Nephrotoxic Evaluation of Aqueous Stem Bark Extract of Dialium guineense in Normal Wistar Rats

ABSTRACT


INTRODUCTION
The kidney participates in whole-body homeostasis, regulating acid-base balance, electrolyte concentrations, extracellular fluid volume, and blood pressure. It accomplishes these homeostatic functions both independently and in concert with other organs, particularly those of the endocrine system [1]. Various endocrine hormones coordinate these endocrine functions: renin, angiotensin II, aldosterone, antidiuretic hormone, and atrial natriuretic peptide, among others. Many of the kidney's functions are accomplished by relatively simple mechanisms of filtration, reabsorption, and secretion, which take place in the nephron [2]. Filtration is the process by which cells and large proteins are filtered from the blood to make an ultrafiltrate that eventually becomes urine. It takes place in renal corpuscle. The kidney generates 180 L of filtrate a day, while reabsorbing a large percentage, allowing for the generation of only approximately 2 L of urine [3,4]. Reabsorption is the transport of molecules from this ultrafiltrate into the blood. Secretion is the reverse process, in which molecules are transported in the opposite direction, from the blood into the urine.The kidneys are responsible for the elimination of unmodified drugs and metabolites. Alterations in kidney structure and function are frequently found in severe liver disease and once liver function falls below a critical threshold, sodium retention occurs followed by ascites, associated with profound disturbances of splanchnic and systemic hemodynamic which in turn may affect renal function [5,6]. Nephrotoxicity refers to injury to the kidneys or impairment of kidney function caused by exposure to xenobiotics such as drugs, food additives, alcohol, chlorinated solvents, peroxidized fatty acids, fungal toxins, radioactive isotopes, environmental toxicants, and even some medicinal plants [7]. With the extensive use and deepening pharmacological research on medicinal plants, the adverse effects of herbal medicines have also been determined. Plant-derived materials used in herbal medicines are considered to have slight side effects, and can be taken for a long time or at a large dose. However, in recent years, reports of adverse reactions caused by herbal medicine and its preparations have increased [8 -10]. Nephrotoxicity is one of the main toxicities of herbal medicines [8]. Dialium guineense is a medicinal plant that is used in parts of Africa for the treatment of various ailments [11]. This plant contains bioactive substances such as alkaloids, tannins, saponins and phenolics [12,13]. Some of these bioactive compounds may have adverse effects on the kidney. Thus assessment of renal status of Wistar rats administered extract of Dialium guineense may shed light on the safety of the acclimatized to the laboratory environment for one week. Standard experimental protocol was followed for this study.

Experimental Design
The rats were assigned to 7 groups (5 rats per group): One group served as control, while rats in other groups received graded doses of extract (200 -5000 mg/kg bwt) for a period of 28 days. Blood samples were collected before treatment (basal samples) and at the end of the 28th day. Blood sample collected in plain or heparin containers was centrifuged at 3000 rpm for 10 min to obtain plasma which was used for kidney function tests.

Kidney Function Tests
Kidney function tests (KFTs) such as urea, creatinine, sodium ion, potassium ion, chloride ion and bicarbonate ion were performed in plasma [15 -17]. Urease activity was determined as shown below: Urease activity (U/L) = [urea]/time

Statistical Analysis
Data are expressed as mean ± SEM (n = 5). The statistical analysis was performed using SPSS (version 20). Groups were compared using Duncan multiple range test. Statistical significance was assumed at p < 0.05.

Effect of Graded Doses of Aqueous Extract of D. guineense Stem Bark on Weight Parameters
As shown in Table 1, percentage increases in body weights of rats treated with aqueous extract of D. guineense stem bark were significantly reduced, when compared with control group (p < 0.05), but there were no significant differences in the corresponding relative organ weights among the groups (p > 0.05). Data are percentage weight increase and relative kidney weight, and are expressed as mean ± SEM (n = 3). a p < 0.05, when compared with control group; b p < 0.05, when compared with the 200 mg/kg bwt group.

Indices of Kidney Function
There were no significant differences in the plasma concentrations of creatinine, urea, electrolytes and urea/creatinine in rats treated with aqueous extract, when compared with the control group (p > 0.05). These results are shown in Tables 2 and 3.  Data are indices of kidney function and are expressed as mean ± SEM (n = 5). B = Basal means; and T = Test means.

Table 3: Concentrations of Plasma Electrolytes in Rats Treated with Aqueous Extract of D. guineense Stem Bark
Data are concentrations of plasma electrolytes and are expressed as mean ± SEM (n = 5).

Effect of Graded Doses of Aqueous Extract of D. guineense Stem Bark on Urease Activity
There were no significant differences in urease activity before and after treatment, among the groups (p > 0.05; Figure 1).  Kidney, an organ that metabolizes harmful substances besides liver, is constantly perfused with huge volume of blood carrying different kinds of compounds, thereby making it at high risk of toxicity [22,23]. High levels of blood creatinine are found in renal dysfunction or muscle injury [24]. Levels of specific ions such as sodium (Na + ), potassium (K + ), chloride (Cl − ) and bicarbonate (HCO 3− ) are used as biomarkers of electrolyte imbalance [25]. Electrolytes promote fluid balance via maintenance of blood volume, fluid absorption and generation of impulses. In pathological conditions, electrolyte imbalance occurs with increased sodium and chloride, and decreased potassium levels [26,27]. Electrolyte balance is crucial for normal cellular function. Decreased electrolyte levels affects nerve conduction, as well as cell function [28]. Blood urea and creatinine are considered traditional indices of kidney function. Urea is a by-product of protein catabolism. About 90 % of urea produced is excreted through the kidneys [29]. Creatinine, a waste product of muscle catabolism, is excreted exclusively via the kidneys [28]. Therefore, renal damage reduces the kidney's capacity to excrete both urea and creatinine, thereby making them to accumulate in the blood. The results of this study showed that graded doses of aqueous extract of D. guineense stem bark did not significantly alter the levels of electrolytes, urea and creatinine, an indication that it may not be toxic upon prolonged use.

CONCLUSION
The results obtained in this study show that aqueous extract of D. guineense stem bark is not nephrotoxic and may be used in traditional medicine at doses not exceeding 5000 mg/kg bwt. Vanherweghem, J.L., Depierreux, M., Tielemans, C., Abramowicz, D., Dratwa, M. and Jadoul, M. (1993). Rapidly progressive interstitial renal fibrosis in young women: association with slimming regimen including Chinese herbs. Lancet. 341: 387 -391. IX.