Antidiabetic activity of watermelon (Citrullus lanatus) juice in alloxan-induced diabetic rats

Abstract

Introduction: Watermelon is one of the commonly eaten fruit in most homes in Nigeria and has been used in the management of diabetes mellitus traditionally. This study was carried out to explore the antidiabetic potential of watermelon (Citrullus lanatus) juice in alloxan-induced diabetic rats.

Methods: Watermelon juice was used for the determination of in vitro parameters such as 1,1-diphenyl-2-picryl-hydrazil (DPPH), nitric oxide and ferric reducing antioxidant potential (FRAP) as well as phytochemicals such as total phenol, total flavonoids. In vitro, α-glucosidase and α-amylase inhibitory activities were also accessed using standard procedures. Diabetes was induced in the rats by a single intraperitoneal (I.P) injection of freshly prepared alloxan (150 mg/kg body weight). The animals were randomly grouped into five groups of normal control, untreated diabetic control, diabetic rats administered 200 mg/kg body weight of metformin, diabetic rats administered 500 mg/kg body weight of watermelon (Citrullus lanatus) juice and diabetic rats administered 1000 mg/kg body weight of watermelon juice. The rats were sacrificed on the 14th day of the experiment and various in vivo biochemical parameters were also evaluated in the serum and tissue homogenates of diabetic rats.

Results: The watermelon juice exhibits anti-oxidant properties and inhibitory activities against α-glucosidase and α-amylase in a dose-dependent manner. Added to this, the administration of different doses of the watermelon juice significantly (p < 0.05) reduced the fasting blood glucose level, serum lipid profile, glucose-6-phosphatase, lipid peroxidation and anti-inflammatory activities in alloxan-induced diabetic rats. There was a significant (p < 0.05) increase in antioxidant enzyme activities, hexokinase activity as well as glucose transporters (GLUT 2 and GLUT 4) levels in diabetic rats administered different doses of Citrullus lanatus.

Conclusion: Taken together, this study demonstrates that watermelon (Citrullus lanatus) juice exhibits its antidiabetic potential in experimental diabetic animal model via multiple pathways involving modulation of glucose transporters, anti-inflammatory activities as well as antioxidant defense system and inhibition of α-glucosidase and α-amylase. This suggests that the watermelon (Citrullus lanatus) juice may have a useful clinical application in the management of diabetes mellitus and its metabolic complications if developed as adjuvant therapy.

Keywords: Citrullus lanatus; Glucose transporters; Metformin; α-amylase; α-glucosidase.

Fig. 1

In vitro α-amylase inhibitory activity of watermelon juice. Data are presented as mean ± SEM of triplicate determinations (n = 3). ^a mean is significantly different compared to acarbose at p < 0.05. ^bmean is significantly different compared to watermelon juice (WMJ) at p < 0.05

Fig. 2

In vitro α-glucosidase inhibitory activities of WMJ (watermelon Juice). Data are presented as mean ± SEM of triplicate determinations (n = 3)

Fig. 3

Nitric oxide scavenging ability of Watermelon Juice. Data are presented as mean ± SEM of triplicate determinations (n = 3). ^aMean is significantly different compared to gallic acid at p < 0.05. ^bMean is significantly different compared to watermelon juice (WMJ) at p < 0.05

Fig. 4

DPPH scavenging ability of Watermelon Juice. Data are presented as mean ± SEM of triplicate determinations (n = 3). ^aMean is significantly different compared to Vitamin C at p < 0.05. ^b Mean is significantly different compared to watermelon juice (WMJ) at p < 0.05. Legends: WMJ: Watermelon Juice; Vitamin C: Standard drug

Fig. 5

Effect of WMJ on fasting blood glucose level in alloxan-induced diabetic rats. Data are presented as the mean ± standard error of the mean (n = 8). ^aMean is significantly different compared to Control at p < 0.05. ^bMean is significantly different compared to Diabetic control (BBC) at p < 0.05. Legends: WMJ: Watermelon Juice; DBC: Diabetic control; DMF: Diabetic rats administered metformin

Fig. 6

Effect of WMJ on serum insulin levels in alloxan-induced diabetic rats. Data are presented as mean ± SEM (n = 8). ^aMean is significantly different compared to Control at p < 0.05. ^bMean is significantly different compared to Diabetic control (DBC) at p < 0.05. Legends: WMJ: Watermelon Juice; DBC: Diabetic control; DMF: Diabetic rats administered metformin

Fig. 7

Effect of WMJ on some Liver carbohydrate metabolizing enzymes in alloxan-induced diabetic rats. Data are presented as mean ± SEM (n = 8). ^aMean is significantly different compared to Control at p < 0.05. ^bMean is significantly different compared to Diabetic control (DBC) at p < 0.05. Legends: WMJ: Watermelon Juice; DBC: Diabetic control; DMF: Diabetic rats administered metformin; G6PASE: glucose-6-phosphatase

Fig. 8

Effect of WMJ on Glut 2 and Glut 4 in alloxan-induced diabetic rats. Data are presented as the mean ± SEM (n = 8). ^aMean is significantly different compared to Control at p < 0.05. ^bMean is significantly different compared to Diabetic control (DBC) at p < 0.05. Legends: WMJ: Watermelon Juice; DBC: Diabetic control; DMF: Diabetic rats administered with metformin

Fig. 9

Effect of WMJ on some serum lipid profile parameters in alloxan-induced diabetic rats. Data are presented as mean ± SEM (n = 8). ^aMean is significantly different compared to Control at p < 0.05. ^bMean is significantly different compared to Diabetic control (DBC) at p < 0.05. Legends: WMJ: Watermelon Juice; DBC: Diabetic control; DMF: Diabetic rats administered with metformin; TG: triglycerides; TC: Total cholesterol; HDL: High-density lipoprotein

Fig. 10

Effect of WMJ on some pro-inflammatory markers in alloxan-induced diabetic rats. Data are presented as mean ± SEM (n = 8). ^aMean is significantly different compared to Control at p < 0.05. ^bMean is significantly different compared to Diabetic control (DBC) at p < 0.05. Legends: WMJ: Watermelon Juice; DBC: Diabetic control; DMF: Diabetic rats administered with metformin; IL6: Interleukin-6; IL2: Interleukin-2; TNF-α: Tumour necrosis factor-alpha

Fig. 11

Effect of WMJ on liver enzymatic and non-enzymatic antioxidants in alloxan-induced diabetic rats/ Data are presented as mean ± SEM (n = 8). ^aMean is significantly different compared to Control at p < 0.05. ^bMean is significantly different compared to Diabetic control (DBC) at p < 0.05. Legends: WMJ: Watermelon Juice; DBC: Diabetic control; DMF: Diabetic rats administered with metformin; CAT: catalase; SOD: superoxide dismutase; GPX: glutathione peroxidase; GSH: glutathione reduced; GST: glutathione transferase