Prevention of Ethanol-Induced Liver Injury in Rats by an Agonist of Peroxisome Proliferator-Activated Receptor-γ, Pioglitazone

Abstract

Agonists of peroxisome proliferator-activated receptor (PPAR)-γ have been shown to reduce tumor necrosis factor-α (TNF-α)-induced insulin resistance. On the other hand, sensitization of Kupffer cells to lipopolysaccharide (LPS) and their production of TNF-α are critical for progression of alcoholic liver injury. This study was intended to determine whether pioglitazone, a PPAR-γ agonist, could prevent alcohol-induced liver injury. Rats were given ethanol (5 g/kg b.wt.) and pioglitazone (500 μg/kg) once every 24 h intragastrically. Ethanol for 8 weeks caused pronounced steatosis, necrosis, and inflammation in the liver. These pathological parameters were diminished greatly by pioglitazone. Kupffer cells were sensitized to LPS after ethanol for 4 weeks as evidenced by aggravation of liver pathology induced by LPS (5 mg/kg) and enhancement of LPS (100 ng/ml)-induced intracellular Ca²⁺ concentration elevation in Kupffer cells. The parameters were diminished by treatment with pioglitazone. LPS-induced TNF-α production by Kupffer cells from the 4-week ethanol group was 3 to 4 times higher than control. This increase was blunted by 70% with pioglitazone. Gut permeability was 10-fold higher in the 4-week ethanol group, and pioglitazone treatment did not change the value. Inclusion of TNF-α in culture media of Kupffer cells enhanced CD14 expression, LPS-induced intracellular Ca²⁺ concentration response, and production of TNF-α. These results indicate that pioglitazone prevents alcoholic liver injury through abrogation of Kupffer cell sensitization to LPS.