Balloon-assisted remote external iliac artery endarterectomy: A safe and durable technique for the treatment of iliac artery occlusive disease.

BACKGROUND: Historically, the treatment of iliac artery occlusive disease required a surgical bypass usually consisting of an aortobifemoral bypass or an iliofemoral bypass. With the advent of balloon angioplasty and stenting, these procedures are frequently replaced with endovascular options. However, the treatment of diffuse occlusive disease of the external iliac artery (EIA) using balloon angioplasty and/or stenting does not carry a favorable long-term patency rate. Remote endarterectomy of the EIA using ring dissectors with balloon assistance provides a novel, controlled, safe, and durable treatment of the diseased and/or occluded EIA. METHODS: A retrospective review over the past 6 years was performed at our institution identifying patients treated with balloon-assisted remote endarterectomy of the EIA by the current five practicing vascular surgeons. The technique involves exposure of the ipsilateral common femoral artery. With nonocclusive disease, direct access into the common femoral artery is performed, a wire is traversed through the diseased EIA, and a balloon is inflated at the origin of the vessel providing hemostasis and control. A femoral endarterectomy is performed, and a ring dissector is passed over the endarterectomized material including the wire and balloon catheter and advanced remotely through the EIA up to the balloon. The balloon is briefly deflated, repositioned within the ring dissector, and reinflated, thus cutting the plaque. This allows for retraction of the inflated balloon and cutter, removing the endarterectomized core plaque. The procedure is similar for the treatment of an occluded EIA, but wire access across the occluded vessel is normally achieved with contralateral access. In both cases, the balloon provides control and hemostasis and is critically important in the rare treatment of vessel rupture. RESULTS: A total of 101 vessels were treated in 97 patients. The procedure was successful in 98 vessels (97%) with failure related to vessel rupture requiring conversion to an iliofemoral bypass. The estimated patency rate at three years was 94% with a median follow-up of 20 months. Restenosis/occlusion in four patients seemed to be related to a severe sclerotic response. The EIA was occluded 32% of the time. The common iliac artery (CIA) was diseased requiring angioplasty and stenting 29% of the time and a stent was placed at the transition zone between endarterectomized vessel and nontreated proximal most EIA or distal most CIA 58% of the time. There were no perioperative deaths. CONCLUSIONS: Balloon-assisted remote endarterectomy of the diffusely diseased and/or occluded EIA is a safe and durable option. It precludes the need for a prosthetic conduit and the risk of associated infection. It also involves a single groin incision and negates the need for retroperitoneal exposure of the CIA.

Risk Prediction Model for Major Adverse Outcome in Proximal Thoracic Aortic Surgery.

BACKGROUND: Proximal thoracic aortic surgery utilizing hypothermic circulatory arrest carries risks of mortality and major morbidity; however, these risks are not the same for every patient. The goal of the current study was to establish a risk prediction model for risk-stratifying patients undergoing proximal thoracic aortic surgery with hypothermic circulatory arrest for degenerative pathology, to facilitate preoperative physician-patient counseling. METHODS: A retrospective analysis was conducted on 489 patients who underwent proximal thoracic aortic surgery with hypothermic circulatory arrest for degenerative pathology between July 2005 and August 2014 at a single referral institution; patients with acute dissection (n = 139) were excluded. Multivariable logistic regression was used to build a risk prediction model and identify preoperative predictors of major adverse outcome-the composite endpoint of 30-day/inhospital mortality, stroke, acute renal failure, prolonged ventilation, or discharge to a location other than home. The results were validated using an independent cohort of 120 patients operated on from September 2014 to September 2016. RESULTS: Multivariable analysis identified age (p = 0.0002, odds ratio [OR] 2.01), total arch replacement (p ≤ 0.0001, OR 6.75), and procedure status (p = 0.0028; OR 2.73 for urgent, OR 43.58 for emergent) as independent predictors associated with major adverse outcome. The calibration curve for probability of major adverse outcome showed excellent agreement between the model and observations. The concordance index was 0.93 in external validation. CONCLUSIONS: The current study identified risk factors for major adverse outcome after proximal thoracic aortic surgery with hypothermic circulatory arrest for degenerative pathology. The proposed simple, accurate model can quantify risk and facilitate physician-patient counseling before possible surgical intervention.

Untargeted metabolomics identifies trimethyllysine, a TMAO-producing nutrient precursor, as a predictor of incident cardiovascular disease risk.

Using an untargeted metabolomics approach in initial (N = 99 subjects) and replication cohorts (N = 1,162), we discovered and structurally identified a plasma metabolite associated with cardiovascular disease (CVD) risks, N6,N6,N6-trimethyl-L-lysine (trimethyllysine, TML). Stable-isotope-dilution tandem mass spectrometry analyses of an independent validation cohort (N = 2,140) confirmed TML levels are independently associated with incident (3-year) major adverse cardiovascular event risks (hazards ratio [HR], 2.4; 95% CI, 1.7-3.4) and incident (5-year) mortality risk (HR, 2.9; 95% CI, 2.0-4.2). Genome-wide association studies identified several suggestive loci for TML levels, but none reached genome-wide significance; and d9(trimethyl)-TML isotope tracer studies confirmed TML can serve as a nutrient precursor for gut microbiota-dependent generation of trimethylamine (TMA) and the atherogenic metabolite trimethylamine N-oxide (TMAO). Although TML was shown to be abundant in both plant- and animal-derived foods, mouse and human fecal cultures (omnivores and vegans) showed slow conversion of TML to TMA. Furthermore, unlike chronic dietary choline, TML supplementation in mice failed to elevate plasma TMAO or heighten thrombosis potential in vivo. Thus, TML is identified as a strong predictor of incident CVD risks in subjects and to serve as a dietary precursor for gut microbiota-dependent generation of TMAO; however, TML does not appear to be a major microbial source for TMAO generation in vivo.

A human in vitro model of Duchenne muscular dystrophy muscle formation and contractility.

Tongue weakness, like all weakness in Duchenne muscular dystrophy (DMD), occurs as a result of contraction-induced muscle damage and deficient muscular repair. Although membrane fragility is known to potentiate injury in DMD, whether muscle stem cells are implicated in deficient muscular repair remains unclear. We hypothesized that DMD myoblasts are less sensitive to cues in the extracellular matrix designed to potentiate structure-function relationships of healthy muscle. To test this hypothesis, we drew inspiration from the tongue and engineered contractile human muscle tissues on thin films. On this platform, DMD myoblasts formed fewer and smaller myotubes and exhibited impaired polarization of the cell nucleus and contractile cytoskeleton when compared with healthy cells. These structural aberrations were reflected in their functional behavior, as engineered tongues from DMD myoblasts failed to achieve the same contractile strength as healthy tongue structures. These data suggest that dystrophic muscle may fail to organize with respect to extracellular cues necessary to potentiate adaptive growth and remodeling.

A Systematic Investigation of Structure/Function Requirements for the Apolipoprotein A-I/Lecithin Cholesterol Acyltransferase Interaction Loop of High-density Lipoprotein.

The interaction of lecithin-cholesterol acyltransferase (LCAT) with apolipoprotein A-I (apoA-I) plays a critical role in high-density lipoprotein (HDL) maturation. We previously identified a highly solvent-exposed apoA-I loop domain (Leu(159)-Leu(170)) in nascent HDL, the so-called "solar flare" (SF) region, and proposed that it serves as an LCAT docking site (Wu, Z., Wagner, M. A., Zheng, L., Parks, J. S., Shy, J. M., 3rd, Smith, J. D., Gogonea, V., and Hazen, S. L. (2007) Nat. Struct. Mol. Biol. 14, 861-868). The stability and role of the SF domain of apoA-I in supporting HDL binding and activation of LCAT are debated. Here we show by site-directed mutagenesis that multiple residues within the SF region (Pro(165), Tyr(166), Ser(167), and Asp(168)) of apoA-I are critical for both LCAT binding to HDL and LCAT catalytic efficiency. The critical role for possible hydrogen bond interaction at apoA-I Tyr(166) was further supported using reconstituted HDL generated from apoA-I mutants (Tyr(166) → Glu or Asn), which showed preservation in both LCAT binding affinity and catalytic efficiency. Moreover, the in vivo functional significance of NO2-Tyr(166)-apoA-I, a specific post-translational modification on apoA-I that is abundant within human atherosclerotic plaque, was further investigated by using the recombinant protein generated from E. coli containing a mutated orthogonal tRNA synthetase/tRNACUA pair enabling site-specific insertion of the unnatural amino acid into apoA-I. NO2-Tyr(166)-apoA-I, after subcutaneous injection into hLCAT(Tg/Tg), apoA-I(-/-) mice, showed impaired LCAT activation in vivo, with significant reduction in HDL cholesteryl ester formation. The present results thus identify multiple structural features within the solvent-exposed SF region of apoA-I of nascent HDL essential for optimal LCAT binding and catalytic efficiency.

Transmission of atherosclerosis susceptibility with gut microbial transplantation.

Recent studies indicate both clinical and mechanistic links between atherosclerotic heart disease and intestinal microbial metabolism of certain dietary nutrients producing trimethylamine N-oxide (TMAO). Here we test the hypothesis that gut microbial transplantation can transmit choline diet-induced TMAO production and atherosclerosis susceptibility. First, a strong association was noted between atherosclerotic plaque and plasma TMAO levels in a mouse diversity panel (n = 22 strains, r = 0.38; p = 0.0001). An atherosclerosis-prone and high TMAO-producing strain, C57BL/6J, and an atherosclerosis-resistant and low TMAO-producing strain, NZW/LacJ, were selected as donors for cecal microbial transplantation into apolipoprotein e null mice in which resident intestinal microbes were first suppressed with antibiotics. Trimethylamine (TMA) and TMAO levels were initially higher in recipients on choline diet that received cecal microbes from C57BL/6J inbred mice; however, durability of choline diet-dependent differences in TMA/TMAO levels was not maintained to the end of the study. Mice receiving C57BL/6J cecal microbes demonstrated choline diet-dependent enhancement in atherosclerotic plaque burden as compared with recipients of NZW/LacJ microbes. Microbial DNA analyses in feces and cecum revealed transplantation of donor microbial community features into recipients with differences in taxa proportions between donor strains that were transmissible to recipients and that tended to show coincident proportions with TMAO levels. Proportions of specific taxa were also identified that correlated with plasma TMAO levels in donors and recipients and with atherosclerotic lesion area in recipients. Atherosclerosis susceptibility may be transmitted via transplantation of gut microbiota. Gut microbes may thus represent a novel therapeutic target for modulating atherosclerosis susceptibility.

Hydrogel encapsulation to improve cell viability during syringe needle flow.

This work examines pluronic F-127 poloxamer for cell protection during injection through a syringe needle. Direct cell injection is a minimally invasive method for cell transplantation; however, it often results in poor cell viability. We proposed that encapsulating cells in this hydrogel would protect cells from detrimental mechanical forces during injection and increase cell viability. The hydrogel was tested at multiple weights and carbon nanobrush concentrations to determine how gel weight affects cell viability as well as to allow the gels to remain as electrically conductive scaffolds. This work assessed the ability of the hydrogel to prevent cell membrane bursting. We used D1 multipotent mouse bone marrow stromal precursor cells for this study. We found that the pressure drop increases with increasing weight of the gels. However, cell viability also increases as the weight of the gels increases. These results support the proposition that hydrogels can be used to protect cells during syringe needle injection. Since these hydrogels undergo a reverse phase transition, the gels can be used to transplant cells into the body in solution form through injection. The gels will then harden in situ to allow for cell proliferation and tissue regeneration at the desired site.

Myeloperoxidase, paraoxonase-1, and HDL form a functional ternary complex.

Myeloperoxidase (MPO) and paraoxonase 1 (PON1) are high-density lipoprotein-associated (HDL-associated) proteins mechanistically linked to inflammation, oxidant stress, and atherosclerosis. MPO is a source of ROS during inflammation and can oxidize apolipoprotein A1 (APOA1) of HDL, impairing its atheroprotective functions. In contrast, PON1 fosters systemic antioxidant effects and promotes some of the atheroprotective properties attributed to HDL. Here, we demonstrate that MPO, PON1, and HDL bind to one another, forming a ternary complex, wherein PON1 partially inhibits MPO activity, while MPO inactivates PON1. MPO oxidizes PON1 on tyrosine 71 (Tyr71), a modified residue found in human atheroma that is critical for HDL binding and PON1 function. Acute inflammation model studies with transgenic and knockout mice for either PON1 or MPO confirmed that MPO and PON1 reciprocally modulate each other's function in vivo. Further structure and function studies identified critical contact sites between APOA1 within HDL, PON1, and MPO, and proteomics studies of HDL recovered from acute coronary syndrome (ACS) subjects revealed enhanced chlorotyrosine content, site-specific PON1 methionine oxidation, and reduced PON1 activity. HDL thus serves as a scaffold upon which MPO and PON1 interact during inflammation, whereupon PON1 binding partially inhibits MPO activity, and MPO promotes site-specific oxidative modification and impairment of PON1 and APOA1 function.

The low-resolution structure of nHDL reconstituted with DMPC with and without cholesterol reveals a mechanism for particle expansion.

Small-angle neutron scattering (SANS) with contrast variation was used to obtain the low-resolution structure of nascent HDL (nHDL) reconstituted with dimyristoyl phosphatidylcholine (DMPC) in the absence and presence of cholesterol, [apoA1:DMPC (1:80, mol:mol) and apoA1:DMPC:cholesterol (1:86:9, mol:mol:mol)]. The overall shape of both particles is discoidal with the low-resolution structure of apoA1 visualized as an open, contorted, and out of plane conformation with three arms in nascent HDL/dimyristoyl phosphatidylcholine without cholesterol (nHDL(DMPC)) and two arms in nascent HDL/dimyristoyl phosphatidylcholine with cholesterol (nHDL(DMPC+Chol)). The low-resolution shape of the lipid phase in both nHDL(DMPC) and nHDL(DMPC+Chol) were oblate ellipsoids, and fit well within their respective protein shapes. Modeling studies indicate that apoA1 is folded onto itself in nHDL(DMPC), making a large hairpin, which was also confirmed independently by both cross-linking mass spectrometry and hydrogen-deuterium exchange (HDX) mass spectrometry analyses. In nHDL(DMPC+Chol), the lipid was expanded and no hairpin was visible. Importantly, despite the overall discoidal shape of the whole particle in both nHDL(DMPC) and nHDL(DMPC+Chol), an open conformation (i.e., not a closed belt) of apoA1 is observed. Collectively, these data show that full length apoA1 retains an open architecture that is dictated by its lipid cargo. The lipid is likely predominantly organized as a bilayer with a micelle domain between the open apoA1 arms. The apoA1 configuration observed suggests a mechanism for accommodating changing lipid cargo by quantized expansion of hairpin structures.

The low resolution structure of ApoA1 in spherical high density lipoprotein revealed by small angle neutron scattering.

Spherical high density lipoprotein (sHDL), a key player in reverse cholesterol transport and the most abundant form of HDL, is associated with cardiovascular diseases. Small angle neutron scattering with contrast variation was used to determine the solution structure of protein and lipid components of reconstituted sHDL. Apolipoprotein A1, the major protein of sHDL, forms a hollow structure that cradles a central compact lipid core. Three apoA1 chains are arranged within the low resolution structure of the protein component as one of three possible global architectures: (i) a helical dimer with a hairpin (HdHp), (ii) three hairpins (3Hp), or (iii) an integrated trimer (iT) in which the three apoA1 monomers mutually associate over a portion of the sHDL surface. Cross-linking and mass spectrometry analyses help to discriminate among the three molecular models and are most consistent with the HdHp overall architecture of apoA1 within sHDL.

Double superhelix model of high density lipoprotein.

High density lipoprotein (HDL), the carrier of so-called "good" cholesterol, serves as the major athero-protective lipoprotein and has emerged as a key therapeutic target for cardiovascular disease. We applied small angle neutron scattering (SANS) with contrast variation and selective isotopic deuteration to the study of nascent HDL to obtain the low resolution structure in solution of the overall time-averaged conformation of apolipoprotein AI (apoA-I) versus the lipid (acyl chain) core of the particle. Remarkably, apoA-I is observed to possess an open helical shape that wraps around a central ellipsoidal lipid phase. Using the low resolution SANS shapes of the protein and lipid core as scaffolding, an all-atom computational model for the protein and lipid components of nascent HDL was developed by integrating complementary structural data from hydrogen/deuterium exchange mass spectrometry and previously published constraints from multiple biophysical techniques. Both SANS data and the new computational model, the double superhelix model, suggest an unexpected structural arrangement of protein and lipids of nascent HDL, an anti-parallel double superhelix wrapped around an ellipsoidal lipid phase. The protein and lipid organization in nascent HDL envisages a potential generalized mechanism for lipoprotein biogenesis and remodeling, biological processes critical to sterol and lipid transport, organismal energy metabolism, and innate immunity.

The refined structure of nascent HDL reveals a key functional domain for particle maturation and dysfunction.

The cardioprotective function of high-density lipoprotein (HDL) is largely attributed to its ability to facilitate transport of cholesterol from peripheral tissues to the liver. However, HDL may become dysfunctional through oxidative modification, impairing cellular cholesterol efflux. Here we report a refined molecular model of nascent discoidal HDL, determined using hydrogen-deuterium exchange mass spectrometry. The model reveals two apolipoprotein A1 (apoA1) molecules arranged in an antiparallel double-belt structure, with residues 159-180 of each apoA1 forming a protruding solvent-exposed loop. We further show that this loop, including Tyr166, a preferred target for site-specific oxidative modification within atheroma, directly interacts with and activates lecithin cholesterol acyl transferase. These studies identify previously uncharacterized structural features of apoA1 in discoidal HDL that are crucial for particle maturation, and elucidate a structural and molecular mechanism for generating a dysfunctional form of HDL in atherosclerosis.