Nightshade Vegetables: A Dietary Trigger for Worsening Inflammatory Bowel Disease and Irritable Bowel Syndrome?

The Solanaceae family of plants, commonly known as Nightshade vegetables or Nightshades, contains a diverse range of crops of over 2000 members with significant culinary, economic, and cultural importance. Familiar edible Nightshades include tomatoes, peppers, eggplants, and white potatoes. Many pharmacologically active compounds used in traditional medicine, including atropine and hyoscyamine, are derived from Nightshades. In addition to these beneficial pharmacologic agents, Nightshade-derived glycoalkaloid compounds, a key defense mechanism against predation, have been shown to disrupt intestinal epithelium and to potentially activate mast cells in the gut mucosa, leading to adverse symptoms in humans. There is a new appreciation that mast cell activation is an allergic inflammatory mechanism contributing both to pain in irritable bowel syndrome (IBS) and to gut inflammation in inflammatory bowel disease (IBD). Given their ubiquity in Western diets and their shared glycoalkaloid active compounds, edible Nightshades are attracting new interest as a potential trigger for worsening gut symptoms in functional and inflammatory gastrointestinal disorders. Here, we review the limited existing literature on the adverse effects of Nightshade consumption, including the effects of Nightshade-derived glycoalkaloids on IBD gut inflammation, and the under-recognized contribution of Nightshades to food allergies and allergic cross-reactivity. We then highlight new evidence on the contributions of mast cell activation to GI disorder pathogenesis, including potential linkages between Nightshade antigens, intestinal mast cells, and GI dysfunction in IBS and IBD.

A TRAF3-NIK module differentially regulates DNA vs RNA pathways in innate immune signaling.

Detection of viral genomes by the innate immune system elicits an antiviral gene program mediated by type I interferons (IFNs). While viral RNA and DNA species induce IFN via separate pathways, the mechanisms by which these pathways are differentially modulated are unknown. Here we show that the positive regulator of IFN in the RNA pathway, TRAF3, has an inhibitory function in the DNA pathway. Loss of TRAF3 coincides with increased expression of the alternative NF-κB-inducing molecule, NIK, which interacts with the DNA pathway adaptor, STING, to enhance IFN induction. Cells lacking NIK display defective IFN activation in the DNA pathway due to impaired STING signaling, and NIK-deficient mice are more susceptible to DNA virus infection. Mechanistically, NIK operates independently from alternative NF-κB signaling components and instead requires autophosphorylation and oligomerization to activate STING. Thus a previously undescribed pathway for NIK exists in activating IFN in the DNA pathway.

ASC/caspase-1/IL-1ß signaling triggers inflammatory responses by promoting HMGB1 induction in liver ischemia/reperfusion injury.

UNLABELLED: Apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC), an adaptor protein for inflammasome receptors, is essential for inducing caspase-1 activation and the consequent secretion of interleukin-1ß (IL-1ß), which is associated with local inflammation during liver ischemia/reperfusion injury (IRI). However, little is known about the mechanisms by which the ASC/caspase-1/IL-1ß axis exerts its function in hepatic IRI. This study was designed to explore the functional roles and molecular mechanisms of ASC/caspase-1/IL-1ß signaling in the regulation of inflammatory responses in vitro and in vivo. With a partial lobar liver warm ischemia (90 minutes) model, ASC-deficient and wild-type mice (C57BL/6) were sacrificed at 6 hours of reperfusion. Separate animal cohorts were treated with an anti-IL-1ß antibody or control immunoglobulin G (10 mg/kg/day intraperitoneally). We found that ASC deficiency inhibited caspase-1/IL-1ß signaling and led to protection against liver ischemia/reperfusion (IR) damage, local enhancement of antiapoptotic functions, and down-regulation of high mobility group box 1 (HMGB1)-mediated, toll-like receptor 4 (TLR4)-driven inflammation. Interestingly, the treatment of ASC-deficient mice with recombinant HMGB1 re-created liver IRI. Moreover, neutralization of IL-1ß ameliorated the hepatocellular damage by inhibiting nuclear factor kappa B (NF-κB)/cyclooxygenase 2 signaling in IR-stressed livers. In parallel in vitro studies, the knockout of ASC in lipopolysaccharide-stimulated bone marrow-derived macrophages depressed HMGB1 activity via the p38 mitogen-activated protein kinase pathway and led to the inhibition of TLR4/NF-κB and ultimately the depression of proinflammatory cytokine programs. CONCLUSION: ASC-mediated caspase-1/IL-1ß signaling promotes HMGB1 to produce a TLR4-dependent inflammatory phenotype and leads to hepatocellular injury. Hence, ASC/caspase-1/IL-1ß signaling mediates the inflammatory response by triggering HMGB1 induction in hepatic IRI. Our findings provide a rationale for a novel therapeutic strategy for managing liver injury due to IR.

Polyinosinic-polycytidylic acid suppresses acetaminophen-induced hepatotoxicity independent of type I interferons and toll-like receptor 3.

UNLABELLED: Viral infections are often linked to altered drug metabolism in patients; however, the underlying molecular mechanisms remain unclear. Here we describe a mechanism by which activation of antiviral responses by the synthetic double-stranded RNA ligand, polyinosinic-polycytidylic acid (polyI:C), leads to decreased acetaminophen (APAP) metabolism and hepatotoxicity. PolyI:C administration down-regulates expression of retinoic X receptor-α (RXRα) as well as its heterodimeric partner pregnane X receptor (PXR) in mice. This down-regulation results in suppression of downstream cytochrome P450 enzymes involved in conversion of APAP to its toxic metabolite. Although the effects of polyI:C on drug metabolism are often attributed to interferon production, we report that polyI:C can decrease APAP metabolism in the absence of the type I interferon receptor. Furthermore, we demonstrate that polyI:C can attenuate APAP metabolism through both its membrane-bound receptor, Toll-like receptor 3 (TLR3), as well as cytoplasmic receptors. CONCLUSION: This is the first study to illustrate that in vivo administration of polyI:C affects drug metabolism independent of type I interferon production or in the absence of TLR3 through crosstalk between nuclear receptors and antiviral responses.

Testosterone treatment increases thromboxane function in rat cerebral arteries.

We previously showed that testosterone, administered in vivo, increases the tone of cerebral arteries. A possible underlying mechanism is increased vasoconstriction through the thromboxane A2 (TxA2) pathway. Therefore, we investigated the effect of chronic testosterone treatment (4 wk) on TxA2 synthase levels and the contribution of TxA2 to vascular tone in rat middle cerebral arteries (MCAs). Using immunofluorescence and confocal microscopy, we demonstrated that TxA2 synthase is present in MCA segments in both smooth muscle and endothelial layers. Using Western blot analysis, we found that TxA2 synthase protein levels are higher in cerebral vessel homogenates from testosterone-treated orchiectomized (ORX + T) rats compared with orchiectomized (ORX) control animals. Functional consequences of changes in cerebrovascular TxA2 synthase were determined using cannulated, pressurized MCA segments in vitro. Constrictor responses to the TxA2 mimetic U-46619 were not different between the ORX + T and ORX groups. However, dilator responses to either the selective TxA2 synthase inhibitor furegrelate or the TxA2-endoperoxide receptor (TP) antagonist SQ-29548 were greater in the ORX + T compared with ORX group. In endothelium-denuded arteries, the dilation to furegrelate was attenuated in both the ORX and ORX + T groups, and the difference between the groups was abolished. These data suggest that chronic testosterone treatment enhances TxA2-mediated tone in rat cerebral arteries by increasing endothelial TxA2 synthesis without altering the TP receptors mediating constriction. The effect of in vivo testosterone on cerebrovascular TxA2 synthase, observed here after chronic hormone administration, may contribute to the risk of vasospasm and thrombosis related to cerebrovascular disease.