Effect of proglycosyn and other phenolic compounds on glycogen metabolism in isolated hepatocytes

Abstract

has been investigated. When incubated in the presence of hepatocytes, proglycosyn was metabolized to an 0-demethylated glucuronidated derivative, as determined by fast-atom-bombardment mass spectrometry and enzymic analysis. This metabolite accumulated almost linearly inside the cells to reach a concentration of approximately 3 pmol/g protein after 50 min, without apparent release into the medium. In confirmation of previous work, proglycosyn decreased the level of phosphorylase a and increased that of synthase a in hepatocytes. Washing of cells incubated with proglycosyn for 30 min considerably decreased the concentration of the drug without significantly modifying the intracellular concentration of the metabolite and the activation state of glycogen synthase.Several compounds bearing structural analogy with proglycosyn were also tested for their effect on glycogen metabolism. At millimolar or submillimolar concentrations, resorcinol, m-anisidine, phenol, 3-hydroxyacetophenone, and 3-acetamidophenol, although not 4-acetamidophenol, stimulated the incorporation of ['"C]glucose into glycogen, decreased the level of phosphorylase a and increased the level of synthase a. In the case of phenol, the effect on the glycogen enzymes paralleled the intracellular accumulation of phenylglucuronide. Furthermore, ethanol and D-galactosamine, which decreased the conversion of phenol to phenylglucuronide and the intracellular concentration of phenylglucuronide, counteracted the effect of phenol on the synthase and on the phosphorylase.From these results, it is suggested that the effect of proglycosyn and of simpler phenol derivatives is mediated by glucuronidated metabolites, which act on an intracellular target.

Quantification of the glycogen 13C‐1 NMR signal during glycogen synthesis in perfused rat liver

“…16 As the active metabolites of these compounds persist in the liver, 15,16 BAY R3401 and proglycosyn were only added to buffer A.…”

“…We did the pulse-chase experiment in livers treated with the phosphorylase inhibitor BAY R3401 15 and the phosphorylase kinase inhibitor proglycosyn, 16 to reduce futile glycogen turnover. Any residual glycogen turnover was evaluated from the accumulation of 13 C-enriched metabolites in the recirculating perfusate during the chase phase.…”

Involvement of Phosphorylase Kinase Inhibition in the Effect of Resorcinol and Proglycosyn on Glycogen Metabolism in the Liver

“…Isolated hepatocytes convert proglycosyn to a polar compound (Yamanouchi et al, 1992), which proved to be a demethylated, glucuronidated metabolite (Van Schaftingen and de Hoffmann, 1993). Evidence was provided for this metabolite being the compound that acts intracellularly on glycogen metabolism (Van Schaftingen and de Hoffmann, 1993).…”

“…Isolated hepatocytes convert proglycosyn to a polar compound (Yamanouchi et al, 1992), which proved to be a demethylated, glucuronidated metabolite (Van Schaftingen and de Hoffmann, 1993). Evidence was provided for this metabolite being the compound that acts intracellularly on glycogen metabolism (Van Schaftingen and de Hoffmann, 1993). Several other phenol compounds, including phenol itself and resorcinol, which are known to be glucuronidated in the liver, were also found to cause the inactivation of phosphorylase and the activation of synthase and to stimulate glycogen synthesis in isolated hepatocytes (Van Schaftingen and de Hoffmann, 1993).…”

“…Evidence was provided for this metabolite being the compound that acts intracellularly on glycogen metabolism (Van Schaftingen and de Hoffmann, 1993). Several other phenol compounds, including phenol itself and resorcinol, which are known to be glucuronidated in the liver, were also found to cause the inactivation of phosphorylase and the activation of synthase and to stimulate glycogen synthesis in isolated hepatocytes (Van Schaftingen and de Hoffmann, 1993). Since the effect on phosphorylase precedes the effect on synthase (Harris et al, 1989), it was suggested that the primary action of the glucuronidated metabolite was at the level of phosphorylase kinase or phosphorylase phosphatase (Van Schaftingen and de Hoffmann, The purpose of this study was to identify the target of the glucuronidated metabolites of proglycosyn and resorcinol and to understand the mechanism of the decrease in the concentration of fructose 2,6-bisphosphate.…”