Understanding methiopropamine, a new psychoactive substance: an in-depth review on its chemistry, pharmacology and implications to human health.

Methiopropamine or 1-(thiophen-2-yl)-2-methylaminopropane (MPA) is a thiophene ring-based structural analogue of methamphetamine, first synthesized in 1942 but become popular when it started to be available for purchase on websites selling 'legal highs' since 2010. While it is legally controlled in many countries, it remains readily accessible and frequently encountered in recreational settings. The growing prevalence of MPA use results in new therapeutic challenges. Relatively few studies have focused on its pharmacodynamics and pharmacokinetics, making it important to better understand its potential risks and harmful effects in humans in terms of its toxicity. This review provides a comprehensive profiling of MPA toxicological properties, including its chemical properties, analytical methods, prevalence, patterns of use, and legal status. Additionally, it discusses the drug's effects on the central nervous system, its potential for addiction, and its adverse physical and mental health effects. Improving the understanding of safety aspects of MPA and how it imposes health threats for public health will guide the development of therapeutic approach of its intoxication and guide the authorities in deciding its legal status.

Potential Roles of 5-HT3 Receptor Antagonists in Reducing Chemotherapy-induced Peripheral Neuropathy (CIPN).

5-HT3 receptor antagonists corresponding to ondansetron, granisetron, tropisetron, and palonosetron are clinically accustomed to treating nausea and emesis in chemotherapy patients. However, current and previous studies reveal novel potentials of those ligands in other diseases involving the nervous system, such as addiction, pruritus, and neurological disorders, such as anxiety, psychosis, nociception, and cognitive function. This review gathers existing studies to support the role of 5-HT3 receptors in CIPN modulation. It has been reported that chemotherapy drugs increase the 5-HT content that binds with the 5-HT3 receptor, which later induces pain. As also shown in pre-clinical and clinical studies that various neuropathic pains could be blocked by the 5-HT3 receptor antagonists, we proposed that 5-HT3 receptor antagonists via 5- HT3 receptors may also inhibit neuropathic pain induced by chemotherapy. Our review suggests that future studies focus more on the 5-HT3 receptor antagonists and their modulation in CIPN to reduce the gap in the current pharmacotherapy for cancer-related pain.

Tapping into 5-HT3 Receptors to Modify Metabolic and Immune Responses.

5-hydroxytryptamine type 3 (5-HT3) receptors are ligand gated ion channels, which clearly distinguish their mode of action from the other G-protein coupled 5-HT or serotonin receptors. 5-HT3 receptors are well established targets for emesis and gastrointestinal mobility and are used as adjunct targets in treating schizophrenia. However, the distribution of these receptors is wider than the nervous system and there is potential that these additional sites can be targeted to modulate inflammatory and/or metabolic conditions. Recent progress in structural biology and pharmacology of 5-HT3 receptors have provided profound insights into mechanisms of their action. These advances, combined with insights into clinical relevance of mutations in genes encoding 5-HT3 subunits and increasing understanding of their implications in patient's predisposition to diseases and response to the treatment, open new avenues for personalized precision medicine. In this review, we recap on the current status of 5-HT3 receptor-based therapies using a biochemical and physiological perspective. We assess the potential for targeting 5-HT3 receptors in conditions involving metabolic or inflammatory disorders based on recent findings, underscoring the challenges and limitations of this approach.

Visualising functional 5-HT3 receptors containing A and C subunits at or near the cell surface.

Five different subunits of the human serotonin 3 (5-hydroxytrptamine 3; 5-HT3) receptor exist and these are present in both central and peripheral systems. Different subunits alter the efficacy of 5-HT3 receptor antagonists used to treat diarrhoea predominant-irritable bowel syndrome, chemotherapy induced nausea and vomiting and depression. Cell surface arrangement of 5-HT3 receptor complexes and the contribution of C, D and E subunits to receptor function is poorly understood. Here, we examine interactions of A and C subunits using 5-HT3 receptor subunits containing fluorescent protein inserts between the 3rd and 4th transmembrane spanning region. HEK293T cells that do not normally express 5-HT3 receptor subunits, were transiently transfected with A or C or both subunits. Patch clamp experiments show that cells transfected with either fluorescent protein tagged A or A and C subunits generate whole cell currents in response to 5-HT. These findings correlate with the apparent distribution of fluorescent protein tagged A and C subunits at or near cell surfaces detected using TIRF microscopy. In co-transfected cells, the A and C subunits are associated forming AC heteromer complexes at or near the cell surface and a proportion can also form A or C homomers. In conclusion, it is likely that both A homomers and AC heteromers contribute to whole cell currents in response to 5-HT with minimal contribution from C homomers.

Potential roles of 5-HT3 receptor (5-HT3R) antagonists in modulating the effects of nicotine.

5-HT3R antagonists such as ondansetron, granisetron and tropisetron have been clinically used to treat nausea and vomiting in chemotherapy patients. However, current study and research revealed novel potentials of these ligands in other diseases like inflammation, Alzheimer's, and drug abuse. Towards utilising these drugs as anti-smoking agents to treat nicotine dependence problem, there are conflicting reports regarding the potential of these ligands in modulating the effects of nicotine in both human and animal behavioural studies. This is complicated by the heterogeneity of 5-HT3R itself, cross regulation between nicotinic acetylcholinergic receptor (nAChR) and distinct pharmacological profiles of 5-HT3R antagonists. This review gathered existing studies conducted investigating the potential of "-setron" class of 5-HT3R antagonists in modulating nicotine effects. We proposed that the mechanism where 5-HT3R antagonists mediate the effects of nicotine could be attributed by both direct at 5-HT3R and indirect mechanism in nicotine addiction downstream regulation. The indirect mechanism mediated by the 5-HT3R antagonist could be through α7 nAChR, 5-HT1B receptor (5-HT1BR), 5-HT1C receptor (5-HT1CR), calcineurin activity, p38 MAPK level, PPAR-γ and NF-κß. Our review suggested that future studies should focus on newer 5-HT3R antagonist with superior pharmacological profile or the one with multitarget action rather than high selectivity at single receptor.

The C and E subunits of the serotonin 5-HT3 receptor subtly modulate electrical properties of the receptor.

Serotonin type 3 (5-hydroxytrptamine-3, 5-HT3) receptors are ligand-gated cation channels present in both central and peripheral nervous systems. In humans there are five different subunits (A, B, C, D and E) of 5-HT3 receptors which can form homomeric or heteromeric receptors that may account for discrepancies in patient responses to treatments. The present study commences characterisation of the profiles of human 5-HT3 receptors containing C and/or E subunits. Recombinant 5-HT3 receptors were expressed transiently in HEK293T cells and expression was checked via immunocytochemistry staining against each epitope-tagged subunits. Functional characterisation of different combinations of 5-HT3 receptor complexes was studied via patch clamp whole cell recordings. In this study, increased current was seen in cells containing A and C subunits but only subtle changes were seen in the electrical properties of cells expressing A, AE, or ACE subunits in response to the ligand, 5-HT. Both di- and tri-heteromeric 5-HT3 receptors were significantly inhibited by the antagonists, ondansetron and palonosetron. Notably, palonosetron exerted stronger and more rapid inhibition on the 5-HT3 receptor ACE tri-heteromer compared to homomeric and di-heteromeric counterparts. This study demonstrated that the C and E subunits when assembled as simple or complex heteromeric 5-HT3 receptors may alter efficacies of 5-HT and clinically used antagonists such as ondansetron and palonosetron, and this in turn may have implications for patient responses to therapies.

Distribution of 5-HT3, 5-HT4, and 5-HT7 Receptors Along the Human Colon.

BACKGROUND/AIMS: Several disorders of the gastrointestinal tract are associated with abnormal serotonin (5-HT) signaling or metabolism where the 5-HT3 and 5-HT4 receptors are clinically relevant. The aim was to examine the distribution of 5-HT3, 5-HT4, and 5-HT7 receptors in the normal human colon and how this is associated with receptor interacting chaperone 3, G protein coupled receptor kin-ases, and protein LIN-7 homologs to extend previous observations limited to the sigmoid colon or the upper intestine. METHODS: Samples from ascending, transverse, descending, and sigmoid human colon were dissected into 3 separate layers (mucosa, lon-gitudinal, and circular muscles) and ileum samples were dissected into mucosa and muscle layers (n = 20). Complementary DNA was synthesized by reverse transcription from extracted RNA and expression was determined by quantitative or end point polymerase chain reaction. RESULTS: The 5-HT3 receptor subunits were found in all tissues throughout the colon and ileum. The A subunit was detected in all sam-ples and the C subunit was expressed at similar levels while the B subunit was expressed at lower levels and less frequently. The 5-HT3 receptor E subunit was mainly found in the mucosa layers. All splice variants of the 5-HT4 and 5-HT7 receptors were expressed throughout the colon although the 5-HT4 receptor d, g, and i variants were expressed less often. CONCLUSIONS: The major differences in 5-HT receptor distribution within the human colon are in relation to the mucosa and muscular tissue layers where the 5-HT3 receptor E subunit is predominantly found in the mucosal layer which may be of therapeutic relevance.

Low-dose photon irradiation response of Ge and Al-doped SiO2 optical fibres.

We have investigated the thermoluminescent response and fading characteristics of germanium- and aluminium-doped SiO(2) optical fibres. These optical fibres were placed in a solid phantom and irradiated using 6 and 10 MV photon beams at doses ranging from 0.02 to 0.24 Gy delivered using a linear accelerator. In fading studies, the TL measurements were continued up to 14 days post-irradation. We have investigated the linearity of TL response as a function of dose for Ge-, Al-doped optical fibre and TLD-100 obtained for 6 and 10 MV photon irradiations. We have concentrated on doses that represent a small fraction of that delivered to the tumour to establish sensitivity of measurement for peripheral exposures in external beam radiotherapy.