Disposition of Mycophenolic Acid and Its Glucuronide Metabolites in Subjects with Glomerulonephritis: Implications of Genes and Effects on Kidney Outcomes

Glomerulonephritis is the third most frequent cause of end-stage kidney disease in the U.S. population. Treatments include immunosuppressant agents such as mycophenolate mofetil. The purpose of undertaking the studies included in this dissertation were to assess the pharmacokinetic alterations of mycophenolic acid in glomerulonephritis, to evaluate the role of patient-level demographic data, clinical data, and genomic alterations on pharmacokinetics, and to evaluate determinants of treatment-related outcomes. We evaluated the pharmacokinetics of mycophenolic acid in 45 patients receiving maintenance mycophenolic acid therapy. Pharmacogenomic assessments were conducted in 85 patients to evaluate genotype frequencies of drug metabolizing enzymes (uridine diphosphate glucuronosyltransferases; UGTs) and drug transporters (including multidrug resistance protein; MDR1) and mycophenolic acid disposition and relative risk of autoimmune diseases. mRNA expression patterns and their relationships to genomics were conducted in 45 patients. The pharmacokinetics showed enhanced oral clearance and reduced metabolic ratios in glomerulonephritis patients. Pharmacokinetics were more highly influenced by serum creatinine/creatinine clearance, urinary protein excretion, race, and gender, than single nucleotide polymorphisms in the UGTs or MDR1. The expression of transcript for drug metabolizing genes and transporter genes was variable across SLE and SVV treated versus untreated patients and healthy controls. The drug transporters were expressed in most patients, while the UGTs were expressed in only 50% of patients. Differences in transcript expression by race, treatment, disease, and genotypes were demonstrated. A disease-gene association risk was found in the study; the relative risk of SVV was increased in patients who were heterozygous or homozygous for the UGT2B7 C802T polymorphism. Kidney-related outcomes, as assessed by urinary protein to creatinine ratio, were worsened in patients with the UGT1A7 C622T polymorphism and improved with the MDR1 C3435T polymorphism. Composite outcomes (dialysis, death, or transplantation) were increased in patients who had reduced transcript expression for ABCB1 in peripheral blood leukocytes. The conducted studies demonstrated the highly complex relationships between drug disposition, patient-level clinical and demographic data, and genome-level variability. Numerous opportunities exist to further delineate these relationships in cell-based assays, animal models of glomerulonephritis, and larger translational studies that assess serial measurements of drug exposure and transcript expression

Population Pharmacokinetics of Mycophenolic Acid and Metabolites in Patients With Glomerulonephritis

Mycophenolic acid (MPA) is an inosine monophosphate dehydrogenase inhibitor used for glomerulonephritis treatment. The objective of the current study was to develop a population pharmacokinetic model for MPA and metabolites in glomerulonephritis in order to enable appropriate design of MPA regimens in these patients with alterations in kidney structure and function

Validation and application of a liquid chromatography–tandem mass spectrometric method for quantification of the drug transport probe fexofenadine in human plasma using 96-well filter plates

A rapid method to determine fexofenadine concentrations in human plasma using protein precipitation in 96-well plates and liquid chromatography-tandem mass spectrometry was validated. Plasma proteins were precipitated with acetonitrile containing the internal standard fexofenadine-d6, mixed briefly, and then filtered into a collection plate. The resulting filtrate was diluted and injected onto a Phenomenex Gemini C18 (50 × 2.0 mm, 5 micron) analytical column. The mobile phase consisted of 0.1% formic acid, 5 mM ammonium acetate in deionized water and methanol (35:65, v/v). The flow rate was 0.2 ml/min and the total run time was 2 min. Detection of the analytes was achieved using positive ion electrospray ionization and high resolution multiple reaction monitoring mode (H-SRM). The linear standard curve ranged from 1 to 500 ng/ml and the precision and accuracy (intra- and inter-run) were within 4.3% and 8.0%, respectively. The method has been applied successfully to determine fexofenadine concentrations in human plasma samples obtained from subjects administered a single oral dose of fexofenadine. The method is rapid, sensitive, selective and directly applicable to human pharmacokinetic studies involving fexofenadine

Predialysis chronic kidney disease: Evaluation of quality of life in clinic patients receiving comprehensive anemia care

Anemia is common in chronic kidney disease (CKD), and suboptimal management of anemia can lead to serious health complications and poor quality of life

Pharmacogenomic Variants May Influence the Urinary Excretion of Novel Kidney Injury Biomarkers in Patients Receiving Cisplatin

Nephrotoxicity is a dose limiting side effect associated with the use of cisplatin in the treatment of solid tumors. The degree of nephrotoxicity is dictated by the selective accumulation of cisplatin in renal tubule cells due to: (1) uptake by organic cation transporter 2 (OCT2) and copper transporter 1 (CTR1); (2) metabolism by glutathione S-transferases (GSTs) and γ-glutamyltransferase 1 (GGT1); and (3) efflux by multidrug resistance-associated protein 2 (MRP2) and multidrug and toxin extrusion protein 1 (MATE1). The purpose of this study was to determine the significance of single nucleotide polymorphisms that regulate the expression and function of transporters and metabolism genes implicated in development of acute kidney injury (AKI) in cisplatin treated patients. Changes in the kidney function were assessed using novel urinary protein biomarkers and traditional markers. Genotyping was conducted by the QuantStudio 12K Flex Real-Time PCR System using a custom open array chip with metabolism, transport, and transcription factor polymorphisms of interest to cisplatin disposition and toxicity. Traditional and novel biomarker assays for kidney toxicity were assessed for differences according to genotype by ANOVA. Allele and genotype frequencies were determined based on Caucasian population frequencies. The polymorphisms rs596881 (SLC22A2/OCT2), and rs12686377 and rs7851395 (SLC31A1/CTR1) were associated with renoprotection and maintenance of estimated glomerular filtration rate (eGFR). Polymorphisms in SLC22A2/OCT2, SLC31A1/CTRI, SLC47A1/MATE1, ABCC2/MRP2, and GSTP1 were significantly associated with increases in the urinary excretion of novel AKI biomarkers: KIM-1, TFF3, MCP1, NGAL, clusterin, cystatin C, and calbindin. Knowledge concerning which genotypes in drug transporters are associated with cisplatin-induced nephrotoxicity may help to identify at-risk patients and initiate strategies, such as using lower or fractionated cisplatin doses or avoiding cisplatin altogether, in order to prevent AKI

Influence of Clinical and Demographic Variables on Mycophenolic Acid Pharmacokinetics in Antineutrophil Cytoplasmic Antibody–Associated Vasculitis

Mycophenolic acid (MPA) is used off-label to treat many forms of glomerulonephritis

Pharmacokinetics of Mycophenolic Acid in Patients with Lupus Nephritis

Lupus nephritis is associated with urinary protein excretion, hypoalbuminemia, and renal function declines, which may impact the pharmacokinetics (PK) of mycophenolic acid (MPA)

Quantitative Profiling of Human Renal UDP-glucuronosyltransferases and Glucuronidation Activity: A Comparison of Normal and Tumoral Kidney Tissues

Renal metabolism by UDP-glucuronosyltransferase (UGT) enzymes is central to the clearance of many drugs. However, significant discrepancies about the relative abundance and activity of individual UGT enzymes in the normal kidney prevail among reports, whereas glucuronidation in tumoral kidney has not been examined. In this study, we performed an extensive profiling of glucuronidation metabolism in normal (n = 12) and tumor (n = 14) kidneys using targeted mass spectrometry quantification of human UGTs. We then correlated UGT protein concentrations with mRNA levels assessed by quantitative polymerase chain reaction and with conjugation activity for the major renal UGTs. Beyond the wide interindividual variability in expression levels observed among kidney samples, UGT1A9, UGT2B7, and UGT1A6 are the most abundant renal UGTs in both normal and tumoral tissues based on protein quantification. In normal kidney tissues, only UGT1A9 protein levels correlated with mRNA levels, whereas UGT1A6, UGT1A9, and UGT2B7 quantification correlated significantly with their mRNA levels in tumor kidneys. Data support that posttranscriptional regulation of UGT2B7 and UGT1A6 expression is modulating glucuronidation in the kidney. Importantly, our study reveals a significant decreased glucuronidation capacity of neoplastic kidneys versus normal kidneys that is paralleled by drastically reduced UGT1A9 and UGT2B7 mRNA and protein expression. UGT2B7 activity is the most repressed in tumors relative to normal tissues, with a 96-fold decrease in zidovudine metabolism, whereas propofol and sorafenib glucuronidation is decreased by 7.6- and 5.2-fold, respectively. Findings demonstrate that renal drug metabolism is predominantly mediated by UGT1A9 and UGT2B7 and is greatly reduced in kidney tumors