Ž . Comparative Biochemistry and Physiology Part C 130 2001 315323 Cyclodiene organochlorine insecticide-induced alterations in the sulfur-redox cycle in CHO-K1 cells A.E. Bayoumi a , A.J. Garcıa-Fernandez b , C. Ordonez c , Y. Perez-Pertejo c , ´ ´ ´˜ ´ J.C. Cubrıa c , R.M. Reguera c , R. Balana-Fouce c , D. Ordonez c,  ´ ˜ ´˜ a Department of Plant Protection, Faculty of Agriculture, Uni  ersity Aim Shams, Cairo, Egypt b Departmento de Ciencias Socio-sanitarias, Uni  ersidad de Murcia, Campus de Espinardo, Murcia, Spain c ( ) Departmento de Farmacologıa y Toxicologıa INTOXCAL , Uni  ersidad de Leon, Campus de Vegazana s  n, 24071 Leon, ´ ´ ´ ´ Spain Received 23 March 2001; received in revised form 25 July 2001; accepted 30 July 2001 Abstract The effect of the cyclodiene organochlorine pesticides aldrin, dieldrin and endosulfan was assessed on CHO-K1 Ž . Ž cultures at fractions of their lethal doses, determined by the neutral red NRI incorporation assay NRI , NRI and 6.25 12.5 . NRI . Glutathione peroxidase, reductase and S-transferase, and total and oxidised glutathione were evaluated along 25 the standard growth curve of the cultures. After a 24-h incubation with each insecticide, glutathione peroxidase incurred a large increase, while glutathione reductase and S-transferase activities were slightly higher than untreated controls. Unlike oxidised glutathione, the content of total glutathione declined significantly after exposure to cyclodiene Ž . insecticides. Changes in cell membrane integrity were assessed by the lactate dehydrogenase LDH release assay and lipid peroxidation for a wide range of pesticide concentrations. Membrane leakage and peroxide production were significantly enhanced at concentrations of aldrin and as low as 12.5 gml, whereas dieldrin and endosulfan increased membrane fragility at much higher concentrations.  2001 Elsevier Science Inc. All rights reserved. Keywords: Cyclodiene organochlorine insecticides; Cytotoxicity; Membrane permeability; Sulfur-redox cycle 1. Introduction Organochlorine cyclodiene insecticides owe their environmental significance to their strong persistence and ability to biomagnify in the trophic Abbre  iations: LDH, lactate dehydrogenase; GSSG, oxidised glutathione; SOD, superoxide dismutase; ROS, reactive oxy- gen species  Corresponding author. Tel.: 34-87-291590; fax: 34-87- 291252. Ž . E-mail address: dftrbf@isidoro.unileon.es D. Ordonez . ´˜ Ž . chain WHO, 1984 . The acute and chronic toxic effects of these compounds in non-target animals are not completely clear. The signs and symptoms observed in experimental animals exposed to cy- clodiene insecticides include: hypothyroidism, porphyria, hypertension, myocarditis, neurotoxic- Ž ity and estrogenic effects see reviews by Naqvi . and Vaishnavi, 1993; Stevenson et al., 1999 , but the principal molecular mechanism involved in these processes is still unclear. Ž . Bagchi and colleagues 1992 proved that the toxicity of endrin, one of the most toxic of cyclo- 1532-045601$ - see front matter  2001 Elsevier Science Inc. All rights reserved. Ž . PII: S 1 5 3 2 - 0 4 5 6 01 00257-5