About beta glucans and lectins and starch and more

What is a glucan?

These are polysaccharides (chains made of sugars like glucose) that are linked to each other by beta 1,3 glycosidic bonds.

Unless you are a chemistry student it is unlikely that you will know what this  means but I can give you an example. The way that sugars are linked to each other makes a big difference in the way that a polysaccharide behaves. Just thing of two polysaccharides made of the same sugar, glucose. There are two polysaccharides that you are very familiar with: starch and cellulose. Starch is in your bread, cellulose is in your newspaper (assuming you still read one). You can get nutrition out of the bread but not from the paper. A cow can use cellulose, though, because her G.I. has bacteria that can break down the bonds between sugars, allowing them to be used in glycolysis and respiration).

Why are beta glucans useful in skin care? Two beta glucans are used in the industry.

Beta glucan (oat)

Many organisms make beta glucans, i.e. sugars linked to each other by beta 1,3 glycosidic bonds. The beta glucan from oat has anti-inflammatory properties.

Beta glucan (yeast)

This polysaccharide is similar in structure to the glucan in Maitake mushroom. The cell wall of yeast is very complex , with a structure that is still being studied and seems to include beta(1–> 3)-glucan, beta(1–> 6)-glucan, chitin, and mannoprotein. Apparently, the effect of these carbohydrates on our immune system is innate, i.e. present in our genetic make-up. When we come in contact with these very special carbohydrates, our immune system seems to activate so that, when we come in contact with a pathogen, we are better able to deal with it and stop an infection. Apparently, this response may also prepare us to stop our own “gone bad” cells, those that have lost the capacity to control cell division and have become cancer cells.

A great advantage to allergy sufferers: yeast beta glucan (and beta glucans from other fungi) seems to decrease the tendency to allergic responses and inflammation.  As an added bonus,  it tightens the skin.

The orientation of a linkage (as alpha or beta) changes the properties of the resulting oligo o polysaccharide. Starch, for example, has glucose monomers linked to each other in alpha linkages. Conversely, cellulose has them linked in beta. We can digest starch but can’t digest cellulose.

Our body can recognize other glycans.

Lectins and the skin
The first human lectin was identified in 1974, but the work on skin lectin receptors lags well behind that on receptors present in other human organs. There is a receptor lectin in fibroblasts and keratinocytes that recognizes rhamnose (a methyl pentose) not synthesized by humans. From the point of view of skin aging, an issue so dear to the skin care industry (including us at SAS!), it is known that applying rhamnose containing glycans to the skin stimulates cell proliferation, decreases elastase-type activity, stimulates collagen biosynthesis, and protects hyaluronan against free radical mediated degradation. This is a very useful effect, even if we don’t know what the primary function of this receptor lectin is. Based on what we know about lectin receptors, we can hypothesize that they have something to do with the beneficial bacteria that live on our skin, but the receptor could also be just an evolutionary leftover. Living organisms, and even viruses, possess sophisticated enzymatic systems devoted to making the glycans, and also the lectins that recognize them.

People with skin conditions characterized by excessive cell division, like psoriasis, should avoid glycans that promote cell division. However, glycans that modulate the immune response, like fucoidans and yeast beta glucans, should be fine.

Lectins may be implicated in allergy: galectin-3 is highly expressed in epithelial cells, including keratinocytes, and is involved in the pathogenesis of inflammatory skin diseases by affecting the functions of immune cells. For example, galectin-3 can contribute to atopic dermatitis and may also be involved in the development of contact hypersensitivity by regulating migration of antigen presenting cells. Human milk contains non-digestible oligosaccharides and modulates allergy, another connection to the role of glycans in allergy.

References:
Faury G, Ruszova E, Molinari J, Mariko B, Raveaud S, Velebny V, Robert L. (2008) The alpha-1-rhamnose recognizing lectin site of human dermal fibrolasts functions as a signal transducer. Modulation of Ca++ fluxes and gene expression. Biochim.Biophys.Acta. 2008. pp. 1388-1394.
Larsen, Larissa, Chen, Huan-Yuan; Saegusa, Jun, Liu, Fu-Tong (2011) Galectin-3 and the skin. J Dermatological Science, 64: 85-91.
Oh JH, Kim YK, Jung JY, Shin JE, Chung JH.(2011) Changes in glycosaminoglycans and related proteoglycans in intrinsically aged human skin in vivo. Experimental Dermatology. 20:454-6
Sharon, N. and Lis H. (2004) History of lectins: from hemagglutinins to biological recognition molecules, in Glycobiology, 14: 53R–62R.