Continuous left ventricular assist devices (LVADs) offer hemodynamic support in advanced and decompensated heart failure but are often complicated by gastrointestinal bleeding (GIB) in medically fragile patients.We performed a retrospective analysis of 475 consecutive patients who underwent LVAD implantation at the Massachusetts General Hospital and Tufts Medical Center from 2008 to 2019 and identified 128 patients with clinically significant GIB. Clinical characteristics of each bleeding event, including procedures and interventions, were recorded. We examined LVAD patients with overt and occult presentations to determine diagnostic endoscopic yield and analyzed predictors of recurrent GIB.We identified 128 unique patients with LVAD implantation complicated by GIB. No significant difference was observed based on study center, underlying cardiomyopathy, race/ethnicity, serum indices, and medications used. Overt bleeders presented more commonly during LVAD implantation admission ( P = 0.001) than occult bleeders. Occult bleed presentations had only 1 lower and no middle GI bleed source identified, despite similar workups to overt bleeds. Destination therapy (e.g., among nontransplant candidates) LVAD implantation (odds ratio 2.38, 95% confidence interval 1.05-5.58) and a history of GIB (odds ratio 3.85, 95% confidence interval 1.29-12.7) were independently associated with an increased risk of recurrent GIB-related hospitalization.Our findings confirm a high rate of GIB, especially in destination LVAD patients, and show a low diagnostic yield for colonoscopy and middle GI bleed assessments in LVAD patients with occult bleeds. Overt bleeding was more common and associated with vascular malformations. Although endoscopic interventions stopped active hemorrhage, GIB often recurred.
The anthracycline doxorubicin (Dox) is a highly effective anti-tumour agent, however, its use is limited by its severe cardiotoxic effects that manifests as heart failure. The decline in cardiac performance induced by doxorubicin remains poorly defined. A critical survival role for the canonical IKKβ -mTOR-NF-κB signaling pathway has been demonstrated in ventricular myocytes. In this report, we demonstrate that, Dox impairs IKKβ-mTOR- NF-κB signaling in ventricular myocytes accompanied by mitochondrial perturbations including mPTP, loss of mitochondrial membrane potential and ROS production. IKKβ- NF-κB signaling involves TRAF 2 mediated ligation of K63- ubiquitin chains to RIP1 (Receptor Interacting Protein 1) which serves as scaffold for recruitment of ubiquitylated Tak1 complexes and phosphorylation-dependent activation of IKKβ -NF-kB signaling. Interestingly, ventricular myocytes treated with dox demonstrated reduction in expression levels of TRAF2 and TAK1, in vivo and in vitro. This was accompanied by a decline in K63- and concomitant increase in K-48 linked polyubiquitination on RIP1, impaired NF-kB activation and necrotic cell death of cardiac myocytes. Interestingly, inhibiting the kinase activity of RIP1 with Necrostatin-1, (Nec1) suppressed necrotic cell injury induced by dox but not NF-kB activation. Concordant with these findings was a marked increase in necrotic cell death in cardiac myocytes defective for IKKB signaling or MEF cells deficient for p65 treated with dox. Notably, mitochondrial perturbations, including PT-pore opening , ROS production, calcium uptake, LDH, Tn(T) and HMGB-1 release and necrotic cell injury induced by dox were completely abrogated by restoring NF-kB signaling in cardiac myocytes or Nec-1. Herein, we provide novel evidence that K-48 linked poly ubiquitylation of RIP1 provides a functional switch that impairs NF-kB activation and signals necrosis in cells treated with dox. Interventions that modulate NF-kB activity may prove beneficial in mitigating the cardiotoxic effects of dox.
Autophagy is an evolutionary conserved process that allows cells to recycle or discard macromolecular constituents or damaged organelles during times of metabolic crisis. Alternative mRNA splicing is a versatile mechanism by which cells generate proteins with different or even antagonistic properties. Herein, we show that inclusion or skipping of exon3 of Bnip3 mRNA generates proteins with distinct and opposing actions on autophagy and cell survival. Metabolic stress imposed by hypoxia or nutrient deprivation resulted in the synthesis of two Bnip3 mRNA isoforms in post-natal ventricular myocytes in vitro and in vivo. Notably, one Bnip3 mRNA comprised of exons 1 through 6 encoded a protein of 26kDa, while a second mRNA generated by the fusion of exon2 and exon4 encoded a truncated Bnip3 protein of 8.2kDa. Sequence analysis revealed the truncated isoform encodes a conserved C-terminus domain that exclusively targets Bnip3 to the endoplasmic reticulum (ER) and not mitochondrion. While the 26kDa Bnip3 induced mitochondrial perturbations and autophagy, the spliced isoform suppressed Bnip3 induced mitochondrial defects and autophagy. Interestingly switching from glucose to fatty metabolism by supplementing nutrient deprived ventricular myocytes with carnitine but not pyruvate preferentially accumulated the spliced isoform of Bnip3 and the association of Bcl-2/Beclin-1 complexes at the ER, while suppressing autophagy. Furthermore, C-terminal domain mutations of the spliced variant defective for ER targeting sensitized cardiac myocytes to mitochondrial perturbations and apoptosis. To our knowledge our data provide the first direct evidence for a novel survival mechanism whereby the metabolic status of the cell programs autophagy or apoptosis by preferentially targeting Bnip3 isoforms to mitochondria or ER during metabolic stress.
Background/Introduction: A long-acting vasodilatory peptide, Adrenomedullin (AM), is secreted and expressed in the kidneys, lung, vasculature, and heart, but recent studies have demonstrated that adipocytes also secrete AM.However, the pathophysiological role of AM secreted by adipose tissue remains elusive.Purpose/Method: To clarify the function of adipocytes-derived AM, we generated two adipocyte-specific AM knockout mice by crossing aP2-cre mice with AMfloxed mice (aP2-AM KO) and adiponectin-Cre mice with AM-floxed mice (adi-AM KO).We evaluated blood pressure in aP2-AM KO and adi-AM KO at 8, 20, and 32 weeks of age.Results: We first noticed that in control mice the AM expression at adipose tissues was highest among all tissues including kidneys, lung, vasculature, and heart.Under normal chow diet condition, systolic blood pressure (SBP) was increased age-dependently in aP2-AM KO (91.5±1.6 vs 87.2±2.0,n.s.,at 8 weeks, 97.3±1.8 vs 88.8±1.8,p<0.05, at 20 weeks, 104.1±3.0 vs 96.8±1.9, p<0.05, at 32 weeks) and in adi-AM KO (89.0±2.5 vs 89.7±2.6,n.s.,at 8 weeks, 100.0±1.3 vs 94.3±1.9,N.S. at 20weeks, 104.8±2.0 vs 95.8±3.9, p<0.05 at 32weeks) compared to control mice.Under high-fat-diet (HFD) condition, SBP was more significantly increased in aP2-AM KO (88.3±1.4 vs 87.1±0.9, n.s.,at 8 weeks, 106.9±1.6 vs 100.2±1.1, p<0.01, at 20 weeks, 119.2±1.7 vs 108.5±2.0,p<0.001, at 32 weeks) and in adi-AM KO (92.7±2.1 vs 90.7±2.1,n.s.,at 8 weeks, 106.5±1.7 vs 101.0±1.7,p<0.05. at 20weeks, 119.4±1.3 vs 104.8±2.2, p<0.001 at 32weeks) compared to control mice.Compared to control mice, plasma AM concentrations was significantly lower under HFD conditions in aP2-AM KO (129.8±17.0vs 213±33.0,p<0.05)and adi-AM KO (115.1±2.9 vs 159.0±10.0pg/ml, p<0.05) at 32 weeks of age.AM deficiency in adipocytes did not significantly affect body weight, heart rate, angiotensin-aldosterone system activity, renal sympathetic activity, and echocardiographic assessment of cardiac function.In addition, aP2-AM KO crossed with AM transgenic mice, in which AM is over-secreted by the liver, improved age-and obesity-related increase in SBP under HFD conditions at 32weeks of age (118.0±1.4 99.6±2.6mmHg,p<0.001). Conclusion:These results demonstrate that adipocytes produce a substantial amount of AM and that adipocyte-derived AM plays a compensatory role in both age-and obesity-related increase in SBP.
