Statins action mechanisms

Mechanism of action of statins cholesterol synthesis pathway... 

HMG-CoA-Reductase Inhibitors. Figure 1 Mechanism of action of statins - cholesterol synthesis pathway. The conversion of acetyl CoA to cholesterol in the liver. The step of cholesterol biosynthesis inhibited by HMG-CoA reductase inhibitors (statins) is shown. 

Garlic s proven mechanisms of action include (a) inhibition of platelet function, (b) increased levels of two antioxidant enzymes, catalase and glutathione peroxidase, and (c) inhibition of thiol enzymes such as coenzyme A and HMG coenzyme A reductase. Garlic s anti-hyperlipidemic effects are believed to be in part due to the HMG coenzyme A reductase inhibition since prescription medications for hyperlipidemia have that mechanism of action (statins). It is unknown whether garlic would have the same drug interactions, side effects, and need for precautions as the statins. 

Prenylation has been implicated in the prevention of HIV infection. Statins have been used to inhibit HIV infection by interacting with Rho GTPases and suppress the intercellular adhesion required for viral entry. In another study with statins and HIV the mechanism of action was elucidated. The lypophilic statins... 

The lowered concentration of bile acids returning to the liver by the enterohepatic circulation results in derepression of 7-a-hydroxylase, the rate-limiting enzyme for conversion of cholesterol to bile acids. This results in increased use of cholesterol to replace the excreted bile acids and lowering of hepatic cholesterol (mechanism VI in Fig. 23.2). Thus, similar to the statins, the ultimate actions of the bile acid-sequestering resins are up-regulation of transcription of the LDL receptor gene, increased hepatic receptor activity, and lowering of plasma LDL cholesterol (mechanism VII in Fig. 23.2). 

Duriez P. Mecanismes d action des statines et des fibrates. [Mechanisms of actions of statins and fibrates.] Therapie 2003 58(1) 5-14. 

What is the mechanism of action of commonly used lipid-lowering drugs, such as statins and ezetimibe ... 

PUFAs are potent inhibitors of the HMG-CoA reductase enzyme and similar to statins are useful in the treatment of hyperlipidemias (99-102). Statins enhance plasma AA levels and decrease the ratio of EPA to AA significantly (100). This finding suggests that PUFAs mediate many actions of statins (103) and that this could be one mechanism by which they lower cholesterol levels. Statins and PUFAs have many overlap actions such as the inhibition of IL-6 and TNF-a production and NF-kB activation plus the ability to enhance eNO production thus, both possess anti-inflammatory actions and both are useful in atherosclerosis, coronary heart disease, osteoporosis, stroke, Alzheimer s disease, and inflammatory conditions such as lupus and cancer (3, 4, 94, 104-121). These similar and overlap actions strongly indicate that the molecular mechanisms of actions of statins and PUFAs are similar, if not identical. Furthermore, when a combination of statins and PUFAs are given together, a synergistic beneficial effect was seen in patients with combined hyperlipemia (122). 

If the patient with coronary artery disease also develops cardiac dysfunction, the same medications would be expected to apply, but for additional reasons. The re-instation of preconditioning mechanisms by ACEI administration has already been described. (I-blockers have additional mechanisms, such as an antiapoptotic and antioxidant action.276 In this situation oxidative stress is also predominant and may further exacerbate apoptotic mechanisms.277 The only drugs predictably diminishing oxidative stress in clinical usage are carvedilol and statins. The latter drug family is also used in heart failure. Exercise is also a standard preventive and therapeutic intervention in both the above categories. 

Despite inhibition of HMG-CoA reductase by statins, cells compensate by increasing enzyme expression several fold. However, the total body cholesterol is reduced by 20-40% due to increased expression of LDL-receptors after statin administration this enhances LDL (the major cholesterol carrying lipoprotein) clearance from serum with a net reduction of serum cholesterol (Chapter 20). Individuals who lack functional LDL-receptors (homozygous familial hypercholesterolemia. Chapter 20) do not benefit from statin therapy. However, statin therapy is useful in the treatment of heterozygous familial hypercholesterolemia. Since HMG-CoA reductase plays a pivotal role in the synthesis of many products vital for cellular metabolism, inhibitors of the enzyme may have toxic effects. Monitoring of liver and muscle function may be necessary to detect any toxicity of statin drug therapy. A decreased risk of bone fractures with statin therapy has been observed in subjects age 50 years or older, who are being treated for hypercholesterolemia. The mechanism of action of statins in bone metabolism may involve inhibition of prenylation... 

MECHANISM OF ACTION The bUe-acid sequestrants are highly positively charged and bind negatively charged bile acids. The resins are not absorbed, and the bound bile acids are excreted in the stool. Since >95% of bile acids are normally reabsorbed, interruption of this process depletes the pool of bile acids and increases hepatic bile-acid synthesis. As a result, hepatic cholesterol content declines, stimulating the production of LDL receptors. The increase in hepatic LDL receptors increases LDL clearance and lowers LDL-C levels, but this effect is partially offset by the enhanced cholesterol synthesis caused by upregulation of HMG-CoA reductase. Inhibition of reductase activity by a statin substantially increases the effectiveness of the resins. 

Background It is well known that hypercholesterolemia is a major risk factor in the progression of atherosclerosis, the major cause of cardiovascular diseases. Statins are widely used to treat hypercholesterolemia. The mechanism of action of these drugs is to reduce the endogenous production of cholesterol by inhibiting 3-hydroxy-3-methylglutaryl coenzyme (HMG-CoA) reductase. Atorvastatin (ATV, Lipitor) is one of the top-selling prescribed oral medications. The only known adverse effect is skeletal muscle toxicity (myopathy) that may be related to the formation of the lactone of the acidic side chain on the molecule. 

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