The effect of aliphatic, naphthenic, and aromatic hydrocarbons on production of reactive oxygen species and reactive nitrogen species in rat brain synaptosome fraction: the involvement of calcium, nitric oxide synthase, mitochondria, and phospholipase A

Citation
O. Myhre et F. Fonnum, The effect of aliphatic, naphthenic, and aromatic hydrocarbons on production of reactive oxygen species and reactive nitrogen species in rat brain synaptosome fraction: the involvement of calcium, nitric oxide synthase, mitochondria, and phospholipase A, BIOCH PHARM, 62(1), 2001, pp. 119-128
Citations number
80
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Pharmacology & Toxicology
Journal title
BIOCHEMICAL PHARMACOLOGY
ISSN journal
0006-2952 → ACNP
Volume
62
Issue
1
Year of publication
2001
Pages
119 - 128
Database
ISI
SICI code
0006-2952(20010701)62:1<119:TEOANA>2.0.ZU;2-X
Abstract
This study investigated the effects of C7 and C9 aliphatic (n-heptane, n-no nane), naphthenic (methylcyclohexane, 1,2,4-trimethylcyclohexane (TMCH)) an d aromatic (toluene, 1,2,4-trimethylbenzene (TMB)) hydrocarbons on the prod uction of reactive oxygen species (ROS) and reactive nitrogen species (RNS) in rat brain synaptosome fraction. Methyl mercury (MeHg) was included as a positive control. Exposure of the synaptosomes to the hydrocarbons produce d a concentration-dependent linear increase in the formation of the fluores cence of 2',7'-dichlorofluorescein (DCF) as a measure of the production of ROS and RNS. Formation of RNS was demonstrated by preincubation of the syna ptosome fraction with the neuronal nitric oxide synthase (nNOS) inhibitor N omega -nitro-L-arginine methyl ester (L-NAME), which reduced the MeHg and TMCH-stimulated fluorescence by 51% and 65%, respectively. The naphthenic h ydrocarbon TMCH showed the strongest potential for ROS and RNS formation in rat brain synaptosomes, followed by TMB, toluene, n-nonane, n-heptane, and methylcyclohexane, respectively. TMCH was selected for mechanistic studies of the formation of ROS. Both MeHg and TMCH induced an increase in intrace llular calcium concentration [Ca2+](i) as measured with Fura-2. Blockade of voltage-dependent Ca2+ channels with lanthanum prior to stimulation with M eHg and TMCH led to a reduction in the ROS/RNS formation of 72% and 70%, re spectively. Furthermore, addition of cyclosporin A (CSA), a blocker of the mitochondrial permeability transition pore (MTP), lowered both the MeHg and TMCH-elevated DCF fluorescence by 72% and 59%. Preincubation of the synapt osome fraction with the protein tyrosine kinase inhibitor genistein lowered the MeHg and TMCH-stimulated fluorescence by 85% and 91%, respectively. Ad dition of the extracellular signal-regulated protein kinase (MEK)-1 and -2 inhibitor U0126 reduced the fluorescence stimulated by MeHg and TMCH by 62% and 63%. Furthermore, the protein kinase C inhibitor bisindolylmaleimide r educed the fluorescence stimulated by MeHg and TMCH by 52% and 56%. The com pound 1-(6-[17beta-3-methoxyestra-1,3,5(10)-trien-17-yl]-aminohexyl)-1H-pyr role-2,5-dione (U73122), which inhibits phospholipase C, was shown to decre ase the ROS and RNS formation induced by MeHg and TMCH by 49% and 64%, resp ectively. The phospholipase A(2) (PLA(2)) inhibitor 7,7-dimethyl eicosadien oic acid (DEDA) reduced fluorescence in response to MeHg and TMCH by 49% an d 54%. Simultaneous addition of L-NAME, CSA, and DEDA to the synaptosome fr action totally abolished the DCF fluorescence. In conclusion, C7 and C9 ali phatic, naphthenic, and aromatic hydrocarbons stimulated formation of ROS a nd RNS in rat brain synaptosomes. The naphthenic hydrocarbon TMCH stimulate d formation of ROS and RNS in the synaptosomes through Ca2+-dependent activ ation of PLA(2) and nNOS, and through increased transition permeability of the MTP. Exposure of humans to the naphthenic hydrocarbon TMCH may stimulat e formation of free radicals in the brain, which may be a key factor leadin g to neurotoxicity. (C) 2001 Elsevier Science Inc. All rights reserved.