Temporal differences in the influence of ischemic factors and deformation on the metabolism of engineered skeletal muscle

Prolonged periods of tissue compression may lead to the development of pressure ulcers, some of which may originate in, for example, skeletal muscle tissue and progress underneath intact skin, representing deep tissue injury. Their etiology is multi-factorial and the interaction between individual causal factors and their relative importance remain unknown. The present study addressed the relative contributions of deformation and ischemic factors to altered metabolism and viability.Engineered muscle tissue was prepared as previously detailed (Gawlitta et al., 2006) and subjected to a combination of factors including 0% oxygen, lactic acid concentrations resulting in pH from 5.3-7.4, 34% compression, and low glucose levels. Deformation had an immediate effect on tissue viability (LDH release, MTT), which increased with time. By contrast, hypoxia evoked metabolic responses (glucose and lactate levels) within 24 hours, but viability was only reduced after prolonged periods. In addition, lactic acidification down-regulated tissue metabolism up to an acid concentration where metabolism was arrested and cell death enhanced. A similar tissue response was observed during glucose deprivation which, at negligible concentration, resulted in both a cessation of metabolic activity and a reduction in cell viability.The combination of results suggests that in a short term (