Mechanisms of pathogenesis in drug hepatotoxicity putting the stress on mitochondria

Comparison of toxic reaction of Tripterygium wilfordii multiglycoside in normal and adjuvant arthritic rats

AIM OF THE STUDY

Tripterygium wilfordii multiglycoside (GTW), an authorized Chinese patent drug, is used for treatment of rheumatoid arthritis and other immune disease. This study was to determine whether GTW induced different toxic reactions in adjuvant arthritis rats (AA rats) compared to those in normal rats.

MATERIALS AND METHODS

To prepare arthritic rat model, male Sprague-Dawley (SD) rats were immunized by injecting complete Freund's Adjuvant into right hind footpad. And then, GTW was given to rats intragastrically at dosage of 7 or 105 mg kg(-1)day(-1) from day 15 to day 28 after immunization. Routine clinical parameters and histopathologic changes of liver, kidney and testis were examined. Metabolic profiling in serum of groups was analyzed by LC-MS. A principal component analysis (PCA) and partial-least-squares discriminate analysis (PLS-DA) were carried out combined with mass spectrometry (MS) data set. All the quantitative data were performed by two-way ANOVA analysis following Student's t-test.

RESULTS AND CONCLUSIONS

Treatment with GTW at both doses could diminish the right and left hind paws swelling. There was slight lipoid degeneration in hepatic tissue of normal rats treated by high dose of GTW, but there were not distinctly pathological changes in hepatic tissue of AA rats treated by GTW. Compared normal rats administered with GTW, no statistically significant difference in the serum alanine aminotransferase (ALT), creatinine (CRE), and blood urea nitrogen (BUN) levels were observed. However, the serum aspartate aminotransferase (AST) level was significant decreased in AA rats under exposure GTW compared with normal rats in the same conditions (p<0.05), which indicated that GTW could offer a different liver toxic reaction in normal and AA rats. The metabolic analysis showed that a clear separation of PCA and PLS-DA score spot in normal rats, but not separation was seen in AA rats perturbed with low dosage GTW. The result indicated low dosage GTW might arouse a general toxic in normal rats but not in AA rats. The biomarker analysis showed that the level of lysophosphatidylcholines (LPCs) was down-regulated, but the level of ursodeoxycholic acid (UDCA) and chenodexycholic acid (CDCA) was up-regulated in AA rats compared with normal rats under exposure GTW. According to pathway analysis of metabolic markers, we conceived that LPC, UDCA and CDCA were the critical intermediates of choline and fatty acid metabolism. And the lipid metabolism was a correlative outcome of GTW induced toxicity in the liver in physiological condition animals. Taken together, GTW could induce different toxic reactions between normal and AA rats, and the lipid metabolism might be part of the mechanism for the hepatic lipidosis or the other liver injury.

Drug-induced liver injury: a summary of recent advances

INTRODUCTION

The knowledge base of drug-induced liver injury (DILI) continues to grow each year as additional drugs are identified as hepatotoxins. There is still a need to improve our ability to predict and diagnose DILI in the preclinical and post-approval settings.

AREAS COVERED

This article presents the new and updated DILI registries for 2010, including the latest information on the causes and outcomes of non-acetaminophen DILI cases in the US Acute Liver Failure Study Group database. As DILI is still largely a diagnosis of exclusion, it is appropriate that causality assessment instruments are again the subject of considerable discussion.

EXPERT OPINION

DILI research remains extremely active including studies aimed at being better able to identify causative agents, utilize potential biomarkers, predict who is at greatest risk of injury and manage outcomes. With respect to identifying DILI risk factors at the genetic level, the field is rapidly approaching the day where 'personalized medicine' (based on pharmacogenomics) will become a reality. A large single-center series from India reminds us that geography can influence the drugs responsible for liver injury; however, Hy's law remains universal. As our DILI knowledge continues to grow, it remains essential to keep abreast of the important changes reported each year.

Drug-induced toxicity on mitochondria and lipid metabolism: mechanistic diversity and deleterious consequences for the liver

Numerous investigations have shown that mitochondrial dysfunction is a major mechanism of drug-induced liver injury, which involves the parent drug or a reactive metabolite generated through cytochromes P450. Depending of their nature and their severity, the mitochondrial alterations are able to induce mild to fulminant hepatic cytolysis and steatosis (lipid accumulation), which can have different clinical and pathological features. Microvesicular steatosis, a potentially severe liver lesion usually associated with liver failure and profound hypoglycemia, is due to a major inhibition of mitochondrial fatty acid oxidation (FAO). Macrovacuolar steatosis, a relatively benign liver lesion in the short term, can be induced not only by a moderate reduction of mitochondrial FAO but also by an increased hepatic de novo lipid synthesis and a decreased secretion of VLDL-associated triglycerides. Moreover, recent investigations suggest that some drugs could favor lipid deposition in the liver through primary alterations of white adipose tissue (WAT) homeostasis. If the treatment is not interrupted, steatosis can evolve toward steatohepatitis, which is characterized not only by lipid accumulation but also by necroinflammation and fibrosis. Although the mechanisms involved in this aggravation are not fully characterized, it appears that overproduction of reactive oxygen species by the damaged mitochondria could play a salient role. Numerous factors could favor drug-induced mitochondrial and metabolic toxicity, such as the structure of the parent molecule, genetic predispositions (in particular those involving mitochondrial enzymes), alcohol intoxication, hepatitis virus C infection, and obesity. In obese and diabetic patients, some drugs may induce acute liver injury more frequently while others may worsen the pre-existent steatosis (or steatohepatitis).

The evaluation of drug rechallenge: the casopitant Phase III program

Drug rechallenge (or reinitiation), following an event of drug-induced liver injury, is associated with 13% mortality in prospective series. Rechallenge generally results in much more rapid injury than the initial liver event. The neurokinin-1 antagonist casopitant or its placebo was administered cyclically with ondansetron and dexamethasone in two randomized chemotherapy-induced nausea and vomiting clinical trials in nearly 3000 subjects. Grade 3 ALT elevations were observed in up to 2% of subjects receiving casopitant or placebo treatment. Similar rates of positive rechallenge were observed in the casopitant 8/29 (28%) and placebo groups 2/8 (25%), with no Grade 4 ALT elevations, hypersensitivity or liver-related serious adverse events. Publishing available rechallenge data (positive and negative) will advance our clinical understanding. Rechallenge should only be considered when the potential drug benefit exceeds the risk.