(-)-Deprenyl treatment restores serum insulin-like growth factor-I (IGF-I) levels in aged rats to young rat level.

We studied the effects of treatment with (-)-deprenyl, a monoamine oxidase B inhibitor, on plasma levels of insulin-like growth factor-I (IGF-I) (as indicator of growth hormone (GH) secretion), levels of monoamines and their metabolites, and the activity and content of tyrosine hydroxylase - the rate-limiting enzyme in the biosynthesis of catecholamines - in the hypothalamus and hypophysis of old male rats. Male Wistar rats (22 months old) were treated with 2 mg deprenyl/kg body weight s.c. three times a week for 2 months. At the end of the treatment period, blood was collected for measurement of plasma IGF-I levels by radioimmunoassay (RIA). The concentrations of dopamine, serotonin (5-HT) and their main metabolites were determined by high performance liquid chromatography (HPLC) with electrochemical detection, and the tyrosine hydroxylase content in hypothalamus and hypophysis was determined by enzyme-linked immunoabsorbent assay (ELISA). (-)-Deprenyl treatment produced a pronounced increase in dopamine and 5-HT in both the hypothalamus and hypophysis (P < 0.01). The main dopaminergic metabolite, 3,4-dihydroxyphenylacetic acid (DOPAC), decreased in hypothalamus but not in hypophysis, and treatment had no effect on the concentration of 5-hydroxyindole-3-acetic acid (5-HIAA). The tyrosine hydroxylase activity and tyrosine hydroxylase content increased in hypothalamus and hypophysis (P < 0.05). In the hypophysis the increase in tyrosine hydroxylase activity was consistent with the increase in tyrosine hydroxylase amount. Moreover, (-)-deprenyl treatment restored the IGF-I plasma levels in old rats to a concentration similar to those found in young animals. Postulated anti-aging effects of (-)-deprenyl could hence be due to restoration of hypothalamic hormones such as GH.

Protection of the aged substantia nigra of the rat against oxidative damage by (-)-deprenyl.

1. We have studied the effect of (-)-deprenyl on the oxidative damage that the rat substantia nigra suffers during aging. 2. (-)-Deprenyl (2 mg kg-1, three times a week) administered for two months, beginning at 22 months of age, produced a significant increase in tyrosine hydroxylase (TH) activity (2.67 +/- 0.40 and 3.64 +/- 0.38 nmol mg-1 protein h-1 in untreated aged rats and treated aged rats respectively, P < 0.05) and in TH amount (0.072 +/- 0.012 and 0.128 +/- 0.38 absorbance 405 nm in untreated aged and treated aged rats respectively, P < 0.05). 3. The proteins of aged rat substantia nigra showed a significant decrease of carbonyl groups in treated animals compared with saline-injected control rats (136.2 +/- 21.8 and 71.5 +/- 13.2 c.p.m. microgram-1 protein in untreated aged and treated aged rats respectively, P < 0.05). 4. The carbonyl groups measured in TH enzyme showed a statistically significant decrease (42.3%) after (-)-deprenyl treatment (471.4 +/- 73.0 and 271.9 +/- 50.00 c.p.m. in untreated aged and treated aged rats respectively, P < 0.001). 5. All these results suggest that oxidative damage produced during aging is prevented by (-)-deprenyl treatment and could explain the effect of this drug in Parkinson's disease (PD) and other degenerative diseases such as Alzheimer's disease.

Oxidative inactivation of tyrosine hydroxylase in substantia nigra of aged rat.

Study of the tyrosine hydroxylase enzyme from substantia nigra and striatum during the aging period of the rat has discovered a significant decrease (55%) of TH activity in substantia nigra between 12 and 24 mo of age. The amount of TH in substantia nigra also decreased (30%) during aging. This loss in TH activity of substantia nigra appears to be produced by the decrease in TH content along with an inactivation process. Our finding showed a significant increase of carbonyl groups in the proteins of rat substantia nigra with aging. A statistically significant increase of carbonyl groups in TH enzyme was found in aged rat brain substantia nigra, indicating that oxidative damage could be the inactivation process that explains the decrease in TH activity found during aging. This hypothesis was corroborated by the fact that when rat striatal homogenate was incubated with hydrogen peroxide, there was a time-dependent decrease in TH activity, which highly correlated with measurements of carbonyl groups content of TH enzyme. The importance of these results may be in their relationship, considering that substantia nigra is preferentially affected in many neurodegenerative disorders.

Increase in dopamine turnover and tyrosine hydroxylase enzyme in hippocampus of rats fed on low selenium diet.

We have studied the turnover of dopamine, noradrenaline, and serotonin and their metabolites in hippocampus of adult female rats that were fed control or selenium-deficient diets during 15 days. Under these circumstances, there was an increase of dopamine turnover (4-fold) in rats fed with selenium-deficient diet with respect to controls and also an increase in the tyrosine hydroxylase activity (75.8%), which was the result of the increase of the amount of the enzyme (2-fold), without significant change in the phosphorylation of the tyrosine hydroxylase. In addition the glutathione peroxidase, glutathione reductase, catalase, and superoxide dismutase activities have been studied. After selenium-deficient diet, the enzymatic activities of superoxide dismutase and catalase did not show change with respect to the controls; however glutathione reductase and glutathione peroxidase significantly decreased 15% and 29%, respectively. It is concluded that the increase in dopamine turnover seems to be associated with the induction of tyrosine hydroxylase enzyme. In these conditions the decrease in antioxidant capacity may produce a cascade of events, which accelerates the degenerative process, since the increase in dopamine turnover produces an increase in oxygen radical by monoamine oxidase activity.

Effect of intraventricular injection of 1-methyl-4-phenylpyridinium: protection by acetyl-L-carnitine.

1-methyl-4-phenylpyridinium (MPP+) is the bioactivated product of 1-methyl-4-phenyl- 1, 2, 3, 6-tetrahydropyridine (MPTP). The neurotoxic action of MPP+ injected intracerebroventricularly (ICV) in the rat has been studied, using dopaminergic systems in the substantia nigra, striatum, olfactory bulb, median eminence and hypophysis. The following results were obtained: (1) Rats with ICV administration of 1 microliter MPP+ solution (62.5 micrograms of MPP+ rat) showed 50% mortality; (2) The ICV administration of MPP+ produced a decrease in dopamine (DA) concentration in different areas of rat CNS studied: striatum (83%), hypophysis (95%) and median eminence (70%). However, olfactory bulb and substantia nigra were not affected; (3) MPP+ by ICV administration produced neurotoxic effect on the dopaminergic system. We also studied the possible protective action of acetyl-L-carnitine (ALC) against the neurotoxic action of MPP+. Rats were intraperitoneally injected daily for 8 days with 100 mg kg-1 of ALC and 3 days from the beginning of the MPP+ treatment; (4) We found that the ALC treatment significantly protected against mortality produced by the ICV injection of MPP+. Rats treated with ALC showed no mortality; (5) We did not find a protective effect on the dopaminergic system studying either catecholamine concentration or measuring tyrosine hydroxylase, neurofilament or glial fibrillary acid protein; (6) The results suggest that the ALC protective action could be related to energy metabolism.

Changes in the histidine residues of Cu/Zn superoxide dismutase during aging.

Cu/Zn-Superoxide dismutase activity (Cu/Zn-SOD) was studied in liver from 3- and 24-month-old rat. A significant decrease of enzyme activity in liver of the aged rat was found. Various amino acid residues and protein carbonyl groups (CO) were measured in purified young and old enzyme. It was found that the 'old' enzyme had one histidine fewer and higher CO content than the 'young' Cu/Zn-SOD. Inactivation 'in vitro' of purified commercial bovine erythrocyte Cu/Zn-SOD led to a decrease in the enzymatic activity, an increase in the CO and one histidine residue modified. A similar behavior between aging and oxidation was suggested.