成都和兰州地区成熟母乳中唾液酸的含量及分布研究

目的 研究母乳中唾液酸的含量及分布，了解生命早期婴幼儿对不同形式唾液酸的需求。方法 在兰州及成都两地招募240位单胎足月分娩的健康乳母，收集母乳样本240例，其中产后40～45 d、200～240 d和300～400 d母乳各80例，使用高效阴离子交换色谱-脉冲安培检测器测定母乳中游离态、结合态及两种低聚糖结合态唾液酸的水平。结果 40～400 d成熟乳中97%～99%的唾液酸以结合态存在，游离态唾液酸仅占1%～3%。3’-唾液酸乳糖（3’ - sialyllactose, 3’ - SL）和6’ - 唾液酸乳糖（6’ - sialyllactose, 6’ - SL）结合的唾液酸占总唾液酸质量浓度的28%～31%。总唾液酸的质量浓度在40～400 d母乳中为233～613 mg/L, 游离唾液酸质量浓度为5～6 mg/L，3’ - SL和6’ - SL结合态唾液酸的总质量浓度为65～187 mg/L。总唾液酸（H = 142.884, P＜0.001）、结合态唾液酸（H = 143.020, P＜0.001）及两种低聚糖结合态（3’ - SL和6’ - SL）唾液酸（H = 127.814, P＜0.001）的含量在三个阶段的母乳中的差异有统计学意义，产后40～45 d的母乳中总唾液酸、结合态唾液酸和两种低聚糖结合态唾液酸的含量均高于200～240 d和300～400 d。游离态唾液酸的水平在三个阶段的母乳中的差异无统计学意义。在产后40～45 d，兰州地区母乳中总唾液酸（Z = 2.124, P＜0.001）、结合态唾液酸（Z = 2.124, P＜0.001）、游离态唾液酸（Z = 1.735, P = 0.005）及结合在3’ - SL和6’ - SL的唾液酸（Z = 2.980, P＜0.001）的含量均高于成都地区，而在200～240 d和300～400 d的母乳中差异均无统计学意义。结论 母体在泌乳早期提供子代较高水平的唾液酸，在泌乳后期含量降低并趋于稳定。成熟母乳中结合态唾液酸占绝对优势，游离态唾液酸的水平较为有限。3’ - SL和6’ - SL是结合态唾液酸的重要形式，其对婴幼儿的健康益处值得进一步研究。除泌乳阶段外，地区因素也影响母乳中唾液酸的含量。

The concentration and distribution pattern of sialic acid in mature breast milk from Lanzhou and Chengdu

Objective To investigate the content and distribution of sialic acid in breast milk and to understand the demand for different forms of sialic acid in infants in early life. Methods A total of 240 healthy mothers who gave birth to full term singletons were recruited in Lanzhou and Chengdu. A total of 240 milk samples were collected at 40 to 45 days, 200 to 240 days, and 300 to 400 days postpartum, 80 for each of the lactation stages. High Performance Anion Exchange Chromatography-Pulsed Amperometric Detector (HPAEC-PAD) was used to determine the levels of free, bound and sialylated oligosaccharides (3’-sialyllactose (3’-SL) and 6’-sialyllactose (6’-SL)) in breast milk. Results For mature breast milk, 97% to 99% of sialic acid existed in a bound form of which 3’-SL and 6’-SL accounted for 28% to 31% of the total sialic acid content, while 1% to 3% was present as free sialic acid. During 40 to 400 days, the M value ranges of total sialic acid were 233 to 613 mg/L including 5 to 6 mg/L as free sialic acid and 65 to 187 mg/L as (3’-SL& 6’-SL)-bound sialic acid. The level of total sialic acid (H=142.884, P<0.001), bound-sialic acid (H=143.020, P<0.001) and (3’-SL& 6’-SL)-bound sialic acid (H=127.814, P<0.001) in breast milk was significantly different among the three stages of mature milk. The contents of total sialic acid, bound-sialic acid and (3’-SL& 6’-SL)-bound sialic acid in breast milk at 40 to 45 days postpartum were higher than those at 200 to 240 days and 300 to 400 days postpartum. The content of free sialic acid was not significantly different among the three stages of mature milk. For the 40 to 45 days postpartum, the level of total sialic acid (Z=2.124, P<0.001), bound-sialic acid (Z=2.124, P<0.001) free sialic acid (Z=1.735, P=0.005) and (3’-SL& 6’-SL)-bound sialic acid (Z=2.980, P<0.001) in Lanzhou mother’s milk was significantly higher compared to mother’s milk in Chengdu, respectively, but comparable at 200 to 240 and 300 to 400 days postpartum. Conclusion The mothers provide the offspring with a higher level of sialic acid in the early lactation, and the content decreases and tends to be stable in the late lactation. Bound sialic acid is the most abundant form of sialic acid while free sialic acid is limited. 3’-SL and 6’-SL are abundant forms of bound sialic acid, and their health benefits in infants warrant further study. In addition to the lactational stage, geographical factors affect the concentration of sialic acid in breast milk.