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Iranian Journal of Basic Medical Sciences logoLink to Iranian Journal of Basic Medical Sciences
. 2023 Jan;26(1):76–84. doi: 10.22038/IJBMS.2022.66255.14553

Elucidation of flavonoids from potent Iranian Scutellaria species against Influenza A (H1N1) virus

Mostafa Pirali Hamedani 1, Mahtab Ahmad Kashi 1, Saied Goodarzi 2, Hadiseh Shokouhi 3, Mahdi Shafiee Ardestani 4, Abbas Hadjiakhoondi 1,2, Morteza Pirali Hamedani 5, Mohammad Hosein Ghahremani 6, Parvaneh Mehrbod 3,*, Zahra Tofighi 1,2,*
PMCID: PMC9790063  PMID: 36594062

Abstract

Objective(s):

Influenza A virus (IAV) is a contagious illness. Different species of Scutellaria genus are used as a traditional remedy to reduce influenza symptoms. This study aimed to investigate the anti-influenza capacity of several species of Iranian Scutellaria and identify active compounds of the most potent species for the first time.

Materials and Methods:

Some Iranian species of Scutellaria were collected from different regions of Iran, including S. pinnatifida with mucida, viridis, and alpina subspecies; S. tournefortii; S. tomentosa; S. persica. They were fractionated to chloroform and methanol. The total phenols and flavonoids of samples were examined by the folin-ciocalteau and aluminum-flavonoid complex methods, respectively. The 50% cytotoxic concentrations (CC50) on MDCK cells and non-cytotoxic concentrations (NCTC) were determined by MTT assay. The percentage of cell protection against IAV and their effect on virus titer were investigated in pre-, post-, and co-penetration treatment groups. Phytochemicals of the most effective species were isolated by various chromatographic methods and identified by different spectroscopic methods.

Results:

Methanol fraction of S. pinnatifida subsp. viridis demonstrated the highest amounts of flavonoid content and best activity against influenza A virus in all combination treatments, which reduced the virus titer by 5 logs with no cytotoxicity. Kaempferol-3-O-glucoside, quercetin-3-O-glucoside, apigenin-4′-methoxy-7-O-glucoside, luteolin, and luteolin-7-O-glucoside were purified and identified from this species.

Conclusion:

Scutellaria pinnatifida subsp. viridis can be introduced as a source of flavonoids with acceptable anti-influenza activity. S. tomentosa also showed potent antiviral effects and is a candidate for elucidation in further studies.

Key Words: Antiviral, Flavonoids, Folin-ciocalteau reagent, Influenza A virus, MTT assay, Scutellaria

Introduction

Influenza virus can cause dangerous illnesses due to the high potential of mutations (antigenic drifts and shifts) in viral genes, and flu infection can result in hospitalization and death (1). H1N1 is a subtype of influenza A virus (IAV) that can cause upper and lower respiratory tract infections. Symptoms like fever, chills, cough, shortness of breath, myalgia, and gastrointestinal symptoms like abdominal pain and vomiting have been reported in some cases (2). Currently, two classes of influenza antiviral drugs are available in the market; first, M2 proton channel blockers (amantadine and rimantadine) and second, neuraminidase inhibitors (oseltamivir, zanamivir, etc.) (3), however, because of drug resistance concerns, it is crucial to discover and improve new compounds (4).

Medicinal plants have represented great potential for antiviral activity against different types of viruses (5). Numerous studies have shown that natural compounds derived from herbal sources can be used as lead compounds for novel drugs. Anti-influenza studies have been done using different plants, and some of those like Sambucus nigra, Kaempferia parviflora, Curcuma longa, Ephedra sinica, Eleutherococcus senticosus, Glycyrrhiza glabra, Brassica juncea, and Scutellaria baicalensis showed significant antiviral activity against influenza virus affecting different pathways (6-10).

Scutellaria (Lamiaceae), with the common name of “Skullcap” in English and “Kolah-khoodi” in Persian, includes more than 350 species in several regions like East Asia, Europe, and North America. It is a traditional herbal medicine with a long history of treating various diseases like diarrhea, hypertension, insomnia and respiratory infection for thousands of years (11, 12). The Iranian flora includes more than 20 species distributed in different regions (13).

In recent years different activities of the Scutellaria genus have been studied. Anti-tumor action against breast and colon cancer, an anti-oxidant activity that can decrease cell damage by inhibiting oxidative stress (14), anti-inflammatory activity via different pathways (15), antibacterial and antiviral effects against various pathogens, effects on vascular diseases (cerebrovascular and cardiovascular) (16), and some other pharmacological activities like hepatoprotective and neuroprotective have been reported (15). Thus, modern pharmacology has proved some of the traditional usages of these plants and confirmed the value and potential of Scutellaria species. The presence of lots of flavonoids and other compounds seems to be the main reason for these effects (17).

One of the major groups of secondary metabolites which plants produce is phenolic compounds. The health benefits of fruits and vegetables are related to their high phenolic content (18). One of the beneficial effects of phenolic compound derivatives is their antiviral effects (19). About half of the phenolic compounds are presented in the flavonoids group, which are responsible for some plant activities. For example, attracting insects through attractive colors is probably due to the presence of flavones, flavonols and anthocyanidins, which leads to their pollination by insects. Also, catechins and some flavonols are responsible for defending plants against harmful insects (20). Flavonoids play a fundamental role in plant development and survival and can be used to prevent and treat some diseases in humans. Some of these properties are anti-atherosclerotic, anti-inflammatory, anti-thrombogenic, anti-tumor, anti-osteoporotic, antiviral, antibacterial and anti-fungal effects. Also, flavonoids are known as anti-oxidant, hepato-protectant, cardio-protectant, anti-diabetic, and anxiolytic compounds (21). In this study, the phenolic and flavonoid contents and antiviral activity of some Iranian Scutellaria species were studied to find the potent species and also the isolation and identification of phytochemicals of the potent species.

Materials and Methods

Plant materials

Four species of Scutellaria were collected from different regions of Iran. The identity of three species was verified by the botanist Dr Y Ajani with voucher specimen and registered in the Herbarium of the Faculty of Pharmacy, Tehran University of Medical Sciences, Tehran, Iran. The voucher specimen of the other species was registered in the Herbarium of Institute of Medical Plants, Karaj, Iran and identified by Dr M Ghorbani Nohooji (Table 1).

Table 1.

Profile of location of various Scutellaria species from Iran

Scientific name Voucher No. Elevation Location Code
Scutellaria pinnatifida
subsp. mucida (Stapf) Rech.f.		 7043-TEH** 1600 m* Barajin, Qazvin Province Barajin
Scutellaria pinnatifida
subsp. viridis (Boiss.) Rech.f.		 7040-TEH 1650 m Zarabad, Qazvin Province Zarabad
Scutellaria pinnatifida
subsp. viridis (Boiss.) Rech.f.		 7042-TEH 1800 m Bahram abad, Qazvin Province Bahram abad
Scutellaria pinnatifida
subsp. viridis (Boiss.) Rech.f.		 7039-TEH 1500 m Kamard, Tehran Province Kamard
Scutellaria pinnatifida
subsp. alpina (Bornn.) Rech.f.		 7117-TEH 2300 m Shahroud, Semnan province Shahroud
Scutellaria tournefortii Benth. 7037-TEH 550 m Galikesh, Golestan Province Gorgan
Scutellaria tournefortii Benth. 7046-TEH 500 m Ramsar, Mazandaran Province Ramsar
Scutellaria tomentosa Bertol. 7116-TEH 2000 m Kashan, Isfahan Province Kashan
Scutellaria persica Bornm. 7078-IMPH*** 2500 m Takab, West Azarbaijan Province Takab
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*m: meter; **TEH: Herbarium of Faculty of Pharmacy, Tehran University of Medical Sciences, Tehran, Iran; ***IMPH: Herbarium of Iranian Institute of Medicinal Plants, Karaj, Iran

Extraction and fractionation

All collected species of Scutellaria were dried in the shade at room temperature. When the final moisture level of the plants was minimized, the plants were pulverized and the extraction process was accomplished with methanol: water (8:2) solvent by maceration method (total extract). Then, the extracts were fractionated by chloroform (chloroform fractions) and the residues were named methanol fractions.

Total phenol content assay

The Folin-ciocalteau method was selected for determining the total phenol content of all fractions of Scutellaria species. The concentration of the samples was equal to 500 μg/ml, diluted with methanol. Folin-ciocalteau reagent (1.5 ml) (1:10 diluted with deionized water) was mixed with 200 μl of each sample. After 5 min, 1.5 ml of sodium bicarbonate (6 g/l was dissolved in distilled water) was added. The absorption of these solutions was measured after 90 min incubation in a dark place at room temperature. Followed by that, the absorbance was measured at 725 nm by the spectrophotometer. Methanol was considered as control. The calibration curve of Gallic acid (0, 25, 50, 100 mg/ml) was plotted as a standard curve. The total phenol content of the fractions was expressed as mg of Gallic acid per gram of fraction (22).

Total flavonoid content assay

Among several methods for determining the total flavonoid content, the aluminum-flavonoid complexing method was selected. The volume of 1 ml of each sample (100 μg/ml) was diluted with 4 ml distilled water, and then 0.3 ml sodium nitrite 5% w/v was added. After 5 min, 0.3 ml of aluminum chloride 10% w/v was added. Five minutes later, 2 ml sodium hydroxide 4% w/v was added and the final volume of the solution reached 10 ml with distilled water. The absorbance of samples was measured at 510 nm after 30 min. Preparing the blank sample was the same as other samples, except there was no analyte and aluminum chloride in the blank sample and methanol was substituted instead (23).

Catechin (25, 75, 125, 150, 500 μg/ml) was used as positive control and the results of the total flavonoid content of Scutellaria species were reported as mg of catechin per gram of fraction.

Cell culture and influenza virus multiplication

The cell line of Madin Darby Canine Kidney (MDCK) was used to propagate the influenza virus. MDCK cells were maintained in Dulbecco’s Modified Eagle’s Medium (DMEM) (Mediatech Cellgro, USA) plus 10% Fetal Bovine Serum (FBS) (PAA, Austria) and 100 μg/ml of Penicillin and 100 μg/ml of streptomycin (Pen/Strep 1% (Sigma Co.)). IAV [A/Puerto Rico/8/1934 (H1N1) (ATCC VR-1469™)] was provided by the Influenza and Respiratory Viruses Department, Pasteur Institute of Iran. The virus infectivity dose as the 50% cell culture infectious dose (CCID50) was determined using the Karber method (24, 25).

Cytotoxicity assay

All the fractions were exposed to the MDCK cells at different concentrations (3.125, 1.562, 0.781, 0.390, 0.195, 0.097, 0.048, 0.024, 0.012, 0.006, and 0.003 mg/ml) and incubated at 37°C, 5% CO2 incubator for 48 hr. Then, the culture medium was removed, and 100 μl of MTT 1X [3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide; Sigma, USA] was added to the cells and incubated for 3 to 4 hr in the dark. Following this time, 100 μl of DMSO was added to dissolve the precipitates of formazan in purple color. A microplate reader (BioTek EL 800, US) was set to record the optical density (OD) at 540 nm, and the cell viability was measured based on the following formula:

Cell viability = (mean OD of treated cells/mean OD of control cells) × 100

The concentration that caused visible morphological changes in 50% of the cells was defined as CC50. MTT data were analyzed with SPSS software, and related graphs were plotted to find NCTC for each sample. Also, the selectivity index (SI) that represents the safety of each extract was calculated by the division of CC50 to NCTC (26).

Antiviral assay

Three combination treatments of co-, pre-, and post-penetration were evaluated to determine the antiviral ability of the fractions. For the co-penetration treatment, 100TCID50 (Tissue Culture Infectious Dose 50%, which is defined as the dilution of virus required to infect 50% of a given cell culture) of the virus was mixed with NCTCs for 30 min and then exposed to MDCK cells in 96-well plates and incubated for 1 hr. For the other two procedures, the virus was added to the cells after (pre-) and before (post-) the fractions following 1 hr incubation. Finally, unabsorbed viruses were replaced by Tosyl phenylalanyl chloromethyl ketone (TPCK)-containing medium (1 µg/ml), and all the plates were incubated for 48 hrs. The MTT assay was performed to measure cellular protection against virus infection in an antiviral assay. Concurrently, the hemagglutination assay (HA) was used to determine the virus titer in the supernatants (25).

The percentage of protection was calculated by SPSS using MTT data of cell viabilities after 48 hrs of exposure by the following formula:

Percentage of protection= [(ODT) V − (ODC) V] / [(ODC)M − (ODC) V] × 100

Where (ODT) V, (ODC) V and (ODC) M represent the absorbance of the treated sample, the virus-infected control (no compound) and the negative control (mock) (27).

Hemagglutination assay (HA)

HA assay was used to determine the virus titer. Briefly, 100 μl of each supernatant was added to a 96-well U-shaped microplate, and 2-fold serial dilutions were prepared using 50 μl PBS in each well. Then, chicken RBC (cRBC) 1% was added to all wells and stayed at room temperature for 1 hr. The formation of clots showed the absence of the virus. HA units were the reciprocal of the highest dilution giving complete agglutination with cRBC (28).

Hemagglutination inhibition assay (HI)

Two-fold serial dilutions from CC50 of each fraction were prepared to investigate the inhibitory outcome of the fractions on the hemagglutinin (HA) glycoprotein activity and then 4HA units of the virus particles were added to each well. Forty-five min of pre-incubation at room temperature was needed. Then, cRBC was added to each well. After 1 hr, the physical interaction between the fractions and virus surface HA glycoprotein was measured.

Statistical analysis

The results of cell protection and the logarithm of HA decrement were analyzed by one-way ANOVA and Fisher’s LSD post hoc test using IBM SPSS Statistics 23 (P-value <0.05).

Separation, isolation, and identification

According to the results of total phenol, flavonoid content, and antiviral assays, S. pinnatifida subsp. viridis was considered as the potent species collected from the Zarabad region, Qazvin province, Iran. Therefore, this species was selected for the phytochemical analysis. First, Diaion HP-20 resin was used for the purification of polyphenols. It adsorbed 10 g of the total extract. Non-phenolic compounds were washed out with distilled water, and phenolic compounds were eluted by methanol (100%), which was named methanol fraction.

Separation and isolation of the methanol fraction of S. pinnatifida subsp. viridis was as follows: 3 g of methanol fraction (A) was loaded on a reversed-phase silica gel column (3 × 30 cm) and eluted with water: methanol (8:2) to methanol 100%. Compound 1 (21.2 mg) was elucidated from sub-fraction No. 16. Sub-fraction No. 8 (A8; 271.1 mg) was selected for the next stage. Sub-fraction A8 was loaded on reversed-phase silica gel (2 × 35 cm) and washed out by water: methanol (8:2) to pure methanol. According to the TLC investigation, sub-fraction A8f (3.2 mg) was a pure compound (Compound 2).

Sub-fraction A4 (165.7 mg) and A28 (48 mg) were loaded on Sephadex LH-20 (1.5 cm × 60 cm), respectively. The columns were rinsed with methanol (100%). Compound 3 (28.1 mg) and compound 4 (2 mg) appeared as one spot on TLC paper under UV radiation and by coloring with an anisaldehyde solution reagent. A4b (48 mg) was loaded on a reversed-phase silica gel column (3 × 30 cm) with gradient solvent from pure water to pure methanol and compound 5 (3.4 mg) was elucidated as A4b (15 mg).

After separation, isolation and purification steps, the compounds were identified by different spectroscopic methods, including UV, 1H-NMR, and 13C-NMR.

Results

Total phenol content

The total phenol content of different species of Scutellaria was determined by the Folin-ciocalteau method and reported based on the Gallic acid equivalent.

Total flavonoid content

The presence of flavonoids in fractions caused an orange color in the sample due to the formation of an aluminum-flavonoid complex. Data were reported as mg of catechin per gram of fraction. The total phenol and flavonoid content of each species of Scutellaria is summarized in Table 2.

Table 2.

Total phenol and flavonoid contents of different species of Scutellaria

Scutellaria samples* Total Phenol Contents
(mg gallic acid/ g fraction)		 Total flavonoid Contents
(mg catechin/ g fraction)
Chloroform Barajin 224.4±1.6 41.9±4.6
Zarabad 160.6±5. 9 226.7±6.3
Bahram abad 118.6±5.9 226.4±5.7
Tehran 95.2±2.5 199.9±2.0
Shahroud 117.1±7.5 168.1±3.8
Gorgan 89.0±2.3 54.7±8.9
Ramsar 89.7±0.6 88.9±9.5
Kashan 158.4±4.2 164.1±0.8
Takab 141.9±4.1 121.1±2.7
Methanol Barajin 616.1±4.6 283.9±4.1
Zarabad 284.6±2.2 402.5±9.5
Bahram abad 413.3±7.8 397.2±1.6
Tehran 224.7±5.9 253.9±4.5
Shahroud 348.9±3. 6 236.4±3.4
Gorgan 72.7±1.5 30.1±3.5
Ramsar 59.7±1.3 83.6±5.3
Kashan 250.0±2.6 352.6±1.6
Takab 216.6±5.6 253.9±1.7
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* Barajin: S. pinnatifida subsp. mucida, Zarabad: S. pinnatifida subsp. viridis, Bahram abad: S. pinnatifida subsp. viridis, Pardis: S. pinnatifida subsp. viridis, Shahroud: S. pinnatifida subsp. alpina, Gorgan: S. tournefortii, Ramsar: S. tournefortii, Kashan: S. tomentosa, Takab: S. persica

Cytotoxicity and antiviral activity of the compounds

This study tested the efficacy of chloroform and methanol fractions of the selected traditional Iranian plants against IAV. The cytotoxicity of the fractions was evaluated. The CC50 and NCTC of the fractions were defined before the antiviral assay. The ability of different fractions to reduce viral titer and the viral cytopathic effects varied as determined by the HA and MTT assays. The cytotoxicity profile of the fractions used in this study is listed in Table 3.

Table 3.

Cytotoxicity evaluation of different fractions of Scutellaria species

Scutellaria samples CC 50 ± (SD) (µg/ml) * NCTC ± (SD) (µg/ml) ** Selectivity Index
Chloroform
Fraction 		Barajin 37.07±(0.71) 18.50±(0.0) 2
Zarabad 344.86±(58.43) 43.12±(0.0) 8
Bahram abad 239.41±(0.90) 3.73±(0.0) 64.18
Pardis 164.03±(0.62) 82.00±(0.0) 2
Shahroud 159.419±(0.55) 79.50±(0.0) 2
Gorgan 771.74±(2.89) 386.00±(0.0) 2
Ramsar 92.97±(1.16) 23.25±(0.0) 4
Kashan 169.01±(0.26) 2.64±(0.0) 64.02
Takab 54.23±(0.49) 27.00±(0.0) 2
Methanol
Fraction 		Barajin 44.25±(1.33) 6.00±(0.0) 7.37
Zarabad 225.04±(0.15) 14.06±(0.0) 16
Bahram abad 5064.27±(1.27) 633.00±(0.0) 8
Pardis 41.99±(2.15) 21.00±(0.0) 2
Shahroud 80.19±(2.84) 40.00±(0.0) 2
Gorgan 3.07±(0.19) 1.50±(0.0) 2
Ramsar 6157.12±(1.02) 384.81±(0.0) 16
Kashan 142.94±(8.68) 35.75±(0.0) 4
Takab 141.97±(2.26) 97.00±(0.0) 1.46
Amantadine hydrochloride 197.01±(1.53) 98.50 2
Oseltamivir carboxylate 788.50±(6.01) 394.25 2
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*CC50: Cytotoxic concentration 50 %; **NCTC: Non-cytotoxic concentration, Barajin: S. pinnatifida subsp. mucida, Zarabad: S. pinnatifida subsp. viridis, Bahram abad: S. pinnatifida subsp. viridis, Pardis: S. pinnatifida subsp. viridis, Shahroud: S. pinnatifida subsp. alpina, Gorgan: S. tournefortii, Ramsar: S. tournefortii, Kashan: S. tomentosa, Takab: S. persica

Among the chloroform fractions, S. tournefortii (Gorgan) and S. pinnatifida subsp. mucida (Barajin) showed the highest (771.74±2.89 µg/ml) and the lowest (37.07±0.71 µg/ml) CC50 values, respectively. Among methanol fractions, the highest and the lowest CC50 values were obtained with S. tournefortii (Ramsar) (6157.12±1.02 µg/ml) and S. tournefortii (Gorgan) (3.07±0.19 µg/ml), respectively.

The percentage of cell protection was a factor in demonstrating cell viability in the presence of the influenza virus. All samples, except the methanol fraction of S. pinnatifida subsp. viridis (Zarabad) (17.36±3.72 %), and chloroform fraction of S. persica (Takab) (23.16±6.29 %) showed optical absorption over 0.5 in co-penetration treatment. In pre-penetration treatment, all samples demonstrated optical absorption above 0.5. In post-penetration treatment, methanol fraction of S. pinnatifida subsp. viridis (Kamard) (29.17±1.53 %) and S. percisa (Takab) (33.78±3.84 %) showed optical absorption over 0.5, which represents cell protection. Oseltamivir as positive control had optical absorption over 1.00 in all treatments. Statistical analyses demonstrated significant differences between pre-, co-, and post-penetration treatment groups and the control group in cell viability percentage with P-value<0.05 (Figure 1). So, the samples with a cell protection percentage over 40% were suitable candidates for the anti-influenza effect. Therefore, to obtain the potent extracts or fractions of Scutellaria with an anti-influenza effect, the percentage of cell protection was examined along with the hemagglutination.

Figure 1.

Figure 1

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Percentage of cell protection of different fractions of Scutellaria species in combination treatment against influenza A virus (S: Scutellaria, Chl: Chloroform, Met: Methanol, F: Fraction. Barajin: S. pinnatifida subsp. mucida, Zarabad: S. pinnatifida subsp. viridis, Bahram abad: S. pinnatifida subsp. viridis, Pardis: S. pinnatifida subsp. viridis, Shahroud: S. pinnatifida subsp. alpina, Gorgan: S. tournefortii, Ramsar: S. tournefortii, Kashan: S. tomentosa, Takab: S. persica, a: Significant difference between treatment group and control with P<0.01, b: Significant difference between treatment group and control with P<0.05)

The fractions could decrease viral hemagglutinin activity, and HA logarithm decrement demonstrated the potency of the extracts or fractions. Regarding HA results, in co-penetration treatment, methanol fraction of Zarabad (5.00±0.82) and S. tomentosa (Kashan) (5.00±0.82) reduced the virus titer by 5 logs, and amantadine reduced the virus titer by 7 logs. In pre-penetration treatment, the methanol fraction of S. pinnatifida subsp. viridis (Bahram abad) and Takab reduced the virus titer by 4.5 logs. In post-penetration treatment, the methanol fraction of Takab, and chloroform fraction of Zarabad reduced the virus titer by 5 logs. Oseltamivir reduced virus titers by 8 logs in all treatments. Statistical analyses demonstrated significant differences between pre-, co-, and post-penetration treatment groups and the control group in HA-log decrement with P-value < 0.05 (Figure 2).

Figure 2.

Figure 2

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Anti-influenza A effects of different fractions of Scutellaria species (Log HA: Logarithm of Hemagglutinin, S: Scutellaria, Chl: Chloroform, Met: Methanol, F: Fraction. Barajin: S. pinnatifida subsp. mucida, Zarabad: S. pinnatifida subsp. viridis, Bahram abad: S. pinnatifida subsp. viridis, Pardis: S. pinnatifida subsp. viridis, Shahroud: S. pinnatifida subsp. alpina, Gorgan: S. tournefortii, Ramsar: S. tournefortii, Kashan: S. tomentosa, Takab: S. persica, a: Significant difference between treatment group and control with P<0.01, b: Significant difference between treatment group and control with P<0.05)

Phytochemical study

Ultraviolet and 1H-NMR spectra of the compounds were investigated and demonstrated as follows:

Compound 1: Kaempferol-3-O-glucoside or Astragalin, brownish yellow color, UV λmax-nm MeOH: 265, 348 nm, 1H-NMR (500 MHz, DMSO-d6): δ 8.08 (2H, dd, J=8, 2 Hz, H-2′, H-6′), 7.60 (2H, dd, J=8, 2 Hz, H-3′, H-5′), 7.06 (1H, d, J=2 Hz, H-8), 7.01 (1H, d, J=2 Hz, H-6), 5.18 (1H, d, J=7.7 Hz, anomeric hydrogen of glucose), 3.5-4.5 (hydrogens of glucose) (Suppl. Figure 1).

Compound 2: Quercetin-3-O-glucoside, brownish yellow color, UV λmax-nm MeOH: 275, 335 nm, 1H-NMR (500MHz, DMSO-d6): δ 7.50 (2H, d, J=2 Hz, H-2′, H-6′), 6.93 (1H, d, J=8 Hz, H-5′), 6.72 (1H, d, J=2 Hz, H-8), 6.64 (1H, d, J=2 Hz, H-6), 4.94 (1H, d, J=7.5 Hz, anomeric hydrogen of glucose), 3.5-4.5 (hydrogens of glucose) (Suppl. Figure 2).

Compound 3: Luteolin-7-O-glucoside, dark yellow color UV λmax-nm MeOH: 255, 349 nm, 1H-NMR (500 MHz, DMSO-d6): δ 7.43 (2H, dd, J=8, 2 Hz, H-2′, H-6′), 6.90 (2H, d, J=8 Hz, H-5′), 6.80 (1H, d, J=2 Hz, H-8), 6.74 (1H, s, H-3), 6.45 (1H, d, J=2 Hz, H-6), 5.19 (1H, d, J=7.5 Hz, anomeric hydrogen of glucose), 3.5-4.5 (hydrogens of glucose) (Suppl. Figure 3).

Compound 4: Luteolin, yellow color, UV λmax-nm MeOH: 264, 357 nm, 1H-NMR (500 MHz, DMSO-d6): δ 7.40 (1H, dd, J=8, 2 Hz, H-6′), 7.36 (1H, d, J=2 Hz, H-2′), 6.82 (1H, d, J=8 Hz, H-5′), 6.60 (1H, s, H-3), 6.39 (1H, d, J=2 Hz, H-8), 6.13 (1H, d, J=2 Hz, H-6) (Suppl. Figure 4).

Compound 5: Tilianin or Acacetin-7-O-glucoside or Apigenin-4′-methoxy-7-O-glucoside, pale yellow color, UV λmax-nm MeOH: 272, 341 nm, 1H-NMR (500 MHz, DMSO-d6): δ 7.45 (2H, dd, J=8, 2 Hz, H-2′, H-6′), 7.06 (1H, s, H-3), 6.90 (2H, dd, J=8 , 2 Hz, H-3′, H-5′), δ 6.67 ppm (1H, d, J=2 Hz, H-8), δ 6.36 ppm (1H, d, J=2 Hz, H-6), δ 5.18 ppm (1H, d, J=7.7 Hz, anomeric hydrogen of glucose), δ 3.5-4.5 ppm (hydrogens of glucose), δ 3.81 ppm (3H, s, 4′-OCH3) (Suppl. Figure 5). The structures of the flavonoid compounds are demonstrated in Figure 3.

Figure 3.

Figure 3

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Elucidated compounds from Scutellaria pinnatifida subsp. viridis

Discussion

Medicinal plants have been used against various ailments, particularly infectious diseases. Medicinal plants have progressively been noticed as suitable alternatives to synthetic antiviral agents.

One of the important effects of the Scutellaria genus has been the antiviral effect in East Asia, especially in Traditional Chinese Medicine (TCM) (29). Scutellaria species have different uses in traditional and folklore medicine. In this study, various Iranian endemic species of Scutellaria were compared based on the total phenol and flavonoid contents and their antiviral capacity against the IAV (H1N1). This genus was introduced as a source of flavonoids, so until 2010, out of 295 identified compounds, 164 belonged to the flavonoids class (11). Several literatures investigated the antiviral activity of some flavonoids such as baicalin, baicalein, wogonin, ganhuangenin, oroxylin A, scutellarin isolated from Scutellaria baicalensis (11). Flavonoids, as a secondary metabolite of plants, are found in all parts of the plants (root, stem, leaf, and flower). Flavonoids have shown protective potential against injuries, pathogens, and UV radiation (30). In humans, this class of phenolic compounds participates in anti-inflammatory, anti-allergic, anti-thrombotic, anti-diabetic, antiviral, antimicrobial, anti-carcinogenic, hepatoprotective, cardioprotective, neuroprotective, and anti-oxidant properties (21). Also, flavonoids have shown anti-platelet aggregation activities (31) and cancer-preventive effects (32). Flavonoids are composed of two pathways. The A ring is synthesized from the acetate pathway, including resorcinol or phloroglucinol molecules, and the B ring is synthesized from the shikimate pathway, including shikimic acid (33, 34). Flavonoids are potent anti-oxidants due to the presence of hydroxyl groups in the A and B rings, a 4-oxo functional group in the C ring, their ability to chelate divalent and trivalent cations, and changing the redox chemistry of chelating agents (35). The results of this study demonstrated that methanol fractions of different varieties of S. pinnatifida subsp. viridis have considerable amounts of phenols and flavonoids. Due to the polarity of flavonoids, they were more likely to present in methanol than in chloroform fraction. Each sample of Scutellaria species with a selectivity index of 2 or above, cell protection percentage of 40 % or above, and log HA decrement of 4.00 or above was considered a suitable candidate for the potential anti-influenza activity. The current study indicated that treatment of IAV with the selected extracts and compounds reduced the hemagglutination activity of the virus, which may result from the physical interaction of the extracts with the virus hemagglutinin. Five flavonoids were isolated and identified by different spectroscopic methods: luteolin and luteolin-7-O-glucoside, quercetin-3-O-glucoside, kaempferol-3-O-glucoside, and apigenin-4′-methoxy-7-O-glucoside.

Luteolin and luteolin derivatives are the most common flavonoids in edible plants such as Daucus carota L. (carrot), Capsicum annuum L. (peppers), Apium graveolens L. (celery), Olea europaea L. (olive), Lactuca sativa L. (lettuce), Punica granatum L. (pomegranate), Theobroma cacao L. (cacao), Capparis spinosa L. (capers), and Cucumis sativus L. (cucumber). Literature has attributed neuroprotective, anti-inflammatory, anti-diabetic, anti-oxidant, and anti-cancer effects to luteolin and luteolin derivatives (36). The addition of a double bond between carbon 2 and 3 in the C ring of eriodictyol by flavone synthase results in luteolin formation. Another pathway to luteolin formation is adding a hydroxyl group to apigenin by flavonoid 3′-hydroxylase (37). Luteolin can be absorbed in the small intestine and its metabolism pathway, including glucuronidation and sulfation, occurs in the liver (38). The excretion of luteolin in urine is very low. Therefore, the main route of luteolin elimination is via feces (39). The antiviral mechanism of luteolin is unclear yet. But, due to the structural similarity between quercetin and luteolin, the ability to binding to the S2 protein of coronavirus is expected (40).

Quercetin is another flavonoid that is present in Scutellaria genus. Quercetin and its derivatives showed several effects, such as anti-microbial, anti-cancer, anti-oxidant, and prevention of cardiovascular and immunomodulatory diseases (41, 42). Also, quercetin has demonstrated a considerable effect on SARS and MERS viruses, which has been suggested for treating the coronavirus known as COVID-19 (43). Theobroma cacao L. (cacao), Vaccinium myrtillus L. (cranberry),  V. vitis-idaea L. (lingonberry), Brassica oleracea L. (kale, broccoli), Apium graveolens L. (celery), Lactuca sativa L. (lettuce), Solanum lycopersicum L. (tomato), Daucus carota L. (carrot), and Ginkgo biloba L. (Maidenhair tree) are foods rich in quercetin (44). This flavonoid is formed from two biosynthesis pathways. In the first pathway, kaempferol is formed as an intermediate compound. A hydroxyl group is added to kaempferol by kaempferol 3′-monooxygenase enzyme and 3′,4′-dihydroxy kaempferol is formed as quercetin. In the second pathway, dihydrokaempferol 3′-hydroxylase synthesizes taxifolin. Then, taxifolin is converted to quercetin by quercetin synthase (45). Research has shown the microflora of the large intestine can cleave flavonoids into phenylpropionic acid, phenylacetic acid, and some other compounds (46). According to previous studies, quercetin is eliminated through feces as aglycone (42). One possible mechanism of quercetin has been found to be the inhibition of mRNA synthesis and M2 protein expression in IAV infection (47).

Astragalin (kaempferol-3-O-glucoside) is widely distributed in plants. The source of kaempferol and its derivatives in edible plants is Allium cepa L. (onion), Brassica oleracea L. (broccoli), Petroselinum crispum (Mill.) Fuss. (parsley), Lactuca sativa L. (lettuce), Spinacia oleracea L. (spinach), Rubus idaeus L. (raspberry), Fragaria vesca L. (strawberry), Malus domestica Borkh. (apple), Solanum lycopersicum L. (tomato), Citrus paradisi Macfad. (grapefruit), Pistacia vera L. (pistachio), and Vitis vinifera L. (grape). (48). Kaempferol and its derivatives showed anti-oxidant, anti-inflammatory, anti-cancer, anti-diabetic, cardioprotective, and neuroprotective effects (48, 49). Recent studies demonstrated that kaempferol and quercetin might execute beneficial effects on the treatment or control of coronavirus (COVID-19) by inhibiting and phosphorylating protein kinase A (50). In the biosynthesis pathway of kaempferol, flavonone-3-dioxygenase enzyme adds a hydroxyl group to C3, and dihydrokaempferol is formed. Then, flavone synthase enzyme forms a double bond in C2-C3 position to produce kaempferol. Adding a glucose molecule by flavonol-3-O-glucosyltrasferase led to the formation of astragalin (51). Kaempferol (IC50= 0.5 μM) was a potent anti-oxidant by scavenging free radicals and reducing the hydroxyl ions (52, 53). Kaempferol and its derivatives are absorbed in the small intestine by facilitated or passive diffusion or active transport. The kaempferol is metabolized by glucuronidation in the liver and colon microflora and its excretion occurs through urine (54).

Acacetin and other apigenin derivatives are abundant in Achillea millefolium L. (Yarrow), Apium graveolens L. (Celery), Artemisia dracunculus L. (Tarragon), Coriandrum sativum L. (Cilantro), Digitalis purpurea L. (Purple foxglove), Gingko biloba (Maidenhair tree), Glycyrrhiza glabra L. (Licorice), Linum usitatissimum L. (flax), Matricaria chamomilla L. (chamomile), Mentha spicata L. (Spearmint), Ocimum basilicum L. (Basil), and Origanum vulgare L. (Oregano) (55). Apigenin and its derivatives have shown anti-oxidant, anti-cancer, anti-inflammatory, anti-mutagenic, hepatoprotective, anti-microbial, and neuroprotective effects (44, 56). Apigenin 4′-O-methyltransferase synthesizes 4′-methoxy apigenin, known as acacetin. This flavonoid is isolated from Chrysanthemum morifolium for the first time (57). Apigenin is absorbed in the small intestine and is metabolized by glucuronidation and sulfation in liver tissue (58). The elimination of apigenin is through urine and feces (59). A study showed the antiviral effect of apigenin on influenza virus type A, which protected cells from death and suppressed replication of IAV by inhibiting the neuraminidase of the virus (60).

Conclusion

Based on this scientific confirmation, the Methanol fraction of S. pinnatifida subsp. viridis and methanol fraction of S. tomentosa that showed the best antiviral activity might have the capacity to ease the symptoms and burden of the flu infection. Recommendations are proposed for strategizing the future role and place for medicinal plants against influenza infection and other infectious diseases prevention and therapy in national, regional, and international health policies and programs. Antiviral effects of Scutellaria species and also isolation and identification of some flavonoids such as apigenin, kaempferol, quercetin, and luteolin and their derivatives from Iranian species of Scutellaria, introduced this genus, especially S. pinnatifida due to wide geographical distribution in Iran, as a potent candidate for the treatment of influenza A virus/H1N1. Also, these flavonoids can be used as supplements to prevent viral diseases such as influenza, and COVID-19. For the first time, anti-influenza virus effect of some Iranian species of Scutellaria was investigated and these flavonoids (kaempferol, apigenin, quercetin, and luteolin) were isolated from Scutellaria pinnatifida subsp. viridis. The next focus of this study will be the purification of pure compounds responsible for the bioactivity against IAV infection and their mode of action. As well, S. pinnatifida can be introduced as a new source for treating or preventing influenza virus as an alternative medicine or in combination with other anti-influenza drugs.

Authors’ Contributions

ZT, and PM Study conception and design; MPH, and MAK Data processing, collection, perform experiment; MPH, and HSh Analysis and interpretation of results; MPH, MAK, HSh Draft manuscript preparation; SG, MShA, AH, MPH, and MHGh Critical revision or editing of the article; ZT, and PM Final approval of the version to be published; ZT, and SG Supervision funding acquisition.

Conflicts of Interest

The authors declare that there is no conflict of interest.

Acknowledgment

This research was part of PharmD and PhD theses and supported by Tehran University of Medical Sciences and Health Services Grants (No. 98-01-33-41878) and (No. 99-3-12050930).

References

  • 1.Ding Y, Dou J, Teng Z, Yu J, Wang T, Lu N, et al. Antiviral activity of baicalin against influenza A (H1N1/H3N2) virus in cell culture and in mice and its inhibition of neuraminidase. Arch Virol. 2014;159:3269–3278. doi: 10.1007/s00705-014-2192-2. [DOI] [PubMed] [Google Scholar]
  • 2.Kshatriya R, Khara N, Ganjiwale J, Lote S, Patel S, Paliwal R. Lessons learnt from the Indian H1N1 (swine flu) epidemic: Predictors of outcome based on epidemiological and clinical profile. J Family Med Primary Care. 2018;7:1506–1509. doi: 10.4103/jfmpc.jfmpc_38_18. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 3.Boltz DA, Aldridge JR, Webster RG, Govorkova EA. Drugs in development for influenza. Drugs. 2010;70:1349–1362. doi: 10.2165/11537960-000000000-00000. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 4.Kim Y, Narayanan S, Chang KO. Inhibition of influenza virus replication by plant-derived isoquercetin. Antiviral Res. 2010;88:227–235. doi: 10.1016/j.antiviral.2010.08.016. [DOI] [PubMed] [Google Scholar]
  • 5.Mehrbod P, Hudy D, Shyntum D, Markowski J, Łos MJ, Ghavami S. Quercetin as a natural therapeutic candidate for the treatment of influenza virus. Biomol. 2021;11:10–38. doi: 10.3390/biom11010010. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 6.Lee JY, Abundo MEC, Lee CW. Herbal medicines with antiviral activity against the influenza virus, a systematic review. Am J Chin Med. 2018;46:1663–1700. doi: 10.1142/S0192415X18500854. [DOI] [PubMed] [Google Scholar]
  • 7.Lee NK, Lee JH, Lim SM, Lee K, Kim Y, Chang PS, et al. Antiviral activity of subcritical water extract of Brassica juncea against influenza virus A/H1N1 in nonfat milk. J Dairy Sci. 2014;97:5383–5386. doi: 10.3168/jds.2014-8016. [DOI] [PubMed] [Google Scholar]
  • 8.Torabian G, Valtchev P, Adil Q, Dehghani F. Anti-influenza activity of elderberry (Sambucus nigra) J Funct Food. 2019;54:353–560. [Google Scholar]
  • 9.Akram M, Tahir IM, Shah SMA, Mahmood Z, Altaf A, Ahmad K, et al. Antiviral potential of medicinal plants against HIV, HSV, influenza, hepatitis, and coxsackievirus: A systematic review. Phytother Res. 2018;32:811–822. doi: 10.1002/ptr.6024. [DOI] [PubMed] [Google Scholar]
  • 10.Ji S, Li R, Wang Q, Miao WJ, Li ZW, Si LL, et al. Anti-H1N1 virus, cytotoxic and Nrf2 activation activities of chemical constituents from Scutellaria baicalensis. J Ethnopharmacol. 2015;176:475–484. doi: 10.1016/j.jep.2015.11.018. [DOI] [PubMed] [Google Scholar]
  • 11.Shang X, He X, He X, Li M, Zhang R, Fan P, et al. The genus Scutellaria an ethnopharmacological and phytochemical review. J Ethnopharmacol. 2010;128:279–313. doi: 10.1016/j.jep.2010.01.006. [DOI] [PubMed] [Google Scholar]
  • 12.Pirali Hamedani M, Yousefi H, Tajabadi F, Tofighi Z, Hadjiakhoundi A, Goodarzi S. Chemical composition of the essential oils and aromatic waters of some native Scutellaria species from Iran. J Med Plant. 2022;21:12–21. [Google Scholar]
  • 13.Ghannadi A, Mehregan I. Essential oil of one of the Iranian skullcaps. Zeitschrift für Naturforschung C. 2003;58:316–318. doi: 10.1515/znc-2003-5-604. [DOI] [PubMed] [Google Scholar]
  • 14.Cai YZ, Sun M, Xing J, Luo Q, Corke H. Structure–radical scavenging activity relationships of phenolic compounds from traditional Chinese medicinal plants. Life Sci. 2006;78:2872–2888. doi: 10.1016/j.lfs.2005.11.004. [DOI] [PubMed] [Google Scholar]
  • 15.EghbaliFeriz S, Taleghani A, Tayarani-Najaran Z. Central nervous system diseases and Scutellaria: a review of current mechanism studies. Biomed Pharmacother. 2018;102:185–195. doi: 10.1016/j.biopha.2018.03.021. [DOI] [PubMed] [Google Scholar]
  • 16.J ian X, Liu Y, Zhao Z, Zhao L, Wang D, Liu Q. The role of traditional Chinese medicine in the treatment of atherosclerosis through the regulation of macrophage activity. Biomed Pharmacother. 2019;118:109375. doi: 10.1016/j.biopha.2019.109375. [DOI] [PubMed] [Google Scholar]
  • 17.Shen J, Li P, Liu S, Liu Q, Li Y, Sun Y, et al. Traditional uses, ten-years research progress on phytochemistry and pharmacology, and clinical studies of the genus Scutellaria. J Ethnopharmacol. 2021;265:113198. doi: 10.1016/j.jep.2020.113198. [DOI] [PubMed] [Google Scholar]
  • 18.Hertog MG, Feskens EJ, Kromhout D, Hollman P, Katan M. Dietary anti-oxidant flavonoids and risk of coronary heart disease: the Zutphen Elderly Study. Lancet. 1993;342:1007–1011. doi: 10.1016/0140-6736(93)92876-u. [DOI] [PubMed] [Google Scholar]
  • 19.Zhang XL, Guo YS, Wang CH, Li GQ, Xu JJ, Chung HY, et al. Phenolic compounds from Origanum vulgare and their anti-oxidant and antiviral activities. Food Chem. 2014;152:300–306. doi: 10.1016/j.foodchem.2013.11.153. [DOI] [PubMed] [Google Scholar]
  • 20.Mazza G, Miniati E. CRC Press: Boca Raton. 1993. Small fruits; pp. 85–129. [Google Scholar]
  • 21.Tapas AR, Sakarkar D, Kakde R. Flavonoids as nutraceuticals: a review. Trop J Pharm Res. 2008;7:1089–1099. [Google Scholar]
  • 22.Yassa N, Beni HR, Hadjiakhoondi A. Free radical scavenging and lipid peroxidation activity of the Shahani black grape. Pak J Biol Sci. 2008;11:2513–2516. doi: 10.3923/pjbs.2008.2513.2516. [DOI] [PubMed] [Google Scholar]
  • 23.Sulaiman C, Balachandran I. Total phenolics and total flavonoids in selected Indian medicinal plants. Indian J Pharm Sci. 2012;74:258–260. doi: 10.4103/0250-474X.106069. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 24.Faisst S. Propagation of viruses Animal. Encyclopedia of Virology. 1999. pp. 1408–1413. [Google Scholar]
  • 25.Mehrbod P, Abdalla MA, Njoya EM, Ahmed AS, Fotouhi F, Farahmand B, et al. South African medicinal plant extracts active against influenza A virus. BMC Complementary Altern Med. 2018;18:1–10. doi: 10.1186/s12906-018-2184-y. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 26.Chattopadhyay D, Chawla-Sarkar M, Chatterjee T, Dey RS, Bag P, Chakraborti S, et al. Recent advancements for the evaluation of antiviral activities of natural products. New Biotechnol. 2009;25:347–368. doi: 10.1016/j.nbt.2009.03.007. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 27.Shigeta S, Mori S, Watanabe J, Soeda S, Takahashi K, Yamase T. Synergistic anti-influenza virus A (H1N1) activities of PM-523 (polyoxometalate) and ribavirin in vitro and in vivo. Antimicrob Agents Chemother. 1997;41:1423–1427. doi: 10.1128/aac.41.7.1423. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 28.Hirst GK. The quantitative determination of influenza virus and antibodies by means of red cell agglutination. J Exp Med. 1942;75:49–64. doi: 10.1084/jem.75.1.49. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 29.Organization WH. Index of Pharmacopoeias. World Health Organization; 2002. [Google Scholar]
  • 30.Falcone Ferreyra ML, Rius S, Casati P. Flavonoids: biosynthesis, biological functions, and biotechnological applications. Front Plant Sci. 2012;3:222–236. doi: 10.3389/fpls.2012.00222. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 31.Faggio C, Sureda A, Morabito S, Sanches-Silva A, Mocan A, Nabavi SF, et al. Flavonoids and platelet aggregation: A brief review. Euro J Pharmacol. 2017;807:91–101. doi: 10.1016/j.ejphar.2017.04.009. [DOI] [PubMed] [Google Scholar]
  • 32.Romagnolo DF, Selmin OI. Flavonoids and cancer prevention: a review of the evidence. J Nut Gerontol Geriatrics. 2012;31:206–238. doi: 10.1080/21551197.2012.702534. [DOI] [PubMed] [Google Scholar]
  • 33.Croft KD. The chemistry and biological effects of flavonoids and phenolic acids a. Ann N Y Acad Sci. 1998;854:435–442. doi: 10.1111/j.1749-6632.1998.tb09922.x. [DOI] [PubMed] [Google Scholar]
  • 34.Harborne JB, Grayer RJ. The anthocyanins. The flavonoids. Springer: 1988. pp. 1–20. [Google Scholar]
  • 35.Gao Z, Huang K, Yang X, Xu H. Free radical scavenging and anti-oxidant activities of flavonoids extracted from the radix of Scutellaria baicalensis Georgi. Biochim Biophys Acta (BBA)-General Subjects. 1999;1472:643–650. doi: 10.1016/s0304-4165(99)00152-x. [DOI] [PubMed] [Google Scholar]
  • 36.Nabavi SF, Braidy N, Gortzi O, Sobarzo-Sanchez E, Daglia M, Skalicka-Woźniak K, et al. Luteolin as an anti-inflammatory and neuroprotective agent: A brief review. Brain Res Bull. 2015;119:1–11. doi: 10.1016/j.brainresbull.2015.09.002. [DOI] [PubMed] [Google Scholar]
  • 37.Grignon-Dubois M, Rezzonico B. First phytochemical evidence of chemotypes for the seagrass Zostera noltii. Plant. 2012;1:27–38. doi: 10.3390/plants1010027. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 38.Boersma MG, Van der Woude H, Bogaards J, Boeren S, Vervoort J, Cnubben NH, van Iersel ML, van Bladeren PJ, Rietjens IM. Regioselectivity of phase II metabolism of luteolin and quercetin by UDP-glucuronosyl transferases. Chem Res Toxicol. 2002;15:662–670. doi: 10.1021/tx0101705. [DOI] [PubMed] [Google Scholar]
  • 39.Sarawek S, Derendorf H, Butterweck V. Pharmacokinetics of luteolin and metabolites in rats. Nat Prod Commun. 2008;3:1934578X0800301218. [Google Scholar]
  • 40.Yi L, Li Z, Yuan K, Qu X, Chen J, Wang G, et al. Small molecules blocking the entry of severe acute respiratory syndrome coronavirus into host cells. J Virol. 2004;78:11334–11339. doi: 10.1128/JVI.78.20.11334-11339.2004. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 41.Rauf A, Imran M, Khan IA, ur‐Rehman M, Gilani SA, Mehmood Z, et al. Anticancer potential of quercetin: A comprehensive review. Phytother Res. 2018;32:2109–2130. doi: 10.1002/ptr.6155. [DOI] [PubMed] [Google Scholar]
  • 42.Wang W, Sun C, Mao L, Ma P, Liu F, Yang J, et al. The biological activities, chemical stability, metabolism and delivery systems of quercetin: A review. Trends Food Sci Technol. 2016;56:21–38. [Google Scholar]
  • 43.Derosa G, Maffioli P, D’Angelo A, Di Pierro F. A role for quercetin in coronavirus disease 2019 (COVID‐19) Phytother Res. 2021;35:1230–1236. doi: 10.1002/ptr.6887. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 44.Gupta A, Birhman K, Raheja I, Sharma SK, Kar HK. Quercetin: A wonder bioflavonoid with therapeutic potential in disease management. Asian Pac J Trop Dis. 2016;6:248–252. [Google Scholar]
  • 45.Castro JC, Maddox JD, Cobos M, Paredes JD, Fasabi AJ, Vargas-Arana G, et al. Medicinal Plants of the Peruvian Amazon: Bioactive Phytochemicals, Mechanisms of Action, and Biosynthetic Pathways. Pharmacogn Med Plant. 2018:27–48. [Google Scholar]
  • 46.Brown J. A review of the genetic effects of naturally occurring flavonoids, anthraquinones and related compounds. Mut Res Rev Genet Toxicol. 1980;75:243–277. doi: 10.1016/0165-1110(80)90029-9. [DOI] [PubMed] [Google Scholar]
  • 47.Choi JG, Lee H, Kim YS, Hwang YH, Oh YC, Lee B, et al. Aloe vera and its components inhibit influenza A virus-induced autophagy and replication. Am J Chin Med. 2019;47:1307–1324. doi: 10.1142/S0192415X19500678. [DOI] [PubMed] [Google Scholar]
  • 48.Devi KP, Malar DS, Nabavi SF, Sureda A, Xiao J, Nabavi SM, et al. Kaempferol and inflammation: From chemistry to medicine. Pharmacol Res. 2015;99:1–10. doi: 10.1016/j.phrs.2015.05.002. [DOI] [PubMed] [Google Scholar]
  • 49.Chen AY, Chen YC. A review of the dietary flavonoid, kaempferol on human health and cancer chemoprevention. Food Chem. 2013;138:2099–2107. doi: 10.1016/j.foodchem.2012.11.139. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 50.Khazdair MR, Anaeigoudari A, Agbor GA. Antiviral and anti-inflammatory effects of kaempferol and quercetin and COVID-2019: A scoping review. Asian Pac J Trop Biomed. 2021;11:327–334. [Google Scholar]
  • 51.M Calderon-Montano J, Burgos-Morón E, Pérez-Guerrero C, López-Lázaro M. A review on the dietary flavonoid kaempferol. Mini Rev Med Chem. 2011;11:298–344. doi: 10.2174/138955711795305335. [DOI] [PubMed] [Google Scholar]
  • 52.Wang L, Tu YC, Lian TW, Hung JT, Yen JH, Wu MJ. Distinctive anti-oxidant and anti-inflammatory effects of flavonols. J Agric Food Chem. 2006;54:9798–9804. doi: 10.1021/jf0620719. [DOI] [PubMed] [Google Scholar]
  • 53.Mira L, Tereza Fernandez M, Santos M, Rocha R, Helena Florêncio M, Jennings KR. Interactions of flavonoids with iron and copper ions: a mechanism for their anti-oxidant activity. Free Radical Res. 2002;36:1199–1208. doi: 10.1080/1071576021000016463. [DOI] [PubMed] [Google Scholar]
  • 54.Crespy V, Morand C, Besson C, Cotelle N, Vézin H, Demigné C, et al. The splanchnic metabolism of flavonoids highly differed according to the nature of the compound. Am J Physiol Gastrointestinal Liver Physiol. 2003;284:G980–G988. doi: 10.1152/ajpgi.00223.2002. [DOI] [PubMed] [Google Scholar]
  • 55.Patel D, Shukla S, Gupta S. Apigenin and cancer chemoprevention: progress, potential and promise. Int J Oncol. 2007;30:233–245. [PubMed] [Google Scholar]
  • 56.Wang M, Firrman J, Liu L, Yam K. A review on flavonoid apigenin: Dietary intake, ADME, antimicrobial effects, and interactions with human gut microbiota. Bio Med Res Int. 2019;2019:1–18. doi: 10.1155/2019/7010467. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 57.Hu CQ, Chen K, Shi Q, Kilkuskie RE, Cheng YC, Lee K-H. Anti-AIDS agents 10 Acacetin-7-o-β-D-galactopyranoside, an anti-HIV principle from Chrysanthemum morifolium and a structure-activity correlation with some related flavonoids. J Nat Prod. 1994;57:42–51. doi: 10.1021/np50103a006. [DOI] [PubMed] [Google Scholar]
  • 58.Cai H, Boocock DJ, Steward WP, Gescher AJ. Tissue distribution in mice and metabolism in murine and human liver of apigenin and tricin, flavones with putative cancer chemopreventive properties. Cancer Chemother Pharmacol. 2007;60:257–266. doi: 10.1007/s00280-006-0368-5. [DOI] [PubMed] [Google Scholar]
  • 59.Scalbert A, Williamson G. Dietary intake and bioavailability of polyphenols. J Nut. 2000;130:2073S–2085S. doi: 10.1093/jn/130.8.2073S. [DOI] [PubMed] [Google Scholar]
  • 60.Xu X, Miao J, Shao Q, Gao Y, Hong L. Apigenin suppresses influenza A virus‐induced RIG‐I activation and viral replication. J Med Virol. 2020;92:3057–3066. doi: 10.1002/jmv.26403. [DOI] [PubMed] [Google Scholar]

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