Inhibitory effects of quercetin and its major metabolite quercetin-3-O-β-D-glucoside on human UDP-glucuronosyltransferase 1A isoforms by liquid chromatography-tandem mass spectrometry

Quercetin is a flavonoid that is widely present in plant-derived food. Quercetin-3-O-β-D-glucoside (Q3GA) is a predominant metabolite of quercetin in animal and human plasma. The inhibitory effects of the UDP-glucuronosyl transferases (UGTs) caused by herbal components may be a key factor for the clinical assessment of herb-drug interactions (HDIs). The present study aimed to investigate the inhibitory profile of quercetin and Q3GA on recombinant UGT1A isoforms in vitro. The metabolism of the nonspecific substrate 4-methylumbelliferone (4-MU) by the UGT1A isoforms was assessed by liquid chromatography-tandem mass spectrometry. Preliminary screening experiments indicated that quercetin exhibited stronger inhibitory effects on UGT1A1, UGT1A3, UGT1A6 and UGT1A9 enzymes than Q3GA. Kinetic experiments were performed to characterize the type of inhibition caused by quercetin and Q3GA towards these UGT isoforms. Quercetin exerted non-competitive inhibition on UGT1A1 and UGT1A6, with half maximal inhibitory concentration (IC₅₀) values of 7.47 and 7.07 µM and inhibition kinetic parameter (K_i) values of 2.18 and 28.87 µM, respectively. Quercetin also exhibited competitive inhibition on UGT1A3 and UGT1A9, with IC₅₀ values of 10.58 and 2.81 µM and K_i values of 1.60 and 0.51 µM, respectively. However, Q3GA displayed weak inhibition on UGT1A1, UGT1A3 and UGT1A6 enzymes with IC₅₀ values of 45.21, 106.5 and 51.37 µM, respectively. In the present study, quercetin was a moderate inhibitor of UGT1A1 and UGT1A3, a weak inhibitor of UGT1A6, and a strong inhibitor on UGT1A9. The results of the present study suggested potential HDIs that may occur following quercetin co-administration with drugs that are mainly metabolized by UGT1A1, UGT1A3 and UGT1A9 enzymes.

Disease Status-Dependent Drug-Herb Interactions: NASH Lowered the Risk of Hepatotoxicity in Rats Coadministered With Simvastatin and Gardenia jasminoides J. Ellis

Concurrent use of simvastatin (SV) and Gardenia jasminoides J. Ellis (GJ) was adopted in patients with multi-morbidity, such as stroke rehabilitation patients with NASH. Although hepatotoxicity has been reported in both of them and NASH could alter the pharmacokinetics of drugs/herbs, the interaction between SV and GJ and the related hepatotoxicity remained uninvestigated under neither healthy nor NASH condition. The current study aimed to evaluate the potential hepatotoxicity resulted from the interactions between SV and GJ in both healthy and NASH rats. Both healthy and NASH rats received two-week SV (p. o., 8.66 mg/kg, once daily) and/or GJ (p.o., 325 mg/kg, twice daily). Pharmacokinetic profiles of SV, simvastatin acid (SVA, active metabolite of SV), and geniposide (major component in GJ); hepatic Cyp2c11/Oatp1b2/P-gp expression; and biomarker levels of liver function, lipid levels, and liver histology were compared to demonstrate the interactions in rats. To explore the mechanism of the interaction-mediated hepatotoxicity, hepatic genipin-protein adduct content and iNOS/COX-1/COX-2 expressions from related groups were compared. Moreover, liver histology of healthy/NASH rats at 90 days after discontinuation of two-week GJ in the absence and presence of SV was evaluated to estimate the long-term impact of the interactions. GJ reduced the systemic exposures of SV and SVA by up-regulating the hepatic P-gp expression in healthy but not NASH rats. Meanwhile, SV increased the systemic exposure of geniposide via inhibiting the activity of P-gp in both healthy and NASH rats. Although neither SV nor GJ induced hepatotoxicity in healthy rats, their co-treatment elevated serum ALT and AST levels, which may attribute to the aggravated genipin-protein adduct formation, inflammation infiltration, and iNOS/COX-1 expressions in the liver. In NASH rats, SV and/or GJ reduced serum ALT, AST, LDL/vLDL, and TC levels via alleviating hepatic inflammation infiltration and iNOS/COX-1 expressions. Moreover, in comparison to NASH rats, more severe fibrosis was observed in the livers of healthy rats at 90 days after discontinuation of two-week SV and GJ coadministration. Although interactions between SV and GJ induced short-term and long-term liver injuries in healthy rats, NASH condition in rats could lower such risk.

Formal comment on "Systematic review of the predictors of statin adherence for the primary prevention of cardiovascular disease"

Statins have been prescribed for primary prevention of cardiovascular disease (CVD) for nearly 3 decades. Throughout this period key opinion leaders in the field have been dismayed by the high rate of non-adherence of patients to follow their statin regimen. Hope et al., [1] have addressed this issue by providing a systematic review of research on predictors of statin adherence for primary prevention of CVD. However, their review does not address the ongoing debate as to whether statin treatment is warranted for primary prevention of CVD, nor does it adequately address concerns regarding adverse effects of statins. We have therefore written a commentary which provides a broader perspective on the benefits versus harms of statin therapy. Our perspective of the literature is that non-adherence to statin treatment for primary prevention of CVD is justified because the meager benefits are more than offset by the extensive harms.

Pharmacological Options in Atherosclerosis: A Review of the Existing Evidence

Coronary heart disease (CHD) is the leading cause of mortality worldwide and high low-density lipoprotein (LDL) cholesterol levels have been shown to be key in the pathogenesis of this condition. Lipid control has therefore been the subject of decades of research and has led to many large and robust randomized controlled trials, as well as the highest grossing drug of all time—Lipitor (atorvastatin). Statin therapy has long been indicated for secondary and more recently primary prevention. However, despite the large-scale use of statins, CHD prevalence remains high, and some patients do not respond to statin therapy. There has been a large push to find and test alternative lipid-lowering agents, these include fibrates, cholesterol absorption inhibitors, and proprotein convertase subtilisin/kexin type 9 (PCSK-9) inhibitors. It is the aim of this review to assess the literature surrounding each of these groups of drugs.

Association study of UGT1A9 promoter polymorphisms with DILI based on systematically regional variation screen in Chinese population

Drug-induced liver injury (DILI) is caused by unpredictable adverse drug reaction due mainly to the accumulation of hepatotoxic compounds in the liver resulting in significant damage. Drug-metabolizing enzymes have been prime targets for molecular studies relevant to DILI. The gene UGT1A9 mainly expresses in the liver and has an important role in drug metabolism. The Han Chinese has a very long and complex demographic history, and the population stratification arising from the interplay of different geographic areas may influence the polymorphism pattern. We selected 260 healthy subjects in three different geographic areas (including Xian, Shanghai and Liuzhou) for systemic screening and analysis of single-nucleotide polymorphisms (SNPs) in the promoter region of UGT1A9. Eight SNPs were identified and no regional disparity exists among the three populations. Based on these results, 213 DILI patients from all over the Chinese mainland were further recruited to investigate possible association between UGT1A9 and DILI. We observed statistically significant associations between SNP rs2741045 and DILI at both allele and genotype levels (allele: P=0.032; genotype: P=0.029; after Bonferroni correction). Also, multivariate interaction analysis discovered the interaction between rs2741045 and age associated with DILI significantly. This is the first such screening study to investigate the association between UGT1A9 promoter polymorphisms and DILI in the Chinese population and it could provide the basis for further study of DILI mechanisms.

A reappraisal of the risks and benefits of treating to target with cholesterol lowering drugs

Atherosclerotic cardiovascular disease (CVD) is the number one cause of death globally, and lipid modification, particularly lowering of low density lipoprotein cholesterol (LDLc), is one of the cornerstones of prevention and treatment. However, even after lowering of LDLc to conventional goals, a sizeable number of patients continue to suffer cardiovascular events. More aggressive lowering of LDLc and optimization of other lipid parameters like triglycerides (TG) and high density lipoprotein cholesterol (HDLc) have been proposed as two potential strategies to address this residual risk. These strategies entail use of maximal doses of highly potent HMG CoA reductase inhibitors (statins) and combination therapy with other lipid modifying agents. Though statins in general are fairly well tolerated, adverse events like myopathy are dose related. There are further risks with combination therapy. In this article, we review the adverse effects of lipid modifying agents used alone and in combination and weigh these effects against the evidence demonstrating their efficacy in reducing cardiovascular events, cardiovascular mortality, and all cause mortality. For patients with established CVD, statins are the only group of drugs that have shown consistent reductions in hard outcomes. Though more aggressive lipid lowering with high dose potent statins can reduce rates of non fatal events and need for interventions, the incremental mortality benefits remain unclear, and their use is associated with a higher rate of drug related adverse effects. Myopathy and renal events have been a significant concern with the use of high potency statin drugs, in particular simvastatin and rosuvastatin. For patients who have not reached target LDL levels or have residual lipid abnormalities on maximal doses of statins, the addition of other agents has not been shown to improve clinical outcomes and carries an increased risk of adverse events. The clinical benefits of drugs to raise HDLc remain unproven. In patients without known cardiovascular disease, there is conflicting evidence as to the benefits of aggressive pursuit of numerical lipid targets, particularly with respect to all cause mortality. Certainly, in statin intolerant patients, alternative agents with a low side effect profile are desirable. Bile acid sequestrants are an effective and safe choice for decreasing LDLc, and omega-3 fatty acids are safe agents to decrease TG. There remains an obvious need to design and carry out large scale studies to help determine which agents, when combined with statins, have the greatest benefit on cardiovascular disease with the least added risk. These studies should be designed to assess the impact on clinical outcomes rather than surrogate endpoints, and require a comprehensive assessment and reporting of safety outcomes.

A unifying ontology to integrate histological and clinical observations for drug-induced liver injury

Drug-induced liver injury (DILI) may present any morphologic characteristic of acute or chronic liver disease with no standardized terminology in place. Defining lexemes of DILI histopathology would allow the development of advanced knowledge discovery and data mining tools for across comparisons of publicly available information. For these purposes, a DILI ontology (DILIo) was developed by using the Unified Medical Language System tool and the standardized terminology of the Systematized Nomenclature of Medicine-Clinical Terms (SNOMED CT). The DILIo was entrained on findings of 114 US Food and Drug Administration-approved drugs by extracting all clinically DILI-related histopathologic descriptions for 1082 liver biopsy samples, which were then analyzed using the Unified Medical Language System MetaMap and subsequently mapped to the SNOMED CT. The DILIo provides a standard means to describe and organize liver injury induced by drugs, enabling comparative analysis of drugs within and across histopathologic terms. The analysis showed that flutamide, troglitazone, diclofenac, isoniazid, and tamoxifen were reported to have the most diverse histopathologic observations in liver biopsy. Necrosis, cholestasis, fatty degeneration, fibrosis, infiltrate, and hepatic necrosis were the most frequent terms used as descriptors of histopathologic features of DILI. In conclusion, DILIo entrains different algorithms for an efficient meta-analysis of published findings for an improved understanding of mechanisms and clinical characteristics of DILI.

Ezetimibe therapy: mechanism of action and clinical update

The lowering of low-density lipoprotein cholesterol (LDL-C) is the primary target of therapy in the primary and secondary prevention of cardiovascular events. Although statin therapy is the mainstay for LDL-C lowering, a significant percentage of patients prescribed these agents either do not achieve targets with statin therapy alone or have partial or complete intolerance to them. For such patients, the use of adjuvant therapy capable of providing incremental LDL-C reduction is advised. One such agent is ezetimibe, a cholesterol absorption inhibitor that targets uptake at the jejunal enterocyte brush border. Its primary target of action is the cholesterol transport protein Nieman Pick C1 like 1 protein. Ezetimibe is an effective LDL-C lowering agent and is safe and well tolerated. In response to significant controversy surrounding the use and therapeutic effectiveness of this drug, we provide an update on the biochemical mechanism of action for ezetimibe, its safety and efficacy, as well as the results of recent randomized studies that support its use in a variety of clinical scenarios.

Hepatotoxicity associated with statins: reports of idiosyncratic liver injury post-marketing

BACKGROUND & AIMS

Limited data exist on drug-induced liver injury (DILI) associated with statins.

METHODS

Reports on adverse reactions suspected to be due to statins received by the Swedish Adverse Drug Reactions Advisory Committe 1988-2010 were analyzed. Only cases with >5×upper limit of normal (ULN) in aminotransferases and/or alkaline phosphatase >2×ULN were included.

RESULTS

The most common types of ADRs suspected were DILI in 124/217 (57%) cases. A total of 73/124 (59%) cases had at least possible relationship, median age 64 years (57-73), 55% males, whereas 25/124 cases (20%) were excluded due to mild elevations of liver tests and 26 due to unlikely relationship and/or lack of data. A statin-related DILI episode was reported in 1.2/100,000 users. Atorvastatin was implicated in 30/73 (41%) cases, simvastatin in 28 (38%), fluvastatin (15%), and others. Two patients died of acute liver failure, one underwent liver transplantation and 25 (34%) had jaundice. Three patients were rechallenged with the same statin producing similar patterns of liver injury. The median duration of therapy was 90 days (30-120), 120 (39-248) for atorvastatin, and 75 (30-150) for simvastatin (NS). Cholestatic/mixed injury was more common with atorvastatin, 17/30 (56%) than with simvastatin, 7/28 (24%) (p=0.018).

CONCLUSIONS

Idiosyncratic liver injury associated with statins is rare but can be severe. After recovery, a similar pattern of liver injury can be reproduced on re-exposure. Most patients experience liver injury 3-4 months after start of therapy. Atorvastatin is mostly associated with cholestatic liver injury whereas hepatocellular injury is more common with simvastatin.

Statins in primary biliary cirrhosis: are they safe?

BACKGROUND AND AIM

Although cholesterol levels are elevated in patients with primary biliary cirrhosis (PBC), most PBC patients are not at increased risk of dying from atherosclerotic heart disease. There is, however, a subgroup, approximately 10%, who have additional disorders of lipid metabolism. They might benefit from a cholesterol-lowering agent. However, there is concern about using statins in patients with pre-existing liver disease. We therefore reviewed our experience with statins in a large cohort of PBC patients who were seen at Tufts Medical Center during the past decade.

METHODS

From January 1, 1996, until June 30, 2006, 603 patients with PBC were seen by one of us (M.M.K.). Fifty-eight were on statins and five were on ezetimibe. The mean duration of usage was 41 months (range 3-125 months). Alanine aminotransferase (ALT) levels were measured at 3-month intervals.

RESULTS

Statins were well tolerated. No patient complained of muscle pain or weakness. There was no increase in ALT levels. ALT levels were slightly elevated at the time that statins were begun (41.7 +/- 25.1 U/l), and were normal at the last time these patients were seen (39.0 +/- 21.0 U/l) (P <or= 0.303). Serum cholesterol levels decreased by 30%, from 262 +/- 45 mg/dl to 181 +/- 14 mg/dl (P < 0.01). Ezetimibe was also well tolerated.

CONCLUSION

Statins are safe in PBC patients who might benefit from their use.

Molecular mechanisms of toxicity of simvastatin, widely used cholesterol-lowering drug. A review

Statins are widely used and well tolerated cholesterol-lowering drugs, and when used for therapy purposes reduce morbidity and mortality from coronary heart disease. Simvastatin is one of nine known statins, specific inhibitors of hepatic enzyme 3-hydroxy-3-methylglutaryl-coenzyme A reductase, the rate-limiting step of cholesterol biosynthesis, and is believed to reduce plasma cholesterol levels by decreasing the activity of this enzyme. Statin drugs represent the major improvement in the treatment of hypercholesterolemia that constitutes the main origin of atherosclerosis, leading to coronary heart disease. Although statins are generally safe, minor and severe adverse reactions are well known complications of statin use. Adverse events associated with simvastatin therapy are uncommon, but potentially serious. In this review some details about statins including their adverse effects in humans and animals, the effects of simvastatin on various intracellular and mitochondrial processes, and molecular mechanisms underlying simvastatin cytotoxicity are discussed.

Drug-induced liver injury: what was new in 2008?

BACKGROUND

Given the number of publications appearing annually regarding drug-induced liver injury (DILI), there remains a need to concisely summarize each year's new crop of case series and reports as well as the advances in mechanisms of liver injury and in the field of pharmacogenomics relating to DILI.

OBJECTIVE

To present an up-to-date review of the past year's most important clinical studies and reports of DILI, placing them into context of previous publications.

METHODS

A Medline search was conducted of all manuscripts appearing in the fields "hepatotoxicity" and "drug-induced liver injury" during the calendar year 2008. The most clinically relevant English language case reports and studies exploring mechanisms and risk factors for DILI were then chosen for review, and supplemented with older literature where appropriate.

CONCLUSIONS

As in past years, 2008 was replete with publications dealing with virtually all facets of DILI, including updated incidence and prevalence data, as well as the latest information regarding mechanisms of liver injury. Data from the first 300 patients in the National Institute of Health-sponsored DILI Network registry of > 100 non-acetaminophen causes were presented. Antimicrobials and CNS drugs were responsible for > 60% of cases, with herbals and dietary supplements being increasingly reported. Identification of genetic predispositions to DILI is coming of age with the FDA calling for the testing of human leukocyte antigen B(*)5701 before the use of abacavir to reduce the risk of hypersensitivity reactions. Several groups emphasized the pitfalls in utilizing Roussel Uclaf Causality Assessment Method and other causality assessment methodologies, and an updated review appeared on the use of potentially hepatotoxic medications in patients with underlying liver disease.

Drug-induced hepatotoxicity or drug-induced liver injury

Drug-induced hepatotoxicity is underreported and underestimated in the United States. It is an important cause of acute liver failure. Common classes of drugs causing drug-induced hepatotoxicity include antibiotics, lipid lowering agents, oral hypoglycemics, psychotropics, antiretrovirals, acetaminophen, and complementary and alternative medications. Hepatotoxic drugs often have a signature or pattern of liver injury including patterns of liver test abnormalities, latency of symptom onset, presence or absence of immune hypersensitivity, and the course of the reaction after drug withdrawal.

Safety and effectiveness of ezetimibe in liver transplant recipients with hypercholesterolemia

Hypercholesterolemia is a common problem among transplant recipients. Despite package-insert warnings about the potential side effects of the use of statins in patients with chronic liver disease, they are often prescribed for liver transplant recipients. Unlike statins, ezetimibe acts through inhibition of enterohepatic recirculation of lipids. We report the effectiveness and safety of ezetimibe among liver transplant recipients because this has been evaluated previously only in kidney and heart transplant patients. A consecutive cohort of 25 liver graft recipients with serum low-density lipoprotein (LDL) levels > 100 mg/dL (2.5 mmol/L) after a mean (+/-standard deviation) of 55 +/- 21 months following liver transplantation received ezetimibe (10 mg orally every day) for at least 6 months. Serum lipid profiles, liver and renal function tests, and dosages and blood levels of the immunosuppression drugs at baseline, 3 months, and 6 months were prospectively collected. The overall mean age was 58 +/- 12 years, and 56% were males. Statin therapy and fibrates were already being used in 32% and 20% of recipients for elevated LDL and/or triglycerides, respectively. The immunosuppression regimen included cyclosporine in 48% of subjects, tacrolimus in 32%, sirolimus in 48%, and mycophenolate mofetil in 44%; only 12% were on oral prednisone with a maximum daily dose of 5 mg. After ezetimibe was started, an 18% reduction in LDL values was observed [at baseline, 147 +/- 35 mg/dL (3.8 +/- 0.9 mmol/L), and at 6 months, 120 +/- 31 mg/dL (3.1 +/- 0.8 mmol/L); P = 0.010]. After 6 months, an additional 32% achieved the target LDL level of <100 mg/dL. None of the remaining variables, including immunosuppression drug levels, varied significantly during ezetimibe therapy. None of the subjects required adjustments in their pharmacological dosages. One discontinued ezetimibe 3 months later because of cost, 2 subjects had minimal nausea, 1 subject had myalgias without a rise in creatine phosphokinase, and 1 subject had a transient elevation (3-5 times) in liver enzymes from baseline with increases in the total and indirect bilirubin levels. In conclusion, among liver transplant recipients, hypercholesterolemia can be effectively treated with ezetimibe with few side effects and no interaction with immunosuppressive regimens.

Statin adverse effects : a review of the literature and evidence for a mitochondrial mechanism

HMG-CoA reductase inhibitors (statins) are a widely used class of drug, and like all medications, have potential for adverse effects (AEs). Here we review the statin AE literature, first focusing on muscle AEs as the most reported problem both in the literature and by patients. Evidence regarding the statin muscle AE mechanism, dose effect, drug interactions, and genetic predisposition is examined. We hypothesize, and provide evidence, that the demonstrated mitochondrial mechanisms for muscle AEs have implications to other nonmuscle AEs in patients treated with statins. In meta-analyses of randomized controlled trials (RCTs), muscle AEs are more frequent with statins than with placebo. A number of manifestations of muscle AEs have been reported, with rhabdomyolysis the most feared. AEs are dose dependent, and risk is amplified by drug interactions that functionally increase statin potency, often through inhibition of the cytochrome P450 3A4 system. An array of additional risk factors for statin AEs are those that amplify (or reflect) mitochondrial or metabolic vulnerability, such as metabolic syndrome factors, thyroid disease, and genetic mutations linked to mitochondrial dysfunction. Converging evidence supports a mitochondrial foundation for muscle AEs associated with statins, and both theoretical and empirical considerations suggest that mitochondrial dysfunction may also underlie many nonmuscle statin AEs. Evidence from RCTs and studies of other designs indicates existence of additional statin-associated AEs, such as cognitive loss, neuropathy, pancreatic and hepatic dysfunction, and sexual dysfunction. Physician awareness of statin AEs is reportedly low even for the AEs most widely reported by patients. Awareness and vigilance for AEs should be maintained to enable informed treatment decisions, treatment modification if appropriate, improved quality of patient care, and reduced patient morbidity.