Application of Imaging Techniques to Cases of Drug-Induced Crystal Nephropathy in Preclinical Studies.

A number of drugs can cause precipitates within renal tubules leading to crystal nephropathy. Crystal nephropathy is usually an exposure-related finding and is not uncommon in preclinical studies, where high doses are tested. An understanding of the nature of precipitates is important for human risk assessment and further development. Our aim was to investigate the ability of various imaging techniques to detect the presence of drugs or metabolites in renal crystals. We applied matrix-assisted laser desorption/ionization-Fourier transform ion cyclotron resonance mass spectrometry (MALDI-FTICR MS) imaging, Raman and infrared microspectroscopy, scanning electron microscopy coupled with energy dispersive X-ray (SEM/EDX) spectroscopy and standard histopathology to cases of drug-induced crystal nephropathy, induced in rodents and primates by 4 compounds. MALDI-FTICR MS imaging enabled the identification of the drug-related crystal content in all 4 cases of nephropathy, without reference material and with high accuracy. Crystals were composed of unchanged parent drug and/or metabolites. Similar results were obtained using Raman and infrared microspectroscopy for 2 compounds. In the absence of reference standards of metabolites, Raman and infrared microspectroscopy showed that the crystals consisted of components similar, but not identical, to the administered drug for the other compounds, a limitation for these techniques. SEM/EDX showed which counter ions were colocalized with the identified drug-related material, complementing the MALDI-FTICR MS findings. Therefore, we recommend MALDI-FTICR MS as a first-line methodology to characterize crystal nephropathies. Raman and infrared microspectroscopy may be useful when MALDI-FTICR MS imaging cannot be applied. SEM/EDX could be considered as a complementary technology.

Minimizing the risk of chemically reactive metabolite formation of new drug candidates: implications for preclinical drug design.

Many pharmaceutical companies aim to reduce reactive metabolite formation by chemical modification at early stages of drug discovery. A practice often applied is the detection of stable trapping products of electrophilic intermediates with nucleophilic trapping reagents to guide rational structure-based drug design. This contribution delineates this strategy to minimize the potential for reactive metabolite formation of clinical candidates during preclinical drug optimization, exemplified by the experience at Roche over the past decade. For the majority of research programs it was possible to proceed with compounds optimized for reduced covalent binding potential. Such optimized candidates are expected to have a higher likelihood of succeeding throughout the development processes, resulting in safer drugs.

Reduction of the genomic damage level in haemodialysis patients by folic acid and vitamin B12 supplementation.

BACKGROUND: Cancer incidence and genomic damage of peripheral lymphocytes are elevated in patients with end-stage renal failure. Among other uraemic toxins, homocysteine (Hcy) levels are increased in most of these patients. In healthy individuals, plasma Hcy correlates with the degree of genomic damage observed in peripheral blood lymphocytes (PBL). The accumulation of Hcy can be reduced by supplementation with folic acid and vitamin B12. The aim of this study was to analyse whether this supplementation can also lower the genomic damage in PBL of haemodialysis patients. This may ultimately help to reduce cancer incidence in renal patients. METHODS: In a prospective study with 27 patients, we analysed the genomic damage in dialysis patients before and at different time points after the initiation of folate/vitamin B12 supplementation. Genomic damage was measured by the frequency of micronuclei, a subset of chromosomal aberrations, in PBL. RESULTS: Supplementation with folic acid and vitamin B12 (more markedly with both) reduced the micronucleus frequency in PBL of dialysis patients. This was not mediated by altered lymphocyte proliferation capacity or changes in DNA cytosine-methylation. Plasma-Hcy was lowered more efficiently by the combined folic acid/vitamin B12 supplementation, and lymphocyte DNA of this group exhibited a nonsignificant trend for a reduction of 1,N(6)-etheno-2'-deoxyadenosine, a marker for oxidative stress. CONCLUSIONS: A reduction of the genomic damage in PBL can be achieved in dialysis patients by supplementation with folic acid and vitamin B12. This may be mediated by Hcy reduction.