Abstract
Background
The continued usage of plants for treatment of diseases and healthcare purposes dates back from time immemorial, including for treatment of respiratory viral infections. The current study was aimed at the evaluation of the antioxidant, anti-neuraminidase and anti-inflammatory properties of selected medicinal plants (Artemisia afra, Lippia javanica, Tetradenia riparia and Tulbaghia violacea) used traditionally for treatment of respiratory viral infections.
Methods
The plants were extracted using water and 80% ethanol. Phytochemical screening of the plant extracts was evaluated using standard protocols. The quantitative antioxidant activity evaluation was performed using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay, ferric reducing antioxidant power (FRAP) assay and the hydrogen peroxide (H2O2) assay. Anti-viral potential was evaluated using anti-neuraminidase inhibition assay. The anti-inflammatory effect of the plant extracts was determined by their activity against cyclooxygenase-2 (COX-2) using colorimetric COX-2 inhibitor screening assay kit.
Results
The phytochemical screening results of extracts tested showed the presence of different classes of secondary metabolites that included coumarins, flavonoids, terpenoids, saponins, steroids, glycosides, and phenolic compounds. The results showed possession of antioxidant activity by the leaf extracts of the selected medicinal plants through dose dependent inhibition of DPPH, H2O2 and FRAP free radicals. The possessed antioxidant activity was shown at varying strengths amongst different plants as demonstrated by differences in determined IC50s. In addition, the plant extracts showed notable inhibitory activity on the enzymatic action of viral neuraminidase with the lowest IC50 of 50 µg/ml recorded. Furthermore, the plant extracts showed possession of anti-inflammation activity demonstrated by C0X-2 inhibition activity.
Conclusions
The results of the current study showed possession of antioxidant, anti-neuraminidase, and anti-inflammatory properties by the extracts of Artemisia afra, Lippia javanica, Tetradenia riparia and Tulbaghia violacea.
Keywords: Phytochemical screening, antioxidant; Anti-neuraminidase; Anti-inflammation; Cyclooxygenase; Respiratory viral infections
Background
The continued usage of plants for treatment of diseases and healthcare purposes dates back from time immemorial [1]. Despite the progress made in the treatment and therapeutic strategies by modern medicine, the incidence, morbidity, and mortality caused by respiratory viral infections remains a major global challenge [2, 3]. Several plants are reported to be ethnobotanically used for treatment of respiratory viral infections and such medicinal plants included A. afra, L. javanica, T. riparia and T. violacea. However, the efficacy or potential efficacy of many such medicinal plants traditionally used for treatment of respiratory complications emanating from viral infections remains not evaluated. In addition, the possible anti-viral mechanisms of many of these plants extracts or their phytochemical compounds remains not yet characterized, which informed their current selection for investigation in the current study [4–6]. Plants efficacy against respiratory viral infections is usually evaluated through assays that involve evaluation of activity based on the two anti-viral mechanisms of action, namely the viral infection inhibition and the post-infection anti-inflammatory properties. Some plants components or bioactive ingredients may possess or exhibit either of the two mechanisms or both. As such, plants that possess inhibitory effects against viral infection aiding proteins/enzymes like neuraminidase and/ or anti-inflammatory properties are regarded to have efficacy against respiratory viral infections [7, 8].
There are different types of diseases caused by respiratory viral infections, and several traditional medicines have been tested on these viruses for their presumed antiviral activity. Several phytochemicals from medicinal plants extracts, including the coumarins, flavonoids, organosulfur compounds, thiophenes, terpenoids, polyphenolics, saponins, peptides and proteins have been found to possess antiviral activity via different mechanisms [9, 10]. Therefore, the phytochemical composition screening of medicinal plants provides invaluable information in the justification for the continued investigation of their potential anti-viral properties. The antiviral mechanism of these phytochemicals found in medicinal plants may follow various pathways, including their antioxidant activities, scavenging capacities, inhibition of the virus penetration into the host cell, or inhibiting the viral reproduction and by competing for pathways that activate intracellular signals such as anti-inflammatory activity [9, 11]. Therefore, the pathways that can be investigated when determining potential efficacy of medicinal plants against respiratory viral infections as is the case for influenzae virus, is through evaluation of the medicinal plants extracts or phytoconstituents’ antioxidant potential, ability to inhibit neuraminidase activity and exhibition or possession of anti-inflammatory properties.
Respiratory viral infections can, therefore, be targeted directly or indirectly. One of the indirect viral reduction targeting looks to address the host response rather than solely focusing on the virus, this is done by the plant’s antioxidants restoring the redox imbalance that act against amplifying the spread of the virus. Oxidative stress occurs due to increase in reactive oxygen species (ROS) production during viral (e.g., influenza virus) infection. This viral infection-induced oxidative stress may contribute to several aspects of pathogenesis of respiratory viral infection, including tissue damage, inflammatory response, and apoptosis. Antioxidants that can block oxidative damage may alleviate respiratory viral infection [12, 13]. Therefore, evaluation of possession of antioxidant properties by medicinal plants extracts or phytoconstituents investigated for anti-viral potential becomes of importance.
The influenzae virus is one of the most implicated respiratory complications causing virus upon human infection. Influenzae virus infection can affect the respiratory tract directly or through the damage that results from the response of the immune system [14]. The enzyme, neuraminidase, has been reported to play a deciding role during the influenzae virus host infection. The inhibition of neuraminidase is an attractive direct target for anti-influenza drug design as it halts viral propagation by interfering with effective shedding. Virus neuraminidase influences the release of newly synthesised progeny virion from the infected host cells. It also encourages virus replications and spread within the infected cells [15]. The evaluation of medicinal plants’ possession of anti-neuraminidase activity is thus informative on the phytoconstituents from such plants’ exhibition of anti-viral activity and potential inhibition of influenzae virus replications. Such bioassay, the anti-neuraminidase activity assay, could therefore, be applicable universally for indication of potential anti-viral activity against respiratory viral infections.
One other anti-viral activity mechanism or pathway is the targeting of the host post-infection inflammatory response in the search for new therapeutics against intense viral respiratory infections [14]. Most of the antiviral herbs have built-in immune-stimulating and inflammation-modulating effects, meaning they can help prevent or regulate immune overreaction (“cytokine storm”) resulting from respiratory viral infections while simultaneously helping fight infections [16]. Prostaglandins are important mediators of the body’s response to pain and inflammation and are formed from essential fatty acids found in cell membranes. This reaction is catalysed by cyclooxygenase, a membrane-associated enzyme occurring in two isoforms, cyclooxygenase-1 (COX-1) that is constitutively expressed and cyclooxygenase-2 (COX-2) that gets induced in the inflamed tissue [17]. Therefore, inhibition of cyclooxygenase presents a therapeutic target for post-infection cytokine storm induced hyperinflammation and an indication of anti-inflammation properties.
The search for new therapeutic agents against respiratory infections is needed to date, more especially with viral respiratory related pandemics such as the swine influenza and the recent COVID-19, which include evaluation of several medicinal plants for that purpose [16, 18–20]. Also, there is a need to fill the gap regarding the elucidation of the anti-viral mechanisms for therapeutic agents that possess antiviral potency. Such mechanisms could include the viral interaction mode through inhibition of viral infection and/or post infection mode through anti-inflammatory properties. The elucidation of the antiviral activity mechanisms would be important in informing antiviral product development and application strategies. The current study was therefore, aimed at the evaluation of the antioxidant, anti-neuraminidase and anti-inflammatory properties in selected medicinal plants used traditionally for treatment of respiratory complications. The findings of the current study contribute to knowledge regarding the anti-viral mode of action exhibited by phytoconstituents within the extracts of the selected medicinal plants different parts or tissues.
Methods
Plant material preparation and extraction
The study was approved by the Sefako Makgatho Health Sciences University Research Ethics Committee (SMUREC/S/498/2023 PG). Plants materials were collected from wild habitations in different communal land non-protected areas of KwaZulu Natal, South Africa; A. afra and L. javanica were collected in Ladysmith (28°28’47.3"S 29°45’19.0"E), T. riparia in Durban (29°47’47.0"S 30°53’49.6"E) and T. violacea in Ladysmith (28°35’40.5"S 29°47’47.4"E). Collection of the plant material was done in compliance with the Guidelines for integrating the conservation and sustainable use of biodiversity in access and benefit-sharing approaches in South Africa [21]. The plants were authenticated by plant taxonomists based at the South African National Biodiversity Institution (SANBI) Pretoria herbarium and voucher specimen were prepared and deposited: T. violacea Harv. (Confirmed by Mothogoane MS; 5/2024; Voucher specimen number: PRE2024-0003), A. afra Jacq. ex Willd. (Confirmed by Makhoba TC; 8/2024; Voucher Specimen number: PRE2024-0001), L. javanica (Burm.f.) Spreng. (Confirmed by Simali S; 8/2024; Voucher Specimen number: PRE2024-0002), T. riparia (Hochst.) Codd (Confirmed by Simali S; 10/2024; Voucher Specimen number: PRE2024-0004). The plant material was then dried at room temperature and ground to fine powder. The ground plant material was then extracted using water and 80% ethanolic (v/v) as solvents applying serial cold maceration for 24 h on an orbital shaker. Resultant extracts were filtered using a Whatman No. 1 filter paper. The filtered ethanolic extracts were evaporated using a rotatory evaporator and dried under a stream of air while aqueous extracts were concentrated using a freeze dryer. Concentrated extracts were then stored in airtight containers and kept in the dark until further usage.
Phytochemical analysis
The plants extracts were subjected to qualitative phytochemical analysis using relevant standard chemical screening tests for determination of the presence of coumarins [22], flavonoids [23], glycosides [24], quinones [22], steroids [25], terpenoids [24] and saponins [26]. The results were recorded in a tabular form indicating presence or absence based on a positive or negative test outcome, respectively. Quantitative phytochemical analysis was also done for the determination of total phenolic content of the plants’ extracts using the Folin-Ciocalteu method [27].
Evaluation of antioxidant activity
The 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay
The ability of plant extracts to donate hydrogen atoms for radical scavenging activity was tested by decolorizing a purple methanol solution of 2,2-diphenyl-1- picrylhydrazyl (DPPH). In the presence of antioxidants, DPPH generates a purple colour in methanol solution and diminishes to shades of yellow. DPPH assay evaluation of the aqueous and ethanolic extracts was done using a method described by Baliyan et al., [28]. The aqueous and ethanolic extracts, including the positive control standards (ascorbic acid and quercetin) were dissolved in ethanol then serially diluted to different concentrations. A volume of 150 µL (250, 125, 62.5, 31.3, 15.6, 7,8 (µg/ml)) for all the plant extracts of different concentrations was then put in the 96 well plate. Then, 50 µL ethanol solution of DPPH (0,2 mg/ml) was added into all the wells and incubated at room temperature for 1 h. Absorbance was then measured at 517 nm using a SpectraMax iD3 microtiter plate reader (Molecular devices, USA). The percentage inhibition of the extracts was calculated using the formula:
 |
Hydrogen peroxide (H2O2) assay
The scavenging activity of natural antioxidants found in plant extracts against hydrogen peroxide (H2O2) has been widely tested by detecting the decrement of H2O2 in an incubation system containing H2O2 and the scavenger using the classical UV absorbance. H2O2 assay evaluation of the aqueous and ethanolic extracts was determined using the method described by Ngonda [29]. with minor modifications. A solution of H2O2 (20 mM) was prepared in phosphate buffer saline (PBS), pH 7.4. The aqueous and ethanolic extracts and the positive control standards, ascorbic acid and quercetin were dissolved in ethanol then serially diluted to different concentrations. An amount of 100 µL for all the diluted samples of different concentrations (1000, 500, 250, 125, 62.5, 31.3, 15.6, 7,8 (µg/ml)) was then put in the 96 well plate. Then, 100 µL of PBS and H2O2 solution of was added into all the wells and incubated at room temperature for 10 min. The absorbance was measured at 560 nm against a blank solution containing phosphate buffer without hydrogen peroxide using a SpectraMax iD3 microtiter plate reader (Molecular devices, USA). The percentage of hydrogen peroxide scavenging by the extracts, standard reagents was calculated using the given formula:
 |
Ferric Reducing Antioxidant Power (FRAP) assay
At low pH, reduction of Fe3+/ferricyanide complex to the ferrous (Fe2+) form (which has an intense blue colour) can be monitored by measuring the change in absorption at 593 nm. The change in absorbance is therefore, directly related to the combined or total reducing power of the electron donating antioxidants of the plant extracts present in the reaction mixture. FRAP assay evaluation of the aqueous and ethanolic extracts was done using a method by Lim et al. [30], . with minor modifications. The extracts and the positive control standards, ascorbic acid and quercetin were dissolved in ethanol then serially diluted to different concentrations. About 30 µl of the plant extract solution were added to a microtiter plate (1000, 500, 250, 125, 62.5, 31.3, 15.6, 7,8 (µg/ml)). Then, 40 µl potassium phosphate buffer (0.2 M, pH 7.2) and 40 µl potassium ferricyanide (1% in phosphate buffer, w/v) was added to each well of the microtiter plate. The microtiter plate was then covered with foil and incubated at 50 °C for 20 min. After the incubation period, 40 µl trichloroacetic acid (10% in phosphate buffer, w/v), 100 µl dH2O and 100 µl FeCl3 (0.1% in phosphate buffer, w/v) was added to the microtiter plate and the plate was recovered with foil and further incubated at room temperature for 30 min. The antioxidant activity was monitored by measuring the change in absorption at 593 nm using a SpectraMax iD3 microtiter plate reader (Molecular devices, USA).
 |
Anti-viral neuraminidase inhibition activity assay
The Amplex Red Neuraminidase (Sialidase) assay kit utilizes Amplex Red to detect H2O2 generated by galactose oxidase action, the end result of neuraminidase action. The H2O2 then, in the presence of horseradish peroxidase (HRP), reacts with a 1:1 stoichiometry with Amplex Red reagent to generate the red-fluorescent oxidation product, resorufin. Resorufin has absorption and fluorescence emission maxima of approximately 571 nm and 585 nm. Samples of different concentrations of the extracts were prepared using a DMSO and Deionized water solvent mixture (10:90). A volume of 50 µL (1000, 500, 250, 125 (µg/ml)) of each extract was pipetted into separate wells of a 96-well microplate. Then added 50 µL of the working solution containing 50 µM Amplex Red reagent, 0.1 U/mL HRP, 2 U/mL galactose oxidase, 250 µg/mL fetuin and a 1X reaction buffer to each microplate well containing the samples and controls. Incubated the reaction for 30 min at 37 °C, protected from light. Oseltamivir was used as the control or anti-neuraminidase standard compound. The absorbance was measured in a microplate at 560 nm. The percentage inhibition of the extracts was calculated as follows:
 |
Anti-inflammatory COX-2 Inhibition activity assay
The anti-inflammatory effect of the selected plant extracts and the formulated concoction against cyclooxygenase-2 (COX-2) inhibition was determined using colorimetric COX-2 inhibitor screening assay kit (Item No. 701080, Cayman Chemical).
The COX reaction Procedure
The Cox-2 enzyme was prepared by mixing 80 µl of enzyme with 320 µl of reaction buffer. Heme solution was prepared by mixing 40 µl of heme with 960 µl of reaction buffer. Arachidonic acid solution with a concentration of 200 µM was prepared by combining 50 µl of arachidonic acid with 50 µl of potassium hydroxide. Stannous chloride solution was prepared by dissolving 125 mg of stannous chloride in 2.5 ml of hydrochloric acid. COX reactions were performed by boiling 10 µl of COX-2 enzyme for 3 min to inactivate it. Then Mixing 160 µl reaction buffer, 10 µL Heme, and 10 µL inactivated enzyme for the background wells. Combined 160 µL reaction buffer, 10 µL Heme, and 10 µL active COX-2 enzyme for the initial activity wells. Added 10 µL of prepared extract/inhibitor (50 µg/ml) to the above mixture. For controls, added 10 µL of inhibitor vehicle instead for the inhibitor wells. All wells were incubated at 37 °C for 10 min. Added 10 µL arachidonic acid to each well to start the reaction, which was then mixed and incubate for 2 min at 37 °C. To stop the reaction 30 µL of stannous chloride solution was added to each well. Incubate for 15 min at 37 °C. The ELISA Procedure was then followed and after incubating the plate in the dark on an orbital shaker the absorbance was read at 412 nm. The following equation was used to calculate the percentage inhibition.
 |
Where, [Initial activity] control is Prostaglandin F2alpha (PGF2α) produced in blank solution (without extracts) and [Inhibitor]sample is PGF2α produced in test sample solution (with extracts). The test compounds, dissolved in DMSO, were evaluated at a concentration of 50 µg/ml. Indomethacin was used as the control or anti-COX activity standard compound.
Statistical analysis
Experiments were carried out in triplicates with the results presented as mean ± standard deviation. Statistical analysis was done using Microsoft (2024) Copilot program. A one-way analysis of variance (ANOVA) was used to determine the differences in means of the antioxidant activity, anti-neuraminidase activity and percentage inhibition of COX by the extracts, with the differences considered significant if the p ≤ 0.05. The quantitative data analysed was assigned groupings (A, B, C, D) using the K-means cluster analysis. Spearman’s rank correlation was used to assess correlation of extracts antioxidant activity with anti-neuraminidase activity and cox-2 inhibition.
Results
The aqueous and ethanolic extracts of different plant parts in A. afra, L. javanica, T. riparia and T. violacea were subjected to phytochemical screening using chemical tests and the results are presented in Tables 1 and 2. The phytochemical screening results showed the presence of different classes of secondary metabolites that included coumarins, flavonoids, terpenoids, saponins, steroids, glycosides and phenolic compounds, although detected at varying intensities.
Table 1.
Phytochemical screening of aqueous extracts from different plant parts of A. afra, L. javanica, T. riparia and T. violacea
| Phytochemical group | Plant part | Coumarins | Flavonoids | Glycosides | Quinones | Terpenoids | Steroids | Saponins |
|---|---|---|---|---|---|---|---|---|
| Artemisia Afra | Leaves | + | ++ | + | - | ++ | + | ++ |
| Lippia javanica | +++ | + | +++ | - | - | - | +++ | |
| Tetradenia riparia | ++ | ++ | ++ | - | - | - | ++ | |
| Tulbaghia violacea | ++ | ++ | ++ | - | - | + | ++ | |
| Artemisia Afra | Stems | ++ | ++ | ++ | - | + | - | ++ |
| Lippia javanica | ++ | ++ | ++ | - | + | - | + | |
| Tetradenia riparia | ++ | ++ | ++ | - | - | - | ++ | |
| Tulbaghia violacea | + | + | + | + | + | + | - | |
| Artemisia Afra | Roots | ++ | + | ++ | - | - | - | - |
| Lippia javanica | ++ | + | ++ | - | + | + | ++ | |
| Tetradenia riparia | + | + | - | - | + | + | +++ | |
| Tulbaghia violacea | + | + | + | + | + | + | - |
[(+) mildly present, (++) moderately present, (+++) highly present; (-) indicate absence)]
Table 2.
Phytochemical composition of ethanolic extracts from different plant parts of A. afra, L. javanica, T. riparia and T. violacea
| Phytochemical group | Plant part | Coumarins | Flavonoids | Glycosides | Quinones | Terpenoids | Steroids | Saponins |
|---|---|---|---|---|---|---|---|---|
| Artemisia Afra | Leaves | +++ | +++ | +++ | ˗ | ++ | + | +++ |
| Lippia javanica | +++ | +++ | +++ | - | ++ | - | - | |
| Tetradenia riparia | ++ | +++ | ++ | + | - | - | ++ | |
| Tulbaghia violacea | ++ | ++ | ++ | + | - | + | ++ | |
| Artemisia Afra | Stems | ++ | +++ | ++ | + | + | - | +++ |
| Lippia javanica | +++ | +++ | +++ | - | ++ | - | ++ | |
| Tetradenia riparia | ++ | ++ | ++ | + | - | + | ++ | |
| Tulbaghia violacea | ++ | ++ | ++ | + | + | + | + | |
| Artemisia Afra | Roots | +++ | ++ | +++ | + | - | - | + |
| Lippia javanica | +++ | +++ | +++ | - | ++ | +++ | +++ | |
| Tetradenia riparia | ++ | + | - | ++ | ++ | + | + | |
| Tulbaghia violacea | ++ | ++ | ++ | ++ | ++ | ++ | ++ |
[(+) mildly present, (++) moderately present, and (+++) highly present; (-) indicate absence)]
Quantitative phytochemical analysis was used for the determination of the total phenolic content (TPC) for the different plant parts and the results depicting the relative TPC distribution amongst the plant species are shown in Fig. 1. All the different plant parts showed possession of some quantifiable total phenolic content, with the A. afra roots and stem extracts having the relative higher distribution of the total phenolic content, respectively.
Fig. 1.
Comparison of the relative distributive Total Phenolic Content (TPC) of the different plant parts (A.A S: A. afra stems; A.A R: A. afra roots; L.J R: L. javanica roots; L.J L: L. javanica leaves; T.R L: T. riparia leaves; T.R S: T. riparia stems; T.V. R: T. violacea roots; T.V S: T. violacea stems)
The antioxidant activity of A. afra, L. javanica, T. riparia and T. violacea aqueous and ethanolic extracts was evaluated through different assays and the results are shown in Tables 3 and 4 for aqueous and ethanolic extracts, respectively. All the extracts revealed to contain certain levels of antioxidant properties when evaluated against the DPPH, H2O2 and FRAP assays. The highest inhibition activity from all the extracts tested for DPPH evaluated antioxidant activity was from the A. afra ethanolic stem extract, which has an IC50 of 0,65 µg/ml. While the most active H2O2 evaluated antioxidant activity was seen with the T. violacea aqueous leaves extract with the recorded IC50 value of 10,18 µg/ml, and for the FRAP evaluation it was the A. afra ethanolic stem extract with recorded IC50 value of 0,40 µg/ml. The A. afra (IC50 value 0.41 µg/ml) FRAP evaluated antioxidant activity was higher than the positive controls, ascorbic acid (IC50 value 0,51 µg/ml) and quercetin (IC50 value 0,64 µg/ml).
Table 3.
Comparison of the antioxidant activity strength (EC50) in aqueous extracts from different plant parts of A. afra, L. javanica, T. riparia and T. violacea with ascorbic acid and quercetin used as positive controls
| Sample | Plant part | DPPH | H2O2 | FRAP |
|---|---|---|---|---|
| EC50 (µg/ml ± SD) | ||||
| Artemisia afra | Leaves | 7,31 ± 0,06b | 73,19 ± 2,80b | 0,59 ± 0,02a |
| Lippia javanica | 22,94 ± 1,12c | 254,01 ± 3,22d | 0,66 ± 0,01a | |
| Tetradenia riparia | 9,18 ± 0,05b | 253,40 ± 5,90d | 42,35 ± 0,81c | |
| Tulbaghia violacea | 17,88 ± 0,75c | 10,18 ± 0,60a | 100,63 ± 2,43d | |
| Artemisia afra | Stems | 8,02 ± 0,29b | 50,63 ± 2,76b | 0,41 ± 0,00a |
| Lippia javanica | 11,44 ± 0,50b | 41,03 ± 1,24b | 1,44 ± 0,08b | |
| Tetradenia riparia | 1,91 ± 0,02a | 44,38 = 1,90b | 1,59 ± 0,01b | |
| Tulbaghia violacea | 40,79 ± 2,57c | 83,92 ± 2,17d | 78,95 ± 2,16d | |
| Artemisia afra | Roots | 7,05 ± 0,05b | 30,55 ± 0,67a | 0,46 ± 0,00a |
| Lippia javanica | 223,00 ± 6,88d | 159,57 ± 3,70c | 8,16 ± 0,34c | |
| Tetradenia riparia | 48,84 ± 1,52c | 73,76 ± 3,36b | 9,27 ± 0,17c | |
| Tulbaghia violacea | 197,17 ± 5,99d | 78,405 ± 2,75b | 7,16 ± 0,32c | |
| Ascorbic acid | 0,05 ± 0,00a | 153,93 ± 3,15c | 0,51 ± 0,01a | |
| Quercetin | 0,06 ± 0,00a | 27,72 ± 0,17a | 0,64 ± 0,01a | |
(p ≤ 0.05) the % DPPH, H2O2, FRAP inhibition is grouped in clusters using alphabetical denotation by a k-means test, cluster denotation is based on natural breaks and spacing in the different groups
Table 4.
Comparison of the antioxidant activity strength (EC50) in ethanolic extracts from different plant parts of A. afra, L. javanica, T. riparia and T. violacea with ascorbic acid and quercetin used as positive controls
| Sample | Plant part | DPPH | H2O2 | FRAP |
|---|---|---|---|---|
| EC50 (µg/ml ± SD) | ||||
| Artemisia afra | Leaves | 5,40 ± 0,04b | 251,32 ± 5,98d | 0,42 ± 0,00a |
| Lippia javanica | 8,19 ± 0,28c | 244,67 ± 0,18d | 0,66 ± 0,02b | |
| Tetradenia riparia | 4,11 ± 0,23b | 211,73 ± 5,19c | 5,43 ± 0,28d | |
| Tulbaghia violacea | 57,53 ± 2,99d | 176,75 ± 5,01b | 4,88 ± 0,23d | |
| Artemisia afra | Stems | 0,65 ± 0,01a | 191,32 ± 3,17c | 0,40 ± 0,00a |
| Lippia javanica | 6,63 ± 0,54b | 180,81 ± 3,47b | 0,71 ± 0,01b | |
| Tetradenia riparia | 5,96 ± 0,45b | 278,73 ± 1,12d | 1,33 ± 0,02c | |
| Tulbaghia violacea | 123,77 ± 4,09d | 190,84 ± 5,15c | 0,94 ± 0,06b | |
| Artemisia afra | Roots | 4,16 ± 0,08b | 199,91 ± 5,90c | 0,51 ± 0,00a |
| Lippia javanica | 8,67 ± 0,20c | 179,33 ± 3,01b | 0,46 ± 0,01a | |
| Tetradenia riparia | 3,37 ± 0,14b | 85,87 ± 2,09a | 4,30 ± 0,07d | |
| Tulbaghia violacea | 21,09 ± 0,94c | 180,00 ± 2,02b | 0,63 ± 0,01b | |
| Ascorbic acid | 0,05 ± 0,00a | 153,93 ± 3,15b | 0,51 ± 0,01a | |
| Quercetin | 0,06 ± 0,00a | 27,72 ± 0,17a | 0,64 ± 0,01a | |
(p ≤ 0.05) the % DPPH, H2O2, FRAP inhibition is grouped in clusters using alphabetical denotation by a k-means test, cluster denotation is based on natural breaks and spacing in the different groups
The anti-neuraminidase activity evaluation results are shown in Table 5. The results have indicated some level of exhibited activity for all plant species under investigation as shown through IC50 values that were mostly below 1 mg/ml. All aqueous extracts showed higher inhibition of neuraminidase activity when compared to the ethanolic extracts. The A. afra extract with the most inhibition activity was the stem aqueous extract with an IC50 of 160 µg/ml. The aqueous root extract of L. javanica showed the lowest IC50 at 50 µg/ml for the inhibitory activity of the viral neuraminidase, followed by the aqueous water extract of T. riparia and the aqueous stem extract of A. afra with IC50 160 µg/ml and 160 µg/ml, respectively.
Table 5.
Neuraminidase (NA) inhibition (IC50) by A. afra, L. javanica, T. riparia and T. violacea extracts from different plant parts using aqueous and ethanol as solvents. Oseltamivir was used as a positive control
| Plant part | Extraction Solvent | A. afra | L. javanica | T. riparia | T. violacea |
|---|---|---|---|---|---|
| NA IC50 (µg/ml ± SD) | |||||
| Leaves | 280 ± 3.0b | 250 ± 2.8a | 160 ± 0.7a | 630 ± 4.1b | |
| Stem | Water | 160 ± 0.1a | 360 ± 2.9b | 430 ± 1.8b | 360 ± 3.3b |
| Roots | 210 ± 4.0a | 50 ± 0.4a | 440 ± 2.6b | 250 ± 2.3a | |
| Leaves | 600 ± 5.4b | 1080 ± 7.4c | 1290 ± 14.4c | 700 ± 11c | |
| Stem | Ethanol | 1930 ± 11.9d | 2620 ± 20.9d | 910 ± 8.7c | 750 ± 5.9c |
| Roots | 1500 ± 10.6d | 1040 ± 15.7c | 540 ± 8.2b | 790 ± 4.4c | |
| Oseltamivir | 1.3 ± 0.0a | ||||
(p ≤ 0.05) the % Neuraminidase inhibition is grouped in clusters using alphabetical denotation by a k-means test, cluster denotation is based on natural breaks and spacing in the different groups
The results for % COX-2 inhibition are shown in Table 6. All the extracts were evaluated at a constant concentration of 50 µg/ml and the extract that showed the highest % COX-2 inhibition was the T. riparia showing an inhibition of 77.43% and 77.18% for the leaf and stem extracts, respectively that was higher than the positive control indomethacin that showed 72.37% of COX-2 inhibition.
Table 6.
COX-2 inhibition activity of aqueous extracts at 50 µg/ml with indomethacin was used as a positive control
| Plant Extract | %COX-2 inhibition |
|---|---|
| Artemisia afra Stem | 72.05 ± 0.13a |
| Artemisia afra Roots | 73.97 ± 0.13b |
| Lippia javanica Roots | 71.60 ± 0.45a |
| Lippia javanica Leaves | 75.96 ± 0.06b |
| Tetradenia riparia Leaves | 77.43 ± 0.26c |
| Tetradenia riparia Stem | 77.18 ± 0.22c |
| Tulbaghia violacea Roots | 72.63 ± 0.06a |
| Tulbaghia violacea Stem | 75.32 ± 0.19b |
| Indomethacin | 72.37 ± 0.58a |
(p ≤ 0.05) the % C0X-2 inhibition is grouped in clusters using alphabetical denotation by a k-means test, cluster denotation is based on natural breaks and spacing in the different groups
Discussion
Phytochemical screening
The medicinal plants selected for investigation in the current study, namely A. afra, L. javanica, T. riparia and T. violacea, are amongst plants used traditionally for treatment of respiratory infections. However, their efficacy or potential efficacy to alleviate complications associated with respiratory viral infections is not adequately explored. Therefore, the current study was aimed at the evaluation of antiviral activity indicators possessed or exhibited by phytochemical compounds within the extracts from the four selected plant species, which contribute information to establish their potential efficacy against respiratory viral infections. The phytochemical screening of the aqueous and ethanolic extracts from the different plants’ parts (leaves, stem, roots) of the selected medicinal plants showed the presence of different classes of secondary metabolites that included coumarins, flavonoids, terpenoids, saponins, steroids, glycosides and phenolic compounds. The results also showed that the presence of the detected plant secondary metabolites/phytochemicals were recorded at different intensities amongst the different selected medicinal plants and, at times, among the different plants parts of the same plant species. For example, quinones were not detected in the leaf extracts of A. afra, whereas in was detected to be present in both the stem and roots extracts. It is not uncommon for different plant parts of the same plant species to show a certain level of disparity in the possessed secondary metabolites during phytochemical screening as it was also reported in several previous studies for different plants species than those selected for the current study [31–34]. It should also be factored in that the phytochemical compositions of extracts from different sources are depended on the properties of solvents used for extraction and the method or procedure employed for extraction [35]. Therefore, the reported phytochemicals detected in the plant materials from the samples of the selected medicinal plants is limited to those that are extractable through the used extraction solvents and the extraction method in the current study.
Antioxidant activity
Evaluation of free radical scavenging properties of the aqueous and ethanolic extracts of the different plants’ parts (leaves, stem, roots) showed exhibition of inhibitory activity against free radicals’ test reagents (DPPH, H2O2 and FRAP) in all plants. The results of the current study agree with the findings of previous studies that reported antioxidant properties in A. afra, L. javanica, T. riparia and T. violacea [36–39]. The results of the current study thus confirm the antioxidant properties of the selected medicinal plants reported in previous studies. Phytochemical screening of the extracts from the selected medicinal plants materials showed the presence of the different phytochemicals that included coumarins, flavonoids, terpenoids, saponins, steroids, glycosides and phenolic compounds. All these phytochemicals detected in presence have been reported to possess strong antioxidant properties [37, 40]. Therefore, the exhibited antioxidant properties of the different plant parts of the selected medicinal plants in the current study could be attributed to the phytochemicals that were detected to be in possession thereof.
Neuraminidase activity inhibition
Evaluation of anti-neuraminidase activity of the aqueous and ethanolic extracts showed possession of some certain levels of neuraminidase inhibition properties in all plants under investigation. All aqueous extracts showed higher inhibition of neuraminidase activity when compared to the ethanolic extracts. The results therefore suggest that the anti-neuraminidase activity exhibited by the extracts of the selected medicinal plants are contributed for mainly by the phytoconstituents of relative higher polarity. The results of the current study confirm the findings of a study done by Monto [41] on the anti-neuraminidase activity of A. afra. However, the anti-neuraminidase activity of the three other selected medicinal plants, namely, L. javanica, T. riparia and T. violacea is reported for the first time through this study. Possession or exhibition of anti-neuraminidase activity by medicinal plants is an indication of potential anti-viral properties and it is an attractive target for anti-influenza related drug design. Neuraminidase (NA) is found in all wild-type influenza viruses, and its inhibition halts viral propagation by interfering with effective shedding [42]. The observed anti-neuraminidase activity in this study could be attributed to the nature of phytochemicals possessed by the selected medicinal plants. For example, saponins were amongst the detected phytochemicals in the medicinal plants selected for the current study and compounds of saponin nature have been reported to possess antiviral activity [40]. The results of current thus places anti-neuraminidase activity as one possible antiviral mechanism of action exhibited by saponin compounds. Therefore, the findings indicate that the selected medicinal plants possess phytoconstituents with anti-neuraminidase activity, which demonstrates potential anti-viral activity through the inhibition of viral propagation against influenzae virus and other respiratory infectious microorganisms.
Cox-2 activity inhibition
Two plant parts extracts of each of the selected medicinal plants that showed higher anti-neuraminidase activity in the current study were evaluated for Cox-2 inhibition activity. The results showed possession of some Cox-2 inhibition activity by all the plant parts extracts evaluated, which was more similar in strength to the positive control, Indomethacin. Phytochemicals such as flavonoids, terpenoids, saponins and coumarins are well known for anti-inflammatory properties [43], as such their presence in the selected medicinal plants extracts that was revealed through phytochemical analysis suggest their contribution to the observed anti-inflammatory activity of the plant’s extracts observed in this study. The exhibition of Cox-2 inhibition activity by the extracts from various plant parts of the selected medicinal plants, namely A. afra and L. javanica, is reported in this study for the first time. Inhibition of the activity of Cox enzyme is one of the ways for demonstration of anti-inflammatory properties. Anti-inflammatory agents mainly inhibit the cyclooxygenase (Cox) enzyme responsible for synthesizing inflammatory mediators by converting arachidonic acid to prostaglandins. Prostaglandin G2 (PGG2) is converted into prostaglandin H2 (PGH2) together by the enzyme peroxidase, which creates long membrane channels [44, 45]. Due to the release of chemical mediators, membrane channel opening causes the release of arachidonic acid from the membrane and is then converted to prostaglandin. This also plays part in acute and chronic inflammation [46]. Therefore, the results suggest that the different plant parts of selected medicinal plants for the current study possess phytoconstituents with Cox-2 inhibition activity and thus anti-inflammation properties.
Evaluation of correlation relationship between pharmacological properties
A correlation relationship was tested between antioxidant activity versus anti-neuraminidase activity, antioxidant activity versus Cox-2 inhibition activity and between anti-neuraminidase versus Cox-2 inhibition activities using the Spearman’ correlation rank test. The Spearman’s correlation rank test demonstrated a negative correlation outcome between antioxidant activity and anti-neuraminidase activity for the selected medicinal plants, with ρ (rho) ≈ -0.45 for DPPH antioxidant assay activity; -0.50 for H2O2 assay activity and − 0.07 for FRAP assay activity. The outcome, therefore, suggest that plant extracts with strong antioxidant activity are likely to also have strong anti-neuraminidase activity, since as the EC50 antioxidant concentration gets lower, the higher the % neuraminidase inhibition. When spearman’s rank correlation was done between DPPH, H2O2 and FRAP reduction activities versus COX-2 inhibition, a positive correlation of ρ (rho) ≈ + 0.36 was found between DPPH and COX-2 inhibition activity. The outcome, therefore, suggest that plant extracts with strong antioxidant activity are likely to also have strong COX-2 inhibition. The outcome of the testing of the correlation relationship between anti-neuraminidase and COX-2 inhibition resulted in the correlation ρ (rho) ≈ − 0.10, which indicated a very weak to negative correlation between anti-neuraminidase and COX-2 inhibition or anti-inflammatory properties. It is important to note that correlation does not equate to causation. More tests would need to be done to account for causation. The correlation outcome between anti-neuraminidase activity versus Cox-2 inhibition activity could be arising from the distinction in the viral infection stage of the two invoked anti-viral mechanisms. For example, anti-neuraminidase action is invoked during the viral infection stage to thwart the propagation of the virus to mount effective infection. On the other hand, Cox-2 inhibition is linked to anti-inflammation activity following the post infection cytokine immune-response storm leading to high inflammation state [47]. The findings of the study, therefore, suggest that the phytoconstituents within the selected medicinal plants have inherent anti-viral properties that arise from two distinct mechanisms that occur at the different viral infection stages. The findings further suggest strong correlation between antioxidant activity and anti-neuraminidase activity inherent in the plants’ phytoconstituents. Antioxidant activity reverses oxidative stress and immune response cytokine storm in living systems and therefore alleviates post viral infection hyperinflammation. In contrast, anti-neuraminidase activity stops viral infection and propagation, which prevents the elevation of the immune cytokine storm and thus prevents hyperinflammation.
Ultimately, the Spearman rank correlation was determined between the TPC and the antioxidant, anti-neuraminidase and anti-COX activities. The resultant correlation between TPC and DPPH, H2O2 and FRAP inhibition EC50s dataset was generally weak with ρ ≈ − 0.05; − 0.12 and – 0.60, respectively. The Spearman rank correlation between TPC and anti-neuraminidase IC50s dataset was moderately weak (ρ ≈ − 0.67). Similarly, the Spearman rank correlation between TPC and % COX-2 inhibition dataset was also moderately negative (ρ ≈ − 0.52). the outcome, therefore, suggest that there is no correlation between the phenolic content and the antioxidant, anti-neuraminidase and anti-COX activities exhibited by the phytoconstituents of the different plant parts extracts of A. afra, T. riparia, L. javanica and T. violacea.
Conclusion
Phytochemical screening confirmed the presence of important phytochemical group compounds within the extracts from medicinal plants selected for the current study. The different plant parts of the various selected medicinal plants exhibited antioxidant activity, which is a validation of their health beneficial properties. The extracts showed exhibition of good anti-neuraminidase and Cox-2 inhibition activities, although no correlation between the two mechanisms was demonstrated. Therefore, the results of the current study suggest that the investigated medicinal plants, namely, A. afra, L. javanica, T. riparia and T. violacea, possess properties to mitigate against respiratory viral infections through the different mechanisms, including the viral propagation inhibition properties demonstrated by anti-neuraminidase activity and post-infection anti-inflammatory properties evidenced by Cox-2 inhibition activity. Higher anti-neuraminidase activity was seen with aqueous plants extracts, which suggest that the active components against neuraminidase activity could be of extremely high polar in nature. Compound-level identification, biosafety and direct antiviral testing such as cell-based assays are recommended in future studies to strengthen the current findings. In conclusion, the study has demonstrated that the phytoconstituents possessed by the selected medicinal plants have the potential to be developed into products for usage against respiratory viral infections.
Acknowledgements
Not applicable.
Authors’ contributions
SL carried out the experimental work and analyzed the data, VS analyzed and interpreted the data, SS Interpreted the data also participated in the manuscript drafting. All authors have read and approved the final manuscript.
Funding
None.
Data availability
All data generated or analysed during this study are included in this published article.
Declarations
Ethics approval and consent to participate
Not applicable.
Consent for publication
Not applicable.
Competing interests
The authors declare no competing interests.
Footnotes
Publisher’s note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
References
- 1.Petrovska BB. Historical review of medicinal plants’ usage. Pharmacogn Rev. 2012;6(11):1–5. PMID: 22654398; PMCID: PMC3358962. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 2.Furman D, Campisi J, Verdin E. Chronic inflammation in the etiology of disease across the life span. Nat Med. 2019;25:1822–32. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 3.Okeke IN, Laxmaninarayan R, Bhutta ZA, Duse AG, Jenkins P, O’Brien TF, et al. Antimicrobial resistance in developing countries. Part 1: recent trends and current status. Lancet Infect Dis. 2005;5:481–93. [DOI] [PubMed] [Google Scholar]
- 4.Shimira F. Tetradenia riparia, an ethnobotanical plant with diverse applications, from antimicrobial to anti-proliferative activity against cancerous cell lines: A systematic review. J Herb Med. 2022;32:100537. [Google Scholar]
- 5.Liu NQ, Van der Kooy F, Verpoorte R. Artemisia afra: A potential flagship for African medicinal plants? S Afr J Bot. 2009;75(2):185–95. [Google Scholar]
- 6.Gaidamashvili M, van Staden J. Prostaglandin inhibitory activity by lectin-like proteins from South African medicinal plants. S Afr J Bot. 2006;72(4):661–3. [Google Scholar]
- 7.Schultz F, Osuji F, Wack B, Anywar G, Garbe LA. Antiinflammatory medicinal plants from the Ugandan Greater Mpigi Region act as potent inhibitors in the COX-2 / PGH2 pathway. Plants. 2021;10(2):351. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 8.Rojas-Quintero J, Wang X, Tipper J, Burkett PR, Zuniga J, Ashtekar AR. Matrix metalloproteinase-9 deficiency protects mice from severe influenza A viral infection. JCI Insight. 2018;3(24):e130771. [DOI] [PMC free article] [PubMed]
- 9.Mukhtar M, Arshad M, Ahmad M, Pomerantz RJ, Wigdahl B, Parveen Z. Antiviral potentials of medicinal plants. Virus Res. 2008;131(2):111–20. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 10.Li SY, Chen C, Zhang HQ, Guo HY, Wang H, Wang L, et al. Identification of natural compounds with antiviral activities against SARS-associated coronavirus. Antivir Res. 2005;67(1):18–23. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 11.Liu AL, Du GH. Antiviral properties of phytochemicals. In: Dietary Phytochemicals and Microbes. 2012:93–126.
- 12.Liu M, Chen F, Liu T, Chen F, Liu S, Yang S. The role of oxidative stress in influenza virus infection. Microbes Infect. 2017;19:580–6. [DOI] [PubMed] [Google Scholar]
- 13.Nencioni L, Sgarbanti R, De Chiara G, Garaci E, Palamara AT. Influenza virus and redox mediated cell signaling: a complex network of virus/host interaction. New Microbiol. 2007;30:367–75. [PubMed] [Google Scholar]
- 14.Kalil AC, Thomas PG. Influenza virus-related critical illness: pathophysiology and epidemiology. Crit Care. 2019;23(1):258. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 15.Stoner TD, Krauss S, DuBois RM, Negovetich NJ, Stallknecth DE, Senne DA, et al. Antiviral susceptibility of avian and swine influenza virus of the N1 neuraminidase subtype. J Virol. 2010;84(19):9800–9. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 16.Yarnell E. Herbs for viral respiratory infections. Altern Complement Ther. 2018;24(1):35–43. [Google Scholar]
- 17.Taylor JLS, van Staden J, Jäger AK. COX-1 and COX-2 inhibitory activity in extracts prepared from Eucomis species. S Afr J Bot. 2002;68(1):80–5. [Google Scholar]
- 18.Ali SI, Sheikh WM, Rather MA, Venkatesalu V, Bashir SM, Nabi SU. Medicinal plants: treasure for antiviral drug discovery. Phytother Res. 2021;35(7):3447–83. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 19.Sonia G. Pandemics and traditional plant-based remedies: a historical-botanical review in the era of COVID-19. Front Plant Sci. 2020;11:571042. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 20.Reddy JGM, Prathyusha K, Venkataswarmy M, Ramesh A. Spreading of swine flu disease: past and present. Res J Pharm Dosage Forms Technol. 2018;10(2):70–8. [Google Scholar]
- 21.Wynberg R, Crouch N, Lavelle J, van Niekerk J, Ndwandwe S. Guidelines for integrating the conservation and sustainable use of biodiversity in access and benefit-sharing approaches in South Africa. Department of Forestry, Fisheries and the Environment, University of Cape Town, South African National Biodiversity Institute, GIZ and Bioinnovation Africa. 2022.
- 22.Roghini R, Vijayalakshmi K. Phytochemical screening, quantitative analysis of flavonoids and minerals in ethanolic extract of Citrus paradisi. Int J Pharm Sci Res. 2018;11:4859–64. [Google Scholar]
- 23.Jaradat N, Hussen F, Anas AA. Preliminary phytochemical screening, quantitative estimation of total flavonoids, total phenols and antioxidant activity of Ephedra alata. J Mater Environ Sci. 2015;6:1771–8. [Google Scholar]
- 24.Rao USM, Abdurrazak M, Mohd KS. Phytochemical screening, total flavonoid and phenolic content assays of tepal of Musa paradisiaca. Malays J Anal Sci. 2016;20(5):1181–90. [Google Scholar]
- 25.Dauda H, Uba G, Ali U. Preliminary phytochemical screening, quantitative analysis of flavonoids from the stem bark extract of Commiphora africana. BES Sci Med. 2020;4(1):25–7. [Google Scholar]
- 26.Sasikala M, Sundaraganapathy R. Qualitative analysis of alkaloids in the hydroalcoholic extract of Ipomoea aquatica. Int J ChemTech Res. 2017;10:446–54. [Google Scholar]
- 27.Molole GJ, Gure A, Abdissa N. Determination of total phenolic content and antioxidant activity of Commiphora mollis (Oliv.) Engl. resin. BMC Chem. 2022;16:48. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 28.Baliyan S, Mukherjee R, Priyadarshini A, Vibhuti A, Gupta A, Pandey RP, Chang CM. Determination of antioxidants and quantitative phytochemical analysis of Ficus religiosa. Molecules. 2022;27(4):1326. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 29.Ngonda F. In-vitro antioxidant activity and scavenging potential of roots of Trichodesma zeylanicum. Asian J Biomed Pharm Sci. 2013;3(20):21. [Google Scholar]
- 30.Lim TY, Lim YY, Yule CM. Antioxidant, antibacterial and anti-tyrosinase activities of four Macaranga species. Food Chem. 2009;114(2):594–9. [Google Scholar]
- 31.Barbouchi M, Benzidia B, Elamrani K, Sabiri M, El Idrissi M, Choukrad M. Antioxidant properties of extracts from three Ruta species. Kuwait J Sci. 2024;51(4):100287. [Google Scholar]
- 32.Pant DR, Joshi GP, Aryal B. Phytochemical screening and antioxidant potential of Nepalese medicinal plants. Tribhuvan Univ J. 2024;39(1):1–15. [Google Scholar]
- 33.Khan M, Khan M, Al-Hamoud K, Adil SF, Shaik MR, Alkhathlan HZ. Phytochemical analysis and biological activities of Artemisia judaica. Life (Basel). 2022;12(11):1885. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 34.Agidew MG. Phytochemical analysis of some selected traditional medicinal plants in Ethiopia. Bull Natl Res Cent. 2022;46:87. [Google Scholar]
- 35.Hlatshwayo S, Thembane N, Krishna SBN, Gqaleni N, Ngcobo M. Extraction and Processing of Bioactive Phytoconstituents from Widely Used South African Medicinal Plants for the Preparation of Effective Traditional Herbal Medicine Products: A Narrative Review. Plants (Basel). 2025;14(2):206. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 36.Agrawal PK, Agrawal C, Blunden G. Quercetin: Antiviral Significance and Possible COVID-19 Integrative Considerations. Nat Prod Commun. 2020;15(12):e1934578X20976293.
- 37.Benarba B, Pandiella A. Medicinal plants as sources of actives against COVID-19. Front Pharmacol. 2020;11:1189. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 38.Sena JDS, Rodrigues SA, Sakumoto K, Inumaro RS, González-Maldonado P, Mendez-Scolari E, Piau R Jr, Gonçalves DD, Mandim F, Vaz J, Gonçalves JE, Sotelo PH, Valle JSD, Gazim ZC. Antioxidant Activity, Antiproliferative Activity, Antiviral Activity, NO Production Inhibition, and Chemical Composition of Essential Oils and Crude Extracts of Leaves, Flower Buds, and Stems of Tetradenia riparia. Pharmaceut (Basel). 2024;17(7):888. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 39.Madike LN, Pillay M, Popat KC. Antithrombogenic properties of Tulbaghia violacea aqueous leaf extracts: assessment of platelet activation and whole blood clotting kinetics. RSC Adv. 2021;11(48):30455–64. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 40.Kumar A, P N, Kumar M, Jose A, Tomer V, Oz E, Proestos C, Zeng M, Elobeid T, Oz KS. Major Phytochemicals: Recent Advances in Health Benefits and Extraction Method. Mol. 2023;28(2):887. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 41.Arnold S, Monto, Effectiveness of the Neuraminidase Inhibitors. The Supporting Evidence Increases. J Infect Dis. 2020;221(3):340–2. [DOI] [PubMed] [Google Scholar]
- 42.Ortigoza MB, Mobini CL, Rocha HL, Bartlett S, Loomis CA, Weiser JN. Inhibiting influenza virus transmission using a broadly acting neuraminidase that targets host sialic acids in the upper respiratory tract. mBio. 2024;15(2):02203–23. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 43.Gonfa YM, Fekade BT, Bachheti A, Rai N, Tadesse MG, Singab AN, Chaubey KK. Rakesh Kumar Bachheti RK. Anti-inflammatory activity of phytochemicals from medicinal plants and their nanoparticles: A review. Curr Res Biotech. 2023;6:100152. [Google Scholar]
- 44.Wautier JL, Wautier MP. Pro- and Anti-Inflammatory Prostaglandins and Cytokines in Humans: A Mini Review. Int J Mol Sci. 2023;24(11):9647. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 45.Kamal DAM, Abidin SZ, Saudi WSW, et al. Roles of Prostaglandins and Cyclooxygenases in Autism Spectrum Disorder: A Comprehensive Review. Curr Behav Neurosci Rep. 2025;12:2. [Google Scholar]
- 46.Maddipati KR. Distinct etiology of chronic inflammation – implications on degenerative diseases and cancer therapy. Front Immunol. 2024;15:1460302. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 47.Yamaya M, Kikuchi A, Sugawara M, Nishimura H. Anti-inflammatory effects of medications used for viral infection-induced respiratory diseases. Respir Investig. 2023;61(2):270–83. [DOI] [PMC free article] [PubMed] [Google Scholar]
Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Data Availability Statement
All data generated or analysed during this study are included in this published article.