Preparation of Selenoinsulin as a Long‐Lasting Insulin Analogue

Abstract

Synthetic insulin analogues with al ong lifetime are current drug targets for the therapyo fd iabetic patients.T he replacement of the interchain disulfide with adiselenide bridge, which is more resistant to reduction and internal bond rotation, can enhance the lifetime of insulin in the presence of the insulin-degrading enzyme (IDE) without impairing the hormonal function. The [C7U A ,C7U B ]v ariant of bovine pancreatic insulin (BPIns) was successfully prepared by using two selenocysteine peptides (i.e., the C7U analogues of A-and Bchains,r espectively). In ab uffer solution at pH 10 they spontaneously assembled under thermodynamic control to the correct insulin fold. The selenoinsulin (Se-Ins) exhibited ab ioactivity comparable to that of BPIns.I nterestingly, degradation of Se-Ins with IDE was significantly decelerated (t 1/2 % 8hvs. % 1hfor BPIns). The lifetime enhancement could be due to both the intrinsic stability of the diselenide bond and local conformational changes induced by the substitution.Insulin, as mall globular protein (5.8 kDa), comprises two peptide chains,t he A-chain (Ins-A, 21 amino acid residues) and B-chain (Ins-B,3 0a mino-acid residues). Then ative structure in am onomeric active state is stabilized by two interchain disulfide bridges,Cys A7 -Cys B7 and Cys A20 -Cys B19 ,in addition to one intrachain disulfide linkage,C ys A6 -Cys A11 . [1] Considerable efforts have been directed toward development of various insulin analogues [2] which imitate either bolus secretion of insulin for expeditiously reducing postprandial blood glucose levels [3] or basal secretion of insulin to control the glucose level for an entire day. [4] Thel atter long-acting analogues have been designed so that insulin forms infusible precipitates or soluble oligomers (hexamer or dihexamer) under physiological conditions and slowly releases active insulin monomers.In contrast, the insulin-degrading enzyme (IDE) is ap ossible alternative target for diabetes therapy.I DE, which is involved in clearance of insulin and amyloid b (Ab), [5] is found in the liver and kidneys.Recent research has revealed that synthetic IDE inhibitors increase circulation of insulin by preventing its degradation in the liver,t hus resulting in improvement of the postprandial glucose tolerance. [6] However,other research suggests that IDE inhibitors could induce accumulation of Ab in the brain, [7] and would lead to Ab-mediated cognitive impairment. Hence,the design of long-lasting insulin analogues resistant against IDE would be desirable. [8] In this study,wehave attempted anew approach to alonglasting insulin analogue by exploiting the unique chemical properties of adiselenide bond. Namely,i ntroduction of two juxtaposed selenium atoms to the insulin analogue could lead to ah igher kinetic and thermodynamic stability than that of the wild-type without affecting the bioactivity.T his new strategy is based primarily on the higher rotational barrier of aSe À Se bond (ca. 4kcal mol À1 )than that of an S À Sbond (ca. 3kcal mol À1 ), [9] and se...

Substitution of an Internal Disulfide Bridge with a Diselenide Enhances both Foldability and Stability of Human Insulin

“…The observed mass corresponded to the expected mass with three crosslinks (two disulfides and one diselenide bonds, see below). The yield of human Se‐insulin[C6U A , C11U A ] was similar to that reported by Iwaoka and co‐workers in the synthesis of bovine Se‐insulin[C7U A , C7U B ], except that our reaction used 1.2 m m concentrations of the two chains versus 184 μ m concentration in the synthesis of bovine Se‐insulin[C7U A , C7U B ] …”

“…The synthesis of the A chain[C6U, C11U] employed stepwise Fmoc‐SPPS, wherein Sec residues were inserted manually (Figure S1), and A chain[C6U, C11U] was isolated in 8 % yield, similar to that achieved in the synthesis of A chain[C7U] by Iwaoka and co‐workers …”

“…Bioactivity similar to that of WT bovine insulin was demonstrated in a cell‐based assay but only at high hormone concentration (1 μ m ), beyond the physiological range (0.1–10 n m ); the relative affinity of the analogue for the insulin receptor was not reported. The interchain diselenide bonds likewise improved the efficiency of chain combination and increased resistance to degradation by insulin‐degrading enzyme (IDE) (relative to bovine insulin) . We note in passing that bovine insulin is remarkable for its lower stability and higher propensity to form fibrils (relative to human or porcine insulins) …”

“…While our work was in progress, Arai et al. exploited Sec to prepare an analogue of bovine insulin with a diselenide bridge on the surface of insulin . Containing substitutions [C7U A , C7U B ], the insulin analogue was obtained with a yield of up to 27 % .…”

“…exploited Sec to prepare an analogue of bovine insulin with a diselenide bridge on the surface of insulin . Containing substitutions [C7U A , C7U B ], the insulin analogue was obtained with a yield of up to 27 % . Bioactivity similar to that of WT bovine insulin was demonstrated in a cell‐based assay but only at high hormone concentration (1 μ m ), beyond the physiological range (0.1–10 n m ); the relative affinity of the analogue for the insulin receptor was not reported.…”