Types of Lipids IV

Suaib Luqman

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  1. Objectives
  • v To know about the sterols
  • v What are their significance
  • v How they act in a system
  1. Concept Map
  1. Description

 

3.1 Types of Lipids IV

 

 

Complex Lipids

 

 

Sterols

 

 

Cholesterol (Greek: chole-bile)

 

 

Is the main sterol (C27 alcohol) in the tissues of vertebrates rich in adrenals (10% w/w), gall stones, liver (0.2% w/w) and nervous tissues (2% w/w). Brain is principally cholesterol rich covering on-fourth of total free cholesterol avaialble in the vertebrate cadaver. Cyclopentanoperhydrophenanthrene ring (sterane) is a carbon structure of cholesterol and it is the first sterol isolated by FP Poulletier de La Salle (1758) from gall stones. In 1815, ME Chevreul isolated Cholesterine (Greek: khole-bile, stereos-solid) from the unsaponifiable fraction of animal fats. F Reinitzer (1888) proposed the accurate formula (C27H46O) but exact steric depiction of cholesterol structural came after the work of HO Wieland who won Nobel Prize in Chemistry (1927) for his work on the establishment of the bile acids and related substances and AOR Windaus who got the Nobel Prize in 1928 for establishing the connection of sterols with vitamins. RK Callow and FG Young (1936) have voted that steroids chemically allied to cholesterol. In 1913, D Steinberg proposed the central role of cholesterol in atherogenesis.

 

Cholesterol

 

 

In animal cell membrane, the concentration of cholesterol is usually high ranging from 30 to 50% (molar percentage of total lipids) in erythrocytes and as elevated as 80% in the membranes of ocular lens. Accordingly, cholesterol has numerous task in membranes varying from the control of phase behavior, offering mechanical strength, to precursor of hormones and vitamins and in scheming raft arrangement and membrane protein activity. Minor modifications of the side chain led to the replacement of cholesterol by sterols such as campesterol, b-sitosterol at cellular level. In the femoral gland of Acanthodactylus boskianus (male lizard) cholesterol is present in abundance and used as a scent blotching pheromone to ascertain dominance. In addition, cholesterol can also silhouette ester connections with secreted polypeptide and signaling molecules encoded by the hedgehog gene family that function in some molding actions amid metazoan evolvement. Sponges signify the richest source of peculiar sterols i.e. cholesterol and sterols, but bearing 1-3 extra carbon atoms at C24 with unusual features as quaternary alkyl groups, acetylenes, allenes, cyclopropene and cyclopropane rings. In class Demospongiae, 24-Isopropylcholesterol (with its analogue unsaturated at C22-C23) is abundant and characteristic of Neoproterozoic era (542-1000 million years) sediments and is the primeval  proof of fossil record for animals but absent the eumetazoans (bilaterian and cnidarians). In Calyx nicaensis, Nicasterol was identified.

 

In higher plants, the presence of cholesterol is mostly accepted and detected in vegetal oils in a diminutive percentage (5% of the total sterols) however, a high cholesterol content has been reported in the oil of Camelina (~200 mg per kg). Nevertheless, numerous investigation have divulged the presence of cholesterol in chloroplasts, pollens, higher plant leaves (~72% of the total sterols in that fraction). It is the only sterol of Laurencia paniculata and also foremost in most Rhodophyceae algae.

 

Lanosterol, the common precursor in the synthesis of cholesterol, is also found as a foremost component of the unsaponifiable fraction of wool fat (lanoline, ~15%). Gemmata obscuriglobus, a bacterium of Planctomycete, is capable to produce lanosterol and its unusual isomer, parkeol. Derivatives of lanosterol have been reported in methanotrophic bacteria. 4- methylcholestan-8 (14), 24-dien-3b-ol, an abundant derivative was first reported in Methylococcus capsulatus and afterward in other analogous bacteria.

 

 

Structure of 4-Methylcholestan-8(14), 24-dien-3b-ol

 

 

Compound with lanostane core (lucidenates, ganoderates) have been successfully isolated from a mushroom (Ganoderma lucidum). The presence of these sterols have led to the utilization of mushroom for curing bronchitis, cardiovascular, diabetes, gastritis, hepatitis, hypercholesterolemia, hypertension related pathologies in traditional Chinese and Japanese medicine.

 

In animal tissues, 7-dehydrocholesterol is present in minute amounts which get transformed to cholecalciferol (vitamin D3) on UV exposure. 24-dehydrocholesterol (Desmosterol), an intermediate product amid cholesterol and lanosterol is associated with myelination processes with an elevated echelon noticed in the brain of young animals and no desmosterol in adults. In astrocytes and spermatozoa of mammalian cells, it is an abundant membrane component. In red algae, 22-dehydrocholesterol and desmosterol are present in high concentrations. Desmosterolosis is a severe cognitive impairment and developmental defect in humans where desmosterol fails to get converted to cholesterol. In 1943, Gorgosterol was revealed by Bergmann from coral like animals (intracellular photosynthetic dinoflagellate symbionts belonging to zooxanthellae). The inventive structure abides a cyclopropane ring in the sidechain and unusual C-23 methyl groups refurbishing interest in marine sterols. Dinosterol (4a, 23, 24-trimethyl-5a-cholest-22E-en-3b-ol) is a unswerving biomarker usually found in dinoflagellates.

 

Structure of Dinosterol

 

In diatoms, 23-methyl sterols and their sterane counterpart were too explicitly recognized from the Jurassic era onwards.

 

Oxysterol

 

 

In the brain tissues, 24S-Hydroxycholesterol (a type of oxysterol) is primarily synthesized. In 1953, it was noticed in horse brain and named as cerebrosterol. 24S-Hydroxycholesterol has been proposed as a biochemical marker for Alzheimer disease protecting formation of b-amyloid peptide found in plaques. Other aspects of oxysterols have also been reviewed and reported.

In animal kingdom, starfishes have oxysterols illustrated by several hydroxylations with no complement. From the Henricia leviuscula (a Far Eastern starfish), the structure of 5a-cholestane-hexaol is revealed and specified underneath.

 

Chlorinated cholesterol

 

 

a-chlorohydrins (6-b-chloro-cholestane-(3b, 5a)-diol) and other chlorinated products are generated by myeloperoxidase–H2O2–Cl system after reaction with double bond of cholesterol second ring. Chlorohydrins are relatively firm, and have been found valuable as a lipoproteins markers oxidatively damaged by triggered phagocytes secreting myeloperoxidase. These stuffs were also produced in LDL and membrane of the cell ensuing exposure to myeloperoxidase system or HOCl. The chlorohydrins formation in cells might be unruly to membranes resulting in the lysis of the cell and death. They might also be used as biomarkers for monocyte / neutrophil activated oxidative damage.

 

  1. Summary

 

 

In this lecture we learnt about:

 

  • The Types of Sterols
  • Their Presence and Importance
you can view video on Types of Lipids IV

 

Weblinks

 

Books

 

1.       The Biology of Cholesterol and Related Steroids by Myant NB. 2014. Page 856 https://books.google.co.in/books?isbn=148328123X

2. Cholesterol by Sabine JR. 1977. https://books.google.co.in/books?isbn=0824765168

3. Desmosterol in Human Lactation by Fey MB. 1983. https://books.google.co.in/books?id=0e6KNwAACAAJ

4.   Biochemistry and Function of Sterols by Parish EJ, Nes WD. 1997. Page 194 https://books.google.co.in/books?isbn=0849376742

5.   An Investigation of Lanosterol 14[alpha]-demethylase by Zadlo JR. 1991. https://books.google.co.in/books?id=3W7nPgAACAAJ

 

 

Journals

 

  1. Deuel HJ. Lipid metabolism. Calif Med. 1950 Apr; 72 (4): 197-200.
  2. Vainio, S.; Jansen, M.; Koivusalo, M.; Rog, T.; Karttunen, M.; Vattulainen, I.; Ikonen, E. 2005. Significance of Sterol Structural Specificity: DESMOSTEROL CANNOT REPLACE CHOLESTEROL IN LIPID RAFTS. Journal of Biological Chemistry 281 (1): 348–355.
  3. Keber, R.; Rozman, D.; Horvat, S. 2012. Sterols in spermatogenesis and sperm maturation. The Journal of Lipid Research 54 (1): 20–33.Schroepfer, GJ, Jr. 2000. Oxysterols: modulators of cholesterol metabolism and other processes. Physiological reviews 80 (1): 361–554.
  4. Björkhem, I. 2002. Do oxysterols control cholesterol homeostasis? The Journal of Clinical Investigation 110 (6): 725–30.
  5. Ingemar Björkhem; Ulf Diczfalusy (2002). Oxysterols: Friends, Foes, or Just Fellow Passengers Arteriosclerosis, Thrombosis, and Vascular Biology 22 (5): 734–42.
  1. Russell DW. 2000. Oxysterol biosynthetic enzymes. Biochim. Biophys. Acta 1529 (1–3): 126–35.
  2. E. J. Corey, W. E. Russey, P. R. Ortiz de Montellano. 1966. 2,3-Oxidosqualene, an Intermediate in the Biological Synthesis of Sterols from Squalene. Journal of the American Chemical Society 88 (20): 4750–4751.
  3. Wright AD, Goclik E, König GM. Oxygenated analogues of gorgosterol and ergosterol from the soft coral Capnella lacertiliensis. J Nat Prod. 2003 Feb; 66 (2): 157-60.