Longitudinal assessment of rabbit renal fibrosis induced by unilateral ureteral obstruction using two-dimensional susceptibility weighted imaging

Quantitative susceptibility mapping for detection of kidney stones, hemorrhage differentiation, and cyst classification in ADPKD

BACKGROUND AND PURPOSE

The objective is to demonstrate feasibility of quantitative susceptibility mapping (QSM) in autosomal dominant polycystic kidney disease (ADPKD) patients and to compare imaging findings with traditional T1/T2w magnetic resonance imaging (MRI).

METHODS

Thirty-three consecutive patients (11 male, 22 female) diagnosed with ADPKD were initially selected. QSM images were reconstructed from the multiecho gradient echo data and compared to co-registered T2w, T1w, and CT images. Complex cysts were identified and classified into distinct subclasses based on their imaging features. Prevalence of each subclass was estimated.

RESULTS

QSM visualized two renal calcifications measuring 9 and 10 mm and three pelvic phleboliths measuring 2 mm but missed 24 calcifications measuring 1 mm or less and 1 larger calcification at the edge of the field of view. A total of 121 complex T1 hyperintense/T2 hypointense renal cysts were detected. 52 (43%) Cysts appeared hyperintense on QSM consistent with hemorrhage; 60 (49%) cysts were isointense with respect to simple cysts and normal kidney parenchyma, while the remaining 9 (7%) were hypointense. The presentation of the latter two complex cyst subtypes is likely indicative of proteinaceous composition without hemorrhage.

CONCLUSION

Our results indicate that QSM of ADPKD kidneys is possible and uniquely suited to detect large renal calculi without ionizing radiation and able to identify properties of complex cysts unattainable with traditional approaches.

Advances in imaging techniques to assess kidney fibrosis

As a sign of chronic kidney disease (CKD) progression, renal fibrosis is an irreversible and alarming pathological change. The accurate diagnosis of renal fibrosis depends on the widely used renal biopsy, but this diagnostic modality is invasive and can easily lead to sampling error. With the development of imaging techniques, an increasing number of noninvasive imaging techniques, such as multipara meter magnetic resonance imaging (MRI) and ultrasound elastography, have gained attention in assessing kidney fibrosis. Depending on their ability to detect changes in tissue stiffness and diffusion of water molecules, ultrasound elastography and some MRI techniques can indirectly assess the degree of fibrosis. The worsening of renal tissue oxygenation and perfusion measured by blood oxygenation level-dependent MRI and arterial spin labeling MRI separately is also an indirect reflection of renal fibrosis. Objective and quantitative indices of fibrosis may be available in the future by using novel techniques, such as photoacoustic imaging and fluorescence microscopy. However, these imaging techniques are susceptible to interference or may not be convenient. Due to the lack of sufficient specificity and sensitivity, these imaging techniques are neither widely accepted nor proposed by clinicians. These obstructions must be overcome by conducting technology research and more prospective studies. In this review, we emphasize the recent advancement of these noninvasive imaging techniques and provide clinicians a continuously updated perspective on the assessment of kidney fibrosis.

Yiqi Huoxue Tongluo recipe regulates NR4A1 to improve renal mitochondrial function in unilateral ureteral obstruction (UUO) rats

CONTEXT

Yiqi Huoxue Tongluo recipe (YHTR) is a traditional Chinese medicine for the treatment of chronic kidney disease, but its exact mechanism is not clear.

OBJECTIVES

To monitor the potential improvement of renal mitochondrial function in unilateral ureteral obstruction (UUO) rats by regulating NR4A1 using the YHTR.

MATERIALS AND METHODS

Wistar rats were randomly divided into four groups: sham, UUO (left ureteral ligation for 14 days), eplerenone (EPL) (UUO + EPL), and YHTR (UUO + YHTR). UUO rats were established and intragastrically administered EPL (100 mg/day/kg) or YHTR (11.7 g/day/kg) for 14 days. The expression of related proteins in kidneys was detected by immunohistochemistry, western blot, RT-PCR, and chemical colorimetric assay, respectively.

RESULTS

In vivo, YHTR treatment reduced the levels of BUN and Scr (by 17.9% and 23.5%) in UUO rats. Moreover, YHTR improved the renal mitochondrial function via increasing key enzymes of the tricarboxylic acid (TCA) cycle (p < 0.05) and activity of the mitochondrial complex (I-V) (by 30.8%, 29.1%, 19.7%, 35.9%, and 22.4%) in UUO rats. Compared with the UUO group, the expression of NR4A1 and Bcl-2 were significantly increased (p < 0.05), the expression of caspase-3 and caspase-9 were significantly decreased (p < 0.05) in the YHTR group. YHTR could upregulate key enzymes of the TCA cycle via promoting NR4A1 expression in HK2 cells, leading to inhibition of TGF-β1 induced cell apoptosis.

CONCLUSIONS

YHTR significantly improved the development of CKD; this study may provide new ideas for the pathogenesis of CKD and new strategies for the development of new drugs against CKD.

Expression Profiles of Kidney Mitochondrial Proteome during the Progression of the Unilateral Ureteral Obstruction: Focus on Energy Metabolism Adaptions

Kidney diseases encompass many pathologies, including obstructive nephropathy (ON), a common clinical condition caused by different etiologies such as urolithiasis, prostatic hyperplasia in males, tumors, congenital stenosis, and others. Unilateral ureteral obstruction (UUO) in rodents is an experimental model widely used to explore the pathophysiology of ON, replicating vascular alterations, tubular atrophy, inflammation, and fibrosis development. In addition, due to the kidney’s high energetic demand, mitochondrial function has gained great attention, as morphological and functional alterations have been demonstrated in kidney diseases. Here we explore the kidney mitochondrial proteome differences during a time course of 7, 14, and 21 days after the UUO in rats, revealing changes in proteins involved in three main metabolic pathways, oxidative phosphorylation (OXPHOS), the tricarboxylic acid cycle (TCA), and the fatty acid (FA) metabolism, all of them related to bioenergetics. Our results provide new insight into the mechanisms involved in metabolic adaptations triggered by the alterations in kidney mitochondrial proteome during the ON.

Telmisartan inhibits bladder smooth muscle fibrosis in neurogenic bladder rats

Hypertension is associated with bladder symptoms. The present study investigated whether an angiotensin receptor blocker could improve the symptoms and pathological changes associated with a neurogenic bladder (NB). A Sprague-Dawley rat model of NB was constructed. Rats in the sham and model groups were gavaged with saline, and rats in the treatment group were gavaged with telmisartan. Urodynamic parameters, including maximum cystometric capacity, residual urine volume, bladder wet weight, bladder compliance and detrusor pressure, were detected. Masson and H&E staining were performed to assess bladder fibrosis and histopathological changes. The expression levels of basic fibroblast growth factor (bFGF), TGF-β1, Collagen I, Collagen III, and α-smooth muscle actin (α-SMA) were also measured by reverse transcription-quantitative PCR, western blotting and immunohistochemistry. The model rats exhibited symptoms and pathological changes associated with NB. Treatment with telmisartan reduced maximum cystometric capacity, residual urine volume, bladder compliance and bladder wet weight, and increased detrusor pressure in model rats. The tissue staining results showed that telmisartan exerted an antifibrotic effect. In addition, telmisartan inhibited the expression of bFGF, TGF-β1, Collagen I, Collagen III and α-SMA in model rats. Therefore, the results of the present study indicated that telmisartan may serve as a potential therapeutic agent for NB.

Advanced non-invasive diagnostic techniques for visualization and estimation of kidney fibrosis

Kidney fibrosis is marked by excessive extracellular matrix deposition during disease progression. Unfortunately, existing kidney function parameters do not predict the extent of kidney fibrosis. Moreover, the traditional histology methods for the assessment of kidney fibrosis require liquid and imaging biomarkers as well as needle-based biopsies, which are invasive and often associated with kidney injury. The repetitive analyses required to monitor the disease progression are therefore difficult. Hence, there is an unmet medical need for non-invasive and informative diagnostic approaches to monitor kidney fibrosis during the progression of chronic kidney disease. Here, we summarize the modern advances in diagnostic imaging techniques that have shown promise for non-invasive estimation of kidney fibrosis in pre-clinical and clinical studies.

Susceptibility weighted imaging (SWI) for evaluating renal dysfunction in type 2 diabetes mellitus: a preliminary study using SWI parameters and SWI-based texture features

Background

Susceptibility weighted imaging (SWI) could reflect tissue blood oxygen levels, and then whether it could be used to evaluate renal injury remains to be further studied. This study aimed to examine the performance of SWI parameters and SWI-based texture features in evaluating renal dysfunction of type 2 diabetes mellitus (T2DM).

Methods

Forty-five patients with T2DM were included. With the estimated glomerular filtration rate (eGFR), the patients were divided into non-moderate-severe renal injured group (non-msRI, eGFR >60 mL/min/1.73 m²) and moderate-severe renal injured group (msRI, eGFR ≤60 mL/min/1.73 m²). The 3 SWI parameters and 16 SWI-based texture features between non-msRI and msRI were compared. The correlation between the parameters and BUN, Scr was analyzed.

Results

The signal intensity ratio of the medulla to psoas muscle (MPswi) was significantly lower than the signal intensity ratio of the cortex to psoas muscle (CPswi) in non-msRI and msRI group (t=8.619, 3.483, respectively, P<0.05). MPswi was higher, and the signal intensity ratio of the cortex to the medulla (CMswi), Skewness, Correlation were lower in msRI than in non-msRI (P<0.05). These parameters showed similar diagnostic efficacies for msRI (P>0.05), and AUCs were 0.703–0.854. CMswi was an independent protective factor for msRI (OR =0.026, P=0.003). MPswi and CMswi were correlated with BUN (r=0.416, −0.545, P<0.05). CMswi and Correlation were correlated with Scr (r=−0.645, −0.411, P<0.05).

Conclusions

SWI was valuable for assessing renal dysfunction, which may be helpful for the evaluation of moderate-severe renal injured patients with T2DM.

Podocyte Injury Through Interaction Between Tlr8 and Its Endogenous Ligand miR-21 in Obstructed and Its Collateral Kidney

While chronic kidney disease is prevalent in adults, obstructive nephropathy (ON) has been reported in both young and old patients. In ON, tubulointerstitial lesions (TILs) have been widely investigated, but glomerular lesions (GLs) have been largely neglected. Here, we show a novel mechanism underlying GL development in ON in young and old mice. TILs develop earlier than GLs owing to infiltration of inflammatory cells in the tubulointerstitium, but GLs develop following the activation of Toll-like receptor 8 (Tlr8) even though the absence of inflammatory cells infiltrating the glomerulus. TLR8 and interleukin 1 beta (IL1β) proteins colocalize with reducing podocyte function markers (PFMs), indicating the activation of TLR8 signaling in injured podocytes. Furthermore, glomerular and serum levels of miR-21, an endogenous ligand for Tlr8, were higher in the ON mouse model than in the sham control. The glomerular expression of Tlr8 positively correlates with miR-21 and the downstream cytokines Il1b and Il6 and negatively correlated with PFMs (Nphs1 and Synpo). We also show the colocalization of TLR8 and IL1β proteins with reducing PFMs in both obstructed and collateral kidney of young and old mice. Furthermore, in vitro study results revealed higher expression of Tlr8 and its downstream cytokines in glomeruli from obstructed kidneys following treatment with miR-21 mimic than in the control. In conclusion, the overexpression of Tlr8 may serve as a plausible mechanism underlying GL development in ON through podocyte injury.

Recent advances in medical image processing for the evaluation of chronic kidney disease

Assessment of renal function and structure accurately remains essential in the diagnosis and prognosis of Chronic Kidney Disease (CKD). Advanced imaging, including Magnetic Resonance Imaging (MRI), Ultrasound Elastography (UE), Computed Tomography (CT) and scintigraphy (PET, SPECT) offers the opportunity to non-invasively retrieve structural, functional and molecular information that could detect changes in renal tissue properties and functionality. Currently, the ability of artificial intelligence to turn conventional medical imaging into a full-automated diagnostic tool is widely investigated. In addition to the qualitative analysis performed on renal medical imaging, texture analysis was integrated with machine learning techniques as a quantification of renal tissue heterogeneity, providing a promising complementary tool in renal function decline prediction. Interestingly, deep learning holds the ability to be a novel approach of renal function diagnosis. This paper proposes a survey that covers both qualitative and quantitative analysis applied to novel medical imaging techniques to monitor the decline of renal function. First, we summarize the use of different medical imaging modalities to monitor CKD and then, we show the ability of Artificial Intelligence (AI) to guide renal function evaluation from segmentation to disease prediction, discussing how texture analysis and machine learning techniques have emerged in recent clinical researches in order to improve renal dysfunction monitoring and prediction. The paper gives a summary about the role of AI in renal segmentation.

Acute renal impairment characterization using diffusion magnetic resonance imaging: Validation by histology

Diffusion magnetic resonance imaging has been demonstrated to be a simple, noninvasive and accurate method for the detection of renal microstructure and microcirculation, which are closely linked to renal function. Moreover, serum endothelin-1 (ET-1) was also reported as a good indicator of early renal injury. The aim of this study was to evaluate the feasibility and capability of diffusion MRI and ET-1 to detect acute kidney injury by an operation simulating high-pressure renal pelvic perfusion, which is commonly used during ureteroscopic lithotripsy. Histological findings were used as a reference. Fourteen New Zealand rabbits in an experimental group and 14 in a control group were used in this study. Diffusion tensor imaging and intravoxel incoherent motion diffusion-weighted imaging were acquired by a 3.0 T MRI scanner. Significant corticomedullary differences were found in the values of the apparent diffusion coefficient (ADC), pure tissue diffusion, volume fraction of pseudo-diffusion (fp) and fractional anisotropy (FA) (P < 0.05 for all) in both preoperation and postoperation experimental groups. Compared with the control group, the values of cortical fp_mean , medullary ADC_mean and FA_mean decreased significantly (P < 0.05) after the operation in the experimental group. Also, the change rate of medullary ADC_mean in the experimental group was more pronounced than that in the control group (P = 0.018). No significant change was found in serum ET-1 concentration after surgery in either the experimental (P = 0.80) or control (P = 0.17) groups. In the experimental group, histological changes were observed in the medulla, while no visible change was found in the cortex. This study demonstrated the feasibility of diffusion MRI to detect the changes of renal microstructure and microcirculation in acute kidney injury, with the potential to evaluate renal function. Moreover, the sensitivity of diffusion MRI to acute kidney injury appears to be superior to that of serum ET-1.

Noninvasive assessment of renal fibrosis by magnetic resonance imaging and ultrasound techniques

Renal fibrosis is a useful biomarker for diagnosis and guidance of therapeutic interventions of chronic kidney disease (CKD), a worldwide disease that affects more than 10% of the population and is one of the major causes of death. Currently, tissue biopsy is the gold standard for assessment of renal fibrosis. However, it is invasive, and prone to sampling error and observer variability, and may also result in complications. Recent advances in diagnostic imaging techniques, including magnetic resonance imaging (MRI) and ultrasonography, have shown promise for noninvasive assessment of renal fibrosis. These imaging techniques measure renal fibrosis by evaluating its impacts on the functional, mechanical, and molecular properties of the kidney, such as water mobility by diffusion MRI, tissue hypoxia by blood oxygenation level dependent MRI, renal stiffness by MR and ultrasound elastography, and macromolecule content by magnetization transfer imaging. Other MR techniques, such as T1/T2 mapping and susceptibility-weighted imaging have also been explored for measuring renal fibrosis. Promising findings have been reported in both preclinical and clinical studies using these techniques. Nevertheless, limited specificity, sensitivity, and practicality in these techniques may hinder their immediate application in clinical routine. In this review, we will introduce methodologies of these techniques, outline their applications in fibrosis imaging, and discuss their limitations and pitfalls.

Unilateral Ureteral Obstruction as a Model to Investigate Fibrosis-Attenuating Treatments

Renal fibrosis is the common pathway for most forms of progressive renal disease. The Unilateral Ureteral Obstruction (UUO) model is used to cause renal fibrosis, where the primary feature of UUO is tubular injury as a result of obstructed urine flow. Furthermore, experimental UUO in rodents is believed to mimic human chronic obstructive nephropathy in an accelerated manner. Renal fibrosis is the common pathway for most forms of progressive renal disease. Removing the obstruction may not be sufficient to reverse fibrosis, so an accompanying treatment may be of benefit. In this review, we have done a revision on treatments shown to ameliorate fibrosis in the context of the UUO experimental model. The treatments inhibit the production of fibrotic and inflammatory proteins such as Transforming Growth Factor β1 (TGF-β₁), Tumor Necrosis Factor α (TNF-α), collagen and fibronectin, Heat Shock Protein 47 (HSP47), suppress the proliferation of fibroblasts, prevent epithelial-to-mesenchymal transition, reduce oxidative stress, inhibit the action of the Nuclear Factor κB (NF-κB), reduce the phosphorylation of mothers against decapentaplegic homolog (SMAD) family members 2 and 3 (Smad2/3) or Mitogen-Activated Protein Kinases (MAPKs), inhibit the activation of the renin-angiotensin system. Summaries of the UUO experimental methods and alterations observed in the UUO experiments are included.

Evaluation of renal dysfunction using texture analysis based on DWI, BOLD, and susceptibility-weighted imaging

OBJECTIVE

To explore the value of texture analysis based on diffusion-weighted imaging (DWI), blood oxygen level-dependent MRI (BOLD), and susceptibility-weighted imaging (SWI) in evaluating renal dysfunction.

METHODS

Seventy-two patients (mean age 53.72 ± 13.46 years) underwent MRI consisting of DWI, BOLD, and SWI. According to their estimated glomerular filtration rate (eGFR), the patients were classified into either severe renal function impairment (sRI, eGFR < 30 mL/min/1.73 m²), non-severe renal function impairment (non-sRI, eGFR ≥ 30 mL/min/1.73 m², and < 80 mL/min/1.73 m²), or control (CG, eGFR ≥ 80 mL/min/1.73 m²) groups. Thirteen texture features were extracted and then were analyzed to select the most valuable for discerning the three groups with each imaging method. A ROC curve was performed to compare the capacities of the features to differentiate non-sRI from sRI or CG.

RESULTS

Six features proved to be the most valuable for assessing renal dysfunction: 0.25Quantile_DWI, 0.5Quantile_DWI, Homogeneity_DWI, Entropy_BOLD, Skewness_SWI, and Correlation_SWI. Three features derived from DWI (0.25Quantile_DWI, 0.5Quantile_DWI, and Homogeneity_DWI) were smaller in sRI than in non-sRI; Entropy_BOLD and Correlation_SWI were smaller in non-sRI than in CG (p < 0.05). 0.25Quantile_DWI, 0.5Quantile_DWI, and Homogeneity_DWI showed similar capacities for differentiating sRI from non-sRI. Similarly, Entropy_BOLD and Correlation_SWI showed equal capacities for differentiating non-sRI from CG.

CONCLUSION

Texture analysis based on DWI, BOLD, and SWI can assist in assessing renal dysfunction, and texture features based on BOLD and SWI may be suitable for assessing renal dysfunction during early stages.

KEY POINTS

• Texture analysis based on MRI techniques allowed for assessing renal dysfunction. • Texture features based on BOLD and SWI, but not DWI, may be suitable for assessing renal function impairment during early stages. • SWI exhibited a similar capacity to BOLD for assessing renal dysfunction.