Comparison of the Effects of Acute and Chronic Administration of Tetrahydroisoquinoline Amines on the In Vivo Dopamine Release: A Microdialysis Study in the Rat Striatum

New frontiers in the biosynthesis of psychoactive specialized metabolites

The recent relaxation of psychedelic drug regulations has prompted extensive clinical investigation into their potential use to treat diverse mental health conditions including anxiety, depression, post-traumatic stress, and substance-abuse disorders. Most clinical trials have relied on a small number of known molecules found in nature, such as psilocybin, or long-known synthetic analogs of natural metabolites, including lysergic acid diethylamide (LSD). Elucidation of biosynthetic pathways leading to several psychedelic compounds has established an opportunity to use synthetic biology as a complement to synthetic chemistry for the preparation of novel derivatives with potentially superior pharmacological properties compared with known drugs. Herein we review the metabolic biochemistry of pathways from plants, fungi and animals that yield the medicinally important hallucinogenic specialized metabolites ibogaine, mescaline, psilocybin, lysergic acid, and N,N-dimethyltryptamine (DMT). We also summarize the reconstitution of these pathways in microorganisms and comment on the integration of native and non-native enzymes to prepare novel derivatives.

Medicinal chemistry perspectives of 1,2,3,4-tetrahydroisoquinoline analogs - biological activities and SAR studies

Isoquinoline alkaloids are a large group of natural products in which 1,2,3,4-tetrahydroisoquinolines (THIQ) form an important class. THIQ based natural and synthetic compounds exert diverse biological activities against various infective pathogens and neurodegenerative disorders. Due to these reasons, the THIQ heterocyclic scaffold has garnered a lot of attention in the scientific community which has resulted in the development of novel THIQ analogs with potent biological activity. The present review provides a much-needed update on the biological potential of THIQ analogs, their structural-activity relationship (SAR), and their mechanism of action. In addition, a note on commonly used synthetic strategies for constructing the core scaffold has also been discussed.

Addressing the instability issue of dopamine during microdialysis: the determination of dopamine, serotonin, methamphetamine and its metabolites in rat brain

Dopamine is a catecholamine neurotransmitter that degrades rapidly in aqueous solutions; hence, its analysis following brain microdialysis is challenging. The aim of the current study was to develop and validate a new microdialysis coupled LC-MS/MS system with improved accuracy, precision, simplicity and turnaround time for dopamine, serotonin, methamphetamine, amphetamine, 4-hydroxymethamphetamine and 4-hydroxyamphetamine analysis in the brain. Dopamine degradation was studied with different stabilizing agents under different storage conditions. The modified microdialysis system was tested in vitro, and was optimized for best probe recovery, assessed by %gain. LC-MS/MS assay was developed and validated for the targeted compounds. Stabilizing agents (ascorbic acid, EDTA and acetic acid) as well as internal and cold standards were added on-line to the dialysate flow. Assay linearity range was 0.01-100 ng/mL, precision and accuracy passed criteria, and LOQ and LLOQ were 0.2 and 1.0 pg, respectively. The new microdialysis coupled LC-MS/MS system was used in Wistar rats striatum after 4 mg/kg subcutaneous methamphetamine. Methamphetamine rapidly distributed to rat striatum reaching an average ~200 ng/mL maximum, ~82.5 min post-dose. Amphetamine, followed by 4-hydroxymethamphetamine, was the most abundant metabolite. Dopamine was released following methamphetamine injection, while serotonin was not altered. In conclusion, we proposed and tested an innovative and simplified solution to improve stability, accuracy and turnover time to monitor unstable molecules, such as dopamine, by microdialysis.

Pro-cognitive effect of 1MeTIQ on recognition memory in the ketamine model of schizophrenia in rats: the behavioural and neurochemical effects

RATIONALE

Schizophrenia is a mental illness which is characterised by positive and negative symptoms and by cognitive impairments. While the major prevailing hypothesis is that altered dopaminergic and/or glutamatergic transmission contributes to this disease, there is evidence that the noradrenergic system also plays a role in its major symptoms.

OBJECTIVES

In the present paper, we investigated the pro-cognitive effect of 1-methyl-1,2,3,4-tetrahydroisoquinoline (1MeTIQ) an endogenous neuroprotective compound, on ketamine-modelled schizophrenia in rats.

METHODS

We used an antagonist of NMDA receptors (ketamine) to model memory deficit symptoms in rats. Using the novel object recognition (NOR) test, we investigated the pro-cognitive effect of 1MeTIQ. Additionally, olanzapine, an atypical antipsychotic drug, was used as a standard to compare the pro-cognitive effects of the substances. In vivo microdialysis studies allowed us to verify the changes in the release of monoamines and their metabolites in the rat striatum.

RESULTS

Our study demonstrated that 1MeTIQ, similarly to olanzapine, exhibits a pro-cognitive effect in NOR test and enhances memory disturbed by ketamine treatment. Additionally, in vivo microdialysis studies have shown that ketamine powerfully increased noradrenaline release in the rat striatum, while 1MeTIQ and olanzapine completely antagonised this neurochemical effect.

CONCLUSIONS

1MeTIQ, as a possible pro-cognitive drug, in contrast to olanzapine, expresses beneficial neuroprotective activity in the brain, increasing concentration of the extraneuronal dopamine metabolite, 3-methoxytyramine (3-MT), which plays an important physiological role in the brain as an inhibitory regulator of catecholaminergic activity. Moreover, we first demonstrated the essential role of noradrenaline release in memory disturbances observed in the ketamine-model of schizophrenia, and its possible participation in negative symptoms of the schizophrenia.

Effect of Electroacupuncture on 99mTc-Sodium Pertechnetate Uptake and Extracellular Fluid Free Molecules in the Stomach in Acupoint ST36 and ST39

Electroacupuncture (EA) is a therapeutic modality in which the electrical stimulation is integrated with concepts of acupuncture to treat diseases. This study was designed to evaluate the connection between the electro-acupuncture induced increase in Na^99mTcO4 uptake in the stomach wall, and the ionic molecule levels in the extracellular fluid in the acupoints. Wistar rats were treated by 2 or 100 Hz EA at Zusanli (ST 36) and Xiajuxu (ST 39) bilaterally for 60 minutes. The accumulation of Na^99mTcO4 in the gastric wall and the free ions, including Ca²⁺, K⁺, Na⁺, and Cl⁻, in the acupoints were measured every 60 minutes. The radioactivity uptake in the stomach was significantly increased during EA, reaching peak at 180 minutes after the EA. The concentration of extracellular ions was also significantly increased during EA. The Ca²⁺ level continued to rise until 60 minutes after EA, then started to decrease at 120 minutes post-EA. The results suggest this up-regulatory effect of EA on gastric activity might be triggered by the increase of the extracellular ion levels, this effect lasts longer than stimulating the release of transmembrane Ca²⁺ flow alone. This might aid in providing a better understanding of the long-lasting effect claimed in acupuncture treatment.

Multiple Administration of Endogenous Amines TIQ and 1MeTIQ Protects Against a 6-OHDA-Induced Essential Fall of Dopamine Release in the Rat Striatum: In Vivo Microdialysis Study

Parkinson’s disease (PD) represents one of the neurodegenerative disorders which are caused by degeneration of dopaminergic neurons in the nigrostriatal pathway. Different toxins, e.g., 6-hydroxydopamine (6-OHDA), are used to model PD in animals. 6-OHDA is a neurotoxin which damages catecholaminergic neurons via production of oxygen radicals. Tetrahydroisoquinolines (TIQs) are endogenous amines which are present in the mammalian brain. Some of them, like TIQ and 1-methyl-1,2,3,4-tetrahydroisoquinoline (1MeTIQ), demonstrate neuroprotective properties. These compounds act as reversible MAO inhibitors and this way block free radical formation. To continue our previous experiments, we evaluated the effect of acute and chronic treatment with TIQ and 1MeTIQ on locomotor/exploratory activity and the release of dopamine as well as its metabolite 3-methoxytyramine (3-MT) in the striatum of unilaterally 6-OHDA-lesioned and sham-operated rats using in vivo microdialysis methodology. Additionally, the changes in the concentration of tyrosine hydroxylase in the substantia nigra were measured. A unilateral 6-OHDA lesion in the substantia nigra produces a strong reduction in the release of dopamine (approx. 70%) and 3-MT (approx. 50%) in the rat striatum. This effect was completely inhibited by multiple administration of TIQ and 1MeTIQ. The results obtained from the in vivo microdialysis study suggest that multiple treatment with both endogenous amines, TIQ and 1MeTIQ, protects dopaminergic neurons against a 6-OHDA-induced deficit of dopamine release. Furthermore, these amines were able to maintain physiological functions of striatal dopamine neurons damaged by a unilateral 6-OHDA lesion.

The mechanism of neuroprotective action of natural compounds

Disturbance of cerebral redox homeostasis is the primary cause of human neurodegenerative disorders, such as Parkinson's disease or Alzheimer's disease. Well known experimental research demonstrates that oxidative stress is a main cause of cell death. A high concentration of reactive oxygen and nitrogen species leads to damage of a lot of proteins, lipids and also DNA. Synthetic compounds used for the treatment in the neurodegenerative diseases failed to meet the hopes they had raised and often exhibit a number of side effects. Therefore, in recent years interest in natural compounds derived from plants appears to be on the rise. This review describes a few natural compounds (1MeTIQ, resveratrol, curcumin, vitamin C and Gingko biloba) which revealed neuroprotective potential both in experimental studies and clinical trials. 1MeTIQ has a privileged position because, as opposed to the remaining compounds, it is an endogenous amine synthesized in human and animal brain. Based on evidence from research, it seems that a common protective mechanism for all the above-mentioned natural compounds relies on their ability to inhibit or even scavenge the excess of free radicals generated in oxidative and neurotoxin-induced processes in nerve cells of the brain. However, it was demonstrated that further different molecular processes connected with neurotoxicity (e.g. the inhibition of mitochondrial complex I, activation of caspase-3, apoptosis) follow later and are initiated by the reactive oxygen species. What is more, these natural compounds are able to inhibit further stages of apoptosis triggered by neurotoxins in the brain.