Angiogenesis in the pathobiology and treatment of vascular and malignant diseases

Cardiovascular disease and cancer account for the majority of adult disease in the developed world. This review focuses on current concepts in the study of angiogenesis (new vessel formation) as related to these conditions and highlights the role of vascular endothelial growth factor. Developments in therapeutic angiogenesis have raised the possibility that pharmacologic or gene-directed interventions, based on the ability of vascular endothelial growth factor to promote new vessel formation, may soon gain clinical application for the treatment of occlusive vascular disease. Similarly, the future treatment of malignant disease is likely to involve antiangiogenic agents that, in preliminary animal work, have demonstrated an efficacy that is not limited by adverse affects. Aside from these potential applications, current investigations have enhanced our understanding of mechanisms involved in the development of atherosclerotic and malignant disease.

Selective inhibition of nitric oxide production during cardiac allograft rejection causes a small increase in graft survival

Nitric oxide production is increased in allograft rejection and may have both beneficial and deleterious effects on graft function and survival. In animal models, conventional immunosuppressive agents have been shown to decrease nitric oxide production. The aim of our study was to determine what effect augmentation and selective inhibition of nitric oxide production may have on graft survival by using the model of heterotopic cardiac transplantation in the rat. L-Arginine, the naturally occurring substrate for nitric oxide production, was administered subcutaneously at 200 mg/kg/day. L-NG-monomethyl-L-arginine (L-NMMA) is a selective inhibitor of nitric oxide synthase and was administered at 500 mg/kg/day to allograft recipients from the day of operation. Endogenous nitric oxide production was quantified by analysis of urinary nitrate excretion, and time to rejection was determined by graft palpation. L-Arginine did not significantly alter urinary nitrate excretion by iso- or allografts, suggesting that nitric oxide production is not a substrate-limited process in this model. Graft survival in this group was unchanged. L-NMMA produced a small increase in graft survival from 5.1 +/- 0.1 to 6.3 +/- 0.3 days compared with control allografts (P = 0.001) and abolished the rise in urinary nitrate excretion seen with control allografts. Lower doses of L-NMMA produced dose-related decrements in urinary nitrate excretion, but did not alter graft survival. We found that allograft rejection can proceed to graft loss despite complete inhibition of the increase in nitric oxide production that occurs during untreated rejection. The small increase in graft survival suggests that nitric oxide plays a minor role as a cytotoxic effector molecule in this model of acute rejection.

Urinary nitrate excretion is a noninvasive indicator of acute cardiac allograft rejection and nitric oxide production in the rat

Cytokine induction of calcium-independent nitric oxide synthase is associated with production of large amounts of nitric oxide (NO). NO is a free radical that is rapidly degraded to nitrite and nitrate. Measurement of plasma and urinary nitrate is an indirect marker of NO production and previous studies have demonstrated that plasma nitrate rises with allograft rejection. The purpose of this study was to examine the temporal relationship between the rise in urinary nitrate excretion and the onset of graft rejection, and to determine the effect of conventional immunosuppression on nitrate excretion. The heterotropic model of cardiac transplantation in the rat was used, with Brown-Norway to Lewis allografts and Lewis to Lewis isograft controls. Twenty-four-hour urine specimens were collected before and after transplantation. Urinary nitrate excretion was measured by gas chromatography/mass spectrometry. Each group was treated with (1) no immunosuppression, (2) dexamethasone (3 mg/kg), or (3) CsA (10 mg/kg) on days 0, 1, and 2. Time to rejection for untreated allografts was 5.1 +/- 0.1 days, extending to 8.4 +/- 0.5 and 9.6 +/- 0.4 days with dexamethasone and CsA treatment, respectively. There was a significant rise in nitrate excretion on days 4, 7, and 9 for control, dexamethasone-treated, and CsA-treated allografts, respectively, preceding evidence of rejection. Untreated allograft rejection was associated with a peak in nitrate excretion 8 times that of basal excretion by isografts. Treatment of the allografts with dexamethasone and CsA significantly attenuated peak nitrate excretion compared with untreated allografts with a only a 2- to 3-fold rise preceding rejection. Results indicate that allograft rejection is associated with a dramatic increase in peak urinary nitrate excretion that is attenuated by standard immunosuppressive therapy. An increase in nitrate excretion precedes evidence of graft rejection, and may serve as a noninvasive marker of graft rejection.

Increased nitric oxide production in heart failure

The role of nitric oxide in heart failure is unknown. The high-capacity inducible isoform of nitric oxide synthase is present in the myocardium of patients with idiopathic dilated cardiomyopathy. Plasma nitrate, the stable end-product of nitric oxide production, was significantly increased in patients with heart failure compared with normal controls (means 51.3 and 24.6 mumol/L). Vasodilation caused by increased nitric oxide may compensate for the vasoconstrictor effect of neurohumoral adaptions to heart failure. Alternatively, excess production may be detrimental to the heart by a direct negative inotropic effect.