The HMG-CoA reductase gene and lipid and lipoprotein levels: the multi-ethnic study of atherosclerosis

Changing the triglyceride diagnostic criteria of metabolic syndrome for African Americans

The incidence and prevalence of metabolic syndrome has been increasing globally with no signs of abating. Individuals with metabolic syndrome are at increased risk of multiple comorbidities, including cardiovascular disease and type 2 diabetes mellitus. Studies show that there is a paradoxical relationship in African Americans however, as they experience a higher rate of cardiovascular disease and type 2 diabetes mellitus despite having a lower prevalence of metabolic syndrome when compared to whites. The triglyceride paradox, an unusual phenomenon in which African Americans consistently express a more normal triglyceride status even when having conditions known to be characterized by high triglyceride levels, is believed to account for this paradoxical relationship. In this manuscript, we review the history and pathophysiology of metabolic syndrome while also discussing the importance of the triglyceride paradox in explaining the inverse relationship that exists between metabolic syndrome, cardiovascular disease, and type 2 diabetes mellitus in African Americans. In addition, we advocate for decreasing the triglyceride cutoff value when diagnosing metabolic syndrome in this population to more precisely determine who is at risk for developing type 2 diabetes mellitus and cardiovascular disease.

Genetic Polymorphisms in the HMGCR Gene and Associations with Cognitive Decline in Parkinson's Disease Patients

Parkinson's disease (PD) is a common neurodegenerative disease characterized by motor and non-motor symptoms including cognitive impairment and dementia. The etiopathogenesis of PD, as well as its protective and susceptibility factors, are still elusive. 3-Hydroxy-3-methyglutaryl coenzyme A reductase (HMGCR) is an enzyme regulating cholesterol synthesis. Single-nucleotide polymorphisms (SNPs) in the gene coding HMGCR have recently been correlated with the risk of Alzheimer's disease. Alternative splicing of exon 13 of the HMGCR transcript and its strongly associated HMGCR haplotype 7 (H7: rs17244841, rs3846662, rs17238540) may downregulate protein activity and cholesterol synthesis, with lower low-density lipoprotein cholesterol (LDL) levels associated with PD that may affect cognitive abilities. We genotyped three SNPs in the H7 HMGCR gene in 306 PD patients divided into three groups-without cognitive decline, with mild cognitive impairment (MCI), and with PD dementia-and in 242 healthy participants. A correlation between the rs17238540 genotype and PD susceptibility as well as a minor association between rs3846662 and cognitive status in PD patients was observed; however, the two-sided analysis of these groups did not reveal any significance. We observed a statistically significant elevated high-density lipoprotein cholesterol (HDL) plasma level in the minor allele carriers of rs17238540 and rs17244841 among PD patients. This study should be replicated in a larger population.

Vitamin D/Bone Mineral Density and Triglyceride Paradoxes Seen in African Americans: A Cross-Sectional Study and Review of the Literature

Vitamin D is known to have a positive effect on bone health. Despite the greater frequency of vitamin D deficiency in African Americans (AA), they have a higher bone mineral density (BMD) compared to whites, demonstrating a disconnect between BMD and vitamin D levels in AA. Another intriguing relationship seen in AA is the triglyceride (TG) paradox, an unusual phenomenon in which a normal TG status is observed even when patients house conditions known to be characterized by high TG levels, such as Type II diabetes. To the best of our knowledge, no study has examined whether these two paradoxical relationships exist simultaneously in AA subjects with Type II diabetes. In this study, we compared levels of blood markers, including HbA1c, TG, and vitamin D, measured as serum 25-hydroxyvitamin D [25(OH)VD] µM/mL, [25(OH)VD]/TG, calcium, and BMD in AA (n = 56) and white (n = 26) subjects with Type II diabetes to see whether these relationships exist concurrently. We found that AA subjects had significantly lower TG and [25(OH)VD] levels and a significantly higher BMD status compared to white subjects, even when the ages, BMI, duration of diabetes, HbA1c, and calcium levels were similar between the two groups. This demonstrates that these two paradoxical relationships exist simultaneously in Type II diabetic AA subjects. In addition to these findings, we discuss the current hypotheses in the literature that attempt to explain why these two intriguing relationships exist. This review also discusses four novel hypotheses, such as altered circulating levels and the potential role of estrogen and hydrogen sulfide on BMD and HMG-CoA reductase as a possible contributor to the TG paradox in AA subjects. This manuscript demonstrates that there are still many unanswered questions regarding these two paradoxical relationships and further research is needed to determine why they exist and how they can be implemented to improve healthcare.

Pharmacogenomics of lipid-lowering agents: the impact on efficacy and safety

Hyperlipidemia is a significant risk factor for cardiovascular disease morbidity and mortality. The lipid-lowering drugs are considered the cornerstone of primary and secondary prevention of atherosclerotic cardiovascular disease. Unfortunately, the lack of efficacy and associated adverse effects, ranging from mild-to-moderate to potentially life-threatening, lead to therapy discontinuation. Numerous reports support the role of gene polymorphisms in drugs' pharmacokinetic parameters and their associated adverse reactions. Therefore, this study aims to understand the pharmacogenomics of lipid-lowering drugs and the impact of genetic variants of key genes on the drugs' efficacy and toxicity. Indeed, genetically guided lipid-lowering therapy enhances overall safety, improves drug adherence and achieves long-term therapy.

A method to account for covariate-specific treatment effects when estimating biomarker associations in the presence of endogenous medication use

In the modern era, cardiovascular biomarkers are often measured in the presence of medication use, such that the observed biomarker value for the treated participants is different than their underlying natural history value. However, for certain predictors (e.g. age, gender, and genetic exposures) the observed biomarker value is not of primary interest. Rather, we are interested in estimating the association between these predictors and the natural history of the biomarker that would have occurred in the absence of treatment. Nonrandom medication use obscures our ability to estimate this association in cross-sectional observational data. Structural equation methodology (e.g. the treatment effects model), while historically used to estimate treatment effects, has been previously shown to be a reasonable way to correct endogeneity bias when estimating natural biomarker associations. However, the assumption that the effects of medication use on the biomarker are uniform across participants on medication is generally not thought to be reasonable. We derive an extension of the treatment effects model to accommodate effect modification. Based on several simulation studies and an application to data from the Multi-Ethnic Study of Atherosclerosis, we show that our extension substantially improves bias in estimating associations of interest, particularly when effect modifiers are associated with the biomarker or with medication use, without a meaningful cost of efficiency.

The pharmacogenomics of statins

The statin class of cholesterol-lowering drugs have been used for decades to successfully lower plasma cholesterol concentrations and cardiovascular risk. Adverse effects of statins are generally considered mild, but increase with age of patients and polypharmacy. One aspect of statin therapy that is still difficult for prescribers to predict is the individual's response to statin therapy. Recent advances in the field of pharmacogenomics have indicated variants of candidate genes that affect statin efficacy and safety. In this review, a number of candidates that affect statin pharmacokinetics and pharmacodynamics are discussed. Some of these candidates, in particular those involved in import and efflux of statins, have now been linked to increased risk of side effects. Furthermore, pharmacogenomic studies continue to reveal new players that are involved in the fine-tuning of the complex regulation of cholesterol homeostasis and response to statins.

The effects of age and gender on the relationship between HMGCR promoter-911 SNP (rs33761740) and serum lipids in patients with coronary heart disease

BACKGROUND

Hydroxymethylglutaryl-Coenzyme A Reductase (HMGCR) catalyzes the rate-limiting step of cholesterol biosynthesis. This enzyme is the target of the widely available cholesterol lowering statins. In this population-based case-control study, the frequencies of -911 C>A polymorphism (rs3761740) of the HMGCR gene in patients with coronary heart disease (CHD) and healthy subjects were investigated and the correlations between the different genotypes and hypercholesterolemia with cardiovascular risk factors were analyzed.

METHODS

The HMGCR genotypes were determined in 365 patients with CHD and 365 controls by PCR-RFLP assay. Anthropometric measurements were measured in all participants.

RESULTS

There was no significant difference in the genotype frequencies of the HMGCR polymorphism between the male subjects of both patient and control groups, however, the HMGCR-CC genotype was found to be more frequent in female patients with CHD than female controls (p=0.002). The HMGCR-CC genotype showed higher total-cholesterol (TC) and LDL-cholesterol (LDL-C) levels than the CA+AA genotypes in male CHD patients (p=0.018). Due to this significant sex interaction, a multivariate analysis was conducted on the patient group. In the multivariate logistic regression analysis, the HMGCR-CC genotype was significantly associated with age<55 (OR=2.837, p=0.001) and TC ≥ 5.18 mmol/L (OR=1.970, p=0.027) in male subjects. However, this association was not observed in female patients (p>0.05). This analysis confirmed that the HMGCR-CC genotype was associated with elevated TC levels in male CHD patients with age<55 years.

CONCLUSION

These results suggest that age and sex modify the contribution of the HMGCR-911 polymorphism to fasting serum TC, LDL-C levels and risk of CHD.

Extract of Wax Gourd Peel Prevents High-Fat Diet-Induced Hyperlipidemia in C57BL/6 Mice via the Inhibition of the PPARγ Pathway

Wax gourd is a popular vegetable in East Asia. In traditional Chinese medicine, wax gourd peel is used to prevent and treat metabolic diseases such as hyperlipidemia, hyperglycemia, obesity, and cardiovascular disease. However, there is no experimental evidence to support these applications. Here, we examined the effect of the extract of wax gourd peel (EWGP) on metabolic disorders in diet-induced C57BL/6 obese mice. In the preventive experiment, EWGP blocked body weight gain and lowered serum total cholesterol (TC), low-density lipoprotein cholesterol (LDL-c), liver TG and TC contents, and fasting blood glucose in mice fed with a high-fat diet. In the therapeutic study, we induced obesity in the mice and treated with EWGP for two weeks. We found that EWGP treatment reduced serum and liver triglyceride (TG) contents and fasting blood glucose and improved glucose tolerance in the mice. Reporter assay and gene expression analysis showed that EWGP could inhibit peroxisome proliferator-activated receptor γ (PPAR γ ) transactivities and could decrease mRNA levels of PPAR γ and its target genes. We also found that HMG-CoA reductase (HMGCR) was downregulated in the mouse liver by EWGP. Our data suggest that EWGP lowers hyperlipidemia of C57BL/6 mice induced by high-fat diet via the inhibition of PPAR γ and HMGCR signaling.

Individualized risk for statin-induced myopathy: current knowledge, emerging challenges and potential solutions

Skeletal muscle toxicity is the primary adverse effect of statins. In this review, we summarize current knowledge regarding the genetic and nongenetic determinants of risk for statin induced myopathy. Many genetic factors were initially identified through candidate gene association studies limited to pharmacokinetic (PK) targets. Through genome-wide association studies, it has become clear that SLCO1B1 is among the strongest PK predictors of myopathy risk. Genome-wide association studies have also expanded our understanding of pharmacodynamic candidate genes, including RYR2. It is anticipated that deep resequencing efforts will define new loci with rare variants that also contribute, and sophisticated computational approaches will be needed to characterize gene-gene and gene-environment interactions. Beyond environment, race is a critical covariate, and its influence is only partly explained by geographic differences in the frequency of known pharmacodynamic and PK variants. As such, admixture analyses will be essential for a full understanding of statin-induced myopathy.

Inflammation-induced atherosclerosis as a target for prevention of cardiovascular diseases from early life

Atherogenesis starts from the fetal life, and its natural course consists of interrelations between traditional risk factors and inflammatory, immune, and endothelial biomarkers. Even the early-stages of atherosclerotic lesions, i.e. fatty streaks present the features of chronic inflammation. Markers of inflammation are associated with insulin resistance and major atherosclerosis risk factors. Several studies have confirmed a relationship between surrogate markers of future cardiovascular disease with childhood obesity, notably abdominal obesity, as well as with the degree of obesity. Moreover, functional and structural changes are documented in arteries of children with a familial predisposition to atherosclerotic diseases; these changes are associated with clusters of inflammatory factors and markers of oxidation. In addition to the development of atheromatous plaques, inflammation also plays an essential role in the destabilization of artery plaques, and in turn in the occurrence of acute thrombo-embolic disorders. Markers of inflammation can provide predictive clinical information about outcomes of patients with acute coronary syndromes, independent of the extent of myocardial damage. Moreover, serum levels of the inflammatory markers might add prognostic information provided by traditional risk factors. Platelets have an important role in vascular inflammation and atherosclerosis and in the formation of mural thrombi. As lifestyle modification trials have been successful in decreasing endothelial dysfunction and the level of markers of inflammation among children and adolescents, it is suggested that in addition to expanding pharmacological therapies considered for secondary prevention of atherosclerotic diseases aiming to control the inflammatory process, the importance of primordial/primary prevention of atherosclerosis should be underscored.

Association of the functional variant in the 3-hydroxy-3-methylglutaryl-coenzyme a reductase gene with low-density lipoprotein-cholesterol in Japanese

BACKGROUND

The association between single nucleotide polymorphisms (SNPs) at 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR) and low-density lipoprotein-cholesterol (LDL-C) levels has been well replicated in genome-wide association studies (GWAS) of white populations. Recently, the common intronic SNP of HMGCR (rs3846662) has been reported to be a functional variant, influencing the alternative splicing of exon 13. The aim of this study was to examine the association between rs3846662 of HMGCR and the level of LDL-C in Japanese.

METHODS AND RESULTS

Significant differences in LDL-C levels were observed among the genotypes of rs3846662 (P=0.0002 (n=2,686) and P=0.004 (n=2,110)) for the Suita and Ehime samples, respectively. The G allele of rs3846662 was associated with higher LDL-C levels (beta, 3.56; P=4.91x10(-5)). Consistent with this observation, the risk G allele at rs3846662 was more prevalent in subjects with myocardial infarction (MI) (n=701) than in subjects without MI (n=3,118); 0.559 and 0.511 in MI cases and controls, respectively (nominal P=0.0038). The odds ratio adjusted for age, sex, diabetes, hypertension, and drinking and smoking habits was 1.15 (95% confidence interval 1.04-1.28; P=0.0075).

CONCLUSIONS

The previously reported association of rs3846662 with LDL-C levels was replicated in the present Suita and Ehime samples. The LDL-associated SNP, rs3846662, appears to confer susceptibility to MI in Japanese.