GROWTH-PROMOTING AND METABOLIC-ACTIVITY OF THE HUMAN INSULIN ANALOG [GLY(A21),ARG(B31),ARG(B32)]INSULIN (HOE-901) IN MUSCLE-CELLS

[Gly(A21), Arg(B31), Arg(B32)]insulin (HOE 901) represents a biosynthe tic human insulin analogue that, due to its isoelectric point, precipi tates at neutral tissue pH leading to a retarded absorption rate and a corresponding longer duration of action. In the present investigation we have evaluated the growth promoting and metabolic activity of this analogue in muscle tissue using exponentially growing H9c2 cardiac my oblasts and adult rat ventricular cardiomyocytes. Equilibrium binding studies of I-125-labelled IGF-I (insulin-like growth factor I) to diff erentiating myoblasts revealed the presence of 7x10(3) IGF-I receptors per cell. In contrast, no specific binding of insulin could be detect ed. Competition binding experiments showed a slightly higher affinity of HOE 901 for the IGF-I receptor when compared to regular human insul in with IC50 (half-inhibitory concentration) values of 70 and 101 nM, respectively. However, the supernitogenic insulin analogue [Asp(B10)]i nsulin competed significantly more efficiently for IGF-I binding (IC50 : 44 nM). Maximum growth promoting activity of the peptides was then d etermined in serum-starved myoblasts by an incubation with the peptide s (5 x 10(-7) M) for 16 h in the presence of [H-3]thymidine. [Asp(B10) ]Insulin produced a stimulation of DNA synthesis (about 3-fold) which was comparable to the effect of IGF-I and significantly (P <0.005) hig her than the effect of HOE 901 with the latter being essentially equip otent to native insulin. Comparable results were obtained at lower con centrations of the peptides (10(-9) to 10(-8) M). Metabolic activity o f HOE 901 was determined by measuring the dose-dependent stimulation o f 3-O-methylglucose transport in adult cardiomyocytes. Maximum transpo rt stimulation was identical for insulin and HOE 901 with EC(50) (half -effective concentration) values of 0.7 x 10(-10) and 1.9 x 10(-9) M, respectively. We concluded that the IGF-I receptor-mediated growth pro moting activity of HOE 901 in muscle cells and the maximal metabolic a ctivity of this analogue are not different from those of native human insulin. It is suggested that differential interaction with IGF-I rece ptors significantly contributes to the action profile of insulin analo gues.