A fungal metabolite zearalenone as a CFTR inhibitor and potential therapy of secretory diarrheas

Discovery of Fungus-Derived Nornidulin as a Novel TMEM16A Inhibitor: A Potential Therapy to Inhibit Mucus Secretion in Asthma

Introduction

Inhibition of Ca2+-activated transmembrane protein 16A (TMEM16A) Cl- channels has been proposed to alleviate mucus secretion in asthma. In this study, we identified a novel class of TMEM16A inhibitors from natural sources in airway epithelial Calu-3 cells and determine anti-asthmatic efficacy of the most potent candidate in a mouse model of asthma.

Methods

For electrophysiological analyses, IL-4-primed Calu-3 cell monolayers were mounted in Ussing chamber and treated with various fungus-derived depsidones prior to the addition of UTP, ionomycin, thapsigargin, or Eact to stimulate TMEM16A Cl- current. Ca2+-induced mucus secretion in Calu-3 cell monolayers was assessed by determining MUC5AC protein remaining in the cells using immunofluorescence staining. OVA-induced female BALB/c mice was used as an animal model of asthma. After the course of induction, cellular and mucus components in bronchoalveolar lavage were analyzed. Lungs were fixed and undergone with H&E and PAS staining for the evaluation of airway inflammation and mucus production, respectively.

Results

The screening of fungus-derived depsidones revealed that nornidulin completely abolished the UTP-activated TMEM16A current in Calu-3 cell monolayers with the IC50 and a maximal effect being at ~0.8 µM and 10 µM, respectively. Neither cell viability nor barrier function was affected by nornidulin. Mechanistically, nornidulin (10 µM) suppressed Cl- currents induced by ionomycin (a Ca2+-specific ionophore), thapsigargin (an inhibitor of the endoplasmic reticulum Ca2+ ATPase), and Eact (a putative TMEM16A activator) without interfering with intracellular Ca2+ ([Ca2+]i) levels. These results suggest that nornidulin exerts its effect without changing [Ca2+]i, possibly through direct effect on TMEM16A. Interestingly, nornidulin (at 10 µM) reduced Ca2+-dependent mucus release in the Calu-3 cell monolayers. In addition, nornidulin (20 mg/kg) inhibited bronchoalveolar mucus secretion without impeding airway inflammation in ovalbumin-induced asthmatic mice.

Discussion and Conclusion

Our study revealed that nornidulin is a novel TMEM16A inhibitor that suppresses mucus secretion without compromising immunologic activity. Further development of nornidulin may provide a new remedy for asthma or other diseases associated with allergic mucus hypersecretion without causing opportunistic infections.

The Cystic Fibrosis Transmembrane Conductance Regulator Gene (CFTR) Is under Post-Transcriptional Control of microRNAs: Analysis of the Effects of agomiRNAs Mimicking miR-145-5p, miR-101-3p, and miR-335-5p

(1) Background: MicroRNAs are involved in the expression of the gene encoding the chloride channel CFTR (Cystic Fibrosis Transmembrane Conductance Regulator); the objective of this short report is to study the effects of the treatment of bronchial epithelial Calu-3 cells with molecules mimicking the activity of pre-miR-145-5p, pre-miR-335-5p, and pre-miR-101-3p, and to discuss possible translational applications of these molecules in pre-clinical studies focusing on the development of protocols of possible interest in therapy; (2) Methods: CFTR mRNA was quantified by Reverse Transcription quantitative Polymerase Chain Reaction (RT-qPCR). The production of the CFTR protein was assessed by Western blotting; (3) Results: The treatment of Calu-3 cells with agomiR-145-5p caused the highest inhibition of CFTR mRNA accumulation and CFTR production; (4) Conclusions: The treatment of target cells with the agomiR pre-miR-145-5p should be considered when CFTR gene expression should be inhibited in pathological conditions, such as polycystic kidney disease (PKD), some types of cancer, cholera, and SARS-CoV-2 infection.

The Roots of Neorautanenia mitis (A. Rich) Verdcourt: Further Evidence of Its Antidiarrhoeal Activity

Despite the current management options and therapeutics used in the treatment of diarrhoea, in Africa and Asia, diarrhoea remains a major concern, especially in children under the age of 5 years. Traditional knowledge of medicinal plants used in the management of diarrhoea symptoms can be explored for their efficacy. In Nigeria, the TMPs (Traditional Medicine Practitioners) have, over the years, employed medicinal plants in the management of diarrhoea symptoms. In our current and previous studies, we aimed at validating the effectiveness of Neorautanenia mitis in the management of diarrhoea as claimed by the TMPs. Out of the 20 compounds isolated from N. mitis, the compounds neodulin, pachyrrhizine, neotenone and dolineone were the most abundant, and in this study, neodulin showed a pronounced relaxation of the rhythmic contraction of the isolated rabbit jejunum in an organ bath in a concentration-dependent manner, with a complete relaxation at 60 µg/mL. Neotenone and dolineone showed a dose-dependent inhibition of defecation of 65.07%, and 50.01%, respectively, at 20 mg/kg in a castor-oil-induced diarrhoea model. This is a strong indication that compounds from N. mitis possess antidiarrhoeal properties, thereby giving credence to its traditional usage in diarrhoea therapy, and therefore validating its antidiarrhoeal activity and its being worthy of further investigation.

Natural statin derivatives as potential therapy to reduce intestinal fluid loss in cholera

As a leading cause of death in children under 5 years old, secretory diarrheas including cholera are characterized by excessive intestinal fluid secretion driven by enterotoxin-induced cAMP-dependent intestinal chloride transport. This study aimed to identify fungal bioactive metabolites possessing anti-secretory effects against cAMP-dependent chloride secretion in intestinal epithelial cells. Using electrophysiological analyses in human intestinal epithelial (T84) cells, five fungus-derived statin derivatives including α,β-dehydrolovastatin (DHLV), α,β-dehydrodihydromonacolin K, lovastatin, mevastatin and simvastatin were found to inhibit the cAMP-dependent chloride secretion with IC50 values of 1.8, 8.9, 11.9, 11.4 and 5 μM, respectively. Being the most potent statin derivatives, DHLV was evaluated for its pharmacological properties including cellular toxicity, mechanism of action, target specificity and in vivo efficacy. DHLV at concentrations up to 20 μM did not affect cell viability and barrier integrity of T84 cells. Electrophysiological analyses indicated that DHLV inhibited cystic fibrosis transmembrane conductance regulator (CFTR), a cAMP-dependent apical chloride channel, via mechanisms not involving alteration of intracellular cAMP levels or its negative regulators including AMP-activated protein kinases and protein phosphatases. DHLV had no effect on Na+-K+ ATPase activities but inhibited Ca2+-dependent chloride secretion without affecting intracellular Ca2+ levels. Importantly, intraperitoneal (2 mg/kg) and intraluminal (20 μM) injections of DHLV reduced cholera toxin-induced intestinal fluid secretion in mice by 59% and 65%, respectively without affecting baseline intestinal fluid transport. This study identifies natural statin derivatives as novel natural product-derived CFTR inhibitors, which may be beneficial in the treatment of enterotoxin-induced secretory diarrheas including cholera.

Total Synthesis and Biological Evaluation of Mutolide and Analogues

The convergent total syntheses of three 14-membered macrolide natural products, mutolide, nigrosporolide and (4S,7S,13S)-4,7-dihydroxy-13-tetradeca-2,5,8-trienolide have been achieved. The key synthetic features include Shiina macrolactonization to assemble the 14-membered macrocyclic core, Wittig or Still-Gennari olefination and selective reduction of propargylic alcohol to construct the E- or Z-olefins. Cross metathesis was also highlighted as an efficient tool to forge the formation of E-olefin. The three synthetic macrolides were evaluated for their cytotoxic activity against three human cancer cell lines as well as for inhibitory effect on CFTR-mediated chloride secretion in human intestinal epithelial (T84) cells. Mutolide displayed significant cytotoxic activity against HCT116 colon cancer cells with an IC₅₀ of ∼12 μM as well as a potent CTFR inhibitory effect with an IC₅₀ value of ∼1 μM.

β-eudesmol but not atractylodin exerts an inhibitory effect on CFTR-mediated chloride transport in human intestinal epithelial cells

Oriental herbal medicine with the two bioactive constituents, β-eudesmol (BE) and atractylodin (AT), has been used as a remedy for gastrointestinal disorders. There was no scientific evidence reporting their antidiarrheal effect and underpinning mechanisms. Therefore, we aimed to investigate the anti-secretory activity of these two compounds in vitro. The inhibitory effect of BE and AT on cAMP-induced Cl^- secretion was evaluated by Ussing chamber in human intestinal epithelial (T84) cells. Short-circuit current (I_SC) and apical Cl^- current (I_Cl-) were measured after adding indirect and direct cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel activator. MTT assay was used to determine cellular cytotoxicity. Protein-ligand interaction was investigated by in silico molecular docking analysis. BE, but not AT concentration-dependently (IC₅₀ of ~1.05 µM) reduced cAMP-mediated, CFTR_inh-172 inhibitable Cl^- secretion as determined by transepithelial I_SC across a monolayer of T84 cells. Potency of CFTR-mediated I_Cl- inhibition by BE did not change with the use of different CFTR activators suggesting a direct blockage of the channel active site(s). Pretreatment with BE completely prevented cAMP-induced I_Cl-. Furthermore, BE at concentrations up to 200 µM (24 h) had no effect on T84 cell viability. In silico studies indicated that BE could best dock onto dephosphorylated structure of CFTR at ATP-binding pockets in nucleotide-binding domain (NBD) 2 region. These findings provide the first evidence for the anti-secretory effect of BE involving inhibition of CFTR function. BE represents a promising candidate for the therapeutic or prophylactic intervention of diarrhea resulted from intestinal hypersecretion of Cl^.

Isolation of CFTR and TMEM16A inhibitors from Neorautanenia mitis (A. Rich) Verdcourt: Potential lead compounds for treatment of secretory diarrhea

A phytochemical study on the root extracts of Neorautanenia mitis, a Nigerian medicinal plant used in the management of diarrhea, led to the isolation of one new and 19 known natural products. These compounds and crude extracts were evaluated for Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) Cl^- channel and calcium-activated Cl^- channel (TMEM16A) inhibitory activities in T84 and Calu-3 cells, respectively. Four compounds namely dolineon, neodulin, pachyrrhizine, and neotenone inhibited cAMP-induced Cl- secretion across T84 cell monolayers with IC₅₀ values of ~0.81 μM, ~2.42 μM, ~2.87 μM, and ~4.66 μM, respectively. Dolineon having the highest inhibitory activity also inhibited a Ca + activated Cl^- channel (TMEM16A) with an IC₅₀ value of ~4.38 μM. The in vitro antidiarrheal activity of dolineon was evaluated on cholera toxin (CT) induced chloride secretion in T84 cells, where it inhibited CT-induced chloride secretion by >70% at 100 μM. Dolineon also inhibited CT-induced fluid secretion by ~70% in an in vivo mouse closed loop model at a dose of 16.9 μg/loop. The cytotoxicity of the extracts and compounds was evaluated on KB, Vero and BHK21 cells, dolineon showed low cytotoxicity of >29.6 μM and 57.30 + 6.77 μM against Vero and BHK21 cells, respectively. Our study revealed that several compounds isolated from N. mitis showed antidiarrheal activity. The most active compound dolineon can potentially serve as a lead compound towards the development of CFTR and TMEM16A inhibitors as future therapeutics for secretory diarrhea.

A comprehensive review of therapeutic approaches available for the treatment of cholera

Objectives

The oral rehydration solution is the most efficient method to treat cholera; however, it does not interfere in the action mechanism of the main virulence factor produced by Vibrio cholerae, the cholera toxin (CT), and this disease still stands out as a problem for human health worldwide. This review aimed to describe therapeutic alternatives available in the literature, especially those related to the search for molecules acting upon the physiopathology of cholera.

Key findings

New molecules have offered a protection effect against diarrhoea induced by CT or even by infection from V. cholerae. The receptor regulator cystic fibrosis channel transmembrane (CFTR), monosialoganglioside (GM1), enkephalinase, AMP-activated protein kinase (AMPK), inhibitors of expression of virulence factors and activators of ADP-ribosylarginine hydrolase are the main therapeutic targets studied. Many of these molecules or extracts still present unclear action mechanisms.

Conclusions

Knowing therapeutic alternatives and their molecular mechanisms for the treatment of cholera could guide us to develop a new drug that could be used in combination with the rehydration solution.