Glargine and degludec: Solution behaviour of higher dose synthetic insulins

Abstract

Single, double and triple doses of the synthetic insulins glargine and degludec currently used in patient therapy are characterised using macromolecular hydrodynamic techniques (dynamic light scattering and analytical ultracentrifugation) in an attempt to provide the basis for improved personalised insulin profiling in patients with diabetes. Using dynamic light scattering and sedimentation velocity in the analytical ultracentrifuge glargine was shown to be primarily dimeric under solvent conditions used in current formulations whereas degludec behaved as a dihexamer with evidence of further association of the hexamers ("multi-hexamerisation"). Further analysis by sedimentation equilibrium showed that degludec exhibited reversible interaction between mono- and-di-hexamer forms. Unlike glargine, degludec showed strong thermodynamic non-ideality, but this was suppressed by the addition of salt. With such large injectable doses of synthetic insulins remaining in the physiological system for extended periods of time, in some case 24-40 hours, double and triple dose insulins may impact adversely on personalised insulin profiling in patients with diabetes.

Figure 1

Volume (%) against hydrodynamic radius of insulin obtained from dynamic light scattering of (a) Insulin glargine (single and triple dose) and (b) Insulin degludec (single and double dose at 0.0, 0.1 and 0.2 M ionic strength).

Figure 2

The sedimentation coefficient distribution c(s) plotted against sedimentation coefficient s (corrected for solvent conditions) for insulin samples obtained through AUC-SV. (a) Insulin glargine; (b) Insulin degludec at 0.0, 0.1 and 0.2 M ionic strength.

Figure 3

BM estimated by the INVEQ algorithm of insulin preparations. (a) glargine AUC-SE profile measured at 25 000 rpm (inset, S = single dose, T = triple dose), with the second virial coefficient factor BM fitted at different radial positions for single (grey) and triple (white) dose. (b–d) Degludec measured at 15 000 rpm (insets, S = single dose, D = double dose), with (b) unmodified ‘0.0 M’ ionic strength, (c) 0.1 M ionic strength; and (d) 0.2 M ionic strength. BM was fitted at different radial positions for single (grey) and double (white) dose. Standard error of regression indicated with error bars which represents how closely the fit matches the raw data. Note the 30x difference between the BM scales of (b) and (c,d).

Figure 4

Molar mass as a function of concentration (expressed in fringe displacement units), with number (☐), weight (◯) and z (Δ) averages. Darker contours represent higher proportion of solute in solution. (a) IGS; (b) IGT; (c) IDS 0.1 M; (d) IDD 0.1 M; (e) IDS 0.2 M; (f) IDD 0.2 M.

Figure 5

(a) and (b); contour probability distributions of glargine and degludec (respectively) from SINGLEHYDFIT where low Δ represents the lowest error of parameters. (c) and (d); to-scale ellipsoid representations of glargine and degludec (respectively) as fitted from SINGLEHYDFIT.