Biochemical abnormalities in erythrocytes from patients with Duchenne muscular dystrophy and multiple sclerosis
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(1) Duchenne Muscular Dystrophy (DHD) Muscle fibres and erythrocytes in DMD exhibit many abnormalities of me membrane-associated properties which have led to the 'Membrane Hypothesis'. The Membrane Hypothesis states that the primary lesion in DMD involves a generalized defect in the plasma membrane. Since phospholipids play a crucial part in the structure, organization and function of membranes, subtle changes in these lipids could well be responsible for the observed abnormalities. One possible alteration is a perturbation of the asymmetric distribution of phospholipids in the plasma membrane. Such asymmetry may be studied in erythrocytes using phospholipases. In this work, bee venom phospholipase A2 was used to treat intact cells and derived ghosts. Two-dimensional TLC was used to separate the extracted lipids, which were quantified by phosphorus assay. Results showed the lipid composition is normal but the degradation of PC in DMD erythrocytes was higher and the differences were highly significant (P < 0.01). Increased PC degradation in erythrocytes may be explained in at least two ways: (i) transbilayer translocation of PC occurs more readily during the course of the experiment, or (ii) more PC is localized in the outer leaflet. If the results can be explained by (i) then spectrin, which is essential in maintaining lipid asymmetry, may be of abnormal structure and in fact, abnormalities of spectrin in DMD erythrocytes have already been reported. If the explanation for the results is (ii), lipid rearrangement and changes in viscosity and fluidity can be expected, which would also result in abnormalities in spectroscopic data, osmotic fragility, ion transport and enzyme activities reported in DMD erythrocytes. Na+ -K+ ATPase activity of normal erythrocytes was reported to become 'Duchenne like' after incubation of cells with DMD plasma. A circulating factor from necrotic muscle was proposed to be responsible. The effect of DMD plasma on the asymmetry of membrane lipid was investigated but results showed that DMD plasma did not result in altered asymmetry in control cells. So the factor, if one exists, is not responsible for the increased PC degradation found in DMD erythrocytes and also the change in Na+-K+ ATPase activity is not due to a change in lipid asymmetry of the erythrocytes. (2) Multiple Sclerosis (MS) MS is a demyelinating disease of unknown cause. A dietary defect and abnormal immune response have been proposed. Lipid organization of the membrane of MS erythrocytes was investigated in this work to explore whether the reported abnormal physical properties in MS erythrocytes were due to abnormal lipid asymmetry. Results showed the membrane lipid composition and asymmetrical organization of MS is normal. So the reported increased cell size, increased osmotic fragility and reduced electrophoretic mobility of erythrocytes as well as increased platelet stickiness in MS patients is not due to changes in lipid organization in the MS erythrocyte membrane. Glutathione peroxidase, one of the enzymes which protects against membrane lipid peroxidation was reported to be decreased in MS erythrocytes. This might result in increased subsceptibility to lipid peroxidation of MS erythrocytes. The peroxidisability (using H2 O2 as stressor) and the activities of the four enzymes, glutathione peroxidase, glutathione reductase, catalase and superoxide dismutase, were investigated. Results showed the per-oxidisability of MS erythrocytes was significantly decreased (P < 0.001) which indicates that the membrane lipids of MS erythrocytes are less susceptible to peroxidation. This may be due to increased content of antioxidants (e.g. vitamin E, etc.) in the cells since the activities of the antioxidant enzymes were found to be normal in this work. Hyperbaric oxygen (HBO) treatment has been proposed for treatment of MS patients. The effect of HBO treatment on the four antioxidant enzymes were investigated. Only catalase activity was found to be increased in erythrocytes of MS patients after HBO treatment. So raised catalase may be an important effect and outweigh the potentially damaging increased lipid peroxidation which may also accompany HBO treatment.
Thesis, PhD Doctor of Philosophy
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