The purpose of this study was to investigate the protective effect of hyperbaric oxygen therapy (HBO) in diabetic kidney and thus reverse the metabolic derangement as a consequence of renal hypoxia associated with diabetes. Hyperpolarised [1-13C]pyruvate MRI was used to asses metabolic changes in renal metabolism of pyruvate after HBOT in healthy and diabetic rats.Twenty-eight female wistar rats (mean age ten weeks) were included. The rats were randomly assigned into four groups – two diabetes groups and two control groups. Diabetes was induced with an intravenous injection of streptozotocin (STZ; 55 mg/kg body weight; Sigma-Aldrich, St. Louis, USA) dissolved in a cold citrate buffer (10mmol/L, pH 4.5) in two groups. Blood glucose was measured with a ContourXT blood glucose meter (Bayer Diabetes Care, Copenhagen, Denmark). Rats were included as diabetics if the blood glucose was higher than 15mmol/L 48 hours after induction of diabetes with STZ. One diabetes group and one healthy group were treated with HBO consisted of five daily pressurizations to 2.5 ATA for one hour using pure oxygen. The two control groups (a healthy group and a diabetic group) were kept in the pressure chamber for the same amount of time as the two HBO treated groups, but were kept at normal pressure and atmospheric air. STZ was given 11 days prior to treatment of HBO. Prior to MRI, each rat was anaesthetized with sevoflurane and a catheter was placed in the tail vein for injection of 1.5 mL of [1-13C]pyruvate which were hyperpolarized in a SpinLab (GE Healthcare). MRI was performed on a 3T clinical scanner (GE Healthcare, USA). A dual tuned 1H/13C quadrature volume transmit/receive coil (GE healthcare, USA) was used for 1H/13C excitation/reception. The kidneys were localized by a standard gradient-echo sequence, and a slice covering both kidneys was shimmed automatically. A slice-selective 13C IDEAL spiral sequence was used for hyperpolarized [1-13C]pyruvate imaging acquiring images every 5 s initiated 20 s after the start of injection. flip angle=10º, 11 IDEAL echoes and one initial spectrum per IDEAL encoding, TR/TE/ΔTE=100 ms/0.9 ms/0.9 ms, FOV=80x80 mm2, 5 x 5 mm real resolution and an axial slice thickness of 15 mm covering both kidneys. Temperature, oxygen saturation and respiration frequency were monitored (SA instruments) throughout MRI examinations. Data was transferred to OsiriX (Pixmeo, Geneva, Switzerland) where region of interest (ROI) analysis was performed covering both kidneys.

Rats were only included in diabetic groups if their blood glucose level exceeded 15mmol/L 48 hours following the STZ injection. A tendency of a reduced blood glucose level during the experiment period was found in the HBO treated diabetic group compared with the untreated diabetic group. The endpoint blood glucose level was significantly different between the untreated diabetic group and the HBO treated diabetic group (figure 1). Our data confirmed an increase in lactate in diabetic rat kidneys¹. However, we found no change in the metabolism of either pyruvate-to-lactate/alanine/bicarbonate in the healthy HBO treated group compared with the healthy untreated group were observed. It corresponds to, that HBO is found safe in healthy rats². A tendency towards a decreasing lactate-to-pyruvate ratio was found with HBO (figure 2).

HBO seems to reduce blood glucose level in diabetic rats. And HBO shows a tendency to decrease the metabolism in the healthy rat kidney and attenuates the derangement of metabolism in the diabetic kidney. More studies are required to confirm the presented hypotheses.