Biological basis of water quality assessment : the Kavango river, Namibia

Le fleuve Kavango prend sa source dnas les hauts plateaux d'Angola, se dirige vers le sud formant la frontière Angola-Namibie sur 415 km de direction Ouest-Est, et coule ensuite vers le sud pendant 65 km avant de former le delta de l'Okavango au Botswana. La portion moyenne de la rivière le long de la frontière est caractéristique des fleuves de faible pente des plaines d'inondation. Les crues sont d'environ 6 m au-dessus du niveau normal, avec un lit majeur de 5 km de large. Le fleuve est vital pour les populations locales dont 85% vivent à moins de 10 km du fleuve. Compte tenu des prévisions d'accroissement de la population, des besoins en eau, des programmes de redistribution des terres, de l'évolution des pratiques agricoles et d'une sécheresse chronique, le ministère des Pêches et des Ressources marines prépare les bases d'une gestion durable des ressources dont les populations locales sont directement dépendantes. C'est dans ce cadre qu'une recherche a été mise en place pour définir un protocole de suivi de la qualité des eaux en Namibie, protocole basé sur des critères biologiques. L'utilisation de critères biologiques pour suivre la qualité des cours des rivières dans les pays tempérés est commune. C'est moins le cas pour les pays tropicaux. L'indice d'intégrité biologique (IBI) est utilisé depuis plus de 10 ans en Europe et en Amérique du Nord. Il permet une estimation de la santé d'une rivière par l'analyse de son peuplement de poissons. Des données sur le peuplement de la portion namibienne du Kavango, obtenues en 1992, sont utilisées ici pour base d'un indice approprié. Les limites de l'approche sont analysées et des recommandations pour son extension à d'autres pays au sud du Sahara sont présentés. (Résumé d'auteur

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 pi-I 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.Articl

PR - Proposed Procurement Marketing Framework For Potato Processing Companies

The potato processing industry production has increased over the last few years with as much as 143% within 10 years; together with this there is also an increased growth in the import of frozen fries. This puts direct pressure on the processing companies to procure good quality potatoes at reasonable prices, in order to remain competitive. The aim of this paper is to develop a procurement marketing framework that will assist processing companies with the establishment of longer term contracts and relationships with producers as suppliers. This framework is constructed by evaluating the needs of producers, transaction costs, the profit margins, price risks and incentives such as Decision Support Models

Characteristics of potato contract producers in the South African potato processing industry

Imports in the South African processing and frozen fries industry are on the increase. Thus, procurement for processing companies becomes more complex and the competition for local producers is increased. Local processors need to find adequate supplies at the lowest price whereas producers need to deliver at the best price. In order for processing companies to ensure sufficient quality and quantity, a good procurement strategy such as contract marketing is required. However, the characteristics of producers willing to adopt contract marketing must be identified. In order to do so, characteristics of contract producers in the Eastern Free State who used two different governance structures (contract and spot-market) were interviewed. A questionnaire was used and data were analysed with a Principal Component Regression combined with a Logit model. Out of 26 possible characteristics, nine were identified as significant (P < 0.1 or P < 0.5). The characteristics included less marketing cost, market information, only channel, less quality penalties, transport, price certainty, negotiation period, number of contacts, and less risk. Processing companies wanting to establish marketing strategies, target producers, and improve current contracts can use the nine characteristics. The characteristics can also be used to negotiate long-term contracts with producers

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 Fe3+-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.Articl

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 &lt; 3 μM) 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 Fe2+-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.Articl

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.Articl

Isoniazid-mediated irreversible inhibition of the myeloperoxidase antimicrobial system of the human neutrophil and the effect of thyronines

During aerobic myeloperoxidase-catalysed oxidation of isoniazid at pH 7.8, compound III was generated. Oxidation of isoniazid or hydrazine sulphate at pH valu7es of 6.5 or 7.8 in a myeloperoxidase-H2O2 system caused considerable haem loss, which was associated with compound III formation. Haem loss and also compound III formation could be inhibited when 8 μM thyroxine was included in the reaction mixtures. During the reaction with isoniazid, an intense pink-coloured pigment with maximum absorbance at 500 nm was formed which could be bleached with ascorbate or hypochlorous acid. The pigment was more stable at pH 7.8 than at pH 6.5. A similar pink colour was generated when a mixture of isoniazid and thyroxine in alkaline solution was irradiated with light of wavelength &gt; 300 nm. A possible product of thyroxine oxidation, 3,5-diiodotyrosine, could not protect the enzyme against isoniazid-mediated haem loss and no colour formation was observed. Haem loss was most extensive when isoniazid was oxidised in a myeloperoxidase system at pH 7.8 in the presence of 0.1 M NaCl. Thyroxine (8 μM), however, could still inhibit haem loss under these conditions. A good correlation was found between haem loss and irreversible loss of peroxidase activity.Articl

Activation of chlorpromazine by the myeloperoxidase system of the human neutrophil

The univalent oxidation of chlorpromazine (CPZ) by the myeloperoxidase (MPO-H2O2 system led to the formation of a cation free radical (CPZ+.) which was observed optically at 527 nm. CPZ protected MPO against loss of catalytic activity when co-oxidized in a MPO-Cl--H2O2 system. Due to the stability of CPZ+. either further oxidation, or reduction back to the mother compound, become important mechanisms for disappearance of the free radical. Thus, the rate of formation and decay of CPZ+. were higher in the presence of Cl- than in its absence, since the radical can also be oxidized further by hypochlorous acid (HOCl), which is formed in the MPO-Cl--H2O2 system. Decay of CPZ+. can also be due to electron acceptance from ascorbic acid or oxygenated haemoglobin (HbO2), resulting in regeneration of CPZ. When CPZ+. was generated in the MPO-H2O2 system, addition of HbO2 resulted in a sudden decrease in CPZ+. absorbance at 527 nm and a concomitant formation of metHb. When HbO2 was not added, the decay of CPZ+. was much slower. CPZ (in the absence of the MPO system) also stimulated the oxidation of HbO2 in the presence of 20 μM H2O2, but this reaction was considerably slower than when CPZ+. (generated by the MPO system) was allowed to react directly with HbO2. These results suggest that HbO2 was oxidized by CPZ+. To study the effect of CPZ intermediates, thyroglobulin (TG) was used as a model polypeptide. Chlorinated oxidants formed in the MPO system (in the absence of CPZ) induced TG peptide bond splitting. In contrast, CPZ metabolites generated by the MPO system (in the absence of Cl-) induced polymerization of TG, as revealed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE).Articl

Free radical scavenging effects of melatonin and serotonin: Possible mechanism

Melatonin has been reported to be a potent free radical scavenger, but the mechanism by which it protects membranes from lipid peroxidation is poorly understood. The present study addresses this problem by comparing the free radical scavenging properties of melatonin and serotonin, two indoles with similar structure, but differing solubilities. Both serotonin and melatonin significantly prevented lipid peroxidation of platelet membranes. Additionally, melatonin significantly decreased the microviscosity (increased the fluidity) of platelet membranes, while serotonin had the opposite effect. These data led us to postulate that serotonin exerts its free radical scavenging action in the aqueous phase, or at the water-membrane interface, while melatonin positions itself within the lipid bilayer where it protects membrane phospholipids against free radical attack.Articl