The conversion of glutamate by glutamine synthase in neocortical astrocytes from juvenile rat is important to limit glutamate spillover and peri/extrasynaptic activation of NMDA receptors

Glutamate transporters (EAATs) are important to maintain spatial and temporal specificity of synaptic transmission. Their efficiency to uptake and transport glutamate into the intracellular space depends on several parameters including the intracellular concentrations of Na⁺ and glutamate, the elevations of which may slow down the cycling rate of EAATs. In astrocytes, glutamate is maintained at low concentration due to the presence of specific enzymes such as glutamine synthase (GS). GS inhibition results in cytosolic accumulation of glutamate suggesting that the conversion of glutamate by GS is important for EAATs operation. Here we recorded astrocytes from juvenile rat neocortical slices and analyzed the consequences of elevated intracellular glutamate concentrations and of GS inhibition on the time course of synaptically evoked transporter current (STC). In slices from rats treated with methionine sulfoximine (MSO), a GS inhibitor, STC evoked by short burst of high frequency stimulation (HFS; 100 Hz for 100 ms) but not by low frequency stimulation (LFS; 0.1 Hz) was twice slower than STC evoked from saline injected rats. Same results were obtained for astrocytes recorded with pipette containing 3–10 mM glutamate and compared with cells recorded with 0 or1 mM glutamate in the patch pipette. We also showed that HFS elicited significantly larger NMDAR‐excitatory postsynaptic currents (EPSCs) with a stronger peri/extrasynaptic component in pyramidal cells from MSO‐treated compared with saline treated rats. Taken together our data demonstrate that the conversion of glutamate by GS is fundamental to ensure an efficient clearance of glutamate by EAATs and to prevent glutamate spillover. GLIA 2017;65:401–415     

Functional and anatomical evaluation of the effect of nepafenac in prevention of macular edema after phacoemulsification in diabetic patients

AIM: To evaluate the effect of prophylactic administration of nepafenac in prevention of macular edema occurring in diabetic patients after phacoemulsification and to investigate the correlation between optical coherence tomography (OCT) foveal thickness and multifocal electroretinogram (MF-ERG) parameters. METHODS: The study included two groups. Group 1 included 50 diabetic patients with senile cataract (50 eyes, 30 females, 20 males, aged 55±7y) received nepafenac 0.1% eye drop. Group 2 included another 50 diabetic patients with senile cataract (50 eyes, 22 female, 28 males, aged 53.8±8y) did not receive nepafenac. All patients were followed up for 3mo postoperatively. OCT and MF-ERG were done preoperative and at 1wk, 1, 2 and 3mo. RESULTS: The mean foveal thickness was statistically significantly lower in Group 1. Five eyes in Group 2 developed clinical cystoid macular oedema (CMO) (10%), and no patients in Group 1 developed central macular thickening more than 50 μm. There were insignificant differences in MF-ERG amplitudes and latencies between the two groups except in the five eyes that developed CMO, there statistically significant reduction of MF-ERG amplitude with increase in foveal thickness. CONCLUSION: Perioperative nepafenac reduces the incidence of CMO following uncomplicated phacoemulsification significantly. Nepafenac has no side effects.     

Primary and secondary hyperoxaluria: Understanding the enigma

Hyperoxaluria is characterized by an increased urinary excretion of oxalate. Primary and secondary hyperoxaluria are two distinct clinical expressions of hyperoxaluria. Primary hyperoxaluria is an inherited error of metabolism due to defective enzyme activity. In contrast, secondary hyperoxaluria is caused by increased dietary ingestion of oxalate, precursors of oxalate or alteration in intestinal microflora. The disease spectrum extends from recurrent kidney stones, nephrocalcinosis and urinary tract infections to chronic kidney disease and end stage renal disease. When calcium oxalate burden exceeds the renal excretory ability, calcium oxalate starts to deposit in various organ systems in a process called systemic oxalosis. Increased urinary oxalate levels help to make the diagnosis while plasma oxalate levels are likely to be more accurate when patients develop chronic kidney disease. Definitive diagnosis of primary hyperoxaluria is achieved by genetic studies and if genetic studies prove inconclusive, liver biopsy is undertaken to establish diagnosis. Diagnostic clues pointing towards secondary hyperoxaluria are a supportive dietary history and tests to detect increased intestinal absorption of oxalate. Conservative treatment for both types of hyperoxaluria includes vigorous hydration and crystallization inhibitors to decrease calcium oxalate precipitation. Pyridoxine is also found to be helpful in approximately 30% patients with primary hyperoxaluria type 1. Liver-kidney and isolated kidney transplantation are the treatment of choice in primary hyperoxaluria type 1 and type 2 respectively. Data is scarce on role of transplantation in primary hyperoxaluria type 3 where there are no reports of end stage renal disease so far. There are ongoing investigations into newer modalities of diagnosis and treatment of hyperoxaluria. Clinical differentiation between primary and secondary hyperoxaluria and further between the types of primary hyperoxaluria is very important because of implications in treatment and diagnosis. Hyperoxaluria continues to be a challenging disease and a high index of clinical suspicion is often the first step on the path to accurate diagnosis and management.     

Vascular endothelial growth factor in neonates with perinatal asphyxia

Background: Vascular endothelial growth factor (VEGF) is a polypeptide growth factor that is activated by tissue hypoxia. The role of VEGF in perinatal asphyxia in human neonates is yet to be clarified. In infants who develop moderate to severe acute hypoxic ischemic encephalopathy (HIE) it is crucial to clearly understand physiologic and biochemical changes that accompany HIE before a novel treatment can be developed. Objectives: To assess VEGF in cord blood of infants suffering from perinatal asphyxia, and to determine whether an association exists between increased concentrations of VEGF and the risk for development of encephalopathy. Study design: We prospectively studied 40 full term infants; of them 20 infants suffered from perinatal asphyxia, and 20 control infants of comparable age and sex. We obtained cord blood samples from all subjects immediately after delivery. Neurological examination and grading of HIE were performed during the first day of life. Results: Birth weight, gestational age and gender did not differ between the control (n = 20) and asphyxia (n = 20) groups. Within the asphyxia group four infants developed HIE; one with severe encephalopathy who died shortly after birth, while the other three infants had moderate HIE. Concentrations of VEGF were increased in infants with asphyxia when compared to controls (P  0.001). Within the asphyxia group, infants with HIE had significantly increased concentrations of VEGF when compared to non-HIE asphyxiated infants (P = 0.008). In the logistic regression model, VEGF inversely correlated with pH and PO₂ in cord blood, and Apgar scores at 1 min, while it did not associate with gestational age and birth weight. Conclusions: This study indicates that VEGF is increased in cord blood of neonates following birth asphyxia, and that VEGF is specifically most increased in infants who later developed encephalopathy. Further studies are required to determine the role of VEGF in brain insult. Such studies will help determine whether a therapeutic role for VEGF or VEGF inhibitors can exist for HIE infants.     

Evaluation of enzymatic biomarkers and lipoperoxidation level in Hediste diversicolor exposed to copper and benzo[a]pyrene

This study aims to evaluate the effects of exposure to copper, benzo[a]pyrene, and to their mixture on enzymatic and lipid peroxidation biomarkers in Hediste diversicolor. Worms were submitted to 1 μM of both single compounds and to their mixture during a period of test of 12, 24, 36, and 48 h. The biomarkers selected in this work were the activities of cytochrome P450-dependent NADPH cytochrome c reductase (NADPH red) as phase I enzyme, glutathione-S-transferase (GST) as phase II enzyme, and the acetylcholinesterase (AChE) activity as neurotoxicity marker. Oxidative stress was evaluated using catalase activity (CAT) and malondialdehyde accumulation (MDA). The NADPH red activity was not significantly affected by copper exposure; it shows a drastic increase in both B[a]P and mixture-exposed organisms. GST activities were significant in B[a]P-exposed worms only after 36 h, and in animals exposed to the mixture after 12 and 48 h. The ACHE activity was inhibited only in B[a]P-exposed worms.