Urothelial Cytotoxicity and Regeneration Induced by Dimethylarsinic Acid in Rats

Abstract

Inorganic arsenic is a known human carcinogen of the skin and respiratory tract. Epidemiologic evidence indicates that it is also carcinogenic to the urinary bladder and other internal organs. Lack of an animal model has limited progress on understanding the mechanism of arsenic carcinogenesis. It was recently reported that high doses of an organic arsenical, dimethylarsinic acid (DMA), increased urinary bladder tumors in rats when administered in the diet or in the drinking water for 2 years, with the female being more sensitive than the male. We previously showed that high doses of DMA (40 or 100 ppm of the diet) fed for 10 weeks increased urothelial cell proliferation in the rat. Treatment with DMA also increased renal calcification and increased urinary calcium concentration. In 2 experiments, we examined the urothelial proliferative effects of treatment with 100 ppm DMA in the diet in female F344 rats for 2 and 10 weeks and for 6 and 24 h, and 3, 7, and 14 days. Cytotoxic changes in the urothelium were evident by SEM as early as 6 h after treatment was begun. Foci of cellular necrosis were detected after 3 days of treatment, followed by widespread necrosis of the urothelium after 7 days of treatment. The bromodeoxyuridine (BrdU) labeling index was not increased until after 7 days of treatment, suggesting that administration of DMA results in cytotoxicity with necrosis, followed by regenerative hyperplasia of the bladder epithelium. Although the rat provides an animal model to study the urothelial effects of DMA, the relevance of this finding to inorganic arsenic carcinogenesis in humans must be extrapolated cautiously, due to the high doses of DMA necessary to produce these changes in the rat and the differences in metabolism of arsenicals in rodents, especially rats, compared to humans.

Dimethylarsinic Acid in Drinking Water Changed the Morphology of Urinary Bladder but Not the Expression of DNA Repair Genes of Bladder Transitional Epithelium in F344 Rats

“…In the present study, 100 ppm DMA(V) induced severe damage to mitochondria, likely rendering these organelles unable to support energy-dependent apoptosis. This situation could lead to necrosis, rather than apoptosis, consistent with previous reports of urothelial toxicity from high concentrations of DMA(V) (Cohen et al 2001; Shen et al 2006). Rats exposed to low concentrations of DMA(V) have increased apoptosis indices in the urothelium (Kinoshita et al 2007).…”

“…At concentrations that produced no apparent clinical toxicity, dimethylarsinic acid induced morphological changes in urinary bladder transitional epithelium, a target of arsenic carcinogenesis, but no alterations in the expression of DNA repair genes. Although vacuolation, hyperchromatin, and hyperplasia in the transitional epithelium have been reported (Cohen et al 2001;Sen et al 2005;Shen et al 2006), the present study is the first to show organelle damage, particularly mitochondrial damage, after DMA(V) exposure in a dose-response manner. The mRNA levels of DNA repair genes involved in excision repair or double-strand break repair (ATM, ERCC3/XPB, Polb, and XRCC1) were not altered by DMA(V) in transitional cells.…”

Dimethylarsinic Acid in Drinking Water Changed the Morphology of Urinary Bladder but Not the Expression of DNA Repair Genes of Bladder Transitional Epithelium in F344 Rats

“…In the present study, 100 ppm DMA(V) induced severe damage to mitochondria, likely rendering these organelles unable to support energy-dependent apoptosis. This situation could lead to necrosis, rather than apoptosis, consistent with previous reports of urothelial toxicity from high concentrations of DMA(V) (Cohen et al 2001; Shen et al 2006). Rats exposed to low concentrations of DMA(V) have increased apoptosis indices in the urothelium (Kinoshita et al 2007).…”

“…At concentrations that produced no apparent clinical toxicity, dimethylarsinic acid induced morphological changes in urinary bladder transitional epithelium, a target of arsenic carcinogenesis, but no alterations in the expression of DNA repair genes. Although vacuolation, hyperchromatin, and hyperplasia in the transitional epithelium have been reported (Cohen et al 2001;Sen et al 2005;Shen et al 2006), the present study is the first to show organelle damage, particularly mitochondrial damage, after DMA(V) exposure in a dose-response manner. The mRNA levels of DNA repair genes involved in excision repair or double-strand break repair (ATM, ERCC3/XPB, Polb, and XRCC1) were not altered by DMA(V) in transitional cells.…”

Subchronic Urinary Bladder Effects of Muraglitazar in Male Rats1

“…That is, the urinary bladder mucosa of high-dose young male animals on normal diet contained areas of multifocal urothelial injury proximal to urothelial hyperplasia. A profile of urothelial necrosis and associated regenerative hyperplasia is consistent with an indirect, nongenotoxic mode of urinary bladder tumorigenesis (Cohen et al, 2001). Importantly, when urinary pH was lowered by dietary acidification, there was no evidence of urothelial necrosis or proliferation by any endpoint as previously reported in cases involving calcium-containing urinary solids and resultant microabrasion of the urothelium (Chappel, 1992).…”

Gene expression profiling of responses to dimethylarsinic acid in female F344 rat urothelium

“…Transcripts for other stress related proteins such as heat shock proteins (Hsp70, Hsp10, Hsp60), hemeoxygenase 2 (HO-2) and stress inducible molecular chaperone (GrpE#1) were all increased in response to DMA. These changes are consistent with the oxidative stress response that has been reported following DMA exposure both in vitro and in vivo (Cohen et al, 2001(Cohen et al, , 2002. Gene expression associated with proliferation control was altered in response to DMA treatment (Table 1).…”

Dimethylarsinic Acid in Drinking Water Changed the Morphology of Urinary Bladder but Not the Expression of DNA Repair Genes of Bladder Transitional Epithelium in F344 Rats

“…In the present study, 100 ppm DMA(V) induced severe damage to mitochondria, likely rendering these organelles unable to support energy-dependent apoptosis. This situation could lead to necrosis, rather than apoptosis, consistent with previous reports of urothelial toxicity from high concentrations of DMA(V) (Cohen et al 2001; Shen et al 2006). Rats exposed to low concentrations of DMA(V) have increased apoptosis indices in the urothelium (Kinoshita et al 2007).…”

“…At concentrations that produced no apparent clinical toxicity, dimethylarsinic acid induced morphological changes in urinary bladder transitional epithelium, a target of arsenic carcinogenesis, but no alterations in the expression of DNA repair genes. Although vacuolation, hyperchromatin, and hyperplasia in the transitional epithelium have been reported (Cohen et al 2001;Sen et al 2005;Shen et al 2006), the present study is the first to show organelle damage, particularly mitochondrial damage, after DMA(V) exposure in a dose-response manner. The mRNA levels of DNA repair genes involved in excision repair or double-strand break repair (ATM, ERCC3/XPB, Polb, and XRCC1) were not altered by DMA(V) in transitional cells.…”

Subchronic Urinary Bladder Effects of Muraglitazar in Male Rats1

“…That is, the urinary bladder mucosa of high-dose young male animals on normal diet contained areas of multifocal urothelial injury proximal to urothelial hyperplasia. A profile of urothelial necrosis and associated regenerative hyperplasia is consistent with an indirect, nongenotoxic mode of urinary bladder tumorigenesis (Cohen et al, 2001). Importantly, when urinary pH was lowered by dietary acidification, there was no evidence of urothelial necrosis or proliferation by any endpoint as previously reported in cases involving calcium-containing urinary solids and resultant microabrasion of the urothelium (Chappel, 1992).…”

Gene expression profiling of responses to dimethylarsinic acid in female F344 rat urothelium

“…Transcripts for other stress related proteins such as heat shock proteins (Hsp70, Hsp10, Hsp60), hemeoxygenase 2 (HO-2) and stress inducible molecular chaperone (GrpE#1) were all increased in response to DMA. These changes are consistent with the oxidative stress response that has been reported following DMA exposure both in vitro and in vivo (Cohen et al, 2001(Cohen et al, , 2002. Gene expression associated with proliferation control was altered in response to DMA treatment (Table 1).…”

Dimethylarsinic Acid in Drinking Water Changed the Morphology of Urinary Bladder but Not the Expression of DNA Repair Genes of Bladder Transitional Epithelium in F344 Rats

“…In the present study, 100 ppm DMA(V) induced severe damage to mitochondria, likely rendering these organelles unable to support energy-dependent apoptosis. This situation could lead to necrosis, rather than apoptosis, consistent with previous reports of urothelial toxicity from high concentrations of DMA(V) (Cohen et al 2001; Shen et al 2006). Rats exposed to low concentrations of DMA(V) have increased apoptosis indices in the urothelium (Kinoshita et al 2007).…”

“…At concentrations that produced no apparent clinical toxicity, dimethylarsinic acid induced morphological changes in urinary bladder transitional epithelium, a target of arsenic carcinogenesis, but no alterations in the expression of DNA repair genes. Although vacuolation, hyperchromatin, and hyperplasia in the transitional epithelium have been reported (Cohen et al 2001;Sen et al 2005;Shen et al 2006), the present study is the first to show organelle damage, particularly mitochondrial damage, after DMA(V) exposure in a dose-response manner. The mRNA levels of DNA repair genes involved in excision repair or double-strand break repair (ATM, ERCC3/XPB, Polb, and XRCC1) were not altered by DMA(V) in transitional cells.…”

Subchronic Urinary Bladder Effects of Muraglitazar in Male Rats1

“…That is, the urinary bladder mucosa of high-dose young male animals on normal diet contained areas of multifocal urothelial injury proximal to urothelial hyperplasia. A profile of urothelial necrosis and associated regenerative hyperplasia is consistent with an indirect, nongenotoxic mode of urinary bladder tumorigenesis (Cohen et al, 2001). Importantly, when urinary pH was lowered by dietary acidification, there was no evidence of urothelial necrosis or proliferation by any endpoint as previously reported in cases involving calcium-containing urinary solids and resultant microabrasion of the urothelium (Chappel, 1992).…”

Gene expression profiling of responses to dimethylarsinic acid in female F344 rat urothelium

“…Transcripts for other stress related proteins such as heat shock proteins (Hsp70, Hsp10, Hsp60), hemeoxygenase 2 (HO-2) and stress inducible molecular chaperone (GrpE#1) were all increased in response to DMA. These changes are consistent with the oxidative stress response that has been reported following DMA exposure both in vitro and in vivo (Cohen et al, 2001(Cohen et al, , 2002. Gene expression associated with proliferation control was altered in response to DMA treatment (Table 1).…”