Biochemical changes in sciatic nerve of hens treated with tri-o-cresyl phosphate: increased phosphorylation of cytoskeletal proteins

Sex-Based Differences in Plasma Autoantibodies to Central Nervous System Proteins in Gulf War Veterans versus Healthy and Symptomatic Controls

Veterans from the 1991 Gulf War (GW) have suffered from Gulf War illness (GWI) for nearly 30 years. This illness encompasses multiple body systems, including the central nervous system (CNS). Diagnosis and treatment of GWI is difficult because there has not been an objective diagnostic biomarker. Recently, we reported on a newly developed blood biomarker that discriminates GWI from GW healthy controls, and symptomatic controls with irritable bowel syndrome (IBS) and myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS). The present study was designed to compare levels of these biomarkers between men and women with GWI, as well as sex-specific effects in comparison to healthy GW veterans and symptomatic controls (IBS, ME/CFS). The results showed that men and women with GWI differ in 2 of 10 plasma autoantibodies, with men showing significantly elevated levels. Men and women with GWI showed significantly different levels of autoantibodies in 8 of 10 biomarkers to neuronal and glial proteins in plasma relative to controls. In summary, the present study addressed the utility of the use of plasma autoantibodies for CNS proteins to distinguish among both men and women veterans with GWI and other healthy and symptomatic control groups.

Common Structural Lesions of the Peripheral Nervous System

This review illustrates common lesions of peripheral nerve myelinated fibers that occur in toxic neuropathy. These distinctive structural changes help to define the site of toxicant activity and thus predict the course of neurotoxic disease and recovery. Neuronopathy is the condition where the primary injury is directed to the neuronal cell body giving rise to a peripheral nerve axon. Axonopathy occurs when the axon is the primary target, and myelinopathy develops where the Schwann cell and/or myelin sheath is the primary target; these conditions can be discriminated early during the course of nerve fiber degeneration, but reciprocal influences between axon and myelin result in degeneration of both structures late in the disease.

Sarin (GB, O-isopropyl methylphosphonofluoridate) neurotoxicity: critical review

Sarin (GB, O-isopropyl methylphosphonofluoridate) is a potent organophosphorus (OP) nerve agent that inhibits acetylcholinesterase (AChE) irreversibly. The subsequent build-up of acetylcholine (ACh) in the central nervous system (CNS) provokes seizures and, at sufficient doses, centrally-mediated respiratory arrest. Accumulation of ACh at peripheral autonomic synapses leads to peripheral signs of intoxication and overstimulation of the muscarinic and nicotinic receptors, which is described as "cholinergic crisis" (i.e. diarrhea, sweating, salivation, miosis, bronchoconstriction). Exposure to high doses of sarin can result in tremors, seizures, and hypothermia. More seriously, build-up of ACh at neuromuscular junctions also can cause paralysis and ultimately peripherally-mediated respiratory arrest which can lead to death via respiratory failure. In addition to its primary action on the cholinergic system, sarin possesses other indirect effects. These involve the activation of several neurotransmitters including gamma-amino-butyric acid (GABA) and the alteration of other signaling systems such as ion channels, cell adhesion molecules, and inflammatory regulators. Sarin exposure is associated with symptoms of organophosphate-induced delayed neurotoxicity (OPIDN) and organophosphate-induced chronic neurotoxicity (OPICN). Moreover, sarin has been involved in toxic and immunotoxic effects as well as organophosphate-induced endocrine disruption (OPIED). The standard treatment for sarin-like nerve agent exposure is post-exposure injection of atropine, a muscarinic receptor antagonist, accompanied by an oxime, an AChE reactivator, and diazepam.

Assessment of neurotoxic effects of tri-cresyl phosphates (TCPs) and cresyl saligenin phosphate (CBDP) using a combination of in vitro techniques

Environmental exposures to tri-cresyl phosphates (TCPs) and the possible formation of toxic metabolites (e.g. cresyl saligenin phosphate; CBDP) may cause a variety of neurotoxic effects in humans. As reported for other organophosphorus compounds (OPs), the inhibition of acetylcholine esterase (AChE) has also been proposed as the underlying mechanism for TCP neurotoxicity. The ortho-isomer, ToCP and its metabolite CBDP are also known to affect neuropathy target esterase (NTE) leading to organophosphate-induced delayed neuropathy (OPIDN). Recently, in vitro testing has led to the identification of other molecular targets and alternative mechanisms of ToCP toxicity. The metabolite CBDP and other isomers, as well as commercial mixtures have not been tested for such additional modes of actions. Accordingly, the present study investigates alterations of neurobiological correlates of central nervous processes using different in vitro techniques. The three symmetric TCP isomers - ToCP, TpCP, and TmCP - that contain a methyl group at the ortho-, para-, or meta-position of the aromatic ring system, respectively, together with a commercial TCP mixture, and CBDP were all tested using concentrations not exceeding their cytotoxic concentrations. Isolated cortical neurons were kept in culture for 6days followed by 24h incubation with different concentrations of the test compounds. Thus, all endpoints were assessed after 7days in vitro (DIV 7), at which time cell viability, neurite microstructure, and the function of glutamate receptors and voltage-gated calcium cannels (VGCC) were measured. While the cytotoxic potential of the TCP isomers and their mixture were comparable (IC₅₀≥80μM), CBDP was more cytotoxic (IC₅₀: 15μM) to primary cortical neurons. In contrast, CBDP (up to 10μM) did not compromise the microstructure of neurites. Ten μM of ToCP significantly reduced the size and complexity of neurite networks, but neither TmCP and TpCP nor the mixture affected this second endpoint of neurotoxicity assessment. TCPs and their mixture significantly reduced the Ca²⁺ influx in response to glutamate and KCl stimulation in concentrations of 10μM. Only ToCP showed a specific effect on glutamate receptors with 100nM reducing the evoked Ca²⁺ influx. The effects of CBDP on the provoked Ca²⁺ influx were much weaker than those observed for TCPs. These results confirmed that ToCP has a unique mode of action on glutamate receptors that are not observed with the metabolite CBDP and the other symmetric TCP isomers. In addition, the TmCP isomer seems to have the lowest potency with respect to inducing neurotoxic effects. CBDP did not affect the neurospecific endpoints investigated in this study. Therefore, the specific affinity of CBDP for NTE and the reported general cytotoxicity might be the most relevant modes of action of this toxic metabolite in the context of ToCP-induced neurotoxicity, including OPIDN.

Identification of differentially expressed proteins related to organophosphorus-induced delayed neuropathy in the brains of hens

Some organophosphorus compounds can cause organophosphate-induced delayed neuropathy (OPIDN). Incidents have been documented for decades, however, little is known about which proteins contribute to the initiation, progression and development of OPIDN. In this study, 51 hens were divided into three groups. The tri-ortho-cresyl-phosphate (TOCP) group was treated with 1000 mg kg(-1) TOCP whereas the control group was treated with an equivalent volume of vehicle. The PMSF + TOCP group was treated subcutaneously with 40 mg kg(-1) phenylmethylsulfonyl fluoride (PMSF), followed by 1000 mg kg(-1) TOCP 24 h later. Proteins in the brains of hens were separated by two-dimensional polyacrylamide gel electrophoresis on day 5 after TOCP administration. Mass spectrometry identified eight differentially expressed proteins. Among these proteins, downregulated expression of glutamine synthetase (GS) in the brains of hens after TOCP treatment was further confirmed by real time RT-PCR and ELISA. Moreover, the brains of hens exposed to TOCP exhibited increased levels of glutamate (Glu) and cytosolic calcium concentration ([Ca(2+)](i)), and a decreased level of glutamine (Gln). However, there were no significant differences in GS expression or levels of Glu, Gln, and [Ca(2+)](i) in the brains of hens among the groups on day 21 after TOCP administration. These results indicate that TOCP exposure downregulates GS expression in the brains of hens, and that downregulation of GS is accompanied by increased levels of Glu and [Ca(2+)](i) in the early stage after TOCP administration. It is also suggested that the downregulated expression of GS might be associated with OPIDN through the disruption of homeostasis of the Glu-Gln cycle and [Ca(2+) ](i).

Autoantibodies to nervous system-specific proteins are elevated in sera of flight crew members: biomarkers for nervous system injury

This descriptive study reports the results of assays performed to detect circulating autoantibodies in a panel of 7 proteins associated with the nervous system (NS) in sera of 12 healthy controls and a group of 34 flight crew members including both pilots and attendants who experienced adverse effects after exposure to air emissions sourced to the ventilation system in their aircrafts and subsequently sought medical attention. The proteins selected represent various types of proteins present in nerve cells that are affected by neuronal degeneration. In the sera samples from flight crew members and healthy controls, immunoglobin (IgG) was measured using Western blotting against neurofilament triplet proteins (NFP), tubulin, microtubule-associated tau proteins (tau), microtubule-associated protein-2 (MAP-2), myelin basic protein (MBP), glial fibrillary acidic protein (GFAP), and glial S100B protein. Significant elevation in levels of circulating IgG-class autoantibodies in flight crew members was found. A symptom-free pilot was sampled before symptoms and then again afterward. This pilot developed clinical problems after flying for 45 h in 10 d. Significant increases in autoantibodies were noted to most of the tested proteins in the serum of this pilot after exposure to air emissions. The levels of autoantibodies rose with worsening of his condition compared to the serum sample collected prior to exposure. After cessation of flying for a year, this pilot's clinical condition improved, and eventually he recovered and his serum autoantibodies against nervous system proteins decreased. The case study with this pilot demonstrates a temporal relationship between exposure to air emissions, clinical condition, and level of serum autoantibodies to nervous system-specific proteins. Overall, these results suggest the possible development of neuronal injury and gliosis in flight crew members anecdotally exposed to cabin air emissions containing organophosphates. Thus, increased circulating serum autoantibodies resulting from neuronal damage may be used as biomarkers for chemical-induced CNS injury.

Expression changes of neurofilament subunits in the central nervous system of hens treated with tri-ortho-cresyl phosphate (TOCP)

Tri-ortho-cresyl phosphate (TOCP) could induce degeneration of long, large diameter axons within the central and peripheral nervous system of susceptible species including human being and hens, which is referred to as organophosphorus-ester induced delayed neuropathy (OPIDN). The mechanisms involved are not understood. Neuropathologic observations suggested that neurofilament subunits (NFs) could be a main target of TOCP in the peripheral nervous system. Our previous study also showed that NFs in protein levels significantly decreased in sciatic nerves of hens treated with TOCP. In this study, to determine whether the decrement of NFs proteins in sciatic nerves was due to reductions in NF gene expression or protein degradation, hens were treated with a single dose of 750 mg/kg body weight TOCP by gavage, and sacrificed on 21 day post-exposure. Cerebral cortexes and spinal cords were sampled. Transcriptional changes of NFs including high molecular weight neurofilament (NF-H), middle molecular weight neurofilament (NF-M), low molecular weight neurofilament (NF-L), and glyceraldehydes-3-phoaphate dehydrogenase (GAPDH) as inner inference in cerebral cortexes and spinal cords were analyzed by semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR). Results showed that all of three NFs mRNA in cerebral cortexes down-regulated significantly. However, in spinal cords, there was only NF-M decreased, both of NF-H and NF-L kept unaffected. The protein levels of NFs in pellet and supernatant fractions of cerebral cortexes and spinal cords were also determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and immunoblotting. We noticed that all NFs protein declined in pellet of cerebral cortexes, but NF-M reduction was not significant compared with that of control hens. NF-H and NF-M proteins in supernatant of cerebral cortexes exhibited significant increase, while NF-L level showed remarkable decline. In spinal cords, apart from NF-L in pellet were significantly increased, both of NF-H and NF-M in pellet and supernatant, as well as NF-L in supernatant fractions were manifested dramatic reduction compared with the pattern of control. The quantitative analyses revealed that the change magnitude in protein levels was much greater than that in mRNA levels in hens' central nervous system after TOCP administration. These findings suggest that the NFs disturbance in protein levels is closely associated with the decreases in sciatic nerves observed in our previous work after TOCP exposure, rather than that in mRNA levels, and the NFs alterations in protein levels may be one of the responsible factors for the OPIDN.

Neuropathological studies of rats following multiple exposure to tri-ortho-tolyl phosphate, chlorpyrifos and stress

Adult male Long-Evans rats were exposed to 2 neurotoxic organophosphates in a setting of chronic stress, over a 63-day period. The organophosphates were tri-ortho-tolyl phosphate (TOTP) administered in 14 gavage doses of 75, 150 or 300 mg/kg, and chlorpyrifos, given in two 60 mg/kg subcutaneous exposures. Corticosterone was added to the drinking water at 400 microg/ml, to model aspects of chronic stress. These compounds/dosages were administered individually and in combination, with appropriate controls, giving rise to 16 experimental groups. The major neuropathologic change was the presence of axonal degeneration progressing to myelinated fiber degeneration, mainly in distal regions of selected fiber tracts and peripheral nerve, seen in animals sacrificed on experimental day 63. The cervical spinal cord and medullary levels of the sensory gracile fasciculus were most prominently affected. This axonopathy/fiber degeneration was TOTP dose-related at the 300 and 150 mg/kg levels. There was association of this lesion with inhibition of the enzyme neurotoxic esterase in hippocampal tissue from TOTP-treated rats. Such an association categorizes this disease process as organophosphate ester-induced delayed neuropathy. Neither chlorpyrifos nor corticosterone appeared to contribute to the neuropathic events or the enzyme inhibition. A cohort of rats was maintained on the corticosterone dosing, but without additional exposure to TOTP or chlorpyrifos, for an additional 27 days. When these rats were examined on day 90, the nerve fiber degeneration had progressed in all experimental groups administered the 300 mg/kg dose of TOTP (lower doses were not studied at the 90-day interval), although hippocampal neurotoxic esterase had returned to control values.

Mechanisms of toxic injury in the peripheral nervous system: neuropathologic considerations

The anatomical distribution and organization of the peripheral nervous system as well as its frequent ability to reflect neurotoxic injury make it useful for the study of nerve fiber and ganglionic lesions. Contemporary neuropathologic techniques provide sections with excellent light-microscopic resolution for use in making such assessments. The histopathologist examining such peripheral nerve samples may see several patterns of neurotoxic injury. Most common are axonopathies, conditions in which axonal alterations are noted; these axonopathies often progress toward the Wallerian-like degeneration of affected fibers. These are usually more severe in distal regions of the neurite, and they affect both peripheral and central fibers. Examples of such distal axonopathies are organophosphorous ester-induced delayed neuropathy, hexacarbon neuropathy, and p-bromophenylacetylurea intoxication. These axonopathies may have varying pathologic features and sometimes have incompletely understood toxic mechanisms. In such neuropathies with fiber degeneration, peripheral nerve axons may regenerate, which can complicate pathologic interpretation of neurotoxicity. On occasion neurotoxins elicit more severe injury in proximal regions of the fiber (not included in this review). Axonal pathology is also a feature of the neuronopathies, toxic states in which the primary injuries are found in neuronal cell bodies. This is exemplified by pyridoxine neurotoxicity, where there is sublethal or lethal damage to larger cytons in the sensory ganglia, with failure of such neurons to maintain their axons. Lastly, one may encounter myelinopathies, conditions in which the toxic effect is on the myelin-forming cell or sheath. An example of this is tellurium intoxication, where demyelination noted in young animals is coincident with toxin-induced interference of cholesterol synthesis by Schwann cells. In this paper, the above-noted examples of toxic neuropathy are discussed, with emphasis on mechanistic and morphologic considerations.

Tau phosphorylation by diisopropyl phosphorofluoridate (DFP)-treated hen brain supernatant inhibits its binding with microtubules: role of Ca2+/Calmodulin-dependent protein kinase II in tau phosphorylation

Diisopropyl phosphorofluoridate (DFP) produces organophosphorus ester-induced delayed neurotoxicity (OPIDN) in hen, human, and other sensitive species. This is characterized by mild ataxia, which progresses to severe ataxia or paralysis in a few days. Ultrastructurally, OPIDN is associated with the degeneration of axons in central and peripheral nervous systems. Bacterially expressed longest human tau protein (htau40) phosphorylated by DFP-treated hen brain supernatant showed a decrease in microtubule binding in a shorter time than that phosphorylated by control hen brain supernatant. The decrease in htau40-microtubule binding observed on htau40 phosphorylation by the recombinant Ca2+/calmodulin (CaM)-dependent protein kinase II (CaM kinase II) alpha-subunit showed that CaM kinase II present in brain supernatant could participate in tau phosphorylation even in the absence of Ca2+/CaM and decrease tau-microtubule binding. In addition, use of htau40 mutants, htau40m1 (Ala416) and htau40m6 (Asp416), suggested that replacement of Ser416 by neutral or acidic amino acid produced some change in htau40 conformation that caused diminished binding with microtubules phosphorylated by brain supernatant in the presence of ethylene glycol bis(beta-aminoethyl ether) N, N'tetraacetic acid (EGTA). The change in conformation produced by Ser416 phosphorylation, however, was different from that produced by mutants since only nonmutated htau40 showed a significant decrease in binding with microtubules on phosphorylation by recombinant CaM kinase II in the presence of Ca2+/CaM compared to that obtained by phosphorylation in the presence of EGTA. This study showed that enhanced Ca2+/CaM-dependent protein kinase activity in DFP-treated hen brain supernatant may cause decreased tau-microtubule binding and destabilization of microtubules and may be involved in axonal degeneration in OPIDN.

Tau proteins-enhanced Ca2+/calmodulin (CaM)-dependent phosphorylation by the brain supernatant of diisopropyl phosphorofluoridate (DFP)-treated hen: tau mutants indicate phosphorylation of more amino acids in tau by CaM kinase II

Diisopropyl phosphorofluoridate (DFP) produces organophosphorus ester-induced delayed neurotoxicity (OPIDN) in hen, human, and other sensitive species. A single dose of DFP (1.7 mg/kg, s.c.) produces mild ataxia in 7-14 days in hens, followed by progression to severe ataxia or paralysis. We studied the effect of DFP administration on Ca2+/calmodulin-dependent phosphorylation of tau proteins by the brain supernatants of control and DFP-treated hens. Brain supernatants from DFP-treated hens showed enhanced in vitro phosphorylation of htau40 and its various mutants, but no change in the two-dimensional phosphopeptide pattern, when compared to control hen brain supernatants. Analysis of tau mutants phosphorylated by brain supernatant and recombinant CaM kinase II alpha-subunit showed that (1) brain supernatant CaM kinase II is mainly responsible for the phosphorylation of Ser416, (2) Ser356, but probably not Ser262, is phosphorylated by CaM kinase II, (3) no amino acid between Lys395-Ala437 except Ser416 is phosphorylated by CaM kinase II, (4) a number of amino acids in the tau molecule, which are phosphorylated by the brain supernatant in the absence of Ca2+/calmodulin are also mildly phosphorylated by CaM kinase II. The enhanced Ca2+/calmodulin-dependent phosphorylation of tau proteins by brain supernatant of DFP-treated hens that includes phosphorylation of a number of amino acids is likely to alter the functional properties of tau proteins in OPIDN. The hyperphosphorylated tau may destabilize microtubules, alter axonal transport, and result in degeneration of axons in OPIDN.

cDNA cloning and sequencing of Ca2+/calmodulin-dependent protein kinase IIalpha subunit and its mRNA expression in diisopropyl phosphorofluoridate (DFP)-treated hen central nervous system

Diisopropyl phosphorofluoridate (DFP) produces delayed neurotoxicity, known as organophosphorus ester-induced delayed neurotoxicity (OPIDN), in hen, human, and other sensitive species. A single dose of DFP (1.7 mg/kg, se.) produces first mild ataxia followed by paralysis in 7-14 days in hens. DFP treatment also increases in vitro autophosphorylation of Ca2+ calmodulin-dependent protein kinase II (CaM kinase II) and the phosphorylation of several cytoskeletal proteins in the hen brain. To investigate whether increase in CaM kinase II activity is associated with increased expression of its mRNA, we cloned and sequenced CaM kinase II alpha subunit cDNA, and used it to study CaM kinase II expression in brain regions and spinal cord. Hen CaM kinase II alpha subunit differs in 7 amino acids from that of rat CaM kinase II. Its mRNA occurs predominantly as a 6.7 kb message, which is very close to that of human CaM kinase II alpha subunit. Northern blot analysis showed a transient increase in CaM kinase II alpha subunit mRNA in the cerebellum and spinal cord of DFP-treated chickens. The increase in CaM kinase II mRNA expression is consistent with the previously reported increase in its activity in brain and spinal cord, and its increased expression only in cerebellum and spinal cord, which are sensitive to the Wallerian-type degeneration characteristic of OPIDN, suggests the probable role of this enzyme in delayed neurotoxicity.

Activation of NMDA receptors and Ca2+/calmodulin-dependent protein kinase participate in phosphorylation of neurofilaments induced by protein kinase C

Aberrant phosphorylation of neurofilaments, similar to that occurring in various motor neuron diseases, is produced in cultured motor neurons by activation of protein kinase C (PKC). Following exposure to synthetic diacylglycerol, persistent change in the phosphorylation state of C-terminal domains of neurofilament proteins was detected by increased perikaryal immunoreactivity with the antibody SMI34; this antibody recognizes NF-M/NF-H when C-terminal KSP repeat domains are highly phosphorylated. SMI34 labeling of perikarya and dendrites was prevented by pretreatment with either the NMDA receptor antagonist APV or by the Ca2+/calmodulin-dependent protein kinase (CaMK) inhibitor KN-62, but not by antagonists of AMPA/kainate or metabotropic glutamate receptors or by inhibitors of arachidonic acid metabolic pathways. Thus, activation of PKC may induce neurofilament phosphorylation in motor neurons by acting in cooperation with stimulation of NMDA receptors and activation of CaMK. These mechanisms may be relevant to motor neuron disease and other neuronal injuries in which increased PKC activity has been measured.

Alteration in neurofilament axonal transport in the sciatic nerve of the diisopropyl phosphorofluoridate (DFP)-treated hen

Diisopropyl phosphorofluoridate (DFP) is an organophosphorus ester that produces organophosphorus ester-induced delayed neurotoxicity (OPIDN) in hens 7-14 days after a single s.c. dose of 1.7 mg/kg. In this study, hens were treated with a single dose of DFP (1.7 mg/kg, s.c.) 24 hr after [35S]methionine injection into the sacrolumbar region of their spinal cord, and killed 3, 7, 14, or 27 days post-DFP treatment. The rates of transport of labeled high (NF-H), medium (NF-M), and low (NF-L) molecular weight neurofilaments, and tubulin were faster in DFP-treated birds than in controls after 3 days. Subsequently, the rate of transport of these proteins started falling, so that the peaks of labeled proteins in control and DFP-treated hens were overlapping after 7 days. At 14 days, the peaks of NF-H, NF-M, and NF-L in treated hens were distinctly behind the corresponding peaks in control hens. This was again followed by an increase in transport of NF-H and NF-L, but not of NF-M, so that the labeled NF-H and NF-L showed the same pattern in control and treated hens after 27 days. The transient decrease in NF-H and NF-L axonal transport rate, and recovery correlated in a temporal manner with the previously reported increase of Ca2+/calmodulin-dependent protein kinase-mediated phosphorylation of neurofilament proteins and inhibition of calpain activity in the sciatic nerve in OPIDN. Proteinase inhibition has been reported recently to result in enhanced phosphorylation of neurofilaments in some cells. The present study suggests that the enhanced phosphorylation of neurofilaments by DFP-increased Ca2+/calmodulin-dependent protein kinase activity may be contributing toward alteration in NF axonal transport and the development of OPIDN.

Protein phosphorylation in human peripheral nerve: altered phosphorylation of a 25-kDa glycoprotein in leprosy

Protein phosphorylation in a low speed supernatant of human peripheral nerve (tibial and sural) homogenate was investigated. The major phosphorylated proteins had molecular mass in the range of 70, 55, 45, and 25 kDa. Mg2+ or Mn2+ was essential for maximum phosphorylation although Zn2+, Co2+, and Ca2+ could partially support phosphorylation. External protein substrates casein and histone were also phosphorylated. The protein phosphatase inhibitor orthovanadate enhanced the phosphorylation of the 45 and 25 kDa proteins significantly. Concanavalin A-Sepharose chromatography of the phosphorylated peripheral nerve proteins showed that the 25 kDa protein was a glycoprotein. Protein phosphorylation of peripheral nerves from leprosy affected individuals was compared with normals. The phosphorylation of 25 kDa protein was decreased in most of the patients with leprosy.

Neurofilament phosphorylation and [125I]calmodulin binding by Ca2+/calmodulin-dependent protein kinase in the brain subcellular fractions of diisopropyl phosphorofluoridate (DFP)-treated hen

Diisopropyl phosphorofluoridate (DFP) produces organophosphorus ester-induced delayed neurotoxicity (OPIDN) in humans and sensitive animal species, e.g., adult chicken. The chickens were sacrificed 18 days after a single dose of DFP (1.7 mg/kg, s.c.), which produced severe ataxia or paralysis in 10-14 days. We studied Ca2+/calmodulin-dependent in vitro neurofilament phosphorylation by the brain subcellular fractions of control and DFP-treated hens. There was enhanced phosphorylation of all three NF subunits by the brain supernatant of treated hens. This was accompanied by enhanced autophosphorylation of both Ca2+/CaM-dependent protein kinase II (CaM-kinase II) subunits and increased calmodulin binding using either 125I-CaM or biotinylated calmodulin to only alpha subunit without concomitant increase in the amount of this enzyme. This enhanced phosphorylation of neurofilament subunits was completely and partially inhibited by mastoparan and KN-62, respectively. There was no alteration in the distribution of CaM-kinase II activity in treated hens and the activity was not related to its concentration in different subcellular fractions. The difference in 125I-CaM binding to CaM-kinase II alpha subunit in the brain supernatants of control and DFP-treated hens was not altered by its phosphorylation or dephosphorylation. The increased CaM-kinase II activity in the soluble fraction of DFP-treated hen brain may be involved in the aberrant phosphorylation of axonal neurofilaments, and thus play a role in OPIDN.

The cytoskeleton as a target for organophosphorus ester-induced delayed neurotoxicity (OPIDN)

Although the immediate action of organophosphorus esters is the inhibition of acetylcholinesterase, some of these compounds also produce a neurodegenerative disorder known as organophosphorus ester-induced delayed neurotoxicity (OPIDN). Tri-o-cresyl phosphate (TOCP) first produced this condition in humans and later in sensitive animal species. OPIDN is characterized by a delay period prior to onset of ataxia and paralysis. The neuropathologic lesions are Wallerian-type degeneration of the axon and myelin in the distal parts of the large tracts in both the central and peripheral nervous systems. In the past decade we have demonstrated that the pathognomonic features of OPIDN are an aberrant increase in autophosphorylation of calcium/calmodulin kinase II (CaM kinase II) and an increase in phosphorylation of cytoskeletal proteins, i.e., MAPs, tubulin, neurofilament triplet proteins, and myelin basic protein. Protein kinase-mediated phosphorylation of cytoskeletal proteins plays a critical role in regulating the growth and maintenance of the axon. We hypothesize that, in OPIDN, hyperphosphorylation of cytoskeletal proteins and axonal swelling are causally linked. Hyperphosphorylation of cytoskeletal proteins decreases their transport rate down the axon relative to their rate of entry into the axon, thus leading to their accumulation. Consistent with this hypothesis is our finding of the anomalous accumulation of phosphorylated neurofilament aggregates in the central and peripheral axons of hens treated with TOCP.

Enhanced calmodulin binding concurrent with increased kinase-dependent phosphorylation of cytoskeletal proteins following a single subcutaneous injection of diisopropyl phosphorofluoridate in hens

Diisopropyl phosphorofluoridate (DFP) produces Type I organophosphorus compound-induced delayed neurotoxicity (OPIDN) in adult female chickens. We have proposed that calcium/calmodulin protein kinase II (CaM kinase II) plays a role in the development of OPIDN by increasing the phosphorylation of cytoskeletal proteins. We investigated in vivo the effects of treatment of DFP on CaM kinase II-dependent phosphorylation. In isolated brain supernatants from DFP-treated hens, calmodulin binding increased concurrent with increases in CaM kinase II-dependent autophosphorylation and phosphorylation of cytoskeleton proteins. There were no changes in the relative amounts of the enzyme based on immunobinding studies of antibodies to the CaM kinase II. In the absence of any exogenously added substrate. CaM kinase II and microtubule associated protein-2 (MAP-2) exhibited substantially increased phosphorylation, 833 and 275%, respectively, over brain supernatants from untreated hens. Moreover, isolated brain supernatants from treated hens with exogenously added cytoskeletal proteins and myelin basic protein (MBP) exhibited significant increases in phosphorylation over control, 233, 332 and 60%, for MAP-2, tubulin, and MBP, respectively. 125I-Calmodulin binding studies revealed a 136% increase in calmodulin binding to CaM kinase II in treated hens when compared to control groups. The data suggest that in vivo DFP treatment increases the percentage of unphosphorylated, active CaM kinase II resulting in increased calmodulin binding and subsequent enhanced phosphorylation of cytoskeletal proteins that leads to their aggregation and the production of axonal degeneration.