Clinical and experimental approaches for imaging of acute kidney injury

New approaches to acute kidney injury

Acute kidney injury (AKI) is a common and serious clinical syndrome that involves complex interplay between different cellular, molecular, metabolic and immunologic mechanisms. Elucidating these pathophysiologic mechanisms is crucial to identify novel biomarkers and therapies. Recent innovative methodologies and the advancement of existing technologies has accelerated our understanding of AKI and led to unexpected new therapeutic candidates. The aim of this review is to introduce and update the reader about recent developments applying novel technologies in omics, imaging, nanomedicine and artificial intelligence to AKI research, plus to provide examples where this can be translated to improve patient care.

Protective effects of lupeol in rats with renal ischemia‑reperfusion injury

Acute kidney injury (AKI) caused by ischemia and, exogenous or endogenous nephrotoxic agents poses a serious health issue. AKI is seen in 1% of all hospital admissions, 2-5% of hospitalizations and 67% of intensive care unit (ICU) patients. The in-hospital mortality rates for AKI is 40-50, and >50% for ICU patients. Ischemia-reperfusion (I/R) injury in the kidney can activate inflammatory responses and oxidative stress, resulting in AKI. The common endpoint in acute tubular necrosis is a cellular insult secondary to ischemia or direct toxins, which results in effacement of brush border, cell death and decreased function of tubular cells. The aim of the present study was to assess if the reported antioxidant and anti-inflammatory agent lupeol can exert any effects against renal I/R damage. In total, 24 Wistar Albino rats were randomly assigned into four groups of 6, namely Sham, lupeol, ischemia and therapy groups. In the lupeol group, intraperitoneal administration of 100 mg/kg lupeol was given 1 h before laparotomy, whilst only laparotomy was conducted in the sham group. The renal arteries of both kidneys were clamped for 45 min, 1 h after either intraperitoneal saline injection (in the ischemia group) or 100 mg/kg lupeol application (in the therapy group). The blood samples and renal tissues of all rats were collected after 24 h. In blood samples, blood urea nitrogen (BUN) was measured by the urease enzymatic method, and creatinine was measured by the kinetic Jaffe method. Using ELISA method, TNF-α and IL-6 levels were measured in the blood samples, whereas malondialdehyde (MDA), glutathione (GSH), caspase-3 levels were measured in kidney tissues. In addition, kidney histopathological analysis was performed by evaluating the degree of degeneration, tubular dilatation, interstitial lymphocyte infiltration, protein cylinders, necrosis and loss of brush borders. It was determined that renal damage occurred due to higher BUN, creatinine, MDA, TNF-α and caspase-3 values observed in the kidney tissues and blood samples of rats in ischemia group compared with the Sham group. Compared with those in the ischemia group, rats in the therapy group exhibited increased levels of GSH and reduced levels of BUN, TNF-α, MDA. Furthermore, the ischemia group also had reduced histopathological damage scores. Although differences in creatinine, IL-6 and caspase-3 levels were not statistically significant, they were markedly reduced in the treatment group. Taken together, these findings suggest that lupeol can prevent kidney damage as mainly evidenced by the reduced histopathological damage scores, decreased levels of oxidative stress and reduced levels of inflammatory markers. These properties may allow lupeol to be used in the treatment of AKI.

Prevalence of acute kidney injury following percutaneous nephrolithotomy

Background

The objective is to evaluate the prevalence of acute kidney injury (AKI) as an early complication of the percutaneous nephrolithotomy (PCNL) procedure.

Materials and Methods

From May 2022 to October 2022, we conducted a retrospective study on patients undergoing PCNL procedures in two of the tertiary medical centers affiliated with Isfahan University of Medical Sciences. Patients' baseline characteristics, laboratory values, perioperative data, and stone features were documented. AKI was defined either as a ≥0.3 mg/dL increase in the serum creatinine level within 2 days, or a ≥1.5-fold increase in baseline serum creatinine level within 7 days after the operation. Laboratory values were measured 1 day before PCNL and daily thereafter until discharge. Patients were followed 1 week later to detect all of the possible cases of AKI.

Results

The final analysis was performed on 347 individuals. AKI developed in 16 (4.61%) cases. The two groups were comparable regarding age (P = 0.887), gender (P = 0.566), and underlying comorbidities including diabetes mellitus (P = 0.577) and hypertension (P = 0.383). The mean body mass index (BMI) (P < 0.001) and both frequency and severity of hydronephrosis (P < 0.001) were significantly different. A higher mean PCNL duration (P < 0.001), period of hospitalization (P < 0.001), and blood loss volume (P < 0.001) were observed in those who developed AKI. Overall, 56.3% (9) of patients in the AKI group and 2.7% (9) in the non-AKI group required the establishment of more than one access tract, during the procedure (P < 0.001). A lower preoperative hemoglobin level was observed in the AKI group (P < 0.001). Those with AKI had significantly larger stones (3.08 ± 0.46 vs. 2.41 ± 0.23 cm, P < 0.001) and higher Hounsfield units (P < 0.001). In addition, in the AKI group, most of the calculi (81.3%, 13) were of staghorn type, whereas in the non-AKI group, calculi were most frequently located in the middle calyx (30.2%, 100), (P < 0.001).

Conclusion

The prevalence of post-PCNL AKI is approximately 4.61%. The mean BMI, preoperative hemoglobin level, PCNL duration, intraoperative blood loss volume, and hospitalization period were significantly higher among patients who developed AKI. Those with AKI had significantly larger stones with higher Hounsfield units and more frequently of staghorn type. The two groups were not statistically different regarding age, gender, and presence of comorbidities (hypertension and diabetes mellitus).

Severity of polycystic kidney disease revealed by multiparametric MRI

PURPOSE

We aimed to compare multiple MRI parameters, including relaxation rates (R 1 $$ {R}_1 $$ ,R 2 $$ {R}_2 $$ , andR 1 ρ $$ {R}_{1\rho } $$ ), ADC from diffusion weighted imaging, pool size ratio (PSR) from quantitative magnetization transfer, and measures of exchange from spin-lock imaging (S ρ $$ {S}_{\rho } $$ ), for assessing and predicting the severity of polycystic kidney disease (PKD) over time.

METHODS

Pcy/Pcy mice with CD1 strain, a mouse model of autosomal dominant PKD, were imaged at 5, 9, and 26 wk of age using a 7T MRI system. Twelve-week normal CD1 mice were used as controls. Post-mortem paraffin tissue sections were stained using hematoxylin and eosin and picrosirius red to identify histological changes.

RESULTS

Histology detected segmental cyst formation in the early stage (week 5) and progression of PKD over time in Pcy kidneys. InT 2 $$ {T}_2 $$ -weighted images, small cysts appeared locally in cystic kidneys in week 5 and gradually extended to the whole cortex and outer stripe of outer medulla region from week 5 to week 26. Regional PSR,R 1 $$ {R}_1 $$ ,R 2 $$ {R}_2 $$ , andR 1 ρ $$ {R}_{1\rho } $$ decreased consistently over time compared to normal kidneys, with significant changes detected in week 5. Among all the MRI measures,R 2 $$ {R}_2 $$ andR 1 ρ $$ {R}_{1\rho } $$ allow highest detectability to PKD, while PSR andR 1 $$ {R}_1 $$ have highest correlation with pathological indices of PKD. Using optimum MRI parameters as regressors, multiple linear regression provides reliable prediction of PKD progression.

CONCLUSION

R 2 $$ {R}_2 $$ ,R 1 $$ {R}_1 $$ , and PSR are sensitive indicators of the presence of PKD. Multiparametric MRI allows a comprehensive analysis of renal changes caused by cyst formation and expansion.

A Comparative Study of 18F-FAPI-42 and 18F-FDG PET/CT for Evaluating Acute Kidney Injury in Cancer Patients

PURPOSE

Compare the value of imaging using positron ¹⁸F-labeled fibroblast activation protein inhibitor-42 (¹⁸F-FAPI-42) and ¹⁸F-labeled deoxyglucose (¹⁸F-FDG) for assessment of AKI.

PROCEDURES

This study analyzed cancer patients who received ¹⁸F-FAPI-42 and ¹⁸F-FDG PET/CT imaging. Eight patients had AKI with bilateral ureteral obstruction (BUO), eight had BUO (CKD1-2) with no acute kidney disease (AKD), and eight had no ureteral obstruction (UO) with normal renal function. The average standardized uptake value (SUV_ave) of the renal parenchyma (RP-SUV_ave), the blood pool SUV_ave (B- SUV_ave), SUV_ave in the highest region of the renal collective system (RCS-SUV_ave), and the highest serum creatinine level (top SCr) were recorded.

RESULTS

The ¹⁸F-FAPI-42 and ¹⁸F-FDG results showed that radiotracer of renal parenchyma was more concentrated in the AKI group than in the other two groups, whereas the RP-SUV_ave from ¹⁸F-FAPI-42 was higher than that from ¹⁸F-FDG in the AKI group (all P < 0.05). ¹⁸F-FAPI-42 imaging in the AKI group showed uptake by the renal parenchyma with a diffuse increase, but very little radiotracer in the renal collecting system, similar to a "super kidney scan." The renal parenchyma also had an increase of SUV_ave, with accumulation of radiotracer in the renal collecting system. AKI was more severe when a patient had a "super kidney scan" in both kidneys (P < 0.05). The B-SUV_ave level was higher in the AKI group than in the other two groups in ¹⁸F-FAPI-42 (both P < 0.05).

CONCLUSIONS

¹⁸F-FAPI-42 imaging had higher RP-SUV_ave than ¹⁸F-FDG imaging in cancer patients who had BUO with AKI. An increased renal parenchyma uptake in both kidneys and low radiotracer distribution in the collecting system suggest more severe AKI.

Quantitative Analysis of Renal Perfusion in Rhabdomyolysis-Induced Acute Kidney Injury Using Contrast-Enhanced Ultrasound: An Experimental Study

The aim of this study was to evaluate renal perfusion changes in rats with acute kidney injury induced by rhabdomyolysis, using quantitative parameters obtained with contrast-enhanced ultrasound (CEUS). Sprague-Dawley (SD) rats were randomly divided into an experimental group (n = 40) and a control group (n = 20). Each group was further divided into four subgroups (0.5-, 6-, 24- and 72-h groups). Time-intensity curves and related quantitative parameters of the renal cortex and medulla were obtained by CEUS, and the contrast characteristics analyzed for different time points. In the experimental group, the CEUS quantitative parameters for the renal medulla of time to peak (TTP), descending time/2 (DT/2) and area under the curve (AUC) increased, whereas ascending slope (AS) and descending slope (DS) decreased. Similarly, renal cortical AS, DS and AUC in the experimental group differed significantly from those in the control group. With respect to the CEUS quantitative parameters for the renal cortex, AUC increased, and AS and DS decreased. These parameters differed significantly between the experimental and control groups. CEUS is sensitive to change in renal perfusion in rhabdomyolysis-induced acute kidney injury and, thus, has diagnostic value.

Advances in Optical Sensors of N-Acetyl-β-d-hexosaminidase (N-Acetyl-β-d-glucosaminidase)

N-Acetyl-β-d-hexosaminidases (EC 3.2.1.52) are exo-acting glycosyl hydrolases that remove N-acetyl-β-d-glucosamine (Glc-NAc) or N-acetyl-β-d-galactosamine (Gal-NAc) from the nonreducing ends of various biomolecules including oligosaccharides, glycoproteins, and glycolipids. The same enzymes are sometimes called N-acetyl-β-d-glucosaminidases, and this review article employs the shorthand descriptor HEX(NAG) to indicate that the terms HEX or NAG are used interchangeably in the literature. The wide distribution of HEX(NAG) throughout the biosphere and its intracellular location in lysosomes combine to make it an important enzyme in food science, agriculture, cell biology, medical diagnostics, and chemotherapy. For more than 50 years, researchers have employed chromogenic derivatives of N-acetyl-β-d-glucosaminide in basic assays for biomedical research and clinical chemistry. Recent conceptual and synthetic innovations in molecular fluorescence sensors, along with concurrent technical improvements in instrumentation, have produced a growing number of new fluorescent imaging and diagnostics methods. A systematic summary of the recent advances in optical sensors for HEX(NAG) is provided under the following headings: assessing kidney health, detection and treatment of infectious disease, fluorescence imaging of cancer, treatment of lysosomal disorders, and reactive probes for chemical biology. The article concludes with some comments on likely future directions.