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Introduction Cardiac implantable electronic devices (CIEDs) are increasing in prevalence. Exposing patients with CIEDs to magnetic resonance imaging (MRI) can lead to adverse outcomes. This has led certain radiology departments to not accept MRI referrals related to patients with CIEDs. Patients with MR-conditional CIEDs can be safely scanned under specific conditions. Our institution has accepted such referrals since 2014. The aim of this study was to systematically identify and reduce risk in our CIED-MRI protocol using failure mode and effects analysis (FMEA). Methods A multidisciplinary FMEA team was assembled and included senior stakeholders from the CIED-MRI protocol. A process map was constructed followed by risk analysis and scoring. Targeted interventions were formulated and implemented; high-risk failure modes were prioritized. A new process map and protocol were drafted and repeat risk analysis was performed. Monitoring and re-evaluation of the CIED-MRI pathway were instigated at departmental quality assurance (QA) meetings. Results Interventions included direct CIED characterization using wireless technology pre-MRI, CIED programming and reprogramming in the MRI suite before and immediately after MRI reducing device downtime and continuous patient monitoring during MRI by a cardiac physiologist. The cumulative risk priority number (RPN) decreased from 1190 pre-FMEA to 492 post-FMEA. Discussion Despite the risk of exposing CIEDs to the MR environment, patients with MR-conditional CIEDs can be safely scanned with an appropriate multidisciplinary support. We found FMEA an indispensable tool in identifying and minimizing risk with no adverse events recorded since FMEA recommendations were implemented.

Summary Impaired hepatic glucose and lipid metabolism are hallmarks of type 2 diabetes. Increased sulfide production or sulfide donor compounds may beneficially regulate hepatic metabolism. Disposal of sulfide through the sulfide oxidation pathway (SOP) is critical for maintaining sulfide within a safe physiological range. We show that mice lacking the liver- enriched mitochondrial SOP enzyme thiosulfate sulfurtransferase (Tst−/− mice) exhibit high circulating sulfide, increased gluconeogenesis, hypertriglyceridemia, and fatty liver. Unexpectedly, hepatic sulfide levels are normal in Tst−/− mice because of exaggerated induction of sulfide disposal, with associated suppression of global protein persulfidation and nuclear respiratory factor 2 target protein levels. Hepatic proteomic and persulfidomic profiles converge on gluconeogenesis and lipid metabolism, revealing a selective deficit in medium-chain fatty acid oxidation in Tst−/− mice. We reveal a critical role of TST in hepatic metabolism that has implications for sulfide donor strategies in the context of metabolic disease., Graphical abstract, Highlights • TST deficiency elevates sulfide, invoking exaggerated hepatic sulfide disposal • Exaggerated sulfide disposal triggers global hepatic protein underpersulfidation • Skewed persulfidation is associated with higher gluconeogenesis and impaired fat oxidation • Diabetogenic hepatic metabolism dominates over apparent peripheral insulin sensitization, Carter et al. show that mice lacking the mitochondrial sulfide oxidation pathway enzyme TST have high systemic sulfide levels that invoke an alternative hepatic sulfide disposal strategy. Consequently, hepatic metabolism is dominantly skewed toward a diabetogenic profile despite peripheral insulin sensitization. This has implications for sulfide donor therapeutic agents.

Induction of an inflammatory monocyte phenotype by activated platelets is implicated in the pathogenesis of inflammatory diseases, including atherosclerosis. In this study, we investigated the early signaling events associated with this platelet-induced inflammatory phenotype. We report that coculture of human monocytes with activated platelets induces phosphorylation of Akt, together with rapid mobilization of intracellular Ca2+, and show that these signaling events can be uncoupled from monocyte binding to activated platelets. Specifically, Ab-inhibition studies and incubation of monocytes with activated platelet supernatant highlighted a role for secreted product(s) of activated platelets. We also identified a role for pertussis toxin–sensitive G protein–coupled receptors and excluded key candidates platelet-activating factor receptor and CCR5. Our results suggest that inhibition of monocyte–platelet interactions via PSGL-1 or P-selectin is not sufficient to prevent platelet-mediated monocyte activation in an inflammatory context. These findings have important implications for the development of therapeutics to treat diseases in which platelet–monocyte complexes are implicated in pathogenesis.

Background Hydrogen sulfide (H2S) is increasingly recognised as a key cardiovascular mediator with effects on the heart and vasculature in health and disease [1] , [2] . H2S is generated endogenously via cystathionine gamma-lyase (CSE) and cystathionine beta-synthase (CBS), whilst bioavailability can also be increased by H2S donors. The mitochondrial enzyme, thiosulfate sulfurtransferase (TST) participates in metabolism of H2S to thiosulfate and targeting of this pathway represents an alternative means to increase H2S bioavailability. The present study aimed to investigate the potential role of TST in the cardiovascular system by characterising (i) expression of TST in the murine heart and vasculature and (ii) the cardiovascular phenotype of Tst null (Tst−/−) mice generated using homologous recombination to delete the entire TST gene. Methods To investigate the expression of TST in the cardiovascular system, RNA and protein were prepared from heart and aorta collected from 12 week old male C57BL/6 mice for qRT-PCR and Western blotting. Tissue was formalin fixed, wax embedded and sectioned before immunohistochemical staining. TST activity was assessed in tissue homogenates as previously described [3] . Hepatic tissue expresses TST highly and was used as a positive control for TST expression. Adult male Tst−/− and C57BL/6 N controls underwent high frequency ultrasound scanning (Visualsonics Vevo770) to determine cardiac dimensions and functional performance under 1% isofluorane. Blood pressure (BP) was measured in 12–15wk old male Tst−/− and wild type mice using a Millar catheter inserted into the right carotid artery under ketamine (50 mg/kg)/ medatomidate (0.5 mg/kg) i.p. anaesthesia. Results qRT-PCR showed there was high relative gene expression for TST in the heart compared to liver (n = 4). Western blots confirmed the presence of TST in the heart and aorta, although at significantly lower levels than that found in the liver (n = 3, p = 0.003). Immunohistochemistry localised TST to vascular smooth muscle and cardiomyocytes. All Tst−/− mice survived to adulthood. Deletion of Tst was confirmed with qRT-PCR, Western blotting and enzyme activity assays. Western blotting revealed down-regulation of the H2S synthesising enzymes CSE and CBS in Tst−/− mice compared to WT controls (n = 5/ group). Ultrasound scanning at 6 & 10 weeks of age showed no difference between Tst−/− vs. WT groups for LV ejection fraction, myocardial performance index, LV end systolic or diastolic areas (n = 6/ group, p > 0.05). Systolic BP (Tst−/− 100.5 ± 5.1 mmHg vs. WT 103.5 ± 3.8 mmHg, n = 5/group, p = 0.67) was unchanged in Tst−/− mice relative to WT mice. Conclusion TST is present in the myocardium and in vascular smooth muscle of healthy mice. Although expression is absent in Tst−/− mice, their baseline cardiovascular function appears normal, at least in young healthy males. Down-regulated expression of the synthetic enzymes CSE and CBS reveals a potential feedback system that may serve to reduce H2S synthesis and prevent accumulation when removal through TST-mediated metabolism is reduced, resulting in maintenance of vascular tone and cardiac function.

Background New interventions are required to prevent the loss of cardiomyocytes associated with myocardial ischemia and with the reperfusion injury that follows revascularisation. Recent studies have shown that compounds releasing hydrogen sulfide (H2S) can have cardioprotective effects [1] . However, these compounds are generally effective only at high (μM) concentrations and release is not well controlled, increasing the potential for cytotoxicity. H2S is produced endogenously and targeting the pathways that regulate availability in heart may be a more promising therapeutic approach. The present study aimed to characterise the distribution of the H2S synthesising enzymes, cystathionine beta-synthase (CBS), cystathionine gamma-lyase (CSE) and mercaptopyruvate sulfurtransferase (MPST), and of H2S degrading enzyme, thiosulfate sulfurtransferase (TST) in the murine heart and in liver, an important site of H2S metabolism. Methods RNA and protein were prepared from heart and liver collected from 10 week old male C57BL/6J mice for quantitative RT-PCR and Western blotting. Further tissue was formalin fixed, processed and wax embedded before sectioning for immunohistochemistry. Results qRT-PCR showed high relative gene expression for all H2S metabolising enzymes in the liver. Cardiac tissue displayed high relative gene expression of TST & CSE, moderate expression of CBS and low expression of MPST. Western blots confirmed the presence of protein for TST & all H2S synthesising enzymes within heart & liver homogenates. Immunohistochemical staining of fixed tissue sections located CSE to vascular smooth muscle in the heart, while CBS & MPST were found in the vascular endothelium. Cardiomyocytes were immunoreactive for all enzymes. In hepatocytes, immunoreactive TST, CBS & MPST are found in hepatocytes throughout the liver, while CSE immunoreactivity is notably intensified around the central vein, responsible for hepatic venous return. Conclusion The murine myocardium and liver have the capacity to regulate local H2S availability via three separate synthetic pathways at least one degradative pathway which have distinctive cellular localisations. Future studies will investigate whether metabolic & synthetic enzyme expression and H2S availability is differentially regulated following ischaemia and reperfusion.

Background Increased H 2 S availability, through use of H 2 S donors, or in mice overexpressing the H 2 S synthetic enzyme cystathionine gamma-lyase (CSE), reduces injury associated with myocardial ischemia (MI) and ischemia-reperfusion. The mitochondrial enzyme thiosulfate sulfurtransferase (TST) has a putative role in removal of H 2 S and inhibition may provide an alternative means of therapeutically increasing H 2 S bioavailability. This study investigated the hypothesis that deletion of TST in mice ( Tst -/- ) would reduce infarct size and improve outcome following MI. Methods TST expression was assessed by qRT-PCR and Western blotting. Tst -/- and wild-type (WT) mice were anaesthetised for assessment of cardaic structure and function by high frequency ultrasound and for measurement of blood pressure. MI was induced by coronary artery ligation in vivo , or ex vivo in perfused hearts, when 30 mins ischemia was followed by 120 min reperfusion. Results qRT-PCR and Western blots confirmed the presence of TST in the murine heart and also deletion in Tst -/- . Tst -/- mice survived to adulthood, had no change in blood pressure relative to WT and and had normal cardiac structure and function. Expression of the H 2 S synthesising enzyme, cystathionine gamma-lyase (CSE), was reduced in Tst -/- relative to WT hearts (n = 5, p -/- mice (66%, vs 20% in WT). Studies in isolated hearts revealed increased infarct size in Tst -/- (88 ± 2% area at risk, vs 65 ± 6% in WT, n = 6, p = 0.01). Discussion TST is present in the heart and deletion does not influence structure or function. Tst -/- mice have reduced cardiac CSE expression, suggesting reduced H 2 S synthetic capacity. This may underlie the increased susceptibility of Tst -/- mice to myocardial injury and increased mortality. Conclusion TST may act with CSE to regulate H 2 S availability. Alteration in the balance of these enzymes has no overt physiological effect, but is associated with reduced capacity of the heart to resist ischaemic stress. This study was supported by a BHF 4 PhD studentship to BE and by a BHF Centre of Research Excellence Award.

Background Increased H2S availability reduces injury associated with myocardial ischemia (MI) and ischemia–reperfusion. The mitochondrial enzyme thiosulfate sulfurtransferase (TST) has a putative role in removal of H2S and is a potential target to increase H2S bioavailability. This study investigated the hypothesis that TST deletion (Tst−/−) would improve outcome following MI. Methods TST expression was assessed by qRT-PCR and Western blotting. Tst−/− and WT mice were examined in vivo by ultrasound. MI was induced by coronary artery ligation in vivo, or ex vivo inperfused hearts, when 30 min ischemia was followed by 120 min reperfusion. Results qRT-PCR and Western blots confirmed the presence of TST in the murine heart and deletion in Tst−/−. Tst−/− mice survived to adulthood and had normal cardiac function. Expression of the H2S synthesising enzyme, cystathionine gamma-lyase (CSE), was reduced in Tst−/− relative to WT hearts (n = 5, p Discussion TST is present in the heart and deletion does not influence function. Tst−/− mice have reduced cardiac CSE expression, suggesting reduced H2S synthetic capacity. This may underlie the increased susceptibility of Tst−/− mice to myocardial injury and increased mortality. Conclusion TST may act with CSE to regulate H2S availability. Alteration in the balance of these enzymes has no overt physiological effect, but is associated with reduced capacity of the heart to resist ischemic stress.

Hydrogen sulphide (H2S) is a novel endogenously produced gasotransmitter. H2S donor compounds protect the heart from ischaemia-reperfusion injury. However the potential for the heart to regulate endogenous H2S availability to provide cardioprotection is not well characterised. The present study aimed to determine the expression, distribution and sub-cellular localisation of the H2S synthesising enzymes cystathionine β-synthase (CBS), cystathionine gamma-lyase (CSE) and mercaptopyruvate sulfurtransferase (MPST) in the heart. Heart, aorta and liver were collected from 10 wk old C57BL/6J mice. Quantitative RT-PCR confirmed high gene expression (Ct 35cycles, n=4). Western blots confirmed the presence of protein within liver and heart homogenates for all enzymes. CSE, CBS and MPST were all localised to the cytosolic component of heart and liver homogenates. Immunohistochemical staining of fixed tissue sections located CSE to vascular smooth muscle in heart and thoracic aorta, while CBS and MPST were found in the vascular endothelium. Cardiomyocytes were immunoreactive for all enzymes. The murine myocardium has the capacity to regulate local H2S availability, via at least three separate synthetic pathways, that have differential cellular locations. Future studies will investigate whether synthetic enzyme expression and H2S availability is regulated following ischaemia and reperfusion. References 1. Elsey DJ, et al. Cell biochemistry and function 2010; 28 (2):95–106. 2. Johansen D, et al. Basic research in cardiology 2006; 101 (1):53–60.