β‐Oxidation of [1‐¹⁴C]palmitic acid by mouse astrocytes in primary culture: Effects of agents implicated in the encephalopathy of Reye's syndrome

β‐Oxidation of [1‐¹⁴C]palmitic acid was examined in homogenates of astrocytes cultured from neonatal mouse brain. Under optimal reaction conditions (≤50 μg protein, 10 min at 37°C), oxidation increased as a function of palmitate concentration (15 μM to 2 mM) and reached a maximum rate of 1.98 ± 0.29 nmol/min/mg protein (mean ± SEM) at 0.2 mM substrate. Eadie‐Hofstee analysis of data from four experiments yielded apparent values for V_max of 1.87 nmol/min/mg protein, and for K_m, 35–40 μM. There were no dramatic changes in the oxidation rate in cells between 10 and 36 days in culture. During the 10‐min assays, less than 0.05% of the radioactivity was converted to ¹⁴CO₂ by the astrocytes; water‐soluble products accounted for 1–2% of the total substrate added. Studies with KCN indicated that 60–70% of the total activity occurred in the mitochondria. We have been studying the structural and functional changes associated with the cerebral encephalopathy of Reye's syndrome (RS). Three‐week‐old astrocytes exposed to serum from RS children for the final 7 days of culture exhibited minor mitochondrial pleomorphism and had increased numbers of other intracellular organelles. Examination of the effects of agents implicated in RS indicated that oxidation of [1‐¹⁴C]palmitate was not altered by Na⁺ salicylate (1–3 mM), but was inhibited by the industrial surfactant, Toximul MP‐8 (≥10 μg/ml), 4‐pentenoic acid (≥01 μM), or with 4 days' exposure to ammonia (10 mM). The latter treatment also resulted in an increase in protein synthesis, cell volume, and malondialdehyde formation. These results suggest that some of the “toxins” implicated in RS inhibit fattyacid oxidation in the astrocytes and produce other lipid‐related abnormalitities that could be related to encephalopathy. © Wiley‐Liss, Inc.