Ask-the-Expert: Explore a new human milk oligosaccharide (HMO) review revealing how HMO combinations can support infant health

• It is now possible to manufacture and combine a select number of human milk oligosaccharides (HMOs)—a key component of human breast milk, the gold standard for infant nutrition—to fortify nutrition solutions for early life.
• Growing pre-clinical and clinical evidence reveals how HMO blends may offer health benefits for infants.
• In this blog, lead author of a new review paper on the biological effects of structurally diverse HMO combinations,¹ Dr. Anita Wichmann, Lead Expert in Regulatory Affairs for Early Life Nutrition and Medical Nutrition at dsm-firmenich, explains how the structures of different HMOs influence their health benefits, and how we can support better infant nutrition with combinations of HMOs.

HMOs are a diverse group of carbohydrates that contribute greatly to infant health and development, particularly in shaping the infant microbiota.² More recent evidence indicates that HMOs also play important roles in protecting against pathogens, supporting the immune system, and potentially influencing brain and cognitive development.^3,4,5

Until recently, these fundamental compounds were only available to breastfed infants. However, technological developments in the last decade have made it possible to produce certain HMOs at scale to fortify infant nutrition—and clinical studies show these solutions positively influence infant health.⁶

As the number of HMOs that can be manufactured at scale grows, there is a pressing need to better understand the unique and differential effects of individual HMOs, and HMO blends. Dr. Anita Wichmann recently published a review paper in Frontiers in Pediatrics examining the current evidence and potential health benefits of combining multiple HMOs with diverse structures.¹ We sat down with Dr. Wichmann to discuss her findings, and learn what the future holds for early life nutrition HMO innovation.

1. What is known about different HMO structures, and how does this affect their function?

“Over 200 different HMOs have been detected in human breast milk. These carbohydrates are each made up of a lactose core (which features the two sugar units, glucose and galactose), and additional sugar molecules—such as fucose, N-acetylglucosamine or sialic acid—arranged in different structures. HMOs vary greatly in size, with the smallest made up of only three sugar units (lactose plus fucose, e.g. 2’-fucosyllactose, or lactose plus sialic acid, e.g. 3’-sialyllactose) and the largest containing up to 14 (Figure 1). Importantly, these structures affect how each HMO functions and the benefits they provide.

“HMOs are generally classified as belonging to one of three major structural classes, based on their sugar composition:

• Fucosylated—containing fucose
• Neutral core—containing N-acetylglucosamine
• Sialylated—containing sialic acid

Figure 1. (A) All HMOs have a lactose backbone that can be extended with fucose, sialic acid, or units of N-acetylglucosamine and galactose. (B) 2’-fucosyllactose (2’-FL) is an example of a fucosylated HMO. (C) Complex HMOs can be branched and modified with fucose, sialic acid and/or N-acetylglucosamine.

“In human breast milk, types and levels of different HMO structures vary by individual and throughout lactation as infants’ needs evolve, but fucosylated HMOs tend to account for the greatest proportion (60-70%) of the HMO pool.^7,8

“HMOs are broken down by bacteria in the infant’s gut, ‘feeding’ the gut microbiome and releasing the different sugar units. Some bacterial species in the gut can utilize a wide range of structurally diverse HMOs, whereas others have more limited capacity. Then, depending on their specific structures, the released sugar units can function as growth substrates for other intestinal bacteria (i.e. cross-feeding), modulate intestinal processes such as inflammation, or be absorbed and affect other areas of the body including the brain.”

2. How could increasing the number of HMOs in infant nutrition solutions better support health?

“Given how HMO structure impacts how they function, it’s hypothesized that increasing the number and structural diversity of HMOs would provide a wider array of health benefits—and there is a growing body of scientific evidence to support this theory.

“For example, a recent in vitro study reported that a mix of six HMOs—two from each structural class—promoted greater abundance and diversity of Bifidobacteriacaea (the dominant group of bacteria in breastfed infants’ gut microbiota), compared to just one or two HMOs.⁹ These findings have been further substantiated by clinical studies in infants, which found that blends of five HMOs brought the gut microbiota composition closer to that of breastfed infants.^10,11

“In relation to neonatal immune health, HMO function is highly dependent on structure, even within the major classes. Interestingly, 3’-sialyllactose (3’-SL) and 6’-sialyllactose (6’-SL)—which are made up of the same three sugar units but with different 3D structural conformations—differ in their ability to reduce infectivity of specific respiratory viruses in vitro.¹² Moreover, data from pre-clinical research indicate that 2’-fucosyllactose (2’-FL)—a fucosylated HMO—as well as 3’-SL and 6’-SL, sialylated HMOs, could play important roles in brain development and cognition, but through distinct mechanisms.¹³

“Together, this evidence suggests that fortifying infant nutrition solutions with a greater number of HMOs would provide a broader range of health benefits, although more clinical intervention studies are needed to better support this.”

3. What are the major challenges associated with investigating the effects of individual HMOs and HMO mixtures?

“Conducting high quality clinical trials in young infants requires robust study design, adequate sample sizes, complex logistics, and significant financial resources. Due to this complexity and expense, it is not possible to perform clinical trials comparing the physiological effects of every HMO and every combination. Therefore, pre-clinical studies are key for understanding the individual and synergistic effects of HMOs and selecting the mixtures with the greatest potential to support infant health and development. This sets the stage for clinical trials and gives us the best chance for success.”

4. Which HMOs can currently be manufactured at scale and what are the barriers to manufacturing more?

“Currently, seven HMOs are available for large-scale production:

• 2’-FL
• 3-fucosyllactose (3-FL)
• 2’-FL/Difucosyllactose (DFL)
• Lacto-N-tetraose (LNT)
• Lacto-N-neotetraose (LNnT)
• 3’-SL
• 6’-SL

“These represent some of the most abundant HMOs from each of the three major structural classes, and are also among the smallest HMO structures, all being composed of only three to four sugar units.

“These smaller HMOs are produced by genetically engineered bacteria in a limited number of enzymatic steps. However, the production of larger HMOs—consisting of five or more sugar units—poses technical challenges, as more enzymatic steps are required, and the larger structures are harder for the bacteria to excrete. Therefore, in order to support the commercial production of these larger, more complex HMOs, alternative technologies need to be developed and optimized. At dsm-firmenich, we are developing this area to build on promising research indicating potentially unique and important health benefits for some larger HMO structures.”

5. In order to better understand the benefits of HMO combinations, which areas of research need particular focus in the future?

“Current knowledge on the mechanisms and health benefits of HMOs is mostly based on smaller HMO structures, due to their greater availability. However, the HMO field would benefit greatly from pre-clinical screenings of a wider variety of structures—and combinations of structures—to better map their differential and unique roles. In addition, clinical studies are needed to validate the benefits (indicated by pre-clinical data) of combining multiple HMOs for immunity and brain development. Further investigations could also reveal the potential of HMO mixtures for other health areas, such as metabolic function.  

“With ongoing investment in HMO production and research, we can find the combinations that provide the broadest range of benefits possible, transforming early life nutrition for infants worldwide.”