Interactions between nitric oxide and arachidonic acid in lung epithelial cells: possible roles for peroxynitrite and superoxide

GABA and Glutamate Uptake and Metabolism in Retinal Glial (Müller) Cells

Müller cells, the principal glial cells of the retina, support the synaptic activity by the uptake and metabolization of extracellular neurotransmitters. Müller cells express uptake and exchange systems for various neurotransmitters including glutamate and γ-aminobutyric acid (GABA). Müller cells remove the bulk of extracellular glutamate in the inner retina and contribute to the glutamate clearance around photoreceptor terminals. By the uptake of glutamate, Müller cells are involved in the shaping and termination of the synaptic activity, particularly in the inner retina. Reactive Müller cells are neuroprotective, e.g., by the clearance of excess extracellular glutamate, but may also contribute to neuronal degeneration by a malfunctioning or even reversal of glial glutamate transporters, or by a downregulation of the key enzyme, glutamine synthetase. This review summarizes the present knowledge about the role of Müller cells in the clearance and metabolization of extracellular glutamate and GABA. Some major pathways of GABA and glutamate metabolism in Müller cells are described; these pathways are involved in the glutamate-glutamine cycle of the retina, in the defense against oxidative stress via the production of glutathione, and in the production of substrates for the neuronal energy metabolism.

Synergistic action of hypoosmolarity and glutamine in inducing acute swelling of retinal glial (Müller) cells

High blood ammonia, elevated glutamine, and hyponatremia are pathogenic factors contributing to astrocytic swelling and brain edema in liver failure. We investigated the effects of hypoosmolarity, ammonia, and glutamine on the induction of glial cell swelling in freshly isolated slices of the rat retina. Glutamine, but not ammonia or hypoosmolarity per se, evoked a rapid (within one minute) swelling of retinal glial (Müller) cell bodies under hypoosmotic conditions. Under isoosmotic conditions, glutamine evoked a delayed swelling after 10 min of exposure. The effect of glutamine was concentration-dependent, with half-maximal and maximal effects at ∼ 0.1 and 0.5 mM. Glutamine in hypoosmotic solution induced a dissipation of the mitochondrial membrane potential. The effects on the mitochondrial membrane potential and the glial soma size were reduced by (i) agents which inhibit the transfer of glutamine into mitochondria and its hydrolysis there, (ii) inhibition of the mitochondrial permeability transition, (iii) inhibitors of oxidative-nitrosative stress, and (iv) inhibitors of phospholipase A(2) and cyclooxygenase. Glutamine-induced glial swelling was also prevented by ATP and adenosine, acting at adenosine A(1) receptors. The data suggest that hypoosmolarity accelerates the swelling-inducing effect of glutamine on retinal glial cells, and that swelling induction by glutamine is mediated by inducing oxidative-nitrosative stress, inflammatory lipid mediators, and mitochondrial dysfunction.

Airway nitric oxide in patients with cystic fibrosis is associated with pancreatic function, Pseudomonas infection, and polyunsaturated fatty acids

BACKGROUND

Airway nitric oxide (NO) is low or normal in cystic fibrosis (CF) patients. This may affect bacterial status since NO has antimicrobial properties. Arachidonic acid (AA), which is increased in the serum and airways of CF patients, has been shown to reduce NO levels. The aim of this study was to investigate whether airway NO level correlates with genotype and pancreatic function, and whether low airway NO level is associated with bacterial infection and increased serum AA level in CF patients.

METHOD

Nasal NO (nNO) and exhaled NO (eNO) were measured according to the European Respiratory Society/American Thoracic Society standard in 59 CF patients aged 7 to 55 years, 80% of whom were pancreatic insufficient (PI) and 51% were chronically infected with Pseudomonas aeruginosa.

RESULTS

PI CF patients had significantly lower nNO levels than pancreatic-sufficient (PS) patients. Airway NO level did not correlate with lung function or inflammatory parameters. PI patients chronically infected with P aeruginosa had significantly lower nNO levels than noninfected PI patients. nNO level correlated inversely with the AA/docosahexaenoic acid ratio, and eNO with the essential fatty acid (FA) deficiency index, which is the ratio between mead acid and AA.

CONCLUSIONS

CF patients with PI, which is associated with more severe genotypes, had lower airway NO levels than patients with PS. Low NO level was correlated to chronic P aeruginosa infection, and an association was found between airway NO level and the abnormal serum phospholipid FA pattern.

Neuroprotective effects of trolox in global cerebral ischemia in gerbils

Stroke is a third leading cause of death and oxygen free radicals have been shown to be involved in its pathophysiology. In the present study, we have investigated neuroprotective potential of trolox, a free radical scavenger in bilateral carotid arteries occlusion (5 min) model of global cerebral ischemia in Mongolian gerbils. Gerbils were treated with trolox (3, 10 or 30 mg/kg, i.p.) 30 min prior to occlusion. There was a significant increase in neurological symptoms and locomotor activity in ischemic animals as compared with the sham-operated animals. These effects were attenuated by trolox 30 mg/kg, i.p. Significant increase in the number of the surviving neurons in the hippocampal CA1 pyramidal region was observed in ischemic animals treated with trolox 30 mg/kg, i.p. There was significant increase in the level of malondialdehyde (MDA) in ischemic animals indicating oxidative stress. Elevated levels of MDA in ischemic animals (25.79+/-3.34 microM/mg of protein) were reduced (16.43+/-3.32 microM/mg of protein) and (8.98+/-0.89 microM/mg of protein) by trolox 10 and 30 mg/kg, i.p., respectively. This study demonstrates the neuroprotective potential of trolox in global cerebral ischemia in gerbils.