Modulation of hepatocyte thiol content by medium composition: implications for toxicity studies

Formation of epichlorohydrin, a known rodent carcinogen, following oral administration of 1,3-dichloro-2-propanol in rats

The observed toxicity and carcinogenicity of 1,3-dichloro-2-propanol (DCP) in rodents is thought to be due to the formation of reactive metabolites, epichlorohydrin (ECH) and dichloroacetone (DCA). However, there is no direct evidence for the formation of these metabolites from exposure to DCP in rodents due to the challenges of measuring these reactive intermediates directly in vivo. The objective of this work was to investigate the metabolism of DCP to ECH and DCA in vivo by first developing a sensitive analytical method in a suitable biological matrix and analyzing samples from rats administered DCP. DCA reacted rapidly in vitro in rat blood, plasma, and liver homogenate, precluding its detection. Because ECH rapidly disappeared in liver homogenate, but was relatively long-lived in plasma and blood in vitro, blood was selected for analysis of this metabolite. Following a single oral dose of 50 mg/kg DCP in male or female Harlan Sprague-Dawley rats, ECH was detected in blood with a maximum concentration reached at ≤13.7 min. ECH was cleared rapidly with a half-life of ca. 33 and 48 min in males and females, respectively. Following a single oral dose of 25 mg/kg ECH in male and female rats, the elimination half-life of ECH was ca. 34 and 20 min, respectively; the oral bioavailability of ECH was low (males, 5.2%; females, 2.1%), suggesting extensive first pass metabolism of ECH following oral administration. The area under the concentration vs time curve for ECH following oral administration of DCP and intravenous administration of ECH was used to estimate the percent of the DCP dose converted to ECH in rats. On the basis of this analysis, we concluded that in male and female rats following oral administration of 50 mg/kg DCP, ≥1.26% or ≥1.78% of the administered dose was metabolized to ECH, respectively.

High hydrostatic pressure enhances whey protein digestibility to generate whey peptides that improve glutathione status in CFTR-deficient lung epithelial cells

Whey protein isolates (WPI) may provide anti-inflammatory benefits to cystic fibrosis (CF), which could be mediated via peptides, as proteolytic digests of WPI enhance intracellular glutathione (GSH) concentrations. The objectives of this study were to investigate whether high hydrostatic pressure can (i) improve the in vitro digestibility of WPI; and (ii) generate low molecular weight (< 1 kDa) peptides from WPI hydrolysates that exert GSH-enhancing and anti-inflammatory properties in wild type and mutant CF transmembrane conductance regulator (CFTR) tracheal epithelial cells. Hydrostatic pressure processing enhanced the in vitro digestibility of WPI to proteolytic enzymes resulting in altered peptide profiles as assessed by CZE and GC-MS. The exposure of mutant CFTR cells to low molecular weight (< 1 kDa) peptides isolated from WPI hydrolysates exposed to pressure processing (pressurized WPI hydrolysates, pWPH), showed increased intracellular levels of reduced GSH and total GSH relative to treatment with peptides obtained from native WPI hydrolysates (nWPH). A tendency for decreased interleukin-8 secretion was associated with the pWPH and nWPH treatments in mutant CFTR cells, which was not observed in wild type cells. Hydrostatic pressure processing of whey proteins appears to enhance their impact on cellular GSH status in cells with the mutant CFTR condition.

N-Acetylcysteine Partially Reverses Oxidative Stress and Apoptosis Exacerbated by Mg-Deficiency Culturing Conditions in Primary Cultures of Rat and Human Hepatocytes

OBJECTIVE

The effects of magnesium (Mg) deficiency on the rate of oxidative stress and apoptosis in primary cultures of human hepatocytes were compared to cultured rat hepatocytes. The possible reversion by N-acetylcysteine (NAC) in Mg-deficient culturing conditions was evaluated.

METHODS

Incubations were conducted for up to 72 h in media containing a deficient (0-0.4 mM) or a physiological (0.8 mM) Mg concentration, and in the presence or absence of NAC after 24 h of culture in these Mg concentration conditions.

RESULTS

We obtained similar profiles in terms of apoptosis and oxidative stress in primary cultures of human hepatocytes, as compared to rat hepatocytes, i.e. a Mg concentration-dependent effect on the caspase-3 activity and GSH levels after 72 h of culture, caspase-3 activity being highest and GSH levels being lowest in Mg-free cultures. The addition of NAC to culture media after the first 24 h of culture increased GSH concentrations. This was accompanied in Mg-deficient cultures by a decrease in both the caspase-3 activity and the lipid peroxidation. However, when culturing hepatocytes with physiological Mg concentrations, an increase in both caspase-3 activity and lipid peroxidation was observed.

CONCLUSIONS

Our results indicate that Mg deficiency exacerbates the rate of apoptosis in cultured hepatocytes, associated with an increase in oxidative stress, the sensitivity of human hepatocytes being equivalent to that of rat hepatocytes. They also indicate a dual role of NAC and/or GSH, i.e. protective for hepatocytes placed in a Mg-deficient environment, while deleterious for hepatocytes placed in a Mg-physiological environment.

Phenotypic anchoring of arsenic and cadmium toxicity in three hepatic-related cell systems reveals compound- and cell-specific selective up-regulation of stress protein expression: implications for fingerprint profiling of cytotoxicity

Exposure of cells to toxic chemicals is known to up-regulate the expression of a number of stress proteins (SPs), including metallothionein (MT) and members of the heat shock protein (HSP) family, and this response may allow the development of a fingerprint profile to identify mechanisms of toxicity in an in vitro toxicology setting. To test this hypothesis, three hepatic-derived cell culture systems (rat hepatoma FGC4 cell line, rat hepatocytes, human hepatoma HepG2 cell line) were exposed to cadmium (as CdCl2) and arsenic (as NaAsO2), two compounds believed to exert their toxicity through an oxidative stress mechanism, under conditions of phenotypic anchoring defined as minimal and mild toxicity (approximately 5 and 25% reduction in neutral red uptake, respectively). The expression of six SPs--MT, HSP25/27, HSP40, HSP60, HSP70, and HSP90--was then determined by ELISA. Expression of four of these SPs--MT, HSP25/27, HSP40 and HSP70--was up-regulated in at least one experimental condition. However, the patterns of expression of these four SPs varied across the experimental conditions, according to differences in toxicant concentration and/or level of toxicity, cell-type and toxicant itself. This lack of uniformity in response of a focussed set of mechanistically defensible targets suggests that similar problems may emerge when using more global approaches based on genomics and proteomics, in which problems of redundancy in targets and uncertain mechanistic relevance will be greater.

Cytotoxicity of the phytosterol diosgenin and its derivatives in rat cultured hepatocytes and V79 fibroblasts

In this work, the cytotoxic effects of some spirostane derivatives were examined in cultured hepatocytes and V79 fibroblasts using different viability assays. The derivatives were obtained by modifying the A and B rings of diosgenin. Diosgenin and its derivatives were more toxic in V79 fibroblasts (IC50 40-300 microM) than in hepatocytes (IC50 280-1000 microM). Inhibition of cytochrome P450IIIA in cultured hepatocytes by incubation with 1 mM cimetidine did not alter the toxicity of these compounds in these cells. These observations suggest that other pathways of detoxification may be involved in hepatocytes. In conclusion, the compounds studied merit investigation for their potential pharmacological and industrial applicability.

Glutathione: its implications for animal health, meat quality, and health benefits of consumers

There has been an increasing focus on the role of antioxidants for human health. This review outlines associations of the most predominant antioxidant, glutathione (GSH), in the body and some ageing-related diseases. Strategies to replete GSH, particularly developing animal-source food products, are discussed. Potentials to alter GSH content in the animal’s body and its possible effects on health are also explored.

Magnesium deficiency induces apoptosis in primary cultures of rat hepatocytes

The effects of extracellular magnesium (Mg) concentration on the rate of apoptosis in rat hepatocytes in primary culture were examined. After overnight attachment, incubations were conducted for up to 72 h in serum-free media containing low (0-0.4 mmol/L), physiological (0.8 mmol/L) or high (2 and 5.6 mmol/L) Mg concentrations. At 72 h, we observed numerous rounded hepatocytes on top of a shrunken cell monolayer at extracellular Mg concentrations < 0.8 mmol/L. These morphological features were associated with Mg-dependent differences in the total protein levels. The various Mg concentrations did not affect DNA synthesis; however, at a concentration < 0.8 mmol/L, the susceptibility of cultured rat hepatocytes to oxidative stress was increased as shown by the reduced glutathione concentration (10.6 +/- 2.8 vs. 37.3 +/- 4.1 nmol/mg protein with 0 and 0.8 mmol/L, respectively; P < 0.05) and increased lipid peroxidation (0.36 +/- 0.03 vs. 0.21 +/- 0.01 nmol malondialdehyde/mg protein with 0 and 0.8 mmol/L, respectively; P < 0.05). Fluorescence microscopy after Hoechst dye staining revealed numerous apoptotic figures in Mg-free monolayers compared with 0.8 and 5.6 mmol/L Mg conditions. These observations were confirmed quantitatively by flow-cytometric analysis after propidium iodide staining. The proportion of subdiploid cells decreased with increasing Mg concentration; for example, it was greater at 72 h in Mg-free cultures (76%) than in cultures containing 0.8 mmol/L or 5.6 mmol/L Mg (28%; P < 0.05). Caspase-3 was highly activated in Mg-free cultures after 48 h of treatment compared with 0.8 and 5.6 mmol/L conditions (P < 0.05). Overall, these results show that extracellular Mg deficiency has a negative effect on the survival of cultured rat hepatocytes by inducing apoptosis; however, supplementation of extracellular Mg did not reduce the spontaneous apoptosis that occurred over time in rat hepatocyte cultures.