PhD Scientific Days 2023

Molecular Sciences - Posters B

Neutrophil Effector Functions are Significantly Enhanced in the Presence of Bicarbonate

Text of the abstract

Background: Recent studies have suggested, that bicarbonate has far more diverse effects than a simple buffer system. It has been described that it inhibits the growth and biofilm formation of different pathogen bacteria, increases the activity of antimicrobial peptides, and enhances bacterial susceptibility to certain antibiotics. Although HCO3- has been shown to regulate neutrophil extracellular trap (NET) formation, there is no data about its effects on other important neutrophil functions. Therefore, in our current study, we aim to investigate the impact of HCO3- on these functions using human polymorphonuclear leukocytes (PMN).
Methods: PMNs were isolated from the blood of healthy volunteers. The phagocytosis of serum opsonized S. Aureus was detected with flow cytometry. Superoxide burst of neutrophils was measured with lucigenin luminescence assay upon opsonized zymosan stimulus. The S. aureus killing capacity of PMN was assessed using the bacterium survival assay. The migration capacity of neutrophils was measured using transwell assay and IL-8 production was determined with the use of an ELISA kit. In each set of experiments, we used the following conditions: plain Hank’s Balanced Salt Solution (HBSS), or HBSS supplemented with 25 or 50 mM NaHCO3 in a 5% CO2 environment, and as adequate controls, plain HBSS or HBSS supplemented with 25 or 50 mM NaCl in an ambient air environment.
Results: Both 25 and 50 mM NaHCO3 significantly increased the phagocytosis capacity of neutrophils compared to osmotic controls, and this difference proved to be pH independent. Intracellular superoxide production and bacterium-killing capacity of PMN were also elevated by HCO3-. We found no effect of bicarbonate on the transmigrating capability and IL-8 production of neutrophils.
Conclusions: Apart from the previously described antibacterial properties of bicarbonate, our data suggest that HCO3- stimulates important effector functions of PMNs. We believe that these beneficial effects of HCO3- could complement each other making bicarbonate a very effective therapeutic agent in infectious diseases where clearance of bacteria by neutrophils is especially important (e.g., in cystic fibrosis).
Funding: EFOP-3.6.3-VEKOP-16-2017-00009, NKFIH FK_18/128376, TKP2021-EGA-24, Semmelweis 250+ Excellence PhD Scholarship