Low hepatic lipase activity is a novel risk factor for coronary artery disease

BACKGROUND

The crucial function of hepatic lipase (HL) in lipid metabolism has been well established, but the relationship between HL activity and coronary artery disease (CAD) is disputed.

METHODS AND RESULTS

We measured HL activity in the postheparin plasma of 200 consecutive men undergoing elective coronary angiography and determined the degree of CAD with the extent score, which has been shown to be better correlated with known risk factors than other measures of CAD extent. We found a significant inverse correlation between HL activity and the extent of CAD (r=-0.19, P<0.01). This association was mainly due to patients with HDL levels >0.96 mmol/L (n=94, r=-0.30, P<0.005). HL activity was lower in 173 patients with CAD than in 40 controls with normal angiograms (286+/-106 versus 338+/-108 nmol. mL(-1). min(-1), P<0.01). To correct for potential confounding factors, we performed multivariate analyses that confirmed the independent association of HL activity with CAD extent. In addition, the presence of the T allele at position -514 in the HL promoter, which leads to a reduced HL promoter activity, was associated with lower HL activity (r=0.30, P<0.001) and higher CAD extent (42.2+/-20.8 versus 35.3+/-23.6 [extent score], P<0.05). In patients with heterozygous familial hypercholesterolemia, calcified lesions in ECG-gated spiral computed tomography were higher in patients with low HL activity (6.3+/-6.8 versus 1.5+/-3.1, P=0.01).

CONCLUSIONS

Our data show that low HL activity is associated with CAD. Therefore, HL might be useful for CAD risk estimation and might be a target for pharmacological intervention.

Mechanism of thrombin clearance by human astrocytoma cells

Astroglial cells secrete a variety of factors that contribute to the regulation of neurite initiation and continued outgrowth, among them proteases and protease inhibitors. An alteration in the balance between these proteins has been implicated in Alzheimer's disease, resulting in an accumulation of thrombin:protease nexin 1 (PN1) complexes in the brains of these patients. This report aims at providing a biochemical explanation for this phenomenon. We show that human astrocytoma cells bind and internalize thrombin and thrombin:PN1 complexes efficiently by a PN1-dependent mechanism. Binding was potently inhibited by soluble heparin and did not occur with the mutant PN1 (K7E) deficient in heparin binding. Receptor-associated protein, an antagonist of the low-density lipoprotein receptor-related protein (LRP), inhibited internalization of thrombin by the astrocytoma cells, but did not affect cell-surface binding. The results are consistent with a mechanism by which astrocytoma cells clear thrombin in a sequential manner: thrombin is first complexed with PN1, then bound to cell-surface heparins, and finally internalized by LRP. This mechanism provides a link between the neuronal growth regulators thrombin and PN1 and proteins genetically associated with Alzheimer's disease, such as LRP.