Acetylcysteine in random skin flap in rats 1 Acetilcisteína em retalho cutâneo randômico em ratos

Purpose: Analyze the ability of Acetylcysteine to reduce distal necrosis in a random skin flap, in the rat. Methods: The present study utilized 28 adult male Wistar-EPM rats distributed, at random, in two groups of 14 animals. Control group rats (CG) received distilled water and Acetylcysteine group animals (NACG) received NAC (300 mg/kg) by oral infusion, 15 minutes before flap elevation. On the seventh postoperative day, percentage of distal necrosis was determined and skin samples collected in order to allow determination of MDA levels. Results: The mean necrotic area in CG group (control) was 66 % and in NACG group (Acetylcysteine) 52 %, a statistically significant difference according to the Mann-Whitney test (U calc = 25; U crit = 45). MDA levels were lower in the CG flap skin samples than in the NACG samples (U calc = 24; U crit = 45), the oposite being true in the normal skin samples (U calc = 10; U crit = 45). Conclusion: Acetylcysteine was effective, according to the model used, reducing the percentage of distal necrosis in NACG rats.


Introduction
The risk of skin slough after elevation of a random flap is a matter of preocupation in Plastic Surgery 1, 2 .Experimental works foccusing on the reduction of skin necrosis have been done and the benefic role of antioxidant drugs discussed 3, 4   .Acetylcysteine, a well known antioxidant substance, had been used before with favorable results 3, 5 .
Therefore, the role of Acetylcysteine in the protection of random skin flaps in rats was studied.

Methods
Twenty-eight adult male Wistar-EPM rats were divided, at random, into two groups of 14 animals.Animals in the control group (CG) received distilled water and rats in group NACG received Acetylcysteine (300 mg/kg) by oral infusion, 15 minutes before flap elevation.Pentobarbital (40 mg/kg) was used intraperitoneally to provide anesthesia.After that, the rats were shaved and a cranially based random pattern skin flap was elevated (10x4 cm) on the back of the animals 6 .
A plastic barrier was then interposed between the flap and its bed 7 .The wound was closed with simple nylon 4-0 stitches .
On the seventh postoperative day, necrosis on the distal portion of the flaps was estimated by means of the paper template method 8 .Skin samples were obtained to permit analyzis of malondyaldehyde (MDA) levels 9 . One sample was collected from the transition area between viable and necrotic tissue and the other, distant from the flap, from a normal skin area.

Results
Necrotic area in CG group (control) ranged between 51 % and 77 % (average 66 %), while that in NACG group (Acetylcysteine) ranged between 38 % and 70 % (average 52 %).MDA concentrations in normal skin samples ranged between 1255 and 3345 ng/ml (average 2038 ng/ml) in CG and between 177 and 1889 ng/ml (average 935 ng/ml) in NACG.MDA levels in the viable to necrotic transiton skin samples ranged between 417 and 1915 ng/ml (average 1235 ng/ml) in CG and between 1051 and 4465 ng/ml (average 2346 ng/ml) in NACG.Mann-Whitney test for independent groups showed statistically significant differences (Tables 1-3).Mann-Whitney test (statistically significant) * two rats died in the postoperative period.

Discussion
Random pattern skin flaps represent valuable and common procedures in Plastic Surgery.Nevertheless, the risk of ischemia and necrosis is allways present, justifying the need of research for protective measures.Free radicals produce deleterious effects on skin flaps and continue to be intensivelly studied.Recent works have foccused on the antioxidant drugs.
Acetylcysteine (NAC) is a very well known antioxidant compound, used extensivelly in Pneumology.Easily obtainable and manipulated, it has low toxicity and the advantage of oral administration 3, 5 .The dosis herein utilized (300 mg/kg/day) was two times higher than that previously presented 3 and was chosen in view of the low toxicity of this drug.It must be stressed that this is a high dose, not readily applicable to human beings, but considered necessary in order to promote adequate antioxidant effect in this experimental model.The herein revisited McFarlane-like skin flap represents a practical experimental tool to study distal necrosis.The plastic barrier interposed between the flap and the donor bed (a latter contribution), prevents flap revascularization through the bed vessels.The percentage of necrosis was determined via the paper template method, another very usefull procedure.
In CG group (control) rats, the average percentage of necrosis was 66 %; in NACG group (Acetylcysteine) it was 52 %.Acetylcysteine was effective, according to the model used, reducing the percentage of distal necrosis on the flap in NACG animals in relation to CG rats.
The antioxidant role of Acetylcysteine was studied through the determination of MDA levels in skin samples.MDA was measured from two skin samples of each animal from both groups, using normal and viable to necrotic transition skin.

TABLE 1 -
Percentage of necrotic area on the seventh postoperative day.Mann-Whitney test (statistically significant)

TABLE 2 -
Concentration * two rats died in the postoperative period.Mann-Whitney test (statistically significant) * two rats died in the postoperative period.

TABLE 3 -
Concentration of malondyaldehyde (ng/ml) from the viable to necrotic transition skin samples on the seventh postoperative day.