Defining the physiological range of 25(OH)D2 and 25(OH)D3 in the serum of healthy giant pandas using UPLC-MS/MS

Vitamin D plays crucial roles in maintaining bone health, regulating immune function, preventing cardiovascular diseases and energy metabolism. However, the bamboo, which is giant panda's main diet, doesn't contain vitamin D. To investigate the vitamin D nutritional status of giant pandas, this study successfully established a UPLC-MS/MS method for simultaneously detecting 25(OH)D 2 and 25(OH)D 3 levels in giant panda serum. The physiological ranges of 25(OH)D 2 and 25(OH)D 3 in serum of giant panda were defined by percentile method. The separation was performed on an ACQUITY UPLC HSS T3 column with a gradient elution. Mass spectrometry detection employed the electrospray ionization (ESI) positive mode and multiple reaction monitoring (MRM). The limits of detection (LOD) for 25(OH)D 3 and 25(OH)D 2 were 0.1 ng/mL, and the limits of quantification (LOQ) were 0.5 ng/mL. Both compounds exhibited a linear concentration range of 1–100 ng/mL. By analyzing 27 serum samples from giant pandas, the study determined that the serum concentration of 25(OH)D 2 in healthy female pandas ranged from 4.29 to 32.23 ng/mL, while in males, the concentration ranged from 14.33 to 44.34 ng/mL, showing a significant difference between sexes. In contrast, the concentration of 25(OH)D 3 in both sexes ranged from 1.25 to 9.57 ng/mL. The results revealed that 25(OH)D 2 concentrations in giant panda serum were markedly higher than those of 25(OH)D 3 , which is in stark contrast to findings in most other mammalian species. These findings provide critical insights for future research on the giant panda and have significant implications for its conservation and medical management.