Dynamic light scattering study of heat aggregation of insulin

An unnatural amino acid modified human insulin derivative for visual monitoring of insulin aggregation

Insulin often forms toxic fibrils during production and transportation, which are deposited as amyloids at repeated injection sites in diabetic patients. Distinguishing early fibrils from non-fibrillated insulin is difficult. Herein, we introduce a chemically modified human insulin derivative with a distinct visual colour transition upon aggregation, facilitating insulin quality assessment.

Mechanism of insulin aggregation and stabilization in agitated aqueous solutions

Undesirable aggregation of aqueous insulin solutions remains a serious obstacle in the development of alternative methods of diabetes therapy. We investigated the fundamental nature of the aggregation mechanism and proposed stabilization strategies based on a mathematical model for the reaction scheme. Insulin aggregation kinetics in the presence of solid-liquid and air-liquid interfaces were monitored using UV spectroscopy and quasielastic light scattering (QELS). Experimental observations were consistent with our model of monomer denaturation at hydrophobic surfaces followed by the formation of stable intermediate species which facilitated subsequent macroaggregation. The model was used to predict qualitative trends in insulin aggregation behavior, to propose stabilization strategies, and to elucidate mechanisms of stabilization. In the absence of additives, insulin solutions aggregated completely (more than 95% of the soluble protein lost) within 24 h; with sugar-based nonionic detergents, no detectable loss occurred for more than 6 weeks.

Multivariate calibration of covalent aggregate fraction to the raman spectrum of regular human insulin

Insulin aggregates were prepared by exposing samples of formulated regular human insulin to agitation at 60 degrees C. Aliquots were drawn from the samples periodically over a time range spanning 192 h, and their aggregate compositions were determined with size exclusion chromatography. The complete data set was composed of 39 separate aliquots. The Raman spectra of three separate 10 microL volumes from each aliquot were measured using the drop-coat deposition Raman (DCDR) method. The spectra were calibrated to aggregate composition by partial least squares regression (PLS), resulting in linear calibration (R(2) = 0.997) with a root mean squared error of calibration (RMSEC) of 1.3% and a root mean squared error of cross validation (RMSECV) of 5.1% in aggregate composition. Though the time required for aggregates to form under stressed conditions showed substantial sample-to-sample variation, the correlation between aggregate composition and Raman spectrum was remarkably consistent, indicating that Raman spectroscopy may be a viable screening method for aggregation of protein drugs.

Heat aggregation studies of phycobilisomes, ferritin, insulin, and immunoglobulin by dynamic light scattering

Dynamic laser light scattering studies on the heat aggregation behavior of phycobilisomes (PBS), ferritin, insulin, and immunoglobulin (IgG) in dilute aqueous solutions has been reported. Except for PBS, results are reported for heat aggregation trends in these proteins for three different pH environments (4.0, 7.5, 9.1). For PBS, studies were performed only in the neutral buffer medium (pH 7.5). The experiments were performed in the very dilute concentration regime (between 0.23 and 1.8 gL-1). For all these samples heat aggregation and dissociation trends were found to be linear with temperature. Upon temperature reversal (self-cooling), hysteresis-like behavior observed in insulin was found to be predominantly large at pH 7.5. PBS, ferritin, and IgG showed no such behavior at any of three pH values, and retraced their path of aggregation while dissociating on temperature reversal. Heat aggregation and dissociation processes in ferritin were found to be independent of pH. The IgG samples showed smooth aggregation tendency only up to 35 degrees C in the buffer media pH 4.0 and 9.1, whereas for pH 7.0 the same could be observed until 60 degrees C. Low polydispersity in the correlation spectra was observed in case of all these samples.