Asiatic acid ameliorates dextran sulfate sodium-induced murine experimental colitis via suppressing mitochondria-mediated NLRP3 inflammasome activation

Asiatic acid inhibits lung cancer cell growth in vitro and in vivo by destroying mitochondria

Asiatic acid (AA), a pentacyclic triterpene found in Centella asiatica, displays significant anti-proliferative effects on cancer cells in vitro although the underlying mechanism of this effect remains unknown. This study investigated the efficacy and mechanism of action of AA against lung cancer both in vivo and in vitro. Using the MTT assay, AA was found to induce apoptosis in a dose- and time-dependent manner, an effect enhanced by pretreatment with an autophagy inhibitor. It also elevated expression of microtubule-associated protein 1 light chain 3 (LC3) and decreased the expression of p62. Furthermore, exposure to AA resulted in collapse of the mitochondrial membrane potential and generation of reactive oxygen species (ROS), suggesting mitochondria are the target of AA. In the mouse lung cancer xenograft model, oral administration of AA significantly inhibited tumor volume and weight accompanied by significant apoptosis of lung cancer cells. In addition, it led to a significant decrease in the expression of proliferating cell nuclear antigen (PCNA). In summary, the results show that AA significantly reduces lung cancer cell growth both in vitro and in vivo and that the associated apoptosis is mediated through mitochondrial damage.

Mitochondria and the NLRP3 inflammasome: physiological and pathological relevance

The NLRP3 inflammasome is assembled and activated in certain types of myeloid cells upon sensing microbe-derived toxins or host-derived danger signals. Activation of the NLRP3 inflammasome by endogenous ligands has been discovered in various disorders, including metabolic syndrome, type 2 diabetes, atherosclerosis, gout, reperfusion injury of the heart, neurodegeneration, such as Alzheimer's disease, chronic kidney diseases, and macular degeneration of the eyes. Despite the potential significance of the NLRP3 inflammasome in the pathogenesis of several diseases, details on the activation mechanism of the NLRP3 inflammasome by a variety of stimulators have yet to be reported. Emerging evidence suggests that mitochondrial events are associated with NLRP3 activation in disease conditions. Mitochondrial dysfunction acts upstream of NLRP3 activation by providing reactive oxygen species (ROS) to trigger NLRP3 oligomerization or by inducing α-tubulin acetylation to relocate mitochondria to the proximity of NLRP3. In addition, mitochondria work as a platform for inflammasome assembly. Mitochondrial events may also lie downstream of NLRP3 activation. While the molecular mechanisms of mitochondrial dysfunction associated with NLRP3 activation are still unclear, they may involve the perturbation of mitochondria by K⁺ efflux and subsequent intracellular disequilibrium. Thus, mitochondria and NLRP3 machinery appear to be closely interwoven at multiple levels.

Hydroxysafflor Yellow A Inhibits LPS-Induced NLRP3 Inflammasome Activation via Binding to Xanthine Oxidase in Mouse RAW264.7 Macrophages

Hydroxysafflor yellow A (HSYA) is an effective therapeutic agent for inflammatory diseases and autoimmune disorders; however, its regulatory effect on NLRP3 inflammasome activation in macrophages has not been investigated. In this study, we predicted the potential interaction between HSYA and xanthine oxidase (XO) via PharmMapper inverse docking and confirmed the binding inhibition via inhibitory test (IC50 = 40.04 μM). Computation docking illustrated that, in this HSYA-XO complex, HSYA was surrounded by Leu 648, Leu 712, His 875, Leu 873, Ser 876, Glu 879, Phe 649, and Asn 650 with a binding energy of -5.77 kcal/M and formed hydrogen bonds with the hydroxyl groups of HSYA at Glu 879, Asn 650, and His 875. We then found that HSYA significantly decreased the activity of XO in RAW264.7 macrophages and suppressed LPS-induced ROS generation. Moreover, we proved that HSYA markedly inhibited LPS-induced cleaved caspase-1 activation via suppressing the sensitization of NLRP3 inflammasome and prevented the mature IL-1β formation from pro-IL-1β form. These findings suggest that XO may be a potential target of HSYA via direct binding inhibition and the combination of HSYA-XO suppresses LPS-induced ROS generation, contributing to the depression of NLRP3 inflammasome and inhibition of IL-1β secretion in macrophages.

Axis of immune response and energy metabolism mediated by Notch/mTOR signaling pathway: Pivotal mechanism of traditional Chinese medicine for preventing inflammatory bowel disease

Inflammatory bowel disease (IBD) is a kind of worldwide refractory disease with a high recurrence rate. However, traditional Chinese medicine for IBD is associated with a better therapeutic effect and a lower recurrence rate, although the mechanism is still unclear. It is known that the Notch signaling pathway interacts with mTOR and regulates the body's immune level and cell energy, which is closely related with morbidity of IBD. These hint that axis of immune response and energy metabolism mediated by the Notch/mTOR signaling pathway is possibly a pivotal mechanism for traditional Chinese medicine to prevent IBD.

Asiatic Acid Protects against Cardiac Hypertrophy through Activating AMPKα Signalling Pathway

Background: AMPactivated protein kinase α (AMPKα) is closely involved in the process of cardiac hypertrophy. Asiatic acid (AA), a pentacyclic triterpene, was found to activate AMPKα in our preliminary experiment. However, its effects on the development of cardiac hypertrophy remain unclear. The present study was to determine whether AA could protect against cardiac hypertrophy.

Methods: Mice subjected to aortic banding were orally given AA (10 or 30mg/kg) for 7 weeks. In the inhibitory experiment, Compound C was intraperitoneally injected for 3 weeks after surgery.

Results: Our results showed that AA markedly inhibited hypertrophic responses induced by pressure overload or angiotensin II. AA also suppressed cardiac fibrosis in vivo and accumulation of collagen in vitro. The protective effects of AA were mediated by activation of AMPKα and inhibition of the mammalian target of rapamycin (mTOR) pathway and extracellular signal-regulated kinase (ERK) in vivo and in vitro. However, AA lost the protective effects after AMPKα inhibition or gene deficiency.

Conclusions: AA protects against cardiac hypertrophy by activating AMPKα, and has the potential to be used for the treatment of heart failure.

Neuroprotective effect of asiatic acid against spinal cord injury in rats

AIMS

The present study investigated the therapeutic efficacy of asiatic acid (AA) on spinal cord injury (SCI) as well as the underlying mechanisms.

MAIN METHODS

Sprague-Dawley rats (n=150) were randomly assigned to five groups: sham, SCI, SCI+methylprednisolone (30mg/kg), SCI+AA (30mg/kg), and SCI+AA (75mg/kg). Motor function, histological changes, neutrophil infiltration, proinflammatory cytokine production, and oxidative stress as well as nuclear factor erythroid 2-related factor (Nrf)2, heme oxygenase (HO)-1, and nucleotide-binding domain-like receptor protein (NLRP)3 levels were evaluated.

KEY FINDINGS

AA treatment increased Basso, Beattie and Bresnahan scores and inclined plane test scores that were reduced by SCI. In addition, AA suppressed myeloperoxidase activity and reduced the levels of interleukin-1β, -18, and -6 and tumor necrosis factor-α as well as reactive oxygen species (ROS), H2O2, and malondialdehyde levels while increasing superoxide dismutase activity and glutathione production. AA treatment results in the upregulation in Nrf2/HO-1 levels and downregulation of NLRP3 inflammasome protein expression in SC tissue.

SIGNIFICANCE

AA protects against SCI via suppression of inflammation and oxidative stress. The underlying mechanism likely involves activation of Nrf2 and HO-1 and inhibition of ROS and the NLRP3 inflammasome pathway. AA has therapeutic potential for SCI treatment.

NLRP3 inflammasome and its inhibitors: a review

Inflammasomes are newly recognized, vital players in innate immunity. The best characterized is the NLRP3 inflammasome, so-called because the NLRP3 protein in the complex belongs to the family of nucleotide-binding and oligomerization domain-like receptors (NLRs) and is also known as “pyrin domain-containing protein 3”. The NLRP3 inflammasome is associated with onset and progression of various diseases, including metabolic disorders, multiple sclerosis, inflammatory bowel disease, cryopyrin-associated periodic fever syndrome, as well as other auto-immune and auto-inflammatory diseases. Several NLRP3 inflammasome inhibitors have been described, some of which show promise in the clinic. The present review will describe the structure and mechanisms of activation of the NLRP3 inflammasome, its association with various auto-immune and auto-inflammatory diseases, and the state of research into NLRP3 inflammasome inhibitors.

Antioxidant therapy for treatment of inflammatory bowel disease: Does it work?

Oxidative stress (OS) is considered as one of the etiologic factors involved in several signals and symptoms of inflammatory bowel diseases (IBD) that include diarrhea, toxic megacolon and abdominal pain. This systematic review discusses approaches, challenges and perspectives into the use of nontraditional antioxidant therapy on IBD, including natural and synthetic compounds in both human and animal models. One hundred and thirty four papers were identified, of which only four were evaluated in humans. Some of the challenges identified in this review can shed light on this fact: lack of standardization of OS biomarkers, absence of safety data and clinical trials for the chemicals and biological molecules, as well as the fact that most of the compounds were not repeatedly tested in several situations, including acute and chronic colitis. This review hopes to stimulate researchers to become more involved in this fruitful area, to warrant investigation of novel, alternative and efficacious antioxidant-based therapies.

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Major biomarkers used for evaluation of antioxidant therapy were MPO, TBARS/MDA and glutathione levels.

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Challenges were identified for the yet poor use of antioxidant therapy in IBD.

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This review stimulates the investigation of alternative and efficacious antioxidant therapies.

Abnormal epithelial cell energy metabolism influences pathogenesis of inflammatory bowel disease

Etiology and pathogenesis of inflammatory bowel disease (IBD) are not clear, but colonic mucosal damage is known to be a critical factor. In recent decades, many studies suggest that interfering with the energy metabolism of epithelial tissue could result in the widening of intestinal epithelial cell gap, increased bacterial translocation across the epithelium, decreased mucus secretion, and intestinal mucosal barrier dysfunction. Bacteria and antigens adhere to the intestinal mucosa, enter into the lamina propria, activate inflammation, and initiate the pathogenesis of IBD. The lack of energy fuel butyrate and mitochondrial dysfunction are the causes of abnormal energy metabolism of the intestinal epithelium. Improving energy metabolism and protection of mitochondrial function can alleviate the seriousness of IBD, reduce recurrence, and provides a new strategy for the treatment of IBD.