Background Matrix metalloproteinases (MMPs) are a group of zinc-dependent-endopeptidases that play a key-role in the degradation of extracellular matrix (ECM). The expression of MMP and theirs tissue inhibitors (TIMP) in human milk (HM) was demonstrated in term but not in preterm infants.

Aim To measure the amounts of MMP and TIMP in milk obtained from mothers of preterm infants.

Methods We collected three samples of expressed HM from 18 mothers of PI (28–33 weeks’ gestation) and from 13 mothers of full term infants: one ⩽72 hours postpartum (colostrum) and once at 1 and 2 weeks postpartum (transitional and mature milk, respectively). MMPs activities and TIMP expression were measured by zymography using substrate-impregnated gels.

Results There was a decrease in MMP-2 activity between the colostrum and the transitional and mature milk samples. MMP-9 activity was greater in the colostrum samples than the others. There was a significant increase in TIMP expression over time, that was maximal at mature milk samples. TIMP expression was significantly higher in preterm compared to term milk at all 3 sampling times. Regression analysis revealed that TIMP expression correlated significantly with gestational age (R2 = 19%, p = 0.003).

Conclusion MMP-2, MMP-9 and TIMP expressions differ between colostrum and mature milk in both preterm and term milk. The balance between these extracellular proteases and their inhibitors might contribute to the beneficial biological effects of HM upon the developing gut, especially in preterm infants, possibly through modulation of growth and maturation.