In this study, we have evaluated anti-inflammatory activities of the oyster mushroom concentrate (OMC). Here we show that i) OMC markedly suppressed LPS-dependent production of TNF-α, IL-6, and IL-12 in macrophages; ii) OMC inhibited LPS-induced production of PGE2 and NO through the downregulation of expression of COX-2 and iNOS in macrophages, respectively; iii) OMC suppressed LPS-dependent activation of AP-1 and NF-κB; iv) OMC inhibited plasma levels of TNF-α and IL-6 in a mouse model of LPS-induced endotoxemia; v) OMC inhibited ConA-induced splenocyte proliferation and production of IFN-γ, IL-2, and IL-6; and vi) chemical analysis demonstrated the presence of α- and β-glucans, isoleucine, leucine, tyrosine, phenylalanine, AMP, CMP, GMP, and vitamin B2 in OMC. The results presented in this study are the first to demonstrate that OMC inhibits the inflammatory response in macrophages, possesses immunosuppressive activity, and inhibits inflammation in mice.
The immunomodulatory effects of mushrooms are usually associated with the stimulation of the immune system by a variety of polysaccharides. These effects include maturation of dendritic cells, stimulation of natural killer (NK) cell activity, and the activation of T and B lymphocytes [18, 41]. On the other hand an acidic polysaccharide isolated from Phellinus linteus (PL) decreased IL-2, IFN-γ, and TNF-α production in splenocytes . Methanol extract from Pleurotus florida demonstrated anti-inflammatory activities in vivo; however, the mechanism of its activity was not addressed . Interestingly, Yu et al recently demonstrated an induction of the immune response by the stimulation of the TNF-α production in RAW264.7 cells treated with the oyster mushroom Pleurotus eryngii . In contrast to Yu et al our data with the oyster mushroom Pleurotus ostreatus (oyster mushroom concentrate, OMC) demonstrates the opposite effect, inhibition of LPS-induced TNF-α production in RAW264.7 cells treated with OMC. Moreover, OMC demonstrated its anti-inflammatory effect by the inhibition of IL-6, IL-12, PGE2, and NO production in RAW264.7 cells. Mechanistically, these effects were mediated by the downregulation of expression of COX-2 and iNOS through the inhibition of transcriptional activity of AP-1 and NF-κB. In addition, OMC also suppressed plasma levels of TNF-α and IL-6 in mice challenged with LPS. Although Yu et al did not detect any changes in the ConA-induced secretion of IFN-γ from splenocytes isolated from mice fed with 1% oyster mushroom for 4 weeks, our data demonstrate that OMC suppressed ConA-induced proliferation as well as the secretion of IFN-γ, IL-2, and IL-6 from mouse splenocytes. The opposing results from the Yu et al study  and our study could be caused by several factors. Although the preparation of the oyster mushrooms in both studies is practically identical (freeze drying of the fresh mushrooms), in our study, we used a different strain of the oyster mushroom, Pleurotus ostreatus. In addition, we used a water extract (OMC) where insoluble particles were removed by the filtration, whereas Yu et al dissolved freeze-dried oyster mushroom in DMSO and used the whole, unfiltered extract. If, however, the same strain of mushroom had been used, the presence and amount of the biologically active compounds could be different. As mentioned above, the chemical composition of different lineages of the same mushroom could be dissimilar [36–38]. In addition, the conditions of growing, harvesting, processing, and storaging also affect the composition, and, therefore, the biological activity of the mushrooms [39, 40].
In our study, we analyzed the chemical composition of OMC, and we identified the water-soluble α- and β-glucans and small organic molecules. Therefore, this analysis could help develop a specific "fingerprint" for the biologically active mushrooms with particular activities. We previously tested the biological activities of Pleurotus ostreatus from different sources and identified the mushroom with the highest biological activity, which we then selected for use in our study (unpublished results). A more comprehensive chemical analysis of the OMC and further bioguided fractionation would enable a better understanding of the bioactives.
The anti-inflammatory activity of OMC can be attributed to different compounds. As previously mentioned, OMC contains the amino acids isoleucine, leucine, tyrosine, and phenylalanine. Interestingly, the original study published 25 years ago, demonstrated anti-inflammatory activity of isoleucine and leucine and suggested that this anti-inflammatory activity is related to interference with the action and/or synthesis of prostaglandins . Another compound with anti-inflammatory activity that we identified in OMC is vitamin B2. As recently demonstrated, vitamin B2 suppressed TNF-α, IL-1, IL-6, and NO plasma levels and downregulated expression of iNOS in livers in mice challenged with LPS [45, 46]. As previously mentioned, the most abundant compounds in mushrooms are glucans, and their presence is associated with the stimulation of the immune system . However, OMC contains 5.8% of water-soluble glucans (5.56% of β-glucans and 0.26% of α-glucans). Therefore, it is possible that these glucans are responsible for the anti-inflammatory activity of the oyster mushroom. As recently demonstrated, water soluble β-glucans from other edible mushrooms demonstrated anti-inflammatory activity through the inhibition of NO production in activated macrophages (Collybia dryophila) , the inhibition of leukocyte migration to injured tissues (Pleurotus pulmonarius) , and the inhibition of edema (Agaricus blazei) . In addition, an insoluble β-glucan (pleuran) from Pleurotus ostreatus suppressed inflammation in an animal model of colitis .