Preterm human milk contains a large pool of latent TGF-β, which can be activated by exogenous neuraminidase

Abstract

Human milk contains substantial amounts of transforming growth factor (TGF)-β, particularly the isoform TGF-β2. We previously showed in preclinical models that enterally administered TGF-β2 can protect against necrotizing enterocolitis (NEC), an inflammatory bowel necrosis of premature infants. In this study we hypothesized that premature infants remain at higher risk of NEC than full-term infants, even when they receive their own mother's milk, because preterm human milk contains less bioactive TGF-β than full-term milk. Our objective was to compare TGF-β bioactivity in preterm vs. full-term milk and identify factors that activate milk-borne TGF-β. Mothers who delivered between 23 0/7 and 31 6/7 wk or at ≥37 wk of gestation provided milk samples at serial time points. TGF-β bioactivity and NF-κB signaling were measured using specific reporter cells and in murine intestinal tissue explants. TGF-β1, TGF-β2, TGF-β3, and various TGF-β activators were measured by real-time PCR, enzyme immunoassays, or established enzymatic activity assays. Preterm human milk showed minimal TGF-β bioactivity in the native state but contained a large pool of latent TGF-β. TGF-β2 was the predominant isoform of TGF-β in preterm milk. Using a combination of several in vitro and ex vivo models, we show that neuraminidase is a key regulator of TGF-β bioactivity in human milk. Finally, we show that addition of bacterial neuraminidase to preterm human milk increased TGF-β bioactivity. Preterm milk contains large quantities of TGF-β, but most of it is in an inactive state. Addition of neuraminidase can increase TGF-β bioactivity in preterm milk and enhance its anti-inflammatory effects.

Maternal breast milk transforming growth factor-beta and feeding intolerance in preterm infants

“…Although these high levels of TGF-beta, particularly in colostrum, could possibly afford the preterm infant protection against excessive inflammation, emerging evidence indicates that most of the TGF-beta in preterm milk exists in an inactive, latent state (19). We speculate that in utero inflammation associated with prematurity and low birth weight may trigger a counter-regulatory anti-inflammatory response that leads to increased maternal TGF-beta production, but the at-risk preterm infant may not always be able to derive full advantage from milk-borne TGF-beta because preterm milk is relatively deficient in the mechanisms that normally activate TGF-beta in milk.…”

“…Perhaps a larger study would have enough power to detect a difference with regards to feeding intolerance and maternal breast milk TGF-beta levels. Of interest, we recently published a separate study in which we report that although there is indeed a large pool of TGF-beta in preterm breast milk, the majority is latent, and preterm infants may be deficient in their ability to activate TGF-beta to the bioactive form (19). …”

Pathogenesis of NEC: Role of the innate and adaptive immune response

“…Third, breast milk contains immunoregulatory cytokines, such as IL-10 and TGF-β 57,58 . Monocytes obtained from preterm infants also seem to have lower ability to produce IL-10 59 and TGF-β 60 , potentially putting them at greater risk for inflammatory diseases.…”

Cytokines and growth factors in the developing intestine and during necrotizing enterocolitis

“…75–78 TGF-β2 is the primary determinant of TGF-β bioactivity in the preterm intestine (unlike plasma, where TGF-β1 is the dominant isoform), but is developmentally regulated and is expressed at low levels in the midgestation intestine. Orally-ingested milk-borne TGF-β2 could possibly patch this deficiency, but there are several physiological constraints: (1) preterm human milk contains a large pool of TGF-β2, but most of it exists in a latent form or sequestered by chondroitin sulfate proteoglycans 79,80 and (2) mothers who give birth to growth-restricted preterm infants may produce very low levels of TGF-β 2 in milk. 81 This deficiency is further accentuated in infants receiving formula that contains no TGF-β 2 .…”