Relationship between serum preheparin lipoprotein lipase mass, plasma glucose and metabolic syndrome in older subjects

ELISA system for human endothelial lipase

BACKGROUND

Endothelial lipase (EL) regulates the metabolism of HDL cholesterol (HDL-C). However, the role of EL in regulating plasma HDL-C concentrations and EL's potential involvement in atherosclerosis in humans has not been fully investigated due to the lack of reliable assays for EL mass. We developed an ELISA system for serum EL mass.

METHODS

Human recombinant EL proteins, purified from cultured media of human EL-transfected Chinese hamster ovary cells, were used as antigen and calibrator. Two specific monoclonal antibodies were generated in mice against recombinant EL protein for a sandwich ELISA. We measured EL mass in human serum using EL recombinant protein as a calibration standard.

RESULTS

The EL antibodies did not cross-react with lipoprotein lipase and hepatic triglyceride lipase. The detection limit of the ELISA was 20 pg/mL, which is approximately 10 times lower than that of previous ELISA systems. Recovery of spiked EL in serum was 90%-105%. Assay linearity was intact with a >4-fold dilution of serum. Intra- and interassay CVs were <5%. The serum EL mass in 645 human subjects was [mean (SE)] 344.4 (7.7) pg/mL (range 55.2-1387.7 pg/mL). Interestingly, serum EL mass was increased in patients with diagnosed cardiovascular disease and inversely correlated with serum HDL-C concentrations. There was no difference in EL mass between pre- and postheparin plasma samples.

CONCLUSIONS

This ELISA should be useful for clarifying the impact of EL on HDL metabolism and EL's potential role in atherosclerosis.

Triglyceride lipases and atherosclerosis

PURPOSE OF REVIEW

There are strong epidemiologic connections between plasma triglycerides and atherosclerosis. We will consider to what extent this goes back to derangements of the lipoprotein lipase (LPL) system. The roles of hepatic lipase and endothelial lipase will also be touched upon.

RECENT FINDINGS

Understanding of LPL action has taken major steps with the discovery of lipase maturation factor 1 as a specific endoplasmic reticulum chaperon needed for proper folding of the lipases, glycosylphosphatidylinositol-anchored HDL-binding protein 1 as an endothelial cell protein needed for transport and binding of LPL and some angiopoietin-like proteins that can modulate LPL activity. Studies of genetic variants continue to support the important roles of the lipases in lipoprotein metabolism and in atherosclerosis.

CONCLUSION

There are several ways by which derangement of the lipases may contribute to atherogenesis. Lipase actions are major determinants of plasma lipoprotein patterns. LPL activity must be modulated in relation to the physiological situation (feeding, fasting, exercise, etc.). Fatty acids and monoglycerides generated must be efficiently removed so that they do not endanger the integrity of the endothelium, cause lipotoxic reactions or both. In addition, the lipases may cause binding and endocytosis of lipoprotein particles in the artery wall.