Effects of carbamylcholine and pyridostigmine on cytoskeleton-bound and cytosolic phosphofructokinase and ATP levels in different rat tissues

Regulation of mammalian muscle type 6-phosphofructo-1-kinase and its implication for the control of the metabolism

Phosphofructokinase (PFK) is a major regulatory glycolytic enzyme and is considered to be the pacemaker of glycolysis. This enzyme presents a puzzling regulatory mechanism that is modulated by a large variety of metabolites, drugs, and intracellular proteins. To date, the mammalian enzyme structure has not yet been resolved. However, it is known that PFK undergoes an intricate oligomerization process, shifting among monomers, dimers, tetramers, and more complex oligomeric structures. The equilibrium between PFK dimers and tetramers is directly correlated with the enzyme regulation, because the dimer exhibits very low catalytic activity, whereas the tetramer is fully active. Several PFK ligands modulate the enzyme, favoring the formation of its dimers or tetramers. The present review integrates recent findings regarding the regulatory aspects of muscle type PFK and discusses their relation to the control of metabolism.

Clotrimazole potentiates the inhibitory effects of ATP on the key glycolytic enzyme 6-phosphofructo-1-kinase

Clotrimazole (CTZ) has been proposed as a potential anti-neoplastic agent, which inhibits glucose metabolism. The present work aimed to evaluate the effects of CTZ on the kinetic mechanism of 6-phosphofructo-1-kinase (PFK). We show that CTZ promotes a dose-dependent inhibition of PFK, presenting a K(i) of 28 +/- 2 microM. Inhibition occurs through the dissociation of the enzyme tetramers, as demonstrated through fluorescence spectroscopy and gel filtration chromatography. Moreover, the affinities of the enzyme for ATP and fructose-6-phosphate are reduced 50% and 30%, respectively. Furthermore, the affinity of PFK for ATP at the inhibitory site becomes 2-fold higher. Altogether, the results presented here suggest that PFK inhibition by CTZ involves a decrease in the affinity of PFK for its substrates at the catalytic site with the concomitant potentiation of the inhibitory properties of ATP.

Chromosomal aberrations in human lymphocytes exposed to the anticholinesterase pesticide isofenphos with mechanisms of leukemogenesis

Human lymphocytes were exposed to the leukemogenic pesticide isofenphos (IFP) to investigate its effects on chromosomal DNA and cholinergic homeostasis using cholinesterase activity as a marker. Isolated peripheral lymphocytes were administered concentrations of IFP ranging from 0.1 ng/ml to 10 microg/ml. The absence (Group 1) and presence (Group 2) of DNA repair inhibitors 4 mM hydroxyurea (HU), 40 microM cytosine arabinoside (ARA-C) and an NADPH regenerating system (NRS) (Group 3) were analyzed at 1, 6 and 24 h by single cell gel electrophoresis using the comet assay. Significant damage to DNA directly from IFP at 1 h by remarkably low concentrations was observed in Group 1, escalating in Group 2 with DNA repair inhibition, while Group 3 disruptions were highest due to the presence of the NRS P-450 microsomal fraction conducive to producing reactive IFP-oxon and N-desalkyl metabolites. The extent of DNA aberrations increased further in parallel within the groups at 6 and 24 h. Male and female chemical sensitivities were similar on average (P < 0.01). Cholinesterase activity measured in a satellite group was inhibited with 0.1 microg/ml IFP by 69, 62, and 48% at 1, 6, and 24 h, respectively, indicating gradual induction of compensatory synthesis. Restoration of cholinergic homeostasis may be exceptionally impaired at higher IFP concentrations from acetyl-CoA depletion [Leuk. Res. 25 (2001) 883]. In summary, these studies reveal that exposure to the organophosphate pesticide isofenphos induces human DNA mutation beyond endogenous repair capacity and disrupts cholinergic nuclear signaling affectively constructing the mutator phenotype of leukemogenesis.

Disruption of the Blood–Brain Barrier and Neuronal Cell Death in Cingulate Cortex, Dentate Gyrus, Thalamus, and Hypothalamus in a Rat Model of Gulf-War Syndrome

We investigated the effects of a combined exposure to restraint stress and low doses of chemicals pyridostigmine bromide (PB), N, N-diethyl-m-toluamide (DEET), and permethrin in adult male rats, a model of Gulf-War syndrome. Animals were exposed daily to one of the following for 28 days: (i) a combination of stress and chemicals (PB, 1.3 mg/kg/day; DEET, 40 mg/kg/day; and permethrin, 0.13 mg/kg/day); (ii) stress and vehicle; (iii) chemicals alone; and (iv) vehicle alone. All animals were evaluated for: (i) the disruption of the blood-brain barrier (BBB) using intravenous horseradish peroxidase (HRP) injections and endothelial barrier antigen (EBA) immunostaining; (ii) neuronal cell death using H&E staining, silver staining, and glial fibrillary acidic protein (GFAP) immunostaining; and (iii) acetylcholinesterase (AChE) activity and m2-muscarinic acetylcholine receptors (m2-AChR). Animals subjected to stress and chemicals exhibited both disruption of the BBB and neuronal cell death in the cingulate cortex, the dentate gyrus, the thalamus, and the hypothalamus. Other regions of the brain, although they demonstrated some neuronal cell death, did not exhibit disruption of the BBB. The neuropathological changes in the above four brain regions were highly conspicuous and revealed by a large number of HRP-positive neurons (21-40% of total neurons), a decreased EBA immunostaining (42-51% reduction), a decreased number of surviving neurons (27-40% reduction), the presence of dying neurons (4-10% of total neurons), and an increased GFAP immunostaining (45-51% increase). These changes were also associated with decreased forebrain AChE activity and m2-AchR (19-25% reduction). In contrast, in animals exposed to stress and vehicle or chemicals alone, the above indices were mostly comparable to that of animals exposed to vehicle alone. Thus, a combined exposure to stress and low doses of PB, DEET, and permethrin leads to significant brain injury. The various neurological symptoms reported by Gulf-War veterans could be linked to this kind of brain injury incurred during the war.

Reactive oxygen species mediate pyridostigmine-induced neuronal apoptosis: involvement of muscarinic and NMDA receptors

Pyridostigmine bromide (PB) is a reversible cholinesterase inhibitor used for treatment of myasthenia gravis and for prophylactic protection against organophosphate nerve agent. We previously showed PB can induce apoptotic death in rat brain following systemic treatment. To study mechanisms by which PB induces brain cell death, cultured rat cerebellar granule cells were used. Cytotoxicity was determined after exposure to PB (10-1000 microM) for 24 h; a high concentration of PB (>500 microM) significantly increased lactate dehydrogenase release, which was reduced by pretreatment with the antioxidant, N-t-butyl-alpha-phenyl-nitrone (PBN). Apoptosis, as determined by TUNEL staining, was concentration dependent (10-250 microM) after a 24-h exposure and cytotoxicity was confirmed by gel electrophoresis of DNA, release of cytochrome c from mitochondria, elevation of caspase activity, and electron microscopy. The oxidant-sensitive fluorescent dye 2',7'-dichlorofluorescin diacetate was used to detect reactive oxidative species (ROS) generation. Pretreatment with PBN, superoxide dismutase, catalase, or the nitric oxide synthase inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME) blocked PB-induced ROS generation and apoptotic cell death. Pretreatment with atropine or MK-801 blocked ROS generation and the subsequent neurotoxicity, showing that both muscarinic and NMDA receptors mediate the response. DNA extracted from PB-treated cells revealed oligonucleosomal fragmentation on gel electrophoresis and antioxidants attenuated the DNA fragmentation, providing further evidence for a link of ROS generation and apoptosis. These results indicate that muscarinic receptor-mediated ROS generation is an initiating factor in PB-induced apoptotic cell death and activation of the NMDA glutamate receptor is directly linked to the response.