Protection and reversal by memantine and atropine of carbofuran-induced changes in biomarkers

Carbofuran in water: Subchronic toxicity to rats

Carbofuran toxicity on rats was studied during subchronic exposure. Female and male rats were administered carbofuran in drinking water in concentrations of 25, 100 and 400ppm for a period of 90 days. Clinical symptoms, water consumption, body weight gain, organ weight, pathological and histopathological changes in the liver and kidneys were observed and biochemical and haematological examinations were carried out. The results obtained show that carbofuran administered to rats caused a significant decrease in water consumption as well as in brain, serum and erythrocyte cholinesterase activities. Statistically significant increases in relation to the control were found in the serum enzyme activities. The haematological data showed that carbofuran had no significant effect on Hb concentration and total RBC, but total WBC showed a significant statistical decrease. The histopathological changes in liver and kidneys were observed. However, cell regeneration in the liver and kidneys was found in all test groups.

Neuronal oxidative injury and dendritic damage induced by carbofuran: protection by memantine

Carbamate insecticides mediate their neurotoxicity by acetylcholinesterase (AChE) inactivation. Male Sprague-Dawley rats acutely intoxicated with the carbamate insecticide carbofuran (1.5 mg/kg, sc) developed hypercholinergic signs within 5-7 min of exposure, with maximal severity characterized by seizures within 30-60 min, lasting for about 2 h. At the time of peak severity, compared with controls, AChE was maximally inhibited (by 82-90%), radical oxygen species (ROS) markers (F(2)-isoprostanes, F(2)-IsoPs; and F(4)-neuroprostanes, F(4)-NeuroPs) were elevated 2- to 3-fold, and the radical nitrogen species (RNS) marker citrulline was elevated 4- to 8-fold in discrete brain regions (cortex, amygdala, and hippocampus). In addition, levels of high-energy phosphates (HEPs) were significantly reduced (ATP, by 43-56%; and phosphocreatine, by 37-48%). Values of total adenine nucleotides and total creatine compounds declined markedly (by 41-56% and 35-45%, respectively), while energy charge potential remained unchanged. Quantitative morphometric analysis of pyramidal neurons of the hippocampal CA1 region revealed significant decreases in dendritic lengths (by 64%) and spine density (by 60%). Pretreatment with the N-methyl-D-aspartate (NMDA) receptor antagonist memantine (18 mg/kg, sc), in combination with atropine sulfate (16 mg/kg, sc), significantly attenuated carbofuran-induced changes in AChE activity and levels of F(2)-IsoPs and F(4)-NeuroPs, declines in HEPs, as well as the alterations in morphology of hippocampal neurons. MEM and ATS pretreatment also protected rats from carbofuran-induced hypercholinergic behavioral activity, including seizures. These findings support the involvement of ROS and RNS in seizure-induced neuronal injury and suggest that memantine by preventing carbofuran-induced neuronal hyperactivity blocks pathways associated with oxidative damage in neurons.

Memantine Alleviates Toxicity Induced by Dichlorvos in Rats

The changes of N-methyl-D-aspartate (NMDA) receptor and protective efficacy of memantine (MEM) in rats poisoned with dichlorvos were studied. Dichlorvos evoked down-regulation of the affinity and density of [(3)H]MK-801 binding to NMDA receptor in the brain of rats receiving dichlorvos (15 and 25 mg/kg bw, i.p.). The binding capacity of NMDA receptor and acetylcholinesterase activity were determined at 4 h, 8 h, 16 h, 24 h and 48 h after treatment. When rats were given a different doses of MEM (5, 15 and 45 mg/kg bw) after poisoning (dichlorvos 25 mg/kg bw), the latency of onset of signs was postponed and the magnitude of muscular fasciculation was alleviated as the dose of MEM increased. The lower doses of MEM (5 and 15 mg/kg bw) could antagonize the dichlorvos-evoked down-regulation of NMDA receptor, while the highest dose (45 mg/kg bw) decreased the Bmax and Kd values of NMDA receptors. These results show the dichlorvos-evoked down-regulation of NMDA receptor might be self-regulation by the body to protect the central nervous system. MEM could antagonize the down-regulation of NMDA receptors, and alleviated signs of poisoning, especially reducing the magnitude of muscular fasciculation. We suggest that the role of NMDA receptor in organophosphates (OP) poisoning should receive more attention, and, that MEM treatment in acute OP poisoning, as a supplement to atropine and oxime, should be considered.

Carbofuran-induced oxidative stress in slow and fast skeletal muscles: prevention by memantine and atropine

Acute toxic effects of acetylcholinesterase (AChE) inhibitors on skeletal muscles are thought to involve oxidative stress with increased generation of free radicals such as reactive oxygen species (ROS) and reactive nitrogen species (RNS). Muscle hyperactivity with its increased oxygen and energy consumption appear to be the primary cause of oxidative stress. The present investigation was therefore undertaken to establish the normal levels of F(2)-isoprostanes (F(2)-IsoPs, specific markers of ROS/oxidative stress), citrulline (determinant of NO/NOS and marker of RNS), and high-energy phosphates (HEP: adenosine triphosphate, ATP and phosphocreatine, PCr) in slow (soleus) and fast (extensor digitorum longus, EDL) muscles of rats. In addition, we aimed to determine if memantine HCl (MEM), in combination with atropine sulfate (ATS), prevents carbofuran-induced changes in markers of oxidative stress. Control values were not significantly different for F(2)-IsoPs (1.142 +/- 0.027 and 1.177 +/- 0.092 ng/g) and citrulline (469.7 +/- 31.8 and 417.8 +/- 18.5 nmol/g) in soleus and EDL muscles, while the values were different for HEP (ATP, 3.66 +/- 0.11 and 5.85 +/- 0.14 micromol/g; PCr, 7.91 +/- 0.26 and 13.14 +/- 0.31 micromol/g). Rats acutely intoxicated with carbofuran (1.5 mg/kg, s.c.) showed the signs of maximal toxicity including muscle hyperactivity within 60 min of exposure. At this time, F(2)-IsoPs (177 and 153%) and citrulline (267 and 304%) levels were significantly increased, while ATP (46 and 43%) and PCr (44 and 46%) levels were decreased in soleus and EDL, respectively. Rats pretreated with MEM (18 mg/kg, s.c.) and ATS (16 mg/kg, s.c.), 60 and 15 min prior to carbofuran, respectively, showed no signs of toxicity. MEM in combination with ATS protected muscles from carbofuran-induced hyperactivity and attenuated increases in F(2)-IsoPs and citrulline, and depletion of HEP. Carbofuran-induced changes and protection by MEM and ATS were of similar magnitude in both muscles. These findings indicate that carbofuran-induced muscle hyperactivity produces oxidative stress as measured by increased ROS and RNS generation, and HEP depletion. MEM and ATS prevent the carbofuran-induced chain of events involved in oxidative stress.

Cholinergic and noncholinergic brain biomarkers of insecticide exposure and effects

The objective of this investigation was to determine the distribution of cholinergic and noncholinergic biomarkers in discrete brain regions (cortex, stem, striatum, hippocampus, and cerebellum) of rats treated with dimethyl sulfoxide (DMSO, controls), and insecticides such as carbofuran (CARB, 1.5 mg/kg, sc), or methyl parathion (MPTH, 5 mg/kg, ip). Both insecticides produced characteristic signs of anticholinesterase nature within 5-7 min after injection. In controls, analyses of the brain regions revealed a wide variability in the values of cholinergic (acetylcholinesterase, AChE) and noncholinergic (creatine kinase, CK; and lactic dehydrogenase, LDH, and their isoenzymes) biomarkers. The highest activities of AChE and LDH were found in the striatum (1661+/-23 micromol/g/h and 57,720+/-478 IU/l, respectively) and lowest in the cerebellum (118+/-6 micromol/g/h) and 39,480+/-918 IU/l, respectively). However, the activity of CK was found highest in the cerebellum (742,560+/-798 IU/l) and lowest in the hippocampus (353,400+/-11,696 IU/l). Each brain region showed a characteristic profile of CK and LDH isoenzymes. Among the CK isoenzymes, activity of CK-BB was highest (77.5-89.3%), followed by CK-MM (6.7-15.6%), and least CK-MB (0-6.9%). The cerebellum had no CK-MB activity. In all brain regions, CK-MM isoenzyme had only the CK-MM3 subform. Among the LDH isoenzymes, activity of LDH-4 was highest in all brain regions (23-40%), except the cerebellum in which LDH-1 was highest (29%). Compared to the brain, control serum contained very little CK and LDH activity, but serum had three distinct CK and five distinct LDH isoenzymes. Unlike brain regions, serum had three CK-MM subforms. Each insecticide induced characteristic alterations in brain biomarkers. AChE activity was maximally inactivated in cortex (90. 6%) with CARB, and in cerebellum (95.3%) with MPTH. With either insecticide, the least inhibition of AChE occurred in the striatum. Unlike AChE, carboxylesterase (CarbE) did not show brain regional variability in controls, and its activity was uniformly inhibited in all brain regions by CARB and comparatively greater by MPTH. CARB- or MPTH-induced characteristic alterations in CK, LDH, and their isoenzymes in the brain, which were also reflected in serum, as a result of their leakage from the brain by increased permeability due to depletion of ATP (38-57% and 33-47%, respectively) and phosphocreatine (PCr, 23-42% and 56-65%, respectively).

Memantine is a clinically well tolerated N-methyl-D-aspartate (NMDA) receptor antagonist--a review of preclinical data

N-methyl-D-aspartate (NMDA) receptor antagonists have therapeutic potential in numerous CNS disorders ranging from acute neurodegeneration (e.g. stroke and trauma), chronic neurodegeneration (e.g. Parkinson's disease, Alzheimer's disease, Huntington's disease, ALS) to symptomatic treatment (e.g. epilepsy, Parkinson's disease, drug dependence, depression, anxiety and chronic pain). However, many NMDA receptor antagonists also produce highly undesirable side effects at doses within their putative therapeutic range. This has unfortunately led to the conclusion that NMDA receptor antagonism is not a valid therapeutic approach. However, memantine is clearly an uncompetitive NMDA receptor antagonist at therapeutic concentrations achieved in the treatment of dementia and is essentially devoid of such side effects at doses within the therapeutic range. This has been attributed to memantine's moderate potency and associated rapid, strongly voltage-dependent blocking kinetics. The aim of this review is to summarise preclinical data on memantine supporting its mechanism of action and promising profile in animal models of chronic neurodegenerative diseases. The ultimate purpose is to provide evidence that it is indeed possible to develop clinically well tolerated NMDA receptor antagonists, a fact reflected in the recent interest of several pharmaceutical companies in developing compounds with similar properties to memantine.

Carbofuran toxicity

Carbofuran, an anticholinesterase carbamate, is commonly used as an insecticide, nematicide, and acaricide in agricultural practice throughout the world. Due to its widespread use in agriculture, contamination of food, water, and air has become imminent, and consequently adverse health effects are inevitable in humans, animals, wildlife, and fish. Currently, carbofuran's involvement is most frequently encountered in malicious poisoning. The literature on chemical properties, acute toxicity data, poisoning incidences, pharmacokinetics, and mechanism of toxicity of carbofuran is briefly reviewed. Much emphasis is given to the metabolism of carbofuran, and the impact of carbofuran and its two major metabolites (3-hydroxycarbofuran and 3-ketocarbofuran) on overall toxicity. Biochemical (cholinergic and noncholinergic), hematological, and immunological effects induced by carbofuran are discussed in detail. Carbofuran and/or its major metabolites can cross the placental barrier and produce serious effects on the maternal-placental-fetal unit. Carbofuran's toxicity can be potentiated by simultaneous exposure with other cholinesterase inhibitors. Literature on various biomarkers of carbofuran exposure and on induced adverse health effects is also presented. To date, a combination of atropine and memantine remains the most effective antidotal treatment against acute carbofuran toxicity.

Cholinergic and noncholinergic changes in skeletal muscles by carbofuran and methyl parathion

The objective of this investigation was to determine the distribution of cholinergic (acetyl-cholinesterase, AChE) and noncholinergic markers in slow-, fast-, and mixed-fiber containing muscles (soleus, SOL; extensor digitorum longus, EDL; and diaphragm, DIA, respectively). Noncholinergic markers included high-energy phosphates (adenosine triphosphate, ATP; phosphocreatine, PCr; and their metabolites), and the activity of creatine kinase (CK) and lactate dehydrogenase (LDH) and their isoenzymes and subforms. All three types of muscles had only one CK isoenzyme, CK-MM, which totally consisted of MM3 subform. Levels of these determinants were highest in EDL followed by DIA and least in SOL. Another objective was to determine alterations of these markers under the influence of acute carbofuran (1.5 mg/kg) or methyl parathion (MPTH, 5 mg/kg) toxicity. Rats receiving either insecticide showed cholinergic signs with maximal severity including muscle fasciculations and convulsions within 15-30 min that lasted for about 2 h. At 1 h postinsecticide injection, when AChE was maximally inhibited (81-96%), significant depletion of ATP and PCr was evident in muscles (DIA > SOL > EDL), and activities of CK-MM and LDH were elevated in muscles and consequently in serum. Serum CK-MM3 activity was markedly reduced with sequential increase in MM2 and MM1 subforms, probably due to induced higher carboxypeptidase activity. These findings suggested that (1) the differences in levels of biochemical constituents in muscles depend upon the fiber type, (2) anticholinesterase insecticide-induced increased muscle activity produces characteristic changes in CK and LDH isoenzymes patterns, and (3) leakage of these enzymes/isoenzymes into serum is due to depletion of ATP and PCr, which are required to maintain the cell membrane permeability.