Department of Pharmaceutical Chemistry, University of Kansas, 2095 Constant Avenue, Lawrence, Kansas 66047, USA.
Pharm Res. 2012 Jan;29(1):121-33. doi: 10.1007/s11095-011-0519-1. Epub 2011 Jul 12.
Exposure of protein pharmaceuticals to light can result in chemical and physical modifications, potentially leading to loss of potency, aggregation, and/or immunogenicity. To correlate these potential consequences with molecular changes, the nature of photoproducts and their mechanisms of formation must be characterized. The present study focuses on the photochemical degradation of insulin in the solid state.
Solid insulin was characterized by solid-state NMR, polarized optical microscopy and scanning electron microscopy; various insulin preparations were exposed to UV light prior to product analysis by mass spectrometry.
UV-exposure of solid human insulin results in photodissociation of the C-terminal intrachain disulfide bond, leading to formation of a CysS(•) thiyl radical pair which ultimately disproportionates into thiol and thioaldehyde species. The high reactivity of the thioaldehyde and proximity to the thiol allow the formation of a dithiohemiacetal structure. Dithiohemiacetal is formed during the UV-exposure of both crystalline and amorphous insulin.
Dithiohemiacetals represent novel structures generated through the photochemical modification of disulfide bonds. This is the first time that such structure is identified during the photolysis of a protein in the solid state.
蛋白质药物暴露于光线下会导致化学和物理性质的改变，可能导致效力丧失、聚集和/或免疫原性。为了将这些潜在后果与分子变化相关联，必须对光产物的性质及其形成机制进行表征。本研究集中于固态胰岛素的光化学降解。
通过固态 NMR、偏光显微镜和扫描电子显微镜对固态胰岛素进行了表征；在通过质谱进行产物分析之前，将各种胰岛素制剂暴露于紫外光下。
固态人胰岛素的 UV 照射导致 C 末端链内二硫键的光解，形成 CysS(•)硫自由基对，最终歧化为巯基和硫醛物种。硫醛的高反应性和与巯基的接近允许形成二硫代半缩醛结构。二硫代半缩醛在结晶和无定形胰岛素的 UV 照射下形成。
二硫代半缩醛代表通过二硫键的光化学修饰产生的新型结构。这是首次在蛋白质的固态光解过程中鉴定出这种结构。
