Chronic intrastriatal L-pyroglutamate: neuropathology and neuron sparing like Huntington's disease

Acute administration of 5-oxoproline induces oxidative damage to lipids and proteins and impairs antioxidant defenses in cerebral cortex and cerebellum of young rats

5-Oxoproline accumulates in glutathione synthetase deficiency, an autossomic recessive inherited disorder clinically characterized by hemolytic anemia, metabolic acidosis, and severe neurological symptoms whose mechanisms are poorly known. In the present study we investigated the effects of acute subcutaneous administration of 5-oxoproline to verify whether oxidative stress is elicited by this metabolite in vivo in cerebral cortex and cerebellum of 14-day-old rats. Our results showed that the acute administration of 5-oxoproline is able to promote both lipid and protein oxidation, to impair brain antioxidant defenses, to alter SH/SS ratio and to enhance hydrogen peroxide content, thus promoting oxidative stress in vivo, a mechanism that may be involved in the neuropathology of gluthatione synthetase deficiency.

5-Oxoproline reduces non-enzymatic antioxidant defenses in vitro in rat brain

5-Oxoproline (pyroglutamic acid) accumulates in glutathione synthetase deficiency, an inborn metabolic defect of the gamma-glutamyl cycle. This disorder is clinically characterized by hemolytic anemia, metabolic acidosis and severe neurological disorders. Considering that the mechanisms of brain damage in this disease are poorly known, in the present study we investigated whether oxidative stress is elicited by 5-oxoproline. The in vitro effect of (0.5-3.0 mM) 5-oxoproline was studied on various parameters of oxidative stress, such as total radical-trapping antioxidant potential, total antioxidant reactivity, chemiluminescence, thiobarbituric acid-reactive substances, sulfhydryl content, carbonyl content, and 2',7'-dichlorofluorescein fluorescence, as well as on the activities of the antioxidant enzymes catalase, superoxide dismutase and glutathione peroxidase in cerebral cortex and cerebellum of 14-day-old rats. Total radical-trapping antioxidant potential and total antioxidant reactivity were significantly reduced in both cerebral structures. Carbonyl content and 2',7'-dichlorofluorescein fluorescence were significantly enhanced, while sulfhydryl content was significantly diminished. In contrast, chemiluminescence and thiobarbituric acid-reactive substances were not affected by 5-oxoproline. The activities of catalase, superoxide dismutase and glutathione peroxidase were also not altered by 5-oxoproline. These results indicate that 5-oxoproline causes protein oxidation and reactive species production and decrease the non-enzymatic antioxidant defenses in rat brain, but does not cause lipid peroxidation. Taken together, it may be presumed that 5-oxoproline elicits oxidative stress that may represent a pathophysiological mechanism in the disorder in which this metabolite accumulates.

L-pyroglutamic acid inhibits energy production and lipid synthesis in cerebral cortex of young rats in vitro

In the present study we investigated the effects of L-pyroglutamic acid (PGA), which predominantly accumulates in the inherited metabolic diseases glutathione synthetase deficiency (GSD) and gamma-glutamylcysteine synthetase deficiency (GCSD), on some in vitro parameters of energy metabolism and lipid biosynthesis. We evaluated the rates of CO2 production and lipid synthesis from [U-14C]acetate, as well as ATP levels and the activities of creatine kinase and of the respiratory chain complexes I-IV in cerebral cortex of young rats in the presence of PGA at final concentrations ranging from 0.5 to 3 mM. PGA significantly reduced brain CO2 production by 50% at the concentrations of 0.5 to 3 mM, lipid biosynthesis by 20% at concentrations of 0.5 to 3 mM and ATP levels by 52% at the concentration of 3 mM. Regarding the enzyme activities, PGA significantly decreased NADH:cytochrome c oxireductase (complex I plus CoQ plus complex III) by 40% at concentrations of 0.5-3.0 mM and cytochrome c oxidase activity by 22-30% at the concentration of 3.0 mM, without affecting the activities of succinate dehydrogenase, succinate:DCPIP oxireductase (complex II), succinate:cytochrome c oxireductase (complex II plus CoQ plus complex III) or creatine kinase. The results strongly indicate that PGA impairs brain energy production. If these effects also occur in humans, it is possible that they may contribute to the neuropathology of patients affected by these diseases.

Hereditary non-spherocytic haemolytic anaemia due to red blood cell glutathione synthetase deficiency in four unrelated patients from Spain: clinical and molecular studies

In four unrelated patients with chronic haemolysis and markedly reduced red blood cell (RBC) glutathione (49.5%, 12.6%, 11.5% and 15% of the normal concentration respectively), a severe glutathione synthetase (GSH-S, EC 6.3.2.3) deficiency was found. One case exhibited a neonatal haemolytic anaemia associated with oxoprolinuria, but without neurological manifestations. The family study revealed GSH-S activity in both parents to be around half the normal level, a finding consistent with the presumed autosomal recessive mode of inheritance of this enzymopathy. Two cases exhibited a well-compensated haemolytic syndrome without anaemia or splenomegaly at steady state. One of these cases was diagnosed after an episode of acute haemolytic anaemia after fava bean ingestion. The remaining patient suffered from moderate to severe chronic non-spherocytic haemolytic anaemia and splenomegaly, and required occasional blood transfusion for a haemolytic crisis associated with drug ingestion. In this patient, the anaemia was corrected by splenectomy. In addition to GSH-S, a panel of 16 other RBC enzyme activities was also studied in all the patients. Hexokinase, aldolase, glucose-6-phosphate dehydrogenase and pyruvate kinase activities all increased; these increases were to be expected, given the rise in the number of circulating reticulocytes. In two patients, the incubation of RBCs with hydrogen peroxide revealed an enhanced production of malonyldialdehyde. DNA analysis showed a homozygous state for 656 A-->G mutation in patients 2 and 3. The GSH-S gene of patient 1, studied elsewhere, revealed an 808 T-->C. The GSH-S gene of patient 4 was not available for study. The present study demonstrates that GSH-S deficiency is also present in Spain and further supports the molecular and clinical heterogeneity of this enzymopathy

Time-course analysis and comparison of acute and chronic intrastriatal quinolinic acid administration on forelimb reaching deficits in the rat

Rats were trained to use a single forelimb for a food pellet retrieval task. During baseline testing all rats exhibited > 90% use of a preferred limb for the task. Following baseline, rats were subjected to chronic administration (18 day) or acute injection of quinolinic acid (QUIN) or vehicle to the striatum contralateral to the preferred limb. Rats were tested 48 h after insertion of chronic delivery probes or after acute injection and retested every 48 h over an 18-day period. Compared to vehicle, rats receiving chronic QUIN (7.6 nmol/h) exhibited an increase in the number of reach attempts required to meet task criteria. Chronic QUIN did not produce a significant change in latency to initiate the task or an increase in latency to complete the task. No rats exposed to chronic QUIN exhibited a switch in limb preference for the task. Unlike animals exposed to chronic QUIN, a significant number of animals receiving acute QUIN injections switched to exclusive use of the ipsilateral (nonpreferred) limb for the task. Quantitative histological analysis revealed no significant difference in lesion volume between acute and chronic lesion animals. These findings suggest that behavioral manifestations of histopathologically similar lesions may be vastly different depending on the methods used to produce these lesions. More specifically, the acute injection model resulted primarily in forelimb disuse, whereas the chronic model resulted in continued abnormal use of the affected limb. Understanding adaptive strategies used in these models may be particularly important when testing newly developed transgenic models of neurodegenerative diseases and the therapeutic potential of newly developed neuroprotectants.

Neurochemical effects of L-pyroglutamic acid

The effect of L-pyroglutamic acid, a metabolite that accumulates in pyroglutamic aciduria, on different neurochemical parameters was investigated in adult male Wistar rats. Glutamate binding, adenylate cyclase activity and G protein coupling to adenylate cyclase were assayed in the presence of the acid. L-pyroglutamic acid decreased Na(+)-dependent and Na(+)-independent glutamate binding. Basal and GMP-PNP stimulated adenylate cyclase activity were not affected by the acid. Furthermore, rats received unilateral intrastriatal injections of 10-300 nmol of buffered L-pyroglutamic acid. Vehicle (0.25 M Tris-Cl, pH 7.35-7.4) was injected into the contralateral striatum. Neurotoxic damage was assessed seven days after the injection by histological examination and by weighing both cerebral hemispheres. No difference in histology or weight could be identified between hemispheres. These results suggest that, although capable of interfering with glutamate binding, pyroglutamate did not cause a major lesion in the present model of neurotoxicity.

A novel device for chronic intracranial drug delivery via microdialysis

A system is described for chronic intracranial drug administration in the rat using a modified in vivo microdialysis probe coupled to an Alzet model 2002 osmotic minipump. The results presented demonstrate that this system can be used for the chronic administration of quinolinic acid with minimal non-specific damage. Each pump delivered approximately 225 microliters of solution over a period of 19-20 days when tested in vitro. The dialysis units were uniform in function, delivering greater than 93% of the [3H]quinolinic acid initially loaded into the minipump. For in vivo analysis of this apparatus the dose of quinolinic acid tested produced extensive destruction of the striatum. The present system allows reliable drug diffusion over a relatively large area without pressure injection variability. In conclusion, we have developed a simple and inexpensive technique for administration of drugs into brain parenchyma with substantial advantages over previously used techniques.

Dopaminergic modulation of excitotoxicity in rat striatum: evidence from nigrostriatal lesions

Considerable evidence indicates that dopamine may, under certain circumstances, play a role in the mediation of central nervous system tissue damage. Furthermore, recent studies suggest a synergistic role between the neurotoxic effects of excitatory amino acids and dopamine. To address this issue, rats received a unilateral injection of 6-hydroxydopamine or vehicle into the medial forebrain bundle. After recovery (18 days), both groups of animals received an ibotenic acid injection of the ipsilateral striatum. Seven days later the brains were removed and the size of the striatal lesion was assessed histologically and by means of receptor autoradiography. Regional analysis of profound D1 receptor loss was determined using [3H]SCH 23390, and extent of astrocytic proliferation was examined using autoradiography with the peripheral benzodiazepine receptor ligand [3H]R05-4864. Prior interruption of the nigrostriatal pathway (resulting in dopaminergic denervation of the ipsilateral striatum) partially protected this latter structure from subsequent injection of ibotenic acid (the extent of the lesion was reduced by 28%, P less than .05). The findings indicate that endogenous dopamine release may modulate (and intensify) the excitotoxic effects of ibotenic acid.

Nigral dopamine type-1 receptors are reduced in Huntington's disease: a postmortem autoradiographic study using [3H]SCH 23390 and correlation with [3H]forskolin binding

Intrastriatal injection of excitatory amino acids, particularly quinolinic acid, has been proposed as an animal model of Huntington's disease. Such neurotoxic lesions of caudate-putamen result in marked dopamine type-1 (D1) receptor losses in the injected nuclei as well as in the ipsilateral substantia nigra pars reticulata. Postmortem human substantia nigra from Huntington's disease brains and from control brains were examined using in vitro autoradiography. A marked reduction in [3H]SCH 23390 binding (labeling D1 receptors) in the substantia nigra of postmortem brains of Huntington's patients was identified, thus paralleling the alterations seen in the animal models. A positive, statistically significant correlation was also encountered between D1 receptor binding (labeled by [3H]SCH 23390) and [3H]forskolin binding (which identifies adenylate cyclase, a second messenger system linked to D1 receptor activation). The results suggest that in the human--as in lower vertebrates--D1 receptors are located on striatonigral terminals and that D1 receptor loss tends to be paralleled by a reduction in adenylate cyclase. Radioactive agents selective for the D1 receptor may prove useful in future studies of Huntington's disease using positron emission tomography scanning.