Nitrocompounds produce striking focal lesions in the auditory centers of the brainstem and deep cerebellar roof nuclei of rats. These lesions initially involve astrocytes and oligodendrocytes, and only later affect neurons. The biochemical basis of the selective involvement of these brain regions and these cell types is unknown. Lipophilic nitrocompounds enter the brain across the endothelia and astrocytes and are metabolized to amines by single-electron addition. The single-electron reduction product readily reduces oxygen, yielding superoxide radical. The regional nitroreductive capacity of astrocytes or other brain cell populations is unknown. The brainstem nuclei affected by nitrocompounds have a high requirement for glucose and are particularly susceptible to perturbations in glucose metabolism. Perturbation of mitochondrial energy metabolism may be a primary consequence of nitrocompound-induced radical reactions. However, the connection between energy metabolism and nitrocompound-induced encephalopathy is unclear. We hypothesize that regional differences in astrocytic nitroreductive capacity render specific populations of astrocytes susceptible to toxic nitrocompounds. It is further postulated that modulation of regional basal metabolic rates within the brainstem alters the degree of damage produced by concomitant alteration of nitroreductive capacity. These hypotheses will be tested by addressing the following specific questions: 1) Are there regional differences in nitroreductive capacity in brain? 2) Do differences in nitroreductive capacity in astrocytes, neurons and endothelial cells underlie regional susceptibility to nitrocompounds? 3) Does modulation of regional energy metabolism result in changes in nitroreductive capacity? 4) Does culture of astrocytes from vulnerable brain regions with neurons or endothelial cells alter their response to nitrocompound-induced toxicity? Models of nitrocompound-induced oxidative stress will be examined in isolated cell preparations, cell cultures of astrocytes, neurons and endothelial cells and in co-cultures of these cells. Nitroreductive capacity and oxidative stress will be monitored using spectrophotometric and HPLC techniques. Both biochemical and morphological indices of cytotoxicity will be used to assess relative regional and cellular susceptibility and damage. The long-term goal of these studies is to understand regional cellular responses to neurotoxicants.
| Philbert, M A; Billingsley, M L; Reuhl, K R (2000) Mechanisms of injury in the central nervous system. Toxicol Pathol 28:43-53 |
