No abstract

Vanadate and pervanadate (pV) are protein tyrosine phosphatase (PTP) inhibitors that mimic insulin to stimulate glucose transport. To determine whether phosphatidylinositol (PI) 3-kinase is required for vanadate and pV, as it is for insulin, cultured L6 myotubes were treated with vanadate and pV. The two compounds stimulated glucose transport to levels similar to those stimulated by insulin; however, while PI 3-kinase activity and the increase in the lipid products PI 3,4-bisphosphate and PI 3,4,5-trisphosphate were inhibited by wortmannin after stimulation by all three agents--insulin, vanadate, and pV--wortmannin blocked glucose transport stimulated by insulin but not vanadate or pV. Vanadate and pV stimulated the translocation of GLUTs from an intracellular compartment to the plasma membrane; this stimulation was not blocked by wortmannin, but insulin-induced GLUT translocation was inhibited. Similar results were obtained in cultured H9c2 cardiac muscle cells in which wortmannin did not inhibit glucose transport or the vanadate-induced translocation of GLUT4 in c-myc-GLUT4 transfected cells. The ser/thr kinase PKB (Akt/PKB/RAC-PK) is activated by insulin, lies downstream of PI 3-kinase, and has been implicated in signaling of glucose transport. Insulin and pV stimulated PKB activity, and both were inhibited by wortmannin. In contrast, vanadate, at concentrations that maximally stimulated glucose transport, did not significantly increase PKB activity. To determine the potential role of protein kinase C (PKC), L6 cells were incubated chronically with phorbol myristate acetate (PMA) or acutely with the PKC inhibitors calphostin C and bisindolylmaleimide. There was no inhibition of glucose transport stimulation by insulin, vanadate, or pV, and a combination of wortmannin and PKC inhibitors also failed to block the effect of vanadate and pV. In contrast, disassembly of the actin network with cytochalasin D blocked the stimulation of glucose transport by all three agents. In conclusion, vanadate and pV are able to stimulate glucose transport and GLUT translocation by a mechanism independent of PI 3-kinase and PKC. Similar to that by insulin, glucose transport stimulation by vanadate and pV requires the presence of an intact actin network.

Pyridoxine dependent epilepsy (PDE) is caused by mutations in the ALDH7A1 gene (PDE-ALDH7A1) encoding α-aminoadipic-semialdehyde-dehydrogenase enzyme in the lysine catabolic pathway resulting in an accumulation of α-aminoadipic-acid-semialdehyde (α-AASA).We present the one-year treatment outcome of a patient on a lysine-restricted diet. Serial cerebral-spinal-fluid (CSF) α-AASA and CSF pipecolic-acid levels showed decreased levels but did not normalize. He had a normal neurodevelopmental outcome on a lysine-restricted diet. Despite normal CSF and plasma tryptophan levels and normal tryptophan intake, he developed mild CSF serotonin deficiency at one year of therapy.Stricter lysine restriction would be necessary to normalize CSF α-AASA levels, but might increase the risks associated with the diet. Patients are at risk of cerebral serotonin deficiency and should be monitored by CSF neurotransmitter measurements.