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THERAPEUTIC HEATING OF COLLAGEN

Collagen

Collagen synthesis is produced in the fibroblast from a forerunner polymer known as tropocollagen which is formed by three chains of polypeptides constituted by a black reception of three amino acids (hydroxyproline, hydroxylysine and glycine). Hydroxyproline is present in the collagen molecule in a percentage of 10 to 12%; the amount of hydroxyproline defines the type of collagen. Glycine is an amino acid that favours the collagen molecule packaging in a counter clockwise rotation. And hydroxylysine stabilises the spiral conformation of the three chains due to its rigid ring-shaped structure. The hydrogen bridges link the three chains of the triple helix and the three chains also unite through links between some amino acids known as cross links.

The polypeptide chains are synthesised in the ribosomes linked to RER of the fibroblasts and are freed onto the luminal cell, containing additional amino acids in the extreme amino and carboxyl-terminals. The proline and lysin residues are hydroxylated and then some are also glycosylated in the Golgi apparatus, these hydroxylations are the ones that later allow for the creation of hydrogen bridges between the three polypeptide chains. These polypeptides are secreted by the fibroblasts and are degraded through proteases that convert them into tropocollagen molecules assembled in extracellular space forming the collagen fibres, driven by the tendency of the procollagen molecules to autonomously assemble through covalent bonds between the lysin residues.

There are several types of collagen, ranging from Collagen I to Collagen XIII. The dermis mainly contains:

• Collagen I (85%) with the main function of providing resistance to stretching.
• Collagen II (15%) whose main function is resistance to intermittent pressure.

With the heating of the collagen, the heat-sensitive hydrogen links responsible for maintaining the clockwise triple helix of the three polypeptidic collagen chains are altered; so that it converts from a protein in a highly organised crystalline state to a disorganised and denatured gel (gelatine). Collagen contraction is produced with the unfolding of the triple helix by the denaturation of the links between the chains and the tension of the residual intrahelicoidal and intramolecular cross links.

When the temperature of the collagen increases, a separation of the fibrils is produced with a dislocation of the spirals, obtaining individual protein chains, although preserving the helicoidal structure. If heating is maintained, the spiral structure is lost and a random structure is obtained in which all the chains interact and are known as gelatine. The temperature at which half of the dissolved collagen molecules have lost their spiral structure is known as melting temperature (Tm). The equivalent in vivo is Ts (shrinkage temperature).

The temperature at which collagen is denatured depends on the proline and hydroxyproline content: the larger the content, greater is the needed temperature. In this sense, there is a major difference in proline content and in denaturation temperature between the collagen of warm-blooded animals and that of fish. Collagen denaturation temperature in mammals is typically at 65 ºC.

Dissolved collagen molecule fusion curve:

Elastin

• Elastin is the second most important polymer in the connective tissue. Another fibrous protein which also contains a large amount of glycine, although different from collagen in that it has no hydroxyproline and is rich in alanine.
• With respect to the structural differences, elastin has a large number of cross links that give it an elasticity that allows it to stretch up to three time its initial length.
• During the heating, the elastin swells but is not dissolved: elastin is very abundant in the walls of the arteries and in tissues such as lung tissue which require great elasticity.

Adipocytes

• This technology can also induce the disruption of the adipocytes by increase in their temperature. (Del Pino-Rosado)¹⁹, (Ruiz Esparza)²⁰.
• Adipocytes are completely full of lipids, the stored triglycerides are encapsulated in a fine covering of a dense weave of lipids and proteins (with a structure similar to that of caviar). Lipids are in a liquid state, normally at a body temperature of 37 ºC, although they have a somewhat viscid structure. Selective heating damages the external envelope, the exact temperature required for the destruction of the external envelope of lipidic vacuole (LCI) is 50º C and the coagulation of the fibrous matrix temperature (60º C). In the adipose tissue, the adipocytes contain more than 90% fat and are grouped closely in the shape of lobules. There are structures interleafed between the lobules such as septa, nerves, vessels, capillaries and elements of connective tissue which are basically made up of water. The structures high in water content are arranged in the fat tissue in a more uniform manner than in the fat lobules.
• Adipose tissue is a unique type of connective tissue comprised of adipocytes, blood vessels and fibrous septa. It is made up of approximately 75-85% lipids and 15-25% water and proteins. The unilocular white adipose tissue (WAT) is the most common type in adult humans and is composed mostly of mature adipocytes measuring 2-150 microns (75 µ on average) and that contain one large droplet of lipids (triglycerides).
• The adipocyte cytoplasm is divided from the surrounding interstitial spaces by an external lamina of a glycoprotein envelope that superficially resembles the basal lamina of epithelia. In addition, the lipid droplets are not surrounded by a membrane, although its interface surface with the cytoplasm contains a layer of 5 to 10 nm lipid reinforced by microfilaments measuring 5 nm in diameter.. This interface is known as LCI (Lipid Cytoplasm Interface).
• Adipocytes are surrounded by a loose network of fine reticular fibres containing collagen fibrils, fibroblasts, lymphoid cells, eosinophils and some mast cells. Adipocytes are nourished by blood and lymphatic capillaries and appear oval or polyhedral with the nucleus flattened and pushed towards the periphery. The larger diameter of the adipocyte is conditioned by the volume of accumulated lipid in the cells and ranges from 25 to 125 microns. The volume ratio of lipid to the surrounding cytoplasm appears to be as the cytoplasm in the adipocyte is barely visible and is completely taken up by the lipid droplets. (J.Childs)²¹

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