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Articles by S Sayed
Total Records ( 2 ) for S Sayed
  A Abdel Nazeer , S Saito , S Sayed , L Hassan , F Askar , W Al jahdari , T Seki and O. Hideaki
  Background

Local anaesthetics exhibit direct neurotoxic effects on neurones. Numerous studies have investigated the factors that may reverse this neuropathology, but the effects of glucose conditions on neuronal regeneration after lidocaine-induced injury have not been examined by observing living neurones. The present study investigated the effects of different glucose conditions on neurite length, growth cone regeneration, and cell death in dorsal root ganglia (DRG) neurones after lidocaine-induced injury in vitro.

Methods

DRG explants were isolated from chick embryos at embryonic day 8 and cultured in media containing low, normal, or high glucose concentrations (10, 25, or 40 mM) for 24 h. Tissues were exposed to lidocaine 8 mM for 1 h, then rinsed and incubated for a further 24 h. Neurite length and growth cone collapse assays were performed to assess neuronal growth and regeneration. Lactate dehydrogenase (LDH) and caspase assays were also performed to detect neuronal cell death.

Results

Addition of lidocaine for 1 h resulted in >97% growth cone collapse and neurite destruction under all three glucose conditions. Two hours after rinsing out the lidocaine, significant reversal of growth cone collapse and neurite elongation was observed under all glucose conditions. Growth cone collapse was higher under low-glucose condition (P<0.05). High glucose negatively affected neurite length more than growth cone collapse. At 24 h, LDH release with both low- and high-glucose conditions was higher than with normal glucose (P<0.05). Low- and high-glucose conditions increased caspase 3/7 activation.

Conclusions

Normal glucose is optimal for neuronal recovery after lidocaine-induced injury in vitro.

  S Sayed , D. R Langdon , S Odili , P Chen , C Buettger , A. B Schiffman , M Suchi , R Taub , J Grimsby , F. M Matschinsky and C. A. Stanley
  OBJECTIVE

Heterozygous activating mutations of glucokinase have been reported to cause hypoglycemia attributable to hyperinsulinism in a limited number of families. We report three children with de novo glucokinase hyperinsulinism mutations who displayed a spectrum of clinical phenotypes corresponding to marked differences in enzyme kinetics.

RESEARCH DESIGN AND METHODS

Mutations were directly sequenced, and mutants were expressed as glutathionyl S-transferase–glucokinase fusion proteins. Kinetic analysis of the enzymes included determinations of stability, activity index, the response to glucokinase activator drug, and the effect of glucokinase regulatory protein.

RESULTS

Child 1 had an ins454A mutation, child 2 a W99L mutation, and child 3 an M197I mutation. Diazoxide treatment was effective in child 3 but ineffective in child 1 and only partially effective in child 2. Expression of the mutant glucokinase ins454A, W99L, and M197I enzymes revealed a continuum of high relative activity indexes in the three children (26, 8.9, and 3.1, respectively; wild type = 1.0). Allosteric responses to inhibition by glucokinase regulatory protein and activation by the drug RO0281675 were impaired by the ins454A but unaffected by the M197I mutation. Estimated thresholds for glucose-stimulated insulin release were more severely reduced by the ins454A than the M197I mutation and intermediate in the W99L mutation (1.1, 3.5, and 2.2 mmol/l, respectively; wild type = 5.0 mmol/l).

CONCLUSIONS

These results confirm the potency of glucokinase as the pancreatic β-cell glucose sensor, and they demonstrate that responsiveness to diazoxide varies with genotype in glucokinase hyperinsulinism resulting in hypoglycemia, which can be more difficult to control than previously believed.

 
 
 
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