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 %.

The effect of stress on the antioxidative potential of serum: implications for Alzheimer's disease.

There is growing consensus in the literature that oxidation status is increased in Alzheimer's disease (AD), and that antioxidant supplementation as prevention or treatment strategy should be investigated further. In the present study the total antioxidant status (TAS) was found to be highly significantly lower in 22 AD patients (p < 0.0001) than in 22 age- and gender matched non-demented controls. The TAS was also lower than controls in 22 patients with vascular dementia, but not significantly. The increased oxidation status in AD was verified using the benzoate hydroxylation method. The origin of the enhanced oxidation status in AD has not been elucidated. To determine whether a causal effect between stress and oxidative status of serum can be demonstrated, a rat model was used with two different kinds of stressors, swim stress (exercise) and restraint stress (non-exercise stress). Following swim stress the maximum oxidative effect was observed at one hour post stress (p < 0.001). At 24 h the oxidative status had recovered significantly to below control values. Restraint stress, however, showed progressively increased oxidation which attained significance after 24 h (p < 0.005). It is postulated that stress may contribute to the higher oxidation status in AD patients.

A comparative study of the effects of cholesterol, beta-sitosterol, beta-sitosterol glucoside, dehydroepiandrosterone sulphate and melatonin on in vitro lipid peroxidation.

The free radical scavenging abilities of the structurally related steroids beta-sitosterol, beta-sitosterol glucoside (plant sterols and sterolins), cholesterol, and dehydroepiandrosterone sulphate (DHEAS) were compared with melatonin (an efficient free radical scavenger) in an in vitro system which measures lipid peroxidation of platelet membranes in the presence of iron (Fe2+). Lipid peroxidation is a process whereby cellular membranes are damaged due to the oxidative deterioration of polyunsaturated lipids, which may lead to cell death and disease in living organisms. Substances such as vitamin E protect cellular membranes against oxidative damage due to their chemical structures. The steroids cholesterol, beta-sitosterol, beta-sitosterol glucoside and dehydroepiandrosterone (DHEA) are structurally related to each other. During aging, serum concentrations of DHEA, DHEAS and melatonin decrease, while the concentration of cholesterol tends to increase. The aim of the present study was to compare the role these substances play in lipid peroxidation over a wide concentration range. At concentrations lower than the free iron in the reaction mixture, all the steroids investigated decreased lipid peroxidation. At higher concentrations, cholesterol and beta-sitosterol increased lipid peroxidation, while DHEAS and melatonin continued to decrease lipid peroxidation.

Melatonin prevents beta-amyloid-induced lipid peroxidation.

Beta-amyloid is a major constituent of senile plaques that occur in the brains of Alzheimer's disease (AD) patients. Cell culture studies have shown that high concentrations of beta-amyloid are toxic and damage biological macromolecules. A number of experiments have shown that melatonin is a potent antioxidant. Melatonin not only neutralizes oxygen-derived free radicals but can also scavenge species of other types such as carbon-centered free radicals. The present study was designed to determine whether beta-amyloid toxicity would cause lipid peroxidation of human platelet membranes. Since aluminum has been implicated in the etiology of AD, we investigated the effects of aluminum on lipid peroxidation and whether the harmful effects of beta-amyloid are aggravated by aluminum. We also investigated whether melatonin had the ability to protect against beta-amyloid toxicity. Our results indicate that both beta-amyloid and aluminum dose-dependently increased lipid peroxidation in platelet membranes. Aluminum was more potent than beta-amyloid. Incubation of platelet membranes with increasing concentrations of aluminum in the presence of 100 microM beta-amyloid (fragment 25-35) resulted in lipid peroxidation levels of similar magnitude as the two substances, respectively. Prior administration of melatonin dose-dependently inhibited this effect. These results confirm the toxic effects of beta-amyloid to biological membranes. While aluminum itself damages membranes, its presence did not exacerbate the toxic effects of beta-amyloid. Melatonin effectively reduced the lipid peroxidation induced by beta-amyloid and aluminum, suggesting that its supplementation to AD patients may be beneficial.

A new model for the pathophysiology of Alzheimer's disease. Aluminium toxicity is exacerbated by hydrogen peroxide and attenuated by an amyloid protein fragment and melatonin.

OBJECTIVES: Although Alzheimer's disease (AD) is the leading cause of dementia in developed countries, there is an as yet unexplained lower prevalence of the disease in parts of Africa. AD is characterised by a catastrophic loss of neurons; free radicals (oxidative toxins) have been implicated in the destruction of the cells through the process of lipid peroxidative damage of cell membranes. Previously aluminium (Al) and a fragment of beta amyloid (A beta 25-35) were shown to exacerbate free-radical damage, while melatonin reduced this effect. The aim of the present study was: (i) to investigate the conditions determining the toxicity of Al and A beta 25-35; and (ii) to assess whether melatonin could attenuate the damage done by both aluminium and the amyloid fragment, thus suggesting a pathway for the aetiology of AD. DESIGN: An in vitro model system was used in which free radicals were generated, causing lipid peroxidation of platelet membranes, thus simulating the disease process found in the brain. RESULTS: 1. Al and A beta 25-35 caused lipid peroxidation in the presence of the iron (II) ion (Pe2+), Al being more toxic than A beta 25-35. 2. A beta 25-35 attenuated the lipid peroxidation promoted by Al. 3. Hydrogen peroxide (H2O2) greatly exacerbated the toxicity of Al and A beta 25-35. 4. Melatonin prevented lipid peroxidation by Al and A beta 25-35 in the absence of H2O2, but only reduced the process when H2O2 was present. CONCLUSIONS: In the light of the results obtained from the present study, the following hypotheses are formulated. 1. In AD, excessive quantities of Al are taken up into the brain, where the Al exacerbates iron-induced lipid peroxidation in the lysosomes. 2. In response, the normal synthetic pathway of amyloid protein is altered to produce A beta fragments which attenuate the toxicity of Al. In the process of sequestering the Al and iron, immature plaques are formed in the brain. 3. Microglia are activated, in an attempt to destroy the plaques by secreting reactive oxygen species such as H2O2. At this point in the disease process, lipid peroxidation causes a catastrophic loss of brain cells. 4. Melatonin, together with other free radical scavengers in the brain, reduces the free-radical damage caused by Al and A beta, except in the latter stages of the disease process. Since melatonin is produced by the pineal gland only in the dark, the excess of electric light in developed countries may help explain why AD is more prevalent in these countries than in rural Africa.

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.

An evaluation of strategic and threshold control measures against the Karoo paralysis tick, Ixodes rubicundus (Acari: Ixodidae) in South Africa.

Paralysis caused by feeding female Ixodes rubicundus ticks is a major problem in large areas of South Africa. As the life cycle of the tick extends over a period of 2 years, it was hypothesized that strategic treatment of sheep with an acaricide over a 2 year period, timed to kill most engorging females, should markedly lower the biotic potential of the tick. Two flocks of sheep grazing in separate paddocks known to be infested with I. rubicundus were treated either strategically or on a threshold basis (i.e. only when tick challenge exceeded a predetermined critical level in terms of paralysis) for a 2 year period. The tick burdens of untreated control sheep running with the two flocks were monitored over a 4 year period and their seasonal dynamics determined. The times at which peak infestations occurred were similar for both flocks of sheep, but significant differences in mean tick burdens between the two flocks were recorded. Tick numbers on sheep in the strategically treated flock did not decrease during the third and fourth years of the trial as was expected. Possible reasons for this were low stocking densities, especially during times of peak abundance of adults and the presence of wild hosts which maintained tick populations.

Preoperative nutritional status and prognostic nutritional index in patients with benign disease undergoing abdominal operations--Part I.

OBJECTIVE: The aim of the first part of this study was to detect the incidence of preoperative malnutrition of clinical importance in patients with benign disease. METHODS: The preoperative nutritional status of 52 consecutive adult patients undergoing abdominal operations for benign conditions was studied prospectively by objective and subjective nutritional criteria. The postoperative outcome was monitored until discharge or death. The preoperative nutritional status was correlated with the postoperative outcome. RESULTS: Protein energy malnutrition was identified in 20 (38%) of the 52 patients. Of these 20 malnourished patients, 15 (75%) developed complications after surgery, compared with 7 (22%) of the 32 well-nourished patients (p < 0.01). The most common abnormal values were serum transferrin concentration (n = 8), subscapula skinfold (n = 11), serum urea:serum creatinine ratio (n = 17), loss of appetite for more than 5 days (n = 24), and preoperative stay in hospital of longer than 5 days (n = 19). CONCLUSION: These results indicate that a combination of objective and subjective criteria may be important in the identification of clinical malnutrition.

Preoperative nutritional status and prognostic nutritional index in patients with benign disease undergoing abdominal operations--Part II.

OBJECTIVES: Part II of this study was undertaken to develop a prognostic nutritional index for the identification of high risk patients with benign disease undergoing abdominal operations at the Universitas Hospital in Bloemfontein. METHODS: To accomplish this goal, 52 consecutive adult non-cancer surgical patients, admitted to the Universitas Hospital for a period of one year, were studied prospectively. The postoperative outcome was monitored until discharge or death. Various discriminant analyses were performed on the obtained data. Four prognostic indexes were compiled, including two nutritional and two mixed models. A short and medium length index were derived for both the nutritional and the mixed models. RESULTS/DISCUSSION: The results suggest that the short nutritional index may be the most practical for the prediction of surgical outcome in this specific set of patients. The short nutritional index included diet risk, serum albumin, body mass index, % ideal body weight, triceps skinfold and grip strength. It is further suggested that these indices be tested in another set of patients and be compared with other available prognostic models.

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.

Different oxidative pathways of isonicotinic acid hydrazide and its meta-isomer, nicotinic acid hydrazide.

1. Superoxide was generated during the auto-oxidation of the antituberculous drug, isonicotinic acid hydrazide (INH), but not with its meta-isomer, nicotinic acid hydrazide (NH). During Fe(3+)-stimulated oxidation of INH and NH, aromatic hydroxylation occurred which was inhibited by the chelating agent, phytic acid. 2. A mixture of myeloperoxidase (MPO) and a hydrazide induced formation of compound III (oxyperoxidase) and aromatic hydroxylation which was stimulated by phytic acid. INH was considerably more potent than NH. 3. Co-oxidation of a hydrazide and thyroxine (T4) in the MPO system resulted in the formation of a pink-coloured product (maximum absorbance at 504 nm) which was more stable with NH than with INH. 4. The hydrazides and Cl- acted synergistically on MPO haem modification when co-oxidised in the MPO-H2O2 system. INH was more destructive than NH. 5. The different oxidative pathways of the hydrazides are consistent with the fact that an acyl intermediate of INH, unlike that of NH, is resonance stabilized.

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.

The appetence behaviour of two South African paralysis-inducing ixodid ticks.

The appetence responses of the ixodid ticks Ixodes rubicundus and Rhipicephalus punctatus to various stimuli were quantified under laboratory conditions. A greater percentage of I. rubicundus generally responded to the different stimuli at lower than at higher temperatures while the converse was usually true for R. punctatus. Radiation heat and shadowing evoked a response in the greatest percentage of I. rubicundus, whereas CO2 and host odour were responsible for a similar reaction in R. punctatus. A single perturbation of the substrate caused more than 50% of I. rubicundus to respond while constant perturbation resulted in a progressive decrease in the proportion of ticks reacting. Significantly more R. punctatus than I. rubicundus were attracted to a CO2 trap and the R. punctatus were also attracted to the trap over a greater distance. Significantly more older than younger ticks of both species responded to the various stimuli.

Thyroxine-supported oxidation in the myeloperoxidase system.

Thyroxine and other iodothyronines (concentrations in the nanomolar range) stimulated the oxidation of NADH in the myeloperoxidase-H2O2-Cl- system. In the absence of chloride, thyroxine had only a marginal effect. This suggests that thyroxine increased the generation of chlorinating oxidants. A peroxidase-catalysed oxidation product of thyroxine, 3,5-diiodotyrosine, was inactive. Pre-incubation of thyroxine in the myeloperoxidase system showed that thyroxine was oxidized to a product capable of stimulating NADH oxidation. Reduction and alkylation of myeloperoxidase under nondenaturing conditions also increased the oxidative activity of the enzyme. It is postulated that both iodoacetamide and a thyroxine-derived oxidation product (presumably a quinone) alkylate sulphydryl groups near the active centre of myeloperoxidase making it more accessible for its substrate.

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.

Interaction of methyl-xanthines with myeloperoxidase. An anti-inflammatory mechanism.

1. Inhibition of myeloperoxidase (MPO)-catalyzed reactions by methyl-substituted xanthines has been investigated. 2. Except for theobromine and caffeine, all xanthines tested were potent inhibitors of the MPO-H2O2-Cl- system. 3. In contrast to methyl substitution in the 1 or 8 position of xanthine, substitution in the 3 or 7 position had a marked effect on the inhibition of MPO catalysis. 4. Two different inhibitory mechanisms were induced; scavenging of hypochlorous acid (HOCl) generated by the MPO system and accumulation of Compound II (ferryl MPO) which is inactive as a catalyst of Cl- oxidation.

Seasonal occurrence of Karoo paralysis in Angora goats in relation to the infestation density of female Ixodes rubicundus.

The seasonal occurrence of Karoo paralysis in relation to the infestation density of female Ixodes rubicundus was investigated in an enzootic area of the southwestern Orange Free State, South Africa. Young and adult Angora goats were exposed to infestation during two paralysis tick seasons. Only the young goats became paralysed and their infestation densities (female ticks kg-1 host body weight) were significantly higher than those of healthy animals. The infestation densities on paralysed goats varied between 0.64 and 3.56 ticks kg-1. During the 1988 season, 30% of the naive young goats became paralysed compared with 67% the following season. Twenty-nine percent of previously paralysed goats were paralysed again during the same season. Paralysis occurred during periods of peak tick activity (April-June).

Sites of attachment and intraspecific infestation densities of the brown paralysis tick (Rhipicephalus punctatus) on Angora goats.

Significant differences in the distribution of brown paralysis ticks on various age classes of Angora goats were recorded. In kids, most (greater than 98%) of the ticks attached to the head and ears, whereas in older groups, in addition to the ears, a high proportion (greater than 20%) of ticks also attached to the ventral side of the neck. There were significant differences in the mean infestation densities of both male and female R. punctatus in kids and older animals. These differences were, however, only significant for the first two sample dates involving kids, and are probably related to behavioural attributes of the kids which enhance tick/host contact. Newly born Angora goat kids are considered a high-risk group with regard to paralysis caused by the brown paralysis tick. Methods of avoiding mortality amongst kids are suggested.

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.

Spatial distribution of the Karoo paralysis tick Ixodes rubicundus (Acari: Ixodidae) within a false upper Karoo veld type.

Spatial distribution of the Karoo paralysis tick (Ixodes rubicundus) has been studied in a paralysis enzootic area of the southwestern Orange Free State. Significantly more females than males were collected from the vegetation. Most ticks (99%) used grass as questing sites at a height of approximately 45 cm (range 10-97 cm), which correlates with the size of host animals. No significant differences between the questing height of male and female ticks were evident. The ticks were found on most of the grass species present and, except for the genus Eragrostis, no specific preference was evident. When questing, the capitulum of I. rubicundus is usually (90%) directed towards the ground. Seventy-eight percent of the ticks occurred singly on a specific grassblade or flowerhead. In those cases where two ticks occurred together, no sexual aggregation was evident. Most ticks occurred under or close (mean = 62 cm) to the crown cover of specific shrub or tree species. These plant species were characterized by a dense crown cover with a mat of decaying leaf litter underneath. The preference of the tick for wild olive trees (Olea europaea africana) suggests that, except for the physical characteristics of this tree species, host factors may also be important. Significantly more ticks were distributed on the cooler, more protected southern sides of vegetation in comparison to the northern sides.