Effects of polyoxyethylene chain length on erythrocyte hemolysis induced by poly[oxyethylene (n) nonylphenol] non-ionic surfactants.

The effects of three different poly[oxyethylene (n) nonylphenols], n = 9.5, 20 and 100 oxyethylene (EO) units, on erythrocyte hemolysis and on the fluidity of the erythrocyte membrane were studied. The three different surfactants showed different effects. The surfactant with average n = 9.5 EO units (C9E9) shows a biphasic effect: at low concentrations it protects erythrocytes against hypotonic hemolysis, but at higher concentrations it induces hemolysis both in isotonic and hypotonic buffers. C9E20 does not affect the erythrocyte membrane resistance to hemolysis, independent of the buffer osmolarity; this detergent did not show a hemolytic effect. C9E100 is an effective protective agent against hypotonic hemolysis, in concentration > 2 x 10(-4) M. EPR spectroscopy of spin-labeled stearic acid indicated that the three different surfactants increase the fluidity of erythrocyte ghost membranes. At the higher C9E20 and C9E100 surfactant concentrations in the presence of membrane ghosts, spin-label is located in the surfactant micelles. In the case of the hemolytic concentrations of C9E9, mixed (surfactant plus phospholipid) micelles are formed. These results suggest that C9E9 has a higher affinity for membrane phospholipids, which accounts for its lytic activity. The protective effect of C9E100 is assigned to the osmotic buffering of the liquid surrounding the cell membrane, due to the large polar chains anchored to the membrane outer monolayer but other mechanisms previously considered in the literature may also be effective.