Angiogenic effects of low molecular weight heparin in patients with stable coronary artery disease: a pilot study

The essential role for endothelial cell sprouting in coronary collateral growth

RATIONALE

Coronary collateral growth is a natural bypass for ischemic heart diseases. It offers tremendous therapeutic benefit, but the process of coronary collateral growth isincompletely understood due to limited preclinical murine models that would enable interrogation of its mechanisms and processes via genetic modification and lineage tracing. Understanding the processes by which coronary collaterals develop can unlock new therapeutic strategies for ischemic heart disease.

OBJECTIVE

To develop a murine model of coronary collateral growth by repetitive ischemia and investigate whether capillary endothelial cells could contribute to the coronary collateral formation in an adult mouse heart after repetitive ischemia by lineage tracing.

METHODS AND RESULTS

A murine model of coronary collateral growth was developed using short episodes of repetitive ischemia. Repetitive ischemia stimulation resulted in robust collateral growth in adult mouse hearts, validated by high-resolution micro-computed tomography. Repetitive ischemia-induced collateral formation compensated ischemia caused by occlusion of the left anterior descending artery. Cardiac function improved during ischemia after repetitive ischemia, suggesting the improvement of coronary blood flow. A capillary-specific Cre driver (Apln-CreER) was used for lineage tracing capillary endothelial cells. ROSA mT/mG reporter mice crossed with the Apln-CreER transgene mice underwent a 17 days' repetitive ischemia protocol for coronary collateral growth. Two-photon and confocal microscopy imaging of heart slices revealed repetitive ischemia-induced coronary collateral growth initiated from sprouting Apelin⁺ endothelial cells. Newly formed capillaries in the collateral-dependent zone expanded in diameter upon repetitive ischemia stimulation and arterialized with smooth muscle cell recruitment, forming mature coronary arteries. Notably, pre-existing coronary arteries and arterioles were not Apelin⁺, and all Apelin⁺ collaterals arose from sprouting capillaries. Cxcr4, Vegfr2, Jag1, Mcp1, and Hif1⍺ mRNA levels in the repetitive ischemia-induced hearts were also upregulated at the early stage of coronary collateral growth, suggesting angiogenic signaling pathways are activated for coronary collaterals formation during repetitive ischemia.

CONCLUSIONS

We developed a murine model of coronary collateral growth induced by repetitive ischemia. Our lineage tracing study shows that sprouting endothelial cells contribute to coronary collateral growth in adult mouse hearts. For the first time, sprouting angiogenesis is shown to give rise to mature coronary arteries in response to repetitive ischemia in the adult mouse hearts.

The Coronary ARteriogenesis with combined Heparin and EXercise therapy in chronic refractory Angina (CARHEXA) trial: A double-blind, randomized, placebo-controlled stress echocardiographic study

BACKGROUND

Coronary collateral circulation exerts protective effects on myocardial ischaemia due to coronary artery disease and can be promoted by exercise with heparin co-administration. Whether this arteriogenetic effect is accompanied by functional improvement of left ventricle during stress and lessening of angina symptoms remains unknown.

AIMS

To evaluate the anti-ischaemic efficacy of heparin plus exercise in coronary artery disease.

METHODS

In a prospective, single-centre, randomized, double-blind study we recruited 32 'no-option' patients (27 males; mean age 61 ± 8 years) with stable angina, exercise-induced ischaemia and coronary artery disease not suitable for revascularization. All underwent a two-week cycle of exercise (two exercise sessions per day, five days per week) and were randomized (n = 16 per group) to intravenous placebo (0.9% saline) versus unfractionated heparin (5.000 IU intravenously), 10 min prior to exercise. We assessed Canadian Cardiovascular Society angina class, stress electrocardiogram and echo parameters (wall motion score index) and computed tomography angiography for collaterals.

RESULTS

After two-week cycle, Canadian Cardiovascular Society class statistically decreased in both groups (heparin plus exercise group: 2.6 ± 0.7 to 1.9 ± 0.7, p < 0.001, exercise group: 2.4 ± 0.7 to 2.1 ± 0.9, p = 0.046). Only the heparin plus exercise group improved time-to-ST segment depression (before 270, 228-327 s vs. after 339, 280-360 s, p = 0.012) and wall motion score index (before 1.38 ± 0.25 vs. after 1.28 ± 0.18, p = 0.005). By multi-slice computed tomography angiography, collaterals improved in 12/15 (80%) in the heparin plus exercise group versus 2/16 (12.5%) in the exercise group (p < 0.001).

CONCLUSION

A two-week, 10-test cycle of heparin plus exercise is better than exercise in improving angina class, myocardial ischaemia and collaterals by computed tomography angiography.

Perspectives On: Local and Sustained Delivery of Angiogenic Growth Factors

This review emphasizes the role of angiogenesis in tissue engineering, introduces various angiogenic growth factors, and highlights current status of delivery systems for angiogenic growth factors using natural and synthetic biomaterials. A short overview of angiogenic growth factors is presented, followed by the introduction of emerging strategies for designing smart delivery carriers.

Wound healing gene therapy: cartilage regeneration induced by vascular endothelial growth factor plasmid

AIMS

The identification of growth factors and cytokines with angiogenic activity has enabled new therapeutic treatments for a variety of diseases; this concept is called therapeutic angiogenesis. The vascular endothelial growth factor (VEGF) is the most critical regulator of vascular formation. In the present study, we were interested in the therapeutic angiogenesis effect using plasmid transfer of human complementary DNA VEGF(165) (phVEGF(165)) in experimental skin and cartilage trauma.

METHODS

Ten BALB/c mice were used for cartilage injury model. At 6 weeks of age, all mice were ear-punched, resulting in 2-mm-diameter puncture through the center of both pinnae. Each mouse got phVEGF(165) injection into the first ear and vector without insert or saline injection into the second one. The healing process was followed. The hollow diameter was measured on days 0, 14, and 42. Histological sections of experimental and control pinnae were taken from days 1, 3, 5, 7, 9, 11, 13, 15, 20, and 30 after experimental injury for hematoxylin and eosin and periodic acid Schiff staining and for human VEGF immunocytochemistry. The expression of human VEGF was also checked by real-time polymerase chain reaction in formalin-fixed, paraffin-embedded tissue sections.

KEY FINDINGS

In BALB/c mouse strain, a significant angiogenesis promotion and cartilage repair were observed after phVEGF(165) injection into the punched ear area.

SIGNIFICANCE

We suggest that administering phVEGF(165) leads to faster cartilage regeneration even if not only on the angiogenic basis.

Dalteparin, a low-molecular-weight heparin, promotes angiogenesis mediated by heparin-binding VEGF-A in vivo

Tumors are angiogenesis dependent and vascular endothelial growth factor-A (VEGF-A), a heparin-binding protein, is a key angiogenic factor. As chemotherapy and co-treatment with anticoagulant low-molecular-weight heparin (LMWH) are common in cancer patients, we investigated whether angiogenesis in vivo mediated by VEGF-A is modulated by metronomic-type treatment with: (i) the LMWH dalteparin; (ii) low-dosage cytostatic epirubicin; or (iii) a combination of these two drugs. Using the quantitative rat mesentery angiogenesis assay, in which angiogenesis was induced by intraperitoneal injection of very low doses of VEGF, dalteparin sodium (Fragmin(®) ) and epirubicin (Farmorubicin(®) ) were administered separately or in combination by continuous subcutaneous infusion at a constant rate for 14 consecutive days. Dalteparin was administered at 27, 80, or 240 IU/kg/day, i.e., doses that reflect the clinical usage of this drug, while epirubicin was given at the well-tolerated dosage of 0.4 mg/kg/day. While dalteparin significantly stimulated angiogenesis in an inversely dose-dependent manner, epirubicin did not significantly affect angiogenesis. However, concurrent treatment with dalteparin and epirubicin significantly inhibited angiogenesis. The effect of dalteparin is the first demonstration of a proangiogenic effect of any LMWH in vivo. The fact that co-treatment with dalteparin and epirubicin significantly inhibited angiogenesis suggests a complex drug effect.

An endogenously deposited fibrin scaffold determines construct size in the surgically created arteriovenous loop chamber model of tissue engineering

BACKGROUND

An arteriovenous loop (AVL) enclosed in a polycarbonate chamber in vivo, produces a fibrin exudate which acts as a provisional matrix for the development of a tissue engineered microcirculatory network.

OBJECTIVES

By administering enoxaparin sodium - an inhibitor of fibrin polymerization, the significance of fibrin scaffold formation on AVL construct size (including the AVL, fibrin scaffold, and new tissue growth into the fibrin), growth, and vascularization were assessed and compared to controls.

METHODS

In Sprague Dawley rats, an AVL was created on femoral vessels and inserted into a polycarbonate chamber in the groin in 3 control groups (Series I) and 3 experimental groups (Series II). Two hours before surgery and 6 hours post-surgery, saline (Series I) or enoxaparin sodium (0.6 mg/kg, Series II) was administered intra-peritoneally. Thereafter, the rats were injected daily with saline (Series I) or enoxaparin sodium (1.5 mg/kg, Series II) until construct retrieval at 3, 10, or 21 days. The retrieved constructs underwent weight and volume measurements, and morphologic/morphometric analysis of new tissue components.

RESULTS

Enoxaparin sodium treatment resulted in the development of smaller AVL constructs at 3, 10, and 21 days. Construct weight and volume were significantly reduced at 10 days (control weight 0.337 +/- 0.016 g [Mean +/- SEM] vs treated 0.228 +/- 0.048, [P < .001]: control volume 0.317 +/- 0.015 mL vs treated 0.184 +/- 0.039 mL [P < .01]) and 21 days (control weight 0.306 +/- 0.053 g vs treated 0.198 +/- 0.043 g [P < .01]: control volume 0.285 +/- 0.047 mL vs treated 0.148 +/- 0.041 mL, [P < .01]). Angiogenesis was delayed in the enoxaparin sodium-treated constructs with the absolute vascular volume significantly decreased at 10 days (control vascular volume 0.029 +/- 0.03 mL vs treated 0.012 +/- 0.002 mL [P < .05]).

CONCLUSION

In this in vivo tissue engineering model, endogenous, extra-vascularly deposited fibrin volume determines construct size and vascular growth in the first 3 weeks and is, therefore, critical to full construct development.

Combination of enoxaparin and fibroblast growth factor-1 increases myocardial blood flow and capillary density after myocardial infarction in rabbits

OBJECTIVE

The effect of enoxaparin and fibroblast growth factor-1 (FGF-1) on post-infarction capillary density and regional myocardial blood flow (RMBF) was examined.

METHODS

New Zealand White rabbits received an intramyocardial injection of either physiological saline, FGF-1 + enoxaparin, FGF-1 or enoxaparin directly after ligation of the left anterior descending artery. RMBF and capillary density were investigated using fluorescent microspheres and histological examination.

RESULTS

One week after infarction a significant difference in the number of capillaries could be demonstrated within the FGF-1 + enoxaparin group (p < 0.001 versus the control group), the FGF-1 group (p < 0.01) and the enoxaparin group (p < 0.05). Treatment with FGF-1 + enoxaparin resulted in a significantly increased number of capillaries compared to treatment with FGF-1 (p < 0.05) and enoxaparin (p < 0.05) alone. Additionally, all groups treated with FGF-1 and/or enoxaparin showed a significant increase of microvessel density in the treated ischemic border zone compared to the non-treated ischemic border zone (p < 0.001 for FGF-1 + enoxaparin, p < 0.01 for FGF-1, p < 0.05 for enoxaparin). RMBF was significantly increased within the FGF-1 + enoxaparin group compared to the control group (p < 0.05). Moreover, perfusion rates within the FGF-1 + enoxaparin-treated area did not significantly differ from the pre-infarction values.

CONCLUSION

Treatment with either enoxaparin or FGF-1 or FGF-1 + enoxaparin resulted in increased microvessel growth. However, only the combination of enoxaparin with FGF-1 promotes capillary growth and RMBF. Thus, we conclude that enoxaparin enhances the angiogenic potential of intramyocardially injected FGF-1 in the acutely infarcted rabbit heart.

Low-molecular-weight heparins and angiogenesis

The involvement of the vascular system in malignancy encompasses not only angiogenesis, but also systemic hypercoagulability and a pro-thrombotic state, and there is increasing evidence that pathways of blood coagulation and angiogenesis are reciprocally linked. In fact, cancer atients often display hypercoagulability resulting in markedly increased thromboembolism, which requires anti-coagulant treatment using heparins, for example. Clinical trials reveal that treatment with various low-molecular-weight heparins (LMWHs) improves the survival time in cancer patients receiving chemotherapy compared with those receiving unfractionated standard heparin (UFH) or no heparin treatment, as well as in cancer patients receiving LMWH as thrombosis prophylaxis during primary surgery. This anti-tumor effect of the heparins appears to be unrelated to their anti-coagulant activity, but the mechanisms involved are not fully understood. Tumor growth and spread are dependent on angiogenesis and it is noteworthy that the most potent endogenous pro- and anti-angiogenic factors are heparin-binding proteins that may be affected by systemic treatment with heparins. Heparin and other glycosaminoglycans play a role in vascular endothelial cell function, as they are able to modulate the activities of angiogenic growth factors by facilitating the interaction with their receptor and promoting receptor activation. To date, preclinical studies have demonstrated that only LMWH fragments produced by the heparinase digestion of UFH, i.e. tinzaparin, exert anti-angiogenic effects in any type of tissue in vivo. These effects are fragment-mass-specific and angiogenesis-type-specific. Data on the effect of various LMWHs and UFH on endothelial cell capillary tube formation and proliferation in vitro are also presented. We hope that this paper will stimulate and facilitate future research designed to elucidate whether the anti-angiogenic or anti-tumor effects of commercial LMWHs in their own right are agent specific and whether anti-angiogenic properties increase the anti-tumor properties of the LMWHs in the clinic.

Prophylaxis of Thromboembolism in Critical Care (PROTECT) Trial: a pilot study

PURPOSE

There is no randomized trial comparing low-molecular weight heparin (LMWH) and unfractionated heparin (UFH) for thromboprophylaxis in medical-surgical ICU patients. The primary objective of this randomized pilot study on LMWH vs UFH was to assess the feasibility of conducting a large randomized trial with respect to timely enrollment and blinded study drug administration, practicality of twice-weekly lower limb ultrasounds to screen for deep venous thrombosis, LMWH bioaccumulation and dose adjustment in renal insufficiency, and recruitment rates for a future trial in medical-surgical intensive care unit (ICU) patients. Its additional goals were to evaluate the suitability of the exclusion criteria and to document the range of research activities that precede accrual of patients into a trial to plan multisite management.

MATERIALS AND METHODS

By computerized telephone randomization, we allocated 129 medical-surgical ICU patients to treatment with dalteparin 5,000 IU QD SC or that with UFH 5,000 IU BID SC. Within each clinical center, only the study pharmacist was not blinded. We performed bilateral lower limb compression ultrasounds within 48 hours of ICU admission, twice weekly, on suspicion of deep venous thrombosis, and 7 days after ICU discharge. Research coordinators and investigators at 7 centers reported the time they engaged in all research activities before the first patient was randomized.

RESULTS

Timely complete study drug administration occurred after enrollment. More than 99% of scheduled doses were administered in a blinded fashion. Scheduled ultrasounds were performed without exception. No bioaccumulation of dalteparin was observed when creatinine clearance decreased to lower than 30 mL/min. Average recruitment was 2 patients/center per month before the study exclusion criteria were modified. Study startup activities required, on average, 65.5 hours of combined investigator and research coordinator time at each center. Careful examination of the accrual in the pilot study led to a reexamination of the Prophylaxis of Thromboembolism in Critical Care Trial (PROTECT) study exclusion criteria.

CONCLUSIONS

This pilot study suggests that a multicenter randomized clinical trial comparing LMWH with UFH in critically ill medical-surgical patients is feasible. Pilot studies can improve the design of larger trials and may enhance successful timely completion.

Low molecular weight heparin and unfractionated heparin are both effective at accelerating pulmonary vascular maturation in neonatal rabbits

BACKGROUND

Creation of a bi-directional cavopulmonary shunt after the Norwood procedure for hypoplastic left heart syndrome is delayed to allow pulmonary vascular resistance to fall with maturation of the pulmonary vascular bed. We hypothesized that unfractionated heparin (UFH) and low molecular weight heparin (LMWH), which promote angiogenesis and inhibit smooth muscle cell growth, could accelerate this process.

METHODS AND RESULTS

Fifty-six newborn rabbits were randomly selected to receive UFH 225U/kg (n=12), LMWH 1 mg/kg (n=14), LMWH 10 mg/kg (n=16), or saline (n=14) by subcutaneous injection every 12 hours for 14 days. Treatment with heparin reduced mean pulmonary artery (PA) pressure by 12% to 16% relative to controls [9.0+/-0.2 (UFH), 9.4+/-0.1 (LMWH 1 mg/kg), 9.2+/-0.2 (LMWH 10 mg/kg) versus 10.7+/-0.2 mm Hg (saline), P=0.0001]. Lower PA pressures were associated with reduced alveolar:arterial ratio consistent with enhanced pulmonary angiogenesis in heparin treated animals [8+/-1 (UFH), 13+/-2 (LMWH 1 mg/kg), 12+/-2 (LMWH 10 mg/kg) versus 23+/-5 (saline), P<0.03]. Reduced PA medial wall thickness and muscularization, two additional features of pulmonary vascular maturation, were also more evident in heparin treated animals. Mean PA pressures in 14-day-old rabbits treated with heparin were lower than those measured in control rabbits less than 7 weeks of age suggesting that heparin shortens the pulmonary vascular maturation process by over 60%.

CONCLUSIONS

These results indicate that both UFH and LMWH are effective at accelerating pulmonary vascular maturation in newborn rabbits. This raises the possibility that administration of heparin to children after the Norwood procedure might allow for earlier conversion to a bi-directional cavopulmonary shunt.

Refractory angina pectoris: mechanism and therapeutic options

As the survival of patients with primary coronary events continues to increase, the number of patients presenting with coronary artery disease unsuitable to further revascularization techniques and symptoms refractory to medical therapy also continues to rise. The aims of this review were to define the population of patients with refractory angina pectoris and to present the therapeutic options currently available for this condition. Refractory angina pectoris is defined, and traditional medical therapies are discussed. Then, current therapeutic options for patients with refractory angina are extensively reviewed. A multitude of therapeutic options exist for patients with refractory angina pectoris. Small, uncontrolled studies have shown a potential benefit for additional antiplatelet and antithrombotic therapy. In randomized trials, neurostimulation has been shown to be effective in reducing angina symptoms. Enhanced external counterpulsation is a viable treatment option for select patients with refractory angina. In many randomized trials, laser revascularization has been shown to diminish angina symptoms, although no placebo-controlled studies exist to date. Gene therapy is a promising area of research in this field. Percutaneous in situ coronary venous arterialization is in its infancy, but may be able to treat many patients if proved successful. No data support the role of chelation therapy in this population. Heart transplantation remains a final option for these patients. Further research of the techniques mentioned in this review is warranted. The importance of randomized, double-blinded, placebo-controlled trials cannot be overemphasized, as the placebo effect of these therapies is probably marked.

Alleviation of myocardial ischemia after Kawasaki disease by heparin and exercise therapy

BACKGROUND

Heparin promotes angiogenesis. We evaluated the effects of combined treatment with heparin and exercise on myocardial ischemia in the chronic stage of Kawasaki disease.

METHODS AND RESULTS

This study was conducted in 7 patients (aged 6 to 19 years) who had a totally occluded coronary artery and stress-induced myocardial ischemia in the collateral-dependent areas. Twice-daily exercise using a bicycle ergometer was performed with increments of 0.5 W/kg every 3 minutes up to maximal exertion for 10 days. Heparin, which immediately increased circulating hepatocyte growth factor, was given intravenously 10 minutes before each exercise period. Newly developed myocardial infarction, ventricular tachyarrhythmia, anginal attack, or hemorrhagic complication was not observed in any patient. Dipyridamole-loading single photon emission computed tomography documented improved myocardial perfusion in the collateral-dependent areas and a significant reduction in total defect scores in all patients after the completion of 20 sessions (P=0.01). In control patients who did not receive the heparin-exercise therapy, however, stress defect scores remained unchanged (n=1) or increased (n=2) during follow-up. Computerized quantitative coronary angiography provided evidence that the heparin-exercise therapy increased the diameter of the occluded artery to which collaterals terminated (P=0.001) but not that of the reference artery with which collaterals were not connected (P=0.96).

CONCLUSIONS

The findings suggest that a series of heparin and exercise treatments over 10 days may have a dramatic effect on the alleviation of myocardial ischemia in collateral-dependent regions. This may be a safe, noninvasive revascularization therapy for patients with coronary artery occlusion in the chronic stage of Kawasaki disease.

Role of platelet-activating factor in cardiovascular pathophysiology

Platelet-activating factor (PAF) is a phospholipid mediator that belongs to a family of biologically active, structurally related alkyl phosphoglycerides. PAF acts via a specific receptor that is coupled with a G protein, which activates a phosphatidylinositol-specific phospholipase C. In this review we focus on the aspects that are more relevant for the cell biology of the cardiovascular system. The in vitro studies provided evidence for a role of PAF both as intercellular and intracellular messenger involved in cell-to-cell communication. In the cardiovascular system, PAF may have a role in embryogenesis because it stimulates endothelial cell migration and angiogenesis and may affect cardiac function because it exhibits mechanical and electrophysiological actions on cardiomyocytes. Moreover, PAF may contribute to modulation of blood pressure mainly by affecting the renal vascular circulation. In pathological conditions, PAF has been involved in the hypotension and cardiac dysfunctions occurring in various cardiovascular stress situations such as cardiac anaphylaxis and hemorrhagic, traumatic, and septic shock syndromes. In addition, experimental studies indicate that PAF has a critical role in the development of myocardial ischemia-reperfusion injury. Indeed, PAF cooperates in the recruitment of leukocytes in inflamed tissue by promoting adhesion to the endothelium and extravascular transmigration of leukocytes. The finding that human heart can produce PAF, expresses PAF receptor, and is sensitive to the negative inotropic action of PAF suggests that this mediator may have a role also in human cardiovascular pathophysiology.

Effects of the repeated administration of adenosine and heparin on myocardial perfusion in patients with chronic stable angina pectoris

The mechanism by which ischemia stimulates angiogenesis is unknown. Adenosine is released during myocardial ischemia and may be a mediator of this process. Experimental data suggest that heparin may enhance this effect. The purpose of this open-labeled, placebo-controlled trial was to determine whether repeated intravenous administration of adenosine and heparin could mimic physiologic angiogenesis and reduce the amount of exercise-induced myocardial ischemia in patients with coronary artery disease. Subjects with chronic stable angina refractory to conventional medical therapy and not suitable for revascularization received either adenosine (140 microg/kg/min for 6 minutes) and heparin (10,000 U bolus), (n = 14), or placebo, (n = 7) daily for 10 days. All patients underwent baseline and follow-up exercise testing with thallium-201 single-photon emission computed tomography myocardial perfusion imaging. A semiquantitative assessment of the extent and severity of the perfusion abnormalities was calculated by 2 blinded investigators. There was no significant change in exercise duration or in the peak heart rate systolic blood pressure product associated with adenosine and heparin compared with placebo treatment. There was, however, a 9% reduction in the extent (60.6 +/- 4.0 vs 54.9 +/- 4.1, p = 0.03) and a 14% improvement in severity (41.5 +/- 3.2 vs 35.7 +/- 2.9, p = 0.01) of the myocardial perfusion abnormalities seen in patients who received adenosine and heparin compared with placebo. Thus, in this pilot study, repeated administration of adenosine and heparin reduced the amount of exercise-induced ischemia in patients with chronic stable angina refractory to conventional treatment.

Heparin potentiates collateral growth but not growth of intramyocardial endarteries in dogs with repeated coronary occlusion

Heparin accelerates coronary collateral development in various animal models of myocardial ischemia. The purpose of this study was to clarify the beneficial effect of heparin on canine collateral development. Seventeen adult mongrel dogs were instrumented for measurements of a subendocardial segment length in the central area perfused by the left circumflex coronary artery, its flow, and left ventricular pressure. A pulsed Doppler flow probe and an externally inflatable pneumatic occluder were placed around the proximal circumflex artery. After the recovery from surgery, 2-min circumflex coronary artery occlusions were repeated eight times at 58-min intervals daily. After excluding seven dogs with well-developed preexisting collateral circulation, ten dogs were randomized into two groups with (n = 5) and without (n = 5) heparin treatment. The total occlusion time until adequate collateral development (an index of collateral growth) was 164+/-34 (SD) min in dogs with heparin treatment, being significantly less than 289+/-49 min in dogs without heparin (p<0.01). In contrast, the extent of the reduction in resting blood flow of the repeatedly occluded circumflex artery (an index of neovascularization toward the ischemic area) was comparable in dogs with and without heparin (15.4+/-12.4% vs. 21.1+/-13.6%, p=NS). Heparin promotes nonsprouting angiogenesis (arteriogenesis) of preformed collateral vessels but not neovascularization toward the ischemic area in dogs with brief repetitive coronary occlusions.

Low molecular weight heparins: current use and indications

Thromboembolic complications are associated with significant morbidity and mortality in postoperative patients. For many years, unfractionated heparin has been used successfully in primary and secondary prophylaxis of these complications. In recent times, however, the usefulness of LMWHs has caught the attention of clinicians because of improved bioavailability, predictable anticoagulation, ease of administration, and the lack of need for monitoring anticoagulation. In clinical situations, LMWHs have been tested and proved to be safe and equipotent or supe rior when compared with unfractionated heparin or warfarin (Table 5). It is clear from clinical trials that LMWHs are superior in primary prophylaxis of DVT in orthopaedic surgical procedures, treatment of unstable angina, and in patients with multiple traumas. LMWHs were also tested and found to be an acceptable alternative to unfractionated heparin in both the primary prophylaxis of DVT in high risk general surgical procedures and in the treatment of patients with DVT and pulmonary embolism. However, the role of LMWHs in ischemic heart diseases, valvular heart diseases, postcoronary angioplasty, and vascular surgery remains to be proved. The major impact of LMWHs would be in allowing clinicians to treat PE and DVT in an outpatient setting, which would directly impact medical economics. LMWHs are associated with similar complications as unfractionated heparin is, but the complications occur less frequently. Currently, the main limitation in using LMWHs in place of unfractionated heparin or warfarin is its cost. However, taking into account the cost incurred by hospitalization and longterm monitoring of anticoagulation in patients treated with unfractionated heparin, certain trials have proved the cost of LMWHs to be the same or less than the cost of unfractionated heparin overall. We envision that LMWHs will be widely used in the future and will bring welcomed change in the treatment of thromboembolic diseases.

The coronary angiogenetic effect of heparin: experimental basis and clinical evidence

Heparin is a highly sulfated polysaccharide consisting of a repeating disaccharide structure as found in other glycosaminoglycanes. The intravenous and subcutaneous formulation of the drug is routinely used for its well-known, time-honored antithrombotic effect. However, available evidences linking heparin to angiogenesis raise the possibility of a therapeutically relevant antiischemic effect of the drug. Molecular biology data show that in a hypoxic milieu heparin could facilitate angiogenesis through interactions with a family of polypeptide growth factor mitogens that stimulate endothelial cell proliferation. Experimental data suggest that heparin can augment collateral circulation when combined with other potentially angiogenetic factors, such as repeated ischemia, coronary occlusion, or physical exercise. Clinical data, although very initial, encompassing a total of only 41 heparin-treated patients with coronary artery disease, suggest that heparin facilitates collateral development stimulated by exercise-induced myocardial ischemia in humans. According to the heparin-collateral hypothesis, the mechanism of action of heparin as an antiischemic medication would be independent of its anticoagulant action. The molecular targets of heparin are Factor Xa and IIa for antithrombotic action, heparin-binding growth factors (including fibroblast growth factor and vascular endothelial growth factor) for angiogenesis. The antithrombotic effect is not linked to a cellular target, whereas the angiogenetic effect directly stimulates endothelial cells. The molecular cofactor required for effect is antithrombin III for antithrombosis, and possibly endogenous adenosine for angiogenesis. The therapeutic effect is achieved within minutes or hours for antithrombosis, and within weeks or months for angiogenesis.

Refractory angina pectoris in end-stage coronary artery disease: evolving therapeutic concepts

Refractory angina pectoris in coronary artery disease is defined as the persistence of severe anginal symptoms despite maximal conventional antianginal combination therapy. Further, the option to use an invasive revascularization procedure such as percutaneous coronary balloon angioplasty or aortocoronary bypass grafting must be excluded on the basis of a recent coronary angiogram. This coronary syndrome, which represents end-stage coronary artery disease, is characterized by severe coronary insufficiency but only moderately impaired left ventricular function. Almost all patients demonstrated severe coronary triple-vessel disease with diffuse coronary atherosclerosis, had had one or more myocardial infarctions, and had undergone aortocoronary bypass grafting (70% of cases). We present three new approaches with antiischemic properties: long-term intermittent urokinase therapy, transcutaneous and spinal cord electrical nerve stimulation, and transmyocardial laser revascularization.

Effect of basic fibroblast growth factor on myocardial angiogenesis in dogs with mature collateral vessels

OBJECTIVES

We sought to evaluate the potential of basic fibroblast growth factor (bFGF) to enhance coronary collateral perfusion in dogs with chronic single-vessel coronary occlusion. A secondary goal was to examine whether the salutary effects of bFGF treatment, previously proved effective in the short term, would be maintained in the long term (6 months).

BACKGROUND

bFGF, an angiogenic growth factor, is currently the subject of a Phase I trial in patients with ischemic heart disease. It has been shown to promote collateral development in dogs with progressive coronary occlusion when given during the period of natural collateralization. The effect of bFGF on quiescent collateral vessels, a subject of significant clinical importance, is uncertain.

METHODS

Dogs were subjected to ameroid-induced occlusion of the left circumflex coronary artery and randomized to bFGF (1.74 mg/day for 7 days), a regimen previously proved effective, or to saline solution. Maximal collateral perfusion was assessed 6 months later, and the dogs were reassigned to a course of bFGF or saline solution. Collateral perfusion was reevaluated after the second treatment course.

RESULTS

At 6 months, collateral function was identical in the groups treated initially with bFGF and saline solution. The subsequent course of bFGF did not induce further collateralization.

CONCLUSIONS

Although we previously demonstrated the salutary effects of this bFGF regimen in the short term (5 weeks), collateral flow in control dogs reached parity with that of bFGF-treated dogs after 6 months. bFGF did not induce further collateralization in dogs with mature collateral vessels, underscoring the priming role of ischemia for bFGF-induced collateral development.

Dalteparin: a low-molecular-weight heparin

OBJECTIVE

To discuss the chemistry, pharmacology, and pharmacokinetics of dalteparin, a low-molecular-weight heparin (LMWH), and to review the comparative clinical trial data evaluating the efficacy and safety of dalteparin and unfractionated heparin (UH) for the prophylaxis and treatment of venous thromboembolism.

DATA SOURCES

A MEDLINE search identified pertinent English-language publications on dalteparin and venous thromboembolism. Key search terms were dalteparin, Fragmin, LMWH, and venous thromboembolism. The search was supplemented by review articles, articles obtained from the bibliographies of the review articles, and the dalteparin approval database.

STUDY SELECTION

The most pertinent studies describing the pharmacology and pharmacokinetics of dalteparin in humans were selected; all abstracts and clinical evaluating the use of dalteparin for antithrombotic therapy were reviewed. Review articles by authors of international reputation were selected.

DATA EXTRACTION

Pertinent information from the review articles on the pharmacology of LMWHs and UH was summarized. Clinical trial data were extracted for study design, patient demographics, therapeutic regimens, methods of evaluation, and outcomes.

DATA SYNTHESIS

Dalteparin is an LMWH indicated for patients undergoing abdominal surgery who are considered to be at risk for deep-vein thrombosis (DVT), which may lead to pulmonary embolism (PE). In this population, numerous clinical trials have demonstrated comparable efficacy between dalteparin and fixed-dose UH for DVT prophylaxis. Dalteparin has a predictable dose response and can be administered as a standard single daily subcutaneous dose for all patients. In therapeutic doses, dalteparin does not alter coagulation tests and therefore does not require routine laboratory monitoring, in contrast with adjusted-dose UH. Bleeding risks with dalteparin are comparable with and possibly less than those associated with UH. Preliminary studies suggest that dalteparin may be effective for other indications, including DVT prophylaxis for hip replacement surgery and the treatment of DVT and PE. Comparative cost-effectiveness data are not yet available.

CONCLUSIONS

Dalteparin is the second LMWH to receive approval by the Food and Drug Administration. Dalteparin is indicated for prophylaxis against DVT in patients undergoing abdominal surgery. Clinical studies have shown that single daily doses of dalteparin provide a safe and effective alternative to fixed-dose UH therapy. Additional studies are needed to determine the cost-effectiveness of dalteparin compared with UH and other LMWHs.

Antithrombotic treatment in stable coronary syndromes: long-term intermittent urokinase therapy in end-stage coronary artery disease and refractory angina pectoris

Interventions that modify lipid metabolism and blood coagulation have been shown to favourably influence the natural course of coronary artery disease in terms of the primary prevention and treatment of acute cardiovascular events. Various findings suggest that such interventions may also preserve and enhance myocardial perfusion in the chronic stage of the disease. Long-term intermittent urokinase therapy was developed for patients with end-stage coronary artery disease and refractory angina pectoris. A dose of 500,000 IU of urokinase given intravenously as a bolus three times a week for of 12 weeks reduced symptoms by 70% and was accompanied by objective improvements in myocardial perfusion and an increase of ergometric exercise capacity. The possible therapeutic mechanisms of long-term intermittent urokinase therapy-improvement of rheological blood properties mediated by fibrinogen reduction, thrombolysis of non-occlusive subclinical thrombi, and regression of atherosclerotic plaques-are discussed in the context of other antithrombotic approaches.

Exercise training and heparin pretreatment in patients with coronary artery disease

The purpose of this study was to evaluate whether combined treatment with a cardiovascular exercise rehabilitation program and low doses of heparin can induce changes in ergometric parameters of ischemia in patients with coronary artery disease (CAD). Heparin may potentiate the development of new vessels promoted by ischemia and therefore may produce important clinical improvement. Thirty-six patients with stable CAD and evidence of myocardial ischemia on exercise testing were randomized into three groups: a control group (n = 11) received the usual medical treatment; another group (n = 11) underwent three exercise sessions per week during 12 weeks; and a third group (n = 14) undertook this exercise program and also received calcium heparin 12,500 IU subcutaneously 20 to 30 minutes before each exercise session. Pretreatment and posttreatment exercise tests were compared. Patients who underwent the rehabilitation program had an increase in exercise duration and workload at the onset of 1 mm ST-segment depression, but only patients who received calcium heparin showed a significant increase in rate-pressure product at the ST-segment ischemic threshold (p = 0.035). This result suggests that higher levels of myocardial oxygen consumption were now tolerated, a change that may be related to an improvement in myocardial perfusion.

Long-term intermittent urokinase therapy in patients with end-stage coronary artery disease and refractory angina pectoris: a randomized dose-response trial

OBJECTIVES

This dose-response study was designed to test two low dose regimens of urokinase administered over a prolonged time period in patients with chronic refractory angina pectoris with respect to effects on clinical symptoms and objective variables of myocardial ischemia.

BACKGROUND

Patients with severe and chronic refractory angina pectoris in end-stage coronary artery disease represent an increasing clinical problem. Favorable therapeutic effects on myocardial ischemia have been reported for long-term application of low dose urokinase.

METHODS

Ninety-eight patients with chronic refractory and end-stage coronary artery disease were randomly assigned to two treatment groups: group A (49 patients) received 50,000 IU and group B (49 patients) 500,000 IU of urokinase as an intravenous bolus infection three times a week over a period of 12 weeks. Variables evaluated were number of weekly anginal events, data from ergometric exercise testing with simultaneous electrocardiographic registration, semiquantitative evaluation of Tc-99m 2-methoxy isobutyl isonitrile (MIBI) scans and rheologic variables.

RESULTS

After 12 weeks of treatment, anginal symptoms (events/week) were reduced significantly in group B by 70% compared with 24% in group A (p < 0.001). Fibrinogen decreased by 3% in group A and by 33% in group B (p < 0.001). Plasma viscosity and red blood cell aggregation were reduced by 6.4% (p < 0.001) and 19.9% (p < 0.001), respectively, in group B. Objective variables of myocardial ischemia were improved significantly in group B only. No cumulation of coronary ischemic events was observed in group B.

CONCLUSIONS

Long-term intermittent urokinase therapy in an applied dose of 3 X 500,000 IU/week represents an effective anti-ischemic and antianginal approach for patients with refractory angina pectoris and end-stage coronary artery disease. Apart from rheologic improvement, antithrombotic properties and plaque regression are likely anti-ischemic mechanisms.

Chronic-intermittent urokinase therapy in patients with end-stage coronary artery disease and refractory angina pectoris--a pilot study

Patients with coronary artery disease and severe angina pectoris refractory to conventional medical treatment (beta blockers, nitrates, calcium antagonists) and without the option for invasive revascularization procedures represent an increasing clinical problem. For these patients, chronic-intermittent urokinase therapy has been developed. Twenty patients received 500,000 IU urokinase as intravenous bolus injection 3 times a week over a period of 12 weeks. The average reduction in anginal symptoms in 19 patients was 74%, from 23.5 +/- 10.8 to 5.2 +/- 4.8 events/week (p < 0.001); 1 patient was excluded from further treatment because of an increase of > 66% in anginal events. Fibrinogen decreased by 34% from 370 +/- 57 to 244 +/- 44 mg/dl (p < 0.001), the rheological parameters plasma viscosity by 6.1% from 1.39 +/- 0.04 to 1.31 +/- 0.03 mPas (< 0.001), and red blood cell aggregation by 18% from 13.9 +/- 2.4 to 11.2 +/- 2.2 (p < 0.001). Exercise tolerance increased by 51%. Average ST-segment depression decreased from 0.16 +/- 0.10 to 0.12 +/- 0.09 (p < 0.01). After 12 weeks of follow-up, angina pectoris and fibrinogen levels were still significantly reduced compared with baseline values. Chronic-intermittent urokinase therapy represents an effective anti-ischemic and antianginal approach in patients with refractory angina pectoris and end-stage coronary artery disease. Improvement of rheological blood properties and thrombolytic effects are likely therapeutic mechanisms.

Angiogenesis: mechanistic insights, neovascular diseases, and therapeutic prospects

This review of angiogenesis aims to describe (a) stimuli that either elicit or antagonize angiogenesis, (b) the response of the vasculature to angiogenic or anti-angiogenic stimuli, i.e., processes required for the formation of new vessels, (c) aspects of angiogenesis relating to tissue remodeling and disease, and (d) the potential of angiogenic or antiangiogenic therapeutic measures. Angiogenesis, the formation of new vessels from existing microvessels, is important in embryogenesis, wound healing, diabetic retinopathy, tumor growth, and other diseases. Hypoxia and other as yet ill-defined stimuli drive tumor, inflammatory, and connective tissue cells to generate angiogenic molecules such as vascular endothelial growth factor (VEGF), fibroblast growth factor (FGF), transforming growth factor-beta (TGF-beta), platelet-derived growth factor (PDGF), and others. Natural and synthetic angiogenesis inhibitors such as angiostatin and thalidomide can repress angiogenesis. Angiogenic and antiangiogenic molecules control the formation of new vessels via different mechanisms. VEGF and FGF elicit their effects mainly via direct action on relevant endothelial cells. TGF-beta and PDGF can attract inflammatory or connective tissue cells which in turn control angiogenesis. Additionally, PDGF may act differently on specific phenotypes of endothelial cells that are engaged in angiogenesis or that are of microvascular origin. Thus phenotypic traits of endothelial cells committed to angiogenesis may determine their cellular responses to given stimuli. Processes necessary for new vessel formation and regulated by angiogenic/antiangiogenic molecules include the migration and proliferation of endothelial cells from the microvasculature, the controlled expression of proteolytic enzymes, the breakdown and reassembly of extracellular matrix, and the morphogenic process of endothelial tube formation. In animal models some angiogenesis-dependent diseases can be controlled via induction or inhibition of new vessel formation. Life-threatening infantile hemangiomas are a first established indication for antiangiogenic therapy in humans. Treatment of other diseases by modulation of angiogenesis are currently tested in clinical trials. Thus the manipulation of new vessel formation in angiogenesis-dependent conditions such as wound healing, inflammatory diseases, ischemic heart and peripheral vascular disease, myocardial infarction, diabetic retinopathy, and cancer is likely to create new therapeutic options.

Basic view on the pathobiology of myocardial ischemia during coronary angioplasty: implications for cardiac protection

PTCA is not only an effective therapeutic tool but a unique opportunity to study the pathobiology of the human myocardium during ischemia and reperfusion. In addition, it is a good model to assess potential therapeutic interventions. Studies performed during PTCA contributed significantly to the understanding of the metabolic, electrophysiologic, hemodynamic, and coronary perfusion changes in the human heart following coronary occlusion. Combining the data from experimental models and human patients may lead to better techniques for myocardial protection during PTCA and consequently reduce the risk of patients undergoing mechanical revascularization.

Prospective, randomized, placebo-controlled, double-blind, multicenter study of exercise with enoxaparin pretreatment for stable-effort angina

In this double-blind, placebo-controlled, multicenter trial, we examined the combined effects of repeated exercise and intravenous enoxaparin (low-molecular-weight heparin) on treadmill exercise capacity and angiographic collateral growth and compared them with the effect of repeated exercise with placebo. Fifty-two patients with stable-effort angina were randomly assigned to receive one of two doses of enoxaparin (40 or 60 mg) or placebo. In each patient, 20 treadmill exercise sessions were performed with the pretreatment of enoxaparin or placebo for 2 to 3 weeks. Before and after treatment, coronary cineangiography was repeated to evaluate the changes in coronary and collateral circulation. Improvement of rate-pressure product (RPP) at the onset of angina was taken as an index of enhanced collateral flow reserve. Although the mean differences in the magnitude of increase in RPP were not significantly different between the 3 groups, a heterogeneous response was observed: 1620 beats/min.mm Hg in 40 mg (p = 0.12), 3060 beats/min.mm Hg in 60 mg (p = 0.02), and 1090 beats/min.mm Hg in placebo (p = 0.44). The end-points of the exercise test were changed from chest discomfort to leg fatigue or dyspnea in 10 (28%) of 36 enoxaparin-treated patients but in only 1 (6%) of 16 placebo patients (p = value not significant (NS)). Similarly, the extent of coronary and collateral circulation to the completely obstructed coronary artery was increased in 17 (47%) of 36 enoxaparin-treated patients but only in 4 (25%) of 16 placebo patients (p = NS).(ABSTRACT TRUNCATED AT 250 WORDS)

Site-specific therapeutic angiogenesis after systemic administration of vascular endothelial growth factor

PURPOSE

Recent experimental studies have established the feasibility of therapeutic angiogenesis; in all cases, this has been achieved with local administration of angiogenic growth factors. This study was designed to investigate the hypothesis that systemic administration of an angiogenic growth factor specifically mitogenic for endothelial cells--vascular endothelial growth factor (VEGF)--could augment collateral vessel development in a rabbit ischemic hindlimb model.

METHODS

Ten days after the ligation of the external iliac artery and excision of the common and superficial femoral arteries in one limb of New Zealand white rabbits, heparin (800 IU, n = 13), VEGF (1 mg, n = 3; 5 mg, n = 5), heparin (800 IU) + VEGF (1 mg, n = 5; 5 mg, n = 7), or saline solution (n = 8) was injected as a single bolus in a marginal ear vein. Collateral vessel formation and limb perfusion were assessed 10 and 30 days after treatment.

RESULTS

Animals in both VEGF-treated groups had a significantly higher (p < 0.01) increase in calf blood pressure ratio at day 10 (control, 0.44 +/- 0.02; heparin, 0.47 +/- 0.02; VEGF, 0.60 +/- 0.01; heparin+VEGF, 0.61 +/- 0.02) and day 30 (control, 0.49 +/- 0.05; heparin, 0.48 +/- 0.02; VEGF, 0.70 +/- 0.03; heparin+VEGF, 0.73 +/- 0.03). Both VEGF-treated groups had a significantly higher (p < 0.05) angiographic score at day 30 (control, 0.28 +/- 0.01; heparin, 0.28 +/- 0.01; VEGF, 0.37 +/- 0.01; heparin+VEGF, 0.38 +/- 0.02). Maximum flow reserve at day 30 in the ischemic limb was higher (p < 0.05) in VEGF-treated rabbits (control, 1.87 +/- 0.07; heparin, 1.92 +/- 0.08; VEGF, 2.42 +/- 0.16; heparin+VEGF, 2.33 +/- 0.12). Capillary density was higher (p < 0.01) in the ischemic muscles of VEGF-treated rabbits (control, 156 +/- 10/mm2; heparin, 178 +/- 8/mm2; VEGF, 230 +/- 10/mm2; heparin+VEGF, 233 +/- 8/mm2).

CONCLUSIONS

This series of in vivo experiments demonstrates that intravenous administration of VEGF, with or without heparin, results in both anatomic and physiologic evidence of enhanced collateral vessel formation in the rabbit ischemic hindlimb. Single-bolus systemic administration of VEGF may be a feasible therapeutic strategy in patients with lower-extremity ischemia.

Effect of coronary collateral circulation on myocardial ischemia and ventricular dysfunction

Although a functional role of coronary collaterals has been continuously debated, we observed the following facts in our studies during intracoronary thrombolytic therapy: (a) Myocardial ischemia is important for the development of collateral circulation, (b) collaterals can perfuse the infarcted myocardium, and (c) the presence of collaterals prevents the left ventricular aneurysm formation in acute myocardial infarction, even when the amount of the salvaged tissue is small. Thus, coronary collaterals are not merely markers of severe ischemia but help to preserve the functional integrity of the myocardium in the presence of coronary obstruction. We then attempted to promote collateralization to treat patients with angina pectoris. Patients with chronic stable effort angina were treated with heparin followed by treadmill exercise twice a day for 10 days. Treadmill capacity was found to improve in association with an increase in coronary collateral circulation. Heparin treatment of ischemic patients was found to be a noninvasive alternative to percutaneous transluminal coronary angioplasty and coronary bypass surgery for patients who are not candidates for invasive procedures.