Vector-mediated l-3,4-dihydroxyphenylalanine delivery reverses motor impairments in a primate model of Parkinson's disease.

Ever since its introduction 40 years ago l-3,4-dihydroxyphenylalanine (l-DOPA) therapy has retained its role as the leading standard medication for patients with Parkinson's disease. With time, however, the shortcomings of oral l-DOPA treatment have become apparent, particularly the motor fluctuations and troublesome dyskinetic side effects. These side effects, which are caused by the excessive swings in striatal dopamine caused by intermittent oral delivery, can be avoided by delivering l-DOPA in a more continuous manner. Local gene delivery of the l-DOPA synthesizing enzymes, tyrosine hydroxylase and guanosine-tri-phosphate-cyclohydrolase-1, offers a new approach to a more refined dopaminergic therapy where l-DOPA is delivered continuously at the site where it is needed i.e. the striatum. In this study we have explored the therapeutic efficacy of adeno-associated viral vector-mediated l-DOPA delivery to the putamen in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-treated rhesus monkeys, the standard non-human primate model of Parkinson's disease. Viral vector delivery of the two enzymes, tyrosine hydroxylase and guanosine-5'-tri-phosphate-cyclohydrolase-1, bilaterally into the dopamine-depleted putamen, induced a significant, dose-dependent improvement of motor behaviour up to a level identical to that obtained with the optimal dose of peripheral l-DOPA. Importantly, this improvement in motor function was obtained without any adverse dyskinetic effects. These results provide proof-of-principle for continuous vector-mediated l-DOPA synthesis as a novel therapeutic strategy for Parkinson's disease. The constant, local supply of l-DOPA obtained with this approach holds promise as an efficient one-time treatment that can provide long-lasting clinical improvement and at the same time prevent the appearance of motor fluctuations and dyskinetic side effects associated with standard oral dopaminergic medication.

A novel therapeutic approach to depression via supplement with tyrosine hydroxylase.

Tyrosine hydroxylase (tyrosine 3-monooxygenase, EC 1.14.16.2, TH) is the rate-limiting enzyme in the biosynthesis of catecholamine neurotransmitters, dopamine (DA), noradrenaline (NE), and adrenaline, in the neurons. The regulated activity of TH is thought to play a critical role in modulating the functional activity of catecholaminergic neuronal systems in the brain. It is well known that the catecholaminergic neuronal systems are associated with depression. Here we showed that TH, delivered by protein transduction domain (PTD), passed through the blood-brain barrier and entered the neurons. Systemic TH treatment improved the behavioral despair in the forced swim test (FST) and the tail suspension test (TST), the two models widely used to screen the potential anti-depressant efficacy. The results indicated a novel and potential therapeutic use of TH in the depression disorder.

A novel therapeutic approach to 6-OHDA-induced Parkinson's disease in rats via supplementation of PTD-conjugated tyrosine hydroxylase.

The present study aimed to evaluate whether the protein transduction domain (PTD)-conjugated human tyrosine hydroxylase (TH) fusion protein was effective on the 6-hydroxydopamine (6-OHDA)-induced Parkinson's disease (PD) model rats. An expression vector pET-PTD-TH harbouring the PTD-TH gene was constructed and transformed to the Escherichia coli BL21 cells for expression. The expressed recombinant PTD-TH with a molecular weight of 61 kD was successfully transduced (1 microM) into the dopaminergic SH-sy5y human neuroblastoma cells in vitro and visualized by immunohistochemical assay. An in vivo experiment in rats showed that the iv administered PTD-TH protein (8 mg/kg) permeated across the blood-brain barrier, penetrated into the striatum and midbrain, and peaked at 5-8 h after the injection. The behavioral effects of PTD-TH on the apomorphine-induced rotations in the PD model rats 8 weeks after the 6-OHDA lesion showed that a single bolus of PTD-TH (8 mg/kg) iv injection caused a decrement of 60% of the contralateral turns on day 1 and 40% on days 5-17. The results imply that iv delivery of PTD-TH is therapeutically effective on the 6-OHDA-induced PD in rats, the PTD-mediated human TH treatment opening a promising therapeutic direction in treatment of PD.

Potentiation of hyperphagia and relief of hypothermia in the genetically obese mouse (genotype, ob/ob) by alpha-methyl tyrosine.

DL-alpha-methyl-p-tyrosine methyl ester hydrochloride affected the hyperphagia and hypothermia characteristic of the genetically obese mouse (genotype, ob/ob) throughout an experimental period of 5 days. Intraperitoneal injections of 100 mg/kg body weight, daily, resulted in a significant increase in the average daily food consumption by 60 per cent, already elevated 35 per cent above that of lean litter-mates. The drug, administered at the same dose, caused a similar percentage elevation of food intake in the lean litter-mates. Rectal temperatures of obese mice were raised significantly throughout the 5-day period by an average of 0.95 degrees C, following administration of the drug. There was a significant rise of 0.75 degrees C in the rectal temperature of lean mice on 2 of the 5 days in the period. Body weight remained unchanged. Further experiments are necessary to determine the site of action at which DL-alpha-methyl-p-tyrosine brings about these effects at this dose in lean and obese mice.