Gerald Stephen Brooke

Modifications in the B10 and B26–30 regions of the B chain of human insulin alter affinity for the human IGF-I receptor more than for the insulin receptor

Summary Inversion of the natural sequence of the B chain of human insulin (HI) from ProB28LysB29 to LysB28ProB29 generates an insulin analogue with reduced tendency to self-associate. Since this substitution increases the homology of insulin to insulin-like growth factor-I (IGF-I), we have examined the affinity of a series of insulin analogues with the general modified structure XaaB28ProB29 HI for binding to both human placental insulin and IGF-I receptors. The XaaB28ProB29 HI series is approximately equipotent to HI in binding to the insulin receptor with the exception of when Xaa = Phe, Trp, Leu, Ile, and Gly (40–60 % relative to HI). Substitution with basic residues in the B28 position increased the relative affinity to the IGF-I receptor approximately 1.5−2-fold (ArgB28ProB29 > OrnB28ProB29 = LysB28ProB29). Substitution with acidic residues reduced relative affinity for the IGF-I receptor approximately 2-fold (CyaB28ProB29 = GluB28ProB29 > AspB28ProB29). Combination of AspB10 substitution in conjunction with a modification in the B28–29 position (e.g. AspB10LysB28ProB29 HI) showed an additional 2-fold selective increase in affinity for the IGF-I receptor, suggesting that these two effects are additive. Addition of Arg residues at B31–32, on the backbone of either HI or AspB10 HI, increased affinity for the IGF-I receptor 10 and 28 fold, respectively, compared to HI, confirming the significance of enhanced positive charge at the C-terminal end of the insulin B-chain in increasing selectivity for the IGF-I receptor. This relative increase in IGF-I receptor affinity correlated largely, but not completely, with enhanced growth promoting activity in human mammary epithelial cells. In the case of LysB28ProB29 HI, growth activity correlated with dissociation kinetics from the insulin receptor which were shown to be identical with those of human insulin. [Diabetologia (1997) 40: S 54–S 61]

Human and rat amylin have no effects on insulin secretion in isolated rat pancreatic islets

Amylin, an islet amyloid peptide secreted by the pancreatic beta cell, has been proposed as a humoral regulator of islet insulin secretion. Four separate preparations of amylin were tested for effects on hormone secretion in both freshly isolated and cultured rat islets and in HIT-T15, hamster insulinoma cells. With all three experimental models, exposure to human amylin acid and human and rat amylin at concentrations as high as 100 nM had no significant effect on rates of insulin or glucagon secretion. These observations suggest that amylin, even at concentrations appreciably higher than those measured in peripheral plasma, is not a significant humoral regulator of islet hormone secretion.

Insulin and IGF-I Analogs: Novel Approaches to Improved Insulin Pharmacokinetics

Current insulin formulations do not mimic the normal glucose-induced release of insulin by the pancreas in a physiological manner.1 One limitation is the delayed absorption of hexameric insulin from the subcutaneous site of injection, such that soluble insulins (currently the most rapid acting formulations) are too slow and have too long a duration of action.2 Another limitation is that longer acting insulin formulations, such as human ultralente, exhibit too short a duration of action, show a pronounced peak in activity and are suspensions, resulting in variability in administration.3 The use of recombinant DNA technology and peptide chemistry have allowed the generation of insulin analogs with a wide variety of amino acid substitutions, which in turn halve been useful in mapping regions of the insulin nucleus that are associated with Zn2+ binding, dimer formation and insulin receptor interaction. This report will review the physical, biological and clinical characterization of several insulin analogs that have been designed to improve absorption characteristics and pharmacodynamics. Because of the structural homology between insulin and insulin-like growth factor-I (IGF-I), we have investigated specific IGF-like modifications in the insulin sequence to determine if these will transfer to pharmacokinetic differences in insulin absorption and clearance.