Tuesday, June 17, 2008

Sphingosomes and sphingolipids

Sphingosomes are similar in structure to liposomes but in sphingosomes, lipids namely sphingolipids are responsible for making up the bilayer of sphingosomes.

Figure: Sphingolipids
(Murray S. Webb et al.) The formulations have enhanced stability and thus are used in methods for improved drug delivery and effective treatment.

Sphingolipids:
They belong to a class of lipids i.e. Membrane lipids. Sphingolipids come from the combination of sphingosine (a long chain base), which is an amino alcohol (and aliphatic in nature), and fatty acid.It is the simplest sphingolipid and is also referred to as sphingoid base. They have a head, which is polar in nature, and two tails, which are nonpolar.

The following mnemonic will help you a lot in remembering the structure of shingosine.

Sphingolipids are present in plasma membranes.

Types of sphingolipids:

1. Ceramide:
It consists of Fatty acid chain and sphingosine linked through amide linkage. It is ordinarily present in all sphingolipids.

These are the precursors of glycolipids and phospholipids having a wide range of function in the tissues.

2. Sphingophosphlipids
    a. Sphingomyelin
    It consists of Phosphoethanolamine or phosphocholine and 1-hydroxy group of a ceramide linked through ester linkage.Sphingomyelin is structurally similar to phosphatidylcholine but biologically and physically it is different.

3. Glycosphingolipids:
     a. Cerebrosides
     b. Sulfatides (Sulfated cerebrosides)
     c. Globosides
     d. Gangliosides




Synthesis of sphingolipids:
Synthesis of sphingolipids takes place in Endoplasmic reticulum. Following is the pathway for the synthesis of sphingolipids.

In the first step, Palmitoyl-CoA alongwith serine results into beta ketosphinganine to sphinganine to N-acylsphinganine to Ceramide containing sphingosine to Cerebroside and sphingomyelin.

Sphingomyelin cycle:
Sphingomyelin cycle is used to show a relationship between the metabolic products of sphingolipids.



Free sphingosine and certain other long chain bases work as mediators for many of the cellular processes. Sphingosine 1-phosphate and ceramide 1-phosphate increases mitosis.

Degradation of sphingolipids:
These are degraded by lysosomal enzymes.

Presence of sphingolipids in Micro-organisms:
Sphingolipids are also found in some genera of bacteria like sphingomonas and sphingobacterium.

Uses of sphingolipids:
They work as the site of adhesion of extracellular proteins. Sphingolipids are important in cell recognition and signal transmission/transduction.
Sphingolipids form the myelin sheath around the nerves in central nervous system.

Diseases in which sphingolipids are involved:
1. Microbial infections
2. Diabetes
3. Alzheimer's disease
4. Certain cancers
5. Some diseases of the respiratory and cardiovascular systems and
6. Some of the neurological syndromes

References:
Murray S. Webb, Marcel B. Bally, Lawrence D. Mayer, James J. Miller, Paul G. Tardi, Sphingosomes for enhanced drug delivery. Patent number: 5814335.

Further Reading:
Delivery System Handbook for Personal Care and Cosmetic Products : Technology, Applications and Formulations (Breakthroughs in Personal Care and Cosmetic Technology) by Meyer R. Rosen

Encyclopedia of Pharmaceutical Technology by James Swarbrick

Hannun, Y. A. 1994. The sphingomyelin cycle and the second messenger function of ceramide. Journal of Biological Chemistry, Vol. 269, No. 5.

http://lipidlibrary.aocs.org/lipids/introsph/index.htm

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