Diet-induced metabolic endotoxemia is an important factor in the development of many chronic diseases in animals and man. The gut epithelium is an efficient barrier that prevents the absorption of liposaccharide (LPS). Structural changes to the intestinal epithelium in response to dietary alterations allow LPS to enter the bloodstream, resulting in an increase in the plasma levels of LPS (termed metabolic endotoxemia). LPS activates Toll-like receptor-4 (TLR4) leading to the production of numerous pro-inflammatory cytokines and, hence, low-grade systemic inflammation. Thus, metabolic endotoxemia can lead to several chronic inflammatory conditions. Obesity, diabetes, and non-alcoholic fatty liver disease (NAFLD) can also cause an increase in gut permeability and potential pharmacological and dietary interventions could be used to reduce the chronic low-grade inflammation associated with endotoxemia.
Background and Purpose There are no medications currently available to treat metabolic inflammation. Bruton's tyrosine kinase (BTK) is highly expressed in monocytes and macrophages and regulates NF‐κB and NLRP3 inflammasome activity; both propagate metabolic inflammation in diet‐induced obesity. Experimental Approach Using an in vivo model of chronic inflammation, high‐fat diet (HFD) feeding, in male C57BL/6J mice and in vitro assays in primary murine and human macrophages, we investigated if ibrutinib, an FDA approved BTK inhibitor, may represent a novel anti‐inflammatory medication to treat metabolic inflammation. Key Results HFD‐feeding was associated with increased BTK expression and activation, which was significantly correlated with monocyte/macrophage accumulation in the liver, adipose tissue, and kidney. Ibrutinib treatment to HFD‐fed mice inhibited the activation of BTK and reduced monocyte/macrophage recruitment to the liver, adipose tissue, and kidney. Ibrutinib treatment to HFD‐fed mice decreased the activation of NF‐κB and the NLRP3 inflammasome. As a result, ibrutinib treated mice fed HFD had improved glycaemic control through restored signalling by the IRS‐1/Akt/GSK‐3β pathway, protecting mice against the development of hepatosteatosis and proteinuria. We show that BTK regulates NF‐κB and the NLRP3 inflammasome specifically in primary murine and human macrophages, the in vivo cellular target of ibrutinib. Conclusion and Implications We provide “proof of concept” evidence that BTK is a novel therapeutic target for the treatment of diet‐induced metabolic inflammation and ibrutinib may be a candidate for drug repurposing as an anti‐inflammatory agent for the treatment of metabolic inflammation in T2D and microvascular disease.
We previously reported the Bruton's tyrosine kinase (BTK) inhibitors ibrutinib and acalabrutinib improve outcomes in a mouse model of polymicrobial sepsis. Now we show that genetic deficiency of the BTK gene alone in Xid mice confers protection against cardiac, renal, and liver injury in polymicrobial sepsis and reduces hyperimmune stimulation (“cytokine storm”) induced by an overwhelming bacterial infection. Protection is due in part to enhanced bacterial phagocytosis in vivo , changes in lipid metabolism and decreased activation of NF-κB and the NLRP3 inflammasome. The inactivation of BTK leads to reduced innate immune cell recruitment and a phenotypic switch from M1 to M2 macrophages, aiding in the resolution of sepsis. We have also found that BTK expression in humans is increased in the blood of septic non-survivors, while lower expression is associated with survival from sepsis. Importantly no further reduction in organ damage, cytokine production, or changes in plasma metabolites is seen in Xid mice treated with the BTK inhibitor ibrutinib, demonstrating that the protective effects of BTK inhibitors in polymicrobial sepsis are mediated solely by inhibition of BTK and not by off-target effects of this class of drugs.
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