Ziprasidone metabolism, aldehyde oxidase, and clinical implications

Optimisation of pharmacotherapy in psychiatry through therapeutic drug monitoring, molecular brain imaging and pharmacogenetic tests: focus on antipsychotics

BACKGROUND

For psychotic disorders (i.e. schizophrenia), pharmacotherapy plays a key role in controlling acute and long-term symptoms. To find the optimal individual dose and dosage strategy, specialized tools are used. Three tools have been proven useful to personalize drug treatments: therapeutic drug monitoring (TDM) of drug levels, pharmacogenetic testing (PG), and molecular neuroimaging.

METHODS

In these Guidelines, we provide an in-depth review of pharmacokinetics, pharmacodynamics, and pharmacogenetics for 50 antipsychotics. Over 30 international experts in psychiatry selected studies that have measured drug concentrations in the blood (TDM), gene polymorphisms of enzymes involved in drug metabolism, or receptor/transporter occupancies in the brain (positron emission tomography (PET)).

RESULTS

Study results strongly support the use of TDM and the cytochrome P450 (CYP) genotyping and/or phenotyping to guide drug therapies. Evidence-based target ranges are available for titrating drug doses that are often supported by PET findings.

CONCLUSION

All three tools discussed in these Guidelines are essential for drug treatment. TDM goes well beyond typical indications such as unclear compliance and polypharmacy. Despite its enormous potential to optimize treatment effects, minimize side effects and ultimately reduce the global burden of diseases, personalized drug treatment has not yet become the standard of care in psychiatry.

Ontogeny of Human Liver Aldehyde Oxidase: Developmental Changes and Implications for Drug Metabolism

Despite the increasing importance of aldehyde oxidase (AO) in the drug metabolism of clinical candidates, ontogeny data for AO are limited. The objective of our study was to characterize the age-dependent AO content and activity in the human liver cytosolic fraction (HLC) and human hepatocytes (HH). HLC (n = 121 donors) and HH (n = 50 donors) were analyzed for (1) AO protein content by quantitative proteomics and (2) enzyme activity using carbazeran as a probe substrate. AO activity showed high technical variability and poor correlation with the content in HLC samples, whereas hepatocyte samples showed a strong correlation between the content and activity. Similarly, AO content and activity showed no significant age-dependent differences in HLC samples, whereas the average AO content and activity in hepatocytes increased significantly (∼20-40-fold) from the neonatal levels (0-28 days). Based on the hepatocyte data, the age at which 50% of the adult AO content is reached (age50) was 3.15 years (0.32-13.97 years, 95% CI). Metabolite profiling of carbazeran revealed age-dependent metabolic switching and the role of non-AO mechanisms (glucuronidation and desmethylation) in carbazeran elimination. The content-activity correlation in hepatocytes improved significantly (R2 = 0.95; p < 0.0001) in samples showing <10% contribution of glucuronidation toward the overall metabolism, confirming that AO-mediated oxidation and glucuronidation are the key routes of carbazeran metabolism. Considering the confounding effect of glucuronidation on AO activity, AO content-based ontogeny data are a more direct reflection of developmental changes in protein expression. The comprehensive ontogeny data of AO in HH samples are more reliable than HLC data, which are important for developing robust physiologically based pharmacokinetic models for predicting AO-mediated metabolism in children.

Risk Assessment of Psychotropic Drugs on Mitochondrial Function Using In Vitro Assays

Mitochondria are potential targets responsible for some drug- and xenobiotic-induced organ toxicities. However, molecular mechanisms of drug-induced mitochondrial toxicities are mostly unknown. Here, multiple in vitro assays were used to investigate the effects of 22 psychotropic drugs on mitochondrial function. The acute extracellular flux assay identified inhibitors of the electron transport chain (ETC), i.e., aripiprazole, phenytoin, and fluoxetine, an uncoupler (reserpine), substrate inhibitors (quetiapine, carbamazepine, buspirone, and tianeptine), and cytotoxic compounds (chlorpromazine and valproic acid) in HepG2 cells. Using permeabilized HepG2 cells revealed minimum effective concentrations of 66.3, 6730, 44.5, and 72.1 µM for the inhibition of complex-I-linked respiration for quetiapine, valproic acid, buspirone, and fluoxetine, respectively. Assessing complex-II-linked respiration in isolated rat liver mitochondria revealed haloperidol is an ETC inhibitor, chlorpromazine is an uncoupler in basal respiration and an ETC inhibitor under uncoupled respiration (IC50 = 135 µM), while olanzapine causes a mild dissipation of the membrane potential at 50 µM. This research elucidates some mechanisms of drug toxicity and provides some insight into their safety profile for clinical drug decisions.

Advancing Our Understanding of Pyranopterin-Dithiolene Contributions to Moco Enzyme Catalysis

The pyranopterin dithiolene ligand is remarkable in terms of its geometric and electronic structure and is uniquely found in mononuclear molybdenum and tungsten enzymes. The pyranopterin dithiolene is found coordinated to the metal ion, deeply buried within the protein, and non-covalently attached to the protein via an extensive hydrogen bonding network that is enzyme-specific. However, the function of pyranopterin dithiolene in enzymatic catalysis has been difficult to determine. This focused account aims to provide an overview of what has been learned from the study of pyranopterin dithiolene model complexes of molybdenum and how these results relate to the enzyme systems. This work begins with a summary of what is known about the pyranopterin dithiolene ligand in the enzymes. We then introduce the development of inorganic small molecule complexes that model aspects of a coordinated pyranopterin dithiolene and discuss the results of detailed physical studies of the models by electronic absorption, resonance Raman, X-ray absorption and NMR spectroscopies, cyclic voltammetry, X-ray crystallography, and chemical reactivity.

Clinically important alterations in pharmacogene expression in histologically severe nonalcoholic fatty liver disease

Polypharmacy is common in patients with nonalcoholic fatty liver disease (NAFLD) and previous reports suggest that NAFLD is associated with altered drug disposition. This study aims to determine if patients with NAFLD are at risk for altered drug response by characterizing changes in hepatic mRNA expression of genes mediating drug disposition (pharmacogenes) across the histological NAFLD severity spectrum. We utilize RNA-seq for 93 liver biopsies with histologically staged NAFLD Activity Score (NAS), fibrosis stage, and steatohepatitis (NASH). We identify 37 significant pharmacogene-NAFLD severity associations including CYP2C19 downregulation. We chose to validate CYP2C19 due to its actionability in drug prescribing. Meta-analysis of 16 independent studies demonstrate that CYP2C19 is significantly downregulated to 46% in NASH, to 58% in high NAS, and to 43% in severe fibrosis. Our data demonstrate the downregulation of CYP2C19 in NAFLD which supports developing personalized medicine approaches for drugs sensitive to metabolism by the CYP2C19 enzyme.

In vitro degradation of ziprasidone in human whole blood

A systematic study was performed into the degradation of ziprasidone in simulated postmortem blood. Fifteen potential degradation products not previously reported in the literature were observed. Four resulted from degradation in human blood, whereas the remaining products resulted from reaction with solvents: four from alkaline degradation, four from reaction with acetaldehyde, and three from reaction with acetone. To identify possible degradation products, a liquid chromatograph-diode array detector (LC-DAD) and liquid chromatograph quadrupole-time-of-flight mass spectrometer (LC-QTOF-MS) operating in auto-MS/MS mode were used. It was indicated from red-shifted UV-Vis spectra, accurate mass data, mass fragmentation data, and a deuteration experiment that the site of ziprasidone degradation, in the in vitro blood experiments, was the methylene carbon of the oxindole moiety. The major in vitro blood degradation products were proposed to be E/Z isomers of 3-ethylidene-ziprasidone. Further, another in vitro degradation product in microbially inoculated blood specimens was proposed to be 3-ethyl-ziprasidone. 3-Ethylidene-ziprasidone was hypothesized to form from the reaction of ziprasidone with acetaldehyde derived from the ethanol used to spike ziprasidone into the in vitro blood experiments. Data from two postmortem investigations were available for retrospective reanalysis. Attempts were made to detect degradation products of ziprasidone, but none were found.

Racial/Ethnic Differences in the Pharmacokinetics of Antipsychotics: Focusing on East Asians

Empirical clinical studies have suggested that East Asian patients may require lower dosages of psychotropic drugs, such as antipsychotics, lithium, and antidepressants, than non-Asians. Both the pharmacokinetic and pharmacodynamic properties of a drug can affect the clinical response of an illness. The levels of antipsychotics used for the treatment of schizophrenia may affect patient clinical responses; several factors can affect these levels, including patient medication adherence, body weight (BW) or body mass index, smoking habits, and sex. The cytochrome P450 (CYP) system is a major factor affecting the blood levels of antipsychotics because many antipsychotics are metabolized by this system. There were notable genetic differences between people of different races. In this study, we determined the racial or ethnic differences in the metabolic patterns of some selected antipsychotics by reviewing therapeutic drug monitoring studies in East Asian populations. The plasma concentrations of haloperidol, clozapine, quetiapine, aripiprazole, and lurasidone, which are metabolized by specific CYP enzymes, were determined to be higher, under the same daily dose, in East Asian populations than in Western populations.

A Pan-Cancer Analysis of Transcriptome and Survival Reveals Prognostic Differentially Expressed LncRNAs and Predicts Novel Drugs for Glioblastoma Multiforme Therapy

Numerous studies have identified various prognostic long non-coding RNAs (LncRNAs) in a specific cancer type, but a comprehensive pan-cancer analysis for prediction of LncRNAs that may serve as prognostic biomarkers is of great significance to be performed. Glioblastoma multiforme (GBM) is the most common and aggressive malignant adult primary brain tumor. There is an urgent need to identify novel therapies for GBM due to its poor prognosis and universal recurrence. Using available LncRNA expression data of 12 cancer types and survival data of 30 cancer types from online databases, we identified 48 differentially expressed LncRNAs in cancers as potential pan-cancer prognostic biomarkers. Two candidate LncRNAs were selected for validation in GBM. By the expression detection in GBM cell lines and survival analysis in GBM patients, we demonstrated the reliability of the list of pan-cancer prognostic LncRNAs obtained above. By constructing LncRNA-mRNA-drug network in GBM, we predicted novel drug-target interactions for GBM correlated LncRNA. This analysis has revealed common prognostic LncRNAs among cancers, which may provide insights into cancer pathogenesis and novel drug target in GBM.

Precision Medicine into Clinical Practice: A Web-Based Tool Enables Real-Time Pharmacogenetic Assessment of Tailored Treatments in Psychiatric Disorders

The management of neuropsychiatric disorders involves different pharmacological treatments. In order to perform efficacious drug treatments, the metabolism of CYP genes can help to foresee potential drug–drug interactions. The NeuroPGx software is an open-source web-based tool for genotype/diplotype/phenotype interpretation for neuropharmacogenomic purposes. The software provides information about: (i) the genotypes of evaluated SNPs (single nucleotide polymorphisms); (ii) the main diplotypes in CYP genes and corresponding metabolization phenotypes; (iii) the list of neuropsychiatric drugs with recommended dosage adjustment (according to CPIC and DPWG guidelines); (iv) the list of possible (rare) diplotypes and corresponding metabolization phenotypes. The combined application of NeuroPGx software to the OpenArray technology results in an easy, quick, and highly automated device ready to be used in routine clinical practice.

A comprehensive review of in silico approaches for the prediction and modulation of aldehyde oxidase-mediated drug metabolism: The current features, challenges and future perspectives

The importance of aldehyde oxidase (AOX) in drug metabolism necessitates the development and application of the in silico rational drug design methods as an integral part of drug discovery projects for the early prediction and modulation of AOX-mediated metabolism. The current study represents an up-to-date and thorough review of in silico studies of AOX-mediated metabolism and modulation methods. In addition, the challenges and the knowledge gap that should be covered have been discussed. The importance of aldehyde oxidase (AOX) in drug metabolism is a hot topic in drug discovery. Different strategies are available for the modulation of the AOX-mediated metabolism of drugs. Application of the rational drug design methods as an integral part of drug discovery projects is necessary for the early prediction of AOX-mediated metabolism. The current study represents a comprehensive review of AOX molecular structure, AOX-mediated reactions, AOX substrates, AOX inhibition, approaches to modify AOX-mediated metabolism, prediction of AOX metabolism/substrates/inhibitors, and the AOX related structure-activity relationship (SAR) studies. Furthermore, an up-to-date and thorough review of in silico studies of AOX metabolism has been carried out. In addition, the challenges and the knowledge gap that should be covered in the scientific literature have been discussed in the current review.

How Can Drug Metabolism and Transporter Genetics Inform Psychotropic Prescribing?

Many genetic variants in drug metabolizing enzymes and transporters have been shown to be relevant for treating psychiatric disorders. Associations are strong enough to feature on drug labels and for prescribing guidelines based on such data. A range of commercial tests are available; however, there is variability in included genetic variants, methodology, and interpretation. We herein provide relevant background for understanding clinical associations with specific variants, other factors that are relevant to consider when interpreting such data (such as age, gender, drug-drug interactions), and summarize the data relevant to clinical utility of pharmacogenetic testing in psychiatry and the available prescribing guidelines. We also highlight areas for future research focus in this field.

A Comprehensive Review on Importance and Quantitation of Atypical Antipsychotic Drugs and their Active Metabolites in Commercial Dosage Forms

Background:

Schizophrenia is a severe mental illness that affects more than twenty-one million people throughout the world. Schizophrenia also causes early death. Schizophrenia and other related psychotic ailments are controlled by the prescription of antipsychotic drugs, which act by blocking certain chemical receptors in the brain and thus relieves the symptoms of psychotic disorder. These drugs are present in the different dosage forms in the market and provided in a certain amount as per the need of the patients.

Objective:

Since such medications treat mental disorders, it is very important to have a perfect and accurate dose so that the risk factor is not affected by a higher or lower dose, which is not sufficient for the treatment. For accurate assay of these kinds of drugs, different analytical methods were developed ranging from older spectrophotometric techniques to latest hyphenated methods.

Results:

The current review highlights the role of different analytical techniques that were employed in the determination and identification of antipsychotic drugs and their metabolites. Techniques such as spectrophotometry, fluorimetry, liquid chromatography, liquid chromatography-mass spectrometry, gas chromatography, and gas chromatography-mass spectrometry employed in the method development of such antipsychotic drugs were reported in the review. Different metabolites, identified using the hyphenated techniques, were also mentioned in the review. The synthesis pathways of few of the metabolites were mentioned.

Conclusion:

The review summarizes the analyses of different antipsychotic drugs and their metabolites. A brief introduction of illnesses and their symptoms and possible medications were highlighted. Synthesis pathways of the associated metabolites were also mentioned.

Drug Metabolism by the Mitochondrial Amidoxime Reducing Component (mARC): Rapid Assay and Identification of New Substrates

For the development of new drugs, the investigation of their metabolism is of central importance. In the past, the focus was mostly on the consideration of established enzymes leading to oxidations such as cytochrome P450. However, reductive metabolism by the mARC enzyme system can play an important role in particular for nitrogen containing functional groups. A rapid test was established to give developers of new drugs in the preclinical stage the opportunity to test the metabolism by mARC. To demonstrate the relevance and validity of the new test system, known and potential substrates were applied to this new assay. All known substrates could be detected by the system. Furthermore, several new substrates were found including long-established drugs such as hydroxyurea and new compounds in development such as epacdadostat.

The use of ziprasidone in clinical practice: Analysis of pharmacokinetic and pharmacodynamic aspects from data of a drug monitoring survey

This study related clinical effects to daily doses and serum concentrations of ziprasidone by retrospective analysis of data from a therapeutic drug monitoring (TDM) survey established for patients treated with the new antipsychotic drug. In the total sample of 463 patients ziprasidone doses ranged between 20 and 320 mg/d and correlated significantly (r2 = 0.093, P < 0.01) with serum concentrations. The latter were highly variable within and between individual patients (between patients median 67 ng/ml, 25–75th percentile 40–103 ng/ml). Pharmacokinetic interactions with comedication played a minor role. According to the clinical global impressions (CGI) scale most of the 348 patients who were under antipsychotic monotherapy with ziprasidone were either much or very much improved (43.3 and 17.3%, respectively). The previously proposed therapeutic range of 50–130 ng/ml ziprasidone in serum or plasma, which can in effect be used interchangeable, was confirmed. In patients who were at least much improved and defined as “responders” mean serum concentrations of ziprasidone were 80 ng/ml and 78 ng/ml in patients who did not reach this improvement score. In patients with serum levels above or below 50 ng/ml, the number of responders was 66 or 63%, respectively. The difference between the two groups was not significant (P = 0.375), and improvement or side effects did not correlate significantly (P > 0.05) with doses or serum levels. It is concluded that TDM of ziprasidone may be useful for treatment optimization because of highly variable serum concentrations resulting under therapeutically recommended doses of the drug.

Immunoendocrine Peripheral Effects Induced by Atypical Antipsychotics

Atypical antipsychotics (AAP) or second-generation antipsychotics are the clinical option for schizophrenia treatment during acute psychoses, but they are also indicated for maintenance during lifetime, even though they are being used for other psychiatric conditions in clinical practice such as affective disorders and autism spectrum disorder, among others. These drugs are differentiated from typical antipsychotics based on their clinical profile and are a better choice because they cause fewer side effects regarding extrapyramidal symptoms (EPS). Even though they provide clear therapeutic benefits, AAP induce peripheral effects that trigger phenotypic, functional, and systemic changes outside the Central Nervous System (CNS). Metabolic disease is frequently associated with AAP and significantly impacts the patient's quality of life. However, other peripheral changes of clinical relevance are present during AAP treatment, such as alterations in the immune and endocrine systems as well as the intestinal microbiome. These less studied alterations also have a significant impact in the patient's health status. This manuscript aims to revise the peripheral immunological, endocrine, and intestinal microbiome changes induced by AAP consumption recommended in the clinical guidelines for schizophrenia and other psychiatric disorders.

Metabolism by Aldehyde Oxidase: Drug Design and Complementary Approaches to Challenges in Drug Discovery

Aldehyde oxidase (AO) catalyzes oxidations of azaheterocycles and aldehydes, amide hydrolysis, and diverse reductions. AO substrates are rare among marketed drugs, and many candidates failed due to poor pharmacokinetics, interspecies differences, and adverse effects. As most issues arise from complex and poorly understood AO biology, an effective solution is to stop or decrease AO metabolism. This perspective focuses on rational drug design approaches to modulate AO-mediated metabolism in drug discovery. AO biological aspects are also covered, as they are complementary to chemical design and important when selecting the experimental system for risk assessment. The authors' recommendation is an early consideration of AO-mediated metabolism supported by computational and in vitro experimental methods but not an automatic avoidance of AO structural flags, many of which are versatile and valuable building blocks. Preferably, consideration of AO-mediated metabolism should be part of the multiparametric drug optimization process, with the goal to improve overall drug-like properties.

Aldehyde oxidase and its role as a drug metabolizing enzyme

Aldehyde oxidase (AO) is a cytosolic enzyme that belongs to the family of structurally related molybdoflavoproteins like xanthine oxidase (XO). The enzyme is characterized by broad substrate specificity and marked species differences. It catalyzes the oxidation of aromatic and aliphatic aldehydes and various heteroaromatic rings as well as reduction of several functional groups. The references to AO and its role in metabolism date back to the 1950s, but the importance of this enzyme in the metabolism of drugs has emerged in the past fifteen years. Several reviews on the role of AO in drug metabolism have been published in the past decade indicative of the growing interest in the enzyme and its influence in drug metabolism. Here, we present a comprehensive monograph of AO as a drug metabolizing enzyme with emphasis on marketed drugs as well as other xenobiotics, as substrates and inhibitors. Although the number of drugs that are primarily metabolized by AO are few, the impact of AO on drug development has been extensive. We also discuss the effect of AO on the systemic exposure and clearance these clinical candidates. The review provides a comprehensive analysis of drug discovery compounds involving AO with the focus on developmental candidates that were reported in the past five years with regards to pharmacokinetics and toxicity. While there is only one known report of AO-mediated clinically relevant drug-drug interaction (DDI), a detailed description of inhibitors and inducers of AO known to date has been presented here and the potential risks associated with DDI. The increasing recognition of the importance of AO has led to significant progress in predicting the site of AO-mediated metabolism using computational methods. Additionally, marked species difference in expression of AO makes it is difficult to predict human clearance with high confidence. The progress made towards developing in vivo, in vitro and in silico approaches for predicting AO metabolism and estimating human clearance of compounds that are metabolized by AO have also been discussed.

Effects of Phenothiazines on Aldehyde Oxidase Activity Towards Aldehydes and N-Heterocycles: an In Vitro and In Silico Study

BACKGROUND

Aldehyde oxidase (AOX) is an important molybdenum-containing enzyme with high similarity with xanthine oxidase (XO). AOX involved in the metabolism of a large array of aldehydes and N-heterocyclic compounds and its activity is highly substrate-dependent.

OBJECTIVES

The aim of this work was to study the effect of five important phenothiazine drugs on AOX activity using benzaldehyde and phenanthridine as aldehyde and N-heterocyclic substrates, respectively.

METHODS

The effect of trifluperazine, chlorpromazine, perphenazine, thioridazine and promethazine on rat liver AOX was measured spectrophotometrically. To predict the mode of interactions between the studied compounds and AOX, a combination of homology modeling and a molecular docking study was performed.

RESULTS

All phenothiazines could inhibit AOX activity measured either by phenanthridine or benzaldehyde with almost no effect on XO activity. In the case of benzaldehyde oxidation, the lowest and highest half-maximal inhibitory concentration (IC₅₀) values were obtained for promethazine (IC₅₀ = 0.9 µM), and trifluoperazine (IC₅₀ = 3.9 µM), respectively; whereas perphenazine (IC₅₀ = 4.3 µM), and trifluoperazine (IC₅₀ = 49.6 µM) showed the strongest and weakest inhibitory activity against AOX-catalyzed phenanthridine oxidation, respectively. The in silico findings revealed that the binding site of thioridazine is near the dimer interference, and that hydrophobic interactions are of great importance in all the tested phenothiazines.

CONCLUSION

The five studied phenothiazine drugs showed dual inhibitory effects on AOX activity towards aldehydes and N-heterocycles as two major classes of enzyme substrates. Most of the interactions between the phenothiazine-related drugs and AOX in the binding pocket showed a hydrophobic nature.

Physiologically-based pharmacokinetics of ziprasidone in pregnant women

AIMS

Pregnancy is associated with physiological changes that alter the pharmacokinetics (PK) of drugs. The aim of this study was to predict the PK of ziprasidone in pregnant women.

METHODS

A full physiologically-based pharmacokinetic (PBPK) model of ziprasidone was developed and validated for the non-pregnant population (healthy adults, paediatrics, geriatrics), and this was extended to the pregnant state to assess the change in PK profile of ziprasidone throughout pregnancy.

RESULTS

The PBPK model successfully predicted the ziprasidone disposition in healthy adult volunteers, wherein the predicted and observed AUC, C_max and t_max were within the fold-difference of 0.94-1.09, 0.89-1.40 and 0.80-1.08, respectively. The paediatric and geriatric population, also showed predicted AUC, C_max and t_max within a two-fold range of the observed values. The simulated exposure in pregnant women using a p-PBPK model showed no significant difference when compared to non-pregnant women.

CONCLUSIONS

The PBPK model predicted the impact of physiological changes during pregnancy on PK and exposure of ziprasidone, suggesting that dose adjustment is not necessary in this special population.

Quantitative Prediction of Human Hepatic Clearance for P450 and Non-P450 Substrates from In Vivo Monkey Pharmacokinetics Study and In Vitro Metabolic Stability Tests Using Hepatocytes

Accurate prediction of human pharmacokinetics for drugs remains challenging, especially for non-cytochrome P450 (P450) substrates. Hepatocytes might be suitable for predicting hepatic intrinsic clearance (CL_int) of new chemical entities, because they can be applied to various compounds regardless of the metabolic enzymes. However, it was reported that hepatic CL_int is underestimated in hepatocytes. The purpose of the present study was to confirm the predictability of human hepatic clearance for P450 and non-P450 substrates in hepatocytes and the utility of animal scaling factors for the prediction using hepatocytes. CL_int values for 30 substrates of P450, UDP-glucuronosyltransferase, flavin-containing monooxygenase, esterases, reductases, and aldehyde oxidase in human microsomes, human S9 and human, rat, and monkey hepatocytes were estimated. Hepatocytes were incubated in serum of each species. Furthermore, CL_int values in human hepatocytes were corrected with empirical, monkey, and rat scaling factors. CL_int values in hepatocytes for most compounds were underestimated compared to observed values regardless of the metabolic enzyme, and the predictability was improved by using the scaling factors. The prediction using human hepatocytes corrected with monkey scaling factor showed the highest predictability for both P450 and non-P450 substrates among the predictions using liver microsomes, liver S9, and hepatocytes with or without scaling factors. CL_int values by this method for 80% and 90% of all compounds were within 2- and 3-fold of observed values, respectively. This method is accurate and useful for estimating new chemical entities, with no need to care about cofactors, localization of metabolic enzymes, or protein binding in plasma and incubation mixture.

Success stories of natural product-based hybrid molecules for multi-factorial diseases

Complex diseases comprises of highly complicated etiology resulting in limited applicability of conventional targeted therapies. Consequently, conventional medicinal compounds suffer major failure when used for such disease conditions. Additionally, development of multidrug resistance (MDR), adverse drug reactions and clinical specificity of single targeted drug therapy has increased thrust for novel drug therapy. In this rapidly evolving era, natural product-based discovery of hybrid molecules or multi-targeted drug therapies have shown promising results and are trending now a days. Historically, nature has blessed human with different sources viz. plant, animal, microbial, marine and ethnopharmaceutical sources which has given a wide variety of medicinally active compounds. These compounds from natural origin are always choice of interest of medicinal chemists because of their minimum side effects. Hybrid molecules synthesized by fusing or conjugating different active molecules obtained from these sources are reported to synergistically block different pathways which contribute in the pathogenesis of complex diseases. This review strives to encompass all natural product-derived hybrid molecules which act as multi-targeting agents striking various targets involved in different pathways of complex diseased conditions reported in literature.

Direct comparison of the four aldehyde oxidase enzymes present in mouse gives insight into their substrate specificities

Mammalian aldehyde oxidases (AOXs) are molybdo-flavoenzymes which are present in many tissues in various mammalian species, including humans and rodents. Different species contain a different number of AOX isoforms. In particular, the reasons why mammals other than humans express a multiplicity of tissue-specific AOX enzymes is unknown. In mouse, the isoforms mAOX1, mAOX3, mAOX4 and mAOX2 are present. We previously established a codon-optimized heterologous expression systems for the mAOX1-4 isoforms in Escherichia coli that gives yield to sufficient amounts of active protein for kinetic characterizations and sets the basis in this study for site-directed mutagenesis and structure-function studies. A direct and simultaneous comparison of the enzymatic properties and characteristics of the four enzymes on a larger number of substrates has never been performed. Here, thirty different structurally related aromatic, aliphatic and N-heterocyclic compounds were used as substrates, and the kinetic parameters of all four mAOX enzymes were directly compared. The results show that especially mAOX4 displays a higher substrate selectivity, while no major differences between mAOX1, mAOX2 and mAOX3 were identified. Generally, mAOX1 was the enzyme with the highest catalytic turnover for most substrates. To understand the factors that contribute to the substrate specificity of mAOX4, site-directed mutagenesis was applied to substitute amino acids in the substrate-binding funnel by the ones present in mAOX1, mAOX3, and mAOX2. An increase in activity was obtained by the amino acid exchange M1088V in the active site identified to be specific for mAOX4, to the amino acid identified in mAOX3.

An Inter-Ethnic Comparison Study of Ziprasidone Plasma Levels, Dosage and Clinical Response in Patients with Schizophrenia

OBJECTIVE

The aim of this study was to investigate ziprasidone plasma concentration, daily dose and clinical efficacy and safety in Han Chinese and Mongolian patients with first-episode schizophrenia.

METHODS

A total of 123 inpatients affected by schizophrenia were recruited from the Mental Health Center of Inner Mongolia in China. Ziprasidone plasma concentration, clinical efficacy and side effects were systematically evaluated at baseline, and at 1, 2, 4, and 6 weeks. Metabolic measures such as changes in weight, body mass index (BMI), fasting blood glucose (FBG), triglycerides, and cholesterol, were also recorded.

RESULTS

90 patients completed the study. Compared with Han patients, on average, Mongolian patients received a significantly higher ziprasidone dosage for adequate symptom control during the 6-week period and had a lower plasma concentration-to-dose ratio. The Mongolian patients also experienced greater increases in weight and BMI. No significant differences between the two ethnic groups were found in the rate of reduction in the Positive and Negative Syndrome Scale (PANSS) score, Treatment Emergent Symptom Scale (TESS) total score, FBG, triglycerides, cholesterol or Q-Tc interval.

CONCLUSION

Compared to Han Chinese patients, Mongolian patients appeared to have increased ziprasidone clearance and require higher doses to achieve effective treatment for schizophrenia.

Ziprasidone induces cytotoxicity and genotoxicity in human peripheral lymphocytes

It has been stated that some antipsychotic drugs might cause genotoxic and carcinogenic effects. Ziprasidone (ZIP) is commonly used an antipsychotic drug. However, its genotoxicity and carcinogenicity data are very limited. The cytotoxicity and genotoxicity of ZIP on human peripheral blood lymphocytes were examined in vitro by sister chromatid exchange (SCE), chromosome aberration (CA) and micronucleus (MN) tests in this study. Lymphocyte cultures were treated with 50, 75 and 100 μg/ml of ZIP in the presence and absence of a metabolic activator (S9 mix). Dimethylsulfoxide was used as a solvent control. While the cells were treated with ZIP for 24 h and 48 h in cultures without S9 mix, the cultures with S9 mix were exposed to ZIP for 3 h. ZIP and its metabolites can exert cytotoxic activities due to significant decreases in mitotic index, proliferation index and nuclear division index in the presence and absence of S9 mix. Statistically significant increases in CAs, aberrant cells and MN values in the presence and absence of S9 mix were found in cultures treated with ZIP. While ZIP significantly increased the SCE values in the absence of S9 mix at all concentrations, increased SCE values in cultures with S9 mix were not found to significantly at all concentrations tested. Our results indicated that both ZIP and its metabolites have cytotoxic, cytostatic and genotoxic potential on lymphocyte cultures under the experimental conditions. Further studies are necessary to make a possible risk assessment in patients receiving therapy with this drug.

Interspecies differences in the metabolism of methotrexate: An insight into the active site differences between human and rabbit aldehyde oxidase

Several drug compounds have failed in clinical trials due to extensive biotransformation by aldehyde oxidase (AOX) (EC 1.2.3.1). One of the main reasons is the difficulty in scaling clearance for drugs metabolised by AOX, from preclinical species to human. Using methotrexate as a probe substrate, we evaluated AOX metabolism in liver cytosol from human and commonly used laboratory species namely guinea pig, monkey, rat and rabbit. We found that the metabolism of methotrexate in rabbit liver cytosol was several orders of magnitude higher than any of the other species tested. The results of protein quantitation revealed that the amount of AOX1 in human liver was similar to rabbit liver. To understand if the observed differences in activity were due to structural differences, we modelled rabbit AOX1 using the previously generated human AOX1 homology model. Molecular docking of methotrexate into the active site of the enzyme led to the identification of important residues that could potentially be involved in substrate binding and account for the observed differences. In order to study the impact of these residue changes on enzyme activity, we used site directed mutagenesis to construct mutant AOX1 cDNAs by substituting nucleotides of human AOX1 with relevant ones of rabbit AOX1. AOX1 mutant proteins were expressed in Escherichia coli. Differences in the kinetic properties of these mutants have been presented in this study.

Evaluation of the pharmacokinetics, safety and clinical efficacy of ziprasidone for the treatment of schizophrenia and bipolar disorder

INTRODUCTION

Multiple strategies exist for the pharmacological treatment of schizophrenia and related disorders. In the last 20 years, several 'new' compounds have been introduced, called 'atypical antipsychotics', which have higher efficacy and better tolerability than first-generation neuroleptics. Among them, ziprasidone (ZPR) is currently finding widespread use, and it has also been shown to be active as an augmenter in bipolar disorder therapy.

AREAS COVERED

This review aims to provide the latest information on ZPR, an 'atypical' agent for the pharmacological therapy of schizophrenia and bipolar disorder. A literature search has been carried out with the keywords 'ziprasidone', 'schizophrenia', 'psychosis', 'bipolar', 'pharmacokinetics' and 'clinical trials'. In this process, particular attention has been paid to the drug pharmacokinetic characteristics and its safety in clinical use.

EXPERT OPINION

ZPR shares most advantages and disadvantages with other atypical antipsychotics. However, it can be useful for its low tendency to cause metabolic syndrome and hyperprolactinaemia, especially in patients suffering from excess weight, hyperlipidaemia, diabetes or who have suffered from hyperprolactinaemia when using other antipsychotics. However, there are serious doubts as to whether ZPR should be administered to patients suffering from arrhythmias or QTc prolongation, and even more for administration to bipolar patients undergoing polypharmacy with antidepressants.

Evaluation of the potential for a pharmacokinetic drug-drug interaction between armodafinil and ziprasidone in healthy adults

BACKGROUND

Armodafinil has been studied as adjunctive therapy for major depressive episodes associated with bipolar I disorder. This open-label, single-centre, 2-period study evaluated the effect of armodafinil, a moderate inducer of cytochrome-P450 (CYP) isoenzyme CYP3A4, on the pharmacokinetics and safety of ziprasidone, an atypical antipsychotic used to treat bipolar I disorder and metabolized in part by CYP3A4.

METHODS

Thirty-five healthy subjects received ziprasidone (20 mg) alone and after armodafinil pretreatment (titrated to 250 mg/day); of those, 25 were evaluable for pharmacokinetics. Pharmacokinetic parameters were derived from plasma concentrations of ziprasidone collected prior to and over the 48 h after each ziprasidone administration. Plasma concentrations of armodafinil and its circulating metabolites, R-modafinil acid and modafinil sulfone, were also obtained after repeated daily dosing of armodafinil alone. Safety and tolerability were assessed.

RESULTS

Systemic exposure to ziprasidone was similar following administration alone or after pretreatment with armodafinil, as assessed by mean peak plasma concentration (C max, 52.1 vs 50.4 ng/mL) and area under the plasma concentration-time curve from time 0 to infinity (AUC0-∞, 544.6 vs 469.1 ng·h/mL). Geometric mean ratios of systemic exposure (ziprasidone alone: ziprasidone after pretreatment with armodafinil) were close to unity, with associated 90 % confidence intervals (CIs) within the range of 0.80-1.25 (C max, 0.97; 90 % CI, 0.87-1.08; AUC0-∞, 0.86; 90 % CI, 0.82-0.91). Adverse events were consistent with the known safety profiles of each agent.

CONCLUSION

Systemic exposure to ziprasidone was not affected by pretreatment with armodafinil. Both drugs were generally safe and well tolerated under the conditions studied.

CYP450 pharmacogenetic treatment strategies for antipsychotics: a review of the evidence

Although a number of first- and second-generation antipsychotics are available, achieving optimal therapeutic response for patients with schizophrenia can be challenging. The presence of polymorphic alleles for cytochrome P (CYP) 450 may result in lack of expression, altered levels of expression, or altered function of CYP450 enzymes. CYP2D6, CYP1A2, and CYP3A4/5 are major enzymes in the metabolism of antipsychotics and polymorphisms of alleles for these proteins are associated with altered plasma levels. Consequently, standard dosing may result in drug plasma concentrations that are subtherapeutic or toxic in some patients. Patient CYP450 genotype testing can predict altered pharmacokinetics, and is currently available and relatively inexpensive. Evidence-based guidelines provide dose recommendations for some antipsychotics. To date few studies have demonstrated a significant association with genotype-guided antipsychotic use and clinical efficacy. However, many studies have been small, retrospective or cohort designs, and many have not been adequately powered. Numerous studies have shown a significant association between genotype and adverse effects, such as CYP2D6 polymorphisms and tardive dyskinesia. This review summarizes evidence for the role of CYP450 genetic variants in the response to antipsychotic medications and the clinical implications of pharmacogenetics in the management of patients with schizophrenia.

Evaluation of rhesus monkey and guinea pig hepatic cytosol fractions as models for human aldehyde oxidase

Aldehyde oxidase (AOX) is a cytosolic enzyme expressed across a wide range of species, including guinea pig and rhesus monkey. These species are believed to be the best preclinical models for studying human AOX-mediated metabolism. We compared AOX activity in rhesus monkeys, guinea pigs, and humans using phthalazine and N-[2-(dimethylamino)ethyl]acridone-4-carboxamide (DACA) as substrates and raloxifene as an inhibitor. Michaelis-Menten kinetics was observed for phthalazine oxidation in rhesus monkey, guinea pig, and human liver cytosol, whereas substrate inhibition was seen with DACA oxidase activity in all three livers. Raloxifene inhibited phthalazine and DACA oxidase activity uncompetitively in guinea pig, whereas mixed-mode inhibition was seen in rhesus monkey. Our analysis of the primary sequence alignment of rhesus monkey, guinea pig, and human aldehyde oxidase isoform 1 (AOX1) along with homology modeling has led to the identification of several amino acid residue differences within the active site and substrate entrance channel of AOX1. We speculate that some of these residues might be responsible for the differences observed in activity. Overall, our data indicate that rhesus monkeys and guinea pigs would overestimate intrinsic clearance in humans and would be unsuitable to use as animal models. Our study also showed that AOX metabolism in species is substrate-dependent and no single animal model can be reliably used to predict every drug response in humans.

Pharmacokinetics, Safety, and Tolerability of Intramuscular Ziprasidone in Healthy Volunteers

Little has been published regarding the pharmacokinetics of the intramuscular (IM) formulation of Ziprasidone. The authors report results from 2 early phase I studies in healthy volunteers: a trial of single 5-, 10-, or 20-mg IM doses of ziprasidone in 24 subjects and an open-label 3-way crossover trial of 5-mg intravenous (IV), 5-mg IM, and 20-mg oral ziprasidone in 12 subjects. Absorption of IM ziprasidone was rapid (Tmax < 1 hour). The IM pharmacokinetic profile was consistent between studies and linear, with dose-related increases in exposure observed. The mean IM elimination t(1/2) was short and approximately 2.5 hours. The mean bioavailability for the 5-mg IM ziprasidone dose was approximately 100%. Adverse events were generally mild to moderate, and no subjects were discontinued from the study. No significant effects on renal function or other laboratory values were noted. These results support the use of IM ziprasidone in treating acutely agitated patients with schizophrenia.

Predicting intrinsic clearance for drugs and drug candidates metabolized by aldehyde oxidase

Metabolism by aldehyde oxidase (AO) has been responsible for a number of drug failures in clinical trials. The main reason is the clearance values for drugs metabolized by AO are underestimated by allometric scaling from preclinical species. Furthermore, in vitro human data also underestimates clearance. We have developed the first in silico models to predict both in vitro and in vivo human intrinsic clearance for 8 drugs with just two chemical descriptors. These models explain a large amount of the variance in the data using two computational estimates of the electronic and steric features of the reaction. The in vivo computational models for human metabolism are better than in vitro preclinical animal testing at predicting human intrinsic clearance. Thus, it appears that AO is amenable to computational prediction of rates, which may be used to guide drug discovery, and predict pharmacokinetics for clinical trials.

Clinical pharmacology of dopamine-modulating agents in Tourette's syndrome

Forty years of research and clinical practice have proved dopamine (DA) receptor antagonists to be effective agents in the treatment of Tourette's syndrome (TS), allowing a significant tic reduction of about 70%. Their main effect seems to be mediated by the blockade of the striatal DA-D2 receptors. Various typical and atypical agents are available and there is still discord between experts about which of them should be considered as first choice. In addition, there are suggestions to use DA receptor agonists such as pergolide or non-DA-modulating agents. The present chapter is focusing on the clinical pharmacology of DA-modulating agents in the treatment of TS. The introduction outlines their clinical relevance and touches on the hypotheses of the role of DA in the pathophysiology of TS. Subsequently, general information about the mechanisms of action and adverse effects are provided. The central part of the chapter forms a systematic review of all DA-modulating agents used in the treatment of TS, including an overview of studies on their effectiveness, and a critical discussion of their specific adverse effects. The present chapter closes with a summary of the body of evidence and a description of the resulting recommendations for the pharmacological treatment of TS.

The role of aldehyde oxidase and xanthine oxidase in the biotransformation of a novel negative allosteric modulator of metabotropic glutamate receptor subtype 5

Negative allosteric modulation (NAM) of metabotropic glutamate receptor subtype 5 (mGlu₅) represents a therapeutic strategy for the treatment of childhood developmental disorders, such as fragile X syndrome and autism. VU0409106 emerged as a lead compound within a biaryl ether series, displaying potent and selective inhibition of mGlu₅. Despite its high clearance and short half-life, VU0409106 demonstrated efficacy in rodent models of anxiety after extravascular administration. However, lack of a consistent correlation in rat between in vitro hepatic clearance and in vivo plasma clearance for the biaryl ether series prompted an investigation into the biotransformation of VU0409106 using hepatic subcellular fractions. An in vitro appraisal in rat, monkey, and human liver S9 fractions indicated that the principal pathway was NADPH-independent oxidation to metabolite M1 (+16 Da). Both raloxifene (aldehyde oxidase inhibitor) and allopurinol (xanthine oxidase inhibitor) attenuated the formation of M1, thus implicating the contribution of both molybdenum hydroxylases in the biotransformation of VU0409106. The use of ¹⁸O-labeled water in the S9 experiments confirmed the hydroxylase mechanism proposed, because ¹⁸O was incorporated into M1 (+18 Da) as well as in a secondary metabolite (M2; +36 Da), the formation of which was exclusively xanthine oxidase-mediated. This unusual dual and sequential hydroxylase metabolism was confirmed in liver S9 and hepatocytes of multiple species and correlated with in vivo data because M1 and M2 were the principal metabolites detected in rats administered VU0409106. An in vitro-in vivo correlation of predicted hepatic and plasma clearance was subsequently established for VU0409106 in rats and nonhuman primates.

The impact of single nucleotide polymorphisms on human aldehyde oxidase

Aldehyde oxidase (AO) is a complex molybdo-flavoprotein that belongs to the xanthine oxidase family. AO is active as a homodimer, and each 150-kDa monomer binds two distinct [2Fe2S] clusters, FAD, and the molybdenum cofactor. AO has an important role in the metabolism of drugs based on its broad substrate specificity oxidizing aromatic aza-heterocycles, for example, N(1)-methylnicotinamide and N-methylphthalazinium, or aldehydes, such as benzaldehyde, retinal, and vanillin. Sequencing the 35 coding exons of the human AOX1 gene in a sample of 180 Italian individuals led to the identification of relatively frequent, synonymous, missense and nonsense single-nucleotide polymorphisms (SNPs). Human aldehyde oxidase (hAOX1) was purified after heterologous expression in Escherichia coli. The recombinant protein was obtained with a purity of 95% and a yield of 50 μg/l E. coli culture. Site-directed mutagenesis of the hAOX1 cDNA allowed the purification of protein variants bearing the amino acid changes R802C, R921H, N1135S, and H1297R, which correspond to some of the identified SNPs. The hAOX1 variants were purified and compared with the wild-type protein relative to activity, oligomerization state, and metal content. Our data show that the mutation of each amino acid residue has a variable impact on the ability of hAOX1 to metabolize selected substrates. Thus, the human population is characterized by the presence of functionally inactive hAOX1 allelic variants as well as variants encoding enzymes with different catalytic activities. Our results indicate that the presence of these allelic variants should be considered for the design of future drugs.

Inhibition of human liver aldehyde oxidase: implications for potential drug-drug interactions

During the course of our research efforts to understand the kinetics of human aldehyde oxidase as a xenobiotic-clearing enzyme, we investigated the effect of eight different inhibitors on the oxidation of the probe substrate phthalazine. Saturation kinetic parameters for phthalazine oxidation in human liver cytosol were found to be the following: K(m) = 8.0 ± 0.4 μM and V(max) = 4.3 ± 0.1 nmol · min(-1) · mg protein(-1). Inhibitory potency of the inhibitors tested ranged from 0.1 to 5 μM. Of the eight different inhibitor compounds tested, seven were observed to inhibit through a mixed mode and one through a strictly competitive mode. A ratio of the K(ii) and K(is) values was used to assess the relative competitiveness of each inhibitor. For the mixed inhibitors, the mode of inhibition varied from mostly uncompetitive to predominantly competitive (K(ii)/K(is) values ranging from 0.1 to 15). The implications for potential drug-drug interactions and inhibition mechanism are discussed. We found two inhibitors, clozapine and chlorpromazine, that have a moderate predicted risk of drug-drug interactions based on the K(i) value relative to the inhibitor concentration in human plasma, having a calculated [I]/K(i) value of 0.4 and 0.8, respectively.

Role of CYP pharmacogenetics and drug-drug interactions in the efficacy and safety of atypical and other antipsychotic agents

Cytochrome P450 (CYP) drug oxidases play a pivotal role in the elimination of antipsychotic agents, and therefore influence the toxicity and efficacy of these drugs. Factors that affect CYP function and expression have a major impact on treatment outcomes with antipsychotic agents. In particular, aspects of CYP pharmacogenetics, and the processes of CYP induction and inhibition all influence in-vivo rates of drug elimination. Certain CYPs that mediate the oxidation of antipsychotic drugs exhibit genetic variants that may influence in-vivo activity. Thus, single nucleotide polymorphisms (SNPs) in CYP genes have been shown to encode enzymes that have decreased drug oxidation capacity. Additionally, psychopharmacotherapy has the potential for drug-drug inhibitory interactions involving CYPs, as well as drug-mediated CYP induction. Literature evidence supports a role for CYP1A2 in the clearance of the atypical antipsychotics clozapine and olanzapine; CYP1A2 is inducible by certain drugs and environmental chemicals. Recent studies have suggested that specific CYP1A2 variants possessing individual SNPs, and possibly also SNP combinations (haplotypes), in the 5′-regulatory regions may respond differently to inducing chemicals. CYP2D6 is an important catalyst of the oxidation of chlorpromazine, thioridazine, risperidone and haloperidol. Certain CYP2D6 allelic variants that encode enzymes with decreased drug oxidation capacity are more common in particular ethnic groups, which may lead to adverse effects with standard doses of psychoactive drugs. Thus, genotyping may be useful for dose optimization with certain psychoactive drugs that are substrates for CYP2D6. However, genotyping for inducible CYPs is unlikely to be sufficient to direct therapy with all antipsychotic agents. In-vivo CYP phenotyping with cocktails of drug substrates may assist at the commencement of therapy, but this approach could be complicated by pharmacokinetic interactions if applied when an antipsychotic drug regimen is ongoing.

The mammalian aldehyde oxidase gene family

Aldehyde oxidases (EC 1.2.3.1) are a small group of structurally conserved cytosolic proteins represented in both the animal and plant kingdoms. In vertebrates, aldehyde oxidases constitute the small sub-family of molybdo-flavoenzymes, along with the evolutionarily and structurally related protein, xanthine oxidoreductase. These enzymes require a molybdo-pterin cofactor (molybdenum cofactor, MoCo) and flavin adenine dinucleotide for their catalytic activity. Aldehyde oxidases have broad substrate specificity and catalyse the hydroxylation of N-heterocycles and the oxidation of aldehydes to the corresponding acid. In humans, a single aldehyde oxidase gene (AOX1) and two pseudogenes clustering on a short stretch of chromosome 2q are known. In other mammals, a variable number of structurally conserved aldehyde oxidase genes has been described. Four genes (Aox1, Aox3, Aox4 and Aox3l1), coding for an equivalent number of catalytically active enzymes, are present in the mouse and rat genomes. Although human AOX1 and its homologous proteins are best known as drug metabolising enzymes, the physiological substrate(s) and function(s) are as yet unknown. The present paper provides an update of the available information on the evolutionary history, tissue- and cell-specific distribution and function of mammalian aldehyde oxidases.

The potential relationship between QTc interval prolongation and ziprasidone treatment: three cases

QTc interval prolongation may appear as a consequence of both typical and atypical antipsychotic treatments. Ziprasidone, which is effective in treating schizophrenia, is associated with QTc prolongation. Although the prolongation of QTc with ziprasidone treatment is often pronounced, there is a scarce number of cases reported about the relationship between ziprasidone and QTc prolongation. Of the three cases presented in this case series, two cases showed values exceeding 0.50 s with ziprasidone treatment.

Role of the molybdoflavoenzyme aldehyde oxidase homolog 2 in the biosynthesis of retinoic acid: generation and characterization of a knockout mouse

The mouse aldehyde oxidase AOH2 (aldehyde oxidase homolog 2) is a molybdoflavoenzyme. Harderian glands are the richest source of AOH2, although the protein is detectable also in sebaceous glands, epidermis, and other keratinized epithelia. The levels of AOH2 in the Harderian gland and skin are controlled by genetic background, being maximal in CD1 and C57BL/6 and minimal in DBA/2, CBA, and 129/Sv strains. Testosterone is a negative regulator of AOH2 in Harderian glands. Purified AOH2 oxidizes retinaldehyde into retinoic acid, while it is devoid of pyridoxal-oxidizing activity. Aoh2(-/-) mice, the first aldehyde oxidase knockout animals ever generated, are viable and fertile. The data obtained for this knockout model indicate a significant role of AOH2 in the local synthesis and biodisposition of endogenous retinoids in the Harderian gland and skin. The Harderian gland's transcriptome of knockout mice demonstrates overall downregulation of direct retinoid-dependent genes as well as perturbations in pathways controlling lipid homeostasis and cellular secretion, particularly in sexually immature animals. The skin of knockout mice is characterized by thickening of the epidermis in basal conditions and after UV light exposure. This has correlates in the corresponding transcriptome, which shows enrichment and overall upregulation of genes involved in hypertrophic responses.

Genetic determinants of variable metabolism have little impact on the clinical use of leading antipsychotics in the CATIE study

PURPOSE

To evaluate systematically in real clinical settings whether functional genetic variations in drug metabolizing enzymes influence optimized doses, efficacy, and safety of antipsychotic medications.

METHODS

DNA was collected from 750 patients with chronic schizophrenia treated with five antipsychotic drugs (olanzapine, quetiapine, risperidone, ziprasidone, and perphenazine) as part of the Clinical Antipsychotic Trials of Intervention Effectiveness study. Doses for each of the medicines were optimized to 1, 2, 3, or 4x units in identically appearing capsules in a double-blind design. We analyzed 25 known functional genetic variants in the major and minor metabolizing enzymes for each medication. These variants were tested for association with optimized dose and other relevant clinical outcomes.

RESULTS

None of the tested variants showed a nominally significant main effect in association with any of the tested phenotypes in European-Americans, African-Americans, or all patients. Even after accounting for potential covariates, no genetic variant was found to be associated with dosing, efficacy, overall tolerability, or tardive dyskinesia.

CONCLUSION

There are no strong associations between common functional genetic variants in drug metabolizing enzymes and dosing, safety, or efficacy of leading antipsychotics, strongly suggesting merely modest effects on the use of these medicines in most patients in typical clinical settings.

Single-dose pharmacokinetics and safety of ziprasidone in children and adolescents

OBJECTIVE

The purpose of this study was to provide single-dose pharmacokinetic, safety, and tolerability data for ziprasidone in youths with tic disorder, for comparison to adult studies to discern whether ziprasidone pediatric dosing could be modeled from adult data.

METHOD

A single-dose, open-label study of ziprasidone was conducted in youths (ages 7-16 years) with Tourette's disorder or chronic tic disorder. Dosing of ziprasidone oral suspension (40 mg/mL) was weight adjusted: >60 kg, 20 mg (group 1, n = 8); 31 to 60 kg, 10 mg (group 2, n = 8); and 16 to 30 kg, 5 mg (group 3, n = 8). Patients were assessed for serum ziprasidone concentration, safety, tolerability, and electrocardiogram pre- and postdose.

RESULTS

Twenty-four patients were evaluated for safety and tolerability, and 23 were evaluated for pharmacokinetics. Regression analysis of AUC(0-infinity) and Cmax values versus weight-normalized dose showed linear, dose-related changes in ziprasidone exposure. Ziprasidone was well tolerated with frequent, although transient, somnolence. No clinically significant change from baseline was observed in Bazett's or Fridericia's corrected QT(c) interval, and change in QT(c) interval was not related to serum ziprasidone concentration.

CONCLUSIONS

Oral ziprasidone exhibited linear pharmacokinetics and dose-related exposure in youths with Tourette's disorder or chronic tic disorder, which are comparable to adult data. A single dose of ziprasidone was well tolerated without clinically significant effects on electrocardiograms collected around the time of maximum serum concentration.

Drug-Metabolizing Ability of Molybdenum Hydroxylases

Molybdenum hydroxylases, which include aldehyde oxidase and xanthine oxidoreductase, are involved in the metabolism of some medicines in humans. They exhibit oxidase activity towards various heterocyclic compounds and aldehydes. The liver cytosol of various mammals also exhibits a significant reductase activity toward nitro, sulfoxide, N-oxide and other moieties, catalyzed by aldehyde oxidase. There is considerable variability of aldehyde oxidase activity in liver cytosol of mammals: humans show the highest activity, rats and mice show low activity, and dogs have no detectable activity. On the other hand, xanthine oxidoreductase activity is present widely among species. Interindividual variation of aldehyde oxidase activity is present in humans. Drug-drug interactions associated with aldehyde oxidase and xanthine oxidoreductase are of potential clinical significance. Drug metabolizing ability of molybdenum hydroxylases and the variation of the activity are described in this review.

From clinical research to clinical practice: a 4-year review of ziprasidone

Ziprasidone is a second-generation antipsychotic that received Food and Drug Administration approval in February 2001. It has a unique receptor profile that includes high-affinity antagonist activity at dopamine D2 receptors, inverse agonist activity at serotonin (5-HT)2A receptors, agonist activity at 5-HTlA receptors, and a relatively high affinity for the serotonin and norepinephrine transporters. The 5-HTIA affinity, together with the inhibitory effect on mono-amine reuptake, may underlie the hypothesized beneficial effects on comorbid affective and cognitive abnormalities in schizophrenia and schizoaffective disorder. The short-term efficacy of ziprasidone for core positive symptoms of schizophrenia appears to be comparable to other conventional and atypical antipsychotics. The short-term efficacy of ziprasidone in acute mania has been established based on two 3-week, double-blind, placebo-controlled trials.Open-label treatment for up to 52 weeks confirms the sustained efficacy and safety of ziprasidone in bipolar disorder. Maintenance studies in schizophrenia and schizoaffective disorder indicate that long-term ziprasidone therapy is effective in preventing relapse, while maintaining cognitive and psychosocial benefits. The safety database suggests that the overall cardiovascular and cerebrovascular risk associated with ziprasidone is lower than with other atypicals, with notably lower risk of drug-related increases in weight, glucose, or lipids. The data also suggest a modestly increased risk of QTc prolongation that is not dose related or linked to torsades de pointes. Switching to ziprasidone from other atypicals appears to improve both clinical symptoms and metabolic parameters, though more studies are needed to fully characterize these benefits. This monograph summarizes the efficacy, tolerability, and safety of oral ziprasidone in the treatment of schizophrenia, schizoaffective disorder, and bipolar mania.

An in vitro approach to detect metabolite toxicity due to CYP3A4-dependent bioactivation of xenobiotics

Many adverse drug reactions are caused by the cytochrome P450 (CYP) dependent activation of drugs into reactive metabolites. In order to reduce attrition due to metabolism-mediated toxicity and to improve safety of drug candidates, we developed two in vitro cell-based assays by combining an activating system (human CYP3A4) with target cells (HepG2 cells): in the first method we incubated microsomes containing cDNA-expressed CYP3A4 together with HepG2 cells; in the second approach HepG2 cells were transiently transfected with CYP3A4. In both assay systems, CYP3A4 catalyzed metabolism was found to be comparable to the high levels reported in hepatocytes. Both assay systems were used to study ten CYP3A4 substrates known for their potential to form metabolites that exhibit higher toxicity than the parent compounds. Several endpoints of toxicity were evaluated, and the measurement of MTT reduction and intracellular ATP levels were selected to assess cell viability. Results demonstrated that both assay systems are capable to metabolize the test compounds leading to increased toxicity, compared to their respective control systems. The co-incubation with the CYP3A4 inhibitor ketoconazole confirmed that the formation of reactive metabolites was CYP3A4 dependent. To further validate the functionality of the two assay systems, they were also used as a "detoxification system" using selected compounds that can be metabolized by CYP3A4 to metabolites less toxic than their parent compounds. These results show that both assay systems can be used to screen for metabolic activation, or de-activation, which may be useful as a rapid and relatively inexpensive in vitro assay for the prediction of CYP3A4 metabolism-mediated toxicity.