Toxic effects of D-galactose on thymus and spleen that resemble aging.

Continuous low-dose injection of d-galactose induces changes in mice that resemble accelerated aging. As such, these mice have been used as models to study mechanisms of aging. Here, we examined whether repeated (daily, for 60 days) subcutaneous injections (at 50 mg D-galactose/kg) into young adult (i.e., 2-month-old) mice induced changes in key immune system organs that were on par with those associated with aging. The results showed that galactose-treated mice develop histologic changes in their thymic cortical and medullary regions; immunohistochemical analysis revealed unorganized distributions of keratin-5 and keratin-8 proteins in the thymus of these hosts. These histological changes in the thymus of D-galactose-treated mice were also observed in the organs of aged (i.e., 24-month-old control mice); however, in this latter group, these changes were accompanied by a strong infiltration of adipose cells. Galactose-treated mice also evinced alterations within their splenic white and red pulp. Further, ultrastructural analyses of the thymus and spleen of the treated mice revealed increases in irregularly shaped lymphocytes bearing visible pyknosis. It was also seen that levels of autophagy within thymic epithelial cells were greatly decreased in the tissues of the galactose-treated mice, an outcome also seen in aged mice. Lastly, the level of memory T-lymphocytes and percentage of IgM-B220-B-lymphocytes in spleens of the galactose-treated mice were both increased (albeit insignificantly so) relative to values among splenocytes of age-matched control; however, these levels were not clearly as elevated as would be expected in "elderly" mice. Taken together, our results strongly suggest that d-galactose treatment can induce structural changes in the thymus and spleen, and some changes in organ-associated cell phenotypes, that are similar to several effects seen with aging. However, the fact that many endpoints do not appear to be truly reflective of what should be seen in immune system organs/cells of "elderly" mice now calls into question the appropriateness of the use of d-galactose (i.e., is it histologically/immunotoxicologically-proper?) to create age-mimicry in mice.