The site specificity and sensitivity of the rat liver to butylated hydroxytoluene-induced damage

Search for Potential Inducible Nitric Oxide Synthase Inhibitors with Favorable ADMET Profiles for the Therapy of Helicobacter pylori Infections

Background:

Helicobacter pylori is a gram-negative bacterium related to chronic gastritis, peptic ulcer and gastric carcinoma. During its infection process, promotes excessive inflammatory response, increasing the release of reactive species and inducing the production of pro-inflammatory mediators. Inducible Nitric Oxide Synthase (iNOS) plays a crucial role in the gastric carcinogenesis process and a key mediator of inflammation and host defense systems, which is expressed in macrophages induced by inflammatory stimuli. In chronic diseases such as Helicobacter pylori infections, the overproduction of NO due to the prolonged induction of iNOS is of major concern.

Objective:

In this sense, the search for potential iNOS inhibitors is a valuable strategy in the overall process of Helicobacter pylori pathogeny.

Method:

In silico techniques were applied in the search of interesting compounds against Inducible Nitric Oxide Synthase enzyme in a chemical space of natural products and derivatives from the Analyticon Discovery databases.

Results:

The five compounds with the best iNOS inhibition profile were selected for activity and toxicity predictions. Compound 9 (CAS 88198-99-6) displayed significant potential for iNOS inhibition, forming hydrogen bonds with residues from the active site and an ionic interaction with heme. This compound also displayed good bioavailability and absence of toxicity/or from its probable metabolites.

Conclusion:

The top-ranked compounds from the virtual screening workflow show promising results regarding the iNOS inhibition profile. The results evidenced the importance of the ionic bonding during docking selection, playing a crucial role in binding and positioning during ligand-target selection for iNOS.

Protective effects of Ligustrum lucidum fruit extract on acute butylated hydroxytoluene-induced oxidative stress in rats

Nuzhenzi, the fruit of Ligustrum lucidum Ait. (Oleaceae), is commonly used as tonic for kidney and liver in the traditional Chinese medicine prescription. The present study aimed to investigate the antioxidant activities of ethanol extract of Ligustrum lucidum fruits (ELL) and its effects on butylated hydroxytoluene (BHT)-induced oxidative stress in rats. Results showed that ELL possesses weak antioxidant activities. Compared to the BHT (1000mg/kg)-treated group, results showed that ELL at 250, 500 and 1000mg/kg significantly reduced the levels of blood urea nitrogen (BUN), serum glutamic pyruvic transaminase (sGPT), glutamic oxaloacetic transaminase (sGOT), alkaline phosphatase (sALP), lactate dehydrogenase (LDH), triglyceride (TG) and creatinine (Cr), as well as LDH in bronchoalveolar lavage fluid (BALF). It also significantly decreased the level of lipid peroxides in liver and lung. In addition, ELL significantly enhanced the levels of catalase (CAT), superoxide dismutase (SOD) and glutathione peroxidase (GPx) in these organs. Histopathological evaluation of the tissues revealed that ELL reduced the incidence of lung lesions, while the liver and kidney tissues were not affected by BHT administration. Taken together, the protective effect of ELL against acute BHT-induced oxidative stress in rats could be through the upregulation of antioxidant enzymes.

Final report on the safety assessment of BHT(1)

BHT is the recognized name in the cosmetics industry for butylated hydroxytoluene. BHT is used in a wide range of cosmetic formulations as an antioxidant at concentrations from 0.0002% to 0.5%. BHT does penetrate the skin, but the relatively low amount absorbed remains primarily in the skin. Oral studies demonstrate that BHT is metabolized. The major metabolites appear as the carboxylic acid of BHT and its glucuronide in urine. At acute doses of 0.5 to 1.0 g/kg, some renal and hepatic damage was seen in male rats. Short-term repeated exposure to comparable doses produced hepatic toxic effects in male and female rats. Subchronic feeding and intraperitoneal studies in rats with BHT at lower doses produced increased liver weight, and decreased activity of several hepatic enzymes. In addition to liver and kidney effects, BHT applied to the skin was associated with toxic effects in lung tissue. BHT was not a reproductive or developmental toxin in animals. BHT has been found to enhance and to inhibit the humoral immune response in animals. BHT itself was not generally considered genotoxic, although it did modify the genotoxicity of other agents. BHT has been associated with hepatocellular and pulmonary adenomas in animals, but was not considered carcinogenic and actually was associated with a decreased incidence of neoplasms. BHT has been shown to have tumor promotion effects, to be anticarcinogenic, and to have no effect on other carcinogenic agents, depending on the target organ, exposure parameters, the carcinogen, and the animal tested. Various mechanism studies suggested that BHT toxicity is related to an electrophillic metabolite. In a predictive clinical test, 100% BHT was a mild irritant and a moderate sensitizer. In provocative skin tests, BHT (in the 1% to 2% concentration range) produced positive reactions in a small number of patients. Clinical testing did not find any depigmentation associated with dermal exposure to BHT, although a few case reports of depigmentation were found. The Cosmetic Ingredient Review Expert Panel recognized that oral exposure to BHT was associated with toxic effects in some studies and was negative in others. BHT applied to the skin, however, appears to remain in the skin or pass through only slowly and does not produce systemic exposures to BHT or its metabolites seen with oral exposures. Although there were only limited studies that evaluated the effect of BHT on the skin, the available studies, along with the case literature, demonstrate no significant irritation, sensitization, or photosensitization. Recognizing the low concentration at which this ingredient is currently used in cosmetic formulations, it was concluded that BHT is safe as used in cosmetic formulations.

Dietary butylated hydroxytoluene protects against aflatoxicosis in Turkeys

Turkeys are among the most sensitive species to the toxic effects of the mycotoxin aflatoxin B(1) (AFB(1)). In mammals, dietary antioxidants, such as butylated hydroxytoluene (BHT), have been shown to lessen the toxic effects of AFB(1) by various mechanisms. To test whether BHT protects against aflatoxicosis in turkeys, we supplemented the feed of 10-day-old male white turkeys with low (1000 ppm) and high (4000 ppm) BHT for 20 days. AFB(1) (1 ppm) was then added to the diets and continued for another 10 days. Birds in the AFB(1)-only group had a lower weight gain, a condition that had returned to near control in groups fed diets containing AFB(1) + BHT. Significant elevations in serum aspartate transaminase, alanine aminotransferase, and lactate dehydrogenase, which were evident in the AFB(1) group, were reversed in the AFB(1) + BHT groups. Histopathology revealed hepatic submassive necrotic lesions and biliary hyperplasia, the severity of which was lessened in the AFB(1) + BHT-treated birds. Hepatocellular hydropic degeneration was observed in the BHT-only group, but not in the AFB(1) + BHT groups. This condition associated with BHT treatment was found in a separate study to be reversible and without any long-term adverse effects. These results indicate that BHT counteracts many of the deleterious effects caused by AFB(1) and that this antioxidant may prove to be a viable feed additive for the reduction of aflatoxicosis in turkeys.

Comparison of paracetamol-induced hepatotoxicity in the rat in vivo with progression of cell injury in vitro in rat liver slices

The flux in rat hepatic ratio of adenosine triphosphate levels to adenosine diphosphate levels (ATP/ADP) during the onset and progression of paracetamol-induced cell injury both in vivo and in vitro were investigated and compared. Leakage of lactate dehydrogenase (LDH) and potassium (K+), and mg water/mg dry weight quantified cell injury. ATP and ADP levels were determined using the luciferin-luciferase bioluminescence assay. For in vitro studies, liver slices obtained from phenobarbitone-induced rats were exposed to 10 mM paracetamol for 120 min (T0-T120) and, then incubated without paracetamol up to a further 240 min (T120-T360). For in vivo studies, groups of four phenobarbitone-induced rats received i.p. injections of 800 mg/kg paracetamol. ATP/ADP ratios fall upon exposure to paracetamol both in vitro and in vivo. However, unlike the in vitro situation where the fall in ATP/ADP ratios precedes and accompanies the progression of cell injury, the in vivo fall in ATP/ADP ratios is shown to occur as cell injury measurements begin to recover to control levels. However, despite these differences classic paracetamol-induced centrilobular necrosis is observed to occur both in vitro and in vivo. This study demonstrates that the liver slice model is a simple and useful technique to investigate the underlying mechanisms of paracetamol-induced cell injury.

Immunochemical visualization and identification of rat liver proteins adducted by 2,6-di-tert-butyl-4-methylphenol (BHT)

Several alkylphenols (e.g., 2,6-di-tert-butyl-4-methylphenol, BHT) form reactive quinone methide intermediates (e.g., 2,6-di-tert-butyl-4-methylene-2,5-cyclohexadienone, BHT-QM) upon oxidation by cellular enzymes. In order to pursue the role of protein alkylation in alkylphenol toxicity, we used an immunochemical approach to identify protein targets alkylated by BHT. Synthetic BHT-N-acetylcysteine (BHT-NAC) was coupled to keyhole limpet hemocyanin and used as an antigen from which polyclonal antibodies were raised in New Zealand white rabbits. Rabbit serum contained an antibody which was highly specific for BHT-NAC, as determined by competitive ELISA. The BHT antibody was used as a probe to look for the presence of BHT-protein adducts in in vitro incubations with rat liver microsomes or tissue slices and also in vivo in liver tissue from male Sprague-Dawley rats exposed to BHT. Western blotting of protein gels revealed BHT-dependent protein alkylation over a wide molecular weight range. Prominent recurrent bands were observed at approximately 34.5, 52, 64.5, 74, and 97 kDa. Detection of adducts was inhibited in microsomal incubations by cytochrome P450 inhibitors, deuterated BHT, and the omission of NADPH. Similar protein alkylation patterns were observed in rat liver microsomes exposed to synthetically prepared BHT-QM as in the enzyme-mediated incubations. In rats gavaged with up to 1000 mg/kg BHT, the amount of protein alkylation observed was maximal at 24 h postdosing and was dose-dependent. Two alkylated proteins were isolated and identified by N-terminal sequencing: a mitochondrial beta-oxidation enzyme, enoyl-CoA hydratase, and a plasma membrane/cytoskeletal linker protein from the ezrin/moesin/radixin family.

Congenital malformations in experimental diabetic pregnancy: aetiology and antioxidative treatment. Minireview based on a doctoral thesis

Diabetes mellitus in pregnancy causes congenital malformations in the offspring. The aim of this work was to characterize biochemical and morphologic anomalies in the conceptus of an animal model of diabetic pregnancy. In addition, a preventive treatment against diabetes-induced dysmorphogenesis was developed. Congenital cataract was often found in the offspring of diabetic rats. The fetal lenses had increased water accumulation, sorbitol concentration and aldose reductase activity compared to control lenses. The results suggest that the cataracts form via osmotic attraction of water due to sorbitol accumulation in the fetal lens. Another set of malformations, with possible neural crest cell origin, occurred frequently in offspring of diabetic rats. These included low set ears, micrognathia, hypoplasia of the thymus, thyroid and parathyroid glands, as well as anomalies of the heart and great vessels. Furthermore, diabetes caused intrauterine death and resorptions more frequently in the late part of gestation. When the pregnant diabetic rats were treated with the antioxidants butylated hydroxytoluene, vitamin E or vitamin C, the occurrence of gross malformations was reduced from approximately 25% to less than 8%, and late resorptions from 17% to 7%. This suggests that an abnormal handling of reactive oxygen species (ROS) is involved in diabetes-induced dysmorphogenesis in vivo. Indeed, an increased concentration of lipid peroxides, indicating damage caused by ROS, was found in fetuses of diabetes rats. In addition, embryos of diabetic rats had low concentrations of the antioxidant vitamin E compared to control embryos. These biochemical alterations were normalized by vitamin E treatment of the pregnant diabetic rats. The antioxidants are likely to have prevented ROS injury in the embryos of the diabetic rats, in particular in the neural crest cells, thereby normalizing embryonic development. These results provide a rationale for developing new anti-teratogenic treatments for pregnant women with diabetes mellitus.

Effect of butylated hydroxytoluene on alpha-tocopherol content in liver and adipose tissue of rats

Female rats were fed an antioxidant supplemented diet containing butylated hydroxytoluene (BHT; 0.5% and 1.0%) with or without vitamin E acetate (0.4%) for 4 weeks, after which the contents of BHT and alpha-tocopherol in the liver and abdominal adipose tissue were analysed. The body weight gain was similar in all groups independent of the diet after the first week of treatment. At the end of the experiment the liver weights of the BHT-supplemented rats were increased compared to the liver weights of the control groups, and this difference was unaffected by vitamin E treatment. The liver concentration of alpha-tocopherol was decreased and inversely proportional to the BHT concentration in the diet. This attenuating effect of BHT on the hepatic alpha-tocopherol concentration was present both in animals with and without vitamin E supplementation. In contrast, BHT treatment did not alter the concentration of alpha-tocopherol in abdominal adipose tissue. The results show that BHT has adverse effects in the liver. BHT is metabolized by the cytochrome P450 system in the liver and may be converted to prooxidative compounds during this process. Adipose tissue lacks the cytochrome P450 system. Therefore, the decreased hepatic concentration of alpha-tocopherol may be a consequence of a BHT-induced, free oxygen radical mediated, depletion of this antioxidant.

Differential induction of isozymes of drug-metabolizing enzymes by butylated hydroxytoluene in mice and Chinese hamsters

Induction of isozymes of drug-metabolizing enzymes by butylated hydroxytoluene (BHT) was studied in the male ddY mouse and Chinese hamster. In mice given 0.05 and 0.15% BHT in the diet for 14 days cytochrome P-450 contents and the activities of uridine diphosphate-glucuronyl transferase (UDP-GT) and pentoxyresorufin O-dealkylase were markedly increased, while in those fed 0.15% BHT testosterone 6 alpha-, 16 alpha- and 16 beta-hydroxylases were greatly increased, which indicated induction of cytochrome P-450 isozymes of the CYP2B family. Western blot analysis also showed an increased level of the isozyme immunorelated to rat CYP2B2 by BHT feeding. The activities of aryl hydrocarbon hydroxylase, ethoxycoumarin O-deethylase (ECOD), erythromycin N-demethylase and glutathione S-transferase (GST) remained unchanged. In Chinese hamsters given 0.05 and 0.15% BHT in the diet for 14 days activities of ECOD and GST were induced, but cytochrome P-450 contents and the activities of other enzymes were unaffected. Testosterone 15 alpha-hydroxylase was induced in hamsters fed 0.15% BHT. These findings suggested that BHT administration in the hamster induced CYP2A2-type isozyme, which was confirmed by Western blot analysis. BHT treatment enhanced activation of benzo[a] pyrene (B[a]P) as determined by the mutagenicity test, especially in Chinese hamsters. The results suggest that BHT treatment induces specific isozymes of drug-metabolizing enzymes and might modify the expression of toxicities of other chemicals.

Comparison of in vivo and in vitro rat hepatic toxicity of coumarin and methyl analogues, and application of quantitative morphometry to toxicity in vivo

The rat hepatic toxicity of coumarin and methyl analogues (3-,4-methyl coumarin and 3,4-dimethylcoumarin) has been determined in vivo and in vitro (freshly-isolated cells). Coumarin at a dose of approximately 1 mmol/kg produced clear histological evidence of centrilobular necrosis, while the methyl analogues at an equivalent dose were much less toxic. By use of a systematic random sampling protocol and quantitative morphometry it was determined that there was a lobar variation in the extent of hepatic damage but that this exhibited random inter-animal variation. The order of cytotoxicity in vitro was identical to that observed in vivo. In hepatocytes depleted of glutathione the toxicity of all four compounds was increased. This was particularly marked for the 3-methyl analogues, such that the order of toxicity was different to that observed in vivo and in hepatocytes not depleted of glutathione.

Haemorrhages due to defective blood coagulation do not occur in mice and guinea-pigs fed butylated hydroxytoluene, but nephrotoxicity is found in mice

Groups of ten male Slc:ddY mice were fed a purified diet containing butylated hydroxytoluene (BHT) at levels of 0, 1.35, 1.75, 2.28, 2.96, 3.85 or 5.00%. They were kept in cages with soft-wood chips as bedding for 30 days. Groups of five Slc:ddY male mice were kept in cages with stainless-steel wire-mesh bottoms (without wood-chip bedding) and fed BHT at 0, 0.5, 1.0 or 2.0% in the diet for 21 days. Male Crj:Hartley guinea-pigs were given a purified ration containing BHT at levels of 0, 0.125 or 0.25% (five animals per group) for 14 days, or at 0, 0.5, 1.0 or 2.0% for 17 days (six animals per group). When BHT was given to mice housed in the mesh-bottomed cages there were one, one and two deaths during the experiment in the 0.5, 1.0 and 2.0% dose groups, respectively. Lung haemorrhages were observed in these dead mice, but in all other mice and guinea-pigs no haemorrhages were found. Indices of prothrombin time and kaolin-activated partial thromboplastin time were significantly decreased by up to 30 and 40%, respectively, in the mice kept on wood-chip bedding, and by up to 40 and 60% in the mice kept in cages with wire bottoms. In guinea-pigs, the prothrombin index was significantly reduced only in the 1.0% BHT group. We conclude that the BHT-induced lung haemorrhages in mice are not caused by a severe reduction in the coagulation process, as they are in rats, and that BHT does not cause bleeding like that observed in rats. However, dose-related toxic nephrosis was found in mice given 1.35-5.0% BHT in the diet. The nephrotoxic ED50(1 month) was 2.3 g/kg body weight/day. The results suggest that an extremely large dose of BHT can cause renal toxicity in mice.