Characterization of Nitric Oxide Modulatory Activities of Alkaline-Extracted and Enzymatic-Modified Arabinoxylans from Corn Bran in Cultured Human Monocytes

Abstract

The ingestion of foods and food-derived substances that may mediate the immune system is widely studied. Evidence suggests cereal arabinoxylans (AXs) have immunomodulatory activities that may impart health benefits in terms of immune enhancement. This study extracted AXs from corn bran using alkali and developed a modification process using three endoxylanases to obtain fractions of lower molecular weight ranges. In vitro studies showed extracted and modified AXs significantly (P < 0.05) elevated nitric oxide (NO) synthesis by the human U937 monocytic cell line (ranging from 53.7 ± 1.1 to 62.9 ± 1.2 μM per million viable cells) at all concentrations tested (5-1000 μg/mL), indicative of immune enhancement compared to an untreated control (43.7 ± 1.9 μM per million viable cells). The study suggested the dose range and Mw distribution of AXs are key determinants of immune-modulatory activity. AXs in the low Mw range (0.1-10 KDa) were the most effective at inducing NO secretion by U937 macrophages at low AX concentration ranges (5-50 μg/mL), with NO production peaking at 62.9 ± 1.2 μM per million viable cells with 5 μg/mL of AX (P = 0.0009). In contrast, AXs in the high Mw range (100-794 kDa) were most effective at inducing NO at high AX concentration ranges (500-1000 μg/mL) with NO production reaching a maximum of 62.7 ± 1.3 μM per million viable cells at 1000 μg/mL of AX (P = 0.0011). The findings suggest that dietary AXs from corn bran may heighten innate immune responses in the absence of infection or disease.

Regulation of inducible nitric oxide synthase by arabinoxylans with molecular characterisation from wheat flour in cultured human monocytes

“…This is consistent with the NO stimulatory activities of corn bran AXs with low and large Mw in U937 cells (Zhang et al, 2016). Although the peak NO secretion for the WEAX treatment may not have been reached in the assay, the findings suggest the maximum NO secretion was being approached and was substantially below that of E-WEAX.…”

“…The composition assessment was performed as previously described by Zhang et al (2016). The mobile phase was HPLC grade water for the HPLC, and isocratic elution was achieved using a Shimadzu LC-10ADvp pump.…”

“…The LPS and solubilised AX samples were diluted in RPMI-1640 medium to yield a series of typical concentrations (1, 5, 10, 50, 500 and 1000 lg mL À1 ) (Zhang et al, 2016) for the subsequent cell culture testing. The LPS and solubilised AX samples were diluted in RPMI-1640 medium to yield a series of typical concentrations (1, 5, 10, 50, 500 and 1000 lg mL À1 ) (Zhang et al, 2016) for the subsequent cell culture testing.…”

“…After 24-h incubation (Ghoneum & Gollapudi, 2003;Zhang et al, 2016), 40 lL from each well was mixed with 40 lL of trypan blue (Sigma-Aldrich, UK) for 1 min prior to analysis on a TC10 automated cell counter (Bio-Rad, UK). A 100 lL cell suspension at 1 9 10 6 viable cells per mL was pipetted into each well of a 96-well microplate.…”

“…In addition, the molecular characteristics, such as the molecular weight (Mw) and substitution degree (A/X) of cereal AXs, appear to affect their NO-inducing activities (Zhou et al, 2010;Zhang et al, 2016). The endo-b-(1,4)-xylanases (EC 3.2.1.8) are commonly involved in cereal AXs isolation and structural modification (Zhang et al, 2014).…”