Epithelial CaSR deficiency alters intestinal integrity and promotes proinflammatory immune responses

Prognosis and factors related to severe secondary hyperparathyroidism in long-term peritoneal dialysis patients

Secondary hyperparathyroidism (SHPT) can progress to severe SHPT (sSHPT), which affects the survival rate and quality of life of patients. This retrospective cohort study investigated risk factors for sSHPT and the association between SHPT and mortality (all-cause and infection-related) among 771 clinically stable patients (421 male patients; mean age, 51.2 years; median dialysis vintage, 28.3 months) who underwent >3 months of regular peritoneal dialysis (PD) between January 2013 and March 2021. The sSHPT and non-sSHPT groups comprised 75 (9.7%) (median progression, 35 months) and 696 patients, respectively. sSHPT was defined as a serum intact parathyroid hormone (PTH) level >800 pg/mL observed three times after active vitamin D pulse therapy. The influence of sSHPT on the prognosis of and risk factors for sSHPT progression were evaluated using logistic and Cox regression analyses. After adjusting for confounding factors, higher (each 100-pg/mL increase) baseline PTH levels (95% confidence interval (CI) 1.206-1.649, p < .001), longer (each 1-year increase) dialysis vintages (95% CI 1.013-1.060, p = .002), higher concomitant diabetes rates (95% CI 1.375-10.374, p = .010), and lower (each 1-absolute unit decrease) Kt/V values (95% CI 0.859-0.984, p = .015) were independent risk factors for progression to sSHPT in patients on PD. During follow-up, 211 deaths occurred (sSHPT group, n = 35; non-sSHPT group, n = 176). The sSHPT group had significantly higher infection-related mortality rates than the non-sSHPT group (12.0% vs. 4.3%; p < .05), and sSHPT was associated with increased infection-related mortality. In conclusion, patients with sSHPT are at higher risk for death and infection-related mortality than patients without sSHPT.

A novel bacterium-like particles platform displaying antigens by new anchoring proteins induces efficacious immune responses

Bacterium-like particles (BLP) are the peptidoglycan skeleton particles of lactic acid bacteria, which have high safety, mucosal delivery efficiency, and adjuvant effect. It has been widely used in recent years in the development of vaccines. Existing anchoring proteins for BLP surfaces are few in number, so screening and characterization of new anchoring proteins are necessary. In this research, we created the OACD (C-terminal domain of Escherichia coli outer membrane protein A) to serve as an anchoring protein on the surface of BLP produced by the immunomodulatory bacteria Levilactobacillus brevis 23017. We used red fluorescent protein (RFP) to demonstrate the novel surface display system's effectiveness, stability, and ability to be adapted to a wide range of lactic acid bacteria. Furthermore, this study employed this surface display method to develop a novel vaccine (called COB17) by using the multi-epitope antigen of Clostridium perfringens as the model antigen. The vaccine can induce more than 50% protection rate against C. perfringens type A challenge in mice immunized with a single dose and has been tested through three routes. The vaccine yields protection rates of 75% for subcutaneous, 50% for intranasal, and 75% for oral immunization. Additionally, it elicits a strong mucosal immune response, markedly increasing levels of specific IgG, high-affinity IgG, specific IgA, and SIgA antibodies. Additionally, we used protein anchors (PA) and OACD simultaneous to show several antigens on the BLP surface. The discovery of novel BLP anchoring proteins may expand the possibilities for creating mucosal immunity subunit vaccines. Additionally, it may work in concert with PA to provide concepts for the creation of multivalent or multiple vaccines that may be used in clinical practice to treat complex illnesses.

Association between dietary calcium to Phosphorus Ratio and the odds of ulcerative colitis: A case-control study

Background & aims

Ulcerative colitis (UC) is a recurrent, inflammatory, autoimmune intestinal disease. The dietary calcium to phosphorus (Ca:P) ratio is suggested to affect the inividuals' normal metabolic and inflammatory pathways. The present study aimed to investigate the association between dietary Ca:P ratio and the odds of developing UC in a case-control format.

Methods

The study included sixty-two currently diagnosed UC patients and one hundred twenty-four matched controls, designed as a case-control study. The dietary intakes of the participants were assessed by a food frequency questionnaire (FFQ), and the dietary Ca:P ratio was calculated. The association between tertiles of Ca:P ratio and UC was examined using the logistic regression. P-values <0.05 were considered as significant.

Results

The study sample consisted of participants with an average age of 36.63 ± 12.42 years and a mean body mass index (BMI) of 25.39 ± 3.82 kg/m2. The overall energy-adjusted ratio of Ca:P was 0.74 ± 0.11. In the multivariate model, after adjustment for potential confounders, participants in the third tertile of dietary Ca:P ratio had a lower odds of developing UC compared to the lowest tertlie (OR: 0.34, 95% CI: 0.13-0.87; p = 0.026).

Conclusion

Our results indicate that a higher ratio of dietary Ca:P ratio might be protective against developing UC. However, further studies are warranted to examine this association in various populations.

Calcium/calcimimetic via calcium-sensing receptor ameliorates cholera toxin-induced secretory diarrhea in mice

BACKGROUND

Enterotoxins produce diarrhea through direct epithelial action and indirectly by activating the enteric nervous system. Calcium-sensing receptor (CaSR) inhibits both actions. The latter has been well documented in vitro but not in vivo. The hypothesis to be tested was that activating CaSR inhibits diarrhea in vivo.

AIM

To determine whether CaSR agonists ameliorate secretory diarrhea evoked by cholera toxin (CTX) in mice.

METHODS

CTX was given orally to C57BL/6 mice to induce diarrhea. Calcium and calcimimetic R568 were used to activate CaSR. To maximize their local intestinal actions, calcium was administered luminally via oral rehydration solution (ORS), whereas R568 was applied serosally using an intraperitoneal route. To verify that their actions resulted from the intestine, effects were also examined on Cre-lox intestine-specific CaSR knockouts. Diarrhea outcome was measured biochemically by monitoring changes in fecal Cl- or clinically by assessing stool consistency and weight loss.

RESULTS

CTX induced secretory diarrhea, as evidenced by increases in fecal Cl-, stool consistency, and weight loss following CTX exposure, but did not alter CaSR, neither in content nor in function. Accordingly, calcium and R568 were each able to ameliorate diarrhea when applied to diseased intestines. Intestinal CaSR involvement is suggested by gene knockout experiments where the anti-diarrheal actions of R568 were lost in intestinal epithelial CaSR knockouts (villinCre/Casrflox/flox) and neuronal CaSR knockouts (nestinCre/Casrflox/flox).

CONCLUSION

Treatment of acute secretory diarrheas remains a global challenge. Despite advances in diarrhea research, few have been made in the realm of diarrhea therapeutics. ORS therapy has remained the standard of care, although it does not halt the losses of intestinal fluid and ions caused by pathogens. There is no cost-effective therapeutic for diarrhea. This and other studies suggest that adding calcium to ORS or using calcimimetics to activate intestinal CaSR might represent a novel approach for treating secretory diarrheal diseases.

Role of micronutrients in inflammatory bowel disease

Inflammatory bowel disease (IBD) is an autoimmune intestinal disease that includes ulcerative colitis, Crohn's disease, and indeterminate colitis. Patients with IBD are often at risk for malnutrition, including micronutrient deficiencies, due to dietary restrictions and poor intestinal absorption. Micronutrients, including vitamins and minerals, play an important role in the human body's metabolism and maintenance of tissue functions. This article reviews the role of micronutrients in IBD. Micronutrients can affect the occurrence and progression of IBD by regulating immunity, intestinal flora, oxidative stress, intestinal barrier function, and other aspects. Monitoring and timely supplementation of micronutrients are important to delay progression and improve clinical symptoms in IBD patients.

Calcium-Sensitive Receptors Alters Intestinal Microbiota Metabolites Especially SCFAs and Ameliorates Intestinal Barrier Damage in Neonatal Rat Endotoxemia

Purpose

The calcium-sensing receptor (CaSR) acts as a major modulator of tissue responses related to calcium homeostasis and expresses highly in the mammalian intestine. Endotoxemia tends to impair intestinal barrier function and poses significant obstacles in clinical treatment. This work is designed to decipher whether CaSR can protect lipopolysaccharide (LPS)-induced intestinal barrier dysfunction in neonatal rats by targeting intestinal metabolites.

Patient and Methods

In this study, we utilized gas chromatography (GC) combined with liquid chromatography-mass spectrometry (LC-MS) to quantitatively analyze SCFAs and metabolites in fecal samples of 24 neonatal rats with LPS induced endotoxemia.

Results

Our results showed that CaSR alleviated endotoxin damage to the intestinal tight junction structure and upregulated the levels of butyric acid, propionic acid, valeric acid, and isovaleric acid in short-chain fatty acids (SCFAs). Non-targeted metabolomics analysis indicated that CaSR improved intestinal metabolic disorders by regulating glycerophospholipid metabolism, α-linolenic acid metabolism, as well as sphingolipids metabolism.

Conclusion

CaSR can alter intestinal microbiota metabolites, especially SCFAs, and improve intestinal barrier damage in neonatal rat endotoxemia.

Impact of Diet on Colorectal Cancer Progression and Prevention: From Nutrients to Neoplasms

Colorectal cancer (CRC), one of the most common cancers worldwide, continues to increase in incidence and mortality rates. This trend is closely linked to changes in dietary habits, which are major risk factors for colorectal cancer. The increase in the incidence of CRC in countries previously considered low-risk and with low socioeconomic status is most likely due to lifestyle and dietary changes. Understanding the influence of dietary factors on the onset of colorectal cancer is essential for prevention and treatment. This review explores the complex interplay between dietary factors and colorectal cancer, focusing on the key nutrients and dietary habits that influence disease onset and progression. The impact of diet on colorectal microbiota and the influence of diet on early-onset colorectal cancer are also reviewed, reviewing recent research on how dietary interventions affect the treatment and recurrence of colorectal cancer. Finally, the future research directions for developing and applying effective dietary intervention strategies are discussed.

The calcium-sensing receptor modulates the prostaglandin E2 pathway in intestinal inflammation

Introduction: The prostaglandin E2 (PGE2) pathway is one of the main mediators of intestinal inflammation. As activation of the calcium-sensing receptor (CaSR) induces expression of inflammatory markers in the colon, we assessed the impact of the CaSR on the PGE2 pathway regulation in colon cancer cells and the colon in vitro and in vivo. Methods and Results: We treated CaSR-transfected HT29 and Caco-2 colon cancer cell lines with different orthosteric ligands or modulators of the CaSR and measured gene expression and PGE2 levels. In CaSR-transfected HT29CaSR-GFP and Caco-2CaSR-GFP cells, the orthosteric CaSR ligand spermine and the positive allosteric CaSR modulator NPS R-568 both induced an inflammatory state as measured by IL-8 gene expression and significantly increased the expression of the PGE2 pathway key enzymes cyclooxygenase (COX)-2 and/or prostaglandin E2 synthase 1 (PGES-1). Inhibition of the CaSR with the calcilytic NPS 2143 abolished the spermine- and NPS R-568-induced pro-inflammatory response. Interestingly, we observed cell-line specific responses as e.g. PGES-1 expression was affected only in HT29CaSR-GFP but not in Caco-2CaSR-GFP cells. Other genes involved in the PGE2 pathway (COX-1, or the PGE2 receptors) were not responsive to the treatment. None of the studied genes were affected by any CaSR agonist in GFP-only transfected HT29GFP and Caco-2GFP cells, indicating that the observed gene-inducing effects of spermine and R-568 were indeed mediated by the CaSR. In vivo, we had previously determined that treatment with the clinically approved calcimimetic cinacalcet worsened symptoms in a dextran sulfate sodium (DSS)-induced colitis mouse model. In the colons of these mice, cinacalcet significantly induced gene expression of PGES-2 and the EP3 receptor, but not COX-2; while NPS 2143 increased the expression of the PGE2-degrading enzyme 15-hydroxyprostaglandin dehydrogenase (15-PGDH). Importantly, neither treatment had any effect on the colons of non-DSS treated mice. Discussion: Overall, we show that activation of the CaSR induces the PGE2 pathway, albeit with differing effects in vitro and in vivo. This may be due to the different microenvironment in vivo compared to in vitro, specifically the presence of a CaSR-responsive immune system. Since calcilytics inhibit ligand-mediated CaSR signaling, they may be considered for novel therapies against inflammatory bowel disease.

Nano selenium-enriched probiotic Lactobacillus enhances alum adjuvanticity and promotes antigen-specific systemic and mucosal immunity

Nano selenium-enriched probiotics have been identified to improve immune responses, such as alleviating inflammation, antioxidant function, treatment of tumors, anticancer activity, and regulating intestinal flora. However, so far, there is little information on improving the immune effect of the vaccine. Here, we prepared nano selenium-enriched Levilactobacillus brevis 23017 (SeL) and heat-inactivated nano selenium-enriched L. brevis 23017 (HiSeL) and evaluated their immune enhancing functions on the alum-adjuvanted, inactivated Clostridium perfringens type A vaccine in mouse and rabbit models, respectively. We found that SeL enhanced immune responses of the vaccine by inducing a more rapid antibody production, eliciting higher immunoglobulin G (IgG) antibody titers, improving secretory immunoglobulin A (SIgA) antibody level and cellular immune response, and regulating Th1/Th2 immune response, thus helping to induce better protective efficacy after challenge. Moreover, we confirmed that the immunoenhancement effects are related to regulating oxidative stress, cytokine secretion, and selenoprotein expression. Meanwhile, similar effects were observed in HiSeL. In addition, they show enhanced humoral immune response at 1/2 and 1/4 standard vaccine doses, which confirms their prominent immune enhancement effect. Finally, the effect of improving vaccine immune responses was further confirmed in rabbits, which shows that SeL stimulates the production of IgG antibodies, generates α toxin-neutralizing antibodies rapidly, and reduces the pathological damage to intestine tissue. Our study demonstrates that nano selenium-enriched probiotics improve the immune effect of the alum adjuvants vaccine and highlight its potential usage in remedying the disadvantages of alum adjuvants.

The calcium-sensing receptor in inflammation: Recent updates

The Calcium-Sensing Receptor (CaSR) is a member of the class C of G-proteins coupled receptors (GPCRs), it plays a pivotal role in calcium homeostasis by directly controlling calcium excretion in the kidneys and indirectly by regulating parathyroid hormone (PTH) release from the parathyroid glands. The CaSR is found to be ubiquitously expressed in the body, playing a plethora of additional functions spanning from fluid secretion, insulin release, neuronal development, vessel tone to cell proliferation and apoptosis, to name but a few. The present review aims to elucidate and clarify the emerging regulatory effects that the CaSR plays in inflammation in several tissues, where it mostly promotes pro-inflammatory responses, with the exception of the large intestine, where contradictory roles have been recently reported. The CaSR has been found to be expressed even in immune cells, where it stimulates immune response and chemokinesis. On the other hand, CaSR expression seems to be boosted under inflammatory stimulus, in particular, by pro-inflammatory cytokines. Because of this, the CaSR has been addressed as a key factor responsible for hypocalcemia and low levels of PTH that are commonly found in critically ill patients under sepsis or after burn injury. Moreover, the CaSR has been found to be implicated in autoimmune-hypoparathyroidism, recently found also in patients treated with immune-checkpoint inhibitors. Given the tight bound between the CaSR, calcium and vitamin D metabolism, we also speculate about their roles in the pathogenesis of severe acute respiratory syndrome coronavirus-19 (SARS-COVID-19) infection and their impact on patients' prognosis. We will further explore the therapeutic potential of pharmacological targeting of the CaSR for the treatment and management of aberrant inflammatory responses.

Tryptophan Promotes Intestinal Immune Defense through Calcium-Sensing Receptor (CaSR)-Dependent Metabolic Pathways

The gastrointestinal tract forms a robust line of defense against invading pathogens through the production of endogenous antimicrobial peptides (AMPs), which are crucial molecules of the innate defense system. Tryptophan could modulate intestinal immunity through promoting the expression of AMPs. However, the precise mechanism needs to be further clarified. In this study, we show that treatment with tryptophan for 24 h triggers (p < 0.05) the expression of porcine β-defensin (pBD) 1 (62.67 ± 3.10 pg/mL) and pBD2 (74.41 ± 1.33 pg/mL) in the porcine intestinal epithelial cells (IPEC-J2) though calcium-sensing receptor (CaSR)-tryptophan metabolic pathways. Meanwhile, tryptophan alleviates (p < 0.05) intestinal inflammation induced by lipopolysaccharide (LPS) through induction of the defensins and activation of the CaSR-AMP-activated protein kinase (AMPK) pathways in vitro and in vivo. Moreover, the activation of CaSR induces the expression of defensins and decreases the levels of IL-1β (75.26 ± 2.74 pg/mL) and TNF-α (449.8 ± 23.31 pg/mL) induced by LPS (p < 0.05). Importantly, tryptophan maintains kynurenine homeostasis through the activation of CaSR during the inflammatory response. To that end, the work identifies a regulatory circuit between CaSR signaling and tryptophan metabolic pathways involved in the tryptophan-trigged AMP expression, which contributes to improving intestinal immune defense.

Calcium-sensing receptor protects intestinal integrity and alleviates the inflammatory response via the Rac1/PLCγ1 signaling pathway

This study aimed to test the hypothesis that the calcium-sensing receptor (CaSR) can protect intestinal epithelial barrier integrity and decrease inflammatory response mediated by the Ras-related C3 botulinum toxin substrate 1 (Rac1)/phospholipase Cγ1 (PLC-γ1) signaling pathway. IPEC-J2 monolayers were treated without or with TNF-α in the absence or presence of CaSR antagonist (NPS 2143), CaSR overexpression, and Rac1 silencing, PLCγ1 silencing or spermine. Results showed that spermine increased transepithelial electrical resistance (TER), tight junction protein levels, the protein concentration of Rac1/PLC-γ1 signaling pathway, and decreased paracellular permeability in the presence of TNF-α. NPS2143 inhibited spermine-induced change in above-mentioned parameters. CaSR overexpression increased TER, the levels of tight junction proteins and the protein concentration of CaSR, phosphorylated PLCγ1, Rac1, and IP3, and decreased paracellular permeability and contents of interleukin-8 (IL-8) and TNF-α after TNF-α challenge. Rac1 and PLCγ1 silencing inhibited CaSR-induced increase in barrier function and the protein concentration of phosphorylated PLCγ1, Rac1, and IP3, and decrease in contents of IL-8 and TNF-α after TNF-α challenge. These results suggest that CaSR activation protects intestinal integrity and alleviates the inflammatory response by activating Rac1 and PLCγ1 signaling after TNF-α challenge, and spermine can maintain barrier function via CaSR/Rac1/PLC-γ1 pathway.

Tryptophan Ameliorates Barrier Integrity and Alleviates the Inflammatory Response to Enterotoxigenic Escherichia coli K88 Through the CaSR/Rac1/PLC-γ1 Signaling Pathway in Porcine Intestinal Epithelial Cells

Background

Impaired intestinal barrier integrity plays a crucial role in the development of many diseases such as obesity, inflammatory bowel disease, and type 2 diabetes. Thus, protecting the intestinal barrier from pathological disruption is of great significance. Tryptophan can increase gut barrier integrity, enhance intestinal absorption, and decrease intestinal inflammation. However, the mechanism of tryptophan in decreasing intestinal barrier damage and inflammatory response remains largely unknown. The objective of this study was to test the hypothesis that tryptophan can enhance intestinal epithelial barrier integrity and decrease inflammatory response mediated by the calcium-sensing receptor (CaSR)/Ras-related C3 botulinum toxin substrate 1 (Rac1)/phospholipase Cγ1 (PLC-γ1) signaling pathway.

Methods

IPEC-J2 cells were treated with or without enterotoxigenic Escherichia coli (ETEC) K88 in the absence or presence of tryptophan, CaSR inhibitor (NPS-2143), wild-type CaSR overexpression (pcDNA3.1-CaSR-WT), Rac1-siRNA, and PLC-γ1-siRNA.

Results

The results showed that ETEC K88 decreased the protein concentration of occludin, zonula occludens-1 (ZO-1), claudin-1, CaSR, total Rac1, Rho family member 1 of porcine GTP-binding protein (GTP-rac1), phosphorylated phospholipase Cγ1 (p-PLC-γ1), and inositol triphosphate (IP3); suppressed the transepithelial electrical resistance (TEER); and enhanced the permeability of FITC-dextran compared with the control group. Compared with the control group, 0.7 mM tryptophan increased the protein concentration of CaSR, total Rac1, GTP-rac1, p-PLC-γ1, ZO-1, claudin-1, occludin, and IP3; elevated the TEER; and decreased the permeability of FITC-dextran and contents of interleukin-8 (IL-8) and TNF-α. However, 0.7 mM tryptophan+ETEC K88 reversed the effects induced by 0.7 mM tryptophan alone. Rac1-siRNA+tryptophan+ETEC K88 or PLC-γ1-siRNA+tryptophan+ETEC K88 reduced the TEER, increased the permeability of FITC-dextran, and improved the contents of IL-8 and TNF-α compared with tryptophan+ETEC K88. NPS2143+tryptophan+ETEC K88 decreased the TEER and the protein concentration of CaSR, total Rac1, GTP-rac1, p-PLC-γ1, ZO-1, claudin-1, occludin, and IP3; increased the permeability of FITC-dextran; and improved the contents of IL-8 and TNF-α compared with tryptophan+ETEC K88. pcDNA3.1-CaSR-WT+Rac1-siRNA+ETEC K88 and pcDNA3.1-CaSR-WT+PLC-γ1-siRNA+ETEC K88 decreased the TEER and enhanced the permeability in porcine intestine epithelial cells compared with pcDNA3.1-CaSR-WT+ETEC K88.

Conclusion

Tryptophan can improve intestinal epithelial barrier integrity and decrease inflammatory response through the CaSR/Rac1/PLC-γ1 signaling pathway.

Stereo-Specific Modulation of the Extracellular Calcium-Sensing Receptor in Colon Cancer Cells

Pharmacological allosteric agonists (calcimimetics) of the extracellular calcium-sensing receptor (CaSR) have substantial gastro-intestinal side effects and induce the expression of inflammatory markers in colon cancer cells. Here, we compared the effects of both CaSR-specific (R enantiomers) and -unspecific (S enantiomers) enantiomers of a calcimimetic (NPS 568) and a calcilytic (allosteric CaSR antagonists; NPS 2143) to prove that these effects are indeed mediated via the CaSR, rather than via off-target effects, e.g., on β-adrenoceptors or calcium channels, of these drugs. The unspecific S enantiomer of NPS 2143 and NPS S-2143 was prepared using synthetic chemistry and characterized using crystallography. NPS S-2143 was then tested in HEK-293 cells stably transfected with the human CaSR (HEK-CaSR), where it did not inhibit CaSR-mediated intracellular Ca²⁺ signals, as expected. HT29 colon cancer cells transfected with the CaSR were treated with both enantiomers of NPS 568 and NPS 2143 alone or in combination, and the expression of CaSR and the pro-inflammatory cytokine interleukin 8 (IL-8) was measured by RT-qPCR and ELISA. Only the CaSR-selective enantiomers of the calcimimetic NPS 568 and NPS 2143 were able to modulate CaSR and IL-8 expression. We proved that pro-inflammatory effects in colon cancer cells are indeed mediated through CaSR activation. The non-CaSR selective enantiomer NPS S-2143 will be a valuable tool for investigations in CaSR-mediated processes.

Calcium-Sensing Receptor Polymorphisms at rs1801725 Are Associated with Increased Risk of Secondary Malignancies

Dysregulation of systemic calcium homeostasis during malignancy is common in most patients with high-grade tumors. However, it remains unclear whether single nucleotide polymorphisms (SNPs) that alter the sensitivity of the calcium-sensing receptor (CaSR) to circulating calcium are associated with primary and/or secondary neoplasms at specific pathological sites in patients of European and African ancestry. Multivariable logistic regression models were used to analyze the association of CASR SNPs with circulating calcium, parathyroid hormone, vitamin D, and primary and secondary neoplasms. Circulating calcium is associated with an increased risk for breast, prostate, and skin cancers. In patients of European descent, the rs1801725 CASR SNP is associated with bone-related cancer phenotypes, deficiency of humoral immunity, and a higher risk of secondary neoplasms in the lungs and bone. Interestingly, circulating calcium levels are higher in homozygous patients for the inactivating CASR variant at rs1801725 (TT genotype), and this is associated with a higher risk of secondary malignancies. Our data suggest that expression of CaSR variants at rs1801725 is associated with a higher risk of developing secondary neoplastic lesions in the lungs and bone, due in part to cancer-induced hypercalcemia and/or tumor immune suppression. Screening of patients for CASR variants at this locus may lead to improved management of high calcium associated tumor progression.

The role of calcium-sensing receptor signaling in regulating transepithelial calcium transport

The calcium-sensing receptor (CaSR) plays a critical role in sensing extracellular calcium (Ca²⁺) and signaling to maintain Ca²⁺ homeostasis. In the parathyroid, the CaSR regulates secretion of parathyroid hormone, which functions to increase extracellular Ca²⁺ levels. The CaSR is also located in other organs imperative to Ca²⁺ homeostasis including the kidney and intestine, where it modulates Ca²⁺ reabsorption and absorption, respectively. In this review, we describe CaSR expression and its function in transepithelial Ca²⁺ transport in the kidney and intestine. Activation of the CaSR leads to G protein dependent and independent signaling cascades. The known CaSR signal transduction pathways involved in modulating paracellular and transcellular epithelial Ca²⁺ transport are discussed. Mutations in the CaSR cause a range of diseases that manifest in altered serum Ca²⁺ levels. Gain-of-function mutations in the CaSR result in autosomal dominant hypocalcemia type 1, while loss-of-function mutations cause familial hypocalciuric hypercalcemia. Additionally, the putative serine protease, FAM111A, is discussed as a potential regulator of the CaSR because mutations in FAM111A cause Kenny Caffey syndrome type 2, gracile bone dysplasia, and osteocraniostenosis, diseases that are characterized by hypocalcemia, hypoparathyroidism, and bony abnormalities, i.e. share phenotypic features of autosomal dominant hypocalcemia. Recent work has helped to elucidate the effect of CaSR signaling cascades on downstream proteins involved in Ca²⁺ transport across renal and intestinal epithelia; however, much remains to be discovered.

Therapeutic Opportunities of Targeting Allosteric Binding Sites on the Calcium-Sensing Receptor

The CaSR is a class C G protein-coupled receptor (GPCR) that acts as a multimodal chemosensor to maintain diverse homeostatic functions. The CaSR is a clinical therapeutic target in hyperparathyroidism and has emerged as a putative target in several other diseases. These include hyper- and hypocalcaemia caused either by mutations in the CASR gene or in genes that regulate CaSR signaling and expression, and more recently in asthma. The development of CaSR-targeting drugs is complicated by the fact that the CaSR possesses many different binding sites for endogenous and exogenous agonists and allosteric modulators. Binding sites for endogenous and exogenous ligands are located throughout the large CaSR protein and are interconnected in ways that we do not yet fully understand. This review summarizes our current understanding of CaSR physiology, signaling, and structure and how the many different binding sites of the CaSR may be targeted to treat disease.

The food additive EDTA aggravates colitis and colon carcinogenesis in mouse models

Inflammatory bowel disease is a group of conditions with rising incidence caused by genetic and environmental factors including diet. The chelator ethylenediaminetetraacetate (EDTA) is widely used by the food and pharmaceutical industry among numerous other applications, leading to a considerable environmental exposure. Numerous safety studies in healthy animals have revealed no relevant toxicity by EDTA. Here we show that, in the presence of intestinal inflammation, EDTA is surprisingly capable of massively exacerbating inflammation and even inducing colorectal carcinogenesis at doses that are presumed to be safe. This toxicity is evident in two biologically different mouse models of inflammatory bowel disease, the AOM/DSS and the IL10^−/− model. The mechanism of this effect may be attributed to disruption of intercellular contacts as demonstrated by in vivo confocal endomicroscopy, electron microscopy and cell culture studies. Our findings add EDTA to the list of food additives that might be detrimental in the presence of intestinal inflammation, but the toxicity of which may have been missed by regulatory safety testing procedures that utilize only healthy models. We conclude that the current use of EDTA especially in food and pharmaceuticals should be reconsidered. Moreover, we suggest that intestinal inflammatory models should be implemented in the testing of food additives to account for the exposure of this primary organ to environmental and dietary stress.

Effects of pharmacological calcimimetics on colorectal cancer cells over-expressing the human calcium-sensing receptor

The calcium-sensing receptor (CaSR) is a ubiquitously expressed multifunctional G protein-coupled receptor. Several studies reported that the CaSR plays an anti-inflammatory and anti-tumorigenic role in the intestine, and that it is down-regulated during colorectal carcinogenesis. We hypothesized that positive allosteric CaSR modulators (type II calcimimetics) selectively targeting the intestinal cells could be used for the treatment of intestinal pathologies. Therefore, the aim of this study was to determine the effect of pharmacological stimulation of CaSR on gene expression in vitro and on tumor growth in vivo. We stably transduced two colon cancer cell lines (HT29 and Caco2) with lentiviral vectors containing either the CaSR fused to GFP or GFP only. Using RNA sequencing, RT-qPCR experiments and ELISA, we determined that CaSR over-expression itself had generally little effect on gene expression in these cells. However, treatment with 1 μM of the calcimimetic NPS R-568 increased the expression of pro-inflammatory factors such as IL-23α and IL-8 and reduced the transcription of various differentiation markers in the cells over-expressing the CaSR. In vivo, neither the presence of the CaSR nor p.o. treatment of the animals with the calcimimetic cinacalcet affected tumor growth, tumor cell proliferation or tumor vascularization of murine HT29 xenografts. In summary, CaSR stimulation in CaSR over-expressing cells enhanced the expression of inflammatory markers in vitro, but was not able to repress colorectal cancer tumorigenicity in vivo. These findings suggest potential pro-inflammatory effects of the CaSR and type II calcimimetics in the intestine.

International Union of Basic and Clinical Pharmacology. CVIII. Calcium-Sensing Receptor Nomenclature, Pharmacology, and Function

The calcium-sensing receptor (CaSR) is a class C G protein-coupled receptor that responds to multiple endogenous agonists and allosteric modulators, including divalent and trivalent cations, L-amino acids, γ-glutamyl peptides, polyamines, polycationic peptides, and protons. The CaSR plays a critical role in extracellular calcium (Ca2+ o) homeostasis, as demonstrated by the many naturally occurring mutations in the CaSR or its signaling partners that cause Ca2+ o homeostasis disorders. However, CaSR tissue expression in mammals is broad and includes tissues unrelated to Ca2+ o homeostasis, in which it, for example, regulates the secretion of digestive hormones, airway constriction, cardiovascular effects, cellular differentiation, and proliferation. Thus, although the CaSR is targeted clinically by the positive allosteric modulators (PAMs) cinacalcet, evocalcet, and etelcalcetide in hyperparathyroidism, it is also a putative therapeutic target in diabetes, asthma, cardiovascular disease, and cancer. The CaSR is somewhat unique in possessing multiple ligand binding sites, including at least five putative sites for the "orthosteric" agonist Ca2+ o, an allosteric site for endogenous L-amino acids, two further allosteric sites for small molecules and the peptide PAM, etelcalcetide, and additional sites for other cations and anions. The CaSR is promiscuous in its G protein-coupling preferences, and signals via Gq/11, Gi/o, potentially G12/13, and even Gs in some cell types. Not surprisingly, the CaSR is subject to biased agonism, in which distinct ligands preferentially stimulate a subset of the CaSR's possible signaling responses, to the exclusion of others. The CaSR thus serves as a model receptor to study natural bias and allostery. SIGNIFICANCE STATEMENT: The calcium-sensing receptor (CaSR) is a complex G protein-coupled receptor that possesses multiple orthosteric and allosteric binding sites, is subject to biased signaling via several different G proteins, and has numerous (patho)physiological roles. Understanding the complexities of CaSR structure, function, and biology will aid future drug discovery efforts seeking to target this receptor for a diversity of diseases. This review summarizes what is known to date regarding key structural, pharmacological, and physiological features of the CaSR.

Intestinal Ca2+ absorption revisited: A molecular and clinical approach

Ca2+ has an important role in the maintenance of the skeleton and is involved in the main physiological processes. Its homeostasis is controlled by the intestine, kidney, bone and parathyroid glands. The intestinal Ca2+ absorption occurs mainly via the paracellular and the transcellular pathways. The proteins involved in both ways are regulated by calcitriol and other hormones as well as dietary factors. Fibroblast growth factor 23 (FGF-23) is a strong antagonist of vitamin D action. Part of the intestinal Ca2+ movement seems to be vitamin D independent. Intestinal Ca2+ absorption changes according to different physiological conditions. It is promoted under high Ca2+ demands such as growth, pregnancy, lactation, dietary Ca2+ deficiency and high physical activity. In contrast, the intestinal Ca2+ transport decreases with aging. Oxidative stress inhibits the intestinal Ca2+ absorption whereas the antioxidants counteract the effects of prooxidants leading to the normalization of this physiological process. Several pathologies such as celiac disease, inflammatory bowel diseases, Turner syndrome and others occur with inhibition of intestinal Ca2+ absorption, some hypercalciurias show Ca2+ hyperabsorption, most of these alterations are related to the vitamin D endocrine system. Further research work should be accomplished in order not only to know more molecular details but also to detect possible therapeutic targets to ameliorate or avoid the consequences of altered intestinal Ca2+ absorption.

Tojapride prevents CaSR-mediated NLRP3 inflammasome activation in oesophageal epithelium irritated by acidic bile salts

Impairment of the oesophageal epithelium in patients with reflux oesophagitis (RE) is a cytokine-mediated injury rather than a chemical burn. The present study was conducted to explore CaSR/NLRP3 inflammasome pathway activation and cytokines IL-1β and IL-18 release in oesophageal epithelia injured by refluxates and the effects of Tojapride on that signal regulation. Using a modified RE rat model with Tojapride administration and Tojapride-pretreated SV40-immortalized human oesophageal epithelial cells (HET-1A) exposed to acidic bile salts pretreated with Tojapride, we evaluated the therapeutic effects of Tojapride on oesophageal epithelial barrier function, the expression of CaSR/NLRP3 inflammasome pathway-related proteins and the release of downstream cytokines in response to acidic bile salt irritation. In vivo, Tojapride treatment ameliorated the general condition and pathological lesions of the oesophageal epithelium in modified RE rats. In addition, Tojapride effectively blocked the CaSR-mediated NLRP3 inflammasome activation in modified RE rats. In vitro, Tojapride treatment can reverse the harmful effect of acidic bile salts, which reduced transepithelial electrical resistance (TEER), up-regulated the CaSR-mediated NLRP3 inflammasome pathway and increased caspase-1 activity, LDH release and cytokines secretion. Taken together, these data show that Tojapride can prevent CaSR-mediated NLRP3 inflammasome activation and alleviate oesophageal epithelial injury induced by acidic bile salt exposure.

Switching to a Healthy Diet Prevents the Detrimental Effects of Western Diet in a Colitis-Associated Colorectal Cancer Model

Inflammatory bowel disease increases the odds of developing colitis-associated cancer. We hypothesized that Western-style diet (WD) aggravates azoxymethane (AOM)/dextran sulfate sodium salt (DSS)-induced colitis-associated tumorigenesis and that switching to the standard AIN93G diet will ameliorate disease symptoms even after cancer initiation. Female BALB/c mice received either WD (WD group) or standard AIN93G diet (AIN group) for the whole experimental period. After five weeks, the mice received 12.5 mg/kg AOM intraperitoneally, followed by three DSS cycles. In one group of mice, the WD was switched to AIN93G the day before starting the first DSS cycle (WD/AIN group). Feeding the WD during the whole experimental period aggravated colitis symptoms, shortened the colon (p < 0.05), changed microbiota composition and increased tumor promotion. On molecular level, the WD reduced proliferation (p < 0.05) and increased expression of the vitamin D catabolizing enzyme Cyp24a1 (p < 0.001). The switch to the AIN93G diet ameliorated this effect, reflected by longer colons, fewer (p < 0.05) and smaller (p < 0.01) aberrant colonic crypt foci, comparable with the AIN group. Our results show that switching to a healthy diet, even after cancer initiation is able to revert the deleterious effect of the WD and could be an effective preventive strategy to reduce colitis symptoms and prevent tumorigenesis.

Nutritional and Pharmacological Targeting of the Calcium-Sensing Receptor Influences Chemically Induced Colitis in Mice

The calcium-sensing receptor (CaSR) is the main regulator of extracellular Ca2+ homeostasis. It has diverse functions in different tissues, including the intestines. Intestine-specific knockout of the CaSR renders mice more susceptible to dextran sulphate sodium (DSS)-induced colitis. To test our hypothesis that the CaSR reduces intestinal inflammation, we assessed the effects of nutritional and pharmacological agonists of the CaSR in a colitis model. We treated female Balb/C mice with dietary calcium and protein (nutritional agonists of the CaSR) or pharmacological CaSR modulators (the agonists cinacalcet and GSK3004774, and the antagonist NPS-2143; 10 mg/kg), then induced colitis with DSS. The high-protein diet had a strong pro-inflammatory effect-it shortened the colons (5.3 ± 0.1 cm vs. 6.1 ± 0.2 cm normal diet, p < 0.05), lowered mucin expression and upregulated pro-inflammatory cytokines, such as interferon-γ, (4.2-fold, p < 0.05) compared with the normal diet. Cinacalcet reduced mucin expression, which coincided with an increase in tumor necrosis factor-α (4.4-fold, p < 0.05) and IL-6 (4.9-fold, p < 0.05) in the plasma, compared with vehicle. The CaSR antagonist, NPS-2143, significantly reduced the cumulative inflammation score compared with the vehicle control (35.3 ± 19.1 vs. 21.9 ± 14.3 area under the curve, p < 0.05) and reduced infiltration of inflammatory cells. While dietary modulation of the CaSR had no beneficial effects, pharmacological inhibition of the CaSR may have the potential of a novel add-on therapy in the treatment of inflammatory bowel diseases.

Factors inhibiting intestinal calcium absorption: hormones and luminal factors that prevent excessive calcium uptake

Besides the two canonical calciotropic hormones, namely parathyroid hormone and 1,25-dihydroxyvitamin D [1,25(OH)2D3], there are several other endocrine and paracrine factors, such as prolactin, estrogen, and insulin-like growth factor that have been known to directly stimulate intestinal calcium absorption. Generally, to maintain an optimal plasma calcium level, these positive regulators enhance calcium absorption, which is indirectly counterbalanced by a long-loop negative feedback mechanism, i.e., through calcium-sensing receptor in the parathyroid chief cells. However, several lines of recent evidence have revealed the presence of calcium absorption inhibitors present in the intestinal lumen and extracellular fluid in close vicinity to enterocytes, which could also directly compromise calcium absorption. For example, luminal iron, circulating fibroblast growth factor (FGF)-23, and stanniocalcin can decrease calcium absorption, thereby preventing excessive calcium uptake under certain conditions. Interestingly, the intestinal epithelial cells themselves could lower their rate of calcium uptake after exposure to high luminal calcium concentration, suggesting a presence of an ultra-short negative feedback loop independent of systemic hormones. The existence of neural regulation is also plausible but this requires more supporting evidence. In the present review, we elaborate on the physiological significance of these negative feedback regulators of calcium absorption, and provide evidence to show how our body can efficiently restrict a flood of calcium influx in order to maintain calcium homeostasis.

Immunolocalization of calcium sensing and transport proteins in the murine endolymphatic sac indicates calciostatic functions within the inner ear

An exceptionally low calcium (Ca²⁺) concentration in the inner ear endolymph ([Ca²⁺]_endolymph) is crucial for proper auditory and vestibular function. The endolymphatic sac (ES) is believed to critically contribute to the maintenance of this low [Ca²⁺]_endolymph. Here, we investigated the immunohistochemical localization of proteins that are presumably involved in the sensing and transport of extracellular Ca²⁺ in the murine ES epithelium. Light microscopic and fluorescence immunolabeling in paraffin-embedded murine ES tissue sections (male C57BL/6 mice, 6–8 weeks old) demonstrated the presence of the calcium-sensing receptor CaSR, transient receptor potential cation channel subtypes TRPV5 and TRPV6, sarco/endoplasmic reticulum Ca²⁺-ATPases SERCA1 and SERCA2, Na⁺/Ca²⁺ exchanger NCX2, and plasma membrane Ca²⁺ ATPases PMCA1 and PMCA4 in ES epithelial cells. These proteins exhibited (i) membranous (apical or basolateral) or cytoplasmic localization patterns, (ii) a proximal-to-distal labeling gradient within the ES, and (iii) different distribution patterns among ES epithelial cell types (mitochondria-rich cells (MRCs) and ribosome-rich cells (RRCs)). Notably, in the inner ear membranous labyrinth, CaSR was exclusively localized in MRCs, suggesting a unique role of the ES epithelium in CaSR-mediated sensing and control of [Ca²⁺]_endolymph. Structural loss of the distal ES, which is consistently observed in Meniere’s disease, may therefore critically disturb [Ca²⁺]_endolymph and contribute to the pathogenesis of Meniere’s disease.

Physiology of Electrolyte Transport in the Gut: Implications for Disease

We now have an increased understanding of the genetics, cell biology, and physiology of electrolyte transport processes in the mammalian intestine, due to the availability of sophisticated methodologies ranging from genome wide association studies to CRISPR-CAS technology, stem cell-derived organoids, 3D microscopy, electron cryomicroscopy, single cell RNA sequencing, transgenic methodologies, and tools to manipulate cellular processes at a molecular level. This knowledge has simultaneously underscored the complexity of biological systems and the interdependence of multiple regulatory systems. In addition to the plethora of mammalian neurohumoral factors and their cross talk, advances in pyrosequencing and metagenomic analyses have highlighted the relevance of the microbiome to intestinal regulation. This article provides an overview of our current understanding of electrolyte transport processes in the small and large intestine, their regulation in health and how dysregulation at multiple levels can result in disease. Intestinal electrolyte transport is a balance of ion secretory and ion absorptive processes, all exquisitely dependent on the basolateral Na⁺ /K⁺ ATPase; when this balance goes awry, it can result in diarrhea or in constipation. The key transporters involved in secretion are the apical membrane Cl^- channels and the basolateral Na⁺ -K⁺ -2Cl^- cotransporter, NKCC1 and K⁺ channels. Absorption chiefly involves apical membrane Na⁺ /H⁺ exchangers and Cl^- /HCO₃ ^- exchangers in the small intestine and proximal colon and Na⁺ channels in the distal colon. Key examples of our current understanding of infectious, inflammatory, and genetic diarrheal diseases and of constipation are provided. © 2019 American Physiological Society. Compr Physiol 9:947-1023, 2019.

Impaired butyrate absorption in the proximal colon, low serum butyrate and diminished central effects of butyrate on blood pressure in spontaneously hypertensive rats

AIM

Butyrate is a major gut microbiota-derived metabolite. Reduced butyrate-producing bacteria has been reported in the spontaneously hypertensive rat (SHR), a model of hypertension characterized by dysfunctional autonomic nervous system and gut dysbiosis. Here, we demonstrate a potential mechanism for butyrate in blood pressure regulation.

METHODS

High-performance liquid chromatography and liquid chromatography-mass spectrometry were performed to measure butyrate levels in feces and serum. Ussing chamber determined butyrate transport in colon ex vivo. Real-time PCR and immunohistochemistry evaluated expression of butyrate transporter, Slc5a8, in the colon. Mean arterial blood pressure was measured in catheterized anesthetized rats before and after a single butyrate intracerebroventricular injection. Activity of cardioregulatory brain regions was determined by functional magnetic resonance imaging to derive neural effects of butyrate.

RESULTS

In the SHR, we demonstrated elevated butyrate levels in cecal content, but diminished butyrate levels in circulation, possibly due to reduced expression of Slc5a8 transporter in the colon. In addition, we observed lower expression levels of butyrate-sensing receptors in the hypothalamus of SHR, likely leading to the reduced effects of centrally administered butyrate on blood pressure in the SHR. Functional magnetic resonance imaging revealed reduced activation of cardioregulatory brain regions following central administration of butyrate in the SHR compared to control.

CONCLUSION

We demonstrated a reduced availability of serum butyrate in the SHR, possibly due to diminished colonic absorption. Reduced expression of butyrate-sensing receptors in the SHR hypothalamus may explain the reduced central responsiveness to butyrate, indicating microbial butyrate may play a role in blood pressure regulation.

G-Protein Coupled Receptor Targeting on Myeloid Cells in Atherosclerosis

Atherosclerosis, the underlying cause of the majority of cardiovascular diseases (CVDs), is a lipid-driven, inflammatory disease of the large arteries. Gold standard therapy with statins and the more recently developed proprotein convertase subtilisin/kexin type 9 (PCSK9) inhibitors have improved health conditions among CVD patients by lowering low density lipoprotein (LDL) cholesterol. Nevertheless, a substantial part of these patients is still suffering and it seems that 'just' lipid lowering is insufficient. The results of the Canakinumab Anti-inflammatory Thrombosis Outcome Study (CANTOS) have now proven that inflammation is a key driver of atherosclerosis and that targeting inflammation improves CVD outcomes. Therefore, the identification of novel drug targets and development of novel therapeutics that block atherosclerosis-specific inflammatory pathways have to be promoted. The inflammatory processes in atherosclerosis are facilitated by a network of immune cells and their subsequent responses. Cell networking is orchestrated by various (inflammatory) mediators which interact, bind and induce signaling. Over the last years, G-protein coupled receptors (GPCRs) emerged as important players in recognizing these mediators, because of their diverse functions in steady state but also and specifically during chronic inflammatory processes - such as atherosclerosis. In this review, we will therefore highlight a selection of these receptors or receptor sub-families mainly expressed on myeloid cells and their role in atherosclerosis. More specifically, we will focus on chemokine receptors, both classical and atypical, formyl-peptide receptors, the chemerin receptor 23 and the calcium-sensing receptor. When information is available, we will also describe the consequences of their targeting which may hold promising options for future treatment of CVD.

Activation of the calcium sensing receptor attenuates TRPV6-dependent intestinal calcium absorption

Plasma calcium (Ca2+) is maintained by amending the release of parathyroid hormone and through direct effects of the Ca2+ sensing receptor (CaSR) in the renal tubule. Combined, these mechanisms alter intestinal Ca2+ absorption by modulating 1,25-dihydroxy vitamin D3 production, bone resorption, and renal Ca2+ excretion. The CaSR is a therapeutic target in the treatment of secondary hyperparathyroidism and hypocalcemia a common complication of calcimimetic therapy. The CaSR is also expressed in intestinal epithelium, however, a direct role in regulating local intestinal Ca2+ absorption is unknown. Chronic CaSR activation decreased expression of genes involved in Ca2+ absorption. In Ussing chambers, increasing extracellular Ca2+ or basolateral application of the calcimimetic cinacalcet decreased net Ca2+ absorption across intestinal preparations acutely. Conversely, Ca2+ absorption increased with decreasing extracellular Ca2+ concentration. These responses were absent in mice expressing a non-functional TRPV6, TRPV6D541A. Cinacalcet also attenuated Ca2+ fluxes through TRPV6 in Xenopus oocytes when co-expressed with the CaSR. Moreover, the phospholipase C inhibitor, U73122, prevented cinacalcet-mediated inhibition of Ca2+ flux. These results reveal a regulatory pathway whereby activation of the CaSR in the basolateral membrane of the intestine directly attenuates local Ca2+ absorption via TRPV6 to prevent hypercalcemia and help explain how calcimimetics induce hypocalcemia.

Design and implementation of novel nutraceuticals and derivatives for treating intestinal disorders

Gastrointestinal illnesses pose a significant worldwide disease burden and are associated with an array of medicinal and surgical therapies. Standard pharmaceutical options have adverse effects, prompting the rise of nutraceutical or food-derivative therapies. Here, we present an overview of the current nutraceutical therapies in gastrointestinal disease. We then introduce the calcium-sensing receptor (CaSR) as a novel therapeutic target. A G-protein-coupled receptor found in apical and basal intestinal cells, the CaSR modulates intestinal fluid secretion and mucosal integrity. Applying nutraceuticals that upregulate the CaSR may alleviate symptoms seen across a spectrum of illnesses. At last, we discuss how nanoparticle technology can be implemented to effectively deliver nutraceuticals to diseased regions of the intestine, thereby minimizing systemic side effects.

Calcium Intake and Risk of Colorectal Cancer According to Tumor-infiltrating T Cells

Calcium intake has been associated with a lower risk of colorectal cancer. Calcium signaling may enhance T-cell proliferation and differentiation, and contribute to T-cell-mediated antitumor immunity. In this prospective cohort study, we investigated the association between calcium intake and colorectal cancer risk according to tumor immunity status to provide additional insights into the role of calcium in colorectal carcinogenesis. The densities of tumor-infiltrating T-cell subsets [CD3⁺, CD8⁺ , CD45RO (PTPRC) ⁺ , or FOXP3⁺ cell] were assessed using IHC and computer-assisted image analysis in 736 cancer cases that developed among 136,249 individuals in two cohorts. HRs and 95% confidence intervals (CI) were calculated using Cox proportional hazards regression. Total calcium intake was associated with a multivariable HR of 0.55 (comparing ≥1,200 vs. <600 mg/day; 95% CI, 0.36-0.84; P _trend = 0.002) for CD8⁺ T-cell-low but not for CD8⁺ T-cell-high tumors (HR = 1.02; 95% CI, 0.67-1.55; P _trend = 0.47). Similarly, the corresponding HRs (95% CIs) for calcium for low versus high T-cell-infiltrated tumors were 0.63 (0.42-0.94; P _trend = 0.01) and 0.89 (0.58-1.35; P _trend = 0.20) for CD3⁺ ; 0.58 (0.39-0.87; P _trend = 0.006) and 1.04 (0.69-1.58; P _trend = 0.54) for CD45RO⁺ ; and 0.56 (0.36-0.85; P _trend = 0.006) and 1.10 (0.72-1.67; P _trend = 0.47) for FOXP3⁺ , although the differences by subtypes defined by T-cell density were not statistically significant. These potential differential associations generally appeared consistent regardless of sex, source of calcium intake, tumor location, and tumor microsatellite instability status. Our findings suggest a possible role of calcium in cancer immunoprevention via modulation of T-cell function.

The calcium-sensing receptor in physiology and in calcitropic and noncalcitropic diseases

The Ca²⁺-sensing receptor (CaSR) is a dimeric family C G protein-coupled receptor that is expressed in calcitropic tissues such as the parathyroid glands and the kidneys and signals via G proteins and β-arrestin. The CaSR has a pivotal role in bone and mineral metabolism, as it regulates parathyroid hormone secretion, urinary Ca²⁺ excretion, skeletal development and lactation. The importance of the CaSR for these calcitropic processes is highlighted by loss-of-function and gain-of-function CaSR mutations that cause familial hypocalciuric hypercalcaemia and autosomal dominant hypocalcaemia, respectively, and also by the fact that alterations in parathyroid CaSR expression contribute to the pathogenesis of primary and secondary hyperparathyroidism. Moreover, the CaSR is an established therapeutic target for hyperparathyroid disorders. The CaSR is also expressed in organs not involved in Ca²⁺ homeostasis: it has noncalcitropic roles in lung and neuronal development, vascular tone, gastrointestinal nutrient sensing, wound healing and secretion of insulin and enteroendocrine hormones. Furthermore, the abnormal expression or function of the CaSR is implicated in cardiovascular and neurological diseases, as well as in asthma, and the CaSR is reported to protect against colorectal cancer and neuroblastoma but increase the malignant potential of prostate and breast cancers.

Involvement of calcium-sensing receptor activation in the alleviation of intestinal inflammation in a piglet model by dietary aromatic amino acid supplementation

Ca2+-sensing receptor (CaSR) represents a potential therapeutic target for inflammatory bowel diseases and strongly prefers aromatic amino acid ligands. We investigated the regulatory effects of dietary supplementation with aromatic amino acids - tryptophan, phenylalanine and tyrosine (TPT) - on the CaSR signalling pathway and intestinal inflammatory response. The in vivo study was conducted with weanling piglets using a 2 × 2 factorial arrangement in a randomised complete block design. Piglets were fed a basal diet or a basal diet supplemented with TPT and with or without inflammatory challenge. The in vitro study was performed in porcine intestinal epithelial cell line to investigate the effects of TPT on inflammatory response using NPS-2143 to inhibit CaSR. Dietary supplementation of TPT alleviated histopathological injury and decreased myeloperoxidase activity in intestine challenged with lipopolysaccharide. Dietary supplementation of TPT decreased serum concentration of pro-inflammatory cytokines (IL-1β, IL-6, IL-8, IL-12, granulocyte-macrophage colony-stimulating factor, TNF-α), as well as the mRNA abundances of pro-inflammatory cytokines in intestine but enhanced anti-inflammatory cytokines IL-4 and transforming growth factor-β mRNA levels compared with pigs fed control diet and infected by lipopolysaccharide. Supplementation of TPT increased CaSR and phospholipase Cβ2 protein levels, but decreased inhibitor of NF-κB kinase α/β and inhibitor of NF-κB (IκB) protein levels in the lipopolysaccharide-challenged piglets. When the CaSR signalling pathway was blocked by NPS-2143, supplementation of TPT decreased the CaSR protein level, but enhanced phosphorylated NF-κB and IκB levels in IPEC-J2 cells. To conclude, supplementation of aromatic amino acids alleviated intestinal inflammation as mediated through the CaSR signalling pathway.

Lactobacillus brevis 23017 Relieves Mercury Toxicity in the Colon by Modulation of Oxidative Stress and Inflammation Through the Interplay of MAPK and NF-κB Signaling Cascades

Aims: Lactobacillus strains have protective effects against heavy metals while relieving oxidative stress and modulating the immune response. Mechanisms that ameliorate heavy metal toxicity and the relationship between probiotics and gut barrier protection in the process of heavy metal pathogenesis was poorly understood. Methods and Results: In this study, Lactobacillus brevis 23017 (LAB, L. brevis 23017), a selected probiotics strain with strong mercury binding capacities, was applied to evaluate the efficiency against mercury toxicity in a mouse model. Histopathological results along with HE stains show that L. brevis 23017 protects the integrity of the small intestinal villus, which slows weight loss in response to Hg exposure. The qRT-PCR results demonstrate that L. brevis 23017 maintains a normal mucosal barrier via modulation of tight junction proteins. Importantly, the present study demonstrates that L. brevis 23017 effectively ameliorates injury of the small intestine by reducing intestinal inflammation and alleviating oxidative stress in animal models. Moreover, L. brevis 23017 blocks oxidative stress and inflammation through MAPK and NF-κB pathways, as shown by western blot. Conclusions: Together, these results reveal that L. brevis 23017 may have applications in the prevention and treatment of oral Hg exposure with fermented functional foods by protecting gut health in daily life.

Calcium-sensing receptor in colorectal inflammation and cancer: Current insights and future perspectives

The extracellular calcium-sensing receptor (CaSR) is best known for its action in the parathyroid gland and kidneys where it controls body calcium homeostasis. However, the CaSR has different roles in the gastrointestinal tract, where it is ubiquitously expressed. In the colon, the CaSR is involved in controlling multiple mechanisms, including fluid transport, inflammation, cell proliferation and differentiation. Although the expression pattern and functions of the CaSR in the colonic microenvironment are far from being completely understood, evidence has been accumulating that the CaSR might play a protective role against both colonic inflammation and colorectal cancer. For example, CaSR agonists such as dipeptides have been suggested to reduce colonic inflammation, while dietary calcium was shown to reduce the risk of colorectal cancer. CaSR expression is lost in colonic malignancies, indicating that the CaSR is a biomarker for colonic cancer progression. This dual anti-inflammatory and anti-tumourigenic role of the CaSR makes it especially interesting in colitis-associated colorectal cancer. In this review, we describe the clinical and experimental evidence for the role of the CaSR in colonic inflammation and colorectal cancer, the intracellular signalling pathways which are putatively involved in these actions, and the possibilities to exploit these actions of the CaSR for future therapies of colonic inflammation and cancer.

Current Perspectives and Mechanisms of Relationship between Intestinal Microbiota Dysfunction and Dementia: A Review

BACKGROUND

Accumulating data suggest a crucial role of the intestinal microbiota in the development and progression of neurodegenerative diseases. More recently, emerging reports have revealed an association between intestinal microbiota dysfunctions and dementia, a debilitating multifactorial disorder, characterized by progressive deterioration of cognition and behavior that interferes with the social and professional life of the sufferer. However, the mechanisms of this association are not fully understood.

SUMMARY

In this review, I discuss recent data that suggest mechanisms of cross-talk between intestinal microbiota dysfunction and the brain that underlie the development of dementia. Potential therapeutic options for dementia are also discussed. The pleiotropic signaling of the metabolic products of the intestinal microbiota together with their specific roles in the maintenance of both the intestinal and blood-brain barriers as well as regulation of local, distant, and circulating immunocytes, and enteric, visceral, and central neural functions are integral to a healthy gut and brain.

KEY MESSAGES

Research investigating the effect of intestinal microbiota dysfunctions on brain health should focus on multiple interrelated systems involving local and central neuroendocrine, immunocyte, and neural signaling of microbial products and transmitters and neurohumoral cells that not only maintain intestinal, but also blood brain-barrier integrity. The change in intestinal microbiome/dysbiome repertoire is crucial to the development of dementia.

Calcium-sensing receptor in nutrient sensing: an insight into the modulation of intestinal homoeostasis

The animal gut effectively prevents the entry of hazardous substances and microbes while permitting the transfer of nutrients, such as water, electrolytes, vitamins, proteins, lipids, carbohydrates, minerals and microbial metabolites, which are intimately associated with intestinal homoeostasis. The gut maintains biological functions through its nutrient-sensing receptors, including the Ca-sensing receptor (CaSR), which activates a variety of signalling pathways, depending on cellular context. CaSR coordinates food digestion and nutrient absorption, promotes cell proliferation and differentiation, regulates energy metabolism and immune response, stimulates hormone secretion, mitigates secretory diarrhoea and enhances intestinal barrier function. Thus, CaSR is crucial to the maintenance of gut homoeostasis and protection of intestinal health. In this review, we focused on the emerging roles of CaSR in the modulation of intestinal homoeostasis including related underlying mechanisms. By elucidating the relationship between CaSR and animal gut homoeostasis, effective and inexpensive methods for treating intestinal health imbalance through nutritional manipulation can be developed. This article is expected to provide experimental data of the effects of CaSR on animal or human health.

The Calcium-Sensing Receptor Gene Polymorphism rs1801725 and Calcium-Related Phenotypes in Hemodialysis Patients

BACKGROUND/AIMS

The calcium-sensing receptor gene (CASR) rs1801725 variant is responsible for a non-conservative amino-acid change (A986S) in the calcium-sensing receptor cytoplasmic tail. We hypothesized that rs1801725 polymorphism might be helpful in understanding Ca-related abnormalities in HD patients.

METHODS

In 1215 subjects (245 on cinacalcet), we determined the associations of rs1801725 with secondary hyperparathyroidism (sHPT)-related laboratory parameters, PTH-decreasing effect of cinacalcet hydrochloride, coronary artery disease (CAD), myocardial infarction (MI), nephrolithiasis-related ESRD, and mortality. CASR rs7652589(AT) haplotypes and rs1801725 epistatic interactions with vitamin D signaling pathway genes were examined for associations with selected phenotypes.

RESULTS

The rs1801725 variant allele showed an increasing independent effect on plasma PTH (Pcorrected = 0.009). CASR rs7652589_rs1801725 AT haplotype was associated with 1.7-fold higher frequency of PTH levels over 437 pg/mL than the reference haplotype GG (P = 0.001). CASR rs7652589_rs1801725 AG haplotype was 1.5-fold more frequent in nephrolithiasis-related ESRD than the GG haplotype (P = 0.004). There were no significant associations between rs1801725, CAD, MI, and response to cinacalcet. Variant homozygosity of rs1801725 correlated independently with higher infection-related mortality compared with heterozygosity (HR 7.95, 95%CI 2.15 - 29.37, P = 0.003) and major homozygosity (HR 5.89, 95%CI 1.69 - 20.55, P = 0.040). CASR rs1801725 did not show epistatic interactions with vitamin D signaling pathway genes concerning tested associations.

CONCLUSION

The variant allele of CASR rs1801725 solely and together with the variant allele of rs7652589 increases risk of more advanced sHPT. Homozygosity of the rs1801725 variant allele contributes to infection-related mortality in HD patients.

Inability to reduce morbidity of diarrhea by ORS: can we design a better therapy?

Diarrheal disease is a worldwide problem that still causes significant morbidity and mortality among children. Currently, oral rehydration solution (ORS) is the standard of care for acute diarrhea in pediatric patients. Although effective in reducing mortality, ORS does not alleviate diarrheal symptoms, thus reducing caregiver compliance and therapeutic efficacy. This article will briefly review the current problem of pediatric diarrhea and the shortcomings of current therapies; however, the focus of this review is to examine the intestinal calcium-sensing receptor (CaSR). The author summarizes the evidence suggesting that targeting the CaSR will enable clinicians to address all four major pathophysiological mechanisms of diarrheal disease, and substantiates the need for future research regarding this therapy.

Functions and Signaling Pathways of Amino Acids in Intestinal Inflammation

Intestine is always exposed to external environment and intestinal microorganism; thus it is more sensitive to dysfunction and dysbiosis, leading to intestinal inflammation, such as inflammatory bowel disease (IBD), irritable bowel syndrome (IBS), and diarrhea. An increasing number of studies indicate that dietary amino acids play significant roles in preventing and treating intestinal inflammation. The review aims to summarize the functions and signaling mechanisms of amino acids in intestinal inflammation. Amino acids, including essential amino acids (EAAs), conditionally essential amino acids (CEAAs), and nonessential amino acids (NEAAs), improve the functions of intestinal barrier and expressions of anti-inflammatory cytokines and tight junction proteins but decrease oxidative stress and the apoptosis of enterocytes as well as the expressions of proinflammatory cytokines in the intestinal inflammation. The functions of amino acids are associated with various signaling pathways, including mechanistic target of rapamycin (mTOR), inducible nitric oxide synthase (iNOS), calcium-sensing receptor (CaSR), nuclear factor-kappa-B (NF-κB), mitogen-activated protein kinase (MAPK), nuclear erythroid-related factor 2 (Nrf2), general controlled nonrepressed kinase 2 (GCN2), and angiotensin-converting enzyme 2 (ACE2).

Extracellular Calcium Dictates Onset, Severity, and Recovery of Diarrhea in a Child with Immune-Mediated Enteropathy

Diarrhea causes monovalent and divalent ion losses that can influence clinical outcome. Unlike the losses of monovalent ions, such as Na⁺, K⁺, Cl^-, and [Formula: see text], which are generally large in quantity (osmoles) and therefore determine the severity of diarrhea, the losses of divalent ions are relatively small in osmoles and are often overlooked during diarrheal treatment. Studies now suggest that despite divalent ions being small in osmoles, their effects are large due to the presence of divalent ion-sensing receptors and their amplifying effects in the gut. As a result, losses of these divalent ions without prompt replacement could also significantly affect the onset, severity, and/or recovery of diarrheal disease. Herein, we report a case of a malnourished child with an immune-mediated enteropathy who developed episodes of "breakthrough" diarrhea with concurrent hypocalcemia while on appropriate immunotherapy. Interestingly, during these periods of diarrhea, stool volume fluctuated with levels of blood Ca²⁺. When Ca²⁺ was low, diarrhea occurred; when Ca²⁺ levels normalized with replacement, diarrhea stopped. Based on this and other observations, a broader question arises as to whether the Ca²⁺ lost in diarrhea should be replaced promptly in these patients.

Tumor expression of calcium sensing receptor and colorectal cancer survival: Results from the nurses' health study and health professionals follow-up study

Although experimental evidence suggests calcium-sensing receptor (CASR) as a tumor-suppressor, the prognostic role of tumor CASR expression in colorectal carcinoma remains unclear. We hypothesized that higher tumor CASR expression might be associated with improved survival among colorectal cancer patients. We evaluated tumor expression levels of CASR by immunohistochemistry in 809 incident colorectal cancer patients within the Nurses' Health Study and the Health Professionals Follow-up Study. We used Cox proportional hazards regression models to estimate multivariable hazard ratio (HR) for the association of tumor CASR expression with colorectal cancer-specific and all-cause mortality. We adjusted for potential confounders including tumor biomarkers such as microsatellite instability, CpG island methylator phenotype, LINE-1 methylation level, expressions of PTGS2, VDR and CTNNB1 and mutations of KRAS, BRAF and PIK3CA. There were 240 colorectal cancer-specific deaths and 427 all-cause deaths. The median follow-up of censored patients was 10.8 years (interquartile range: 7.2, 15.1). Compared with patients with no or weak expression of CASR, the multivariable HRs for colorectal cancer-specific mortality were 0.80 [95% confidence interval (CI): 0.55-1.16] in patients with moderate CASR expression and 0.50 (95% CI: 0.32-0.79) in patients with intense CASR expression (p-trend = 0.003). The corresponding HRs for overall mortality were 0.85 (0.64-1.13) and 0.81 (0.58-1.12), respectively. Higher tumor CASR expression was associated with a lower risk of colorectal cancer-specific mortality. This finding needs further confirmation and if confirmed, may lead to better understanding of the role of CASR in colorectal cancer progression.

Identification of potent, nonabsorbable agonists of the calcium-sensing receptor for GI-specific administration

Modulation of gastrointestinal nutrient sensing pathways provides a promising a new approach for the treatment of metabolic diseases including diabetes and obesity. The calcium-sensing receptor has been identified as a key receptor involved in mineral and amino acid nutrient sensing and thus is an attractive target for modulation in the intestine. Herein we describe the optimization of gastrointestinally restricted calcium-sensing receptor agonists starting from a 3-aminopyrrolidine-containing template leading to the identification of GI-restricted agonist 19 (GSK3004774).

Fatty acid and mineral receptors as drug targets for gastrointestinal disorders

Nutrient-sensing receptors, including fatty acid receptors (FFA1–FFA4), Ca2+-sensing receptors and Zn2+-sensing receptors, are involved in several biological processes. These receptors are abundantly expressed in the GI tract, where they have been shown to play crucial roles in regulating GI function. This review provides an overview of the GI functions of fatty acid and mineral receptors, including the regulation of gastric and enteroendocrine functions, GI motility, ion transport and cell growth. Recently, several lines of evidence have implicated these receptors as promising therapeutic targets for the treatment of GI disorders, for example, inflammatory bowel disease, colorectal cancer, metabolic syndrome and diarrheal diseases. A future perspective on drug discovery research targeting these receptors is discussed.

The Extracellular Calcium-Sensing Receptor in the Intestine: Evidence for Regulation of Colonic Absorption, Secretion, Motility, and Immunity

Different from other epithelia, the intestinal epithelium has the complex task of providing a barrier impeding the entry of toxins, food antigens, and microbes, while at the same time allowing for the transfer of nutrients, electrolytes, water, and microbial metabolites. These molecules/organisms are transported either transcellularly, crossing the apical and basolateral membranes of enterocytes, or paracellularly, passing through the space between enterocytes. Accordingly, the intestinal epithelium can affect energy metabolism, fluid balance, as well as immune response and tolerance. To help accomplish these complex tasks, the intestinal epithelium has evolved many sensing receptor mechanisms. Yet, their roles and functions are only now beginning to be elucidated. This article explores one such sensing receptor mechanism, carried out by the extracellular calcium-sensing receptor (CaSR). In addition to its established function as a nutrient sensor, coordinating food digestion, nutrient absorption, and regulating energy metabolism, we present evidence for the emerging role of CaSR in the control of intestinal fluid homeostasis and immune balance. An additional role in the modulation of the enteric nerve activity and motility is also discussed. Clearly, CaSR has profound effects on many aspects of intestinal function. Nevertheless, more work is needed to fully understand all functions of CaSR in the intestine, including detailed mechanisms of action and specific pathways involved. Considering the essential roles CaSR plays in gastrointestinal physiology and immunology, research may lead to a translational opportunity for the development of novel therapies that are based on CaSR's unique property of using simple nutrients such as calcium, polyamines, and certain amino acids/oligopeptides as activators. It is possible that, through targeting of intestinal CaSR with a combination of specific nutrients, oral solutions that are both inexpensive and practical may be developed to help in conditioning the gut microenvironment and in maintaining digestive health.

Calcium-sensing receptor: A new target for therapy of diarrhea

Management of acute diarrhea remains a global challenge, particularly in resource-limiting countries. Oral rehydration solution (ORS), a passive rehydrating therapy developed approximately 40 years ago, remains the mainstay treatment. Although ORS is effective for hydration, since it does not inhibit enterotoxin-mediated excessive secretion, reduced absorption and compromised barrier function - the primary mechanisms of diarrhea, ORS does not offer a rapid relief of diarrhea symptom. There are a few alternative therapies available, yet the use of these drugs is limited by their expense, lack of availability and/or safety concerns. Novel anti-diarrheal therapeutic approaches, particularly those simple affordable therapies, are needed. This article explores intestinal calcium-sensing receptor (CaSR), a newly uncovered target for therapy of diarrhea. Unlike others, targeting this host antidiarrheal receptor system appears “all-inclusive”: it is anti-secretory, pro-absorptive, anti-motility, and anti-inflammatory. Thus, activating CaSR reverses changes of both secretory and inflammatory diarrheas. Considering its unique property of using simple nutrients such as calcium, polyamines, and certain amino acids/oligopeptides as activators, it is possible that through targeting of CaSR with a combination of specific nutrients, novel oral rehydrating solutions that are inexpensive and practical to use in all countries may be developed.

Chitosan Oligosaccharide Reduces Intestinal Inflammation That Involves Calcium-Sensing Receptor (CaSR) Activation in Lipopolysaccharide (LPS)-Challenged Piglets

Chitosan oligosaccharide (COS) is a degradation product of chitosan with antioxidative, anti-inflammatory, and antibacterial effects. This study was conducted to investigate the effects of dietary COS on the intestinal inflammatory response and the calcium-sensing receptor (CaSR) and nuclear transcription factor kappa B (NF-κB) signaling pathways that may be involved using a lipopolysaccharide (LPS)-challenged piglet model. A total of 40 weaned piglets were used in a 2 × 2 factorial design; the main factors were dietary treatment (basal or 300 μg/kg COS) and inflammatory challenge (LPS or saline). On the morning of days 14 and 21 after the initiation of treatment, the piglets were injected intraperitoneally with Escherichia coli LPS at 60 and 80 μg/kg body weight or the same amount of sterilized saline, respectively. Blood and small intestine samples were collected on day 14 or 21, respectively. The results showed that piglets challenged with LPS have a significant decrease in average daily gain and gain:feed and histopathological injury in the jejunum and ileum, whereas dietary supplementation with COS significantly alleviated intestinal injury induced by LPS. Piglets fed the COS diet had lower serum concentrations of tumor necrosis factor alpha (TNF-α), interleukin (IL) 6, and IL-8 as well as lower intestinal abundances of pro-inflammatory cytokine mRNA but higher anti-inflammatory cytokine mRNA compared with piglets fed the basal diet among LPS-challenged piglets (p < 0.05). Dietary COS increased intestinal CaSR and PLCβ2 protein expressions in both saline- and LPS-treated piglets, but decreased p-NF-κB p65, IKKα/β, and IκB protein expressions in LPS-challenged piglets (p < 0.05). These findings indicate that COS has the potential to reduce the intestinal inflammatory response, which is concomitant with the activation of CaSR and the inhibition of NF-κB signaling pathways under an inflammatory stimulus.