Abstract
Background
Gongronema latifolium leaf is used traditionally to treat diabetes and other diseases. The present study aimed to provide the modulatory effect of G. latifolium on hyperglycemia, inhibitory effect of redox imbalance and inflammation in alloxan-induced nephropathy in Wistar rats.
Methods
Alloxan monohydrate was used to induce diabetes by an intraperitoneal injection of (150 mg/kg). Three diabetic groups were administered aqueous leaf extract of G. latifolium at 6.36, 12.72 and 25.44 mg/kg bodyweight (BW) respectively; a group was administered with metformin (5 mg/kg BW), while the other two were served as positive and negative control. Thereafter, fasting blood glucose, antioxidant enzymes, malondialdehyde (MDA) level, interleukin 2 and 6 were determined.
Results
G. latifolium leaf significantly (p < 0.05) reduced the alloxan-induced increases in blood glucose, MDA, interleukin 2 and interleukin 6 level and increased the alloxan-induced decreases in superoxide dismutase, catalase, glutathione peroxidase, glutathione reduced and glutathione transferase activity. All these changes compared with those of metformin-treated diabetic rats.
Conclusion
The data from this study suggest that G. latifolium modulates glucose homeostasis as well as inhibiting redox imbalance and inflammation in diabetic rats, which may be attributed to the effects of its phytochemical constituents such as saponins, flavonoids and alkaloids. It also indicated that inhibition of inflammatory cytokines and redox imbalance are likely mechanisms by which G. latifolium leaf exert its antidiabetic action.
Keywords: Gongronema latifolium, Diabetic nephropathy, Oxidative stress, Reactive oxygen species, And antioxidant activity
Introduction
Diabetes mellitus (DM) is a metabolic disease characterized by the deficiency of insulin production, insulin action or both, thus leading to hyperglycemia [1]. Its deficiency results in chronic hyperglycemia (high blood glucose) with disorders of major macromolecules metabolism. Implications of diabetes mellitus are long term injury, dysfunction and failure of various organs, especially the pancreas, liver, kidney, eyes (retinopathy), kidneys (nephropathy), nerves (neuropathy), liver, hearts, and blood vessels [2]. Recent estimate revealed that about 455 million people have diabetes worldwide in 2017, a figure that is expected to increase to 693 million by 2045. It was further revealed that about half of the people living with diabetes are undiagnosed. In terms of cost, an estimated USD 850 billion was expended globally on people with diabetes in the same year [3]. In Nigeria, about 11.2 million people are reported to live with diabetes with a prevalence rate of 5.77% [4]. Alloxan induces diabetes by damaging the insulin secreting cells of the pancreas leading to hyperglycemia. It also inhibits the antioxidant enzymes resulting in the activation of free radicals leading to oxidative damage and fragmentation of DNA [5]. Hyperglycemia is central to the pathogenesis of diabetic nephropathy. Diabetic nephropathy results in chronic kidney disease ultimately leads to end stage renal disease (ESRD) which requires renal replacement therapy (RRT) or kidney transplantation [6]. Oxidative stress is a contributing factor to kidney damage by increasing the generation of oxidants due to insufficiency of endogenous antioxidants [6–8].
Oxidative stress and inflammation has been involved in the pathogenic micro- and macro-vascular complications related to type 2 diabetes [9–11]. Excessive production of reactive oxygen species triggers cytokines production, apoptotic proteins, and transcription factors, leading to chronic inflammation and elevated apoptosis, an underlying factor in the development of diabetic complications [12]. Evidence suggests that oxidative damage, pro-inflammatory responses, and apoptosis are key players in pathological conditions relating to diabetic nephropathy [6]. The progression of diabetes mellitus to diabetic nephropathy involves the interplay of several mechanisms: oxidative damage, inflammation, apoptosis and renal dysfunction.
Inflammation is a type of defense and protection from infections and organ damage; though, the unrestrained regulation of immune systems can result in massive tissue damage [13, 14]. Proinflammatory.
cytokines with other indices of inflammation have been revealed to be raised in the kidneys of type-2 diabetes (T2D) patients [15, 16]. Diabetes activates lower levels of systemic inflammation in the nephrocytes as an early response to renal injury because of the overproduction of reactive oxygen species. This systemic inflammation triggers the enlistment of leukocytes and causes the secretion of pro-inflammatory cytokines such as interleukin IL-2 and IL-6 [17]. Furthermore, studies indicate that patients with type 2 diabetes who have no history of coronary artery disease have the same risk for cardiac events as do non-diabetic patients with preexisting coronary artery disease. Therefore, the search for a drug having twofold properties, that is lowering of blood lipids and glucose and mitigating oxidative stress together is of great demand. Despite the remarkable achievement in the management of diabetes by synthetic drugs, there has been a renewed interest in medicinal plants because they do not elicit any side effects.
Gongronema latifolium, generally called “utazi” in Igbo and “arokeke” in Yoruba communities in Nigeria, is a native of south eastern Nigeria [18]. G. latifolium has been widely used in folk medicine as a spice and vegetable and for maintaining healthy blood glucose levels [18, 19]. The south-eastern inhabitants of Nigeria are known for their high consumption of vegetables and some of these vegetables form part of foods consumed on special conditions, including ill health and times of convalescence [20]. This stresses the role of plants in the life of man from past till date. As an old companion of man, it has provided food, shelter, wealth and has helped to maintain a relatively disease free state when properly utilized as herbal medicine [21]. Ugochukwu et al. [22] documented the ethno-medical usage of this plant in managing diabetes mellitus. There are some evidences on normoglycemic, hypolipidemic and antioxidative activity of the plant [23], but not on the uses of this plant based on ethnobotanical survey dosage in managing of diabetes mellitus. Ajiboye et al., [24] also documented the antihyperglycaemia and related gene expressions of aqueous extract of Gongronema latifolium leaf in alloxan-induced diabetic rats. Ogundipe et al. [25] reported that aqueous and ethanolic G. latifolium extracts had hypoglycemic, hypolipidemic and antioxidative properties while Morebise et al. [18] showed that it has anti-inflammatory properties. Also, phytochemical analysis of the leaves extract of Gongronema latifolium revealed the presence of saponins (asterglycosides), flavonoids, glycosides, essential oil, alkaloids [26] as well as vitamins, proteins, fatty acid and minerals like calcium, phosphorus, magnesium, copper and potassium [27, 28]. Since, one of the microvascular complications of diabetes is diabetic nephropathy, it is imperative to use this medicinal plant the way it is being used locally to serve as scientific evidence for used doses (local dosage) in managing diabetic nephropathy in rats. Hence, this study was conducted to assess the ability of Gongronema latifolium leaf extract in modulating hyperglycaemia, inhibiting redox imbalance and inflammation in alloxan-induced diabetic nephropathy in Wistar rats.
Materials and methods
Plant materials and authentication
Gongronema latifolium leaf was purchased in January, 2019 at Ekpoma market, Ekpoma, Edo State, Nigeria. It was recognized and authenticated by a taxonomist at Forestry Research Institute of Nigeria (FRIN), Ibadan, Nigeria with Herbarium number FHI: 112032.
Chemicals and reagents
Alloxan as a diabetogenic agent was purchased from Sigma Chemical Co., St Louis, MO, USA. All other chemicals used in this experiment were secured from Sigma- Aldrich, Inc. (St Louis, MO, USA), while all enzymes assay kits were procured from Randox Laboratories Ltd., Antrim, UK.
Gongronema latifolium aqueous leaf extract preparataion
G. latifolium leaf was dried at 25 °C for 30 days. Then pulverized into powder by an electric blender. The powder sample (200 g) was soaked in 2000 mL of distilled H2O for a day, filtered, and freeze dried to obtain the dried extract. A cup (based on ethnobotanical survey) of the filtrate (250 mL) was freeze dried and the yield obtained was equivalent to the intake of a 70 kg man. This was then extrapolated to get 12.72 mg/kg body weight (equivalent dose of 70 kg man), then multiply by 2 and divided by 2 to get high and low ethnobotanical doses respectively; 25.44 and 6.36 mg/kg body weight according to Yakubu et al. [29]. The extract was weighed in a universal bottle using a weighing balance. The universal bottle containing the weighed extract (88.5 g) was closed and kept at 4 °C for further studies.
Experimental animals
Forty-eight (48) Wistar rats of 120–135 g, acquired from the Animal Holding unit of Afe Babalola University, Ado-Ekiti, Nigeria. The rats were placed on drinkable water, food and room temperature at 25 °C under laboratory conditions (12 h light/dark cycle). This study was approved by ABUAD Animal Ethical Committee (Approval number 19/ABUADSCI/016).
Diabetes induction
Fasting blood glucose levels of each rats were assessed subject to overnight fasting. Then 5 g of alloxan monohydrate was liquefied in 9% saline solution, which was used to induce diabetes mellitus into the rats (by single intraperitoneal injection) at a dose of 150 mg/kg body weight. Forty-eight hours after the induction, fasting blood glucose levels were evaluated via ACCU check glucometer. Rats whose fasting blood glucose level greater than or equal to 250 mg/dL were used [30].
Animal grouping and administration of extract
Forty-eight Wistar rats were randomized into six groups of eight animals as follows:
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Group A:
Non-diabetic rats + distilled water
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Group B:
Diabetic rats + distilled water
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Group C:
Diabetic rats +5 mg/kg body weight of metformin
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Group D:
Diabetic rats +6.36 mg/kg body weight of Gongronema latifolium leaf aqueous extract
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Group E:
Diabetic rats +12.72 mg/kg body weight of Gongronema latifolium leaf aqueous extract
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Group F:
Diabetic rats +25.44 mg/kg body weight of Gongronema latifolium leaf aqueous extract
Treatment of animals with plant extracts and metformin
The plant extract was administered at a dose of (6.36, 12.72 and 25.44 mg/kg) body weight by oral gavage (that is through oesophageal cannula) as well as metformin (5 mg/kg) to the diabetic rats daily for 13 days.
Collection and processing of samples
The rats were sacrificed on the 14th day of administration using cervical dislocation. Then blood was collected from rats for serum analysis. Then allowed to stand at 25 °C for 1800 s (clotting process), centrifuged at 3000 g for 600 s and collected the supernatant. The excised kidney was rinsed with buffer, homogenized with 0.1 M phosphate buffer (pH 6.4) and centrifuged at 4000 g for 15 min. Thereafter, both the serum and obtained homogenate supernatant were properly labelled and kept for different analysis.
Determination of fasting blood glucose
The fasting blood glucose level was determined using the procedure described by [31]. In this method, blood was collected from the tips of the rat’s tail and a drop was placed on the strip inserted into the glucometer to obtain the fasting blood glucose of each rat.
Biochemical analysis
Uric acid, urea, Creatinine determination
Serum uric acid, urea, creatinine and BUN levels were evaluated using the method described by [32].
Catalase determination
Catalase activity was determined based on the method described by [33]. Briefly, 4 mL of H2O2 solution was added to 5 mL of phosphate buffer at pH 7.0 in a 10-mL flat bottom flask. Then, 1 mL of the properly diluted sample was mixed with the reaction mixture by a gentle swirling motion at 25 °C (room temperature). Thereafter, 1-mL portion of the reaction mixture was withdrawn and blown into 2 mL of dichromate/acetic acid reagent at 60-s intervals. The hydrogen peroxide contents of the withdrawn samples were determined by reading the absorbance at 570 nm.
Superoxide dismutase determination
Superoxide dismutase activity was determined based on the method described by [34]. Briefly, an aliquot of the sample was added to 2.5 mL of 0.05 M carbonate buffer at (pH 10.2) to equilibrate in the spectrophotometer. The reactions were inhibited by the addition of 0.3 mL freshly prepared 0.3 mM adrenaline to the mixture which was quickly mixed by inversion. The reference cuvette contained 2.5 mL buffer, 0.3 mL of adrenaline, and 0.2 mL of water. The increase in absorbance was read at 480 nm at every 30 s for 150 s.
Glutathione peroxidase determination
The method described by [35] was adopted for the determination of glutathione peroxidase activity. GPx activity was estimated by using NADPH, and the reduction in absorbance was read at 340 nm for every minute to obtain at least 5 time points.
Glutathione reduced determination
Reduced glutathione was measured spectrophotometrically as described by [36].
Glutathione transferase determination
The glutathione-S-transferase activity was measured according to the method of Habig et al. [37].
Malondialdehyde level determination
Lipid peroxidation marker in the liver homogenate was determined by measuring the malondialdehyde.
(MDA) levels as described by Ohkawa et al. [38]. The MDA concentration was calculated per mg protein and expressed as nanomoles of MDA per mg protein.
Serum Interleukin-2 and interleukin-6 determination
Serum interleukin-2 and interleukin-6 were estimated using the methods of [39].
Data analysis
Data analysis was done using graph pad prism version 8.0. Results were expressed as the mean ± SEM (n = 8). One-way analysis of variance (ANOVA) was used for the analysis of the biochemical indices followed by Tukey’s post-hoc test. Results were considered significant at p < 0.05.
Results
Changes in the fasting blood glucose of diabetic rats administered aqueous extract of G. latifolium leaf
Animals treated with 150 mg/kg body weight of alloxan had their glucose greater than 250 mg/dl after 48 h and was sustained throughout the 14 days of administration, climaxing at 300.01 mg/dl from 90.23 mg/dl (Table 1). Administration of aqueous extract of Gongronema latifolium leaf at 6.36, 12.72 and 25.44 mg/kg body weight significantly (p < 0.05) and progressively reduced the blood glucose levels by 69%, 69% and 70% respectively as against 68% by metformin. The reduction in the fasting blood glucose of animals administered 6.36, 12.72 and 25.44 mg/kg body weight compared well with that of distilled water treated non-diabetic control animals by the end of treatment period.
Table 1.
Fasting blood glucose levels (mg/dL) in alloxan-induced diabetic rats administered aqueous leaf extract of G. latifolium
| Groups | IFBGL (mg/dL) | FBGL (mg/dL) at 48 h of induction | FBGL (mg/dL) at 14th day of AEGLL administration |
|---|---|---|---|
| Normal Control | 90.23 ± 3.45a | 94.89 ± 5.38a | 93.20 ± 5.78a |
| Diabetic control | 94.34 ± 2.15a | 286.34 ± 2.19b | 300.01 ± 6.46b |
| Diabetic +5 mg/kg Metformin | 90.13 ± 2.41a | 295.79 ± 2.56b | 95.37 ± 2.69a |
| Diabetic +6.36 mg/kg AEGLL | 93.10 ± 1.79a | 289.32 ± 3.21b | 93.45 ± 2.90a |
| Diabetic +12.72 mg/kg AEGLL | 94.17 ± 3.15a | 290.10 ± 2.65b | 93.12 ± 4.23a |
| Diabetic +25.44 mg/kg AEGLL | 90.29 ± 2.27a | 296.29 ± 4.12b | 90.27 ± 2.59a |
Values are expressed as mean ± standard deviation (SD) of 8 replicate
Column with different superscript are significant difference at p > 0.05
IFBGL- Initial fasting blood glucose level, FBGL- Fasting blood glucose level, AEGLL – Aqueous extract of G. latifolium leaf
G. latifolium leaf extract effect on some kidney functional indices of diabetic rats
Administration of alloxan significantly (P < 0.05) increased the concentrations of serum uric acid urea, creatinine and BUN levels (Figs. 1, 2, 3, and 4). In contrast, the extract dose-dependently reduced the levels of uric acid, urea, creatinine and BUN in the serum of the animals in a fashion similar to those of metformin-treated diabetic rats. The 25.44 mg/kg body weight of the extract completely restored the levels of uric acid, urea, creatinine and BUN to those of distilled water treated non-diabetic control rats (Figs. 1, 2, 3, and 4).
Fig. 1.
Serum Uric acid concentration of alloxan-induced diabetic rats after administration of aqueous extract of Gongronema latifolium leaf
Values are expressed as mean ± standard deviation (SD); n = 8.
Bar with the same * are not significant difference at p ˃ 0.05.
Bar with different * are significant difference at p < 0.05.
Legends: NC: Normal control; DC: Diabetic control; Met: Metformin
Fig. 2.
Serum Urea concentration of alloxan-induced diabetic rats after administration of aqueous extract of Gongronema latifolium leaf
Values are expressed as mean ± standard deviation (SD); n = 8.
Bar with the same * are not significant difference at p ˃ 0.05.
Bar with different * are significant difference at p < 0.05.
Legends: NC: Normal control; DC: Diabetic control; Met: Metformin
Fig. 3.
Serum Creatinine concentration of alloxan-induced diabetic rats after administration of aqueous extract of Gongronema latifolium leaf
Values are expressed as mean ± standard deviation (SD); n = 8.
Bar with the same * are not significant difference at p ˃ 0.05.
Bar with different * are significant difference at p < 0.05.
Legends: NC: Normal control; DC: Diabetic control; Met: Metformin
Fig. 4.
Serum BUN concentration of alloxan-induced diabetic rats after administration of aqueous extract of Gongronema latifolium leaf
Values are expressed as mean ± standard deviation (SD); n = 8.
Bar with the same * are not significant difference at p ˃ 0.05.
Bar with different * are significant difference at p < 0.05.
Legends: NC: Normal control; DC: Diabetic control; Met: Metformin
Biochemical changes in the oxidative markers in diabetic rats administered G. latifolium leaf extract
Administration of alloxan resulted in significant (p < 0.05) depletion in the levels of superoxide dismutase, catalase, glutathione peroxidase, glutathione (reduced) and glutathione transferase as well as increased the MDA level in the kidney (Figs. 5, 6, 7, 8, 9, and 10). Oral administration of aqueous extract of Gongronema latifolium leaf at 6.36, 12.72 and 25.44 mg/kg body weight significantly (p < 0.05) elevated the activities of superoxide dismutase, catalase, glutathione peroxidase, glutathione (reduced) and glutathione transferase when compared with the distilled water treated diabetic rats. Metformin treatment similarly increased the activities of SOD, CAT, GPx, GSH, GST and reduced significantly the levels of MDA compared with distilled water treated diabetic animals. The 25.44 mg/kg body weight produced the most pronounced increase in the activities of the enzymes and reduction in the MDA levels. Furthermore, the 25.44 mg/kg body weight of the extract restored the levels of SOD, CAT, GPx, GSH, GST and MDA to those of distilled water treated non diabetic rats (Figs. 5, 6, 7, 8, 9, and 10).
Fig. 5.
Superoxide dismutase activity of alloxan-induced diabetic rats after administration of aqueous extract of Gongronema latifolium leaf
Values are expressed as mean ± standard deviation (SD); n = 8.
Bar with the same * are not significant difference at p ˃ 0.05.
Bar with different * are significant difference at p < 0.05.
Legends: NC: Normal control; DC: Diabetic control; Met: Metformin
Fig. 6.
Catalase activity of alloxan-induced diabetic rats after administration of aqueous extract of Gongronema latifolium leaf
Values are expressed as mean ± standard deviation (SD); n = 8.
Bar with the same * are not significant difference at p ˃ 0.05.
Bar with different * are significant difference at p < 0.05.
Legends: NC: Normal control; DC: Diabetic control; Met: Metformin
Fig. 7.
Glutathione peroxidase activity of alloxan-induced diabetic rats after administration of aqueous extract of Gongronema latifolium leaf
Values are expressed as mean ± standard deviation (SD); n = 8.
Bar with the same * are not significant difference at p ˃ 0.05.
Bar with different * are significant difference at p < 0.05.
Legends: NC: Normal control; DC: Diabetic control; Met: Metformin
Fig. 8.
Reduced glutathione level of alloxan-induced diabetic rats after administration of aqueous extract of Gongronema latifolium leaf
Values are expressed as mean ± standard deviation (SD); n = 8.
Bar with the same * are not significant difference at p ˃ 0.05.
Bar with different * are significant difference at p < 0.05.
Legends: NC: Normal control; DC: Diabetic control; Met: Metformin
Fig. 9.
Glutathione transferase activity of alloxan-induced diabetic rats after administration of aqueous extract of Gongronema latifolium leaf
Values are expressed as mean ± standard deviation (SD); n = 8.
Bar with the same * are not significant difference at p ˃ 0.05.
Bar with different * are significant difference at p < 0.05.
Legends: NC: Normal control; DC: Diabetic control; Met: Metformin
Fig. 10.
Malondialdehyde level of alloxan-induced diabetic rats after administration of aqueous extract of Gongronema latifolium leaf
Values are expressed as mean ± standard deviation (SD); n = 8.
Bar with the same * are not significant difference at p ˃ 0.05.
Bar with different * are significant difference at p < 0.05.
Legends: NC: Normal control; DC: Diabetic control; Met: Metformin
G. latifolium leaf extract modulatory role on anti-inflammatory biomarkers in diabetic rats
Administration of alloxan significantly (p < 0.05) increased the concentration of interleukin IL-2 and interleukin IL-6 in the serum of the animals when compared with those of non-diabetic distilled water treated control rats (Figs. 11, and 12). The aqueous extract of Gongronema latifolium leaf significantly (p < 0.05) lowered the levels of IL-2 and IL-6 when compared with distilled water treated diabetic animals in a manner similar to those obtained with metformin treated diabetic rats. The dose at 25.44 mg/kg of aqueous extract of Gongronema latifolium leaf exhibited the most pronounced reversal in the alloxan treatment related increases in the levels of IL-2 and IL6.
Fig. 11.
Serum Interleukin-2 concentration of alloxan-induced diabetic rats after administration of aqueous extract of Gongronema latifolium leaf
Values are expressed as mean ± standard deviation (SD); n = 8.
Bar with the same * are not significant difference at p ˃ 0.05.
Bar with different * are significant difference at p < 0.05.
Legends: NC: Normal control; DC: Diabetic control; Met: Metformin
Fig. 12.
Serum interleukin-6 concentration of alloxan-induced diabetic rats after administration of aqueous extract of Gongronema latifolium leaf
Values are expressed as mean ± standard deviation (SD); n = 8.
Bar with the same * are not significant difference at p ˃ 0.05.
Bar with different * are significant difference at p < 0.05.
Legends: NC: Normal control; DC: Diabetic control; Met: Metformin
Discussion
Alloxan-induced diabetes has been described as a useful experimental model to study antidiabetic activity of several agents [30]. The mechanism by which alloxan brings about diabetes includes destruction of β-cells and redox imbalance which make cells less active, leading to poor sensitivity of insulin for glucose uptake by tissues [5]. However, the reference anti-diabetic agent, metformin, is a commonly used drug which act through various mechanisms such as reduced glucose production, increased fatty acid oxidation in hepatocytes, and/or increased glucose uptake in skeletal muscle [40, 41]. The increase in blood glucose level observed after 48 h of administration of alloxan may be attributed to the cytotoxicity of alloxan on the pancreas leading to generation of free radicals [42]. The reduction in serum glucose level by the aqueous extract of Gongronema latifolium leaf could be due to potentiating the pancreatic secretion of insulin from β-cells of islets or the increased uptake of glucose [17, 40]. It may also be due to increased glycolysis. The increased activity of hexokinase helps in increasing glycolysis and increasing utilization of glucose for energy production [40]. Hence, the aqueous extract may be considered to have good antihyperglycemic active principles without causing any hypoglycemic effect. Drugs that normalize function, without causing hypoglycemia, would make attractive targets for diabetes [43]. The phytochemical analysis of G. latifolium aqueous extract showed the presence of saponins, glycosides, flavonoids, phenols and alkaloids etc. The antidiabetic effect of G. latifolium aqueous extract may be due to the presence of more than one antihyperglycemic principle and their synergistic properties. Several phytocompounds including flavonoids, alkaloids, glycosides, saponins, glycolipids, dietary fibres, polysaccharides, carbohydrates, amino acids and others obtained from various plant sources have been documented as potent hypoglycemic agents [43]. Such a phenomenon of low hypoglycemic response at higher dose is common with indigenous plants and has been observed earlier with many plants like Boswellia ovalifoliolata [44], Syzygium paniculatum [45], Homalium zeylanicum [46], Andrographis echioides [47] Helianthus annuus root [48], Artocarpus altilis fruit [49].
Hyperuremia and hypercreatininemia, have been reported to occur in alloxan-induced diabetic rats [29, 50], and such elevated levels of biomolecules in this study did not only suggest disturbance in the metabolism of these substances, but also agree with other previously published works [51]. The restoration of these biomolecules by the extract of Gongronema latifolium leaf relative to the control levels further corroborate the earlier position of recovery of the animals from some metabolic disorders associated with diabetes by the aqueous extract of Gongronema latifolium leaf. This study is consistent with the report of [17, 30].
Antioxidant enzymes (SOD, CAT, GPx, GSH and GST) perform crucial role in the maintenance of physiological concentrations of oxygen and hydrogen peroxide by enhancing the dismutation of oxygen radicals and mopping up organic peroxides generated from exposure to alloxan [41, 49]. The data obtained from this study suggested that alloxan-induced diabetes disrupted the activities of renal antioxidant enzymes [17]. The decrease in the activities of SOD, CAT, GPx, GSH and GST in the kidney of diabetic rats may be due to the glucose oxidation, formation of free radical generation, and nitric oxide donor property of alloxan [52, 53]. Furthermore, it may also be that the free radicals produced inactivated the activities of these enzymes [54]. This may be responsible for the insufficiency of antioxidant defenses in mitigating ROS mediated damage [55]. The increased activities of the antioxidant enzymes by aqueous extract of Gongronema latifolium leaf reduced the imbalance between the generation of ROS and antioxidant activities in diabetic rats. Therefore, the ability of aqueous extract of Gongronema latifolium leaf to restore the altered levels of antioxidant enzymes in alloxan-induced diabetic rats indicates its free radical scavenging property.
Certain serum cytokines serve as markers of systemic inflammation, including interleukin-2 (IL-2) and interleukin-6 (IL-6) [56]. Measurement of inflammatory markers has two main functions: to detect acute inflammation that might indicate specific diseases, or to give a marker of treatment response. The increased levels of inflammation observed in alloxan-induced diabetic rats could be due to increased oxidative stress. Furthermore, it may be due to induction of nuclear factor kappa B (NF-κB) that is responsible for the production of some pro-inflammatory cytokines including IL-6 [17, 57]. IL-6 can also mediate as an anti-inflammatory agent in local and systemic inflammation [58, 59]. Thus, the decrease in IL-6 levels in normal and diabetic rats placed on G. latifolium can suggestively be attributed to the anti-inflammatory modulation by G. latifolium. In this study, improved inflammatory parameters in response to aqueous extract of Gongronema latifolium leaf can be attributed to antioxidant activity of compounds present in the extract of Gongronema latifolium leaf that prevents the development of reactive oxygen species. This correlates with the reports of Adeneye and Adeyemi [60]; Adeneye et al. [61] as Hunteria umbellate reduced the inflammatory parameters in diabetic rats.
Conclusion
The data obtained from this study show that various doses of aqueous extract of Gongronema latifolium leaf possess antidiabetic activity via modulating hyperglycaemia, inhibiting redox imbalance and inflammation in alloxan-induced diabetic nephropathy in rats.
Compliance with ethical standards
Animal ethics
All of the animals received humane care according to the criteria outline in the Guide for the Care and the Use of Laboratory Animals prepared by the National Academy Science and published by the National Institute of Health (USA). The ethic regulations have been followed in accordance with national and institutional guidelines for the protection of animals’ welfare during experiments. The experiment was carried out at the Phytomedicine, Biochemical Toxicology and Biotechnology Research Laboratory, Department of Biochemistry, Afe Babalola University, Ado-Ekiti, Ekiti State, Nigeria.
Conflict of interest
Authors declare no conflict of interest all through the compilation of this manuscript.
Footnotes
Publisher’s note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
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