Long-Term Combinatorial Exposure to Trichloroethylene and Inorganic Arsenic in Genetically Heterogeneous Mice Results in Renal Tubular Damage and Cancer-Associated Molecular Changes

Abstract

Trichloroethylene (TCE) and inorganic arsenic (iAs) are environmental contaminants that can target the kidney. Chronic exposure to TCE is associated with increased incidence of renal cell carcinoma, while co-exposure to TCE and iAs likely occurs in exposed human populations, such as those near Superfund sites. In order to better understand the kidney health consequences of TCE and/or iAs exposure, a genetically heterogeneous mouse population derived from FVB/NJ and CAST/EiJ mouse strains and deficient for multidrug resistance genes (Abcb1a^tm1Bor , Abcb1b^tm1Bor ) was chronically exposed for 52-weeks to varying concentrations of TCE and iAs. Although no exposure group resulted in primary renal cell tumors, kidneys from exposed mice did have significant increases in histologic and biochemical evidence of renal tubular disease with each toxicant alone and with combined exposure, with males having significantly higher levels of damage. Although no added increase in tubular disease was observed with combination exposure compared to single toxicants, molecular changes in kidneys from mice that had the combined exposure were similar to those previous observed in an embryonic stem cell assay for the P81S TCE-induced renal cell carcinoma mutation in the Von Hippel-Lindau syndrome (VHL) gene. While this model more accurately reflects human exposure conditions, development of primary renal tumors observed in humans following chronic TCE exposure was not reproduced even after inclusion of genetic heterogeneity and co-carcinogenic iAs.

Keywords: arsenic; environmental exposure; renal toxicity; trichloroethylene.

Figure 1

Kaplan-Meier survival plots by dose group.

Figure 2

Representative examples of renal pathologies and non-renal tumors. (A) Male. High As/High TCE exposure group. Tubular dilation (asterisk), degeneration and regeneration. One tubule has a necrotic tubular epithelial cell (arrow). (B) Male. No As/Low TCE exposure group. Chronic progressive nephropathy lesions. There are areas of relatively well demarcated tubular change consisting of basophilic tubules with thickened basement membranes. A glomerulus in the section is expanded by presumed amyloidosis. (C) Female. Low As/High TCE exposure group. Lymphoma. (D) Female. High As/High TCE exposure group. Histiocytic sarcoma. Hyaline droplets in renal tubular epithelium support the diagnosis (inset, lower right).

Figure 3

Renal disease scores. (A) Mean (+SE) tubular disease score in each dose group. Number of mice analyzed from each group is shown above. No As/No TCE group was used as control for comparisons: **** P < 0.0001; ** P = 0.0068; * P = 0.0184. (B) Mean (+SE) tubular disease score by toxicant exposure or co-exposure. Number of mice in each group is noted at the bottom. No Toxicant group used as control for comparisons: **** P < 0.0001, *** P = 0.0003.

Figure 4

Renal parameters separated by sex. (A) Mean (+SE) tubular damage across all dose groups. Male n = 171; female n = 278 (P < 0.0001). (B) Mean (+SE) urine protein/creatinine ratio across all dose groups. Male n = 113, female n = 233 (P < 0.0001). (C) Mean (+SE) BUN across all dose groups. Male n = 156, female n = 264 (P < 0.0001). (D) Mean (+SE) NGAL normalized to creatinine across all dose groups. Male n = 113, female n = 233 (P = 0.0027).

Figure 5

Clinical biomarkers of kidney injury. (A) BUN levels for each exposure group were analyzed and compared to the No iAs/No TCE group. Significance was reached only in the Low iAs/No TCE group (P = 0.0137) and the High iAs/No TCE group (P = 0.0333) when compared to the No iAs/No TCE group used as the control for this analysis. (B) Urine protein/carnitine ratios for male and female mice across the entire study population. Male n = 113, female n = 233 (P < 0.0001). (C) Urine protein/carnitine ratios for male and female mice in the No As/No TCE group. Male n = 12, female n = 31 (P < 0.0001).

Figure 6

Molecular changes in kidney from exposed mice. (A) Hierarchical clustering of differentially expressed genes. (B) Ingenuity Pathway Analysis of genes differentially expressed in Low iAs/Low TCE exposure groups. (C) Pathway enrichment analysis of genes differentially expressed in Low iAs/Low TCE exposure groups.