Metallothionein 1+2 protect the CNS during neuroglial degeneration induced by 6-aminonicotinamide.

6-Aminonicotinamide (6-AN) is a niacin antagonist, which leads to degeneration of gray matter astrocytes. Metallothionein 1+2 (MT-1+2) are neuroprotective factors in the central nervous system (CNS), and to determine the roles for MT after 6-AN, we have examined transgenic mice overexpressing MT-1 (TgMTI* mice) after an i.p. injection with 6-AN. In control mice injected with 6-AN, astrocytes in specific gray matter areas of the brainstem showed degeneration. Reactive astrocytes surrounded the degenerated areas, which were heavily infiltrated by macrophages and T lymphocytes. MT-1+2 expression was significantly decreased in the damaged brainstem areas, but it increased in reactive astrocytes surrounding these areas and also in infiltrating macrophages. The levels of oxidative stress, as determined by immunoreactivity for inducible nitric-oxide synthase (iNOS), malondialdehyde (MDA), and nitrotyrosine (NITT), and the number of terminal deoxynucleotidyl transferase [TdT]-mediated deoxyuridine triphosphate [dUTP]-digoxigenin nick end labeling-positive (TUNEL+), caspase-3+ apoptotic cells were significantly increased in the brainstem of normal mice after 6-AN. In the TgMTI* mice, the 6-AN-induced tissue damage was decreased in comparison to control mice, and they showed significantly reduced numbers of recruited macrophages and T lymphocytes, and a drastic reduction of oxidative stress and apoptotic cell death. In addition, the accompanying reactive astrogliosis was increased in the transgenic mice. To further study the potential protective role of MT, we administered intraperitoneally Zn-MT-2 to 6-AN-injected normal mice and found essentially the same results as those obtained in TgMTI* mice. Thus, we hereby report that endogenous MT-1 overexpression and exogenous MT-2 treatment have significant neuroprotective roles during CNS pathological conditions.