Comparative effectiveness of 4 natural and chemical activators of Nrf2 on inflammation, oxidative stress, macrophage polarization, and bactericidal activity in an in vitro macrophage infection model.

Inflammation plays a crucial role in the defense response of the innate immune system against pathogen infection. In this study, we selected 4 compounds for their potential or proven anti-inflammatory and/or anti-microbial properties to test on our in vitro model of bacteria-infected THP-1-derived macrophages. We first compared the capacity of sulforaphane (SFN), wogonin (WG), oltipraz (OTZ), and dimethyl fumarate (DMF) to induce the nuclear factor erythroid 2-related factor 2 (Nrf2), a key regulator of the antioxidant, anti-inflammatory response pathways. Next, we performed a comparative evaluation of the antioxidant and anti-inflammatory efficacies of the 4 selected compounds. THP-1-derived macrophages and LPS-stimulated macrophages were treated with each compound and expression levels of genes coding for inflammatory cytokines IL-1ß, IL-6, and TNF-α were quantified by RT-qPCR. Moreover, expression levels of genes coding for M1 (IL-23, CCR7, IL-1ß, IL-6, and TNF-α) and M2 (PPARγ, MRC1, CCL22, and IL-10) markers were determined in classically-activated M1 macrophages treated with each compound. Finally, the effects of each compound on the intracellular bacterial survival of gram-negative E. coli and gram-positive S. aureus in THP-1-derived macrophages and PBMC-derived macrophages were examined. Our data confirmed the anti-inflammatory and antioxidant effects of SFN, WG, and DMF on LPS-stimulated THP-1-derived macrophages. In addition, SFN or WG treatment of classically-activated THP-1-derived macrophages reduced expression levels of M1 marker genes, while SFN or DMF treatment upregulated the M2 marker gene MRC1. This decrease in expression of M1 marker genes may be correlated with the decrease in intracellular S. aureus load in SFN- or DMF-treated macrophages. Interestingly, an increase in intracellular survival of E. coli in SFN-treated THP-1-derived macrophages that was not observed in PBMC-derived macrophages. Conversely, OTZ exhibited pro-oxidant and proinflammatory properties, and affected intracellular survival of E. coli in THP-1-derived macrophages. Altogether, we provide new potential therapeutic alternatives in treating inflammation and bacterial infection.

Sulforaphane reduces intracellular survival of Staphylococcus aureus in macrophages through inhibition of JNK and p38 MAPK­induced inflammation.

Macrophages are active contributors to the innate immune defense system. As macrophage activation is clearly affected by the surrounding microenvironment, the present study investigated the effect of sulforaphane (SFN) on the bactericidal activity of macrophages and the underlying molecular mechanisms involved in this process. Human THP­1­derived macrophages, primary human peripheral blood mononuclear cell­derived macrophages, and primary mouse bone marrow derived­macrophages (BMDMs) pretreated with SFN or DMSO were utilized in a model of Staphylococcus aureus infection. The results suggested that SFN pretreatment of macrophages effectively repressed the intracellular survival of S. aureus through modulation of p38/JNK signaling and decreased S. aureus­induced caspases­3/7­dependent cell apoptosis, potentially through downregulation of microRNA (miR)­142­5p and miR­146a­5p. As SFN is a well­known activator of nuclear factor erythroid 2­related factor 2 (Nrf2), Nrf2­/­ BMDMs were used to demonstrate that the SFN­mediated inhibitory effect was independent of Nrf2. Nevertheless, an increase in intracellular bacterial survival in Nrf2­deficient macrophages was observed. In addition, SFN pretreatment suppressed S. aureus­induced transcriptional expression of genes coding for the proinflammatory cytokines interleukin (IL)­1ß, IL­6, and tumor necrosis factor­α (TNF­α), as well as for the M1 markers C­C motif chemokine receptor 7, IL­23 and inducible nitric oxide synthase (iNOS). Western blot analysis indicated that S. aureus challenge activated p38 mitogen­activated protein kinase (MAPK) (p38) and c­Jun N­terminal kinase (JNK) MAPK signaling pathways, while SFN pretreatment prevented p38 and JNK phosphorylation. Pretreatment with 2 specific inhibitors of p38 and JNK, SB203580 and SP600125, respectively, resulted in a decrease in S. aureus­induced proinflammatory gene expression levels compared with those observed in the SFN­pretreated macrophages. Furthermore, THP­1­derived macrophages pretreated with SB203580 or SP600125 prior to bacterial infection exhibited a significant inhibition in intracellular S. aureus survival. In conclusion, we hypothesize that concomitant targeting of the p38/JNK­inflammatory response and the S. aureus­induced apoptosis with SFN may be a promising therapeutic approach in S. aureus infection.