Fasting augments PCB impact on liver metabolism in anadromous arctic char

Department of Biology, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada.
Toxicological Sciences (Impact Factor: 4.48). 07/2006; 91(2):431-9. DOI: 10.1093/toxsci/kfj154
Source: PubMed

ABSTRACT Anadromous arctic char (Salvelinus alpinus) undertake short feeding migrations to seawater every summer and accumulate lipids, while the rest of the year is spent in fresh water where the accumulated lipid reserves are mobilized. We tested the hypothesis that winter fasting and the associated polychlorinated biphenyls' (PCBs) redistribution from lipid depots to critical tissues impair the liver metabolic capacity in these animals. Char were administered Aroclor 1254 (0, 1, 10, and 100 mg/kg body mass) orally and maintained for 4 months without feeding to mimic seasonal winter fasting, while fed groups (0 and 100 mg Aroclor 1254/kg) were maintained for comparison. A clear dose-related increase in PCB accumulation and cytochrome P4501A (CYP1A) protein content was observed in the livers of fasted fish. This PCB concentration and CYP1A response with the high dose of Aroclor were 1.5-fold and 3-fold greater in the fasted than in the fed fish, respectively. In fed fish, PCB exposure lowered liver glycogen content, whereas none of the other metabolic indicators were significantly affected. In fasted fish, PCB exposure depressed liver glycogen content and activities of glucose-6-phosphate dehydrogenase, alanine aminotransferase, lactate dehydrogenase, and phosphoenolpyruvate carboxykinase and elevated 3-hydroxyacylcoA dehydrogenase activity and glucocorticoid receptor protein expression. There were no significant impacts of PCB on heat shock protein 70 (hsp70) and hsp90 contents in either fed or fasted fish. Collectively, our study demonstrates that winter emaciation associated with the anadromous lifestyle predisposes arctic char to PCB impact on hepatic metabolism including disruption of the adaptive metabolic responses to extended fasting.

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    • "On the other hand, several studies reported that Hsp concentrations not only differ between the tissues of the same species, but also between different species and stimuli (Dietz 1994; Currie et al. 2000; Deane and Woo 2003; Feidantsis et al. 2009, 2012). For example , in white muscle tissue of fishes exposed to extended fasting (Dicentrarchus labrax, antonopoulou et al. 2013; Salvelinus alpines; Vijayan et al. 2006) and heat stress (Acipenser transmontanus, Han et al. 2012) lower Hsp90 levels have been found, which has been linked to metabolic disruption due to adaptive responses. If protein synthesis is decreased by hypoxia, less Hsp will be needed for various aspects of protein metabolism such as repairing or translocation of newly synthesized protein within or between cells (Hendrick and Hartl 1993), which also might explain the decrease in Hsp90 observed in the mantle tissue of D. gigas under metabolic suppression. "
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    • "On the other hand, increased CS would suggest an increased oxidative flux which may explain the apparent increase in uptake of extracellular FFAs, possibly for its incorporation into the TCA cycle and generation of ATP (Gagnon, 2002). PCB exposed Arctic char are reported to increase β-oxidation as measured by HOAD activities (Vijayan et al., 2006) which would support this hypothesis, although HOAD activity did not change in this study. "
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    • "In this study however, the influx of free amino acids from food (Ronnestad et al., 1999) and consequent amino acid restriction associated with food-deprivation, was not severe enough to elicit a heat shock response in all the examined organs of the sea bass between the imposed experimental feeding trials. More similar to the results from the present investigation, extended fasting can lead to metabolic disruption of adaptive responses resulting to decreased levels of Hsps in the white muscle of the anadromous arctic char (Salvelinus alpinus) (Vijayan et al., 2006) and in the white sturgeon (Acipenser transmontanus) under the effect of heat stress (Han et al., 2012) and sub-optimal feeding (Deng et al., 2009). Concerning the Hsp70 transcript levels, feed deprivation did not significantly affect the abundance of Hsp70 mRNA in channel catfish (Ictalurus punctatus) muscle (Weber and Bosworth, 2005) and in juvenile Atlantic salmon (Salmo salar) gills (Zarate and Bradley, 2003). "
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