Chemical-gas Sterilization of External Surface of Polymer-based Prefilled Syringes and Its Effect on Stability of Model Therapeutic Protein.

To reduce the risk of infection during intravitreal injections, the external surface of prefilled syringes (PFSs) must be sterilized. Usually, ethylene oxide (EO) gas or vaporized hydrogen peroxide (VHP) is used for sterilization. More recently, nitrogen dioxide (NO2) gas sterilization has been developed. It is known that gas permeability is approximately zero into glass-PFSs. However, polymer-PFSs (P-PFSs) have relatively high gas permeability. Therefore, there are concerns about the potential impact of external surface sterilization on drug solutions in P-PFSs. In this study, P-PFSs [filled with water for injection (WFI) or human serum albumin (HSA) solution] were externally sterilized using EO, VHP, and NO2 gases. For the WFI-filled syringes, the concentration of each gas that ingressed into the WFI was measured. For the HSA solution-filled syringes, the physical and chemical degradation of HSA molecules by each sterilant gas was quantified. For the EO- or VHP-sterilized syringes, the ingressed EO or hydrogen peroxide (H2O2) molecules were detected in the filled WFI. Additionally, EO-adducted or oxidized HSA molecules were observed in the HSA-filled syringes. In contrast, the NO2-sterilized WFI-filled syringes exhibited essentially immeasurable ingressed NO2, and protein degradation was not detected in HSA-filled syringes.

Effect of UVC Irradiation on the Oxidation of Histidine in Monoclonal Antibodies.

We oxidized histidine residues in monoclonal antibody drugs of immunoglobulin gamma 1 (IgG1) using ultraviolet C irradiation (UVC: 200-280 nm), which is known to be potent for sterilization or disinfection. Among the reaction products, we identified asparagine and aspartic acid by mass spectrometry. In the photo-induced oxidation of histidine in angiotensin II, 18O atoms from H218O in the solvent were incorporated only into aspartic acid but not into asparagine. This suggests that UVC irradiation generates singlet oxygen and induces [2 + 2] cycloaddition to form a dioxetane involving the imidazole Cγ - Cδ2 bond of histidine, followed by ring-opening in the manner of further photo-induced retro [2 + 2] cycloaddition. This yields an equilibrium mixture of two keto-imines, which can be the precursors to aspartic acid and asparagine. The photo-oxidation appears to occur preferentially for histidine residues with lower pKa values in IgG1. We thus conclude that the damage due to UVC photo-oxidation of histidine residues can be avoided in acidic conditions where the imidazole ring is protonated.