Manipulation of the Renin Angiotensin System in Peripheral Arterial Disease

Pioneering new frontiers in circadian medicine chronotherapies for cardiovascular health

Cardiovascular disease (CVD) is a global health concern. Circadian medicine improves cardiovascular care by aligning treatments with our body's daily rhythms and their underlying cellular circadian mechanisms. Time-based therapies, or chronotherapies, show special promise in clinical cardiology. They optimize treatment schedules for better outcomes with fewer side effects by recognizing the profound influence of rhythmic body cycles. In this review, we focus on three chronotherapy areas (medication, light, and meal timing) with potential to enhance cardiovascular care. We also highlight pioneering research in the new field of rest, the gut microbiome, novel chronotherapies for hypertension, pain management, and small molecules that targeting the circadian mechanism.

Circadian Influences on Myocardial Ischemia-Reperfusion Injury and Heart Failure

The impact of circadian rhythms on cardiovascular function and disease development is well established, with numerous studies in genetically modified animals emphasizing the circadian molecular clock's significance in the pathogenesis and pathophysiology of myocardial ischemia and heart failure progression. However, translational preclinical studies targeting the heart's circadian biology are just now emerging and are leading to the development of a novel field of medicine termed circadian medicine. In this review, we explore circadian molecular mechanisms and novel therapies, including (1) intense light, (2) small molecules modulating the circadian mechanism, and (3) chronotherapies such as cardiovascular drugs and meal timings. These promise significant clinical translation in circadian medicine for cardiovascular disease. (4) Additionally, we address the differential functioning of the circadian mechanism in males versus females, emphasizing the consideration of biological sex, gender, and aging in circadian therapies for cardiovascular disease.

Long-term mortality benefit of renin-angiotensin system inhibitors in patients with chronic limb-threatening ischemia undergoing vascular intervention

OBJECTIVE

The beneficial effect of renin-angiotensin system (RAS) inhibitors has been well-established in patients with cardiovascular disease; however, their effectiveness in patients with chronic limb-threatening ischemia (CLTI), a selected disease-burdened population, is largely unknown. The purpose of this study was to evaluate long-term outcomes of RAS inhibitor use in patients with CLTI undergoing a vascular intervention.

METHODS

For this study, all patients with CLTI undergoing a first-time revascularization (bypass or endovascular) were analyzed at our institution between 2005 and 2014. Patients discharged on an RAS inhibitor (angiotensin-converting enzyme inhibitor or angiotensin receptor blocker) were compared with those not on an RAS inhibitor. The inverse probability of treatment weighting with additional regression analyses were used to determine the long-term risk of mortality and major adverse events. A sensitivity analysis was performed to assess the dose-related therapeutic response of RAS inhibitors (low-dose vs high-dose therapy).

RESULTS

Between 2005 and 2014, 1303 limbs from 1161 patients were identified. Of these patients, 52% were discharged on an RAS inhibitor, with 67% discharged on a high-dose therapy and 33% on a low-dose therapy. Patients discharged on an RAS inhibitor suffered more frequently from diabetes, hypertension, and myocardial infarction, whereas those not on an RAS inhibitor had more chronic kidney disease (all P < .05). There was no difference in the proportion of patients presenting with tissue loss. After adjustment for these and other baseline covariates, RAS inhibitor use was associated with less late mortality (hazard ratio [HR], 0.78; 95% confidence interval [CI], 0.65-0.94). Discharge on a high-dose RAS inhibitor was associated with lower mortality (HR, 0.70; 95% CI, 0.57-0.86), whereas a low-dose RAS inhibitor was not associated with less mortality (HR, 0.95; 95% CI, 0.73-1.24) compared with patients not prescribed an RAS inhibitor. This association remained significant when comparing high-dose with low-dose therapy (HR, 0.74; 95% CI, 0.55-0.98). No associations were found between RAS inhibitor use and major adverse limb event (HR, 0.95; 95% CI, 0.73-1.22), major amputation (HR, 0.82; 95% CI, 0.57-1.18), or reintervention (HR, 1.05; 95% CI, 0.85-1.31). These point estimates were not different for those on angiotensin-converting enzyme inhibitors vs angiotensin receptor blockers, nor were they affected by the type of revascularization.

CONCLUSIONS

Patients with CLTI prescribed an RAS inhibitor at discharge demonstrated significantly less long-term mortality, whereas limb events were unaffected. These data indicate that, in these heavily burdened patients, the benefit is restricted to those on a high dose, which underscores the importance of attaining these doses.

Randomized clinical trial of angiotensin-converting enzyme inhibitor, ramipril, in patients with intermittent claudication

Background

The aim was to investigate the effect of ramipril on clinical parameters in patients with peripheral arterial disease.

Methods

Patients with intermittent claudication were randomized to receive ramipril or placebo for 24 weeks in a double-blind study. Outcome measures were walking distance, arterial stiffness measurement and quality of life (QoL).

Results

A total of 33 patients were included (25 men; mean(s.d.) age 64·6(7.8) years); 14 received ramipril and 19 placebo. After 24 weeks, ramipril improved maximum treadmill walking distance by an adjusted mean (95 per cent confidence interval, c.i.) of 131 (62 to 199) m (P = 0·001), improved treadmill intermittent claudication distance by 122 (56 to 188) m (P = 0·001) and improved patient-reported walking distance by 159 (66 to 313) m (P = 0·043) compared with placebo. Ramipril reduced carotid femoral pulse wave velocity by –1·47 (95 per cent c.i. –2·40 to –0·57) m/s compared with placebo (P = 0·002). Resting ankle : brachial pressure index (ABPI) improved slightly in both ramipril and placebo groups (0·02 (95 per cent c.i. –0·08 to 0·11) versus 0·03 (–0·05 to 0·10); P = 0·830). Ramipril had a slight, non-significant effect on QoL physical domains compared with placebo.

Conclusion

Ramipril improved walking distance in patients with claudication; however, this improvement was not related to improved ABPI but might have been due to ramipril reducing arterial stiffness. Registration number: NCT01037530 (http://www.clinicaltrials.gov).

The primary benefits of angiotensin-converting enzyme inhibition on cardiac remodeling occur during sleep time in murine pressure overload hypertrophy

OBJECTIVES

Our objective was to test the hypothesis that there is a significant diurnal variation for the therapeutic benefit of angiotensin-converting enzyme (ACE) inhibitors on pressure-overload cardiovascular hypertrophy.

BACKGROUND

Physiological and molecular processes exhibit diurnal rhythms that may affect efficacy of disease treatment (chronotherapy). Evidence suggests that the heart primarily remodels during sleep. Although a growing body of clinical and epidemiological evidence suggests that the timing of therapy, such as ACE inhibition, alters diurnal blood pressure patterns in patients with hypertension, the benefits of chronotherapy on myocardial and vascular remodeling have not been studied.

METHODS

We examined the effects of the short-acting ACE inhibitor, captopril, on the structure and function of cardiovascular tissue subjected to pressure overload by transverse aortic constriction (TAC) in mice. Captopril (15 mg/kg intraperitoneally) or placebo was administered at either murine sleep time or wake time for 8 weeks starting 1 week after surgery.

RESULTS

TAC mice given captopril at sleep time had improved cardiac function and significantly decreased heart: body weight ratios, myocyte cross-sectional areas, intramyocardial vascular medial wall thickness, and perivascular collagen versus TAC mice given captopril or placebo during wake time. Captopril induced similar drops in blood pressure at sleep or wake time, suggesting that time-of-day differences were not attributable to blood pressure changes. These beneficial effects of captopril were correlated with diurnal changes in ACE mRNA expression in the heart.

CONCLUSIONS

The ACE inhibitor captopril benefited cardiovascular remodeling only when administered during sleep; wake-time captopril ACE inhibition was identical to that of placebo. These studies support the hypothesis that the heart (and vessels) remodel during sleep time and also illustrate the importance of diurnal timing for some cardiovascular therapies.

Multilocus analysis in candidate genes ACE, AGT, and AGTR1 and predisposition to peripheral arterial disease: role of ACE D/-240T haplotype

OBJECTIVE

Peripheral arterial disease (PAD) is a common manifestation of systemic atherosclerosis. Apart from traditional cardiovascular risk factors, several novel biologic mediators and genetic predisposing factors appear relevant in determining the atherogenetic process leading to PAD. Genes encoding for renin angiotensin system (RAS) components have been proposed as candidate in atherosclerosis. This study investigated four polymorphisms in angiotensinogen (AGT), angiotensin converting enzyme (ACE), and angiotensin II receptor type 1 (AGTR1), genes of RAS, in both predicting PAD and modulating the severity of the disease.

METHODS

The ACE I/D and -240A>T, AGT M235T, and AGTR1 1166A>C polymorphisms were analyzed in 281 PAD patients and in 485 controls comparable for age and sex.

RESULTS

The ACE D and -240T alleles both significantly influenced the predisposition to PAD. The ACE D, but not -240 T, allele remained associated with PAD after Bonferroni correction (P = .004) and adjustment for cardiovascular risk factors (P = .03). The ACE D allele influenced PAD predisposition with a dose-dependent effect (odds ratio for ACE ID vs II genotype, 1.77; P = .006; ACE DD vs II genotype, 2.15; P = .001). The haplotype reconstruction analysis for the ACE gene showed that the D/-240T haplotype significantly and independently influenced the predisposition to PAD (P = .02). In 190 PAD patients with no additional atherosclerotic localizations (isolated PAD), a significant association between ACE D and -240T alleles and PAD was observed. Only the ACE D allele remained associated with isolated PAD after Bonferroni correction (P = .02) and after adjustment for cardiovascular risk factors (P = .02). The haplotype reconstruction analysis for the ACE gene showed that the D/-240T, but not the D/-240A haplotype significantly influenced the predisposition to PAD (P = .0003). No influence of the polymorphisms analyzed on the severity of the disease, according to Rutherford categories, was found.

CONCLUSIONS

The present study contributes data to highlight the role of the ACED/-240T haplotype in predisposing to PAD, also in the absence of other atherosclerotic comorbidities.

Effect of ramipril on renal function in patients with intermittent claudication

BACKGROUND

The Heart Outcomes Prevention Study (HOPE) demonstrated that ramipril resulted in a blood-pressure-independent 25% reduction in cardiovascular events in patients with peripheral arterial disease (PAD). Despite this, general practitioners and vascular surgeons remain reluctant to prescribe ACE inhibitors in this group of patients because of concerns about renal artery stenosis (RAS). We aimed to define the effect of ramipril on renal function in patients with intermittent claudication (IC).

METHODS AND RESULTS

Of 132 unselected patients with IC entering the study 78 (59%) were excluded due to: current ACE inhibitor use (38%), renal impairment (serum creatinine above normal range) (15%), known severe RAS (1%) or unwillingness to participate (5%). The remaining 54 patients were titrated to 10 mg ramipril and renal function was monitored at 1, 5, and 12 weeks. Treatment was discontinued during titration in 5 patients due to symptoms (3) or lack of compliance (2). In the remainder, median [IQR] serum creatinine increased (94 [85.8-103.3] to 98 [88.0-106.5] micromol/L, p < or = 0.001) and median [IQR] GFR decreased (71.5 [64.6-82.3] to 68.7 [59.8-74.7] mL/min per 1.73 m2, p < or = 0.001) between baseline and 5 weeks. These changes were not considered clinically significant. By 12 weeks these values had returned almost to baseline (Cr 95.5 [88.0-103.25] micromol/L, GFR 71.8 [65.3-77.4] mL/min). No patient had a serum creatinine rise > 30%.

CONCLUSION

Most of patients with IC and a normal serum creatinine can be safely commenced on ramipril provided they are screened, titrated and monitored as described above. Studies in patients with borderline renal impairment (serum creatinine up to 30% above baseline) are on-going.

Optimal medical management of peripheral arterial disease

Patients with peripheral vascular disease are less likely to receive optimal medical management than patients with coronary artery disease. However, early medical treatment is critical because it is profoundly beneficial and the benefits are maximized. Even in patients with advanced disease requiring invasive intervention, medical management has been proven to improve outcome, prolong the success of the intervention, improve functional capacity, and prolong life. The vascular surgeon should be knowledgeable enough to initiate basic medical therapy and to define for their patients the goals that need to be met to optimize their medical management. The vascular surgeon should be instrumental in assuring that the peripheral vascular patient receives medical therapy of the same standard as the patient with coronary disease. The major modifiable risk factors in the vascular patient are: smoking, high blood pressure, hyperlipidemia, physical inactivity, obesity, and diabetes. In addition, the use of beta blockers for patients with coronary disease and antiplatelet therapy as well as angiotensin-converting enzyme (ACE) inhibitors are recommended for all patients with peripheral vascular disease. Statins have favorable effects on multiple interrelated aspects of vascular biology important in atherosclerosis. In particular they have beneficial effects on inflammation, plaque stabilization, endothelial dysfunction, and thrombosis. Statins have also been shown to be beneficial in acute vascular events. Angiotensin-converting enzyme inhibitors have been shown to reduce cardiovascular morbidity and mortality in patients with peripheral arterial disease regardless of the presence or absence of hypertension. A number of the pleiotropic effects of statins are shared by ACE inhibitors. In summary, patients with known vascular disease should be treated aggressively with a combination of a HMG CoA reductase inhibitor, an angiotensin-converting enzyme inhibitor, an antiplatelet agent and a beta blocker if there is a history of coronary disease. They should also receive tight control of their blood pressure and blood sugar. Smokers should be encouraged to stop smoking and should be provided with pharmaceutical and emotional support by their physicians. All of these patients should have their body mass index as close to normal as possible and be on a therapeutic lifestyle diet. Regular aerobic exercise is also indicated. Patients with symptomatic claudication should be considered for cilostazol. Patients with multiple risk factors for vascular disease, but who do not have documented disease should also be on statin therapy. As more studies define the linear relationship between lower LDL-C levels and lowered risk of vascular events, indicating that the lower the LDL-C level, the lower the risk, experts are advocating more aggressive lipid-lowering therapy. In patients with peripheral arterial disease, some experts now advocate lowering the goal of LDL therapy to 70 mg/dL.

Intermittent claudication: an overview

Intermittent claudication (IC) is defined by leg muscle pain, cramping and fatigue brought on by ambulation/exercise; relieved on rest; and caused by inadequate blood supply and is the primary symptom of peripheral arterial disease (PAD). PAD has a detrimental effect on the quality of life. PAD is a debilitating atherosclerotic disease of the lower limbs and is associated with an increased risk of cardiovascular morbidity and mortality. IC is an extremely important marker of atheroma. Up to 60% patients with IC have significant underlying coronary and/or carotid disease and 40% of all patients suffering from IC die or suffer a stroke within 5 years of presentation. The therapeutic intervention of IC essentially aims at providing symptomatic relief and reducing the systemic cardiovascular complications. Although exercise therapy is one of the most efficacious conservative treatments for claudication, the pharmacotherapeutic goals can be best achieved through an increase in the walking capacity to improve quality of life and a decrease in rates of amputation. In the development of treatment for IC, an aggressive non-pharmacological intervention and pharmacological treatment of the risk factors associated with IC are considered. In the next 2 years, the results of major trials of drugs that stabilize and regress atherosclerosis such as statins and angiotensin converting enzyme inhibitors, and anti-platelet agents, recombinant growth factors and immune modulators will be available for IC. Levocarnitine (l-carnitine) and a derivative, propionyl levocarnitine, are emerging agents that increase the pain-free walking and improve the quality of life in IC patients by working at the metabolism and exercise performance of ischemic muscles. This article provides a comprehensive review of the pathophysiology involved, diagnosis of IC and existing and emerging pharmacotherapies with rationale for their use in its treatment.

Treatment for diabetic foot ulcers

People with diabetes develop foot ulcers because of neuropathy (sensory, motor, and autonomic deficits), ischaemia, or both. The initiating injury may be from acute mechanical or thermal trauma or from repetitively or continuously applied mechanical stress. Patients with clinically significant limb ischaemia should be assessed by a vascular surgeon to determine the need for angioplasty, stenting, or femorodistal bypass. When infection complicates a foot ulcer, the combination can be limb or life-threatening. Infection is defined clinically, but wound cultures reveal the causative pathogens. Tissue specimens are strongly preferred to wound swabs for wound cultures. Antimicrobial therapy should be guided by culture results, and should aim to cure the infection, not to heal the wound. Alleviation of the mechanical load on ulcers (off-loading) should always be a part of treatment. Neuropathic ulcers typically heal in 6 weeks with total contact casting, because it effectively relieves pressure at the ulcer site and enforces patient compliance. The success of other approaches to off-loading similarly depends on the patients' adherence to the effectiveness of pressure relief. Surgery to heal ulcers and prevent recurrence can include tenotomy, tendon lengthening, reconstruction, or removal of bony prominences. However, these procedures may result in secondary ulceration and other complications. Ulcer recurrence rates are high, but appropriate education for patients, the provision of posthealing footwear, and regular foot care can reduce rates of re-ulceration.