Receptor affinity, neurochemistry and behavioral characteristics of the enantiomers of thioridazine: evidence for different stereoselectivities at D1 and D2 receptors in rat brain

Repurposing thioridazine for inducing immunogenic cell death in colorectal cancer via eIF2α/ATF4/CHOP and secretory autophagy pathways

BACKGROUND

Colorectal cancer (CRC) is a highly prevalent cancer type with limited targeted therapies available and 5-year survival rate, particularly for late-stage patients. There have been numerous attempts to repurpose drugs to tackle this problem. It has been reported that autophagy inducers could augment the effect of certain chemotherapeutic agents by enhancing immunogenic cell death (ICD).

METHODS

In this study, we employed bioinformatics tools to identify thioridazine (THD), an antipsychotic drug, and found that it could induce autophagy and ICD in CRC. Then in vitro and in vivo experiments were performed to further elucidate the molecular mechanism of THD in CRC.

RESULTS

THD was found to induce endoplasmic reticulum (ER) stress in CRC cells by activating the eIF2α/ATF4/CHOP axis and facilitating the accumulation of secretory autophagosomes, leading to ICD. In addition, THD showed a remarkable ICD-activating effect when combined with oxaliplatin (OXA) to prevent tumor progression in the mouse model.

CONCLUSIONS

Together, our findings suggest that the repurposed function of THD in inhibiting CRC involves the upregulation of autophagosomes and ER stress signals, promoting the release of ICD markers, and providing a potential candidate to enhance the clinical outcome for CRC treatment. Video Abstract.

Serotonin and dopamine modulate aging in response to food odor and availability

An organism's ability to perceive and respond to changes in its environment is crucial for its health and survival. Here we reveal how the most well-studied longevity intervention, dietary restriction, acts in-part through a cell non-autonomous signaling pathway that is inhibited by the presence of attractive smells. Using an intestinal reporter for a key gene induced by dietary restriction but suppressed by attractive smells, we identify three compounds that block food odor effects in C. elegans, thereby increasing longevity as dietary restriction mimetics. These compounds clearly implicate serotonin and dopamine in limiting lifespan in response to food odor. We further identify a chemosensory neuron that likely perceives food odor, an enteric neuron that signals through the serotonin receptor 5-HT1A/SER-4, and a dopaminergic neuron that signals through the dopamine receptor DRD2/DOP-3. Aspects of this pathway are conserved in D. melanogaster. Thus, blocking food odor signaling through antagonism of serotonin or dopamine receptors is a plausible approach to mimic the benefits of dietary restriction.

Repositioning of non-antibiotic drugs as an alternative to microbial resistance: a systematic review

The global spread of microbial resistance coupled with high costs and slow pace in the discovery of a new antibiotic have made drug repositioning an attractive and promising alternative in the treatment of infections caused by multidrug resistant (MDR) microorganisms. The reuse involves the production of compounds with lower costs and development time, using diversified production technologies. The present systematic review aimed to present a selection of studies published in the last 20 years, which report the antimicrobial activity of non-antibiotic drugs that are candidates for repositioning, which could be used against the current microbial multidrug resistance. A search was performed in the PubMed, SciELO and Google Scholar databases using the following search strategies: [(drug repurposing) OR (drug repositioning) OR (repositioning) AND (non-antibiotic) AND (antibacterial activity) AND (antimicrobial activity)]. Overall, 112 articles were included, which explored the antimicrobial activity in antidepressants, antihypertensives, anti-inflammatories, antineoplastics, hypoglycemic agents, among other drugs. It was concluded that they have significant antimicrobial activity in vitro and in vivo, against standard strain and clinical isolates (Gram-negative and Gram-positive) and fungi. When associated with antibacterials, most of these drugs had their antibacterial activity enhanced. It was also a consensus of the studies included in this review that the presence of aromatic rings in the molecular structure contributes to antimicrobial activity. This review highlights the potential repositioning of several classes of non-antibiotic drugs as promising candidates for repositioning in the treatment of severe bacterial infections of MDR bacteria, extensively resistant (XDR) and pan-resistant (PDR) to drugs.

Enantiomeric Separation of Dioxopromethazine and its Stereoselective Pharmacokinetics in Rats by HPLC-MS/MS

Dioxopromethazine (DPZ) is a popular phenothiazine antihistamine that is widely used as a racemic drug in clinical to cure respiratory illness. In our work, a reliable, specific, and rapid enantioselective HPLC-MS/MS method has been established and fully validated for the quantification of R- and S-DPZ in rat plasma. After plasma alkalization (with 1 M Na₂CO₃), DPZ enantiomers and diphenhydramine (IS) were extracted using ethyl acetate. Completely separation of R- and S-DPZ (Rs = 2.8) within 12 min was implemented on Chiralpak AGP column (100 × 4.0 mm i.d., 5 μm) employing ammonium acetate (10 mM; pH 4.5) - methanol (90:10, v/v) as mobile phase. Themultiple reaction monitoring (MRM) mode was used for the detection of DPZ enantiomers and IS. The transitions of m/z 317.2 → 86.1 and 256.2 → 167.1 werechosen for monitoring DPZ enantiomers and IS, respectively. Good linearity (r² > 0.995) was achieved for each DPZ enantiomer over the linear ranges of 1.00 - 80.00 ng/mL, with the lower limit of quantitation (LLOQ) of 1.00 ng/mL. The intra-day and inter-day precisions (RSDs,%) were below 12.3%, and accuracies (REs,%) were in the scope of-10.5% to 6.6%, which were within the admissible criteria. The validated bioanalytical approach was applied to the stereoselective pharmacokinetic (PK) research of DPZ in rat plasma for the first time. It was found that significant differences (p < 0.05) exist between the main PK parameters of R- and S-DPZ, indicating the pharmacokinetic behaviors of DPZ enantiomers in rats were stereoselective. The chiral inversion of the enantiomers did not occur during the assay.

Abnormal dopamine receptor signaling allows selective therapeutic targeting of neoplastic progenitors in AML patients

The aberrant expression of dopamine receptors (DRDs) in acute myeloid leukemia (AML) cells has encouraged the repurposing of DRD antagonists such as thioridazine (TDZ) as anti-leukemic agents. Here, we access patient cells from a Phase I dose escalation trial to resolve the cellular and molecular bases of response to TDZ, and we extend these findings to an additional independent cohort of AML patient samples tested preclinically. We reveal that in DRD2⁺ AML patients, DRD signaling in leukemic progenitors provides leukemia-exclusive networks of sensitivity that spare healthy hematopoiesis. AML progenitor cell suppression can be increased by the isolation of the positive enantiomer from the racemic TDZ mixture (TDZ⁺), and this is accompanied by reduced cardiac liability. Our study indicates that the development of DRD-directed therapies provides a targeting strategy for a subset of AML patients and potentially other cancers that acquire DRD expression upon transformation from healthy tissue.

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Leukemic progenitors are a critical cellular target of DRD2 antagonist TDZ

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DRD2 protein expression is a reliable biomarker of TDZ response

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DRD2 antagonism selectively triggers leukemic maturation programs via cyclic AMP

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An enantiomer of TDZ displays a superior efficacy:risk ratio relative to racemic TDZ

Multidisciplinary assessment and treatment of self-injurious behavior in autism spectrum disorder and intellectual disability: integration of psychological and biological theory and approach

The objective of this review is to consider the psychological (largely behavioral) and biological [neurochemical, medical (including genetic), and pharmacological] theories and approaches that contribute to current thinking about the etiology and treatment of self-injurious behavior (SIB) in individuals with autism spectrum disorder and/or intellectual disability. Algorithms for the assessment and treatment of SIB in this context, respectively, from a multidisciplinary, integrative perspective are proposed and challenges and opportunities that exist in clinical and research settings are discussed.

Differential effects of thioridazine enantiomers on action potential duration in rabbit papillary muscle

The antipsychotic drug thioridazine has potential for treatment of multidrug-resistant microbes including tuberculosis but also causes cardiotoxic QT interval prolongation. Both thioridazine enantiomers have potent antimicrobial effects, but the neuroleptic effect primarily resides with (+)-thioridazine. In this study we for the first time investigate the cardiotoxicity of the isolated thioridazine enantiomers and show their effects on ventricular repolarization. The effects of (+)-thioridazine, (-)-thioridazine, and racemate on the rabbit ventricular action potential duration (APD) were investigated in a randomized controlled blinded experiment. Action potentials were measured in papillary muscles isolated from 21 female rabbits, and the drug effect on 90% APD in comparison with control (ΔΔ-APD90) was evaluated. Increasing concentrations of (+)-thioridazine and the racemate caused significant dose-dependent ΔΔ-APD90 prolongation, while (-)-thioridazine did not. At 0.5 and 2Hz pacing, (+)-thioridazine caused 19.5% and 20.1% ΔΔ-APD90 prolongation, the racemate caused 8.0% and 12.9%, and (-)-thioridazine caused 1.5% and 1.1%. The effect of (-)-thioridazine on APD90 was significantly less than that of the other drugs at both pacing rates (P<0.01 in all cases), and there was no significant difference between (-)-thioridazine and control. The results of this study indicate that the APD prolonging effect of thioridazine is primarily due to the (+)-thioridazine enantiomer. If these results are valid in humans, (-)-thioridazine may be a safer drug for treatment of multidrug-resistant tuberculosis and other microbes.

A comparative analysis of in vitro and in vivo efficacies of the enantiomers of thioridazine and its racemate

A long list of chemotherapeutical drugs used in the treatment of the peripheral and the central nervous systems possess anti-microbial activity. Some of these neurotropic compounds are chiral, with the one stereo isomeric form exaggerating reduced neurotropism. This is the case for the levorotatory form of thioridazine. The phenothiazine thioridazine is an interesting compound, characterized by exhibiting a significant growth inhibiting activity on a wide array of micro-organisms. Thioridazine is characterized by another challenging feature, because the compound is concentrated in certain human tissue cells. The present study describes a comparative study of the two enantiomers as well as the racemic form of thioridazine. The study exploits the stereochemical aspect and the in vitro and in vivo potential of these compounds, with a focus on the effects on Gram negative organism Salmonella enterica serover Typhimurium. In summary, the results of this study yielded a significant antibacterial activity of all forms of thioridazine, indicating the levorotatory (–)- form to be superior in terms of both its in vitro and in vivo efficacies.

Mechanisms of action of antipsychotic drugs of different classes, refractoriness to therapeutic effects of classical neuroleptics, and individual variation in sensitivity to their actions: Part I

Many issues remain unresolved about antipsychotic drugs. Their therapeutic potency scales with affinity for dopamine D2 receptors, but there are indications that they act indirectly, with dopamine D1 receptors (and others) as possible ultimate targets. Classical neuroleptic drugs disinhibit striatal cholinergic interneurones and increase acetyl choline release. Their effects may then depend on stimulation of muscarinic receptors on principle striatal neurones (M4 receptors, with reduction of cAMP formation, for therapeutic effects; M1 receptors for motor side effects). Many psychotic patients do not benefit from neuroleptic drugs, or develop resistance to them during prolonged treatment, but respond well to clozapine. For patients who do respond, there is a wide (>ten-fold) range in optimal doses. Refractoriness or low sensitivity to antipsychotic effects (and other pathologies) could then arise from low density of cholinergic interneurones. Clozapine probably owes its special actions to direct stimulation of M4 receptors, a mechanism available when indirect action is lost.

Reversal of methicillin resistance in Staphylococcus aureus by thioridazine

OBJECTIVES

Thioridazine has been shown to reverse oxacillin resistance in methicillin-resistant Staphylococcus aureus (MRSA) in vitro. The aim of this study was to investigate whether thioridazine alone or in combination with oxacillin affects the transcription of the methicillin resistance gene mecA and the protein level of the encoded protein PBP2a.

METHODS

Viability of MRSA was determined in liquid media in the presence of oxacillin or thioridazine alone or in combination. Transcription of mecA was analysed by primer extension, and the protein level of PBP2a was analysed by western blotting in the presence of thioridazine and oxacillin.

RESULTS

We observed an increased susceptibility of MRSA towards oxacillin in the presence of thioridazine compared with bacteria grown with oxacillin or thioridazine alone. Transcription of mecA was reduced with increasing concentrations of thioridazine in the presence of a fixed amount of oxacillin. Furthermore, the protein level of PBP2a was reduced when bacteria were treated with the combination of oxacillin and thioridazine. The two drugs also affected the mRNA level of the beta-lactamase gene, blaZ.

CONCLUSIONS

The present study indicates that reversal of methicillin resistance by thioridazine in MRSA may be explained by a reduced transcription of mecA and blaZ, resulting in a reduced protein level of PBP2a.

Thioridazine: resurrection as an antimicrobial agent?

The emergence of multiresistant bacterial strains and the continuing burden of infectious disease globally point to the urgent need for novel affordable antimicrobial drugs. Thioridazine is a phenothiazine antipsychotic drug with well-recognized antimicrobial activity, but this property has not been harnessed for clinical use as a result of its central nervous system and cardiac side-effects. The cardiotoxicity of thioridazine has recently been shown to be structurally specific at a molecular level, whereas its antimicrobial properties are shared by a number of phenothiazine analogues. This raises the possibility that its enantiomers or its inactive metabolite, the ring sulphoxide, may act as a lead compound in the future development of antimicrobial drugs to face the new challenges in infectious disease.

Comparison of the Effects of Thioridazine and Mesoridazine on the QT Interval in Healthy Adults After Single Oral Doses

We compared the effects of single doses of thioridazine and mesoridazine on the heart rate-corrected QT (QTc) interval in healthy adult volunteers. QTc intervals and plasma concentrations of thioridazine, mesoridazine, and metabolites were measured after single oral doses of thioridazine hydrochloride 50 mg, mesoridazine besylate 50 mg, or placebo in a double-blind, crossover study. Mean maximum increases in the QTc interval following thioridazine (37.3+/-4.1 ms, P=0.023) and mesoridazine (46.6+/-7.4 ms, P=0.021) were similar and significantly greater than following placebo (12.9+/-8.1 ms). The area under the effect-time curve over 8 h following drug administration was similar between the two drugs (129.3+/-22.1 vs 148.3+/-43.0 ms h). In conclusion, thioridazine and mesoridazine are associated with similar effects on the QTc interval.

HPLC resolution of thioridazine enantiomers from pharmaceutical dosage form using cyclodextrin-based chiral stationary phase

Resolution of racemic thioridazine obtained from Thioril tablets (Cipla Ltd., Goa, India) into its enantiomers has been achieved by HPLC using a beta-cyclodextrin (CD)-bonded stationary phase. Thioridazine was isolated from commercial formulations and was purified using preparative TLC. The purity was ascertained by RP-HPLC. For the resolution of rac-thioridazine using cyclodextrin based CSP and mobile phase of 0.05 M phosphate buffer (pH 6.5)-acetonitrile (50:50) was found to be successful. The optimum conditions of resolution were established by systematically studying the effect of organic modifier, concentration of buffer, pH and flow rate of mobile phase. The detection limit was found to be 10 microg (5 microg of each enantiomer). The enantiomeric purity of each of the resolved isomers was verified by optical rotation.

Synthesis, receptor binding and functional studies of mesoridazine stereoisomers

The four stereoisomers of mesoridazine were synthesized and evaluated in D2, 5-HT1A, 5-HT2A, 5-HT2C, D1, and D3 receptor binding and functional assays. Two isomers demonstrated potent D2 receptor binding (Ki < 3 nM) and functional antagonism (IC50 < or = 10 nM) activities. These two isomers also showed moderate affinity for the 5-HT2A and D3 receptors. A third isomer was devoid of significant D2 receptor binding, but did have moderate affinity for the 5-HT2A and D3 receptors. The fourth isomer demonstrated poor affinity for all the receptors tested. Most significantly, the stereochemistry of the sulfoxide moiety played a dominant role in the observed structure-activity relationship (SAR).

The enantiomer debate: current status and future directions

Psychopharmacology, and the treatment of depression in particular, is one area where there is currently an increasing awareness of chiral drug phenomena. It is now generally agreed that the pharmacological and pharmacokinetic properties of chiral drugs and their enantiomers should be assessed early on in the drug development process. However, issues surrounding the potential advantages and disadvantages of enantiomeric drugs, compared with racemates, continue to be debated. This article highlights some of the key issues raised during one such debate, the aim of which was to address the hypothesis that each enantiomeric drug should be considered on its own merit. The idea is considered both in general terms and specifically in the context of clinical psychiatry, with an emphasis on the treatment of depression. An update on recent developments in enantiomeric antidepressant therapy is also provided. Copyright 2001 John Wiley & Sons, Ltd.

An introduction to enantiomers in psychopharmacology

There is growing scientific, clinical, commercial and regulatory recognition that enantiomers offer benefits over racemates in the management of psychiatric diseases as well as in clinical medicine generally. However, relatively few studies consider enantiomers' individual characteristics. This review considers some of the clinical benefits associated with using stereochemically pure drugs in psychiatric conditions other than depression.A review of the evidence shows that enantiomers offer four main benefits. Firstly, using a single enantiomer may allow a reduction in total dose, while maintaining or improving outcomes. For example, (+)-nefopam's antinociceptive activity is greater than that produced by both the racemate and (-)-nefopam, but with the same level of acute toxicity. Thus, a single enantiomer may offer greater efficacy, dose for dose, than the racemate. Secondly, assessing dose-response relationships is simpler. There is no reason to suppose that a racemate will necessarily contain the isomers' optimum therapeutic ratio, that one of the isomers will be inactive or that the enantiomers' dose-response curves will coincide. For example, the dose-response relationship for the induction of catalepsy in the rat by thioridazine suggested that the racemate was around 12 times more potent than (+)-thioridazine and three times more potent than (-)-thioridazine, when considering the actual concentrations in the striatum. Thirdly, using a single enantiomer may reduce pharmacokinetic and pharmacodynamic variability between patients. For example, the coefficients of variation for some of methadone's pharmacokinetic parameters may reach 70%, which might have clinical consequences. Finally, using a single enantiomer may reduce toxicity arising from the therapeutically inactive stereoisomer. For example, the single enantiomers of bupivacaine and ropivacaine are significantly less cardiotoxic than their respective racemates.This review illustrates why stereochemistry should be considered when assessing the toxicology, pharmacokinetics, metabolism and efficacy of a racemate. Indeed, the differences may be so marked that achiral analyses may be misleading, and clinicians should consider prescribing an enantiomer whenever possible. In many cases, prescribing a single enantiomer improves the benefit:risk ratio. Finally, there is no reason to suppose that a racemate's characteristics will apply to the constituent enantiomers. Copyright 2001 John Wiley & Sons, Ltd.

Direct, preparative enantioselective chromatography of propranolol hydrochloride and thioridazine hydrochloride using carbon dioxide-based mobile phases

In this paper, we describe the direct, preparative enantioselective chromatography of racemic (rac)-propranolol hydrochloride (HCI) and rac-thioridazine.HCl using Chiralpak AD chiral stationary phase and mobile phase systems containing carbon dioxide and methanol without the use of basic or acidic additives. Isolated fractions of propranolol.HCl were positively identified by mass spectrometry, Beilstein flame test, melting point, and chemical analysis to be HCI enantiomers of propranolol-HCl salts exhibited characteristic mass spectra peaks at 36 and 38 mass-to-charge ratio in the expected 3:1 isotopic ratio for the solute that were absent in the mass spectra for the free-base forms. To our knowledge, the direct, preparative enantioselective isolation of HCI enantiomeric salts of rac-propranolol and of rac-thioridazine have not been previously demonstrated and published.

Chirality and drugs used in psychiatry: nice to know or need to know?

1. Many drugs used to treat psychiatric disorders contain a chiral center or a center of unsaturation and are marketed as a mixture of the resultant enantiomers or geometric isomers, respectively. These enantiomers or geometric isomers may differ markedly with regard to their pharmacodynamic and/or pharmacokinetic properties. 2. Examples of the effects of chiral centers or geometric centers on such properties are given for drugs from the following classes: antidepressants (tricyclics, selective serotonin reuptake inhibitors, monoamine oxidase inhibitors, viloxazine, bupropion, trazodone, mianserin, venlaflaxine); benzodiazepines, zoplicone, and antipsychotics. 3. As described in this review, there are several notable examples of psychiatric drugs currently available where the individual enantiomers or geometric isomers differ considerably with regard to factors such as effects on amine transport systems, interactions with receptors and metabolizing enzymes, and clearance rates from the body. Indeed, relatively recent developments in analytical and preparative resolution of racemic and geometric drug mixtures and increased interest in developing new drugs which interact with specific targets, which have been described in detail at the molecular level, have resulted in increased emphasis on stereochemistry in drug development.

Concentration-related pharmacodynamic effects of thioridazine and its metabolites in humans

OBJECTIVE

To measure cardiac and other effects of thioridazine and relate these to the plasma concentration of the parent drug and its principal metabolites.

METHODS

A double-blind, randomized-order crossover study involving nine healthy male subjects compared the effects of single doses of thioridazine (10 mg and 50 mg) with placebo. Plasma concentrations of thioridazine and its ring sulfoxide, side-chain sulfoxide, and side-chain sulfone metabolites were measured, together with effects on the ECG, blood pressure, salivary flow, and a batch of psychomotor tests for 72 hours after administration.

RESULTS

Thioridazine, 50 mg, reduced standing systolic blood pressure (mean peak changes from baseline [95% CI] -32 mm Hg [-55, 10 mm Hg]; p < 0.01 versus placebo) and diastolic blood pressure (-14 mm Hg [-26, -2 mm Hg]; p < 0.05), increased standing heart rate (7 beats/min [-1, 16 beats/min]; p < 0.05), impaired psychomotor function, and prolonged the JT (20 ms1/2 [7, 34 ms1/2]; p < 0.05), QTa (22 ms1/2 [8, 36 ms1/2]; p < 0.05), and QTc (22 ms1/2 [11, 33 ms1/2]; p < 0.01) intervals, but had no effect on QT dispersion (-12 ms1/2 [-31, 6 ms1/2]). Thioridazine, 1.0 mg, also significantly increased QTc, but the effect was less marked (9 ms1/2 [-1, 19 ms1/2]; p < 0.05). Plasma thioridazine and metabolite concentrations did not correlate significantly with these effects. Maximum effects on QTc occurred after peak concentrations of thioridazine but before peak concentrations of the ring sulfoxide and side-chain sulfone metabolites.

CONCLUSIONS

These data suggest that thioridazine has dose-related effects on ventricular repolarization and that the parent drug causes an important proportion of these effects, although its metabolites may also contribute.

Plasma levels of the enantiomers of thioridazine, thioridazine 2-sulfoxide, thioridazine 2-sulfone, and thioridazine 5-sulfoxide in poor and extensive metabolizers of dextromethorphan and mephenytoin

Concentrations of total (R) + (S) and of the enantiomers (R) and (S) of thioridazine and metabolites were measured in 21 patients who were receiving 100 mg thioridazine for 14 days and who were comedicated with moclobemide (450 mg/day). Two patients were poor metabolizers of dextromethorphan and one was a poor metabolizer of mephenytoin. Cytochrome P450IID6 (CYP2D6) is involved in the formation of thioridazine 2-sulfoxide (2-SO) from thioridazine and also probably partially in the formation of thioridazine 5-sulfoxide (5-SO), but not in the formation of thioridazine 2-sulfone (2-SO2) from thioridazine 2-SO. Significant correlations between the mephenytoin enantiomeric ratio and concentrations of thioridazine and metabolites suggest that cytochrome P450IIC19 could contribute to the biotransformation of thioridazine into yet-unknown metabolites, other than thioridazine 2-SO, thioridazine 2-SO2, or thioridazine 5-SO. An enantioselectivity and a large interindividual variability in the metabolism of thioridazine have been shown: measured (R)/(S) ratios of thioridazine, thioridazine 2-SO fast eluting (FE), thioridazine 2-SO slow eluting (SE), thioridazine 2-SO (FE+SE), thioridazine 2-SO2, thioridazine 5-SO(FE), and thioridazine 5-SO(SE) were (mean +/- SD) 3.48 +/- 0 .93 (range, 2.30 to 5.80), 0.45 +/- 0.22 (range, 0.21 to 1.20), 2.27 +/- 8.1 (range, 6.1 to 40.1), 4.64 +/- 0.68 (range, 2.85 to 5.70), 3.26 +/- 0.58 (range, 2.30 to 4.30), 0.049 +/- 0.019 (range, (0.021 to 0.087), and 67.2 +/- 66.2 (range, 16.8 to 248), respectively. CYP2D6 is apparently involved in the formation of (S)-thioridazine 2-SO(FE), (R)-thioridazine 2-SO(SE), and also probably (S)-thioridazine 5-SO(FE) and (R)-thioridazine 5-SO(SE).

Determination of the enantiomers of thioridazine, thioridazine 2-sulfone, and of the isomeric pairs of thioridazine 2-sulfoxide and thioridazine 5-sulfoxide in human plasma

Thioridazine is a commonly prescribed phenothiazine drug administered as a racemate and it is believed that its antipsychotic effect is mainly associated with (R)-thioridazine. A method based on high-performance liquid chromatography has been developed for the determination of the enantiomers of thioridazine and thioridazine 2-sulfone (THD 2-SO2 or sulforidazine) and of the enantiomers of the diastereoisomeric pairs of thioridazine 2-sulfoxide (THD 2-SO or mesoridazine) and thioridazine 5-sulfoxide (THD 5-SO) in the plasma of thioridazine-treated patients. The method involves sequential achiral and chiral HPLC. The limits of quantitation for total (R) + (S) concentrations were found to be 15 ng/ml for thioridazine and 5 ng/ml for its metabolites. The limits for the determination of the (R)/(S) ratios were found to be 60 ng/ml for racemic THD and 10 ng/ml for racemic THD 2-SO, THD 2-SO2, THD 5-SO (FE) and THD 5-SO (SE). The method has been used to determine the concentrations of the enantiomers of thioridazine and of its metabolites in the plasma of a patient treated with 100 mg of racemic thioridazine hydrochloride per os per day for 14 days. The results show a high enantioselectivity in the metabolism of this drug: the (R)/(S) ratios for THD, THD 2-SO (FE), THD 2-SO (SE), THD 2-SO2, THD 5-SO (FE) and THD 5-SO (SE) were found to be 3.90, 1.22, 6.10, 4.10, 0.09 and 28.0, respectively.

Thioridazine enantiomers in human tissues

Enantiomers of thioridazine (TRZ) were determined in postmortem tissues obtained from a patient on chronic TRZ therapy by sequential achiral and chiral high pressure liquid chromatography. Tissue concentrations of (+)-TRZ found in liver, brain, bile and blood were: 6.46, 0.40, 0.48 and 0.07 mg/l or mg/kg, respectively. Concentrations of (-)-TRZ in liver, brain, bile and blood were: 12.2, 0.81, 1.07 and 0.20 mg/l or mg/kg, respectively. These data demonstrate the stereoselective disposition of TRZ in human tissues.

Repeated L-dopa administration reduces the ability of dopamine storage and abolishes the supersensitivity of dopamine receptors in the striatum of intact rat

The "wearing-off" phenomenon is a clinically recognized adverse effect of long-term L-DOPA therapy in Parkinson's disease. Several causes of this phenomenon have been proposed, but no direct evidence has yet been obtained. The present study was therefore conducted to investigate the effects of long-term L-DOPA administration on the dopamine system. We examined in rats the time course of the levels of L-DOPA and its metabolites in the serum and striatum, the activities of tyrosine hydroxylase and catechol O-methyltransferase, and the D1 and D2 dopamine receptor bindings in the striatum until 12 h after the final dose on the 28th day of repeated oral L-DOPA administration, and compared the results with those after a single L-DOPA administration. The results revealed that long-term L-DOPA administration induced (1) acceleration of DOPA absorption at the gut and the blood-brain barrier, (2) reduction of dopamine retention in the striatum, and (3) loss of "supersensitive response" of dopamine receptors. "Supersensitive response" induced by single L-DOPA administration was preceded by the increase of D1 messenger RNA. We suggest that these changes after long-term L-DOPA administration are causes of the "wearing-off" phenomenon in Parkinson's disease.