Amir H. Kashani, Ph.D. - US grants

Project Summary Ischemia and hypoxia play critical roles in the pathophysiology of common blinding diseases such as diabetic retinopathy (DR) and retinal vein occlusions (RVO). Unfortunately, the correlation between impaired capillary perfusion, often called ischemia or ?nonperfusion,? and hypoxia is largely unknown in a clinical setting because of limited imaging methodologies. Impaired capillary perfusion is almost exclusively demonstrated in clinic by fluorescein angiography (FA) but histological studies show that FA underestimates capillary density as much as 30-40% thereby under-diagnosing ?nonperfusion.? Indirect clinical evidence and animal studies suggest that hypoxia underlies sequelae of DR and RVO. For example, contrast sensitivity deficits and retinal thickening are reversed in diabetic subjects breathing oxygen. However, there is little direct evidence of retinal hypoxia in humans because of the invasive methods needed to measure intraretinal oxygen levels. Since there is no direct clinical measure for mild-moderate hypoxia and only limited assessments of impaired capillary perfusion (ischemia), current treatments for DR and RVO presume a direct and static relationship between these two. However, abundant clinical evidence suggests that ischemia and hypoxia are not directly correlated. These observations confirm that the correlation between ischemia, hypoxia and sequelae of retinal vascular diseases are incompletely understood. I hypothesize that the relationship between microvascular hypoxia and ischemia is not static nor necessarily direct; and I suggest that this underlies limitations in current treatments and therapeutic failures. I propose basic and clinical studies that correlate real time intraocular pO2 measurements in animal models of ischemia with non-invasive imaging methods such as optical coherence tomography angiography (OCTA) to assess retinal capillary perfusion and hyperspectral computed tomographic imaging spectroscopy (HCTIS) to assess tissue hypoxia. These methods are then translated to the clinic where they are already shown to be safe and effective imaging modalities in pilot studies I have performed. The combination of these approaches leverages the gold standard intraocular pO2 measurements to validate and calibrate non- invasive methods that can be used safely and effectively in human subjects. Lastly, I propose to use OCTA and HCTIS to correlate the extent and duration of ischemia and hypoxia in human subjects with vision loss from DR and RVO.

Project Summary/Abstract While Alzheimer's disease (AD) is the most common cause of dementia, the contribution of vascular factors to cognitive impairment and dementia is becoming increasingly recognized. Vascular cognitive impairment and dementia (VCID) is most commonly caused by cerebral small vessel disease (SVD). To date, cerebral small vessels including arterioles, capillaries and venules are inaccessible to existing imaging technologies. Characteristic parenchymal lesions on MRI, such as lacunar infarcts, white matter lesions, and microbleeds, have been adopted as markers of SVD. However, these parenchymal lesions are the consequences of SVD rather than the surrogate markers of microvascular changes, and are unsuitable for early interventions to change the course of VCID. During the past few years, our group has spearheaded the development of a suite of cutting edge MRI technologies for in vivo and noninvasive assessment of microvascular structure and function, including (1) high-resolution black blood MRI for direct imaging of perforating arteries; (2) arterial spin labeling (ASL) techniques for mapping microvascular perfusion, arterial stiffness or vascular compliance (VC) of small arteries/arterioles, and water exchange rate across the blood-brain barrier (BBB). Furthermore, we recently developed quantitative metrics for retinal capillary density and morphology using an FDA approved optical coherence tomography angiography (OCTA) platform. This method allows clinically feasible, in vivo and completely noninvasive imaging of retinal arterioles and capillaries with a spatial resolution of ~10 microns. Capitalizing on our extensive technical expertise and longstanding track record of clinical studies on VCID, we propose this UH2/UH3 project to further develop and evaluate a suite of MRI and OCTA markers for assessing the structure and function of cerebral and retinal microvasculature, in a cohort of Latino subjects enrolled in the Los Angeles Latino Eye Study (LALES) and in the study of autosomal dominant AD in persons of Mexican origin (Estudio de Enfermedad de Alzheimer en Jalisciences, or EEAJ). During the UH2 phase, we will further develop and evaluate the proposed MRI and OCTA imaging markers of SVD, establish their test-retest repeatability and clinical utility. We will work with the other participating sites and with the Coordinating Center to establish collaborative parameters and agreements of the consortium. During the UH3 phase, we will contribute to and execute cross-site research studies as designed by the consortium. We will perform unified and comprehensive clinical, cognitive, imaging, genetic and biochemical assessments on the cohort of LALES and EEAJ participants locally and perform data analyses as required by the consortium. At the closing of this project, we expect to develop the suite of microvascular imaging markers to readiness to enter into large-scale multi-site clinical validation studies toward FDA qualification for phase II and phase III clinical trials on small vessel disease to prevent and treat VCID.

Abstract In the clinical diagnosis of diabetic retinopathy (DR), fluorescein angiography (FA) is currently the only method used routinely for the detection and treatment of ischemia, but it is an invasive method and not sensitive to early microvascular changes before the onset of visual symptoms. For the early detection and management of ischemia in DR, Optical Coherence Tomography Angiography (OCTA) is a novel method that has obtained FDA approval in 2015. Compared with FA, OCTA allows non-invasive imaging of both the neurosensory retina as well as the retinal vasculature at ~10?m resolution. Some recent studies have successfully used OCTA to extract quantitative 2D metrics that are well correlated with DR severity. Dr. Kashani?s group has pioneered several of the 2D OCTA metrics for the quantitative assessment of capillary morphology and density. While highly valuable, these 2D OCTA metrics were derived from the en face projection of the 3D OCTA data, and therefore inevitably obscure the geometric and topological information in the original 3D vasculature networks. To overcome this fundamental limitation, Drs. Shi and Kashani will collaborate in this R21 project to develop truly 3D metrics for the automated analysis of OCTA data and apply them for the early diagnosis of DR in large scale eye studies. For brain mapping research, Dr. Shi?s group at Laboratory of Neuro Imaging (LONI) of USC has developed various advanced computational tools for 3D shape analysis based on generally applicable principles from intrinsic geometry. In this project, we will translate and adapt these tools for 3D retinal vasculature modeling and analysis using OCTA data. There are three specific aims in this project: (1) Apply cutting-edge computational algorithms developed in brain imaging to develop novel 3D OCTA metrics for volume- and surface-based quantitation of retinal capillary density and morphology. (2) Define the relationship and reliability of 2D- and 3D-OCTA metrics with clinical severity of DR using our previously published cohorts of healthy and diabetic subjects. (3) Validate the relationship of 2D- and 3D-OCTA metrics with DR severity among a well-characterized population from the NEI funded African American Eye Diseases Study (AFEDS) and identify OCTA metrics associated with currently undetectable (sub-clinical) retinopathy. Given the rich computational tools developed by Dr. Shi?s group at LONI and the already collected, large-scale OCTA data (n=396) from the AFEDS study and Dr. Kashani?s published studies, the risk of this project is low, but the resulting 3D OCTA metrics and associated software tools will be highly valuable to the research and potentially clinical community. We will make all the software tools and source codes developed in this project freely available through the NITRC (http://www.nitrc.org) and LONI website (http://www.loni.usc.edu/Software).

Abstract Diabetes mellitus (DM) and hypertension (HTN) are two prototypical vascular diseases associated with microscopic pathological changes in retinal capillary structure. These changes ultimately lead to capillary dysfunction, capillary closure, ischemia and vision loss. Current clinical methods and diagnostics for staging these diseases are neither effective in detecting the earliest capillary changes nor in detecting incremental capillary changes (improvement or worsening) in later stages of the disease. For example, clinical detection of capillary loss is generally not possible by clinical examination alone. Fluorescein angiography (FA) is an invasive test that has been traditionally used to assess retinal perfusion but human studies show that the resolution and technical limitations of FA is only effective in detecting capillary loss after ~50% or more of capillaries are already non-perfused. In addition, FA is not clinically indicated unless there are already clinical signs of late stage disease and neovascularization. Therefore, reliably detecting and characterizing subclinical retinal capillary changes in DM and HTN represents an important opportunity to decrease disease burden and cost by enabling early diagnosis, clinical trials and interventions before irreversible tissue damage. Optical coherence tomography angiography (OCTA) is a safe, non-invasive and FDA approved method that provides a unique opportunity to achieve these goals. Our group of physicians, scientists and engineers have been pioneers in the development and application of OCTA technology. In this proposal, we seek to shift the current research and clinical practice paradigms in assessment of retinal vascular disease by utilizing cutting-edge commercially available OCTA technology and novel image acquisition methods to identify and measure subclinical changes in capillary structure and function. Our preliminary data shows that subclinical capillary loss occurs in all stages of DR. In this proposal we will (1) further characterize capillary changes in well controlled, non-interventional clinical trial of human subjects across race, age, gender and other possible confounding variables by taking advantage of well-characterized subjects from NIH-funded population based studies. (2) Assess the feasibility and reliability of novel OCTA measures of retinal capillary function. (3) To further characterize the magnitude and physiological relevance of these capillary changes we will use a custom built functional swept-source OCTA (FOCTA) to assess real time and in vivo retinal vascular responses during a focal physiologic light stimulus. The successful outcome of this proposal will develop and implement novel SD- and SS-OCTA based technology in human subjects to identify novel biomarkers of capillary loss or closure in DM and HTN. Application of these biomarkers will improve the diagnosis and management of disease by allowing direct evaluation of capillary changes and ischemia in a clinical setting. Our proposal uses spectral domain (SD) and swept-source (SS)-OCTA devices that are FDA approved so our results will be directly transferable to patient care.

Persons with similar amount of Alzheimer's or vascular brain pathology on imaging or autopsy may have had very different clinical and functional experiences during life. One possible reason could be varying amounts of cognitive reserve, or brain health which protects them from clinical manifestations. Thus, just as a healthy bone mass through life protects from osteoporosis and fractures, having a healthy brain at age 65-85, a consequence of genetic propensity and lifelong environmental, behavioral and disease-related factors, will protect from development of AD, dementia and stroke. How do we define a healthy brain phenotype? Brain health is typically characterized using quantitative measurements MRI and PET brain imaging, cognitive testing and at autopsy. Other dimensions of brain health, often altered in aging, prior to cognition, include retinal structure and vasculature, olfactory, visual, auditory, tactile and sensory perception and motor abilities. Sensory-motor measures are promising early biomarkers of AD and may play a causal role in the development or progression of dementia. An NIA workshop titled ?Sensory and Motor dysfunctions in Aging and AD? concluded that comprehensive sensory motor testing would provide key mechanistic insights into AD pathogenesis. We propose to incorporate multiple such sensory-motor measures in the recently funded 10th exam for 1874 Framingham Heart Study (FHS) Offspring and Omni 1 cohort participants and develop a multi-dimensional sensory-motor Brain Health Index (smBHI), as well as a composite BHI (cBHI) that additionally includes brain MRI and cognitive measures. Predictors and outcomes related to the BHI will be identified using the extensive profiling of risk factors, repeated measures of brain structure and function, information on MCI, dementia (AD and VCID) and stroke outcomes already available in FHS. It will be validated in 3 additional population samples, 200 African- Americans in Jackson, MS, 400 Hispanic participants in San Antonio, Texas and 1650 European ancestry participants in the Great Age Study in Barri, Italy (LOS only, will collect and analyze data with Italian funding. Aim 1: To characterize individual brain health using a multidimensional sensory-motor `Brain Health Index' by assessing olfaction, retina, vision, auditory function, vestibular function, touch sensation, motor function, and examine its association with (i) cross-sectional MRI, PET and cognitive function and (ii) incident mild cognitive impairment (MCI), dementia including AD, VCID, TIA, stroke and all-cause mortality over 3-5 years and subsequent follow-up Aim 2: To investigate the effect of lifelong (20-40+ years) social, behavioral and vascular/metabolic factors, measured previously on these participants, on individual sensory-motor functions, smBHI and cBHI and brain reserve (difference between BH age and chronological age) Aim 3: To examine the association between (1) genetic, (2) putative circulating biomarkers and (3) epigenetic aging and `brain health' Aim 4: To replicate the associations observed in Aims 1, 2 and 3 in our three replication samples.