Glutaric acidemia type I (GA-I) is an inherited
metabolic disease characterized by accumulation of
glutaric acid (GA) and striatal degeneration. Although growing evidence suggests that excitotoxicity and oxidative stress play central role in the neuropathogenesis of this disease, mechanism underlying striatal damage in this disorder is not well established. Thus, we decided to investigate the in vitro effects of GA 10nM (a low concentration that can be present initial development this disorder) on l-[(3)H]
glutamate uptake and
reactive oxygen species (ROS) generation in synaptosomes from striatum of rats. GA reduced l-[(3)H]
glutamate uptake in synaptosomes from 1 up to 30min after its addition. Furthermore, we also provided some evidence that GA competes with the
glutamate transporter inhibitor l-trans-pyrrolidine-2,4-dicarboxylate (PDC), suggesting a possible interaction of GA with
glutamate transporters on synaptosomes. Moreover, GA produced a significant decrease in the V(MAX) of l-[(3)H]
glutamate uptake, but did not affect the K(D) value. Although the GA did not show
oxidant activity per se, it increased the ROS generation in striatal synaptosomes. To evaluate the involvement of reactive species generation in the GA-induced l-[(3)H]
glutamate uptake inhibition,
trolox (0.3, 0.6 and 6muM) was added on the incubation medium. Statistical analysis showed that
trolox did not decrease inhibition of GA-induced l-[(3)H]
glutamate uptake, but decreased GA-induced reactive species formation in striatal synaptosomes (1, 3, 5, 10, 15 and 30min), suggesting that ROS generation appears to occur secondarily to glutamatergic overstimulation in this model of organic acidemia. Since GA induced DCFH oxidation increase, we evaluate the involvement of
glutamate receptor antagonists in oxidative stress, showing that
CNQX, but not
MK-801, decreased the DCFH oxidation increase in striatal synaptosomes. Furthermore, the results presented in this report suggest that excitotoxicity elicited by low concentration of GA, could be in part by maintaining this excitatory
neurotransmitter in the synaptic cleft by non-competitive inhibition of
glutamate uptake. Thus the present data may explain, at least partly, initial striatal damage at birth, as evidenced by acute bilateral destruction of caudate and putamen observed in children with GA-I.