Influence of clinicopathological variables on CYP protein expression in human liver

Predictors of Voriconazole Trough Concentrations in Patients with Child-Pugh Class C Cirrhosis: A Prospective Study

This prospective observational study aimed to clinically describe voriconazole administrations and trough concentrations in patients with Child–Pugh class C and to investigate the variability of trough concentration. A total of 144 voriconazole trough concentrations from 43 Child–Pugh class C patients were analyzed. The majority of patients (62.8%) received adjustments. The repeated measured trough concentration was higher than the first and final ones generally (median, 4.33 vs. 2.99, 3.90 mg/L). Eight patients with ideal initial concentrations later got supratherapeutic with no adjusted daily dose, implying accumulation. There was a significant difference in concentrations among the six groups by daily dose (p = 0.006). The bivariate correlation analysis showed that sex, CYP2C19 genotyping, daily dose, prothrombin time activity, international normalized ratio, platelet, and Model for end-stage liver disease score were significant factors for concentration. Subsequently, the first four factors mentioned above entered into a stepwise multiple linear regression model (variance inflation factor <5), implying that CYP2C19 testing makes sense for precision medicine of Child–Pugh class C cirrhosis patients. The equation fits well and explains the 34.8% variety of concentrations (R² = 0.348). In conclusion, it needs more cautious administration clinically due to no recommendation for Child–Pugh class C patients in the medication label. The adjustment of the administration regimen should be mainly based on the results of repeated therapeutic drug monitoring.

Clinical pharmacokinetics of drugs in cardiopulmonary associated cachexia without hepatorenal pathology: a systematic review

Cachexia not only has a dramatically harmful impact on a patient's life, but also a poor response to therapeutic agents. The purpose of the present review is to provide updated information concerning the pharmacokinetic aspects of drugs used to treat cardiopulmonary cachexia in patients with no signs of hepatic or renal pathology. A systematic search of PubMed, the Cochrane Central Register of Control Trials, Science Direct, and Clinical Trials Registry (ClinicalTrials.gov), encompassing the period between 2000 and 2017, was conducted in accordance to PRISMA guidelines. Seven studies were identified. Collectively, these studies included a total of 196 individuals (19 healthy subjects and 177 diseased patients). This data review found no differences in bisoprolol and prothionamide absorption in cachectic patients with chronic heart failure and tuberculosis, but higher absorption of oflaxocin in the same set of patients was observed. The distribution of bisoprolol, prothionmaide, ceftazidime, and cefipirome was reduced in cardiopulmonary cachexia patients. Hepatic clearance of rifampin was equivalent in cachectic and non-cachectic patients that had normal hepatic function. Similarly in cardiopulmonary cachexia patients, renal clearance of ceftazidime was reduced by 19% but no significant differences in bisorpolol and prothionamide clearance were observed. In the case of cefipirome, both renal clearance and creatinine clearance were higher in cachectic patients with cystic fibrosis. From the limited evidence available, the main drug pharmacokinetic changes seen in cardiopulmonary cachexia patients were a reduction in the volume of distribution and impairment of clearance.

Elevated 4β-hydroxycholesterol/cholesterol ratio in anorexia nervosa patients

Recent studies have shown that the cytochrome P450 (CYP) 3A phenotype marker 4β-hydroxycholesterol/cholesterol (4βOHC/C) ratio is negatively correlated with body weight in healthy volunteers, and that obese patients have lower 4βOHC levels than healthy controls. However, 4βOHC/C ratio in underweight patients has yet to be reported. The aim of this study was to examine potential differences in CYP3A activity between underweight patients with anorexia nervosa and normal-weight volunteers by measuring plasma 4βOHC/C ratio. Furthermore, we wished to describe any association between body mass index (BMI) and 4βOHC/C ratio in underweight patients. A total of 20 underweight patients and 16 normal-weight volunteers were included in the study, all females. Underweight patients had a median 4βOHC/C ratio (molar ratio × 10-5) of 2.52 (range, 0.90-11.3) compared to 1.29 (0.56-2.09) in normal-weight subjects (Mann-Whitney P = 0.0005). 4βOHC/C ratio was negatively correlated with BMI in underweight patients (r = -0.56, P = 0.011), and in the whole study population (r = -0.67, P < 0.0001). This suggests that the negative correlation between 4βOHC/C and BMI, which has previously been reported between 4βOHC/C and body weight in healthy volunteers, extends to underweight patients. The findings indicate that CYP3A activity increases with decreasing BMI, resulting in higher CYP3A activity in underweight patients compared to normal-weight subjects. The potential clinical relevance of this needs to be studied further by comparing pharmacokinetics of drugs subjected to CYP3A-mediated metabolism in underweight vs. normal-weight individuals.

Reduced Clearance of Phenobarbital in Advanced Cancer Patients near the End of Life

BACKGROUND AND OBJECTIVES

Little is known about the pharmacokinetics of phenobarbital in terminally ill cancer patients. We investigated whether phenobarbital clearance alters depending on the length of survival.

METHODS

We retrospectively reviewed the clinical, laboratory, and therapeutic drug monitoring (TDM) records of patients who received parenteral or oral phenobarbital for 21 consecutive days or longer between 2000 and 2016. Patients were divided into non-cancer and cancer groups. Cancer patients were further stratified according to the survival interval after TDM: those who survived > 3 months were classified as long-surviving and the remainders short-surviving cancer patients. Phenobarbital clearance (CL_PB) was calculated at steady state. Multiple comparisons of median CL_PB were conducted among the three groups.

RESULTS

Data were collected from 44 non-cancer patients and 34 cancer patients comprising 24 long-surviving and 10 short-surviving cancer patients. Among 10 short-surviving cancer patients, 4 had hepatic metastasis. Median CL_PB (range) in short-surviving cancer patients [0.076 (0.057‒0.114) L/kg/day] was significantly (p < 0.05) lower than that in non-cancer patients [0.105 (0.060‒0.226) L/kg/day] and in long-surviving cancer patients [0.100 (0.082‒0.149) L/kg/day].

CONCLUSION

Terminally ill patients with advanced cancer may have reduced CL_PB, thereby TDM is recommended for these patients particularly near the end of life.

Pharmacokinetic considerations and recommendations in palliative care, with focus on morphine, midazolam and haloperidol

INTRODUCTION

A variety of medications are used for symptom control in palliative care, such as morphine, midazolam and haloperidol. The pharmacokinetics of these drugs may be altered in these patients as a result of physiological changes that occur at the end stage of life.

AREAS COVERED

This review gives an overview of how the pharmacokinetics in terminally ill patients may differ from the average population and discusses the effect of terminal illness on each of the four pharmacokinetic processes absorption, distribution, metabolism, and elimination. Specific considerations are also given for three commonly prescribed drugs in palliative care: morphine, midazolam and haloperidol).

EXPERT OPINION

The pharmacokinetics of drugs in terminally ill patients can be complex and limited evidence exists on guided drug use in this population. To improve the quality of life of these patients, more knowledge and more pharmacokinetic/pharmacodynamics studies in terminally ill patients are needed to develop individualised dosing guidelines. Until then knowledge of pharmacokinetics and the physiological changes that occur in the final days of life can provide a base for dosing adjustments that will improve the quality of life of terminally ill patients. As the interaction of drugs with the physiology of dying is complex, pharmacological treatment is probably best assessed in a multi-disciplinary setting and the advice of a pharmacist, or clinical pharmacologist, is highly recommended.

A nutrigenomic approach to detect nutritional stress from gene expression in blood samples drawn from Steller sea lions

Gene expression profiles are increasingly being used as biomarkers to detect the physiological responses of a number of species to disease, nutrition, and other stressors. However, little attention has been given to using gene expression to assess the stressors and physiological status of marine mammals. We sought to develop and validate a nutrigenomic approach to quantify nutritional stress in Steller sea lions (Eumetopias jubatus). We subjected 4 female Steller sea lions to 3 feeding regimes over 70-day trials (unrestricted food intake, acute nutritional stress, and chronic nutritional stress), and drew blood samples from each animal at the end of each feeding regime. We then extracted the RNA of white blood cells and measured the response of 8 genes known to react to diet restriction in terrestrial mammals. Overall, we found that the genomic response of Steller sea lions experiencing nutritional stress was consistent with how terrestrial mammals respond to dietary restrictions. Our nutritionally stressed sea lions down-regulated some cellular processes involved in immune response and oxidative stress, and up-regulated pro-inflammatory responses and metabolic processes. Nutrigenomics appears to be a promising means to monitor nutritional status and contribute to mitigation measures needed to assist in the recovery of Steller sea lions and other at-risk species of marine mammals.

The influence of the CYP3A4*22 polymorphism on serum concentration of quetiapine in psychiatric patients

BACKGROUND

Besides dietary, hormonal, or pathological factors, mutations in cytochrome P450 enzymes are thought to be responsible for the interindividual differences in serum concentrations of cytochrome P450 (CYP450)-dependent drugs. Cytochrome P450 3A4 (CYP3A4) is involved in the metabolism of greater than 50% of the prescribed drugs. Recently, a new single-nucleotide polymorphism (SNP) was found (CYP3A4*22), which results in a decreased enzyme activity, in contrast to the other known SNPs in CYP3A4. We investigated to which degree the CYP3A4*22 SNP affects serum concentrations of patients receiving quetiapine, a drug exclusively metabolized by CYP3A4.

METHODS

Two hundred thirty-eight adult patients receiving quetiapine were included in this study, based on availability of DNA, serum quetiapine levels, and information on dose. Patients were genotyped for CYP3A4*22 using allele-specific polymerase chain reaction, and, as a control, restriction fragment length polymorphism analysis.

RESULTS

Carriers of the CYP3A4*22 allele (*1/*22 and *22/*22, n = 31) had 2.5-fold higher serum levels of quetiapine than did wild-type patients (n = 207; P = 0.03) when using a comparable dose (median, 300 mg/d for both wild-type and carriers; P = 0.67). The dose-corrected serum concentration (C/D) was 67% higher in carriers than in wild-type patients (P = 0.01). The number of patients who achieved serum levels above the therapeutic range (>500 µg/L) was also higher in *22-allele carriers (16.1% vs 2.9%; P = 0.007).

CONCLUSION

Being a carrier of the CYP3A4*22 allele increases the serum concentration of quetiapine at comparable doses.

Pharmacokinetics of drugs in cachectic patients: a systematic review

Cachexia is a weight-loss process caused by an underlying chronic disease such as cancer, chronic heart failure, chronic obstructive pulmonary disease, or rheumatoid arthritis. It leads to changes in body structure and function that may influence the pharmacokinetics of drugs. Changes in gut function and decreased subcutaneous tissue may influence the absorption of orally and transdermally applied drugs. Altered body composition and plasma protein concentration may affect drug distribution. Changes in the expression and function of metabolic enzymes could influence the metabolism of drugs, and their renal excretion could be affected by possible reduction in kidney function. Because no general guidelines exist for drug dose adjustments in cachectic patients, we conducted a systematic search to identify articles that investigated the pharmacokinetics of drugs in cachectic patients.

Asenapine pharmacokinetics in hepatic and renal impairment

BACKGROUND AND OBJECTIVE

The effects of hepatic or renal impairment on the pharmacokinetics of atypical antipsychotics are not well understood. Drug exposure may increase in patients with hepatic disease, owing to a reduction of certain metabolic enzymes. The objective of the present study was to study the effects of hepatic or renal impairment on the pharmacokinetics of asenapine and its N-desmethyl and N⁺-glucuronide metabolites.

METHODS

Two clinical studies were performed to assess exposure to asenapine, desmethylasenapine and asenapine N⁺-glucuronide in subjects with hepatic or renal impairment. Pharmacokinetic parameters were determined from plasma concentration-time data, using standard noncompartmental methods. The pharmacokinetic variables that were studied included the maximum plasma concentration (C(max)) and the time to reach the maximum plasma concentration (t(max)). Eligible subjects, from inpatient and outpatient clinics, were aged ≥18 years with a body mass index of ≥18 kg/m² and ≤32 kg/m². Sublingual asenapine (Saphris®) was administered as a single 5 mg dose.

RESULTS

Thirty subjects participated in the hepatic impairment study (normal hepatic function, n = 8; mild hepatic impairment [Child-Pugh class A], n = 8; moderate hepatic impairment [Child-Pugh class B], n = 8; severe hepatic impairment [Child-Pugh class C], n = 6). Thirty-three subjects were enrolled in the renal impairment study (normal renal function, n = 9; mild renal impairment, n = 8; moderate renal impairment, n = 8; severe renal impairment, n = 8). Asenapine and N-desmethylasenapine exposures were unaltered in subjects with mild or moderate hepatic impairment, compared with healthy controls. Severe hepatic impairment was associated with increased area under the plasma concentration-time curve from time zero to infinity (AUC(∞)) values for total asenapine, N-desmethylasenapine and asenapine N⁺-glucuronide (5-, 3-, and 2-fold, respectively), with slight increases in the C(max) of asenapine but 3- and 2-fold decreases in the C(max) values for N-desmethylasenapine and asenapine N⁺-glucuronide, respectively, compared with healthy controls. The mean AUC(∞) of unbound asenapine was more than 7-fold higher in subjects with severe hepatic impairment than in healthy controls. Mild renal impairment was associated with slight elevations in the AUC(∞) of asenapine compared with healthy controls; alterations observed with moderate and severe renal impairment were marginal. N-desmethylasenapine exposure was only slightly altered by renal impairment. No correlations were observed between exposure and creatinine clearance.

CONCLUSION

Severe hepatic impairment (Child-Pugh class C) was associated with pronounced increases in asenapine exposure, but significant increases were not seen with mild (Child-Pugh class A) or moderate (Child-Pugh class B) hepatic impairment, or with any degree of renal impairment. Asenapine is not recommended in patients with severe hepatic impairment; no dose adjustment is needed in patients with mild or moderate hepatic impairment, or in patients with renal impairment.

Rapid identification of CYP2C8 polymorphisms by high resolution melting analysis

BACKGROUND

Cytochrome P450 (CYP) 2C8 is the principal enzyme responsible for the metabolism of arachidonic acid and various drugs, and influences drug-drug interactions and some associated diseases. Large interindividual differences in CYP2C8 enzymatic activity and several nonsynonymous genetic variations have been reported in different races. Therefore, how to identify CYP2C8 polymorphisms efficiently for genotyping in different populations is very important.

METHODS

A high resolution melting (HRM) analysis was used to characterize the CYP2C8 polymorphism. Genomic DNA was extracted from peripheral blood samples from 95 normal individuals in Taiwan. Nine exons of the CYP2C8 gene were screened by HRM analysis. All results were confirmed by direct DNA sequencing.

RESULTS

Five new single nucleotide polymorphisms (SNPs) were found in this study; two SNPs [1189G>A (D397N) and 1230C>T (G410G)] were in exon 8 and the others [1312G>C (E438Q), 1497T>C (A499A) and 1677delT (559delL)] were in exon 9. The 1497T>C (A499A) was the most common variant with an allele frequency of 20.53% but without amino acid substitution.

CONCLUSIONS

HRM analysis is a fast, reliable, accurate and cost-effective screening method for gene mutations, even very similar cDNA sequences with 83% identities, compared with CYP2C8 and CYP2C9.

Inflammation and CYP3A4-mediated drug metabolism in advanced cancer: impact and implications for chemotherapeutic drug dosing

BACKGROUND

The inability to accurately predict treatment outcomes for cancer patients in terms of tumour response and anticancer drug toxicity is a severe limitation inherent in current approaches to chemotherapy. Many anticancer drugs are metabolically cleared by cytochrome P450 3A4 (CYP3A4), the predominant CYP expressed in liver. CYP3A4 expression exhibits marked interindividual variation and is repressed in acute inflammatory states.

OBJECTIVES

(1) To review the relevance of CYP3A4 variability to drug metabolism in the setting of cancer and to understand how inflammation associated with malignancy contributes to both this variability and to adverse treatment outcomes. (2) To examine the relationship between tumour-induced inflammation and repression of CYP3A4 and to explore methods of dosing of anticancer drugs in the setting of advanced cancer.

METHODS

Review of relevant literature covering both human and animal studies as well as in vitro mechanistic studies.

RESULTS/CONCLUSIONS

Interindividual variability in CYP3A4 expression is a major confounding factor for effective cancer treatment and methods to predict CYP3A4-mediated drug clearance may have clinical utility in this setting. Although acute inflammation has long been recognised to repress drug metabolism, it is now becoming apparent that cancer patients exhibiting clinical and laboratory features of an inflammatory response have reduced expression of CYP3A4 and possibly other genes relevant to anticancer drug disposition.

Modification of CYP2E1 and CYP3A4 activities in haemoglobin E-beta thalassemia patients

OBJECTIVE

Thalassemia disease is a genetic haemoglobinopathy usually associated with an iron overload and some degree of organ impairment. The impact of the disease on the drug metabolising enzyme cytochrome P450 (CYP) is not known. CYP2E1 and CYP3A4 are responsible for the metabolism of a large number of drugs and changes in their activities may have clinical consequences.

METHODS

Haemoglobin E-beta thalassemia paediatric, blood transfusion-dependent patients apparently without complications (n = 35) and healthy controls (n = 42) were recruited in this study. The ratios of plasma 6-hydroxychlorzoxazone to chlorzoxazone, and urinary 6-beta-hydroxycortisol (6beta-OHF) to cortisol were used as indices for CYP2E1 and CYP3A4 activities, respectively. Blood and plasma samples were assayed for parameters of clinical biochemistry, oxidants and antioxidants.

RESULTS

There were significant increases in serum iron, protein carbonyl and lipid peroxidation in thalassemia patients, whereas there was a decrease in blood glutathione, but unchanged plasma nitric oxide metabolites. CYP2E1 activity in the patients was unchanged; however, when the patients were stratified by splenectomy status, CYP2E1 activity was increased in non-splenectomised patients in comparison with the controls and splenectomised subjects. On the other hand, 6beta-OHF/cortisol ratios increased markedly in patients associated with depressed growth hormone levels. There were no correlations between CYP2E1 activity and oxidant stress or antioxidant parameters.

CONCLUSIONS

This report is the first demonstration that thalassemia major is associated with an alteration of CYP2E1 and CYP3A4 activities; this could modify the sensitivity of thalassemia patients to the toxic or therapeutic effects of drugs.

Systemic responses to inhaled ozone in mice: cachexia and down-regulation of liver xenobiotic metabolizing genes

Rats or mice acutely exposed to high concentrations of ozone show an immediate and significant weight loss, even when allowed free access to food and water. The mechanisms underlying this systemic response to ozone have not been previously elucidated. We have applied the technique of global gene expression analysis to the livers of C57BL mice acutely exposed to ozone. Mice lost up to 14% of their original body weight, with a 42% decrease in total food consumption. We previously had found significant up-regulation of genes encoding proliferative enzymes, proteins related to acute phase reactions and cytoskeletal functions, and other biomarkers of a cachexia-like inflammatory state in lungs of mice exposed to ozone. These results are consistent with a general up-regulation of different gene families responsive to NF-kappaB in the lungs of the exposed mice. In the present study, we observed significant down-regulation of different families of mRNAs in the livers of the exposed mice, including genes related to lipid and fatty acid metabolism, and to carbohydrate metabolism in this tissue, consistent with a systemic cachexic response. Several interferon-dependent genes were down-regulated in the liver, suggesting a possible role for interferon as a signaling molecule between lung and liver. In addition, transcription of several mRNAs encoding enzymes of xenobiotic metabolism in the livers of mice exposed to ozone was decreased, suggesting cytokine-mediated suppression of cytochrome P450 expression. This finding may explain a previously controversial report from other investigators more than 20 years ago of prolongation of pentobarbital sleeping time in mice exposed to ozone.

Acetaminophen misconceptions

Examination of the pharmacokinetics of acetaminophen can decrease misconceptions involved in clinical evaluation. Enzyme patterns and acetaminophen levels must be related to time and known metabolic phenomena. A careful look at ethanol and nutrition, especially fasting demonstrates that therapeutic doses of acetaminophen do not place patients at a greater risk in either of these instances. An overdose of acetaminophen in a chronic alcohol abuser may result in more severe hepatotoxicity than in the nonalcoholic. CYP2E1 and glutathione must be evaluated simultaneously rather than in isolation. Glucuronidation capacity in humans is not a factor except in massively overdosed patients.

Cytochrome p450 gene expression levels in peripheral blood mononuclear cells in comparison with the liver

Cytochromes p450 (CYPs) compose a superfamily of similar proteins involved in detoxification and elimination, as well as activation of a wide variety of compounds. Most CYP family members are localized in the liver. In order to assess whether peripheral blood leukocytes (PBL) are available as a surrogate for the determination of CYP gene expression levels in the liver, we compared CYP gene expression levels in PBL with those in liver tissues from patients with hepatocellular carcinoma (HCC). We measured CYP1A1, 1A2, 1B1, 2A6, 2B6, 2C8, 2C9, 2C18, 2C19, 2D6, 2E1, 2F1, 2J2, 3A4, 3A5, 3A7, 4A11, 4B1 and CYP27 gene expressions in PBL and in the liver by real-time reverse-transcription (RT)-PCR. We could detect expression of CYP1A1, 1A2, P1B1, 2A6, 2B6 and 2E1 genes in PBL and all the genes except for CYP2F1 in the liver. Although gene expression levels within each subfamily were closely correlated within PBL and within the liver, a clear correlation of gene expression levels between PBL and liver tissues was found only for CYP4B1. Although inter-individual variation of the expression level of each CYP gene was wide, the induced level was proportional to the basal expression level. Therefore, monitoring of CYP gene expression levels in PBL, especially those of CYP4B1, could be available as a biomarker for monitoring of exposure to environmental pollutants and assessing the associated risk. Compared with non-tumor tissue, HCC tissues tended to show overexpression of multiple CYP genes, indicating that individualized selection and more effective administration of chemotherapeutic agents could perhaps be based on the pattern of CYP overexpression.

Pharmacokinetics of cyclosporine pre- and post-liver transplantation

Cyclosporine (CyA) is an immunosuppressant metabolized primarily by the liver and small intestine. The pharmacokinetics (PK) of CyA-were studied in 6 patients prior to and 1 to 3 months after liver transplantation (tx). Sixteen blood samples were collected over 24 hours following a 2-3 mg/kg intravenous dose of CyA. PK parameters, presented as mean +/- SD, were estimated using noncompartmental techniques. Pre-tx AUCs (14,540 +/- 5200 micrograms.h/L) were found to be significantly higher than during the post-tx phase (8120 +/- 2870 micrograms.h/L, p = 0.04). CyA clearance values were lower pre-tx as compared to post-tx (0.21 +/- 0.06 L/h/kg vs. 0.38 +/- 0.14 L/h/kg, respectively). There was no change in volume of distribution. End-stage liver disease can markedly decrease hepatic clearance of CyA relative to patients with stable hepatic function post-liver tx. The degree of impairment in clearance is not consistent or predictable based on liver function tests.

How to calculate the dose of chemotherapy

Body surface area-dosing does not account for the complex processes of cytotoxic drug elimination. This leads to an unpredictable variation in effect. Overdosing is easily recognised but it is possible that unrecognised underdosing is more common and may occur in 30% or more of patients receiving standard regimen. Those patients who are inadvertently underdosed are at risk of a significantly reduced anticancer effect. Using published data, it can be calculated that there is an almost 20% relative reduction in survival for women receiving adjuvant chemotherapy for breast cancer as a result of unrecognised underdosing. Similarly, the cure rate of cisplatin-based chemotherapy for advanced testicular cancer may be reduced by as much as 10%. The inaccuracy of body surface area-dosing is more than an inconvenience and it is important that methods for more accurate dose calculation are determined, based on the known drug elimination processes for cytotoxic chemotherapy. Twelve rules for dose calculation of chemotherapy are given that can be used as a guideline until better dose-calculation methods become available. Consideration should be given to using fixed dose guidelines independent of body surface area and based on drug elimination capability, both as a starting dose and for dose adjustment, which may have accuracy, safety and financial advantages.

Variation in coumarin 7-hydroxylase activity associated with genetic polymorphism of cytochrome P450 2A6 and the body status of iron stores in adult Thai males and females

The relationships between catalytic activity of cytochrome P450 2A6 (CYP2A6), polymorphism of CYP2A6 gene, gender and levels of body iron stores were analysed in a sample group of 202 apparently healthy Thais, aged 19-47 years. Eleven individuals were found to have high activity of CYP2A6, judged by the relatively large amounts (11.2-14.6 mg) of 7-hydroyxcoumarin (7-OHC) excreted 3 h following administration of 15 mg of coumarin. Ten individuals, however, did not excrete any 7-OHC. Of these 10, four were found to have no CYP2A6 gene (whole gene deletion; CYP2A6*4 allele). The frequency of the CYP2A6 alleles; *1A, *1B and *4 in the whole sample group was 52, 40 and 8% while the frequency of the CYP2A6 gene types; *1A/*1A, *1A/*1B, *1B/*1B, *1A/*4, *1B/*4, *4/*4 was 29, 41, 16, 7, 5 and 2%. Subjects having CYP2A6*1A/*1B gene-type group were found to have higher rates of coumarin 7-hydroxylation compared with those of the CYP2A6*1B/*1B and CYP2A6*1A/*4 gene types. The inter-individual variability in CYP2A6 catalytic activity was therefore attributed in part to the CYP2A6 genetic polymorphism. Variation in CYP2A6 activity in this sample group was not associated with gender but, interestingly, it did show an inverse association with plasma ferritin; an indicator of body iron stores. Higher rates of coumarin 7-hydroxylation were found in individuals with low body iron stores (plasma ferritin < 20 microg/l) compared with subjects having normal body iron store status. Subjects (n = 16) with iron overload (plasma ferritin > 300 microg/l) also tended to have elevated rates of coumarin 7-hydroxylation. These results suggest an increased CYP2A6 expression in subjects who have excessive body iron stores. Further investigations into the underlying factors that may lead to increased expression of CYP2A6 in association with abnormal body iron stores are currently in progress in our laboratory.

Associations between human liver and kidney cadmium content and immunochemically detected CYP4A11 apoprotein

This present study was undertaken to assess potential effects of cadmium on CYP4A11 apoprotein in human liver and kidney as detected by Western blotting using a highly specific anti-peptide antibody. Liver and kidney cortex samples were autopsy specimens of 37 individuals (26 males and 11 females) whose ages ranged from 3 to 89 years. All were Caucasians who had not been exposed to cadmium in the workplace. Reduced CYP4A11 apoprotein levels were found in chronic hepatitis samples and in liver samples showing fatty changes. In contrast, increased CYP4A11 apoprotein levels were found in liver samples having higher cadmium content compared to the lower cadmium content samples. Increased CYP4A11 levels were also found in liver samples from female donors, compared to male donors; the difference being attributable to higher female liver cadmium burden. In distinction to liver, lowered CYP4A11 levels were seen in the kidney cortex samples which have high cadmium content. It is proposed here that the difference between the absolute cadmium burden of the liver and kidney samples may be responsible for the different patterns of expression of CYP4A11 in these two tissues. Further, since cadmium exposure may be associated with derangement in blood pressure control, it is interesting to note the possible relationship between altered CYP4A11-dependent production of arachidonic acid hydroxy and epoxy metabolites in kidney cortex and altered control of blood pressure. Our findings provide a possible link between these observations.

Relationships between non-occupational cadmium exposure and expression of nine cytochrome P450 forms in human liver and kidney cortex samples

This study was undertaken to assess associations between age, gender, cigarette smoke and non-workplace cadmium exposure, and liver pathology and inter-individual variation in cytochrome P450 (CYP) expression in human tissues. Autopsy specimens of twenty-eight Queensland residents whose ages ranged from 3 to 89 years were analyzed for the presence of nine CYP protein isoforms by immunoblotting. All subjects were Caucasians and their liver cadmium contents ranged from 0.11 to 3.95 microg/g wet weight, while their kidney cadmium contents were in the range of 2 to 63 microg/g wet weight. CYP1A2, CYP2A6, CYP2D6, CYP3A4, and CYP3A5 were detected in liver but not in kidney, and CYP1A1 and CYP1B1 were not found in liver or kidney. Lowered liver CYP2C8/19 protein contents were found to be associated with liver pathology. Importantly, we show elevated levels of CYP2C9 protein to be associated with cadmium accumulation in liver. No mechanism that explains this association is apparent, but there are two possibilities that require further study. One is that variation in CYP2C9 protein levels may be, in part, attributed to an individual's non-workplace exposure to cadmium, or an individual's CYP2C9 genotype may be a risk factor for cadmium accumulation. A positive correlation was found between liver CYP3A4 protein and subject age. Levels of liver CYP1A2 protein, but not other CYP forms, were increased in people more exposed to cigarette smoke, but there was no association between CYP1A2 protein and cadmium. CYP2A6 protein was found in all liver samples and CYP2A6 gene typing indicated the absence of CYP2A6 null allele (CYP2A6(D)) in this sample group, confirming very low prevalence of homozygous CYP2A6(D) in Caucasians. CYP2A6 gene types W/W, W/C, and C/C were not associated with variations in liver microsomal CYP2A6 protein. CYP2D6 protein was absent in all twenty-five kidney samples tested but was detectable in liver samples of all but two subjects, indicating the prevalence of the CYP2D6 null allele (CYP2D6(D)) in this sample group to be about 7%, typical of Caucasian populations.

Influence of cirrhosis on lamotrigine pharmacokinetics

AIMS

Lamotrigine, an antiepileptic drug, is cleared from the systemic circulation mainly by glucuronidation. The possibility of changes in the pharmacokinetics of lamotrigine in plasma owing to hepatic dysfunction has been evaluated.

METHODS

Thirty-six subjects, including 24 patients with various degrees of liver cirrhosis and 12 healthy volunteers received a single 100 mg dose of lamotrgine. Blood samples were taken for 7 days in all subjects, except nine with severe cirrhosis, who had a 29 day blood sampling period.

RESULTS

The pharmacokinetics of lamotrigine were comparable between the patients with moderate cirrhosis (corresponding to Child-Pugh grade A) and the healthy subjects. Plasma oral clearance mean ratios (90% confidence interval) in patients with severe cirrhosis without or with ascites (corresponding, respectively, to Child-Pugh grade B and C) to healthy subjects were, respectively, 60% (44%, 83%) and 36% (25%, 52%). Plasma half-life mean ratios (90% confidence interval) in these two patient groups to healthy subjects were, respectively, 204% (149%, 278%) and 287% (202%, 408%).

CONCLUSIONS

Lamotrigine administered as a single oral dose of 100 mg was well tolerated in all groups. Initial, escalation and maintenance doses should generally be reduced by approximately 50 or 75% in patients with Child-Pugh Grade B or C cirrhosis. Escalation and maintenance doses should be adjusted according to clinical response.