Rodica Pop-Busui - US grants

DESCRIPTION (provided by applicant): Present in up to 50 % of diabetic patients, diabetic peripheral neuropathy (DPN), is one of the most threatening complications of diabetes mellitus (D), constituting the leading cause of non-traumatic amputations. To date, a viable treatment for human DPN is not available. Although the pathophysiology of DPN is still quite poorly understood, increased oxidative stress and alterations in cyclooxygenase (COX) pathway activity, with subsequent perturbations in prostanoid metabolism, have been involved as critical factors. The overall hypothesis of this application is that in experimental D activation of the COX-2 pathway by oxidative stress, contributes to the biochemical, functional, neurotrophic and structural deficits of DPN. The objective of this proposal is to delineate the relationships between glucose-mediated oxidative stress, components of the COX pathway, and impaired neurotrophic support in the pathogenesis of DPN. Understanding these mechanisms and their relationship, may provide a rationale for the use of COX-2 selective inhibitors as a new and efficient therapeutic approach in patients with DPN. Streptozotocin-diabetic (STZ-D) rats, mice deficient in the expression of the COX-2 gene, and intervention with COX inhibition will be employed. Experimental DPN will be assessed with functional measurements of motor and sensory nerve conduction velocity (NCV) and nerve blood flow (NBF); light and electron microscopic nerve morphometry; biochemical parameters of nerve energy metabolism, oxidative stress, and antioxidative defense; measures of Schwann cell and sensory neuron apoptosis (AP). The Specific Aims are: Aim 1. To characterize the relationships of glucose-mediated oxidative stress to COX-2 pathway activation on the development of selected biochemical, functional, morphometric and neurotrophic defects in STZ-D rats. Aim 2. Determine the time course for the development of selected biochemical, functional, morphometric, apoptotic and neurotrophic defects in STZ-D mice deficient in the human COX-2 gene. These studies will help to elucidate the mechanism by which oxidative stress and COX pathway influence the development of DPN and, facilitate the design of human studies, in which the aim will be the prevention or reversal of DPN.

DESCRIPTION (provided by applicant): In type 1 diabetes (T1DM), left ventricle (LV) dysfunction often precedes or occurs in the absence of coronary artery disease or hypertension. This suggests that diabetes has direct effects on the heart, which can contribute to the development of cardiomyopathy and LV dysfunction through other mechanisms including: microvascular disease, myocardial metabolism and energetic impairment, autonomic neuropathy and oxidative stress. Cardiac autonomic neuropathy (CAN) is associated with an increased prevalence of silent myocardial ischemia, and is an independent predictor of increased cardiac mortality. Sympathetic imbalance associated with CAN may critically influence myocardial glucose utilization and contribute to LV contractile abnormalities and functional deficits. We have previously shown that CAN is associated with diastolic dysfunction in patients with T1DM. Recently, magnetic resonance imaging (MRI) myocardial tagging has been used to demonstrate increased LV torsion in T1DM patients, a measure providing sensitive information on early LV tissue deformation. Our preliminary studies indicated that increased torsion correlates with markers of CAN. Recent evidence also suggests that glycemic variability may influence the risk of cardiovascular complications, possibly through a mechanism mediated by activation of oxidative stress. We have previously found that oxidative stress was highest in CAN subjects, and we hypothesize that this could be secondary to increased glycemic excursions. Based on these data, our hypothesis is that, in T1DM, sympathetic activation induced by acute glycemic fluctuations, in concert with activation of oxidative stress, promotes alterations in myocardial oxidative metabolism and efficiency via catecholamine toxicity. Subsequently, the development of increased LV torsion and strain, diastolic dysfunction, and cardiomyopathy increase the risk of cardiovascular events. We propose to test these hypotheses in a prospective clinical study with two specific aims. Aim 1 will determine the association between sympathetic activation and cardiac metabolic and functional deficits in subjects with T1DM free of coronary artery disease. The manifestations of sympathetic activation will be determined by positron emission tomography (PET) with [11C]meta-hydroxyephedrine ([11C]HED), heart rate variability, and 24-hour blood pressure monitoring in patients with T1DM (5-10 years'diabetes duration). These will be correlated with changes in cardiac oxidative metabolism and efficiency determined by [11C]acetate PET and with LV torsion and strain assessed by cardiac MRI with tagging. Aim 2 will explore the natural history of myocardial dysfunction in T1DM and will identify predictive biomarkers and potential pathways involved in the development of these deficits. Subjects with T1DM recruited in Aim 1 will be followed prospectively for 3 years, while adhering to the current standard of care for T1DM, and re-assessed utilizing the outcome measures described in Aim 1. We will correlate changes in sympathetic function, LV torsion, and efficiency with the magnitude of glycemic excursions and down-stream biomarkers proposed to contribute to the development of small fiber dysfunction and microvascular disease: oxidative stress fingerprints as assessed by gas- chromatography/mass spectrometry, real-time qRT-PCR, poly(ADP-ribose) polymerase activation and deficits of intraepidermal nerve fiber density (IENFD). We will also determine whether these minimally invasive surrogate measures can identify subjects susceptible to the development of sympathetic and cardiac deficits. These studies will help elucidate mechanisms of myocardial dysfunction in T1DM with ultimate goal of designing future studies implementing therapeutic strategies aimed at preventing increased cardiovascular risk in patients with T1DM. PUBLIC HEALTH RELEVANCE: It was shown that the injury to heart nerves in diabetes, called cardiac autonomic neuropathy (CAN), is an independent predictor of cardiovascular disease (CVD) mortality, which is up to 4 fold more in patients with diabetes than the general population. Heart failure contributes to CVD and in type 1 diabetes (T1DM) it may occur in the absence of significant ischemic heart disease. This proposal will test if, in T1DM, wide blood glucose fluctuations lead to diabetic CAN and to impaired heart contractile patterns and will evaluate the natural history of heart failure and enhanced CVD risk in patients with T1DM in the current standard of diabetes care. These studies also seek to characterize minimally invasive and sensitive biomarkers that may predict the development and progression of these deficits in T1DM. Identifying the impact of acute and wide glucose fluctuations in T1DM, and their relationship with CAN and cardiovascular risk, could help clinicians better determine the safe premises for intensifying insulin therapy in this patient population.

DESCRIPTION (provided by applicant): Diabetic neuropathy (DN) is the most common chronic complication of diabetes, ultimately affecting half of patients with type 1 diabetes (T1DM) and leading to severe morbidity, high mortality, major physical disability, poor quality of life and estimated total annual costs of $22 billion. Due to the complex structure and anatomy of the peripheral nervous system, DN presents with a very broad spectrum of clinical symptoms and deficits, including severe pain, sensory deficits, foot ulcers and amputations. Despite the high morbidity associated with DN, most randomized clinical trials evaluating therapies for established DN have been disappointing. To date there is no pathogenetic treatment for this condition. The Diabetes Control and Complications Trial (DCCT) demonstrated that intensive control designed to achieve near-normal glycemia is essential in reducing the risk of DN development in type 1 diabetes. However, attainable intensive glycemic control, although necessary, is insufficient to prevent adverse nervous system effects, justifying a therapeutic need to identify new drug targets to treat DN early in its course. Evidence for an important role of low-grade inflammation and of nuclear factor kappa B (NF-kB) activation in the pathogenesis of DN and in the pain syndrome associated with DN is emerging from both experimental and clinical studies. This suggests that agents with known anti-inflammatory properties, such as salicylates, may prevent the development of DN and the pain associated with DN. Salsalate (Disalcid), a pro-drug form of salicylate, is an FDA approved treatment for osteoarthritis and other rheumatologic conditions. It is a highly effective drug in blocking the IKK2/NF-:B pathway, with a large margin of safety, and low cost. Salsalate has recently been shown to have glucose lowering effects. We propose to develop a clinical trial to evaluate the effect of Salsalate on DN. Our specific aims are: Aim 1: Develop a proposal for a multi-center randomized clinical trial to evaluate the effects of salsalate on measures of DN in patients with T1DM Aim 2: Develop the supporting materials needed to conduct the trial in Aim 1, develop the criteria of site selection, reach out to the sites of interest and finalize the selection process, and develop the general and site specific recruitment strategies. The accomplishment of these aims will allow implementing the proposed clinical trial protocol on a sample of subjects to test documents and procedures during the planning grant phase R34 and allow submission of an application for a multi-center trial grant. PUBLIC HEALTH RELEVANCE: This study is relevant to public health because diabetic neuropathy (DN) is the most common chronic complication of diabetes, ultimately affecting half of patients with diabetes and leading to severe morbidity, high mortality, major physical disability, and poor quality of life. This is relevant to the NIH mission because to date there is still no specific treatment for DN. We propose to use a FDA-approved drug commonly used to treat osteoarthritis, which has recently been shown to have glucose lowering effects, to address inflammation - a critical mediator in the development and progression of peripheral nerve damage in diabetes, and pain- the most common and cumbersome symptom for patients with DN.