Acute hepatotoxicity induced by hepatotoxins in Suncus murinus

Use of 99mTc-mercaptoacetyltriglycine (MAG3)-biocytin hepatobiliary scintigraphy to study the protective effect of a synthetic enzyme inhibitor on acute hepatotoxicity in mice

Recent data suggest that inhibitors of ethanol-inducible cytochrome P450 (CYP2E1) can protect the liver from injury caused by various substrates of CYP2E1. In this study, we measured the protective effect of isopropyl-2-(1,3-dithioetane-2-ylidene)-2[N-(4-methylthiazol -2-yl)-carbamoyl]acetate (YH439), a transcriptional inhibitor of CYP2E1, against carbon tetrachloride (CCl4)-induced hepatotoxicity by using various conventional methods and dynamic scintigraphy with 99mTc-mercaptoacetyltriglycine (MAG3)-biocytin, a recently developed scintigraphic agent. Balb/c mice were pretreated with two doses of YH439 (50 or 150 mg/kg per day) at 48 h and 24 h and one dose of CCl4 (0.25 mL/kg) at 18 h before scintigraphy. The results were compared with those of two other groups, one that received CCl4 but not YH439, and the other that received neither (control). Scintigraphic images were acquired continuously at 15-sec intervals for 30 min. Pharmacokinetic parameters, such as peak liver/heart ratio (r(max)), peak liver uptake time (t(max)), and hepatic half-clearance time (HCT), were obtained from time-activity curves derived from regions-of-interest (ROI) over the liver and the heart. Acute administration of CCl4 alone caused centrilobular necrosis and serum transaminase levels to rise more than 5 times higher than those of the control group. Pharmacokinetic parameters also changed significantly from those of the control group. Administration of YH439 prevented centrilobular necrosis and significantly improved pharmacokinetic parameters. This study demonstrates for the first time that hepatobiliary scintigraphy can be used to study in vivo biochemistry of the CYP2E1 inhibitor (YH439) against liver toxicity.

Effect of ethanol on esophageal cell proliferation and the development of N-methyl-N'-nitro-N-nitrosoguanidine induced-esophageal carcinoma in shrews

The effect of ethanol (EtOH) on esophageal cell proliferation and the development of esophageal cancers induced by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) in shrews were investigated. Sequential histological examination was done, and cell proliferation was assessed by BrdU labeling. At 5 weeks of age, animals were given tap water, 2% EtOH, 50 ppm MNNG, or 50 ppm MNNG plus 2%, 5% or 10% EtOH in the drinking water. Administration of 10% and 5% EtOH simultaneously with MNNG caused death in 40% (10/25) within 4 days and in 20% (6/30) within 7 days respectively, whereas other treatment were well tolerated with no sudden deaths. Administration of 2% EtOH for 30 weeks caused a 2-fold increase, and that of MNNG caused a 4.5-fold increase in the proliferation index of the basal cells of the esophagus compared with control shrews, and MNNG plus 2% EtOH caused a 5.5-fold increase. In MNNG-treated shrews, with or without 2% EtOH administration, sequential histological examination of esophageal tissue revealed a similar change; dysplasia appeared at 30 weeks of age, squamous cell carcinoma occurred at 35 weeks of age, and the depth of invasion extended to adventitia at 45 weeks of age. These finding indicate that treatment with 2% EtOH promoted the proliferation of esophageal basal cells but did not alter the tumor induction period and did not have tumor-promoting activity. EtOH per se was not carcinogenic; no tumors were seen in shrews not administered MNNG.

Liver apoptosis after dimethylnitrosamine administration in shrews

Female house musk shrews (Suncus murinus, Insectivora) were given a single i.p. dose of 30 mg/kg dimethylnitrosamine (DMN) at 8 weeks of age which was lethal 36 to 48 hrs after dosing. Liver tissues were collected from shrews killed 3, 6, 16, 24 and 36 hrs after treatment, and the sequential development of the lesions was characterized. DMN induced acute centrilobular cell injury. In 6 hrs, a few cells became apoptotic in the centrilobular area; the number increased at 16 hrs and 24 hrs, and was prominent at 36 hrs. There was no inflammatory reaction or necrosis and hemorrhage was not obvious. These apoptotic cells as well as normal appearing cells in the centrilobular area were labeled by the TUNEL method. In both hepatocytes and endothelial cells, apoptosis was confirmed electron microscopically as nuclear chromatin condensation at the periphery with no mitochondria swelling. When an i.p. dose of 10 mg/kg DMN was given twice at 8 and 9 weeks of age, no acute toxicity was induced, and the liver of shrews surviving for 50 weeks of age was normal with no tumor formation. These findings indicate that a single i.p. administration of 30 mg/kg DMN induced severe and fatal toxicity on liver tissues in shrews due to apoptosis, whereas 2 x 10 mg/kg DMN had no carcinogenic effect.

Decrease in the content of cytochrome P450IIE by fasting in liver microsomes of house musk shrew (Suncus murinus)

The effects of fasting on hepatic cytochrome P450 in the mature male house musk shrew, Suncus murinus (suncus), were studied by Western blot analyses and enzyme assays. The content of P450IIE protein was decreased, by fasting, to 24% of the control level in contrast to the results with rats, in which P450IIE protein was increased to 172% by fasting. These changes reflected on catalytic activities, such as aniline hydroxylase and N-nitrosodimethylamine demethylase activities, which were decreased to about 45% and 28%, respectively, of the control levels by fasting, while in fasting rats, the catalytic activities of these enzymes were 2-3-fold higher than in controls.

Suncus murinus: a new experimental model in emesis research

Effects of various emetic and antiemetic drugs were studied using Suncus murinus for its potential use as an experimental model in emetic research. Subcutaneous injection of nicotine bitartrate (10-15 mg/kg), veratrine sulfate (0.5-1.0 mg/kg), emetine dihydrochloride (40-80 mg/kg) and oral administration of copper sulfate (20-100 mg/kg) caused dose-dependent emesis in suncus. The ED50 of nicotine, veratrine, emetine and copper sulfate were 7.9, 0.4, 47.6 and 21.4 mg/kg, respectively. However, subcutaneously injected apomorphine hydrochloride (0.1-100 mg/kg), digitoxin (0.5-1.0 mg/kg) and orally administered emetine dihydrochloride (10-80 mg/kg) did not induce the vomiting. Chlorpromazine and promethazine decreased the emetic effect of nicotine, veratrine and copper sulfate, but scopolamine hydrobromide was not effective. These results indicate that the Suncus murinus is sensitive to various emetic and antiemetic drugs and can be used as a new experimental animal model for the emesis. Emetic behavior of suncus was discussed in comparison with other animals.