Metabolism and penetration through blood-brain barrier of parkinsonism-related compounds. 1,2,3,4-Tetrahydroisoquinoline and 1-methyl-1,2,3,4-tetrahydroisoquinoline.

14C-Labeled 1,2,3,4-tetrahydroisoquinoline (TIQ) and 1-methyl-1,2,3,4-tetrahydroisoquinoline (1MeTIQ) were synthesized, and their metabolism and tissue distribution were studied. Both compounds showed similar metabolic patterns. In 24 hr after po administration (50 mg/kg) to rats, 76% of TIQ and 72% of 1MeTIQ were excreted unchanged, and 2.7 and 8.7% were excreted as the 4-hydroxyl derivatives, 4-hydroxy-TIQ and 4-hydroxy-1MeTIQ, respectively. Small amounts of N-methylated metabolites, 2-methyl-TIQ (0.4%) and 2-methyl-1MeTIQ (0.7%) were detected. Isoquinoline (2.5%) also was found as a metabolite of TIQ and 1-methyl-3,4-dihydroisoquinoline (1.0%) was found as a metabolite of 1MeTIQ. The concentration of labeled compounds in the brain was about 4.5-fold higher than the blood concentration at 4 hr after dosing, and over 90% was unchanged TIQ or 1MeTIQ. These data indicated that TIQ and 1MeTIQ easily passed through the blood-brain barrier and were concentrated in the brain. Thus, it appears that TIQ and 1MeTIQ as endogenous or exogenous amines may accumulate in the brain and may be related to the onset of Parkinson's disease.     

Tetrahydroisoquinoline derivatives as possible Parkinson's disease-inducing substances

Parkinson's disease (PD) is believed to be induced by the interaction of genetic predisposition and environmental factors, and a type of neurotoxin is proposed to be one of the environmental factors. We designed and synthesized a molecule, 1-benzyl-1,2,3,4-tetrahydroisoquinoline (1BnTIQ) as a possible PD-eliciting neurotoxin and evaluated its characteristics relevant to PD. 1BnTIQ is an endogenous amine in the brain and the 1BnTIQ content increases in the patients with PD. Repeated administration of 1BnTIQ induced PD-like symptoms in monkeys and mice. 1BnTIQ was biosynthesized from 2-phenylethylamine and phenylacetaldehyde, which is a metabolite of 2-phenylethylamine, and used in in vivo and in vitro studies. 1BnTIQ inhibited [3H] dopamine uptake in HEK293 cells which stably express dopamine transporter. 1BnTIQ also inhibited NADH-ubiquinone oxidoreductase (complex I) in the mitochondrial respiratory chain. Next, we assessed 1BnTIQ neurotoxicity in the organotypic coculture of the ventromedial portion of the mesencephalon and striatum. 1BnTIQ decreased the dopamine content in the mesencephalon in both dose- and time-dependent manners and it irreversibly reduced the dopamine content. Furthermore, it caused morphological changes in tyrosine hydroxylase-positive cells in the mesencephalon and reduced the number of cells. 1-(3',4'-Dihydroxybenzyl)-1,2,3,4-tetrahydroisoquinoline (3'4'DHBnTIQ) is also an endogenous parkinsonism-inducing 1BnTIQ derivative. In vivo and in vitro studies revealed that 3'4'DHBnTIQ was O-methylated by soluble catechol-O-methyltransferase (COMT). The result that COMT inhibitor suppressed 3'4'DHBnTIQ neurotoxicity suggests that 3'4'DHBnTIQ is metabolically activated by COMT to exert toxic effects.     

Synthesis and neurotoxicity of tetrahydroisoquinoline derivatives for studying Parkinson's disease

Parkinson's disease involves the progressive degeneration of dopaminergic neurons in the substantia nigra. However, the etiology of the disease remains to be elucidated. Endogenous amines, such as 1,2,3,4-tetrahydroisoquinoline (TIQ) derivatives present in the mammalian brain, are known to participate in the pathogenesis of Parkinson's disease. These endogenous neurotoxins have been extensively studied because of their structural resemblance to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), an agent widely used for generating animal models of Parkinson's disease-like symptoms. Investigations of the synthesis and pharmacological properties of TIQ derivatives are expected to contribute to the development of new therapeutic agents for treating Parkinson's disease. In the present study, we describe more efficient synthesis methods for TIQ derivatives via Pummerer-type cyclization of the substrate N-acyl sulfoxide. Furthermore, the modified Pummerer reaction provided a convenient and efficient method for synthesizing various TIQs. TIQ and its derivative, 1-benzyl-TIQ, can induce parkinsonism in primates and rodents. On the other hand, one TIQ derivative, 1-methyl-TIQ, has been shown to prevent MPTP, TIQ, and 1-benzyl-TIQ induced behavioral abnormalities. Therefore, TIQ derivatives are considered to play an important role in both the onset and prevention of Parkinson's disease. In this article, we focus on the synthesis and pharmacological aspects of 1,2,3,4-tetrahydroisoquinoline derivatives in Parkinson's disease.     

Parkinsonism-preventing activity of 1-methyl-1,2,3,4-tetrahydroisoquinoline derivatives in C57BL mouse in vivo

1-Methyl-1,2,3,4-tetrahydroisoquinoline (1MeTIQ), an endogenous parkinsonism-preventing substance, and its 5-, 6-, and 7-hydroxylated derivatives are reported to show in vitro neuroprotective activity against toxicity due to salsolinol in SH-SY5Y human neuroblastoma cells. In the present study, we tested the parkinsonism-preventing potential of these derivatives by means of the pole test in C57BL mice in vivo, and measured brain dopamine contents by liquid chromatography-tandem mass spectrometry. Parkinsonism was induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydroisoquinoline(MPTP), and pretreatment with any of the 1MeTIQ derivatives prevented its induction. 6-Hydroxy-1MeTIQ showed the greatest preventive activity. The amount of dopamine in the brain was reduced by MPTP treatment, and this reduction was suppressed by pretreatment with 1MeTIQ derivatives. These hydroxy-1MeTIQ derivatives may have potential for the treatment of Parkinson's disease as well as 1MeTIQ itself.     

Role of noradrenergic system in the mechanism of action of endogenous neurotoxin 1,2,3,4-tetrahydroisoquinoline: biochemical and functional studies

It is well recognized that 1,2,3,4-tetrahydroisoquinoline (TIQ) is a substance capable of inducing in animals a syndrome, regarded as an animal model of Parkinson's disease. This study was designed to evaluate the effect of the endogenous neurotoxin TIQ on the brain noradrenaline (NA) metabolism in mice and on an arterial blood pressure in rats. It was shown for the first time that TIQ significantly increased NA metabolism, induced NA release and raised the level of its final metabolite, 3-methoxy-4-hydroxyphenylglycol (MHPG), in mouse brain. The comparative biochemical studies using specific agonist (clonidine) and antagonist (yohimbine) of alpha2-adrenergic receptors ligands have shown that observed biochemical effects were similar to those produced by alpha2-adrenergic antagonist, yohimbine. In functional studies, the systolic and diastolic blood pressure was measured using a non-invasive blood pressure transducer. Both acute and multiple treatment with TIQ produced a strong hypotensive effect, having decreased both systolic and diastolic blood pressure in rats. Development of tolerance to the hypotensive effect was observed after multiple treatment with TIQ. The data coming from these experimental studies apparently suggest an important role of the noradrenergic system in the mechanism of action of endogenous compounds from TIQ group. The results may also support the hypothesis assuming a causal relationship between noradrenergic dennervation, activity of the nigrostriatal dopamine system, and some clinical manifestation of Parkinson's disease.     

Endogenous risk factors in Parkinson's disease: dopamine and tetrahydroisoquinolines

The cause of chronic nigral cell death in Parkinson's disease (PD) and the underlying mechanisms remain elusive. The selective action of exogenous and endogenous neurotoxic substances can provide partial explanation of these processes. 1-Methyl-4-phenyl- 1,2,3,6-tetrahydropyridine (MPTP) is an exogenous neurotoxin producing parkinsonism in humans, monkeys and various animals as the result of MAOB-catalyzed conversion of it to the 1-methyl-4-phenyl-pyridinium ion (MPP+), which selectively kills the nigrostriatal dopaminergic neurons. On the other hand, various isoquinoline derivatives were found in the brain, and they are considered to be the endogenous neurotoxins with neurochemical properties similar to those of MPTP, which cause PD. Among them, 1,2,3,4-tetrahydroisoquinoline (TIQ), 1-benzyl-TIQ, and 1-methyl-5,6-dihydroxy-TIQ (salsolinol) have the most potent neurotoxic action. Since PD is a slowly progressing neurodegenerative disease, it has been suggested that it could be connected with excitotoxicity and apoptosis. Therapeutic strategies should focused on the search for the drugs exhibiting antiapoptotic potential such as: antioxidants, MAOB inhibitors, dopaminergic drugs and free radical scavengers.     

Influence of acute and chronic 1,2,3,4-tetrahydroisoquinoline administration on the expression of proenkephalin mRNA in the rat striatum

Animal studies have shown that a depletion of dopamine or blockade of dopamine D2 receptors in the striatum produces an increase in striatal proenkephalin (PENK) mRNA expression and an increase in GABAergic transmission in the globus pallidus. Therefore, it has been suggested that an enhanced striatal PENK mRNA expression may reflect to some extent an increase in the activity of the GABAergic striatopallidal pathway whose overactivity has been suggested to take place in the course of Parkinson's disease. Therefore, the aim of the study was to investigate the role of 1,2,3,4-tetrahydroisoquinoline (TIQ), an endogenous substance suspected of producing parkinsonism in humans, in the regulation of the activity of GABAergic striatopallidal pathway in rats. TIQ administered acutely at the dose of 100 mg/kg ip increased the PENK mRNA expression in the dorsal part of the striatum at two levels I and II (rostral and central striatum, respectively). No changes were noticed in the ventral part of the striatum. Moreover, TIQ given chronically to rats for 3 weeks did not modify the level of PENK mRNA in any examined part of the striatum. The present results show that the effect of TIQ on the PENK mRNA expression is different from that described for proparkinsonian model neurotoxins (MPTP, 6-OHDA) as well as for typical neuroleptics, such as haloperidol.     

Comparative behavioral and neurochemical studies of R- and S-1-methyl-1,2,3,4-tetrahydroisoquinoline stereoisomers in the rat

Background1-Methyl-1,2,3,4-tetrahydroisoquinoline (1-MeTIQ) is present in human and mammalian brain as aracemate (R,S) of two stereoisomers: R- and S-1MeTIQ. The racemate is a mixture of the endogenous, synthesized in the brain dextrorotary R-1MeTIQ, and the exogenous, levorotary form, S-1MeTIQ.MethodsIn this study, we compared the effect of these two stereoisomers of 1MeTIQ with the racemate in the context of their influence on dopamine metabolism and in vivo dopamine release in the rat striatum. Additionally, a behavioral study was used to examine the influence of both enantiomers R- and S-1MeTIQ on locomotor activity of rats.ResultsThe behavioral studies showed that both R- and S-1MeTIQ enantiomers, like the racemate, produced biphasic effects: a slight decrease in the exploratory locomotor activity, and then an increase in the basal locomotor activity. Biochemical ex vivo experiments showed that S-1MeTIQ produced a much stronger inhibition of MAO-dependent dopamine oxidation than the racemate. R-1MeTIQ, in opposite to S-isoform and racemate, did not block dopamine oxidation in the structures which contain dopamine nerve endings (striatum, nucleus accumbens), and in fact did not suppress the level of its intraneuronal metabolite, DOPAC in these brain regions. However, an in vivo microdialysis study demonstrated that the racemate and both stereoisomers (R-1MeTIQ to a lesser extent) significantly elevated the concentration of dopamine in the extraneuronal space in the rat striatum. What is more, the concentration of an extraneuronal dopamine metabolite 3-methoxytyramine (3-MT), which is an indicator of its release, was considerably increased by all the compounds.ConclusionsIn summary of the results, it can be stated that S-1MeTIQ, like the racemate and in contrast to R-stereoisomer, inhibits MAO-dependent dopamine oxidation in all investigated brain structures. In addition, both these substances potentiated COMT-dependent O-methylation in the brain, however, also R-1MeTIQ produced such effect but to a lesser extent. In conclusion, we suggest that R- and S-1MeTIQ enantiomers like the racemate may demonstrate neuroprotective properties in the brain via the activation of dopamine O-methylation catabolic pathway and elevation of its methylated product – 3-MT.     

Protective effect of 1-methyl-1,2,3,4-tetrahydroisoquinoline against dopaminergic neurodegeneration in the extrapyramidal structures produced by intracerebral injection of rotenone

The aim of this paper was to investigate whether rotenone, a pesticide causing experimental parkinsonism, causes direct damage to dopaminergic structure when injected intracerebrally and whether this action may be prevented by peripheral administration of 1-methyl-1,2,3,4-tetrahydroisoquinoline (1MeTIQ), an endogenous compound with anti-dopaminergic activity. Male Wistar rats were injected unilaterally into the median forebrain bundle with 2 microg rotenone, and received 1MeTIQ, 50 mg/kg i.p. 1 h before and then daily for 21 d. To compare the effect of intracerebral and peripheral treatment, rotenone was also given once or for 7 d in a dose of 10 mg/kg s.c. Dopamine, serotonin and their metabolites were assessed by HPLC in the substantia nigra and striatum. While a single subcutaneous rotenone dose did not produce any change in striatal dopamine metabolism, the multiple treatments resulted in changes suggesting a shift in the metabolism towards oxidative desamination and reduction of O-methylation. In contrast to systemic injections, intracerebral-administered rotenone produced a decrease in dopamine and its metabolites content in the striatum (dopamine decrease by 70%) and substantia nigra (dopamine decrease by 35%), without affecting the serotonin system. As those changes were observed 21 d after the injection of rotenone, they suggest a durable neurotoxic effect. The treatment with 1MeTIQ strongly reduced the fall of striatal dopamine concentration. The data suggest that rotenone given peripherally affects metabolic processes in dopaminergic neurons, and this seems to result from its neurotoxic action, which may be observed after an intracerebral injection. 1MeTIQ is able to counteract the damaging action of rotenone and seems to be a potential neuroprotective agent.     

Treatment with 1,2,3,4,-tetrahydroisoquinoline affects glutamate release in the striatum but not the binding of [3H]MK-801 to NMDA receptors in the dopaminergic structures of the rat brain

Overactivity of the glutamatergic system is thought to be closely related to the pathogenesis of Parkinson’s disease. This study aimed to examine the effect of acute administration of 1,2,3,4-tetrahydroisoquinoline (TIQ), an endo- and exogenous amine suspected of inducing parkinsonism in humans on the release of glutamate in the striatum as well as to assess the impact of its chronic treatment on the binding of [³H]MK-801 to NMDA receptors in the dopaminergic structures of the rat brain. Striatal release of glutamate was measured in conscious, freely moving rats using a microdialysis method. [³H]MK-801 binding to NMDA receptors was examined in the striatum, nucleus accumbens and prefrontal cortex by autoradiographic method. TIQ administered acutely at a single dose of 100 mg/kg significantly decreased the level of extracellular glutamate, with the concentration decrease starting at 60 min and reaching minimum at 210 min after TIQ injection. TIQ administered chronically at the same dose for 3 weeks did not alter the binding of [³H]MK-801 to NMDA receptors in the examined dopaminergic structures at either 4 or 72 h after the last chronic injection. These results indicate that TIQ can modulate glutamate release in the striatum but that it does not affect the level of NMDAreceptors in that structure. The latter data complete a list of recently published evidence that distinctly suggest that TIQ acts in the mammalian brain rather as a neuromodulator or even as a neuroprotective agent but not as a parkinsonism-inducing neurotoxin.     

Important role of 3-methoxytyramine in the inhibition of cocaine sensitization by 1-methyl-1,2,3,4-tetrahydroisoquinoline: an in vivo microdialysis study

1-Methyl-1,2,3,4-tetrahydroisoquinoline (1MeTIQ) is an endogenous compound with neuroprotective and antidopaminergic activities. Our previous research has shown that 1MeTIQ prevents morphine addiction and abates the expression of the reinstatement of cocaine self-administration. The current study investigated the mechanism of action of 1MeTIQ that is responsible for its considerable anticraving potential. Accordingly, we performed behavioral tests that measured the influence of 1MeTIQ on the locomotor activity of rats (Wistar) after a single cocaine (15 mg/kg, i.p.) dose and during cocaine sensitization (15 mg/kg, i.p.). In a neurochemical study, we examined the influence of 1MeTIQ on dopamine release in the rat striatum after a single cocaine administration and during cocaine sensitization using an in vivo microdialysis methodology. The data showed that 1MeTIQ (50 mg/kg, i.p.) only slightly inhibited cocaine-induced hyperactivity but completely antagonized the expression of locomotor cocaine sensitization. The in vivo microdialysis study demonstrated that the administration of 1MeTIQ before the acute cocaine injection intensified the cocaine-induced increase in dopamine release and produced a huge and long-lasting elevation of the extraneuronal concentration of dopamine (by approximately 1400%, p < 0.01) in the rat striatum. A significant increase in 3-methoxytyramine (3-MT) (by approximately 400%, p < 0.01) was also observed. During the expression of cocaine sensitization, the administration of 1MeTIQ before the reminder dose of cocaine produced an additional elevation of dopamine release but considerably more strongly increased the concentration of 3-MT in the synaptic cleft (by about 800%, p < 0.01). In light of these data and of our earlier in vitro and in vivo experiments showing a physiological role of 3-MT in the inhibitory regulation of excessive stimulation, we suggest that locomotor hyperactivity is dependent not only on dopamine concentration in the extracellular space, but also on the ratio of [DA/3-MT]. 1MeTIQ administered before the reminder dose of cocaine to cocaine-experienced rats plainly normalized the [DA/3-MT] ratio, which was increased by cocaine, and this effect may be responsible for its anti-addictive action. The results strongly support the view that 1MeTIQ may have a more general anti-abuse potential, and the extraneuronal metabolite of dopamine, 3-MT, may play a crucial role in its anti-craving effects.     

Neurotoxins: 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, 1,2,3,4-tetrahydroisoquinoline and 1-methyl-6,7-dihydroxy-tetrahydroisoquinoline as substrates for FAD-containing monooxygenase of porcine liver microsomes.

The activity of FAD-containing monooxygenase (FMO) (EC 1.14.13.8) of porcine liver microsomes was examined with the neurotoxins, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), 1,2,3,4-tetrahydroisoquinoline (TIQ) and 1-methyl-6,7-dihydroxy-tetrahydroisoquinoline (MDTIQ), as substrates. FMO catalyses these neurotoxins. The kinetic parameters of FMO for the neurotoxins and electron donors were determined. Km values for MPTP, TIQ and MDTIQ were determined to be 47 microM, 6.9 mM and 5.6 mM, respectively. The Km for the electron donor, NADPH, was variable from 31 to 200 microM depending on the substrate used. The activities of FMO for these neurotoxins were comparable with that for dimethylaniline.     

1-methyl-1,2,3,4-tetrahydroisoquinoline protects against rotenone-induced mortality and biochemical changes in rat brain

The effect of single and multiple administration of the neurotoxic pesticide, rotenone, and the potentially neuroprotective compound, 1-methyl-1,2,3,4-tetrahydroisoquinoline (1MeTIQ), on the concentration of dopamine and its metabolites (homovanillic acid-HVA, 3,4-dihydroxyphenylacetic acid-DOPAC, and 3-methoxytyramine-3-MT)) in three brain areas was studied by high-performance liquid chromatography (HPLC) with electrochemical detection in Wistar rats. The rate of dopamine catabolism in the striatum along the N-oxidative and O-methylation pathways was assessed by calculation of the ratio of dopamine metabolites to dopamine. In addition, the effect of rotenone on mortality and general behavior of rats was investigated. We have found that the neurotoxic pesticide, rotenone, administered in a single dose (12 mg/kg s.c.) did not produce evident behavioral or biochemical effects. In contrast, repeated administration of rotenone in doses (12-15 mg/kg) causing abnormalities in general behavior, produced considerable mortality and dramatic increases in dopamine metabolism, which may be ascribed to an increase in the oxidative pathway. Interestingly, it depressed the concentration of the extracellular dopamine metabolite, 3-MT. These behavioral and biochemical changes were effectively counteracted by administration of 1MeTIQ before each dose of rotenone. In summary, we demonstrated that multiple systemic rotenone injections are strongly toxic, and induce alterations of cerebral dopamine metabolism, and that 1MeTIQ may be considered as a potential protective agent against environmental factors affecting the function of the dopaminergic system.     

1-Methyl-1,2,3,4-tetrahydroisoquinoline and established uncompetitive NMDA receptor antagonists induce tolerance to excitotoxicity

The aim of this study was to establish the antagonistic effects of 1-methyl-1,2,3,4-tetrahydroisoquinoline (1MeTIQ) on NMDA receptors and its neuroprotective abilities on primary cultures of rat cerebellar granule cells exposed for 30 min to 250 or 100 μM glutamate. Neuronal viability was tested after 24 h with propidium iodide or calcein/ethidium homodimer-1 staining. The neuroprotective potential of 100, 250 or 500 μM 1MeTIQ was compared with established uncompetitive NMDA receptor antagonists, 0.5 μM MK-801, or 5 μM memantine. These substances were applied for 30 min either together with glutamate, 24 or 48 h before glutamate, or 0.5 h, 1 h and 3 h after exposure to the excitotoxin. The results demonstrated that MK-801, memantine and 500 μM 1MeTIQ induced an almost complete neuroprotection when co-applied with glutamate, but lower concentrations of 1MeTIQ were slightly less effective. Similar effects for 1MeTIQ and the established NMDA receptor antagonists were observed in the pretreatment experiments, even with a 48-h lag between the application of the tested substances and the excitotoxic challenge. In the post-treatment experiments, MK-801 and memantine and 500 μM 1MeTIQ applied up to 3 h after the exposure to glutamate significantly reduced the excitotoxic lesion, but 1MeTIQ in lower concentrations was ineffective. These results indicate that 1MeTIQ shares neuroprotective abilities with established uncompetitive NMDA receptor antagonists, which suggests that its inhibitory effect on NMDA receptors plays a key role in its anti-excitotoxic activity. Moreover, our data disclose a new mechanism of 1MeTIQ-evoked neuroprotection based on the induction of neuronal tolerance to excitotoxicity.     

Apoptosis induced by an endogenous neurotoxin, N-methyl(R)salsolinol, in dopamine neurons

A dopamine-derived neurotoxin, 1(R),2(N)-dimethyl-6,7-dihydroxy-1,2, 3,4-tetrahydroisoquinoline [N-methyl(R)salsolinol] was found to cause parkinsonian in rats and to deplete selectively dopamine neurons in the substantia nigra after infusion in the striatum. This isoquinoline occurs enantio-specifically in the nigra-striatum of human brains. The biosynthesis from dopamine is catalyzed by two enzymes, (R)salsolinol synthase and (R)salsolinol N-methyltransferase. The isoquinoline increases in the cerebrospinal fluid from parkinsonian patients, and the increase is ascribed to high activity of its synthesizing neutral (R)salsolinol N-methyltransferase, as shown by analyses in lymphocytes. The cell death caused by this neurotoxin in dopaminergic human neuroblastoma SH-SY5Y cells proved to be apoptotic. Apoptosis by this neurotoxin is mediated by intracellular sequential process, loss of mitochondrial membrane potential, activation of caspases and DNA fragmentation. These results are discussed in relation to the role of apoptosis in neurodegenerative diseases and the involvement of the endogenous toxin in the pathogenesis of Parkinson's disease.     

Salsolinol, a catechol neurotoxin, induces modification of ferritin: Protection by histidine dipeptide

1-Methyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline (salsolinol), an endogenous neurotoxin present in the mammalian brain, is known to perform a role in the pathogenesis of Parkinson's disease. In this study, we evaluated oxidative modifications of ferritin occurring after incubation with salsolinol. When ferritin was incubated with salsolinol, protein aggregation increased in a time-dependent manner. Free radical scavengers inhibited this salsolinol-mediated ferritin modification. The exposure of ferritin to salsolinol also results in the generation of protein carbonyl compounds and the formation of dityrosine. The results of this study show that free radicals may perform a pivotal role in salsolinol-mediated ferritin modification. Histidine dipeptides, such as carnosine, have been proposed to function as antioxidant agents in vivo. In this study, we also attempted to determine whether the histidine dipeptides, carnosine and N-acetyl-carnosine, could prevent salsolinol-mediated oxidative modification of ferritin. Our results showed that both carnosine and N-acetyl-carnosine significantly reduced ferritin aggregation. Both compounds effectively inhibited the formation of both carbonyl compounds and dityrosine. These results suggest that carnosine derivatives can, indeed, protect against salsolinol-mediated ferritin modification, as the consequence of free radical-scavenging activity.     

1-Methyl-1,2,3,4-tetrahydroisoquinoline – The toxicological research on an exo/endogenous amine with antidepressant-like activity – In vivo,in vitro and in silico studies

Background1-Methyl-1,2,3,4-tetrahydroisoquinoline (1MeTIQ) demonstrates significant neuroprotective activity. It can interact with agonistic conformation of dopamine (DA) receptors. 1MeTIQ inhibits the formation of 3,4-dihydroxyphenylacetic acid as well as production of free radicals and shifts DA catabolism toward COMT-dependent O-methylation. 1MeTIQ inhibits both MAO-A and B enzymes activity and increases neurotransmitters levels in the brain. It shows significant antidepressant-like effect in forced swim test (FST) in rats. This compound might be effective for depression therapy in a clinical setting but its success is determined not only by good efficacy, but also by an acceptable its ADMET profile. The use of combination in silico prediction with in vivoand in vitro studies greatly simplifies the search for new, safer and effectively acting drugs.MethodsThe aim of this study was to investigate the degree of histopathological changes in different rats tissues after acute and chronic administration of 1MeTIQ. Additionally, prediction of its properties in terms of absorption, distribution, metabolism, elimination and toxicity in the human body was performed.ResultsThe obtained data did not show extensive and significant toxic effects of tested substance in in vivo and in vitro studies in rats, and in silico ADMET prediction.ConclusionsThese results can help to discover a new effective and safe antidepressant substance and have important significance in the treatment of depression in clinic. Additionally, the use in the treatment of depression substance with neuroprotective, antioxidant and antidepressant-like effects in the CNS and existing endogenously might be also beneficial in controlling the adverse CNS inflammatory processes accompanying depression.     

Accumulation of dopamine by blood platelets from normal subjects and parkinsonian patients under treatment with L-DOPA

1. Human blood platelets have been shown to take up dopamine by an energy-dependent, saturable process that is inhibited by 5-hydroxytryptamine (5-HT), desipramine and other drugs.

2. Platelets from parkinsonian subjects receiving oral L-DOPA also took up dopamine.

3. When the responses of normal and parkinsonian platelets were compared, the parkinsonian cells showed the following differences: increased affinity for the dopamine transport process; decreased equilibrium concentrations of dopamine after incubation for 90 min, and greater efflux of dopamine from loaded platelets during a 10 min incubation.

4. There were no differences in the uptake of 5-HT by parkinsonian platelets, but endogenous 5-HT was significantly reduced; ATP was normal.

5. In two out of three samples of platelets from parkinsonian subjects, traces of a dopamine-like substance were detected, but this finding requires confirmation.

6. If the platelet is a valid model for dopaminergic brain neurones, then the results described would suggest that dopamine uptake and storage may be abnormal in brain neurones in Parkinson's disease.

     

Possible role of interleukin-6 in PC12 cell death induced by MPP+ and tetrahydroisoquinoline

Interleukin (IL)-6 has been shown to protect neuronal cells from cell death induced by various stimulants. Although neuronal cells including PC12 cells were shown to produce IL-6, little is known about the effects of dopaminergic neurotoxins, 1,2,3,4-tetrahydroisoquinoline (TIQ) and 1-methyl-4-phenylpyridinium ion (MPP(+)), on IL-6 expression in PC12 cells. In the present study, we investigated the role of IL-6 in the TIQ- and MPP(+)-induced cell death in PC12 cells. Treatment with 3.2 mM TIQ for 24 h caused a delayed cell death (lactate dehydrogenase (LDH) leakage and nuclear DNA fragmentation) markedly 72 h after the addition. Addition of 0.4 mM MPP(+) caused LDH leakage and nuclear DNA fragmentation 24 h after the addition. The cell death induced by MPP(+) was inhibited by an inhibitor of caspases, z-Val-Ala-Asp(OMe)-fluoromethylketone. The cell death induced by TIQ or MPP(+) was inhibited by nerve growth factor and 10% serum and significantly enhanced by the treatment with anti-IL-6 antibody. Both neurotoxins decreased the IL-6 mRNA level in PC12 cells without changing the other tested mRNA levels (IL-1 alpha, beta-actin, etc.). These findings suggest that dopaminergic neurotoxins cause cell death in PC12 cells at least partially by changing IL-6 expression.     

1,2,3,4-Tetrahydroisoquinoline as the potential antidepressant compound in forced swimming test in rat

1,2,3,4-Tetrahydroisoquinoline (TIQ) is an exo- and endogenous amine present naturally in mammalian brain and may be the natural regulator of monoaminergic systems with a visible neuroprotective potency [Antkiewicz-Michaluk et al., J Neurochem, 2006]. In our study we tested the potential antidepressant properties of TIQ in comparison with a classic antidepressant drug, imipramine by using forced swimming test in rats (FST). Further, we measured the levels of dopamine (DA), noradrenaline (NA), serotonin (5-HT), and their metabolites, as well as the rate of monoamines metabolism in different rats brain structures by HPLC methodology with ED. The locomotor activity test was used to check motor function of rat after investigated drugs administration. All experiments were performed on male Wistar rats weighing 220 –240 g.ResultsFST has shown that TIQ (10 , 25 , 50 mg/kg, ip) significantly reduced immobility time similarly to imipramine (30 mg/kg, ip). TIQ significantly elevated swimming activity (p < 0.01) while imipramine increased climbing time (p < 0.01). Additionally, TIQ (25 mg/kg, ip) and imipramine (15 mg/kg, ip) injected simultaneously decreased immobility time, increased the swimming and did not affect the climbing activity. The biochemical analysis showed that TIQ increased the levels of monoamines: DA, NA and 5-HT in rat brain structures. Moreover, the factor of DA re-uptake inhibition, calculated as the ratio [3-MT]/[DOPAC], was significantly elevated by TIQ administration. The rate of serotonin metabolism was strongly decreased (p < 0.01) while, the rate of noradrenaline metabolism was increased (p < 0.05) after injection of TIQ and imipramine. TIQ did not change the locomotor activity in rats.ConclusionsThe obtained data indicate that TIQ produced antidepressant-like effect in FST with potency comparable to imipramine. Thus, in that light and taking into account its neuroprotective potential of action in the brain TIQ may be useful in clinical practice for therapy of depression.