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Aug 28, 2012

Superbug Succumbs to Vitamin-Boosted Immune System

  • New evidence indicates that the vitamin B3 (nicotinamide, NAM) can directly boost the immune system’s ability to fight serious Staphylococcus infections, including MRSA. In vivo studies in mice and in vitro work with human blood have shown that treatment with NAM administered prophylactically or therapeutically enhances the clearance of staphylococcal infection by up to 1,000-fold. The Cedars-Sinai Medical Center team reporting the studies say that the vitamin acts by increasing expression and activity of the myeloid-specific transcription factor CCAAT/enhancer-binding protein ε (C/EBPε) in myeloid cells, and particularly in the neutrophils that were largely responsible for the NAM-related increase in bacterial cell killing.

    George Y. Liu, M.D., et al., suggest the results not only highlight C/EBPε as a target for boosting the innate immune system’s ability to combat infection, but also indicate that formal clinical trials with NAM are warranted. The researchers report their findings in the Journal of Clinical Investigation, in a paper titled “C/EBPε mediates nicotinamide-enhanced clearance of Staphylococcus aureus in mice.”

    The use of NAM as a modulator of inflammation is well reported, and the vitamin is prescribed topically for treating a number of inflammatory skin conditions. However, while NAM has also been shown to improve survival of experimental mice with Gram-positive and Gram-negative sepsis, its potential role as an antimicrobial agent isn’t well understood.

    The myeloid-specific transcription factor CCAAT/enhancer-binding protein ε (C/EBPε), meanwhile, plays an essential role in the terminal differentiation and functional maturation of neutrophils and monocytes/macrophages. Its potential link with NAM relates to the fact that the vitamin acts as a competitive inhibitor of class III histone deacetylase (HDACs) enzymes, and these enzymes are involved in the regulation of C/EBPε and, potentially, its downstream targets.

    In a series of experiments designed to further investigate the effects of NAM on C/EBPε and antibacterial immune responses, the researchers first turned to a mouse model lacking the Cebpe gene (Cebpe-/- mice) that codes for C/EBPε. Their studies showed that the Cebpe knockout animals were far more severely affected by infection with S. aureus than wild-type mice, and displayed increased systemic spread of bacteria to organs. This lack of ability to clear the infection was associated with reduced neutrophil function. “After S. aureus challenge, C/EBPε-deficient mice exhibited dramatic skin pathology, were unable to clear S. aureus at the infection site, and had permitted systemic spread of the bacteria to spleens and kidneys,” the authors write.

    Conversely, forcing overexpression of Cebpe in myeloid cells in vitro significantly increased the cells’ bactericidal capabilities over and above those of unmodified cells. In this case the Cebpe-overexpressing myeloid cells were capable of killing up to 30-fold more S. aureus than unmodified myeloid cells.

    The team moved on to treat peripheral blood from healthy human volunteers with NAM, and then subsequently infected the blood with S. aureus. They found that NAM pretreatment boosted levels of C/EBPε in neutrophils, and resulted in up to 1,000-fold greater level of pathogen clearance after three hours when compared with untreated blood. Testing the effects of NAM therapy on neutrophil and mononuclear fractions separately confirmed that it was the NAM-treated neutrophils that appeared responsible for the increase in bacterial cell-killing ability. Encouragingly, NAM pretreatment of human peripheral blood also improved the clearance of infection with other pathogens, including K. pneumonia and P. aeruginosa.

    The combined results thus far indicated that increased C/EBPε production boosts the ability of neutrophils in the blood to kill bacterial infections, and that NAM treatment directly impacts on this neutrophil cell-killing activity. However, the experiments had all looked at the effects of C/EBPε levels or NAM treatment prior to infection. To see whether NAM administration could improve the ability of neutrophils to clear an existing infection the team established systemic S. aureus infection in wild-type mice and only 12 hours later started daily treatment with NAM. Again, within 60 hours of infection the number of bacteria recovered from the spleens and kidneys of NAM-treated mice was 30-fold to 1,000-fold lower than the number recovered from untreated controls.

    “Our results constitute a proof of principle that compounds exerting modulatory effects of the myeloid-specific transcription factor C/EBPε may be suitable candidates for antimicrobial therapeutics,” the authors conclude. “Our finding that NAM has an important effect on immune-mediated killing of S. aureus in mouse and in human blood has a number of additional therapeutic implications. In an age when the number of antibiotics in the pipeline is limited and development of resistance occurs rapidly, use of complementary strategies to antibiotic treatment would provide a method of limiting development of antibiotic resistance. Because C/EBPε is a transcriptional activator of a number of important antimicrobial factors, induction of resistance to multiple host factors is less likely. Likewise, the use of an immune-boosting strategy coupled with conventional antibiotics could provide important synergy.”


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