Wool production and quality traits of pure- and crossbred Merino-type sheep.

Very little information is available on the quality of wool produced by terminal crosses out of wool producing dam lines. This study was therefore undertaken to elucidate the wool quality traits of four crossbred lines relative to Merinos and Dohne Merinos, which served as dam lines. Each dam line was mated to rams of their own breed as well as to Dormer or Ile de France rams to create four crossbred lines, namely, Dohne x Dormer, Dohne x Ile de France, Merino x Dormer, and Merino x Ile de France, in addition to the purebred Dohne Merino and Merino lines. Four rams and four ewes from each of these lines were reared up to one year of age under optimal growth conditions and shorn at the end of that time. Fleeces were weighed and samples collected for analysis. Neither sex nor genotype influenced clean fleece weight or clean yield percentage, but fibre diameter differed between genotypes. Purebred Merino had the finest wool (18.26 µm) and the Merino x Dormer cross the coarsest (26.01 µm). However, all lines still produced wool that could be used in manufacturing clothing, while fleeces showed good uniformity. The two purebred lines had the highest comfort factor (> 98%). The crossbred lines produced a similar quantity of wool as the purebreds, although of poorer quality. All genotypes except Merino x Dormer appear to produce wool that could be processed into garments, although the crossbred wool would only be suitable for outerwear.

Application of growth models to South African Boer goat castrates and does under feedlot conditions.

Mathematical models may aid researchers in describing biological processes, like growth, in animals. This study aimed to collect the body weight data of 18 Boer goat castrates and 20 Boer goat does, from birth until maturity, to model growth and determine growth trends. This is a novel investigation as sufficient information on an age-weight database for these two Boer goat sexes from birth to maturity, is lacking. Using age-weight data, four nonlinear models, namely the Brody, Gompertz, Logistic and Von Bertalanffy growth models, were plotted and evaluated. The model parameters of each growth model were compared for differences between the two sexes. The statistical effectiveness of fit was determined for each model using AIC and RMSE, with R2 also being considered. All models except the Brody model, predicted significantly heavier mature weights for castrates. The Brody model was deemed unfit to describe Boer goat growth as the function severely over-predict weights from birth until maturity for both sexes. The Von Bertalanffy (R2 = 91.3) and Gompertz functions (R2 = 91.3) showed the best fit for Boer goat castrates, while the Gompertz model (R2 = 95.1) showed the best fit for Boer goat does. The Gompertz function is the preferred model to depict Boer goat growth overall, as it accurately characterized growth of both sexes. According to the Gompertz model the age at which the inflection point of the growth curve was reached, did not differ significantly between castrates and does (141.80 days versus 136.31 days). There was also no significant difference in maturation rate between the two sexes.

The International Consortium on Primary Graft Dysfunction: Redefining Clinical Risk Factors in the Contemporary Era of Heart Transplantation.

BACKGROUND: Primary graft dysfunction (PGD) is the leading cause of morbidity and mortality early after heart transplantation (HT). The International Consortium on PGD is a multicenter collaboration dedicated to identifying the clinical risk factors for PGD in the contemporary era of HT. The objectives of the current report were (1) to assess the incidence of severe PGD in an international cohort; (2) to evaluate the performance of the most strongly validated PGD risk tool, the RADIAL score, in a contemporary cohort; and (3) to redefine clinical risk factors for severe PGD in the current era of HT. METHODS: This is a retrospective, observational study of consecutive adult HT recipients between 2010 and 2020 in 10 centers in the United States, Canada and Europe. Patients with severe PGD were compared to those without severe PGD (comprising those with no, mild and moderate PGD). The RADIAL score was calculated for each transplant recipient. The discriminatory power of the RADIAL score was evaluated using receiver operating characteristic (ROC) analysis, and its calibration was assessed by plotting the percentage of PGD predicted vs that which was observed. To identify clinical risk factors associated with severe PGD, we performed multivariable mixed-effects logistic regression modeling to account for among-center variability. RESULTS: A total of 2746 patients have been enrolled in the registry to date, including 2015 (73.4%) from North America, and 731 (26.6%) from Europe; 215 participants (7.8%) met the criteria for severe PGD. There was an increase in the incidence of severe PGD over the study period (P value for trend by difference sign test = 0.004). The Kaplan-Meier estimate for 1-year survival was 75.7% (95% CI 69.4-80.9%) in patients with severe PGD as compared to 94.4% (95% CI 93.5-95.2%) in those without severe PGD (log-rank P value < 0.001). The RADIAL score performed poorly in our contemporary cohort and was not associated with severe PGD; it had an AUC of 0.53 (95% CI 0.48-0.58). In the multivariable regression model, acute preoperative dialysis (OR 2.41, 95% CI 1.31-4.43), durable left ventricular assist device support (OR 1.77, 95% CI 1.13-2.77), and total ischemic time (OR 1.20 for each additional hour, 95% CI 1.02-1.41) were associated with an increased risk of severe PGD. CONCLUSIONS: Our consortium has identified an increasing incidence of PGD in the modern transplant era. We identified contemporary risk factors for this early post-transplant complication, which confers a high mortality risk. These results may enable the identification of patients at high risk for developing severe PGD in order to inform peri-transplant donor and recipient management practices.

Modelling and predicting fat deposition rates in various South African sheep crosses using ultrasound technology.

Producers require an accurate predictive tool that can determine the optimal point of slaughter based on fat depth. The modelling of fat deposition with a simple mathematical model could supply in this need. Dohne Merino and Merino ewes were crossed with Dorper, Dormer and Ile de France rams or rams of their own breeds to create two purebred (Dohne Merino and Merino) and six crossbred groups (Dohne x Dorper, Dohne x Dormer, Dohne x Ile de France, Merino x Dorper, Merino x Dormer and Merino x Ile de France) of offspring. Fat deposition of four lambs of each sex per genotypic group was monitored from 80 to 360 days using ultrasound, and the data subsequently fitted to various equations and evaluated for goodness of fit. A linear fitting of fat depth to age (R2 > 0.77) and live weight (R2 > 0.56) were deemed to provide the best fit. The slope parameters of the equations indicated that ewes deposited fat faster than rams and that Dorper crosses had the highest fat deposition rate. An attempt was also made to model loin muscle growth, but the model fit was judged to be unsatisfactory. The predictive models developed here are deemed suitable for inclusion in feedlot management systems to aid in the production of optimally classified lamb carcasses.

Determining and predicting feed intake in crossbred sheep from weaning until maturity.

Access to simple, accurate feed intake models would facilitate decision-making in feedlots as feed costs are a major part of operational expenditure. This study aimed to develop genotype-specific feed intake models for South African feedlot lambs. Four ram and four ewe lambs each of eight genotypes were raised under ideal growth conditions from weaning until 1 year of age. Feed intake and growth were monitored throughout this period. The intake data were then used to fit various models to predict daily feed intake, intake as percentage of body weight, cumulative intake and feed conversion ratio. No satisfactory univariate models could be found for the prediction of daily or percentage intake, but a good fit was found for cumulative intake data (R2 >0.80, P <0.01). The slope parameters of these linear models show a strong correlation (72%) with feed conversion and can therefore also serve as proxies for feed conversion. A model was also developed that can predict feed conversion ratio with a moderate accuracy (R2 =0.5, P <0.05) at a given body weight. The cumulative intake model was deemed accurate and simple enough for practical use.

Outcomes of Neonates Requiring Neonatal Intensive Care Admission for Necrotizing Enterocolitis in a Resource-Restricted Hospital in Cape Town, South Africa.

AIM: The aim of this study is to describe the 30-day mortality, neurodevelopmental outcome and composite outcome (mortality or abnormal neurodevelopmental outcome) of neonates with necrotizing enterocolitis (NEC), requiring neonatal intensive care (NICU) admission, in a resource-restricted environment. METHODS: All neonates admitted to Tygerberg Hospital, NICU, with a presumptive diagnosis of NEC Bell stage IIB or more, over a 5-year period, were included. RESULTS: One hundred and thirty-five neonates were included with a mean gestational age of 29 ± 2.7 weeks and mean birth weight of 1185 g ± 446 g. The 30-day mortality was 52%, neurodevelopment abnormalities occurred in 35% of survivors and adverse composite outcome in 63%. The 30-day mortality and adverse composite outcome risk were increased by small for gestational age, shock, metabolic acidosis, inotrope requirement and first feed >9 days after surgery. CONCLUSION: In resource-restricted environments, mortality and abnormal neurodevelopmental outcome of neonates with NEC, remain high. However, outcomes are comparable with international literature. Neonates with NEC, requiring NICU admission and surgery, require neurodevelopmental follow-up.

Necrotizing enterocolitis remains one of the most common gastrointestinal emergencies in neonates. Neonates admitted to a resource-restricted neonatal intensive care unit with a presumptive diagnosis of advanced NEC were reviewed. We were able to identify risk factors associated with a higher chance of death or poor neurodevelopmental outcomes. Our outcomes are comparable with international literature.

Determining Mancozeb Deposition Benchmark Values on Apple Leaves for the Management of Venturia inaequalis.

Apple scab, caused by Venturia inaequalis, is the most common fruit and foliar disease in commercial apple production worldwide. Early in the production season, preventative contact fungicide sprays are essential for protecting highly susceptible continuously unfolding and expanding young leaves. In South Africa, mancozeb is a key contact fungicide used for controlling apple scab early in the season. The current study developed deposition benchmarks indicative of the biological efficacy of mancozeb against apple scab, using a laboratory-based apple seedling model system. The model system employed a yellow fluorescent pigment that is known to be an effective tracer of mancozeb deposition. A concentration range of mancozeb (0.15 to 1 times the registered dosage) and fluorescent pigment concentrations was sprayed onto seedling leaves, which yielded various fluorescent particle coverage (FPC%) levels. Modeling of the FPC% values versus percent disease control yielded different benchmark values when disease quantification was conducted using two different methods. Thermal infrared imaging (TIRI) disease quantification resulted in a benchmark model where 0.40%, 0.79%, and 1.35 FPC% yielded 50, 75, and 90% apple scab control, respectively. These FPC% values were higher than the benchmarks (0.10, 0.20, and 0.34 FPC%, respectively) obtained with quantitative real-time PCR (qPCR) disease quantification. The qPCR benchmark model is recommended as a guideline for evaluating the efficacy of mancozeb sprays on leaves in apple orchards since the TIRI benchmark model underestimated disease control. The TIRI benchmark model yielded 68% disease control at the lowest mancozeb dosage, yet no visible lesion developed at this dosage. Both benchmark models showed that mancozeb yielded high levels of disease control at very low concentrations; for the qPCR benchmark model the FPC% value of the FPC90 (90% control) corresponded to 0.15 times that of the registered mancozeb concentration in South Africa, i.e., 85% lower than the registered dosage.

Testing in the HIV Counselling and Testing (HCT) campaign, HIV risk behaviours and ART enrolment in South Africa.

OBJECTIVES: To examine the association between testing in the 2010 HIV Testing and Counselling (HCT) campaign with HIV risk behaviours and enrolment on ART. STUDY DESIGN: Data for this study were collected as part of a nationally representative cross-sectional household survey conducted in 2012 in South Africa. METHODS: Consenting participants completed a structured questionnaire and provided a dry blood spot specimen which was tested for HIV antibodies and antiretroviral drugs. Multinomial logistic regression was used to examine the association between HIV testing history and explanatory variables of interest. RESULTS: There was no association between testing in the 2010 HCT campaign and condom use at last sex, number of sexual partnerships or HIV knowledge. Individuals who tested in the HCT campaign were more likely to disclose their status (COR 2.6, 95% CI: 1.71-3.8) and those who tested HIV positive in the campaign were more likely to be receiving ART (COR 1.8, 95% CI: 1.1-2.9). Testing in the HCT campaign was associated with having received both pretest and post-test counselling while testing before the campaign was associated with having received HIV results with no counselling (COR 2.1, 95% CI: 1.2-3.8). CONCLUSION: We highlight the success of the 2010 HCT campaign in improving HIV status disclosure and enrolment on ART as well as shortcomings on HIV risk behaviours and HIV knowledge. These may be related to issues of quality assurance in the counselling process. Our results further highlight possible HCT counselling inconsistencies across sectors requiring stronger public-private partnership in the delivery of HCT in South Africa.

Guidance for the gastrointestinal evaluation and management of iron deficiency in Sub-Saharan Africa.

BACKGROUND: Over 30% of the world's population is anaemic, with a significant proportion of these being iron deficient. As iron deficiency (ID) anaemia in men and post-menopausal women is mostly caused by gastrointestinal blood loss or malabsorption, the initial evaluation of a patient with ID anaemia involves referral to a gastroenterologist. The current drive towards patient blood management in sub-Saharan Africa (SSA)prescribes that we regulate not only the use of blood transfusion but also the management of patients in whom the cause of iron loss or inadequate iron absorption is sought. Recommendations have been developed to: (i) aid clinicians in the evaluation of suspected gastrointestinal iron loss and iron malabsorption, and often a combination of these; (ii) improve clinical outcomes for patients with gastrointestinal causes of ID; (iii) provide current, evidence-based, context-specific recommendations for use in the management of ID; and (iv) conserve resources by ensuring rational utilisation of blood and blood products. METHOD: Development of the guidance document was facilitated by the Gastroenterology Foundation of Sub-Saharan Africa and the South African Gastroenterology Society. The consensus recommendations are based on a rigorous process involving 21 experts in gastroenterology and haematology in SSA. Following discussion of the scope and purpose of the guidance document among the experts, an initial review of the literature and existing guidelines was undertaken. Thereafter, draft recommendation statements were produced to fulfil the outlined purpose of the guidance document. These were reviewed in a round-table discussion and were subjected to two rounds of anonymised consensus voting by the full committee in an electronic Delphi exercise during 2022 using the online platform, Research Electronic Data Capture. Recommendations were modified by considering feedback from the previous round, and those reaching a consensus of over 80% were incorporated into the final document. Finally, 44 statements in the document were read and approved by all members of the working group. CONCLUSION: The recommendations incorporate six areas, namely: general recommendations and practice, Helicobacter pylori, coeliac disease, suspected small bowel bleeding, inflammatory bowel disease, and preoperative care. Implementation of the recommendations is aimed at various levels from individual practitioners to healthcare institutions, departments and regional, district, provincial and national platforms. It is intended that the recommendations spur the development of centre-specific guidelines and that they are integrated with the relevant patient blood management protocols. Integration of the recommendations is intended to promote optimal evaluation and management of patients with ID, regardless of the presence of anaemia.

A model for estimating the medium properties of Avicel to ethanol conversion.

Simultaneous saccharification and fermentation received an increasing level of attention over recent decades, with the primary focus on the development of improved enzyme and organism performance. Little literature is available on the effects of the various fermentation components on the apparent dynamic viscosity of the fermentation broth for use in reactor design and analysis. This work investigates density and settling properties of Avicel PH-101 particles and the effects of base medium composition, yeast concentration and cellulose particles on the apparent dynamic viscosity of the fermentation mixture. Dynamic viscosity measurements were obtained using a rotational viscometer equipped with a DG 26.7 double gap concentric cylinder measuring system. Results indicated that Avicel particles experience a greater drag force compared to similar sized spherical particles and have a measured density of 1,605.7 kg m(-3). The Ostwäld-de Waele formulation was used to describe the dynamic viscosity of the particles due to it shear-thinning nature. Correlation between the predicted particle effects and experimental results deviated with a root mean square error of 8.46 %.

Unusual radar echoes from the greenland ice sheet.

Airborne radar images of part of the Greenland ice sheet reveal icy terrain whose radar properties are unique among radar-studied terrestrial surfaces but resemble those of Jupiter's icy Galilean satellites. The 5.6- and 24-centimeter-wavelength echoes from the Greenland percolation zone, like the 3.5- and 13-centimeter-wavelength echoes from the icy satellites, are extremely intense and have anomalous circular and linear polarization ratios. However, the detailed subsurface configurations of the Galilean satellite regoliths, where heterogeneities are the product of prolonged meteoroid bombardment, are unlikely to resemble that within the Greenland percolation zone, where heterogeneities are the product of seasonal melting and refreezing.

Solubilization of peroxidase from porcine thyroids and characterization by photoaffinity labelling.

Peroxidase was solubilized without proteolysis from porcine thyroid particulate fraction with the nonionic detergent, 1-O-n-octyl-beta-D-glucopyranoside. The enzyme was able to catalyze the oxidation of guaiacol and the iodination of bovine serum albumin (33 atoms of iodine per molecule protein). Binding studies performed with the partially purified enzyme indicated that the substrates thyroxine (T4) and tyrosine compete for the same binding site on the enzyme. Dissociation constants of 0.9 nM and 0.5 nM were found for T4 and tyrosine, respectively. After photoaffinity labelling with underivatized 125I-labelled T4, gel chromatography on Sephacryl S-1000 revealed a relative molecular weight of about 100 000 for the solubilized enzyme. The peroxidase activity and haem-absorbance peak coeluted from the Sephacryl S-1000 column. SDS-polyacrylamide gel electrophoresis under reducing conditions indicated two major radiolabelled polypeptides, Mr 83 000 and Mr 42 600, as well as a smaller peak at Mr 15 400. The 15 400 molecular weight species is probably not part of the peroxidase complex, since it could partially be removed by Sephadex G-25 prechromatography . Further analyses confirmed that the partially purified enzyme is a haemoprotein absorbing maximally at 412 nm. The Soret band is shifted to 423 nm by reducing agents and the haem-cyanide complex has a maximum absorbance at 416 nm.

Assessment of estrogenic recruitment before chemotherapy in advanced breast cancer: a double-blind randomized study. European Organization for Research and Treatment of Cancer Breast Cancer Cooperative Group.

PURPOSE: In the present phase III study, the specific effect of estrogenic recruitment was assessed by comparing two groups of patients with advanced breast cancer receiving either ethinylestradiol (EE2) or placebo (PL) before chemotherapy (CT). PATIENTS AND METHODS: The therapeutic regimen consisted of (1) estrogen suppression by aminoglutethimide (AGL) 1 g/d plus hydrocortisone (HC) 40 mg/d, with surgical castration performed on premenopausal patients; (2) fluorouracil (5-FU) 500 mg/m2, doxorubicin 50 mg/m2, and cyclophosphamide (CPA) 500 mg/m2 (FAC) intravenously (IV) every 3 weeks; (3) following randomization, patients were double-blinded to receive either PL or EE2 50 micrograms exactly 24 hours before receiving FAC. All patients had advanced breast cancer presumably sensitive to endocrine therapy (estrogen receptor-positive [ER+] and/or progesterone receptor-positive [PgR+] status) with measurable lesions; none had received prior systemic antineoplastic therapy for metastatic disease; prior adjuvant hormonal therapy (HT) or CT (without anthracyclines) was allowed if interval since completion was longer than 1 year. RESULTS: Among 154 patients treated according to the protocol, tolerance, response rates, time to progression, and median survival duration were identical in the PL and EE2 groups. Only performance status, dominant metastatic site, and menopausal status seemed to influence response (overall response, 64%), with the highest levels of partial remission (PR) and complete remission (CR) being achieved in premenopausal women (CR plus PR, 26% plus 55%) and in those with dominant soft tissue lesions (CR plus PR, 45% plus 28%). CONCLUSION: We conclude that the validity of the hormonal recruitment concept has not yet been established in clinical practice so that this approach remains experimental. The results achieved by combining (near) complete estrogenic suppression and cyclical FAC chemotherapy are not significantly different from those to be expected with the more conventional use of HT followed by CT in presumably hormone-responsive (ER+) patients.

Randomized comparison of tamoxifen and two separate doses of toremifene in postmenopausal patients with metastatic breast cancer.

PURPOSE: To perform a randomized three-arm comparison of tamoxifen (TAM; 20 mg/d) and two separate doses of toremifene (TOR; 60 mg/d [TOR60] and 200 mg/d [TOR200]) in postmenopausal patients with hormone receptor-positive or -unknown metastatic breast cancer. MATERIALS AND METHODS: Six hundred forty-eight patients with hormone receptor-positive or -unknown metastatic breast cancer were randomly assigned to receive TAM (n = 215), TOR60 (n = 221), or TOR200 (n = 212). RESULTS: The combined response rates (by intent to treat) were as follows;: TAM, 44%; TOR60, 50%; and TOR200, 48%. Complete and partial response rates were as follows: TAM, 19%; TOR60, 21%, and TOR200, 23% (not statistically different). Median times to progression and overall survival were not significantly different. Adverse events (lethal, serious but nonlethal, and important but non-life-threatening) were similar in all three arms, except that patients in the TOR200 arm had a statistically significantly increased rate of nausea (37% v 26% and 26% for TOR200, TAM, and TOR60, respectively; P = .027). Quality-of-life assessments were not different among the three arms. CONCLUSION: The activity, toxicity, and side effects of TOR in postmenopausal women with hormone receptor-positive or -unknown metastatic breast cancer are similar if not equivalent to those of TAM. We detected no clear evidence of a dose-response effect for TOR. TOR60 is an effective and safe agent for the treatment of postmenopausal women with hormone receptor-positive metastatic breast cancer and can be considered an alternative to TAM as first-line treatment for such patients.

Evaluation of mathematic models to assess platelet kinetics.

Twelve mathematic methods used to calculate the mean platelet survival time were compared by determining the "goodness of fit" of the models to the platelet survival curves of 15 reference subjects and 54 patients. Platelets were labeled with [111In]oxine. The linear (LN), exponential, weighted mean, multiple hit (MH), Dornhorst (DH), Meuleman (ML), alpha order (AO), and polynomial (PO) mathematic models were investigated. The goodness of fit for the exponential model was determined by the nonlinear least squares method (EP), and also by the linear least squares method on logarithmically transformed data (EX) as is recommended. The modified weighted mean (MWM) and the usual weighted mean method (WM) obtained with these exponential models were tested. The Dornhorst (DH10) and Meuleman (ML10) models, where the potential age-dependent platelet survival times were kept constant at 10 days, were also evaluated. The goodness of fit results, expressed as % s.d. indicated that the LN (5.2%), EX (5.0%), EP (4.4%), WM (3.7%), DH10 (3.7%), and ML10 (3.7%) models all fitted the data significantly worse than the MWM, MH, DH, ML, AO, and PO models (range 3.2-3.3%). The mean platelet survival time determined with the MH model differed significantly from the results with the DH, ML, and AO models. The results of mean platelet survival time calculated with different mathematic models cannot, therefore, be compared directly. The models that fitted the platelet survival curve well varied slightly in sensitivity to noise as is indicated by the coefficient of variation of the mean platelet survival time estimates for the reference subjects (range 7.9-12.0%). Fitting data to at least two mathematic models has definite advantages. Data on which the calculations are based are probably invalid if the following are true: (a) if the mean platelet survival time estimated with the alpha order model is shorter than that estimated with the EP, MWM, or MH models, or (b) the mean platelet survival time estimated with either the DH, ML, AO, or PO models, is longer than the LN, MWM, or MH estimate of the mean platelet survival time. We conclude that the mean platelet survival time can be reliably estimated by fitting the data to either the MWM method (if limited computing facilities are available) or the MH model. Confidence in the result will be increased if considered in conjunction with the finding obtained with one other model; in those cases where the platelet survival time is very short, the alpha order model is recommended.(ABSTRACT TRUNCATED AT 400 WORDS)

Anti-oxidant properties of H2-receptor antagonists. Effects on myeloperoxidase-catalysed reactions and hydroxyl radical generation in a ferrous-hydrogen peroxide system.

Ulcerogenesis of the gastroduodenal mucosa is caused by the digestive action of gastric juice and initially involves an inflammatory reaction with infiltration of phagocytes. The anti-inflammatory activity of many drugs have been attributed to the inhibition of the leukocyte enzyme, myeloperoxidase (MPO). In this study, the H2-antagonists in clinical use were found to be potent inhibitors of MPO-catalysed reactions (IC50 < 3 microM) under conditions resembling those in experiments with intact neutrophils. Since peak plasma concentrations of cimetidine, ranitidine and nizatidine are well within the micromolar range, after oral therapeutic dosing, our results may be of clinical relevance. The inhibitory actions of cimetidine and nizatidine were largely due to scavenging of hypochlorous acid (HOCl), a powerful chlorinating oxidant produced in the MPO-H2O2-Cl- system. In contrast to famotidine, ranitidine was also a potent scavenger of HOCl, while both drugs inhibited MPO reversibly by converting it to compound II, which is inactive in the oxidation of Cl-. The HOCl scavenging potencies of ranitidine and nizatidine were about three times higher than that of the anti-rheumatic drug, penicillamine, which had a potency similar to that of cimetidine. The rapid HOCl scavenging ability of penicillamine is thought to contribute to its anti-inflammatory effects. Using riboflavin as a probe, the H2-antagonists were found to be inhibitors of hydroxyl radical (.OH) generated in a Fe(2+)-H2O2 reaction mixture. Spectral analyses of the interaction of iron ions with the drugs and studies with chelators, suggest that the drugs were efficient chelators of Fe2+, in addition to their .OH scavenging abilities. Since the gastrointestinal tract can contain potentially reactive iron, the simultaneous presence of H2-antagonists may help to suppress iron-driven steps in tissue damage.

Apparent hydroxyl radical generation without transition metal catalysis and tyrosine nitration during oxidation of the anti-tubercular drug, isonicotinic acid hydrazide.

Aromatic hydroxylation and formation of thiobarbituric acid-reactive substances occurred in a mixture of isonicotinic acid hydrazide (isoniazid) and catalase. Since these reactions were stimulated by phytic acid (a potent metal chelator), rather than inhibited, transition metal-catalysed hydroxyl radical generation was not implicated. Hydroxylation also occurred with isoniazid and phytic acid in the absence of catalase, albeit to a lesser extent. The independent effects of catalase and phytic acid are related to their abilities to catalyse isoniazid oxidation. In the presence of tyrosine, both the isoniazid/phytic acid system and authentic peroxynitrite generated dityrosine. Authentic peroxynitrite, as well as a phytic acid-mediated isoniazid oxidation product, have absorbance maxima at 302 nm. The yield of this isoniazid-derived product increased with pH and in the presence of a superoxide-generating system. A good correlation existed between absorbance at 302 nm and aromatic hydroxylation. Acid-induced decomposition of the 302 nm absorbance in the presence of superoxide dismutase led to the formation of a product absorbing in the same region as peroxynitrite-modified superoxide dismutase (350 nm at acid pH). Catalase catalysed peroxynitrite-mediated, as well as isoniazid/phytic acid-mediated tyrosine nitration, which was accompanied by Compound II formation (ferryl-catalase) in both cases. We postulate that peroxynitrite or a similar species is formed during isoniazid oxidation.

The inhibitory effect of acetaminophen on the myeloperoxidase-induced antimicrobial system of the polymorphonuclear leukocyte.

Acetaminophen binds via its acetamido side chain to purified myeloperoxidase in a pH-dependent manner and maximum binding occurred around pH 6. The H2O2-dependent myeloperoxidase-catalysed polymerization products of acetaminophen had excitation maxima at 304 nm and 334 nm in acid and alkaline solutions, respectively, and an intense blue fluorescence maximum at 426 nm. Acetaminophen can compete effectively with Cl- as myeloperoxidase substrate and thus HOCl formation is suppressed while HOCl, nevertheless present, can be scavenged by the drug. In this way the microbicidal action of the myeloperoxidase-H2O2-Cl- system can be seriously limited in the presence of high concentrations of acetaminophen. To study the effect of acetaminophen on peptide bond splitting in the myeloperoxidase antimicrobial system, thyroglobulin was used as a model peptide. Peptide bond splitting was inhibited at acetaminophen concentrations below the accepted toxic range for plasma values.

Aromatic hydroxylation during the myeloperoxidase-oxidase oxidation of hydrazines.

Benzoic acid was found to be hydroxylated by a mixture of myeloperoxidase (MPO) and the mycobactericidal drug, isoniazid. Aromatic hydroxylation and formation of compound III (oxyperoxidase) were coincident during the MPO-oxidase oxidation of isoniazid which proceeded without augmentation from the reagent hydrogen peroxide. An intermediate of isoniazid reduced ferric MPO to ferrous MPO which associated with dioxygen to form compound III. Aromatic hydroxylation also occurred in a mixture of isoniazid (or phenylhydrazine) and a ferric salt. Hydroxylations in both the enzymatic and nonenzymatic reaction systems were inhibited by the iron chelator, desferal, as well as by the specific hydroxyl radical scavenger, mannitol. To distinguish between the hydroxylating intermediates in the different reaction systems, the unique properties of the natural antioxidant, phytic acid, were exploited. Phytic acid inhibited aromatic hydroxylation in the Fe(3+)-INH system, which is in accordance with its known properties as a powerful inhibitor of iron-driven reactions (.OH formation). By contrast, phytic acid stimulated hydroxylation in the enzymatic system which was accompanied by a concomitant stimulation in the rate of compound III formation. These events were, however, not directly related to each other. Phytic acid had a direct effect on the redox transformation of isoniazid by stimulating superoxide generation during auto-oxidation of the drug. In addition, phytic acid also facilitated compound III decay in the absence of isoniazid, suggesting that it may also regulate the oxygen affinity of MPO, similar to its effect on the oxygenation of haemoglobin. The data on aromatic hydroxylation in the MPO-isoniazid system do not support a role for .OH in the reaction and may fit the model for the P450 mixed oxidase system.

Mechanisms by which clofazimine and dapsone inhibit the myeloperoxidase system. A possible correlation with their anti-inflammatory properties.

The mechanisms by which two anti-leprotic drugs (clofazimine and dapsone), both with anti-inflammatory properties, inhibit myeloperoxidase (MPO)-catalysed reactions, were investigated. The disappearance of NADH fluorescence was used as an assay for its oxidation. Chloride stimulated the oxidation of NADH in the MPO-H2O2 system in a concentration-dependent manner (50-fold at 150 mM NaCl). Under these conditions Cl- is oxidized and the oxidant formed, presumably hypochlorous acid (HOCl), oxidizes NADH. Observations demonstrating the effect of the drugs on the MPO system, are: (1) Inhibition of Cl(-)-stimulated oxidation of NADH. (2) Inhibition of polypeptide modification in a model protein, thyroglobulin (TG). (3) Protection of MPO against loss of catalytic activity caused by chlorinating oxidants generated by the system. (4) Inhibition of haemoglobin oxidation. Only dapsone was active here. HPLC analyses suggested that the drugs were not significantly metabolized in the MPO-H2O2 system in the absence of Cl-. Bleaching of clofazimine was stimulated by Cl- in the MPO system, suggesting the involvement of HOCl. Clofazimine was found to be a more potent scavenger of HOCl than dapsone when the inhibition of NADH oxidation by reagent HOCl was used as an assay. This finding is also supported by HPLC analyses which indicated a greater sensitivity of HOCl for clofazimine than for dapsone. Relatively low concentrations of dapsone inhibited the oxidation of oxygenated haemoglobin (HbO2), suggesting that the drug was not metabolized to its N-hydroxylated derivative which is thought to be responsible for methaemoglobin (metHb) formation in vivo. It is proposed that the inhibitory mechanism of action of clofazimine is to scavenge chlorinating oxidants generated by the MPO-Cl(-)-H2O2 system, while dapsone converts MPO into its inactive compound II (ferryl) form. The different inhibitory mechanisms of clofazimine and dapsone towards the MPO system may contribute to the anti-inflammatory actions of the drugs.