Sirolimus and its Analogs and its Effects on Vascular Diseases

Rapamycin: A Bacteria-Derived Immunosuppressant That Has Anti-atherosclerotic Effects and Its Clinical Application

Atherosclerosis (AS) is the leading cause of stroke and death worldwide. Although many lipid-lowering or antiplatelet medicines have been used to prevent the devastating outcomes caused by AS, the serious side effects of these medicines cannot be ignored. Moreover, these medicines are aimed at preventing end-point events rather than addressing the formation and progression of the lesion. Rapamycin (sirolimus), a fermentation product derived from soil samples, has immunosuppressive and anti-proliferation effects. It is an inhibitor of mammalian targets of rapamycin, thereby stimulating autophagy pathways. Several lines of evidence have demonstrated that rapamycin possess multiple protective effects against AS through various molecular mechanisms. Moreover, it has been used successfully as an anti-proliferation agent to prevent in-stent restenosis or vascular graft stenosis in patients with coronary artery disease. A thorough understanding of the biomedical regulatory mechanism of rapamycin in AS might reveal pathways for retarding AS. This review summarizes the current knowledge of biomedical mechanisms by which rapamycin retards AS through action on various cells (endothelial cells, macrophages, vascular smooth muscle cells, and T-cells) in early and advanced AS and describes clinical and potential clinical applications of the agent.

DNA Damage: A Main Determinant of Vascular Aging

Vascular aging plays a central role in health problems and mortality in older people. Apart from the impact of several classical cardiovascular risk factors on the vasculature, chronological aging remains the single most important determinant of cardiovascular problems. The causative mechanisms by which chronological aging mediates its impact, independently from classical risk factors, remain to be elucidated. In recent years evidence has accumulated that unrepaired DNA damage may play an important role. Observations in animal models and in humans indicate that under conditions during which DNA damage accumulates in an accelerated rate, functional decline of the vasculature takes place in a similar but more rapid or more exaggerated way than occurs in the absence of such conditions. Also epidemiological studies suggest a relationship between DNA maintenance and age-related cardiovascular disease. Accordingly, mouse models of defective DNA repair are means to study the mechanisms involved in biological aging of the vasculature. We here review the evidence of the role of DNA damage in vascular aging, and present mechanisms by which genomic instability interferes with regulation of the vascular tone. In addition, we present potential remedies against vascular aging induced by genomic instability. Central to this review is the role of diverse types of DNA damage (telomeric, non-telomeric and mitochondrial), of cellular changes (apoptosis, senescence, autophagy), mediators of senescence and cell growth (plasminogen activator inhibitor-1 (PAI-1), cyclin-dependent kinase inhibitors, senescence-associated secretory phenotype (SASP)/senescence-messaging secretome (SMS), insulin and insulin-like growth factor 1 (IGF-1) signaling), the adenosine monophosphate-activated protein kinase (AMPK)-mammalian target of rapamycin (mTOR)-nuclear factor kappa B (NFκB) axis, reactive oxygen species (ROS) vs. endothelial nitric oxide synthase (eNOS)-cyclic guanosine monophosphate (cGMP) signaling, phosphodiesterase (PDE) 1 and 5, transcription factor NF-E2-related factor-2 (Nrf2), and diet restriction.

Rapamycin nanoparticles target defective autophagy in muscular dystrophy to enhance both strength and cardiac function

Duchenne muscular dystrophy in boys progresses rapidly to severe impairment of muscle function and death in the second or third decade of life. Current supportive therapy with corticosteroids results in a modest increase in strength as a consequence of a general reduction in inflammation, albeit with potential untoward long-term side effects and ultimate failure of the agent to maintain strength. Here, we demonstrate that alternative approaches that rescue defective autophagy in mdx mice, a model of Duchenne muscular dystrophy, with the use of rapamycin-loaded nanoparticles induce a reproducible increase in both skeletal muscle strength and cardiac contractile performance that is not achievable with conventional oral rapamycin, even in pharmacological doses. This increase in physical performance occurs in both young and adult mice, and, surprisingly, even in aged wild-type mice, which sets the stage for consideration of systemic therapies to facilitate improved cell function by autophagic disposal of toxic byproducts of cell death and regeneration.

Antibiotics acting as neuroprotectants via mechanisms independent of their anti-infective activities

This review considers available evidence that some antibiotics have ancillary neuroprotective effects. Notably, β-lactam antibiotics are believed to increase the expression of glutamate transporter GLT1, potentially relieving the neurological excitotoxicity that characterizes disorders like amyotrophic lateral sclerosis. Minocycline has shown promise in reducing the severity of a number of neurological diseases, including multiple sclerosis, most likely by reducing apoptosis and the expression of inflammatory mediators in the brain. Rapamycin inhibits the activity of a serine/threonine protein kinase that has a role in the pathogenesis of numerous neurologic diseases. Herein we examine the unique neuroprotective aspects of these drugs originally developed as anti-infective agents.

Rapamycin extends life and health in C57BL/6 mice

Target of rapamycin inhibition by rapamycin feeding has previously been shown to extend life in genetically heterogeneous mice. To examine whether it similarly affected mouse health, we fed encapsulated rapamycin or a control diet to C57BL/6Nia mice of both sexes starting at 19 months of age. We performed a range of health assessments 6 and 12 months later. Rapamycin feeding significantly reduced mTOR activity in most but not all tissues. It also reduced total and resting metabolic rate during the light (inactive) phase of the light:dark cycle in females only but had no effect on spontaneous activity or metabolism during the dark (active) phase of either sex. Males only had less fragmented sleep when fed rapamycin, whereas stride length and rotarod performance were improved in both sexes. Survival was also improved by this late-life rapamycin feeding, and some pathological lesions were delayed. We found no adverse health consequences associated with rapamycin treatment.

Sirolimus and cardiovascular disease risk in liver transplantation

BACKGROUND

Two adverse effects of sirolimus are hypertriglyceridemia and hypercholesterolemia. These elevated levels often lead clinicians to discontinue the sirolimus from concerns of an increased cardiovascular disease (CVD) risk; however, evidence suggests that sirolimus might be cardioprotective. There are no published reports of sirolimus CVD in liver transplantation.

METHODS

We reviewed all 1812 liver recipients who underwent transplantation from 1998 to 2010, identifying a cohort using sirolimus as part of the initial immunosuppression (SRL Cohort) and a control group of the remaining patients from this period where SRL was never given (Non-SRL Control). A prospectively maintained database identified all episodes of myocardial infarction (MI), congestive heart failure (CHF), abdominal aortic aneurysm (AAA), and cerebrovascular accident and tracked triglyceride, high-density and low-density lipoproteins, and total cholesterol levels. A Framingham Risk Model calculated the predicted 10-year risk of CVD for both groups.

RESULTS

The SRL Cohort (n=406) is older, more predominantly male, with more pretransplantation hypertension and diabetes and posttransplantation hypertension compared to Non-SRL Controls (n=1005). The SRL Cohort has significantly higher triglyceride, low-density lipoprotein, and cholesterol levels at 6 months and 1 year. There is no difference in MI incidence in the SRL Cohort (1.0% vs. 1.2%) and no difference in AAA, cerebrovascular accident, and CHF. The Framingham Risk Model predicts that the SRL Cohort should have almost double the 10-year risk of CVD compared to the Non-SRL Control (11% vs. 6%).

CONCLUSIONS

Sirolimus causes hypertriglyceridemia and hypercholesterolemia, but it does not increase the incidence of MI or other CVDs. Considering the SRL Cohort has more cardiac risk factors and nearly double 10-year predicted CVD risk, the fact that the CVD incidence is similar suggests that sirolimus is in fact cardioprotective.

Perspectives of Targeting mTORC1-S6K1 in Cardiovascular Aging

The global population aging is accelerating and age-associated diseases including cardiovascular diseases become more challenging. The underlying mechanisms of aging and age-associated cardiovascular dysfunction remain elusive. There are substantial evidences demonstrating a pivotal role of the mammalian target of rapamycin complex 1 (mTORC1) and its down-stream effector S6K1 signaling in mammalian lifespan regulation and age-related diseases such as type II diabetes mellitus and cancer. The role of mTORC1–S6K1 in age-related cardiovascular diseases is, however, largely unknown and the available experimental results are controversial. This review article primarily summarizes the most recent advances toward understanding the role of mTORC1–S6K1 in cardiovascular aging and discusses the future perspectives of targeting mTORC1–S6K1 signaling as a healthy lifespan extension modality in anti-aging and anti-cardiovascular aging.