Statins: Epidrugs with effects on endothelial health?

BACKGROUND

Epigenetic events involving the methylation of CpG cites in DNA, histone modifications and noncoding RNAs correlated with many essential processes in human cells and diseases, such as cancer and cardiovascular diseases. HMG-CoA reductase inhibitors (statins)-the LDL cholesterol-lowering drugs-are broadly used in cardio- and cerebro-vascular diseases. It is well established that statins exert pleiotropic functions, but how they exert effects on epigenetic modifications independently of HMG-CoA reductase inhibition is not yet clear. Thereby, understanding these mechanisms may pave the way for further clinical application of statin therapy.

DESIGN

Following and electronic database search, studies reporting substantial effects of statins on epigenetic reprogramming in both cultured cells and in vivo models were retrieved and reviewed.

RESULTS

Epigenetic mechanisms play an essential role in cellular development and function, and data collected in the past few years have revealed that many of the pleiotropic properties of statins are mediated by epigenetic mechanisms. Furthermore, those 'nonclassical' effects are not limited to CV field but they would extend to other conditions such as malignancies.

CONCLUSION

This review suggests that the epigenetic effects of statins mediate, at least in part, the pleiotropic actions of these drugs but further validation of such effects in clinical studies is yet to be provided.

Pleiotropic and Adverse Effects of Statins-Do Epigenetics Play a Role?

Statins are widely used to prevent major cardiovascular events by lowering serum cholesterol. There is evidence that statins have pleiotropic effects-that is, cholesterol-independent effects-that may also confer protection from cardiovascular disease and potentially numerous other pathologies, including cancer. Statins also have a number of well described adverse effects, including myopathy, rhabdomyolysis, liver damage, and type 2 diabetes. This paper examines the evidence of epigenetic modifications as a contributory factor to the pleiotropic and adverse effects of statins. In vitro and animal studies have shown that statins can inhibit histone deacetylase activity and increase histone acetylation. Similarly, there is evidence that statins may inhibit both histone and DNA methyltransferases and subsequently demethylate histone residues and DNA, respectively. These changes have been shown to alter expression of various genes, including tumor suppressor genes and genes thought to have anti-atherosclerotic actions. Statins have also been shown to influence the expression of numerous microRNAs that suppress the translation of proteins involved in tumorigenesis and vascular function. Whether the adverse effects of statins may also have an epigenetic component has been less widely studied, although there is evidence that microRNA expression may be altered in statin-induced muscle and liver damage. As epigenetics and microRNAs influence gene expression, these changes could contribute to the pleiotropic and adverse effects of statins and have long-lasting effects on the health of statin users.

SIRT1 and SIRT7 expression in adipose tissues of obese and normal-weight individuals is regulated by microRNAs but not by methylation status

BACKGROUND/OBJECTIVE

Given their importance in the regulation of metabolism, sirtuins (SIRTs) constitute promising subjects of research on the pathogenesis of obesity and the metabolic syndrome. The aim of this study was to assess whether obesity in humans is associated with changes in the expression of SIRT genes in adipose tissue and whether epigenetic mechanisms, DNA methylation and microRNA (miRNA) interference, mediate in this phenomenon.

SUBJECTS/METHODS

The expression of SIRTs and of SIRT1 and SIRT7 mRNA-interacting miRNAs was evaluated by real-time PCR in visceral adipose tissue (VAT) and subcutaneous adipose tissue (SAT) of 58 obese (body mass index (BMI) >40 kg m^-2) and 31 normal-weight (BMI 20-24.9 kg m^-2) individuals. The methylation status of SIRTs was studied by the methylation-sensitive digestion/real-time PCR method.

RESULTS

SIRT1 mRNA levels were lower in adipose tissues of obese patients than of normal-weight controls (VAT: P=0.0002, SAT: P=0.008). In contrast, expression of SIRT7 was higher in adipose tissues of obese patients than in the control group (VAT: P=0.001, SAT: P=0.008). The mean methylation of the SIRT1 and SIRT7 CpG islands was similar in tissues with high and low expression of these genes, and there was no correlation between the level of expression and the level of methylation. On the other hand, expression of SIRT1 in VAT of obese subjects correlated negatively with the expression of miR-22-3p (P<0.0001, r_s=-0.514), miR-34a-5p (P=0.01, r_s=-0.326) and miR-181a-3p (P<0.0001, r_s=-0.536). In turn, expression of SIRT7 in VAT of slim individuals correlated negatively with the expression of miR-125a-5p (P=0.003, r_s=-0.562) and miR-125b-5p (P=0.018, r_s=-0.460).

CONCLUSIONS

We observed obesity-associated downregulation of SIRT1 and upregulation of SIRT7 mRNA levels that were not associated with the methylation status of their promoters. We found a negative correlation between mRNA levels of SIRT1 in VAT of obese individuals and SIRT7 in VAT of the normal-weight subjects and expression of the relevant miRNAs.