The aims of this projects are: 1. to understand the neurotoxic effect of lead (Pb), a heavy metal that binds with high affinity to glutathione and metallothionein; 2. to study the mechanisms involved in the increased Pb-toxicity in a serum free-medium condition; 3. to analyze the neuroprotective role of glial cells during Pb treatment. Metallothionein-I/II and glutathione are, predominantly, expressed in astrocytes and play an important role in heavy metal scavenging and oxidative stress response. The breakdown of their function may be linked to the etiology of various progressive neurological diseases. A 24 h exposure of mesencephalic primary culture to 25 mM Pb, in serum-containing medium, increased the metallothionein-I/II level by 2 fold. A similar treatment of cells increased glutathione concentration by 2 fold. In contrast Pb exposure (3-25 mM Pb) in serum-free medium increased Pb uptake in the cells 2-4 time above the levels found in 10% serum-containing medium, reduced the glutathione level and obliterated the metallothionein-I/II protein band. When mesencephalic cells were exposed for 3h to Pb in serum-free NM followed by a 21 h incubation in serum-free NM, the metallothionein-I/II protein band was obliterated. In contrast, when cells were recovered in serum-containing NM, after the same Pb-exposure period in absence of serum, the metallothionein-I/II band was increased above that of the control group. These data suggest that metallothionein-I/II induction required a serum factor besides the increase of intracellular Pb concentration. In absence of serum, Pb-exposure increased the carbonyl groups of proteins extracted from mesencephalic cultures, indicating an increase in oxygen free radicals. The increase in protein oxidation may associated with decreased levels of free radical scavengers such as metallothionein and glutathione. The rapid decrease of metallothionein-I/II levels in serum-free medium implies that its regulation may depend on a serum factor operative in inducing immediate early genes.
