Vitamin A modulation of xenobiotic-induced hepatotoxicity in rodents

Comparative Hepatoprotective Effect of Vitamins A and E Against Gasoline Vapor Toxicity in Male and Female Rats

Background

Plasma alanine transferase(ALT), aspartate transferase(AST), α-glutamyl transferase(GGT), and alkaline phosphatase(ALP) activities are known biomarkers in assessing hepatic functional integrity. A remarkable rise in the activities of these enzymes normally signifies hepatotoxicity of chemical agent(s) in the biological system. Exposure to 17.8 cm³h^-1m^-3 of PMS blend unleaded gasoline vapors (UGV) for 6 hr/day, 5 days/week for 20 weeks have been reported to cause hepatotoxicity in rats.

Methods

In this study, the comparative hepatoprotective effect of vitamins A (retinol) and E (α-tocopherol) against UGV-induced toxicity was assessed in male and female rats. Retinol and α-tocopherol at prophylactic dosage (400 and 200 IU/kg/day, respectively) were separately administered orally to the test rats concomitant with exposure to UGV in the last two weeks of the experiment.

Results

The results of this study indicated that exposure to UGV caused significant increase (P < 0.05) in the activities of serum ALT, AST, ALP, GGT and bilirubin in male and female rats. Oral administration of prophylactic doses of retinol and α-tocopherol produced a significant decrease (P < 0.05) in the activities of these parameters in male and female test rats, compared with the non-treated test rats; but insignificant increase(P ≥ 0.05), compared with the control. However, the hepatoprotective effect of α-tocopherol was observed to be more potent than that of retinol.

Conclusions

The result of this study demonstrated that the hepatoprotective potency of α-tocopherol against gasoline vapors toxicity was higher than that of retinol in male and female rats, although the female gender of the animal model responded to treatment with both vitamins better than the males. Hence, the work suggested the beneficial effects of both vitamins against hepatotoxicity in individuals frequently exposed to gasoline vapors.

The Hepatoprotective Effect of Vitamin A against Gasoline Vapor Toxicity in Rats

Background

Changes in the activities of plasma alanine amino transferase (ALT), aspartate amino transferase (AST), gamma glutamyl transferase (GGT), and alkaline phosphatase (ALP) are used to assess the functional state of the liver. Significant increase in the activities of these enzymes commonly indicates the hepatotoxicity of chemical agent(s) in the body. Exposure of male and female rats to 17.8 cm³h^-1m^-3 of Premium Motor Spirit (PMS) blend unleaded gasoline (UG) vapors for 6 hr/day, 5 days/week for 20 weeks have been observed to cause hepatotoxicity. In this study, the potential hepatoprotective effect of vitamin A (retinol) against gasoline vapours-induced toxicity was investigated in male and female rats.

Methods

Retinol (400 IU/kg/day) was orally administered to the test rats concomitant with the gasoline vapor exposure in the last two weeks of the experiment.

Results

The results obtained from this study showed that exposure to gasoline vapors caused significant increase (P < 0.05) in the activities of serum ALT, AST, ALP, GGT and bilirubin in both male and female rats. The treatment of the male and female test rats with vitamin A produced a significant decrease (P < 0.05) in the activities of these parameters, compared with the test rats without treatment; but insignificant increase(P ≥ 0.05), compared with the control.

Conclusions

The result of this study demonstrates the beneficial effects of retinol, at prophylactic dosage, against gasoline vapours hepatotoxicity in male and female rats, thereby suggesting that retinol may be used to prevent hepatotoxicity in individuals frequently exposed to gasoline vapours.

Chloroplast microsatellites markers to assess genetic diversity in wild and cultivated grapevines of Iran

To assess the haplotype diversity and genetic relationship between them, A set of 69 Iranian cultivated accessions, six European cultivars and an accession of Vitis labrusca along with 63 wild grapevine individuals were studied using chloroplast microsatellite markers. Results showed that among analyzed cpssr loci only ccmp 3 and ccmp10 were polymorphic within cultivars and only ccmp3 was polymorphic in wild grape individuals. The size variants of both loci combine in a total of 4 different haplotypes. All the 4 haplotype are displayed in the cultivars while only 2 are presented in wild grapes. Sultani or keshmeshi Bidane cultivar has the haplotype III that there is not this haplotype among the wild grapes of studied regions. Concerning to existence of both haplotypes I and II in the number of Iranian cultivated and wild grapes, it is possible to consider that the wild grapes are ancestor of some of our native cultivars.

Retinol potentiates acetaminophen-induced hepatotoxicity in the mouse: mechanistic studies

This study was designed to elucidate the mechanism of retinol's potentiation of acetaminophen-induced hepatotoxicity. To accomplish this, the major bioactivation and detoxification pathways for acetaminophen were investigated following retinol (75 mg/kg/day, 4 days), acetaminophen (400 mg/kg), and retinol + acetaminophen treatment. Hepatic microsomes were used to determine the catalytic activity and polypeptide levels of cytochrome P450 enzymes involved in the murine metabolism of acetaminophen. Results showed that the catalytic activity and polypeptide levels of CYP1A2, CYP2E1, and CYP3A were unchanged in the treatment groups compared to vehicle and untreated controls. In combination, retinol + acetaminophen caused a significantly greater depletion of GSH compared to corn oil + acetaminophen (0.36 +/- 0.11 vs 0.89 +/- 0.19 micromol/g, respectively, p < 0.05). This greater GSH depletion correlated with a higher degree of hepatic injury in the retinol + acetaminophen-treated animals but is probably not the cause of the potentiated injury since the results showed that retinol treatment itself did not alter hepatic glutathione (3.34 +/- 0.43 vs 3.44 +/- 0.46 micromol/g for retinol vs vehicle, respectively). However, hepatic UDPGA stores were decreased in the retinol-treated group compared to untreated and corn oil controls (54.6 +/- 10.6 vs 200.6 +/- 17.6 nmol/g for retinol and untreated control, respectively, p < 0.001). This demonstrates that there is significantly less hepatic UDPGA available for conjugation following retinol administration. The results suggest that decreased hepatic UDPGA is likely the cause of retinol's potentiation of acetaminophen-induced hepatic injury.

Chlorinated methanes and liver injury: highlights of the past 50 years

The chlorinated methanes, particularly carbon tetrachloride and chloroform, are classic models of liver injury and have developed into important experimental hepatoxicants over the past 50 years. Hepatocellular steatosis and necrosis are features of the acute lesion. Mitochondria and the endoplasmic reticulum as target sites are discussed. The sympathetic nervous system, hepatic hemodynamic alterations, and role of free radicals and biotransformation are considered. With carbon tetrachloride, lipid peroxidation and covalent binding to hepatic constituents have been dominant themes over the years. Potentiation of chlorinated methane-induced liver injury by alcohols, aliphatic ketones, ketogenic compounds, and the pesticide chlordecone is discussed. A search for explanations for the potentiation phenomenon has led to the discovery of the role of tissue repair in the overall outcome of liver injury. Some final thoughts about future research are also presented.

Protection against carbon tetrachloride hepatotoxicity by oleanolic acid is not mediated through metallothionein

Oleanolic acid is a triterpenoid compound that has been shown to protect against liver injury produced by some hepatotoxicants. This study was designed to characterize the protective effects of oleanolic acid on carbon tetrachloride-induced hepatotoxicity, and the role of metallothionein in the protection. Oleanolic acid pretreatment (100-400 micromol/kg, s.c.) protected Sprague-Dawley rats and mice from carbon tetrachloride-induced liver injury in a dose- and time-dependent manner, as evidenced by serum alanine aminotransferase and sorbitol dehydrogenase activities, as well as by histopathology. The protection against carbon tetrachloride hepatotoxicity was not evident until animals were pretreated with oleanolic acid 12 h, and lasted for 72 h after a single injection. This suggests that the protection might be due to induction of some adaptive mechanisms. Metallothionein (MT), an acute-phase protein proposed to decrease carbon tetrachloride-induced liver injury, was dramatically induced following oleanolic acid treatment. To examine whether oleanolic acid protection is mediated through MT, MT-I and II knock-out (MT-null) mice were utilized. Oleanolic acid pretreatment increased MT levels in control mice (20-fold), but not in MT-null mice, however, it protected equally against carbon tetrachloride-induced hepatotoxicity in both control and MT-null mice. These data indicate that oleanolic acid is effective in protecting rats and mice from the hepatotoxicity produced by carbon tetrachloride, and the protection is not mediated through induction of MT.

Suppression of Kupffer cell function prevents cadmium induced hepatocellular necrosis in the male Sprague-Dawley rat

Exposure of humans to toxic metals and metalloids is a major environmental problem. Many metals, such as cadmium, can be hepatotoxic. However, the mechanisms by which metals cause acute hepatic injury are in many cases unknown. Previous reports suggest a major role for inflammation in acute cadmium induced hepatotoxicity. In initial experiments we found that a non-hepatotoxic dose of cadmium chloride (CdCl2; 2.0 mg/kg, i.v.) markedly increased the clearance rate of colloidal carbon from the blood, which is indicative of enhanced phagocytic activity by Kupffer cells (resident hepatic macrophages). Thus. the objective these studies was to determine the involvement of Kupffer cells in cadmium induced liver injury by inhibiting their function with gadolinium chloride (GdCl3). Male Sprague-Dawley rats were administered GdCl3 (10 mg/kg, i.v.) followed 24 h later by a single dose of CdCl2 (3.0 and 4.0 mg/kg, i.v.). Twenty four hours after CdCl2 administration animals were killed and the degree of liver toxicity was assessed using plasma alanine aminotransferase (ALT), as well as light microscopy. Cadmium chloride administration produced multifocal hepatocellular necrosis and increased plasma ALT activity. Pretreatment with GdCl3 significantly reduced both the morphological changes and hepatic ALT release caused by CdCl2. However, the protection was specific to the liver, and did not alter CdCl2 induced testicular injury, as determined by histopathological damage. In many cases, the inducible cadmium-binding protein, metallothionein (MT) is often an essential aspect of the acquisition of cadmium tolerance in the liver. Although cadmium caused a dramatic induction of hepatic MT (32-fold), GdCl3 caused only a minor increase (2-fold). Combined CdCl2 and GdCl3 treatment did not induce levels to an extent greater than CdCl2 alone. As expected, GdCl3 also caused a slight increase in the amount of cadmium associated with the liver. In cultured hepatocytes isolated from GdCl3 pretreated rats, CdCl2 induced cytotoxicity was not significantly altered compared to control hepatocytes, indicating that the mechanism of tolerance required the presence of other cell types. Thus, GdCl3 attenuation of CdCl2 induced hepatotoxicity does not appear to be caused by increased tissue MT content or a decreased susceptibility of hepatocytes to cadmium. From these data, we concluded that tolerance to cadmium induced hepatotoxicity involves the inhibition of Kupffer cell function which results in a decreased inflammatory response and an altered progression of hepatic injury. These data further indicate that Kupffer cell function is critical to cadmium induced hepatocellular necrosis.

Modulation of Kupffer cell and peripheral blood monocyte activity by in vivo treatment of rats with all-trans-retinol

Previous studies have shown that large doses of vitamin A potentiate chemical-induced liver injury and that the Kupffer cell is directly involved in this potentiation. Therefore, these studies were designed to determine if Kupffer cells isolated from vitamin A treated male Sprague-Dawley rats (75 mg/kg/day for 3-7 days as all- trans-retinol) had altered activity and function. Respiratory activity of Kupffer cells isolated from rats treated with vitamin A for 3 to 7 days markedly increased. Similarly, phagocytic activity was significantly elevated (up to 9-fold) after exposure to vitamin A for 3 to 7 days. Production of reactive oxygen species, measured by luminol-enhanced chemiluminescence of Kupffer cells isolated after 7 days of vitamin A exposure, was significantly higher than that of control cells when stimulated with opsonized zymosan. Also, the release of superoxide anion by individual Kupffer cells isolated from vitamin A treated rats was nearly three times greater than that of control cells. Basal production of tumor necrosis factor-alpha (TNF-alpha) and prostaglandin E2 (PGE2) production were significantly elevated in Kupffer cells isolated from rats treated with vitamin A. Lastly, peripheral blood monocytes (PBMC) isolated from rats treated with vitamin A for 7 days had a significantly greater respiratory activity, as well as TNF-alpha and PGE2 production, than PBMC isolated from control rats. Our data suggest that large doses of vitamin A enhance both Kupffer cell and PBMC function. Upregulation of the activity by these phagocytic cells may play a role in the vitamin A potentiation of chemical-induced liver injury.

Plasma and hepatic antioxidant control and vitamin A nutritional status

Twenty-seven rats were divided into three groups and fed on diets containing 0.3, 6 or 60 RE (retinol equivalent) retinyl palmitate/g food. After 7 weeks, hepatic vitamin A uptake was found to be more efficient in vitamin A-deficient rats than in rats given adequate vitamin A. We showed that during the metabolic adaptation of the animals to the level of vitamin A in the diet, extensive modifications occur in the antioxidant defences of the organism. In parallel with the increase in the level of vitamin A, the decrease in the level of alpha-tocopherol in the plasma can bring about a greater susceptibility of the lipoproteins to oxidative stress. Similarly, the decrease in the hepatic alpha-tocopherol level and in glutathione peroxidase activity leads to the weakening of the liver's antioxidant defences.

Alterations in chemically induced tissue injury related to all-trans-retinol pretreatment in rodents

Retinol (vitamin A) is an essential nutrient which has many physiological effects throughout the body. Our studies have demonstrated that retinol modulation of immune response, through alteration of macrophage and neutrophil function, can have dramatic effects on the toxicity of some compounds. Based on these studies, our current hypothesis for retinol potentiation of chemical-induced liver injury is that retinol administered to rats prior to the hepatotoxicant (CCl4 and AA in rats; and AA, APAP, and GalN in mice) primes the Kupffer cells to a more active state. This may occur in part as a result of increases in chemical mediators such as TNF from these Kupffer cells. Following hepatocyte damage by a toxicant, Kupffer cells are activated to release reactive oxygen species, immune mediators, and chemotactic factors which all serve to enhance the inflammatory response. This increased inflammatory response then results in increased injury to the already toxicant-damaged hepatocytes. In addition, retinol modulation of toxicant activation and detoxification may also make important contributions to the potentiation of some toxicants such as AA. Retinol protection of CCl4 hepatotoxicity in mice is more difficult to explain at this time but is possibly related to alterations in CCl4 metabolism in this species. Differences in response between pulmonary and liver macrophages (Kupffer cells) may explain the retinol protection from 1-NN pulmonary toxicity. Retinol may decrease the inflammatory response through downregulation of pulmonary macrophage function, thus resulting in decreased pulmonary injury. Finally, since retinol protection of cadmium toxicity in the liver and testis requires 7 days of retinol pretreatment, we suspect that retinol is inducing protective protein(s) in these organs. Aside from its normal biological role in rhe body, clinical medicine has found new uses for retinol in the treatment and prevention of some cancers, and in the treatment of certain dermatologic conditions. Since these patients are frequently administered or exposed to other potentially toxic compounds, it is obviously prudent and necessary to continue research into the effects of retinol on immune modulation and interaction with other compounds. More importantly, these studies demonstrate the modulation of immune function is one mechanism by which one chemical can influence the toxicity of another.