Drug-induced liver disease

Mitochondria as the Target of Hepatotoxicity and Drug-Induced Liver Injury: Molecular Mechanisms and Detection Methods

One of the major mechanisms of drug-induced liver injury includes mitochondrial perturbation and dysfunction. This is not a surprise, given that mitochondria are essential organelles in most cells, which are responsible for energy homeostasis and the regulation of cellular metabolism. Drug-induced mitochondrial dysfunction can be influenced by various factors and conditions, such as genetic predisposition, the presence of metabolic disorders and obesity, viral infections, as well as drugs. Despite the fact that many methods have been developed for studying mitochondrial function, there is still a need for advanced and integrative models and approaches more closely resembling liver physiology, which would take into account predisposing factors. This could reduce the costs of drug development by the early prediction of potential mitochondrial toxicity during pre-clinical tests and, especially, prevent serious complications observed in clinical settings.

Drug-induced liver injury through mitochondrial dysfunction: mechanisms and detection during preclinical safety studies

Mitochondrial dysfunction is a major mechanism whereby drugs can induce liver injury and other serious side effects such as lactic acidosis and rhabdomyolysis in some patients. By severely altering mitochondrial function in the liver, drugs can induce microvesicular steatosis, a potentially severe lesion that can be associated with profound hypoglycaemia and encephalopathy. They can also trigger hepatic necrosis and/or apoptosis, causing cytolytic hepatitis, which can evolve into liver failure. Milder mitochondrial dysfunction, sometimes combined with an inhibition of triglyceride egress from the liver, can induce macrovacuolar steatosis, a benign lesion in the short term. However, in the long term this lesion can evolve in some individuals towards steatohepatitis, which itself can progress to extensive fibrosis and cirrhosis. As liver injury caused by mitochondrial dysfunction can induce the premature end of clinical trials, or drug withdrawal after marketing, it should be detected during the preclinical safety studies. Several in vitro and in vivo investigations can be performed to determine if newly developed drugs disturb mitochondrial fatty acid oxidation (FAO) and the oxidative phosphorylation (OXPHOS) process, deplete hepatic mitochondrial DNA (mtDNA), or trigger the opening of the mitochondrial permeability transition (MPT) pore. As drugs can be deleterious for hepatic mitochondria in some individuals but not in others, it may also be important to use novel animal models with underlying mitochondrial and/or metabolic abnormalities. This could help us to better predict idiosyncratic liver injury caused by drug-induced mitochondrial dysfunction.

Review article: The use of potentially hepatotoxic drugs in patients with liver disease

BACKGROUND

Misconceptions surround the use of hepatotoxic drugs in chronic liver disease. While many prescription and over-the-counter (OTC) agents can be used safely, this often runs counter to labelled warnings/contraindications, especially for the statins and other commonly used agents.

AIM

To evaluate published data on the use of hepatotoxic drugs in chronic liver disease including pharmacokinetic changes in cirrhosis and drug interactions, where available, to formulate recommendations on their use.

METHODS

Using a combination of PubMed searches, review texts, the Physicians' Desk Reference and expert opinion, drugs considered at higher risk of hepatotoxicity in chronic liver disease were evaluated.

RESULTS

Most drugs and OTC products including herbals have not been formally studied in chronic liver disease, but available data suggest that several of the most commonly used agents, especially the statins, can be used safely. While there is an increased risk of drug-induced liver injury for drugs used in the treatment of tuberculosis and HIV patients with hepatitis B or C, recommendations for their safe use are emerging.

CONCLUSIONS

Although many clinicians remain hesitant to use hepatotoxic drugs in chronic liver disease, the database supporting this view is limited to just a few agents. Most medications can be used safely in patients with chronic liver disease with appropriate monitoring.

Incidence of statin hepatotoxicity in patients with hepatitis C

BACKGROUND AND AIMS

Statins are considered contraindicated in patients with chronic liver disease. Our objective was to determine the risk of developing hepatotoxicity from statin therapy in hyperlipidemic patients with hepatitis C.

METHODS

Changes in liver biochemistry values within 12 months compared with baseline were determined in 3 cohorts matched for age, sex, and body mass index: (I) 166 anti-hepatitis C virus (HCV)-positive hyperlipidemic veterans who were initiated on statin therapy; (II) 332 anti-HCV-positive veterans who had not received statin therapy; and (III) 332 anti-HCV-negative hyperlipidemic veterans who were initiated on statin therapy. An increase in liver biochemistry values was defined as mild-moderate or severe as proposed in a previous study on statin hepatotoxicity in a non-hepatitis C population.

RESULTS

In patients with hepatitis C, statin therapy (cohort I) was associated with a higher incidence of mild-moderate liver biochemistry value increases compared with those not on statin therapy (cohort II) (22.9% vs 13.3%, respectively, P = .009), but a lower incidence of severe increases (1.2% vs 6.6%, respectively, P = .015). Among patients started on statin therapy (cohorts I and III), the incidence of mild-moderate liver biochemistry value increases (22.9% vs 16.3%, respectively, P = .094), severe increases (1.2% vs 1%, respectively, P = .874), or discontinuation of statin therapy as a result of hepatotoxicity (21.6% vs 9.2%, respectively, P = .147) were similar in hepatitis C-positive and hepatitis C-negative patients.

CONCLUSIONS

Statin therapy was not associated with a higher risk of severe hepatotoxicity in patients with chronic hepatitis C and appeared safe.

Drug-induced liver disease 2004

PURPOSE OF REVIEW

To summarize the salient reviews, studies and case reports and series that dealt with clinical, pathological, methodological, and epidemiological descriptions of drug-induced liver disease in the calendar year 2004.

RECENT FINDINGS

While no new causes of drug-induced liver injury were reported for 2004, several new reports of previously recognized hepatotoxins, including herbal products, were published. These include the antiretroviral drugs for HIV and agents to manage tuberculosis. Acetaminophen (APAP) retained its preeminent position as the leading cause of drug-induced acute liver failure, currently accounting for nearly 50% of cases according to the latest figures from the U.S. Acute Liver Failure Study Group. Not surprisingly, APAP also heads the list of drugs and toxins leading to liver transplantation for acute hepatic failure. Efforts to reduce the number of cases of intentional APAP poisonings by restricting the number of tablets sold at any one time in the UK are ongoing, but the success of the program may be lessening, as was pointed out this year. The use of potentially hepatotoxic medications in patients with underlying liver disease was examined with the statins, and they emerged as a safe class for use in this setting.

SUMMARY

Given the apparent increasing incidence of acute liver failure attributable to APAP in the US, additional efforts are still needed to better define the risks associated with its use and to further reduce the incidence of severe liver injury from this widely used agent.

Workshop Overview: Hepatotoxicity Assessment for Botanical Dietary Supplements

Botanical dietary supplements (herbal products) have flooded the market in the United States over the past decade, and studies show a significant percentage of Americans use them. With increasing frequency and duration of exposure, some serious adverse effects, though relatively uncommon, have been reported. Among the most troublesome is the association of some botanicals with serious hepatotoxicity. In some cases, hepatotoxicity has been linked to the consumption of botanicals with recognized hepatotoxic components (e.g., pyrrolizidine alkaloids). However, in other cases, the causative agent(s) is less clear and, overall, the mechanisms of hepatotoxicity are poorly understood. To help create a scientific basis for understanding botanical-induced hepatotoxicity and better tools for hepatotoxicity assessment and prediction, the National Center for Natural Product Research (NCNPR) hosted a workshop (September 8 and 9, 2003) in cooperation with the Center for Food Safety and Applied Nutrition (CFSAN) of the Food and Drug Administration (FDA). The workshop featured presentations by 22 experts and was attended by 65 individuals. The agenda can be found in the supplementary data at www.toxsci.oupjournals.org.

Drug-induced liver disease in 2003

Drug-induced liver disease remains an important topic of concern for all prescribers as well as drug manufacturers. The withdrawal of troglitazone (Rezulin) and bromfenac (Duract) a few years ago remains fresh in the minds of regulatory authorities as well as clinicians and researchers who are focusing renewed attention on ways to better understand mechanisms of injury to predict and avert serious drug-induced liver disease in the future from drugs under development as well as existing agents known to cause liver injury. As in past years, this review describes new and first-time reports of various aspects of drug-induced liver disease for several classes of compounds, including herbal products (such as kava kava), reviews the risk factors seen with antiretroviral and antituberculosis agents among others. It provides a sampling of experimental hepatoprotection studies that may hold the key to treatment and prevention of drug-induced liver disease in the future and discusses the ongoing approaches to be taken to restrict the availability of acetaminophen that have proved successful in reducing the number of overdoses, deaths, and liver transplantations from this drug in the United Kingdom. Given the fact that acetaminophen is the single most important cause of acute liver failure here and abroad, such efforts to limit its use seem appropriate for other nations as well.

Drug- and chemical-induced cholestasis

Cholestasis caused by medicinal and chemical agents is an increasingly well-recognized cause of liver disease. Clinical drug-induced cholestatic syndromes producing jaundice and bile duct injury can mimic extrahepatic biliary obstruction, primary biliary cirrhosis, and sclerosing cholangitis, among others. This article updates the various forms of drug-induced cholestasis, focusing on the clinicopathologic features of this form of hepatic injury and on the known or putative mechanisms by which drugs and chemicals lead to cholestasis.