Steroid

A steroid is a terpenoid lipid characterized by a carbon skeleton with four fused rings, generally arranged in a 6-6-6-5 fashion.

Steroids can vary by the functional groups attached to these rings and the oxidation state of the rings. Hundreds of distinct steroids are found in plants, animals, and fungi. All steroids are biosynthetically derived either from the sterol lanosterol (animals and fungi) or the sterol cycloartenol (plants). Both sterols are derived from the cyclization of the triterpene squalene.^[1]

Origin

Steroids include estrogen (U.S spelling) or oestrogen (UK spelling), progesterone and androgen. Oestrogen and progesterone are made primarily in the ovary and in the placenta during pregnancy and testosterone in the testes. Certain neurons and glia in the central nervous system (CNS) express the enzymes that are required for the local synthesis of pregnane neurosteroids, either de novo or from peripherally derived sources.

Classification

Taxonomical/Functional

Some of the common categories of steroids:

Animal steroids
- Insect steroids
  - Ecdysteroids such as ecdysterone
- Vertebrate steroids
  - Steroid hormones
  - *Sex steroids are a subset of sex hormones that produce sex differences or support reproduction. They include androgens, estrogens, and progestagens.
  - *Corticosteroids include glucocorticoids and mineralocorticoids. Glucocorticoids regulate many aspects of metabolism and immune function, whereas mineralocorticoids help maintain blood volume and control renal excretion of electrolytes.
  - *Anabolic steroids are a class of steroids that interact with androgen receptors to increase muscle and bone synthesis. There are natural and synthetic anabolic steroids. These are the steroids used by athletes to increase performance.
  - Cholesterol which modulates the fluidity of cell membranes and is the principle constituent of the plaques implicated in atherosclerosis.
Plant steroids
- Phytosterols
- Brassinosteroids
Fungus steroids
- Ergosterols

Structural

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.

External links

Michael W. King's Medical Biochemistry. Steroids and retinoids are both terpenes which are hydrophobic, pass through cell membranes and bind to intracellular receptors. However, retinoic acid is not a steroid because is does not have the defining ring structure. See: Steroids and Related Hydrophobic Molecules.
"Biochemistry" by Jeremy M. Berg, John L. Tymoczko and Lubert Stryer (2002) W. H. Freeman and Co. steroid topics in this

References

Agis-Balboa RC. et al. (2006). "Characterization of brain neurons that express enzymes mediating neurosteroid biosynthesis". Proc Natl Acad Sci U S A 103, 14602-14607. PMID 16984997

Belelli D. and Lambert JJ. (2005). "Neurosteroids: endogenous regulators of the GABA<sub>A</sub> receptor". Nature Reviews Neuroscience 6, 565-575. PMID 15959466. Review

Pinna G. et al. (2005). "Fluoxetine and norfluoxetine stereospecifically and selectively increase brain neurosteroid content at doses that are inactive on 5-HT reuptake". Psychopharmacology (Berl) 186, 362-372. PMID 16432684. Review

Dubrovsky BO. (2005). "Steroids, neuroactive steroids and neurosteroids in psychopathology". Prog Neuropsychopharmacol Biol Psychiatry 29, 169-192, PMID 15694225. Review

Mellon SH. and Griffin LD. (2002) "Neurosteroids: biochemistry and clinical significance". Trends Endocrinol Metab 13, 35-43. PMID 11750861. Review

Citations

[1] http://www.chem.qmul.ac.uk/iubmb/enzyme/reaction/terp/lanost.html

The actual descriptive text portion of the article above (and its Contents menu) are licensed under the GNU Free Documentation License then in effect published by the Free Software Foundation. The text article uses material from http://en.wikipedia.org/wiki/Steroid (retrieval date: 2007-05-27) and is provided "as-is" and without warranty. Permission is granted to copy, distribute and/or modify only the actual descriptive text portion of the article above (and its Contents Box) under the GNU Free Documentation License. A copy of the license is available at: http://en.wikipedia.org/wiki/Wikipedia:Text_of_the_GNU_Free_Documentation_License. Any advertisements (or active links not embedded in the actual article) and the layout or selection thereof are excluded from such license.
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