Comparative effect of ursodeoxycholic acid and calcium antagonists on the binding, uptake and degradation of LDL in isolated hamster hepatocytes

Calcium antagonists as inhibitors of in vitro low density lipoprotein oxidation and glycation

The peroxidation step in lipid transformation is considered to be essential in the pathogenesis of atherosclerosis. Calcium antagonists (CA) appear to have antioxidant effects in addition to their potent vasorelaxant properties. In the present study, we compared the antioxidative efficacy of CA (amlodipine, lacidipine, nifedipine, isradipine, diltiazem, and semotiadil) in the copper-catalysed oxidation of low-density lipoprotein (LDL) with that of glycated(g)/glycoxidated(go) LDL. This issue is of great importance when considering the potential therapeutic use of antioxidant drugs in diabetes-associated vasculopathy. Oxidation of native LDL was inhibited most efficiently (>90%) by lacidipine and semotiadil in the concentration range 10(-4)-10(-3) M. We found, however, a dramatic decrease in antioxidant activity towards g/goLDL as compared to native LDL in all the CA tested. Only lacidipine significantly inhibited copper-mediated oxidation of g/goLDL in the whole concentration range tested (10(-5) M-10(-3) M). This probably resulted from the increased auto-oxidative potential introduced by early and advanced glycation end products (AGE) into the g/goLDL. We noted that coincubation of LDL with 10(-3) M CA and 0.5 M glucose under oxidative/non-oxidative conditions partially or fully restored the antioxidant capacity of the different CA to inhibit the subsequent copper-catalysed oxidation of the modified LDL. This is a clear indication that CA inhibit glycative or glycoxidative LDL changes during the preceding long-term glycation period. The notion that both oxidative changes and long-term glycation effects were reduced by CA was corroborated by fluorescence analysis, AGE-ELISA, quantitation of lipid peroxidation, and thiobarbituric acid reactive substance (TBARS) measurement of long-term g/goLDL. The strongest antioxidative effects during long-term glycation of LDL were seen with isradipine, lacidipine, nifedipine, and semotiadil. Diltiazem was the only CA that could not prevent TBARS formation in LDL during the long-term glycation period. In contrast, Amadori product formation, as measured by the generation of fructosamines, was not significantly reduced by any CA tested. Thus CA, like other antioxidants, significantly retard AGE formation, while initial glycation reactions, such as Amadori product formation, are only weakly inhibited.

Effect of ursodeoxycholic acid on hepatic LDL binding and uptake in dietary hypercholesterolemic hamsters

Administration of ursodeoxycholic acid (UDCA) has been shown to decrease serum total and low density lipoprotein (LDL) cholesterol in hypercholesterolemic patients with primary biliary cirrhosis. Results of previous studies prompted us to postulate that the cholesterol-lowering effect of UDCA may be due, at least in part, to a direct increment in hepatic LDL receptor binding [Bouscarel et al., Biochem J, 1991;280:589; Bouscarel et al., Lipids 1995;30:607]. The aim of the present investigation was to determine the ability of UDCA to enhance hepatocellular LDL receptor recruitment, as determined by its effect in vivo on LDL uptake, and its effect in vitro on LDL binding, under conditions of moderately elevated serum cholesterol. Study groups consisted of male golden Syrian hamsters fed either a standard chow diet (control), a 0.15% cholesterol-containing diet, or a 0.15% cholesterol-containing diet supplemented with either 0.1% UDCA, or 0.1% chenodeoxycholic acid (CDCA). Cholesterol feeding increased (P<0.01) total serum cholesterol by 44%, and was associated with a 10-fold accumulation of cholesteryl esters in the liver (P<0.01). In vivo, hepatic uptake of [U-(14)C]sucrose-labeled hamster LDL was increased (P<0.05) to a level of 454+/-101 microl in animals fed a cholesterol-containing diet supplemented with UDCA, compared to that either without UDCA (337+/-56 microl), or with CDCA (240+/-49 microl). The hepatic uptake of [U-(14)C]sucrose-labeled methylated human LDL, a marker of LDL receptor-independent LDL uptake, was unaffected by bile acid feeding. In vitro, specific binding of [125I]hamster LDL to isolated hepatocytes was determined at 4 degrees C, in presence and absence of 700 micromol/l UDCA. The K(D) ranged from 25 to 31 microg/ml, and was not affected by either cholesterol feeding or UDCA. In the presence of UDCA, the B(max) was increased by 19% (P<0.05) in cells isolated from control animals and by 29% (P<0.01) in cells isolated from hamsters fed a cholesterol-supplemented diet. In conclusion, in dietary hypercholesterolemic hamsters, both chronic in-vivo and acute in-vitro treatments with UDCA resulted in restoration of hepatic LDL binding and uptake to levels observed in control hamsters.