硫代乙酰胺诱导大鼠肝纤维化的研究

目的研究硫代乙酰胺对大鼠肝纤维化模型的诱导作用。方法采用0．03％的硫代乙酰胺腹腔注射,每周2次,构建大鼠肝纤维化模型;观察大鼠肝纤维化形成情况。结果与空白组比较,模型组大鼠血清谷丙转氨酶（ALT）、谷草转氨酶（AST）、透明质酸（HA）明显升高（P〈0．01）;层粘连蛋白（LN）升高（P〈0．05）。组织病理提示模型组大鼠肝细胞大量坏死,假小叶形成。结论硫代乙酰胺能诱导大鼠形成肝纤维化。     

Application of metabonomics on an experimental model of fibrosis and cirrhosis induced by thioacetamide in rats

Metabonomics has already been used to discriminate different pathological states in biological fields. The metabolic profiles of chronic experimental fibrosis and cirrhosis induction in rats were investigated using (1)H NMR spectroscopy of liver extracts and serum combined with pattern recognition techniques. Rats were continuously administered with thioacetamide (TAA) in the drinking water (300 mg TAA/L), and sacrificed on 1st, 2nd, and 3rd month of treatment. (1)H NMR spectra of aqueous and lipid liver extracts, together with serum were subjected to Principal Component Analysis (PCA). Liver portions were also subjected to histopathological examination and biochemical determination of malondialdehyde (MDA). Liver fibrosis and cirrhosis were progressively induced in TAA-treated rats, verified by the histopathological examination and the alterations of MDA levels. TAA administration revealed a number of changes in the (1)H NMR spectra compared to control samples. The performance of PCA in liver extracts and serum, discriminated the control samples from the fibrotic and cirrhotic ones. Metabolic alterations revealed in NMR spectra during experimental liver fibrosis and cirrhosis induction, characterize the stage of fibrosis and could be illustrated by subsequent PCA of the spectra. Additionally, the PCA plots of the serum samples presented marked clustering during fibrosis progression and could be extended in clinical diagnosis for the management of cirrhotic patients.     

Toxicokinetics and toxicity of thioacetamide sulfoxide: a metabolite of thioacetamide

Thioacetamide (TA) is bioactivated by CYP2E1 to TA sulfoxide (TASO), and to the highly reactive sulfdioxide (TASO₂), which initiates hepatic necrosis by covalent binding. Previously, we have established that TA exhibits saturation toxicokinetics over a 12-fold dose range, which explains the lack of dose–response for bioactivation-based liver injury. In vivo and in vitro studies indicated that the second step (TASO → TASO₂) of TA bioactivation is less efficient than the first one (TA → TASO). The objective of the present study was to specifically test the saturation of the second step of TA bioactivation by directly administering TASO, which obviates the contribution from first step, i.e. TA → TASO. Male SD rats were injected with low (50 mg/kg, ip), medium (100 mg/kg) and high (LD₇₀, 200 mg/kg) doses of TASO. Bioactivation-mediated liver injury that occurs in the initial time points (6 and 12 h), estimated by plasma ALT, AST and liver histopathology over a time course, was not dose-proportional. Escalation of liver injury thereafter was dose dependent: low dose injury subsided; medium dose injury escalated upto 36 h before declining; high dose injury escalated from 24 h leading to 70% mortality. TASO was quantified in plasma by HPLC at various time points after administration of the three doses. With increasing dose (i.e., from 50 to 200 mg/kg), area under the curve (AUC) and C_max increased more than dose proportionately, indicating that TASO bioactivation exhibits saturable kinetics. Toxicokinetics and initiation of liver injury of TASO are similar to that of TA, although TASO-initiated injury occurs at lower doses. These findings indicate that bioactivation of TASO to its reactive metabolite is saturable in the rat as suggested by previous studies with TA.     

解毒口服液对大鼠实验性肝损伤内毒素血症的防护作用

目的:探讨中医药对肝损伤大鼠内毒素血症的防治作用。方法:应用硫代乙酰胺灌胃建立暴发性肝衰竭大鼠模型,观察解毒口服液对实验性肝损伤大鼠血浆内毒素、肝功能及肝组织病理学指标的影响。结果:解毒口服液组在降低血浆内毒素、缩短凝血酶原时间、改善肝脏病理损伤程度方面,与损伤组比较均有非常显著的差异(P<0.01);解毒护肝口服液组次之(P<0.05)。在改善肝功酶系指标方面,解毒口服液与损伤组比较亦有显著差异(P<0.05),略差于解毒护肝口服液组。结论:解毒口服液有较好改善肝脏功能、防治内毒素血症的功效。     

Contrasting effects of thioacetamide-induced liver damage on the brain uptake indices of ornithine,arginine and lysine: Modulation by treatment with ornithine aspartate

The dibasic amino acids arginine (ARG), ornithine (ORN) and lysine (LYS) are transported by a common saturable transporter (system ⁺) at the blood-brain barrier (BBB). In the present study we compared the brain uptake index (BUI) for radiolabelled ORN, ARG and LYS in control rats and in rats treated with thioacetamide (TAA) to induce hepatic encephalopathy (HE). Some animals received i.v. ornithine aspartate (OA), a drug structurally related to the ⁺ substrates that ameliorates neurological symptoms following liver damage by improving detoxification of ammonia in peripheral tissues: the compound was administered either by continuous infusion for 6h at a concentration of 2 g/kg (final blood concentration ranging from 0.19–0.5 mM), or as a 15 sec. bolus together with the radiolabelled amino acids, at a concentration of 0.35 mM. TAA treatment resulted in a delayed and progressive increase of BUI for ORN, to 186% of control at 7d post-treatment and to 345% of control at 21d post-treatment, when despite sustained liver damage, HE symptoms were already absent. In contrast, the BUI for ARG decreased to 30% of control at 7d post-treatment and remained low (42% of control) at 21d post-treatment. A 6h infusion of OA to untreated rats resulted in a reduction of the BUI for ARG and ORN to 51% and 62% of the control levels, respectively. Reductions of a similar magnitude were noted with both amino acids following the 15 sec OA bolus, indicating direct interaction of OA with the transport site in both cases. OA administered by either route abolished the enhancement of BUI for ORN, but did not further inhibit the BUI for ARG in the TAA-treated animals. The results indicate that some as yet unspecified factors released from damaged liver either modify the structure or conformation of the ⁺ transporter at the BBB from the normally ARG-preferring to the ORN-preferring state, or activate (induce) a different transporter specific for ORN which is normally latent.     

硫代乙酰胺诱导大鼠急性肝性脑病模型建立的用药时间研究

目的通过硫代乙酰胺（TAA,300mg·kg^-1·d^-1）不同用药时间诱导A型肝性脑病,比较大鼠的行为学、生物化学以及组织学改变,探讨造模最适时间。方法将大鼠分为A、B、C、D四组,其中A组为正常对照组;B、C、Di组用TAA（300mg·kg^-1·d^-1）分别连续灌胃2d、3d、4d,A组用相等量生理盐水灌胃4d。比较各组大鼠行为学变化、脑功能评分、AHE的诱导率和致死率,并分析各组给药结束24h后血氨、ALT、AST、TBIL的差异。结果C、D组比B组大鼠脑功能评分高,差异有统计学意义（P〈0．0083）;C、D组比B组诱导率高（P〈0．0083）,而D组比B、C组的大鼠致死率高,差异有统计学意义（P〈0．0083）;C、D组血氨及ALT、AST、TBIL肝功能指标比B组高,差异有统计学意义（P〈0．0083）;C、D组TAA用药后肝组织学观察炎症浸润、坏死、纤维化等损害最明显。结论300mg·kg^-1·d^-1的TAA连续灌胃3d,行为学改变显著．致死率较低．血氨较高．肝功能损害明显．为TAA诱导大鼠急性肝性脑病适宜时间。     

Chronic liver injury by thioacetamide and promotion of hepatic carcinogenesis

Summary To verify whether a mild, but prolonged liver injury by chemicals needing bioactivation causes both hepatic cirrhosis and the appearance of hepatocyte nodules and tumors (providing the liver has been exposed previously to initiating stimuli), diethylnitrosamine-initiated and uninitiated rats were administered thioacetamide at low dose (250 mg/l drinking water) for 6 months. Hepatocyte nodule incidence as well as changes in the drug-metabolizing system were followed at monthly intervals. In the uninitiated rats a micronodular liver cirrhosis slowly developed upon thioacetamide chronic administration; a few hepatocyte focal lesions of small size were seen from the 3rd month onward. By contrast in the diethylnitrosamine-initiated thioacetamide-treated rats the liver was macronodular because of the appearance and growth of many hepatocyte nodules; some hepatomas were also seen. During thioacetamide administration both uninitiated and diethylnitrosamine-initiated rats underwent a progressive decrease of the cytochrome P-450 liver content as well as of the activity of aminopyrine N-demethylase, ethoxycoumarin O-deethylase and ethoxyresorufin O-deethylase. On the other hand, most components of the phase II of the drug-metabolizing system were markedly enhanced. In conclusion, chronic administration of thioacetamide at low doses provided strong promoting stimuli for previously initiated hepatocytes.     

Type 2 diabetic rats are sensitive to thioacetamide hepatotoxicity

Previously, we reported high hepatotoxic sensitivity of type 2 diabetic (DB) rats to three dissimilar hepatotoxicants. Additional work revealed that a normally nonlethal dose of CCl4 was lethal in DB rats due to inhibited compensatory tissue repair. The present study was conducted to investigate the importance of compensatory tissue repair in determining the final outcome of hepatotoxicity in diabetes, using another structurally and mechanistically dissimilar hepatotoxicant, thioacetamide (TA), to initiate liver injury. A normally nonlethal dose of TA (300 mg/kg, ip), caused 100% mortality in DB rats. Time course studies (0 to 96 h) showed that in the non-DB rats, liver injury initiated by TA as assessed by plasma alanine or aspartate aminotransferase and hepatic necrosis progressed up to 48 h and regressed to normal at 96 h resulting in 100% survival. In the DB rats, liver injury rapidly progressed resulting in progressively deteriorating liver due to rapidly expanding injury, hepatic failure, and 100% mortality between 24 and 48 h post-TA treatment. Covalent binding of 14C-TA-derived radiolabel to liver tissue did not differ from that observed in the non-DB rats, indicating similar bioactivation-based initiation of hepatotoxicity. S-phase DNA synthesis measured by [3H]-thymidine incorporation, and advancement of cells through the cell division cycle measured by PCNA immunohistochemistry, were substantially inhibited in the DB rats compared to the non-DB rats challenged with TA. Thus, inhibited cell division and compromised tissue repair in the DB rats resulted in progressive expansion of liver injury culminating in mortality. In conclusion, it appears that similar to type 1 diabetes, type 2 diabetes also increases sensitivity to dissimilar hepatotoxicants due to inhibited compensatory tissue repair, suggesting that sensitivity to hepatotoxicity in diabetes occurs in the absence as well as presence of insulin.     

Hepatotoxin-induced hypertyrosinemia and its toxicological significance

A ¹H Nuclear Magnetic Resonance (NMR) spectroscopic investigation of the effects of single doses of four model hepatotoxins on male Sprague–Dawley rats showed that hypertyrosinemia was induced by three of the treatments (ethionine 300 mg/kg, galactosamine hydrochloride 800 mg/kg and isoniazid 400 mg/kg) but not by the fourth (thioacetamide 200 mg/kg). Concomitant histopathological and clinical chemistry analyses showed that hypertyrosinemia could occur with or without substantial hepatic damage and that substantial hepatic damage could occur without hypertyrosinemia. However, in the rats dosed with galactosamine hydrochloride, which showed highly variable amounts of liver damage at ca. 24 h after dosing, a clear relationship was found between the degree of hypertyrosinemia and the extent of the hepatic necrosis induced. In line with the cause of clinically observed Type II Tyrosinemia, we consider that the critical event in the onset of hepatotoxin-induced hypertyrosinemia is likely to be a reduction in hepatic tyrosine aminotransferase (TAT) activity. We discuss mechanisms by which TAT activity could be lost with special consideration given to pyridoxal 5′-phosphate (P5P) depletion and to the inhibition of protein synthesis. This analysis may have implications for the interpretation of clinical measures of liver status such as Fischer’s ratio and the branched-chain tyrosine ratio (BTR).     

Investigation of antioxidant,anti-inflammatory and DNA-protective properties of eugenol in thioacetamide-induced liver injury in rats

The present study investigated the preventive effect of eugenol, a naturally occurring food flavouring agent on thioacetamide (TA)-induced hepatic injury in rats. Adult male Wistar rats of body weight 150–180 g were used for the study. Eugenol (10.7 mg/kg b.w./day) was administered to rats by oral intubation for 15 days. TA was administered (300 mg/kg b.w., i.p.) for the last 2 days at 24 h interval and the rats were sacrificed on the 16th day. Markers of liver injury (aspartate transaminase, alanine transaminase, alkaline phosphatase, γ-glutamyl transferase and bilirubin), inflammation (myeloperoxidase, tumor necrosis factor-α and interleukin-6), oxidative stress (lipid peroxidation indices, protein carbonyl and antioxidant status) and cytochrome P4502E1 activity were assessed. Expression of cyclooxygenase-2 (COX-2) and the extent of DNA damage were analyzed using immunoblotting and comet assay, respectively. Liver injury and collagen accumulation were assessed using histological studies by hematoxylin and eosin and Masson trichrome staining. Rats exposed to TA alone showed increased activities of hepatocellular enzymes in plasma, lipid peroxidation indices, inflammatory markers and pro-inflammatory cytokines and decreased antioxidant status in circulation and liver. Hepatic injury and necrosis were also evidenced by histology. Eugenol pretreatment prevented liver injury by decreasing CYP2E1 activity, lipid peroxidation indices, protein oxidation and inflammatory markers and by improving the antioxidant status. Single-cell gel electrophoresis revealed that eugenol pretreatment prevented DNA strand break induced by TA. Increased expression of COX-2 gene induced by TA was also abolished by eugenol. These findings suggest that eugenol curtails the toxic effects of TA in liver.