Circulating factors and insulin resistance. II. The action of the novel myo-inositol cyclic 1,2-inositol phosphate phosphoglycan insulin antagonist from human plasma in regulating pyruvate dehydrogenase phosphatase.

Abstract

A novel low mol wt inositol phosphoglycan antagonist of insulin action of oxidative glucose metabolism in isolated rat adipocytes was partially purified from normal human plasma and shown to be increased in type II diabetic plasma. It was characterized chemically as a myo-inositol phosphoglycan containing a cyclic 1,2-phosphate. This antagonist, termed fraction V3, is now shown to inhibit the action of an inositol glycan insulin pH 2.0 mediator that stimulates pyruvate dehydrogenase phosphatase in a similar manner to insulin. In addition, fraction V3 inhibits stimulation of the pyruvate dehydrogenase (PDH) phosphatase by Mg2+, the enzyme's required metal, and by spermine, a polyamine. Fraction V3 does not inhibit active PDH itself. The inhibitory effect is dose dependent and apparently noncompetitive or nonsurmountable for the insulin inositol glycan pH 2.0 mediator, thus comparing kinetically with its insulin antagonistic action on intact adipocytes. Its inhibitory action on PDH phosphatase is dose dependent and competitive for Mg2+ stimulation of the phosphatase. Additionally, fraction V3 is shown to inhibit stimulation by Mg2+ of cloned recombinant PDH phosphatase catalytic subunit. Inhibition by fraction V3 of Mg(2+)-stimulated PDH phosphatase and its cloned catalytic subunit helps explain its mechanism of action to inhibit insulin-stimulated oxidative glucose metabolism in adipocytes and its potential clinical significance in insulin resistance.

Locally released small (non‐protein) ninhydrin‐reacting molecules underlie developmental differences of cultured medullary versus spinal dorsal horn neurons

“…To identify potential factors released from cells that may be responsible for the greater cell death in Vc, we examined conditioned media used by cultures of Vc, SDH, and Hip tissues isolated from embryonic rats, respectively. Based on previous findings that a group of non‐peptide ninhydrin‐reacting small molecules in human plasma is involved in cell signaling (Galasko et al. 1995, 1996), we isolated the ninhydrin‐reacting fractions in Vc, SDH, and Hip‐conditioned media by column chromatography using Sephadex G‐25 followed by G‐15.…”

“…Using size exclusion chromatography on Sephadex G‐25 followed by Sephadex G‐15, Galasko and her colleagues isolated two fractions containing non‐protein, ninhydrin‐reacting small molecules from human plasma, called Fractions V3A and V3 (Galasko et al. 1995, 1996).…”

“…As described previously by Galasko (Galasko et al. 1995, 1996), the small (non‐protein) ninhydrin‐reacting molecules were isolated by using size exclusion chromatography at first on a Sephadex G25 (GE Healthcare, Uppsala, Sweden) column (∼19 × 950 mm).…”

Insulin mediators in man: effects of glucose ingestion and insulin resistance

“…4). Galasko et al [16,17] recently characterized an IPG isolated from plasma of NIDDM patients that inhibited PDH phosphatase to a greater extent than did IPG isolated from control plasma. We therefore repeated the analysis of the samples obtained in the basal state (all in the same run) using more concentrated samples (equivalent to 10 m l of stock).…”

“…Again, there was no significant difference between groups (data not shown). Our PDH complex inhibitor has not been characterized, and has been isolated by procedures different from those employed by Galasko Values are means ± SEM for n = 6 (healthy men) or 7 (insulin resistant men) a p < 0.05, b p < 0.01, c p < 0.001 vs 0 min in corresponding group by ANOVA followed by Newman-Keuls test et al [16,17]. Therefore, a direct comparison between studies is currently not possible.…”