1-Methyl- 1,2,3,4-Tetrahydroisoquinoline, Decreasing in 1-Methyl-4-Phenyl-1,2,3,6-Tetrahydropyridine-Treated Mouse, Prevents Parkinsonism-Like Behavior Abnormalities

In 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated mouse brain, there was no significant increase or decrease in the content of an endogenous amine, 1,2,3,4-tetrahydroisoquinoline (TIQ), which is well noted for inducing parkinsonism, whereas another endogenous amine, 1-methyl-1,2,3,4-tetrahydroisoquinoline (1-MeTIQ), was markedly reduced. This result agrees with the finding in human idiopathic parkinsonianism, confirmed by our previous research. In addition, pretreatment with 1-MeTIQ completely prevented MPTP- or TIQ-inducing bradykinesia, a symptom of parkinsonism. This study confirmed that 1-MeTIQ plays an important role in preventing the pathogenesis of parkinsonism and is a possible leading compound of anti-parkinsonism agents.     

Inhibition of mitochondrial respiration by 1,2,3,4-tetrahydroisoquinoline-like endogenous alkaloids in mouse brain

Since the discovery of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced parkinsonism, it has been postulated that (a) MPTP-like toxin(s) such as 1,2,3,4-tetrahydroisoquinoline (TIQ) may induce Parkinson's disease. As the neuronal degeneration in MPTP-induced parkinsonism is thought to be caused by the inhibition of the mitochondrial respiration by 1-methyl-4-phenylpyridinium ion (MPP⁺), we studied the effects of TIQ-like alkaloids including dopaminederived ones on the mitochondrial respiration using mouse brains. TIQ, tetrahydropapaveroline (THP), and tetrahydropapaverine (THPV) produced significant inhibition of the state 3 and 4 respiration and respiratory control ratio supported by glutamate + malate, the activity of Complex 1 and the ATP synthesis. Among those compounds, THPV was most potent. Toxic properties of these compounds on mitochondria were quite similar to that of MPP⁺. Our results support the hypothesis that (a) MPTP- or MPP⁺-like substance(s) may be responsible for the nigral degeneration in Parkinson's disease.Abbreviations used MPTP 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine - MPP⁺ 1-methyl-4-phenylpyridinium ion - ATP adenosine triphosphate - ADP Adenosine diphosphate - TCL tricarboxylic acid - TIQ cycle: 1,2,3,4-Tetrahydroisoquinoline - THPV Tetrahydropapaverine - THP Tetrahydropaveroline     

Simultaneous analysis of 1,2,3,4-tetrahydroisoquinolines by high-performance liquid chromatography using 4-(5,6-dimethoxy-2-phthalimidinyl)-2-methoxyphenylsulfonyl chloride as a fluorescent labeling reagent

A highly sensitive high-performance liquid chromatographic method for the simultaneous analysis of 1,2,3,4-tetrahydroisoquinolines (TIQs) in the rat brain was developed. 1,2,3,4-Tetrahydroisoquinoline (TIQ), 1-methyl-1,2,3,4-tetrahydroisoquinoline (1-MeTIQ) and 1-benzyl-1,2,3,4-tetrahydroisoquinoline (1-BeTIQ) were derivatized with 4-(5,6-dimethoxy-2-phthalimidinyl)-2-methoxyphenylsulfonyl chloride to produce fluorescent sulfonamides. The labeling reaction was carried out at 50 degrees C for 15 min at pH 8.5. The fluorescent derivatives were separated on a reversed-phase column by gradient elution using (A) water-(B) acetonitrile/methanol (55:45) at 55 degrees C and detected by fluorescence measurement at 318 nm (excitation) and 398 nm (emission). The detection limits (signal-to-noise ratio=3) were 8-9 fmol per injection. The relative standard deviations (n=6) of TIQs were 2.6-10.5% and the recoveries were 87.6, 101.8 and 75.2%, respectively. The concentrations of TIQ, 1-MeTIQ and 1-BeTIQ in normal rat brains (n=6) were 0.7+/-0.3 (0.10+/-0.04), 3.4+/-1.5 (0.50+/-0.22) and 1.3+/-1.8 pmol/g (0.30+/-0.41 ng/g), respectively.     

Presence of tetrahydroisoquinoline and 1-methyl-tetrahydro-isoquinoline in foods: compounds related to Parkinson's disease

This is the first report confirming the presence of 1,2,3,4-tetrahydroisoquinoline (TIQ) and 1-methyl-1,2,3,4-tetrahydroisoquinoline(1MeTIQ) in a number of foods with a high 2-phenylethylamine content. These compounds were determined by gas chromatography-mass spectrometry. This study also confirmed that 1MeTIQ and TIQ can cross the blood-brain barrier in rat. Thus, these compounds, suspected to have relation to parkinson's disease, may accumulate in the brain from food sources.     

N-Methylation of Dopamine-Derived 6,7-Dihydroxy-1,2,3,4-Tetrahydroisoquinoline, (R)-Salsolinol, in Rat Brains: In Vivo Microdialysis Study

N-Methylation of (R)-1-methyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline [(R)-salsolinol] derived from dopamine was proved by in vivo microdialysis study in the rat brain. The striatum was perfused with (R)-salsolinol and N-methylated compound was identified in the dialysate using HPLC and electrochemical detection with multichanneled electrodes. N-Methylation of (R)-salsolinol was confirmed in three other regions of the brain, the substantia nigra, hypothalamus, and hippocampus. In the substantia nigra, the amount of N-methylated (R)-salsolinol was significantly larger than in the other three regions. These results indicate that around dopaminergic neurons, particularly in the substantia nigra, (R)-salsolinol was methylated into N-methyl-(R)-salsolinol, which has a chemical structure similar to that of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, the selective dopaminergic neurotoxin. N-Methylation of tetrahydroisoquinolines and beta-carbolines have already been proven to increase their toxicity to dopaminergic neurons and N-methylation might be an essential step for these alkaloids to increase their toxicity. On the other hand, after perfusion of (R)-salsolinol, release of dopamine and 5-hydroxytryptamine was observed and inhibition of monoamine oxidase was indicated. (R)-Salsolinol and its derivatives may be candidates for being dopaminergic neurotoxins.     

Presence of tetrahydroisoquinoline and 2-methyl-tetrahydroquinoline in parkinsonian and normal human brains

1,2,3,4-Tetrahydroisoquinoline (TIQ) and 2-methyl-1,2,3,4-tetrahydroquinoline (2-Me-TQ) were identified for the first time by gas chromatography-mass spectrometry in the parkinsonian and normal human brains. TIQ, an analogue of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), was markedly increased in the parkinsonian brain and could be an endogenous neurotoxin to induce Parkinson's disease.     

An Endogenous Dopaminergic Neurotoxin, N-Methyl-(R)-Salsolinol, Induces DNA Damage in Human Dopaminergic Neuroblastoma SH-SY5Y Cells

Abstract: Recently, an endogenous neurotoxin, 1( R ),2( N )-dimethyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline [ N -methyl-( R )-salsolinol], was found to elicit parkinsonism in rats with selective depletion of dopamine neurons in the substantia nigra without necrotic tissue reaction. The mechanism of the cell death was examined by detection of DNA damage using a single-cell gel electrophoresis (comet) assay in human dopaminergic neuroblastoma SH-SY5Y cells. Only N -methylsalsolinol was found to induce DNA damage, whereas other catechol isoquinolines, such as ( R )-salsolinol, ( S )-salsolinol, and 1,2-dimethyl-6,7-dihydroxyisoquinolinium ion, did not. The ( R )-enantiomer of N -methylsalsolinol damaged DNA much more profoundly than the ( S )-enantiomer. Cycloheximide protected the cells from DNA damage, suggesting that an apoptotic process may account for the DNA damage. Morphological changes indicating apoptotic cell death were also confirmed. Antioxidants and deprenyl reduced DNA damage, indicating that the damage was initiated by oxidative stress and that neuroprotection by deprenyl may be partially ascribed to its prevention of DNA damage. Apoptosis induced by neurotoxins may be a mechanism underlying the cell death of dopamine neurons in the substantia nigra of Parkinson's disease.     

Presence of methyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinolines, derivatives of the neurotoxin isoquinoline, in parkinsonian lumbar CSF.

The TIQ derivatives 2-methyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline (2-MDTIQ) and 1-methyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline (1-MDTIQ, salsolinol) were identified the first time as possible endogenous neurotoxins in parkinsonian but not in normal human lumbar cerebrospinal fluid by high performance liquid chromatography with electrochemical detection. Additionally, MDTIQ analogues were incubated with a monoamine oxidase (MAO) assay. MAO was able to metabolize dose-dependently 2-MDTIQ, whereas 1-MDTIQ was not modified by the enzyme.     

Tetrahydroisoquinoline alkaloids of the Mexican columnar cactus Pachycereus Weberi

Eight tetrahydroisoquinoline alkaloids have been crystallized and identified from the nonphenolic and phenolic extracts of the giant Mexican cereoid cactus, Pachycereus weberi (Coult.) Br. and R. The identities were established as 5,6,7-trimethoxy-1,2,3,4- tetrahydroisoquinoline (nortehuanine) 1; 7,8-dimethoxy-1,2,3,4-tetrahydroisoquinoline (lemaireocercine) 2; 7-methoxy-1, 2,3,4-tetrahydroisoquinoline (weberidine) 3; 5,6,7,8-tetramethoxy-1,2,3,4-tetrahydroisoquinoline (weberine) 4; 6,7- dimethoxy-1,2,3,4-tetrahydroisoquinoline (heliamine) 5; 2-methyl-6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline (N- methylheliamine or oxymethyl-corypalline) 6; 2-methyl-5,6,7-trimethoxy-1,2,3,4-tetrahydroisoquinoline (tehuanine) 7; and 1,2-dimethyl-6,7-dimethoxy-8-hydroxy-1,2,3,4-tetrahydroisoquinoline (pellotine) 8. Compounds 1- 4 have not been identified previously as natural compounds, while compounds 5-8 are previously known cactus alkaloids.     

Presence of 2-methyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline and 1,2-dimethyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline, novel endogenous amines, in parkinsonian and normal human brains

2-Methyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline and 1,2-dimethyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline were identified for the first time as novel endogenous amines in parkinsonian and normal human brains by gas chromatography-mass spectrometry. It is of interest that these tetrahydroisoquinolines are analogues of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) which produces Parkinson's disease.     

Pharmacological characterization of mammalian D1 and D2 dopamine receptors expressed in Drosophila Schneider-2 cells

Mammalian D1 and D2 dopamine receptors were stably expressed in Drosophila Schneider-2 (S2) cells and screened for their pharmacological properties. Saturable, dose-dependent, high affinity binding of the D1-selective antagonist [3H]SCH-23390 was detected only in membranes from S2 cells induced to express rat dopamine D1 receptors, while saturable, dose-dependent, high affinity binding of the D2-selective antagonist [3H]methylspiperone was detected only in membranes from S2 cells induced to express rat dopamine D2 receptors. No specific binding of either radioligand could be detected in membranes isolated from uninduced or untransfected S2 cells. Both dopamine D1 and D2 receptor subtypes displayed the appropriate stereoselective binding of enantiomers of the nonselective antagonist butaclamol. Each receptor subtype also displayed the appropriate agonist stereoselectivities. The dopamine D1 receptor bound the (+)-enantiomer of the D1-selective agonist SKF38393 with higher affinity than the (-)-enantiomer, while the dopamine D2 receptor bound the (-)-enantiomer of the D2-selective agonist norpropylapomorphine with higher affinity than the (+)-enantiomer. At both receptor subtypes, dopamine binding was best characterized as occurring to a single low affinity site. In addition, the low affinity dopamine binding was also found to be insensitive to GTPgammaS and magnesium ions. Overall, the pharmacological profiles of mammalian dopamine D1 and D2 receptors expressed in Drosophila S2 cells is comparable to those observed for these same receptors when they are expressed in mammalian cell lines. A notable distinction is that there is no evidence for the coupling of insect G proteins to mammalian dopamine receptors. These results suggest that the S2 cell insect G system may provide a convenient source of pharmacologically active mammalian D1 and D2 dopamine receptors free of promiscuous G protein contaminants.     

Detection of 1-phenyl-N-methyl-1,2,3,4-tetrahydroisoquinoline and 1-phenyl-1,2,3,4-tetrahydroisoquinoline in human brain by gas chromatography—tandem mass spectrometry

1-Phenyl-N-methyl-1,2,3,4-tetrahydroisoquinoline and 1-phenyl-1,2,3,4-tetrahydroisoquinoline were detected for the first time in parkinsonian human brain using gas chromatography-tandem mass spectrometry (GC-MS-MS). Since these compounds are structural analogues of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) that produces parkinsonism in humans, they might be candidates for endogenous MPTP-like neurotoxins.     

Determination of 1-methyl-1,2,3,4-tetrahydroisoquinoline in mouse brain after treatment with haloperidol by gas chromatography–selected ion monitoring

The content of the endogenous amine, 1-methyl-1,2,3,4-tetrahydroisoquinoline (1-MeTIQ), in mouse brain, treated with the antipsychotic agent haloperidol (HP) was determined by GC–SIM (selected ion monitoring) system. 1-MeTIQ in brain was extracted with chloroform at pH 11–12 and was detected as PFP derivative by GC–SIM. The 1-MeTIQ contents in mouse brains following intraperitoneal administration of HP or its dehydrated product, HPTP (1 and 4 mg/kg per day, for four days), were markedly reduced compared with control groups. This result agrees well with the findings in human idiopathic parkinsonianism and in MPTP-treated mouse brain. In addition, this finding suggests that the change of the endogenous amine 1-MeTIQ content in the brain plays an important role in the pathogenesis of toxin-induced parkinsonism.     

Enzymatic condensation of dopamine and acetaldehyde: a salsolinol synthase from rat brain

Salsolinol (1-methyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline; Sal) is structurally similar to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, which is supposed to have a role in the development of Parkinson-like syndrome in both human and non-human subjects. In the human brain, the amount of (R)-enantiomer of Sal is much higher than (S)-enantiomer, suggesting that a putative enzyme may participate in the synthesis of (R)-salsolinol, called (R)-salsolinol synthase. In this study, the (R)-salsolinol synthase activity in the condensation of dopamine and acetaldehyde was investigated in the crude extracts from the brains of Sprague Dawley rats. Identification of the enzymatic reaction products and enzyme activity detection were achieved by HPLC-electrochemical detection. The discovery of this enzyme activity in rat’s brain indicates the natural existence of (R)-salsolinol synthase in the brains of humans and rats, and it is distributed in most brain regions of rat with higher activity in soluble proteins extracted from striatum and substantia nigra.     

The mechanism of 1,2,3,4-tetrahydroisoquinolines neuroprotection: the importance of free radicals scavenging properties and inhibition of glutamate-induced excitotoxicity

1-Methyl-1,2,3,4-tetrahydroisoquinoline (1MeTIQ), unlike several other tetrahydroisoquinolines, displays neuroprotective properties. To elucidate this action we compared the effects of 1MeTIQ with 1,2,3,4-tetrahydroisoquinoline (TIQ), a compound sharing many activities with 1MeTIQ (among them reducing free radicals formed during dopamine catabolism), but offering no clear neuroprotection. We found that the compounds similarly inhibit free-radical generation in an abiotic system, as well as indices of neurotoxicity (caspase-3 activity and lactate dehydrogenase release) induced by glutamate in mouse embryonic primary cell cultures (a preparation resistant to NMDA toxicity). However, in granular cell cultures obtained from 7-day-old rats, 1MeTIQ prevented the glutamate-induced cell death and 45Ca2+ influx, whereas TIQ did not. This suggested a specific action of 1MeTIQ on NMDA receptors, which was confirmed by the inhibition of [3H]MK-801 binding by 1MeTIQ. Finally, we demonstrated in an in vivo microdialysis experiment that 1MeTIQ prevents kainate-induced release of excitatory amino acids from the rat frontal cortex. Our results indicate that 1MeTIQ, in contrast to TIQ, offers a unique and complex mechanism of neuroprotection in which antagonism to the glutamatergic system may play a very important role. The results suggest the potential of 1MeTIQ as a therapeutic agent in various neurodegenarative illnesses of the central nervous system.     

Synthesis, resolution, stereochemistry, and molecular modeling of (R)- and (S)-2-acetyl-1-(4'-chlorophenyl)-6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline AMPAR antagonists

Recently we identified (R,S)-2-acetyl-1-(4'-chlorophenyl)-6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline (6) as a potent non-competitive AMPA receptor antagonist able to prevent epileptic seizures. We report here the optimized synthesis of compound 6, its resolution by chiral preparative HPLC, and the absolute configuration of (R)-enantiomer established by X-ray diffractometry. The biological tests of the single enantiomers revealed that higher anticonvulsant and antagonistic effects reside in (R)-enantiomer as also suggested by molecular modeling studies.     

A N-methyltransferase in human brain catalyses N-methylation of 1,2,3,4-tetrahydroisoquinoline into N-methyl-1,2,3,4-tetrahydroisoquinoline, a precursor of a dopaminergic neurotoxin, N-methylisoquinolinium ion

N-methylation of 1,2,3,4-tetrahydroisoquinoline (TIQ) present in human brain was found by a N-methyltransferase in human brain homogenate. Formation of N-methyl-1,2,3,4-tetrahydroisoquinoline (NMTIQ) from TIQ was quantitatively assayed by high-performance liquid chromatography with electrochemical detection. The reaction required S-adenosyl-L-methionine (SAM) as a methyl donor and in terms of SAM the value of the Michaelis constant, Km, and of the maximal velocity, Vmax, were 5.11 +/- 1.69 microM and 7.31 +/- 0.21 pmol/min/mg protein, respectively. The value of Km and Vmax in terms of TIQ were 20.9 +/- 5.5 microM and 7.98 +/- 1.21 pmol/min/mg protein, respectively. The optimal pH of the reaction was 8.25. A major part of the N-methyltransferase activity was found in the cytosolic fraction of human cortex. Enzymatic formation of NMTIQ indicates that in human brain this compound may be an intermediate of biosynthesis of a potent neurotoxin of dopamine metabolism, N-methylisoquinolinium ion, from naturally-occurring TIQ.     

Benzylic alcohols as stereospecific substrates and inhibitors for aryl sulfotransferase

Aryl sulfotransferase IV catalyzes the 3'-phosphoadenosine-5'-phosphosulfate (PAPS)-dependent formation of sulfuric acid esters of benzylic alcohols. Since the benzylic carbon bearing the hydroxyl group can be asymmetric, the possibility of stereochemical control of substrate specificity of the sulfotransferase was investigated with benzylic alcohols. Benzylic alcohols of known stereochemistry were examined as potential substrates and inhibitors for the homogeneous enzyme purified from rat liver. For 1-phenylethanol, both the (+)-(R)- and (-)-(S)-enantiomers were substrates for the enzyme, and the kcat/Km value for the (-)-(S)-enantiomer was twice that of the (+)-(R)-enantiomer. The enzyme displayed an absolute stereospecificity with ephedrine and pseudoephedrine, and with 2-methyl-1-phenyl-1-propanol; that is, only (-)-(1R,2S)-ephedrine, (-)-(1R,2R)-pseudoephedrine, and (-)-(S)-2-methyl-1-phenyl-1-propanol were substrates for the sulfotransferase. In the case of 1,2,3,4-tetrahydro-1-naphthol, only the (-)-(R)-enantiomer was a substrate for the enzyme. Both (+)-(R)-2-methyl-1-phenyl-1-propanol and (+)-(S)-1,2,3,4-tetrahydro-1-naphthol were competitive inhibitors of the aryl sulfotransferase-catalyzed sulfation of 1-naphthalenemethanol. Thus, the configuration of the benzylic carbon bearing the hydroxyl group determined whether these benzylic alcohols were substrates or inhibitors of the rat hepatic aryl sulfotransferase IV. Furthermore, benzylic alcohols such as (+)-(S)-1,2,3,4-tetrahydro-1-naphthol represent a new class of inhibitors for the aryl sulfotransferase.     

The endogenous amine 1-methyl-1,2,3,4- tetrahydroisoquinoline prevents the inhibition of complex I of the respiratory chain produced by MPP(+)

The endogenous monoamine 1-methyl-1,2,3,4-tetrahydroisoquinoline has been shown to prevent the neurotoxic effect of MPP(+) and other endogenous neurotoxins, which produce a parkinsonian-like syndrome in humans. We have tested its potential protective effect in vivo by measuring the protection of 1-methyl-1,2,3,4-tetrahydroisoquinoline in the neurotoxicity elicited by MPP(+) in rat striatum by tyrosine hydroxylase immunocytochemistry. Because we know that cellular damage caused by MPP(+) is primarily the result of mitochondrial respiratory inhibition at the complex I level, we have extended the study further to understand this protective mechanism. We found that the inhibitory effect on the mitochondrial respiration rate induced by MPP(+) in isolated rat liver mitochondria and striatal synaptosomes was prevented by addition of 1-methyl-1,2,3,4-tetrahydroisoquinoline. This compound has no antioxidant capacity; therefore, this property is not involved in its protective effect. Thus, we postulate that the preventive effect that 1-methyl-1,2,3,4-tetrahydroisoquinoline has on mitochondrial inhibition for MPP(+) could be due to a "shielding effect," protecting the energetic machinery, thus preventing energetic failure. These results suggest that this endogenous amine may protect against the effect of several parkinsonism-inducing compounds that are associated with progressive impairment of the mitochondrial function.     

1-Benzyl-1,2,3,4-Tetrahydroisoquinoline as a Parkinsonism-Inducing Agent: A Novel Endogenous Amine in Mouse Brain and Parkinsonian CSF

Abstract: 1-Benzyl-1,2,3,4-tetrahydroisoquinoline (1BnTIQ) was detected as a novel endogenous amine in mouse brain and parkinsonian CSF by using the gas chromatography-selected ion-monitoring method. The level of 1BnTIQ was very high in CSF of some parkinsonian patients compared with that of controls with other neurological diseases, the mean value being three times higher (parkinsonians: 1.17 ± 0.35 ng/ml of CSF, n = 18; vs. controls: 0.40 ± 0.10 ng/ml of CSF, n = 11; mean ± SEM, not significantly different). The pole test, a toxicological examination to evaluate behavior abnormalities related to Parkinson's disease, was used to examine the pharmacological effect of 1BnTIQ in mice. Repeated administration of 1BnTIQ induced behavior abnormalities, which pretreatment with 1-methyl-1,2,3,4-tetrahydroisoquinoline could prevent. We suggest that 1BnTIQ may be related to the idiopathic Parkinson's disease.