Ocular blood flow measurements in healthy human myopic eyes

Background. To evaluate the haemodynamic features of young healthy myopes and emmetropes, in order to ascertain the perfusion profile of human myopia and its relationship with axial length prior to reaching a degenerative state. Methods The retrobulbar, microretinal and pulsatile ocular blood flow (POBF) of one eye of each of twenty-two high myopes (N=22, mean spherical equivalent (MSE) =-5.00D), low myopes (N=22, MSE-1.00 to-4.50D) and emmetropes (N=22, MSE±0.50D) was analyzed using color Doppler Imaging, Heidelberg retinal flowmetry and ocular blood flow analyser (OBF) respectively. Intraocular pressure, axial length (AL), systemic blood pressure, and body mass index were measured. Results. When compared to the emmetropes and low myopes, the AL was greater in high myopia (p<0.0001). High myopes showed higher central retinal artery resistance index (CRA RI) (p=0.004), higher peak systolic to end diastolic velocities ratio (CRA ratio) and lower end diastolic velocity (CRA EDv) compared to low myopes (p=0.014, p=0.037). Compared to emmetropes, high myopes showed lower OBFamplitude (OBFa) (p=0.016). The POBF correlated significantly with the systolic and diastolic blood velocities of the CRA (p=0.016, p=0.036). MSE and AL correlated negatively with OBFa (p=0.03, p=0.003), OBF volume (p=0.02, p<0.001), POBF (p=0.01, p<0.001) and positively with CRA RI (p=0.007, p=0.05). Conclusion. High myopes exhibited significantly reduced pulse amplitude and CRA blood velocity, the first of which may be due to an OBF measurement artefact or real decreased ocular blood flow pulsatility. Axial length and refractive error correlated moderately with the ocular pulse and with the resistance index of the CRA, which in turn correlated amongst themselves. It is hypothesized that the compromised pulsatile and CRA haemodynamics observed in young healthy myopes is an early feature of the decrease in ocular blood flow reported in pathological myopia. Such vascular features would increase the susceptibility for vascular and age-related eye diseases.

Relationship between ocular perfusion pressure and retrobulbar blood flow in patients with glaucoma with progressive damage

PURPOSE: To evaluate the relationship between ocular perfusion pressure and color Doppler measurements in patients with glaucoma. MATERIALS AND METHODS: Twenty patients with primary open-angle glaucoma with visual field deterioration in spite of an intraocular pressure lowered below 21 mm Hg, 20 age-matched patients with glaucoma with stable visual fields, and 20 age-matched healthy controls were recruited. After a 20-minute rest in a supine position, intraocular pressure and color Doppler measurements parameters of the ophthalmic artery and the central retinal artery were obtained. Correlations between mean ocular perfusion pressure and color Doppler measurements parameters were determined. RESULTS: Patients with glaucoma showed a higher intraocular pressure (P <.0008) and a lower mean ocular perfusion pressure (P <.0045) compared with healthy subjects. Patients with deteriorating glaucoma showed a lower mean blood pressure (P =.033) and a lower end diastolic velocity in the central retinal artery (P =.0093) compared with normals. Mean ocular perfusion pressure correlated positively with end diastolic velocity in the ophthalmic artery (R = 0.66, P =.002) and central retinal artery (R = 0.74, P <.0001) and negatively with resistivity index in the ophthalmic artery (R = -0.70, P =.001) and central retinal artery (R = -0.62, P =.003) in patients with deteriorating glaucoma. Such correlations did not occur in patients with glaucoma with stable visual fields or in normal subjects. The correlations were statistically significantly different between the study groups (parallelism of regression lines in an analysis of covariance model) for end diastolic velocity (P =.001) and resistivity index (P =.0001) in the ophthalmic artery, as well as for end diastolic velocity (P =.0009) and resistivity index (P =. 001) in the central retinal artery. CONCLUSIONS: The present findings suggest that alterations in ocular blood flow regulation may contribute to the progression in glaucomatous damage.

Investigation into bilateral distribution of cerebral blood flow using a multidetector scintillating system

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Regional variation in peripapillary retinal blood flow in primary open angle glaucoma:a follow-up study

Purpose: To investigate whether regional long-term changes in peripapillary retinal flow, measured by scanning laser Doppler flowmetry (SLDF), occur in patients with primary open angle glaucoma (POAG). Methods: 31 healthy volunteers (mean age: 65 8.3 years) and 33 POAG patients (mean age: 71.2 7.6 years) were followed up every 4 months for 16 months. Using SLDF, three images of the superior and inferior optic nerve head were obtained for each subject. A 1010-pixel frame was used to measure blood flow, volume and velocity in the four quadrants of the peripapillary retina. Central 24-2 visual field testing was carried out at each visit. Repeated measures analysis of covariance was used to assess change over time between the normal and POAG groups for the SLDF parameters. Univariate linear regression analysis for mean deviation and glaucoma change probability (GCP) analysis were used to identify visual field progression. Results: Blood volume, flow and velocity measured in the inferior nasal quadrant of the peripapillary retina decreased significantly over time for the POAG group compared to the normal group (p=0.0073, 0.0097, 0.0095 respectively). Overall, 2 glaucoma patients showed a significantly deteriorating MD slope, while 7 patients showed visual field progression with GPA. All of the patients progressing with GPA, showed change in the superior hemifield and, of those, 14% showed change in the inferior hemifield. Conclusion: Glaucoma patients showed a decrease in blood flow, volume and velocity in the inferior nasal peripapillary retina. A regional variation in microvascular retinal capillary blood flow may provide insight into the pathogenesis of glaucomatous optic neuropathy. Keywords: 331 blood supply • 554 retina • 624 visual fields

Individual variability analysis of fluorescence parameters measured in skin with different levels of nutritive blood flow

Fluorescence spectroscopy has recently become more common in clinical medicine. However, there are still many unresolved issues related to the methodology and implementation of instruments with this technology. In this study, we aimed to assess individual variability of fluorescence parameters of endogenous markers (NADH, FAD, etc.) measured by fluorescent spectroscopy (FS) in situ and to analyse the factors that lead to a significant scatter of results. Most studied fluorophores have an acceptable scatter of values (mostly up to 30%) for diagnostic purposes. Here we provide evidence that the level of blood volume in tissue impacts FS data with a significant inverse correlation. The distribution function of the fluorescence intensity and the fluorescent contrast coefficient values are a function of the normal distribution for most of the studied fluorophores and the redox ratio. The effects of various physiological (different content of skin melanin) and technical (characteristics of optical filters) factors on the measurement results were additionally studied.The data on the variability of the measurement results in FS should be considered when interpreting the diagnostic parameters, as well as when developing new algorithms for data processing and FS devices.

Use of the retinal vessel analyzer in ocular blood flow research

The present article describes a standard instrument for the continuous online determination of retinal vessel diameters, the commercially available retinal vessel analyzer. This report is intended to provide informed guidelines for measuring ocular blood flow with this system. The report describes the principles underlying the method and the instruments currently available, and discusses clinical protocol and the specific parameters measured by the system. Unresolved questions and the possible limitations of the technique are also discussed. © 2009 Acta Ophthalmol.

Glutaredoxin-1 up-regulation induces soluble vascular endothelial growth factor receptor 1, attenuating post-ischemia limb revascularization

Glutaredoxin-1 (Glrx) is a cytosolic enzyme that regulates diverse cellular function by removal of GSH adducts from S-glutathionylated proteins including signaling molecules and transcription factors. Glrx is up-regulated during inflammation and diabetes. Glrx overexpression inhibits VEGF-induced endothelial cell (EC) migration. The aim was to investigate the role of up-regulated Glrx in EC angiogenic capacities and in vivo revascularization in the setting of hind limb ischemia. Glrx overexpressing EC from Glrx transgenic mice (TG) showed impaired migration and network formation and secreted higher level of soluble VEGF receptor 1 (sFlt), an antagonizing factor to VEGF. After hind limb ischemia surgery Glrx TG mice demonstrated impaired blood flow recovery, associated with lower capillary density and poorer limb motor function compared to wild type littermates. There were also higher levels of anti-angiogenic sFlt expression in the muscle and plasma of Glrx TG mice after surgery. Non-canonical Wnt5a is known to induce sFlt. Wnt5a was highly expressed in ischemic muscles and EC from Glrx TG mice, and exogenous Wnt5a induced sFlt expression and inhibited network formation in human microvascular EC. Adenoviral Glrx-induced sFlt in EC was inhibited by a competitive Wnt5a inhibitor. Furthermore, Glrx overexpression removed GSH adducts on p65 in ischemic muscle and EC, and enhanced nuclear factor kappa B (NF-kB) activity which was responsible for Wnt5a-sFlt induction. Taken together, up-regulated Glrx induces sFlt in EC via NF-kB -dependent Wnt5a, resulting in attenuated revascularization in hind limb ischemia. The Glrx-induced sFlt may be a part of mechanism of redox regulated VEGF signaling.

Glutathione adducts induced by ischemia and deletion of glutaredoxin-1 stabilize HIF-1α and improve limb revascularization

Reactive oxygen species (ROS) are increased in ischemic tissues and necessary for revascularization; however, the mechanism remains unclear. Exposure of cysteine residues to ROS in the presence of glutathione (GSH) generates GSH-protein adducts that are specifically reversed by the cytosolic thioltransferase, glutaredoxin-1 (Glrx). Here, we show that a key angiogenic transcriptional factor hypoxia-inducible factor (HIF)-1α is stabilized by GSH adducts, and the genetic deletion of Glrx improves ischemic revascularization. In mouse muscle C2C12 cells, HIF-1α protein levels are increased by increasing GSH adducts with cell-permeable oxidized GSH (GSSG-ethyl ester) or 2-acetylamino-3-[4-(2-acetylamino-2-carboxyethylsulfanyl thiocarbonylamino) phenylthiocarbamoylsulfanyl] propionic acid (2-AAPA), an inhibitor of glutathione reductase. A biotin switch assay shows that GSSG-ester-induced HIF-1α contains reversibly modified thiols, and MS confirms GSH adducts on Cys520 (mouse Cys533). In addition, an HIF-1α Cys520 serine mutant is resistant to 2-AAPA–induced HIF-1α stabilization. Furthermore, Glrx overexpression prevents HIF-1α stabilization, whereas Glrx ablation by siRNA increases HIF-1α protein and expression of downstream angiogenic genes. Blood flow recovery after femoral artery ligation is significantly improved in Glrx KO mice, associated with increased levels of GSH-protein adducts, capillary density, vascular endothelial growth factor (VEGF)-A, and HIF-1α in the ischemic muscles. Therefore, Glrx ablation stabilizes HIF-1α by increasing GSH adducts on Cys520 promoting in vivo HIF-1α stabilization, VEGF-A production, and revascularization in the ischemic muscles

Regulation of neovascularization by S-glutathionylation via the Wnt5a/sFlt-1 pathway

S-glutathionylation occurs when reactive oxygen or nitrogen species react with protein-cysteine thiols. Glutaredoxin-1 (Glrx) is a cytosolic enzyme which enzymatically catalyses the reduction in S-glutathionylation, conferring reversible signalling function to proteins with redox-sensitive thiols. Glrx can regulate vascular hypertrophy and inflammation by regulating the activity of nuclear factor κB (NF-κB) and actin polymerization. Vascular endothelial growth factor (VEGF)-induced endothelial cell (EC) migration is inhibited by Glrx overexpression. In mice overexpressing Glrx, blood flow recovery, exercise function and capillary density were significantly attenuated after hindlimb ischaemia (HLI). Wnt5a and soluble Fms-like tyrosine kinase-1 (sFlt-1) were enhanced in the ischaemic-limb muscle and plasma respectively from Glrx transgenic (TG) mice. A Wnt5a/sFlt-1 pathway had been described in myeloid cells controlling retinal blood vessel development. Interestingly, a Wnt5a/sFlt-1 pathway was found also to play a role in EC to inhibit network formation. S-glutathionylation of NF-κB components inhibits its activation. Up-regulated Glrx stimulated the Wnt5a/sFlt-1 pathway through enhancing NF-κB signalling. These studies show a novel role for Glrx in post-ischaemic neovascularization, which could define a potential target for therapy of impaired angiogenesis in pathological conditions including diabetes.

Cystathionine γ-lyase regulates arteriogenesis through NO-dependent monocyte recruitment

AIMS: Hydrogen sulfide (H2S) is a vasoactive gasotransmitter that is endogenously produced in the vasculature by the enzyme cystathionine γ-lyase (CSE). However, the importance of CSE activity and local H2S generation for ischaemic vascular remodelling remains completely unknown. In this study, we examine the hypothesis that CSE critically regulates ischaemic vascular remodelling involving H2S-dependent mononuclear cell regulation of arteriogenesis. METHODS AND RESULTS: Arteriogenesis including mature vessel density, collateral formation, blood flow, and SPY angiographic blush rate were determined in wild-type (WT) and CSE knockout (KO) mice at different time points following femoral artery ligation (FAL). The role of endogenous H2S in regulation of IL-16 expression and subsequent recruitment of monocytes, and expression of VEGF and bFGF in ischaemic tissues, were determined along with endothelial progenitor cell (CD34/Flk1) formation and function. FAL of WT mice significantly increased CSE activity, expression and endogenous H2S generation in ischaemic tissues, and monocyte infiltration, which was absent in CSE-deficient mice. Treatment of CSE KO mice with the polysulfide donor diallyl trisulfide restored ischaemic vascular remodelling, monocyte infiltration, and cytokine expression. Importantly, exogenous H2S therapy restored nitric oxide (NO) bioavailability in CSE KO mice that was responsible for monocyte recruitment and arteriogenesis. CONCLUSION: Endogenous CSE/H2S regulates ischaemic vascular remodelling mediated during hind limb ischaemia through NO-dependent monocyte recruitment and cytokine induction revealing a previously unknown mechanism of arteriogenesis.