Immunomodulatory properties of water soluble arabinoxylans from extruded rice bran and wheat pentosan in an in vitro model of human monocytes and macrophages

Fadel, Abdulmannan Mohamad (2017) Immunomodulatory properties of water soluble arabinoxylans from extruded rice bran and wheat pentosan in an in vitro model of human monocytes and macrophages. Doctoral thesis (PhD), Manchester Metropolitan University.

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Abstract

Arabinoxylans (AXs) are major components of non-starch polysaccharides (NSPs). Recently, AXs have attracted a great deal of attention, because of their possible antitumor and immunomodulation activities. These activities have been suggested to be related to the content of low molecular weight (Mw) AXs, in particular those with a Mw below 32 kDa. Rice bran and wheat pentosan are rich sources of AXs. However, extraction of AXs is difficult and often gives low yield. Various methods have been used to increase the extraction yield of AXs with varying degrees of success, such as alkaline hydrolysis and enzymatic treatment. However, some of these treatments have been reported to be either expensive or produce hazardous wastes and non-environmentally friendly. Extrusion processing has been used to increase the solubility of cereal dietary fibre, however, these studies used alkaline or enzyme treatments with the extrusion to maximise the extraction yield. The use of extrusion alone as a pre-treatment method to increase the extraction yield and reduce the molecular weight (Mw) of AXs from rice bran or wheat endosperm pentosan has not been investigated. Hence, the current study aimed to determine if extrusion alone could change the extraction yield and Mw of the AXs. Wheat endosperm pentosan and rice bran were extruded with a twin-screw extruder at screw speeds of 80 and 160 revolutions per minute (rpm). It was found that the extraction yield of AXs increased with an increase in screw speed and was accompanied by a decrease in the Mw of the AXs. In vitro studies using immunoassays to measure proinflammatory markers showed that AXs from extruded rice bran and wheat pentosan significantly (P<0.05) increased nitric oxide (NO) and tumour necrosis factor α (TNFα) production from both U937 monocytes and macrophages in a concentration-dependent manner at (50, 500 and 1000 μg/ml), respectively. Moreover, the immunomodulatory activity of AXs was associated with the very low Mw of AXs. Moreover, inhibition of toll like receptor 4 (TLR4), which is known to be the receptor for bacterial lipopolysaccharides (LPS), significantly inhibited the AXs-induced increase in NO and TNFα production in both U937 monocytes and macrophages (P<0.05), suggesting the actions of AXs may be mediated at least in part through TLR4. The findings of this study indicate that AXs may compete with LPS for the same receptor TLR4, resulting in decreasing the inflammatory response that LPS produces during the infection. Thus AXs can produce a non-detrimental moderate increase in the inflammatory response.