Cystic fibrosis (CF) is a catabolic, recessive genetic disease whose prognosis is highly dependent on maintenance of adequate nutritional status. As life expectancy increases, co-morbidities such as CF-related diabetes (CFRD) become more prevalent. It is thus increasingly important to identify pathophysiologic pathways that will inform nutritional therapies for adult patients with CF. Recent advances in metabolomics analysis provide a novel opportunity to broadly explore metabolism and underlying pathways relevant to disease exacerbation and recovery in CF. The PI, Jessica A. Alvarez, PhD, RD, will use high-resolution, liquid chromatography-mass spectrometry (LC-MS) metabolomics methods as a tool to interrogate the plasma metabolome in cohorts of adult CF patients, with or without CFRD, in collaboration with a multidisciplinary team of expert mentors (including Lead Mentor Dr. Thomas R. Ziegler and Co-Mentors Drs. Dean P. Jones, Vin Tangpricha, Arlene A. Stecenko, and Nael A. McCarty). Based on preliminary clinical and metabolomics research findings by the PI and the mentoring team, the working hypotheses of this project are: 1) aminothiol redox imbalance in CF contributes to impaired fatty acid ?-oxidation, and 2) vitamin D supplementation normalizes the redox system and, subsequently, ?-oxidation. Specific Aim 1 is to confirm a defect in ?- oxidation in adult CF subjects using high-resolution targeted plasma metabolomics analysis and complementary in vivo bioenergetic assessment methods (indirect calorimetry,31phosphorus-magnetic resonance spectroscopy) in a cross-sectional study of adult subjects with CF compared to healthy, age matched controls. Specific Aim 2 will determine if plasma aminothiol redox status is associated with ?-oxidation in this cross-sectional study. Specific Aim 3 is a pilot study to determine the impact of high-dose oral vitamin D3 on indexes of ?-oxidation and aminothiol redox in adult CF patients hospitalized for pulmonary exacerbation and followed during clinical recovery in an ongoing, double-blind, randomized controlled trial. Emory University boasts an intellectually rich research environment whose resources will be used to carry out the proposed research, including an NIH-funded Atlanta Clinical and Translational Science Institute Clinical Research Network site. The primary goal of this K01 career development proposal is for Dr. Alvarez to develop expertise in high-resolution metabolomics for use in clinically oriented nutrition research, which will highly complement her nutrition and metabolism training to-date. The proposed research, in combination with a structured mentoring and training plan that includes didactic courses and workshops, is designed to facilitate Dr. Alvarez's long-term goal of developing an independently-funded clinical and translational nutrition research program in chronic catabolic diseases, such as CF, consistent with the mission of the NIDDK.