PPARalpha and PPARbeta are differentially affected by ethanol and the ethanol metabolite acetaldehyde in the MCF-7 breast cancer cell line

Effects of acetaldehyde on hepatocyte glycerol uptake and cell size: implication of aquaporin 9

BACKGROUND

The effects of ethanol and acetaldehyde on uptake of glycerol and on cell size of hepatocytes and a role Aquaporin 9 (AQP9), a glycerol transport channel, were evaluated.

METHODS

The studies were done in primary rat and mouse hepatocytes. The uptake of [(14) C] glycerol was determined with hepatocytes in suspension. For determination of cell size, rat hepatocytes on coated dishes were incubated with a lipophilic fluorochrome that is incorporated into the cell membrane and examined by confocal microscopy. A three-dimensional z scan of the cell was performed, and the middle slice of the z scan was used for area measurements.

RESULTS

Acute exposure to acetaldehyde, but not to ethanol, causes a rapid increase in the uptake of glycerol and an increase in hepatocyte size, which was inhibited by HgCl(2) , an inhibitor of aquaporins. This was not observed in hepatocytes from AQP9 knockout mice, nor observed by direct application of acetaldehyde to AQP9 expressed in Xenopus Laevis oocytes. Prolonged 24-hour exposure to either acetaldehyde or ethanol did not result in an increase in glycerol uptake by rat hepatocytes. Acetaldehyde decreased AQP9 mRNA and AQP9 protein, while ethanol decreased AQP9 mRNA but not AQP9 protein. Ethanol, but not acetaldehyde, increased the activities of glycerol kinase and phosphoenolpyruvate carboxykinase.

CONCLUSIONS

The acute effects of acetaldehyde, while mediated by AQP9, are probably influenced by binding of acetaldehyde to hepatocyte membranes and changes in cell permeability. The effects of ethanol in enhancing glucose kinase, and phosphoenolpyruvate carboxykinase leading to increased formation of glycerol-3-phosphate most likely contribute to alcoholic fatty liver.

Peroxisome proliferator-activated receptor and retinoic x receptor in alcoholic liver disease

A growing number of new studies demonstrate that nuclear receptors are involved in the development of alcoholic liver disease (ALD). Ethanol metabolism and RXR/PPAR functions are tightly interconnected in the liver. Several ethanol metabolizing enzymes are potently regulated by RXR and PPARα after alcohol consumption. The increased ethanol metabolism, in turn, leads to alteration of the redox balance of the cells and impairment of RXR/PPAR functions by direct and indirect effects of acetaldehyde, resulting in deranged lipid metabolism, oxidative stress, and release of proinflammatory cytokines. The use of animal models played a crucial role in understanding the molecular mechanisms of ALD. In this paper we summarize the reciprocal interactions between ethanol metabolism and RXR/PPAR functions. In conclusion, RXR and PPAR play a central role in the onset and perpetuation of the mechanisms underling all steps of the clinical progression in ALD.

PPAR-alpha L162V and PGC-1 G482S gene polymorphisms, but not PPAR-gamma P12A, are associated with alcohol consumption in a Spanish Mediterranean population

BACKGROUND

Peroxisome Proliferator-Activated Receptors (PPARs) and its co-activators are regulatory elements of the cellular lipid homeostasis and have been associated with feeding behavior modulation. Animal models suggest that these genes may be involved in alcohol consumption regulation. However, no studies in humans exist. Our aim is to estimate the possible association between polymorphisms in the PPAR-alpha, PPAR-gamma and PPAR-gamma co-activator 1A (PGC-1A) genes and alcohol consumption in humans.

METHODS

We have conducted a cross-sectional study between the PPAR-alpha L162V, PPAR-gamma P12A and PGC-1A G482S polymorphisms, and alcohol consumption in a general Mediterranean Spanish population (303 men and 443 women).

RESULTS

We have found an association between the L162V polymorphism and alcohol consumption in which, carriers of the V allele were more prevalent among alcohol consumers (19.4% vs. 9.8%; OR 2.69; 95% CI: 1.31-5.54, p=0.007). The G482S polymorphism showed a significantly higher frequency in the group of high alcohol drinkers than in non-high alcohol drinkers (33.4% vs. 20.6%; OR 2.28; 95% CI: 1.07-4.88, p=0.034). Mean alcohol consumption was higher as the number of G alleles increased (GG 8.6+/-12.8 g/day, GS 6.6+/-9.2 g/day, SS 5.6+/-7.8 g/day, p=0.003). These results remained statistically significant after covariate adjustment.

CONCLUSIONS

PPAR-alpha L162V and PGC-1A G482S polymorphisms are associated with alcohol consumption in the Mediterranean population.