Inducible nitric oxide synthase expression in smooth muscle cells and macrophages of human transplant coronary artery disease

BACKGROUND

The inducible isoform of the nitric oxide synthase (iNOS) produces large amounts of nitric oxide in response to cytokine stimulation. Previous investigations have demonstrated iNOS expression in the setting of acute and chronic rejection in experimental cardiac transplant models. The goal of this study was to investigate whether iNOS is upregulated in human transplant coronary artery disease (TCAD), a major cause of late mortality after cardiac transplantation.

METHODS AND RESULTS

We studied 15 patients with TCAD and 10 with normal coronary arteries. In situ hybridization and immunohistochemistry were used in tissue sections to localize iNOS mRNA and protein, respectively. The presence of peroxynitrite was indirectly assessed by immunostaining with an anti-nitrotyrosine antibody. Normal coronary arteries had no evidence of iNOS expression. In contrast, 30 of 36 coronary artery segments with TCAD (83%) were immunostained by the iNOS antibody. The presence of iNOS mRNA was demonstrated in these vessels by in situ hybridization. Specific cell markers identified iNOS-positive cells as neointimal macrophages and smooth muscle cells. Nitrotyrosine immunoreactivity colocalized with iNOS expression in arteries with TCAD, distributed in macrophages and smooth muscle cells.

CONCLUSIONS

iNOS mRNA and protein are expressed in human arteries with TCAD, where they are associated with extensive nitration of protein tyrosines. These findings indicate that the high-output nitric oxide pathway and possibly the oxidant peroxynitrite might be involved in the process leading to the development of TCAD.

Apoptosis and increased expression of inducible nitric oxide synthase in human allograft rejection

BACKGROUND

The mechanisms of myocyte death during cardiac allograft rejection are incompletely understood. In a previous study using a rat heterotopic cardiac allograft model, we showed that cardiac myocyte apoptosis, inducible nitric oxide synthase (iNOS) mRNA, protein and enzyme activity, and nitrotyrosine increased simultaneously during cardiac allograft rejection. This study was designed to investigate whether apoptosis and expression of iNOS occur in human cardiac allograft rejection.

METHODS

Right ventricular endomyocardial biopsies from 30 cases of allograft rejection (International Society of Heart and Lung Transplantation grade 3A/B) were compared with 12 biopsies with no rejection (International Society of Heart and Lung Transplantation grade 0). Samples were co-labeled for apoptosis and muscle actin. Serial sections were stained for iNOS, nitrotyrosine, and the leukocyte markers CD3, CD4, CD8, and CD68 to identify T-cell subpopulations and macrophages.

RESULTS

Biopsies with cardiac allograft rejection showed a 30-fold increase of apoptotic cells when compared with controls. Most apoptotic cardiac myocytes were found in proximity to macrophage (CD68+)-rich inflammatory infiltrates. iNOS immunoreactivity was strongest in macrophages and adjacent myocytes, which also showed high levels of nitrotyrosine, representing damage by peroxynitrite.

CONCLUSIONS

Apoptosis is a major form of myocyte death during human cardiac allograft rejection. Cardiac myocyte apoptosis is closely associated with expression of iNOS in macrophages and myocytes and with nitration of myocyte proteins by peroxynitrite.

Persistent allopeptide reactivity and epitope spreading in chronic rejection of organ allografts

The role of the indirect allorecognition pathway in acute allograft rejection has been documented both in organ recipients and in experimental models. However, it is unknown whether self-restricted recognition of donor alloantigens also contributes to chronic allograft rejection. The aim of this study was to determine the relationship between allopeptide reactivity, epitope spreading, and chronic rejection. Using synthetic peptides corresponding to the hypervariable region of 32 HLA-DR alleles, we have followed the specificity of self-restricted T cell alloresponses to the donor in a population of 34 heart allograft recipients. T cells from sequential samples of blood collected from the patients up to 36 mo after transplantation were studied in limiting dilution analysis for allopeptide reactivity. The incidence of coronary artery vasculopathy (CAV) was significantly higher in patients who displayed persistent alloreactivity late after transplantation than in patients who showed no alloreactivity after the first 6 mo after transplantation. Both intra- and intermolecular spreading of epitopes was observed with an increased frequency in patients developing CAV in less than 2 yr, compared with patients without CAV; this suggests that diversification of the immune response against the graft contributes to chronic rejection. These data provide a strategy for identifying patients at risk of developing CAV and a rationale for therapeutic intervention aimed to prevent the progression of the rejection process.

L-arginine prevents xanthoma development and inhibits atherosclerosis in LDL receptor knockout mice

BACKGROUND

The potential antiatherosclerotic actions of NO were investigated in four groups of mice (n = 10 per group) lacking functional LDL receptor genes, an animal model of familial hypercholesterolemia. Group 1 was fed a regular chow diet. Groups 2 through 4 were fed a 1.25% high-cholesterol diet. In addition, group 3 received supplemental L-arginine and group 4 received L-arginine and N omega-nitro-L-arginine (L-NA), an inhibitor of NO synthase (NOS).

METHODS AND RESULTS

Animals were killed at 6 months; aortas were stained with oil red O for planimetry and with antibodies against constitutive and inducible NOSs. Plasma cholesterol was markedly increased in the animals receiving the high-cholesterol diet. Xanthomas appeared in all mice fed the high-cholesterol diet alone but not in those receiving L-arginine. Aortic atherosclerosis was present in all mice on the high-cholesterol diet. The mean atherosclerotic lesion area was reduced significantly (P < .01) in the cholesterol-fed mice given L-arginine compared with those receiving the high-cholesterol diet alone. The mean atherosclerotic lesion area was significantly larger (P < .01) in cholesterol-fed mice receiving L-arginine + L-NA than in those on the high-cholesterol diet alone. Within the atherosclerotic plaques, endothelial cells immunoreacted for endothelial cell NOS; macrophages, foam cells, and smooth muscle cells immunostained strongly for inducible NOS and nitrotyrosine residues.

CONCLUSIONS

The data indicate that L-arginine prevents xanthoma formation and reduces atherosclerosis in LDL receptor knockout mice fed a high-cholesterol diet. The abrogation of the beneficial effects of L-arginine by L-NA suggests that the antiatherosclerotic actions of L-arginine are mediated by NOS. The data suggest that L-arginine may be beneficial in familial hypercholesterolemia.

Increased immunoreactive endothelin-1 in human transplant coronary artery disease

BACKGROUND

The pathogenesis of transplant coronary artery disease (TCAD) is unknown, but it is thought to derive from an interaction between immune and nonimmune factors, leading to smooth muscle cell proliferation and accumulation in the expanded neointima. Endothelin-1 (ET-1), a potent vasoconstrictor with mitogenic properties for vascular smooth muscle cells, has recently been demonstrated in native vessel atherosclerosis. The present study used immunohistochemistry to investigate the role of ET-1 in TCAD.

METHODS AND RESULTS

ET-1 immunoreactivity and cellular localization were assessed in human coronary arteries with TCAD (n = 13) and in normal coronary arteries (n = 10) with single- and double-label immunohistochemistry. The intensity of immunostaining was determined by a semiquantitative method. Diffuse and intense ET-1 immunoreactivity was found in 11 of 13 patients with TCAD (85%), mainly in myointimal cells and, in lesser amounts, in macrophages and endothelial cells. In contrast, normal coronary arteries had only faint immunostaining localized to the endothelial layer. Mean semiquantitative grade was significantly higher in TCAD than in normal arteries (1.8 versus 0.7; P < .05). ET-1 was more frequently present in lipid-rich, atheromatous lesions than in lipid-poor, proliferative ones. Intimal neovessels consistently immunostained for ET-1.

CONCLUSIONS

Immunoreactivity for ET-1 is significantly increased in TCAD, possibly as a result of stimulatory cytokines and growth factors that are upregulated in the posttransplant state. The results suggest a role for this mitogenic peptide in the pathogenesis of graft arteriosclerosis.

Interleukin 8 is induced by cholesterol loading of macrophages and expressed by macrophage foam cells in human atheroma

In order to identify novel genes expressed in macrophage-derived foam cells, we used a multigene assay to examine the expression of genes in control versus cholesterol-loaded macrophages. We compared THP-1 macrophages incubated with or without acetylated LDL (acLDL) +/- acyl-CoA:cholesterol O-acyltransferase (ACAT) inhibitor (compound 58035) for 20 h and assessed changes in mRNA of chemokines, growth factors, interleukins, and adhesion molecules. Among 49 genes examined, an increase in mRNA was observed only for interleukin 8 (IL-8) in THP-1 macrophages. Northern analysis confirmed a 3- to 4-fold increase of IL-8 mRNA and an enzyme-linked immunosorbent assay (ELISA) revealed a corresponding increase in IL-8 in conditioned medium. Oxidized LDL (oxLDL) also induced IL-8 mRNA, but native LDL had no effect. 58035 had a moderate effect on IL-8 induction by acLDL. AcLDL-induced IL-8 expression was concentration- and time-dependent. The time course of IL-8 induction paralleled that of cholesterol loading. MCP-1, a chemokine implicated in recruiting monocytes in atherogenesis, was also induced by acLDL. The induction of MCP-1, however, peaked at 1 h after addition of acLDL and returned to basal level by 20 h while IL-8 induction peaked at 8 h and was still 2-fold higher than basal level at 20 h. IL-8 induction was also observed in fresh human monocyte-derived macrophage cells treated with acLDL. Finally, immunohistochemistry and in situ hybridization studies using specimens of human coronary atheromas showed expression of IL-8 mRNA in a macrophage-rich area. We conclude that IL-8 is induced in macrophage foam cells as a response to cholesterol loading. The chemoattractant and/or mitogenic effects of IL-8 on neutrophils, T cells, smooth muscle, or vascular endothelial cells may contribute to the progression and complications of atherosclerosis.

Intravascular ultrasound imaging of human cerebral arteries

The aim of this study was to assess the feasibility of imaging cerebral arteries in vitro with intravascular ultrasound and to establish a correlation between echographic images and corresponding histological architecture. Intravascular ultrasound imaging was performed using a 30-MHz, 4.3F ultrasound probe. Twenty-two arterial segments were obtained at autopsy from 6 patients and were imaged fresh. Arteries were then processed for histological examination and comparisons were made between echographic and histological findings. The correlation between luminal area measurements as determined histologically and by intravascular ultrasound was tested by linear regression analysis. Intravascular ultrasound demonstrated a three-layered appearance in normal cerebral arteries but not in those affected by severe atherosclerosis. Overall, ultrasound correctly identified the presence of a plaque in 83% of patients. Intravascular ultrasound sensitivity and specificity, respectively, were 100 and 80% for calcium deposits and 83 and 75% for fibrous tissue. Intravascular ultrasound and histological measurements correlated well for the determination of luminal area (r = 0.89). Intravascular ultrasound provides accurate characterization of the arterial lumen and geometry, as well as the presence and histological features of atherosclerotic plaque. Thus, it appears to have a great potential for an earlier and more accurate diagnosis of atherosclerosis and may serve to guide new interventional techniques being utilized in the treatment of cerebrovascular diseases.

Immunohistochemical demonstration of 15-lipoxygenase in transplant coronary artery disease

15-Lipoxygenase (15-LO) catalyzes the oxygenation of arachidonic and linoleic acids and has been implicated in the oxidative modification of low-density lipoproteins (LDL). 15-LO mRNA and protein have previously been demonstrated in macrophages of rabbit and human atherosclerotic lesions. The purpose of this study was to investigate whether 15-LO is also present in the accelerated form of coronary artery disease that can complicate cardiac transplantation (TCAD). Immunohistochemical analysis of coronary arteries with TCAD was carried out by using a rabbit polyclonal antibody raised against human recombinant 15-LO and an avidin-biotin-immunoperoxidase system. Normal coronary and pulmonary arteries showed no immunostaining for 15-LO. Two different types of TCAD were observed. One type consisted of concentric intimal proliferation of smooth muscle cells, without lipid or calcium deposits. No immunoreactivity for 15-LO was present in these lesions. The second type of graft arteriosclerosis consisted of complex atheromatous lesions, containing myointimal cells, lipid-laden foam cells, fragmented internal elastic laminae, and calcifications. 15-LO immunostaining of myointimal cells, lipid-laden foam cells, and endothelial cells was consistently present in these atheromatous lesions. The majority of the myointimal and foam cells positive for 15-LO were recognized by antisera to alpha-smooth muscle actin; the others were identified as macrophages. The results indicate that 15-LO expression is present in endothelial, myointimal, and foam cells in complex atheromatous lesions of TCAD, and suggest that 15-LO may play a role in the pathogenesis of this form of the disease.

Gastrointestinal neoplasia in young HIV antibody-positive patients

In a period of less than one year, the authors observed three young patients in whom primary gastrointestinal carcinomas developed. Two of them had acquired immune deficiency syndrome and the other one was human immunodeficiency virus (HIV) antibody-positive drug abuser. This report is intended to alert the medical profession to gastrointestinal malignancy as a possible complication of HIV infection.