Interactive pathway map
Click on genes, proteins and metabolites below to link to respective articles. [§ 1]
Statin Pathway edit
- ↑ The interactive pathway map can be edited at WikiPathways: "Statin_Pathway_WP430".
The discovery of HMG-CoA (3-hydroxy-3-methylglutaryl-CoA) reductase inhibitors, called statins, was a breakthrough in the prevention of hypercholesterolemia and related diseases. Hypercholesterolemia is considered to be one of the major risk factors for atherosclerosis which often leads to cardiovascular, cerebrovascular and peripheral vascular diseases. [1] The statins inhibit cholesterol synthesis in the body and that leads to reduction in blood cholesterol levels, which is thought to reduce the risk of atherosclerosis and diseases caused by it. [2]
In the mid-19th century, a German pathologist named Rudolf Virchow discovered that cholesterol was to be found in the artery walls of people that died from occlusive vascular diseases, like myocardial infarction. The cholesterol was found to be responsible for the thickening of the arterial walls and thus decreasing the radius in the arteries which leads in most cases to hypertension and increased risk of occlusive vascular diseases. [2]
In the 1950s the Framingham heart study led by Dawber revealed the correlation between high blood cholesterol levels and coronary heart diseases. Following up from that study the researchers explored a novel way to lower blood cholesterol levels without modifying the diet and lifestyle of subjects suffering with elevated blood cholesterol levels. The primary goal was to inhibit the cholesterol biosynthesis in the body. Hence HMG-CoA reductase (HMGR) became a natural target. HMGR was found to be the rate-limiting enzyme in the cholesterol biosynthetic pathway. There is no build-up of potentially toxic precursors when HMGR is inhibited, because hydroxymethylglutarate is water-soluble and there are alternative metabolic pathways for its breakdown. [2] [3]
In the 1970s the Japanese microbiologist Akira Endo first discovered natural products with a powerful inhibitory effect on HMGR in a fermentation broth of Penicillium citrinum, during his search for antimicrobial agents. The first product was named compactin (ML236B or mevastatin). Animal trials showed very good inhibitory effect as in clinical trials, however in a long term toxicity study in dogs it resulted in toxic effects at higher doses and as a result was believed to be too toxic to be given to humans. In 1978, Alfred Alberts and colleagues at Merck Research Laboratories discovered a new natural product in a fermentation broth of Aspergillus terreus , their product showed good HMGR inhibition and they named the product mevinolin, which later became known as lovastatin. [2] [3] [4]
The cholesterol controversy began in the early promotion of statins. [2]
Statins are a competitive antagonists of HMG CoA, as they directly compete with the endogenous substrate for the active site cavity of HMGR. Statins are also noncompetitive with the cosubstrate NADPH (nicotinamide adenine dinucleotide phosphate). [5] By blocking the HMGR enzyme they inhibit the synthesis of cholesterol via the mevalonate pathway. The end result is lower LDL (Low Density Lipoprotein), TG (Triglycerides) and total cholesterol levels as well as increased HDL (High Density Lipoprotein) levels in serum. [2] [3] [4]
Click on genes, proteins and metabolites below to link to respective articles. [§ 1]
The ideal statin should have the following properties: [6]
One of the main design objectives of statin design is the selective inhibition of HMGR in the liver, as cholesterol synthesis in non-hepatic cells is needed for normal cell function and inhibition in non-hepatic cells could possibly be harmful. [7]
The essential structural components of all statins are a dihydroxyheptanoic acid unit and a ring system with different substituents. The statin pharmacophore is modified hydroxyglutaric acid component, which is structurally similar to the endogenous substrate HMG CoA and the mevaldyl CoA transition state intermediate (Figure 1). The statin pharmacophore binds to the same active site as the substrate HMG-CoA and inhibits the HMGR enzyme. It has also been shown that the HMGR is stereoselective and as a result all statins need to have the required 3R,5R stereochemistry. [8]
The statins differ with respect to their ring structure and substituents. These differences in structure affect the pharmacological properties of the statins, such as: [6]
Statins have sometimes been grouped into two groups of statins according to their structure. [9]
Type 1 statins Statins that have substituted decalin-ring structure that resemble the first statin ever discovered, mevastatin have often been classified as type 1 statins due to their structural relationship. Statins that belong to this group are: [9]
Type 2 statins Statins that are fully synthetic and have larger groups linked to the HMG-like moiety are often referred to as type 2 statins. One of the main differences between the type 1 and type 2 statins is the replacement of the butyryl group of type 1 statins by the fluorophenyl group of type 2 statins. This group is responsible for additional polar interactions that causes tighter binding to the HMGR enzyme. Statins that belong to this group are: [9]
Lovastatin is derived from a fungus source and simvastatin and pravastatin are chemical modifications of lovastatin and as a result do not differ much in structure from lovastatin. [7] All three are partially reduced napthylene ring structures. Simvastatin and lovastatin are inactive lactones which must be metabolized to their active hydroxy-acid forms in order to inhibit HMGR. [7] Type 2 statins all exist in their active hydroxy-acid forms. Fluvastatin has indole ring structure, while atorvastatin and rosuvastatin have pyrrole and pyrimidine based ring structure respectively. The lipophilic cerivastatin has a pyridine-based ring structure.
Studies have shown that statins bind reversibly to the HGMR enzyme. The affinity of statins for HGMR enzyme is in the nanomolar range, while the natural substrate's affinity is in the micromolar range. [10] Studies have shown that statins use the conformational flexibility of the HMGR enzyme that causes a shallow hydrophobic groove that the statins exploit and is used to accommodate their hydrophobic moieties. [11] The specificity and the tight binding of statins is due to orientation and bonding interactions that form between the statin and the HMGR enzyme. [9] Polar interactions are formed between the HMG-moiety and residues that are located in the cis loop of the enzyme. These polar interactions are between Ser684, Asp690, Lys691 and Lys692 (Figure 4). The terminal carboxylate of the HMG moiety forms a salt bridge with the cationic Lys735 of the enzyme. In addition to the polar interaction, Lys691 participates in a hydrogen bonding network with Glu559, Asp767 and the O5 hydroxyl group of the hydroxyglutartic acid component of the statins. Van der Waals interactions are formed between the hydrophobic side chains of the enzyme, which involve the Leu562, Val683, Leu853, Ala856 and Leu857 and the statins. [9] Type 2 statins form polar interaction between the fluorine atom on the fluorophenyl group and the guanidinium group of Arg590. [11] In addition to these interactions atorvastatin and rosuvastatin also form unique hydrogen bonds between Ser565 residue and either a carbonyl oxygen atom (atorvastatin) or a sulfone oxygen atom (rosuvastatin). A unique polar interaction between the Arg568 side chain and the electronegative sulfone group on rosuvastatin makes it the statin that has the greatest number of bonding interactions with HGMR. [9]
All statins have the same pharmacophore so the difference in their pharmacodynamic effect is mostly based on the substituents. The activity of each statin is dependent on the binding affinity of the compound for the substrate site and the length of time it binds to the site. [5] Type 2 statins have unique fluorophenyl group that causes additional polar interaction between the enzyme and the statins, which results in a tighter binding to the enzyme. The newest statin, rosuvastatin has a unique polar methane sulfonamide group, which is quite hydrophilic and confers low lipophilicity. The sulfonamide group forms a unique polar interaction with the enzyme. As a result, rosuvastatin has superior binding affinity to the HMGR enzyme compared to the other statins, which is directly related to its efficiency to lower LDL cholesterol. [6]
Lipophilicity of the statins is considered to be quite important since the hepatoselectivity of the statins is related to their lipophilicity. The more lipophilic statins tend to achieve higher levels of exposure in non-hepatic tissues, while the hydrophilic statins tend to be more hepatoselective. The difference in selectivity is because lipophilic statins passively and non-selectively diffuse into both hepatocyte and non-heptatocyte, while the hydrophilic statins rely largely on active transport into hepatocyte to exert their effects. [5] [12] High hepatoselectivity is thought to translate into reduced risk of adverse effects. [7] It has been reported that the organic anion transporting polypeptide (OATP) is important for the hepatic uptake of hydrophilic statins such as rosuvastatin and pravastatin. [5] [12] OATP-C is expressed in liver tissue on the basolateral membrane of hepatocytes and is considered to be a potential contributor for the low IC50 for rosuvastatin in hepatocytes. Of the marketed statins, cerivastatin was the most lipophilic and also had the largest percentage of serious adverse effects due to its ability to inhibit vascular smooth muscle proliferation and as a result was voluntarily removed from the market by the manufacturer. [5]
| Cerivastatin | Simvastatin | Fluvastatin | Atorvastatin | Rosuvastatin | Pravastatin | |
|---|---|---|---|---|---|---|
| Log D Class | 1,50–1,75 | 1,50–1,75 | 1,00–1,25 | 1,00–1,25 | -0,25–(-0,50) | -0,75–(-1,0) |
All statins are metabolized by the liver, which causes their low systemic bioavailability. [13] Lovastatin and simvastatin are administered in their lactone forms, which is more lipophilic than their free acid forms, and therefore they have to be activated by hydrolysis to the active anionic carboxylate form. [8] [13] Cytochrome P450(CYP) isoenzymes are involved in the oxidative metabolism of the statins, with CYP3A4 and CYP2C9 isoenzymes being the most dominant. CYP3A4 isoenzyme is the most predominant isoform involved in metabolism of lovastatin, simvastatin, atorvastatin and cerivastatin. [8] [13] CYP2C9 isoenzyme is the most predominant isoform involved in metabolism of Fluvastatin, but CYP3A4 and CYP2C8 isoenzymes also contribute to the metabolism of Fluvastatin. [13] Rosuvastatin is metabolized to a small degree by CYP2C9 and to a lesser extent by CYP2C19 isoenzymes. Pravastatin is not metabolized by CYP isoenzymes to any appreciable extent. [6] [8] [13] The statins that have the ability to be metabolized by multiple CYP isoenzymes may therefore avoid drug accumulation when one of the pathways is inhibited by co-administered drugs. [13]
| Drug | Reduction in LDL-C (%) | Increase in HDL-C (%) | Reduction in TG (%) | Reduction in TC (%) | Metabolism | Protein binding (%) | T1/2 (h) | Hydrophilic | IC50 (nM) [6] |
|---|---|---|---|---|---|---|---|---|---|
| Atorvastatin | 26 – 60 | 5 – 13 | 17 – 53 | 25 – 45 | CYP3A4 | 98 | 13–30 | No | 8 |
| Lovastatin | 21 – 42 | 2 – 10 | 6 – 27 | 16 – 34 | CYP3A4 | >95 | 2 – 4 | No | NA |
| Simvastatin | 26 – 47 | 8 – 16 | 12 – 34 | 19 – 36 | CYP3A4 | 95 – 98 | 1 – 3 | No | 11 |
| Fluvastatin | 22 – 36 | 3 – 11 | 12 – 25 | 16 – 27 | CYP2C9 | 98 | 0,5 – 3,0 | No | 28 |
| Rosuvastatin | 45 – 63 | 8 – 14 | 10 – 35 | 33 – 46 | CYP2C9 | 88 | 19 | Yes | 5 |
| Pravastatin | 22 – 34 | 2 – 12 | 15 – 24 | 16 – 25 | Sulfation | 43 – 67 | 2 – 3 | Yes | 44 |
With the recent elucidation of the structures of the catalytic portion of human HMGR enzyme complexed with six different statins by a series of crystallography studies, new possibilities have opened up for the rational design and optimization of even better HGMR inhibitors. [15]
A new study using comparative molecular field analysis (CoMFA) to establish three-dimensional quantitative structure-activity relationship (3D QSAR), while searching for novel active pharmacophores as potentially potent HGMR inhibitors, was recently published. Using this novel technique researchers were able to screen for compounds with high screening scores. In addition to the conventional statin-like compounds with HMG-like moiety, eight additional compounds with completely different pharmacophore structure were found. This structure-based virtual screening procedure is considered promising for rational quest and optimization of potential novel HGMR inhibitors. [15]
Statins, also known as HMG-CoA reductase inhibitors, are a class of lipid-lowering medications that reduce illness and mortality in those who are at high risk of cardiovascular disease. They are the most commonly prescribed cholesterol-lowering drugs.
Dyslipidemia is a metabolic disorder characterized by abnormally high or low amounts of any or all lipids or lipoproteins in the blood. Dyslipidemia is a risk factor for the development of atherosclerotic cardiovascular diseases (ASCVD), which include coronary artery disease, cerebrovascular disease, and peripheral artery disease. Although dyslipidemia is a risk factor for ASCVD, abnormal levels don't mean that lipid lowering agents need to be started. Other factors, such as comorbid conditions and lifestyle in addition to dyslipidemia, is considered in a cardiovascular risk assessment. In developed countries, most dyslipidemias are hyperlipidemias; that is, an elevation of lipids in the blood. This is often due to diet and lifestyle. Prolonged elevation of insulin resistance can also lead to dyslipidemia. Likewise, increased levels of O-GlcNAc transferase (OGT) may cause dyslipidemia.
The mevalonate pathway, also known as the isoprenoid pathway or HMG-CoA reductase pathway is an essential metabolic pathway present in eukaryotes, archaea, and some bacteria. The pathway produces two five-carbon building blocks called isopentenyl pyrophosphate (IPP) and dimethylallyl pyrophosphate (DMAPP), which are used to make isoprenoids, a diverse class of over 30,000 biomolecules such as cholesterol, vitamin K, coenzyme Q10, and all steroid hormones.
Atorvastatin, sold under the brand name Lipitor among others, is a statin medication used to prevent cardiovascular disease in those at high risk and to treat abnormal lipid levels. For the prevention of cardiovascular disease, statins are a first-line treatment. It is taken by mouth.
Simvastatin, sold under the brand name Zocor among others, is a statin, a type of lipid-lowering medication. It is used along with exercise, diet, and weight loss to decrease elevated lipid levels. It is also used to decrease the risk of heart problems in those at high risk. It is taken by mouth.
Fluvastatin is a member of the statin drug class, used to treat hypercholesterolemia and to prevent cardiovascular disease.
Rosuvastatin, sold under the brand name Crestor among others, is a statin medication, used to prevent cardiovascular disease in those at high risk and treat abnormal lipids. It is recommended to be used together with dietary changes, exercise, and weight loss. It is taken orally.
Pravastatin, sold under the brand name Pravachol among others, is a statin medication, used for preventing cardiovascular disease in those at high risk and treating abnormal lipids. It is suggested to be used together with diet changes, exercise, and weight loss. It is taken by mouth.
Lovastatin, sold under the brand name Mevacor among others, is a statin medication, to treat high blood cholesterol and reduce the risk of cardiovascular disease. Its use is recommended together with lifestyle changes. It is taken by mouth.
Cerivastatin is a synthetic member of the class of statins used to lower cholesterol and prevent cardiovascular disease. It was marketed by the pharmaceutical company Bayer A.G. in the late 1990s, competing with Pfizer's highly successful atorvastatin (Lipitor). Cerivastatin was voluntarily withdrawn from the market worldwide in 2001, due to reports of fatal rhabdomyolysis.
Ezetimibe is a medication used to treat high blood cholesterol and certain other lipid abnormalities. Generally it is used together with dietary changes and a statin. Alone, it is less preferred than a statin. It is taken by mouth. It is also available in the fixed combinations ezetimibe/simvastatin, ezetimibe/atorvastatin, ezetimibe/rosuvastatin, and ezetimibe/bempedoic acid.
HMG-CoA reductase is the rate-controlling enzyme of the mevalonate pathway, the metabolic pathway that produces cholesterol and other isoprenoids. HMGCR catalyzes the conversion of HMG-CoA to mevalonic acid, a necessary step in the biosynthesis of cholesterol. Normally in mammalian cells this enzyme is competitively suppressed so that its effect is controlled. This enzyme is the target of the widely available cholesterol-lowering drugs known collectively as the statins, which help treat dyslipidemia.
Ezetimibe/simvastatin is a drug combination used for the treatment of dyslipidemia. It is a combination of ezetimibe and the statin drug simvastatin.
Mevastatin is a hypolipidemic agent that belongs to the statins class.
Monascus purpureus is a species of mold that is purplish-red in color. It is also known by the names ang-khak rice mold, corn silage mold, maize silage mold, and rice kernel discoloration.
Pitavastatin is a member of the blood cholesterol lowering medication class of statins.
Mexazolam is a drug which is a benzodiazepine derivative. Mexazolam has been trialed for anxiety and was found to be effective in alleviating anxiety at one week follow-up. Mexazolam is metabolised via the CYP3A4 pathway. HMG-CoA reductase inhibitors including simvastatin, simvastatin acid, lovastatin, fluvastatin, atorvastatin and cerivastatin inhibit the metabolism of mexazolam, but not the HMG-CoA reductase inhibitor pravastatin. Its principal active metabolites are chlorodesmethyldiazepam and chloroxazepam.
Lanosterol synthase (EC 5.4.99.7) is an oxidosqualene cyclase (OSC) enzyme that converts (S)-2,3-oxidosqualene to a protosterol cation and finally to lanosterol. Lanosterol is a key four-ringed intermediate in cholesterol biosynthesis. In humans, lanosterol synthase is encoded by the LSS gene.
Bruce D. Roth is an American organic and medicinal chemist who trained at Saint Joseph's College, Iowa State University and the University of Rochester, and, at the age of 32, discovered atorvastatin, the statin-class drug sold as Lipitor that would become the largest-selling drug in pharmaceutical history. His honours include being named a 2008 Hero of Chemistry by the American Chemical Society, and being chosen as the Perkin Medal awardee, the highest honour given in the U.S. chemical industry, by the Society of Chemical Industry, American section in 2013.
A steroidogenesis inhibitor, also known as a steroid biosynthesis inhibitor, is a type of drug which inhibits one or more of the enzymes that are involved in the process of steroidogenesis, the biosynthesis of endogenous steroids and steroid hormones. They may inhibit the production of cholesterol and other sterols, sex steroids such as androgens, estrogens, and progestogens, corticosteroids such as glucocorticoids and mineralocorticoids, and neurosteroids. They are used in the treatment of a variety of medical conditions that depend on endogenous steroids.