Lotte Bonde Bertelsen

Renal ischemia and reperfusion assessment with three‐dimensional hyperpolarized 13C,15N2‐urea

The aim of this work was to investigate whether hyperpolarized 13C,15N2‐urea can be used as an imaging marker of renal injury in renal unilateral ischemic reperfusion injury (IRI), given that urea is correlated with the renal osmotic gradient, which describes the renal function.

Hyperpolarized 13C urea relaxation mechanism reveals renal changes in diabetic nephropathy.

Our aim was to assess a novel 13C radial fast spin echo golden ratio single shot method for interrogating early renal changes in the diabetic kidney, using hyperpolarized (HP) [13C,15N2]urea as a T2 relaxation based contrast bio‐probe.

Antioxidant treatment attenuates lactate production in diabetic nephropathy

The early progression of diabetic nephropathy is notoriously difficult to detect and quantify before the occurrence of substantial histological damage. Recently, hyperpolarized [1-13C]pyruvate has demonstrated increased lactate production in the kidney early after the onset of diabetes, implying increased lactate dehydrogenase activity as a consequence of increased nicotinamide adenine dinucleotide substrate availability due to upregulation of the polyol pathway, i.e., pseudohypoxia. In this study, we investigated the role of oxidative stress in mediating these metabolic alterations using state-of-the-art hyperpolarized magnetic resonance (MR) imaging. Ten-week-old female Wistar rats were randomly divided into three groups: healthy controls, untreated diabetic (streptozotocin treatment to induce insulinopenic diabetes), and diabetic, receiving chronic antioxidant treatment with TEMPOL (4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl) via the drinking water. Examinations were performed 2, 3, and 4 wk after the induction of diabetes by using a 3T Clinical MR system equipped with a dual tuned 13C/1H-volume rat coil. The rats received intravenous hyperpolarized [1-13C]pyruvate and were imaged using a slice-selective 13C-IDEAL spiral sequence. Untreated diabetic rats showed increased renal lactate production compared with that shown by the controls. However, chronic TEMPOL treatment significantly attenuated diabetes-induced lactate production. No significant effects of diabetes or TEMPOL were observed on [13C]alanine levels, indicating an intact glucose-alanine cycle, or [13C]bicarbonate, indicating normal flux through the Krebs cycle. In conclusion, this study demonstrates that diabetes-induced pseudohypoxia, as indicated by an increased lactate-to-pyruvate ratio, is significantly attenuated by antioxidant treatment. This demonstrates a pivotal role of oxidative stress in renal metabolic alterations occurring in early diabetes.

Acute porcine renal metabolic effect of endogastric soft drink administration assessed with hyperpolarized [1‐13c]pyruvate

Our aim was to determine the quantitative reproducibility of metabolic breakdown products in the kidney following intravenous injection of hyperpolarized [1‐13C]pyruvate and secondly to investigate the metabolic effect on the pyruvate metabolism of oral sucrose load using dissolution dynamic nuclear polarization. By this technique, metabolic alterations in several different metabolic related diseases and their metabolic treatment responses can be accessed.

Vascular effects of plinabulin (NPI-2358) and the influence on tumour response when given alone or combined with radiation.

Abstract Purpose: This study investigated the anti-tumour effects of the novel vascular disrupting agent plinabulin (NPI-2358) when given alone or combined with radiation. Materials and methods: Foot implanted C3H mammary carcinomas or leg implanted KHT sarcomas were used, with plinabulin injected intraperitoneally. Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) measurements were made with gadolinium-diethylenetriamine pentaacetic acid (Gd-DTPA) on a 7-tesla magnet. Treatment response was assessed using regrowth delay (C3H tumours), clonogenic survival (KHT sarcomas) or histological estimates of necrosis for both models. Results: Plinabulin (7.5 mg/kg) significantly reduced the initial area under curve (IAUC) and the transfer constant (Ktrans) within 1 hour after injection, reaching a nadir at 3 h, but returning to normal within 24 h. A dose-dependent decrease in IAUC and Ktrans, was seen at 3 h. No significant anti-tumour effects were observed in the C3H tumours until doses of 12.5 mg/kg were achieved, but started at 1.5 mg/kg in the KHT sarcoma. Irradiating tumours 1 h after injecting plinabulin enhanced response in both models. Conclusions: Plinabulin induced a time- and dose-dependent decrease in tumour perfusion. The KHT sarcoma was more sensitive than the C3H tumour to the anti-tumour effects of plinabulin, while radiation response was enhanced in both models.

Diabetes induced renal urea transport alterations assessed with 3D hyperpolarized 13C,15N-Urea

In the current study, we investigated hyperpolarized urea as a possible imaging biomarker of the renal function by means of the intrarenal osmolality gradient.

In situ lactate dehydrogenase activity: a novel renal cortical imaging biomarker of tubular injury?

Renal ischemia-reperfusion injury is the state of which a tissue experiences injury after a phase of restrictive blood supply and recirculation. Ischemia-reperfusion injury (I/R-I) is a leading cause of acute kidney injury (AKI) in several disease states, including kidney transplantation, sepsis, and hypovolemic shock. The most common methods to evaluate AKI are creatinine clearance, plasma creatinine, blood urea nitrogen, or renal histology. However, currently, there are no precise methods to directly assess renal injury state noninvasively. Hyperpolarized 13C-pyruvate MRI enables noninvasive accurate quantification of the in vivo conversion of pyruvate to lactate, alanine, and bicarbonate. In the present study, we investigated the in situ alterations of metabolic conversion of pyruvate to lactate, alanine, and bicarbonate in a unilateral I/R-I rat model with 30 min and 60 min of ischemia followed by 24 h of reperfusion. The pyruvate conversion was unaltered compared with sham in the 30 min I/R-I group, while a significant reduced metabolic conversion was found in the postischemic kidney after 60 min of ischemia. This indicates that after 30 min of ischemia, the kidney maintains normal metabolic function in spite of decreased kidney function, whereas the postischemic kidney after 60 min of ischemia show a generally reduced metabolic enzyme activity concomitant with a reduced kidney function. We have confidence that these findings can have a high prognostic value in prediction of kidney injury and the outcome of renal injury.

Early diabetic kidney maintains the corticomedullary urea and sodium gradient.

Early diabetic nephropathy is largely undetectable before substantial functional changes have occurred. In the present study, we investigated the distribution of electrolytes and urea in the early diabetic kidney in order to explore whether pathophysiological and metabolic changes appear concomitantly with a decreased sodium and urea gradient. By using hyperpolarized 13C urea it was possible to measure the essential intrarenal electrolyte gradients and the acute changes following furosemide treatment. No differences in either intrarenal urea or sodium gradients were observed in early diabetes compared to healthy controls. These results indicate that the early metabolic and hypertrophic changes occurring in the diabetic kidney prelude the later functional alterations in diabetic kidney function, thus driving the increased metabolic demand commonly occurring in the diabetic kidney.

Fumarase activity: an in vivo and in vitro biomarker for acute kidney injury.

Renal ischemia/reperfusion injury (IRI) is a leading cause of acute kidney injury (AKI), and at present, there is a lack of reliable biomarkers that can diagnose AKI and measure early progression because the commonly used methods cannot evaluate single-kidney IRI. Hyperpolarized [1,4-13C2]fumarate conversion to [1,4-13C2]malate by fumarase has been proposed as a measure of necrosis in rat tumor models and in chemically induced AKI rats. Here we show that the degradation of cell membranes in connection with necrosis leads to elevated fumarase activity in plasma and urine and secondly that hyperpolarized [1,4-13C2]malate production 24 h after reperfusion correlates with renal necrosis in a 40-min unilateral ischemic rat model. Fumarase activity screening on bio-fluids can detect injury severity, in bilateral as well as unilateral AKI models, differentiating moderate and severe AKI as well as short- and long-term AKI. Furthermore after verification of renal injury by bio-fluid analysis the precise injury location can be monitored by in vivo measurements of the fumarase activity non-invasively by hyperpolarized [1,4-13C]fumarate MR imaging. The combined in vitro and in vivo biomarker of AKI responds to the essential requirements for a new reliable biomarker of AKI.

Imaging porcine cardiac substrate selection modulations by glucose, insulin and potassium intervention: A hyperpolarized [1-13C]pyruvate study

Cardiac metabolism has received considerable attention in terms of both diagnostics and prognostics, as well as a novel target for treatment. As human trials involving hyperpolarized magnetic resonance in the heart are imminent, we sought to evaluate the general feasibility of detection of an imposed shift in metabolic substrate utilization during metabolic modulation with glucose–insulin–potassium (GIK) infusion, and thus the limitations associated with this strategy, in a large animal model resembling human physiology. Four [1‐13C]pyruvate injections did not alter the blood pressure or ejection fraction over 180 min. Hyperpolarized [1‐13C]pyruvate conversion showed a generally high reproducibility, with intraclass correlation coefficients between the baseline measurements at 0 and 30 min as follows: lactate to pyruvate, 0.85; alanine to pyruvate, 1.00; bicarbonate to pyruvate, 0.83. This study demonstrates that hyperpolarized [1‐13C]pyruvate imaging is a feasible technique for cardiac studies and shows a generally high reproducibility in fasted large animals. GIK infusion increases the metabolic conversion of pyruvate to its metabolic derivatives lactate, alanine and bicarbonate, but with increased variability.