Rationale for targeting multiple lipid pathways for optimal cardiovascular risk reduction

Prevention of cardiovascular complications of the metabolic syndrome: focus on pharmacotherapy

The metabolic syndrome increases the risk of atherothrombotic cardiovascular disease (CVD) and diabetes. In turn, diabetes promotes the development of atheroma and is regarded as a coronary heart disease risk equivalent. A multifactorial therapeutic strategy is advocated for patients with the metabolic syndrome to improve cardiovascular risk factor profiles and to reduce the chances of developing type 2 diabetes. Individual components of the syndrome must be addressed using safe, efficacious, and cost-effective measures. There is general agreement that lifestyle modifications, including control of body weight, avoidance of central adiposity, adoption of an antiatherogenic diet, and regular physical activity, are crucial. However, as the magnitude of the individual components of the metabolic syndrome increases with time, lifestyle measures are often insufficient. An individual with metabolic syndrome will often require drug treatment for hyperglycemia, atherogenic dyslipidemia, and high blood pressure, together with antiplatelet therapy. Reducing the need for polypharmacy is an increasingly important consideration for clinicians and the pharmaceutical industry; to date, no single therapy has emerged that targets the root cause(s) of the syndrome. HMG-CoA reductase inhibitors are important agents that reduce CVD morbidity and mortality, in people with impaired fasting glucose or metabolic syndrome. Selective cannabinoid receptor antagonists appear promising because they improve or attenuate several key defects of the syndrome. Thiazolidinediones and metformin are presently licensed for treatment of type 2 diabetes but may prove to have a broader role in future. Novel insulin-sensitizing drugs are under investigation. Drugs that act to prevent or reverse endothelial dysfunction may be of particular utility in preventing cardiovascular disease, especially if initiated before tissue damage has become irreversible. Insulin therapy, which has antiinflammatory and endothelial protective properties, has been shown to reduce morbidity and mortality in high-risk nondiabetic patients during critical illness. Potential synergy between different classes of drugs with metabolic and/or cardiovascular protective properties merits further investigation.

Is combination therapy an effective way of reaching lipid goals in type 2 diabetes mellitus?

Type 2 diabetes mellitus is associated with a specific pattern of plasma lipid and lipoprotein abnormalities. Lipid goals are often not attained with statins alone, and combination lipid-lowering strategies may need to be considered in an attempt to further reduce the residual cardiovascular risk. Combination therapy utilizes various classes of lipid-lowering medications with different mechanisms of action and different effects on lipid levels. Clinical trial data support the efficacy of combining statins with fibrates, niacin, ezetimibe (cholesterol absorption inhibitor) and colesevelam (bile acid sequestrant) with the caveat that there are insufficient clinical trial data to show a further robust benefit on cardiovascular outcomes. Of the different combination therapy options to potentiate low-density lipoprotein cholesterol lowering in combination with a statin, colesevelam provides additional beneficial effects by further reducing hemoglobin A1c levels in Type 2 diabetes mellitus.

Ezetimibe/simvastatin 10/20 mg versus simvastatin 40 mg in coronary heart disease patients

BACKGROUND

Reducing low-density lipoprotein cholesterol (LDL-C) is the primary goal of therapy in patients with hypercholesterolemia and coronary heart disease (CHD).

METHODS

This double blind placebo-controlled study enrolled patients 18 to 75 years of age with primary hypercholesterolemia and established CHD who were taking a stable daily dose of simvastatin 20 mg. Patients were randomized to ezetimibe/simvastatin 10/20 mg (eze/simva; n = 56) or simvastatin 40 mg (simva; n = 56) for 6 weeks. Percent change from baseline in LDL-C, total cholesterol, high-density lipoprotein cholesterol (HDL-C), and triglycerides were assessed by use of the Student t test. The percent of patients achieving LDL-C less than 100 mg/dL (<2.6 mmol/L) or less than 80 mg/dL (<2.0 mmol/L) was analyzed via logistic regression with terms for treatment, baseline LDL-C, age, and gender.

RESULTS

Baseline characteristics were similar between groups. Treatment with eze/simva combination resulted in significantly greater reductions in LDL-C, total cholesterol, and triglycerides versus doubling the dose of simva to 40 mg (all P < .01). Significantly more patients achieved LDL-C less than 100 mg/dL (<2.6 mmol/L) and less than 80 mg/dL (<2.0 mmol/L) with ezetimibe/simvastatin versus doubling the dose of simva to 40 mg (73.2% vs 25.0%; P < .001) for simvastatin. Changes in HDL-C were similar between treatments. Both treatments were generally well tolerated.

CONCLUSION

In high-risk CHD patients with hypercholesterolemia, treatment with eze/simva combination resulted in significantly greater reductions in LDL-C, total cholesterol and triglycerides, as well as greater achievement of recommended LDL-C targets, compared with doubling the simvastatin dose to 40 mg over the 6-week period. (

CLINICAL TRIAL REGISTRATION NUMBER

NCT00423579).

Myriocin-mediated up-regulation of hepatocyte apoA-I synthesis is associated with ERK inhibition

Sphingolipids including sphingomyelin have been implicated as potential atherogenic lipids. Studies in apoE (apolipoprotein E)-null mice have revealed that the serine palmitoyltransferase inhibitor myriocin reduces plasma levels of sphingomyelin, ceramide, sphingosine-1-phosphate and glycosphingolipids and that this is associated with potent inhibition of atherosclerosis. Interestingly, hepatic apoA-I (apolipoprotein A-I) synthesis and plasma HDL (high-density lipoprotein)-cholesterol levels were also increased in apoE-null mice treated with myriocin. Since myriocin is a known inhibitor of ERK (extracellular-signal-related kinase) phosphorylation, we assessed the possibility that myriocin may be acting to increase hepatic apoA-I production via this pathway. To address this, HepG2 cells and primary mouse hepatocytes were treated with 200 muM myriocin for up to 48 h. Myriocin increased apoA-I mRNA and protein levels by approx. 3- and 2-fold respectively. Myriocin also increased apoA-I secretion up to 3.5-fold and decreased ERK phosphorylation by approx. 70%. Similar findings were obtained when primary hepatocytes were isolated from apoE-null mice that were treated with myriocin (intraperitoneal injection at a dose of 0.3 mg/kg body weight). Further experiments revealed that the MEK (mitogen-activated protein kinase/ERK kinase) inhibitor PD98059 potently inhibited ERK phosphorylation, as expected, and increased primary hepatocyte apoA-I production by 3-fold. These results indicate that ERK phosphorylation plays a role in regulating hepatic apoA-I expression and suggest that the anti-atherogenic mechanism of action for myriocin may be linked to this pathway.

Review of side-effect profile of combination ezetimibe and statin therapy in randomized clinical trials

Effective treatment to achieve target lipid parameters in high-risk patients may require combination drug therapies. Concerns regarding risks associated with such combination therapies may limit their use. A systematic overview of randomized controlled trials to assess risks associated with combination statin and ezetimibe therapy was performed. Eighteen trials were identified, including 14,471 patients. Follow-up ranged from 6 to 48 weeks. Compared with statin monotherapy, combination therapy did not result in significant absolute increases in risks of myalgias (risk difference -0.033, 95% confidence interval [CI] -0.06 to -0.01), creatine kinase increases (risk difference 0.011, 95% CI -0.02 to 0.04), rhabdomyolysis (risk difference -0.003, 95% CI -0.01 to 0.004), transaminase increases (risk difference -0.003, 95% CI -0.01 to 0.005), gastrointestinal adverse events (risk difference 0.005, 95% CI -0.03 to 0.04), or discontinuations because of an adverse event (risk difference -0.005, 95% CI -0.03 to 0.02). In conclusion, based on available randomized trials, the addition of ezetimibe to statin therapy did not increase the risk of myalgias, creatine kinase increases, rhabdomyolysis, transaminase increases, gastrointestinal adverse events, or discontinuations because of an adverse event. Additional trials are necessary to ensure that results of clinical trials are consistent with routine clinical practice, particularly in older patients with more co-morbid conditions and patients on higher statin doses.

Dual mechanisms for the fibrate-mediated repression of proprotein convertase subtilisin/kexin type 9

Proprotein convertase subtilisin/kexin type 9 (PCSK9) is associated with familial autosomal dominant hypercholesterolemia and is a natural inhibitor of the LDL receptor (LDLr). PCSK9 is degraded by other proprotein convertases: PC5/6A and furin. Both PCSK9 and the LDLr are up-regulated by the hypocholesterolemic statins. Thus, inhibitors or repressors of PCSK9 should amplify their beneficial effects. In the present study, we showed that PPARalpha activation counteracts PCSK9 induction by statins by repressing PCSK9 promoter activity and by increasing PC5/6A and furin expression. Quantification of mRNA and protein levels showed that various fibrates decreased PCSK9 and increased PC5/6A and furin expression. Fenofibric acid (FA) reduced PCSK9 protein content in immortalized human hepatocytes (IHH) as well as its cellular secretion. FA suppressed PCSK9 induction by statins or by the liver X receptor agonist TO901317. PCSK9 repression is occurring at the promoter level. We showed that PC5/6A and furin fibrate-mediated up-regulation is PPARalpha-dependent. As a functional test, we observed that FA increased by 30% the effect of pravastatin on the LDLr activity in vitro. In conclusion, fibrates simultaneously decreased PCSK9 expression while increasing PC5/6A and furin expression, indicating a broad action of PPARalpha activation in proprotein convertase-mediated lipid homeostasis. Moreover, this study validates the functional relevance of a combined therapy associating PCSK9 repressors and statins.

NCX 6560, a nitric oxide-releasing derivative of atorvastatin, inhibits cholesterol biosynthesis and shows anti-inflammatory and anti-thrombotic properties

We compared the lipid-lowering, vasodilating, anti-thrombotic and anti-inflammatory properties of NCX 6560, a novel NO-releasing derivative of atorvastatin, with those of atorvastatin. NCX 6560 and atorvastatin induced similar inhibition of cholesterol biosynthesis in rat smooth muscle cells (IC(50)=1.9+/-0.4 and 3.9+/-1.0 microM, respectively). However, in hyperlipidemic mice, a 5-week oral treatment with NCX 6560 (46.8 mg/kg/day, p.o.) was more effective than equivalent atorvastatin (40 mg/kg/day, p.o.) at lowering serum cholesterol (NCX 6560: -21% vs controls, P<0.05; atorvastatin: -14% vs control, P=NS). In norepinephrine-precontracted rabbit aortic rings, NCX 6560-induced vasodilation (EC(50)=53.5+/-8.3 microM) and in PC12 cells it stimulated cGMP formation (EC(50)=1.8+/-0.7 microM), while atorvastatin was inactive. In lipopolysaccharide from Escherichia coli (LPS)-treated RAW 264.7 macrophages, NCX 6560 reduced iNOS expression and dimer assembly more efficiently than atorvastatin and inhibited nitrite accumulation (IC(50)=6.7+/-1.6 microM) and TNFalpha release. U46619- or collagen plus epinephrine-induced platelet pulmonary thromboembolism in mice was reduced by NCX 6560 at 46.8 mg/kg p.o. (mortality: -44% and -56% vs vehicle, respectively; P<0.05), but not by atorvastatin 40 mg/kg, p.o. In the U46619-induced mortality model, isosorbide mononitrate (ISMN) (20 mg/kg, p.o.), a pure NO-donor, was also active (mortality: -40%, P<0.05). NCX 6560 significantly reduced ex vivo platelet adhesion to collagen at high shear (-31+/-1.3% vs vehicle), and so did ISMN (-33.3+/-1.7% vs vehicle). Atorvastatin was ineffective. NCX 6560, but not atorvastatin, reduced blood pressure in eNOS knockout mice (-16%, P<0.001 vs vehicle), an effect not observed in wild type mice. On the contrary, ISMN provoked a significant drop of blood pressure both in wild type (-20%, P<0.05 vs vehicle) and in eNOS-/- mice (-21%, P<0.05 vs vehicle). In conclusion, NCX 6560 exerts greater lipid-lowering, anti-thrombotic and anti-inflammatory effects than atorvastatin, due to a large extent to NO release.

Drug Insight: the role of statins in combination with ezetimibe to lower LDL cholesterol

The cardiovascular benefits of therapy with the 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins) are well documented. Undertreatment of dyslipidemia remains pervasive, however, and the introduction of more-aggressive optional LDL-cholesterol targets in US guidelines only heightens the challenges of reaching the target values. Combination therapy with a statin and the cholesterol absorption inhibitor ezetimibe could help in the management of patients who have an inadequate reduction in cholesterol after making changes to lifestyle or taking statins alone. The effects of the combination on cardiovascular risk remain speculative, however, and clinical trials are in development. In this Review we consider the rationale for combination therapy in the context of achieving LDL-cholesterol goals.