Assessment of skin viability: is it necessary to use different methodologies?

Background/aim: Skin is complex and may display variable structural and metabolic change 'ex vivo'. The present study aimed to follow measures of skin viability and evaluate their usefulness as markers of viability. Materials and methods: We evaluated the viability of skin samples fresh or after being frozen and subsequently thawed. Assessments included histopathological appearance, lactate dehydrogenase (LDH) activity, oxygen consumption and skin pH. Results: Morphological investigations of fresh and frozen skin samples using light and electron microscopy showed samples with relatively well-defined epidermis and dermis. Frozen samples showed some sign of stratum corneum fragmentation, although this was not obvious. LDH activity measured in fresh samples kept at 4degreesC was low, but it was stable up to 7 days. Fresh samples kept at 32degreesC had a comparable LDH activity to the ones kept in the fridge up to 4 days. Frozen samples, thawed and then kept at 4degreesC showed a stable LDH activity after 24 h of incubation. However, frozen samples incubated at 32degreesC demonstrated a high variability in results, with up to 800 U/L of LDH activity after 5 days of incubation. Freshly excised as well as freshly thawed samples showed the highest respiration rates. Fresh and thawed samples stored for a long period of time had a significantly lower (sometimes non-existent) oxygen consumption rate. Our results also showed an increase in the oxygen consumption rate of fresh samples being incubated at 32degreesC for 24 h. The oxygen consumption rate for all samples reached a plateau within the 15-min measurement period and even the fresh samples did not deplete all the oxygen from the medium. Skin samples ex vivo showed a significantly higher pH than human skin in vivo, and when incubated for 46 h at 32degreesC, fresh samples had a significantly lower pH than frozen samples. All protocols were reproducible and freshly excised and freshly thawed skin samples showed the highest rates of viability. Conclusion: ex vivo skin shows variation of several parameters over time. It is recommended to use two or three techniques for evaluation of skin viability including at least oxygen measurement and an enzyme assay.