Role of acetylcholine in pyridostigmine-induced myocardial injury: possible involvement of parasympathetic nervous system in the genesis of cardiomyopathy

Intermittent exposure to chlorpyrifos results in cardiac hypertrophy and oxidative stress in rats

Forbidden in some countries due to its proven toxicity to humans, chlorpyrifos (CPF) still stands as an organophosphate pesticide (OP) highly used worldwide. Cardiotoxicity assessment is an unmet need in pesticide regulation and should be deeply studied through different approaches to better inform and generate an appropriate regulatory response to OP use. In the present study, we used our 4-week intermittent OP exposure model in rats to address the CPF effects on cardiac morphology allied with cardiovascular functional and biomolecular evaluation. Rats were intermittently treated with CPF at doses of 7 mg/kg and 10 mg/kg or saline (i.p.) and assessed for cardiac morphology (cardiomyocyte diameter and collagen content), cardiopulmonary Bezold-Jarisch reflex (BJR) function, cardiac autonomic tone, left ventricle (LV) contractility, cardiac expression of NADPH oxidase (Nox2), catalase (CAT), superoxide dismutase 1 (SOD1), superoxide dismutase 2 (SOD2) and cardiac levels of advanced oxidation protein products (AOPP) and thiobarbituric acid reactive substances (TBARS). Plasma butyrylcholinesterase (BuChE) and brainstem acetylcholinesterase (AChE) were also measured. Intermittent exposure to CPF induced cardiac hypertrophy, increasing cardiomyocyte diameter and collagen content. An impairment of cardioinhibitory BJR responses and an increase in cardiac vagal tone were also observed in CPF-treated animals without changes in LV contractility. CPF exposure increased cardiac Nox-2, CAT, SOD1, and TBARS levels and inhibited plasma BuChE and brainstem AChE activities. Our data showed that intermittent exposure to CPF induces cardiac hypertrophy together with cardiovascular reflex impairment, imbalance of autonomic tone and oxidative stress, which may bring significant cardiovascular risk to individuals exposed to OP compounds seasonally.

New insights on brain stem death: From bedside to bench

As much as brain stem death is currently the clinical definition of death in many countries and is a phenomenon of paramount medical importance, there is a dearth of information on its mechanistic underpinnings. A majority of the clinical studies are concerned only with methods to determine brain stem death. Whereas a vast amount of information is available on the cellular and molecular mechanisms of cell death, rarely are these studies directed specifically towards the understanding of brain stem death. This review presents a framework for translational research on brain stem death that is based on systematically coordinated clinical and laboratory efforts that center on this phenomenon. It begins with the identification of a novel clinical marker from patients that is related specifically to brain stem death. After realizing that this "life-and-death" signal is related to the functional integrity of the brain stem, its origin is traced to the rostral ventrolateral medulla (RVLM). Subsequent laboratory studies on this neural substrate in animal models of brain stem death provide credence to the notion that both "pro-life" and "pro-death" programs are at work during the progression towards death. Those programs (mitochondrial functions, nitric oxide, peroxynitrite, superoxide anion, coenzyme Q10, heat shock proteins and ubiquitin-proteasome system) hitherto identified from the RVLM are presented, along with their cellular and molecular mechanisms. It is proposed that outcome of the interplay between the "pro-life" and "pro-death" programs (dying) in this neural substrate determines the final fate of the individual (being dead). Thus, identification of additional programs in the RVLM and delineation of their regulatory mechanisms should shed new lights on future directions for clinical management of life-and-death.

DEPRESSION OF MITOCHONDRIAL RESPIRATORY ENZYME ACTIVITY IN ROSTRAL VENTROLATERAL MEDULLA DURING ACUTE MEVINPHOS INTOXICATION IN THE RAT

We investigated possible changes in bioenergetics at the rostral ventrolateral medulla (RVLM), a medullary site where sympathetic vasomotor tone originates and where the organophosphate poison mevinphos (Mev) acts to elicit cardiovascular intoxication. In Sprague-Dawley rats maintained under propofol anesthesia, microinjection bilaterally of Mev (10 nmol) into the RVLM induced progressive hypotension that was accompanied by an early augmentation (80-100 min post-Mev; Phase I), followed by a decrease (>100 min post-Mev; Phase II) in the power density of the vasomotor components (0-0.8 Hz) in systemic arterial pressure (SAP) signals. Enzyme assay revealed that local application of Mev into the RVLM also significantly and progressively depressed the activity of NADH cytochrome c reductase (marker for Complexes I and III) and cytochrome c oxidase (marker for Complex IV) in the mitochondrial respiratory chain of the RVLM, but not the heart. On the other hand, the activity of succinate cytochrome c reductase (marker for Complexes II and III) remained unaltered. Both the cardiovascular consequences and depression of mitochondrial respiratory chain enzymes elicited by Mev were significantly antagonized on comicroinjection of atropine (3.5 or 7 nmol) bilaterally into the RVLM. We conclude that Mev adversely effects cardiovascular control by acting as a cholinesterase inhibitor in the RVLM, whose neuronal activity is intimately related to the death process. The resulting accumulation of acetylcholine and prolonged activation of muscarinic receptors in the RVLM is manifested by a selective dysfunction of respiratory enzyme Complexes I and IV in the mitochondrial respiratory chain that underlies cardiovascular toxicity associated with organophosphate poisons such as Mev.

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

1. The effects of carbamylcholine (CaCh) (acetylcholine agonist) and pyridostigmine (Pyr) (acetylcholinesterase inhibitor), on the activity of cytoskeleton-bound and cytosolic phosphofructokinase (PFK), the rate-limiting enzyme in glycolysis, and ATP levels, were studied in rat tibialis anterior (TA) muscle, heart, and brain. 2. In the TA muscle, a marked (about three-fold) increase in the allosteric activity of cytosolic (soluble) PFK was found, 3-5 min following the injection of CaCh or Pyr. The intracellular distribution of the enzyme was not affected by both drugs. Stimulation of glycolysis in this muscle was also expressed by a significant increase in the concentrations of glycolytic intermediates and lactate. Glucose 1,6-bisphosphate (Glc-1,6-P2) levels were unchanged, whereas fructose-2,6-bisphosphate (Fru-2,6-P2) was increased. Glycogenolysis was also stimulated, as deduced from the decrease in glycogen content. The stimulation of glycolysis, induced by both drugs, was accompanied by an increase in ATP level in the TA muscle. 3. In contrast to the stimulatory action of CaCh or Pyr on glycolysis in the TA muscle, both drugs had no effect on cytosolic and cytoskeletal PFK in heart and brain. However, ATP content in both heart and brain was markedly reduced by these drugs, most probably due to their reported harmful effects on mitochondrial function, leading to tissue damage. 4. Electron microscopic studies of TA muscle and heart from rats treated with CaCh or Pyr, revealed severe damage of heart but no harmful effects on TA muscle, which is a muscle with high glycolytic and low oxidative capacity. The present experiments suggest that the accelerated glycolysis in this muscle induced by both drugs, supplies ATP, thus preventing muscle damage.

Cardiomyopathy and angiopathy in patients with mitochondrial myopathy, encephalopathy, lactic acidosis, and strokelike episodes

In four patients with mitochondrial myopathy, encephalopathy, lactic acidosis, and strokelike episodes (MELAS) in which mutated mitochondrial deoxyribonucleic acid was seen, hypertrophic cardiomyopathy and angiopathy was demonstrated by echocardiography, dipyridamole stress scintigraphy, and cardiac catheterization. On stress scintigraphy with dipyridamole, three patients showed hypoperfusion in the early image and a "filling-in" pattern in the late image. However, coronary angiography did not demonstrate narrowing of the large vessels in these patients. Light and electron microscopy of endomyocardial biopsy specimens indicated abnormal mitochondria, with marked increase in the number and size of mitochondria in endothelium. Modified Gomori's trichrome staining in biopsied endomyocardial specimens revealed a red-purple deposit similar in appearance of the ragged-red fibers in skeletal muscle, a characteristic finding of mitochondrial disease. Deterioration of complex I in the mitochondrial electron transfer system, which is widely observed in various mitochondrial diseases, appeared in biopsied skeletal muscle of our patients, indicating deficiency of some subunits of complex I. These results indicate that mitochondrial diseases such as MELAS show not only cardiomyopathy but also angiopathy. We speculate that proliferation of mitochondria leads to narrowing of the lumen of arterioles, which might be responsible for the ischemic findings observed scintigraphically.

Changes in myocardial mitochondrial electron transport activity in rats administered with acetylcholinesterase inhibitor

This study was designed to elucidate harmful effects of acetylcholine on myocardial mitochondrial electron transport activity. Rats were cervically dislocated 3 h and 6 h after oral administration of pyridostigmine, an acetylcholinesterase inhibitor. The myocardial mitochondrial electron-transport activity (NADH-cytochrome c reductase, succinate-cytochrome c reductase and cytochrome c oxidase), and myocardial acetylcholine and norepinephrine concentrations were measured. Activities of cytochrome c oxidase were significantly decreased in the pyridostigmine-3h and the pyridostigmine-6h groups compared with untreated rats. Activity of NADH-cytochrome c reductase was significantly decreased 6 h after administration. No significant changes were observed in those of succinate-cytochrome c reductase among all groups. Pyridostigmine increased significantly myocardial acetylcholine concentration, however, no significant changes of myocardial norepinephrine concentrations were observed among all groups. It is indicated that these mitochondrial injuries might be dependent on an increase in acetylcholine level and independent of norepinephrine.