Uremic Toxin Lanthionine Interferes with the Transsulfuration Pathway, Angiogenetic Signaling and Increases Intracellular Calcium.

(1) The beneficial effects of hydrogen sulfide (H2S) on the cardiovascular and nervous system have recently been re-evaluated. It has been shown that lanthionine, a side product of H2S biosynthesis, previously used as a marker for H2S production, is dramatically increased in circulation in uremia, while H2S release is impaired. Thus, lanthionine could be classified as a novel uremic toxin. Our research was aimed at defining the mechanism(s) for lanthionine toxicity. (2) The effect of lanthionine on H2S release was tested by a novel lead acetate strip test (LAST) in EA.hy926 cell cultures. Effects of glutathione, as a redox agent, were assayed. Levels of sulfane sulfur were evaluated using the SSP4 probe and flow cytometry. Protein content and glutathionylation were analyzed by Western Blotting and immunoprecipitation, respectively. Gene expression and miRNA levels were assessed by qPCR. (3) We demonstrated that, in endothelial cells, lanthionine hampers H2S release; reduces protein content and glutathionylation of transsulfuration enzyme cystathionine-ß-synthase; modifies the expression of miR-200c and miR-423; lowers expression of vascular endothelial growth factor VEGF; increases Ca2+ levels. (4) Lanthionine-induced alterations in cell cultures, which involve both sulfur amino acid metabolism and calcium homeostasis, are consistent with uremic dysfunctional characteristics and further support the uremic toxin role of this amino acid.

Zebrafish, a Novel Model System to Study Uremic Toxins: The Case for the Sulfur Amino Acid Lanthionine.

The non-proteinogenic amino acid lanthionine is a byproduct of hydrogen sulfide biosynthesis: the third endogenous vasodilator gas, after nitric oxide and carbon monoxide. While hydrogen sulfide is decreased in uremic patients on hemodialysis, lanthionine is increased and has been proposed as a new uremic toxin, since it is able to impair hydrogen sulfide production in hepatoma cells. To characterize lanthionine as a uremic toxin, we explored its effects during the early development of the zebrafish (Danio rerio), a widely used model to study the organ and tissue alterations induced by xenobiotics. Lanthionine was employed at concentrations reproducing those previously detected in uremia. Light-induced visual motor response was also studied by means of the DanioVision system. Treatment of zebrafish embryos with lanthionine determined acute phenotypical alterations, on heart organogenesis (disproportion in cardiac chambers), increased heart beating, and arrhythmia. Lanthionine also induced locomotor alterations in zebrafish embryos. Some of these effects could be counteracted by glutathione. Lanthionine exerted acute effects on transsulfuration enzymes and the expression of genes involved in inflammation and metabolic regulation, and modified microRNA expression in a way comparable with some alterations detected in uremia. Lanthionine meets the criteria for classification as a uremic toxin. Zebrafish can be successfully used to explore uremic toxin effects.

Regulatory elements retained during chordate evolution: coming across tunicates.

Understanding the role of conserved noncoding elements (CNEs) throughout the genome is taking advantage of the improved efficiency of genome-sequencing techniques and bioinformatics tools. Tunicates diverged before the vertebrate whole genome duplications and, therefore, represent an optimal model system to study the evolution of complex regulatory networks. Here, we review the current knowledge on the characterization of CNEs during embryonic development, focusing on the evolutionary similarity and divergence between tunicates and other chordates. Many vertebrate specific CNEs that regulate developmental processes were identified based on high level of sequence conservation, but only few of them have been recognized in tunicates or other invertebrates because of genomic sequences divergence. We discuss recent studies demonstrating that a combination of different methodologies, based not only on high sequence identity, can collectively be used to identify CNEs with regulatory activity in phylogenetically distant species. Here, a low sequence constraints approach was successfully used to search orthologous chordate gene regions for cross-species conserved regulatory elements that control developmental genes.

Novel Applications of Lead Acetate and Flow Cytometry Methods for Detection of Sulfur-Containing Molecules.

Hydrogen sulfide (H2S) is the most recently established gaseous vasodilator, enzymatically produced from cysteine metabolism, involved in a number of pathophysiological processes. However, its accurate detection in vivo is critical due to its volatility and tendency to form sulfane sulfur derivatives, thus limiting the data interpretation of its biological roles. We developed new applications of the simple and rapid method to measure H2S release in cell culture systems, based on the lead acetate strip test. This test, previously prevalently used in microbiology, was compared with the agar trap method, applied, in parallel, on both cell cultures and cell-free samples. Sulfane sulfur represents the major species derived from intracellular H2S. Various fluorescent probes are available for quantitation of H2S derivatives intracellularly. We present here an alternative to the classic imaging method for sulfane sulfur evaluation, running on a flow cytometer, based on SSP4 probe labeling. Flow cytometry turned out to be more direct, fully quantitative and less time-consuming compared to microscopy and more precise with respect to the fluorescence multi-plate reader assay. The new application methods for H2S determination appear to be fully suitable for the analysis of H2S release and sulfane sulfur content in biological samples.

The role of the intestinal microbiota in uremic solute accumulation: a focus on sulfur compounds.

The gut microbiota is considered to be a novel important factor to take into account in the pathogenesis of chronic kidney disease and uremia. Much attention has been paid to specific uremic retention solutes of microbial origin, such as indoxyl sulfate, p-cresyl sulfate, and trimethylamine-N-oxide. However, other novel less well studied compounds, such as hydrogen sulfide and related sulfur metabolites (sulfane sulfur, lanthionine, etc.), should be included in a more comprehensive appraisal of this topic, in light of the potential therapeutic opportunities for the future.

Lanthionine and Other Relevant Sulfur Amino Acid Metabolites: Detection of Prospective Uremic Toxins in Serum by Multiple Reaction Monitoring Tandem Mass Spectrometry.

In the context of the vascular effects of hydrogen sulfide (H2S), it is known that this gaseous endogenous biological modulator of inflammation, oxidative stress, etc. is a potent vasodilator. Chronic renal failure, a common disease affecting the aging population, is characterized by low levels of H2S in plasma and tissues, which could mediate their typical hypertensive pattern, along with other abnormalities. Lanthionine and homolanthionine, natural non-proteinogenic amino acids, are formed as side products of H2S production. Also in consideration of the intrinsic difficulties in H2S measuring, these compounds have been proposed as reliable and stable markers of H2S synthesis. However, in the setting of chronic renal failure patients on hemodialysis, they represent typical retention products (without ruling out the possibility of an increased intestinal synthesis) and prospective novel uremic toxins. Here, a method utilizing liquid chromatography-electrospray tandem mass spectrometry (LC-MS/MS) in multiple reaction monitoring ion mode has been developed and evaluated for the determination of these key H2S metabolites in plasma, by using a triple quadrupole mass spectrometer.

SoxB2 in sea urchin development: implications in neurogenesis, ciliogenesis and skeletal patterning.

BACKGROUND: Current studies in evolutionary developmental biology are focused on the reconstruction of gene regulatory networks in target animal species. From decades, the scientific interest on genetic mechanisms orchestrating embryos development has been increasing in consequence to the fact that common features shared by evolutionarily distant phyla are being clarified. In 2011, a study across eumetazoan species showed for the first time the existence of a highly conserved non-coding element controlling the SoxB2 gene, which is involved in the early specification of the nervous system. This discovery raised several questions about SoxB2 function and regulation in deuterostomes from an evolutionary point of view. RESULTS: Due to the relevant phylogenetic position within deuterostomes, the sea urchin Strongylocentrotus purpuratus represents an advantageous animal model in the field of evolutionary developmental biology. Herein, we show a comprehensive study of SoxB2 functions in sea urchins, in particular its expression pattern in a wide range of developmental stages, and its co-localization with other neurogenic markers, as SoxB1, SoxC and Elav. Moreover, this work provides a detailed description of the phenotype of sea urchin SoxB2 knocked-down embryos, confirming its key function in neurogenesis and revealing, for the first time, its additional roles in oral and aboral ectoderm cilia and skeletal rod morphology. CONCLUSIONS: We concluded that SoxB2 in sea urchins has a neurogenic function; however, this gene could have multiple roles in sea urchin embryogenesis, expanding its expression in non-neurogenic cells. We showed that SoxB2 is functionally conserved among deuterostomes and suggested that in S. purpuratus this gene acquired additional functions, being involved in ciliogenesis and skeletal patterning.