Cigarette smoking, coffee drinking, and ingestion of charcoal-broiled beef as potential modifiers of drug therapy and confounders of clinical trials

Interindividual Variability in Cytochrome P450 3A and 1A Activity Influences Sunitinib Metabolism and Bioactivation

Sunitinib is an orally administered tyrosine kinase inhibitor associated with idiosyncratic hepatotoxicity; however, the mechanisms of this toxicity remain unclear. We have previously shown that cytochromes P450 1A2 and 3A4 catalyze sunitinib metabolic activation via oxidative defluorination leading to a chemically reactive, potentially toxic quinoneimine, trapped as a glutathione (GSH) conjugate (M5). The goals of this study were to determine the impact of interindividual variability in P450 1A and 3A activity on sunitinib bioactivation to the reactive quinoneimine and sunitinib N-dealkylation to the primary active metabolite N-desethylsunitinib (M1). Experiments were conducted in vitro using single-donor human liver microsomes and human hepatocytes. Relative sunitinib metabolite levels were measured by liquid chromatography-tandem mass spectrometry. In human liver microsomes, the P450 3A inhibitor ketoconazole significantly reduced M1 formation compared to the control. The P450 1A2 inhibitor furafylline significantly reduced defluorosunitinib (M3) and M5 formation compared to the control but had minimal effect on M1. In CYP3A5-genotyped human liver microsomes from 12 individual donors, M1 formation was highly correlated with P450 3A activity measured by midazolam 1'-hydroxylation, and M3 and M5 formation was correlated with P450 1A2 activity estimated by phenacetin O-deethylation. M3 and M5 formation was also associated with P450 3A5-selective activity. In sandwich-cultured human hepatocytes, the P450 3A inducer rifampicin significantly increased M1 levels. P450 1A induction by omeprazole markedly increased M3 formation and the generation of a quinoneimine-cysteine conjugate (M6) identified as a downstream metabolite of M5. The nonselective P450 inhibitor 1-aminobenzotriazole reduced each of these metabolites (M1, M3, and M6). Collectively, these findings indicate that P450 3A activity is a key determinant of sunitinib N-dealkylation to the active metabolite M1, and P450 1A (and potentially 3A5) activity influences sunitinib bioactivation to the reactive quinoneimine metabolite. Accordingly, modulation of P450 activity due to genetic and/or nongenetic factors may impact the risk of sunitinib-associated toxicities.

Low serum vitamin C correlates with an increased risk of peripheral arterial disease in current smokers: Results from NHANES 2003-2004

Background

Cigarette smoking is one of the most critical risk factors for peripheral arterial disease (PAD) and inversely correlated Vitamin C. Here we determine whether serum vitamin C correlates with the risk of PAD, especially among current smokers.

Methods

A cross-sectional analysis of 2383 individuals ≥40 y was performed from the U.S. National Health and Nutrition Examination Survey (NHANES 2003–2004), including measurement of ankle-brachial index (ABI), smoking status and serum vitamin C. We examined the interactions between plasma vitamin C and exposure to smoking on the risk of PAD.

Results

912 (38.2%) were current smokers while 207 participants were diagnosed with PAD based on ABI(ABI≤0.9). Current smokers in the lowest vitamin C quartile had the highest prevalence of PAD (14.1%) compared to other quartiles. However, this trend was not significant in nonsmokers. Current smokers in the lowest quartile had a 2.32-fold risk (95% CI, 1.03–5.32; P = 0.04) for PAD after weighted adjustment for potential confounders, including vitamin D and C-reactive protein. In contrast, non-smokers did not have a differing risk of PAD as a function of vitamin C (P for interaction = 0.019).

Conclusions

As an anti-oxidant and anti-inflammatory, low serum vitamin C appears to associates with the risk of PAD in smokers. A relationship between PAD and vitamin C in non-current smokers is not apparent. Modulating vitamin C in current smokers may help mitigate the risk of PAD and should be a target of mechanistic study.

Impact of switching to a heat-not-burn tobacco product on CYP1A2 activity

Background

Cigarette smoking induces cytochrome P450 1A2 (CYP1A2) expression and activity, while smoking cessation normalizes the levels of this enzyme. The aim of this publication is to summarize the data on CYP1A2 gene expression and activity in preclinical and clinical studies on the Tobacco Heating System (THS), currently marketed as IQOS® with HEETs®, and to summarize the potential effects on CYP1A2 to be expected upon switching to reduced-risk products (RRPs).

Methods

We summarized PMI’s preclinical and clinical data on the effects of switching from cigarette smoking to THS.

Results

Data from four preclinical mouse and rat studies showed that, upon either cessation of cigarette smoke exposure or switching to THS exposure, the upregulation of CYP1A2 observed with exposure to cigarette smoke reverted close to fresh-air levels. Data from four clinical studies yielded similar results on CYP1A2 activity within a time frame of five days. Furthermore, the effects of switching to THS were similar to those seen after smoking cessation.

Conclusions

Because smoking cessation and switching to either electronic cigarettes or THS seem to have similar effects on CYP1A2 activity, the same measures taken for patients treated with narrow therapeutic index drugs that are metabolized by CYP1A2 and who quit smoking should be recommended for those switching to RRPs.

Clinical Pharmacokinetic and Pharmacodynamic Profile of Riociguat

Oral riociguat is a soluble guanylate cyclase (sGC) stimulator that targets the nitric oxide (NO)–sGC–cyclic guanosine monophosphate pathway with a dual mode of action: directly by stimulating sGC, and indirectly by increasing the sensitivity of sGC to NO. It is rapidly absorbed, displays almost complete bioavailability (94.3%), and can be taken with or without food and as crushed or whole tablets. Riociguat exposure shows pronounced interindividual (60%) and low intraindividual (30%) variability in patients with pulmonary arterial hypertension (PAH) or chronic thromboembolic pulmonary hypertension (CTEPH), and is therefore administered using an individual dose-adjustment scheme at treatment initiation. The half-life of riociguat is approximately 12 h in patients and approximately 7 h in healthy individuals. Riociguat and its metabolites are excreted via both renal (33–45%) and biliary routes (48–59%), and dose adjustment should be performed with particular care in patients with moderate hepatic impairment or mild to severe renal impairment (no data exist for patients with severe hepatic impairment). The pharmacodynamic effects of riociguat reflect the action of a vasodilatory agent, and the hemodynamic response to riociguat correlated with riociguat exposure in patients with PAH or CTEPH in phase III population pharmacokinetic/pharmacodynamic analyses. Riociguat has a low risk of clinically relevant drug interactions due to its clearance by multiple cytochrome P450 (CYP) enzymes and its lack of effect on major CYP isoforms and transporter proteins at therapeutic levels. Riociguat has been approved for the treatment of PAH and CTEPH that is inoperable or persistent/recurrent after surgical treatment.

Cytochromes P450 1A2 and 3A4 Catalyze the Metabolic Activation of Sunitinib

Sunitinib is a multitargeted tyrosine kinase inhibitor associated with idiosyncratic hepatotoxicity. The mechanisms of this toxicity are unknown. We hypothesized that sunitinib undergoes metabolic activation to form chemically reactive, potentially toxic metabolites which may contribute to development of sunitinib-induced hepatotoxicity. The purpose of this study was to define the role of cytochrome P450 (P450) enzymes in sunitinib bioactivation. Metabolic incubations were performed using individual recombinant P450s, human liver microsomal fractions, and P450-selective chemical inhibitors. Glutathione (GSH) and dansylated GSH were used as trapping agents to detect reactive metabolite formation. Sunitinib metabolites were analyzed by liquid chromatography-tandem mass spectrometry. A putative quinoneimine-GSH conjugate (M5) of sunitinib was detected from trapping studies with GSH and dansyl-GSH in human liver microsomal incubations, and M5 was formed in an NADPH-dependent manner. Recombinant P450 1A2 generated the highest levels of defluorinated sunitinib (M3) and M5, with less formation by P450 3A4 and 2D6. P450 3A4 was the major enzyme forming the primary active metabolite N-desethylsunitinib (M1). In human liver microsomal incubations, P450 3A inhibitor ketoconazole reduced formation of M1 by 88%, while P450 1A2 inhibitor furafylline decreased generation of M5 by 62% compared to control levels. P450 2D6 and P450 3A inhibition also decreased M5 by 54 and 52%, respectively, compared to control. In kinetic assays, recombinant P450 1A2 showed greater efficiency for generation of M3 and M5 compared to that of P450 3A4 and 2D6. Moreover, M5 formation was 2.7-fold more efficient in human liver microsomal preparations from an individual donor with high P450 1A2 activity compared to a donor with low P450 1A2 activity. Collectively, these data suggest that P450 1A2 and 3A4 contribute to oxidative defluorination of sunitinib to generate a reactive, potentially toxic quinoneimine. Factors that alter P450 1A2 and 3A activity may affect patient risk for sunitinib toxicity.

Interethnic differences in pharmacokinetics of antibacterials

BACKGROUND

Optimal antibacterial dosing is imperative for maximising clinical outcome. Many factors can contribute to changes in the pharmacokinetics of antibacterials to the extent where dose adjustment may be needed. In acute illness, substantial changes in important pharmacokinetic parameters such as volume of distribution and clearance can occur for certain antibacterials. The possibility of interethnic pharmacokinetic differences can further complicate attempts to design an appropriate dosing regimen. Factors of ethnicity, such as genetics, body size and fat distribution, contribute to differences in absorption, distribution, metabolism and elimination of drugs. Despite extensive previous work on the altered pharmacokinetics of antibacterials in some patient groups such as the critically ill, knowledge of interethnic pharmacokinetic differences for antibacterials is limited.

OBJECTIVES

This systematic review aims to describe any pharmacokinetic differences in antibacterials between different ethnic groups, and discuss their probable mechanisms as well as any clinical implications.

METHODS

We performed a structured literature review to identify and describe available data of the interethnic differences in the pharmacokinetics of antibacterials.

RESULTS

We found 50 articles that met our inclusion criteria and only six of these compared antibacterial pharmacokinetics between different ethnicities within the same study. Overall, there was limited evidence available. We found that interethnic pharmacokinetic differences are negligible for carbapenems, most β-lactams, aminoglycosides, glycopeptides, most fluoroquinolones, linezolid and daptomycin, whereas significant difference is likely for ciprofloxacin, macrolides, clindamycin, tinidazole and some cephalosporins. In general, subjects of Asian ethnicity achieve drug exposures up to two to threefold greater than Caucasian counterparts for these antibacterials. This difference is caused by a comparatively lower volume of distribution and/or drug clearance.

CONCLUSION

Interethnic pharmacokinetic differences of antibacterials are likely; however, the clinical relevance of these differences is unknown and warrants further research.

Effect of vitamin C on endothelial function in health and disease: a systematic review and meta-analysis of randomised controlled trials

BACKGROUND

Observational studies indicate that higher vitamin C intake is associated with reduced risk for cardiovascular diseases. However, randomised controlled trials (RCT) examining the effect of vitamin C on endothelial function (EF) have reported inconsistent results. The aims of this systematic review and meta-analysis were to determine the effect of vitamin C supplementation on EF and to investigate whether the effect was influenced by health status, study duration, dose and route of vitamin C administration.

METHODS

We searched the Medline, Embase, Cochrane Library, and Scopus databases from inception to May 2013 for studies that met the following criteria: 1) RCT with adult participants, 2) vitamin C administered alone, 3) studies that quantified EF using commonly applied methods including ultrasound, plethysmography and pulse wave analysis.

RESULTS

Pooling the data from 44 clinical trials showed a significant positive effect of vitamin C on EF (SMD: 0.50, 95% CI: 0.34, 0.66, P < 0.001). Stratification of the analysis by health outcome revealed improved EF in atherosclerotic (SMD: 0.84, 95% CI: 0.41, 1.26, P < 0.001), diabetic (SMD: 0.52, 95% CI: 0.21, 0.82, P < 0.001) and heart failure patients (SMD: 0.48, 95% CI: 0.08, 0.88, P < 0.02) after vitamin C supplementation. The effect size appeared to be unaffected by study design, duration, baseline plasma vitamin C concentration or route of administration of vitamin C. The meta-regression showed a significant positive association between vitamin C dose and improvement in EF (β: 0.00011, 95% CI: 0.00001, 0.00021, P = 0.03).

CONCLUSIONS

Vitamin C supplementation improved EF. The effect of vitamin C supplementation appeared to be dependent on health status, with stronger effects in those at higher cardiovascular disease risk. PROSPERO Database registration: CRD42013004567, http://www.crd.york.ac.uk/prospero/

The next therapeutic challenge in HIV: polypharmacy

With the adoption of combination antiretroviral therapy (ART), most HIV-infected individuals in care are on five or more medications and at risk of harm from polypharmacy, a risk that likely increases with number of medications, age, and physiologic frailty. Established harms of polypharmacy include decreased medication adherence and increased serious adverse drug events, including organ system injury, hospitalization, geriatric syndromes (falls, fractures, and cognitive decline) and mortality. The literature on polypharmacy among those with HIV infection is limited, and the literature on polypharmacy among non-HIV patients requires adaptation to the special issues facing those on chronic ART. First, those aging with HIV infection often initiate ART in their 3rd or 4th decade of life and are expected to remain on ART for the rest of their lives. Second, those with HIV may be at higher risk for age-associated comorbid disease, further increasing their risk of polypharmacy. Third, those with HIV may have an enhanced susceptibility to harm from polypharmacy due to decreased organ system reserve, chronic inflammation, and ongoing immune dysfunction. Finally, because ART is life-extending, nonadherence to ART is particularly concerning. After reviewing the relevant literature, we propose an adapted framework with which to address polypharmacy among those on lifelong ART and suggest areas for future work.