Validation and stability analysis of a modified lactate dehydrogenase (LDH) test method to be employed for an in vitro viable skin model

In view of increasing numbers of dermatological disorders, transdermal drug delivery along with in vitro research is becoming increasingly popular. Herefore, qualified in vitro skin models are required. The objective of this study was the optimization and validation of a modified lactate dehydrogenase (LDH) release assay during the establishment of an in vitro viable human skin model, employable for a variety of skin associated disorders. Firstly, the most suitable LDH isoform for the study was determined. Subsequently, a stability study was conducted to investigate the best storage conditions of the LDH enzyme. Finally, the test system was validated in terms of linear range, range limits and system suitability. The results indicate LDH-5 as most suitable isoform due to its predominance in skin. The stability samples stored at −20 °C in the presence of polyethylene glycol (PEG) as cryoprotector displayed the targeted recovery of 100% ± 15 % until the end of the four-week study in contrast to other investigated conditions. A six-point calibration without PEG and a seven-point calibration with PEG including evaluation of system suitability and quantification limits were established with both correlation coefficients r(2) above 0.99 and all deviations below 15%. Concluding from those results, this method can be considered valid and useful for its employment in viability determination of viable in vitro skin models.