Volume 86, Issue 1, Pages 67-74 (July 2014) High altitude may alter oxygen availability and renal metabolism in diabetics as measured by hyperpolarized [1-13C]pyruvate magnetic resonance imaging  Christoffer Laustsen, Sara Lycke, Fredrik Palm, Jakob A. Østergaard, Bo M. Bibby, Rikke Nørregaard, Allan Flyvbjerg, Michael Pedersen, Jan H. Ardenkjaer-Larsen  Kidney International  Volume 86, Issue 1, Pages 67-74 (July 2014) DOI: 10.1038/ki.2013.504 Copyright © 2014 International Society of Nephrology Terms and Conditions

Figure 1 Oxygen availability measurements with microelectrodes and blood oxygen level–dependent (BOLD) magnetic resonance imaging (MRI). (a) pO2 (tissue oxygen partial pressure) mean values from the microelectrode experiments from the medulla and cortex in control and diabetic rats during altered oxygen content in the inspired air. (b) R2* mean values from the 1H BOLD MRI from the medulla and cortex in control and diabetic rats during altered oxygen content in the inspired air. Data are presented as mean±s.e.m. *P<0.05 compared with corresponding control, whereas (x-y) denotes P<0.05 compared between the two states x and y within the same group. Kidney International 2014 86, 67-74DOI: (10.1038/ki.2013.504) Copyright © 2014 International Society of Nephrology Terms and Conditions

Figure 2 Anatomical 1H magnetic resonance imaging (MRI) overlaid with metabolic maps of lactate, alanine, pyruvate, and bicarbonate in control and diabetic rats during altered oxygen content in the inspired air. The metabolic maps are normalized individually to show the biodistribution of each metabolite in the kidney and surrounding tissue. Kidney International 2014 86, 67-74DOI: (10.1038/ki.2013.504) Copyright © 2014 International Society of Nephrology Terms and Conditions

Figure 3 Individual metabolite ratio plots of lactate, alanine, pyruvate, and bicarbonate in control and diabetic rats during altered oxygen content in the inspired air. *P<0.05 compared with corresponding control, whereas (x-y) denotes P<0.05 compared between the two states x and y within the diabetes group. Data are presented as mean±s.e.m. Kidney International 2014 86, 67-74DOI: (10.1038/ki.2013.504) Copyright © 2014 International Society of Nephrology Terms and Conditions

Figure 4 Boxplot illustration of biochemical analysis of diabetic and kidney cortex of rats exposed to 15min of hypoxia (10% O2:90% N2). (a) mRNA expression of lactate dehydrogenase (LDH) is significantly increased in the diabetic kidney. (b) mRNA expression of alanine aminotransferase (ALT) is similar between the diabetic and the control kidney. (c) mRNA expression of pyruvate dehydrogenase (PDH) is significantly decreased in the diabetic kidney compared with the control kidney. (d) LDH activity is not significantly different in the diabetic kidney compared to the control kidney. (e) ALT activity is significantly increased in the diabetic kidney compared with the control kidney. (f) The NAD+/NADH (oxidized and reduced nicotinamide adenine dinucleotides) ratio is significantly decreased in the diabetic kidney compared with the control. *P<0.05 compared with corresponding control. The central mark is the median, the boxes are the 25th and 75th percentiles, and outliers are plotted individually +. Kidney International 2014 86, 67-74DOI: (10.1038/ki.2013.504) Copyright © 2014 International Society of Nephrology Terms and Conditions

Figure 5 Proposed hypothesis for how reduced oxygen content in the inspired air accentuates the development of diabetic nephropathy. Classical hyperglycemia-induced pseudohypoxia inducing reduced NAD+/NADH (oxidized and reduced nicotinamide adenine dinucleotides) ratio, resulting in increased lactate formation, despite sufficient oxygen level to run oxidative phosphorylation, which promotes diabetic nephropathy via activation of protein kinase C (PKC), increased oxidative stress, and metabolic alterations (left). Reduced oxygen content in the inspired air accelerates the pseudohypoxia by magnifying the reduced NAD+/NADH ratio, evident from increased lactate formation, and accelerated development of diabetic nephropathy. Kidney International 2014 86, 67-74DOI: (10.1038/ki.2013.504) Copyright © 2014 International Society of Nephrology Terms and Conditions

Figure 6 Experimental magnetic resonance imaging (MRI) setup consists of three different oxygen levels in the inspired air. At all levels of oxygen, 1H blood oxygen level–dependent magnetic resonance imaging (BOLD MRI) and 13C chemical shift imaging (CSI) hyperpolarized experiments were performed at 5 and 15min after the start of the intervention, respectively. Thus, a total of six measurements were performed in each animal. Kidney International 2014 86, 67-74DOI: (10.1038/ki.2013.504) Copyright © 2014 International Society of Nephrology Terms and Conditions