EFFECT OF NOS INHIBITION ON RETINAL ARTERIAL AND CAPILLARY CIRCULATION IN EARLY ARTERIAL HYPERTENSION:

Oxidative Stress, Vascular Endothelium, and the Pathology of Neurodegeneration in Retina

Oxidative stress (OS) is an imbalance between free radicals/ROS and antioxidants, which evokes a biological response and is an important risk factor for diseases, in both the cardiovascular system and central nervous system (CNS). The underlying mechanisms driving pathophysiological complications that arise from OS remain largely unclear. The vascular endothelium is emerging as a primary target of excessive glucocorticoid and catecholamine action. Endothelial dysfunction (ED) has been implicated to play a crucial role in the development of neurodegeneration in the CNS. The retina is known as an extension of the CNS. Stress and endothelium dysfunction are suspected to be interlinked and associated with neurodegenerative diseases in the retina as well. In this narrative review, we explore the role of OS-led ED in the retina by focusing on mechanistic links between OS and ED, ED in the pathophysiology of different retinal neurodegenerative conditions, and how a better understanding of the role of endothelial function could lead to new therapeutic approaches for neurodegenerative diseases in the retina.

Clinical Significance of Endothelial Dysfunction in Essential Hypertension

The endothelium is recognized as a major determinant of vascular physiology and pathophysiology. Over the last few decades, a plethora of studies have implicated endothelial dysfunction in the progression of atherosclerosis and the subclinical target organ damage observed in essential hypertension. However, the clinical significance of diagnosing endothelial dysfunction in patients with essential hypertension remains under investigation. Although a number of vascular and non-vascular markers of endothelial dysfunction have been proposed, there is an ongoing quest for a marker in the clinical setting that is optimal, inexpensive, and reproducible. In addition, endothelial dysfunction emerges as a promising therapeutic target of agents that are readily available in clinical practice. In this context, a better understanding of its role in essential hypertension becomes of great importance. Here, we aim to investigate the clinical significance of endothelial dysfunction in essential hypertension by accumulating novel data on (a) early diagnosis using robust markers with prognostic value in cardiovascular risk prediction, (b) the association of endothelial dysfunction with subclinical vascular organ damage, and (c) potential therapeutic targets.

Endothelial dysfunction in glaucoma

Glaucoma is a group of ocular diseases characterized by optic neuropathy associated with loss of the retinal nerve fibre layer and re-modelling of the optic nerve head, and a subsequent particular pattern of visual field loss. Increased intraocular pressure is the most important risk factor for the disease, but the pathogenesis of glaucoma is not monofactorial. Among other factors, ischaemia and vascular dysregulation have been implicated in the mechanisms underlying glaucoma. The vascular endothelium plays an important role in the regulation of ocular blood flow and pathological alterations of vascular endothelial cells may induce ischaemia and dysregulation. The present review summarizes our current evidence of endothelial dysfunction in glaucoma. This is of interest because endothelial dysfunction is a good prognostic factor for progression in several diseases. Although such data are lacking for glaucoma, endothelial dysfunction may provide an attractive target for therapeutic intervention in open-angle glaucoma and other vascular disorders of the eye.

Fourier Analysis of the Envelope of the Ophthalmic Artery Blood Flow Velocity

The harmonic content of the envelope waveform of the blood flow velocity in the ophthalmic artery was analyzed in aging and arterial hypertension. The case-control study enrolled 98 healthy men (age: 44.0±15.6 years), 100 healthy women (age: 44.5±19.1 years), which is group 1, and overall 199 hypertensive patients with increased systolic and diastolic blood pressure (in millimeters of mercury) before registration of the blood flow velocity using pulsed Doppler sonography. Group 2 was sufficiently treated (≤140/≤90), group 3 (>140/≤90) and group 5 (>140/>90) were insufficiently treated, and group 4 (>140/≤90) and group 6 (>140/>90) were untreated. Cronbach-α reliability of the calculated spectral coefficient and SI (SI) was 0.88 and 0.93, respectively. In control subjects, the SI was influenced by age (men: 45.1%; women: 50.2%; P <0.001 each) and in women additionally by mean arterial pressure (13.1%; P <0.001). The SI differed in subjects >43 years of age (men: 0.37±0.11; women: 0.26±0.08; P <0.001 each) as compared with subjects ≤43 years of age (men: 0.60±0.18; women: 0.48±0.13). All of these changes were lacking for the resistance index. In both men and women with hypertension, the SI decreases, whereas the mean arterial pressure increases, but the resistance index did not change. The SI of the ophthalmic artery allows an assessment of the ocular circulation in consideration of age and arterial blood pressure in contrast to the resistance index.

Plasma asymmetric dimethylarginine and retinal vessel diameters in middle-aged men

It has been suggested that asymmetric dimethylarginine (ADMA), an endogenous nitric oxide synthase inhibitor, is linked to hypertension and vascular reactivity. Retinal arteriolar narrowing has been observed to associate early with increased risk of hypertension. The objective of this study was to evaluate the role of ADMA as a biomarker for early vascular changes of retinal vessels and thus as a possible biomarker of hypertension risk. Thirty-five healthy white men aged 50.1 years (range, 45-55 years) were studied. Using digitized fundus photography, the following diameters of retinal arterioles and venules were measured 1 disc diameter from the optic disc edge: the mean arteriole width (MAW) and venule width (MVW), the sum of squares of widths of arterioles (SSWA) and venules (SSWV), and the central retinal artery equivalent (CRAE) and venous equivalent (CRVE). Arteriovenous ratio was determined using MAW/MVW, SSWA/SSWV, and CRAE/CRVE. Blood pressure was measured by 24-hour ambulatory recordings and also by resting measurements. Plasma ADMA was determined by a high-performance liquid chromatography tandem mass spectrometry. Plasma ADMA had a strong negative association with MAW, MVW, SSWA, SSWV, CRAE, and CRVE. Arteriovenous ratio measurements did not associate with plasma ADMA or with l-arginine to ADMA ratio, but arteriovenous ratios had a strong association with blood pressure. In a multivariate linear model, plasma ADMA concentration was the most significant predictor of arteriole and venule diameter measurements. These results suggest that plasma ADMA is associated with vascular phenomenon seen in early hypertension and that ADMA may be a potential biomarker candidate for development of hypertension.