A proposed mechanism for chlorpromazine jaundice--defective hepatic sulphoxidation combined with rapid hydroxylation

Interaction of cigarette smoke condensate and some of its components with chlorpromazine toxicity on Saccharomyces cerevisiae

Chlorpromazine (CPZ) is an antipsychotic phenothiazine which is still commonly prescribed though it causes idiosyncratic toxicity such as cholestasis. CPZ toxicity mechanisms involve oxidative stress among others. Cigarette smoke (CS) causes deleterious effects through diverse mechanisms such as oxidative stress. CS alters drug metabolizing enzymes expression and drug transporters expression and activity in animal cell models as well as in Saccharomyces cerevisiae. CS therefore alters pharmacokinetic and pharmacodynamics of many drugs including CPZ and caffeine whose toxicity is promoted by CS condensate (CSC). CSC interaction with CPZ toxicity deserves investigation. In this study, CSC exerted mild toxicity on Saccharomyces cerevisiae which resisted to this chemical stress after several hours. CPZ toxicity on yeast was dose-dependent and the cells resisted to CPZ up to 40 µM after 24 h of treatment. Yeast cells treated simultaneously with CPZ and a nontoxic CSC dose were less sensitive to CPZ. CSC probably triggers cross-resistance to CPZ. Using Sod1 mutant strain, we showed that this gene is potentially involved in the potential cross-resistance. Other genes encoding stress-related transcription factors could be involved in this process. Nicotine and cadmium chloride, which caused a dose-dependent toxicity individually, acted with CPZ in an additive or synergistic manner in terms of toxicity. Although our results cannot be extrapolated to humans, they clearly show that CSC and its components interact with CPZ toxicity.

Phenylalanine 4-monooxygenase: the "sulfoxidation polymorphism"

1. Consistent differences in the proportion of an orally administered dose of S-carboxymethyl-l-cysteine subsequently excreted in the urine as S-oxide metabolites were reported 40 years ago. This observation suggested the existence of inter-individual variation in the ability to undertake the enzymatic S-oxygenation of this compound. Pedigree studies and investigations employing twin pairs indicated a genetically controlled phenomenon overlaid with environmental influences. It was reproducible and not related to gender or age.2. Studies undertaken in several healthy volunteer cohorts always provided similar results that were not significantly different when statistically analysed. However, when compared to these healthy populations, a preponderance of subjects exhibiting the characteristic of poor sulfoxidation of S-carboxymethyl-l-cysteine was found within groups of patients suffering from various disease conditions. The most striking of these associations were witnessed amongst subjects diagnosed with neurodegenerative disorders; although, underlying mechanisms were unknown.3. Exhaustive investigation has identified the enzyme responsible for this S-oxygenation reaction as the tetrahydrobiopterin-dependent aromatic amino acid hydroxylase, phenylalanine 4-monooxygenase classically assigned the sole function of converting phenylalanine to tyrosine. The underlying principle is discussed that enzymes traditionally associated solely with intermediary metabolism may have as yet unrecognised alternative roles in protecting the organism from potential toxic assault.

Transcriptional, Functional, and Mechanistic Comparisons of Stem Cell-Derived Hepatocytes, HepaRG Cells, and Three-Dimensional Human Hepatocyte Spheroids as Predictive In Vitro Systems for Drug-Induced Liver Injury

Reliable and versatile hepatic in vitro systems for the prediction of drug pharmacokinetics and toxicity are essential constituents of preclinical safety assessment pipelines for new medicines. Here, we compared three emerging cell systems-hepatocytes derived from induced pluripotent stem cells, HepaRG cells, and three-dimensional primary human hepatocyte (PHH) spheroids-at transcriptional and functional levels in a multicenter study to evaluate their potential as predictive models for drug-induced hepatotoxicity. Transcriptomic analyses revealed widespread gene expression differences between the three cell models, with 8148 of 17,462 analyzed genes (47%) being differentially expressed. Expression levels of genes involved in the metabolism of endogenous as well as xenobiotic compounds were significantly elevated in PHH spheroids, whereas genes involved in cell division and endocytosis were significantly upregulated in HepaRG cells and hepatocytes derived from induced pluripotent stem cells, respectively. Consequently, PHH spheroids were more sensitive to a panel of drugs with distinctly different toxicity mechanisms, an effect that was amplified by long-term exposure using repeated treatments. Importantly, toxicogenomic analyses revealed that transcriptomic changes in PHH spheroids were in compliance with cholestatic, carcinogenic, or steatogenic in vivo toxicity mechanisms at clinically relevant drug concentrations. Combined, the data reveal important phenotypic differences between the three cell systems and suggest that PHH spheroids can be used for functional investigations of drug-induced liver injury in vivo in humans.

Development of HepG2-derived cells expressing cytochrome P450s for assessing metabolism-associated drug-induced liver toxicity

The generation of reactive metabolites from therapeutic agents is one of the major mechanisms of drug-induced liver injury (DILI). In order to evaluate metabolism-related toxicity and improve drug efficacy and safety, we generated a battery of HepG2-derived cell lines that express 14 cytochrome P450s (CYPs) (1A1, 1A2, 1B1, 2A6, 2B6, 2C8, 2C9, 2C18, 2C19, 2D6, 2E1, 3A4, 3A5 and 3A7) individually using a lentiviral expression system. The expression/production of a specific CYP in each cell line was confirmed by an increased abundance of the CYP at both mRNA and protein levels. Moreover, the enzymatic activities of representative CYPs in the corresponding cell lines were also measured. Using our CYP-expressed HepG2 cells, the toxicity of three drugs that could induce DILI (amiodarone, chlorpromazine and primaquine) was assessed, and all of them showed altered (increased or decreased) toxicity compared to the toxicity in drug-treated wild-type HepG2 cells. CYP-mediated drug toxicity examined in our cell system is consistent with previous reports, demonstrating the potential of these cells for assessing metabolism-related drug toxicity. This cell system provides a practical in vitro approach for drug metabolism screening and for early detection of drug toxicity. It is also a surrogate enzyme source for the enzymatic characterization of a particular CYP that contributes to drug-induced liver toxicity.

Chlorpromazine-induced hepatotoxicity during inflammation is mediated by TIRAP-dependent signaling pathway in mice

Inflammation is a major component of idiosyncratic adverse drug reactions (IADRs). To understand the molecular mechanism of inflammation-mediated IADRs, we determined the role of the Toll-like receptor (TLR) signaling pathway in idiosyncratic hepatotoxicity of the anti-psychotic drug, chlorpromazine (CPZ). Activation of TLRs recruits the first adaptor protein, Toll-interleukin 1 receptor domain containing adaptor protein (TIRAP) to the TIR domain of TLRs leading to the activation of the downstream kinase, c-Jun-N-terminal kinase (JNK). Prolonged activation of JNK leads to cell-death. We hypothesized that activation of TLR2 by lipoteichoic acid (LTA) or TLR4 by lipopolysaccharide (LPS) will augment the hepatotoxicity of CPZ by TIRAP-dependent mechanism involving prolonged activation of JNK. Adult male C57BL/6, TIRAP(+/+) and TIRAP(-/-) mice were pretreated with saline, LPS (2 mg/kg) or LTA (6 mg/kg) for 30 min or 16 h followed by CPZ (5 mg/kg) or saline (vehicle) up to 24h. We found that treatment of mice with CPZ in presence of LPS or LTA leads to ~3-4 fold increase in serum ALT levels, a marked reduction in hepatic glycogen content, significant induction of serum tumor necrosis factor (TNF) α and prolonged JNK activation, compared to LPS or LTA alone. Similar results were observed in TIRAP(+/+) mice, whereas the effects of LPS or LTA on CPZ-induced hepatotoxicity were attenuated in TIRAP(-/-) mice. For the first time, we show that inflammation-mediated hepatotoxicity of CPZ is dependent on TIRAP, and involves prolonged JNK activation in vivo. Thus, TIRAP-dependent pathways may be targeted to predict and prevent inflammation-mediated IADRs.

Drug-induced liver injury: insights from genetic studies

Drug-induced liver injury (DILI) is an increasing health problem and a challenge for physicians, regulatory bodies and the pharmaceutical industry, not only because of its potential severity and elusive pathogenesis but also because it is often inaccurately diagnosed, commonly missed entirely and more often not reported. The general view is that idiosyncratic DILI, which is not predictable whether based on the pharmacology of the drug or on the dose administered, is determined by the presence in the recipient of variants in, or expression of, genes coding for key metabolic pathways and/or the immune response, and the interaction of these genetic variants with environmental variables. Furthermore, idiosyncratic DILI is an example of a complex-trait disease with two or more susceptibility loci, as reflected by the frequency of genetic variants in the population often being higher than the occurrence of significant liver injury. Polymorphisms of bioactivation/toxification pathways via the CYP450 enzymes (Phase I), detoxification reactions (Phase II) and excretion/transport (Phase III), together with immunological factors that might determine DILI are reviewed. Challenges such as gene-trait association studies and whole-genome studies, and future approaches to the study of DILI are explored. Better knowledge of the candidate genes involved could provide further insight for the prospective identification of susceptible patients at risk of developing drug-induced hepatotoxicity, development of new diagnostic tools and new treatment strategies with safer drugs.

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.

Hepatic metabisulfite sensitivity in a patient with sclerosing cholangitis

BACKGROUND

Primary sclerosing cholangitis is an uncommon chronic cholestatic liver disease with a poor prognosis in symptomatic cases. Genetic and immunologic alterations have been identified, and many possible etiologies have been entertained. Most treatments have limited benefit, and primary sclerosing cholangitis is a common cause for liver transplantation.

OBJECTIVE

To describe a patient with documented primary sclerosing cholangitis associated with chronic ulcerative colitis, who developed hepatic toxicity following ingestion of metabisulfite.

RESULTS

A placebo-controlled oral challenge suggested metabisulfite hypersensitivity with liver toxicity. He was treated with cobalamin (to prevent sulfite toxicity), low-sulfite diet, steroids, and antibiotics and has had an unusually benign course for 19 years.

CONCLUSIONS

The hypersensitivity to oral metabisulfite in our patient appeared to be a significant trigger to flare-ups of his disease. Controlling the response to metabisulfite (along with recurrent antibiotic and steroid therapy) may have contributed significantly to the remarkably good outcome in this patient.

Potential Cholestatic Activity of Various Therapeutic Agents Assessed by Bile Canalicular Membrane Vesicles Isolated from Rats and Humans

The active transport of solutes mediated by the bile salt export pump (BSEP/ABCB11) and multidrug resistance associated protein-2 (MRP2/ABCC2) are thought to involve bile acid-dependent and -independent bile formation, respectively. To evaluate the potential of therapeutic agents as inhibitors of such transporters on bile canalicular membranes, we examined the inhibition of the primary active transport of typical substrates by 15 drugs, clinically known to cause cholestasis in canalicular membrane vesicles. The inhibition by most of the compounds in rat canalicular membrane vesicles (CMVs) was minimal or observed at much higher concentrations than obtained in clinical situations. However, cloxacillin, cyclosporin A and midecamycin inhibited BSEP, and cyclosporin A and midecamycin inhibited MRP2 with an inhibition constant close to the clinical concentration. By comparing the inhibition potential between rat and human CMVs, the inhibition of BSEP- and MRP2-mediated transport by midecamycin and cyclosporin A was relatively similar whereas the inhibitory effect on BSEP-mediated transport by cloxacillin and glibenclamide was more marked in humans than in rats. These results suggest that the majority of cholestasis-inducing drugs have a minimal inhibitory effect on rat BSEP and MRP2 although species differences in inhibitory potential should be considered, especially in the case of BSEP.

Three-dimensional visualization and physiologic evaluation of bile canaliculi in the rat liver slice by confocal laser scanning microscopy

We evaluated the morphology and physiologic function of the bile canaliculi (BC) in the rat liver slice (RLS) by confocal laser scanning microscopy (CLSM). Lucifer yellow (LY) dye was injected into the RLS, and the distribution of LY was serially evaluated. After the injection of LY, hepatocytes were initially visualized, followed by visualization of the BC. There was no significant difference in the distribution of LY between zones 1 and 3 in the hepatic lobule. In zone 1, the reticular distribution of the BC was observed, whereas the part of BC was linearly visualized in zone 3 along the course of sinusoids. When changes in the bile canalicular fluorescence (BCF) were serially evaluated, the BCF was decreased to the minimal level (88% of the value obtained immediately after the LY injection) 10 min after the LY injection, and it tended to increase thereafter. The intralobular hepatocyte fluorescence (ILHF) was decreased to 58.9% of the initial value during the first 40 min. However, the ILHF was transiently increased 30 min after the LY injection, suggesting the possibility of reabsorption of LY by hepatocytes. Three-dimensional (3-D) reconstruction images of the BC facilitated the evaluation of the stereoscopic structure of BC. Confocal laser scanning microscopy facilitated the evaluation of structures and physiologic function of the BC.

Drug-induced liver disease

The incidence of drug-induced liver disease appears to be increasing, reflecting the increasing number of new agents that have been introduced into clinical use over the past several decades. Among the topics covered, the author discusses incidence, diagnosis, risk factors, clinical presentations, hepatitis, and vascular injury. The author also reviews the hepatic injury seen with commonly prescribed drugs, emphasizing newer developments in the field and recent publications and reports.

Drug- and chemical-induced cholestasis

Cholestasis resulting from drugs is an increasingly recognized cause of liver disease. It produces a broad clinical-pathologic spectrum of injury that includes simple jaundice, cholestatic hepatitis, and bile duct injury that can mimic extrahepatic biliary obstruction, primary biliary cirrhosis, and sclerosing cholangitis. Although the risk of drug-induced cholestasis leading to a fatal outcome is quite rare, knowledge and recognition of the various forms of cholestatic injury assumes an importance whenever clinicians are confronted with jaundice or other manifestations of liver disease in patients receiving medicinal or chemical agents.

Xenobiotic-induced hepatotoxicity: mechanisms of liver injury and methods of monitoring hepatic function

Xenobiotic-induced liver injury is a clinically important etiology of hepatic disease that, if not recognized, can lead to hepatic failure. In this article we discuss the mechanisms of xenobiotic-induced liver injury, various factors that can alter the risk and severity of injury, the clinical and laboratory manifestations of injury, and the methods used to detect the presence of injury and (or) functioning liver mass.

Genetic predisposition to drug-induced hepatotoxicity

Drug-induced hepatitis is uncommon and generally unpredictable. Hepatotoxicity may be related to the drug itself, or to chemically reactive metabolites which can bind covalently to hepatic macromolecules and may lead to either idiosyncratic, toxic hepatitis or to immunoallergic hepatitis. There is now evidence indicating that genetic variations in systems of biotransformation or detoxication may modulate either the toxic or sensitizing effects of some drugs. Thus, the genetic deficiency in a particular hepatic cytochrome P 450 isozyme (CYP 2D6) is involved in per-hexiline liver injury. The deficiency in CYP 2C19 might also contribute to Atrium hepatotoxicity. Slow acetylation related to N-acetyltransferase 2 deficiency contributes to sulfonamide hepatitis. The genetic deficiency in glutathione synthetase may increase the susceptibility to several drugs including acetaminophen. A constitutional deficiency in another cell defense mechanism, still not characterized, seems to increase significantly the risk of hepatotoxicity with halothane, phenytoin, carbamazepine, phenobarbital, sulfamides and amineptine.

Phenotypic variation in xenobiotic metabolism and adverse environmental response: focus on sulfur-dependent detoxification pathways

Proper bodily response to environmental toxicants presumably requires proper function of the xenobiotic (foreign chemical) detoxification pathways. Links between phenotypic variations in xenobiotic metabolism and adverse environmental response have long been sought. Metabolism of the drug S-carboxymethyl-L-cysteine (SCMC) is polymorphous in the population, having a bimodal distribution of metabolites, 2.5% of the general population are thought to be nonmetabolizers. The researchers developing this data feel this implies a polymorphism in sulfoxidation of the amino acid cysteine to sulfate. While this interpretation is somewhat controversial, these metabolic differences reflected may have significant effects. Additionally, a significant number of individuals with environmental intolerance or chronic disease have impaired sulfation of phenolic xenobiotics. This impairment is demonstrated with the probe drug acetaminophen and is presumably due to starvation of the sulfotransferases for sulfate substrate. Reduced metabolism of SCMC has been found with increased frequency in individuals with several degenerative neurological and immunological conditions and drug intolerances, including Alzheimer's disease, Parkinson's disease, motor neuron disease, rheumatoid arthritis, and delayed food sensitivity. Impaired sulfation has been found in many of these conditions, and preliminary data suggests that it may be important in multiple chemical sensitivities and diet responsive autism. In addition, impaired sulfation may be relevant to intolerance of phenol, tyramine, and phenylic food constituents, and it may be a factor in the success of the Feingold diet. These studies indicate the need for the development of genetic and functional tests of xenobiotic metabolism as tools for further research in epidemiology and risk assessment.

Possible association between poor metabolism of mephenytoin and hepatotoxicity caused by Atrium, a fixed combination preparation containing phenobarbital, febarbamate and difebarbamate

Drug hepatotoxicity is partially determined by genetic factors involved in drug metabolism, which may involve the debrisoquine oxidation polymorphism mediated by cytochrome (CYP) 2D6. The purpose of this study was to assess the relationship between drug hepatotoxicity and another genetic polymorphism of drug oxidation, namely that of S-mephenytoin metabolism mediated by CYP2CMP. Mephenytoin hydroxylation capacity was assessed by a hydroxylation index in 24 patients with drug-induced hepatitis and in 23 healthy controls. Hydroxylation index was calculated as the ratio of S-mephenytoin dose to the (0-10 h) urinary excretion of 4-hydroxymephenytoin after oral administration of 100 mg racemic mephenytoin. The test was performed following the patient's recovery. In three patients, hepatitis was related to Atrium, a drug containing phenobarbital, febarbamate and difebarbamate. The mean hydroxylation index (+/- SD) value in patients with Atrium hepatitis (12.4 +/- 8.3) was markedly higher than that found in healthy controls (1.8 +/- 0.4) or in patients with other drug-induced hepatitis (2.5 +/- 3.3). Mean hydroxylation index values were similar in the two latter groups. Considered individually, oxidation capacity was low (hydroxylation index > 9) in two of the three patients with Atrium hepatitis and intermediate (hydroxylation index between 4 and 9) in the third patient. In contrast, all 23 healthy subjects exhibited a high oxidation capacity (hydroxylation index < 4). In the 21 patients with other drug-induced hepatitis, oxidation capacity was high in 19 subjects, intermediate in one subject with chlorpromazine hepatitis, and low in one subject with dapsone hepatitis.(ABSTRACT TRUNCATED AT 250 WORDS)

Metabolic polymorphisms

Polymorphisms have been detected in a variety of xenobiotic-metabolizing enzymes at both the phenotypic and genotypic level. In the case of four enzymes, the cytochrome P450 CYP2D6, glutathione S-transferase mu, N-acetyltransferase 2 and serum cholinesterase, the majority of mutations which give rise to a defective phenotype have now been identified. Another group of enzymes show definite polymorphism at the phenotypic level but the exact genetic mechanisms responsible are not yet clear. These enzymes include the cytochromes P450 CYP1A1, CYP1A2 and a CYP2C form which metabolizes mephenytoin, a flavin-linked monooxygenase (fish-odour syndrome), paraoxonase, UDP-glucuronosyltransferase (Gilbert's syndrome) and thiopurine S-methyltransferase. In the case of a further group of enzymes, there is some evidence for polymorphism at either the phenotypic or genotypic level but this has not been unambiguously demonstrated. Examples of this class include the cytochrome P450 enzymes CYP2A6, CYP2E1, CYP2C9 and CYP3A4, xanthine oxidase, an S-oxidase which metabolizes carbocysteine, epoxide hydrolase, two forms of sulphotransferase and several methyltransferases. The nature of all these polymorphisms and possible polymorphisms is discussed in detail, with particular reference to the effects of this variation on drug metabolism and susceptibility to chemically-induced diseases.

Psychopharmacology in patients with hepatic and gastrointestinal disease

Psychotropic drugs often need to be prescribed to patients who also have pre-existing gastrointestinal (GI) and/or hepatic disease. This paper addresses the effect of GI and hepatic disease on the pharmacokinetics of psychotropic drugs, the effect of psychotropic drugs on pre-existing GI and hepatic diseases, the adverse GI and hepatic effects of psychotropic medications, the effects of GI medications on mental status, and the potential drug interactions between commonly prescribed GI medications and psychotropic drugs. Drug selection and dosage modification based on these considerations should allow safe and effective psychotropic treatment for patients with pre-existing GI and/or hepatic disease.

Drug-induced jaundice

A large number of drugs may be associated with impaired bile flow. Drug-associated cholestasis presents like other forms of cholestasis with pale stools, dark urine, pruritus and jaundice. Abdominal pain may be present in some instances and can be so severe as to lead to a false diagnosis of acute cholecystitis. Biochemically, drug-associated cholestasis resembles other forms of cholestasis although the presence of eosinophilia may suggest drug involvement. Many types of drug-induced cholestasis run a benign course with resolution of signs and symptoms within 3 months but occasionally the jaundice can take a year or more to resolve. Progression to cirrhosis is uncommon. Some patients may develop a syndrome resembling primary biliary cirrhosis. The mechanisms of drug-associated cholestasis are uncertain but may arise from alteration of bile formation within the hepatocyte or bile excretion at the level of the canaliculus or the extrahepatic ducts. Histological examination of the liver may be helpful in classifying the types of jaundice but the diagnosis of drug-induced cholestasis is usually one of temporal association and exclusion of other causes.

Pharmacogenetics of the S-oxidation of S-carboxymethyl-L-cysteine

The pharmacogenetics of S-carboxymethyl-L-cysteine (SCMC) have been studied in detail. When results from administration of SCMC to 200 volunteers were analysed, there was seen to be a wide interindividual variation in the percentage of sulphoxide metabolites excreted. Computer assisted analysis suggested that the population distribution observed could be most economically represented as two overlapping Gaussian distributions with the smaller mode representing poor sulphoxidisers. This phenomenon appears to be largely genetic in origin and to behave as though controlled by one autosomal recessive gene, but environmental factors may also be important. Poor sulphoxidisers seem to be overrepresented in certain patient populations with chronic diseases. These findings are discussed in terms of oxidative metabolism of sulphur-containing compounds.