Alterations in rabbit kidney protein expression following lead exposure as analyzed by two-dimensional gel electrophoresis.

It was recently reported that low blood lead levels impaired kidney function in men. To develop a set of molecular markers of renal lead exposure and effect, we investigated changes in renal protein expression while approximating occupational lead exposure at subchronic, low blood levels. Lead was administered to male Dutch Belted rabbits as a lead acetate solution adjusted weekly to achieve and maintain the target blood lead levels of 0, 20, 40, and 80 microg/dL for 15 weeks. Lead exposure did not affect kidney or body weights. The effect of increasing blood lead on protein expression was evaluated in rabbit kidney by large-scale two-dimensional electrophoresis (2-DE). Significant quantitative changes (p < 0.05) occurred in a dose-related manner in 12 proteins at 20 microg/dL exposure, 25 at 40 microg/dL, and 102 at 80 microg/dL. At a higher level of significance (p < 0.001), 40 microg/dL blood lead resulted in one protein alteration and 80 microg/dL affected 14 proteins. A set of quantitatively altered charge variants was tentatively identified as glutathione-S-transferase (GST), based on similar observations in rodents subjected to short-term, very high lead exposure. The significance of the protein alterations observed as markers of toxicity awaits their conclusive identification. Investigation of the kidney 2-DE profile in lead-exposed rabbit may be useful in understanding the mechanism of lead nephrotoxicity in humans.

Regional protein alterations in rat kidneys induced by lead exposure.

Lead is a potent neuro- and nephrotoxin in humans and a renal carcinogen in rats. Previous studies have detected lead-induced increases in the activities of specific detoxification enzymes in distinct kidney cell types preceding irreversible renal damage. While preferential susceptibility of the highly vascularized cortex to the effects of lead is clear, lead effects on the medullary region have remained unexplored. The present study was undertaken to investigate the extent to which regional renal protein expression differs and to determine which, if any, regionally distinct protein markers indicative of lead's renotoxic mechanism might be detected in kidney cortical and medullary cytosols. We examined protein expression in these two functionally and anatomically distinct regions, and identified several proteins that are differentially expressed in those regions and were significantly altered by lead. Kidney cytosols from rats injected with lead acetate (114 mg/kg, three consecutive daily injections) were separated by two-dimensional electrophoresis. Lead exposure significantly (P<0.001) altered the abundance (either or) of 76 proteins in the cortex and only 13 in the medulla. Eleven of the proteins altered in the protein patterns were conclusively identified either by matrix-assisted laser desorption/ionization mass spectrometry/electrospray ionization-mass spectrometry (MALDI-MS/ESI-MS) analysis of peptide digests, immunological methods, or by gel matching. Several of the cortical proteins altered by lead were unchanged in the medulla while others underwent similar but lesser alterations. These observations reflect the complexity of lead's nephrotoxicity and endorse the application of proteomics in mechanistic studies as well as biomarker development in a variety of toxicologic paradigms.

Differential expression of cytosolic proteins in the rat kidney cortex and medulla: preliminary proteomics.

The rodent kidney is a target of many xenobiotics and is typified by regionally specific structure and function. This renders distinct regions of the kidney differentially susceptible to toxic exposure and effect. To characterize these differences at the proteome level, protein patterns from male rat kidney cortex and medulla cytosols were examined by two-dimensional electrophoresis (2-DE) and image analysis and prominent proteins identified immunologically or by matrix-assisted laser desorption/ionization-mass spectrometry (MALDI-MS) and electrospray/ionization-tandem mass spectrometry (ESI-MS/MS) sequence tag identification. An average of 727 protein spots were resolved and matched to the cortex cytosol reference pattern, and 716 in the medulla. Of this total, 127 proteins were found to differ in abundance (86 higher in cortex; 41 higher in medulla) (P < 0.001). Of those proteins that were detectable in both cortex and medulla, the abundance of 97 differed significantly while 30 proteins were found to be unique to one region or the other (26 in cortex, 4 in medulla). Twenty protein spots were identified and their regional differences are discussed. These results both confirm and expand our understanding of the molecular heterogeneity characterizing structurally and functionally distinct regions of the kidney and serve as a useful foundation for future nephrotoxicologic studies.

Glutathione S-transferases: two-dimensional electrophoretic protein markers of lead exposure.

Glutathione S-transferases (GST) are a family of detoxification isoenzymes that catalyze the conjugation of xenobiotics and their metabolites with reduced glutathione. Lead exposure in rats is known to induce GST isoenzymes in the liver and kidney. These changes in expression have potential use as biomarkers of lead exposure. Because two-dimensional electrophoresis (2-DE) enables one to analyze both protein abundance changes and chemical changes in protein structure, 2-DE was used to determine the effect of in vivo lead exposure on GST isoform expression in rat kidney cytosols. Male Sprague-Dawley rats were exposed to inorganic lead, and proteins were separated by conventional ISO-DALT and NEPHGE-DALT techniques and blotted for immunological identification. Lead exposure caused detectable inductions in both GSTP1 and GSTM1 and quantifiable charge modification in GSTP1. These preliminary data confirm the utility of 2-D electrophoretic GST analysis as indicative of lead exposure and toxicity and support its use for further elaboration of lead's effects on renal protein expression.

Two-dimensional electrophoresis of precision-cut testis slices: toxicologic application.

Advances in tissue slice technology and a recent novel application of this technique to reproductive toxicology using bovine testis have demonstrated the remarkable utility of this approach. The objective of the present study was to combine this in vitro toxicity test system with large-scale two-dimensional polyacrylamide gel electrophoresis (2-DE) to detect and study alterations in testicular-slice protein patterns as molecular correlates of 1,3,5-trinitrobenzene (TNB) and 1,3-dinitrobenzene (DNB) toxicity. Previous studies have shown that testicular slices remain viable for > 24 h and, as measured by protein synthesis inhibition, TNB causes dose-related injury. Tissue-slices were prepared from bovine testicles incubated for 2, 4 or 6 h and exposed to either 100 microM, 500 microM or 1 mM DNB or TNB in the incubation medium. Slices were collected, solubilized, and separated by large scale 2-DE. Resulting protein patterns were then examined by image analysis, which revealed coefficients of variation in protein spot abundance comparable to patterns from fresh rodent tissue samples. Furthermore, specific protein alterations indicated dose-related inductions and declines in protein abundance, some progressive over time. The results of this investigation demonstrate the potential toxicologic utility of combining in vitro tissue-slice technology with high-resolution 2-DE protein mapping. The consolidation of these methods offers a novel approach for toxicity screening and testing, reduces experimental cost, and reduces the use of laboratory animals.

Two-dimensional electrophoretic analysis of compartment-specific hepatic protein charge modification induced by thioacetamide exposure in rats.

Thioacetamide (TA) is a well-known hepatotoxicant. It has been reported that an obligate intermediate of TA binds to proteins with the formation of acetylimidolysine derivatives that are responsible for TA-induced hepatotoxic effects. TA has also been reported to cause chemically induced cell death via both apoptosis and necrosis. The objective of this study was 2-fold: first, to investigate the effect of TA exposure on protein charge modifications in the rat liver and second, to study the role of these molecular correlates in the regulation of cell death. Male Sprague-Dawley rats (200-225 g, 7-8 weeks old) were divided into four major groups and treated intraperitoneally with a 12-fold dose range of TA (50, 150, 300, and 600 mg TA/kg) dissolved in water. Using whole liver extracts, alterations in the hepatic protein pattern following treatment with the 12-fold dose range of TA were studied using high-resolution, two-dimensional polyacrylamide gel electrophoresis and computerized image analysis. The results indicate that charge modification was clearly evident as early as 2 hr with the lowest dose of 50 mg TA/kg. At this dose and time endoplasmic reticulum proteins, calreticulin, grp78, and ER6O exhibited acidic charge variants. The effect of TA became more prominent with dose and time. Generally the elevation of charge modification indices (CMI) by TA appeared to reach a peak between 4 and 6 hr and then while CMI either leveled off or declined in the lower two doses of 50 and 150 mg TA/kg, it continued to remain elevated with the higher doses of 300 and 600 mg TA/kg. This dichotomy in the elevation of CMI is in close correspondence to the pattern of cell death observed with a similar dose range of TA, where lower doses (50 and 150 mg TA/kg) predominantly cause cell death via apoptosis while higher doses cause cell death via necrosis. Delayed charge modification was observed with the cytosolic hsc70s with the 300 and 600 mg TA/kg treatments, indicating that the reactive metabolite(s) slowly leak out into the cytosol from the endoplasmic reticulum. There were no alterations in the mitochondrial proteins hsp60 and grp75, suggesting that TA has no effect on the mitochondrion, its effects primarily being confined to the endoplasmic reticulum. The concept of looking at these proteins as biomarkers of tissue injury has validity. These changes may be indicators of bioactivation and adduct formation and also may be signaling events in the regulation of the mode of cell death.

Toxicant-induced alterations in two-dimensional electrophoretic patterns of hepatic and renal stress proteins.

Recent studies in this laboratory and by others suggest that two-dimensional polyacrylamide gel electrophoresis of proteins (2-DE) possesses significant utility in the detection of chemical toxicity and in providing information regarding toxic mechanism. After having identified a set of specific heat-shock and glucose-regulated proteins whose expression in rodent liver and kidney is highly conserved and constitutive, we compared the effect of in vivo exposure to perfluoro-n-octanoic acid and perfluoro-n-decanoic acid on their expression. The following stress proteins were identified, their x, y coordinate positions mapped, and abundance statistically analyzed and compared: hsp32, hsp60, hsc70, hsp70, hsp90, grp75, grp94, protein disulfide isomerase (PDI), and ER60. We report here that the stress response to perfluorocarboxylic acids is tissue-, toxicant-, and stress protein class-specific and dose-related. Furthermore, because nearly all of the proteins studied were constitutively expressed at detectable levels in both liver and kidney, the 2-DE stress protein pattern may be suitable to future toxicologic screening applications.