Extract of Woodfordia fruticosa flowers ameliorates hyperglycemia, oxidative stress and improves β-cell function in streptozotocin–nicotinamide induced diabetic rats

Abstract

Ethnopharmacological relevance

The art of Ayurveda and the traditional healing system in India have reflected the ethnomedicinal importance of the plant Woodfordia fruticosa Kurtz, which demonstrates its vast usage in the Ayurvedic preparations as well as in the management of diabetes by the traditional healers.

Aims of study

The study aimed to ascertain the antidiabetic potential of W. fruticosa flower methanolic extract (WF) on Streptozotocin (STZ)–nicotinamide-induced diabetic rat model.

Materials and methods

Diabetes was induced in Sprague Dawley (SD) rats by STZ–nicotinamide and thereafter diabetic rats were treated with three different doses of WF (100, 200 and 400 mg/kg body weight) respectively and glibenclamide as a positive control. Biochemical parameters such as blood glucose, serum insulin and C-peptide levels were measured with oxidative stress markers. Furthermore, histology of liver and pancreas was carried out to evaluate glycogen content and β-cell structures. Moreover, immunohistochemistry and western blot analysis were performed on kidney and pancreas tissues to determine renal Bcl-2, pancreatic insulin and glucose transporter (GLUT-2, 4) protein expression in all the experimental groups.

Results

The acute toxicity study showed non-toxic nature of all the three doses of WF. Further, studies on diabetic rats exhibited anti-hyperglycemic effects by upregulating serum insulin and C-peptide levels. Similarly, WF shown to ameliorate oxidative stress by downregulating LPO levels and augmenting the antioxidant enzyme (ABTS). Furthermore, histopathological analysis demonstrate recovery in the structural degeneration of β-cells mass of pancreas tissue with increase in the liver glycogen content of the diabetic rats. Interestingly, protective nature of the extract was further revealed by the immunohistochemical study result which displayed upregulation in the insulin and renal Bcl-2 expression, the anti apoptosis protein. Moreover, western blot result have shown slight alteration in the GLUT-2 and GLUT-4 protein expression with the highest dose of WFc treatment, that might have stimulated glucose uptake in the pancreas and played an important role in attenuating the blood glucose levels.

Conclusion

The overall study result have demonstrated the potential of WF in the management of diabetes and its related complications, thus warrants further investigation on its major compounds with in depth mechanistic studies at molecular level.

Introduction

There is a growing research interest in the management of diabetes mellitus (DM) and its associated complications due to the unabated increase in the incidence of this metabolic syndrome. At present DM is one of the alarming global threat giving rise to complications such as retinopathy, neuropathy, heart attack and atherosclerotic vascular disease (Gandhi et al., 2014, Irudayaraj et al., 2012, Laakso, 1999). The impairment in carbohydrate, lipid and protein metabolism and defects in insulin signaling leads to hyperglycemia, a known characteristic of DM, which is associated with oxidative stress by increasing the formation of reactive oxygen species (ROS) causing reduction in the antioxidant levels. Under the oxidative stress condition, an increased level of malondialdehyde (MDA), a highly toxic by-product is released by lipid peroxidation and ROS and consequently causing oxidative damage in the pancreas, liver and kidney (Evans, 2007).

According to WHO estimation, herbal medicinal plants have started to gain more attention in recent years for the management of diabetes owing to their less side effects compared to the synthetic pharmaceutical drugs which are more costly (Chavre et al., 2010). These ethnomedicinal plant species are known to exert anti-diabetic effect by ameliorating blood glucose levels and oxidative stress and improving the pancreatic expressions of insulin and glucose transporter proteins (Taha et al., 2014). The presence of glycosides, alkaloids, terpenoids, flavonoids, carotenoids, etc account for the antidiabetic properties of the plants. As the search for more effective and less expensive anti-diabetic plant extract is still ongoing, there is a renewed research interest on the traditionally used antidiabetic plants. One such plant is Woodfordia fruticosa, the flower of which have been traditionally used in the Beed district of Maharashtra as anti-diabetic agent (Patil et al., 2011, Chavre et al., 2010, Das et al., 2007).

W. fruticosa Kurtz, the well-known plant belong to the family Lythraceae and located abundantly in the tropical and subtropical region of India growing upto an altitude of 1500 m and have been in use for a long time by the traditional practitioners of South East Asian countries. The flower fulfills huge demand of both domestic and international markets even though other parts of the plant also behold some medicinal values. The flowers which is specialized in the preparation of herbal medicines are brilliant red in color, pungent, acrid and it exerts uterine sedative and anthelmintic effect. The other therapeutic values of the dried flowers of W. fruticosa act against dysentery, sprue, bowel complaint, rheumatism, dysuria, hematuria, wounds, bleeding injuries, otorrhoea, leucorrhea and dysmenorrhea. The flowers also contribute in the preparation of Ayurvedic fermented drugs named as ‘Aristhas’ and ‘Asavas’ and was made patented against diabetics and calorie conscious non-diabetics by Brindavanam et al. (2003). The anti-diabetic property of the plant was due to the phytochemicals such as tannins, flavonoids, anthraquinone glycosides and polyphenols present in flowers and leaves (Chavre et al., 2010; Das et al., 2007). The immunomodulatory activity of the Ayurvedic drug ‘Nimba Aristha’, possessing W. fruticosa flowers was demonstrated by Kroes et al. (1993). The presence of glycosides, quercetin and myricetin in WF attribute to the anti-inflammatory effect of the plant and it is validated by its ability to inhibit the two pivotal enzymes, lipoxygenase and cycloxygenase of pelargonidin, which play dominant role in regulating the pathophysiology of inflammation.

Although various interesting pharmacological aspects have been identified in previous studies to reflect the antioxidant, anti-inflammatory, anti-microbial and anticancer properties of different parts of this plant, two recent studies demonstrated the antihyperglycemic potential of the methanolic and ethanolic extract of the flower on alloxan induced diabetic mice and STZ-induced diabetic rats (Bhatia and Khera, 2013, Verma et al., 2012). However, lack of scientific report on the anti-diabetic mechanism including the pancreatic expression of insulin and glucose transporters by the methanolic extract of W. fruticosa flower (WF) warrants further investigation. Keeping this in view, the present study attempts to understand the mechanism involved in antihyperglycemic activity of the flower methanolic extract, WF, associated with important biochemical parameters, oxidative stress markers, hepatic glycogen content, pancreatic β-cell mass, insulin and targeted GLUT-2 and 4 protein expressions and the renal Bcl2 protein analysis in STZ–nicotinamide induced diabetic rat model.