No abstract

Calcium oxalate monohydrate (COM) is the major crystalline component found in kidney stones and its adhesion to renal tubular cells provokes tubular injury, which in turn enhances COM crystal adhesion. However, COM-induced toxic effects in these tubular cells remain largely unknown. We performed a proteomics study to characterize changes in the cellular proteome in MDCK distal renal tubular cells after an exposure to high-dose (1000 microg/mL) COM crystals for 48 h, at which percentage of cell death was significantly increased. Proteins were extracted from MDCK cells cultured with COM-containing or COM-free medium ( n = 5 individual flasks per group), resolved in individual 2-D gels, and stained with SYPRO Ruby fluorescence dye. Quantitative and statistical analyses revealed 53 proteins whose abundance levels were altered (25 were increased, whereas other 28 were decreased) by COM-induced toxicity. Among these, 50 were successfully identified by quadrupole time-of-flight (Q-TOF) mass spectrometry (MS) and/or tandem MS (MS/MS) analyses. The proteomic data were clearly confirmed by 2-D Western blot analysis. While three chaperones (GRP78, Orp150 and Hsp60) were increased, other proteins involved in protein biosynthesis, ATP synthesis, cell cycle regulator, cellular structure, and signal transduction were decreased. These data provide some novel mechanistic insights into the molecular mechanisms of COM crystal-induced tubular toxicity.

To our knowledge these data provide the first direct evidence that urinary trefoil factor 1 is a novel potent inhibitor of calcium oxalate crystal growth and aggregation, and can transform calcium oxalate monohydrate crystals to the dihydrate type.

The interaction between crystals and renal tubular cells has been proposed to be a crucial event that elicits subsequent cellular responses, leading to kidney stone formation. Nevertheless, the molecular mechanisms of these cellular responses remain poorly understood. We performed a gel-based differential proteomics study to examine cellular responses (as determined by altered protein expression) in Madin-Darby canine kidney (MDCK) cells, which were derived from dog kidney and exhibited distal renal tubule phenotype, during calcium oxalate dihydrate (COD) crystal adhesion. MDCK cells were grown in a medium without or with COD crystals (100 microg/ml) for 48 h. Crystal adhesion was illustrated by phase-contrast and scanning electron microscopy. Flow cytometry using annexin V/propidium iodide double staining showed that the percentage of cell death did not significantly differ between cells with and without COD crystal adhesion. Cellular proteins were then extracted, resolved with two-dimensional gel electrophoresis (2-DE), and visualized by SYPRO Ruby staining ( n = 5 gels per group). Quantitative intensity analysis revealed 11 significantly altered proteins, 10 of which were successfully identified by quadrupole time-of-flight peptide mass fingerprinting (MS) and/or tandem MS (MS/MS), including metabolic enzymes, cellular structural protein, calcium-binding protein, adhesion molecule, protein involved in RNA metabolism, and chaperone. An increase in annexin II was confirmed by 2-D Western blot analysis. These data may lead to better understanding of the cellular responses in distal renal tubular cells during COD crystal adhesion.

Efficacy of peritoneal dialysis is determined by solute transport through peritoneal membranes. With the use of the peritoneal equilibration test (PET), peritoneal membranes can be classified as high (H), high average (HA), low average (LA), and low (L) transporters, based on the removal or transport rate of solutes, which are small molecules. Whether there is any difference in macromolecules (i.e., proteins) removed by different types of peritoneal membranes remains unclear. We performed a gel-based differential proteomics study of peritoneal dialysate effluents (PDE) obtained from chronic peritoneal dialysis (CPD) patients with H, HA, LA, and L transport rates (n = 5 for each group; total n = 20). Quantitative analysis and ANOVA with Tukey's posthoc multiple comparisons revealed five proteins whose abundance in PDE significantly differed among groups. These proteins were successfully identified by matrix-assisted laser desorption ionization quadrupole time-of-flight (MALDI-Q-TOF) mass spectrometry (MS) and tandem mass spectrometry (MS/MS) analyses, including serum albumin in a complex with myristic acid and triiodobenzoic acid, α1-antitrypsin, complement component C4A, immunoglobulin κ light chain, and apolipoprotein A-I. The differences among groups in PDE levels of C4A and immunoglobulin κ were clearly confirmed in a validation set of the other 24 patients (n = 6 for each group) using ELISA. These data may lead to better understanding of the physiology of peritoneal membrane transport in CPD patients. Extending the study to a larger number of patients with subgroup analyses may yield additional information of the peritoneal dialysate proteins in association with dialysis adequacy, residual renal function, nutritional status, and risk of peritoneal infection. Keywords: dialysate • kidney • membranes • peritoneal dialysis • proteome • renal failure • solute clearance

Adhesion of calcium oxalate (CaOx) crystals to renal tubular cells is a critical event that triggers a cascade of responses, leading to the development of kidney stones. However, the molecular mechanisms of these cellular responses remain largely unknown. We performed gel-based, differential proteomics study to examine cellular responses (as determined by altered protein expression) in Madin-Darby Canine Kidney (MDCK) cells during CaOx monohydrate (COM) crystal adhesion. Approximately 3-million MDCK cells were inoculated in each culture flask and maintained for 24 h. A total of 10 semiconfluent flasks were then divided into two groups (n = 5 per group) and the culture medium was replaced by either COM-containing (with 100 μg/mL COM crystals) or COM-free medium. The cells were grown further for 48 h. Crystal adhesion on the cell surface was clearly demonstrated using phase-contrast and scanning electron microscopy. Cell death assay using annexin V/propidium iodide double staining showed that all these samples had comparable % cell death. Cellular proteins were then extracted, resolved with 2-DE, and visualized by SYPRO Ruby staining (n = 5 gels per group). Quantitative intensity analysis revealed significantly increased abundance of 15 protein spots, whereas the other 5 were decreased. These altered proteins were then identified by quadrupole TOF (Q-TOF) MS and/or MS/MS analyses, including transcription/translation regulators, signal transduction proteins, metabolic enzymes, nuclear membrane proteins, carrier protein, cellular structural protein, chaperones, and proteins involved in biosynthesis, enzyme activation, and growth regulation. These data may lead to better understanding of the cellular responses in distal renal tubular cells during COM crystal adhesion.

Anionic or acidic proteins are the main compositions of normal urinary proteome. Efforts to characterize human urinary proteome, thus, have focused mainly on the anionic compartment. The information of cationic or basic proteins present in the normal urine is virtually unknown. In the present study, we applied different methods to enrich cationic urinary proteome. Efficacies of these methods were compared using equal volume (1 L) of urine samples from the same pool obtained from 8 normal healthy individuals. Cation exchange chromatography using RESOURCE-S column provided the least amount of the recovered proteins, whereas batch adsorption using SP Sepharose 4 Fast Flow beads equilibrated with acetic acid (pH 4.8) provided the greatest yield of protein recovery. The recovered proteins were then resolved with 2-DE (pI 7-11) and identified by peptide mass fingerprinting using MALDI-TOF MS. There were several isoforms of immunoglobulin heavy and light chains enriched by these methods. In addition, three isoforms of interferon alpha-3 (IFNalpha3) and six isoforms of eosinophil-derived neurotoxin (EDN), were also enriched. The enrichment of IFNalpha3 and EDN was particularly effective by batch adsorption using SP Sepharose 4 Fast Flow beads equilibrated with acetic acid (pH 6.0). Initial depletion of anionic components using DEAE batch adsorption reduced the recovery yield of these two proteins and did not improve recovery of any other cationic urinary proteins. We conclude that batch adsorption using SP Sepharose Fast Flow beads equilibrated with acetic acid (pH 6.0) is the method of choice to examine the basic/cationic urinary proteome, as this protocol provided the satisfactory yield of protein recovery and provided the greatest amount as well as maximal number of IFNalpha3 and EDN isoforms. Our data will be useful for further highly focused study targeting on cationic/basic urinary proteins. Moreover, the techniques described herein may be applicable for enrichment of cationic proteomes in other body fluids, cells, and tissues.