Lactational Transfer of Sulforaphane to Activate Nrf2 in Neonatal Mice

Abstract

Respiratory syncytial virus (RSV) is the leading etiological factor for pneumonia, bronchiolitis, and post-bronchiolitic wheeze in children less than five years old. Besides palivizumab, an RSV prophylactic used for premature infants, there are no effective immunoprophylactics for term-infants; therefore, the use of phytochemicals has gained traction as potential therapeutics that may reduce RSV severity in neonates. RSV disease severity is the result of an exaggerated Th2 response from the host immune system, in addition to a substantial production of reactive oxygen species (ROS). RSV has been shown to downregulate several antioxidant-related genes regulated by the transcription factor Nrf2, including Nqo1, Hmox1, Gsta1, and Gpx2. Induction of Nrf2 by the phytochemical sulforaphane (SFN), derived from cruciferous vegetables, has been shown to increase Nqo1 expression, decreasing ROS and RSV severity in an adult mouse model. Currently, very little is known about the lactational transfer of SFN into breast milk and whether transfer can potentially activate Nrf2 to reduce RSV severity in neonates. The in vivo studies of experiment 1 and experiment 2 that included maternal dietary supplementation with sulforaphane, were carried out to assess the lactational transfer of SFN/SFN metabolites and subsequent induction of Nrf2-controlled genes in the nursing offspring. Sub-acute SFN supplementation (for 5 and 14 days, respectively) revealed the presence of SFN-N-Acetyl-cystine (SFN-NAC) in maternal plasma and milk. Nrf2-related gene expression was increased in maternal and neonatal liver and lung tissues. Next, in a survey of human breast milk, we were able to confirm low levels of SFN-NAC in milk from mothers consuming dietary levels of cruciferous vegetables. Last, to determine if the lactational transfer of SFN-NAC could decrease RSV severity, we tested maternal dietary SFN supplementation using an in vivo neonatal RSV model. Viral load and Th2 inflammatory-related genes were evaluated. Overall, there were no differences across all assays in neonates from both experimental groups emphasizing the importance of optimizing maternal/neonatal dose for protection against respiratory infection. In conclusion, this research demonstrates for the first time that the SFN metabolite SFN-NAC can be transferred in breast milk resulting in the induction of Nrf2-controlled genes in neonates. It remains a question whether this induction can reduce RSV-induced inflammation and what the appropriate dosing regimen may be for lactating mothers. In summary, these studies represent important first steps in designing natural therapeutic interventions using novel dosing strategies for infants at risk for respiratory infection.