Effects of organophosphorus compounds on ATP production and mitochondrial integrity in cultured cells

Abstract

Recent studies in vivo and in vitro suggested that mitochondrial dysfunction follows exposure to organophosphorus (OP) esters. As mitochondrial ATP production is important for cellular integrity, ATP production in the presence of OP neurotoxicants was examined in a human neuronal cell line (SH-SY5Y neuroblastoma cells) and primary dorsal root ganglia (DRG) cells isolated from chick embryos and subsequently cultured to achieve maturation with axons. These cell culture systems were chosen to evaluate toxic effects on the mitochondrial respiratory chain associated with exposure to OP compounds that do and do not cause OP-induced delayed neuropathy (OPIDN), a disorder preceded by inhibition of neurotoxic esterase (NTE). Concentration- and time-response studies were done in neuroblastoma cells exposed to phenyl saligenin phosphate (PSP) and mipafox, both compounds that readily induce delayed neuropathy in hens, or paraoxon, which does not. Phenylmethylsulfonyl fluoride (PMSF) was included as a non-neuropathic inhibitor of NTE. Purified neuronal cultures from 9 day-old chick embryo DRG were treated for 12 h with 1 microM PSP, mipafox, or paraoxon. In situ evaluation of ATP production measured by bioluminescence assay demonstrated decreased ATP concentrations both in neuroblastoma cells and chick DRG neurons treated with PSP. Mipafox decreased ATP production in DRG but not in SH-SY5Y cells. This low energy state was present at several levels of the mitochondrial respiratory chain, including Complexes I, II, III, and IV, although Complex I was the most severely affected. Paraoxon and PMSF were not effective at all complexes, and, when effective, required higher concentrations than needed for PSP. Results suggest that mitochondria are an important early target for OP compounds, with exposure resulting in depletion of ATP production. The targeting of neuronal, rather than Schwann cell mitochondria in DRG following exposure to PSP and mipafox was verified by loss of the mitochondrial-specific dye, tetramethylrhodamine, in these cells. No such loss was seen in paraoxon exposed neurons isolated from DRG or in Schwann cells treated with any of the test compounds.

Inhibition of Mitochondrial Respiratory Chain in the Brain of Adult Rats After Acute and Chronic Administration of Methylphenidate

“…Augmented ROS production causes defects in the mitochondrial genome, leading to impaired oxidative phosphorylation, which not only limits ATP generation but also further promotes ROS production [49,50]. Previous works demonstrated an increase in superoxide production due to the inhibition of the respiratory chain complex I after organophosphorus exposure [51]. Moreover, the complex I is the primary source of ROS in a variety of pathological processes [52][53][54].…”

Methyl-parathion decreases sperm function and fertilization capacity after targeting spermatocytes and maturing spermatozoa

“…This result indicates that Me-Pa impairs sperm mitochondrion during their transit through the epididymis. Recent studies suggest that mitochondrion is an important early target for OP compounds resulting in altered ATP production and mitochondrial integrity in cultured neuronal cells (Massicotte et al, 2005). The lack of an effect on MMP at 28 dpt may be due to the fact that structural modifications of many organelles including mitochondria occur during spermatogenesis (Meinhardt et al, 1999); therefore, any change, such as decreased MMP, caused at earlier stages on the testis may not be present at the end of the epididymal maturation.…”

Adverse effects of organophosphorus pesticides on the liver: a brief summary of four decades of research

“…Since, there are limited data about the hepatotoxicity of OPs in humans, it is not certain whether changes in biochemical parameters indicate actual liver damage. (90)(91)(92)(93)(94), energy production (93,(95)(96)(97), and cell death (98)(99)(100). Several studies have found an association between mitochondrial dynamics and malathion-induced drop in mitochondrial ATP synthesis in rat liver (9) or quinalphos and acephate effects on liver succinic dehydrogenase (84,85,101) and ATPase activities (87) -all of them the key enzymes for oxidative phosphorylation.…”