FK409, a spontaneous nitric oxide releaser, attenuates allograft vasculopathy in a rat aortic transplant model

NO donors and NO delivery methods for controlling biofilms in chronic lung infections

Nitric oxide (NO), the highly reactive radical gas, provides an attractive strategy in the control of microbial infections. NO not only exhibits bactericidal effect at high concentrations but also prevents bacterial attachment and disperses biofilms at low, nontoxic concentrations, rendering bacteria less tolerant to antibiotic treatment. The endogenously generated NO by airway epithelium in healthy populations significantly contributes to the eradication of invading pathogens. However, this pathway is often compromised in patients suffering from chronic lung infections where biofilms dominate. Thus, exogenous supplementation of NO is suggested to improve the therapeutic outcomes of these infectious diseases. Compared to previous reviews focusing on the mechanism of NO-mediated biofilm inhibition, this review explores the applications of NO for inhibiting biofilms in chronic lung infections. It discusses how abnormal levels of NO in the airways contribute to chronic infections in cystic fibrosis (CF), chronic obstructive pulmonary disease (COPD), and primary ciliary dyskinesia (PCD) patients and why exogenous NO can be a promising antibiofilm strategy in clinical settings, as well as current and potential in vivo NO delivery methods. KEY POINTS : • The relationship between abnormal NO levels and biofilm development in lungs • The antibiofilm property of NO and current applications in lungs • Potential NO delivery methods and research directions in the future.

Modulating the Bioactivity of Nitric Oxide as a Therapeutic Strategy in Cardiac Surgery

Cardiac surgery, including cardioplegic arrest and extracorporeal circulation, causes endothelial dysfunction, which can lead to no-reflow phenomenon and reduction of myocardial pump function. Nitric oxide (NO) deficiency is involved in this pathologic process, thereby providing a fundamental basis for the use of NO replacement therapy. Presently used drugs and additives to cardioplegic and heart preservation solutions are not able to reliably protect endothelial cells and cardiomyocytes from ischemia-reperfusion injury. This review discusses promising NO-releasing compounds of various chemical classes for cardioplegia and reperfusion, which effectively maintain NO homeostasis under experimental conditions, and presents the mechanisms of their action on the cardiovascular system. Incomplete preclinical studies and a lack of toxicity assessment, however, hinder translation of these drug candidates into the clinic. Perspectives for modulation of endothelial function using NO-mediated mechanisms are discussed. They are based on the cardioprotective potential of targeting vascular gap junctions and endothelial ion channels, intracoronary administration of progenitor cells, and endothelial-specific microRNAs. Some of these strategies may provide important therapeutic benefits for human cardiovascular interventions.

Nitric oxide-mediated injury of interstitial cells of Cajal and intestinal dysmotility under endotoxemia of mice

Gastrointestinal dysmotility is frequently observed under septic conditions, yet its precise mechanisms remain to be elucidated. In this study, we have investigated the mechanisms of intestinal dysmotility by lipopolysaccharides (LPS) and the role of the interstitial cells of Cajal (ICCs) in motility disorders using a mouse endotoxin model. The injection of LPS caused time- and dose-dependent decreases in the intestinal contractility, which was associated with similar time- and dose-dependent decreases in the number of KIT-positive fibroblast-like cells located in the intermuscular layer. iNOS inhibitors, L-NAME and aminoguanidine (AG), but not 7-nitroindazole (7NI), a specific nNOS inhibitor, inhibited the LPS-induced decreases in both the contractility and the number of KIT-positive cells. A spontaneous NO releaser, FK409, not only diminished spontaneous electrical potential and phasic contractions, but also decreased the number of KIT-positive cells. Pretreatment with gadolinium inhibited the activation of macrophages and the induction of iNOS in intestinal resident macrophages, and restored the number of KIT-positive cells and intestinal contractions. These results suggested that NO produced from intestinal macrophages via iNOS induced by LPS, may be involved in the ICCs injury and intestinal dysmotility under septic conditions.

Vascular Access in Hemodialysis: Issues, Management, and Emerging Concepts

This article (1) identifies the types of hemodialysis access, (2) summarizes the clinical standard of care for dialysis access grafts and fistulae, (3) describes the pathology and pathogenesis of venous stenosis in dialysis access grafts and fistulae, (4) tabulates avail-able therapies for hemodialysis vascular access dysfunction and speculates on the rea-sons for the lack of effective therapies, and (5) discusses the development and application of novel therapeutic interventions for this difficult clinical problem. The possibility that dialysis access grafts and fistulae could be the ideal clinical model for testing novel local therapies to block neointimal hyperplasia is discussed.

Appraisal of the extent of chronic allograft vasculopathy in animal models: Proposition of a standardized micromorphometric method

Arterial obstruction due to intimal myproliferation is an outcome used for investigating chronic allograft vasculopathy in animal models. Since harvested tissue may be distorted while processing, discrepancy may happen in the measure of the obstruction. We propose a standardized micromorphometric method for calculating the percentage of obstruction with eliminating the variability in the shape of the vessel cross-section. The mathematical adjustment avoids the overestimation of the percentage of obstruction and improves accuracy.

Aging and Transplant Arteriosclerosis in Absence of Alloreactivity and Immunosuppressive Drugs in a Rat Aortic Model: Recipient Age???s Contribution

BACKGROUND

Almost half of all transplanted vascularized organ grafts will be lost to transplant arteriosclerosis sometime posttransplantation. Organ shortage for primary transplants and retransplants has led to donor-pool expansion to include elderly donors, knowing that aging per se promotes arteriosclerosis. The current understanding that donor age negatively affects organ and/or patient survival outcome is undermined by variables such as the use of immunosuppressive drugs, their toxicity to the graft, degree of donor-recipient histocompatibility, and the resulting chronic rejection. The purpose of this study was to determine whether the donor's age or recipient's age matters the most in transplant arteriosclerosis in the absence of such variables.

METHODS

A syngeneic combination was used where young (2-month-old) and old (22-month-old) donor aortas were injured to initiate neointimal thickening, then transplanted into age-mismatched recipients for 14, 60, and 90 days and then assessed for neointimal thickening. Base level injury response due ischemia and surgery was evaluated in age-matched and noninjured aortic grafts, respectively.

RESULTS

Young aortas invariably developed thicker neointima when transplanted into old recipients than when transplanted into young ones. Correspondingly, old aortas transplanted in young recipients consistently developed less neointimal thickening than when transplanted into old recipients.

CONCLUSIONS

Our findings strongly suggest that the severity of age-related neointima formation is primarily determined by the recipient's age rather than the donor's age. Therefore, in addition to focusing on donor-specific tolerance induction, strategies aiming at increasing the lifespan of vascularized organ grafts also have to take into consideration the recipient's aging milieu.

Immunosuppression and transplant vascular disease: benefits and adverse effects

Cardiac allograft vasculopathy (CAV) occurs within 5 years of transplantation surgery and represents the main cause of death in long-term heart transplant survivors. The detailed pathogenesis of CAV is unknown, but there are strong indications that immunologic mechanisms, which are regulated by nonimmunologic factors, are the major cause of this phenomenon. Cyclosporine A (CsA) is a frequently used immunosuppressive agent in transplant medicine to prevent rejection. The mechanism of action of CsA involves initial binding to cyclophilin to form a complex that then inhibits calcineurin (CN), leading to reduced interleukin (IL)-2 production as part of the signal transduction pathway for the activation of B-lymphocytes and T-lymphocytes. Based on this proposed mechanism, it was expected that CsA should be an effective strategy in attenuating the host immune response against transplanted allograft tissue; however, CsA has not changed the outcome of CAV. Several mechanisms have been suggested for the ineffectiveness of CsA in long-term prevention of CAV. For example, routine therapeutic doses of CsA may block CN incompletely (50%), whereas complete blockade requires doses that are not clinically tolerable. Another explanation is the possible activation of T-cell receptors directly (CN independent) by the immune response, which induces protein kinase C theta (PKCtheta) and leads to IL-2 production and immune rejection. Moreover, there may be a role for nonimmunologic mechanisms, such as complement, which cannot be controlled by CsA, or CsA may cause hypercholesterolemia or induce overexpression of transforming growth factor-beta (TGF-beta). This review also compares the effect of CsA with other immunosuppressants in allograft artery preservation and their clinical efficacy.

The regulatory role of nitric oxide in apoptosis

Nitric oxide (NO) is a multi-faceted molecule with dichotomous regulatory roles in many areas of biology. The complexity of its biological effects is a consequence of its numerous potential interactions with other molecules such as reactive oxygen species (ROS), metal ions, and proteins. The effects of NO are modulated by both direct and indirect interactions that can be dose-dependent and cell-type specific. For example, in some cell types NO can promote apoptosis, whereas in other cells NO inhibits apoptosis. In hepatocytes, NO can inhibit the main mediators of cell death-caspase proteases. Moreover, low physiological concentrations of NO can inhibit apoptosis, but higher concentrations of NO may be toxic. High NO concentrations lead to the formation of toxic reaction products like dinitrogen trioxide or peroxynitrite that induce cell death, if not by apoptosis, then by necrosis. Long-term exposure to nitric oxide in certain conditions like chronic inflammatory states may predispose cells to tumorigenesis through DNA damage, inhibition of DNA repair, alteration in programmed cell death, or activation of proliferative signaling pathways. Understanding the regulatory mechanisms of NO in apoptosis and carcinogenesis will provide important clues to the diagnosis and treatment of tissue damage and cancer. In this article we have reviewed recent discoveries in the regulatory role of NO in specific cell types, mechanisms of pro-apoptotic and anti-apoptotic induction by NO, and insights into the effects of NO on tumor biology.