Atorvastatin, enzyme inhibition

You decide to treat a patient who has very high levels of serum cholesterol with the statin drug Lipitor (atorvastatin). You know that this drug acts in the metabolic pathway leading to the synthesis of cholesterol. The substrate for the enzyme inhibited by the statin drugs is which of the following ... 

An enzyme (see Section 2.6) called HMG-CoA reductase is involved in the biosynthesis of cholesterol. Drugs such as atorvastatin (Lipitor) and simvastatin (Zocor) are competitive inhibitors of HMG-CoA reductase. They inhibit cholesterol synthesis by increasing the number of LDL receptors to take up the LDL. 

The statins, lovastatin (L), simvastatin (S), pravastatin (P), fluvastatin (F), cerivastatin, and atorvastatin, inhibit HMG CoA reductase. The active group of L, S, P, and F (or their metabolites) resembles that of the physiological substrate of the enzyme (A). L and S are lactones that are rapidly absorbed by the enteral route, subjected to extensive first-pass extraction in the liver, and there hydrolyzed into active metabolites. P and F represent the active form and, as acids, are actively transported by a specific anion carrier that moves bile acids from blood into liver and also mediates the selective hepatic uptake of the mycotoxin, amanitin (A), Atorvastatin has the longest duration of action. 

Co-enzyme Q10 concentrations were measured in blood from hypercholesterolemic subjects before and after exposure to atorvastatin 80 mg/day for 14 and 30 days in 34 subjects eligible for statin treatment (11). The mean blood concentration of co-enzyme Q10 was 1.26 pg/ml at baseline, and fell to 0.62 after 30 days of atorvastatin therapy. There was a statistically significant fall detectable after 14 days of treatment. The authors concluded that widespread inhibition of co-enzyme Q10 synthesis could explain the exercise intolerance, myalgia, and myoglobinuria that are observed with statin treatment. 

This category includes atorvastatin (Lipitor), fluvas-tatin (Lescol), lovastatin (Mevacor), pravastatin (Prava-chol), and simvastatin (Zocor) (Table 25-2). These drugs, known commonly as statins, are characterized by their ability to inhibit an enzyme known as 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase.96 This enzyme catalyzes one of the early steps of cholesterol synthesis, and drugs that inhibit HMG-CoA reductase decrease cholesterol produc-... 

One class of antihyperlipidemic drugs is the statins. Statins interfere with the biosynthesis of cholesterol (A.103) and specifically inhibit the enzyme 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase (Scheme A.l). The statins that have been approved by the FDA include lovastatin (Mevacor, A.104), simvastatin (Zocor, A.105), pravastatin (Prava-chol, A.106), atorvastatin (Lipitor, A.107), rosuvastatin (Crestor, A.108), and fluvastatin (Lescol, A.109) (Figure A.29). All six compounds are drawn here to highlight the similarities between HMG-CoA (A.99) and mevalonic acid (A.100), and the top portion of the various statins. As a class, the statins have been extremely successful in terms of sales and effective in decreasing LDL cholesterol levels in the blood. 

The above process has been improved and optimized. An almost 400-fold increase in volumetric productivity relative to the published enzymic reaction conditions has been achieved, resulting in a attractive process that has been run on up to 100-g scale in a single batch at a rate of 30.6 g/L/hr. The catalyst load has been improved by 10-fold as well, from 20 to 2.0 wt % DERA. These improvements were achieved by a combination of the discovery of a DERA with improved activity and reaction optimization to overcome substrate inhibition. The two stereogenic centers are set by DERA, with an ee of >99.9% and a diastereomeric excess of 96.6%. In addition, downstream chemical processes have been developed to convert the enzymic product efficiently to versatile intermediates applicable to the preparation of atorvastatin and rosuvastatin (Greenberg et al., 2004). 

All of these drugs have the same mode of action. They are HMG co-A reductase inhibitors. Simply stated, they inhibit the liver s production of an enzyme that s essential to the manufacture of cholesterol. These are very powerful drugs, the most potent of which are atorvastatin and rosuvastatin, and are capable of reducing cholesterol, especially LDL, by as much as 50 percent or even more. 

E. The statin class of drugs—Lipitor (atorvastatin), Mevacor (lovas-tatin), and Zocor (simvastatin)—is used to treat hypercholesterolemia. This class of drugs lowers cholesterol levels by inhibiting the biosynthesis of cholesterol. Specifically, these drugs inhibit the enzyme P-hydroxy-P-methylglutaryl-CoA (HMG-CoA) reductase, which catalyzes the reaction that converts HMG-CoA to mevalonate. This is the rate-limiting step of cholesterol biosynthesis. 

Lovastatin is a member of a class of drugs (atorvastatin and simvastatin are others in this class) called statins that are used to treat hypercholesterolemia. The statins act as competitive inhibitors of the enzyme HMG-CoA reductase. These molecules mimic the structure of the normal substrate of the enzyme (HMG-CoA) and act as transition state analogues. While the statins are bound to the enzyme, HMG-CoA cannot be converted to mevalonic acid, thus inhibiting the whole cholesterol biosynthetic process. Recent studies indicate that there may be important secondary effects of statin therapy because some of the medical benefits of statins are too rapid to be a result of decreasing atherosclerotic lesions. Statin therapy has been associated with reduced risks of dementia, Alzheimer disease, ischemic cerebral stroke, and other diseases that are not correlated with high cholesterol levels. Although this is still an active area of research, it appears that the pleiotropic effects of statins may be a result of a reduction in the synthesis of isoprenoid intermediates that are formed in the pathway of cholesterol biosynthesis. 

Atorvastatin (Lipitor) Antilipidemic agent Inhibits the enzyme HMG-CoA reductase and reduces the biosynthesis of cholesterol... 

Statins work by reducing the endogenous synthesis of cholesterol in the liver through the inhibition of an enzyme, HMG-CoA reductase (3-hydroxy-3-methylglutaryl-CoA, if you must know). As a result, more DDLs are taken up from the circulation by the liver to provide the cholesterol needed to synthesize bile acids. An example of a statin is atorvastatin and others have similar names. 

Atorvastatin is marketed in combination with the Ca2+-channel blocker amlodipine (Caduet) for patients with hypertension or angina as well as hypercholesterolemia. Atorvastatin is an HMG-CoA reductase inhibitor that increases the rate at which the body removes cholesterol from blood and reduces the production of cholesterol by inhibiting enzymes that catalyze early rate-limiting steps in cholesterol synthesis increases HDL reduces LDL, VLDL, and triglycerides. 

Lovastatin (Mevacor ) (3), simvastatin (Zocor ) (15), pravastatin (Pravachol ) (19), atorvastatin (Lipitor ) (20), cerivastatin (Baycol , withdrawn on August 1, 2003) (21), and fluvastatin (Lescol ) (22) were introduced to lower total cholesterol levels, and especially LDL-cholesterol levels to prevent coronary heart disease. These HMG-CoA inhibitors inhibit de novo synthesis of cholesterol in the liver. The rate-limiting enzyme in cholesterol synthesis is HMG-CoA reductase, which catalyzes the conversion of HMG-CoA to mevalonate. The resulting decrease in hepatic cholesterol synthesis leads to increased synthesis of... 

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