Methylglyoxal May Affect Hydrogen Peroxide Accumulation in
Manuka Honey Through the Inhibition of Glucose Oxidase
Although hydrogen peroxide (H2O2) is one of the major
antibacterial factors in most honeys, it does not accumulate in medical-grade
manuka honey. The goal of this study was to investigate the effect of
artificially added methylglyoxal (MGO) on H2O2 accumulation in natural
non-manuka honeys. H2O2 concentrations in the honey solutions were determined
using a fluorimetric assay. Two, the most potent H2O2 producers honeydew honeys
were mixed with MGO at final concentrations of 250, 500, and 1000 mg/kg, and
incubated for 4 days at 37°C. Subsequently, H2O2 concentrations were determined
in 50% (wt/vol) MGO supplemented honey solutions. In vitro crosslinking of the
enzyme glucose oxidase (GOX) after incubation with MGO was determined by sodium
dodecyl sulfate–polyacrylamide gel electrophoresis. Tested honeys at a
concentration of 50% (wt/vol) accumulated up to 495.8±9.1 μM H2O2 in 24 h. The
most potent producers were the two honeydew honeys, whose 50% solutions
accumulated 306.9±6.8 and 495.8±9.1 μM H2O2, respectively. Levels of H2O2
increased significantly over time in both honey solutions. Contrary to this,
the MGO-treated honeys generated significantly lower amounts of H2O2
(P<.001), and this reduction was dose dependent. In addition, MGO-treated
GOX formed high molecular weight adducts with increasing time of incubation
accompanied by loss of its enzymatic activity. High levels of MGO in manuka
honey, by modifying the enzyme GOX, might be responsible for suppressing H2O2
generation. These data highlight the detrimental effect of MGO on significant
proteinaceous components of manuka honey.
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