Nonvascular Sites Research Articles

Inflammation and atherosclerosis: direct versus indirect mechanisms

It is now widely accepted that the development of atherosclerotic lesions involves a chronic inflammatory response that includes both innate and adaptive immune mechanisms. However, it is still unclear precisely what induces the inflammatory response. Furthermore, inflammation within the blood vessel can be divided into direct mechanisms where the primary inflammatory events occur within the intima of the blood vessel and contribute to both the initiation and progression of the plaques and indirect mechanisms where inflammation at nonvascular sites can contribute to the progression of the lesions. The direct mechanisms include lipid deposition and modification, influx of lipoprotein associated factors and microparticles derived from many different cell types, and possibly bacterial and viral infection of vascular cells. Indirect mechanisms derive from inflammation related to autoimmune diseases, smoking, respiratory infection, and pollution exposure, and possibly periodontal disease and gastric infection. The mechanisms include secretion of cytokines and other inflammatory factors into the circulation with subsequent uptake into the plaques, egress and recruitment of activated inflammatory cells, formation of dysfunctional HDL and crossreactive autoantibodies.

The autoimmune concept of atherosclerosis

This review summarizes the recent data on the 'Autoimmune Concept of Atherosclerosis', according to which the first stage of this disease is due to an autoimmune reaction against arterial endothelial cells expressing heat shock protein 60 (HSP60) and adhesion molecules when stressed by classical atherosclerosis risk factors. Special emphasis is put on oxidized low-density lipoproteins as early endothelial stressors. Plasma cholesterol and LDL levels considered 'normal' by the medical community are possibly too high from an evolutionary viewpoint. The proinflammatory milieu at sites of early atherosclerotic lesions could be conducive to oxidation of LDL in situ. LDL oxidation can also take place at nonvascular sites or in the circulation under general proinflammatory conditions explaining its proatherosclerotic role in 'normocholesterolemic' individuals. We hypothesize that the plasma cholesterol and LDL levels currently considered normal are evolutionarily too high. Cholesterol and/or oxidized low-density lipoprotein, even as a mild HSP60-inducing endothelial stressor, function as a ubiquitous risk factor. If this hypothesis is true, most members of developed societies might be at risk to develop atherosclerotic plaques at anti-HSP60-immunity-triggered intimal inflammatory foci, irrespective of the primary risk-factor(s).

Pathogens and atherosclerosis: Update on the potential contribution of multiple infectious organisms to the pathogenesis of atherosclerosis

It is currently unclear what causes the chronic inflammation within atherosclerotic plaques. One emerging paradigm suggests that infection with bacteria and/or viruses can contribute to the pathogenesis of atherosclerosis either via direct infection of vascular cells or via the indirect effects of cytokines or acute phase proteins induced by infection at non-vascular sites. This paradigm has been supported by multiple epidemiological studies that have established positive associations between the risk of cardiovascular disease morbidity and mortality and markers of infection. It has also been supported by experimental studies showing an acceleration of the development of atherosclerosis following infection of hyperlipidaemic animal models. There are now a large number of different infectious agents that have been linked with an increased risk of cardiovascular disease. These include: Chlamydia pneumoniae, Porphyromonas gingivalis, Helicobacter pylori , influenza A virus, hepatitis C virus, cytomegalovirus, and human immunodeficiency virus. However, there are significant differences in the strength of the data supporting their association with cardiovascular disease pathogenesis. In some cases, the infectious agents are found within the plaques and viable organisms can be isolated suggesting a direct effect. In other cases, the association is entirely based on biomarkers. In the following review, we evaluate the strength of the data for individual or groups of pathogens with regard to atherosclerosis pathogenesis and their potential contribution by direct or indirect mechanisms and discuss whether the established associations are supportive of the infectious disease paradigm. We also discuss the failure of antibiotic trials and the question of persistent infection.

Tissue angiotensin II in the regulation of inflammatory and fibrogenic components of repair in the rat heart

Quantitative in vitro autoradiography has identified high density ACE and AT 1 receptor binding at sites of cardiac injury in the adult rat, implicating Ang II, generated de novo at these sites (tissue Ang II) in contributing to repair. This hypothesis remains to be tested. In the study reported here we used a time-dependent rat model of cardiac injury wherein plasma levels of renin and Ang II are chronically suppressed by means of continuous treatment with aldosterone (0.75 μg/h) and 1% dietary NaCl . To further address a role for tissue Ang II in tissue repair, we administered oral valsartan (10 mg/kg/day) in combination with aldosterone/NaCl. On days 20 and 30 of each regimen, hearts were examined. In coronal sections, we assessed transcription factor NFκB activation (RelA subunit), inflammatory-cell infiltration and appearance of myofibroblasts by immunohistochemistry; mRNA expression of several inflammatory (NFκB-related) and fibrogenic (type I collagen) mediators of repair, using quantitative in situ hybridization; and ACE binding density, detected with quantitative in vitro autoradiography. Blood pressure was measured with a tail cuff. Untreated age- and sex-matched rats served as controls. On day 20, we found no evidence of cardiac injury, inflammation, or repair with aldosterone/NaCl treatment, with or without valsartan. In contrast, on day 30 of aldosterone/NaCl treatment, inflammatory cells and α-SMA–positive myofibroblasts colocalized with high-density ACE binding and histochemical evidence of fibrillar collagen accumulation at sites of microscopic scarring and perivascular fibrosis of intramyocardial coronary arteries that appeared in both right and left ventricles. The activation of NFκB and the increased mRNA expression of ICAM-1, MCP-1, TNF-α, TGF-β 1, PAI-1, and type I collagen were also observed at these sites. Expression of vascular cell adhesion molecule-1 was unchanged. Valsartan significantly reduced ( P < .01) the expression of these mediators and attenuated the expression of MCP-1. It reduced microscopic evidence of tissue damage and the extent of fibrosis. Blood pressure was increased in aldosterone-treated rats on days 20 and 30; this increase was suppressed by valsartan. We thus show that in this rat model of long-term aldosterone/NaCl administration, in which circulating Ang II is suppressed, AT 1 receptor–mediated actions of tissue Ang II are involved in regulating the expression of mediators of repair at vascular and nonvascular sites of cardiac injury, thereby implicating autocrine/paracrine properties of tissue Ang II in inflammatory and healing responses.

Aldosterone-Induced Inflammation in the Rat Heart: Role of Oxidative Stress

Heart failure and hypertension have each been linked to an induction of oxidative stress transduced by neurohormones, such as angiotensin II and catecholamines. Herein, we hypothesized that aldosterone (ALDO) likewise induces oxidative stress and accounts for a proinflammatory/fibrogenic phenotype that appears at vascular and nonvascular sites of injury found in both right and left ventricles in response to ALDO/salt treatment and that would be sustained with chronic treatment. Uninephrectomized rats received ALDO (0.75 micro g/hour) together with 1% dietary NaCl, for 3, 4, or 5 weeks. Other groups received this regimen in combination with an ALDO receptor antagonist, spironolactone (200 mg/kg p.o. daily), or an antioxidant, either pyrrolidine dithiocarbamate (PDTC) (200 mg/kg s.c. daily) or N-acetylcysteine (NAC) (200 mg/kg i.p. daily). Unoperated and untreated age- and gender-matched rats served as controls. We monitored spatial and temporal responses in molecular and cellular events using serial, coronal sections of right and left ventricles. Our studies included: assessment of systolic blood pressure; immunohistochemical detection of NADPH oxidase expression and activity; analysis of redox-sensitive nuclear factor-kappaB activation; in situ localization of intercellular adhesion molecule-1, monocyte chemoattractant protein-1, and tumor necrosis factor-alpha mRNA expression; monitoring cell growth and infiltration of macrophages and T cells; and analysis of the appearance and quantity of fibrous tissue accumulation. At week 3 of ALDO/salt treatment and comparable to controls, there was no evidence of oxidative stress or pathological findings in the heart. However, at weeks 4 and 5 of treatment, increased gp91(phox) and 3-nitrotyrosine expression and persistent activation of RelA were found in endothelial cells and inflammatory cells that appeared in the perivascular space of intramural coronary arteries and at sites of lost cardiomyocytes in both ventricles. Coincident in time and space with these events was increased mRNA expression of intercellular adhesion molecule-1, monocyte chemoattractant protein-1, and tumor necrosis factor-alpha. Macrophages, lymphocytes, and proliferating endothelial and vascular smooth muscle cells and fibroblast-like cells were seen at each of these sites, together with an accumulation of fibrillar collagen, or fibrosis, as evidenced by a significant increase in ventricular collagen volume fraction. Co-treatment with spironolactone, PDTC, or NAC attenuated these molecular and cellular responses as well as the appearance of fibrosis at vascular and nonvascular sites of injury. Furthermore, elevated systolic blood pressure in ALDO-treated rats was partially suppressed by spironolactone or either antioxidant. Thus, chronic ALDO/salt treatment is accompanied by a time-dependent sustained activation of NADPH oxidase with 3-nitrotyrosine generation and nuclear factor-kappaB activation expressed by endothelial cells and inflammatory cells. This leads to a proinflammatory/fibrogenic phenotype involving vascular and nonvascular sites of injury found, respectively, in both normotensive and hypertensive right and left ventricles. Spionolactone, PDTC, and NAC each attenuated these responses suggesting ALDO/salt induction of oxidative/nitrosative stress is responsible for the appearance of this proinflammatory phenotype.

The vesicle content of catecholamine-containing axons in the rectum of the domestic fowl: effect of permanganate and chromaffin fixations

The ultrastructural appearance of catecholamine-containing (CA) axon profiles in the rectum of the domestic fowl was compared following fixation using the chromaffin reaction or potassium permanganate. As described previously [38], after chromaffin fixation CA-axons in the perivascular plexuses contained many small granular vesicles (SGV) and variable numbers of large granular vesicles (LGV), whereas those in the non-vascular sites contained few small vesicles and were characterised by the presence of elongated LGV. Following fixation in potassium permanganate, CA-axons in both the non-vascular and vascular sites contained many SGV. The SGV were accompanied by variable numbers of large round vesicles which were often devoid of a core. Large vesicles comprised 16 and 26%, respectively, of total vesicles in the vascular and non-vascular axon profiles. The total number of vesicles per CA-axon profile in both the vascular and non-vascular site was not dependent on fixation procedure. It is concluded that the vesicle content of CA-axon profiles in the rectum of the domestic fowl is dependent on the fixative employed.

Effects of calcium antagonists on renal hemodynamics

The renal hemodynamic effects of Ca2+ antagonists are considered in the context of their actions on Ca2+ movements during activation of vascular smooth muscle. Observations in intact animals reveal that the renal hemodynamic response to Ca2+ antagonists is highly variable, depending on the neural and hormonal determinants of renal vascular tone. Studies in the isolated perfused kidney and in isolated renal vessels indicate that diverse agonists use different activating mechanisms with differing sensitivities to Ca2+ antagonists. In comparison with other direct-acting vasodilators, Ca2+ antagonists are unique in their ability to maintain or increase glomerular filtration rate. This effect is due, in part, to their selective reduction of afferent arteriolar resistance. This implies that activating mechanisms of the afferent and efferent arterioles differ. The ability of Ca2+ antagonists to augment glomerular filtration rate by concomitant actions on nonvascular sites remains to be elucidated.

Ultrastructure of catecholamine-containing axons in the intestine of the domestic fowl.

Axons in the duodenum, ileum and rectum of the domestic fowl were identified as catecholamine-containing (CA) on the basis of positive reactivity following chromaffin fixation for electron microscopy. CA-axons in association with blood vessels in all regions of the intestine and in non-vascular sites in the small intestine had a 'typical' adrenergic appearance, in that they contained many small granular vesicles (SGV) and variable numbers of large granular vesicles (LGV). In the rectum the non-vascular CA-axon profiles were atypical, in that there were many elongated LGV and few SGV, and the chromaffin reactivity was weak. The nerve profiles in the rectum were dramatically reduced following 6-hydroxydopamine and reserpine treatment and were absent in rectum cultured in the absence of extrinsic ganglia. It was concluded that the profiles, in spite of their low chromaffin reactivity, truely represent CA-axons. The possibility was raised that the atypical morphology and reduced chromaffin reactivity is due to the presence of adrenaline.

Angiotensin I converting enzyme of rat intestinal and vascular surface membrane

High levels of angiotensin I converting enzyme are present in rat intestinal mucosa and in intestinal arteries. Homogenates of both tissues were subfractionated and fractions enriched in vascular plasma membrane or intestinal brush border were prepared. The preparations were identified and their purities established by marker enzyme enrichment and/or electron microscopy. Converting enzyme activity was highly enriched on both the vascular plasma membrane and the intestinal brush border. Subsequently the properties of these membrane-bound enzymes were compared. Both surface membrane-bound enzymes were highly sensitive to inhibition by captopril (SQ 14225) and teprotide (SQ 20881). Similar to converting enzyme isolated from other sources, they were also inhibited by bradykinin, angiotensin I, EDTA and o-phenanthroline. Finally, both membrane-bound enzymes were relatively resistant to activation by sonication, freezing and thawing or detergent. These results demonstrate significant similarities between surface membrane-bound converting enzyme from vascular and non-vascular sites. In addition, in view of the possible relationship of kinins and angiotensins to gastrointestinal function and blood flow, inhibition of gastrointestinal converting enzyme by captopril may affect some aspects of intestinal physiology.