Abstract
Vascular hyperpermeability, the excessive leakage of fluid and proteins from blood vessels to the interstitial space, commonly occurs in traumatic and ischemic injuries. This hyperpermeability causes tissue vasogenic edema, which often leads to multiple organ failure resulting in patient death. Vascular hyperpermeability occurs most readily in small blood vessels as their more delicate physical constitution makes them an easy target for barrier dysfunction. A single layer of endothelial cells, linked to one another by cell adhesion molecules, covers the interior surface of each blood vessel. The cell adhesion molecules play a key role in maintaining barrier functions like the regulation of permeability. Aging is a major risk factor for microvascular dysfunction and hyperpermeability. Apart from age-related remodeling of the vascular wall, endothelial barrier integrity and function declines with the advancement of age. Studies that address the physiological and molecular basis of vascular permeability regulation in aging are currently very limited. There have been many cellular and molecular mechanisms proposed to explain aging-related endothelial dysfunction but their true relationship to barrier dysfunction and hyperpermeability is not clearly known. Among the several mechanisms that promote vascular dysfunction and hyperpermeability, the following are considered major contributors: oxidative stress, inflammation, and the activation of apoptotic signaling pathways. In this review we highlighted (a) the physiological, cellular and molecular changes that occur in the vascular system as a product of aging; (b) the potential mechanisms by which aging leads to barrier dysfunction and vascular hyperpermeability in the peripheral and the blood-brain barrier; (c) the mechanisms by which the age-related increases in oxidative stress, inflammatory markers and apoptotic signaling etc. cause endothelial dysfunction and their relationship to hyperpermeability; and (d) the relationship between aging, vascular permeability and traumatic injuries.
Highlights
Aging and vascular endotheliumThe vascular endothelium is comprised of a single layer of endothelial cells located on the interior surface of blood vessels [1,2]
Vascular hyperpermeability, the excessive leakage of fluid and proteins from blood vessels to the interstitial space, commonly occurs in traumatic and ischemic injuries
Vascular hyperpermeability has been considered as a phenomenon that occurs due to activation of the apoptotic signaling pathway which results in endothelial barrier dysfunction even without the instance of apoptotic cell death [6,8]
Summary
The vascular endothelium is comprised of a single layer of endothelial cells located on the interior surface of blood vessels [1,2] Peroxinitrite has been shown to induce microvascular hyperpermeability by disrupting the adherens junction proteins [24] These described mechanisms in part explain oxidative stress-mediated decrease of eNOS and NO in. It has been suggested that the ageassociated changes occurring in eNOS regulatory proteins such as caveolin-1, pAkt, and heat shock protein 90 (Hsp90) contribute to the decreased activity of eNOS in aged endothelial cells [21] In addition to these regulatory mechanisms, several other factors regulate eNOS activity. Conditions which are commonly associated with aging, such as hypertension and cerebrovascular ischemia, aggravate these age-related alterations in the BBB integrity (refer to the section on BBB)
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