Written by: Sandeep Ravindran, Ph.D. | Issue # 105 | 2021
- Sugars found in human milk, called human milk oligosaccharides (HMOs), have been shown to protect against bacterial pathogens and viruses.
- A new review provides an overview of evidence that HMOs might protect against viruses common in pediatric ICUs, including norovirus and respiratory syncytial virus.
- The findings further highlight the benefits of breastfeeding in protecting infants, while also adding to the potential applications of HMOs.
A surge in viral infections this past summer caused more children to be hospitalized than usual, and it’s not all COVID-19 [1,2]. Other respiratory viruses, including respiratory syncytial virus, have been hitting kids hard, highlighting how vulnerable they can be to viral infections. So it’s a good thing that in addition to providing nutrition, human milk can help protect against these diseases. Sugars called human milk oligosaccharides (HMOs) are abundant in human milk and are one of the human milk components that have been shown to have protective effects against a wide range of pathogens.
Many studies have shown how HMOs protect against bacterial pathogens, and Dr. Steven Townsend of Vanderbilt University wondered whether there was also evidence for their effects against viruses. “We know these compounds have activity against bacteria, so I told my students to start to figure out what’s known in the literature about their antiviral properties,” he says. In a new review article, Townsend and his co-authors present an overview of evidence that HMOs might also protect against several viruses [3]. “It turns out that these compounds do have some interesting antiviral properties,” he says.
Viruses recognize and bind to sugars in our body during infection, and the review article highlights several examples of human milk sugars functioning as a receptor decoy for viral binding and thus preventing viral infection [3]. “These compounds look like a lot of sugars that are on human surfaces, whether it’s in our saliva, on the mucus layer, in our eyes, or on our epithelium, and they become very potent decoy receptors,” says Townsend.
Townsend and his colleagues listed examples of binding between certain HMOs, such as 2-fucosyllactose and 3-fucosyllactose, and several viruses, including influenza, rotavirus, respiratory syncytial virus, human immunodeficiency virus (HIV), and norovirus, as well as evidence of such binding reducing viral infection [1–14]. They also found evidence of a role for HMOs in modulating the immune response, which can reduce infection by these viruses and also prevent necrotizing enterocolitis (NEC), an intestinal disease linked to viral infections [14–18]. Some studies have found disialyllacto-N-tetraose to be the most effective HMO in preventing NEC, although the underlying mechanism is still unclear [19,20].
High concentrations of HMOs present in breast milk have also been shown to reduce the risk of transmission of HIV to the infant through breastfeeding [13]. Researchers are also starting to look into whether SARS-CoV-2, the virus responsible for the COVID-19 pandemic, is transmitted through breastfeeding, and whether HMOs can serve as receptor decoys or have other protective effects against this virus [21].
The review article suggests that the antiviral properties of HMOs may be worth investigating further [3]. Researchers still don’t fully understand the specific structural basis for HMOs’ antiviral properties, and only a small number of known HMOs have been structurally characterized or evaluated for antiviral activity.
Figuring out ways to synthesize more HMOs would help researchers better study the link between their structure and their antiviral activity. “My group and others are figuring out ways to synthesize these compounds,” says Townsend. “I think if we’re careful and we’re smart, there are a lot of strategic applications for most of them,” he says.
The review highlights yet another way that human milk protects infants. “Breastfeeding is super powerful, and if you just go to the literature, you can see breastfed babies typically get sick far less than formula-fed babies, and HMOs are just a small part of that equation,” says Townsend. “Infant formula does not have HMOs, and there are companies that are trying to add them to formula, but they’re not adding 8 to 20 grams, so what we’re able to add at the moment is not even close to what moms can provide,” he says. So when it comes to protecting infants against infections, it seems like there’s no substitute for mother’s milk.
References
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2. Fox M, 2021. Respiratory infections other than Covid-19 are filling up pediatric wards. [online] CNN. Available at: <https://www.cnn.com/2021/08/26/health/respiratory-viruses-kids-rsv-rhinovirus-covid/index.html> [Accessed 18 October 2021].
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