Prophylactic veno-arterial extracorporeal membrane oxygenation in patients undergoing high-risk percutaneous coronary intervention

Netherlands Heart Journal - Complex high-risk percutaneous coronary intervention (PCI) is challenging and frequently accompanied by haemodynamic instability. Veno-arterial extracorporeal membrane...     

Diagnosis of takotsubo cardiomyopathy is increasing over time in patients presenting as ST-elevation myocardial infarction

Background

Takotsubo cardiomyopathy often presents with the clinical signs of ST-elevation myocardial infarction (STEMI). The increase in scientific publications addressing this relatively rare condition may result in higher awareness and diagnosis of takotsubo cardiomyopathy.

Aim

To assess the observed prevalence per year of takotsubo cardiomyopathy in a large registry of patients with STEMI, during a 12-year inclusion period.

Method

All patients presenting with STEMI at a large regional cardiology clinic were entered into a database (n = 8,413, mean age 63 ± 13 years). Takotsubo cardiomyopathy was diagnosed in 42 patients (0.5?%). Years of evaluation were defined as ‘early years’ (January 2002 to December 2007; n = 4350) and ‘later years’ (January 2008 to December 2013). Multivariable analyses were performed to adjust for differences in demographical and clinical variables.

Results

In later years, the age of STEMI patients was slightly higher (64 ± 13 vs. 63 ± 13 years, p < 0.001), with more patients with clinical symptoms of shock (10 vs. 7?%, p < 0.001) or a history of percutaneous coronary intervention or hypertension (10 vs. 8?%, p = 0.001 and 37 vs. 34?%, p < 0.001). Smoking and a positive family history were less often observed during later years (39 vs. 46?%, p < 0.001 and 37 vs. 42?% p < 0.001). Patients with takotsubo cardiomyopathy were more often female (81 vs. 27?%, p = 0.001). Takotsubo cardiomyopathy was more often diagnosed in the later period (0.7 vs. 0.3?%, OR 2.4, 95?% CI 1.2–4.6, p = 0.009). The higher prevalence of takotsubo cardiomyopathy in recent years remained significant after adjustment for differences in patient characteristics (OR 2.1, 95?% CI 1.1–4.3).

Conclusion

Takotsubo cardiomyopathy is currently more often diagnosed in patients with STEMI compared with in earlier years. This is probably due to the increased scientific and clinical awareness among doctors, but the prevalence is still low.

     

Crystal structure of pyruvate dehydrogenase phosphatase 1 and its functional implications

Pyruvate dehydrogenase phosphatase 1 (PDP1) catalyzes dephosphorylation of pyruvate dehydrogenase (E1) in the mammalian pyruvate dehydrogenase complex (PDC), whose activity is regulated by the phosphorylation-dephosphorylation cycle by the corresponding protein kinases (PDHKs) and phosphatases. The activity of PDP1 is greatly enhanced through Ca2+ -dependent binding of the catalytic subunit (PDP1c) to the L2 (inner lipoyl) domain of dihydrolipoyl acetyltransferase (E2), which is also integrated in PDC. Here, we report the crystal structure of the rat PDP1c at 1.8 A resolution. The structure reveals that PDP1 belongs to the PPM family of protein serine/threonine phosphatases, which, in spite of a low level of sequence identity, share the structural core consisting of the central beta-sandwich flanked on both sides by loops and alpha-helices. Consistent with the previous studies, two well-fixed magnesium ions are coordinated by five active site residues and five water molecules in the PDP1c catalytic center. Structural analysis indicates that, while the central portion of the PDP1c molecule is highly conserved among the members of the PPM protein family, a number of structural insertions and deletions located at the periphery of PDP1c likely define its functional specificity towards the PDC. One notable feature of PDP1c is a long insertion (residues 98-151) forming a unique hydrophobic pocket on the surface that likely accommodates the lipoyl moiety of the E2 domain in a fashion similar to that of PDHKs. The cavity, however, appears more open than in PDHK, suggesting that its closure may be required to achieve tight, specific binding of the lipoic acid. We propose a mechanism in which the closure of the lipoic acid binding site is triggered by the formation of the intermolecular (PDP1c/L2) Ca2+ binding site in a manner reminiscent of the Ca2+ -induced closure of the regulatory domain of troponin C.     

Conformational Changes in BAK,a Pore-forming Proapoptotic Bcl-2 Family Member,upon Membrane Insertion and Direct Evidence for the Existence of BH3-BH3 Contact Interface in BAK Homo-oligomers

During apoptosis, the pro-apoptotic Bcl-2 family proteins BAK and BAX form large oligomeric pores in the mitochondrial outer membrane. Apoptotic factors, including cytochrome c, are released through these pores from the mitochondrial intermembrane space into the cytoplasm where they initiate the cascade of events leading to cell death. To better understand this pivotal step toward apoptosis, a method was developed to induce membrane permeabilization by BAK in the membrane without using the full-length protein. Using a soluble form of BAK with a hexahistidine tag at the C terminus and a liposomal system containing the Ni²⁺-nitrilotriacetic acid lipid analog that can bind hexahistidine-tagged proteins, BAK oligomers were formed in the presence of the activator protein p7/p15Bid. In this system, we determined the conformational changes in BAK upon membrane insertion by applying the site-directed spin labeling method of EPR to 13 different amino acid locations. Upon membrane insertion, the BH3 domains were reorganized, and the α5-α6 helical hairpin structure was partially exposed to the membrane environment. The monomer-monomer interface in the oligomeric structure was also mapped by measuring the distance-dependent spin-spin interactions for each residue location. Spin labels attached in the BH3 domain were juxtaposed within 5–10 Å distance in the oligomeric form in the membrane. These results are consistent with the current hypothesis that BAK or BAX forms homodimers, and these homodimers assemble into a higher order oligomeric pore. Detailed analyses of the data provide new insights into the structure of the BAX or BAK homodimer.     

X-Ray Crystallographic and Kinetic Analysis of Human Purine Nucleoside Phosphorylase Complexes with 1-β-D-Ribofuranosyl-1,2,4-triazole-3-carobxamide and 1-β-D-Ribofuranosyl-1,2,4-triazole-3-carboxamidine

Abstract

The three-dimensional structures of the complexes between human erythrocytic purine nucleoside phosphorylase (PNP) and both 1-β-D-ribofuranosyl-1,2,4-triazole-3-carboxamide (ribavirin) and 1-β-D-ribofuranosyl-1,2,4-triazole-3-carboxamidine (TCNR) have been determined using X-ray crystallographic techniques. The structures have been refined at 2.9 Å resolution using simulated annealing and conjugate-gradient minimization techniques to an R value of 21.8% for ribavirin and 20.8% for TCNR. Ribavirin and TCNR are truncated nucleosides corresponding to adenosine and inosine, respectively, and are of potential interest as PNP inhibitors. Kinetic parameters have been determined for recombinant wild-type PNP and for a mutant PNP in which Asn 243 is converted to Asp. The K_i value for ribavirin is 4.9 mM with wild-type PNP and 4.7 mM with the Asn243Asp mutant, while the K_i values for TCNR are 17.6 μM and 3.8 μM with wild-type and mutant, respectively. X-ray crystallographic studies showed that the binding geometry for both of these substrate analogues was similar to that seen for natural substrates. The glycosidic torsion angles (χ) were ?34° for ribavirin and ?39° for TCNR which are in good agreement with values seen for other studied nucleoside complexes with PNP, but which are unusual when compared to those seen for free nucleic acid derivatives. Based upon the three-dimensional structure, interactions of Asn 243 and Glu 201 with a protonated carboxamidine of TCNR explain the stronger inhibition of PNP observed for TCNR over ribavirin.     

Crystal Structures of Mutant Forms of the Yeast F1 ATPase Reveal Two Modes of Uncoupling

The mitochondrial ATP synthase couples the flow of protons with the phosphorylation of ADP. A class of mutations, the mitochondrial genome integrity (mgi) mutations, has been shown to uncouple this process in the yeast mitochondrial ATP synthase. Four mutant forms of the yeast F₁ ATPase with mgi mutations were crystallized; the structures were solved and analyzed. The analysis identifies two mechanisms of structural uncoupling: one in which the empty catalytic site is altered and in doing so, apparently disrupts substrate (phosphate) binding, and a second where the steric hindrance predicted between γLeu83 and β_DP residues, Leu-391 and Glu-395, located in Catch 2 region, is reduced allowing rotation of the γ-subunit with less impedance. Overall, the structures provide key insights into the critical interactions in the yeast ATP synthase involved in the coupling process.