Changes of Membrane Fluidity in Erythrocytes of Obese Children: A Spin Label Study

Abstract

ABSTRACf. Red blood cells depend on circulating lipoproteins for the turnover of membrane phospholipids. Thus abnormalities in lipid and lipoprotein metabolism are frequently associated with changes in composition and fluidity of erythrocyte membranes. Using the electron spin resonance technique we studied the physical state of erythrocyte membranes from 15 obese children with a body mass index ranging from 22.8 to 34 kg. m"? and slight alterations of plasma lipids. The spin labels used, S-doxylstearate and 16-doxylstearate, have shown an increase of the order parameter and of the correlation time, respectively. These observations indicate a decrease of fluidity at the surface and in the hydrophobic core of erythrocyte membranes from obese subjects. The results are statistically significant and they are discussed in relation to clinical aspects of childhood obesity. Studies on erythrocyte membrane molecular organization could represent a sensitive way to find out small metabolic alterations hardly detectable with compositional studies. (Pediatr Res 22:141-144,1987) Abbreviations LPL, lipoprotein lipase LCAT, lecithin-cholesterol acyl transferase ESR, electron spin resonance BMI, body mass index SoNS, S-doxylstearate 16-NS, 16-doxylstearate LDL, low-density lipoproteins HDL, high-density lipoproteins RBC, red blood cells Several studies on metabolic and fun ctional alterations in obesity are limited to obese adults; less att ention has been devoted to the pediatric obese subjects. In adult obese pat ients modifications of the activity of the LPL (I) and of the LCAT (2) suggest the hypothesis that obesit y could be associated with alterations of the lipoprotein metabolism.It is known that in certain specific pathological states , inborn errors of metabolism and/or dietary or hormonal disturbances are associated with changes in the surface of lipids of circulating lipoproteins and several lines of evidence correlate these changes with abnormalities in the lipids of erythrocyte membrane (3-7).Because the molecular organization of the erythrocyte membrane is known in detail, it is possible to correlate changes in membrane composition with modifications in membrane fluid- Received September 8, 1986; accepted February 19, 1987. Correspond ence should be addr essed to Prof. Giovanna Curatola, Istituto di Biochimi ca, Facolta di Medicina e Chirurgia, Via Ran ieri, 60 131 Ancona, Italy.Supported by a grant from Regione Marche, Ricerca Sanita ria Finalizzata, n. 213 22-5-1985. ity, moreover it is well known that membrane fluidity affects membrane-bound enzyme activities (8, 9), A reduced level of erythrocyte membrane tocopherol ( 10) which could explain the erythrocyte sensitivity to pero xidative damage, a lower concentration of insulin receptors (II), and a reduced Na +K+ pump ( 12) have been shown in erythrocytes of obese ch ildren. However until now there is no evidence for their direct or indirect involvement in the pathogenesis of obesity.The possible correlations between obesity and membrane physical state wer...

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