Does repeated exposure to fenitrothion alter phospholipid composition of erythrocyte membrane?

Abstract

Sir, Erythrocytes have acetylcholinesterase (AchE), and its activity is often used as an indicator of intoxication with cholinesterase inhibitors. The physiological function(s) of AchE in erythrocytes, however, have not been clarified. The enzyme is entirely membrane bound and located in the outer side of the membrane (see Igisu et al. 1981). On the other hand, the outer leaflet of the erythrocyte membrane is rich in choline-containing phospholipids, i.e., phosphatidylcholine and sphingomyelin (Rothman and Lenard 1977). Hence, one may speculate that AchE might play a role in the metabolism of phospholipids of the membrane, especially those containing choline. Furthermore, in the brain, cholinergic activity and phosphatidylcholine content appears related (Buyukuysal and Wurtman 1990). We therefore examined whether or not repeated exposure to a potent inhibitor of cholinesterase (fenitrothion) affects phospholipid composition of erythrocyte membrane. Male Wistar rats weighing 150-190 g were used. The animals were exposed to fenitrothion (Sumithion) powder for 2 h a day, 5 times a week for 4 -6 weeks. The fenitrothion powder was generated by an apparatus which can produce powder with a fairly constant concentration over a long period (Tanaka and Akiyama 1984). The exposure concentration, aerodynamic median diameter of the powder, and geometric standard deviation were 12.9+ 17.9 (mg/m3, mean _+ SD), 4.9 Bm, and 2.3, respectively. Three hours after the final exposure, blood was obtained by cardiac puncture under ether anesthesia. Preparation of the erythrocyte membrane and measurement of AchE activity were done as described previously (Igisu et al. 1981 ). Lipids were extracted by the method of Folch et al. (1957) and partitioned with water. Lower-phase lipid was applied to a high performance thin-layer chromatogram (HPTLC) plate (Merck 5641) and developed in a mixture of chloroform-methanol-water (65 : 25 : 4, v/v/v). After visualization by spraying cupric acetate and heating (Fewster et al. 1969), the plate was scanned by a Shimadzu Fig. 1. Thin-layer chromatograms of lipids of erythrocyte membrane from rats of control (1), 4-week exposure (2) and 6-week exposure to fenitrothion (3). Spots of cholesterol (Ch), ethanolamine phospholipids (E), phosphatidylcholine (Pc), serine phospholipid (+ phosphatidylinositol) (S) and sphingomyelin (Sp) are seen