Autoantibodies against cytochromes P-450 in drug-induced autoimmune hepatitis

Long-term sequelae of drug-induced liver injury

Drug-induced liver injury (DILI) has a very variable clinical and biochemical phenotype and differs widely in severity, from mild injury to life-threatening liver failure. Chronic injury has also been reported to occur at a variable frequency, ranging from 3.4% to 39%, 6-12 months after discontinuing the implicated agent. This wide range is probably related to various definitions of chronic liver injury and variable selection of patients. The long-term sequalae of this chronic injury in terms of morbidity and mortality are unclear, although rare vanishing bile duct syndrome is associated with an unfavourable prognosis, with increased risk of chronic liver failure and need for liver transplantation. Other forms of long-term sequalae associated with DILI are progressive fibrosis, autoimmune-like hepatitis, secondary sclerosing cholangitis, sinusoidal obstruction syndrome and, as a common final stage, the development of cirrhosis, portal hypertension and its complications. Immune checkpoint inhibitors, which can cause an autoimmune-like phenotype have also recently been shown to cause sclerosing cholangitis with cytotoxic T CD8+ cell infiltration in biliary tracts. DILI has been shown to have a significant impact on health-related quality of life but very little is known about its psychological consequences in the long-term. Further investigations with structured long-term follow-up and periodic quality of life surveys are needed to assess the impact of DILI on psychological outcomes, particularly in those with chronic sequelae.

Transitioning from Idiopathic to Explainable Autoimmune Hepatitis

Autoimmune hepatitis lacks an identifiable cause, and its diagnosis requires the exclusion of etiologically defined diseases that resemble it. Insights into its pathogenesis are moving autoimmune hepatitis from an idiopathic to explainable disease, and the goal of this review is to describe the insights that are hastening this transition. Two types of autoimmune hepatitis are justified by serological markers, but they also have distinctive genetic associations (DRB1 and DQB1 genes) and autoantigens. DRB1 alleles are the principal susceptibility factors in white adults, and a six amino acid sequence encoded in the antigen-binding groove of class II molecules of the major histocompatibility complex can influence the selection of autoantigens. Polymorphisms, including variants of SH2B3 and CARD10 genes, may affect immune reactivity and disease severity. The cytochrome mono-oxygenase, CYP2D6, is the autoantigen associated with type 2 autoimmune hepatitis, and it shares homologies with multiple viruses that might promote self-intolerance by molecular mimicry. Chemokines, especially CXCL9 and CXCL10, orchestrate the migration of effector cells to sites of injury and are associated with disease severity. Cells of the innate and adaptive immune responses promote tissue damage, and possible deficiencies in the number and function of regulatory T cells may facilitate the injurious process. Receptor-mediated apoptosis is the principal mechanism of hepatocyte loss, and cell-mediated and antibody-dependent mechanisms of cytotoxicity also contribute. Insights that explain autoimmune hepatitis will allow triggering exogenous antigens to be characterized, risk management to be improved, prognostic indices to be refined, and site-specific therapeutic interventions to emerge.

Relationship between characteristics of medications and drug-induced liver disease phenotype and outcome

BACKGROUND & AIMS

It is not known whether specific characteristics of medication are associated with type of drug-induced liver injury (DILI) or outcome. We examined the relationships among select characteristics of medications and DILI phenotype and outcome.

METHODS

We analyzed 383 cases of DILI caused by a single orally administered prescription agent from the DILI Network Prospective Study with causalities of definite, highly likely, or probable. Relationship of daily dosage (≥50 mg vs ≤49 mg), preponderance of hepatic metabolism (≥50% vs <50%), or Biopharmaceutics Drug Disposition Classification System (BDDCS) class (1-4, based on solubility and metabolism of the drug) were compared with clinical characteristics and outcomes.

RESULTS

Compared with cases of DILI in the ≤49 mg/day group, those associated with daily dosages ≥50 mg had shorter latency (median, 38 days vs 56 days; P = .03) and a different biochemical pattern of liver injury (P = .04); no differences in recovery, severity, or outcome were observed. Patients with DILI caused by medications with or without preponderant hepatic metabolism did not differ in clinical characteristics or outcomes. Compared with other classes of BDDCS, DILI caused by BDDCS class 1 medications had significantly longer latency (P < .001) and greater proportion of hepatocellular injury (P = .001). However, peak liver biochemical values and patients' time to recovery, disease severity, and outcomes did not differ among the 4 BDDCS classes.

CONCLUSIONS

Characteristics of medications (dosage, hepatic metabolism, and solubility) are associated with features of DILI such as latency and pattern of liver injury, but not with recovery, severity, or outcome.

Autoimmune hepatitis: the role of environmental risk factors: a population-based study

PURPOSE

The etiology of autoimmune hepatitis (AIH) likely involves a complex interaction of genetic and environmental factors. We aim to investigate the associations between exposure to putative environmental factors and AIH and to quantify AIH risk in a first-degree relative.

METHODS

We conducted a population-based case-control study. Cases were AIH patients who were alive and resided in Canterbury, New Zealand, between 1 July 2011 and 30 June 2012. Controls were randomly selected from the Electoral Roll and were matched 2:1 to each case by age and gender. Self-reporting questionnaires that cover lifestyle factors, childhood factors and family history were used.

RESULTS

72 AIH cases and 144 controls were included. We found that exposure to antibiotics within 12 months prior to AIH diagnosis (OR 12.98, 95 % CI 2.49-67.67, p < 0.01) was an independent risk factor for the development of AIH. Alcohol consumption (OR 0.43, 95 % CI 0.28-0.68, p < 0.01) and childhood home with wood heating (OR 0.30, 95 % CI 0.14-0.63, p < 0.01) were independently associated with reduced risks of later development of AIH. The crude risk of AIH in first-degree relatives of a patient with AIH was 0.2 % (95 % CI <0.1-2.0).

CONCLUSIONS

We found that antibiotics are an independent risk factor for the development of AIH, whereas alcohol consumption and living in a childhood home with wood heating are independent protective factors against the later development of AIH.

Drug-induced autoimmune hepatitis: clinical characteristics and prognosis

Drug-induced autoimmune hepatitis (DIAIH) has been reported to be caused by several drugs. There is a lack of data comparing these patients with other patients with autoimmune hepatitis (AIH). A search was performed using the Mayo Clinic diagnostic medical index for AIH patients and DIAIH patients identified over 10 years. Individuals with overlap syndromes and decompensated liver disease were excluded. Overall, 261 patients (204 females, median age 52) were identified, and 24 (9.2%) were DIAIH cases with a median age of 53 (interquartile range, 24-61). Two drugs, nitrofurantoin (n = 11) and minocycline (n = 11), were the main causes. A similar proportion of DIAIH patients had positive antinuclear antibodies (83% versus 70%) and smooth muscle antibodies (50% versus 45%) as compared with AIH patients. Histological grade and stage were similar in patients with DIAIH versus AIH; however, none of the DIAIH patients had cirrhosis at baseline; this was present in 20% of matched AIH cases. Liver imaging was normal in all minocycline cases. Eight of 11 (73%) nitrofurantoin patients had abnormalities on hepatic imaging (mainly liver atrophy), a finding seen in only 8 of 33 (24%) of a random sample of the rest of the AIH group (P = 0.0089). Corticosteroid responsiveness was similar in DIAIH and the AIH patients. Discontinuation of immunosuppression was tried and successful in 14 DIAIH cases, with no relapses (0%), whereas 65% of the AIH patients had a relapse after discontinuation of immunosuppression (P < 0.0001).

CONCLUSION

A significant proportion of patients with AIH have drug-induced AIH, mainly because of nitrofurantoin and minocycline. These two groups have similar clinical and histological patterns. However, DIAIH patients do not seem to require long-term immunosuppressive therapy.

Suggested guidelines for patient monitoring: hepatic and hematologic toxicity attributable to systemic dermatologic drugs

Hepatic and hematologic toxicity are among the most fearful adverse effects that occasionally occur as a result of systemic drugs in the dermatologist's therapeutic armamentarium. Drugs of greatest interest concerning hepatic toxicity include methotrexate, azathioprine, dapsone, and acitretin. Somewhat overlapping are drugs that have important hematologic toxicities, including methotrexate, azathioprine, dapsone, sulfonamides, cyclophosphamide, and chlorambucil. Laboratory tests most commonly used include (1) hepatic monitoring: transaminases (AST/SGOT and ALT/SGPT) and the ultrasound-guided liver biopsy, and (2) hematologic monitoring: CBC with diff and platelets along with occasional use of the reticulocyte count. Important principles and specific guidelines for monitoring by drug group are highlighted.

The role of cytochrome P450 enzymes in hepatic and extrahepatic human drug toxicity

The human cytochrome P450 enzyme system metabolises a wide array of xenobiotics to pharmacologically inactive metabolites, and occasionally, to toxicologically active metabolites. Impairment of cytochrome P450 activity, which may be either genetic or environmental, may lead to toxicity caused by the parent compound itself. In practise, this usually only applies to drugs that have a narrow therapeutic index and when their clearance is critically dependent upon the fraction normally metabolised by that pathway. P450 enzymes may also convert the drug to a chemically reactive metabolite, which, if not detoxified, may lead to various forms of hepatic and extrahepatic toxicity, including cellular necrosis, hypersensitivity, teratogenicity, and carcinogenicity, depending on the site of formation and the relative stability of the metabolite, and the cellular macromolecule with which it reacts. Variation in the regulation and expression of the drug metabolising enzymes may play a key role in both interindividual variation in sensitivity to drug toxicity and tissue-specific damage. Avoidance of toxicity may be possible in rare instances by prediction of individual susceptibility or by designing new chemical entities that are metabolised by a range of enzymes (both cytochromes P450 and others) and do not undergo bioactivation.

Possible role of cytochromes P450 in lupus erythematosus and related disorders

Cytochromes P450 comprise a superfamily of enzymes pivotal in the metabolism of innumerable substrates of both endogenous and exogenous origin. The total number of distinct P450 genes, each encoding a different enzyme in humans, is estimated to be at least 60 and possibly several hundred. The cytochrome P450 (CYP) superfamily nomenclature system is based on divergent evolution of the genes. Most of the enzymes within gene families CYP1, CYP2, CYP3 and CYP4 appear to have evolved as the body's primary defense against the onslaught of chemicals confronted on a daily basis. Whereas P450 enzymes more than 3.5 billion years ago were undoubtedly designed as necessary components of signal transduction pathways, in the past billion years most P450 enzymes have become generally responsible for the detoxification of numerous foreign chemicals. During such oxidative metabolism, it has become increasingly apparent that these enzymes are also capable of functioning in an ambivalent manner, generating toxic intermediates. More than a dozen human P450 polymorphisms have been characterized. Genetic variability in P450 expression is therefore likely to have significant bearing on individual susceptibility to chemical toxicity. In this review, genetic differences in human P450 expression are outlined, and their possible relationship to autoimmune disease is examined. In addition, the speculative role of P450 polymorphisms in several 'lupus-like' disorders is discussed.