Recruitment of a subset of subjects in this cohort has been described in detail elsewhere (supplementary Table A1, available in an online appendix at http://care.diabetesjournals.org/cgi/content/full/dc10-1219/DC1) (¹⁰). Subjects adhered to a sodium replete (>140 mmol/day) and moderate protein (<1.5 g/kg/day) diet during the 7-day period before each experiment (¹⁰,¹¹). A 24-h urine collection on day 6 was used to evaluate dietary adherence through the determination of urinary sodium and urea excretion. Protein intake was calculated from the urea excretion using standard methods (¹⁰,¹¹).

On two consecutive days, brachial artery blood pressure, renal hemodynamic parameters, and a spot urine sample were obtained after a 6-h modified clamp, during euglycemia (day 1, 4–6 mmol/l), and hyperglycemia (day 2, 9–11 mmol/l) (¹⁰,¹¹). In the left arm, a peripheral venous cannula was inserted for infusion of glucose and insulin, and a second cannula was inserted for blood sampling more distally. At the same time, a third intravenous infusion was inserted into the right arm and connected to a syringe infusion pump to measure renal hemodynamic function.

Blood pressure measurements were obtained with an automated Dinamap sphygmomanometer (Critikon, Tampa, FL). Renal hemodynamic function (glomerular filtration rate and effective renal plasma flow) were estimated by steady-state infusion of inulin and paraaminohippurate (¹⁰,¹¹).

Urinary analytes were measured in each urine sample using the 42-Plex Primary Cytokine/Chemokine Panel Luminex Assay (Eve Technologies, Calgary, Alberta, Canada) and included: epidermal growth factor, eotaxin, fibroblast growth factor-2, Fit-3L, fractalkine, granulocyte colony stimulation factor, granulocyte-macrophage colony-stimulating factor, growth-regulated oncogene, interferon (IFN)-α2, IFN-γ, interleukin (IL)-1α, IL-1β, IL-1ra, IL-2, IL-3, IL-4, IL-5, IL-6, IL-7, IL-8, IL-9, IL-10, IL-12 (p40), IL-12 (p70), IL-13, IL-15, IL-17, IP-10, monocyte chemoattractant protein (MCP)-1, MCP-3, macrophage-derived chemokine, macrophage inflammatory protein (MIP)-1α, MIP-1β, platelet-derived growth factor (PDGF)-AA, PDGF-AB/BB, RANTES, sCD40K, sIL-2Rα, transforming growth factor-α, tumor necrosis factor (TNF)-α, TNF-β, and vascular endothelial growth factor (supplementary Table A2). Analytes were corrected for the urinary creatinine concentration.

Baseline clinical parameters were analyzed using parametric methods (two independent sample t tests). Within subject responses to hyperglycemia were determined by repeated measures analysis of variance and were corrected for multiple comparisons using the Tukey-Kramer test. All statistical analyses were performed using SAS 9.2. The University Health Network and Hospital for Sick Children (Toronto, Canada) Research Ethics Boards approved the protocols, and patients gave informed consent.

Supplementary Table A3 describes the clinical characteristics of the cohort (n = 25). Subjects were young, normotensive, normoalbuminuric men and women with type 1 diabetes. Subjects adhered to the controlled sodium and protein diet. Six hours of clamped hyperglycemia was associated with expected increases in glomerular filtration rate and effective renal plasma flow (P < 0.05).

Clamped hyperglycemia was also associated with significant increases in urinary eotaxin (P = 0.0075), fibroblast growth factor-2 (P = 0.0026), granulocyte-macrophage colony-stimulating factor (P = 0.0192), IFN-α2 (P = 0.0045), IL-12 (P = 0.0034), MCP-3 (P = 0.0062), macrophage-derived chemokine (P = 0.0111), MIP-1α (P = 0.0201), PDGF-AB/BB (P = 0.0267), TNF-β (P = 0.0049), sCD40K (P = 0.0080) (Fig. 1A–L). For IL-3, the unadjusted P value was 0.01, which was not significant after adjustment for multiple comparisons (P = 0.058).

The goal of this pilot study was to determine whether acute clamped hyperglycemia activates renal inflammatory pathways in patients with uncomplicated type 1 diabetes. Our rationale was twofold: 1) acute glycemic excursions may contribute to end-organ injury in patients with diabetes, independent of long-term glycemic control; and 2) while acute hyperglycemia is associated with hemodynamic changes and activation of systemic inflammation, the acute effects on renal inflammatory pathways are not described well. We therefore determined whether acute hyperglycemia may contribute to kidney injury by activation of inflammatory pathways in patients with uncomplicated type 1 diabetes by measuring renal hemodynamic function and urinary concentrations of a broad panel of cytokines/chemokines in response to acute clamped hyperglycemia.

Our major finding was that in subjects with uncomplicated type 1 diabetes, clamped hyperglycemia is associated with significant increases in 12/42 cytokines/chemokines included in the pilot study. Urinary cytokines/chemokines excretion is increased in established diabetic nephropathy, and their excretion is influenced by renoprotective medications (⁷,⁸,^{12, B13}–¹⁴). Less is known about the renal excretion of inflammatory biomarkers in response to acute clamped hyperglycemia in humans with uncomplicated type 1 diabetes (¹⁵). Our findings show that acute moderate hyperglycemia induces an increase in urinary excretion of inflammatory mediators. While the factors responsible for this rise were not determined in this study, possible mechanisms include synthesis and/or release of preformed cytokines/chemokines from the kidney or possible spillover from the systemic circulation.

Given the critical role for hyperglycemia in the pathogenesis of diabetic nephropathy, the acute effect of glucose on markers of inflammation and fibrosis is important for two key reasons. First, increases in the urinary excretion of inflammatory factors may give mechanistic insights into disease pathogenesis in humans at a preclinical stage of disease. Our observations are consistent with previous work that demonstrated the deleterious effects of acute glycemic excursions on the renal microvasculature and highlight biological pathways that may be involved. Second, mediators that increase under the influence of acute hyperglycemia may act as markers that can be used to monitor the biological effects of experimental and therapeutic interventions in patients with type 1 diabetes. Although our study involved a small cohort that may never develop clinical diabetic nephropathy, our findings suggest that acute hyperglycemia induces a dynamic molecular signal in the urine that may contribute to progressive kidney injury over time. Future work should involve defining the time course and reversibility of the response and studying other populations, including nondiabetic control subjects and patients with overt nephropathy.

In conclusion, acute moderate hyperglycemia is associated with significant increases in the urinary excretion of inflammatory cytokines/chemokines in subjects with uncomplicated type 1 diabetes.

The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

This work was supported by operating grants from the Canadian Diabetes Association (to D.Z.I.C.). D.Z.I.C. is a recipient of a Kidney Foundation of Canada Scholarship; a Canadian Diabetes Association–Kidney Research Scientist Core Education and National Training (KRESCENT) Program Joint New Investigator Award; and receives operating support from the Canadian Institutes of Health Research (CIHR), the Canadian Diabetes Association, and the Heart and Stroke Foundation of Canada (with H.N.R.). H.N.R. is a recipient of a KRESCENT Program New Investigator Award. J.W.S. is the CIHR/AMGEN Canada Kidney Research Chair at the University Health Network, University of Toronto.

No potential conflicts of interest relevant to this article were reported.

D.Z.I.C. and H.N.R. researched data and wrote the manuscript. J.W.S., E.S., and T.J.B. contributed to discussion and reviewed/edited the manuscript.