Coffee, Renal Oxygenation, Blood Flow and Glomerular Filtration Rate in Early Diabetic Kidney Disease.

Over 1.25 million Americans have Type 1 Diabetes (T1D), increasing risk for early death from cardiovascular disease (CVD). Despite advances in glycemic and blood pressure control, a child diagnosed with T1D is expected to live up to 17 years less than non-diabetic peers. The strongest risk factor for CVD and mortality in T1D is diabetic kidney disease (DKD). Current treatments, such as control of hyperglycemia and hypertension, are beneficial, but only partially protect against DKD. This limited progress may relate to a narrow focus on clinical manifestations of disease, rather than on the initial metabolic derangements underlying the initiation of DKD. Renal hypoxia, stemming from a potential metabolic mismatch between increased renal energy expenditure and impaired substrate utilization, is increasingly proposed as a unifying early pathway in the development of DKD. T1D is impacted by several mechanisms which increase renal adenosine triphosphate (ATP) consumption and decrease ATP generation.

Caffeine, a methylxanthine, is known to alter kidney function by several mechanisms including natriuresis, hemodynamics and renin-angiotensin-aldosterone system. In contrast, to other natriuretic agents, caffeine is thought to fully inhibit the local tubuloglomerular feedback (TGF) response to increased distal sodium delivery. This observation has broad-ranging implications as caffeine can reduce renal oxygen (O2) consumption without impairing effective renal plasma flow (ERPF) and glomerular filtration rate (GFR).

There are also data suggesting that chemicals in coffee besides caffeine may provide important cardio-renal protection. Yet, there are no data examining the impact of coffee-induced natriuresis on intrarenal hemodynamic function and renal energetics in youth-onset T1D. Our overarching hypothesis in the proposed pilot and feasibility trial is that coffee drinking improves renal oxygenation by reducing renal O2 consumption without impairing GFR and ERPF. To address these hypotheses, we will measure GFR, ERPF, renal perfusion and oxygenation in response to 7 days of cold brew coffee (one Starbucks® Cold brew 325ml bottle daily [205mg caffeine]) in an open-label pilot and feasibility trial in 10 adolescents with T1D already enrolled in the CASPER Study (PI: Bjornstad).