Common sequence variant in lipoprotein lipase gene conferring triglyceride response to fibrate treatment

Fibrate pharmacogenomics: expanding past the genome

Fibrates are a medication class prescribed for decades as 'broad-spectrum' lipid-modifying agents used to lower blood triglyceride levels and raise high-density lipoprotein cholesterol levels. Such lipid changes are associated with a decrease in cardiovascular disease, and fibrates are commonly used to reduce risk of dangerous cardiovascular outcomes. As with most drugs, it is well established that response to fibrate treatment is variable, and this variation is heritable. This has motivated the investigation of pharmacogenomic determinants of response, and multiple studies have discovered a number of genes associated with fibrate response. Similar to other complex traits, the interrogation of single nucleotide polymorphisms using candidate gene or genome-wide approaches has not revealed a substantial portion of response variation. However, recent innovations in technological platforms and advances in statistical methodologies are revolutionizing the use and integration of other 'omes' in pharmacogenomics studies. Here, we detail successes, challenges, and recent advances in fibrate pharmacogenomics.

Rare LPL gene variants attenuate triglyceride reduction and HDL cholesterol increase in response to fenofibric acid therapy in individuals with mixed dyslipidemia

OBJECTIVE

Individuals with mixed dyslipidemia have elevated triglycerides (TG), low high-density lipoprotein cholesterol (HDL-C), and increased risk for coronary disease. Fibrate therapy is commonly used to lower TG and increase HDL-C. Common genetic variants are known to affect the response to fibrate therapy. We sought to identify rare genetic variants (frequency ≤ 1%) in genes involved in TG and HDL-C metabolism that affect the response to fenofibric acid (FA) therapy.

METHODS

Four genes with a major role in HDL-C and TG metabolism APOA1, APOC2, APOC-III and LPL were sequenced in 2385 participants with mixed dyslipidemia in a randomized, double-blind, active-controlled study comparing therapy with FA alone, in combination with statins, or statin alone. Rare variants collapsing or SKAT methods were used for the analysis.

RESULTS

Synonymous rare variants in the LPL gene were significantly associated with absolute HDL-C change (P = 9 × 10(-4)) and TG percent change (P = 6.76 × 10(-4)) in those treated with FA only. Participants with these rare variants had a 2 mg/dL increase in HDL-C and 39 mg/dL decrease in TG as compared to 6.2 mg/dL increase in HDL-C and 100 mg/dL decrease in TG in those without these variants. Rare variants in the APOC-III gene were associated with a modest 3 mg/dL less reduction in APOB (P = 8.72 × 10(-4)) in those receiving FA and statin.

CONCLUSION

In individuals with mixed dyslipidemia rare synonymous variants within LPL gene were associated with attenuated response to FA therapy while APOCIII rare variants were associated with a modest effect on APOB response to FA-statin therapy. These results should be replicated in a similar clinical trial for further confirmation.

Pharmacogenomics of lipid-lowering therapies

Statins are the most widely used group of lipid-lowering drugs and they have been shown to be effective in the prevention of cardiovascular disease, primarily by reducing plasma low-density lipoprotein cholesterol concentrations and possibly through other pleiotropic effects. However, there are large variations in lipid responses to statins and some patients have intolerable muscle adverse drug reactions, which may in part be related to genetic factors. In the last decade, pharmacogenetic studies on statins ranging from the candidate gene approach to the more recent genome-wide association studies have provided evidence that genetic variations play an important role in determining statin responses. This review summarizes the current understanding on the pharmacogenomics of statins and other lipid-lowering drugs in current use.

Functional importance of apolipoprotein A5 185G in the activation of lipoprotein lipase

BACKGROUND

Apolipoprotein A5 (APOA5) over-expression enhances lipolysis of triglyceride (TG) through stimulation of lipoprotein lipase (LPL) activity; however, an APOA5 G185C variant was found associated with hypertriglyceridemia. The aim of this study was, therefore, to explore the importance of APOA5 185GG in the activation of LPL.

METHODS

A fragment containing mature human APOA5 cDNA was obtained by RT-PCR and subcloned into pET-15b vector. Site-directed mutagenesis was performed to generate 19 variants. Recombinant human APOA5 wild type and variants were produced in Escherichia coli, and then activation of LPL was measured.

RESULTS

Activity of APOA5 variants on LPL-mediated 1,2-dimyristoyl-sn-glycero-3-phosphocholine hydrolysis was reduced by 17 to 74% in comparison to wild type APOA5 (P<0.0001). All variants also showed reduced activation (P<0.0001) of LPL-mediated hydrolysis of very low-density lipoprotein (VLDL); activation abilities of APOA5 variants ranged from 31 to 81% of wild-type APOA5.

CONCLUSIONS

APOA5 residue 185G is very important in LPL-mediated VLDL hydrolysis, and any mutation at this residue will decrease LPL activation and concomitant TG modulation.