Demers-Mathieu Veronique, Underwood Mark A, Dallas David C
Nutrition Program, School of Biological and Population Health Sciences, College of Public Health and Human Sciences, Oregon State University, Corvallis, OR, United States.
Department of Pediatrics, University of California, Davis, Sacramento, CA, United States.
Front Pediatr. 2022 Aug 9;10:917179. doi: 10.3389/fped.2022.917179. eCollection 2022.
Plasmin in human milk partially hydrolyzes milk proteins within the mammary gland and may enhance the hydrolysis of milk proteins within the infant's stomach. This study examined the effects of extremely preterm (EP)-, very preterm (VP)-, and term-delivery on plasmin activity and the concentrations of plasminogen activators [urokinase-type plasminogen activator (uPA) and tissue-type plasminogen activator (tPA)], plasminogen activator inhibitor type 1 (PAI-1) and the complexes of PAI-1/uPA and PAI-1/tPA in human milk.
Human milk samples were collected from mothers who delivered extremely preterm infants [24-27 weeks gestational age (GA), = 20], very preterm infants (28-32 weeks GA, = 12), and term infants (38-39 weeks GA, = 8) during 2-72 days postnatally. Plasmin activity was determined using fluorometric substrate assay, whereas concentrations of uPA, tPA, PAI-1, the PAI-1/uPA complex and the PAI-1/tPA complex were quantified by ELISA.
Plasmin activity, uPA and tPA were detected in all human milk samples, PAI-1 and the PAI-1/uPA complex were present in 42.5 and 32.5% of milk samples, respectively, and the PAI-1/tPA complex was not detected. Plasmin activity was correlated negatively with postnatal age and postmenstrual age (PMA) in the VP group and positively with postnatal age in the term group. uPA and tPA concentrations decreased with increasing postnatal age in both EP and VP groups but did not correlate in the term group. uPA concentration was correlated positively with GA in the VP group and tended to be elevated with increasing GA in the combined three groups. In contrast, tPA concentrations were correlated negatively with GA and PMA in the combined three groups ( < 0.008) and with PMA in the EP and VP groups. PAI-1 concentration tended to be correlated positively with postnatal age in the combined three groups. No correlation was detected with the PAI-1/uPA complex.
Premature delivery impacted the plasmin activity and the concentrations of uPA, tPA, and PAI-1 in human milk. Whether these changes in milk plasminogen activators and inhibitors have a role in balancing the proteolytic digestion of premature infants remains to be investigated.
人乳中的纤溶酶可部分水解乳腺内的乳蛋白，并可能增强婴儿胃内乳蛋白的水解。本研究检测了极早产（EP）、早产（VP）和足月分娩对人乳中纤溶酶活性、纤溶酶原激活剂[尿激酶型纤溶酶原激活剂（uPA）和组织型纤溶酶原激活剂（tPA）]浓度、纤溶酶原激活剂抑制剂1型（PAI - 1）以及PAI - 1/uPA和PAI - 1/tPA复合物的影响。
收集产后2 - 72天内分娩极早产婴儿[胎龄（GA）24 - 27周，n = 20]、早产婴儿（GA 28 - 32周，n = 12）和足月婴儿（GA 38 - 39周，n = 8）的母亲的人乳样本。采用荧光底物法测定纤溶酶活性，通过酶联免疫吸附测定法（ELISA）对uPA、tPA、PAI - 1、PAI - 1/uPA复合物和PAI - 1/tPA复合物的浓度进行定量分析。
在所有人乳样本中均检测到纤溶酶活性、uPA和tPA，PAI - 1和PAI - 1/uPA复合物分别存在于42.5%和32.5%的乳样本中，未检测到PAI - 1/tPA复合物。在VP组中，纤溶酶活性与出生后年龄和月经后年龄（PMA）呈负相关，在足月组中与出生后年龄呈正相关。在EP组和VP组中，uPA和tPA浓度均随出生后年龄增加而降低，但在足月组中无相关性。VP组中uPA浓度与GA呈正相关，在三组合并分析中随GA增加有升高趋势。相反，三组合并分析中tPA浓度与GA和PMA呈负相关（P < 0.008），在EP组和VP组中与PMA呈负相关。三组合并分析中PAI - 1浓度与出生后年龄呈正相关趋势。未检测到与PAI - 1/uPA复合物的相关性。
早产影响人乳中纤溶酶活性、uPA、tPA和PAI - 1的浓度。母乳中纤溶酶原激活剂和抑制剂的这些变化是否在平衡早产儿的蛋白水解消化中起作用仍有待研究。
