Aqueous extract of Dennettia tripetala ameliorates liver and kidney damage caused by multiple exposures to carbon tetrachloride

A considerable number of people all over the world suffer from liver disease, with a large percentage unable to afford sophisticated treatment. There is therefore the need for effective and affordable drugs with fewer side effects. Many affordable drugs currently in use have their starting source from medicinal plants. Examples of plants that have shown promise in alleviating liver damage in experimental animals include: Silybum marianum [1], Curcuma longa [2, 3], Dacryodes edulis [4, 5] amongst others.

In this report, Dennettia tripetala was investigated for its possible hepatoprotective ability. The plant is widely consumed in West Africa for its spicy taste and medicinal value. It is used traditionally for the management of fever, diabetes, diarrhea, toothache, sore throat, nausea, among other ailments [6]. Research has shown that Dennettia tripetala possesses antimicrobial properties [7‐9], analgesic/anti-inflammatory properties [10], antihyperglycemic properties [11], anticancer properties [12] as well as in vitro antioxidant properties [13‐15].

Recently, we established the fact that pre-administration of the aqueous and ethanolic extracts of Dennettia tripetala can protect the liver and kidney of rats from damage arising from a single administration of carbon tetrachloride [16, 17].

In the present study, we investigated the ability of the aqueous extract of Dennettia tripetala fruits to ameliorate liver and kidney damage induced by pre-exposure of Wistar albino rats to carbon tetrachloride multiple times. It is a well known fact that when the liver is damaged by free radicals (such as those produced during the metabolism of a toxic substance like carbon tetrachloride), the cell membrane can be a target [18]. This causes certain liver marker enzymes to leak out of the cell. Lipid homeostasis is also affected by free radicals eventually leading to lipid accumulation in the cells of the liver [18]. The kidney is also known to be damaged by free radicals resulting from carbon tetrachloride metabolism [19]. In a similar vein as the liver, free radicals can attack the nephron and eventually lead to problems with filtration of waste such as urea and creatinine from the blood into the urine. Therefore the levels of these substances tend to be higher than normal in a situation where there is kidney damage. In this report, we evaluated the activity of liver marker enzymes as well as the concentration of lipids and proteins in the blood and hepatocytes in order to determine the level of carbon tetrachloride-induced liver injury as well as the level of hepatoprotection offered by the aqueous extract of Dennettia tripetala. We also evaluated the levels of urea and creatinine in the blood in order to assess the extent of compromise in kidney function. We measured the activity of antioxidant enzymes as well as the lipid peroxidation status of the liver and kidneys in order to determine the extent of damage and restoration provided by carbon tetrachloride and Dennettia tripetala respectively.

Our earlier studies showed that extracts of Dennettia tripetala fruits can prevent liver and kidney damage when administered prior to a single dose of carbon tetrachloride in rats [16, 17]. The aim of the present study was to investigate the potentials of Dennettia tripetala fruits in restoring the health of the liver and kidney when considerable damage (caused by multiple exposures to carbon tetrachloride) had already occurred. Our results reveal that the aqueous extract of Dennettia tripetala fruits can ameliorate liver and kidney damage posed by multiple exposures to carbon tetrachloride.

ALT, AST and ALP are markers of liver damage. They are majorly localized within hepatocytes. Damage to the membrane of hepatocytes can cause these enzymes to leak out thereby leading to their elevation in the serum [23]. In this study, ALT, AST and ALP which were elevated by carbon tetrachloride were significantly reduced by the plant extract indicating hepatoprotection.

The distribution of lipids in the body is a good indicator of health status. Dyslipidemia which refers to a distortion in plasma lipid pattern is often characterized by a profound drop in HDL-cholesterol levels and a concomitant rise in LDL-cholesterol levels and signals severe problems with lipid metabolism. Such distortions in plasma lipid patterns could be predictive of artherosclerosis and associated cardiovascular complications [24]. In this study, the plant extract was able to dampen the dangerous trends in the levels of HDL-and LDL-cholesterol caused by carbon tetrachloride. The plant also dampened the trends in the levels of serum total cholesterol and triglyceride caused by carbon tetrachloride.

In the liver of the rats that were exposed to carbon tetrachloride, our data revealed an apparent accumulation of lipids. This was also evident from the histopathological evaluations. Other researchers have reported this pathology of lipid accumulation in the liver of animals following carbon tetrachloride administration [25‐27]. The possible mechanism for this lipid accumulation may include: carbon tetrachloride-induced decrease in the secretion of lipids from the liver [28] as well as increase in the synthesis of lipids in the liver [29]. In the present study, the plant extract greatly reduced the accumulation of lipids in the liver as supported by both biochemical and histological evidences.

In this study, there was a large increase in serum total protein in rats treated with carbon tetrachloride. This may be partly due to the leakage of enzymes and other proteins from the liver and possibly other organs of the body into serum. There was also a decrease in serum albumin as well as the albumin: globulin ratio indicating possible compromise in the synthetic capacity of the liver [18]. Dennettia tripetala extract was able to prevent this and boost both the structural and functional integrity of the liver, including its synthetic capacity.

Urea and creatinine are commonly used as markers of kidney function. When the levels of these metabolites increase in serum, it indicates that there is a problem with the kidney [26, 30]. This is because the kidney is responsible for filtration of the blood, and when there is a problem with the kidney, urea and creatinine which are supposed to be filtered into the urine accumulates in the blood [26, 30]. In the present study, the concentration of urea in the serum of rats administered carbon tetrachloride increased by 40%. The histopathology also revealed critical changes in kidney architecture characteristic of acute tubular necrosis. Our data also showed a 28% rise in serum creatinine concentration in the rats treated with carbon tetrachloride. In the present study, Dennettia tripetala extract ameliorated kidney damage as shown by restoration of the normal kidney architecture. At the biochemical level, the plant extract lowered the serum urea and creatinine concentration to levels very similar to those of the control group.

Antioxidant enzymes are natural intrinsic enzymes which living organisms use to combat reactive oxygen species (ROS) produced during normal metabolism. They act by scavenging free radicals and by terminating any free radical-induced chain reaction. When an animal is exposed to an external source of free radicals (e.g., as a result of exposure to a toxic chemical) the animal’s antioxidant defense mechanism steps in and tries to control the rate of deleterious bio-oxidation and molecular damage [31].

Several researchers have observed that the activities and expression of antioxidant enzymes such as SOD, catalase and glutathione peroxidase, drops drastically in the liver and kidney of animals exposed to an external source of free radicals compared to control animals [25, 27, 30, 32‐34]. This may be explained by the fact that these radicals may inhibit (non-specifically) the synthesis as well as the activity of antioxidant enzymes in the liver and kidney at the DNA level and at the protein level respectively [31, 35‐37].

On the other hand, some other researchers have observed that the activities and expression of antioxidant enzymes increases significantly in the liver and kidney of animals exposed to an external source of free radicals compared to control [38, 39]. This is not surprising because the cell may attempt to counteract the effects of radicals by activating genes responsible for encoding antioxidant enzymes [31]. It is also a known fact that certain reactive oxygen species can activate stress-induced transcription factors [31] and these transcription factors may include those that are critical to the expression of antioxidant enzymes. Put together, it stands to reason therefore that host response to oxidant-driven pathology may involve a two-phase process in which the host initially mobilizes its antioxidant defense system until such a time, when such system becomes overwhelmed and begins to suffer a decline.

The mechanism by which carbon tetrachloride causes liver and kidney damage is free radical mediated. In this study, carbon tetrachloride decreased the activities of liver and kidney SOD and catalase. On the other hand, Dennettia tripetala caused an increase in liver and kidney SOD and catalase activities, indicating that one way in which this plant confers protection is by altering the activity of antioxidant enzymes. Further evidence in support of the antioxidant mechanism is seen in the reduction in malondialdehyde levels of the liver and kidney compared to that of the group administered with only carbon tetrachloride. Products of lipid peroxidation such as malondialdehyde, can inactivate many crucial cellular proteins [37]. Our results show that Dennettia tripetala extract was able to manage carbon tetrachloride-induced lipid peroxidation in the liver and kidney.