High metabolic activity of tissue-nonspecific alkaline phosphatase not only in young but also in adult bone as demonstrated using a new histochemical detection protocol

Tissue-nonspecific alkaline phosphatase (TNAP) is playing a key role in bone calcification, as has been demonstrated in different mammalian species including human and rodents. However, to investigate age-related changes during life history, histochemical demonstration of TNAP is severely hampered, particularly in the elderly, by technical difficulties associated with sectioning calcified tissue. Sufficient fixation must precede decalcification since poorly fixed bone tissue is exposed to the deleterious effects of decalcification reagents. In order to find a method that would allow cryosectioning of bone without loss of TNAP activity, we assessed the efficacy of different fixation reagents regarding the effects on structural integrity and TNAP activity using liver and osseous tissue from younger and older horses. The results of this study reveal that glyoxal-based fixatives sufficiently preserved bone tissue for successful cryosectioning without compromising TNAP activity. The method described combines the demonstration of TNAP activity with optimal preservation of tissue morphology in osseous tissue of younger and even of older mammals. As a model species, we selected horse bones in light of potentially higher similarities to ageing history and lifelong locomotion in humans as compared to other, mostly smaller, experimental model species with a much shorter life span and artificial locomotive activity when kept in cages. This may serve as a basis for future studies addressing the impact of different life traits in iconic, domestic and companion animals, which are often patients in veterinary medicine, as well as for basic research on human physiology and pathologies of the musculoskeletal system.