Diabetes mellitus remains a long-standing and global health challenge [1]. Although several therapeutic options are available for the management of the disease, unfortunately the disease is yet to have a cure [2]. This has necessitated the need to continuously search for a drug candidate with a curative potency. As a part of this pursuit, it is also important to take into cognizance common diets or foods that may play critical roles in the prevention or attenuation of the disease.
Vegetables like cucumber (Cucumis sativa) and onions (Allium cepa) are believed to be rich in natural compounds [5] which are capable of playing vital roles in glucose homeostasis or regulation [18]. It is on this basis, the present study was designed to evaluate the relative efficacy of Cucumis sativa and Allium cepa as well as their combined formulation in streptozotocin-induced diabetic rats.
The choice of streptozotocin as a diabetogenic agent in this study was informed by its ability to induce stable and insulin-dependent hyperglycemia in experimental animals. The results obtained indicate that the investigated botanicals could be vital in the fight against diabetes; particularly in terms of management, prevention and natural regression of the disease. Hence, regular consumption of onion (Allium cepa) and cucumber (cucumis sativa) may capacitate the body glucose regulatory machineries, consequently forestalling compromise in lipid homeostasis.
Compromised lipid metabolism is a metabolic disorder which is usually associated with uncontrolled diabetes mellitus and is undoubtedly key in the onset of diabetic complications [19, 20]. The presence of rich amounts of dietary fiber, vitamins, minerals, and phytonutrients (flavonoids, ligands and triterpenes) in Allium cepa and Cucumis sativa may underscore their ability to protect against streptozotocin-induced alterations in the physiological levels of blood glucose and lipoprotein cholesterols (HDL- and LDL-cholesterols) in rats; as noted in this study. Antioxidants such as flavonoids, particularly quercetin, have been associated with blood sugar regulatory properties [21, 22]. Similarly, soluble dietary fibers are well known for their binding roles in up-regulating and down-regulating the synthesis of HDL-cholesterol and LDL-cholesterol levels, respectively [20, 23]
Consumption of vegetables and fruits has been known to contribute to human health and protect against disease [7]. This is evidently due to the fact that they contain both nutrients and phyto-components with disease preventive properties. They are low in calories and capable of lowering the rates at which simple sugars are released from complex carbohydrates into the body system, consequently regulating the blood sugar level [24].
The hypoglycemic potential exhibited by Allium cepa and Cucumis sativa as well as their combined formulation in this study may be suggestive of the botanicals important roles in the improvement and/or regeneration of pancreatic beta cells as well as consequent stimulation of beta cells for insulin release.
There is also a possibility that hypoglycemic effects of Allium cepa and Cucumis sativa may have occurred through covalent modification of some glucose regulatory enzymes; and/or other pathways such as attenuation of endoplasmic reticulum (ER) stress; rather than increasing serum insulin level and creating extra-pancreatic effects. ER stress has been suggested to play a central role in the development of insulin resistance and diabetes by impairing insulin signaling [25].
Moreover, it is important to recall that the total triglycerides level in the serum was surprisingly decreased, howbeit not significantly in the diabetic control animals. This observation may be seen as the body's natural response to the unavailability of glucose for energy generation, hence the need for utilization of tissue triglycerides for energy purposes as an alternative source. Arguably, this ‘biological flexibility’ has the propensity to cause decline in serum total triglycerides as recorded in this study. Little wonder why treatments of the diabetic animals with Allium cepa, Cucumis sativa and their combined formulation which improved glucose assimilation into the body tissues, were noted to restore the serum triglycerides level.
In the same vein, the non-significant increase in serum total cholesterols noted in the diabetic control animals was unexpectedly exacerbated by treatments of the animals with Allium cepa, Cucumis sativa and their combined formulation. The reason for this is unclear. However, it is probably due to the ability of specific compounds in the botanicals to stimulate the synthesis of other high-density components of total cholesterols [5] (such as very high-density cholesterol (VHDL) as noted with HDL-cholesterol in this study.
