Growth promoting and metabolic activity of the human insulin analogue [Gly(A21),Arg(B31),Arg(B32)]insulin (HOE 901) in muscle cells

[Gly(A21), Arg(B31), Arg(B32)]insulin (HOE 901) represents a biosynthetic human insulin analogue that, due to its isoelectric point, precipitates 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 myoblasts and adult rat ventricular cardiomyocytes. Equilibrium binding studies of I-125-labelled IGF-I (insulin-like growth factor I) to differentiating myoblasts revealed the presence of 7x10(3) IGF-I receptors per cell. In contrast, no specific binding of insulin could be detected. Competition binding experiments showed a slightly higher affinity of HOE 901 for the IGF-I receptor when compared to regular human insulin with IC50 (half-inhibitory concentration) values of 70 and 101 nM, respectively. However, the supernitogenic insulin analogue [Asp(B10)]insulin competed significantly more efficiently for IGF-I binding (IC50: 44 nM). Maximum growth promoting activity of the peptides was then determined in serum-starved myoblasts by an incubation with the peptides (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) higher than the effect of HOE 901 with the latter being essentially equipotent to native insulin. Comparable results were obtained at lower concentrations of the peptides (10(-9) to 10(-8) M). Metabolic activity of HOE 901 was determined by measuring the dose-dependent stimulation of 3-O-methylglucose transport in adult cardiomyocytes. Maximum transport 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 promoting activity of HOE 901 in muscle cells and the maximal metabolic activity of this analogue are not different from those of native human insulin. It is suggested that differential interaction with IGF-I receptors significantly contributes to the action profile of insulin analogues.