Lack of formic acid production in rat hepatocytes and human renal proximal tubule cells exposed to chloral hydrate or trichloroacetic acid

Abstract

The industrial solvent trichloroethylene (TCE) and its major metabolites have been shown to cause formic aciduria in male rats. We have examined whether chloral hydrate (CH) and trichloroacetic acid (TCA), known metabolites of TCE, produce an increase in formic acid in vitro in cultures of rat hepatocytes or human renal proximal tubule cells (HRPTC). The metabolism and cytotoxicity of CH was also examined to establish that the cells were metabolically active and not compromised by toxicity. Rat hepatocytes and HRPTC were cultured in serum-free medium and then treated with 0.3-3mM CH for 3 days or 0.03-3mM CH for 10 days respectively and formic acid production, metabolism to trichloroethanol (TCE-OH) and TCA and cytotoxicity determined. No increase in formic acid production in rat hepatocytes or HRPTC exposed to CH was observed over and above that due to chemical degradation, neither was formic acid production observed in rat hepatocytes exposed to TCA. HRPTC metabolised CH to TCE-OH and TCA with a 12-fold greater capacity to form TCE-OH versus TCA. Rat hepatocytes exhibited a 1.6-fold and 3-fold greater capacity than HRPTC to form TCE-OH and TCA respectively. CH and TCA were not cytotoxic to rat hepatocytes at concentrations up to 3mM/day for 3 days. With HRPTC, one sample showed no cytotoxicity to CH at concentrations up to 3mM/day for 10 days, while in another cytotoxicity was seen at 1mM/ day for 3 days. In summary, increased formic acid production was not observed in rat hepatocytes or HRPTC exposed to TCE metabolites, suggesting that the in vivo response cannot be modelled in vitro. CH was toxic to HRPTC at millimolar concentrations/day over 10 days, while glutathione derived metabolites of TCE were toxic at micromolar concentrations/day over 10 days supporting the view that glutathione derived metabolites are likely to be responsible for nephrotoxicity.

In vitro evaluation of human xenobiotic toxicity: Scientific concepts and the novel integrated discrete multiple cell coculture (IdMOC) technology

“…Besides hepatocytes, primary cells cultured from various organs such as kidney (Dietrich et al, 2001;Li et al, 2006;Lock et al, 2007), nervous system (Stair et al, 2005;Guizzetti et al, 2005), heart (Hasinoff et al, 2007), skeletal muscle (Mazno et al, 2003), vascular endothelium (Harlan et al, 1983;Kim et al, 2007), lung (Li, 1986;Li and Myers, 1988;Bakand et al, 2007;Han et al, 2007;Sayes et al, 2007), and blood/bone marrow cells (Deldar and Stevens, 1993;Rich and Hall, 2005) have also been applied towards the evaluation of xenobiotic toxicity. The various primary cell systems used may be representative of the appropriate in vivo target cells for their respective organs.…”