Comparative functional and structural analysis of Pseudomonas aeruginosa d-alanine-d-alanine ligase isoforms as prospective antibiotic targets

Pseudomonas aeruginosa is a major human pathogen in the healthcare setting. The emergence of multi-drug-resistant and extensive drug-resistant P. aeruginosa is of great concern, and clearly indicates that new alternatives to current first-line antibiotics are required in the future. Inhibition of d-alanine-d-alanine production presents as a promising avenue as it is a key component in the essential process of cell wall biosynthesis. In P. aeruginosa, d-alanine-d-alanine production is facilitated by two isoforms, d-alanine-d-alanine ligase A (PaDdlA) and d-alanine-d-alanine ligase B (PaDdlA), but neither enzyme has been individually characterised to date. Here, we present the functional and structural characterisation of PaDdlA and PaDdlB, and assess their potential as antibiotic targets. This was achieved using a combination of in vitro enzyme-activity assays and X-ray crystallography. The former revealed that both isoforms effectively catalyse d-alanine-d-alanine production with near identical efficiency, and that this is effectively disrupted by the model d-alanine-d-alanine ligase inhibitor, d-cycloserine. Next, each isoform was co-crystallised with ATP and either d-alanine-d-alanine or d-cycloserine, allowing direct comparison of the key structural features. Both isoforms possess the same structural architecture and share a high level of conservation within the active site. Although residues forming the d-alanine pocket are completely conserved, the ATP-binding pocket possesses several amino acid substitutions resulting in a differing chemical environment around the ATP adenine base. Together, these findings support that the discovery of dual PaDdlA/PaDdlB competitive inhibitors is a viable approach for developing new antibiotics against P. aeruginosa.

A Single-Run HPLC-MS Multiplex Assay for Therapeutic Drug Monitoring of Relevant First- and Second-Line Antibiotics in the Treatment of Drug-Resistant Tuberculosis

The treatment of drug-resistant Mycobacterium tuberculosis relies on complex antibiotic therapy. Inadequate antibiotic exposure can lead to treatment failure, acquired drug resistance, and an increased risk of adverse events. Therapeutic drug monitoring (TDM) can be used to optimize the antibiotic exposure. Therefore, we aimed to develop a single-run multiplex assay using high-performance liquid chromatography-mass spectrometry (HPLC-MS) for TDM of patients with multidrug-resistant, pre-extensively drug-resistant and extensively drug-resistant tuberculosis. A target profile for sufficient performance, based on the intended clinical application, was established and the assay was developed accordingly. Antibiotics were analyzed on a zwitterionic hydrophilic interaction liquid chromatography column and a triple quadrupole mass spectrometer using stable isotope-labeled internal standards. The assay was sufficiently sensitive to monitor drug concentrations over five half-lives for rifampicin, rifabutin, levofloxacin, moxifloxacin, bedaquiline, linezolid, clofazimine, terizidone/cycloserine, ethambutol, delamanid, pyrazinamide, meropenem, prothionamide, and para-amino salicylic acid (PAS). Accuracy and precision were sufficient to support clinical decision making (≤±15% in clinical samples and ±20-25% in spiked samples, with 80% of future measured concentrations predicted to fall within ±40% of nominal concentrations). The method was applied in the TDM of two patients with complex drug-resistant tuberculosis. All relevant antibiotics from their regimens could be quantified and high-dose therapy was initiated, followed by microbiological conversion. In conclusion, we developed a multiplex assay that enables TDM of the relevant first- and second-line anti-tuberculosis medicines in a single run and was able to show its applicability in TDM of two drug-resistant tuberculosis patients.

Population Pharmacokinetics and Dose Evaluation of Cycloserine among Patients with Multidrug-Resistant Tuberculosis under Standardized Treatment Regimens

Although cycloserine is a recommended drug for the treatment of multidrug-resistant tuberculosis (MDR-TB) according to World Health Organization (WHO), few studies have reported on pharmacokinetics (PK) and/or pharmacodynamics (PD) data of cycloserine in patients with standardized MDR-TB treatment. This study aimed to estimate the population PK parameters for cycloserine and to identify clinically relevant PK/PD thresholds, as well as to evaluate the current recommended dosage. Data from a large cohort with full PK curves was used to develop a population PK model. This model was used to estimate drug exposure in patients with MDR-TB from a multicentre prospective study in China. The classification and regression tree was used to identify the clinically relevant PK/PD thresholds. Probability of target attainment was analyzed to evaluate the currently recommended dosing strategy. Cycloserine was best described by a two-compartment disposition model. A percentage of time concentration above MICs (T>MIC) of 30% and a ratio of area under drug concentration-time curve (AUC0-24h) over MIC of 36 were the valid predictors for 6-month sputum culture conversion and final treatment outcome. Simulations showed that with WHO-recommended doses (500 mg and 750 mg for patients weighing <45 kg and ≥45 kg), the probability of target attainment exceeded 90% at MIC ≤16 mg/L in MGIT for both T>MIC of 30% and AUC0-24h/MIC of 36. New clinically relevant PK/PD thresholds for cycloserine were identified in patients with standardized MDR-TB treatment. WHO-recommended doses were considered adequate for the MGIT MIC distribution in our cohort of Chinese patients with MDR-TB.

Cycloserine-Induced Insomnia and Psychosis in Multidrug-Resistant Pulmonary Tuberculosis - A Case Report

Tuberculosis (TB) is a highly infectious disease due to Mycobacterium tuberculosis. The disease presents as drug-sensitive or drug-resistant TB (DR-TB). DR-TB could be of various types like isoniazid mono-resistant, multidrug-resistant tuberculosis (MDR-TB), MDR-rifampicin mono-resistant (MDR-RR), extensively drug-resistant TB (XDR-TB), or pre-extensively drug-resistant TB (pre-XDR-TB). Management of DR-TB is challenging mainly due to longer treatment duration, high pill burden, and adverse drug reactions (ADR) to the second-line anti-TB drugs. Some of these could be life-threatening and require immediate care. Herein, a case of ADR caused by cycloserine in a pulmonary MDR-TB case is presented. All the antitubercular drugs were put on hold, and the symptoms disappeared, only to reappear with the rechallenge of cycloserine. It is emphasized here that a high degree of suspicion with immediate management is imperative to avoid fatal outcomes.

High Incidence of Psychiatric Disorders Associated with Cycloserine Treatment of Multidrug-Resistant Tuberculosis Patients: A Cohort Study in Beijing, China

Objective

Cycloserine (CS) is a group B anti-tuberculosis (TB) drug endorsed by the World Health Organization (WHO) for the treatment of drug-resistant (DR)-TB. Despite CS widespread acceptance and known efficacy, the high potential of drug-associated psychiatric disorders is a major concern to multidrug-resistant (MDR)-TB patients. In this study, we investigated CS-associated psychiatric disorders in a cohort of MDR-TB patients in Beijing, China. Our aim was to determine psychiatric disorder prevalence rates and associated risk factors in this population.

Methods

This MDR-TB cohort study was conducted at Beijing Chest Hospital between February 2018 and February 2021. All patients received individualized treatment regimens that included CS at some point during the full treatment course. Patient psychological status was assessed using the Symptom Checklist (SCL-90) questionnaire during the post-treatment follow-up period.

Results

Two hundred and thirty-seven MDR-TB patients were included in the final analysis. Overall, psychiatric disorders were recorded in 22 (9.28%) of the 237 patients in our cohort, with severity grades of 1 or 2 observed for the majority (8.44%) of psychiatric adverse events. As compared to results obtained for control group patients who were ≥40 years of age, patients who were <40 years of age (77.3%, 17/22) were more likely to experience psychiatric disorders [adjusted odds ratio (aOR) = 3.060; 95% CI (1.060–8.828)]. Additionally, patients with body mass index (BMI)s of <18.5 kg/m² [aOR = 3.824; 95% CI (1.502–9.739)] had significantly higher odds of being afflicted with psychiatric disorders as compared with patients with BMIs that were ≥18.5 kg/m².

Conclusion

Our results demonstrated that approximately one-tenth of Chinese MDR-TB patients experienced psychiatric disorders during CS treatment, with the majority of adverse events of moderate severity. In addition, low BMI and age <40 years were identified as independent risk factors for psychiatric disorders in MDR-TB patients receiving CS therapy.

Bone Penetration of Cycloserine in Osteoarticular Tuberculosis Patients of China

The cycloserine concentrations in plasma and bone that were collected during operations on 28 osteoarticular tuberculosis (TB) patients treated daily with a 500-mg cycloserine-containing regimen were determined. The median concentrations in plasma and bone were 16.29 μg/mL (interquartile range [IQR], 6.47 μg/mL) and 24.33 μg/g (IQR, 14.68 μg/g), respectively. The median bone/plasma penetration ratio was 0.76 (range, 0.33 to 1.98). Cycloserine could effectively penetrate bone and acquire concentrations comparable to those in plasma, which favors its usage in osteoarticular TB treatment.

D-Cycloserine-Induced Seizure Activity in the Emergency Department: A Case Report

D-cycloserine (DCS) is an anti-tuberculosis medication that has been utilized for years for drug-resistant tuberculosis. DCS works via a centrally acting mechanism which can cause neurotoxic adverse effects which has limited its use. This centrally acting mechanism also allows for DCS to be utilized for various neuropsychiatric purposes. Our patient was on high-dose DCS for autism spectrum disorder and presented to the emergency department (ED) with a seizure. The seizure episode was managed with both anti-epileptics and pyridoxine. With increasing novel use of this older medication, it is imperative for ED clinicians to be aware of the different management strategies that may be required when a patient presents with a neurotoxic effect, specifically seizures, secondary to DCS.

Treatment Outcomes and Adverse Drug Effects of Ethambutol, Cycloserine, and Terizidone for the Treatment of Multidrug-Resistant Tuberculosis in South Africa

Treatment outcomes among multidrug-resistant tuberculosis (MDR-TB) patients receiving ethambutol, cycloserine, or terizidone as part of a standardized regimen were compared, determining occurrence of serious adverse drug events (SADEs). Newly diagnosed adult MDR-TB patients were enrolled between 2000 and 2004, receiving a standardized multidrug regimen for 18 to 24 months, including ethambutol, cycloserine, or terizidone. Cycloserine and terizidone were recorded individually. SADEs and factors associated with culture conversion and unfavorable treatment outcomes (default, death, treatment failure) were determined. Of 858 patients, 435 (51%) received ethambutol, 278 (32%) received cycloserine, and 145 (17%) received terizidone. Demographic and baseline clinical data were comparable. Successful treatment occurred in 56%, significantly more in patients receiving cycloserine (60%) and terizidone (62%) than in those receiving ethambutol (52% [P = 0.03]). Defaults rates were 30% in ethambutol patients versus 15% and 11% for cycloserine and terizidone patients, respectively. Terizidone was associated with fewer unfavorable outcomes (adjusted odds ratio [AOR], 0.4; P = 0.008; 95% confidence interval [CI], 0.2 to 0.8). Patients receiving cycloserine were more likely to achieve culture conversion than those receiving ethambutol or terizidone (AOR, 2.2; P = 0.02; 95% CI, 1.12 to 4.38). Failure to convert increased the odds of unfavorable outcomes (AOR, 23.7; P < 0.001; 95% CI, 13 to 44). SADEs were reported in two patients receiving ethambutol, seven patients receiving cycloserine, and three receiving terizidone (P = 0.05). Ethambutol was associated with high culture conversion and default rates. Cycloserine achieved higher culture conversion rates than terizidone. Fewer patients on terizidone experienced SADEs, with lower default rates. The differences that we observed between cycloserine and terizidone require further elucidation.

Population Pharmacokinetics of Cycloserine and Pharmacokinetic/Pharmacodynamic Target Attainment in Multidrug-Resistant Tuberculosis Patients Dosed with Terizidone

Cycloserine is a WHO group B drug for the treatment of multidrug-resistant tuberculosis (TB). Pharmacokinetic/pharmacodynamic data for cycloserine when dosed as terizidone are sparse. The aim of this analysis was to describe the population pharmacokinetics of cycloserine when administered as terizidone and predict the doses of terizidone attaining cycloserine exposures associated with efficacy. The plasma cycloserine level was measured 2 to 6 weeks after treatment initiation in patients hospitalized for second-line tuberculosis treatment. The pretreatment MICs of cycloserine were determined for the clinical isolates. We enrolled 132 participants with rifampicin-resistant TB; 79 were HIV positive. The median pretreatment MIC was 16 mg/liter. A one-compartment disposition model with two clearance pathways, nonrenal (0.35 liters/h) and renal (0.43 liters/h), described cycloserine pharmacokinetics well. Nonrenal clearance and the volume of distribution were allometrically scaled using fat-free mass. Smoking increased nonrenal clearance by 41%. Simulations showed that with daily doses of terizidone (750 mg and 1,000 mg for patients weighing ≤45 kg and >45 kg, respectively), the probability of maintaining the plasma cycloserine concentration above the MIC for more than 30% of the dosing interval (30% T>MIC) (which is associated with a 1.0-log10-CFU/ml kill in vitro) exceeded 90% at MIC values of ≤16 mg/liter, but the proportion of patients achieving 100% T>MIC (which is associated with the prevention of resistance) was more than 90% only at MICs of ≤8 mg/liter. Based on a target derived in vitro, the WHO-recommended doses of terizidone are effective for cycloserine MICs of ≤8 mg/liter, and higher doses are required to prevent the development of resistance.

Cycloserine enantiomers are reversible inhibitors of human alanine:glyoxylate aminotransferase: implications for Primary Hyperoxaluria type 1

Peroxisomal alanine:glyoxylate aminotransferase (AGT) is responsible for glyoxylate detoxification in human liver and utilizes pyridoxal 5'-phosphate (PLP) as coenzyme. The deficit of AGT leads to Primary Hyperoxaluria Type I (PH1), a rare disease characterized by calcium oxalate stones deposition in the urinary tract as a consequence of glyoxylate accumulation. Most missense mutations cause AGT misfolding, as in the case of the G41R, which induces aggregation and proteolytic degradation. We have investigated the interaction of wild-type AGT and the pathogenic G41R variant with d-cycloserine (DCS, commercialized as Seromycin), a natural product used as a second-line treatment of multidrug-resistant tuberculosis, and its synthetic enantiomer l-cycloserine (LCS). In contrast with evidences previously reported on other PLP-enzymes, both ligands are AGT reversible inhibitors showing inhibition constants in the micromolar range. While LCS undergoes half-transamination generating a ketimine intermediate and behaves as a classical competitive inhibitor, DCS displays a time-dependent binding mainly generating an oxime intermediate. Using a mammalian cellular model, we found that DCS, but not LCS, is able to promote the correct folding of the G41R variant, as revealed by its increased specific activity and expression as a soluble protein. This effect also translates into an increased glyoxylate detoxification ability of cells expressing the variant upon treatment with DCS. Overall, our findings establish that DCS could play a role as pharmacological chaperone, thus suggesting a new line of intervention against PH1 based on a drug repositioning approach. To a widest extent, this strategy could be applied to other disease-causing mutations leading to AGT misfolding.

Steady-state population pharmacokinetics of terizidone and its metabolite cycloserine in patients with drug-resistant tuberculosis

AIMS

Despite terizidone being part of the second-line recommended drugs for treatment of drug-resistant tuberculosis (DR-TB), information on its pharmacokinetics is scarce. The aim of this study was to describe the steady-state population pharmacokinetics (PPK) of terizidone and its primary metabolite cycloserine in patients with DR-TB and determine the effect of patient characteristics.

METHODS

This clinical study involved 39 adult DR-TB patients admitted to Brewelskloof Hospital in Cape Town, South Africa for intensive treatment phase. Blood samples were collected at predose and 0.5, 1, 2, 3, 3.5, 4, 8, 16 and 24 hours after drug administration. The estimation of PPK parameters was performed using nonlinear mixed-effects modelling software Monolix 2018R1. Free-fat mass was used to perform allometric scaling on disposition parameters.

RESULTS

A 1-compartment model best described the pharmacokinetics of terizidone and cycloserine. A modified transit compartment model described the absorption of terizidone. The parameters of terizidone model were mean transit time (1.7 h), absorption rate constant (2.97 h^-1 ), apparent volume of distribution (Vp/F: 13.4 L) and apparent total clearance (0.51 L h^-1 ). In the joint model, apparent fraction of terizidone converted to cycloserine was 0.29 while apparent clearance of terizidone via other routes and apparent cycloserine clearance was 0.1 L h^-1 and 2.94 L h^-1 , respectively. Serum albumin had significant effect on Vp/F.

CONCLUSIONS

The developed PPK model described well the concentration-time profile for terizidone and cycloserine in DR-TB patients. High albumin concentration was associated with low Vp/F.

Cycloserine Population Pharmacokinetics and Pharmacodynamics in Patients with Tuberculosis

Limited pharmacokinetic/pharmacodynamic (PK/PD) data exist on cycloserine in tuberculosis (TB) patients. We pooled several studies into a large PK data set to estimate the population PK parameters for cycloserine in TB patients.

Limited pharmacokinetic/pharmacodynamic (PK/PD) data exist on cycloserine in tuberculosis (TB) patients. We pooled several studies into a large PK data set to estimate the population PK parameters for cycloserine in TB patients. We also performed simulations to provide insight into optimizing the dosing of cycloserine. TB patients were included from Georgia, Bangladesh, and four U.S. sites. Monolix and mlxR package were used for population PK modeling and simulation. We used PK/PD targets for time above MIC of ≥30% and ≥64%, representing bactericidal activity and 80% of the maximum kill, to calculate the probability of target attainment (PTA). Optimal PK/PD breakpoints were defined as the highest MIC to achieve ≥90% of PTA. Data from 247 subjects, including 205 patients with drug-resistant TB, were included. The data were best described by a one-compartment model. In most cases, the PK/PD breakpoints for the simulated regimens were similar for both PK/PD targets. Higher PTA were achieved as the total daily dose was increased. The highest PK/PD breakpoint that resulted from the use of 250 mg dosages was 16 mg/liter. For MICs of >16 mg/liter, doses of at least 500 mg three times daily or 750 mg twice daily were needed. In conclusion, the current dosing for cycloserine, 250 to 500 mg once or twice daily, is not sufficient for MICs of >16mg/liter. Further studies are needed regarding the efficacy and tolerability of daily doses of >1,000 mg. Dividing the dose minimally affected the PK/PD breakpoints while optimizing exposure, which can potentially reduce adverse drug effects.

Efficacy and safety of cycloserine-containing regimens in the treatment of multidrug-resistant tuberculosis: a nationwide retrospective cohort study in China

Background

Our aim was to assess whether the use of cycloserine (CS) would bring additional benefit for multidrug-resistant tuberculosis (MDR-TB) patients, and to estimate the incidence and associated risk factors of adverse drug reactions (ADRs) from CS.

Patients and methods

In this study, we retrospectively reviewed the clinical outcomes and ADRs of MDR-TB patients treated with CS containing regimens between January 2012 and June 2015 in China.

Results

A total of 623 MDR-TB cases enrolled in this study received regimens containing CS. Of these cases, in 411 of the patients 374 (66.0%) were “cured” and 37 (5.9%) “complete treatment” by the end of the study. The elderly, patients with prolonged previous exposure to and history of anti-TB drugs, and pre-existing co-morbidity were more likely to be associated with adverse outcomes of MDR-TB patients (P<0.05). Hyperuricemia (22.8%, 142/623) was the most frequently observed ADR among these cases, while the most noted ADRs associated with the administration of CS was psychiatric symptoms, accounting for 4.3% (27/623) of study population. Nineteen (70.4%) out of 27 cases with psychiatric symptoms occurred before the 6-month timepoint, and were notably, the highest proportion of serious adverse, 29.6% (8/27) of which were noted after discontinuation of CS.

Conclusion

Our study demonstrates that a CS-containing regimen achieved a highly successful outcome in the treatment of MDR-TB and promising tolerance in Chinese population. The potential emergence of serious psychiatric symptoms highlights that patients need to be closely monitored for these conditions during treatment that includes CS.

Cycloserine for treatment of multidrug-resistant tuberculosis: a retrospective cohort study in China

PURPOSE

Cycloserine has been used in multidrug-resistant tuberculosis (MDR-TB) treatment since the 1950s. We evaluated the efficacy and safety of cycloserine and sought to clarify the role of cycloserine for treatment of simple MDR-TB, pre-extensively drug-resistant tuberculosis (pre-XDR-TB), and extensively drug-resistant tuberculosis (XDR-TB).

MATERIALS AND METHODS

A retrospective observational study was performed in Zhejiang Province, China. We enrolled 144 cycloserine-treated and 181 cycloserine-nontreated patients consecutively and determined the treatment outcome as the primary outcome. The proportion of patients with sputum culture conversion and the frequency of adverse drug reactions were also assessed.

RESULTS

One-hundred (69.4%) out of 144 patients in the cycloserine group successfully completed treatment. The HR of any unfavorable treatment outcome after the introduction of cycloserine was 0.58 (95% CI: 0.38-0.86, P=0.008). Subgroup analysis showed that cycloser-ine could benefit simple MDR-TB cases reducing the risk of unfavorable treatment outcomes (HR: 0.43, 95% CI: 0.24-0.76, P=0.004), but not pre-XDR-TB (HR: 0.65, 95% CI: 0.30-1.38, P=0.263) or XDR-TB (HR: 0.73, 95% CI: 0.22-2.37, P=0.589). The culture conversion rate at the intensive phase was similar whether cycloserine was administered or not (P=0.703). Of the 144 patients treated with cycloserine, a total of 16 (11.1%) patients experienced side effects attributed to cycloserine.

CONCLUSION

Cycloserine is an attractive agent for the treatment of MDR-TB, and its safety profile warrants its use in most MDR-TB cases. Cycloserine significantly improved the chance of a favorable outcome for patients with simple MDR-TB but not pre-XDR-TB and XDR-TB. Thus, more aggressive regimens might be required for pre-XDR-TB or XDR-TB patients.

Validation of Cycloserine Efficacy in Treatment of Multidrug-Resistant and Extensively Drug-Resistant Tuberculosis in Beijing, China

Cycloserine (Cs) is recommended by the World Health Organization as a second-line drug to treat multidrug-resistant tuberculosis (MDR-TB); however, its efficacy has never been sufficiently evaluated. To gain some insights into the value of cycloserine for MDR-TB treatment, in vitro bacteriostatic effect was determined and patient validations were performed prospectively. The in vitro activity of Cs against 104 wild-type Mycobacterium tuberculosis strains was determined, and serum Cs concentrations were measured for 73 MDR TB patients 2 h after administration. The treatment outcomes for 27 MDR-TB patients who had baseline isolates and were treated with Cs-containing regimens were followed up. The MICs for 90% of the recruited 104 wild-type strains were below 32 μg/ml. Eighteen out of 52 patients had peak serum concentrations (C_max) below 20 μg/ml at the dosage of 500 mg daily, while 13 out of 21 patients had peak serum concentrations higher than 35 μg/ml at the dosage of 750 mg daily. The percentage of favorable treatment outcomes among patients with a C_max/MIC ratio of ≥1 was statistically significantly higher than that among the group with a C_max/MIC ratio of <1 (P = 0.022). The epidemiological cutoff value for Cs susceptibility testing was 32 μg/ml. A high percentage of patients receiving the recommended dosage of 10 mg/kg for Cs administration could not acquire desirable blood concentrations; therefore, adjusting the dosage according to drug concentration monitoring is necessary. The C_max/MIC ratio might be a good indicator for predicting the treatment outcome for patients with MDR-TB or extensively drug-resistant TB (XDR-TB) who are being administered Cs-containing regimens.

Determination of cycloserine in microdialysis samples using liquid chromatography-tandem mass spectrometry with benzoyl chloride derivatization

A new method for the analysis of cycloserine (4-amino-3-isoxazolidinone, CYC) in rat microdialysis samples has been developed. This method consists of derivatizing the CYC with benzoyl chloride, which transforms primary amines into highly stable derivatives. An attractive feature of this method was that the derivatization reaction is straightforward and can be completed within 10 min. The formed derivative, in contrast to the non-derivatized analyte, exhibited increased chromatographic retention and decreased matrix effects resulting from the co-elution of other components using reversed-phase liquid chromatography and on-line switching. Detection on a quadrupole-linear ion trap mass spectrometer (AB3200 Q-Trap) was performed using electrospray tandem mass spectrometry in multiple reaction monitoring mode. Various derivatization parameters were optimized in order to improve chromatographic separation and minimize ion suppression. In particular, the benzoylation reaction was improved to enhance the reproducibility and sensitivity of the chromatographic method. The transition m/z 207.1 → 105.1 was acquired to monitor the CYC derivatization products. The method was fully validated for its sensitivity, selectivity, matrix effect and stability. A good linearity over the selected range (r > 0.99, range = 22-2200 mg/L), as well as accuracy and precision within ±7% of the target values, was obtained. The assay described herein was successfully applied to quantitatively measure CYC in the lung and blood of anesthetized rats.

Role of Alanine Racemase Mutations in Mycobacterium tuberculosis d-Cycloserine Resistance

A screening of more than 1,500 drug-resistant strains of Mycobacterium tuberculosis revealed evolutionary patterns characteristic of positive selection for three alanine racemase (Alr) mutations. We investigated these mutations using molecular modeling, in vitro MIC testing, as well as direct measurements of enzymatic activity, which demonstrated that these mutations likely confer resistance to d-cycloserine.

Cycloserine induced psychosis with hepatic dysfunction

With the increase in the cases of multidrug resistance tuberculosis, second line anti-tubercular drugs like the cycloserine are being prescribed frequently. Isoniazid and ethambutol are reported to cause psychosis like state; however, few reports of cycloserine induced psychosis are available. To the best of our knowledge, this is the first case of cycloserine induced psychosis with hepatic dysfunction.

Low Serum Concentrations of Moxifloxacin, Prothionamide, and Cycloserine on Sputum Conversion in Multi-Drug Resistant TB

PURPOSE

Low serum concentrations of drugs used to treat multi-drug resistant tuberculosis (MDR-TB) have occasionally been associated with treatment failure. We determined the frequencies of low serum concentrations of anti-MDR-TB drugs, and assessed the effects of these concentrations on 2-month sputum conversion.

MATERIALS AND METHODS

The serum levels of moxifloxacin (MF), prothionamide (PTH), and cycloserine (CS) were determined for 89 serum samples by high-pressure liquid chromatography-tandem mass spectrometry.

RESULTS

Low serum concentrations of MF, PTH, and CS below the minimal levels of the normal ranges were 83.3% (20/24), 59.2% (29/49), and 71.2% (47/66), respectively. There were no significant differences between the 2-month sputum conversion group (n=25) and the 2-month sputum non-conversion group (n=4) in median drug concentrations (μg/mL) of MF (1.46 vs. 1.60), PTH (0.91 vs. 0.70), and CS (14.90 vs. 14.90). However, a poor compliance rate was significantly greater in the 2-month sputum non-conversion group (75.0%, 3/4) than in the 2-month sputum conversion group (0%, 0/25) (p=0.001).

CONCLUSION

The frequency of low serum concentrations of anti-MDR-TB drugs was substantial and might not affect the 2-month sputum conversion rate. Larger prospective studies with timely sampling are needed to investigate the role of therapeutic drug monitoring in MDR-TB.

Tau-mediated NMDA receptor impairment underlies dysfunction of a selectively vulnerable network in a mouse model of frontotemporal dementia

Frontotemporal dementia (FTD) is a neurodegenerative behavioral disorder that selectively affects the salience network, including the ventral striatum and insula. Tau mutations cause FTD, but how mutant tau impairs the salience network is unknown. Here, we address this question using a mouse model expressing the entire human tau gene with an FTD-associated mutation (V337M). Mutant, but not wild-type, human tau transgenic mice had aging-dependent repetitive and disinhibited behaviors, with synaptic deficits selectively in the ventral striatum and insula. There, mutant tau depleted PSD-95, resulting in smaller postsynaptic densities and impaired synaptic localization of NMDA receptors (NMDARs). In the ventral striatum, decreased NMDAR-mediated transmission reduced striatal neuron firing. Pharmacologically enhancing NMDAR function with the NMDAR co-agonist cycloserine reversed electrophysiological and behavioral deficits. These results indicate that NMDAR hypofunction critically contributes to FTD-associated behavioral and electrophysiological alterations and that this process can be therapeutically targeted by a Food and Drug Administration-approved drug.

Role of the solvent on the stability of cycloserine under ESI-MS conditions

The effects of methanol (M) and acetonitrile (A) on the stability of cycloserine (1) have been studied. InfraRed Multiphoton PhotoDissociation (IRMPD) spectroscopy of the ionic species from electrospray ionization tandem mass spectrometry (ESI-MS) of 1/M and 1/A solutions points to extensive dimerization of 1 to cis-3,6-bis(aminooxymethyl)-2,5-piperidinedione (2), while the same process is not observed in the ESI-MS of 1/M solutions. 1D and 2D nuclear magnetic resonance experiments confirmed these findings by showing that partial dimerization of 1 actually takes place at room temperature in acetonitrile even before ESI-MS analysis. Comparison of nuclear magnetic resonance and IRMPD spectroscopic data from the same 1/A solution suggests that dimerization of cycloserine is enhanced in the ESI source.

Structural and biochemical analyses of alanine racemase from the multidrug-resistant Clostridium difficile strain 630

Clostridium difficile, a Gram-positive, spore-forming anaerobic bacterium, is the leading cause of infectious diarrhea among hospitalized patients. C. difficile is frequently associated with antibiotic treatment, and causes diseases ranging from antibiotic-associated diarrhea to life-threatening pseudomembranous colitis. The severity of C. difficile infections is exacerbated by the emergence of hypervirulent and multidrug-resistant strains, which are difficult to treat and are often associated with increased mortality rates. Alanine racemase (Alr) is a pyridoxal-5'-phosphate (PLP)-dependent enzyme that catalyzes the reversible racemization of L- and D-alanine. Since D-alanine is an essential component of the bacterial cell-wall peptidoglycan, and there are no known Alr homologs in humans, this enzyme is being tested as an antibiotic target. Cycloserine is an antibiotic that inhibits Alr. In this study, the catalytic properties and crystal structures of recombinant Alr from the virulent and multidrug-resistant C. difficile strain 630 are presented. Three crystal structures of C. difficile Alr (CdAlr), corresponding to the complex with PLP, the complex with cycloserine and a K271T mutant form of the enzyme with bound PLP, are presented. The structures are prototypical Alr homodimers with two active sites in which the cofactor PLP and cycloserine are localized. Kinetic analyses reveal that the K271T mutant CdAlr has the highest catalytic constants reported to date for any Alr. Additional studies are needed to identify the basis for the high catalytic activity. The structural and activity data presented are first steps towards using CdAlr for the development of structure-based therapeutics for C. difficile infections.

Resistance to antibiotics targeted to the bacterial cell wall

Peptidoglycan is the main component of the bacterial cell wall. It is a complex, three-dimensional mesh that surrounds the entire cell and is composed of strands of alternating glycan units crosslinked by short peptides. Its biosynthetic machinery has been, for the past five decades, a preferred target for the discovery of antibacterials. Synthesis of the peptidoglycan occurs sequentially within three cellular compartments (cytoplasm, membrane, and periplasm), and inhibitors of proteins that catalyze each stage have been identified, although not all are applicable for clinical use. A number of these antimicrobials, however, have been rendered inactive by resistance mechanisms. The employment of structural biology techniques has been instrumental in the understanding of such processes, as well as the development of strategies to overcome them. This review provides an overview of resistance mechanisms developed toward antibiotics that target bacterial cell wall precursors and its biosynthetic machinery. Strategies toward the development of novel inhibitors that could overcome resistance are also discussed.

Metabolomics Reveal d-Alanine:d-Alanine Ligase As the Target of d-Cycloserine in Mycobacterium tuberculosis

Stable isotope-mass spectrometry (MS)-based metabolomic profiling is a powerful technique for following changes in specific metabolite pool sizes and metabolic flux under various experimental conditions in a test organism or cell type. Here, we use a metabolomics approach to interrogate the mechanism of antibiotic action of d-cycloserine (DCS), a second line antibiotic used in the treatment of multidrug resistant Mycobacterium tuberculosis infections. We use doubly labeled 13C α-carbon-2H l-alanine to allow tracking of both alanine racemase and d-alanine:d-alanine ligase activity in M. tuberculosis challenged with DCS and reveal that d-alanine:d-alanine ligase is more strongly inhibited than alanine racemase at equivalent DCS concentrations. We also shed light on mechanisms surrounding d-Ala-mediated antagonism of DCS growth inhibition and provide evidence for a postantibiotic effect for this drug. Our results illustrate the potential of metabolomics in cellular drug-target engagement studies and consequently have broad implications in future drug development and target validation ventures.

Novel chemotherapeutic drugs in sphingolipid cancer research

Sphingolipid-metabolizing enzymes are becoming targets for chemotherapeutic development with an increasing interest in the recent years. In this chapter we introduce the sphingolipid family of lipids, and the role of individual species in cell homeostasis. We also discuss their roles in several rare diseases and overall, in cancer transformation. We follow the biosynthesis pathway of the sphingolipid tree, focusing on the enzymes in order to understand how using small molecule inhibitors makes it possible to modulate cancer progression. Finally, we describe the most used and historically significant inhibitors employed in cancer research, their relationships to sphingolipid metabolism, and some promising results found in this field.

D-cycloserine for Alzheimer's disease

BACKGROUND

Evidence supports a role for the NMDA receptors in learning and memory. These can be modulated by the antibiotic D-cycloserine in such a way that the effect of the excitatory transmitter substance glutamate is enhanced. A study on healthy subjects pretreated with scopolamine to mimic Alzheimer's disease showed a positive effect of D-cycloserine at low doses.

OBJECTIVES

To assess the efficacy and safety of D-cycloserine in patients with Alzheimer's disease.

SEARCH STRATEGY

The trials were identified from a search of the Specialized Register of the Cochrane Dementia and Cognitive Improvement Group on 14 June 2001 using the terms: cycloserine, D-cycloserine, Alzheimer*.

SELECTION CRITERIA

Randomized, double-blinded and unconfounded trials comparing D-cycloserine with a control treatment.

DATA COLLECTION AND ANALYSIS

Two larger and two smaller randomized controlled trials were identified. The clinical global impression scale was used in all studies and was a primary outcome measure.

MAIN RESULTS

It was not possible to extract the results from the first phases of the two crossover studies and therefore the meta-analyses are based on the two parallel group 6-month studies. There was no indication of a positive effect favouring D-cycloserine for the numbers showing improvement at 6 months as assessed by the Clinical Global Impression for any dose. The number of withdrawals for any reason before end of treatment at 6 months was significantly in favour of placebo (fewer withdrawals) compared with D-cycloserine for dose levels of 30 mg/day (OR 2.94, 95% CI 1.52, 5.70) and 100 mg/day (OR 3.23, 95% CI 1.67, 6.25). There was no significant difference between treatment, (2, 10, 30, 100, or 200 mg/day) and placebo for the number of withdrawals due to adverse events by six months.

REVIEWER'S CONCLUSIONS

The lack of a positive effect of D-cycloserine on cognitive outcomes in controlled clinical trials with statistical power high enough to detect a clinically meaningful effect means that D-cycloserine has no place in the treatment of patients with Alzheimer's disease.