Hyaluronate (HA) is a glycosaminoglycan ubiquitously distributed in organisms. It has a linear structure without side chains, and a molecular weight of 10 4 to 10 7 . The huge molecular mass characterizes the physiologic and physicochemical properties of HA. High-molecular-weight HA forms entangled networks, having unique viscoelasticity and waterholding ability.1) The characteristics are molecular-weightsensitive, and yet, high molecular weight HA is easily depolymerized by various physical and chemical factors. There are many reports about HA depolymerization by photo, 2,3) thermal, 2,4) mechanical 2,5) and chemical actions. 6,7) Previously, we described HA depolymerization by phenothiazines and sulfacetamide with UV irradiation. 7) These drugs are known to cause dermatological or ophthalmic phototoxicity in patients receiving them in the long term. We have revealed the hydroxyl radicals and hydrated electrons generated during photodegradation of the drugs to be the active chemicals for HA depolymerization.Tetracyclines have also been reported to exhibit phototoxic and photoallergic reactions, with certain radicals proposed to account for in vivo and in vitro toxicity. 8,9) In this paper, the depolymerization of HA by tetracyclines, expressly oxytetracycline (OTC), was investigated. From depolymerization profiles under various conditions, the probable causative derivative was identified.
ExperimentalMaterials Two sodium HA samples were used: one was extracted from culture medium of Streptococcus equi, with a weight average molecular weight (M w ) of 2.6ϫ10 6 , and the other was isolated from rooster comb, with a M w of 1.1ϫ106 . Sodium alginate of medium viscosity from kelp was a commercial product of Sigma Chemical Co. Tetracycline hydrochlorides were purchased from Sigma Chemical Co. or Wako Chemical Co. They were used without further purification. Their chemical structures are listed in Table 1. Other reagents were of analytical grade. All the water used was distilled once and then Millipore filtered.Sample Preparation Polymer solutions were mixed with tetracycline solutions to make at final concentrations of 0.1% in 0.2 M NaCl. They were incubated in test tubes in a thermostated water bath. At the desired time, a portion was removed, appropriately diluted and after drugs were eliminated by solid-phase extraction on Sep-Pak C 18 cartridges, the molecular weight was measured. For studies under anaerobic conditions, glass ampules were used in place of test tubes. Solutions in ampules were de-aerated by 10-min nitrogen bubbling, immediately before the necks of the ampules were sealed with a burner. For UV irradiation, lamps (100 V, 5 W) with 254 nm or 365 nm for TLC spot detection were employed. The distance of the vessels from the light source was set at 5 cm. In the experiments with 254 nm irradiation, the vessels were squared quartz cells.Molecular Weight Measurement M w of HA was measured using a size exclusion chromatography (SEC) equipped with a low angle laser light scattering (LALLS). SEC-LALLS (Tosoh ...
