Steroid

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Gonane, the simplest possible steroid, shown with its IUPAC-recommended ring-lettering and atom-numbering. The gonane substructure is present in all substances called steroids.[1]
Cholesterol, a prototypical steroid present in all tissues of animals and the precursor to most other animal steroids via steroidogenesis, shown with its approved ring and atom conventions.[1]

A steroid is a type of organic compound that contains a characteristic arrangement of four cycloalkane rings that are joined to each other. Examples of steroids include the dietary lipid cholesterol, the sex hormones estradiol and testosterone and the anti-inflammatory drug dexamethasone.

The core of steroids is composed of seventeen carbon atoms bonded together that take the form of four fused rings: three cyclohexane rings (designated as rings A, B and C in the figure to the right) and one cyclopentane ring (the D ring). The steroids vary by the functional groups attached to this four-ring core and by the oxidation state of the rings. Sterols are special forms of steroids, with a hydroxyl group at position-3 and a skeleton derived from cholestane.[1]

Hundreds of distinct steroids are found in plants, animals and fungi. All steroids are made in cells either from the sterols lanosterol (animals and fungi, see below right) or from cycloartenol (plants). Both lanosterol and cycloartenol are derived from the cyclization of the triterpene squalene.[2]

Lanosterol, the biosynthetic precursor to animal steroids. The total number of carbons (30) reflects its triterpenoid origin.

Nomenclature[edit]

Steroids are a class of organic compounds with a chemical structure that contains the core of gonane or a skeleton derived therefrom. Usually, methyl groups are present at the carbons C-10 and C-13 – an alkyl side-chain at carbon C-17 may also be present.

Gonane, see above, is the simplest possible steroid and is composed of seventeen carbon atoms, bonded together to form four fused rings. The three cyclohexane rings (designated as rings A, B, and C in the figure below) form the skeleton of phenanthrene; ring D has a cyclopentane structure. Hence, together they are called cyclopentaphenanthrene.[3]

The more complex structure of cholic acid, a bile acid.

Commonly, steroids have a methyl group at the carbons C-10 and C-13 and an alkyl side chain at carbon C-17. Further, they vary by the configuration of the side chain, the number of additional methyl groups, and the functional groups attached to the rings. For example, sterols have a hydroxyl group attached at position C-3.

Some exemplary steroids with their structures:

The anabolic steroid testosterone, the principal male sex hormone.
Progesterone, a steroid hormone involved in the female menstrual cycle, pregnancy and embryogenesis.
Medrogestone, a synthetic drug with similar effects as progesterone.
β-Sitosterol, a phytosterol showing the hydroxyl group at C-3.

Types[edit]

Taxonomical/functional[edit]

Some of the common categories of steroids:

Structural[edit]

It is also possible to classify steroids based upon their chemical composition. One example of how MeSH performs this classification is available at the Wikipedia MeSH catalog. Examples from this classification include:

ClassExamplesNumber of carbon atoms
Cholestanescholesterol27
Cholanescholic acid24
Pregnanesprogesterone21
Androstanestestosterone19
Estranesestradiol18

Gonane (or steroid nucleus) is the parent (17-carbon tetracyclic) hydrocarbon molecule without any alkyl sidechains.[4]

Biological significance[edit]

Steroid and their metabolites are frequently used signalling molecules. The most notable examples are the steroid hormones.

Steroids along with phospholipids function as components of cell membranes. Steroids such as cholesterol decrease membrane fluidity.[5]

Similar to lipids, steroids represent highly concentrated energy stores. However steroids are not typically used as sources of energy. In mammals, they are normally metabolized and excreted.

Pharmacological actions[edit]

A number of drugs target the mevalonate pathway:

Biosynthesis and metabolism[edit]

Simplified version of latter part of steroid synthesis pathway, where the intermediates isopentenyl pyrophosphate (PP or IPP) and dimethylallyl pyrophosphate (DMAPP) form geranyl pyrophosphate (GPP), squalene and, finally, lanosterol, the first steroid in the pathways. Some intermediates are omitted for clarity.

Steroid biosynthesis is an anabolic metabolic pathway that produces steroids from simple precursors. A unique biosynthetic pathway is followed in animals compared to many other organisms, making the pathway a common target for antibiotics and other anti-infective drugs. In addition, steroid metabolism in humans is the target of cholesterol-lowering drugs such as statins.

In humans and other animals, the biosynthesis of steroids follows the mevalonate pathway that uses acetyl-CoA as building-blocks to form dimethylallyl pyrophosphate (DMAPP) and isopentenyl pyrophosphate (IPP).[6] In subsequent steps, DMAPP and IPP are joined to form geranyl pyrophosphate (GPP), which in turn is used to synthesize the steroid lanosterol. Further modifications of lanosterol into other steroids are classified steroidogenesis transformations.

Mevalonate pathway[edit]

The mevalonate pathway or HMG-CoA reductase pathway starts with acetyl-CoA and ends with dimethylallyl pyrophosphate (DMAPP) and isopentenyl pyrophosphate (IPP).

DMAPP and IPP in turn donate isoprene units, which are assembled and modified to form terpenes and isoprenoids,[7] which are a large class of lipids that include the carotenoids, and form the largest class of plant natural products.[8]

Here, the isoprene units are joined together to make squalene and then folded up and formed into a set of rings to make lanosterol.[9] Lanosterol can then be converted into other steroids such as cholesterol and ergosterol.[9][10]

Steroidogenesis[edit]

The human steroidogenesis, with the major classes of steroid hormones, individual steroids and enzymatic pathways. Note that changes in molecular structure compared to the respective precursor are highlighted with white circles.

Steroidogenesis is the biological process by which steroids are generated from cholesterol and transformed into other steroids.[11] The pathways of steroidogenesis differ between different species – as an example the pathways of human steroidogenesis are shown in this figure below: The major classes of steroid hormones and some prominent members of the human steroidogenesis are:

Locations of human steroidogenesis:

Regulation[edit]

Several key enzymes can be activated through DNA transcriptional regulation on activation of SREBP (Sterol Regulatory Element-Binding Protein-1 and -2).[citation needed] This intracellular sensor detects low cholesterol levels and stimulates endogenous production by the HMG-CoA reductase pathway, as well as increasing lipoprotein uptake by up-regulating the LDL receptor.[citation needed] Regulation of this pathway is also achieved by controlling the rate of translation of the mRNA, degradation of reductase and phosphorylation.[citation needed]

Alternative pathways[edit]

In plants and bacteria, the non-mevalonate pathway uses pyruvate and glyceraldehyde 3-phosphate as substrates.[7][13]

Metabolism[edit]

Steroids are oxidized mainly by cytochrome P450 oxidase enzymes, such as CYP3A4. These reactions introduce oxygen into the steroid ring and allow the structure to be broken up by other enzymes, to form bile acids as final products.[14] These bile acids can then be eliminated through secretion from the liver in the bile.[15] The expression of this oxidase gene can be upregulated by the steroid sensor PXR when there is a high blood concentration of steroids.[16]

Partial synthesis[edit]

Phytosterols, especially a mixture of soybean phytosterols, as starting materials can be converted into two kinds of steroid hormone intermediates through microbial transformation. Microbial catabolism of phytosterol sidechains yields either C-19 steroids, a precursor to most steroid hormones including sex hormones, or C-22 steroids, a precursor to adrenocortical hormones.

The chemical conversion of sapogenins to steroids — Marker degradation combined with Mexican barbasco trade — is a long established alternative to microbial transformation of phytosterols to steroids. It is however unsustainable since huge tubers of plants growing in the wild were harvested.[17][18]

Determination of structure and methods of analysis[edit]

Methods of isolation[edit]

History[edit]

A number of Nobel Prizes have been awarded for research involving steroids. These prizes include:

See also[edit]

References[edit]

  1. ^ a b c Moss GP (1989). "Nomenclature of Steroids (Recommendations 1989)". Pure & Appl. Chem. 61 (10): 1783–1822. doi:10.1351/pac198961101783.  PDF "IUPAC-IUB Joint Commission on Biochemical Nomenclature (JCBN). The nomenclature of steroids. Recommendations 1989". Eur. J. Biochem. 186 (3): 429–58. December 1989. doi:10.1111/j.1432-1033.1989.tb15228.x. PMID 2606099. 
  2. ^ "Lanosterol biosynthesis". Recommendations on Biochemical & Organic Nomenclature, Symbols & Terminology. International Union Of Biochemistry And Molecular Biology. 
  3. ^ PubChem 130801; 219-08-9 cyclopentaphenanthrene
  4. ^ Edgren RA, Stanczyk FZ (December 1999). "Nomenclature of the gonane progestins". Contraception 60 (6): 313. doi:10.1016/S0010-7824(99)00101-8. PMID 10715364. 
  5. ^ Sadava D, Hillis DM, Heller HC, Berenbaum MR (2011). Life: The Science of Biology 9th Edition. San Francisco: Freeman. pp. 105–114. ISBN 1-4292-4646-4. 
  6. ^ Grochowski L, Xu H, White R (2006). "Methanocaldococcus jannaschii uses a modified mevalonate pathway for biosynthesis of isopentenyl diphosphate". J Bacteriol 188 (9): 3192–8. doi:10.1128/JB.188.9.3192-3198.2006. PMC 1447442. PMID 16621811. 
  7. ^ a b Kuzuyama T, Seto H (2003). "Diversity of the biosynthesis of the isoprene units". Nat Prod Rep 20 (2): 171–83. doi:10.1039/b109860h. PMID 12735695. 
  8. ^ Dubey V, Bhalla R, Luthra R (2003). "An overview of the non-mevalonate pathway for terpenoid biosynthesis in plants". J Biosci 28 (5): 637–46. doi:10.1007/BF02703339. PMID 14517367. 
  9. ^ a b Schroepfer G (1981). "Sterol biosynthesis". Annu Rev Biochem 50: 585–621. doi:10.1146/annurev.bi.50.070181.003101. PMID 7023367. 
  10. ^ Lees N, Skaggs B, Kirsch D, Bard M (1995). "Cloning of the late genes in the ergosterol biosynthetic pathway of Saccharomyces cerevisiae—a review". Lipids 30 (3): 221–6. doi:10.1007/BF02537824. PMID 7791529. 
  11. ^ Hanukoglu I (Dec 1992). "Steroidogenic enzymes: structure, function, and role in regulation of steroid hormone biosynthesis.". J Steroid Biochem Mol Biol 43 (8): 779–804. doi:10.1016/0960-0760(92)90307-5. PMID 22217824. 
  12. ^ Rossier MF (2006). "T channels and steroid biosynthesis: in search of a link with mitochondria". Cell Calcium. 40 (2): 155–64. doi:10.1016/j.ceca.2006.04.020. PMID 16759697. 
  13. ^ Lichtenthaler H (1999). "The 1-Dideoxy-D-xylulose-5-phosphate pathway of isoprenoid biosynthesis in plants". Annu Rev Plant Physiol Plant Mol Biol 50: 47–65. doi:10.1146/annurev.arplant.50.1.47. PMID 15012203. 
  14. ^ Pikuleva IA (2006). "Cytochrome P450s and cholesterol homeostasis". Pharmacol. Ther. 112 (3): 761–73. doi:10.1016/j.pharmthera.2006.05.014. PMID 16872679. 
  15. ^ Zollner G, Marschall HU, Wagner M, Trauner M (2006). "Role of nuclear receptors in the adaptive response to bile acids and cholestasis: pathogenetic and therapeutic considerations". Mol. Pharm. 3 (3): 231–51. doi:10.1021/mp060010s. PMID 16749856. 
  16. ^ Kliewer S, Goodwin B, Willson T (2002). "The nuclear pregnane X receptor: a key regulator of xenobiotic metabolism". Endocr. Rev. 23 (5): 687–702. doi:10.1210/er.2001-0038. PMID 12372848. 
  17. ^ Conner AH, Nagaoka M, Rowe JW, Perlman D (August 1976). "Microbial conversion of tall oil sterols to C19 steroids". Appl. Environ. Microbiol. 32 (2): 310–1. PMC 170056. PMID 987752. 
  18. ^ Wang F-Q, Yao K, Wei D-Z. "From Soybean Phytosterols to Steroid Hormones, Soybean and Health". In El-Shemy H. Soybean and Health. InTech. doi:10.5772/18808. ISBN 978-953-307-535-8. 
  19. ^ "The Nobel Prize in Chemistry 1927". The Nobel Foundation. 
  20. ^ "The Nobel Prize in Chemistry 1928". The Nobel Foundation. 
  21. ^ "The Nobel Prize in Chemistry 1939". The Nobel Foundation. 
  22. ^ "The Nobel Prize in Physiology or Medicine 1950". The Nobel Foundation. 
  23. ^ "The Nobel Prize in Chemistry 1965". The Nobel Foundation. 
  24. ^ "The Nobel Prize in Chemistry 1969". The Nobel Foundation. 
  25. ^ "The Nobel Prize in Chemistry 1975". The Nobel Foundation. 

Further reading[edit]

External links[edit]