ERYTHROCYTE DISAGGREGATION SHEAR-STRESS, SIALIC-ACID, AND CELL AGING IN HUMANS

Erythrocyte aggregation, which plays an important role in the physiolo gical behavior of blood fluidity, was found to be enhanced in hyperten sion and hypercholesterolemia. While the role of macromolecule bridgin g force has been widely described, cellular factors related to membran e sialic acid content, which might contribute to the negative charge o f cell surface causing the repulsion of erythrocytes, have been less s tudied. Cell age-dependent changes in membrane sialic acid content (in micromoles per gram of integral membrane protein) were investigated i n 24 normotensive and 24 hypertensive matched subjects, each divided i nto 2 identical subgroups according to a cutoff of 6.2 mmol/L serum ch olesterol. A progressive and significant (P<0.001) decrease in membran e sialic acid content associated with an increase (P<0.001) of disaggr egation shear rate threshold (laser reflectometry in the presence of d extran) were observed with increased erythrocyte density (erythrocytes fractionated by density using ultracentrifugation) in both normotensi ve and hypertensive groups regardless of the cholesterol level. Howeve r, disaggregation shear rate threshold was significantly higher and si alic acid content was lower (P<0.001) in both hypertensive and normote nsive subjects with hypercholesterolemia compared with either normoten sive or hypertensive subjects with low cholesterol, respectively. A hi gh membrane sialic acid content variance, beginning in the younger ery throcytes, was due mainly to triglyceride and LDL cholesterol levels ( R-2=0.49 for low, R-2=0.43 for middle, and R-2=0.54 for high densities , ie, young, mean, and senescent erythrocytes, respectively). We concl ude that an early decrease in erythrocyte sialic acid content may infl uence the rheological properties of blood by increasing the adhesive e nergy of erythrocyte aggregates.