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Molecular Cardiology, Diabetes Research Institute, Düsseldorf, Germany; and Mitsubishi Chemical Co. (H.T., S.I.), Yokohama, Japan
Address all correspondence and requests for reprints to: Prof. Dr. Jürgen Eckel, Diabetes Research Institute, Aufm Hennekamp 65, D-40225 Düsseldorf, Germany. E-mail: eckel{at}uni-duesseldorf.de
Freshly isolated adult rat ventricular cardiomyocytes have been used to
characterize the action profile of the new thiazolidinedione
antidiabetic drug MCC-555. Preincubation of cells with the compound
(100 µM for 30 min or 10 µM for 2 h)
did not modify basal 3-O-methylglucose transport, but
produced a marked sensitizing effect (2- to 3-fold increase in insulin
action at 3 x 10-11 M insulin) and a
further enhancement of maximum insulin action (1.8-fold). MCC-555 did
not modulate autophosphorylation of the insulin receptor and tyrosine
phosphorylation of insulin receptor substrate-1 (IRS-1). However,
insulin action (10-10 and 10-7 M)
on IRS-1-associated phosphatidylinositol (PI) 3-kinase activity was
enhanced 2-fold in the presence of MCC-555. Association of the p85
adapter subunit of PI 3-kinase to IRS-1 was not modified by the drug.
Immunoblotting experiments demonstrated expression of the peroxisomal
proliferator-activated receptor-
in cardiomyocytes reaching about
30% of the abundance observed in adipocytes. The insulin-sensitizing
effect of MCC-555 was lost after inhibition of protein synthesis by
preincubation of the cells with cycloheximide (1 mM; 30
min). Cardiomyocytes from obese Zucker rats exhibited a completely
blunted response of glucose transport at 3 x 10-11
M insulin. MCC-555 ameliorates this insulin resistance,
producing a 2-fold stimulation of glucose transport, with maximum
insulin action being 1.6-fold higher than that in control cells. This
drug effect was paralleled by a significant dephosphorylation of IRS-1
on Ser/Thr. In conclusion, MCC-555 rapidly sensitizes
insulin-stimulated cardiac glucose uptake by enhancing insulin
signaling resulting from increased intrinsic activity of PI 3-kinase.
Acute activation of protein expression leading to a modulation of the
Ser/Thr phosphorylation state of signaling proteins such as IRS-1 may
be underlying this process. It is suggested that MCC-555 may provide a
causal therapy of insulin resistance by targeted action on the
defective site in the insulin signaling cascade.
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