Non-enzymatic lipid peroxidation of rat liver nuclei and chromatin fractions MoÂnica Marmunti, Angel Catala * Ca Âtedra de BioquõÂmica, Facultad de Ciencias Veterinarias, Universidad Nacional de La Plata, CC 296, 1900 La Plata, Argentina Abstract In the study reported here, the non-enzymatic (ascorbate±Fe 2+ ) lipid peroxidation of rat liver nuclei and chromatin fractions was assayed. Chromatin obtained by sonication of nuclei suspended in 0.25 M sucrose was fractionated by dierential sedimentation according to the following scheme: 3000, 12 000 and 27 500g for 10 min each. The lowest density chromatin fraction was obtained by precipitation with cold ethanol of the supernatant obtained from the last centrifugation. Light emission = chemiluminescence, measured as cpm/mg protein, decreased in the order heavy>low density chromatin fractions during the peroxidation process. Analysis of fatty acids by gas chromatography showed that heavy density chromatin fractions are enriched with C20:4 n6 arachidonic acid, when compared with low density chromatin fractions. The amount of arachidonic acid C20:4 n6 was higher in repressed chromatin fractions as compared to the amount in the transcriptionally active chromatin which correlates with the level of lipid peroxidation. # 1998 Elsevier Science Ltd. All rights reserved. Keywords: Lipid-peroxidation; Chemiluminescence; Rat liver nuclei; Chromatin 1. Introduction The lipid peroxidation process in cell nuclei has been the subject of relatively few studies, some of them presenting con¯icting results. The non-enzymatic and enzymatic cell-driven lipid peroxidation processes have been studied in rat liver nuclei and in isolated nuclear membranes, by evaluating the formation of thiobarbituric acid-chromophore, free malondyaldehide, lypo- fuscin-like pigments and the degradation of poly- unsaturated fatty acids of the nuclear membrane lipids [17]. Although the presence of phospholi- pids associated with chromatin, indicated by his- tochemical analysis has been questioned, various biochemical studies have shown the presence of both phospholipids and neutral lipids in chroma- tin isolated from a variety of tissues [2, 10, 12± 16]. In a recent paper from our laboratory [4] it was demonstrated that polar lipids extracted from rat liver nuclei are more susceptible to lipid peroxidation than are neutral lipids. The juxta- position of DNA to the nuclear membrane and the existence of chromatin nuclear membrane attachment sites [6] suggest the possibility that The International Journal of Biochemistry & Cell Biology 30 (1998) 967±972 1357-2725/98/$19.00 # 1998 Elsevier Science Ltd. All rights reserved. PII: S1357-2725(98)00043-0 The International Journal of Biochemistry & Cell Biology PERGAMON * Corresponding author. Fax: +54-21-253-276; E-mail: acatala@fcv.medvet.unlp.edu.ar