Label-free detection and profiling of individual solution-phase molecules.

Most chemistry and biology occurs in solution, in which conformational dynamics and complexation underlie behaviour and function. Single-molecule techniques1 are uniquely suited to resolving molecular diversity and new label-free approaches are reshaping the power of single-molecule measurements. A label-free single-molecule method2-16 capable of revealing details of molecular conformation in solution17,18 would allow a new microscopic perspective of unprecedented detail. Here we use the enhanced light-molecule interactions in high-finesse fibre-based Fabry-Pérot microcavities19-21 to detect individual biomolecules as small as 1.2 kDa, a ten-amino-acid peptide, with signal-to-noise ratios (SNRs) >100, even as the molecules are unlabelled and freely diffusing in solution. Our method delivers 2D intensity and temporal profiles, enabling the distinction of subpopulations in mixed samples. Notably, we observe a linear relationship between passage time and molecular radius, unlocking the potential to gather crucial information about diffusion and solution-phase conformation. Furthermore, mixtures of biomolecule isomers of the same molecular weight and composition but different conformation can also be resolved. Detection is based on the creation of a new molecular velocity filter window and a dynamic thermal priming mechanism that make use of the interplay between optical and thermal dynamics22,23 and Pound-Drever-Hall (PDH) cavity locking24 to reveal molecular motion even while suppressing environmental noise. New in vitro ways of revealing molecular conformation, diversity and dynamics can find broad potential for applications in the life and chemical sciences.

Metaphyseal Fixation Using Cones and Sleeves for Severe Proximal Tibial Bone Loss.

BACKGROUND: Tibial bone defects are commonly encountered in revision total knee arthroplasty (rTKA) and can be managed with metaphyseal cones or sleeves. Few studies have directly compared tibial cones and sleeves in rTKA, and none have limited this comparison to the most severe tibial defects. The purpose of this study was to evaluate and compare the outcomes of metaphyseal cones and sleeves for tibial reconstruction in rTKA regarding implant fixation and clinical outcomes. METHODS: A retrospective review was conducted on patients undergoing rTKA in which metaphyseal cones or sleeves were utilized for addressing metaphyseal bone loss (34 cones and 18 sleeves). Tibial bone loss was classified according to the Anderson Orthopaedic Research Institute bone defect classification, with types 2B and 3 being included. Patient-reported outcomes and postoperative complications were collected, and a radiographic evaluation of osseointegration or loosening was performed. RESULTS: There were 52 knees included (34 cones, 18 sleeves), with a median follow-up of 41.0 months. All-cause implant survival was 100% at 2 years and 96% (95% confidence interval: 76 to 99%) at 4 years, with 98% of tibial components demonstrating osseointegration at the final follow-up. During follow-up, there were a total 11 revisions, of which 1 sleeve was revised secondary to implant loosening. Tibial sleeves had a higher risk of revision compared to tibial cones (P < .01), and sleeves fixed with a hybrid technique were more likely to need revision than cones fixed by the same method (P = .01). CONCLUSIONS: Porous metaphyseal tibial cones and tibial metaphyseal sleeves both performed well at a 41-month median follow-up with no difference in aseptic survivorship between the 2 constructs. Both demonstrate high rates of osseointegration, low rates of aseptic failure, and significant improvement in Knee Society Scores in patients with severe tibial defects in rTKA.

Novel Technique for the Identification of Hip Implants Using Artificial Intelligence.

BACKGROUND: The anticipated growth of total hip arthroplasty will result in an increased need for revision total hip arthroplasty. Preoperative planning, including identifying current implants, is critical for successful revision surgery. Artificial intelligence (AI) is promising for aiding clinical decision-making, including hip implant identification. However, previous studies have limitations such as small datasets, dissimilar stem designs, limited scalability, and the need for AI expertise. To address these limitations, we developed a novel technique to generate large datasets, tested radiographically similar stems, and demonstrated scalability utilizing a no-code machine learning solution. METHODS: We trained, validated, and tested an automated machine learning-implemented convolutional neural network to classify 9 radiographically similar femoral implants with a metaphyseal-fitting wedge taper design. Our novel technique uses computed tomography-derived projections of a 3-dimensional scanned implant model superimposed within a computed tomography pelvis volume. We employed computer-aided design modeling and MATLAB to process and manipulate the images. This generated 27,020 images for training (22,957) and validation (4,063) sets. We obtained 786 test images from various sources. The performance of the model was evaluated by calculating sensitivity, specificity, and accuracy. RESULTS: Our machine learning model discriminated the 9 implant models with a mean accuracy of 97.4%, sensitivity of 88.4%, and specificity of 98.5%. CONCLUSIONS: Our novel hip implant detection technique accurately identified 9 radiographically similar implants. The method generates large datasets, is scalable, and can include historic or obscure implants. The no-code machine learning model demonstrates the feasibility of obtaining meaningful results without AI expertise, encouraging further research in this area.

Label-free observation of individual solution phase molecules.

The vast majority of chemistry and biology occurs in solution, and new label-free analytical techniques that can help resolve solution-phase complexity at the single-molecule level can provide new microscopic perspectives of unprecedented detail. Here, we use the increased light-molecule interactions in high-finesse fiber Fabry-Pérot microcavities to detect individual biomolecules as small as 1.2 kDa with signal-to-noise ratios >100, even as the molecules are freely diffusing in solution. Our method delivers 2D intensity and temporal profiles, enabling the distinction of sub-populations in mixed samples. Strikingly, we observe a linear relationship between passage time and molecular radius, unlocking the potential to gather crucial information about diffusion and solution-phase conformation. Furthermore, mixtures of biomolecule isomers of the same molecular weight can also be resolved. Detection is based on a novel molecular velocity filtering and dynamic thermal priming mechanism leveraging both photo-thermal bistability and Pound-Drever-Hall cavity locking. This technology holds broad potential for applications in life and chemical sciences and represents a major advancement in label-free in vitro single-molecule techniques.

Total Joint Arthroplasty in Patients With an Implanted Left Ventricular Assist Device.

Left ventricular assist devices (LVADs) may be used as bridge therapy or destination therapy in heart failure patients. Total joint arthroplasty may improve the functional status of patients limited by arthritis. This retrospective case series evaluated patients with an implanted LVAD who underwent a total joint arthroplasty at 1 institution from 2012 to present. Five patients underwent 12 surgeries with 7 primary arthroplasties and 5 revisions. Their mortality, length of stay, coagulopathic events, incidence of infection or revision arthroplasty, and heart transplantation were evaluated, and is the largest study to date of this population. Two patients expired from thrombotic events while 3 progressed to heart transplantation. Joint arthroplasty is feasible in patients with an implanted LVAD with expected risk and perioperative multidisciplinary collaboration.

Predictors of Reinfection in Prosthetic Joint Infections Following Two-Stage Reimplantation.

BACKGROUND: Two-stage reimplantation is an effective treatment for periprosthetic joint infection (PJI). Many factors are involved in the variable success of this procedure. The purpose of this study is to examine the relationship between patient risk factors, comorbidities, and the pathogen on reinfection rates following two-stage reimplantation. METHODS: We evaluated 158 patients treated for PJI from 2008-2019. Only patients who had completed a two-stage exchange were included. Patient demographics, comorbidities, laboratory values, time-to-reimplantation, pathogen, antibiotic sensitivities, host status, and reinfection rates were assessed. Multivariate analysis was performed to identify correlation between risk factors and reinfection. A P-value < .05 was considered statistically significant. RESULTS: 31 patients experienced a reinfection (19.6%). There was a statistically significant association between infection with Methicillin Sensitive Staphylococcus Aureus (MSSA) and reinfection (P = .046). Patients with a reinfection also had a significantly greater median serum C-reactive protein (CRP) level (12.65 g/dL) at the time of diagnosis compared to patients without a reinfection (5.0 g/dL) (P = .010). Median Erythrocyte Sedimentation Rate (ESR) (56 in no re-infection and 69 in re-infection) and time-to-reimplantation (101 days in no reinfection and 141 days in reinfection) demonstrated a trend toward an association with re-infection but were not statistically significant (P = .055 and P = .054 respectively). CONCLUSION: As the number of arthroplasties continue to rise, PJIs are increasing proportionately and represent a significant revision burden. Elevated C-reactive protein (CRP) levels and Methicillin Sensitive Staphylococcus aureus (MSSA) infection were strongly associated with failure of a two-stage reimplantation. While not statistically significant with our numbers, there were strong trends toward an association between elevated Erythrocyte Sedimentation Rate (ESR), longer time-to-reimplantation, and reinfection.

Pain associated with cemented and uncemented long-stemmed tibial components in revision total knee arthroplasty.

AIMS: Stemmed tibial components are frequently used in revision total knee arthroplasty (TKA). The purpose of this study was to evaluate patient satisfaction, overall pain, and diaphyseal tibial pain in patients who underwent revision TKA with cemented or uncemented stemmed tibial components. METHODS: This is a retrospective cohort study involving 110 patients with revision TKA with cemented versus uncemented stemmed tibial components. Patients who underwent revision TKA with stemmed tibial components over a 15-year period at a single institution with at least two-year follow-up were assessed. Pain was evaluated through postal surveys. There were 63 patients with cemented tibial stems and 47 with uncemented stems. Radiographs and Knee Society Scores were used to evaluate for objective findings associated with pain or patient dissatisfaction. Postal surveys were analyzed using Fisher's exact test and the independent-samples t-test. Logistic regression was used to adjust for age, sex, and preoperative bone loss. RESULTS: No statistically significant differences in stem length, operative side, or indications for revision were found between the two cohorts. Tibial pain at the end of the stem was present in 25.3% (16/63) of cemented stems and 25.5% (12/47) of uncemented stems (p = 1.000); 74.6% (47/63) of cemented patients and 78.7% (37/47) of uncemented patients were satisfied following revision TKA (p = 0.657). CONCLUSION: There were no differences in patient satisfaction, overall pain, and diaphyseal tibial pain in cemented and uncemented stemmed tibial components in revision TKA. Patient factors, rather than implant selection and surgical technique, likely play a large role in the presence of postoperative pain. Stemmed tibial components have been shown to be a possible source of pain in revision TKA. There is no difference in patient satisfaction or postoperative pain with cemented or uncemented stemmed tibial components in revision TKA. Cite this article: Bone Joint J 2021;103-B(6 Supple A):165-170.

Orthopaedic Surgery Elicits a Systemic Anti-Inflammatory Signature.

Little information is available on the functional activity of leukocytes after arthroplasty or the expansion of populations with immune suppressive properties during the acute post-operative period. Synovial fluid and matched pre- and post-surgical blood samples were collected from total hip and knee arthroplasty patients (THA and TKA, respectively) to examine the impact of surgery on peripheral blood leukocyte frequency, bactericidal activity, and inflammatory mediator expression. For spinal surgeries, inflammatory mediator production by peripheral blood mononuclear cells (PBMCs) pre- and post-surgery was examined. An expansion of immune suppressive granulocytic myeloid-derived suppressor cells (G-MDSCs) was observed following arthroplasty, which correlated with significantly increased serum interleukin-10 (IL-10) levels. Analysis of synovial fluid from THA and TKAs revealed reduced granulocyte colony-stimulating factor (G-CSF) and soluble CD40 ligand (sCD40L) and increased interleukin-6 (IL-6), monocyte chemoattractant protein 2 (CCL2) and Fms-like tyrosine kinase 3 ligand (Flt-3L) compared to pre- and post-surgical serum. For the spinal surgery cohort, stimulation of PBMCs isolated post-surgery with bacterial antigens produced significantly less pro-inflammatory (IL-1α, IL-1ß, interleukin-1 receptor antagonist (IL-1RA), IL-12p40, growth-related oncogene-α/GRO-α (CXCL1) and 6Ckine (CCL21)) and more anti-inflammatory/tissue repair mediators (IL-10, G-CSF and granulocyte-macrophage colony-stimulating factor (GM-CSF)) compared to PBMCs recovered before surgery. The observed bias towards systemic anti-inflammatory changes without concomitant increases in pro-inflammatory responses may influence susceptibility to infection following orthopaedic surgery in the context of underlying co-morbidities or risk factors.

Current and future trends in the diagnosis of periprosthetic hip infection.

The challenge of confirming the diagnosis of prosthetic hip infection is two-fold. First, the presentation of the patient with a prosthetic hip infection often has limited or few subjective complaints and physical findings, nonconfirmatory inflammatory laboratory markers, and negative culture results. Second, there has not been consistent agreement of the definition of prosthetic join infection. Recent work by the Musculoskeletal Infection Society has created a new uniform definition for research and clinical use that may improve the ability to accurately diagnose prosthetic hip infections individually and share data among different sites for research collaboration.

Acute hematogenous infection following total hip and knee arthroplasty.

Forty consecutive patients (42 joints; 22 TKA, 20 THA) treated for acute hematogenous infections were reviewed. All patients underwent irrigation and debridement and exchange of the modular components. At a mean of 56 months (range, 25-124 months) recurrent infection, requiring surgery, developed in 9 of the 42 joints (21%); 8 of the 9 recurrent infections were in patients with a staphylococcal infection (P = 0.0004). Ten of the 40 patients (25%) died within 2 years of infection. Irrigation and debridement for the treatment of an acute hematogenous infection was successful in the majority of patients (76% survivorship at 2 years). Non-staphylococcal infections had a particularly low failure rate (96% survivorship at 2 years). The 2 year mortality rate among this subset of patients was strikingly high.

What is the long-term survival of impaction allografting of the femur?

BACKGROUND: Revision hip surgery of the femur for patients with substantial bone loss is challenging. We previously reported 41 patients (44 hips) treated with femoral impaction grafting followed for a minimum of 2 years. The survivorship, using femoral reoperation for symptomatic aseptic loosening as the end point, was 97% at 8 years. However, data on longer term survival are crucial to adequately compare this surgical technique with other types of revision hip arthroplasty procedures. QUESTIONS/PURPOSES: We therefore asked what the survivorship of impaction bone grafting was at longer followup, if the severity of bone loss was associated with failure, and finally, if longer length stems had improved survival compared with shorter stems. METHODS: Between 1993 and 2002, 78 femoral revisions were performed in 71 patients using impaction grafting. The average age of the patients was 67 years (range, 33­84 years). Sixty-nine of the 71 patients were available for followup evaluation. We obtained Harris hip scores preoperatively and postoperatively. Radiographs were measured for radiolucent lines. Patients were followed a minimum of 2 years (average, 10.6 years; range, 2-19 years). RESULTS: Survival of the femoral component without revision for any cause was 93% (confidence interval [CI], 83%­97%) and for aseptic loosening was 98% (CI, 87%­100%) at 19 years. Neither severity of bone loss nor the length of the stem predicted failure. CONCLUSIONS: Impaction bone grafting has a high survival of 93% at the 19-year followup for patients with severe bone loss of their femur.

Diagnostic and therapeutic challenges in hepatic epithelioid hemangioendothelioma.

BACKGROUND: Epithelioid hemangioendothelioma is a very rare, low-grade vascular tumor known to arise in soft tissues and visceral organs. Clinical diagnosis of hepatic epithelioid hemangioendothelioma remains a challenge, and although it is frequently managed with a liver transplant due to its multifocal nature, recurrence is a common complication. METHODS: We review recent advances in the diagnosis of hepatic epithelioid hemangioendothelioma, including major genetic breakthroughs, and discuss efforts to reduce post-liver transplant recurrence of hepatic epithelioid hemangioendothelioma.

Infection following total knee arthroplasty: prevention and management.

Despite diligent efforts to prevent infection, prosthetic knee infection occurs in up to 2% of patients treated with total knee arthroplasty. Although the risk of infection is relatively low, the effects are considerable. The number of total knee arthroplasties is projected to increase by more than 600% by 2030, resulting in 3.48 million knee replacements, with a possible 70,000 prosthetic knee infections. Infection will be the most common indication for revision total knee arthroplasty. Prophylactic antibiotics and minimizing patient risk factors are critical in preventing infections. Staphylococcus is the most common organism in infected total knee arthroplasties. Prompt diagnosis and treatment are crucial to the long-term outcomes of patients with prosthetic joint infections. The erythrocyte sedimentation rate, C-reactive protein level, and interleukin-6 serum level should be checked in all patients with clinical signs of infection or unexplained pain or stiffness. The surgical management of a prosthetic knee infection depends on several factors, but none is more important than the timing of infection in relationship to the index surgery. With a success rate of 80% to 90%, two-stage component exchange remains the treatment of choice for chronically infected total knee arthroplasties.

Use of three-dimensional spheroids of hepatocyte-derived reporter cells to study the effects of intracellular fat accumulation and subsequent cytokine exposure.

Non-alcoholic fatty liver disease (NAFLD) is a family of liver diseases associated with obesity. Initial stage of NAFLD is characterized by a fatty liver, referred to as steatosis, which progresses in some individuals to non-alcoholic steatohepatitis (NASH) and liver failure. In order to study and treat the many liver diseases such as NAFLD, an improved in vitro cellular model is needed. Several studies in the past have attempted to elucidate these mechanisms using primary hepatocytes or relevant hepatoma cell lines in two-dimensional (2D) monolayer in vitro cultures. These 2D planar culture systems, unfortunately, do not represent the complex architecture of hepatic tissue in vivo. Therefore, we have engineered an elastin-like polypeptide (ELP)-polyethyleneimine (PEI) copolymer and shown that ELP-PEI coated surfaces influenced H35 rat hepatoma cell morphology to create 3D spheroids. Our reporter cell model recapitulates many cellular features of the human disease, including fatty acid uptake, intracellular triglyceride accumulation, decreased proliferation, decreased liver-specific function, and increased reactive oxygen species accumulation. Finally, to demonstrate the utility of the reporter cells for studying transcriptional regulation, we compared the transcriptional dynamics of nuclear factor κB (NFκB) in response to its classical inducer (tumor necrosis factor-α, TNF-α) under lean and fatty conditions in both 2D and 3D culture configurations. We found that, in 3D spheroids, linoleic acid treatment activated NFκB at earlier time points during the development of steatosis, but suppressed the TNF-mediated NFκB activation at later time points. These studies therefore provide a good starting point to evaluate such relationships observed during NAFLD in a 3D in vitro cell culture.

Continuous versus interrupted suture for end-to-end biliary anastomosis during liver transplantation gives equal results.

Biliary complications following orthotopic liver transplantation have been reported in 10% to 30% of patients. Most surgeons perform an end-to-end choledochocholedochostomy with interrupted sutures for biliary reconstruction. The goal of this study was to compare biliary complications between interrupted suture (IS) and continuous suture (CS) techniques during liver transplantation in which an end-to-end choledochocholedochostomy over an internal biliary stent was performed. A retrospective cohort study of 100 consecutive liver transplants occurring between December 2003 and July 2005 was conducted. An end-to-end choledochocholedochostomy over an internal biliary stent was performed during liver transplantation. Data were analyzed using Kaplan-Meier methods, t tests, and chi-square tests of proportions. IS and CS techniques were used in 59 and 41 patients, respectively, for biliary reconstruction during liver transplantation. Mean follow-up time for the CS group was 17 +/- 8 months and 15 +/- 7 months for the IS group (P = .21). The overall biliary complication rate was 15%. There was no difference in the proportion of leaks (CS = 7.3%, IS = 8.5%; P = .83) or strictures (CS = 9.8%, IS = 5.1%; P = .37) between groups. Kaplan-Meier event rates show no difference in leaks (P = .79), strictures (P = .41), graft survival (P = .52), and patient survival (P = .32) by anastomosis type. In conclusion, there was no difference in biliary complications, graft survival, or patient survival between the 2 groups. CS and IS techniques for biliary reconstruction during liver transplantation yield comparable outcomes.

Beta-adrenergic and muscarinic cholinergic receptor densities in the human sinoatrial node: identification of a high beta 2-adrenergic receptor density.

The objective of this study was to measure autonomic receptor densities in the human sinoatrial node and adjacent atrial myocardium to gain further insights into autonomic regulation of sinoatrial node function in the human heart. Sinoatrial nodes (n = 9) were acquired from human donors. Quantitative light microscopic autoradiography of radioligand binding sites in tissue sections was used to compare beta-adrenergic and muscarinic cholinergic receptor densities within specific tissue compartments of the sinoatrial node and adjacent myocardium. Total beta-adrenergic receptors were measured with the nonsubtype selective radioligand [125I]iodocyanopindolol. beta 2-Adrenergic receptors were determined by measuring the amount of radioactivity bound to sections incubated with radioligand in the presence of the highly beta 1-selective antagonist CGP-20712A. Specific autoradiographic grain densities were normalized to myocyte area/unit tissue area. Myocytes in the sinoatrial node occupied 47.7% +/- 0.1% of the total tissue area compared with 92.8% +/- 0.1% in myocardium (P < 0.001). Total specific beta-adrenergic receptor density per unit myocyte area was 3.5 +/- 0.9 times greater in the sinoatrial node than in myocardium (P < 0.001). The relative densities of beta 1-(4.2, P < 0.002), beta 2-(2.6, P < 0.002), and muscarinic (3.3, P < 0.001) receptors were significantly greater in the sinoatrial node than in the atrium. Thus, total beta-adrenergic and muscarinic cholinergic receptor densities are > 3-fold higher in the sinoatrial node than adjacent atrial myocardium, reflecting their specialized roles in regulating cardiac rate and rhythm. The beta 1-subtype is predominant in both regions. The beta 2-subtype, however, is > 2.5-fold more abundant in the sinoatrial node than in atrial myocardium. The relatively high beta 2-receptor density in the human sinoatrial node is consistent with physiologic studies that implicate this receptor in regulating cardiac chronotropism.

Relative densities of muscarinic cholinergic and beta-adrenergic receptors in the canine sinoatrial node and their relation to sites of pacemaker activity.

The site of earliest extracellular electrical activation in the sinoatrial node (SAN) is known to shift in response to autonomic stimuli, but the mechanisms underlying this phenomenon and the determinants of the location of dominant pacemaker activity have not been elucidated. The present study was designed to characterize the spatial distribution of muscarinic cholinergic and beta-adrenergic receptors in the canine SAN and to determine whether a consistent relationship exists between autonomic receptor densities and the site of dominant pacemaker activity. We used quantitative light-microscopic autoradiography of radioligand binding sites to characterize the spatial distribution of muscarinic cholinergic and beta-adrenergic receptor subtypes in tissue sections containing the SAN and adjacent right atrial muscle from 18 canine hearts. Muscarinic receptor density was 5.4 times greater in SAN cells than in atrial myocytes (P < .01). Total beta-adrenergic receptor density was more than 3 times greater in SAN cells than in atrial myocytes (P < .0001), due entirely to the significantly greater number of beta 1-adrenergic receptors in the SAN. The region of dominant pacemaker activity, localized in 4 hearts with in vitro mapping, consistently exhibited greater densities of muscarinic and beta 1-adrenergic receptors than other SAN regions. Muscarinic receptor density in the dominant pacemaker region was 18 +/- 2% and 29 +/- 7% higher than in adjacent superior and inferior regions, respectively. beta 1-Receptor density in the dominant site was 53 +/- 5% and 26 +/- 4% higher than in adjacent superior and inferior SAN regions, respectively. Thus, the SAN is richly endowed with both muscarinic cholinergic and beta 1-adrenergic receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Transmural heterogeneity of norepinephrine uptake in failing human hearts.

OBJECTIVES: The aim of this study was to determine whether regional heterogeneity in myocardial sympathetic neural function measured by the uptake of norepinephrine could account for the spatial heterogeneity of beta-adrenergic receptor down-regulation that occurs in the failing human heart. BACKGROUND: Myocardial beta-adrenergic receptor density and function are diminished in patients with chronic heart failure. Down-regulation occurs predominantly in the subendocardium, suggesting that local rather than systemic alterations in sympathetic neural function may be responsible. Although some studies have implicated hypofunction of cardiac sympathetic nerves with defective norepinephrine uptake, others suggest increased cardiac sympathetic nerve activity with unimpaired uptake. METHODS: We measured norepinephrine uptake by incubating transmural slices of the left ventricle from 19 patients who had chronic heart failure and three nonfailing control hearts with [3H]norepinephrine with or without desipramine, a neuronal uptake blocker. The density of uptake sites was measured in subepicardial and subendocardial myocyte regions with light microscopic autoradiography. RESULTS: Although the amount of [3H]norepinephrine uptake varied considerably in failing ventricles, uptake was directly proportional (r = 0.46, p < 0.05) to beta 1-adrenergic receptor density measured in additional slices with radioligand binding assays. In addition, marked transmural heterogeneity in [3H] norepinephrine uptake was consistently observed in failing ventricles. Uptake in subendocardial myocyte regions was significantly less than in subepicardial regions (mean [ +/- SD] subepicardial/subendocardial uptake ratio 4.7 +/- 4.8, p < 0.01). The extent of transmural heterogeneity in norepinephrine uptake was similar in patients with idiopathic and ischemic cardiomyopathy. In contrast, nonfailing hearts exhibited more uniform transmural [3H]norepinephrine uptake (subepicardial/subendocardial uptake ratio 1.8 +/- 1.2, p = NS). CONCLUSIONS: Specific [3H]norepinephrine accumulation is approximately fivefold lower in subendocardial regions of failing left ventricles than in subepicardial regions. These findings support the hypothesis that a subendocardial defect in norepinephrine uptake may chronically elevate local interstitial catecholamine levels and thereby down-regulate beta-adrenergic receptors in a spatially heterogeneous distribution.

Heterogeneous transmural distribution of beta-adrenergic receptor subtypes in failing human hearts.

BACKGROUND: Downregulation of myocardial beta-adrenergic receptor density does not occur in a spatially uniform distribution in patients with congestive heart failure. Rather, it results primarily from loss of receptors in the subendocardium. In patients with dilated cardiomyopathy, beta 1-receptors have been found to be downregulated selectively. These observations suggest that considerable transmural heterogeneity in the distribution of beta-adrenergic receptor subtypes exists in the failing human heart. The present study was designed to test this hypothesis. METHODS AND RESULTS: We used quantitative autoradiography of radioligand binding sites to measure the distribution of beta-adrenergic receptor subtypes in transmural sections of left ventricular myocardium obtained from cardiac transplant patients with ischemic (n = 13) and idiopathic dilated (n = 12) cardiomyopathy and from 4 subjects with no history of cognitive heart failure. Analysis of radioligand binding isotherms revealed a significant reduction in total beta-adrenergic receptor density in hearts of patients with ischemic and idiopathic cardiomyopathy (20.3 +/- 1.9 and 18.2 +/- 2.0 fmol/mg protein, respectively, versus 40.0 +/- 11.4 in control subjects; P < .01 for both). Loss of the beta 1-subtype accounted for 86% of the total reduction in beta-receptor density in failing hearts. Despite the significant decreases in overall tissue receptor content, the densities of total beta-receptors and beta-receptor subtypes in subepicardial myocytes were equivalent in failing and control hearts. However, in contrast to control hearts, in which the transmural distribution of total and beta 1-receptors was uniform (endocardial: epicardial receptor density ratios, 0.97 +/- 0.14 and 1.0 +/- 0.2, respectively), hearts of patients with ischemic and idiopathic dilated cardiomyopathy had significantly lower total beta-receptor and beta 1-receptor densities in the subendocardium (ratios, 0.66 +/- 0.06 and 0.46 +/- 0.09 for total and beta 1-receptors, respectively, in ischemic cardiomyopathy and 0.60 +/- 0.08 and 0.52 +/- 0.11 in dilated cardiomyopathy; P < .001 for all values compared with a ratio of 1). Thus, beta 1: beta 2 receptor density ratios were markedly decreased in the subendocardium of ischemic and idiopathic dilated left ventricles compared with control hearts. CONCLUSIONS: A significant transmural gradient in the density of myocardial beta 1-adrenergic receptors exists in the hearts of patients with ischemic and dilated cardiomyopathy, resulting in a markedly altered beta 1: beta 2 receptor density ratio in the subendocardium.