Molecular imaging of the kidneys

Endothelial NOX5 Obliterates the Reno-Protective Effect of Nox4 Deletion by Promoting Renal Fibrosis via Activation of EMT and ROS-Sensitive Pathways in Diabetes

Chronic hyperglycemia induces intrarenal oxidative stress due to the excessive production of reactive oxygen species (ROS), leading to a cascade of events that contribute to the development and progression of diabetic kidney disease (DKD). NOX5, a pro-oxidant NADPH oxidase isoform, has been identified as a significant contributor to renal ROS in humans. Elevated levels of renal ROS contribute to endothelial cell dysfunction and associated inflammation, causing increased endothelial permeability, which can disrupt the renal ecosystem, leading to progressive albuminuria and renal fibrosis in DKD. This study specifically examines the contribution of endothelial cell-specific human NOX5 expression in renal pathology in a transgenic mouse model of DKD. This study additionally compares NOX5 with the previously characterized NADPH oxidase, NOX4, in terms of their relative roles in DKD. Regardless of NOX4 pathway, this study found that endothelial cell-specific expression of NOX5 exacerbates renal injury, albuminuria and fibrosis. This is attributed to the activation of the endothelial mesenchymal transition (EMT) pathway via enhanced ROS formation and the modulation of redox-sensitive factors. These findings underscore the potential therapeutic significance of NOX5 inhibition in human DKD. The study proposes that inhibiting NOX5 could be a promising approach for mitigating the progression of DKD and strengthens the case for the development of NOX5-specific inhibitors as a potential therapeutic intervention.

Recent developments on nanomaterial-based optical biosensor as potential Point-of-Care Testing (PoCT) probe in carcinoembryonic antigen detection: A review

For the past decades, several cancer biomarkers have been exploited for rapid and accurate prognosis or diagnosis purposes. In this review, the optical biosensor is targeted for carcinoembryonic antigen (CEA) detection. The CEA level is a prominent parameter currently used in clinical cases for the prognosis of cancer-related diseases. Many nanomaterial-based biosensors are invented as alternatives for the commonly used enzyme-linked immunosorbent assays (ELISA) immunoassay method in CEA detection as the traditional approach but they possess certain drawbacks such as tedious procedure, high technical demand, and costly. Nevertheless, the effort appears to be wasted as none of them are being actualised. Generally, the sensor function was carried out by converting bio-signals generated upon the interface of the receptor into light signals. These sensors were popular due to specific advantages such as sensitivity, being free from chemical and electromagnetic interferences, wide dynamic range, and being easy to be monitored. The features of PoC diagnostics are discussed and associated with the various applications of colorimetric-based and chemiluminescent-based biosensors. The roles of nanomaterials in each application were also summarised by comparing the modification, incubation period, lowest detection limit (LOD) and linear range of detection amount. The challenges and future perspectives were highlighted at the end of the review.

CT Angiography Findings Predictive of Kidney Injury in Chronic Aortic Dissection

OBJECTIVE. The purpose of this study was to compare the volume alteration and effective renal plasma flow of kidneys supplied by false lumens (FLs) with those of kidneys supplied by true lumens (TLs), to show the discrepancy in perfusion between the two lumens. We sought to corroborate malperfusion of FL-supplied kidneys with imaging characteristics observed on CT angiography. MATERIALS AND METHODS. A retrospective analysis was conducted using prospectively collected data for 87 patients with a diagnosis of residual chronic aortic dissection between 2005 and 2013 who had one kidney perfused by a TL and the other kidney perfused by a FL. RESULTS. Overall, at follow-up, FL-supplied kidneys had a mean (± SD) effective renal plasma flow (117.5 ± 42.6 vs 146.6 ± 41.0 mL/min; p = 0.004) and volume (131.1 ± 37.1 vs 146.5 ± 33.3 cm³; p = 0.004) that were lower than those of TL-supplied kidneys. Multivariate analysis revealed the presence of a proximal major inlet (odds ratio, 0.306; 95% CI, 0.103-0.910; p = 0.033) and large FL area (odds ratio, 0.104; CI, 0.012-0.880; p = 0.038) as factors protecting against malperfusion of FL-supplied kidneys. In patients with dissected renal arteries, the FL-supplied kidney had low effective renal plasma flow (mean, 88.5 ± 26.8 vs 149.6 ± 43.5 mL/min; p = 0.004) and diminished volume (mean, 120.4 ± 30.4 vs 152.3 ± 24.6 cm³; p = 0.001). CONCLUSION. In the present study, kidneys perfused by FLs showed decreased volume and reduced effective renal plasma flow during follow-up, particularly those kidneys with dissected renal arteries, a small FL area at the renal level, and lack of a proximal major inlet. Further studies are warranted to identify the clinical relevance of malperfusion in FL-supplied kidneys.

11C-PABA as a PET Radiotracer for Functional Renal Imaging: Preclinical and First-in-Human Study

para-Aminobenzoic acid (PABA) has been previously used as an exogenous marker to verify completion of 24-h urine sampling. Therefore, we hypothesized that PABA radiolabeled with ¹¹C might allow high-quality dynamic PET of the kidneys with less radiation exposure than other agents because of its shorter biologic and physical half-life. We evaluated if ¹¹C-PABA can visualize renal anatomy and quantify function in healthy rats and rabbits and in a first-in-humans study on healthy volunteers. Methods: Healthy rats and rabbits were injected with ¹¹C-PABA intravenously. Subsequently, dynamic PET was performed, followed by postmortem tissue-biodistribution studies. ¹¹C-PABA PET was directly compared with the current standard, ^99mTc-mercaptoacetyltriglycin, in rats. Three healthy human subjects also underwent dynamic PET after intravenous injection of ¹¹C-PABA. Results: In healthy rats and rabbits, dynamic PET demonstrated a rapid accumulation of ¹¹C-PABA in the renal cortex, followed by rapid excretion through the pelvicalyceal system. In humans, ¹¹C-PABA PET was safe and well tolerated. There were no adverse or clinically detectable pharmacologic effects in any subject. The cortex was delineated on PET, and the activity gradually transited to the medulla and then pelvis with high spatiotemporal resolution. Conclusion: ¹¹C-PABA demonstrated fast renal excretion with a very low background signal in animals and humans. These results suggest that ¹¹C-PABA might be used as a novel radiotracer for functional renal imaging, providing high-quality spatiotemporal images with low radiation exposure.

Renal statistical map for positron emission tomography with [O-15] water

Image statistics are frequently used for functional and molecular imaging research in which images from a patient group with a specific diagnosis are compared with images from a healthy control group who have been matched for demographic variables. The success of image statistics for brain imaging has encouraged us to develop a method for obtaining volumetrically normalized kidney to perform image statistics so that we can locally visualize the statistical significant difference comparing voxel by voxel between certain groups in terms kidney blood flow kinetic parameters. For the development of this evolutionary process, we first volumetrically normalized all subjects, which include healthy control (HC) and chronic renal failure (CRF) patients, 15O water PET image with respect to one HC subject's MRI image using affine transformation. Then 15O kinetic parametric images of normalized kidneys were obtained through the basis function method. Finally, the statistical map of these parametric images was produced using the threshold-free cluster enhancement based permutation method. Kinetic parameters of kidney namely, uptake rate constant (K1), clearance rate constant (k2) and blood volume (Va), were found to be notably lower in CRF than those of in HC and k2 parameter was found to be more stable compared to K1 and Va. The statistical map of these parametric images allowed us to visualize local significant differences statistically (P<0.05) between HC and CRF groups. Though PET and MRI techniques have enormous potentiality for functional and molecular imaging of kidney, these are, at best, in experimental level. It is speculated that statistical mapping of kidney could play a significant role in the successful implementation of functional and molecular kidney imaging. However, more research involving a larger sample size and improved normalization technique will be needed for the robustness of the process.

Molecular imaging of diabetes and diabetic complications: Beyond pancreatic β-cell targeting

Diabetes is a chronic non-communicable disease affecting over 400 million people worldwide. Diabetic patients are at a high risk of various complications, such as cardiovascular, renal, and other diseases. The pathogenesis of diabetes (both type 1 and type 2 diabetes) is associated with a functional impairment of pancreatic β-cells. Consequently, most efforts to manage and prevent diabetes have focused on preserving β-cells and their function. Advances in imaging techniques, such as magnetic resonance imaging, magnetic resonance spectroscopy, positron emission tomography, and single-photon-emission computed tomography, have enabled noninvasive and quantitative detection and characterization of the population and function of β-cells in vivo. These advantages aid in defining and monitoring the progress of diabetes and determining the efficacy of anti-diabetic therapies. Beyond β-cell targeting, molecular imaging of biomarkers associated with the development of diabetes, e.g., lymphocyte infiltration, insulitis, and metabolic changes, may also be a promising strategy for early detection of diabetes, monitoring its progression, and occurrence of complications, as well as facilitating exploration of new therapeutic interventions. Moreover, molecular imaging of glucose uptake, production and excretion in specified tissues is critical for understanding the pathogenesis of diabetes. In the current review, we summarize and discuss recent advances in noninvasive imaging technologies for imaging of biomarkers beyond β-cells for early diagnosis of diabetes, investigation of glucose metabolism, and precise diagnosis and monitoring of diabetic complications for better management of diabetic patients.

Divergent effects of AKI to CKD models on inflammation and fibrosis

Chronic kidney disease (CKD) is a condition with significant morbidity and mortality that affects 15% of adults in the United States. One cause of CKD is acute kidney injury (AKI), which commonly occurs secondary to sepsis, ischemic events, and drug-induced nephrotoxicity. Unilateral ischemia-reperfusion injury (UIRI) without contralateral nephrectomy (CLN) and repeated low-dose cisplatin (RLDC) models of AKI to CKD demonstrate responses characteristic of the transition; however, previous studies have not effectively compared the pathogenesis. We demonstrate both models instigate renal dysfunction, inflammatory cytokine responses, and fibrosis. However, the models exhibit differences in urinary excretory function, inflammatory cell infiltration, and degree of fibrotic response. UIRI without CLN demonstrated worsening perfusion and function, measured with ^99mTc-mercaptoacetyltriglycine-3 imaging, and physiologic compensation in the contralateral kidney. Furthermore, UIRI without CLN elicited a robust inflammatory response that was characterized by a prolonged polymorphonuclear cell and natural killer cell infiltrate and an early expansion of kidney resident macrophages, followed by T-cell infiltration. Symmetrical diminished function occurred in RLDC kidneys and progressively worsened until day 17 of the study. Surprisingly, RLDC mice demonstrated a decrease in inflammatory cell numbers relative to controls. However, RLDC kidneys expressed increased levels of kidney injury molecule-1 (KIM-1), high mobility group box-1 ( HMGB1), and colony stimulating factor-1 ( CSF-1), which likely recruits inflammatory cells in response to injury. These data emphasize how the divergent etiologies of AKI to CKD models affect the kidney microenvironment and outcomes. This study provides support for subtyping AKI by etiology in human studies, aiding in the elucidation of injury-specific pathophysiologic mechanisms of the AKI to CKD transition.

Accurate Monitoring of Renal Injury State through in Vivo Magnetic Resonance Imaging with Ferric Coordination Polymer Nanodots

It is highly challenging to detect the pathophysiology of the diseased kidneys and achieve precise diagnosis because there are few in vivo noninvasive imaging techniques to quantitatively assess kidney dysfunction. This longstanding challenge is normally attributed to the limited molecular contrast agents which can be addressed with renal clearable nanoprobes. In this report, we demonstrate the use of magnetic resonance imaging along with renal clearable ferric coordination polymer nanodots (Fe-CPNDs) for in vivo monitoring the kidney dysfunction effects following drug (daunomycin)-induced kidney injury. After intravenous injection of Fe-CPNDs, the change of the MR signal in the kidney can be precisely correlated with local pathological lesion which is demonstrated by renal anatomic details and biochemical examinations of urine and blood. This finding opens the door to the possibility of noninvasively assessing kidney dysfunction and local injuries.

Imaging techniques to study drug transporter function in vivo

Transporter systems involved in the permeation of drugs and solutes across biological membranes are recognized as key determinants of pharmacokinetics. Typically, the action of membrane transporters on drug exposure to tissues in living organisms is inferred from invasive procedures, which cannot be applied in humans. In recent years, imaging methods have greatly progressed in terms of instruments, synthesis of novel imaging probes as well as tools for data analysis. Imaging allows pharmacokinetic parameters in different tissues and organs to be obtained in a non-invasive or minimally invasive way. The aim of this overview is to summarize the current status in the field of molecular imaging of drug transporters. The overview is focused on human studies, both for the characterization of transport systems for imaging agents as well as for the determination of drug pharmacokinetics, and makes reference to animal studies where necessary. We conclude that despite certain methodological limitations, imaging has a great potential to study transporters at work in humans and that imaging will become an important tool, not only in drug development but also in medicine. Imaging allows the mechanistic aspects of transport proteins to be studied, as well as elucidating the influence of genetic background, pathophysiological states and drug-drug interactions on the function of transporters involved in the disposition of drugs.

Early kidney damage induced by subchronic exposure to PM2.5 in rats

BACKGROUND

Particulate matter exposure is associated with respiratory and cardiovascular system dysfunction. Recently, we demonstrated that fine particles, also named PM_2.5, modify the expression of some components of the angiotensin and bradykinin systems, which are involved in lung, cardiac and renal regulation. The endocrine kidney function is associated with the regulation of angiotensin and bradykinin, and it can suffer damage even as a consequence of minor alterations of these systems. We hypothesized that exposure to PM_2.5 can contribute to early kidney damage as a consequence of an angiotensin/bradykinin system imbalance, oxidative stress and/or inflammation.

RESULTS

After acute and subchronic exposure to PM_2.5, lung damage was confirmed by increased bronchoalveolar lavage fluid (BALF) differential cell counts and a decrease of surfactant protein-A levels. We observed a statistically significant increment in median blood pressure, urine volume and water consumption after PM_2.5 exposure. Moreover, increases in the levels of early kidney damage markers were observed after subchronic PM_2.5 exposure: the most sensitive markers, β-2-microglobulin and cystatin-C, increased during the first, second, sixth and eighth weeks of exposure. In addition, a reduction in the levels of specific cytokines (IL-1β, IL-6, TNF-α, IL-4, IL-10, INF-γ, IL-17a, MIP-2 and RANTES), and up-regulated angiotensin and bradykinin system markers and indicators of a depleted antioxidant response, were also observed. All of these effects are in concurrence with the presence of renal histological lesions and an early pro-fibrotic state.

CONCLUSION

Subchronic exposure to PM_2.5 induced an early kidney damage response that involved the angiotensin/bradykinin systems as well as antioxidant and immune imbalance. Our study demonstrates that PM_2.5 can induce a systemic imbalance that not only affects the cardiovascular system, but also affects the kidney, which may also overall contribute to PM-related diseases.

Evaluation of 18F-FDG excretion patterns in malignant obstructive uropathy

OBJECTIVES

This study aims to evaluate whether (18)F-FDG excretion patterns reflect renal function in malignant obstructive uropathy and to evaluate if these patterns predict internal ureteral stent success.

METHODS

One hundred twelve patients who underwent PET/CT for abdominal tumors and displayed hydronephrosis on CT and 59 patients who underwent PET/CT for cancer screening were included in a retrospective study. Hydronephrosis was graded by initial CT and correlated with visual analysis of (18)F-FDG renal parenchymal uptake and excretion patterns. Stent insertion was performed for 84 patients after PET. Follow-up CT was reviewed for hydronephrosis improvement.

RESULTS

There were 4 PET patterns in obstructive hydronephrosis which correlated linearly with hydronephrosis severity and serum creatinine levels. Patients with no parenchymal retention and renal excretion (PET pattern 1) showed 97% (28/29) hydronephrosis improvement after stent insertion, and patients with no parenchymal retention and no renal excretion showed 0% (0/9) hydronephrosis improvement after stent insertion. Multivariate analysis showed creatinine levels and PET pattern predicted stent success, but CT hydronephrosis did not.

CONCLUSIONS

There are 4 PET patterns of obstructive hydronephrosis which correlated with hydronephrosis grade and creatinine levels. Some of these PET patterns can be useful in the prediction of hydronephrosis improvement after stent insertion. Recognition of these patterns in obstructive hydronephrosis may be helpful in improving patient prognosis and quality of life.

Assessment of renal function; clearance, the renal microcirculation, renal blood flow, and metabolic balance

Historically, tools to assess renal function have been developed to investigate the physiology of the kidney in an experimental setting, and certain of these techniques have utility in evaluating renal function in the clinical setting. The following work will survey a spectrum of these tools, their applications and limitations in four general sections. The first is clearance, including evaluation of exogenous and endogenous markers for determining glomerular filtration rate, the adaptation of estimated glomerular filtration rate in the clinical arena, and additional clearance techniques to assess various other parameters of renal function. The second section deals with in vivo and in vitro approaches to the study of the renal microvasculature. This section surveys a number of experimental techniques including corticotomy, the hydronephrotic kidney, vascular casting, intravital charge coupled device videomicroscopy, multiphoton fluorescent microscopy, synchrotron-based angiography, laser speckle contrast imaging, isolated renal microvessels, and the perfused juxtamedullary nephron microvasculature. The third section addresses in vivo and in vitro approaches to the study of renal blood flow. These include ultrasonic flowmetry, laser-Doppler flowmetry, magnetic resonance imaging (MRI), phase contrast MRI, cine phase contrast MRI, dynamic contrast-enhanced MRI, blood oxygen level dependent MRI, arterial spin labeling MRI, x-ray computed tomography, and positron emission tomography. The final section addresses the methodologies of metabolic balance studies. These are described for humans, large experimental animals as well as for rodents. Overall, the various in vitro and in vivo topics and applications to evaluate renal function should provide a guide for the investigator or physician to understand and to implement the techniques in the laboratory or clinic setting.

Cumulative radiation dose from medical imaging in kidney transplant patients

BACKGROUND

Although many patients undergoing kidney transplant are exposed to multiple examinations that increase cumulative effective doses (CEDs) of ionizing radiation, no data are available characterizing their total longitudinal radiation burden and relating radiation burden with risk factors for more exposure.

METHODS

We did a retrospective cohort study of 92 patients (mean age 52 years; range: 20-75 years) who underwent kidney transplant at University Hospital, Novara, Italy, that evaluated all following medical imaging procedures involving ionizing radiation undergone beginning June 2007, and all subsequent procedures through August 2011, at the centre.

RESULTS

The mean and median annual CED were 17.2 and 4.9 millisieverts (mSv) per patient-year. The mean and median total CED per patient over the study period were 46.1 and 17.3 mSv, respectively. Twenty-eight and 12% of patients had total CED >50 and 100 mSv, values which are associated with a good or strong evidence of an increased cancer mortality risk, respectively. Computed tomography scanning accounted for 73% of the total CED. The annual CED was significantly higher in incident patients and in patients with ischaemic heart disease and cancer.

CONCLUSION

In this institution, multiple testing of kidney transplant patients was common in many patients associated with high cumulative estimated doses of ionizing radiation.

Functional renal imaging: new trends in radiology and nuclear medicine

The objective of this work is to compare the characteristics of various techniques for functional renal imaging, with a focus on nuclear medicine and magnetic resonance imaging. Even with low spatial resolution and rather poor signal-to-noise ratio, classical nuclear medicine has the advantage of linearity and good sensitivity. It remains the gold standard technique for renal relative functional assessment. Technetium-99m ((99m)Tc)-labeled diethylenetriamine penta-acetate remains the reference glomerular tracer. Tubular tracers have been improved: (123)I- or (131)I-hippuran, (99m)Tc-MAG3 and, recently, (99m)Tc-nitrilotriacetic acid. However, advancement in molecular imaging has not produced a groundbreaking tracer. Renal magnetic resonance imaging with classical gadolinated tracers probably has potential in this domain but has a lack of linearity and, therefore, its value still needs evaluation. Moreover, the advent of nephrogenic systemic fibrosis has delayed its expansion. Other developments, such as diffusion or blood oxygen level-dependent imaging, may have a role in the future. The other modalities have a limited role in clinical practice for functional renal imaging.