Can dynamic elastic therapy be established as the standard protocol of closed reduction for moderately displaced extracapsular condylar fractures?

OBJECTIVE

This study was conducted with the aim to establish standard technique of closed reduction (CR) and compare functional outcomes in patients of moderately displaced unilateral extracapsular condylar fractures.

MATERIAL AND METHODS

This study is a retrospective randomized controlled trial, conducted at a tertiary care hospital setting from August, 2013 to November, 2018. Patients of unilateral extracapsular condylar fractures with ramus shortening < 7mm and deviation < 35° were divided in two groups by drawing lots and were treated by dynamic elastic therapy and maxillomandibular fixation (MMF). Mean and standard deviation were calculated for quantitative variables, and one way analysis of variance (ANOVA) and Pearson's Chi-square test were used to determine significance of outcomes between two modalities of CR. P value < 0.05 was taken as significant.

RESULTS

The numbers of patients treated by dynamic elastic therapy and MMF were 76 (38 in each group). Out of which 48 (63.15%) were male and 28 (36.84%) were female. The ratio of male to female was 1.7:1. The mean ± standard deviation (SD) of age was 32 ± 9.57 years. In patients treated by dynamic elastic therapy, the mean ± SD (at 6-month follow-up) of loss of ramus height (LRH), maximum incisal opening (MIO) and opening deviation were 4.6mm ± 1.08mm, 40.4mm ± 1.57mm and 1.1mm ± 0.87mm respectively. Whereas, LRH, MIO and opening deviation were 4.6mm ± 0.85mm, 40.4mm ± 2.37mm and 0.8mm ± 0.63mm respectively by MMF therapy. One-way ANOVA was statistically insignificant (P value > 0.05) for above mentioned outcomes. Pre-traumatic occlusion was achieved in 89.47% of patients by MMF and in 86.84% patients by dynamic elastic therapy. Pearson's Chi-square test was statistically insignificant (p value < 0.05) for occlusion.

CONCLUSION

Parallel results were obtained for both modalities; thus, the technique as dynamic elastic therapy, which promotes early mobilization and functional rehabilitation, can be favored as standard technique of closed reduction for moderately displaced extracapsular condylar fractures. This technique eases patients' stress associated with MMF and prevents ankylosis.

P–076 Probability of sperm retrieval in azoospermic patients and mRNA expression profile of JMJD1A, TNP2 and PRM2 : in a subset of karachi population

Study question

To access successfulness of sperm retrieval by evaluating the mRNA expression profile of JMJD1A, TNP1, TNP2, PRM1 and PRM2 in patients undergoing surgical sperm retrieval procedure.

Summary answer

Probability of sperm retrieval in azoospermia is decreased when mRNA expression profile of JMJD1A TNP2 and PRM2 in testicular tissue is decreased.

What is known already

Studies have been done on expression of JMJD1A in non-obstructive azoospermic patients in other part of the world with smaller sample size but this is the first study in Pakistan with larger number of patients. Study design, size, duration: Crossectional study, 100 azoospermic patients coming for purpose of sperm retrieval by TESE or micro-TESE in Australian Concept Infertility Medical Center, Karachi,from March, 2018 to December, 2019

Participants/materials, setting, methods

All recruited azoospermic patients were evaluated by history, physical examination, and hormonal assessment. RNA was extracted by pureLink RNA Micro kit and mRNA expression of the JMJD1A, TNP1, TNP2, PRM1 and PRM2 genes was determined using innu-SCRIPT One Step RT_qPCR SyGreen kit. For quantitative variables independent t test and for categorical variables chi-square/ Fisher Exact test was used. Unadjusted and adjusted prevalence ratio were reported by using cox regression algorithm. Main results and the role of chance: The patients were categorized into (i) Group-I: Patients with successful sperm retrieval n = 42, (ii) Group-II: Patients with unsuccessful sperm retrieval n = 58. The patients were categorized into (i) Group-I: Patients with successful sperm retrieval n = 42, (ii) Group-II: Patients with unsuccessful sperm retrieval n = 58. Azoospermic men in the successful sperm retrieval group had significantly decreased expression of JMJD1A (P &lt; 0.001), TNP2(P &lt; 0.001), and PRM2 (P 0.008). In addition to this regarding hormonal parameters: FSH (P 0.004), LH(P &lt; 0.001), TSH(P&lt;.011) were significantly different in azoospermic men with successful and unsuccessful sperm retrieval. In multivariate analysis, after adjusting for the other covariates, a significant association was found between JMJD1A, TNP2, PRM2 and successful sperm retrieval (p-value &lt;0.05).

Limitations, reasons for caution

It is unicentric and outcomes for fertilization were not assessed. Azoospermic patients from multi-centeres were difficult because of lack of facility of sperm retrieval procedures at these centers and it was difficult to follow the fertrilization outcome.

Wider implications of the findings: This will be useful for making the decision in azoospermic men to proceed for ICSI or not. In addition to this, the repetition of unnecessary surgical procedures can be avoided, as the azoospermic men often undergo number of rounds of ICSI, with the hope of becoming biological father.

Trial registration number

non-clinical trials

Workplace mistreatment and mental health in female surgeons in Pakistan

Background

Despite workplace mistreatment, which includes harassment, bullying and gender discrimination(GD)/bias, being serious problems for female surgeons, there are limited data from lower–middle-income countries like Pakistan. This study explored harassment and GD/bias experienced by female surgeons in Pakistan, and the effects of these experiences on mental health and well-being.

Methods

A nationwide survey was conducted between July and September 2019 in collaboration with the Association of Women Surgeons of Pakistan, an organization consisting of female surgeons and trainees in Pakistan. An anonymous online survey was emailed directly, disseminated via social media platforms (such as Facebook, Twitter and Instagram), and sent to surgical programmes in Pakistan.

Results

A total of 146 women surgeons responded to the survey; 67.1 per cent were trainees and the rest attending surgeons. Overall, 57.5 per cent of surgeons reported experiencing harassment, most common being verbal (64.0 per cent) and mental (45.9 per cent), but this mostly went unreported (91.5 per cent). On multivariable analysis adjusted for age and specialty, workplace harassment (odds ratio 2.02 (95 per cent c.i. 1.09 to 4.45)) and bullying (odds ratio 5.14 (95 per cent c.i. 2.00–13.17)) were significantly associated with severe self-perceived burnout, while having a support system was protective against feelings of depression (odds ratio 0.35 (95 per cent c.i. 0.16 to 0.74)). The overwhelming majority (91.3 per cent) believed that more institutional support groups were needed to help surgeons with stress reduction (78.8 per cent), receiving mentorship (74.7 per cent) and work–life balance (67.8 per cent).

Conclusion

Workplace mistreatment, in particular harassment and bullying, has a damaging impact on the mental well-being of female surgeons, particularly trainees. The absence of support groups in Pakistan should be urgently addressed so that surgeons, especially trainees, may cope better with potentially harmful workplace stressors.

Lymph node ratio as a prognostic marker of oral tongue squamous cell carcinoma: a cohort study

INTRODUCTION

Lymph node metastasis is a poor prognostic indicator and is well established in tongue squamous cell carcinoma. Based on the current staging system, accurate risk stratification is difficult. There is thus a need to evaluate an alternate method for predicting recurrence and survival. The objective of the study was to evaluate lymph node ratio as a prognostic marker as compared with N-staging for tongue squamous cell carcinoma.

MATERIALS AND METHODS

We conducted a retrospective cohort study with 56 patients with a lymph node ratio greater than 0.012 (exposed) and 74 patients with a lymph node ratio less than 0.012 (unexposed). Overall five-year survival and disease-free survival were assessed. The Cox proportional hazard model was used to analyse lymph node ratio as a predictor of outcome, together with other covariates.

RESULTS

A total of 130 patients were included in the study. Patients with lymph node ratio greater than 0.012 had a poor overall five-year (mean survival time 52.1 months vs 38.1 months) and disease-free survival (mean survival time 53.6 months vs 39.2 months). The hazard of death among patients with a lymph node ratio greater than 0.012 was 3.24 times higher than the hazard of death among patients with a lymph node ratio less than 0.012 (95% confidence interval 1.82-5.77).

DISCUSSION

Lymph node ratio is a superior prognostic marker compared with the currently used American Joint Committee on Cancer N-staging. Our findings also suggest that the margin status (involved) of the primary tumour resection adversely affects prognosis.

Production of a periplasmic trehalase in Gluconobacter oxydans and growth on trehalose

Gluconobacter strains are specialized in the incomplete oxidation of monosaccharides. In contrast, growth and product formation from disaccharides is either very low or impossible. A pathway that allows growth on trehalose was rationally designed to broaden the substrate range of Gluconobacter oxydans. Expression vectors containing different signal sequences and the gene encoding alkaline phosphatase, phoA, from Escherichia coli were constructed. The signal peptide that exhibited the strongest periplasmic PhoA activity was used to generate a G. oxydans strain able to utilize the model disaccharide trehalose as a carbon and energy source by expressing the periplasmic trehalase TreA from E. coli. The strain had a doubling time of 3.7h and reached a final optical density of 1.7 when trehalose was used as a growth substrate. In comparison, the wild-type harboring the empty vector and the strain expressing treA without a signal sequence grew slowly to a final OD of only 0.15. The trehalose concentration in treA expressing cultures decreased continuously during the exponential growth phase indicating that the substrate was hydrolyzed to glucose by TreA. In contrast to the wild-type growing on glucose, the treA expression strain mainly formed acetate and 5-ketogluconate as end products rather than gluconate.

Potential of chitosan-loaded nanoemulsions to control different Colletotrichum spp. and maintain quality of tropical fruits during cold storage

AIMS

To investigate the antifungal activity of conventional chitosan and chitosan-loaded nanoemulsions against anthracnose caused by Colletotrichum spp. isolated from different tropical fruits.

METHODS AND RESULTS

In vitro results illustrated that conventional chitosan onwards 1·5% concentration inhibited radial mycelial growth, conidial germination, sporulation and dry weight of mycelia for Colletotrichum musae (Berk. & Curt) Arx. isolated from banana, Colletotrichum gloeosporioides (Penz.) Penz and Sacc. isolated from papaya and dragon fruits. For further investigations, chitosan-loaded nanoemulsions were prepared, and chitosan at 2·0% concentration with 200 nm droplet size gave the best results in terms of all the in vitro parameters tested for C. musae and at the same concentration with 600 nm droplet size for both the isolates of C. gloeosporioides. However, the results obtained at 2·0% chitosan concentration with different droplet sizes were nonsignificantly different with 1·0 and 1·5% concentrations. Therefore, for in vivo studies, only 1·0% chitosan with different droplet sizes was used. In terms of fungicidal effects and maintaining postharvest quality of banana, papaya and dragon fruits, chitosan at 1·0% concentration with a droplet size of 200 nm in banana and 600 nm in papaya and dragon fruits showed the best results in delaying the onset of anthracnose and maintaining quality of all the fruits for up to 28 days of cold storage.

CONCLUSION

Chitosan used in a conventional form showed good results but not as effective as in the form of nanoemulsions.

SIGNIFICANCE AND IMPACT OF THE STUDY

The results of this study suggest that instead of applying chitosan in a conventional form, chitosan in the form of nanoemulsions could be more effective as a biofungicide for controlling anthracnose of fresh fruits. Moreover, it could be cost-effective as the amount of chemical used is reduced when applied in the form of nanoemulsions.

Predicting drug-induced agranulocytosis: characterizing neutrophil-generated metabolites of a model compound, DMP 406, and assessing the relevance of an in vitro apoptosis assay for identifying drugs that may cause agranulocytosis

DMP 406 is a clozapine analogue developed by Dupont-Pharma for the treatment of schizophrenia. Unfortunately it caused agranulocytosis in dogs during preclinical studies. Clozapine also causes agranulocytosis and this is believed to be due to a reactive nitrenium ion metabolite produced by neutrophils. We studied the oxidation of DMP 406 by activated neutrophils and found that the major reactive species that is produced is not a nitrenium ion but rather an imine. This metabolite is similar to the reactive metabolite that has been proposed to be responsible for mianserin-induced agranulocytosis. Therefore we also studied the oxidation of mianserin by activated neutrophils and found that, although the major species is an iminium ion, it also bears a lactam moiety in the piperazine ring resulting from further oxidation. We usually find that HOCl is a good model system for the production of reactive metabolites of drugs that are formed by activated neutrophils, but in the case of both DMP 406 and mianserin, the products produced were significantly different than those formed by activated neutrophils. In contrast, the combination of horseradish peroxidase and hydrogen peroxide (HRP/H(2)O(2)) formed a very similar pattern of products, and this system was used to produce sufficient quantities of metabolites to allow for identification. The reactive metabolites of both DMP 406 and mianserin reacted with a range of nucleophiles, but in many cases the reaction was reversible. The best nucleophile for trapping these reactive metabolites was cyanide. It has been demonstrated that the products of clozapine oxidation by HRP/H(2)O(2), presumably the nitrenium ion, induced apoptosis in neutrophils at therapeutic concentrations of clozapine. It has been suggested that this process is involved in the mechanism of clozapine-induced agranulocytosis. We tested DMP 406 and mianserin in this system to see if the ability of a reactive metabolite of a drug to cause apoptosis could predict the ability of that drug to cause agranulocytosis. We used clozapine as a positive control and we also tested olanzapine, a drug that forms a reactive metabolite similar to that of clozapine but is given at a lower dose and does not cause agranulocytosis. We found that DMP 406 did not increase apoptosis at concentrations below 50 microM, and although mianserin did increase apoptosis at 10 microM this is above the therapeutic concentration. Olanzapine caused an increase in apoptosis at the same concentration as clozapine (1 microM), but because its therapeutic concentration is lower, this concentration was above the pharmacological range. There was no increase in apoptosis with any drug in the absence of HRP/H(2)O(2). These results indicate that this assay is unable to reliably predict the ability of different types of drugs to cause agranulocytosis. This is not a surprising result given that different drugs may induce agranulocytosis by different mechanisms.

Bioactivation and covalent binding of hydroxyfluperlapine in human neutrophils: implications for fluperlapine-induced agranulocytosis

The use of fluperlapine and the structurally related clozapine has been associated with the induction of agranulocytosis in humans. Unlike clozapine, fluperlapine is relatively resistant to chemical and biochemical oxidations. In this study we demonstrated that 7-hydroxyfluperlapine, the major metabolite of fluperlapine in humans, is oxidized to a reactive intermediate by HOCl and by myeloperoxidase in the presence of H(2)O(2) and Cl(-). This reactive intermediate was identified as an iminoquinone species with a M + 1 ion at m/z 324 by mass spectrometry. The iminoquinone intermediate was trapped by N-acetyl-L-cysteine (NAC) as well as GSH. NMR spectra of the NAC adducts indicated that the NAC was bound to the 6 and 9 positions of the aromatic ring. This is the same orientation as the binding of nucleophiles to the reactive metabolite of clozapine. We were able to use an antibody against clozapine to demonstrate that 7-hydroxyfluperlapine, but not fluperlapine itself, covalently modifies human myeloperoxidase. Furthermore, we demonstrated that 7-hydroxyfluperlapine is metabolized by activated neutrophils to a reactive intermediate that covalently binds to neutrophils. In the presence of NAC or GSH, such covalent binding was inhibited and the NAC or GSH adducts were formed. Thus, the reactivity and even the orientation of the binding of the reactive metabolite of 7-hydroxyfluperlapine is very similar to that of clozapine. These results provide a mechanism for the formation of a reactive metabolite of fluperlapine similar to clozapine that may explain its ability to induce agranulocytosis.

Hypochlorous acid, a major oxidant produced by activated neutrophils, has low effect on two pyridobenzazepine derivatives, JL 3 and JL 13

JL 13 (5-(4-methylpiperazin-1-yl)-8-chloro-pyrido[2,3-b]- [1,5]benzoxazepine fumarate) and JL 3 (10-(4-methylpiperazin-1- yl)pyrido[4,3-b][1,4]benzothiazepine), two pyridobenzazepine derivatives structurally related to clozapine, were selected for further development. Due to their structural similarity to clozapine, they are haunted by the spectre of clozapine-induced agranulocytosis. In a previous study, JL 13 was shown to be less sensitive to oxidation than clozapine. In the present paper, using an in vitro procedure, we report the effect of hypochlorous acid (HOCl), a major in vivo oxidant, on both drugs. It appears that the oxidations of JL 3 and JL 13, unlike clozapine, are very slow and little secondary product is formed. Moreover, in contrast to clozapine, the products that were formed are not reactive and thus do not react with glutathione or N-acetylcysteine. Thus, if, as postulated for clozapine, drug-induced agranulocytosis is due to a reactive metabolite formed by neutrophils or their precursors, JL 3 and JL 13 would not be expected to cause the same adverse reaction.

Metabolism of trimethoprim to a reactive iminoquinone methide by activated human neutrophils and hepatic microsomes

The antibacterial agent, trimethoprim, is normally used synergistically with sulfonamides. Its use is associated with idiosyncratic reactions including liver toxicity and agranulocytosis. In this study, we demonstrated that trimethoprim was oxidized by activated human neutrophils, as well as a combination of myeloperoxidase/hydrogen peroxide/chloride or hypochlorous acid, to a reactive pyrimidine iminoquinone methide intermediate with a protonated molecular ion of m/z 289 as detected by mass spectrometry. In the presence of N-acetyl-L-cysteine (NAC), the pyrimidine iminoquinone methide could be trapped as three NAC adducts. The three NAC adducts were separable on HPLC, but showed the same protonated molecular ion of m/z 452. The proton NMR spectrum of the major adduct showed that the NAC group was at the 6 position of the pyrimidine ring. The mass spectra of the two minor NAC adducts indicated that they were the two diastereomers in which NAC was attached to the exo-cyclic prechiral carbon of the pyrimidine iminoquinone methide. Incubation of trimethoprim with isolated hepatic microsomes, both human and rat, in presence of NAC gave the same set of trimethoprim-NAC adducts. We propose that the formation of this pyrimidine iminoquinone methide by both hepatic microsomes and neutrophils may be responsible for trimethoprim-induced idiosyncratic hepatotoxicity and agranulocytosis.

A comparison of the covalent binding of clozapine and olanzapine to human neutrophils in vitro and in vivo

Covalent binding of a reactive metabolite of clozapine to neutrophils or their precursors is thought to play a role in the development of clozapine-induced agranulocytosis. Immunoblotting studies with an anti-clozapine antiserum detected covalent binding of clozapine to human neutrophils in vitro when HOCl was used to generate clozapine reactive metabolite (major clozapine adducts of 31, 49, 58, 78, 86, 126, 160, and 204 kDa). In addition, incubating neutrophils with clozapine and H2O2 (major clozapine adducts of 49 and 58 kDa) or clozapine, H2O2, and human myeloperoxidase (major clozapine adducts of 31, 49, 58, and 126 kDa) also resulted in covalent binding of clozapine to the neutrophils. The covalent binding of clozapine to neutrophils was inhibited by extracellular glutathione when HOCl, but not H2O2 was used to generate reactive metabolite. We found that the antiserum against clozapine also recognized olanzapine, an antipsychotic drug that forms a similar reactive metabolite to clozapine but has not been associated with induction of agranulocytosis. Repeating the in vitro experiments with olanzapine revealed that the major olanzapine-modified polypeptides had molecular masses of 96, 130-170, and 218 kDa. Only relatively low levels of 31, 49, and 58 kDa adducts were observed. Clozapine-modified polypeptides also were detected in neutrophils from patients being treated with clozapine. A major 58-kDa clozapine-modified polypeptide was detected in all patients tested. In contrast, no drug-modified polypeptides were detected in neutrophils from patients taking olanzapine. The differences in covalent binding exhibited by the two compounds and, in particular, the lack of olanzapine binding to human neutrophils in vivo may help to explain the difference in toxicity of these two drugs.

A comparison of the oxidation of clozapine and olanzapine to reactive metabolites and the toxicity of these metabolites to human leukocytes

Olanzapine was shown to be oxidized to a reactive intermediate by HOCl, which is the major oxidant produced by activated neutrophils. A mass spectrum obtained using a flow system in which the reactants were fed into a mixing chamber and the products flowed directly into a mass spectrometer revealed a reactive intermediate at m/z 311. This is 2 mass units less than the protonated molecular ion of parent olanzapine and suggests that the reactive intermediate is a nitrenium ion. The reactive intermediate could be trapped with glutathione or N-acetylcysteine to produce two conjugates. These data are analogous to results we reported previously with the structurally related atypical antipsychotic agent clozapine. However, the clozapine and olanzapine reactive metabolites showed differences in their ability to cause toxicity to human neutrophils. Toxicity to neutrophils was observed only at high concentrations of clozapine (>50 microM) when HOCl was used to generate reactive metabolite. In contrast, concentration-dependent toxicity (p < 0.05) was observed when neutrophils were incubated with clozapine (0-20 microM) and H2O2 to generate clozapine reactive metabolite. No toxicity was observed with clozapine alone (at concentrations of > 50 microM). Similar results were observed in monocytes and HL-60 cells. Olanzapine reactive metabolite only seemed to cause slight toxicity at the highest concentrations tested (20 microM), even when the reactive metabolite was generated using H2O2. Neutrophils from two patients with a history of clozapine-induced agranulocytosis seemed to be more sensitive to the toxic effects of the clozapine reactive metabolite; however, the numbers are too small to draw any definite conclusions.

Structural features associated with reactive metabolite formation in clozapine analogues

Clozapine is associated with a high incidence of agranulocytosis. We had previously found that it is oxidized by granulocytes, or simply HOCl, to a reactive metabolite that irreversibly binds to the cells, and we proposed that this reactive metabolite is responsible for clozapine-induced agranulocytosis. The reactive metabolite appeared to be a nitrenium ion formed by chlorination of the nitrogen bridge between the two aromatic rings. If this is correct, analogs that contain this structural feature should also be oxidized to a reactive intermediate while those not possessing this feature would, at least, not form the same type of reactive intermediate and, therefore, may not induce agranulocytosis. We tested the first part of this hypothesis with three clozapine analogs that do contain a nitrogen bridge and three that do not. Consistent with the hypothesis, the three analogs that do contain the nitrogen bridge formed reactive intermediates that could be trapped with glutathione when oxidized by HOCl, myeloperoxidase or activated neutrophils. In contrast, we found no evidence of a reactive intermediate on oxidation of analogs that contained an oxygen or sulfur bridge rather than a nitrogen bridge. If such reactive metabolites are responsible for drug-induced agranulocytosis, it should be possible to use such a simple screening method to test drugs at an early stage in their development for the potential to induce agranulocytosis.

Oxidation of diclofenac to reactive intermediates by neutrophils, myeloperoxidase, and hypochlorous acid

Diclofenac is associated with a low, but significant, incidence of hepatotoxicity and bone marrow toxicity. It has been suggested that this could be due to a reactive acyl glucuronide. An alternative hypothesis is that an oxidative reactive metabolite could be responsible for such reactions and such metabolites formed by the enzymes present in neutrophils could be responsible for bone marrow toxicity. Others had reported the formation of 2,2'-dihydroxyazobenzene during the oxidation of diclofenac by myeloperoxidase/hydrogen peroxide. In contrast, in similar experiments we did not find evidence for the formation of 2,2'-dihydroxyazobenzene, but we did find several products, including a reactive iminoquinone. The same iminoquinone was formed by the oxidation of 5-hydroxydiclofenac. This iminoquinone was also formed by oxidation of diclofenac by HOCl or by activated neutrophils. It reacted with glutathione to form a conjugate. 5-Hydroxydiclofenac is also a major hepatic metabolite of diclofenac, and we found that rat hepatic microsomes oxidized 5-hydroxydiclofenac to the iminoquinone which was trapped with glutathione. This reactive metabolite represents another possible cause of the idiosyncratic reactions associated with the use of diclofenac.

In vitro formation, disposition and toxicity of N-acetoxy-sulfamethoxazole, a potential mediator of sulfamethoxazole toxicity

Variation in the formation and disposition of the hydroxylamine of (SMX-HA) is thought to play an important role in the pathogenesis of sulfamethoxazole (SMX)-induced idiosyncratic adverse drug reactions. We hypothesized that, in analogy to carcinogenic arylamines, SMX-HA might be further converted to an electrophilic N-acetoxy metabolite which could play a role in mediating SMX toxicity. Accordingly, we chemically synthesized N-acetoxy-SMX, and examined the characteristics of its formation, metabolism, cytotoxicity and mutagenicity in human and bacterial test systems. The human arylamine N-acetyl-transferases, (NAT)1 and NAT2, were capable of converting SMX-HA to N-acetoxy-SMX. NAT1 and NAT2 possessed similar affinities for SMX-HA (apparent Km values of 650 and 520 microM, respectively), but the apparent maximal velocity of the NAT1-mediated acetylation was higher than that of NAT2. (1332 vs. 37 nmol/min/U of immunoreactive NAT protein). Human peripheral blood mononuclear cells 12,000 x g supernatant fractions converted N-acetoxy-SMX mainly back to SMX-HA, and also to a lesser extent to SMX, at clinically relevant concentrations. Similar pathways were observed in human hepatic cytosolic fractions. In a cytotoxicity assay, N-acetoxy-SMX was significantly more toxic to human peripheral blood mononuclear cells than SMX-HA (16.6 vs. 11.5% dead cells at a concentration of 300 microM). N-acetoxy-SMX was weakly mutagenic to the Salmonella typhimurium TA100 strain in the Ames test. These data suggest that the N-acetoxy metabolites of sulfonamides could potentially play a role in mediating sulfonamide idiosyncratic adverse drug reactions.

Metabolism of vesnarinone by activated neutrophils: implications for vesnarinone-induced agranulocytosis

Vesnarinone is an important new drug that significantly decreases mortality rates in severe congestive heart failure; however, its use is associated with a relatively high incidence (approximately 1%) of agranulocytosis. The authors studied its metabolism by activated neutrophils, the target for this toxicity, and evidence pointed to a pathway that involved a reactive iminium ion. Hydrolysis of the iminium ion led to a reactive quinone imine. The same pathway was observed with a combination of myeloperoxidase/hydrogen peroxide/chloride, the major oxidizing system of neutrophils, or hypochlorous acid, which is generated by this system. Activation of the neutrophils could be achieved by phorbol ester or by influenza vaccine and there is evidence to suggest that the administration of influenza vaccine during vesnarinone therapy may increase the risk of agranulocytosis. Incubation of radiolabeled vesnarinone with activated neutrophils led to covalent binding of almost 5% of the drug to the cells. Both the iminium ion and quinone imine generated by hypochlorous acid could be trapped with glutathione. It was proposed that these reactive metabolites, generated by neutrophils or neutrophil precursors in the bone marrow, may be responsible for the vesnarinone-induced agranulocytosis. Factors such as infection or vaccination that activate neutrophils may increase the risk of agranulocytosis.

N-chlorination of sulfamethoxazole and dapsone by the myeloperoxidase system

It is known that activation of neutrophils or monocytes leads to the formation of hydrogen peroxide and the release of myeloperoxidase (MPO). We found that sulfamethoxazole was chlorinated by the combination of MPO, hydrogen peroxide, and chloride. The product, N-chlorosulfamethoxazole, is reasonably stable but reacts rapidly with a variety of compounds. The same product was formed by the reaction between sulfamethoxazole and hypochlorous acid, and dapsone was also N-chlorinated by the MPO system or hypochlorous acid. Although N-chlorination was not observed when sulfamethoxazole or dapsone was incubated with activated neutrophils, this is presumably because the chloramine products react rapidly with the cells. When radiolabeled sulfamethoxazole was incubated with activated neutrophils, covalent binding was observed. When radiolabeled sulfamethoxazole was incubated with MPO and hydrogen peroxide in the presence of albumin, covalent binding to the albumin occurred. Although binding to albumin occurred in the absence of chloride, it was increased by the presence of chloride. This suggests that N-chlorosulfamethoxazole may be one of several reactive metabolites of sulfamethoxazole that covalently bind to neutrophils. We suspect that covalent binding of arylamine drugs, such as sulfamethoxazole, to activated leukocytes is responsible for some of the adverse reactions associated with these drugs, especially adverse reactions that involve leukocytes such as agranulocytosis or drug-induced lupus.

N-Chlorination and oxidation of procainamide by myeloperoxidase: toxicological implications

In previous studies we had shown that procainamide is metabolized to reactive metabolites by activated leukocytes, and evidence pointed to involvement of myeloperoxidase (MPO). In this study we examine the metabolism of procainamide by MPO/H2O2, in the presence and absence of chloride ion. In the absence of chloride ion, the metabolism was very similar to that seen with activated leukocytes. The major metabolite was formed by oxidation of the arylamine group to a hydroxylamine. In the presence of chloride ion, a much greater degree of metabolism occurred, and the major product (40% of the starting procainamide) was a reactive species that could not be isolated. This metabolite spontaneously rearranged to 3-chloroprocainamide, and from its mass spectrum and chemical reactions, we deduce its structure to be N-chloroprocainamide. The N-chloroprocainamide metabolite reacted very rapidly with reducing agents, such as ascorbate, and also reacted with protein such as albumin, the major product in both cases being procainamide. This metabolite also chlorinated phenylbutazone. When radiolabeled procainamide was oxidized by MPO/H2O2 in the presence of albumin, covalent binding of the radiolabel to albumin occurred, and binding was greater under conditions in which N-chloroprocainamide was formed. It is probable that the failure to observe N-chloroprocainamide, when procainamide is oxidized by activated leukocytes, is due to its rapid reaction with the cells. We propose that modification of neutrophils (or neutrophil precursors in the bone marrow) by these reactive metabolites is responsible for procainamide-induced agranulocytosis. In a similar manner, procainamide-induced lupus could be due to modification of monocytes by monocyte-generated reactive metabolites.

N-chlorination of phenytoin by myeloperoxidase to a reactive metabolite

Several types of phenytoin toxicity appear to involve leukocytes. We had previously demonstrated that other drugs were metabolized to reactive metabolites by activated neutrophils and monocytes or the combination of myeloperoxidase (MPO) and hydrogen peroxide. In this study we found that phenytoin was chlorinated by MPO/H2O2/Cl- to N,N'-dichlorophenytoin which is chemically reactive. Failure to demonstrate that activated neutrophils also formed N,N'-dichlorophenytoin appeared to be due to the rapid reaction of N,N'-dichlorophenytoin with neutrophils. We were able to demonstrate that phenytoin covalently bound to albumin in the presence of MPO/H2O2/Cl- and to neutrophils, but only if the cells were activated. Such activation leads to the release of MPO and the generation of H2O2. We, therefore, speculate that the toxicity of phenytoin may be due to the formation of N,N'-dichlorophenytoin by activated neutrophils or monocytes.

Metabolism of dapsone to a hydroxylamine by human neutrophils and mononuclear cells

Dapsone is an effective anti-inflammatory agent in conditions in which inflammation is mediated by neutrophils. Dapsone also has been associated with agranulocytosis. We found that neutrophils, which had been activated by a phorbol ester or opsonized zymosan, oxidized dapsone to its nitroderivative. It appears as if this is due to oxidation of dapsone by myeloperoxidase to the hydroxylamine, followed by nonenzymatic oxidation of the hydroxylamine to the nitroderivative. The hydroxylamine can be isolated if ascorbic acid is added to the incubations. Monocytes also contain myeloperoxidase and activated mononuclear leukocytes also metabolize dapsone to the hydroxylamine. Dapsone also causes a mononucleosis-like syndrome. The reactive hydroxylamine could be responsible for both the pharmacologic and toxic properties of dapsone.

Metabolism of procainamide to a hydroxylamine by human neutrophils and mononuclear leukocytes

The chronic use of procainamide is associated with a high incidence of drug-induced lupus and also agranulocytosis. We have previously demonstrated that procainamide is metabolized in the liver to reactive hydroxylamine (PAHA) and nitroso (nitroso-PA) metabolites which covalently bind to protein and are toxic to lymphocytes. We proposed that these metabolites were responsible for the toxicities of procainamide. However, PAHA and nitroso-PA do not appear to escape the liver in significant concentrations. In this paper we describe the metabolism of procainamide to a reactive hydroxylamine by neutrophils and mononuclear leukocytes. Such metabolism only occurs if the cells have been stimulated to have a respiratory burst. These observations have obvious possible implications for the mechanism of procainamide-induced agranulocytosis (formation of a reactive metabolite by neutrophils) and procainamide-induced lupus (formation of a reactive metabolite by monocytes). The metabolism of drugs to reactive metabolites by monocytes may be a general mechanism for hypersensitivity reactions because monocytes play a key role in the processing of antigen and stimulation of antibody synthesis.

Reconstruction of peptidyltransferase activity on 50S and 70S ribosomal particles by peptide fragments of protein L16

Ribosomal protein L16 was digested with Staphylococcus aureus protease V8 and the resulting peptides were separated by reversed-phase high-performance liquid chromatography. One of the fragments, identified by sequence analysis as the N-terminal peptide of L16, was shown to exhibit partial peptide-bond-formation and transesterification activities of peptidyltransferase upon reconstitution with L16-depleted 50S core particles. However, several proteins enhanced these activities. L15 increased both reactions when added to the reconstitution mixture, suggesting a limited capacity of the L16 peptide to incorporate into 50S core particles. In contrast, the interaction of L11 with the N-terminal peptide stimulated the transesterification reaction but not the peptide-bond-forming activity of ribosomes, indicating a different topological domain for these reactions. Also, EF-P, a soluble protein which reconstructs the peptide-bond formation and transesterification reactions on 70S ribosomes, stimulated both peptidyltransferase activities exhibited by the L16 N-terminal peptide.

L16, a bifunctional ribosomal protein and the enhancing effect of L6 and L11

L16 exhibits both peptide bond and transesterification activities when reconstituted into 2 M LiCl core particles. L6 and L11, when reconstituted in a similar manner in the absence of L16, manifest significant transesterification activity. Both L6 and L11 enhance the transesterification activity of L16; L11 being more active than L6 in this respect. However, both L6 and L11 have minimal effect on peptide bond formation when reconstituted with L16 at concentrations more than 2.5 M equivalents. Both L6 and L11 exhibit a differential effect on transesterification. The affinity-labelling agents, like PhCH2SO2F, diisopropylfluorophosphate and ethoxyformic anhydride, have been used to explore the role of residues in peptide bond formation and transesterification. It is proposed that the Ser-Phe combination present in L16, L11 and L6 is involved in transesterification in addition to the single histidine in L16. The single histidine in L16 appears to be important in the catalysis of peptide bond formation and transesterification.

Stimulation of peptidyltransferase reactions by a soluble protein

The requirements for peptide-bond synthesis and transesterification reactions of Escherichia coli 70S ribosomes, 50S native or reconstructed 50S subunits were examined using fMet-tRNA as donor substrate and puromycin or alpha-hydroxypuromycin as acceptors. We report that the soluble protein EF-P, purified to apparent homogeneity, stimulates the synthesis of N-formylmethionylpuromycin or N-formylmethionylhydroxypuromycin by 70S ribosomes or reassociated 30S and 50S subunits. In the presence of EF-P, 70S ribosomes are significantly more efficient than 50S particles in catalysing either peptide-bond synthesis or transesterification. The involvement of 50S subunit proteins in EF-P-stimulated peptide-bond formation and transesterification was studied. 50S subunits were dissociated by 2.0 M LiCl into core particles and 'split' proteins, several of which were purified to homogeneity. When added to 30S X A-U-G X f[35S]Met-tRNA, 50S cores or 50S cores reconstituted with L6 or L11 promoted peptide-bond synthesis or transesterification poorly. EF-P stimulated peptide-bond synthesis by both these types of core particles to approximately the same extent. On the other hand, EF-P stimulated a low level of transesterification by cores reconstituted with L6 and L11. In contrast, core particles reconstituted with L16 exhibited both peptide-bond-forming and transesterification activities and EF-P stimulated both reactions twentyfold and fortyfold respectively. Thus different proteins differentially stimulate the intrinsic or EF-P-stimulated peptide-bond and transesterification reactions of the peptidyl transferase. Ethoxyformylation of either 50S subunits or purified L16 used to reconstitute core particles, resulted in loss of peptide-bond formation and transesterification. Similarly ethoxyformylation of EF-P resulted in a 25-50% loss of its ability to stimulate both reactions. 30S subunits were resistant to treatment by this reagent. These results suggest the involvement of histidine residues in peptidyltransferase activities. The role of EF-P in the catalytic mechanism of peptidyltransferase is discussed.