Changes in glomerular filtration rate during complete ureteral obstruction in rats

Photoacoustic Imaging of Nanoparticle Transport in the Kidneys at High Temporal Resolution

Noninvasive monitoring of kidney elimination of engineered nanoparticles at high temporal and spatial resolution will not only significantly advance our fundamental understandings of nephrology on the nanoscale, but also aid in the early detection of kidney disease, which affects more than 10 % of the worldwide population. Taking advantage of strong NIR absorption of the well-defined Au25 (SG)18 nanocluster, photoacoustic (PA) imaging was used to visualize its transport in situ through the aorta to the renal parenchyma and its subsequent filtration into the renal pelvis at a temporal resolution down to 1 s. High temporal and spatial resolution imaging of Au25 (SG)18 kidney elimination allowed the accurate quantification of the glomerular filtration rate (GFR) of individual kidneys in normal and pathological conditions, broadening the biomedical applications of engineered nanoparticles in preclinical kidney research.

CD40 Generation 2.5 Antisense Oligonucleotide Treatment Attenuates Doxorubicin-induced Nephropathy and Kidney Inflammation

Preclinical and clinical data suggest CD40 activation contributes to renal inflammation and injury. We sought to test whether upregulation of CD40 in the kidney is a causative factor of renal pathology and if reduction of renal CD40 expression, using antisense oligonucleotides (ASOs) targeting CD40, would be beneficial in mouse models of glomerular injury and unilateral ureter obstruction. Administration of a Generation 2.5 CD40 ASO reduced CD40 mRNA and protein levels 75–90% in the kidney. CD40 ASO treatment mitigated functional, transcriptional, and pathological endpoints of doxorubicin-induced nephropathy. Experiments using an activating CD40 antibody revealed CD40 is primed in kidneys following doxorubicin injury or unilateral ureter obstruction and CD40 ASO treatment blunted CD40-dependent renal inflammation. Suborgan fractionation and imaging studies demonstrated CD40 in glomeruli before and after doxorubicin administration that becomes highly enriched within interstitial and glomerular foci following CD40 activation. Such foci were also sites of ASO distribution and activity and may be predominately comprised from myeloid cells as bone marrow CD40 deficiency sharply attenuated CD40 antibody responses. These studies suggest an important role of interstitial renal and/or glomerular CD40 to augment kidney injury and inflammation and demonstrate that ASO treatment could be an effective therapy in such disorders.

Propagation of the electrical impulse in reversible unilateral ureteral obstruction as determined at high electrophysiological resolution

PURPOSE

We investigated the propagation of electrical impulses in a reversible, complete or partial unilateral ureteral obstruction model in vivo.

MATERIALS AND METHODS

In Wistar rats the left mid ureter was completely (8) or partially (7) occluded and released after 24 hours. We recorded electrical activity of the left and right ureter before, during and after obstruction at different stages up to 2 weeks after obstruction using a high resolution, 64 extracellular electrode probe.

RESULTS

Complete obstruction in the left proximal ureter caused an immediate increase in frequency from a mean ± SEM of 14.8 ± 1.3 to 18.6 ± 1.7 per minute (p <0.05), followed by a 1.4 ± 0.9 per minute decrease (p <0.001). Within the first 2 days after reversal velocity gradually decreased from 1.82 ± 0.12 to 0.79 ± 0.17 cm per second (p <0.001). Release of obstruction gradually restored frequency and velocity, which returned to baseline at 2 weeks. Generally the alterations in rats with complete and partial obstruction were similar but they were less marked in those with partial obstruction. Distal to the obstruction site the impulses disappeared (38%) or propagated retrograde (43%) at some stage in the post-obstruction period. These abnormal impulse propagations also gradually disappeared in the post-obstruction stage.

CONCLUSIONS

After complete or partial ureteral obstruction there were immediate, significant changes in the propagation of electrical impulses in the proximal and distal left ureter, which were generally less marked after partial than after complete obstruction. Reversal of obstruction resulted in the gradual disappearance of this abnormality in 2 weeks.

A case of acute kidney injury due to complex, partial, multifocal ureteral strictures

BACKGROUND

An 89-year-old man with a history of prostate cancer who had undergone radical prostatectomy 15 years ago presented with hyperkalemia (serum potassium level 6.9 mmol/l) and kidney failure (serum creatinine level 937 micromol/l [10.6 mg/dl]). Ultrasound scan of his kidneys showed mild bilateral hydronephrosis. Although placement of a bladder catheter led to an initial increase in glomerular filtration rate, the improvement was delayed and incomplete. Subsequently, the patient's glomerular filtration rate decreased acutely. This unusual biphasic course of kidney injury begged explanation.

INVESTIGATIONS

Physical examination, measurements of serum creatinine level and electrolytes, imaging of the urinary tract (ultrasound and CT scans), and nephrostograms.

DIAGNOSIS

Acute kidney injury due to upper (multiple ureteral strictures bilaterally) and lower (urethral) urinary tract obstruction.

MANAGEMENT

Placement of bladder catheter and percutaneous nephrostomy tubes followed by bilateral internal ureteral stents.

Metabolism of Tac (IL2Ralpha): physiology of cell surface shedding and renal catabolism, and suppression of catabolism by antibody binding

The interleukin 2 receptor alpha (IL2Ralpha; CD25; Tac) is the prototypic model for soluble receptor studies. It exists in vivo as a transmembrane complete molecule (TM-Tac) on cell surfaces and as a truncated soluble form (sTac; sIL2R alpha). sTac has been used as a serum marker of T cell activation in immune disorders and of tumor burden in Tac-expressing malignancies. In vivo, serum levels of all soluble proteins depend on the balance between production and catabolism, but little is known about the metabolic features of this class of molecules. We have developed a model for Tac metabolism that incorporates new insights in its production and catabolism. Tac was shed from the surface of malignant and activated human T cells with a model half-life (t1/2) of 2-6h, but which was prolonged under certain circumstances. The rate of shedding is first order overall and nonsaturable over a two order of magnitude range of substrate (TM-Tac) expression. Once shed from cells Tac is subject to catabolic activities in the host. In vivo studies in mice showed that 90% of Tac was catabolized by the kidney with a t1/2 of 1 h and a filtration fraction of 0.11 relative to creatinine. The remaining 10% of catabolism was mediated by other tissues with a t1/2 of 10 h. Approximately 1-3% of sTac is excreted intact as proteinuria with the remaining 97-99% catabolized to amino acids. Antibody to the receptor induced a marked delay in sTac catabolism by preventing filtration of the smaller protein through the renal glomerulus and additionally suppressing other nonrenal catabolic mechanisms. A discrepancy between the catabolic rats for Tac and anti-Tac in the same complex was interpreted as a previously unrecognized differential catabolic mechanism, suggesting features of the Brambell hypothesis and immunoglobulin G transport and catabolism, in which the antigen-in-complex in intracellular vesicles is relatively less protected from catabolism than the associated antibody. In light of the pivotal role played by the kidney in sTac catabolism and the impact of administered antibody, the serum concentration of Tac in the settings of renal dysfunction or antibody therapy is not a suitable surrogate of activated T cells or of the body burden of tumor. These results provide parameters for assessing soluble receptor-ligand interactions generally.

The pathophysiology of ureteral obstruction

Ureteral obstruction can have a variety of causes intrinsic or extrinsic to the kidney. The effects of obstruction are examined from the perspectives of duration, severity, totality, and the presence of complicating factors. There is a difference in the postobstructive pathophysiology depending on whether one or both ureters were obstructed. Atrial natriuretic peptide may be important in postobstructive diuresis, and preliminary evidence suggests a role for it as protection against nephron ischemia in acute obstruction. The potential for recovery of renal function after relief of obstruction depends on the duration and degree of obstruction, the condition of the contralateral kidney, and the presence or absence of infection. Ability to acidify the urine to pH < 6.0 preoperatively may be a good predictor of the recovery potential of an obstructed kidney. Urine concentrations of lysosomal enzymes such as N-acetylglucosaminidase also may be useful for this purpose, as may measurement of creatinine clearance in urine obtained from a nephrostomy tube.

P-31 nuclear magnetic resonance spectral changes in obstructed or dehydrated kidney

Rat kidneys subjected to urinary obstruction or dehydration in vivo both develop marked increases in the area under a peak resonating in the phosphodiester region on their P-31 nuclear magnetic resonance spectra. The chemical species responsible for these changes were assessed using physiologic manipulations which altered the concentration of phosphate in the urine or increased the urine pH. Obstructed kidneys of rats fed a normal diet had a 140 +/- 50% increase in a peak resonating at 3.31 +/- 0.05 ppm after three hours of obstruction (P less than 0.01). Low phosphate diet which decreased urine phosphate concentration by 98% virtually eliminated this increase in peak area, where saline diuresis which decreased urine phosphate concentration by 50% markedly attenuated it. Acute phosphate loading which doubled urine phosphate concentration markedly accentuated the increase in peak area. Alkalinizing the urine with acetazolamide (changing urine pH from 6.2 +/- 0.2 to 8.0 +/- 0.1) shifted the resonance frequency of this increasing peak from 3.31 +/- 0.06 to 5.45 +/- 0.11 ppm (P less than 0.01). Rats fed a normal diet developed increases (57 +/- 15%, P less than 0.05) in a peak resonating at 2.84 +/- 0.03 ppm following 48 hours of dehydration. Rats fed a low phosphate diet had a comparable increase in the relative area of this peak (46 +/- 16%, P less than 0.05). Alkalinization of the urine did not affect the position or intensity of this peak under conditions of dehydration.(ABSTRACT TRUNCATED AT 250 WORDS)

P-31 nuclear magnetic resonance spectroscopic study of obstructive uropathy in the rat

P-31 nuclear magnetic resonance (NMR) spectroscopy of the rat kidney with ureteral ligation resulted in a rapid and major increase in a peak resonating at 7096.63 +/- 0.65 Hz from the reference frequency of phosphorus (32.60 MHz). This corresponded to an increase in the concentration of the substance responsible for peak X from 0.34 +/- 0.04 mumol/g wet weight in normal kidneys to 1.45 +/- 0.27 mumol/g wet weight in unilaterally obstructed kidneys and 2.00 +/- 0.34 mumol/g wet weight in bilaterally obstructed kidneys at 3 h (P less than 0.01). Further NMR studies performed with in vivo kidneys and tissue extracts revealed that inorganic phosphate in the urine, resonating at a lower frequency due to the acid pH environment, was responsible for the increase in this peak. These findings may prove to be of fundamental interest as well as potential clinical significance.

Quantitative ultrastructure of human proximal tubules and cortical interstitium in chronic renal disease (hydronephrosis)

Surgically removed perfusion-fixed human kidneys with chronic renal disease (hydronephrosis) were studied by electron microscopy in order to determine whether there is a quantitative relationship between ultrastructural changes in proximal tubules in atrophy and changes in the surrounding cortical interstitium. Morphometric techniques were applied to montages of electron micrographs each covering several tubular profiles in the cortical labyrinth and to montages representing cross-sections of individual proximal convoluted tubules at a higher magnification. In order to enable a quantification of the spatial relations between individual tubular cross-sections and adjacent peritubular capillaries a tubulo-capillary index (TCI) was defined. This index was based on the mean distances between individual tubular cross-sections and adjacent peritubular capillaries and on the fraction of tubular circumference facing capillaries. Normal tissue from similarly fixed human nephrectomy specimens, which had been removed mainly because of neoplastic disorders, served as control material. In the hydronephrotic kidneys the relative volume of cortical interstitium (excluding capillaries) covered a range from 19.2-70.3%. Inverse correlations were demonstrated between the relative volume of cortical interstitium and various structural variables of proximal convoluted tubules, including tubular wall volume, the volume of mitochondria and the surface area of basolateral membranes. The TCI showed positive correlations with these tubular variables. No significant correlation was found between the volume fractions of cortical interstitium and capillaries. Finally, it was found that an increase in the volume fraction of the cortical interstitium from 16.2% in controls to 24.7% in cortical areas of hydronephrotic kidneys was associated with a 40-50% reduction in the volume of mitochondria and in the surface area of basolateral membranes in proximal tubules. The results are consistent with a pathogenic interrelationship between tubular and interstitial changes. An important factor in this relationship might be disturbed topographic associations between tubules and blood capillaries caused by the increase in cortical interstitium. The results further show that even slight increases in the cortical interstitial volume are associated with significant quantitative changes in tubular fine structure suggesting impaired tubular functions.

Renal blood flow during unilateral ureteral obstruction. Effects of reduced perfusion pressure, acetylcholine, and thromboxane A2 blockers in obstructed and unobstructed rat kidneys

Renal blood flow (RBF) is markedly reduced in kidneys with unilateral ureteral obstruction (UUO), possibly due to vascular constriction. Whether obstructive nephropathy is associated with impaired RBF autoregulation is unknown. We therefore investigated RBF autoregulation in obstructed and contralateral unobstructed rat kidneys during and following release of 24 h and 6 days of UUO, using stepwise reduction of renal arterial pressure and electromagnetic recording of RBF. The lower pressure limit of autoregulation was increased and the maximal vasodilatory ability in response to infusion of acetylcholine into the renal artery was reduced only in the unobstructed kidney at 24 h of UUO. Thus, we conclude that the vasodilatory reactions to both these maneuvres, previously observed to be markedly reduced during acutely elevated ureteral pressure (Hope & Clausen 1982), were reestablished: In the obstructed kidneys in less than 24 h (RBF approximately 70% of control) and in the contralateral unobstructed kidneys in less than 6 days (RBF approximately 140% of control). Infusion of the thromboxane A2 (TXA) synthetase inhibitors imidazole and 3-ethyl pyridine in controls and at 24 h and 6 days of UUO did not produce renal vasodilation. These results do not support the suggestion that TXA contributes directly to the increase in renal vascular resistance observed during or following release of UUO in the rat.

Effect of renal tubular obstruction on stop-flow pressure and glomerular deposition of fibrin during intravascular coagulation in the rat

Intravascular coagulation in the rat kidney was induced by intravenous infusion of thrombin for 1 hr. The proximal tubular free-flow (Pt) and stop-flow (Psf) pressures were measured by micropuncture. Some proximal tubules were obstructed with solid paraffin before infusion of thrombin. In certain rats saralasin or indomethacin was administered for 1 hr starting 30 min after the thrombin infusion, and the effect on the tubular pressures was studied. The deposition of fibrin in the glomeruli was examined by light and electron microscopy. Pt fell from 15 +/- 1 (SE) to 7 +/- 2 mm Hg (P less than 0.05) during the infusion of thrombin. After a brief period of increased pressure the Psf fell rapidly from 37 +/- 1 to 17 +/- 1 mm Hg (P less than 0.05). In the previously obstructed nephrons the pressure (Po) increased parallel to the increase in Psf but remained elevated after the infusion of thrombin, 54 +/- 2 mm Hg. The arterial blood pressure (Pa) increased from 119 +/- 2 to 138 +/- 3 mm Hg (P less than 0.05). Saralasin raised the Psf from 15 +/- 1 to 19 +/- 1 mm Hg (P less than 0.05) but had no effect on Pt, Po, or Pa. Indomethacin did not influence the pressures. Morphological examination revealed fibrin in all glomeruli of normal nephrons. In the previously obstructed nephrons the deposition of fibrin was almost totally prevented. The results suggest that glomerular filtration is important for deposition of fibrin in the kidney.