Gilbert's disease and atazanavir: from phenotype to UDP-glucuronosyltransferase haplotype

Similarities in Structure and Function of UDP-Glycosyltransferase Homologs from Human and Plants

The uridine diphosphate glycosyltransferase (UGT) superfamily plays a key role in the metabolism of xenobiotics and metabolic wastes, which is essential for detoxifying those species. Over the last several decades, a huge effort has been put into studying human and mammalian UGT homologs, but family members in other organisms have been explored much less. Potentially, other UGT homologs can have desirable substrate specificity and biological activities that can be harnessed for detoxification in various medical settings. In this review article, we take a plant UGT homology, UGT71G1, and compare its structural and biochemical properties with the human homologs. These comparisons suggest that even though mammalian and plant UGTs are functional in different environments, they may support similar biochemical activities based on their protein structure and function. The known biological functions of these homologs are discussed so as to provide insights into the use of UGT homologs from other organisms for addressing human diseases related to UGTs.

Cardiovascular risks associated with protease inhibitors for the treatment of HIV

Introduction: Cumulative use of some first-generation protease inhibitors has been associated with higher rates of dyslipidemia and increased risk of cardiovascular disease. The protease inhibitors most commonly in use are atazanavir and darunavir, which have fewer detrimental lipid effects and greater tolerability. This paper aims to review the evidence of a potential association of these contemporary protease inhibitors with the risk of ischemic CVD and atherosclerotic markers.Areas covered: We searched for publications of randomized trials and observational studies on PubMed from 1 January 2000 onwards, using search terms including: protease inhibitors; darunavir; atazanavir; cardiovascular disease; cardiovascular events; dyslipidemia; mortality; carotid intima media thickness; arterial elasticity; arterial stiffness and drug discontinuation. Ongoing studies registered on clinicaltrials.gov as well as conference abstracts from major HIV conferences from 2015-2020 were also searched.Expert opinion: Atazanavir and darunavir are no longer part of first-line HIV treatment, but continue to be recommended as alternative first line, second- and third-line regimens, as part of two drug regimens, and darunavir is used as salvage therapy. Although these drugs will likely remain in use globally for several years to come, baseline CVD risk should be considered when considering their use, especially as the population with HIV ages.

Evaluation of the effect of UGT1A1 polymorphisms on the pharmacokinetics of oral and long-acting injectable cabotegravir

Background

Cabotegravir is an HIV integrase inhibitor in clinical development with both oral and long-acting (LA) injectable formulations. Cabotegravir is primarily metabolized by uridine 5′-diphospho-glucuronosyltransferase (UGT) 1A1, a known polymorphic enzyme with functional variants that can affect drug metabolism and exposure.

Objectives

To investigate the pharmacogenetic effects of the reduced-function alleles UGT1A1*6, UGT1A1*28 and/or UGT1A1*37 on steady-state pharmacokinetics (PK) and safety of oral cabotegravir (30 mg/day) and intramuscular cabotegravir LA (400 mg every 4 weeks or 600 mg every 8 weeks).

Methods

Plasma cabotegravir PK was assessed in 346 UGT-genotyped participants with and without UGT1A1 functional variants across six studies (four Phase I and two Phase II) of oral cabotegravir, including 215 HIV-infected participants who received oral cabotegravir followed by cabotegravir LA. Changes from baseline in total bilirubin and ALT were assessed in one study (LATTE; NCT01641809).

Results

Statistically significant (P < 0.05) associations were observed between UGT1A1 genotype and plasma cabotegravir PK parameters, with 28%–50% increases following oral cabotegravir [plasma cabotegravir concentration at the end of the dosing interval (C_tau), 1.50-fold; AUC_tau, 1.41-fold; and C_max, 1.28-fold] and 16%–24% increases following cabotegravir LA administration (48 week C_tau, 1.24-fold; AUC_tau, 1.16-fold; and C_max, 1.18-fold) among those with low-versus-normal genetically predicted UGT1A1 activity. A statistically significant (P < 10⁻⁵) association between predicted UGT1A1 activity and maximum change in total bilirubin was also observed (2.45-fold asymptomatic increase for low versus normal) without a corresponding change in ALT.

Conclusions

This modest increase in oral and parenteral cabotegravir exposure associated with a reduced function of UGT1A1 is not considered clinically relevant based on accumulated safety data; no dose adjustment is required.

Hepatocellular cancer therapy in patients with HIV infection: Disparities in cancer care, trials enrolment, and cancer-related research

In the highly active antiretroviral therapy (HAART) era, hepatocellular carcinoma (HCC) is arising as a common late complication of human immunodeficiency virus (HIV) infection, with a great impact on morbidity and mortality. Though HIV infection alone may not be sufficient to promote hepatocarcinogenesis, the complex interaction of HIV with hepatitis is a main aspect influencing HCC morbidity and mortality.

Data about sorafenib effectiveness and safety in HIV-infected patients are limited, particularly for patients who are on HAART. However, in properly selected subgroups, outcomes may be comparable to those of HIV-uninfected patients. Scarce data are available for those other systemic treatments, either tyrosine kinase inhibitors, as well as immune checkpoint inhibitors (ICIs), which have been added to our therapeutic armamentarium. This review examines the influence of HIV infection on HCC development and natural history, summarizes main data on systemic therapies, offers some insight into possible mechanisms of T cell exhaustion and reversal of HIV latency with ICIs and issues about clinical trials enrollment. Nowadays, routine exclusion of HIV-infected patients from clinical trial participation is totally inappropriate, since it leaves a number of patients deprived of life-prolonging therapies.

The Functionality of UDP-Glucuronosyltransferase Genetic Variants and their Association with Drug Responses and Human Diseases

UDP-glucuronosyltransferases (UGTs) are phase II drug-metabolizing enzymes that metabolize endogenous fatty acids such as arachidonic acid metabolites, as well as many prescription drugs, such as opioids, antiepileptics, and antiviral drugs. The UGT1A and 2B genes are highly polymorphic, and their genetic variants may affect the pharmacokinetics and hence the responses of many drugs and fatty acids. This study collected data and updated the current view of the molecular functionality of genetic variants on UGT genes that impact drug responses and the susceptibility to human diseases. The functional information of UGT genetic variants with clinical associations are essential to understand the inter-individual variation in drug responses and susceptibility to toxicity.

TaqMan real time PCR for the Detection of the Gilbert's Syndrome Markers UGT1A1*28; UGT1A1*36 and UGT1A1*37

Gilbert's syndrome is characterized by mild unconjugated hyperbilirubinemia. The key of this disease is a diminished activity of UDP-glucuronosyltransferase 1A1 (UGT1A1). TA insertion into the TATA box promoter region of the UGT1A1 gene on chromosome 2 is the genetic basis of Gilbert's syndrome (UGT1A1*28). An extra TA insert leads to eight (TA)8 repeats (UGT1A1*37) resulting in a further reduction of glucuronidation activity. A variant lacking one TA repeat (TA)5 (UGT1A1*36) has been identified. (TA)8 repeats (UGT1A1*37) and (TA)5 (UGT1A1*36) have been detected in Africans (frequency up to 0.07 and 0.08 respectively). We present a real time PCR method for genotyping the UGT1A1 (TA)n polymorphism (UGT1A1*28, UGT1A1*36, UGT1A1*37) using Taqman PCR on 7500 and cfx96 Real-Time PCR System. We present a real time PCR method for genotyping the UGT1A1 (TA)n polymorphism (UGT1A1*28, UGT1A1*36, UGT1A1*37) using Taqman PCR. About clinical validation, all 53 samples collected from patients referred for suspected Gilbert's syndrome were analyzed. We found 21 on the 53 patients (39.6%) were homozygotes (UGT1A1-TATA (TA)6) and referred as wild-type, 13 on the 53 patients (24.5%) were homozygotes (UGT1A1-TATA (TA)7) and referred as mutated, 1 on the 53 patients (1.9%) were homozygotes (UGT1A1-TATA (TA)8) and referred as mutated, 1 on the 53 patients (1.9%) were heterozygotes (UGT1A1-TATA (TA)7/8) and referred as mutated, 1 on the 53 patients (1.9%) were heterozygotes (UGT1A1-TATA (TA)5/6) and referred as mutated, and 16 on the 53 patients (30.2%) were heterozygotes (UGT1A1-TATA (TA)6/7). None were homozygotes UGT1A1-TATA (TA)5, homozygotes UGT1A1-TATA (TA)8, or heterozygotes with (TA)5 or (TA)8 alleles. The newly described technique represents a valid alternative method to sequencing, mainly due to its rapidity, easiness, and minor costs.

UGT1A1 Guided Cancer Therapy: Review of the Evidence and Considerations for Clinical Implementation

Multi-gene assays often include UGT1A1 and, in certain instances, may report associated toxicity risks for irinotecan, belinostat, pazopanib, and nilotinib. However, guidance for incorporating UGT1A1 results into therapeutic decision-making is mostly lacking for these anticancer drugs. We summarized meta-analyses, genome-wide association studies, clinical trials, drug labels, and guidelines relating to the impact of UGT1A1 polymorphisms on irinotecan, belinostat, pazopanib, or nilotinib toxicities. For irinotecan, UGT1A1*28 was significantly associated with neutropenia and diarrhea, particularly with doses ≥ 180 mg/m2, supporting the use of UGT1A1 to guide irinotecan prescribing. The drug label for belinostat recommends a reduced starting dose of 750 mg/m2 for UGT1A1*28 homozygotes, though published studies supporting this recommendation are sparse. There was a correlation between UGT1A1 polymorphisms and pazopanib-induced hepatotoxicity, though further studies are needed to elucidate the role of UGT1A1-guided pazopanib dose adjustments. Limited studies have investigated the association between UGT1A1 polymorphisms and nilotinib-induced hepatotoxicity, with data currently insufficient for UGT1A1-guided nilotinib dose adjustments.

Gilbert's Syndrome, Bilirubin Level and UGT1A1∗28 Genotype in Men of North-West Region of Russia

BACKGROUND/OBJECTIVES

Gilbert's syndrome (GS) is a hereditary pathology that affects approximately 10% of the world's population. In most cases, GS is associated with the UGT1A1∗28 polymorphism of UGT1A1 gene coding the enzyme bilirubin uridine diphosphate glucuronosyltransferase (UGT-1A) which plays a key role in the bilirubin metabolism. The presence of an additional TA repeat in the TATA box of the UGT1A1 gene promoter (the allelic variant of 7TA, abbreviated as UGT1A1∗28) leads to a significant decrease in the enzymatic activity of UGT-1A in the liver and to decrease in glucuronidation process as a consequence. The aim of the study is to estimate the prevalence of the 6TA/6TA, 6TA/7TA, and 7TA/7TA genotypes of UGT1A1 promoter and to analyze the effect of these variants on bilirubin levels in healthy men in North-West Russia and patients with a clinical diagnosis of GS.

METHODS

Genotyping of the UGT1A1 ∗28 (rs8175347) polymorphism was carried out by real-time PCR.

RESULTS

The results obtained indicate an increased probability of GS developing in residents of the North-West region of Russia compared with other representatives of the Caucasians.

CONCLUSIONS

Despite the fact that the level of serum bilirubin increases with the rise in the number of additional TA dinucleotides in the UGT1A1 gene promoter tests of clinical manifestations only (jaundice, fatigue, sleep disturbances, nausea, belching, and so on) and increased bilirubin levels in patients with normal liver function do not allow unequivocally diagnose GS. UGT1A1∗28 genotyping should be used as a prognostic risk factor for such pathology development.

Pharmacogenomics and Pharmacogenetics: In Silico Prediction of Drug Effects in Treatments for Novel Coronavirus SARS-CoV2 Disease

The latest developments in precision medicine allow the modulation of therapeutic approaches in different pathologies on the basis of the specific molecular characterization of the patient. This review of the literature coupled with in silico analysis was to provide a selected screening of interactions between single-nucleotide polymorphisms (SNPs) and drugs (repurposed, investigational, and biological agents) showing efficacy and toxicityin counteracting Covid-19 infection. In silico analysis of genetic variants related to each drug was performed on such databases as PharmGKB, Ensembl Genome Browser, www.drugs.com, and SNPedia, with an extensive literature review of papers (to May 10, 2020) on Covid-19 treatments using Medline, Embase, International Pharmaceutical Abstracts, PharmGKB, and Google Scholar. The clinical relevance of SNPs, known as both drug targets and markers, considering genetic variations with known drug responses, and the therapeutic consequences are discussed. In the context of clinical treatment of Covid-19, including infection prevention, control measures, and supportive care, this review highlights the importance of a personalized approach in the final selection of therapy, which is probably essential in the management of the Covid-19 pandemic.

Association Between Atazanavir-Induced Hyperbilirubinemia and Cardiovascular Disease in Patients Infected with HIV

BACKGROUND:

Serum bilirubin is inversely associated with cardiovascular risk. Atazanavir, an HIV protease inhibitor that competitively inhibits bilirubin conjugation, provides a unique opportunity to examine whether selectively increasing bilirubin is cardioprotective. We sought to determine whether patients receiving atazanavir manifest a reduced risk of cardiovascular disease compared with those receiving darunavir, an HIV protease inhibitor that does not increase serum bilirubin.

METHODS AND RESULTS:

This was a retrospective cohort study of 1020 patients with HIV. The main outcome was time to myocardial infarction or ischemic stroke. Mean follow‐up was 6.6±3.4 years, with 516 receiving atazanavir and 504 darunavir. Atazanavir patients exhibited significantly higher serum total bilirubin (1.7 versus 0.4 mg/dL; P<0.001) and longer mean time to ischemic event (10.2 versus 9.4 years; P<0.001). On Cox regression, atazanavir treatment (hazard ratio [HR], 0.38; 95% CI, 0.21–0.71; P=0.002) and serum bilirubin (HR, 0.60; 95% CI, 0.41–0.89; P=0.011) were independently associated with a lower risk of an ischemic event. Notably, when atazanavir and bilirubin were included together in the Cox regression model, atazanavir lost significance (HR, 0.55; 95% CI, 0.24–1.29; P=0.169) consistent with bilirubin being an intermediate variable on the causal pathway between atazanavir and its effect on cardiovascular disease. Patients on atazanavir also had a significantly lower risk of developing new cardiovascular disease (HR, 0.53; 95% CI, 0.33–0.86; P=0.010) and longer mean time to death (12.2 versus 10.8 years; P<0.001).

CONCLUSIONS:

Patients with HIV on atazanavir manifest a decreased risk of cardiovascular disease when compared with those on darunavir, an effect that appears to be mediated by serum bilirubin.

The correlation between UDP-glucuronosyltransferase polymorphisms and environmental endocrine disruptors levels in polycystic ovary syndrome patients

BACKGROUND

In recent years, there has been an interest in whether environmental endocrine disruptors (EEDs) may contribute to the endocrine disorders in patients with polycystic ovary syndrome (PCOS). The clearance of EEDs from the human body is regulated by the glucuronidation of UDP-glucuronosyltransferases (UGT). This study aimed to analyze the relationship of UGT1A1, UGT2B7, and UGT2B15 polymorphisms with the metabolism of EEDs in patients with PCOS.

METHODS

A total of 357 Chinese women (119 PCOS cases and 238 controls) were genotyped for polymorphisms of UGT1A1, UGT2B7, and UGT2B15. The plasma concentrations of EEDs were measured by the gas chromatography-mass spectrometry method. The association between UGT polymorphisms and the serum level of EEDs in patients with PCOS was analyzed.

RESULTS

The UGT2B7 single nucleotide polymorphism was associated with an increased risk of PCOS. The homozygous polymorphism (TT) of UGT2B7 showed higher bisphenol A and PAEs concentrations in serum. However, a single nucleotide polymorphism on UGT2B15 expression was associated with a decreased risk of PCOS. Subjects homozygous for the T allele of UGT2B15 had a significant effect on phthalates in the blood. In addition, our results also showed that the homozygous polymorphism (TT) of UGT2B7 and UGT2B15 was associated with the capacity of the excretion of androgen in patients with PCOS.

CONCLUSIONS

Our study reported the novel associations between the UGT polymorphisms and EEDs concentrations in patients with PCOS, supporting the relevance of genetic differences in EEDs metabolism, which might be considered as an etiology of PCOS.

Association between the UGT1A1*28 allele and hyperbilirubinemia in HIV-positive patients receiving atazanavir: a meta-analysis

Objectives The uridine diphosphate glucuronosyltransferase 1A1 (UGT1A1)*28 allele in HIV-positive patients receiving atazanavir (ATV) might be associated with the risk of hyperbilirubinemia. Owing to mixed and inconclusive results, a meta-analysis was conducted to systematically summarize and clarify this association.

Methods Based on a comprehensive search of PubMed, Embase and Web of Science databases, studies investigating the association between UGT1A1 alleles and hyperbilirubinemia was retrieved. We evaluated the strength of this relationship using odds ratios (ORs) with 95% confidence intervals (CIs). Sensitivity analysis was performed by removing each study one at a time and calculating the pooled ORs of the remaining studies to test the robustness of the meta-analysis results. The Q statistic and the I² index statistic were used to assess heterogeneity. Publication bias was evaluated using Orwin’s fail-safe N test.

Results A total of six individual studies were included in this meta-analysis. A significantly increased risk of hyperbilirubinemia was observed in HIV-positive patients receiving ATV with the UGT1A1*1/*28 or UGT1A1*28/*28 genotype, and the risk was higher with the UGT1A1*28/*28 genotype than with the UGT1A1*1/*28 genotype. (UGT1A1*28/*28 versus UGT1A1*1/*28: OR = 3.69, 95%CI = 1.82–7.49; UGT1A1*1/*28 versus UGT1A1*1/*1: OR = 3.50, 95%CI = 1.35–9.08; UGT1A1*28/*28 versus UGT1A1*1/*1: OR = 10.07, 95%CI = 4.39–23.10). All of the pooled ORs were not significantly affected by the remaining studies and different modeling methods, indicating robust results.

Conclusions This meta-analysis suggests that the UGT1A1*28 allele represents a biomarker for an increased risk of hyperbilirubinemia in HIV-positive patients receiving ATV.

Liver Disease in Human Immunodeficiency Virus Infection

Liver disease in human immunodeficiency virus (HIV) remains a main cause of morbidity and mortality. Liver-related morbidity and mortality can be caused by multiple etiologic factors, including opportunistic infections, direct and indirect effects of antiretrovirals, direct and indirect effects of HIV, and viral hepatitides. These factors present with varied liver pathophysiologic mechanisms that lead to abnormalities in liver enzymes and synthetic function test, followed by distinct clinical presentations. This article elucidates the direct effects on HIV in the liver and explores the diagnostic and management challenges in patients with HIV in the era of highly active antiretroviral treatment.

The UDP-Glycosyltransferase (UGT) Superfamily: New Members, New Functions, and Novel Paradigms

UDP-glycosyltransferases (UGTs) catalyze the covalent addition of sugars to a broad range of lipophilic molecules. This biotransformation plays a critical role in elimination of a broad range of exogenous chemicals and by-products of endogenous metabolism, and also controls the levels and distribution of many endogenous signaling molecules. In mammals, the superfamily comprises four families: UGT1, UGT2, UGT3, and UGT8. UGT1 and UGT2 enzymes have important roles in pharmacology and toxicology including contributing to interindividual differences in drug disposition as well as to cancer risk. These UGTs are highly expressed in organs of detoxification (e.g., liver, kidney, intestine) and can be induced by pathways that sense demand for detoxification and for modulation of endobiotic signaling molecules. The functions of the UGT3 and UGT8 family enzymes have only been characterized relatively recently; these enzymes show different UDP-sugar preferences to that of UGT1 and UGT2 enzymes, and to date, their contributions to drug metabolism appear to be relatively minor. This review summarizes and provides critical analysis of the current state of research into all four families of UGT enzymes. Key areas discussed include the roles of UGTs in drug metabolism, cancer risk, and regulation of signaling, as well as the transcriptional and posttranscriptional control of UGT expression and function. The latter part of this review provides an in-depth analysis of the known and predicted functions of UGT3 and UGT8 enzymes, focused on their likely roles in modulation of levels of endogenous signaling pathways.

Uridine 5'-diphospho-glucronosyltrasferase: Its role in pharmacogenomics and human disease

Biotransformation is an enzyme-catalyzed process in which the body converts endogenous compounds, xenobiotics and toxic substances into harmless or easily excreted metabolites. The biotransformation reactions are classified as phase I and II reactions. Uridine 5'-diphospho (UDP)-glucuronosyltransferases (UGTs) are a superfamily of phase II enzymes which have roles in the conjugation of xenobiotics or endogenous compounds, including drugs and bilirubin, with glucuronic acid to make them easier to excrete. The method the human body uses to achieve glucuronidation may be affected by a large interindividual variation due to changes in the sequences of the genes encoding these enzymes. In the last five years, the study of the genetic variants of the UGTs at a molecular level has become important due to its association with several diseases and the ability to predict adverse events due to drug metabolism. In the present review, the structure and the prominent genetic variants of the UGT1A subfamily and their metabolic and clinical implications are described.

Germline genetic variants with implications for disease risk and therapeutic outcomes

Genetic testing has multiple clinical applications including disease risk assessment, diagnosis, and pharmacogenomics. Pharmacogenomics can be utilized to predict whether a pharmacologic therapy will be effective or to identify patients at risk for treatment-related toxicity. Although genetic tests are typically ordered for a distinct clinical purpose, the genetic variants that are found may have additional implications for either disease or pharmacology. This review will address multiple examples of germline genetic variants that are informative for both disease and pharmacogenomics. The discussed relationships are diverse. Some of the agents are targeted for the disease-causing genetic variant, while others, although not targeted therapies, have implications for the disease they are used to treat. It is also possible that the disease implications of a genetic variant are unrelated to the pharmacogenomic implications. Some of these examples are considered clinically actionable pharmacogenes, with evidence-based, pharmacologic treatment recommendations, while others are still investigative as areas for additional research. It is important that clinicians are aware of both the disease and pharmacogenomic associations of these germline genetic variants to ensure patients are receiving comprehensive personalized care.

The challenge of polypharmacy in an aging population and implications for future antiretroviral therapy development

: It is estimated that by 2030 nearly three-quarters of persons living with HIV will be 50 years and older. The aging HIV population presents a new clinical concern for HIV providers: adverse effects from polypharmacy. An aging population means more comorbidities and potentially more drug-drug interactions for providers to manage. This review discusses major comorbidities including cardiovascular disease, anticoagulation, hypertension, diabetes mellitus and malignancy and considerations for drug-interactions with antiretrovirals.

Drug metabolism and liver disease: a drug-gene-environment interaction

Despite the central role of the liver in drug metabolism, surprisingly there is lack of certainty in anticipating the extent of modification of the clearance of a given drug in a given patient. The intent of this review is to provide a conceptual framework in considering the impact of liver disease on drug disposition and reciprocally the impact of drug disposition on liver disease. It is proposed that improved understanding of the situation is gained by considering the issue as a special example of a drug-gene-environment interaction. This requires an integration of knowledge of the drug's properties, knowledge of the gene products involved in its metabolism, and knowledge of the pathophysiology of its disposition. This will enhance the level of predictability of drug disposition and toxicity for a drug of interest in an individual patient. It is our contention that advances in pharmacology, pharmacogenomics, and hepatology, together with concerted interests in the academic, regulatory, and pharmaceutical industry communities provide an ideal immediate environment to move from a qualitative reactive approach to quantitative proactive approach in individualizing patient therapy in liver disease.

Pharmacogenetic considerations in the treatment of HIV

After the introduction of highly active antiretroviral therapy in the 1990s, the perception of the diagnosis of HIV infection gradually shifted from a 'death sentence' to a chronic disease requiring long-term treatment. The host genetic variability has been shown to play a relevant role in both antiretroviral drugs bioavailability and adverse effects susceptibility. Knowledge about pharmacogenetics role in HIV infection treatment has largely increased over the last years, and is reviewed in the present report, as well as future perspectives for the inclusion of pharmacogenetics information in the directing of HIV infection treatment.

Bilirubin Binding to PPARα Inhibits Lipid Accumulation

Numerous clinical and population studies have demonstrated that increased serum bilirubin levels protect against cardiovascular and metabolic diseases such as obesity and diabetes. Bilirubin is a potent antioxidant, and the beneficial actions of moderate increases in plasma bilirubin have been thought to be due to the antioxidant effects of this bile pigment. In the present study, we found that bilirubin has a new function as a ligand for PPARα. We show that bilirubin can bind directly to PPARα and increase transcriptional activity. When we compared biliverdin, the precursor to bilirubin, on PPARα transcriptional activation to known PPARα ligands, WY 14,643 and fenofibrate, it showed that fenofibrate and biliverdin have similar activation properties. Treatment of 3T3-L1 adipocytes with biliverdin suppressed lipid accumulation and upregulated PPARα target genes. We treated wild-type and PPARα KO mice on a high fat diet with fenofibrate or bilirubin for seven days and found that both signal through PPARα dependent mechanisms. Furthermore, the effect of bilirubin on lowering glucose and reducing body fat percentage was blunted in PPARα KO mice. These data demonstrate a new function for bilirubin as an agonist of PPARα, which mediates the protection from adiposity afforded by moderate increases in bilirubin.

Role of pharmacogenetics on deferasirox AUC and efficacy

AIM

We evaluated deferasirox pharmacokinetic according to SNPs in genes involved in its metabolism and elimination. Moreover, we defined a plasma area under the curve cut-off value predicting therapy response.

PATIENTS & METHODS

Allelic discrimination was performed by real-time PCR. Drug plasma concentrations were measured by a high performance liquid chromatography system coupled with an ultraviolet method.

RESULTS

Pharmacokinetic parameters were significantly influenced by UGT1A1 rs887829C>T, UGT1A3 rs1983023C>T and rs3806596A>G SNPs. Area under the curve cut-off values of 360 μg/ml/h for efficacy were here defined and 250 μg/ml/h for nonresponse was reported. UGT1A3 rs3806596GG and ABCG2 rs13120400CC genotypes were factors able to predict efficacy, whereas UGT1A3 rs3806596GG was a nonresponse predictor.

CONCLUSION

These data show how screening patient's genetic profile may help clinicians to optimize iron chelation therapy with deferasirox.

UGT genotyping in belinostat dosing

Certain genetic polymorphisms of UDP glucuronosyltransferase 1 family, polypeptide A1 (UGT1A1) can reduce gene expression (*28, *60, *93) or activity (*6), thereby altering the pharmacokinetics, pharmacodynamics, and the risk of toxicities of UGT1A1 substrates, of which irinotecan is a widely-described example. This review presents an overview of the clinical effects of UGT1A1 polymorphisms on the pharmacology of UGT1A1 substrates, with a special focus on the novel histone deacetylase inhibitor belinostat. Belinostat, approved for the treatment of peripheral T-cell lymphoma, is primarily glucuronidated by UGT1A1. Recent preclinical and clinical data showed that UGT1A1*28 was associated with reduced glucuronidation in human liver microsomes, while in a retrospective analysis of a Phase I trial with patients receiving belinostat UGT1A1*60 was predominantly associated with increased belinostat plasma concentrations. Furthermore, both UGT1A1*28 and *60 variants were associated with increased incidence of thrombocytopenia and neutropenia. Using population pharmacokinetic analysis a 33% dose reduction has been proposed for patients carrying UGT1A1 variant alleles. Clinical effects of this genotype-based dosing recommendation is currently prospectively being investigated. Overall, the data suggest that UGT1A1 genotyping is useful for improving belinostat therapy.

Clinically relevant genetic variants of drug-metabolizing enzyme and transporter genes detected in Thai children and adolescents with autism spectrum disorder

Single-nucleotide polymorphisms (SNPs) among drug-metabolizing enzymes and transporters (DMETs) influence the pharmacokinetic profile of drugs and exhibit intra- and interethnic variations in drug response in terms of efficacy and safety profile. The main objective of this study was to assess the frequency of allelic variants of drug absorption, distribution, metabolism, and elimination-related genes in Thai children and adolescents with autism spectrum disorder. Blood samples were drawn from 119 patients, and DNA was extracted. Genotyping was performed using the DMET Plus microarray platform. The allele frequencies of the DMET markers were generated using the DMET Console software. Thereafter, the genetic variations of significant DMET genes were assessed. The frequencies of SNPs across the genes coding for DMETs were determined. After filtering the SNPs, 489 of the 1,931 SNPs passed quality control. Many clinically relevant SNPs, including CYP2C19*2, CYP2D6*10, CYP3A5*3, and SLCO1B1*5, were found to have frequencies similar to those in the Chinese population. These data are important for further research to investigate the interpatient variability in pharmacokinetics and pharmacodynamics of drugs in clinical practice.

Liver safety assessment in special populations (hepatitis B, C, and oncology trials)

The FDA guidance for industry in the premarketing clinical evaluation of drug-induced liver injury (DILI) is the most specific regulatory guidance currently available and has been useful in setting standards for the great majority of clinical indications involving subjects with a low risk of liver disorders. However, liver safety assessment faces challenges in populations with underlying liver disease, such as viral hepatitis or metastatic cancer. This is an important issue because there are currently many promising anti-viral and oncologic therapies in clinical development, with a trend toward oral therapies with reduced side effects. Without clearer guidelines, questions regarding liver safety may become a major factor in regulatory approval and ultimately physician uptake of the new treatments. The lack of consensus in defining stopping rules based on serum alanine aminotransferase (ALT) levels underscores the need for precompetitive data sharing to improve our understanding of DILI in these populations and to allow evidence-based rather than empirical definition of stopping rules. A workshop was convened to discuss best practices for the assessment of drug-induced liver injury (DILI) in clinical trials.

Complicity of haem in some adverse drug-reactions

Genetic variants in haem metabolism enzymes can be predisposition factors for adverse reactions in some individuals. New areas of haem biology may also be associated with idiosyncratic effects which are yet to be identified.

Understanding and preventing drug-drug and drug-gene interactions

Concomitant administration of multiple drugs can lead to unanticipated drug interactions and resultant adverse drug events with their associated costs. A more thorough understanding of the different cytochrome P450 isoenzymes and drug transporters has led to new methods to try to predict and prevent clinically relevant drug interactions. There is also an increased recognition of the need to identify the impact of pharmacogenetic polymorphisms on drug interactions. More stringent regulatory requirements have evolved for industry to classify cytochrome inhibitors and inducers, test the effect of drug interactions in the presence of polymorphic enzymes, and evaluate multiple potentially interacting drugs simultaneously. In clinical practice, drug alert software programs have been developed. This review discusses drug interaction mechanisms and strategies for screening and minimizing exposure to drug interactions. We also provide future perspectives for reducing the risk of clinically significant drug interactions.

The interactions of lenalidomide with human uptake and efflux transporters and UDP-glucuronosyltransferase 1A1: lack of potential for drug-drug interactions

PURPOSE

Lenalidomide is an immunomodulatory agent used for the treatment of myelodysplastic syndromes and multiple myeloma. Renal clearance of lenalidomide is the predominant elimination route and is approximately twofold greater than the glomerular filtration rate (GFR), suggesting the potential contribution of an active secretory mechanism. In vitro studies were conducted to examine whether lenalidomide is a substrate of drug transporters, namely P-glycoprotein (P-gp), human breast cancer resistance protein (BCRP), multidrug resistance proteins (MRP1, MRP2, MRP3), organic anion transporters (OAT1, OAT3), organic cation transporters (OCT1 and OCT2), human organic cation transporter novel 1 and 2 (OCTN1 and OCTN2), multidrug and toxin extrusion (MATE1) and organic anion transporting polypeptide (OATP1B1). Lenalidomide was also evaluated as an inhibitor of P-gp, BCRP, MRP2, OCT2, OAT1, OAT3, OATP1B1, OATP1B3 and bile salt export pump (BSEP). In addition, inhibition of UDP-glucuronosyltransferase 1A1 (UGT1A1) variants by lenalidomide was also assessed.

METHOD

Cells or vesicles expressing each of the human transporters were used for uptake and inhibition studies, with appropriate probe substrates and known inhibitors.

RESULTS

Results of these studies indicate that the lenalidomide is not a substrate for the transporters examined, except that it is weak substrate of P-gp. None of the transporters studied were inhibited by lenalidomide. Lenalidomide is not an inhibitor of UGT1A1*1/*1 or its polymorphic variants UGT1A1*1/*28 and UGT1A1*28/*28.

CONCLUSIONS

Drug interactions are unlikely to occur when lenalidomide is co-administered with substrates or inhibitors of these transporters. In addition, lenalidomide is unlikely to cause interactions when co-administered with substrates of UGT1A1.

Pharmacokinetic drug interactions between drugs of abuse and antiretroviral medications: implications and management for clinical practice

Substance abuse and HIV/AIDS are two of the most serious, yet treatable diseases worldwide. Global access to HIV treatment continues to expand. In settings where both active illicit drug use and HIV treatment are concurrent, potentional problematic pharmacokinetic drug interactions may arise and complicate therapy. Clinical case series and carefully controlled pharmacokinetic interaction studies have been conducted between only a few drugs of abuse and approved antiretroviral therapies. Important pharmacokinetic drug interactions have been described for benzodiazepines, 3,4-methylenedioxymethamphetamine, methadone and buprenorphine; however, most have not been studied and few well-controlled studies have been conducted to adequately address the clinical implications of these interactions. The metabolism of drugs of abuse, description of the known interactions, and clinical implications and management of these interactions are reviewed. Certain interactions between drugs of abuse and antiretroviral therapies are known and others are likely based upon shared metabolic pathways. These may result in important clinical consequences. To optimize care, clinicians must be alert, knowledgeable about known and possible interactions and equipped to clinically manage the medical consequences. Moreover, there is considerable need for carefully controlled studies in this important and emerging area.

Relevance of UDP-glucuronosyltransferase polymorphisms for drug dosing: A quantitative systematic review

UDP-glucuronosyltransferases (UGT) catalyze the biotransformation of many endobiotics and xenobiotics, and are coded by polymorphic genes. However, knowledge about the effects of these polymorphisms is rarely used for the individualization of drug therapy. Here, we present a quantitative systematic review of clinical studies on the impact of UGT variants on drug metabolism to clarify the potential for genotype-adjusted therapy recommendations. Data on UGT polymorphisms and dose-related pharmacokinetic parameters in man were retrieved by a systematic search in public databases. Mean estimates of pharmacokinetic parameters were extracted for each group of carriers of UGT variants to assess their effect size. Pooled estimates and relative confidence bounds were computed with a random-effects meta-analytic approach whenever multiple studies on the same variant, ethnic group, and substrate were available. Information was retrieved on 30 polymorphic metabolic pathways involving 10 UGT enzymes. For irinotecan and mycophenolic acid a wealth of data was available for assessing the impact of genetic polymorphisms on pharmacokinetics under different dosages, between ethnicities, under comedication, and under toxicity. Evidence for effects of potential clinical relevance exists for 19 drugs, but the data are not sufficient to assess effect size with the precision required to issue dose recommendations. In conclusion, compared to other drug metabolizing enzymes much less systematic research has been conducted on the polymorphisms of UGT enzymes. However, there is evidence of the existence of large monogenetic functional polymorphisms affecting pharmacokinetics and suggesting a potential use of UGT polymorphisms for the individualization of drug therapy.

Coadministration of atazanavir-ritonavir and zinc sulfate: impact on hyperbilirubinemia and pharmacokinetics

Atazanavir (ATV) causes an elevation of unconjugated hyperbilirubinemia (HBR) as a result of UDP glucuronyltransferase (UGT) 1A1 inhibition. Zinc sulfate (ZnSO4) reduces unconjugated hyperbilirubinemia in individuals with Gilbert's syndrome. We assessed the changes in total, conjugated, and unconjugated bilirubin and the effect on ATV pharmacokinetics (PK) after single and 14-day dosing of ZnSO(4). HIV patients, stable on ATV/ritonavir (ATV/r)-containing regimens with a total bilirubin level of >25 mmol/liter received 125 mg daily of ZnSO(4) as Solvazinc tablets for 14 days. ATV/r and bilirubin concentrations were measured pre-ATV/r dose and 2, 4, 6, 8, and 24 h post-ATV/r dose; before ZnSO4 initiation (phase 1), after a single dose (phase 2) and after 14 days (phase 3). Changes in bilirubin and ATV/r concentrations in the absence or presence of ZnSO4 were evaluated by geometric mean ratios (GMRs) and 90% confidence intervals (CIs; we used phase 1 as a reference). Sixteen male patients completed the study maintaining virologic suppression; ZnSO(4) was well tolerated. Statistically significant declines in total bilirubin C(max) and AUC(0-24) of 16 and 17% were seen in phase2 and 20% in phase 3. Although there were no significant changes in conjugated bilirubin, unconjugated bilirubin Cmax and AUC(0-24) of were lower (17 and 19%, phase 2; 20 and 23% during phase 3). The ATV GMRs (90% CI) for C(trough), C(max), and AUC(0-24) were 0.74 (0.62 to 0.89), 0.82 (0.70 to 0.97), and 0.78 (0.70 to 0.88). Intake of ZnSO(4) decreases total and unconjugated bilirubin and causes modest declines in ATV exposure. ZnSO(4) supplementation may be useful in management of ATV-related HBR in selected patients.

Effect of the UGT1A1*28 Allele on Unconjugated Hyperbilirubinemia in HIV-Positive Patients Receiving Atazanavir: A Systematic Review

OBJECTIVE

To systematically examine the literature assessing the effect of uridine 5′-diphospho-glucuronosyltransferase (UGT) 1A1*28 genetic polymorphisms on atazanavir-associated hyperbilirubinemia.

DATA SOURCES

MEDLINE (1948–November 2012), EMBASE (1980–November 2012), International Pharmaceutical Abstracts (1970–November 2012), Google, and Google Scholar were searched using combinations of the following terms: glucuronosyltransferase, glucuronosyltransferase 1A1, atazanavir, atazanavir plus ritonavir, or polymorph$. The reference lists of all identified articles were manually searched.

STUDY SELECTION AND DATA EXTRACTION

Studies were included if at least 1 group of patients received atazanavir therapy and assessed the effect of UGT1A1*28 variants on bilirubin concentrations or atazanavir discontinuation rates. The quality of each study was ranked according to the US Preventive Services Task Force 1996 classification system. Information extracted included study design, baseline characteristics, treatment regimens, UGT1A1*28 genotype frequencies, bilirubin concentrations, incidence of hyperbilirubinemia, and atazanavir discontinuation rates.

DATA SYNTHESIS

Our search produced 12 studies, of which 9 were included (6 full manuscripts [level II-2], 2 abstracts, and 1 letter to the editor [level III]). Reported UGT1A1*28 homozygote genotype frequencies (0.8–23.8%) were in general agreement with the literature for the diverse ethnic population captured in the 9 studies. An association between the incidence of hyperbilirubinemia and UGT1A1*28 genotype (homozygotes > heterozygotes > wild-type) was demonstrated in all studies that reported such data (6 of 9 studies). However, the calculated positive predictive value for homozygosity and hyperbilirubinemia from pooled data was low (40.3%). Only 2 studies (levels II-2 and III) reported rates of atazanavir discontinuation due to hyperbilirubinemia and showed some positive correlation with presence of the UGT1A1*28 allele.

CONCLUSIONS

Based on the available evidence, homozygosity of the UGT1A1*28 allele does not strongly predict the incidence of severe hyperbilirubinemia. Thus, until large, prospective trials demonstrate otherwise, UGT1A1*28 testing does not appear to provide additional information to aid clinical decision-making when initiating atazanavir treatment in HIV-infected patients.

Short communication: fasting increases serum concentrations of bilirubin in patients receiving atazanavir: results from a pilot study

Unconjugated hyperbilirubinemia resulting from therapy with atazanavir is physiologically related to hyperbilirubinemia in Gilbert's syndrome (GS). In patients with GS, changes in diet have a significant impact on bilirubinemia. Our aim was to investigate whether changes in diet affect the level of serum bilirubin in patients receiving atazanavir. Thirty patients on stable therapy with ritonavir-boosted atazanavir without evidence of GS were enrolled. Hemolysis and chronic hepatitis were excluded. After a baseline period of normal intake of calories, the patients were randomized to follow a 24-h 400-calorie diet (fasting), then a 48-h period of normal calorie intake and, afterward, a 24-h period of a high-calorie diet, or the same interventions in inverse order. Serum bilirubin concentrations were measured before and after each intervention. A high adherence to the recommended diet was observed. The mean unconjugated bilirubin concentration before the high-calorie diet was 2.79±1.53 mg/dl and after such intervention it was 2.70±1.40 mg/dl. The mean difference between preintervention and postintervention was -0.08±0.69 mg/dl (p=NS). The mean unconjugated bilirubin concentration before the fasting diet was 2.31±1.23 mg/dl and it was 3.84±1.90 mg/dl after. The mean difference between prefasting and postfasting was 1.53±1.17 mg/dl (p=0.001). According to these results, short periods of fasting seem to increase the unconjugated bilirubin concentration in patients on atazanavir. A high-calorie diet did not have any impact in bilirubin probably because most patients follow similar diets in their everyday life.

Polymorphic expression of UDP-glucuronosyltransferase UGTlA gene in human colorectal cancer

Background

Polymorphism of genes encoding drug-metabolizing enzymes is known to play an important role in increased susceptibility of colorectal cancer. UGT1A gene locus has been suggested to define tissue-specific glucuronidation activity. Reduced capacity of glucuronidation is correlated with the development of colorectal cancer. Therefore, we sought to explore polymorphism of UGTlA gene in human colorectal cancer.

Methods

Cancerous and healthy tissues were obtained from selectedpatients. Blood samples were collected and UGTlA mRNA transcriptions were analyzed. Genomic DNA was prepared and UGTlA8 exon-1 sequences were amplified, visualized and purified. The extracted DNA was subcloned and sequenced. Two-tailed Fisher's exact test, Odds ratios (ORs), confidence interval (CIs) and Logistics Regression Analysis were used for statistical analysis.

Results

UGTlA mRNA expression was reduced in cancerous tissues compared with healthy tissues from the same patient . The UGTlA mRNA expression of healthy tissue in study patients was lower than control . The mRNA expression of cancerous tissue was down-regulated in UGTlAl, 1A3, 1A4, lA6, 1A9 and up-regulated in UGTlA8 and UGTlAl0 UGT1A5 and UGT1A7 were not expressed in colonic tissue of either group. The allele frequency of WT UGTlA8*1 was higher (p = 0.000), frequency of UGTlA8*3 was lowered in control group (p = 0.000). The expression of homozygous UGTlA8*1 was higher in control group (p = 0.000). Higher frequency of both heterozygous UGTlA8*1/*3 and UGTlA8*2/*3 were found in study group (p = 0.000; p = 0.000). The occurrence of colorectal cancer was mainly related to the presence of polymorphic UGTlA8*3 alleles (p = 0.000).

Conclusion

Regulation of human UGT1A genes is tissue-specific. Individual variation in polymorphic expressions of UGTlA gene locus was noted in all types of colonic tissue tested, whereas hepatic tissue expression was uniform. The high incidence of UGTlA8 polymorphism exists in colorectal cancer patients. UGTlA8*1 allele is a protective factor and UGTlA8*3 allele is a risk factor.

Drug-induced liver injury: the role of drug metabolism and transport

Many studies have pinpointed the significant contribution of liver-mediated drug metabolism and transport to the complexity of drug-induced liver injury (DILI). Phase I cytochrome P450 (CYP450) enzymes can lead to altered drug metabolism and formation of toxic metabolites, whilst Phase II enzymes are also associated with DILI. The emerging role of hepatic transporters in regulating the movement of endogenous and exogenous chemicals (e.g., bile acids and drugs) across cellular and tissue membranes is critical in determining the pathophysiology of liver disease as well as drug toxicity and efficacy. Genetic and environmental factors can have a significant impact on drug metabolism and transporter proteins, consequently increasing the risk of DILI in susceptible individuals. The assessment of these factors therefore represents an important approach for predicting and preventing DILI, by better understanding the pharmacological profile of a specific drug. This review focuses on the mechanisms of DILI associated with drug metabolism and hepatic transport, and how they can be influenced by underlying factors.

Pharmacogenomics of Viral Diseases

Viral diseases are leading cause of deaths worldwide as WHO report suggests that hepatitis A virus (HAV) infects more than 80 % of the population of many developing countries. Viral hepatitis B (HBV) affects an estimated 360 million people, whereas hepatitis C affects 123 million people worldwide, and last but not least, at current, India has an HIV/AIDS population of approximately 2.4 million people and more than 30 million in whole world and now it has become a reason for 1.8 million death globally; thus, millions of people still struggle for their lives.

The progress in medical science has made it possible in overcoming the various fatal diseases such as small pox, chicken pox, dengue, etc., but human immunodeficiency viruses, influenza, and hepatitis virus have renewed challenge surprisingly. The obstacles and challenges in therapy include existence of antibiotic resistance strains of common organisms due to overuse of antibiotics, lack of vaccines, adverse drug reaction, and last but not least the susceptibility concerns. Emergence of pharmacogenomics and pharmacogenetics has shown some promises to take challenges. The discovery of human genome project has opened new vistas to understand the behaviors of genetic makeup in development and progression of diseases and treatment in various viral diseases. Current and previous decade have been engaged in making repositories of polymorphisms (SNPs) of various genes including drug-metabolizing enzymes, receptors, inflammatory cells related with immunity, and antigen-presenting cells, along with the prediction of risks. The genetic makeup alone is most likely an adequate way to handle the therapeutic decision-making process for previous regimen failure. With the introduction of new antiviral therapeutic agents, a significant improvement in progression and overall survival has been achieved, but these drugs have shown several adverse responses in some individuals, so the success is not up to the expectations. Research and acquisition of new knowledge of pharmacogenomics may help in overcoming the prevailing burden of viral diseases. So it will definitely help in selecting the most effective therapeutic agents, effective doses, and drug response for the individuals. Thus, it will be able to transform the laboratory research into the clinical bench side and will also help in understanding the pathogenesis of viral diseases with drug action, so the patients will be managed more properly and finally become able to fulfill the promise of the future.

Short communication: UGT1A1*28 variant allele is a predictor of severe hyperbilirubinemia in HIV-infected patients on HAART in southern Brazil

Highly active antiretroviral therapy (HAART) has increased the survival of HIV-infected patients. However, adverse effects play a major role in adherence to HAART. Some protease inhibitors (mainly atazanavir and indinavir) act as inhibitors of uridine diphosphate-glucuronosyltransferase (UGT1A1), the enzyme responsible for hepatic conjugation of bilirubin. Variations in the promoter region of the UGT1A1 gene (UGT1A1*28, rs8175347) can influence bilirubin plasma levels, modulating the susceptibility to hyperbilirubinemia. Aiming to analyze the association between UGT1A1*28 allele and hyperbilirubinemia in individuals exposed to HAART, we evaluated 375 HIV-positive individuals on antiretroviral therapy. Individuals carrying the UGT1A1*28 allele had a higher risk of developing severe hyperbilirubinemia [prevalence ratio (PR)=2.43, 95% confidence interval (CI) 1.08-5.45, p=0.032] as well as atazanavir users (PR=7.72, 95% CI=3.14-18.98, p<0.001). This is the first description of such an association in Brazilian HIV patients, which shows that in African-American and Euroamerican HAART users, the UGT1A1*28 allele also predisposes to severe hyperbilirubinemia, especially in those exposed to atazanavir.

Gilbert syndrome: the UGT1A1*28 promoter polymorphism as a biomarker of multifactorial diseases and drug metabolism

Gilbert syndrome belongs to the group of the most common human metabolic disorders and is characterized by an elevated level of bilirubin in blood serum. A polymorphism of the 5´ end of the UGT1A1 gene promoter, a homozygous insertion of TA pairs (genotype UGT1A1*28/*28), results in a decrease in bilirubin glucuronidation activity and therefore leads to an increase in the level of unconjugated bilirubin (hyperbilirubinemia). Genotyping the UGT1A1 promoter is an important step in the determination of the etiology of free hyperbilirubinemia of unknown origin. Molecular diagnosis enables avoiding invasive diagnostic procedures, such as liver biopsy, in establishing the appropriate diagnosis and prognosis, as well as in establishing the correct therapeutic procedures in a variety of diseases (e.g., chemotherapy or bone marrow transplantation). Moreover, the UGT1A1*28/*28 genotype has emerged as an important element in drug tolerance, as well as in multifactorial diseases, such as cancer. However, the role of this polymorphism is still not completely understood. In this review we have summarized current knowledge and attempted to propose directions for further research.

Switching to unboosted atazanavir reduces bilirubin and triglycerides without compromising treatment efficacy in UGT1A1*28 polymorphism carriers

OBJECTIVES

Hyperbilirubinaemia is a frequent complication of atazanavir-containing antiretroviral therapy and its severity is related to UDP-glucuronosyl transferase (UGT) 1A1*28 polymorphism. The aim of this study was to evaluate the safety and outcome of unboosted atazanavir-containing regimens based on the genetic constitution.

METHODS

Fifty-one HIV-1-infected patients on boosted atazanavir were prospectively enrolled in the study. Twenty-five patients with a UGT1A1*28 allele switched to 400 mg of unboosted atazanavir.

RESULTS

At baseline, UGT1A1 heterozygous and homozygous patients had significantly higher bilirubin levels than wild-type (P = 0.012 and P < 0.001, respectively). After ritonavir removal, a reduction was observed in total bilirubin (from 4.09 to 1.82 mg/dL; P < 0.001), γ-glutamyl transpeptidase (P = 0.015), triglycerides (P = 0.03) and total cholesterol (P = 0.05). No significant changes in CD4 T cell count and no increases in viral load were observed 12 months after unboosting. Plasma drug monitoring after ritonavir removal revealed the presence of therapeutic atazanavir concentrations in all patients except one with poor therapy adherence.

CONCLUSIONS

UGT1A1*28 is significantly related to hyperbilirubinaemia in HIV-1 patients receiving atazanavir. Genotyping before the initiation of antiretroviral therapy can reduce the emergence of severe hyperbilirubinaemia. Unboosted atazanavir-containing therapy is safe and efficacious in patients with an undetectable viral load with a UGT1A1*28 polymorphism, allowing the use of atazanavir in patients otherwise likely unable to receive it.

Gilbert syndrome redefined: a complex genetic haplotype influences the regulation of glucuronidation

Gilbert syndrome (GS) is characterized by intermittent unconjugated hyperbilirubinemia without structural liver damage, affecting about 10% of the white population. In GS the UGT1A1*28 variant reduces bilirubin conjugation by 70% and is associated with irinotecan and protease inhibitor side effects. The aim of this study was to characterize potential in vivo consequences of UGT1A gene variability in GS. Three hundred GS patients (UGT1A1*28 homozygous) and 249 healthy blood donors (HBD) were genotyped for UGT1A (UGT1A1*28, UGT1A3-66 T>C, UGT1A6*3a, UGT1A7*3) and transporter single nucleotide polymorphisms (SNPs) (SCLO1B1 p.V174A, SCLO1B1 p.N130D, ABCC2 p.I1324I, ABCC2-24 UTR) using TaqMan-5'-nuclease-assays. A humanized transgenic UGT1A-SNP and corresponding wildtype mouse model were established carrying the GS-associated UGT1A variant haplotype. UGT1A transcript and protein expression, and transcriptional activation were studied in vivo. Homozygous UGT1A1*28 GS individuals were simultaneously homozygous for UGT1A3-66 T>C (91%), UGT1A6*2a (77%), and UGT1A7*3 (77%). Seventy-six percent of GS and only 9% of HBD were homozygous for the variant haplotype spanning four UGT1A genes. SCLO1B1 and ABCC2 SNPs showed no differences. In transgenic humanized UGT1A SNP and wildtype mice this UGT1A haplotype led to lower UGT1A messenger RNA (mRNA) expression and UGT1A protein synthesis. UGT1A transcriptional activation by dioxin, phenobarbital, and endotoxin was significantly reduced in SNP mice.

CONCLUSION

Our data redefine the genetic basis behind GS. In vivo data studying the genotype present in 76% of GS individuals suggest that transcription and transcriptional activation of glucuronidation genes responsible for conjugation and detoxification is directly affected, leading to lower responsiveness. This study suggests that GS should be considered a potential risk factor for drug toxicity.