David P.R. Muller

Oxidative stress and erythrocyte damage in Kenyan children with severe Plasmodium falciparum malaria

Anaemia causes significant morbidity in children with Plasmodium falciparum malaria, but the mechanism(s) are unclear. During malarial infection, increased reactive oxygen species (ROS) are generated that may contribute to erythrocyte damage and anaemia. This study measured the concentrations of α‐tocopherol in plasma and erythrocyte membranes, and the percentage polyunsaturated fatty acid composition (%PUFA) (an indirect marker of ROS damage) in erythrocyte membranes in children with severe P. falciparum malaria from Kilifi, Kenya, and asymptomatic children from the same district. Malarial subjects were stratified into complicated malaria and malaria anaemia. Results demonstrated significant reductions in erythrocyte membrane α‐tocopherol concentration (1·63 ± 0·16 versus 3·38 ± 0·18 μmol/mg protein; P < 0·001) and total %PUFA (30·7 ± 0·49 versus 32·8 ± 0·44% P < 0·005) for the malarial subjects (non‐stratified) compared with controls. Malarial subjects showed a significant positive correlation between membrane α‐tocopherol and haemoglobin concentrations (P < 0·005 r = 0·63 complicated malaria group; P < 0·05 r = 0·36 non‐stratified data). There were no significant differences in plasma α‐tocopherol concentration between malaria patients and controls. In conclusion, malarial infection may be associated with oxidative damage and reduced α‐tocopherol reserve in the erythrocyte membrane, suggesting that local antioxidant depletion may contribute to erythrocyte loss in severe malaria. Erythrocyte membrane α‐tocopherol appeared a better indicator of ROS exposure than plasma.

Lipid peroxidation in neural tissues and fractions from vitamin E-deficient rats.

A severe and chronic deficiency of vitamin E results in a characteristic neurological syndrome in both man and experimental animals. This is presumed to result from increased oxidative stress arising from a reduction in antioxidant capacity. In this study we have examined parameters of endogenous lipid peroxidation and susceptibility to in vitro oxidative stress of neural tissues and fractions, and some non-neural tissues from 1-year-old vitamin E-deficient and control rats. We have shown: (1) an increase in endogenous lipid peroxidation (thiobarbituric acid reactive substances and malondialdehyde) in neural tissues from vitamin E-deficient animals compared to controls. (2) The following order of susceptibility of neural tissues to in vitro oxidative stress in both vitamin E-deficient and control animals: brain >> muscle > cord > nerve. (3) The susceptibility of different brain regions to in vitro oxidative stress varied in a consistent manner with the cortex, striatum, and cerebellum showing the greatest and brainstem and hypothalamus the least susceptibility. (4) Fractions isolated from myelinated nerves of brainstem showed the following order of susceptibility to in vitro oxidative stress: axoplasmic membranes and organelles > axolemma enriched fraction > whole homogenate > = myelin. These results would fit with the characteristic neuropathology associated with severe and chronic vitamin E deficiency.

Nutritional supplementation in down syndrome: theoretical considerations and current status.

Down syndrome (DS) is the most common inherited cause of learning disability1, and affected individuals are more prone to infections, leukaemia, congenital heart disease and other anomalies, thyroid dysfunction, early senescence and Alzheimer’s disease2. These complications create a heavy burden for carers of individuals with DS and the social and health services. Consequently, any intervention that ameliorates some of these complications will have a significant impact on the quality of life of individuals with DS and their carers. However, before investing resources in interventions, it is important to ascertain their scientific validity. The Internet and the lay press make many claims that certain expensive nutritional supplements improve the outcome in DS. These claims have left some health professionals confused and parents of children with DS vulnerable to pressures to spend large amounts of money on nutritional supplements whose benefits have not been proved. This review was undertaken firstly, to determine whether there is a theoretical basis to expect that nutritional supplements may improve the pathology of DS, and secondly, to critically examine published trials of nutritional supplements in DS to determine whether the existing evidence supports claims that nutritional supplements improve the outcome in DS.

New synthesis of (±)-α-CMBHC and its confirmation as a metabolite of α-tocopherol (vitamin E)

Abstract There is currently interest in the metabolism of the various compounds which make up the vitamin E family, especially with regards to the possible use of vitamin E metabolites as markers of oxidative stress and adequate vitamin E supply. A number of vitamin E metabolites have been described to date and we have recently developed a method to extract and quantitate a range of vitamin E metabolites in human urine. During the development of this method a new metabolite of α-tocopherol was identified, which we tentatively characterised as 5-(6-hydroxy-2,5,7,8-tetramethyl-chroman-2-yl)-2-methyl-pentanoic acid (α-CMBHC). 1 Here we describe the synthesis of α-CMBHC as a standard and confirm that it is a metabolite of α-tocopherol.

Cortical Gene Expression in the Vitamin E-Deficient Rat: Possible Mechanisms for the Electrophysiological Abnormalities of Visual and Neural Function

In mammals, severe and chronic deficiency of vitamin E (α-tocopherol) is associated with a characteristic neurological syndrome. Previously, we have shown that this syndrome is accompanied by electrophysiological abnormalities of neural and visual function. To investigate the molecular basis of the observed abnormalities, we used microarrays to monitor the expression of ∼14,000 genes in the cerebral cortex from rats which had received diets containing 0, 1.25 and 5.0 mg/kg diet of all-rac-α-tocopheryl acetate for 14 months. Compared to the groups receiving 1.25 and 5.0 mg/kg α-tocopheryl acetate, a total of 11 genes were statistically significantly upregulated (≧1.3-fold) and 34 downregulated (≤1.3-fold) in the vitamin E-deficient group. Increased expression was observed for the genes encoding the antioxidant enzyme catalase and the axon guidance molecule tenascin-R, while decreased expression was detected for genes encoding protein components of myelin and determinants of neuronal signal propagation. Thus our observations suggest that vitamin E deficiency results in transcriptional alterations in the cerebral cortex of the rat which are consistent with the observed neurological and electrophysiological alterations.

Effect of intravenous lipid emulsions on hepatic cholesterol metabolism

BACKGROUND Total parenteral nutrition offers the chance of survival to children who have had extensive gut resections or gut failure. However, in infants it is often associated with serious complications including cholestatic liver disease. The causes of these complications remain unclear, although it has been suggested that the lipid emulsions used in total parenteral nutrition may be responsible. METHODS An in vitro system was developed to study the effect of lipid emulsions on hepatic cholesterol metabolism using cultured hepatocytes. RESULTS Incubations of Hep G2 cells with medium containing Intralipid (Pharmacia and Upjohn, Milton Keynes, UK) demonstrated that the fat emulsion mediated a powerful dose-dependent but reversible inhibition of cholesterol uptake. In addition Intralipid was shown to stimulate the efflux of cholesterol from Hep G2 cells. The component or components of the Intralipid responsible for these effects and the mechanism by which they act remain to be established. CONCLUSIONS Intravenous lipid emulsions may interfere with hepatic cholesterol metabolism in vivo. This may have implications for the development of total parenteral nutrition-associated cholestasis in neonates.

Retinal abnormalities in experimental vitamin E deficiency.

Physiological and biochemical studies have been carried out longitudinally over a period of 12 months in vitamin E deficient and control rats to gain an understanding of the mechanism whereby vitamin E conserves normal retinal function. Electroretinographic studies indicated that the primary effect of vitamin E deficiency was on the photoreceptors. Ultrastructural studies, however, did not show any morphological changes to the photoreceptors which could explain receptor dysfunction. A 30-40% loss of vitamin A (retinol) was found to be associated with vitamin E deficiency. This could be corrected by repletion with vitamin E, but there was no associated improvement in visual function. An irreversible loss of the long-chain polyunsaturated fatty acids from the retina, increased lipid peroxidation and alterations in membrane fluidity were also detected during vitamin E deficiency. We suggest that a deficiency of vitamin E leads to changes in the membrane microenvironment, which could affect photo transduction by either impairing the ability of rhodopsin to undergo conformational changes to the active form, or by disrupting the hyperpolarising and depolarising processes of the photoreceptors.

Oxidative stress does not appear to be involved in the aetiology of Friedreich's ataxia

The purpose of this study was to investigate the hypothesis that the gene for Friedreichs ataxia (FA) may be involved in the metabolism of α-tocopherol (vitamin E) or in other antioxidant systems. Concentrations of α-tocopherol, parameters of endogenous lipid peroxidation and susceptibility to in vitro oxidative stress were measured in neural tissues from four patients with FA and four controls. In general there were no significant differences in any of the parameters studied, although the brainstem whole homogenate from the FA patients was significantly (p < 0.02) less susceptible to in vitro oxidative stress than control material. These results, therefore, do not support the suggestion that abnormal metabolism of α-tocopherol or increased oxidative stress is involved in the aetiology of FA.

Urinary conjugated α-tocopheronolactone—a biomarker of oxidative stress in children with type 1 diabetes

Increased oxidative stress has been implicated in both the onset and the progression of diabetes mellitus and its complications. The development of easy to measure biomarkers of oxidative stress would, therefore, help in determining in a prospective manner the impact of glycemic control on oxidative stress and macrovascular disease in patients with diabetes. We report the development and validation of a novel method to directly measure the urinary concentrations of the conjugated metabolites of vitamin E (α-tocopherol) and investigate whether the oxidized metabolite α-tocopheronolactone (α-TL) could be used as a biomarker of oxidative stress in children with type 1 diabetes. A novel method using liquid chromatography–tandem mass spectrometry was developed and used to measure directly and rapidly the urinary concentrations of the glucuronidated and sulfated metabolites of α-tocopherol in 32 young patients with type 1 diabetes and age-matched controls. The mean concentrations of the glucuronidated and sulfated conjugates of α-TL were all highly significantly increased in the children with type 1 diabetes (p<0.001). The results suggest that the measurement of the urinary concentrations of α-TL conjugates may provide a useful biomarker of oxidative stress in diabetes and possibly in other clinical conditions in which oxidative stress has been implicated.