Lothar Faerber

Bioavailability of Mycophenolate Mofetil and Enteric‐Coated Mycophenolate Sodium Is Differentially Affected by Pantoprazole in Healthy Volunteers

The influence of pantoprazole 40 mg twice daily on the bioavailability of a single dose of mycophenolate mofetil 1000 mg or enteric‐coated mycophenolate sodium is investigated in healthy volunteers. The plasma concentrations of mycophenolic acid and of the inactive metabolite mycophenolic acid glucuronide are measured by high‐performance liquid chromatography. The pharmacokinetic parameters following sole administration are similar for mycophenolate mofetil and enteric‐coated mycophenolate sodium except for the time to peak concentration, which is longer in the enteric‐coated mycophenolate sodium group. Concomitant treatment with pantoprazole significantly (P < .001) lowers the mycophenolic acid exposure following administration of mycophenolate mofetil. The peak concentrations drop by 57%, and area under the curve decreases from 0 to 12 hours by 27%. In contrast, pantoprazole does not change the pharmacokinetics of enteric‐coated mycophenolate sodium. Given that mycophenolic acid exposure correlates with the incidence of biopsy‐proven acute rejections in renal transplant recipients, these findings may have clinical implications. Administration of pantoprazole in combination with mycophenolate mofetil could possibly result in an insufficient mycophenolic acid exposure, increasing the risk of treatment failure.

Omeprazole Impairs the Absorption of Mycophenolate Mofetil But Not of Enteric‐Coated Mycophenolate Sodium in Healthy Volunteers

In 2 crossover studies, 12 healthy volunteers (6 male/6 female) received a single oral dose of mycophenolate mofetil (MMF) 1000 mg or an equimolar dose of enteric‐coated mycophenolate sodium (EC‐MPS) 720 mg fasting with and without coadministered omeprazole 20 mg bid. The plasma concentrations of mycophenolic acid (MPA) and of the inactive metabolite mycophenolic acid glucuronide (MPA‐G) were measured by high‐performance liquid chromatography (HPLC). In addition, dissolution of MMF 500 mg or EC‐MPS 360 mg tablets was determined using an USP paddle apparatus in aqueous buffer of pH 1 to 7. The bioavailability of MPA following administration of MMF or EC‐MPS was similar except for the time to peak concentration, which was longer in the EC‐MPS group. Concomitant treatment with omeprazole lowered significantly Cmax and AUC12h of MPA following administration of MMF. The pharmacokinetics of EC‐MPS was not affected. Dissolution of MMF in aqueous buffer decreased dramatically at pH above 4.5. The EC‐MPS tablet was stable up to pH 5. Above, EC‐MPS was quantitatively disintegrated and MPS quantitatively dissolved. There is strong evidence that impaired absorption of MMF with concomitant proton pump inhibitors is due to incomplete dissolution of MMF in the stomach at elevated pH.

Pre-Analytical Parameters Affecting Vascular Endothelial Growth Factor Measurement in Plasma: Identifying Confounders.

Background Vascular endothelial growth factor-A (VEGF-A) is intensively investigated in various medical fields. However, comparing VEGF-A measurements is difficult because sample acquisition and pre-analytic procedures differ between studies. We therefore investigated which variables act as confounders of VEGF-A measurements. Methods Following a standardized protocol, blood was taken at three clinical sites from six healthy participants (one male and one female participant at each center) twice one week apart. The following pre-analytical parameters were varied in order to analyze their impact on VEGF-A measurements: analyzing center, anticoagulant (EDTA vs. PECT / CTAD), cannula (butterfly vs. neonatal), type of centrifuge (swing-out vs. fixed-angle), time before and after centrifugation, filling level (completely filled vs. half-filled tubes) and analyzing method (ELISA vs. multiplex bead array). Additionally, intrapersonal variations over time and sex differences were explored. Statistical analysis was performed using a linear regression model. Results The following parameters were identified as statistically significant independent confounders of VEGF-A measurements: analyzing center, anticoagulant, centrifuge, analyzing method and sex of the proband. The following parameters were no significant confounders in our data set: intrapersonal variation over one week, cannula, time before and after centrifugation and filling level of collection tubes. Conclusion VEGF-A measurement results can be affected significantly by the identified pre-analytical parameters. We recommend the use of CTAD anticoagulant, a standardized type of centrifuge and one central laboratory using the same analyzing method for all samples.

Comparative bioavailability of the microemulsion formulation of cyclosporine (Neoral) with a generic dispersion formulation (Cicloral) in young healthy male volunteers.

The aim of this study was to compare the bioavailability of cyclosporine (CyA) from the generic dispersion formulation Cicloral (CIC) with the microemulsion formulation Neoral (NEO) and the original Sandimmune (SIM) capsules after single doses of 100, 300, or 600 mg of drug, respectively. The study was performed according to an open 3-period cross-over design with 12 young healthy male volunteers for each dosage. The concentrations of CyA and its main metabolites were determined by high performance liquid chromatography in whole blood and urine up to 48 hours postdosing. Peak concentrations and area under the time-concentration curve were greater for the NEO and CIC formulations compared with SIM, and the mean bioavailability of CIC was significantly (P<0.05) lower compared with NEO. The bioavailability of SIM compared with NEO was 54% to 71%, in agreement with previous results. Bioequivalence was not demonstrated between CIC (test) and NEO (reference) as the 90% confidence intervals were outside the 80% to 125% guidelines based on log-transformed AUCs, and were 75.2% to 87.7% at 100 mg, 79.2% to 91.8% at 300 mg, and 76.6% to 94.5% at 600 mg doses. The respective values for Cmax were 78.9% to 94.6%, 80.7% to 95.0%, and 71.4% to 84.1%. A good correlation was demonstrated between the urinary recovery of CyA and the AUC4. Therefore, the urinary recovery of CyA may be helpful as a surrogate parameter for the systemic exposure of patients to CyA. Whereas the relative amount of hydroxylated metabolites (AM1, AM9, AM1c) was similar for all formulations and doses, the urinary recovery of the N-demethylated metabolite AM4N decreased with increasing dose indicating saturable metabolism. No relationship could be demonstrated between CYP3A activity using dextromethorphan as a probe for the metabolic clearance of CyA.

Involvement of Cyclic Guanosine Monophosphate-Dependent Protein Kinase I in Renal Antifibrotic Effects of Serelaxin

Introduction: Kidney fibrosis has shown to be ameliorated through the involvement of cyclic guanosine monophosphate (cGMP) and its dependent protein kinase I (cGKI). Serelaxin, the recombinant form of human relaxin-II, increases cGMP levels and has shown beneficial effects on kidney function in acute heart failure patients. Antifibrotic properties of serelaxin are supposed to be mediated via relaxin family peptide receptor 1 and subsequently enhanced nitric oxide/cGMP to inhibit transforming growth factor-β (TGF-β) signaling. This study examines the involvement of cGKI in the antifibrotic signaling of serelaxin. Methods and Results: Kidney fibrosis was induced by unilateral ureteral obstruction in wildtype (WT) and cGKI knock-out (KO) mice. After 7 days, renal antifibrotic effects of serelaxin were assessed. Serelaxin treatment for 7 days significantly increased cGMP in the kidney of WT and cGKI-KO. In WT, renal fibrosis was reduced through decreased accumulation of collagen1A1, total collagen, and fibronectin. The profibrotic connective tissue growth factor as well as myofibroblast differentiation were reduced and matrix metalloproteinases-2 and -9 were positively modulated after treatment. Moreover, Smad2 as well as extracellular signal-regulated kinase 1 (ERK1) phosphorylation were decreased, whereas phosphodiesterase (PDE) 5a phosphorylation was increased. However, these effects were not observed in cGKI-KO. Conclusion: Antifibrotic renal effects of serelaxin are mediated via cGMP/cGKI to inhibit Smad2- and ERK1-dependent TGF-β signaling and increased PDE5a phosphorylation.

Secreted frizzled-related protein 4 predicts progression of autosomal dominant polycystic kidney disease

BACKGROUND Autosomal dominant polycystic kidney disease (ADPKD) is a common autosomal dominant condition associated with renal cysts and development of renal failure. With the availability of potential therapies, one major obstacle remains the lack of readily available parameters that identify patients at risk for disease progression and/or determine the efficacy of therapeutic interventions within short observation periods. Increased total kidney volume (TKV) correlates with disease progression, but it remains unknown how accurate this parameter can predict disease progression at early stages. METHODS To identify additional parameters that help to stratify ADPKD patients, we measured secreted frizzled-related protein 4 (sFRP4) serum concentrations at baseline and over the course of 18 months in 429 ADPKD patients. RESULTS Serum creatinine and sFRP4 as well as TKV increased over time, and were significantly different from baseline values within 1 year. CONCLUSION Elevated sFRP4 levels at baseline predicted a more rapid decline of renal function at 2, 3 and 5 years suggesting that sFRP4 serum levels may provide additional information to identify ADPKD patients at risk for rapid disease progression.

Antifibrotic function of cGKI in the kidney.

Results The cGKIa isozyme is expressed in the renal medullary interstitium. Unilateral ureter kidney was taken as model for the analysis of interstitial kidney fibrosis in wild type, cGKI-KO and cGKIa rescue mice (which express cGKIa solely in smooth muscle in a cGKI-KO background). We tested whether the pharmacological stimulation of the cGMP/cGKI signalling pathway affects the induction of interstitial kidney fibrosis. For this purpose we used a) NO-independent sGC stimulators (YC-1, Bay41-8543) and b) the pregnancy hormone serelaxin which was shown to induce cGMP levels and is currently tested for treatment of acute heart failure. sGC stimulators effectively suppressed TGFb levels, myofibroblast differentiation (SMA) and deposition of extracellular matrix (ECM) (collagen, fibronectin) in wild type mice involving RhoA/ROCK signalling in contrast to cGKI-KO and/or cGKIa rescue mice. Serelaxin treatment by osmotic pumps continuously enhanced cGMP concentrations in the kidney. Serelaxin also strongly reduced interstitial kidney fibrosis via diminished cytokines (TGFb, CTGF), myofibroblasts and ECM and by regulation of matrix metalloproteases (MMP-2, MMP-9) dependent on the presence of cGKI. However, our results indicated that serelaxin might exert different signalling pathways e.g. via MAPK. Conclusion Our results suggest that pharmacological treatment with sGC stimulators or serelaxin enhancing cGMP suppresses interstitial kidney fibrosis via cGMP/cGKI signalling.

Differences in the renal antifibrotic signaling of serelaxin and zaprinast

Background Kidney fibrosis is frequently observed in cardiorenal diseases. Cyclic guanosine monophosphate (cGMP) serves as the most important second messenger of nitric oxide (NO) and has shown antifibrotic effects at enhanced levels in several experimental models of kidney diseases. Antifibrotic effects of cGMP signalling via cGMP-dependent protein kinases (cGK), in particular cGKI, have already been shown. Serelaxin and zaprinast are both able to increase cGMP signalling via influencing two independent pharmacological targets. Serelaxin is currently in phase III development for acute heart failure and has shown antifibrotic properties in several in vitro and in vivo experiments. It is discussed that serelaxin inhibits TGF-b signalling via RXFP1 receptor. Involvement of NO / cGMP in this process has also been revealed. Zaprinast is a selective inhibitor of phosphodiesterase V, which leads to enhanced levels of cGMP by blocking cGMP degradation.