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      Impact of Liver Transplantation on Carbon Monoxide Production as Measured by Arterial Carboxyhemoglobin Levels in Cirrhotic Patients with and without Hepatopulmonary Syndrome

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          Abstract

          Background

          Hepatic dysfunction is associated with increased production of carbon monoxide. End-stage liver disease patients with hepatopulmonary syndrome (HPS) have been shown to have higher blood carbon monoxide levels than those without HPS. The impact of liver transplantation on blood carbon monoxide levels is currently unknown. We assessed the impact of liver transplantation on blood carbon monoxide and whether this is affected by HPS.

          Material/Methods

          Eligible liver transplant recipients had room air arterial blood gas testing performed before and after liver transplantation. The carboxyhemoglobin fraction was obtained from arterial co-oximetry and used as a surrogate for carboxyhemoglobin production. Mean arterial carboxyhemoglobin fraction before transplantation was compared to that after transplantation. Mean absolute and median relative pre- to post-transplant within-patient change in carboxyhemoglobin fraction was compared between those with and without HPS.

          Results

          Thirty-nine transplanted cirrhotic patients were analyzed, of whom 14 (36%) met criteria for hepatopulmonary syndrome. The mean pre-transplant carboxyhemoglobin fraction was higher than the post-transplant fraction (2.6 vs 1.8, difference 0.8 [95% CI 0.4–1.2]; P value 0.0002). Of the 14 patients with HPS, 11 (79%) experienced a decrease in their carboxyhemoglobin fraction after liver transplantation; among the 25 patients without HPS, 16 (64%) experienced such a decrease ( P=0.48). Neither the absolute nor relative within-patient pre- to post-transplant change in carboxyhemoglobin fraction was significantly different between patients with and without HPS.

          Conclusions

          Blood carbon monoxide levels decreased significantly in cirrhotic patients following liver transplantation, but HPS did not affect the magnitude of this change.

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          Most cited references20

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          Targeting heme oxygenase-1 and carbon monoxide for therapeutic modulation of inflammation.

          The heme oxygenase-1 (HO-1) enzyme system remains an attractive therapeutic target for the treatment of inflammatory conditions. HO-1, a cellular stress protein, serves a vital metabolic function as the rate-limiting step in the degradation of heme to generate carbon monoxide (CO), iron, and biliverdin-IXα (BV), the latter which is converted to bilirubin-IXα (BR). HO-1 may function as a pleiotropic regulator of inflammatory signaling programs through the generation of its biologically active end products, namely CO, BV and BR. CO, when applied exogenously, can affect apoptotic, proliferative, and inflammatory cellular programs. Specifically, CO can modulate the production of proinflammatory or anti-inflammatory cytokines and mediators. HO-1 and CO may also have immunomodulatory effects with respect to regulating the functions of antigen-presenting cells, dendritic cells, and regulatory T cells. Therapeutic strategies to modulate HO-1 in disease include the application of natural-inducing compounds and gene therapy approaches for the targeted genetic overexpression or knockdown of HO-1. Several compounds have been used therapeutically to inhibit HO activity, including competitive inhibitors of the metalloporphyrin series or noncompetitive isoform-selective derivatives of imidazole-dioxolanes. The end products of HO activity, CO, BV and BR may be used therapeutically as pharmacologic treatments. CO may be applied by inhalation or through the use of CO-releasing molecules. This review will discuss HO-1 as a therapeutic target in diseases involving inflammation, including lung and vascular injury, sepsis, ischemia-reperfusion injury, and transplant rejection.
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            International Liver Transplant Society Practice Guidelines: Diagnosis and Management of Hepatopulmonary Syndrome and Portopulmonary Hypertension.

            Two distinct pulmonary vascular disorders, hepatopulmonary syndrome (HPS) and portopulmonary hypertension (POPH) may occur as a consequence of hepatic parenchymal or vascular abnormalities. HPS and POPH have major clinical implications for liver transplantation. A European Respiratory Society Task Force on Pulmonary-Hepatic Disorders convened in 2002 to standardize the diagnosis and guide management of these disorders. These International Liver Transplant Society diagnostic and management guidelines are based on that task force consensus and should continue to evolve as clinical experience dictates. Based on a review of over 1000 published HPS and POPH articles identified via a MEDLINE search (1985-2015), clinical guidelines were based on, selected single care reports, small series, registries, databases, and expert opinion. The paucity of randomized, controlled trials in either of these disorders was noted. Guidelines are presented in 5 parts; I. Definitions/Diagnostic criteria; II. Hepatopulmonary syndrome; III. Portopulmonary hypertension; IV. Implications for liver transplantation; and V. Suggestions for future clinical research.
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              HO-1 overexpression and underexpression: Clinical implications

              In this review we examine the effects of both over- and under-production of heme oxygenase-1 (HO-1) and HO activity on a broad spectrum of biological systems and on vascular disease. In a few instances e.g., neonatal jaundice, overproduction of HO-1 and increased HO activity results in elevated levels of bilirubin requiring clinical intervention with inhibitors of HO activity. In contrast HO-1 levels and HO activity are low in obesity and the HO system responds to mitigate the deleterious effects of oxidative stress through increased levels of bilirubin (anti-inflammatory) and CO (anti-apoptotic) and decreased levels of heme (pro-oxidant). Site specific HO-1 overexpression diminishes adipocyte terminal differentiation and lipid accumulation of obesity mediated release of inflammatory molecules. A series of diverse strategies have been implemented that focus on increasing HO-1 and HO activity that are central to reversing the clinical complications associated with diseases including, obesity, metabolic syndrome and vascular disease.
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                Author and article information

                Journal
                Ann Transplant
                Ann Transplant
                Annals of Transplantation
                Annals of Transplantation
                International Scientific Literature, Inc.
                1425-9524
                2329-0358
                2021
                14 September 2021
                02 August 2021
                : 26
                : e932009-1-e932009-7
                Affiliations
                [1 ]Department of Internal Medicine, Westchester Medical Center, Valhalla, NY, USA
                [2 ]Department of Pulmonary, Critical Care and Sleep Medicine, Baystate Medical Center, Springfield, MA, USA
                [3 ]Division of Gastroenterology and Transplant Hepatology, Westchester Medical Center, Valhalla, NY, USA
                [4 ]Division of Pulmonary, Critical Care and Sleep Medicine, Westchester Medical Center, Valhalla, NY, USA
                Author notes
                Corresponding Author: Ralph Llewel Sabang, e-mail: ralph.sabang@ 123456wmchealth.org
                [A]

                Study Design

                [B]

                Data Collection

                [C]

                Statistical Analysis

                [D]

                Data Interpretation

                [E]

                Manuscript Preparation

                [F]

                Literature Search

                [G]

                Funds Collection

                Article
                932009
                10.12659/AOT.932009
                8449510
                34518507
                b98777e0-f7a7-4a8e-871f-cbd1f80717a9
                © Ann Transplant, 2021

                This work is licensed under Creative Common Attribution-NonCommercial-NoDerivatives 4.0 International ( CC BY-NC-ND 4.0)

                History
                : 07 March 2021
                : 13 July 2021
                Categories
                Original Paper

                carbon monoxide,hepatopulmonary syndrome,liver cirrhosis,liver transplantation,oximetry

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