This proposal aims to test two promising new treatments for diabetic neuropathy, Ilepatril and LCZ696. Each of these drugs acts through two mechanisms proposed to preserve peripheral nerves in diabetes: 1) to reduce the effect of angiotensin II on immune-mediated nerve damage and to reduce its effect on vessels supplying peripheral nerves, acting to improve their blood supply, and 2) to inhibit neutral endopeptidase, which will make neuro- and vaso-active peptides more available at nerve endings to maintain vascular and nerve integrity and function. This proposal will also validate the use of corneal nerve morphology and sensory function as valid early small fiber markers of diabetic peripheral neuropathy. The structure and function of corneal nerves are proposed as surrogates for detecting diabetic neuropathy early in humans and animal models and for use as outcome measures for the new treatments proposed. Our long term objective is to conduct pre-clinical trials with the intent of identifying new effective treatments for diabetic neuropathy and to advance this treatment to clinical trials using corneal nerve structure and sensory function as outcome measures. Progress toward this goal has been hampered by the lack of a sensitive and reliable method for diagnosing and monitoring peripheral neuropathy. Recently, corneal confocal microscopy has shown promise as a non-invasive method for quantifying the damage and repair of corneal sensory nerves and to serve as a surrogate marker for diabetic neuropathy. Preliminary studies of corneal nerves in human diabetic patients have been promising, but studies in animal models characterizing diabetic corneal nerve damage by monitoring their structure and sensory function over time have yet to be performed. The immediate goals of this application are to examine the development, progression and repair of corneal neuropathy in animal models of type 2 diabetes. This will be accomplished by investigating the structural integrity of corneal nerves using confocal microscopy and their function by using a Cochet-Bonnet filament esthesiometer. In addition to corneal sensation, rate of tear production will also be monitored using Zone-Quick cotton threads (similar to a Schirmer's test in humans). Corneal structural and functional results will be compared to standard endpoints used to identify diabetic peripheral neuropathy, including motor and sensory nerve conduction velocity, thermal nociception and intraepidermal nerve fiber density in the hindpaw. After validating corneal nerves as a surrogate marker for diabetic neuropathy, we will test the efficacy of two promising new treatment approaches on diabetes-induced corneal nerve damage and function. The treatment hypothesis to be examined is whether diabetic corneal nerve damage is caused to a large extent by modifiable factors targeted by treatment with Ilepatril and/or LCZ696. The first phase of the study will address the hypothesis that type 2 diabetes causes an early and progressive loss of corneal nerves, reduces corneal sensitivity and decreases vascular relaxation in the posterior ciliary artery, which supplies the orbital portion of the trigeminal corneal nerves. It i hypothesized that corneal nerve damage and dysfunction will precede peripheral diabetic neuropathy. A longitudinal study in high fat fed/low dose streptozotocin diabetic rats, an accepted model of type 2 diabetes, will test this hypothesis. These studies will provide an understanding of the progression of diabetic nerve damage. The second phase of the study will address the hypothesis that corneal nerve fiber loss, corneal dysfunction and impaired vascular reactivity of the posterior ciliary artery can be rescued by treating type 2 diabetic rats with Ilepatril and/or LCZ696. Results from these studies will determine whether prevention and intervention therapies can improve diabetes-induced corneal nerve impairment. These studies will provide a basis for the use of non-invasive assessment of structure and function of corneal nerves as a clinical tool for assessing diabetic peripheral neuropathy and its treatment in human clinical trials.
Type 2 diabetes is approaching epidemic levels and is creating a large burden on the financial capabilities of the VA health care system. Current therapies have not prevented the progression of disease, which often results with patients developing severe complications leading to amputations and increased mortality. These poor outcomes impact the quality of life of Veterans and also affect their families. Currently, there exists no quantitative non-invasive standard for detecting and monitoring treatment of diabetic neuropathy, hindering the development of new therapies. We will examine the applicability of using corneal confocal microscopy and measuring a corneal sensory function as a marker for diabetic neuropathy. Applying this methodology, we will test the efficacy of selected treatments for diabetic neuropathy as determined by improving corneal nerve damage and function.
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