Opposite response of blood vessels in the retina to 6° head-down tilt and long-duration microgravity.

The Spaceflight Associated Neuro-ocular Syndrome (SANS), associated with the headward fluid shifts incurred in microgravity during long-duration missions, remains a high-priority health and performance risk for human space exploration. To help characterize the pathophysiology of SANS, NASA's VESsel GENeration Analysis (VESGEN) software was used to map and quantify vascular adaptations in the retina before and after 70 days of bed rest at 6-degree Head-Down Tilt (HDT), a well-studied microgravity analog. Results were compared to the retinal vascular response of astronauts following 6-month missions to the International Space Station (ISS). By mixed effects modeling, the trends of vascular response were opposite. Vascular density decreased significantly in the 16 retinas of eight astronauts and in contrast, increased slightly in the ten retinas of five subjects after HDT (although with limited significance). The one astronaut retina diagnosed with SANS displayed the greatest vascular loss. Results suggest that microgravity is a major variable in the retinal mediation of fluid shifts that is not reproduced in this HDT bed rest model.

Vascular Patterning as Integrative Readout of Complex Molecular and Physiological Signaling by VESsel GENeration Analysis.

The molecular signaling cascades that regulate angiogenesis and microvascular remodeling are fundamental to normal development, healthy physiology, and pathologies such as inflammation and cancer. Yet quantifying such complex, fractally branching vascular patterns remains difficult. We review application of NASA's globally available, freely downloadable VESsel GENeration (VESGEN) Analysis software to numerous examples of 2D vascular trees, networks, and tree-network composites. Upon input of a binary vascular image, automated output includes informative vascular maps and quantification of parameters such as tortuosity, fractal dimension, vessel diameter, area, length, number, and branch point. Previous research has demonstrated that cytokines and therapeutics such as vascular endothelial growth factor, basic fibroblast growth factor (fibroblast growth factor-2), transforming growth factor-beta-1, and steroid triamcinolone acetonide specify unique "fingerprint" or "biomarker" vascular patterns that integrate dominant signaling with physiological response. In vivo experimental examples described here include vascular response to keratinocyte growth factor, a novel vessel tortuosity factor; angiogenic inhibition in humanized tumor xenografts by the anti-angiogenesis drug leronlimab; intestinal vascular inflammation with probiotic protection by Saccharomyces boulardii, and a workflow programming of vascular architecture for 3D bioprinting of regenerative tissues from 2D images. Microvascular remodeling in the human retina is described for astronaut risks in microgravity, vessel tortuosity in diabetic retinopathy, and venous occlusive disease.

Decreased Vascular Patterning in the Retinas of Astronaut Crew Members as New Measure of Ocular Damage in Spaceflight-Associated Neuro-ocular Syndrome.

Purpose: Ocular structural and functional changes, collectively termed spaceflight-associated neuro-ocular syndrome (SANS), have been described in astronauts undergoing long-duration missions in the microgravity environment of the International Space Station. We tested the hypothesis that retinal vascular remodeling, particularly by smaller vessels, mediates the chronic headward fluid shifts associated with SANS. Methods: As a retrospective study, arterial and venous patterns extracted from 30° infrared Heidelberg Spectralis retinal images of eight crew members acquired before and after six-month missions were analyzed with NASA's recently released VESsel GENeration Analysis (VESGEN) software. Output parameters included the fractal dimension and overall vessel length density that was further classified into large and small vascular branching generations. Vascular results were compared with SANS-associated clinical ocular measures. Results: Significant postflight decreases in Df, Lv, and in smaller but not larger vessels were quantified in 11 of 16 retinas for arteries and veins (P value for Df, Lv, and smaller vessels in all 16 retinas were ≤0.033). The greatest vascular decreases occurred in the only retina displaying clinical evidence of SANS by choroidal folds and optic disc edema. In the remaining 15 retinas, decreases in vascular density from Df and Lv ranged from minimal to high by a custom Subclinical Vascular Pathology Index. Conclusions: Together with VESGEN, the Subclinical Vascular Pathology Index may represent a new, useful SANS biomarker for advancing the understanding of SANS etiology and developing successful countermeasures for long duration space exploration in microgravity, although further research is required to better characterize retinal microvascular adaptations.

Overview of the NASA 70-day Bed Rest Study.

PURPOSE: The purpose of this article was to provide an overview of the National Aeronautics and Space Administration (NASA) 70-day Bed Rest Study. The integrated complement of investigations and the standardized bed rest environment that served as the platform for this study complement are described. Outcomes of the studies will not be presented here but will be reported in separate publications. METHODS: A set of studies running in an integrated fashion along the entire period (pre-, in-, and post-bed rest) and using the same subjects is referred in this article as "the campaign" or "complement." NASA selected eight individual studies to participate in the 70-d bed rest campaign. These studies were integrated to increase efficiency in the utilization of resources and to share common measures among the investigations. In addition to the individual studies addressing specific aims, a battery of standardized measures was included. Standard measures target a wide range of physiologic systems and represent some of the testing routinely done on astronauts. Bed rest subjects underwent rigorous medical and psychological screening. Standardized conditions included 70 d of bed rest in a 6° head-down tilt position. Subjects' vital signs, body weight, and fluid intake and output were measured daily. A standardized diet was provided to ensure consistent nutritional intake across subjects. Exercising subjects were prescribed individualized aerobic and resistance training 6 d·wk performed in a horizontal body position. Subjects in the testosterone supplementation countermeasure group received testosterone enanthate injections at 2-wk intervals during bed rest. CONCLUSION: Long-duration head-down tilt bed rest provided a suitable platform for examining physiologic effects of spaceflight and testing countermeasures in a ground-based model. Integrating studies into a complement is an effective way to support multiple investigations while minimizing the number of subjects to answer many research questions.

Inflammatory gene expression signatures in idiopathic intracranial hypertension: possible implications in microgravity-induced ICP elevation.

The visual impairment and intracranial pressure (VIIP) syndrome is a neuro-ophthalmologic condition described in astronauts returning from long duration space missions. Idiopathic intracranial hypertension (IIH), also known as pseudotumor cerebri, is characterized by a chronic elevation of intracranial pressure (ICP) in the absence of an intracranial mass lesion. Because VIIP and IIH share some neurologic and ophthalmologic manifestations, the latter might be used as a model to study some of the processes underlying VIIP. This work constitutes a preliminary investigation of the molecular pathways associated with the elevation of ICP in IIH. Gene expression signatures were obtained from exosomes collected from CSF and plasma in patients with possible signs of IIH. The gene expression targets focused on inflammatory genes and miRNAs. The results suggest that inflammatory cytokine-driven processes and immune cell migration are activated when ICP is elevated in IIH patients, either as a cause or effect of the ICP increase. Several miRNAs appear to be involved in this response, among which miR-9 and miR-16 are upregulated in CSF and plasma of higher ICP subjects. This study provides evidence in support of neurophysiological alterations and neuro-immunomodulation in this condition. If similar changes are seen in astronauts manifesting with the VIIP syndrome, an underlying pathophysiological basis may be discovered.

Ophthalmological Evaluation of Integrated Resistance and Aerobic Training During 70-Day Bed Rest.

INTRODUCTION: We evaluated ophthalmic changes in healthy individuals who underwent integrated resistance and aerobic training (iRAT) during 70-d 6° head-down tilt (HDT) bed rest (BR). METHODS: Participants were selected using NASA standard screening procedures. Standardized NASA BR conditions were implemented. Subjects were randomly assigned to the iRAT protocol or no exercise during HDTBR. Weekly ophthalmic examinations were performed in the sitting (pre/post-BR only) and HDT (BR only) positions. Mixed-effects linear models compared pre- and post-HDTBR intraocular pressure (IOP), Spectralis OCT circumpapillary retinal nerve fiber layer (cpRNFL) thickness, and peripapillary retinal thickness observations between groups. RESULTS: Six controls and nine exercisers completed the study. There was an overall effect of BR on our outcomes. Except Goldmann IOP (mean pre/post difference in controls and exercisers: -0.47 mmHg vs. +1.14 mmHg), the magnitude of changes from baseline was not significantly different between groups. There was a +1.38 mmHg and a +1.63 mmHg iCare IOP increase during BR in controls and exercisers, respectively. Spectralis OCT detected a +1.33 µm average cpRNFL thickness increase in both groups, and a +9.77 µm and a +6.65 µm peripapillary retinal thickening post-BR in controls and exercisers, respectively. Modified Amsler grid, red dot test, confrontational visual field, color vision, and stereoscopic fundus photography were unremarkable. CONCLUSIONS: HDTBR for 70 d induced peripapillary retinal thickening and cpRNFL thickening without visible signs of optic disc edema. The magnitude of such changes was not different between controls and exercisers. A slight IOP increase during BR subsided post-BR. Further study should evaluate whether different physical exercise paradigms may prevent/mitigate the risk of space-related visual impairment.Taibbi G, Cromwell RL, Zanello SB, Yarbough PO, Ploutz-Snyder RJ, Godley BF, Vizzeri G. Ophthalmological evaluation of integrated resistance and aerobic training during 70-day bed rest. Aerosp Med Hum Perform. 2017; 88(7):633-640.

Ocular Outcomes Comparison Between 14- and 70-Day Head-Down-Tilt Bed Rest.

PURPOSE: To compare ocular outcomes in healthy subjects undergoing 14- and/or 70-day head-down-tilt (HDT) bed rest (BR). METHODS: Participants were selected by using NASA standard screening procedures. Standardized NASA BR conditions were implemented. Subjects maintained a 6° HDT position for 14 and/or 70 consecutive days. Weekly ophthalmologic examinations were performed in the sitting (pre/post-BR only) and HDT positions. Mixed-effects linear models compared pre- and post-HDT BR observations between 14- and 70-day HDT BR in best-corrected visual acuity, spherical equivalent, intraocular pressure (IOP), Spectralis OCT retinal nerve fiber layer thickness, peripapillary and macular retinal thicknesses. RESULTS: Sixteen and six subjects completed the 14- and 70-day HDT BR studies, respectively. The magnitude of HDT BR-induced changes was not significantly different between the two studies for all outcomes, except the superior (mean pre/post difference of 14- vs. 70-day HDT BR: +4.69 µm versus +11.50 µm), nasal (+4.63 µm versus +11.46 µm), and inferior (+4.34 µm versus +10.08 µm) peripapillary retinal thickness. A +1.42 mm Hg and a +1.79 mm Hg iCare IOP increase from baseline occurred during 14- and 70-day HDT BR, respectively. Modified Amsler grid, red dot test, confrontational visual field, color vision, and stereoscopic fundus photography were unremarkable. CONCLUSIONS: Seventy-day HDT BR induced greater peripapillary retinal thickening than 14-day HDT BR, suggesting that time may affect the amount of optic disc swelling. Spectralis OCT detected retinal nerve fiber layer thickening post BR, without clinical signs of optic disc edema. A small IOP increase during BR subsided post HDT BR. Such changes may have resulted from BR-induced cephalad fluids shift. The HDT BR duration may be critical for replicating microgravity-related ophthalmologic changes observed in astronauts on ≥6-month spaceflights.

High dietary iron increases oxidative stress and radiosensitivity in the rat retina and vasculature after exposure to fractionated gamma radiation.

Radiation exposure in combination with other space environmental factors including microgravity, nutritional status, and deconditioning is a concern for long-duration space exploration missions. Astronauts experience altered iron homeostasis due to adaptations to microgravity and an iron-rich food system. Iron intake reaches three to six times the recommended daily allowance due to the use of fortified foods on the International Space Station. Iron is associated with certain optic neuropathies and can potentiate oxidative stress. This study examined the response of eye and vascular tissue to gamma radiation exposure (3 Gy fractionated at 37.5 cGy per day every other day for 8 fractions) in rats fed an adequate-iron diet or a high-iron diet. Twelve-week-old Sprague-Dawley rats were assigned to one of four experimental groups: adequate-iron diet/no radiation (CON), high-iron diet/no radiation (IRON), adequate-iron diet/radiation (RAD), and high-iron diet/radiation (IRON+RAD). Animals were maintained on the corresponding iron diet for 2 weeks before radiation exposure. As previously published, the high-iron diet resulted in elevated blood and liver iron levels. Dietary iron overload altered the radiation response observed in serum analytes, as evidenced by a significant increase in catalase levels and smaller decrease in glutathione peroxidase and total antioxidant capacity levels. 8-OHdG immunostaining, showed increased intensity in the retina after radiation exposure. Gene expression profiles of retinal and aortic vascular samples suggested an interaction between the response to radiation and high dietary iron. This study suggests that the combination of gamma radiation and high dietary iron has deleterious effects on retinal and vascular health and physiology.

Ocular outcomes evaluation in a 14-day head-down bed rest study.

INTRODUCTION: We evaluated ocular outcomes in a 14-d head-down tilt (HDT) bed rest (BR) study designed to simulate the effects of microgravity on the human body. METHODS: Healthy subjects were selected using NASA standard screening procedures. Standardized NASA BR conditions were implemented (e.g., strict sleep-wake cycle, standardized diet, 24-hour-a-day BR, continuous video monitoring). Subjects maintained a 6° HDT position for 14 consecutive days. Weekly ophthalmological examinations were performed in the sitting (pre/post-BR) and HDT (in-bed phase) positions. Equivalency tests with optimal-alpha techniques evaluated pre/post-BR differences in best-corrected visual acuity (BCVA), spherical equivalent, intraocular pressure (IOP), Spectral-domain OCT retinal nerve fiber layer thickness (RNFLT), optic disc and macular parameters. RESULTS: 16 subjects (12 men and 4 women) were enrolled. Nearly all ocular outcomes were within our predefined clinically relevant thresholds following HDTBR, except near BCVA (pre/post-BR mean difference: -0.06 logMAR), spherical equivalent (-0.30 D), Tonopen XL IOP (+3.03 mmHg) and Spectralis OCT average (+1.14 µm), temporal-inferior (+1.58 µm) and nasal-inferior RNFLT (+3.48 µm). Modified Amsler grid, red dot test, confrontational visual field, and color vision were within normal limits throughout. No changes were detected on stereoscopic color fundus photography. DISCUSSION: A few functional and structural changes were detected after 14-d HDTBR, notably an improved BCVA possibly due to learning effect and RNFL thickening without signs of optic disc edema. In general, 6° HDTBR determined a small nonprogressive IOP elevation, which returned to baseline levels post-BR. Further studies with different BR duration and/or tilt angle are warranted to investigate microgravity-induced ophthalmological changes.

Effects of 30-day head-down bed rest on ocular structures and visual function in a healthy subject.

INTRODUCTION: We report ocular changes occurring in a healthy human subject enrolled in a bed rest (BR) study designed to replicate the effects of a low-gravity environment. CASE REPORT: A 25-yr-old Caucasian man spent 30 consecutive days in a 6 degrees head-down tilt (HDT) position at the NASA Flight Analogs Research Unit. Comprehensive ophthalmologic exams, optic disc stereo-photography, standard automated perimetry (SAP), and optic disc Spectralis OCT scans were performed at baseline, immediately post-BR (BR+0), and 6 mo post-BR. MAIN OUTCOME MEASURES: changes in best-corrected visual acuity, intraocular pressure (IOP), cycloplegic refraction, SAP, and Spectralis OCT measures. At BR+0 KIOP was 11 and 10 mmHg in the right (OD) and left eye (OS), respectively (a bilateral 4-mmHg decrease compared to baseline); SAP documented a possible bilateral symmetrical inferior scotoma; Spectralis OCT showed an average 19.4 microm (+5.2%) increase in peripapillary retinal thickness, and an average 0.03 mm3 (+5.0%) increase in peripapillary retinal volume bilaterally. However, there were no clinically detectable signs of optic disc edema. At 6 mo post-BR, IOP was 13 and 14 mmHg in OD and OS, respectively, and the scotoma had resolved. Spectralis OCT measurements matched the ones recorded at baseline. DISCUSSION: In this subject, a reduction in IOP associated with subtle structural and functional changes compared to baseline were documented after prolonged head-down BR. These changes may be related to cephalad fluid shifts in response to tilt. Further studies should clarify whether decreased translaminar pressure (i.e., the difference between IOP and intracranial pressure) may be responsible for these findings.

Retinal non-visual photoreception in space.

BACKGROUND: Circadian rhythm disruption occurs during spaceflight, leading to crew health and performance decrements. Spaceflight-related retinal changes, including oxidative stress and neuronal loss, have been previously reported in mice. METHODS: Animal tissue from experiments aboard shuttle missions STS-133 (BALB/cJ mice, albino strain) and STS-135 (C57BL mice, pigmented strain), along with ground controls, was examined to determine survival of intrinsically photosensitive retinal ganglion cells (ipRGC) and melanopsin expression in retinas of mice exposed to the spaceflight environment. Real-time qPCR (RTqPCT) and microarray approaches were used to analyze Opn4 (melanopsin) gene expression, while immunohistologic studies were conducted to detect melanopsin localization in the retina. RESULTS: Opn4 expression was decreased in albino BALB/cJ mice exposed to spaceflight, as measured by RTqPCR, but not in C57BL mice samples as analyzed by microarray. Opn4 expression returned to control levels at 7 d postreturn in the BALB/cJ samples. Melanopsin positive RGCs were found in the expected proportion in all samples, except for the BALB/cJ samples at 1 d after flight, where virtually no immunoreactive cells were found. DISCUSSION: Spaceflight environmental factors may affect the nonvisual function of the retina, mediated by a reduction in melanopsin expression and ipRGC survival, contributing to circadian disruption.

Outcome measure to assess head-down bed rest subject performance.

BACKGROUND: The purpose of the present study was to develop an objective outcome measure to assess the performance of head-down bed rest subjects. The rationale behind the development was that the current outcome measure is subjective and dependent upon how much the clinical psychologist knows about subject behaviors during the study to rate them accurately. METHODS: The behaviorally anchored rating scales (BARS) were developed through the use of the critical incident technique, along with traditional BARS development procedures, and the use of focus groups. RESULTS: Use of these methodologies yielded 86 usable critical incidents, which were used as anchors for the scales. DISCUSSION: Further research will be necessary to determine whether or not associations exist between data from the BARS and psychological screening data.

Identification and distribution of 14.3.3sigma (stratifin) in the human cornea.

We demonstrate for the first time the expression of 14.3.3sigma, an epithelial cell differentiation marker, in human corneal epithelium. 14.3.3sigma appeared at 30 kDa, pI 4-5, in 2D gels of corneal extracts. We found no significant differences in 14.3.3sigma levels between healthy corneas and corneas from keratoconus, corneal dystrophy, and corneal edema patients. 14.3.3sigma immunofluorescence was observed in the cytoplasm and nucleus of epithelial cells and colocalized with cyclin-B1. 14.3.3sigma was secreted by HCE-2 cells; HCE-2-conditioned medium induced matrix metalloproteinase-1 in cultured keratocytes. In summary, our work presents evidence of 14.3.3sigma expression in corneal epithelium and elaborates over its possible implications in corneal pathologic conditions.