INVOLVEMENT OF LIPID-PEROXIDATION IN NECROSIS OF SKIN FLAPS AND ITS SUPPRESSION BY ELLAGIC ACID

To evaluate the pathogenesis of lipid peroxidation in skin-flap necrosis and to select a novel herbal antioxidant to suppress lipid peroxidation and salvage the flaps, in vitro and in vivo experiments were instituted. In vitro studies revealed (1) the potentiality of the cutaneous microsomal system (vesicular fragment of endoplasmic reticulum) to generate oxyradicals by FeCl3 (oxidative agent), since NADPH-dependent lipid peroxidation was elevated time-dependently, (2) suppression of microsomal lipid peroxidation by herbal antioxidants (dose- and time-dependently), further supporting the theory of oxyradical-induced lipid peroxidation in the skin, and (3) that ellagic acid showed the strongest response, with curcumin, chlorogenic acid, and alpha-tocopherol (tocopherol) being moderate, and ferulic acid and gallic acid remaining weakest. Thus ellagic acid, curcumin, chlorogenic acid, and tocopherol at doses of 10, 60, 80 and 100 mu M (twice I-50, the dose which could inhibit lipid peroxidation by 50 percent) were chosen for in vivo assessments, respectively. In vivo studies were performed using rat back skin random flaps (70 X 15 mm and based anteriorly) and circular island flaps (20 mm in diameter and raised on superficial epigastric vessels). Control flaps were painted with a Tris-ethanol solution, and test flaps were painted with either ellagic acid, curcumin, chlorogenic acid, or tocopherol (above-mentioned doses per 250 mu l of Tris-ethanol per 300 mm(2) of flap surface 1 hour before the operation and once a day for 3 postoperative days). Doses, frequency, and period of drug application were based on in vitro and in vivo pilot experiments. The results were as follows: (1) a direct and time-dependent relation was noticed between lipid peroxide levels and the rate of necrosis in both types of flap; (2) time-dependent elevation of lipid peroxide levels of skin, subcutaneous fat, and exudate of island flaps during ischemia and those of skin and subdermal fat after reperfusion indicated pre- and post-reflow states of lipid peroxidation rather than the original conception of merely reperfusion state; and (3) in good agreement with the results of in vitro experiments, ellagic acid exerted the strongest effect to suppress lipid peroxide levels of skin and to augment the viability of random flaps more than that of island flaps. These results suggest (1) that in the field of flap research and testing of flap-salvaging drugs, combined in vitro and in vivo experiments would help not only in better understanding the pathophysiology of the flap necrosis but also in finding the proper method and dose of drug administration; (2) that since even ellagic acid failed to salvage the flaps completely, it seems other factors might be involved, which further studies may aim at; and (3) that more experiments such as topical application of radioisotope-labeled ellagic acid should be done to determine the rate and depth of cutaneous absorption of this compound for clinical use.