Abu OD1*, Awhin EP2 and Ifekwe JC3
Received: June 12, 2023; Published: June 22, 2023
*Corresponding author: Abu OD, Department of Biochemistry, Faculty of Life Sciences, University of Benin, Benin City, Nigeria
Diabetes mellitus is a fast growing metabolic disorder and one of the leading causes of death worldwide. The aim of this study was to evaluate the effect of ethanol extract of Cucumis sativus on liver function in diabetic rats. Adult male Wistar albino rats (n = 25) weighing 200 to 230 g (mean weight = 215 ± 15 g) were used for this study. The rats were randomly assigned to five groups of 5 rats each: normal control group, diabetic control group, metformin group, 200 mg/kg bwt extract and 300 mg/kg bwt extract groups. Diabetes mellitus was induced in the rats via intraperitoneal injection of STZ at a dose of 50 mg/kg bwt. The diabetic rats were then treated for 21 days with either metformin (50 mg/kg bwt) or the extract at doses of 200 and 300 mg/kg bwt, respectively, leaving the diabetic control group untreated. Induction of diabetes mellitus with STZ significantly increased the serum activities of aspartate aminotransferase (AST), alanine aminotransferase (ALT) and alkaline phosphatase (ALP), as well as total protein bilirubin, and Fasting Blood Glucose (FBG) concentrations (p < 0.05). However, treatment of diabetic rats with ethanol extract of C. sativus markedly reduced the activity of the liver enzymes, and the concentrations of total protein, bilirubin and FBG. The results obtained in this study suggest that ethanol extract of C. sativus is effective in ameliorating STZ-induced diabetes mellitus.
Keywords: Aminotransferases; Cucumis Sativus; Hepatocytes; Liver Function; Total Protein
Abbreviations: AST: Aspartate Aminotransferase; ALT: Alanine Aminotransferase; FBG: Fasting Blood Glucose; ALP: Alkaline Phosphatase; T1DM: Type 1 Diabetes Mellitus; T2DM: Type 2 Diabetes Mellitus; BDH: British Drug House; LFTs: Liver Function Test; ROS: Reactive Oxygen Species
Cucurbits are vegetable crops, belonging to the family Cucurbitaceae, which primarily comprises species consumed as food worldwide. Cucurbits are an excellent fruit in nature, composed of all the essential constituents required for good health in humans . They are consumed as vegetables and salads due to their availability at low cost. Cucumbers are botanically categorized as berries, which are available in many different sizes, shapes and colours. They range from thick, stubby little fruits (10 - 12 cm long) to Dutch greenhouse varieties (of up to 50 cm long) . The most common variety is the long cucumber which has a smooth, dark-green skin. The "gherkin" is a cucumber that was harvested when little and pickled in brine. The true gherkin is a different species (Cucumis anguria), which is primarily grown in the West Indies. Cucumbers may not contain a lot of food value, but they make up for this lack of nutrients with a wide variety of healthy substances . The parts of this medicinal plant which are traditionally used are leaves, flowers, seeds, fruits, and bark. These parts contain bioactive compounds responsible for particular pharmacological activity . Cucumis sativus is used in traditional medicine for the treatment of various ailments [3,4]. Diabetes mellitus is a heterogeneous group of syndromes characterized by an increase in fasting blood glucose, caused by a relative or absolute deficiency in insulin .
It is one of the most common metabolic disorders affecting millions of people worldwide . It is a major cause of heart disease and stroke . Death rates for heart disease and the risk of stroke are about 2 – 4 times higher among adults with diabetes than in non-diabetics . In diabetic individuals, high blood pressure, high blood cholesterol, and smoking increase the risk of heart disease and stroke . The most common forms of diabetes mellitus are type 1 diabetes mellitus (T1DM), type 2 diabetes mellitus (T2DM), gestational diabetes, and other types . Biochemical and histochemical analysis have shown that some cucurbits are effective in preventing pancreatic β-cell apoptosis induced by noxious chemicals .
Drugs and Chemicals
The standard antidiabetic drug, metformin, was purchased from Micronova Laboratories (India), and STZ was a product of British Drug House (BDH) Chemicals Ltd. (England). Absolute ethanol, chloroform, syringes, beakers, test tubes, pH meter and other glass wares were obtained from Bell, Sons & Co. (England), and formaldehyde was purchased from Thermo Fisher Scientific Ltd. (USA). All the chemicals and solvents used in this study were of analytical grade.
Plant Preparation and Extraction
Freshly harvested Cucumis sativus fruits were purchased from a major fruit/vegetable market in Benin City, Nigeria and identified by Dr. Henry Akinibosun of Plant Biology and Biotechnology Department, University of Benin. They were thereafter washed and air-dried for about 4 weeks at the Department of Biochemistry. The dry plant was ground with a mechanical blender. The pulverized sample was cold macerated in absolute ethanol for three days (72 h) in a bell jar and filtered using Whatmann filter paper No. 42 (125 mm). The ethanol extract was thereafter concentrated using rotary evaporator and freeze-dried using a lyophilizer [11,12].
Adult male Wistar albino rats (n = 25) weighing 200 to 230 g (mean weight = 215 ± 15 g) were used for this study. The rats were bought from the Department of Anatomy, University of Benin and housed in wooden cages. They were acclimatized for two weeks before commencement of the study, and had free access to feed and water.
The rats were randomly assigned to five groups of 5 rats each: normal control group, diabetic control group, metformin group, 200 mg/kg bwt extract and 300 mg/kg bwt extract groups. Diabetes mellitus was induced in the rats via intraperitoneal injection of STZ at a dose of 50 mg/kg bwt. The diabetic rats were then treated with either metformin (50 mg/kg bwt) or the extract at doses of 200 and 300 mg/kg bwt, respectively, for 21 days.
Collection of Blood
At the end of the treatment, the rats were subjected to mild chloroform an aesthesia after an overnight fast. They were euthanized and blood was collected via retro-orbital sinus puncture and centrifuged for 10 min at 3000 rpm to obtain serum which was used for biochemical analysis.
The biochemical parameters studied were liver function tests such as AST, ALT, ALP, bilirubin and total protein [13-16].
Effect of Ethanol Extract of sativus on Weight and Blood Glucose of Rats
As shown in (Table 1), induction of diabetes mellitus using STZ significantly increased the blood glucose concentrations of the rats (p < 0.05). However, treatment of the diabetic rats with the extract markedly reduced the FBG concentration and body weights of rats (p < 0.05).
Note: Data are weight and FBG parameters and are expressed as mean ± SEM (n = 5).
Effect of Ethanol Extract of sativus on Activities of Liver Enzymes and Total Protein Concentration
Induction of diabetes mellitus with STZ significantly increased the serum activities of AST, ALT and ALP, as well as total protein concentration (p < 0.05). However, treatment of diabetic rats with ethanol extract of C. sativus markedly reduced the activities of the liver enzymes and total protein concentration (p < 0.05). These results are shown in (Tables 2 & 3).
Note: Data are activities of liver enzymes and are expressed as mean ± SEM (n = 5).
Note: Data are activities of ALP and total protein concentration, and are expressed as mean ± SEM (n = 5).
Effect of Ethanol Extract of sativus on Concentrations of Bilirubin
As shown in (Table 4), bilirubin concentration was significantly higher in the diabetic group than in the normal control and extract–treated rats (p < 0.05).
Note: Data are concentrations of bilirubin and are expressed as mean ± SEM (n = 5).
There is presently a growing interest in herbal treatments due to the expansion of medicine. In Africa alone, over 500 plants are known to be used for medicinal purposes, but only a few have been described or studied . A plant is said to be medicinal only when its biological effect has been ethnobotanically or scientifically proven . Plant secondary metabolites are unique resources for pharmaceuticals, food additives, and fine chemicals . An estimated increase in the number of persons with diabetes mellitus is expected over the next decade. Diabetes mellitus is a condition primarily defined by the level of hyperglycemia giving rise to risk of microvascular damage (retinopathy, nephropathy, and neuropathy). It is also associated with increased risk of macrovascular complications (ischemic heart disease, stroke, and peripheral vascular disease), reduced life expectancy, morbidity and reduced quality of life [20,21]. If blood glucose level remains high (hyperglycemia) for a long time, there would be long-term damage to organs such as liver, kidney, eye, nerves, heart and blood vessels [22,23]. Several pathogenic processes are involved in the development of the disease. These range from autoimmune destruction of pancreatic beta cells with consequent insulin deficiency, to abnormalities resulting in resistance to insulin action .
The basis of the abnormalities in carbohydrate, fat, and protein metabolism in diabetes mellitus is reduced action of insulin on target tissues. Deficiency in insulin action results from inadequate insulin secretion and/or diminished tissue responses to insulin at one or more points in the pathways of hormone action. Impairment of insulin secretion and defects in insulin action often coexist in the same patient, and it is often unclear which abnormality, if either alone, is the primary cause of hyperglycemia . Liver Function tests (LFTs) can be used to screen for the presence of liver disease, suggest the underlying cause, estimate the severity, assess prognosis, and monitor effectiveness of therapy. Liver enzymes are released into systemic circulation following cellular necrosis and increased cell membrane permeability and are used as diagnostic measure of liver damage. Most proteins in plasma are synthesized by hepatocytes and secreted into circulation. Bilirubin, a major breakdown product of hemoglobin, rises when there is liver injury or damage, leading to discolouration of the skin; a condition known as jaundice. Elevation of total bilirubin which results from decreased uptake and conjugation of bilirubin by the liver is caused by liver cell dysfunction, while increased levels of direct or conjugated bilirubin is due to decreased secretion from liver or bile ducts obstruction. Increase in albumin, bilirubin and total protein following increase in hemolysis or liver disease or both can lead to jaundice of the skin or kernicterus in the brain .
Diabetes mellitus is generally induced in laboratory animals using streptozotocin or alloxan. Streptozotocin (STZ) is a permanent diabetes-inducing drug that is synthesized by a strain of the soil microbe Streptomyces achromogenes (gram positive bacterium) . The most frequently occurring disorder of carbohydrate metabolism is hyperglycemia . Many of the drugs currently used for the treatment of diabetes mellitus produce adverse effects: sulfonylureas usually stimulate pancreatic islet cells to secrete insulin, while metformin slows down hepatic glucose production . The effectiveness of all these therapies are limited, thereby necessitating the search for novel plant-based compounds that can be used to effectively control hyperglycemia. The antidiabetic effect of plant-derived compounds is due to their ability to alter carbohydrate digestion/absorption, stimulate beta cell function, mimic insulin action, and mop up Reactive Oxygen Species (ROS) . In this study, the intraperitoneal administration of STZ caused a significant elevation in Fasting Blood Glucose (FBG) level. This elevated blood glucose level was significantly reduced after daily treatment with ethanol extract of C. sativus. Similarly, STZ significantly increased the serum activities of AST and ALT, as well as total protein concentration. However, treatment of diabetic rats with ethanol extract of C. sativus markedly reduced the activities of the liver enzymes and total protein concentration. Bilirubin concentration was significantly higher in the diabetic group than in the normal control and extract–treated rats.
The effect of the extract was similar to that of metformin. The evaluation of plasma total protein alone may not tell the actual picture of the metabolic state of an individual, since the concentration of the various proteins are not affected by each other. An elevated level of total protein may be due to dehydration or infection. Plasma concentration may decrease due to impaired synthesis that can result from malnutrition, malabsorption, over-hydration and some forms of liver diseases . It appears that STZ adversely reduced liver functions. It is likely that the extract possesses anti-hyperglycemic effect. It has been reported that ethanol extracts of Cucurbitaceae family fruits like cucumber, white pumpkin, and ridge gourd possess significant anti-hyperglycemic effects . The results of this study are in agreement with previous findings [31-35]. Recent studies validated the presence of antidiabetic agents in Cucumis sativus L. . The antidiabetic agent in Cucumis sativus L. has been identified as a flavonoid called kaempferol . Studies have shown that plant rich in phytochemicals possess important biological and pharmacological activities [36-44].
The results obtained in this study suggest that ethanol extract of C. sativus is effective in ameliorating STZ-induced liver dysfunction.