Role of angiotensin II type 1a receptor in renal injury induced by deoxycorticosterone acetate-salt hypertension

Medicinal (Radio) Chemistry: Building Radiopharmaceuticals for the Future

Radiopharmaceuticals are increasingly playing a leading role in diagnosing, monitoring, and treating disease. In comparison with conventional pharmaceuticals, the development of radiopharmaceuticals does follow the principles of medicinal chemistry in the context of imaging-altered physiological processes. The design of a novel radiopharmaceutical has several steps similar to conventional drug discovery and some particularity. In the present work, we revisited the insights of medicinal chemistry in the current radiopharmaceutical development giving examples in oncology, neurology, and cardiology. In this regard, we overviewed the literature on radiopharmaceutical development to study overexpressed targets such as prostate-specific membrane antigen and fibroblast activation protein in cancer; β-amyloid plaques and tau protein in brain disorders; and angiotensin II type 1 receptor in cardiac disease. The work addresses concepts in the field of radiopharmacy with a special focus on the potential use of radiopharmaceuticals for nuclear imaging and theranostics.

Effects of intrarenal angiotensin 1-7 infusion on renal haemodynamic and excretory function in anaesthetised two-kidney one-clip and deoxycorticosterone acetate-salt hypertensive rats

NEW FINDINGS

What is the central question of this study? Are renal functional responses to intrarenal angiotensin 1-7 (Ang (1-7)) infusion dependent on the level of the endogenous renin-angiotensin system (RAS) in the two-kidney one-clip (2K1C) and deoxycorticosterone acetate (DOCA)-salt animal models of hypertension? What is the main finding and its importance? The renal actions of Ang (1-7) are dependent on the relative endogenous levels of each arm of the classical angiotensin II-angiotensin II type 1 receptor (AT1 R) axis and those of the Ang (1-7)-Mas receptor axis. These findings support the hypothesis that a balance exists between the intrarenal classical and novel arms of the RAS, and in particular the relative abundance of AT1 R to Mas receptor, which may to a large extent determine the renal excretory response to Ang (1-7) infusion.

ABSTRACT

This study investigated the action of angiotensin 1-7 (Ang (1-7)) on renal haemodynamic and excretory function in the two-kidney one-clip (2K1C) and deoxycorticosterone acetate (DOCA)-salt rat models of hypertension, in which the endogenous renin-angiotensin system (RAS) activity was likely to be raised or lowered, respectively. Rats were anaesthetised and prepared for the measurement of mean arterial pressure and kidney function during renal interstitial infusion of Ang (1-7) or saline. Kidney tissue concentrations of angiotensin II (Ang II) and Ang (1-7) were determined. Intrarenal infusion of Ang (1-7) into the clipped kidney of 2K1C rats increased urine flow (UV), absolute (UNa V) and fractional sodium (FENa ) excretions by 110%, 214% and 147%, respectively. Renal Ang II concentrations of the clipped kidney were increased with no major changes in Ang (1-7) concentration. By contrast, Ang (1-7) infusion decreased UV, UNa V, and FENa by 27%, 24% and 21%, respectively in the non-clipped kidney in which tissue Ang (1-7) concentrations were increased, but renal Ang II concentrations were unchanged compared to sham animals. Ang (1-7) infusion in DOCA-salt rats had minimal effects on glomerular filtration rate but significantly decreased UV, UNa V and FENa by ∼30%. Renal Ang (1-7) concentrations were higher and Ang II concentrations were lower in DOCA-salt rats compared to sham rats. These findings demonstrate that the intrarenal infusion of exogenous Ang (1-7) elicits different renal excretory responses the magnitude of which is dependent on the balance between the endogenous renal Ang II-AT1 receptor axis and Ang (1-7)-Mas receptor axis.

Angiotensin II type 1a receptor loss ameliorates chronic tubulointerstitial damage after renal ischemia reperfusion

We investigate whether suppressing the activation of the angiotensin II type 1a receptor (AT1a) can ameliorate severe chronic tubulointerstitial damage (TID) after renal ischemia reperfusion (IR) using AT1a knockout homozygous (AT1a^−/−) male mice. To induce severe chronic TID after renal IR, unilateral renal ischemia was performed via clamping of the right renal pedicle in both AT1a^−/− and wild-type (AT1a^+/+) mice for 45 min. While marked renal atrophy and severe TID at 70 days postischemia was induced in the AT1a^+/+ mice, such a development was not provoked in the AT1a^−/− mice. Although the AT1a^+/+ mice were administered hydralazine to maintain the same systolic blood pressure (SBP) levels as the AT1a^−/− mice with lower SBP levels, hydralazine did not reproduce the renoprotective effects observed in the AT1a^−/− mice. Acute tubular injury at 3 days postischemia was similar between the AT1a^−/− mice and the AT1a^+/+ mice. From our investigations using IR kidneys at 3, 14, and 28 days postischemia, the multiple molecular mechanisms may be related to prevention of severe chronic TID postischemia in the AT1a^−/− mice. In conclusion, inactivation of the AT1 receptor may be useful in preventing the transition of acute kidney injury to chronic kidney disease.

The Possibility of Urinary Liver-Type Fatty Acid-Binding Protein as a Biomarker of Renal Hypoxia in Spontaneously Diabetic Torii Fatty Rats

BACKGROUND

Renal hypoxia is an aggravating factor for tubulointerstitial damage, which is strongly associated with renal prognosis in diabetic kidney disease (DKD). Therefore, urinary markers that can detect renal hypoxia are useful for monitoring DKD.

OBJECTIVE

To determine the correlation between urinary liver-type fatty acid-binding protein (L-FABP) and renal hypoxia using a novel animal model of type 2 diabetes.

METHODS

Male spontaneously diabetic Torii (SDT) fatty rats (n = 6) were used as an animal model of type 2 diabetes. Age- and sex-matched Sprague-Dawley (SD) rats (n = 8) were used as controls. Body weight, systolic blood pressure, and blood glucose levels were measured at 8, 12, 16, and 24 weeks of age. Urine samples and serum and kidney tissues were collected at 24 weeks of age. Microvascular blood flow index (BFI) was measured using diffuse correlation spectroscopy before sampling both the serum and kidneys for the evaluation of renal microcirculation at the corticomedullary junction.

RESULTS

Obesity, hyperglycemia, and hypertension were observed in the SDT fatty rats. Focal glomerular sclerosis, moderate interstitial inflammation, and fibrosis were significantly more frequent in SDT fatty rats than in SD rats. While the frequency of peritubular endothelial cells and phosphoendothelial nitric oxide synthase levels were similar in both types of rats, the degree of renal hypoxia-inducible factor-1α (HIF-1α) expression was significantly higher (and with no change in renal vascular endothelial growth factor expression levels) in the SDT fatty rats. Urinary L-FABP levels were significantly higher and renal microvascular BFI was significantly lower in the SDT fatty rats than in the SD rats. Urinary L-FABP levels exhibited a significant positive correlation with renal HIF-1α expression and a significant negative correlation with renal microvascular BFI.

CONCLUSIONS

Urinary L-FABP levels reflect the degree of renal hypoxia in DKD in a type 2 diabetic animal model. Urinary L-FABP may thus prove useful as a renal hypoxia marker for monitoring DKD in patients with type 2 diabetes in clinical practice.

A modified elliptical formula to estimate kidney collagen content in a model of chronic kidney disease

The extent of scarring or renal interstitial collagen deposition in chronic kidney disease (CKD) can only be ascertained by highly invasive, painful and sometimes risky, tissue biopsy. Interestingly, while CKD-related abnormalities in kidney size can often be visualized using ultrasound, not only does the ellipsoid formula used today underestimate true renal size, but the calculated renal size does not inform tubulointerstitial collagen content. We used coronal kidney sections from healthy mice and mice with kidney disease to develop a new formula for estimating renal parenchymal area. While treating the kidney as an ellipse with the major axis (a) the polar distance, this technique involves extending the minor axis (b) into the renal pelvis to obtain a new minor axis, b_e. The calculated renal parenchymal area is remarkably similar to the true or measured area. Biochemically determined kidney collagen content revealed a strong and positive correlation with the calculated renal parenchymal area. Picrosirius red staining for tubulointerstitial collagen also correlated with calculated renal parenchymal area. The extent of renal scarring, i.e. kidney interstitial collagen content, can now be computed by making just two axial measurements which can easily be accomplished via noninvasive imaging of this organ.