Effect of experimental kidney disease on the functional expression of hepatic reductases

Metabolic Activation of Flavin Monooxygenase-mediated Trimethylamine-N-Oxide Formation in Experimental Kidney Disease

Cardiovascular disease (CVD) remains the leading cause of death in chronic kidney disease (CKD) patients despite treatment of traditional risk factors, suggesting that non-traditional CVD risk factors are involved. Trimethylamine-N-oxide (TMAO) correlates with atherosclerosis burden in CKD patients and may be a non-traditional CVD risk factor. Serum TMAO concentrations are significantly increased in CKD patients, which may be due in part to increased hepatic flavin monooxygenase (FMO)-mediated TMAO formation. The objective of this work was to elucidate the mechanism of increased FMO activity in CKD. In this study, FMO enzyme activity experiments were conducted in vitro with liver microsomes isolated from experimental CKD and control rats. Trimethylamine was used as a probe substrate to assess FMO activity. The FMO activator octylamine and human uremic serum were evaluated. FMO gene and protein expression were also determined. FMO-mediated TMAO formation was increased in CKD versus control. Although gene and protein expression of FMO were not changed, metabolic activation elicited by octylamine and human uremic serum increased FMO-mediated TMAO formation. The findings suggest that metabolic activation of FMO-mediated TMAO formation is a novel mechanism that contributes to increased TMAO formation in CKD and represents a therapeutic target to reduce TMAO exposure and CVD.

Comparative Pharmacokinetics of Gallic Acid, Protocatechuic Acid, and Quercitrin in Normal and Pyelonephritis Rats after Oral Administration of a Polygonum capitatum Extract

Polygonum capitatum Buch.-Ham. ex D. Don is traditionally used by Hmong for the treatment of urinary tract infections and pyelonephritis. Information regarding the pharmacokinetic behavior of the extract in the condition of pyelonephritis is lacking. In the present study, we aimed to compare the pharmacokinetic properties of gallic acid (GA), protocatechuic acid (PCA), and quercitrin (QR)—the main bioactive constituents in the herb—in normal and pyelonephritis rats. The plasma samples were collected at various time points after administration of a single dose of Polygonum capitatum extract. The plasma level of GA, PCA, and QR at the designed time points was determined by ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) and drug concentration versus time plots were constructed to estimate the pharmacokinetic parameters. The AUC_(0-t), AUC_(0-∞), MRT_(0-t), and CL of GA, PCA, and QR in pyelonephritis rats was significantly different from those of the normal rats. The results indicated that the three constituents have higher rate of uptake and slower rate of elimination in the rats with pyelonephritis, suggesting altered rate and extent of drug metabolism.

Warfarin Dosing and Outcomes in Chronic Kidney Disease: A Closer Look at Warfarin Disposition

BACKGROUND

Chronic Kidney Disease (CKD) is a prevalent worldwide health problem. Patients with CKD are more prone to developing cardiovascular complications such as atrial fibrillation and stroke. This warrants the use of oral anticoagulants, such as warfarin, in this population. While the efficacy and safety of warfarin in this setting remain controversial, a growing body of evidence emphasizes that warfarin use in CKD can be problematic. This review discusses 1) warfarin use, dosing and outcomes in CKD patients; and 2) possible pharmacokinetic mechanisms for altered warfarin dosing and response in CKD.

METHODS

Structured search and review of literature articles evaluating warfarin dosing and outcomes in CKD. Data and information about warfarin metabolism, transport, and pharmacokinetics in CKD were also analyzed and summarized.

RESULTS

The literature data suggest that changes in warfarin pharmacokinetics such as protein binding, nonrenal clearance, the disposition of warfarin metabolites may partially contribute to altered warfarin dosing and response in CKD.

CONCLUSION

Although the evidence to support warfarin use in advanced CKD is still unclear, this synthesis of previous findings may help in improving optimized warfarin therapy in CKD settings.

Efficacy and Tolerability of Ombitasvir/Paritaprevir/Ritonavir in HCV Genotype 1-infected Elderly Japanese Patients

INTRODUCTION AND AIM

We assessed the characteristics of virological response to a combination treatment of ombitasvir, paritaprevir, and ritonavir in hepatitis C virus genotype 1-infected elderly Japanese patients.

MATERIAL AND METHODS

This multicenter prospective study was conducted at six locations in Japan. Seventy patients with chronic hepatitis C virus genotype 1b infection were orally administered ombitasvir/paritaprevir/ritonavir once daily for 12 weeks. The primary endpoint was the proportion of elderly patients with sustained virological response (SVR) 12 weeks after the completion of treatment. Adverse events were also recorded to evaluate drug safety and tolerability during the trial period. SVR in elderly patients (age > 65; 94% [47 / 50]) was lower than that in younger patients (100% [20 / 20]).

RESULTS

No significant differences in SVR 12 weeks after the completion of treatment were observed between the age groups (P = 0.153). Adverse events were observed in 16 patients (23.3%). Multivariate analysis confirmed that the change or discontinuation of concomitant drugs owing to drug interactions was independent of risk factors for adverse events associated with this drug combination (P = 0.015; odds ratio, 15.9; 95% confidence interval, 1.79 - 148). Ombitasvir/paritaprevir/ritonavir combination treatment was highly effective in elderly patients.

CONCLUSION

Tolerability should be monitored in older patients for whom concomitant medications are discontinued or changed because of drug interactions.

Decreased Kidney Function Is Associated with Enhanced Hepatic Flavin Monooxygenase Activity and Increased Circulating Trimethylamine N-Oxide Concentrations in Mice

Circulating trimethylamine N-oxide (TMAO) predicts poor cardiovascular outcomes in patients with chronic kidney disease (CKD). Accumulation of serum TMAO has been observed in CKD patients; however, the mechanisms contributing to this finding have been inadequately explored. The purpose of this study was to investigate the mechanisms responsible for TMAO accumulation in the setting of decreased kidney function using a CKD mouse model. Mice were fed a diet supplemented with 0.2% adenine to induce CKD, which resulted in increased serum TMAO concentrations (females: CKD 29.4 ± 32.1 μM vs. non-CKD 6.9 ± 6.1 μM, P < 0.05; males: CKD 18.5 ± 13.1 μM vs. non-CKD 1.0 ± 0.5 μM, P < 0.001). As anticipated, accumulation of circulating TMAO was accompanied by a decrease in renal clearance (females: CKD 5.2 ± 3.8 μl/min vs. non-CKD 90.4 ± 78.1 μl/min, P < 0.01; males: CKD 10.4 ± 8.1 μl/min vs. non-CKD 260.4 ± 134.5 μl/min; P < 0.001) and fractional excretion of TMAO. Additionally, CKD animals exhibited an increase in hepatic flavin monooxygenase (FMO)-mediated formation of TMAO (females: CKD 125920 ± 2181 pmol/mg per 60 minutes vs. non-CKD 110299 ± 4196 pmol/mg per 60 minutes, P < 0.001; males: CKD 131286 ± 2776 pmol/mg per 60 minutes vs. non-CKD 74269 ± 1558 pmol/mg per 60 minutes, P < 0.001), which likely resulted from increased FMO3 expression in CKD mice. The current study provides evidence that both decreased renal clearance and increased hepatic production of TMAO may contribute to increments in serum TMAO in the setting of CKD. Hepatic FMO activity may represent a novel therapeutic target for lowering circulating TMAO in CKD patients.

Stereospecific Metabolism of R- and S-Warfarin by Human Hepatic Cytosolic Reductases

Coumadin (rac-warfarin) is the most commonly used anticoagulant in the world; however, its clinical use is often challenging because of its narrow therapeutic range and interindividual variations in response. A critical contributor to the uncertainty is variability in warfarin metabolism, which includes mostly oxidative but also reductive pathways. Reduction of each warfarin enantiomer yields two warfarin alcohol isomers, and the corresponding four alcohols retain varying levels of anticoagulant activity. Studies on the kinetics of warfarin reduction have often lacked resolution of parent-drug enantiomers and have suffered from coelution of pairs of alcohol metabolites; thus, those studies have not established the importance of individual stereospecific reductive pathways. We report the first steady-state analysis of R- and S-warfarin reduction in vitro by pooled human liver cytosol. As determined by authentic standards, the major metabolites were 9R,11S-warfarin alcohol for R-warfarin and 9S,11S-warfarin alcohol for S-warfarin. R-warfarin (Vmax 150 pmol/mg per minute, Km 0.67 mM) was reduced more efficiently than S-warfarin (Vmax 27 pmol/mg per minute, Km 1.7 mM). Based on inhibitor phenotyping, carbonyl reductase-1 dominated R-and S-warfarin reduction, followed by aldo-keto reductase-1C3 and then other members of that family. Overall, the carbonyl at position 11 undergoes stereospecific reduction by multiple enzymes to form the S alcohol for both drug enantiomers, yet R-warfarin undergoes reduction preferentially. This knowledge will aid in assessing the relative importance of reductive pathways for R- and S-warfarin and factors influencing levels of pharmacologically active parent drugs and metabolites, thus impacting patient dose responses.

Comparative pharmacokinetics of the main compounds of Shanzhuyu extract after oral administration in normal and chronic kidney disease rats

ETHNOPHARMACOLOGICAL RELEVANCE

Pharmacokinetic studies on traditional Chinese medicine are useful to evaluate and predict the drug efficacy and safety. The renal impairment may affect drug clearance and other pharmacokinetic processes which can increase toxicity and drug to drug interactions or cause ineffective therapy. Pharmacokinetic studies in pathological status rats might be meaningful for revealing the action mechanism and improving clinical medication of the herb medicine.

MATERIALS AND METHODS

A highly sensitive and rapid ultra-performance liquid chromatography-mass spectrometry (UPLC-MS) method with multiple-reaction monitoring (MRM) mode was developed and validated for simultaneous quantitation of morroniside and loganin in normal and doxorubicin-induced chronic kidney disease (CKD) rat plasma after oral administration of Shanzhuyu (fruit of Cornus officinalis) extract.

RESULTS

Both calibration curves gave satisfactory linearity (r>0.99) at linear range of 1.96-1962.5ngmL(-1) for morroniside, 1.53-1531.25ngmL(-1) for loganin. The precision and accuracy of the in vivo study were assessed by intra-day and inter-day assays. The percentages of relative standard deviation (RSD) were all within 9.58% and the accuracy (RE) was in the -6.02% to 8.11% range. The extraction recoveries of morroniside, loganin and internal standard (IS) were all >67.62% and the matrix effects ranged from 95.07% to 102.75%.

CONCLUSIONS

The pharmacokinetic behavior of morroniside and loganin in normal and CKD rat plasma was determined in this paper. The significant different pharmacokinetic parameters might partly result from the changes of P-glycoprotein and metabolic enzymes in the pathological state. The pharmacokinetic research in the pathological state might provide more useful information to guide the clinical usage of the herb medicine.