Tetrahydrobiopterin prevents cyclosporine-induced vasomotor dysfunction

The Role of Nitroglycerin and Other Nitrogen Oxides in Cardiovascular Therapeutics

The use of nitroglycerin in the treatment of angina pectoris began not long after its original synthesis in 1847. Since then, the discovery of nitric oxide as a biological effector and better understanding of its roles in vasodilation, cell permeability, platelet function, inflammation, and other vascular processes have advanced our knowledge of the hemodynamic (mostly mediated through vasodilation of capacitance and conductance arteries) and nonhemodynamic effects of organic nitrate therapy, via both nitric oxide-dependent and -independent mechanisms. Nitrates are rapidly absorbed from mucous membranes, the gastrointestinal tract, and the skin; thus, nitroglycerin is available in a number of preparations for delivery via several routes: oral tablets, sublingual tablets, buccal tablets, sublingual spray, transdermal ointment, and transdermal patch, as well as intravenous formulations. Organic nitrates are commonly used in the treatment of cardiovascular disease, but clinical data limit their use mostly to the treatment of angina. They are also used in the treatment of subsets of patients with heart failure and pulmonary hypertension. One major limitation of the use of nitrates is the development of tolerance. Although several agents have been studied for use in the prevention of nitrate tolerance, none are currently recommended owing to a paucity of supportive clinical data. Only 1 method of preventing nitrate tolerance remains widely accepted: the use of a dosing strategy that provides an interval of no or low nitrate exposure during each 24-h period. Nitric oxide's important role in several cardiovascular disease mechanisms continues to drive research toward finding novel ways to affect both endogenous and exogenous sources of this key molecular mediator.

Contemporary Approaches to Modulating the Nitric Oxide-cGMP Pathway in Cardiovascular Disease

Endothelial cells lining the vessel wall control important aspects of vascular homeostasis. In particular, the production of endothelium-derived nitric oxide and activation of soluble guanylate cyclase promotes endothelial quiescence and governs vasomotor function and proportional remodeling of blood vessels. Here, we discuss novel approaches to improve endothelial nitric oxide generation and preserve its bioavailability. We also discuss therapeutic opportunities aimed at activation of soluble guanylate cyclase for multiple cardiovascular indications.

Epidermal Growth Factor–Like Domain 7 Is a Novel Inhibitor of Neutrophil Adhesion to Coronary Artery Endothelial Cells Injured by Calcineurin Inhibition

Background—

We investigated the effect of epidermal growth factor–like domain 7 (Egfl7) on nuclear factor-κB activation, intercellular adhesion molecule-1 expression, and neutrophil adhesion to human coronary artery endothelial cells after calcineurin-inhibition–induced injury.

Methods and Results—

Human coronary endothelial cells were incubated with cyclosporine (CyA) 10 μg/mL with or without Egfl7 (100 ng/mL) or the Notch receptor activator Jagged1 (200 ng/mL) for 6 to 48 hours. CyA upregulated nuclear factor-κB (p65) activity (128±2% of control, P <0.001) in nuclear extracts, as determined with a DNA-binding activity ELISA. This activity was inhibited by Egfl7 (86±3% of control; P <0.001 versus CyA alone). Jagged1 blocked Egfl7-induced nuclear factor-κB inhibition (105±4% of control; P <0.05 versus CyA plus Egfl7). CyA upregulated cell-surface intercellular adhesion molecule-1 expression (215±13% of control; P <0.001), as determined by flow cytometry. This expression was suppressed by Egfl7 (148±5%; P <0.001 versus CyA alone). Jagged1 attenuated the intercellular adhesion molecule-1–suppressive effect of Egfl7 when administered with CyA (193±3% versus 148±5%; P <0.01). CyA increased neutrophil adhesion to human coronary endothelial cells (control 20±5%, CyA 37±3%; P <0.001 versus control) in a nonstatic neutrophil adhesion assay. This increase was attenuated by Egfl7 (22±6%; P <0.001 versus CyA alone). Jagged 1 attenuated the effect of Egfl7 on neutrophil adhesion (31±3%; P <0.001 versus Egfl7 plus CyA).

Conclusions—

Our study reveals that Egfl7 is a potent inhibitor of neutrophil adhesion to human coronary endothelial cells subsequent to calcineurin-inhibition–induced injury. Mechanistically, Egfl7 blocked nuclear factor-κB pathway activation and intercellular adhesion molecule-1 expression, which suggests that it may have significant antiinflammatory properties. Because Jagged1 blocked the effect of Egfl7, Notch receptor antagonism may contribute to the mechanism of action of Egfl7.

Pathogenetic role of eNOS uncoupling in cardiopulmonary disorders

The homodimeric flavohemeprotein endothelial nitric oxide synthase (eNOS) oxidizes l-arginine to l-citrulline and nitric oxide (NO), which acutely vasodilates blood vessels and inhibits platelet aggregation. Chronically, eNOS has a major role in the regulation of blood pressure and prevention of atherosclerosis by decreasing leukocyte adhesion and smooth muscle proliferation. However, a disturbed vascular redox balance results in eNOS damage and uncoupling of oxygen activation from l-arginine conversion. Uncoupled eNOS monomerizes and generates reactive oxygen species (ROS) rather than NO. Indeed, eNOS uncoupling has been suggested as one of the main pathomechanisms in a broad range of cardiovascular and pulmonary disorders such as atherosclerosis, ventricular remodeling, and pulmonary hypertension. Therefore, modulating uncoupled eNOS, in particular eNOS-dependent ROS generation, is an attractive therapeutic approach to preventing and/or treating cardiopulmonary disorders, including protective effects during cardiothoracic surgery. This review provides a comprehensive overview of the pathogenetic role of uncoupled eNOS in both cardiovascular and pulmonary disorders. In addition, the related therapeutic possibilities such as supplementation with the eNOS substrate l-arginine, volatile NO, and direct NO donors as well as eNOS modulators such as the eNOS cofactor tetrahydrobiopterin and folic acid are discussed in detail.

Effect of high intensity exercise on peak oxygen uptake and endothelial function in long-term heart transplant recipients

Coronary allograft vasculopathy is a well-known long-term complication after cardiac transplantation. Endothelial dysfunction is involved and may be prevented by aerobic exercise. The purpose of this study was to examine whether high intensity aerobic exercise improves peak oxygen uptake (VO(2 peak) ) and endothelial function in heart transplant (HT) recipients. Twenty-seven long-term HT recipients were randomized to either 8-weeks high intensity aerobic exercise or no training. Flow mediated dilation of the brachial artery (FMD) was measured by ultrasound and VO(2 peak) by the analysis of expired air. Blood pressure and biomarkers were measured before and after 8 weeks. VO(2 peak) increased significantly in the exercise group (VO(2 peak) 23.9 ± 1.79 to 28.3 ± 1.63 mL/kg/min compared to controls (VO(2 peak) 24.6 ± 1.38 to 23.4 ± 1.58, p < 0.001 exercise vs. control).FMD increased in the exercise group compared to controls (8.3 ± 1.1% to 11.4 ± 1.2% vs. 5.6 ± 1.0% to 5.3 ± 1.7%, p = 0.024). No increase in nitroglycerin-induced vasodilation was observed. Systolic blood pressure fell in the exercise group (142 ±4.2 mmHg to127 ± 3.4 mmHg, p = 0.01) and was unchanged in controls (141 ± 4.2 mmHg to 142 ±6.4 mmHg, NS). High intensity aerobic exercise reduces systolic blood pressure and improves endothelial function in HT recipients.

Tacrolimus preserves vasomotor function and maintains vascular homeostasis

BACKGROUND

Post-transplant immunosuppression is associated with endothelial dysfunction that may lead to vasculopathy. We have previously demonstrated that cyclosporine causes vascular dysfunction. In this we study examined the effect of tacrolimus (Tac) in an identical model.

METHODS

Lewis rats (n = 8 per group) were injected with Tac (low, medium or high dose) or saline (Con) daily for 2 weeks. Segments of thoracic aorta (TAo) were assessed for endothelium-dependent (Edep) and -independent (Eind) vasorelaxation (E(max)) and sensitivity to endothelin (ET)-induced vasoconstriction (C(max)). ET(A) and ET(B) receptor (Rc) expression levels were determined in TAo. Tumor necrosis factor-alpha (TNF-α) and transforming growth factor-beta (TGF-β) expression were determined in myocardial (LV) tissue. Plasma ET levels and tissue oxidative injury were quantified by enzyme-linked immunoassay.

RESULTS

Tac did not impair Edep relaxation when compared with Con (p = 0.69). Impairment of sodium nitroprusside-mediated Eind vasorelaxation was noted with Tac (E(max): Con 69 ± 2%, Tac high 54 ± 2%; p = 0.0001), whereas no such impairment was seen with diltiazem-mediated Eind vasorelaxation (p = 0.06). Tac decreased sensitivity to ET (C(max): Con 222 ± 19%, Tac high 162 ± 11%; p = 0.0002) and ET levels (Con 0.8 ± 0.1 fmol/ml, Tac 0.4 ± 0.1 fmol/ml; p = 0.02). Tac did not alter ET(A) Rc expression (p = 0.28), but increased ET(B) Rc levels (p = 0.02). Oxidative injury was similar in both LV (p = 0.43) and Ao (p = 0.73) tissue. Similarly, TNF-α expression (p = 0.16) was not different between groups, whereas expression of TGF-β demonstrated a significant decrease with Tac treatment (p = 0.02).

CONCLUSION

Our findings suggests that tacrolimus has beneficial effects with respect to endothelial function.

Inhibition of nitric oxide-guanylate cyclase-dependent and -independent signaling contributes to impairment of beta-adrenergic vasorelaxations by cyclosporine

This study investigated the role of endothelium- and smooth muscle-dependent mechanisms in the interaction of cyclosporine (CyA), an immunosuppressant drug, with beta-adrenoceptor (isoprenaline)-mediated relaxations in isolated rat aortas precontracted with phenylephrine. CyA effects were assessed in the absence and presence of NG-nitro-L-arginine methyl ester (L-NAME, nitric oxide synthase inhibitor), methylene blue (guanylate cyclase inhibitor), or propranolol (beta-adrenoceptor antagonist). In aortas with intact endothelium (E+), pretreatment with L-NAME or methylene blue significantly reduced isoprenaline (1 x 10(-9) to 1 x 10(-7)M) relaxations in contrast to no effect for tetraethylammonium (K+ channel blocker), or diclophenac (cyclooxygenase inhibitor), suggesting a major role for the nitric oxide-guanylate cyclase (NO-GC) pathway, but not endothelial hyperpolarizing factor or vasodilator prostanoids, in isoprenaline responses. Isoprenaline relaxations were still evident, though significantly attenuated, in endothelium-denuded aortas (E-) and were resistant to L-NAME or methylene blue. Acute exposure to CyA (2 microM) caused propranolol-sensitive reductions in isoprenaline responses in E+ and E- aortas. The CyA-induced attenuation of isoprenaline responses in E+ aortas largely disappeared in L-NAME-treated aortas and after supplementation with L-arginine, the substrate of nitric oxide. CyA also reduced the endothelium-independent, GC-dependent aortic relaxations evoked by sodium nitroprusside, an effect that was virtually abolished by methylene blue. We conclude that: (i) endothelial and smooth muscle mechanisms contribute to aortic beta-adrenoceptor relaxations and both components are negatively influenced by CyA, and (ii) NO-GC signaling plays an integral role in the vascular CyA-beta-adrenoceptor interaction. The clinical relevance of the present study is warranted given the established role of impaired vascular function in CyA toxicity.

Effect of combined simvastatin and cyclosporine compared with simvastatin alone on cerebral vasospasm after subarachnoid hemorrhage in a canine model

Object

The object of this study was to determine whether the combination of cyclosporine and simvastatin could ameliorate cerebral vasospasm after subarachnoid hemorrhage (SAH) in a canine model to a greater extent than simvastatin alone.

Methods

Animals were assigned to one of three groups: control (five dogs), simvastatin alone (four), or simvastatin and cyclosporine (four). A double SAH model was used. Baseline basilar artery (BA) angiograms were obtained. These were repeated at Days 3, 7, and 10. Measurement of the BA diameter was performed.

Decreased BA diameter was seen on Day 3 in the control and simvastatin/cyclosporine group. A return to baseline diameters was seen by Day 7. An increase from baseline diameter was seen in the simvastatin group at Day 10.

Conclusions

Cyclosporine may interfere with the vasodilatory effects of simvastatin. Vasodilation greater than baseline is seen at Day 10 in the simvastatin group. The combination of simvastatin and cyclosporine does not ameliorate cerebral vasospasm in a canine model to a greater extent than simvastatin alone.

Role of endothelin-1 and nitric oxide bioavailability in transplant-related vascular injury: comparative effects of rapamycin and cyclosporine

BACKGROUND

Cyclosporine (CyA) is associated with many side effects, including endothelial dysfunction and transplant vasculopathy (TxV). We previously demonstrated that CyA results in impairment of nitric oxide bioavailability and enhanced sensitivity to endothelin-1 (ET-1). In this study, we evaluated rapamycin (SRL) for its effects on the endothelium.

METHODS AND RESULTS

Lewis rats (n = 8) were injected with SRL (1.5 mg/kg), CyA (5 mg/Kg), or saline (Con) intraperitoneally daily for 2-weeks. Thoracic aortic segments were assessed for endothelial-dependent (Edep) and independent (Eind) relaxation after exposure to acetylcholine and sodium nitroprusside by deriving the percent maximum relaxation (Emax). ET-1 plasma levels were also measured. Thoracic aortic expression of endothelial nitric oxide synthase (eNOS), ET(A) and ET(B) receptors (Rc), were determined. Oxidative injury was assessed by changes in 8-isoprostane levels. CyA exposure resulted in lower Edep vasorelaxation compared with control and SRL (Emax: SRL, 58+/-4%; CyA, 24+/-7%; Con, 52+/-8%; P=0.001). No differences in Eind vasorelaxation were seen. CyA exposure also increased sensitivity to ET-1 (% maximum contraction [Cmax]: Con, 211+/-8%; SRL, 230+/-5%; CyA, 259+/-3%; P=0.04). Only SRL treatment reduced ET-1 plasma levels. CyA reduced eNOS expression by 30% and increased ETA Rc expression by 34% compared with both Con and SRL (P=0.02). CyA resulted in higher 8-isoprostane levels (CyA, 50+/-2%; SRL, 3+/-3%; Con, 2+/-5%; P=0.02).

CONCLUSIONS

CyA results in vascular dysfunction characterized by impairment of Edep vasorelaxation and enhanced sensitivity to vasospasm. SRL did not impair Edep vasorelaxation or increase sensitivity to vasospasm while lowering ET-1 levels and preserving eNOS protein expression. We conclude that SRL is less deleterious to the vasculature than CyA and may prevent TxV by these mechanisms.

Tetrahydrobiopterin compounds prolong allograft survival independently of their effect on nitric oxide synthase activity

BACKGROUND

In previous work, the four-amino analogue of tetrahydrobiopterin, a novel, selective inhibitor of inducible nitric oxide synthase, has been shown to prolong survival of murine cardiac allografts.

METHODS

To further elucidate the underlying molecular immunosuppressive mechanism, we compared the effect of four-amino tetrahydrobiopterin with that of the unsubstituted parent compound tetrahydrobiopterin and of N-(iminoethyl)-L-lysine (L-NIL), a nonpterin inhibitor of inducible nitric oxide synthase using a murine cardiac transplant model. We analyzed allograft survival, intragraft gene expression in grafts by microarray and real-time polymerase chain reaction, graft nitrotyrosine staining by immunohistochemistry and plasma nitrite plus nitrate levels by high-performance liquid chromatography.

RESULTS

Allograft survival was significantly prolonged by tetrahydrobiopterin and cyclosporin A, but not by L-NIL although decreased plasma nitrite plus nitrate levels confirmed nitric oxide synthase inhibition in vivo. As compared to allogeneic untreated controls, intragraft peroxynitrite formation and hence nitrotyrosine staining was lowered in all groups except in cyclosporine A-treated animals. Gene expression profiles obtained by microarray analysis demonstrated that cyclosporine A was able to counteract the expression changes of more than half of the genes differently expressed in syngeneic grafts versus allografts, whereas tetrahydrobiopterin compounds and L-NIL showed only smaller influences on gene expression profiles.

CONCLUSIONS

These results demonstrate that the four-amino substitution, which is essential for inhibition of nitric oxide synthase, is not required for the immunosuppressive effect of tetrahydrobiopterin compounds. We describe a novel immunosuppressive role of pharmacologically applied tetrahydrobiopterin.

Signalling and regulation of collagen I synthesis by ET-1 and TGF-beta1

Endothelin-1 (ET-1) plays an important role in tissue remodelling and fibrogenesis by inducing synthesis of collagen I via protein kinase C (PKC). ET-1 signals are transduced by two receptor subtypes, the ETA- and ETB-receptors which activate different Galpha proteins. Here, we investigated the expression of both ET-receptor subtypes in human primary dermal fibroblasts and demonstrated that the ETA-receptor is the major ET-receptor subtype expressed. To determine further signalling intermediates, we inhibited Galphai and three phospholipases. Pharmacologic inhibition of Galphai, phosphatidylcholine-phospholipase C (PC-PLC) and phospholipase D (PLD), but not of phospholipase Cbeta, abolished the increase in collagen I by ET-1. Inhibition of all phospholipases revealed similar effects on TGF-beta1 induced collagen I synthesis, demonstrating involvement of PC-PLC and PLD in the signalling pathways elicited by ET-1 and TGF-beta1. ET-1 and TGF-beta1 each stimulated collagen I production and in an additive manner. ET-1 further induced connective tissue growth factor (CTGF), as did TGF-beta1, however, to lower levels. While rapid and sustained CTGF induction was seen following TGF-beta1 treatment, ET-1 increased CTGF in a biphasic manner with lower induction at 3 h and a delayed and higher induction after 5 days of permanent ET-1 treatment. Coincidentally at 5 days of permanent ET-1 stimulation, a switch in ET-receptor subtype expression to the ETB-receptor was observed. We conclude that the signalling pathways induced by ET-1 and TGF-beta1 leading to augmented collagen I production by fibroblasts converge on a similar signalling pathway. Thereby, long-time stimulation by ET-1 resulted in a changed ET-receptor subtype ratio and in a biphasic CTGF induction.

Antioxidant supplementation enhances erythrocyte antioxidant status and attenuates cyclosporine-induced vascular dysfunction

The aim of this study was to determine the effects of dietary antioxidant supplementation with alpha-tocopherol and alpha-lipoic acid on cyclosporine-induced alterations to erythrocyte and plasma redox balance, and cyclosporine-induced endothelial and smooth muscle dysfunction. Rats were randomly assigned to either control, antioxidant, cyclosporine or cyclosporine + antioxidant treatments. Cyclosporine A was administered for 10 days after an 8-week feeding period. Plasma was analyzed for alpha-tocopherol, total antioxidant capacity, malondialdehyde and creatinine. Erythrocytes were analyzed for glutathione, methemoglobin, superoxide dismutase, catalase, glutathione peroxidase, glucose-6-phosphate dehydrogenase, alpha-tocopherol and malondialdehye. Vascular endothelial and smooth muscle function was determined in vitro. Antioxidant supplementation resulted in significant increases in erythrocyte alpha-tocopherol concentration and glutathione peroxidase activity in both of the antioxidant-supplemented groups. Cyclosporine administration caused significant decreases in glutathione concentration, methemoglobin concentration and superoxide dismutase activity. Antioxidant supplementation attenuated the cyclosporine-induced decrease in superoxide dismutase activity. Cyclosporine therapy impaired both endothelium-independent and -dependent relaxation of the thoracic aorta, and this was attenuated by antioxidant supplementation. In summary, dietary supplementation with alpha-tocopherol and alpha-lipoic acid attenuated the cyclosporine-induced decrease in erythrocyte superoxide dismutase activity and attenuated cyclosporine-induced vascular dysfunction.