[Development of L-threo-DOPS, a norepinephrine precursor amino acid].

threo-Dihydroxyphenylserine (DOPS) is a synthetic amino acid which can be decarboxylated by L-aromatic amino acid decarboxylase to yield natural form of norepinephrine (l-NE), a principal neurotransmitter in both central and peripheral (sympathetic) nervous systems. Like L-Dopa as an agent for dopamine precursor therapy, DOPS was expected to have a potential as an agent for NE precursor therapy. Previous studies carried out by several groups in early 1970s, however, reached a negative conclusion that threo-DOPS was not an effective precursor of NE in the brain because of its low NE-increasing activity and weak pharmacological action. Since the latter half of 1970s, on the contrary, three Japanese research groups have successfully shown the possibility of DOPS as a useful NE-precursor. That is, Tanaka (Kobe Univ.) showed that L-threo-DOPS is the real l-NE precursor among four DOPS-enantiomers, and that it has several pharmacological activities such as a slow-onset and long-lasting pressor effect, an inhibitory effect on harmaline-induced tremor and so on. Hayashi and Suzuki (Osaka Univ.) found through the mobility study on familial amyloid polyneuropatchy (FAP) that the progress of the disease develops NE-deficiency (NE-D), that severe orthostatic hypotention in FAP might be due to NE-D, and that L-DOPS has favorable effects on this symptom. Narabayashi (Juntendo Univ.) found that NE-D develops in patients with advanced Parkinson's disease (PD), that a freezing phenomenon in these patients might be associated with NE-D, and that L-DOPS improves the phenomenon. Based on these findings, the development of L-DOPS for registration had been undertaken by Sumitomo Pharmaceuticals Co., and an approval was given to it in 1989 as an agent for the treatment orthostatic hypotention in FAP or Shy-Drager syndrome and freezing phenomenon in PD. Preclinical and clinical studies done in the R&D confirmed that L-DOPS markedly restored NE-D and improved related-syndrome in the NE-deficient animals/patients, and that its actions were slow-onset, long-lasting and gentle. The R & D of L-DOPS described in this paper includes studies on industrial production, efficacy pharmacology (mode of action), metabolism and clinical trial of this agent.

Pharmacological actions of SM-9018, a new neuroleptic drug with both potent 5-hydroxytryptamine2 and dopamine2 antagonistic actions.

Pharmacological studies were undertaken to clarify the profile of cis-2-(4-(4-(1,2-benzisothiazol-3-yl)-1-piperazinyl) butyl) hexahydro-1H-isoindole-1,3-(2H)-dione hydrochloride (SM-9018), a new neuroleptic drug. SM-9018 had very high binding affinities for both 5-hydroxytryptamine2 (5-HT2) and dopamine2 (D2) receptors, unlike many other neuroleptics. SM-9018 also strongly inhibited 5-HT2 receptor-mediated behavior such as tryptamine-induced clonic seizure and D2 receptor-mediated behavior such as methamphetamine-induced hyperactivity, apomorphine-induced stereotypy and climbing behavior. SM-9018 possessed only a weak cataleptogenic activity, which may be clinically related to extrapyramidal side effects, despite its potent D2 antagonistic activity. Moreover, SM-9018 induced weak central depressant effects such as inhibition of spontaneous locomotor activity and motor coordination, as compared with classical neuroleptics (haloperidol and chlorpromazine). These results suggest that SM-9018 is a new neuroleptic drug with both potent 5-HT2 and D2 antagonistic activities and with low cataleptogenic and central depressant activities.

Pharmacological and biochemical assessment of SM-10888, a novel cholinesterase inhibitor.

The effects of the compound SM-10888 (9-amino-8-fluoro-1,2,3,4-tetrahydro-2,4-methanoacridine citrate) in a number of pharmacological and biochemical tests were studied and compared to those of tacrine (THA), amiridin, HP-029 and physostigmine. SM-10888 inhibited cholinesterase activity (IC50: 2.3 x 10(-7) M) in rat cortical P2 fraction with almost the same potency as THA, while SM-10888 was 2-4 times more potent than amiridin and HP-029, but about 10 times less potent than physostigmine. When given to mice p.o., SM-10888 induced central (hypothermia) and peripheral (salivation) cholinergic effects. When the ratio of the ED50 value for hypothermia to that for salivation was regarded as the index of the selectivity to the central nervous system (CNS), SM-10888 was shown to be about 3 times more selective to the CNS than the other four drugs in mice. The minimum effective dose of SM-10888 for its increasing effect on acetylcholine (ACh) content in the mouse cerebral cortex was about 10 times higher than that of physostigmine, but 5-10 times lower than those of THA, amiridin and HP-029. These results suggest that SM-10888 is an adequate drug for increasing the brain ACh content with less peripheral cholinergic side effects than THA, amiridin, HP-029 and physostigmine.

Effect of a novel CNS-selective cholinesterase inhibitor, SM-10888, on habituation and passive avoidance responses in mice.

The effects of the tacrine (THA) derivative SM-10888 (9-amino-8-fluoro-1,2,3,4-tetrahydro-2,4-methanoacridine citrate) on habituation and passive avoidance responses were studied in mice. We examined its effects on habituation of exploratory activity, measured by photo-cell beam interruptions in a small, simple cage and cycloheximide (CXM)- or electroconvulsive shock (ECS)-induced stepdown type passive avoidance response (PAR) failures in comparison with those of THA, amiridin, HP-029 and physostigmine. SM-10888 (6 mg/kg, p.o.) administered post-acquisition session enhanced the retention of habituation. CXM- and ECS-induced PAR failures were improved by SM-10888 (6 mg/kg, p.o.) administered at pre-training or post-training, respectively. THA enhanced the retention of habituation and improved CXM-induced PAR failure at 30 mg/kg, p.o., but did not affect ECS-induced PAR failure at 1-15 mg/kg, p.o. Amiridin and HP-029 were also effective on habituation and CXM-induced PAR failure at 40-50 mg/kg, p.o., but did not affect ECS-induced PAR failure at the tested doses. Physostigmine showed a moderate improvement only in CXM-induced PAR failure. The results indicate that SM-10888 enhanced habituation and improved PAR failures at much lower doses than THA. This seems to depend on its high selectivity to the central nervous system.

Pharmacological properties of SM-3997: a new anxioselective anxiolytic candidate.

Pharmacological properties of SM-3997 (3a alpha,4 beta,7 beta,7a alpha-hexahydro-2-(4-(4-(2-pyrimidinyl)-1- piperazinyl)-butyl)-4,7-methano-1H-isoindole-1,3(2H)-dione dihydrogen citrate) have been examined in rats and mice. SM-3997 showed a dose-related anticonflict activity in rats in a water lick conflict paradigm, and it had no effect on water consumption in a spontaneous water drinking test. The potency of SM-3997 appeared to be equal to that of buspirone and about one-half that of diazepam. No tolerance to the anticonflict activity of SM-3997 was observed following 5 and 10 consecutive days of treatment. Unlike diazepam, SM-3997 had no anticonvulsant effect and had very weak muscle relaxant and hypnotic effects. On the other hand, SM-3997 and buspirone exhibited dopamine antagonistic action, although the potency of SM-3997 was less than one fourth that of buspirone. These results show that SM-3997 is a new anxioselective anxiolytic agent which is weaker than buspirone in the dopaminergic neuron system.

Studies on the activity of L-threo-3,4-dihydroxyphenylserine (L-DOPS) as a catecholamine precursor in the brain. Comparison with that of L-dopa.

L-Threo-3,4-dihydroxyphenylserine (L-DOPS) was compared with L-3,4-dihydroxyphenylalanine (L-DOPA) with respect to their activities as central amine precursors. The apparent Km value (the substrate affinity) of L-DOPS for aromatic L-amino acid decarboxylase was nearly equal to that of L-DOPA, whereas the vmax value (the rate of decarboxylation) of L-DOPS was much smaller than that of L-DOPA, the penetration of L-DOPS into the brain through the blood-brain barrier was found to be smaller (about one-fourth) than that of L-DOPA but, for an amine precursor, it was still substantial. Unlike L-DOPA, L-DOPS did not cause a marked accumulation of norepinephrine (NE), the corresponding catecholamine in the brain, but nialamide, a monoamine oxidase inhibitor significantly enhanced the L-DOPS-induced rise of NE. Moreover, the brain concentration of 3-methoxy-4-hydroxy-phenylethyleneglycol (MHPG), the principal end metabolite of NE, was increased markedly by L-DOPS. These results suggest that L-DOPS may act as an NE precursor in the brain and activate NE neurons by increasing the turnover rate of NE.

Effect of L-threo-3,4-dihydroxyphenylserine(L-threo-DOPS) on brain and serum MHPG levels in mice: evidence for NE formation in CNS.

Effects of L-threo-DOPS on brain and serum concentrations of 3-methoxy-4-hydroxyphenylethyleneglycol (MHPG), a major metabolite of 1-norepinephrine(NE) were studied in mice. An intraperitoneal(i.p.) injection of L-threo-DOPS markedly increased both serum and brain MHPG levels in mice. This increase in the brain was dose-dependent at doses up to 800 mg/kg, and lasted for 4 h or more. Though the increase in serum total-MHPG was 3-4 times greater than that in brain MHPG, the decline was rapid as compared with the case of brain MHPG. The L-threo-DOPS-induced increase in MHPG was inhibited by i.p. pretreatment with benserazide, a peripheral decarboxylase inhibitor, in both serum and brain. This inhibition in the brain, however, was observed at about 20 times higher doses of benserazide than that in serum. On the contrary, an intracerebroventricular(i.c.v.) injection of benserazide inhibited the increase in brain MHPG to about the same degree as that in serum MHPG. These results suggest that the L-threo-DOPS-induced increase in brain MHPG is not likely to originate in peripheral organs including the brain capillary, and that L-threo-DOPS can be converted to NE by aromatic L-amino acid decarboxylase(AADC) in the brain parenchyma.

Studies on the central action of L-threo-3,4-dihydroxyphenyl-serine (L-threo-DOPS) in FLA-63-treated mice.

In order to clarify the central action of L-threo-DOPS, the effect of benserazide on behavioral and biochemical changes by L-threo-DOPS in FLA-63-treated mice was studied. L-threo-DOPS in combination with nialamide markedly increased both the locomotor activity and the concentrations of the brain, heart and kidney norepinephrine (NE) in the FLA-63-treated mice. Benserazide at low doses did not alter either the rise of the brain NE level or the increase in locomotor activity, whereas it significantly inhibited the rise of the heart and kidney NE levels. Benserazide at a high dose significantly inhibited all of them. These results suggested that the increase in locomotor activity might be mediated via activation of the central noradrenergic neurons system by L-threo-DOPS.

Effect of L-threo-3,4-dihydroxyphenylserine (L-DOPS), an immediate precursor of norepinephrine, on the cerebral blood flow in rats.

L-threo-3,4-Dihydroxyphenylserine (L-DOPS), a norepinephrine (NE) precursor, 3 mg/kg, i.v., increased the cerebral blood flow (CBF) in both the striatum and hippocampus as well as the mean arterial blood pressure (MABP) in urethane-anesthetized rats, as NE infusion did. The L-DOPS induced increase in CBF was inhibited by benserazide (3 mg/kg/hour), a peripheral aromatic L-amino acid decarboxylase inhibitor, and propranolol (3 mg/kg, i.p.), a beta-adrenoceptor blocker as well. These results suggest that the effects of L-DOPS may be attributed to the action of NE formed from L-DOPS, and the action may be mediated by stimulation of beta-adrenoceptor.

Reversal by L-threo-3,4-dihydroxyphenylserine (L-threo-DOPS), a L-norepinephrine precursor of reserpine- or tetrabenazine-induced hypothermia.

The effects of L-threo-DOPS on the hypothermia and the decrease of brain norepinephrine (NE) concentration in the mouse pretreated with reserpine or tetrabenazine were studied. Reserpine (5 mg/kg, i.p.) or tetrabenazine (40 mg/kg, i.p.) produced a significant decrease in body temperature. The i.p. injection of L-threo-DOPS (100, 200 and 400 mg/kg) reversed these hypothermia in a dose-dependent manner. These hypothermia were also antagonized by the i.c. injection of NE (5 micrograms/mouse). Both reserpine and tetrabenazine markedly decreased the brain content of NE, and L-threo-DOPS (400 mg/kg, i.p.) recovered it. These results suggested that L-threo-DOPS would reverse the reserpine- or tetrabenazine-induced hypothermia at least in part by the formation of NE in the central nervous system.

Diuretic effect of L-threo-3,4-dihydroxyphenylserine, a noradrenaline precursor, in rats and mice.

L-Threo-DOPS, a noradrenaline (NA) precursor, produced a dose-dependent increase in the volume of urine in mice and rats. It also increased the total output of sodium and chloride ions, but not the excretion of potassium ion. Treatment with peripheral decarboxylase inhibitors antagonized not only the diuretic action, but also the increase in the concentration of kidney NA produced by L-threo-DOPS. These results suggest that the diuretic action of L-threo-DOPS might not be due to its direct action, but largely to NA formed by its decarboxylation in the kidney.

Reversal of the reserpine-induced ptosis by L-threo-3,4-dihydroxy-phenylserine (L-threo-DOPS), a (-)-norepinephrine precursor, and its potentiation by imipramine or nialamide.

The effect of L-threo-DOPS on the reserpine-induced ptosis in mice and its modification by imipramine, a norepinephrine (NE) uptake inhibitor, or nialamide, a monoamineoxidase inhibitor, were studied. Intraperitoneal (i.p.) injection of L-threo-DOPS (800 mg/kg) significantly reduced the severity of the ptosis. This reversal of the ptosis by L-threo-DOPS was markedly potentiated by i.p. injection of either imipramine (2.5 mg/kg) or nialamide (30 mg/kg). Response to L-threo-DOPS was also significantly potentiated by intracerebroventricular (i.c.v.) injection of imipramine (10 micrograms). On the other hand, this treatment with imipramine (10 micrograms, i.c.v.) also significantly potentiated the reversal of the ptosis by NE (20 micrograms, i.c.v.), but the reversal by the subcutaneous (s.c.) injection of NE (1 and 3 mg/kg) was not affected. Reserpine (5 mg/kg, i.p.) markedly decreased the brain content of NE in mice, whereas L-threo-DOPS (400 mg/kg, i.p.) slightly restored it. Moreover, by the pretreatment with nialamide (30 mg/kg, i.p.), L-threo-DOPS produced a significant increase in the brain content of NE in reserpine-treated mice. These results suggested that L-threo-DOPS was capable of reversing the reserpine-induced ptosis due to the formation, at least in part of (-)-NE at the synaptic sites of central noradrenergic neurons.