Candidate: Tamara Isakova received her MD from Downstate College of Medicine, and completed her Internal Medicine Residency at Massachusetts General Hospital. She is currently a research fellow in nephrology at MGH, and a candidate for a Master's degree in human physiological investigation from Harvard Medical School. Mentor: Dr. Ravi Thadhani is a world-renowned clinical investigator with extensive mentorship experience. Dr. Thadhani will ensure the success of Dr. Isakova's training, proposed studies and career development. Research: Secondary hyperparathyroidism (sHPT) is a common and early complication of chronic kidney disease (CKD) that is associated with bone and cardiovascular disease and mortality. While the factors that maintain increased levels of parathyroid hormone (PTH) in advanced CKD are well established, the pathophysiological triggers that initiate increased PTH secretion in early CKD are less clear. Data from our group demonstrated that normocalcemic patients with early CKD developed subtle but significant reductions in serum calcium levels in the postprandial state. The relative hypocalcemia followed an increase in calciuria and was associated with a subsequent increase in postprandial PTH levels. Importantly, fasting PTH levels were not significantly increased in these patients;differences in PTH physiology between CKD and controls were detectable only in the postprandial """"""""stressed"""""""" state. Thus, we hypothesize that postprandial calciuria with episodic, relative hypocalcemia is a previously unreported initiating factor in the pathogenesis of sHPT in early CKD. In the current proposal we will explore this novel hypothesis in a series of human physiological studies and assess the relevance of the physiologic mechanisms at the population level in the Chronic Renal Insufficiency Cohort (CRIC), a large established cohort of CKD patients.
In Aim 1, we will examine the PTH secretory pattern in CKD and its relationship with calciuria, calcemia and dietary calcium intake in response to 3 separate meals over the course of 24-hours to test whether there is a """"""""stacking"""""""" effect from meal to meal on increased PTH secretion.
In Aim 2 A, we will increase separately the meal protein and sodium contents in order to test whether greater calciuria following high protein and sodium meals is associated with worsening hypocalcemia and greater PTH elevation in CKD.
In Aim 2 B, we will test whether augmenting dietary calcium intake or its absorption using calcitriol will blunt the postprandial hypocalcemia and thus prevent subsequent increases in PTH secretion.
In Aim 3, we will examine in CRIC the effects of dietary sodium, calcium, phosphorus and protein, and therapy with diuretics on PTH levels and the risk of developing sHPT in CKD. We believe the results of these studies will provide important insights into novel mechanisms of sHPT in early CKD and lead to improved diagnosis and management of early-stage CKD patients. A K23 award will allow Dr. Isakova to attain new skills in clinical investigation and develop into an independent clinical investigator.

Public Health Relevance

The long term goal of this proposal is to improve the lives of patients with chronic kidney disease (CKD) by studying the mechanisms for development of secondary hyperparathyroidism in CKD. Our results will provide new insights into the initiation of this hormone problem in CKD and guide new treatments to improve clinical outcomes for patients with CKD.

National Institute of Health (NIH)
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Mentored Patient-Oriented Research Career Development Award (K23)
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Diabetes, Endocrinology and Metabolic Diseases B Subcommittee (DDK)
Program Officer
Rankin, Tracy L
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University of Miami School of Medicine
Internal Medicine/Medicine
Schools of Medicine
Coral Gables
United States
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Isakova, Tamara; Cai, Xuan; Lee, Jungwha et al. (2016) Associations of FGF23 With Change in Bone Mineral Density and Fracture Risk in Older Individuals. J Bone Miner Res 31:742-8
Isakova, Tamara; Ix, Joachim H; Sprague, Stuart M et al. (2015) Rationale and Approaches to Phosphate and Fibroblast Growth Factor 23 Reduction in CKD. J Am Soc Nephrol 26:2328-39
Isakova, Tamara; Craven, Timothy E; Scialla, Julia J et al. (2015) Change in estimated glomerular filtration rate and fracture risk in the Action to Control Cardiovascular Risk in Diabetes Trial. Bone 78:23-7
Mehta, Rupal; Ying, Gui Shuang; Houston, Samuel et al. (2015) Phosphate, fibroblast growth factor 23 and retinopathy in chronic kidney disease: the Chronic Renal Insufficiency Cohort Study. Nephrol Dial Transplant 30:1534-41
Scialla, Julia J; Xie, Huiliang; Rahman, Mahboob et al. (2014) Fibroblast growth factor-23 and cardiovascular events in CKD. J Am Soc Nephrol 25:349-60
Contreras, G; Li, H; Gonzalez-Suarez, M et al. (2014) Kidney allograft survival of African American and Caucasian American recipients with lupus. Lupus 23:151-8
Cortazar, Frank; Diaz-Wong, Roque; Roth, David et al. (2013) Corticosteroid and calcineurin inhibitor sparing regimens in kidney transplantation. Nephrol Dial Transplant 28:2708-16
Isakova, T; Xie, H; Messinger, S et al. (2013) Inhibitors of mTOR and risks of allograft failure and mortality in kidney transplantation. Am J Transplant 13:100-10
Isakova, Tamara (2013) Comparison of mineral metabolites as risk factors for adverse clinical outcomes in CKD. Semin Nephrol 33:106-17
Isakova, Tamara; Houston, Jessica; Santacruz, Laura et al. (2013) Associations between fibroblast growth factor 23 and cardiac characteristics in pediatric heart failure. Pediatr Nephrol 28:2035-42

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