# Physicochemical Stability of Insulin and Analogues in Saline Infusion: Screening for Amyloid and Amorphous High-Molecular-Weight Material

## TL;DR

This study examines how insulin and its analogues behave in saline solutions, finding that diluted insulin does not form harmful particles under tested conditions.

## Contribution

The study introduces standardized assays to detect insulin aggregation and clarifies its stability in saline infusions.

## Key findings

- Diluted insulin in saline (1-unit/mL) does not form detectable amyloid or subvisible particles up to 48 hours.
- Amyloid insulin forms within 3 days in saline or phosphate buffer at room temperature.
- Dynamic light scattering can detect subvisible insulin particles at low concentrations.

## Abstract

Insulin is known to form subvisible particles and amyloid
material,
which can lead to iatrogenic amyloidosis and reduced potency necessary
for glycemic control. In the intensive care unit, insulin is commonly
diluted in saline (1-unit/mL) for intravenous infusion. While reports
of insulin aggregation in such dilutions exist, it remains unclear
whether these conditions favor the formation of amyloid or subvisible
particles. Here, we report standardized assays for detecting amorphous
and amyloid insulin aggregation and applied them to investigate these
particles in insulin infusion setups. Amorphous insulin was produced
by heating insulin (100 U/mL) in plastic tubes, while amyloid insulin
formed within 3 days by incubating in saline or sodium phosphate buffer,
pH 7.0. Electron microscopy confirmed the amyloid nature of these
aggregates, and dynamic light scattering detected subvisible particles
as low as 0.05 U/mL. Insulin incubated at 1-unit/mL in saline showed
no detectable amyloid material or subvisible particles up to 48 h
at room temperature. These results suggest that insulin diluted to
1-unit/mL in saline does not form detectable amyloid or subvisible
particles under the tested conditions and that these analytical approaches
may be helpful for other biopharmaceuticals.