Alleviation of fatty liver in a rat model by enhancing N1-methylnicotinamide bioavailability through aldehyde oxidase inhibition.

Nonalcoholic fatty liver disease (NAFLD) has increased worldwide in recent years. NAFLD is classified into two types, nonalcoholic fatty liver (NAFL), with few complications, and nonalcoholic steatohepatitis (NASH), which leads to liver cirrhosis or cancer. This study was based on previous reports that N1-methylnicotinamide (MNA) can stabilise sirtuin 1 protein, leading to decreased lipid levels in the liver. We hypothesised that fatty liver improvement by MNA would be further enhanced by suppressing its rapid metabolism by aldehyde oxidase in the liver. To test this, hydralazine (HYD), a potent aldehyde oxidase inhibitor, was administered orally to NAFL model rats. Liver triglyceride (TG) levels in the model were nearly unchanged by administration of MNA alone. In contrast, TG levels were marked decreased in NAFL rats treated with a combination of MNA and HYD. In addition, TG levels were decreased even in NAFL rats treated with only HYD. These findings supported our hypothesis that maintaining MNA concentrations in the liver, by suppressing MNA metabolism, would at least partially ameliorate fatty liver.

Reduction of fatty liver in rats by nicotinamide via the regeneration of the methionine cycle and the inhibition of aldehyde oxidase.

Nonalcoholic fatty liver disease, which has been rapidly increasing in the world in recent years, is roughly classified into nonalcoholic fatty liver (NAFL) and nonalcoholic steatohepatitis. This study was based on our previous reports that stated that the combination treatment of N1-methylnicotinamide (MNA) and hydralazine (HYD) improves fatty liver in NAFL model rats. This finding was attributed to the MNA metabolism inhibition by HYD, which is a strong inhibitor of aldehyde oxidase (AO); this results in an increase in hepatic MNA and improved fatty liver. We hypothesized that orally administered nicotinamide (NAM), which is the precursor of MNA and is a form of niacin, would be efficiently metabolized by nicotinamide N-methyltransferase in the presence of exogenous S-adenosylmethionine (SAM) in NAFL rats. To address this issue, NAFL model rats were orally administered with NAM, SAM, and/or HYD. As a result, liver triglyceride (TG) and lipid droplet levels were barely altered by the administration of NAM, SAM, NAM+SAM, or NAM+HYD. By contrast, the triple combination of NAM+SAM+HYD significantly reduced hepatic TG and lipid droplet levels and significantly increased hepatic MNA levels. These findings indicated that the combination of exogenous SAM with AO inhibitors, such as HYD, has beneficial effects for improving fatty liver with NAM.

Dehydroepiandrosterone sulfate and cytochrome P450 inducers alleviate fatty liver in male rats fed an orotic acid-supplemented diet.

The effects of the peroxisome proliferator, dehydroepiandrosterone sulfate (DHEAS), and the typical cytochrome P450 (CYP) inducers phenobarbital (PB) and 3-methylcholanthrene (3-MC) on fatty liver were examined in rats. Treating rats with orotic acid caused marked accumulation of lipid droplets in the liver. This effect of orotic acid was almost eradicated by co-treatment with DHEAS and PB. While DHEAS or PB alone also alleviated fatty liver, treatment with 3-MC caused little effect on a reduction in lipid droplets. Histopathological examinations revealed numerous peroxisomes in the liver of rats treated with DHEAS. In addition, a significant increase in the expression on hepatic CYPs was observed in rats the fatty liver of which was attenuated. Regarding other enzymes associated with hepatic fatty acid oxidation, the expression levels of sirtuin 1, sirtuin 6, and carnitine palmitoyltransferase 1 were also upregulated most markedly by treatment with DHEAS alone. Thus, the attenuation in fatty liver observed in the present study is likely due to peroxisome proliferation and the induction of fatty acid-metabolizing enzymes by DHEAS and typical CYP inducers.

Intratracheal administration of bleomycin via a catheter in unanesthetized rats.

In order to ensure a widespread distribution in the lung and to avoid the effect of anesthesia, bleomycin at a total dose of 4.5 or 6.0 mg/kg was administered in four divided doses (0.5 ml/kg/time) at intervals of 2 h to male rats via a catheter (tracheotomy tube) without anesthesia. In comparison to vehicle (saline) controls, bleomycin-treated rats showed a significant suppression of body weight gain that was observed transiently at 4.5 mg/kg and continuously (throughout the 3-week observation period) at 6.0 mg/kg. Histopathologically, interstitial pneumonitis, thickening of alveolar walls, thickening of pulmonary arterial walls, foamy cells in alveoli, and hemorrhage were observed in both 4.5 and 6 mg/kg groups, and also emphysema in the 6 mg/kg group. Both groups exhibited a significant decrease in the partial pressure of arterial oxygen (PaO(2)) and a significant increase in alveolar-arterial oxygen tension difference (AaDO(2)), and a significant increase in erythrocyte count was observed in the 6 mg/kg group. Furthermore, both treated groups showed a significant increase in the ratio of the right ventricular weight versus left ventricle plus septum weights. The significant increase in erythrocyte count might have been caused by diffusion disturbance and ventilation-perfusion imbalance due to the pulmonary damage. These findings suggest that the present experimental method will be useful for clarification of the pulmonary damage induced by bleomycin in rats.

Interlaboratory validation of the modified murine local lymph node assay based on adenosine triphosphate measurement.

INTRODUCTION: The murine local lymph node assay (LLNA) is a well-established alternative to the guinea pig maximization test (GPMT) or Buehler test (BT) for the assessment of the skin sensitizing ability of drugs and chemicals. Daicel Chemical Industries Ltd. has developed a modified LLNA based on the adenosine triphosphate (ATP) content (LLNA-DA). We conducted 2 interlaboratory validation studies to evaluate the reliability and relevance of LLNA-DA. METHODS: The experiment involved 17 laboratories, wherein 14 chemicals were examined under blinded conditions. In the first study, 3 chemicals were examined in 10 laboratories and the remaining 9 were examined in 3 laboratories. In the second study, 1 chemical was examined in 7 laboratories and the remaining 4 chemicals were examined in 4 laboratories. The data were expressed as the ATP content for each chemical-treated group, and the stimulation index (SI) for each chemical-treated group was determined as the increase in the ATP content relative to the concurrent vehicle control group. An SI of 3 was set as the cut-off value for exhibiting skin sensitization activity. RESULTS: The results of the first study obtained in the experiments conducted for the 3 chemicals that were examined in all the 10 laboratories and for 5 of the remaining 9 chemicals were sufficiently consistent with small variations in their SI values. The sensitivity, specificity, and accuracy of LLNA-DA against those of GPMT/BT were 7/8 (87.5%), 3/3 (100%), and 10/11 (90.9%), respectively. In the second study, all the 5 chemicals studied demonstrated acceptably small interlaboratory variations. DISCUSSION: In the first study, a large variation was observed for 2 chemicals; in the second study, this variation was small. It was attributed to the application of dimethylsulfoxide as the solvent for the metallic salts. In conclusion, these 2 studies provide good evidence for the reliability of the LLNA-DA.