Department of Radiation Biology, Institute for Cancer Research, Norwegian Radium Hospital, Oslo University Hospital, Montebello, N-0310 Oslo, Norway.
J Photochem Photobiol B. 2013 May 5;122:7-14. doi: 10.1016/j.jphotobiol.2013.03.001. Epub 2013 Mar 14.
Vitamin B12 (cobalamin) is required for proper red blood cell formation, neurologic function, and DNA synthesis. Cobalamins in solutions are light sensitive, but no comprehensive study has been performed to compare the photostability of different cobalamins under UVA exposure. Their indirect photodegradation due to their antioxidant properties and their photostability in vivo have also not been studied so far. The photodegradation of four cobalamins (methylcobalamin (MeCbl), adenosylcobalamin (AdCbl), hydroxocobalamin (OHCbl) and cyanocobalamin (CNCbl)) under UVA exposure in aqueous solutions (pH=7.4) have been investigated by absorption spectroscopy. The photodegradation of OHCbl in the absence and presence of the endogenous photosensitizer riboflavin was studied. Serum vitamin B12 concentrations before and after summer were measured in four patients with psoriasis. All studied cobalamins are photolabile. The biologically active forms of cobalamin, AdCbl and MeCbl, are converted to OHCbl within seconds during UVA exposure. OHCbl is the most stable cobalamin. However, reactive oxygen species increases the degradation rate of OHCbl. Our pilot study on humans demonstrates that serum vitamin B12 concentrations are not significantly affected during summertime in Norway. Further work is needed to determine vitamin B12 photostability in humans living at lower latitudes or using sunbeds.
维生素 B12（钴胺素）是红细胞形成、神经功能和 DNA 合成所必需的。溶液中的钴胺素对光敏感，但迄今为止尚未进行过全面研究以比较不同钴胺素在 UVA 暴露下的光稳定性。它们由于抗氧化特性而间接光降解及其在体内的光稳定性也尚未得到研究。通过吸收光谱法研究了四种钴胺素（甲钴胺（MeCbl）、腺苷钴胺素（AdCbl）、羟钴胺素（OHCbl）和氰钴胺素（CNCbl））在 UVA 暴露下水溶液（pH=7.4）中的光降解。研究了在不存在和存在内源性光敏剂核黄素的情况下 OHCbl 的光降解。在四名银屑病患者中测量了夏季前后血清维生素 B12 浓度。所有研究的钴胺素都是光不稳定的。在 UVA 暴露下，钴胺素的生物活性形式 AdCbl 和 MeCbl 会在几秒钟内转化为 OHCbl。OHCbl 是最稳定的钴胺素。然而，活性氧会增加 OHCbl 的降解速率。我们对人类的初步研究表明，在挪威的夏季，血清维生素 B12 浓度没有明显受到影响。需要进一步的工作来确定生活在较低纬度地区或使用日光浴床的人类的维生素 B12 光稳定性。
