Digested artificial baby milk, but not breastmilk, kills normal cells

Article written by Dr Susan Tawia, Senior Scientific Information Officer, Breastfeeding Information and Research team, for the October 2013 health professional member eNewsletter.

Scientists have long known that premature infants fed artificial baby milk are more likely to develop necrotising enterocolitis than those fed breastmilk, but the underlying mechanism has not been understood. According to a study by Penn and others (2012), free fatty acids created during the ‘digestion’ of artificial baby milk to mimic what happens in the stomach of an infant, cause cell death that may contribute to necrotising enterocolitis.

Penn and Schmid-Schönbein (2008) found previously that partially-digested food in a mature, adult intestine is cytotoxic (capable of killing cells) due to the presence of free fatty acids that damage cell membranes. The intestines of healthy adults and older children have a mature mucosal barrier that may prevent damage due to free fatty acids. However, the observation that the intestine is leakier at birth, particularly in preterm infants, could explain their increased susceptibility to necrotising enterocolitis. A recent study by Penn and others (2012) compared the ability of ‘digested’ fresh human breastmilk and nine different artificial baby milks to kill neutrophils, intestinal epithelial cells and endothelial cells. They hypothesised that, after enzyme digestion, artificial baby milk, but not breastmilk would contain free fatty acids that would be cytotoxic to cells and cause their death.

The researchers ‘digested’ artificial baby milks marketed for full-term and preterm infants, as well as fresh breastmilk using digestive enzymes. They then tested the artificial baby milk and breastmilk for levels of free fatty acids. They also tested whether these fatty acids killed three types of cells potentially involved in necrotising enterocolitis: epithelial cells that line the intestine, endothelial cells that line blood vessels and neutrophils (a ‘first responder’ to inflammation caused by trauma in the body).

Overwhelmingly, ‘digested’ artificial baby milk led to cell death, or cytotoxicity, in as little as 5 minutes in some cases, while breastmilk did not. For example, ‘digested’ artificial baby milk caused death in 47% to >90% of neutrophils, while only 6% of neutrophils died as a result of exposure to ‘digested’ breastmilk (Table 1). Free fatty acid levels were found to be significantly higher in ‘digested’ artificial baby milk compared to breastmilk and free fatty acid levels were correlated with neutrophil cytotoxicity. ‘Digested’ artificial baby milk was also found to be more cytotoxic than ‘digested’ breastmilk when it was added to intestinal epithelial cells and endothelial cells in vitro.

 

Control

Lipase 'digested'

Fresh breastmilk

3.0 ± 1.7

6.2 ± 7.4

Enfamil Infant

10.1 ± 7.3

60.0 ± 15.6

Similac Advance

8.6 ± 7.3

93.4 ± 3.3

Similac Soy

4.3 ± 2.1

70.8 ± 13.5

Enfamil Premature 20 kcal/oz

9.8 ± 4.9

95.0 ± 3.1

Enfamil EnfaCare 22 kcal/oz

11.6 ± 2.6

46.7 ± 10.1

Similac Special Care 20 kcal/oz

12.6 ± 3.1

97.0 ± 0.4

Similac Expert Care NeoSure 22 kcal/oz

16.5 ± 5.6

90 ± 1.9

Table 1 Neutrophil cell death after 1 hr exposure to control fluid (phosphate-buffered saline) and breastmilk or artificial baby milk that had been ‘digested’ with lipase.

The study found that all ‘digested’ artificial baby milks tested in this way were cytotoxic, but ‘digested’ breastmilk was not. The research team proposed that most food, including artificial baby milk, released high levels of free fatty acids during digestion, but that breastmilk is digested in a manner that does not release cytotoxic free fatty acids.

Breastmilk kills cancer cells

In contrast, two components of breastmilk have been found to be capable of killing cancer cells in vitro.

Human Alpha-lactalbumin Made LEthal to Tumour cells (HAMLET) is a protein-fatty acid complex derived from human milk, which kills cancer cells. Synthetic HAMLET has been shown to reduce papillomas and bladder cancer when applied directly. HAMLET is formed in the laboratory at low pH from α-lactalbumin and oleic acid which are both present in human milk, though the HAMLET complex is not. Researchers have speculated that HAMLET may form in the infant’s stomach and this might contribute to the difference in incidence of cancer between breastfed and artificially-fed infants (Mok et al 2007). (Breastfed infants have a lower incidence of acute myelogenous leukaemia and acute lymphocytic leukaemia than artificially-fed infants [Ip et al 2007]).

TNF-Related Apoptosis-Inducing Ligand (TRAIL) is another component of human milk that is able to kill cancer cells. TRAIL binds to ‘death receptors’ on the surface of cancer cells and sets off the process of cell death or apoptosis. It is not entirely clear why TRAIL doesn’t kill normal cells, but possibly normal cells have many decoy receptors that compete with the active death receptors for binding to TRAIL. TRAIL has other functions too and may be involved in promoting cell differentiation in the gut lining. Researchers are investigating ways to use TRAIL in cancer treatments (Allen & El-Deiry 2012; Stolfi, Pallone & Montelone 2012). TRAIL has been found in human milk at levels 100 times those in serum (Davanzo et al 2012).

Reports of components in breastmilk that have the capacity to kill cancer cells in vitro have given some patients the hope that breastmilk might help them. Rough and others (2009) reported a study of 10 cancer patients’ experiences using human milk. Most of the patients reported feeling some benefit, such as an increase in appetite or less nausea during chemotherapy. However, the study did not use any objective measure of improvement in the patients’ health.

 

References

Allen JE, El-Deiry W 2012, Regulation of the human TRAIL gene. Cancer Biol Ther 13(12): 1–9.

Davanzo R, Zauli G, Monasta L, Brumatti LV, Abate MV, Ventura G, Rimondi E, Secchiero P, Demarini S 2012, Human colostrum and breast milk contain high levels of TNF-Related Apoptosis-Inducing Ligand (TRAIL). J Hum Lact doi:10.1177/0890334412441071.

Ip S, Chung M, Raman G, Chew P, Magula N, DeVine D, Trikalinos T, Lau J 2007, Breastfeeding and maternal and infant health outcomes in developed countries – executive summary. Rockville MD: Agency for Healthcare Research and Quality. Evidence report/technology assessment: No 153.

Mok KH, Pettersson J, Orrenius S, Svanborg C 2007, HAMLET, protein folding and tumour cell death. Biochem Biophys Res Commun 354(1): 1–7.

Penn AH, Altshuler AE, Small JW, Taylor SF, Dobkins KR, Schmid-Schönbein GW 2012, Digested formula but not digested fresh human milk causes death of intestinal cells in vitro: implications for necrotizing enterocolitis. Pediatric Res 72(6): 560–567.

Penn AH, Schmid-Schönbein GW 2008, The intestine as source of cytotoxic mediators in shock: free fatty acids and degradation of lipid-binding proteins. Am J Physiol Heart Circ Physiol 294(4): H1779-1792.

Rough SM, Sakamoto P, Fee CH, Hollenbeck CB 2009, Qualitative analysis of cancer patients' experiences using donated human milk. J Hum Lact 25(2): 211–219.

Stolfi C, Pallone F, Monteleone G 2012, Molecular Targets of TRAIL-Sensitizing Agents in Colorectal Cancer. Int J Mol Sci 13(7): 7886-7901.