Role of nitric oxide and free radicals in the contractile response to non-preactivated leukocytes

Nitric Oxide Generation by NO Donors Is Enhanced Following Balloon Injury in the Porcine Coronary Artery

Vasospasm is a complication of cardiological procedures such as balloon angioplasty and may be related to vascular oxidant stress. Although nitric oxide donor drugs are often administered to prevent vasospasm, the response to these drugs in balloon-injured arteries has not been studied. Pig coronary arteries were balloon-injured in vitro and relaxations to nitric oxide (NO)-donating and NO-independent vasodilators studied. Generation of superoxide in response to injury was assayed using dihydroethidium. NO formation on addition of the NO donor drugs was studied using an amperometric sensor. Expression of nitrotyrosine, a peroxynitrite marker, was probed using immunocytochemistry. In vitro injury enhanced sensitivity to the NO donors SNAP and SpermineNONOate but blunted the response to isoprenaline or chromakalim. With both donors, NO formation was significantly enhanced in the presence of an injured vessel. Vascular superoxide generation was also increased throughout the vessel wall and a small increase in nitrotyrosine was detected in the injured vessel media following addition of SNAP. In conclusion, injured vessels were more sensitive to NO donors and this appears to be due to enhanced NO generation by the donor molecule. Increased formation of peroxynitrite within the injured vessel may contribute to the enhanced relaxation in injured vessels.

Peroxynitrite scavenging activity of indole derivatives: interaction of indoles with peroxynitrite

One of the products of nitrogen-derived free radicals, peroxynitrite (ONOO(-)), is formed by the reaction of superoxide anion (O(2)(*-)) with nitric oxide (NO). ONOO(-) can cause damage to proteins and DNA through nitration. In particular, proteins and their constituent amino acids have been proven to be extremely sensitive to ONOO(-). However, the lack of specific endogenous defense enzymes to protect against ONOO(-) has prompted many researchers to search for endogenous scavengers. We previously found 5-hydroxytryptamine (HT), which is an indole derivative (ID), to be an efficient ONOO(-) scavenger. In the present study, the interaction of several other indoles was further investigated: tryptophan (TRP), 5-hydroxyL-tryptophan (HLT), HT, N-acetyl-5-hydroxytryptamine (AHT), 5-methoxyindole-3-acetate (MIA), 5-methoxytryptamine (MT), and melatonin. The ONOO(-) scavenging activity of ID was assayed by measuring the formation of oxidized dihydrorhodamine-123 (DHR-123). The scavenging efficacy was expressed as the IC(50), denoting the concentration of each indole required to cause 50% inhibition of DHR-123 formation. In a separate in vitro study, the protective effect of IDs against ONOO(-)-induced nitration of bovine serum albumin was investigated. Nitration was quantified using an immunoassay with a monoclonal anti-nitrotyrosine antibody, and a horseradish peroxidase-conjugated anti-mouse secondary antibody from sheep. The results revealed that the inhibitory activities of indoles were as follows: HLT, IC(50) = 0.73 microM; HT, IC(50) = 1.03 microM; and AHT, IC(50) = 0.98 microM), showing relatively strong activities against ONOO(-). Interestingly, TRP, MIA, MT, and melatonin were less effective. Regarding the protection of albumin by IDs, the data showed that the formation of ONOO(-) was inhibited in a dose-dependent manner. Further probing of the mode of the interaction of indoles revealed that the hydroxyl groups in IDs are required for the enhanced scavenging action. It was concluded that several indole derivatives with hydroxyl groups are effective scavengers against ONOO(-), and that the scavenging efficacy depends on the presence of hydroxyl groups located within the indole ring structure.

Modification of 5-hydroxytryptophan-evoked 5-hydroxytryptamine formation of guinea pig colonic mucosa by reactive oxygen species

We studied whether reactive oxygen species (ROS) generated by normal colonic mucosa affect 5-hydroxytryptophan (5-HTP)-evoked 5-HT formation (measured as the sum of 5-HT plus 5-hydroxyindole acetic acid (5-HIAA) accumulation) of guinea pig's isolated colonic mucosa. Catalase (3000-6000 U/ml), a hydrogen peroxide (H2O2) scavenger or diphenylene iodonium (DPI, 10-100 microM), an NADPH oxidase inhibitor, concentration-dependently caused an increase of the sum of 5-HT plus 5-HIAA accumulation in the presence of 5-HTP (10 microM), but these drugs did not significantly affect the 5-HT-metabolite in the colonic mucosa measured as the ratio of 5-HIAA/5-HT. Exogenously applied H2O2 (10-100 microM) concentration-dependently inhibited the sum of 5-HT plus 5-HIAA accumulation. In contrast, neither superoxide dismutase (SOD, 100-300 U/ml), superoxide anion scavenger, nor dimetyl sulfoxide (1-5%, DMSO), a hydroxyl radical scavenger affected the sum of 5-HT plus 5-HIAA accumulation. Moreover, mucosa ROS generation was estimated using the chemiluminescence technique. SOD (100-300 U/ml), catalase (3000-6000 U/ml) or DPI (10-100 microM), concentration-dependently reduced luminol-enhanced chemiluminescence signal from the colonic mucosa, while allopurinol (10-100 microM), a xanthine oxidase inhibitor, did not affect the chemiluminescence signal. These results suggest that ROS is formed through an NADPH oxidase system in the guinea pig colonic mucosa, where it exerts a modulatory effect on mucosal 5-HT formation upon addition of 5-HTP. Thus, ROS formation from normal colonic mucosa could be considered to contribute to the control of 5-HT production in mucosa enterochromaffin cells.

A rapid, quantitative method for measuring leukocyte adhesion to normal and balloon-injured arteries in vitro

Many of the currently available techniques for quantifying leukocyte adhesion require monolayers of cells and are therefore unsuitable for use in ex vivo arterial tissue. Here we describe a rapid method to measure adhesion of leukocytes to intact artery strips and to determine the effect of artery injury on adhesiveness of leukocytes with and without activation. Leukocytes were isolated from rabbit blood, labelled with 51Cr, and added to the luminal face of the left and right subclavian arteries derived from the same animal. In some experiments the endothelium was removed before addition of leukocytes and in another series of experiments the artery was injured by inflating a balloon catheter within the lumen in vitro before leukocyte addition. After washing, the adhesion of labelled leukocytes was quantified by gamma counting. To determine localization of the leukocytes, some arteries were fixed in situ and examined microscopically, with confirmation of leukocyte identification by enzyme cytochemistry. The adhesion of leukocytes increased progressively during 60 min and was inhibited by reducing the temperature to 4 degrees C. Adhesion was increased by the nitric oxide synthase inhibitor L-NAME. Stretching the artery wall in vitro using a balloon catheter increased leukocyte adhesion within 1 h after injury. In contrast, this did not occur following simple arterial denudation. Histological examination of stained en face preparations and transverse sections of the subclavian arteries revealed loosely adherent granulocytic leukocytes on the endothelial surface. This technique is straightforward and allows accurate and rapid measurement of autologous leukocyte adhesion to normal and pathologically altered arteries ex vivo.

Correlation of leukocyte adhesiveness, adhesion molecule expression and leukocyte-induced contraction following balloon angioplasty

1. The aim of this study was to examine the changes in leukocyte adhesion and leukocyte-induced contraction in balloon-injured rabbit subclavian artery and to correlate these changes with vessel morphology and expression of adhesion molecules on the injured arteries. 2. Rabbits were anaesthetized and their left subclavian arteries were injured by balloon inflation and withdrawal followed by sacrifice at 2, 24, 48 h or 8 days after injury. The left and right subclavian arteries were removed and leukocytes were isolated from autologous rabbit blood. Leukocyte-induced contraction was measured in 5-HT precontracted artery rings and leukocyte adhesion was measured using (51)Cr-labelled leukocytes. Immunocytochemistry using paraffin-embedded tissue was employed to detect changes in the expression of adhesion molecules on injured arteries. 3. Autologous leukocytes caused a contraction of rabbit subclavian artery rings, which was prevented by L-NAME (10(-3) M). Balloon-induced injury abolished the contractile response to leukocytes, which correlated with loss of carbachol-induced relaxation 4. Balloon injury markedly enhanced the adhesiveness of the subclavian artery for leukocytes, most notably at 24 and 48 h after injury (1.7 and 1.8 fold respectively). Increased leukocyte adhesion at these two time points correlated with an upregulation of E-selectin, P-selectin and VCAM-1 expression on the remaining endothelium of the injured artery. 5. Vessel morphology revealed that balloon inflation had induced an infiltration of inflammatory cells into the vessel wall, the greatest increase being seen at 24 h after injury. 6. It is concluded that an increase in the expression of E-selectin, P-selectin and VCAM-1 following balloon-induced injury leads to enhanced leukocyte adhesion and migration into the injured vessel.