Protein levels of neurofilament subunits in the hen central nervous system following prevention and potentiation of diisopropyl phosphorofluoridate (DFP)-induced delayed neurotoxicity(1)

Increased oxidative stress is associated with the development of organophosphate-induced delayed neuropathy

Organophosphate-induced delayed neuropathy (OPIDN) is a progressive neuropathic disorder that manifests in days to weeks following exposure to an acute dose of organophosphates. The precise mechanism involved in the development of OPIDN is not clear as it develops after many days of the cessation of cholinergic crisis. The present study has been designed to understand the role of oxidative stress in the development of OPIDN, wherein neuropathy was developed by the administration of acute dose of monocrotophos (MCP) or dichlorvos (2,2-dichlorovinyl dimethyl phosphate (DDVP)) to rats. Significant motor deficits in terms of reduced spontaneous locomotor activity and performance on narrow beam test were observed after 14 days of exposure to MCP or DDVP, which persisted even on day 28, suggesting the development of OPIDN. Rats with OPIDN also exhibited an increase in malondialdehyde levels along with a decrease in thiol content in cerebral cortex, cerebellum and brain stem. Concomitantly, the activities of antioxidant enzymes, superoxide dismutase, catalase, glutathione peroxidase and glutathione reductase were reduced in the three brain regions. The biochemical and functional changes were associated with histological alterations in the brain regions studied. The results clearly indicate that the development of OPIDN is mediated in part through an increased oxidative stress and suggest that the strategies aimed at restoration of antioxidant capacity may be beneficial for the individuals with OPIDN-like symptoms.

Impaired mitochondrial functions in organophosphate induced delayed neuropathy in rats

Acute exposure to organophosphates induces a delayed neurodegenerative condition known as organophosphate-induced delayed neuropathy (OPIDN). The mechanism of OPIDN has not been fully understood as it does not involve cholinergic crisis. The present study has been designed to evaluate the role of mitochondrial dysfunctions in the development of OPIDN. OPIDN was induced in rats by administering acute dose of monocrotophos (MCP, 20 mg/kg body weight, orally) or dichlorvos (DDVP, 200 mg/kg body weight, subcutaneously), 15-20 min after treatment with antidotes [atropine (20 mg/kg body weight) and 2-PAM (100 mg/kg body weight) intraperitoneally]. MDA levels were observed to be higher and thiol content was lower in mitochondria from brain regions of OP exposed animals. This was accompanied by decreased activities of the mitochondrial enzymes; NADH dehydrogenase, succinate dehydrogenase, and cytochrome oxidase. In addition, mitochondrial functions assessed by MTT reduction also confirmed mitochondrial dysfunctions following development of OPIDN. The spatial long-term memory evaluated using elevated plus-maze test was observed to be deficit in OPIDN. The results suggest impaired mitochondrial functions as a mechanism involved in the development of organophosphate induced delayed neuropathy.

Time-dependent changes of lipid peroxidation and antioxidative status in nerve tissues of hens treated with tri-ortho-cresyl phosphate (TOCP)

Tri-ortho-cresyl phosphate (TOCP) could induce a delayed neurodegenerative condition known as organophosphorus easter-induced delayed neurotoxicity (OPIDN) in human beings and sensitive animals. However, the mechanisms of OPIDN remain unknown. This study investigated the time-dependent changes of the lipid peroxidation (malondialdehyde, MDA) and antioxidative status (glutathione, GSH; glutathione peroxidase, GSH-Px; glutathione reductase, GR; superoxide dismutase, SOD and anti-reactive oxygen species, anti-ROS) in nerve tissues for elucidating the mechanism of OPIDN induced by TOCP. Adult hens were treated with TOCP by gavage at a single dosage of 750 mg/kg. TOCP was dissolved in corn oil and administered at 0.65 ml/kg. The control hens received an equivalent volume of corn oil by gavage. Hens were sacrificed after 0, 5, 10, 15 and 21 days of treatment and the cerebrum, spinal cord, sciatic nerve were dissected, homogenized and used for the determination of lipid peroxidation and antioxidative status. The results showed that treatment with TOCP increased lipid peroxidation and reduced the antioxidative status in cerebrum, spinal cord and sciatic nerve. The levels of MDA increased by 33% (P<0.01) in cerebrum on 5th day after TOCP treatment and at clinical sign score of 1-2, and increased respectively by 32% and 15% (P<0.01) in spinal cord and sciatic nerve on 10th day after TOCP treatment and at clinical sign score of 3-4. Further changes of MDA were also observed after 15 and 21 days post-dosing and at clinical sign score of 5-6 and 7-8. There is a decrease in the activities of SOD, GSH-Px, GR, anti-ROS, and GSH content in cerebrum, spinal cord and sciatic nerve of hens after 5, 10, 15 and 21 days post-dosing and at clinical sign score of 1-2, 3-4, 5-6 and 7-8. Thus, OPIDN induced by TOCP was associated with elevation of lipid peroxidation and reduction of antioxidative status, and the time-dependent changes of these indexes in hens nerve tissues occurred. Sciatic nerve was the main target tissue and MDA was most sensitive among all indexes. The time-dependent and tissue specific changes of lipid peroxidation and antioxidative status in cerebrum, spinal cord and sciatic nerve suggest that ROS and concomitant lipid peroxidation, at least in part, are involved in the toxic effects of TOCP on nerve tissues and that oxidative stress may play a role in the occurrence and development of OPIDN induced by TOCP.

Triorthocresyl phosphate-induced neuronal losses in lumbar spinal cord of hens--an immunohistochemistry and ultrastructure study

To investigate the neuronal losses of hens' spinal cords in the model of organophosphate-induced delayed neuropathy (OPIDN) and to analyze the impact of apoptosis on the pathogenesis of OPIDN. Adult hens were challenged with triorthocresyl phosphate (TOCP) at a single dose (750 mg/kg). Neuronal losses in the 3rd lumbar spinal cord (L3) were assessed by light-microscopy and electron-microscopy methods at different days post exposure, respectively. The typical OPIDN signs were seen in the TOCP-exposed hens at about 9th day. The number of large nerve cells declined gradually. And these cells were verified as neurons by immunostained with neuronal marker NeuN. The expression of FasL reached proximal at about 9th day, decreased from 14th day. Neurons in TOCP exposed groups displayed degenerative morphologies in electronic microscopy. Some neurons showed apoptotic-like ultrastructure profiles at 5th day. The nuclear membrane was complete with chromatin condensed to the margins of nuclear membrane like a crescent-shaped body. Mitochondria morphologic changes appeared early (5 d) following exposure to TOCP, and developed in a time-dependent fashion. Apoptosis might be involved in the development of OPIDN, and play a role in the pathogenesis of OPIDN.

Aberrant activation of CDK5 is involved in the pathogenesis of OPIDN

Exposure to triorthocresyl phosphate (TOCP) may result in a late neurological complication, i.e. organophosphate-induced delayed neuropathy (OPIDN). The aim of this study was to examine changes in levels of cyclin-dependent kinase 5 (CDK5) and of its activator, p35/p25, in the spinal cord of hens treated by TOCP. After exposure to a single dose of TOCP, groups of adult hens were examined in 3, 5, 7, 9, 14, and 18 days after exposure. CDK5, p35/p25 expression and distribution in the lumbar spinal cord were evaluated by immunohistochemistry and Western blotting. The hens showed signs of OPIDN around day 9 after exposure. The number of p (phosphorylated) -CDK5 and p35 positive cells increased significantly. Co-localization and mislocalization of p-CDK5 and p35/p25 was identified and became evident in neurons around the 9th day. Meanwhile, CDK5, p-CDK5, p35, p25 protein levels and p25/p35 ratio were increased, and peaked around the 9th day, then decreased. Some hens' unilateral common peroneal was treated by roscovitine 3 days after TOCP exposure. Axonal transport of these nerves was faster than of their opposite side and of those simply treated by TOCP. These findings indicate aberrant activation of CDK5 may be involved in the pathogenesis of OPIDN.

Altered expression of transcripts for ?-tubulin and an unidentified gene in the spinal cord of phenyl saligenin phosphate treated hens (Gallus gallus)

Phenyl saligenin phosphate (PSP) induces a central-peripheral distal axonopathy in domestic fowl that develops 7-21 days after a single exposure. Neurotoxic esterase (NTE) is the initial molecular target for this neurotoxicity. PSP has to covalently bind to NTE and chemically "age" for induction of axonopathy. It was hypothesized that exposure to PSP results in early changes in spinal cord gene expression that do not occur with phenylmethylsulfonyl fluoride, a non-neuropathic compound that also inhibits NTE, or DMSO controls. Targeted display was used to screen approximately 15,000 gel bands. Three candidate genes were identified, but only the transcript designated P1 showed decreased expression following PSP exposure (2 mg/kg i.m.) in subsequent Northern blot and in situ hybridization experiments in samples taken <48 h after exposure. Additional experiments revealed that a approximately 2.5 kb alpha-tubulin transcript had decreased expression at 12-48 h after PSP exposure, with maximum change at 48 h (33%, p = 0.0479). A approximately 4.5 kb alpha-tubulin transcript had increased expression at 12 h (38%, p = 0.0125) and decreased expression at 48 h (28%, p = 0.0576). In situ hybridization on spinal cord revealed neuronal expression of P1 and alpha-tubulin transcripts. Decreased expression of transcripts for P1 and alpha-tubulin was present at 12 and 48 h, respectively. This decrease occurred in all neurons, not just those whose axons degenerate. Results suggest that (1) in PSP-induced OPIDN (organophosphorus-induced delayed neurotoxicity) some gene transcript expression changes are associated with initiation of axonopathy, and (2) PSP modulates spinal cord gene expression in neuronal types that do not undergo axonal degeneration.

The effect of Calcicol as calcium tonic on delayed neurotoxicity induced by organophosphorus compounds

To examine whether delayed neuropathy is prevented or alleviated when Ca is administered to experimental animals before or after organophosphorus compounds (OPs) dosing, we observed the effects of Calcicol administration as a calcium tonic on delayed neurotoxicity by OPs in hens. The hens (n=28) were randomly divided into seven groups (four in each group). One group received glycerol formal as vehicle group, two groups received 30 mg/kg leptophos or 40 mg/kg triortho-cresyl phosphate (TOCP) (L group and T group), two groups received 2.4 mg/kg Ca(2+) (0.3 ml/kg Calcicol) 24 h before leptophos or TOCP administration, and the last two groups received 2.4 mg/kg Ca after leptophos or TOCP administration, respectively. Although delayed polyneuropathy induced by OPs could not be prevented completely by Calcicol, the clinical signs of organophosphorus-induced delayed neuropathy (OPIDN) in hens that received Calcicol soon before or after OPs administration were less severe than those in hens that received only OPs and there were significant differences in OPIDN score between groups (P<0.05). This shows that polyneuropathy and the recovery function of nerves and muscles suffering from polyneuropathy can be alleviated, as long as calcium tonic is administered before the clinical signs develop. This study offers hope of recovery to humans who are exposed to these OPs because of work, attempted suicide, accidental ingestion or other accidents, etc. Meanwhile, our results indicate further that there is a relationship between a decrease in Ca(2+) concentration in tissues and induction of delayed neuropathy.