Therapeutic drug monitoring of mycophenolic acid in kidney transplant patients: a abbreviated sampling strategy

Mycophenolic acid (MPA) levels have demonstrated a good correlation with clinical outcomes, but with great pharmacokinetic variability between patients. Therapeutic drug monitoring (TDM) is recommended to include a 12-hour area under the concentration-time curve (AUC). Since full AUC estimates are not practical for routine monitoring, limited sampling strategies have been suggested. We evaluated MPA pharmacokinetics in 18 stable renal transplant patients receiving mycophenolate mofetil (MMF) as part of their immunosuppressive therapy. The correlation between measured and estimated AUC was assessed using 4 different sparse sampling algorithms. The mean values for C(0) and AUC(0-6h) were 1.8 +/- 1.2 mg/L and 31.1 +/- 14.8 mg*h/L, respectively. The dose-corrected AUC(0-6h) was 35.4 +/- 17.9 mg*h/L. Regarding the single time points, C(0) showed a low correlation with AUC(0-6h) (r(2) = .34); C(1.5), the best correlation (r(2) = .72); and C(3), the worst (r(2) = .07). Sparse sample algorithms used to estimate 12-hour AUC including C(0), C(1), C(2), C(3), C(4), and/or C(6) showed a good correlation with the calculated AUC(0-6) (r(2) = .81-.96). The algorithm that used C(0), C(1), C(2), and C(4) showed the best correlation, but we also found a good correlation (r(2) = .91) with C(0), C(1), and C(2). Based on these results, we have suggested using the 3-point algorithm (C(0), C(1), and C(2)) for MPA TDM in stable renal transplant patients due to the good correlation with drug exposure and better functionality than an algorithm using a 4-hour postdose measurement.

Glyphosate inhibits melanization of Cryptococcus neoformans and prolongs survival of mice after systemic infection

Cryptococcus neoformans is a major fungal pathogen and is a relatively common cause of life-threatening meningoencephalitis. Glyphosate is a widely used herbicide that inhibits the synthesis of aromatic amino acids via the shikimate acid pathway. This study investigated the effects of glyphosate on C. neoformans growth, melanization, and murine infection. C. neoformans was relatively resistant to glyphosate, requiring concentrations >250 microg/mL for inhibition. Melanization of C. neoformans in the presence of L-dopa was inhibited by subinhibitory concentrations of glyphosate. Glyphosate inhibited autopolymerization of L-dopa and oxidation of L-epinephrine by cryptococcal cells, which is mediated by a laccase. Administration of glyphosate to mice infected with C. neoformans delayed melanization of yeast cells in vivo and prolonged average mouse survival. The results suggest that inhibition of melanization in vivo may facilitate control of C. neoformans infection.

Systematic analysis of oxidative degradation of polysaccharides using PAGE and HPLC--MS

Oxidation of polysaccharides yields hydroxyaldehydes and hydroxycarboxylic acids. Aldehydes and carboxylic acids were separately conjugated to 8-aminonaphthalene-1,3,6-trisulfonic acid (ANTS) or tyrosine t-butyl ester (TBT). The ANTS-labeled derivatives were separated by molecular size on PAGE gels and detected by fluorescence. TBT-labeled derivatives were separated by reverse phase chromatography on a C18-HPLC column and analyzed by positive ion electrospray mass spectroscopy (HPLC--MS). This combination of procedures allowed a systematic analysis of carbohydrate oxidation products.

The spheroplast lysis assay for yeast in microtiter plate format

A yeast lysis assay in the microtiter plate format improved precision and throughput and led to an improved algorithm for estimating lag time. The assay reproducibly revealed differences of 10% or greater in the maximal lysis rate and 50% or greater in the lag time. Clonal differences were determined to be the major source of variation. Microtiter-based assays should be useful for screening for drug susceptibility and for analyzing mutant phenotypes.

A spheroplast rate assay for determination of cell wall integrity in yeast

The rate of formation of spheroplasts of yeast can be used as an assay to study the structural integrity of cell walls. Lysis can be measured spectrophotometrically in hypotonic solution in the presence of Zymolyase, a mixture of cell wall-digesting enzymes. The optical density of the cell suspension decreases as the cells lyse. We optimized this assay with respect to enzyme concentration, temperature, pH, and growth conditions for several strains of Saccharomyces cerevisiae. The level of variability (standard deviation) was 1-5% between trials where the replications were performed on the same culture using enzyme prepared from the same lot, and 5-15% for different cultures of the same strain. This assay can quantitate differences in cell wall structure (1) between exponentially growing and stationary phase cells, (2) among different S. cerevisiae strains, (3) between S. cerevisiae and Candida albicans, (4) between parental and mutated lines, and (5) between drug- or chemically-treated cells and controls.

Nonideal size-exclusion chromatography with zwitterions causes a pI-dependent elution of proteins from glycerol propylsilane-modified silica

A potato homogenate containing proteins of similar molecular weights but varying pI values was separated by nonideal size-exclusion chromatography after attempts to resolve the proteins with common size-exclusion chromatography methods failed. The method used a zwitterion buffer to amplify electrostatic interactions between the proteins and the silica matrix. The proteins were sorted on the basis of pI in preference to molecular weight. Subsequent tests with marker proteins of known weight and pI verified the validity of the original findings. The method can be used for separation of isozymes and similarly sized proteins as an alternative to chromatofocusing or isoelectrofocusing.