Oxidative stress-mediated bimodal regulation of polymorphonuclear leukocyte spreading by polyphenolic compounds

Pyrogallol-bearing polyphenolic compounds induce spreading of polymorphonuclear leukocytes (PMNL), although their optimal concentrations for induction of spreading are quite different (2000, 200, and 2 μM for pyrogallol, (−)-epigallocatechin gallate (EGCG), and tannic acid (TA), respectively), and TA tends to inhibit spreading at higher concentrations. In this study, we examined the involvement of oxidative stress in the regulation of PMNL spreading by these compounds. All three compounds in solution generated H2O2 to a similar extent. Adsorption of the polyphenols to cell surfaces and their accumulation within cells were assessed by detection of the H2O2 precursor O2− produced by the compounds through reduction of cytochrome c and p-nitro-blue tetrazolium, respectively. TA showed the highest degree of adsorption. EGCG adhered only to PMNL pre-fixed by paraformaldehyde, whereas pyrogallol did not adhere. None of the compounds caused intracellular O2− generation. A non-pyrogallic compound, 1,2,4-benzenetriol (BT), also produced H2O2; it had no stimulatory effect on PMNL spreading, but inhibited spreading induced by other stimuli. BT did not adhere to PMNL but accumulated within them, and generated O2− in the presence of glycine. Thiol antioxidants abrogated all of the above spreading-regulatory effects of the polyphenolic compounds. We conclude that H2O2-generating polyphenols bimodally regulate the spreading of PMNL by subjecting them to oxidative stress. The ability of polyphenol to adhere to, or accumulate within, PMNL may govern the nature of the oxidative stress and determine the optimal concentration of each compound for induction of spreading, as well as whether spreading is promoted or inhibited.

Research highlights
► The NAA concentration in the hippocampus is significant reduced in patients with schizophrenia.
► Pyrogallic compounds affect cellular functions by generating H2O2 outside them.
► Adhesiveness of pyrogallic compounds to cells governs the strength of their effects.
► 1,2,4-Benzenetriol penetrates into cells and oxidatively inactivate target molecules.