Depolymerization of some polysaccharides and synthetic polymers by L-ascorbic acid

Hyaluronate depolymerization following thermal decomposition of oxytetracycline

Depolymerization of sodium hyaluronate (HA) by tetracyclines was investigated. Reduction in HA molecular weight was followed by size exclusion chromatography with a low angle laser light scattering detector. On mixing with oxytetracycline hydrochloride (OTC) solution and incubating at 37 degrees C, HA was gradually depolymerized. OTC, a representative antibiotic, is known as a photosensitizer, and phototoxic side effects relevant to radicals have been reported. However, HA depolymerization required no irradiation. As time passed, OTC solution incubated at 37 degrees C got colored reddish brown, even in the dark. With reversed-phase HPLC separation, several peaks derived from decomposed OTC appeared. One of the peaks had an absorbance in the visible range. A quantitative correlation between the discoloration and the HA depolymerization rate was obtained. On the other hand, when samples were incubated below 25 degrees C, change of color was slight, and practically no HA depolymerization was observed after up to 4 h. Oxygen depletion by nitrogen saturation or addition of mannitol also prevented the depolymerization. Under anaerobic conditions, the color of the solution did not change, whereas it turned red under aerobic conditions in the presence of mannitol. The mannitol did not inhibit the OTC decomposition, but it preserved HA from damage. On the basis of the known decomposition of OTC and the results of HPLC separation, anhydrooxytetracycline can be proposed as the derivative causing HA depolymerization.

Preparation of cross-linked hyaluronic acid films of low water content

Hyaluronic acid (HA) was chemically cross-linked with poly(ethylene glycol) diglycidyl ether, a diepoxy compound (EX-810), to yield low water content and slowly degradable films when brought into contact with water. The cross-linking reaction was performed under acidic and neutral conditions, since the epoxy group is readily hydrolysed in alkaline media. To allow the reaction to proceed at high HA concentrations, a solution casting method was employed for the cross-linking of HA. The lowest water content of the cross-linked HA films obtained was 60 wt% when swollen with buffered saline at 37 degrees C. Alginic acid and poly(vinyl alcohol), which possess hydroxyl groups, similar to HA, were also found to undergo cross-linking with the diepoxy compound. Since IR spectra of the cross-linked films had no significantly new absorption, intermolecular formation of ether bonds between the hydroxyl groups belonging to different polysaccharide molecules was assumed to take place. It seemed too difficult to detect the ether bonds in the cross-linked HA films, because the virgin HA film itself contained ether bonds in the molecule. The cross-linked HA film with a water content of 60 wt% exhibited practically no weight loss after 10 days of immersion in phosphate-buffered saline (pH 7.4), while this film underwent in vivo degradation by 30% weight loss after 7 days of subcutaneous implantation in rats. The inflammation reaction elicited around the implanted film was not significant.

Pathways to the decisive extension of the human specific lifespan

Three approaches to reversal or removal of gerogenic aggregations of macromolecules have shown promise. Of these the enzyme approach is the most gentle, and can be made specific. Aside from this, the lower the molecular weight of an enzyme, the better chance it will have to be immunologically tolerated as well as replicated synthetically in whole or in part. The chelating approach provides a powerful means for removing a single class of unwanted, random crosslinkages, i.e., those due to extraneous polyvalent metals such as lead, cadmium and aluminum. The free hydroxyl radical approach is the most penetrant and most versatile means for removing otherwise insoluble aggregates, but its very lack of specificity will demand great foresight in control and use. Together, these three methods, when properly applied, might bring some principal objectives of gerontology within closer range.