Imaging- and physiology-guided percutaneous coronary intervention without contrast administration in advanced renal failure: a feasibility, safety, and outcome study

AIMS

The feasibility, safety, and clinical utility of percutaneous coronary intervention (PCI) without radio-contrast medium in patients with advanced chronic kidney disease (CKD) are unknown. In this series, we investigated a specific strategy for 'zero contrast' PCI with the aims of preserving renal function and preventing the need for renal replacement therapy (RRT) in patients with advanced CKD.

METHODS AND RESULTS

A total of 31 patients with advanced CKD [creatinine = 4.2 mg/dL, inter-quartile range (IQR) 3.1-4.8, estimated glomerular filtration rate = 16 ± 8 mL/min/1.73 m²] who had clinical indication for PCI based on a prior minimal contrast coronary angiogram were included. Zero contrast PCI was performed at least 1 week after diagnostic angiography using real-time intravascular ultrasound (IVUS) guidance, with pre- and post-PCI measurements of fractional flow reserve and coronary flow reserve to confirm physiological improvement. This approach resulted in successful PCI, no major adverse cardiovascular events and preservation of renal function without the need for RRT within a follow-up time of 79 days (IQR 33-207) in all patients.

CONCLUSION

In patients with advanced CKD who require revascularization, PCI may safely be performed without contrast using IVUS and physiological guidance with high procedural success and without complications.

Evolution of definitions and understanding of vascular complications related to transcatheter aortic valve replacement

Vascular complications have emerged as a major clinical challenge during transcatheter aortic valve replacement (TAVR). Recent reports demonstrate that major vascular complications not only predict major bleeding, transfusions, and renal failure, but are also associated with increased mortality. During the early development of TAVR, heterogeneous definitions of vascular complications were used in the literature. However, the Valve Academic Research Consortium has made significant progress in standardizing outcomes definitions in the study of this emerging technology. This has resulted in a rapidly expanding body of high-quality clinical research exploring important outcomes of TAVR, including vascular complications. This review seeks to summarize the literature and to explore the current state of knowledge with respect to the incidence, predictors, clinical impact, and management of vascular complications associated with TAVR.

Paravalvular leak after transcatheter aortic valve replacement

Paravalvular leak (PVL) is a frequent complication of transcatheter aortic valve replacement (TAVR) that occurs at a much higher rate after TAVR than after conventional surgical aortic valve replacement. Recent reports indicating that PVL may be associated with increased late mortality have raised significant concern. However, the heterogeneity of methods for assessing and quantifying PVL, in addition to lack of consistency in the timing of this assessment, complicate the understanding of its true prevalence, severity, and clinical implications. The following review is an effort to consolidate current knowledge in this area in order to better understand the incidence, progression, and clinical impact of post-TAVR PVL, as well as to focus future research efforts on the assessment, prevention, and treatment of this important complication.

Concurrent Coronary Artery and Valvular Heart Disease - Hybrid Treatment Strategies in 2013

Concomitant coronary artery disease (CAD) and valvular heart disease is an increasingly common problem in the ageing population. Hybrid procedures combine surgical and transcatheter approaches to facilitate minimally invasive surgery or to transform a single high-risk open surgery into two less risky procedures. In ideal circumstances, this strategy may decrease the surgical risk in elderly, high-risk and reoperative surgical candidates, while improving patient comfort, convenience and cost-effectiveness. Hybrid procedures can be performed in a staged fashion or as a 'one-stop' procedure in a hybrid operating suite. Increasing evidence supports the safety and short-term efficacy of hybrid valve repair or replacement and coronary revascularisation procedures. Nevertheless, important questions remain, including the optimal timing of the individual procedures and the optimal antiplatelet therapy after percutaneous coronary intervention. With ongoing advances in procedural techniques and anticoagulation strategies, as well as the accumulation of long-term outcomes data, hybrid approaches to concomitant CAD and valvular heart disease will likely become increasingly common.

Activity-based probes that target diverse cysteine protease families

Proteases are one of the largest and best-characterized families of enzymes in the human proteome. Unfortunately, the understanding of protease function in the context of complex proteolytic cascades remains in its infancy. One major reason for this gap in understanding is the lack of technologies that allow direct assessment of protease activity. We report here an optimized solid-phase synthesis protocol that allows rapid generation of activity-based probes (ABPs) targeting a range of cysteine protease families. These reagents selectively form covalent bonds with the active-site thiol of a cysteine protease, allowing direct biochemical profiling of protease activities in complex proteomes. We present a number of probes containing either a single amino acid or an extended peptide sequence that target caspases, legumains, gingipains and cathepsins. Biochemical studies using these reagents highlight their overall utility and provide insight into the biochemical functions of members of these protease families.

Characteristics of the caspase-like catalytic domain of human paracaspase

Human paracaspase has been predicted to be a member of the protein structural fold that encompasses protease clan CD. To determine whether paracaspase has catalytic activity we have expressed the region corresponding to the catalytic domain and used protease activity-based chemical probes to profile the putative active site. A leucine-based acyloxymethyl ketone probe that covalently labels cysteine proteases discloses a hydrophobic P 1 preference in the putative active site. The probe covalently labels Cys539, which is not the predicted catalytic site based on structural and sequence comparisons with other clan CD proteases. Using a combinatorial peptide substrate library approach we have been unable to detect amidolytic activity of paracaspase, implying that if it is a protease it must be very specific. We suggest a switch in the use of catalytic residues to generate an enzyme overlapping the canonical clan CD protease active site.

Sequential autolytic processing activates the zymogen of Arg-gingipain

Most proteases are synthesized as inactive precursors to protect the synthetic machinery of the cell and allow timing of activation. The mechanisms used to render latency are varied but tend to be conserved within protease families. Proteases belonging to the caspase family have a unique mechanism mediated by transitions of two surface loops, and on the basis of conservation of mechanism one would expect this to be preserved by caspase relatives. We have been able to express the full-length precursor of the Arg-specific caspase relative from the bacterium Porphyromonas gingivalis, Arg-gingipain-B, and we show that it contains N- and C-terminal extensions that render a low amount of latency, meaning that the zymogen is substantially active. Three sequential autolytic processing steps at the N and C terminus are required for full activity, and the N-propeptide may serve as an intramolecular chaperone rather than an inhibitory peptide. Each step in activation requires the previous step, and an affinity probe reveals that incremental activity enhancements are achieved in a stepwise manner.

Probing structural determinants distal to the site of hydrolysis that control substrate specificity of the 20S proteasome

The 20S proteasome is a large multicomponent protease complex. Relatively little is known about the mechanisms that control substrate specificity of its multiple active sites. We present here the crystal structure at 2.95 A resolution of a beta2-selective inhibitor (MB1) bound to the yeast 20S proteasome core particle (CP). This structure is compared to the structure of the CP bound to a general inhibitor (MB2) that covalently modified all three (beta1, beta2, beta5) catalytic subunits. These two inhibitors differ only in their P3 and P4 residues, thereby highlighting binding interactions distal to the active site threonine that control absolute substrate specificity of the complex. Comparisons of the CP-bound structures of MB1, MB2, and the natural products epoxomycin and TMC-95A also provide information regarding general binding modes for several classes of proteasome inhibitors.

Lysine 188 substitutions convert the pattern of proteasome activation by REGgamma to that of REGs alpha and beta

11S REGs (PA28s) are multimeric rings that bind proteasomes and stimulate peptide hydrolysis. Whereas REGalpha activates proteasomal hydrolysis of peptides with hydrophobic, acidic or basic residues in the P1 position, REGgamma only activates cleavage after basic residues. We have isolated REGgamma mutants capable of activating the hydrolysis of fluorogenic peptides diagnostic for all three active proteasome beta subunits. The most robust REGgamma specificity mutants involve substitution of Glu or Asp for Lys188. REGgamma(K188E/D) variants are virtually identical to REGalpha in proteasome activation but assemble into less stable heptamers/hexamers. Based on the REGalpha crystal structure, Lys188 of REGgamma faces the aqueous channel through the heptamer, raising the possibility that REG channels function as substrate-selective gates. However, covalent modification of proteasome chymotrypsin-like subunits by 125I-YL3-VS demonstrates that REGgamma(K188E)'s activation of all three proteasome active sites is not due to relaxed gating. We propose that decreased stability of REGgamma(K188E) heptamers allows them to change conformation upon proteasome binding, thus relieving inhibition of the CT and PGPH sites normally imposed by the wild-type REGgamma molecule.

Global analysis of proteasomal substrate specificity using positional-scanning libraries of covalent inhibitors

The proteasome is a large protease complex consisting of multiple catalytic subunits that function simultaneously to digest protein substrates. This complexity has made deciphering the role each subunit plays in the generation of specific protein fragments difficult. Positional scanning libraries of peptide vinyl sulfones were generated in which the amino acid located directly at the site of hydrolysis (P1 residue) was held constant and sequences distal to that residue (P2, P3, and P4 positions) were varied across all natural amino acids (except cysteine and methionine). Binding information for each of the individual catalytic subunits was obtained for each library under a variety of different conditions. The resulting specificity profiles indicated that substrate positions distal to P1 are critical for directing substrates to active subunits in the complex. Furthermore, specificity profiles of IFN-gamma-regulated subunits closely matched those of their noninducible counterparts, suggesting that subunit swapping may modulate substrate processing by a mechanism that does require a change in the primary sequence specificity of individual catalytic subunits in the complex. Finally, specificity profiles were used to design specific inhibitors of a single active site in the complex. These reagents can be used to further establish the role of each subunit in substrate processing by the proteasome.