Emerging evidence reveals that adipose tissue-associated inflammation is a main mechanism whereby obesity promotes colorectal cancer risk and progression. Increased inflammasome activity in adipose tissue has been proposed as an important mediator of obesity-induced inflammation and insulin resistance development. Chronic inflammation in tumor microenvironments has a great impact on tumor development and immunity, representing a key factor in the response to therapy. In this context, the inflammasomes, main components of the innate immune system, play an important role in cancer development showing tumor promoting or tumor suppressive actions depending on the type of tumor, the specific inflammasome involved, and the downstream effector molecules. The inflammasomes are large multiprotein complexes with the capacity to regulate the activation of caspase-1. In turn, caspase-1 enhances the proteolytic cleavage and the secretion of the inflammatory cytokines interleukin (IL)-1β and IL-18, leading to infiltration of more immune cells and resulting in the generation and maintenance of an inflammatory microenvironment surrounding cancer cells. The inflammasomes also regulate pyroptosis, a rapid and inflammation-associated form of cell death. Recent studies indicate that the inflammasomes can be activated by fatty acids and high glucose levels linking metabolic danger signals to the activation of inflammation and cancer development. These data suggest that activation of the inflammasomes may represent a crucial step in the obesity-associated cancer development. This review will also focus on the potential of inflammasome-activated pathways to develop new therapeutic strategies for the prevention and treatment of obesity-associated colorectal cancer development.

Background: Inflammasomes maintain tissue homeostasis and their altered regulation in the colon, and the adipose tissue (AT) leads to chronic activation of inflammatory pathways promoting colon cancer (CC) development. We aimed to analyze the potential involvement of inflammasomes in obesity-associated CC. Methods: Ninety-nine volunteers [61 with obesity (OB) and 38 normoponderal (NP)] further subclassified according to the approved protocol for the diagnosis of CC (58 without CC and 41 with CC) were included in the case-control study. Results: CC (P<0.01) and obesity (P<0.01) were accompanied by increased mRNA levels of NLRP3, NLRP6, ASC, IL1B and NOD2 in VAT. Contrarily, patients with CC exhibited a downregulation of NLRP6 and IL18 in their colon. Additionally, we revealed that the decreased Nlrp1 (P<0.05), Nlrp3 (P<0.01) and Nlrp6 (P<0.01) mRNA levels in the colon from obese rats significantly increase (P<0.05) after caloric restriction. Adipocyteconditioned media obtained from subjects with obesity reduced (P<0.01) the mRNA of NLRP3 as well as molecules involved in maintaining the intestinal integrity (MUC2, CLDN1 and TJP1) and the anti-inflammatory factors FGF21, KLF4, and IL33 and in HT-29 cells. We also found that the knockdown of NLRP6 in HT-29 cells significantly upregulated (P<0.05) the mRNA of NLRP1 and NLRP3 and inhibited (P<0.05) the expression levels of MUC2. Finally, we showed that the incubation of HT-29 with Akkermansia muciniphila influence (P<0.05) the inflammasome expression profile as well as intestinal integrity-related genes and aberrant inflammation. Conclusions: These findings provide evidence that the downregulated levels of NLRP6 and IL18 in the colon from patients with CC may be responsible for a reduced intestinal-barrier integrity, triggering local inflammation, which in turn acts on the dysfunctional AT in obesity, increasing the expression of different inflammasome components and flaring up a vicious cycle of uncontrollable inflammatory cascades that favours a pro-tumorigenic microenvironment.

Objective: The protein microfibril-associated glycoprotein (MAGP)-1 constitutes a crucial extracellular matrix protein. We aimed to determine its impact on visceral adipose tissue (VAT) remodelling during obesity-associated colon cancer (CC). Methods: Samples obtained from 79 subjects (29 normoponderal (NP) (17 with CC) and 50 patients with obesity (OB) (19 with CC)) were used in the study. Circulating concentrations of MAGP-1 and its gene expression levels (MFAP2) in VAT were analysed. The impact of inflammation-related factors and adipocyte-conditioned media (ACM) on MFAP2 mRNA levels in colon adenocarcinoma HT-29 cells were further analysed. The effects of MAGP-1 in the expression of genes involved in the extracellular matrix (ECM) remodelling and tumorigenesis in HT-29 cells was also explored. Results: Obesity (p < 0.01) and CC (p < 0.001) significantly decreased MFAP2 gene expression levels in VAT whereas an opposite trend in TGFB1 mRNA levels was observed. Increased mRNA levels of MFAP2 after the stimulation of HT-29 cells with lipopolysaccharide (LPS) (p < 0.01) and interleukin (IL)-4 (p < 0.01) together with a downregulation (p < 0.05) after hypoxia mimicked by CoCl2 treatment was observed. MAGP-1 treatment significantly enhanced the mRNA levels of the ECM-remodelling genes collagen type 6 α3 chain (COL6A3) (p < 0.05), decorin (DCN) (p < 0.01), osteopontin (SPP1) (p < 0.05) and TGFB1 (p < 0.05). Furthermore, MAGP-1 significantly reduced (p < 0.05) the gene expression levels of prostaglandin-endoperoxide synthase 2 (COX2/PTGS2), a key gene controlling cell proliferation, growth and adhesion in CC. Interestingly, a significant decrease (p < 0.01) in the mRNA levels of MFAP2 in HT-29 cells preincubated with ACM from volunteers with obesity compared with control media was observed. Conclusion: The decreased levels of MAGP-1 in patients with obesity and CC together with its capacity to modulate key genes involved in ECM remodelling and tumorigenesis suggest MAGP-1 as a link between AT excess and obesity-associated CC development.

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