Several histochemical and clinical investigations showed the moisturizing activity of low molecular weight precursors of mucopolysaccharides (Hyaluramine) which can penetrate the skin, increase mucopolysaccharides content of the ground substance and as a result improve skin moisturization.
Topical application of 1% Hyaluramine increases the quota of mucopolysaccharides; conversely skin samples treated with cortisone markedly lower the usual content of mucopolysaccharides. Autoradiographic and audioradiometric assays of skin specimens treated with an O/W emulsion containing 1% Hyaluramine labelled with 14C manifested the percutaneous absorption of this precursor of UDP-N-acetylglucosamine and its subsequent incorporation in mucopolysaccharides.
A clinical trial using the same concentration of Hyaluramine showed a 25% increase of skin eutrophism compared to controls.
The assumption that the dry and wrinkled appearance of aging skin is linked to a progressive dehydration has no actual grounds.
The belief of an increased water loss due to an impairment of the stratum corneum barrier in the elderly proved itself inappropriate.
An explanation for the evident decline in the water content has been directed towards an alterated water distribution. It has been focused that the real damage is associated to mucopolysaccharides impoverishment with a connected increase of free water. We started an investigation to check whether the moisturising activity of Hyaluramine affects transport of free water into the dermis or induces redistribution of water molecules between the free and bound state, so altering the conformation of biopolymers in the dermis itself.
Ten years ago our study using Nuclear Magnetic Resonance (NMR) to evaluate the moisturizing effect of Hyaluramine was performed.
NMR is an image diagnostic test close to axial tomography but oppositely using a magnetic field instead of ionic radiation. To scan all the planes not only transversally is one of the advantages of NMR. The magnetic field completed by radio waves created by NMR influences the commonly casual spin of hydrogen ions (protons) in water molecules. At the end of the perturbation the primary equilibrium is reestablished but concurrently energy is released and promptly registered allowing, thanks to computer systems too, the determination of water molecules in the examined tissue.
In our studies it ascertains the measurement of skin moisturization and notably the portion of free and bound water, i.e. free in solution or bound to biopolymers and cellular macrostructures.
Therefore it is not surprising the present attention in using NMR for the evaluation of cosmetics efficacy. Our research was performed following the topical application of a gel formulated with 1% Hyaluramine, 1% Hydroxyethylcellulose (Idroramnosan) and 98% water or a placebo.
Measurements are based on relaxation times T1 (spin coupling) and T2 (spin-spin) correlated to water protons concentration and physical state.
In our investigation changes in spin-relaxation time T2 were too slight to be representative so only results related to T1 were taken into consideration.
Skin samples carefully separated from the subcutaneous adipose pads displayed a strong decrease of T1 (see Table I) following treatment with Hyaluramine. On the contrary, T1 values of the adipose pads obtained from the same biopsies did not change after any treatment. A further trial compared the moisturizing effects of low (Hyaluramine) and high molecular weight mucopolysaccharides. Again T1 values were considerably reduced in skin samples treated with Hyaluramine. Oppositely the high molecular weight mucopolysaccharide had no effect on the T1 relaxation time (see Table II). The absolute values are higher due to fixation of samples in glutaraldehyde allowing a longer storage.
The reduction of relaxation time T1 of hydrogen ions is opposite to the recognized increase in free water concentration. The data obtained allowed to assume that: skin samples devoid of subcutaneous adipose pads have a relaxation time T1 highly influenced by the moisturizing activity of Hyaluramine; T1 decrease in hydrated skin is connected to a substantial redistribution of water molecules following the application of Hyaluramine bringing to a growth in bound water compared to free one, presumably related to structural changes of the biopolymers in the ground substance of the dermis. Such an activity is exclusively associated to the treatment with the low molecular weight precursor.
These data substantiate the effect of Hyaluramine on the skin, while the underlying adipose tissue registers no changes in the water physical state. Hyaluramine as a diffusible precursor of mucopolysaccharides does not cause a plain transport or retention of water in the dermis, but a change in the conformation of the dermal macromolecules influencing the subsequent redistribution of water which increases the ratio of bound molecules.