A generalized mathematical model is developed to describe the transport of fluid and plasma proteins or other macromolecules within the interstitium. To account for the effects of plasma protein exclusion and interstitial swelling, the interstitium is treated as a multiphase deformable porous medium. Fluid flow is assumed proportional to the gradient in fluid chemical potential and therefore depends not only on the local hydrostatic pressure but also on the local plasma protein concentrations through appropriate colloid osmotic pressure relationships. Plasma protein transport is assumed to occur by restricted convection, molecular diffusion, and convective dispersion. A simplified version of the model is used to investigate microvascular exchange of fluid and a single 'aggregate' plasma protein species in mesenteric tissue. The interstitium is approximated by a rigid, rectangular, porous slab displaying two fluid pathways, only one of which is available to plasma proteins. The model is first used to explore the effects the interstitial plasma protein diffusivity, the tissue hydraulic conductivity, the restricted convection of plasma proteins, and the mesothelial transport characteristics have on the steady-state distribution and transport of plasma proteins and flow of fluid in the tissue. The simulations predict significant convective plasma protein transport and complex fluid flow patterns within the interstitium. These flow patterns can produce local regions of high fluid and plasma protein exchange along the mesothelium which might be erroneously identified as 'leaky sites'. Further, the model predicts significant interstitial osmotic gradients in some instances, suggesting that the Darcy expression invoked in a number of previous models appearing in the literature, in which fluid flow is assumed to be driven by hydrostatic pressure gradients alone, may be inadequate. Subsequent transient simulations of hypoproteinemia within the model tissue indicate that the interstitial plasma protein content decreases following this upset. The simulations therefore support (qualitatively, at least) clinical observations of hypoproteinemia. Simulations of venous congestion, however, demonstrate that changes in the interstitial plasma protein content following this upset depends, in part, on the relative sieving properties of the filtering and draining vessels. For example, when the reflection coefficients of these two sets of boundaries are similar, the interstitial plasma protein content increases with time due to an increased plasma protein exchange rate across the filtering boundaries and sieving of interstitial plasma proteins at the draining boundaries. (This effect is supported by the clinical observation that interstitial plasma protein content in liver increases during venous congestion.) As the reflection coefficient of the draining boundaries decreases relative to that of the filtering boundaries, there is a net loss of plasma proteins from the interstitium, resulting in a decrease in the total interstitial plasma protein content over time (i.e., the familiar 'plasma protein washout'). Further, the model predicts increased fluid transfer from the interstitium to the peritoneum during venous congestion, supporting the clinical observation of ascites. Finally, the model is used to study the effects of interstitial plasma protein convection and diffusion, plasma protein exclusion, and the capillary transport properties on the transit times of two macromolecular tracers representative of albumin and γ-globulin within a hypothetical, one-dimensional tissue. As was expected, the transit times of each of the tracers through the model tissue varied inversely with the degree of convective transport. Increasing the interstitial diffusivity of the albumin tracer also led to a moderate decrease in the transit time for that tracer. The capillary wall transport properties, meanwhile, had only a marginal effect on the transit time for the range of capillary permeabilities and reflection coefficients considered. However, these properties (and, in particular, the reflection coefficient) had a more pronounced effect on the ultimate steady-state concentration of the tracer in the outlet stream. It was the interstitial distribution volume of a given tracer that had the greatest impact on the time required for the outlet tracer concentration to reach 50 % of its steady-state value. This was attributed to the increased filling times associated with larger interstitial distribution volumes. These findings suggest that the 'gel chromatographic effect' observed in some tissues could possibly be explained on the basis of varying distribution volumes. / Applied Science, Faculty of / Chemical and Biological Engineering, Department of / Graduate

Thesis (MTech (BioMedical Technology))--Cape Peninsula University of Technology, 2006 / In multiple sclerosis (MS) the myelin sheaths surrounding the axons in the brain are mainly affected by the disease process. Myelin consists for the most part of lipids and proteins. An abnormality in essential fatty acid metabolism is known to be present in patients with MS (Horrobin, 1979), reflected in a high ratio of n-6 to n-3 fatty acids in cell membranes. It has also been established previously that the pathogenesis of inflammatory disorders is aggravated by excessive consumption of n-6 fatty acids relative to n-3 fatty acids (Guesnet et al., 2005),and it has been shown that ingesting a larger proportion of n-3 fatty acids could be crucial in the regulation of cellular physiology and in the prevention of pathologies such as autoimmune and inflammatory diseases. Modern Western medical treatment for autoimmune diseases, which includes MS, involves the administration of immunosuppressive drugs, such as beta interferon, cortisone (prednisone), methotrexate and cytoxan, which reduce the effectiveness of the entire Immune system, and can have serious, sometimes life threatening, side effec1s (Perlmutter, 2006, htlp:/Iwww.msfac1s.org). It would therefore be of interest to investigate other options for treatment Although there is an extensive literature on fatly acids in MS, the actual details of the mechanisms of fatly add imbalances in MS have not been established. It would therefore be advisable to Investigate the abnormality of the MS cell membrane fatly acid profile. Previous studies focused on individual fatty acids, but it would be more relevant to investigate the relationships within and between the n-6 and n-3 series, and their effect on outcome, and to establish any possible cumulative effects, because the metabolism of fatty adds within the two series does have an effect on one another.

Thesis (DTech (Biomedical Technology))--Cape Peninsula University of Technology, 2009 / Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system (CNS), which leads to neuronal demyelination, and eventually to oligodendrocyte and axon loss, with subsequent lesion formation. The wide distribution of lesions in the CNS results in a variety of clinical features, such as cognitive impairment, vertigo, spasticity, ataxia tremors, progressive quadriparesis, pain and depression. Currently no cure exists for CNS disorders, resulting in a decline in quality of life, and an economic burden on society. Metabolic disturbances, especially lipid metabolic abnormalities, have been implicated in the development of MS. Although the disease cannot be cured, disease-modifiers, such as interferon beta, glatiramer acetate and mitoxantrone, as well as fatty acid supplementatlon have been used to delay the progression of the disease. Membrane fatty acids are precursors for mediators of inflammation, the eicosanoids, which are produced soon after stimulation and which regulate a number of inflammatory effects, such as the induction of fever, vasodilation and production of macrophage- and Iymphocyte-derived cytokines. Eicosanoids, in contrast to their fatty acid precursors, have a short half-life and are therefore difficult to measure. The objective in the present study was to determine the role of fatty acids from South African MS patients, by measuring the fatty acid composition of phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylserine (PS), phosphatidylinositol (PI) and sphingomyelin (SM) phospholipids in the plasma, red blood cell (RBC) and peripheral blood mononuclear cell (PBMC) membranes and correlate abnormalities with the neurological outcome as measured by the Kurtzke Expanded Disability Status Scale (EDSS) and inflammation assessed by C-reactive protein (CRP). A second objective was to establish whether possible changes in membrane lipids (phospholipids, fatty acids and cholesterol) would have an effect on membrane fluidity, and whether this would correlate with the EDSS and CRP. The plasma, RBC and PBMC membrane lipid composition from 31 white female patients with MS and 30 age- and gender-matched control subjects were assessed. Fatty acids were quanflfied by gas chromatography (GC), phospholipids by colorimetric and cholesterol by enzymatic assays. Membrane fluidity, as measured by the membrane lipid composition, was calculated, using previously established formulae, and includes the following: the saturated nature of the membrane was measured by the phospholipid PC+PS/PE+PS ratio, fluidity and permeability were measured by the cholesterol concentratlon and the cholesterol to total phospholipid ratio and membrane deformability was measured by the phospholipid PE to PS ratio. Membrane fluidity was also measured by the ordered-erystalline-phase to liquidcrystalline- phase lipid composition, which correlates with the phospholipid PE to PC ratio. The membrane saturated (SATS) to polyunsaturated fatty acid (PUFA) ratio was further used as an indication- of the fluidity status of the membranes. CRP was measured in all participants using a Beckman nephelometer. In MS, the n-6 fatty acids, particularly C18:2n-6, C20:4n-6 and C22:4n-6, were significantly decreased in plasma, RBC and/or PBMC membranes. In addition, the relationship between C20:3n-6 and C20:4n-6 showed a metabolic disturbance in both RBC and PBMC membranes from patients with MS, as compared to the control group. C20:4n-6 showed significant inverse correlations with the EDSS and CRP in MS patients, indicating that loss of these fatty acids from membranes correlated with higher disability as well as with increased inflammation. There were significant increases in free fatty acids C18:2n-6 and C20:4n-6 in plasma from MS patients. Saturated fatty acids, SM C14:0 and PI C22:0 were significantly increased in PBMC membranes from MS patients, and SM C14:0, C16:0 and C20:0 showed inverse correlations with the Functional System Scores. In contrast, the longer-ehain SATS, C22:0 and C24:0 showed positive correlations with the Functional System Scores. Red blood cell membrane fluidity as measured by the SATS to PUFA ratio was significantly higher in patients than in controls. In patients with CRP ~ 5.00 Ilglml the ratio showed significant inverse correlation with disease outcome. The saturated nature correlated positively, whilst the .ordered-erystalline-phase to liquid-crystalline-phase lipid ratio correlated inversely with the Functional System Scores. In this study it was consistently shown that C20:4n-6, or its precursor and elongation products, C18:2n-6 and C22:4n-6 respectively, was lower in plasma, RBC and/or PBMC membranes from MS patients. Red blood cells lack the desaturase enzymes and depend on fatty acids sourced from the plasma. Therefore, lower C20:4n-6 in the RBC membranes from MS patients may be due to depleted plasma stores, or an indication of an increased demand of this fatty acid elsewhere. Furthermore, this study has demonstrated that lower RBC C20:4n-6, with an increase in plasma FFA C20:4n6, resulted in worse disease outcome, perhaps due to the pro-inflammatory effect of eicosanoid production. This. study also characterized the specific SATS, that is, longer-ehain SATS that may increase the risk of developing MS, as higher shorter-ehain SATS, C14:0 and C16:0 reflected better disease outcome, demonstrated by the inverse correlation with the EDSS and FSS. Lastly, this study has shown that in the presence of uncontrolled inflammation such as in MS, the altered lipid composition indirectly compromised cell membrane, structure and fluidity, and thereby contributed to the disease progression in MS patients.