Microcirculation in Acute and Chronic Kidney Diseases

Characterizing hub biomarkers for post-transplant renal fibrosis and unveiling their immunological functions through RNA sequencing and advanced machine learning techniques

BACKGROUND

Kidney transplantation stands out as the most effective renal replacement therapy for patients grappling with end-stage renal disease. However, post-transplant renal fibrosis is a prevalent and irreversible consequence, imposing a substantial clinical burden. Unfortunately, the clinical landscape remains devoid of reliable biological markers for diagnosing post-transplant renal interstitial fibrosis.

METHODS

We obtained transcriptome and single-cell sequencing datasets of patients with renal fibrosis from NCBI Gene Expression Omnibus (GEO). Subsequently, we employed Weighted Gene Co-Expression Network Analysis (WGCNA) to identify potential genes by integrating core modules and differential genes. Functional enrichment analysis was conducted to unveil the involvement of potential pathways. To identify key biomarkers for renal fibrosis, we utilized logistic analysis, a LASSO-based tenfold cross-validation approach, and gene topological analysis within Cytoscape. Furthermore, histological staining, Western blotting (WB), and quantitative PCR (qPCR) experiments were performed in a murine model of renal fibrosis to verify the identified hub genes. Moreover, molecular docking and molecular dynamics simulations were conducted to explore possible effective drugs.

RESULTS

Through WGCNA, the intersection of core modules and differential genes yielded a compendium of 92 potential genes. Logistic analysis, LASSO-based tenfold cross-validation, and gene topological analysis within Cytoscape identified four core genes (CD3G, CORO1A, FCGR2A, and GZMH) associated with renal fibrosis. The expression of these core genes was confirmed through single-cell data analysis and validated using various machine learning methods. Wet experiments also verified the upregulation of these core genes in the murine model of renal fibrosis. A positive correlation was observed between the core genes and immune cells, suggesting their potential role in bolstering immune system activity. Moreover, four potentially effective small molecules (ZINC000003830276-Tessalon, ZINC000003944422-Norvir, ZINC000008214629-Nonoxynol-9, and ZINC000085537014-Cobicistat) were identified through molecular docking and molecular dynamics simulations.

CONCLUSION

Four potential hub biomarkers most associated with post-transplant renal fibrosis, as well as four potentially effective small molecules, were identified, providing valuable insights for studying the molecular mechanisms underlying post-transplant renal fibrosis and exploring new targets.

Interventions for chronic kidney disease in people with sickle cell disease

BACKGROUND

Sickle cell disease (SCD), one of the commonest severe monogenic disorders, is caused by the inheritance of two abnormal haemoglobin (beta-globin) genes. SCD can cause severe pain, significant end-organ damage, pulmonary complications, and premature death. Kidney disease is a frequent and potentially severe complication in people with SCD. Chronic kidney disease (CKD) is defined as abnormalities of kidney structure or function present for more than three months. Sickle cell nephropathy refers to the spectrum of kidney complications in SCD. Glomerular damage is a cause of microalbuminuria and can develop at an early age in children with SCD, with increased prevalence in adulthood. In people with sickle cell nephropathy, outcomes are poor as a result of the progression to proteinuria and chronic kidney insufficiency. Up to 12% of people who develop sickle cell nephropathy will develop end-stage renal disease. This is an update of a review first published in 2017.

OBJECTIVES

To assess the effectiveness of any intervention for preventing or reducing kidney complications or chronic kidney disease in people with sickle cell disease. Possible interventions include red blood cell transfusions, hydroxyurea, and angiotensin-converting enzyme inhibitors (ACEIs), either alone or in combination.

SEARCH METHODS

We searched for relevant trials in the Cochrane Cystic Fibrosis and Genetic Disorders Group Trials Register, CENTRAL, MEDLINE, Embase, seven other databases, and two other trials registers.

SELECTION CRITERIA

Randomised controlled trials (RCTs) comparing interventions to prevent or reduce kidney complications or CKD in people with SCD. We applied no restrictions related to outcomes examined, language, or publication status.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed trial eligibility, extracted data, assessed the risk of bias, and assessed the certainty of the evidence (GRADE).

MAIN RESULTS

We included three RCTs with 385 participants. We rated the certainty of the evidence as low to very low across different outcomes according to GRADE methodology, downgrading for risk of bias concerns, indirectness, and imprecision. Hydroxyurea versus placebo One RCT published in 2011 compared hydroxyurea to placebo in 193 children aged nine to 18 months. We are unsure if hydroxyurea compared to placebo reduces or prevents progression of kidney disease assessed by change in glomerular filtration rate (mean difference (MD) 0.58 mL/min /1.73 m2, 95% confidence interval (CI) -14.60 to 15.76; 142 participants; very low certainty). Hydroxyurea compared to placebo may improve the ability to concentrate urine (MD 42.23 mOsm/kg, 95% CI 12.14 to 72.32; 178 participants; low certainty), and may make little or no difference to SCD-related serious adverse events, including acute chest syndrome (risk ratio (RR) 0.39, 99% CI 0.13 to 1.16; 193 participants; low certainty), painful crisis (RR 0.68, 99% CI 0.45 to 1.02; 193 participants; low certainty); and hospitalisations (RR 0.83, 99% CI 0.68 to 1.01; 193 participants; low certainty). No deaths occurred in either trial arm and the RCT did not report quality of life. Angiotensin-converting enzyme inhibitors versus placebo One RCT published in 1998 compared an ACEI (captopril) to placebo in 22 adults with normal blood pressure and microalbuminuria. We are unsure if captopril compared to placebo reduces proteinuria (MD -49.00 mg/day, 95% CI -124.10 to 26.10; 22 participants; very low certainty). We are unsure if captopril reduces or prevents kidney disease as measured by creatinine clearance; the trial authors stated that creatinine clearance remained constant over six months in both groups, but provided no comparative data (very low certainty). The RCT did not report serious adverse events, all-cause mortality, or quality of life. Angiotensin-converting enzyme inhibitors versus vitamin C One RCT published in 2020 compared an ACEI (lisinopril) with vitamin C in 170 children aged one to 18 years with normal blood pressure and microalbuminuria. It reported no data we could analyse. We are unsure if lisinopril compared to vitamin C reduces proteinuria in this population: the large drop in microalbuminuria in both arms of the trial after only one month on treatment may have been due to an overestimation of microalbuminuria at baseline rather than a true effect. The RCT did not report serious adverse events, all-cause mortality, or quality of life.

AUTHORS' CONCLUSIONS

We are unsure if hydroxyurea improves glomerular filtration rate or reduces hyperfiltration in children aged nine to 18 months, but it may improve their ability to concentrate urine and may make little or no difference to the incidence of acute chest syndrome, painful crises, and hospitalisations. We are unsure if ACEI compared to placebo has any effect on preventing or reducing kidney complications in adults with normal blood pressure and microalbuminuria. We are unsure if ACEI compared to vitamin C has any effect on preventing or reducing kidney complications in children with normal blood pressure and microalbuminuria. No RCTs assessed red blood cell transfusions or any combined interventions to prevent or reduce kidney complications. Due to lack of evidence, we cannot comment on the management of children aged over 18 months or adults with any known genotype of SCD. We have identified a lack of adequately designed and powered studies, although we found four ongoing trials since the last version of this review. Only one ongoing trial addresses renal function as a primary outcome in the short term, but such interventions have long-term effects. Trials of hydroxyurea, ACEIs or red blood cell transfusion in older children and adults are urgently needed to determine any effect on prevention or reduction of kidney complications in people with SCD.

The sublingual microcirculation and frailty index in chronic kidney disease patients

OBJECTIVE

To examine the relationship between sublingual microcirculatory measures and frailty index in those attending a kidney transplant assessment clinic.

METHODS

Patients recruited had their sublingual microcirculation taken using sidestream dark field videomicroscopy (MicroScan, Micro Vision Medical, Amsterdam, the Netherlands) and their frailty index score using a validated short form via interview.

RESULTS

A total of 44 patients were recruited with two being excluded due to microcirculatory image quality scores exceeding 10. The frailty index score indicated significant correlations with total vessel density (p < .0001, r = -.56), microvascular flow index (p = .004, r = -.43), portion of perfused vessels (p = .0004, r = -.52), heterogeneity index (p = .015, r = .32), and perfused vessel density (p < .0001, r = -.66). No correlation was shown between the frailty index and age (p = .08, r = .27).

CONCLUSIONS

There is a relationship between the frailty index and microcirculatory health in those attending a kidney transplant assessment clinic, that is not confounded by age. These findings suggest that the impaired microcirculation may be an underlying cause of frailty.

Non-invasive intradialytic percutaneous perfusion monitoring: a view to the heart through the skin

Introduction

The life-sustaining treatment of hemodialysis (HD) induces recurrent and cumulative systemic circulatory stress resulting in cardiovascular injury. These recurrent insults compound preexisting cardiovascular sequalae leading to the development of myocardial injury and resulting in extremely high morbidity/mortality. This is largely a consequence of challenged microcirculatory flow within the myocardium (evidenced by detailed imaging-based studies). Currently, monitoring during HD is performed at the macrovascular level. Non-invasive monitoring of organ perfusion would allow the detection and therapeutic amelioration of this pathophysiological response to HD. Non-invasive percutaneous perfusion monitoring of the skin (using photoplethysmography-PPG) has been shown to be predictive of HD-induced myocardial stunning (a consequence of segmental ischemia). In this study, we extended these observations to include a dynamic assessment of skin perfusion during HD compared with directly measured myocardial perfusion during dialysis and cardiac contractile function.

Methods

We evaluated the intradialytic microcirculatory response in 12 patients receiving conventional HD treatments using continuous percutaneous perfusion monitoring throughout HD. Cardiac echocardiography was performed prior to the initiation of HD, and again at peak-HD stress, to assess the development of regional wall motion abnormalities (RWMAs). Myocardial perfusion imaging was obtained at the same timepoints (pre-HD and peak-HD stress), utilizing intravenous administered contrast and a computerized tomography (CT)-based method. Intradialytic changes in pulse strength (derived from PPG) were compared with the development of HD-induced RWMAs (indicative of myocardial stunning) and changes in myocardial perfusion.

Results

We found an association between the lowest pulse strength reduction (PPG) and the development of RWMAs (p = 0.03) and also with changes in global myocardial perfusion (CT) (p = 0.05). Ultrafiltration rate (mL/kg/hour) was a significant driver of HD-induced circulatory stress [(associated with the greatest pulse strength reduction (p = 0.01), a reduction in global myocardial perfusion (p = 0.001), and the development of RWMAs (p = 0.03)].

Discussion

Percutaneous perfusion monitoring using PPG is a useful method of assessing intradialytic hemodynamic stability and HD-induced circulatory stress. The information generated at the microcirculatory level of the skin is reflective of direct measures of myocardial perfusion and the development of HD-induced myocardial stunning. This approach for the detection and management of HD-induced cardiac injury warrants additional evaluation.

Prediction of renal recovery following sepsis-associated acute kidney injury requiring renal replacement therapy using contrast-enhanced ultrasonography

BACKGROUND

Microcirculatory dysfunction plays a critical role in sepsis-associated acute kidney injury (S-AKI) development; however, its impact on renal recovery remains uncertain. We investigated the association between cortical microcirculatory function assessed using contrast-enhanced ultrasonography (CEUS) and renal recovery after S-AKI needing renal replacement therapy (RRT).

METHODS

This retrospective study included 23 patients who underwent CEUS among those who underwent acute RRT for S-AKI. In addition, we acquired data from 17 healthy individuals and 18 patients with chronic kidney disease. Renal recovery was defined as sustained independence from RRT for at least 14 days.

RESULTS

Of the CEUS-derived parameters, rise time, time to peak, and fall time were longer in patients with S-AKI than in healthy individuals (p = 0.045, 0.01, and 0.096, respectively). Fourteen patients (60.9%) with S-AKI receiving RRT experienced renal recovery; and these patients had higher values of peak enhancement, wash-in area under the curve (AUC), wash-in perfusion index, and washout AUC than those without recovery (p = 0.03, 0.01, 0.03, and 0.046, respectively). We evaluated the receiver operating characteristic curve and found that the peak enhancement, wash-in AUC, wash-in perfusion index, and wash-out AUC of CEUS derivatives estimated the probability of renal recovery after S-AKI requiring RRT (p = 0.03, 0.01, 0.03, and 0.04, respectively).

CONCLUSION

CEUS-assessed cortical microvascular perfusion may predict renal recovery following S-AKI that requires RRT. Further studies are essential to validate the clinical utility of microcirculatory parameters obtained from CEUS to estimate renal outcomes in various etiologies and severities of kidney disease.

Microcirculatory dysfunction in cardiogenic shock

Cardiogenic shock is usually defined as primary cardiac dysfunction with low cardiac output leading to critical organ hypoperfusion, and tissue hypoxia, resulting in high mortality rate between 40% and 50% despite recent advances. Many studies have now evidenced that cardiogenic shock not only involves systemic macrocirculation, such as blood pressure, left ventricular ejection fraction, or cardiac output, but also involves significant systemic microcirculatory abnormalities which seem strongly associated with the outcome. Although microcirculation has been widely studied in the context of septic shock showing heterogeneous alterations with clear evidence of macro and microcirculation uncoupling, there is now a growing body of literature focusing on cardiogenic shock states. Even if there is currently no consensus regarding the treatment of microcirculatory disturbances in cardiogenic shock, some treatments seem to show a benefit. Furthermore, a better understanding of the underlying pathophysiology may provide hypotheses for future studies aiming to improve cardiogenic shock prognosis.

Diabetic vascular diseases: molecular mechanisms and therapeutic strategies

Vascular complications of diabetes pose a severe threat to human health. Prevention and treatment protocols based on a single vascular complication are no longer suitable for the long-term management of patients with diabetes. Diabetic panvascular disease (DPD) is a clinical syndrome in which vessels of various sizes, including macrovessels and microvessels in the cardiac, cerebral, renal, ophthalmic, and peripheral systems of patients with diabetes, develop atherosclerosis as a common pathology. Pathological manifestations of DPDs usually manifest macrovascular atherosclerosis, as well as microvascular endothelial function impairment, basement membrane thickening, and microthrombosis. Cardiac, cerebral, and peripheral microangiopathy coexist with microangiopathy, while renal and retinal are predominantly microangiopathic. The following associations exist between DPDs: numerous similar molecular mechanisms, and risk-predictive relationships between diseases. Aggressive glycemic control combined with early comprehensive vascular intervention is the key to prevention and treatment. In addition to the widely recommended metformin, glucagon-like peptide-1 agonist, and sodium-glucose cotransporter-2 inhibitors, for the latest molecular mechanisms, aldose reductase inhibitors, peroxisome proliferator-activated receptor-γ agonizts, glucokinases agonizts, mitochondrial energy modulators, etc. are under active development. DPDs are proposed for patients to obtain more systematic clinical care requires a comprehensive diabetes care center focusing on panvascular diseases. This would leverage the advantages of a cross-disciplinary approach to achieve better integration of the pathogenesis and therapeutic evidence. Such a strategy would confer more clinical benefits to patients and promote the comprehensive development of DPD as a discipline.

Artificial Intelligence and Machine Learning in Perioperative Acute Kidney Injury

Acute kidney injury (AKI) is a common complication after a surgery, especially in cardiac and aortic procedures, and has a significant impact on morbidity and mortality. Early identification of high-risk patients and providing effective prevention and therapeutic approach are the main strategies for reducing the possibility of perioperative AKI. Consequently, several risk-prediction models and risk assessment scores have been developed for the prediction of perioperative AKI. However, a majority of these risk scores are only derived from preoperative data while the intraoperative time-series monitoring data such as heart rate and blood pressure were not included. Moreover, the complexity of the pathophysiology of AKI, as well as its nonlinear and heterogeneous nature, imposes limitations on the use of linear statistical techniques. The development of clinical medicine's digitization, the widespread availability of electronic medical records, and the increase in the use of continuous monitoring have generated vast quantities of data. Machine learning has recently shown promise as a method for automatically integrating large amounts of data in predicting the risk of perioperative outcomes. In this article, we discussed the development, limitations of existing work, and the potential future direction of models using machine learning techniques to predict AKI after a surgery.

Effects of Fluids on the Sublingual Microcirculation in Sepsis

Sepsis is one of the most common and deadly syndromes faced in Intensive Care settings globally. Recent advances in bedside imaging have defined the changes in the microcirculation in sepsis. One of the most advocated interventions for sepsis is fluid therapy. Whether or not fluid bolus affects the microcirculation in sepsis has not been fully addressed in the literature. This systematic review of the evidence aims to collate studies examining the microcirculatory outcomes after a fluid bolus in patients with sepsis. We will assimilate the evidence for using handheld intra vital microscopes to guide fluid resuscitation and the effect of fluid bolus on the sublingual microcirculation in patients with sepsis and septic shock. We conducted a systematic search of Embase, CENTRAL and Medline (PubMed) using combinations of the terms "microcirculation" AND "fluid" OR "fluid resuscitation" OR "fluid bolus" AND "sepsis" OR "septic shock". We found 3376 potentially relevant studies. Fifteen studies published between 2007 and 2021 fulfilled eligibility criteria to be included in analysis. The total number of participants was 813; we included six randomized controlled trials and nine non-randomized, prospective observational studies. Ninety percent used Sidestream Dark Field microscopy to examine the microcirculation and 50% used Hydroxyethyl Starch as their resuscitation fluid. There were no clear effects of fluid on the microcirculation parameters. There was too much heterogeneity between studies and methodology to perform meta-analysis. Studies identified heterogeneity of affect in the sepsis population, which could mean that current clinical classifications were not able to identify different microcirculation characteristics. Use of microcirculation as a clinical endpoint in sepsis could help to define sepsis phenotypes. More research into the effects of different resuscitation fluids on the microcirculation is needed.

Effects of perioperative dexmedetomidine infusion on renal function and microcirculation in kidney transplant recipients: a randomised controlled trial

OBJECTIVE

Ischemia-reperfusion injury affects postoperative transplanted kidney function in kidney transplant recipients. Dexmedetomidine was reported to attenuate ischemia-reperfusion injury and improve microcirculation, but its propensity to cause bradycardia and hypotension may adversely affect microcirculation. This study investigated the effect of dexmedetomidine on postoperative renal function and sublingual microcirculation in kidney recipients.

METHODS

The enrolled kidney transplant recipients were randomly allocated to the control group or dexmedetomidine group. After anaesthesia induction, patients in the dexmedetomidine group received dexmedetomidine infusion until 2 h after surgery. Sublingual microcirculation was recorded using an incident dark-field video microscope and analysed. The primary outcomes were the creatinine level on a postoperative day 2 and total vessel density at 2 h after surgery.

RESULTS

A total of 60 kidney recipients were analysed, and the creatinine levels on postoperative day 2 were significantly lower in the dexmedetomidine group than in the control group (1.5 (1.1-2.4) vs. 2.2 (1.7-3.0) mg/dL, median difference -0.6 (95% CI, -0.7 to -0.5) mg/dL, p = .018). On a postoperative day 7, the creatinine levels did not differ significantly between the two groups. Total vessel density at 2 h after surgery did not differ significantly between the two groups.

CONCLUSION

We found that early postoperative renal function was better in kidney transplant recipients receiving dexmedetomidine infusion, but total vessel density was not significantly different between the intervention and control groups. Key messagesIschemia-reperfusion injury affects postoperative transplanted kidney function, and dexmedetomidine was reported to attenuate ischemia-reperfusion injury and improve microcirculation in other clinical conditions.This study showed that early postoperative renal function was better in kidney transplant recipients receiving dexmedetomidine.Dexmedetomidine's side effect of bradycardia and hypotension may affect microcirculation, our results revealed that the perioperative sublingual microcirculation did not differ significantly in kidney transplant recipients receiving dexmedetomidine.

Deep learning and computer vision techniques for microcirculation analysis: A review

The analysis of microcirculation images has the potential to reveal early signs of life-threatening diseases such as sepsis. Quantifying the capillary density and the capillary distribution in microcirculation images can be used as a biological marker to assist critically ill patients. The quantification of these biological markers is labor intensive, time consuming, and subject to interobserver variability. Several computer vision techniques with varying performance can be used to automate the analysis of these microcirculation images in light of the stated challenges. In this paper, we present a survey of over 50 research papers and present the most relevant and promising computer vision algorithms to automate the analysis of microcirculation images. Furthermore, we present a survey of the methods currently used by other researchers to automate the analysis of microcirculation images. This survey is of high clinical relevance because it acts as a guidebook of techniques for other researchers to develop their microcirculation analysis systems and algorithms.

Oxidative stress: An essential factor in the process of arteriovenous fistula failure

For more than half a century, arteriovenous fistula (AVFs) has been recognized as a lifeline for patients requiring hemodialysis (HD). With its higher long-term patency rate and lower probability of complications, AVF is strongly recommended by guidelines in different areas as the first choice for vascular access for HD patients, and its proportion of application is gradually increasing. Despite technological improvements and advances in the standards of postoperative care, many deficiencies are still encountered in the use of AVF related to its high incidence of failure due to unsuccessful maturation to adequately support HD and the development of neointimal hyperplasia (NIH), which narrows the AVF lumen. AVF failure is linked to the activation and migration of vascular cells and the remodeling of the extracellular matrix, where complex interactions between cytokines, adhesion molecules, and inflammatory mediators lead to poor adaptive remodeling. Oxidative stress also plays a vital role in AVF failure, and a growing amount of data suggest a link between AVF failure and oxidative stress. In this review, we summarize the present understanding of the pathophysiology of AVF failure. Furthermore, we focus on the relation between oxidative stress and AVF dysfunction. Finally, we discuss potential therapies for addressing AVF failure based on targeting oxidative stress.

Short-Chain Fatty Acids in Chronic Kidney Disease: Focus on Inflammation and Oxidative Stress Regulation

Chronic Kidney Disease (CKD) is a debilitating disease associated with several secondary complications that increase comorbidity and mortality. In patients with CKD, there is a significant qualitative and quantitative alteration in the gut microbiota, which, consequently, also leads to reduced production of beneficial bacterial metabolites, such as short-chain fatty acids. Evidence supports the beneficial effects of short-chain fatty acids in modulating inflammation and oxidative stress, which are implicated in CKD pathogenesis and progression. Therefore, this review will provide an overview of the current knowledge, based on pre-clinical and clinical evidence, on the effect of SCFAs on CKD-associated inflammation and oxidative stress.

Metabolomic profiling demonstrates evidence for kidney and urine metabolic dysregulation in a piglet model of cardiac surgery-induced acute kidney injury

Acute kidney injury (AKI) is a common cause of morbidity after congenital heart disease surgery. Progress on diagnosis and therapy remains limited, however, in part due to poor mechanistic understanding and a lack of relevant translational models. Metabolomic approaches could help identify novel mechanisms of injury and potential therapeutic targets. In the present study, we used a piglet model of cardiopulmonary bypass with deep hypothermic circulatory arrest (CPB/DHCA) and targeted metabolic profiling of kidney tissue, urine, and serum to evaluate metabolic changes specific to animals with histological acute kidney injury. CPB/DHCA animals with acute kidney injury were compared with those without acute kidney injury and mechanically ventilated controls. Acute kidney injury occurred in 10 of 20 CPB/DHCA animals 4 h after CPB/DHCA and 0 of 7 control animals. Injured kidneys showed a distinct tissue metabolic profile compared with uninjured kidneys (R² = 0.93, Q² = 0.53), with evidence of dysregulated tryptophan and purine metabolism. Nine urine metabolites differed significantly in animals with acute kidney injury with a pattern suggestive of increased aerobic glycolysis. Dysregulated metabolites in kidney tissue and urine did not overlap. CPB/DHCA strongly affected the serum metabolic profile, with only one metabolite that differed significantly with acute kidney injury (pyroglutamic acid, a marker of oxidative stress). In conclusion, based on these findings, kidney tryptophan and purine metabolism are candidates for further mechanistic and therapeutic investigation. Urine biomarkers of aerobic glycolysis could help diagnose early acute kidney injury after CPB/DHCA and warrant further evaluation. The serum metabolites measured at this early time point did not strongly differentiate based on acute kidney injury.

NEW & NOTEWORTHY This project explored the metabolic underpinnings of postoperative acute kidney injury (AKI) following pediatric cardiac surgery in a translationally relevant large animal model of cardiopulmonary bypass with deep hypothermic circulatory arrest. Here, we present novel evidence for dysregulated tryptophan catabolism and purine catabolism in kidney tissue and increased urinary glycolysis intermediates in animals who developed histological AKI. These pathways represent potential diagnostic and therapeutic targets for postoperative AKI in this high-risk population.

Arterial Labeling Ultrasound Subtraction Angiography (ALUSA) Based on Acoustic Phase-Change Nanodroplets

Biomedical imaging technology (like digital subtraction angiography (DSA)) based on contrast agents has been widely employed in the diagnosis of vascular-related diseases. While the DSA achieves the high-resolution observation of specified vessels and their downstream perfusion at the cost of invasive, radioactive operation and hepatorenal toxicity. To address those problems, this study develops arterial labeling ultrasound (US) subtraction angiography (ALUSA) based on a new perfluorobutane (PFB) nanodroplets with a lower vaporization threshold through spontaneous nucleation. The nanodroplets can be selectively vaporized to microbubbles, indicating a highly echogenic signal at B-mode images only using a diagnostic transducer. By labeling a single blood vessel for nanodroplets vaporization and tracking its downstream blood perfusion in segmental renal arteries at a frame rate of 500 Hz. The results demonstrate the color-coded super-resolution ALUSA image, exhibiting the downstream arcuate and interlobular arteries of each segmental renal artery with a resolution of 36 µm in a rabbit kidney. Furthermore, ALUSA could offer the vascular structures, blood flow velocity, and direction of their primary supply vessels in the mouse breast tumor. ALUSA fills the gap of noninvasive labeling angiography in US and opens a broad vista in the diagnosis and treatment of tumor and vascular-related diseases.

Role of TRPC6 in kidney damage after acute ischemic kidney injury

Transient receptor potential channel subfamily C, member 6 (TRPC6), a non-selective cation channel that controls influx of Ca²⁺ and other monovalent cations into cells, is widely expressed in the kidney. TRPC6 gene variations have been linked to chronic kidney disease but its role in acute kidney injury (AKI) is unknown. Here we aimed to investigate the putative role of TRPC6 channels in AKI. We used Trpc6^-/- mice and pharmacological blockade (SH045 and BI-749327), to evaluate short-term AKI outcomes. Here, we demonstrate that neither Trpc6 deficiency nor pharmacological inhibition of TRPC6 influences the short-term outcomes of AKI. Serum markers, renal expression of epithelial damage markers, tubular injury, and renal inflammatory response assessed by the histological analysis were similar in wild-type mice compared to Trpc6^-/- mice as well as in vehicle-treated versus SH045- or BI-749327-treated mice. In addition, we also found no effect of TRPC6 modulation on renal arterial myogenic tone by using blockers to perfuse isolated kidneys. Therefore, we conclude that TRPC6 does not play a role in the acute phase of AKI. Our results may have clinical implications for safety and health of humans with TRPC6 gene variations, with respect to mutated TRPC6 channels in the response of the kidney to acute ischemic stimuli.

Piperazine ferulate prevents high-glucose-induced filtration barrier injury of glomerular endothelial cells

Filtration barrier injury induced by high glucose (HG) levels leads to the development of diabetic nephropathy. The endothelial glycocalyx plays a critical role in glomerular barrier function. In the present study, the effects of piperazine ferulate (PF) on HG-induced filtration barrier injury of glomerular endothelial cells (GEnCs) were investigated and the underlying mechanism was assessed. Immunofluorescence was used to observe the distribution of the glycocalyx as well as the expression levels of syndecan-1 and Zonula occludens-1 (ZO-1). Endothelial permeability assays were performed to assess the effects of PF on the integrity of the filtration barrier. Protein and mRNA expression levels were measured by western blotting and reverse transcription-quantitative PCR analyses, respectively. In vitro experiments revealed that adenosine monophosphate-activated protein kinase (AMPK) mediated HG-induced glycocalyx degradation and endothelial barrier injury. PF inhibited the HG-induced endothelial barrier injury and restored the expression levels of heparanase-1 (Hpa-1), ZO-1 and occludin-1 by AMPK. In vivo assays demonstrated that PF reduced the expression levels of Hpa-1, increased the expression levels of ZO-1 and attenuated glycocalyx degradation in the glomerulus. These data suggested that PF attenuated HG-induced filtration barrier injury of GEnC by regulating AMPK expression.

Kidney Microcirculation as a Target for Innovative Therapies in AKI

Acute kidney injury (AKI) is a serious multifactorial conditions accompanied by the loss of function and damage. The renal microcirculation plays a crucial role in maintaining the kidney’s functional and structural integrity for oxygen and nutrient supply and waste product removal. However, alterations in microcirculation and oxygenation due to renal perfusion defects, hypoxia, renal tubular, and endothelial damage can result in AKI and the loss of renal function regardless of systemic hemodynamic changes. The unique structural organization of the renal microvasculature and the presence of autoregulation make it difficult to understand the mechanisms and the occurrence of AKI following disorders such as septic, hemorrhagic, or cardiogenic shock; ischemia/reperfusion; chronic heart failure; cardiorenal syndrome; and hemodilution. In this review, we describe the organization of microcirculation, autoregulation, and pathophysiological alterations leading to AKI. We then suggest innovative therapies focused on the protection of the renal microcirculation and oxygenation to prevent AKI.

Identification of the Crucial Gene in Overflow Arteriovenous Fistula by Bioinformatics Analysis

Objective: The aim was to study the preliminary screening of the crucial genes in intimal hyperplasia in the venous segment of arteriovenous (AV) fistula and the underlying potential molecular mechanisms of intimal hyperplasia with bioinformatics analysis. Methods: The gene expression profile data (GSE39488) was analyzed to identify differentially expressed genes (DEGs). We performed Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis of DEGs. Gene set enrichment analysis (GSEA) was used to understand the potential activated signaling pathway. The protein-protein interaction (PPI) network was constructed with the STRING database and Cytoscape software. The Venn diagram between 10 hub genes and gene sets of 4 crucial signaling pathways was used to obtain core genes and relevant potential pathways. Furthermore, GSEAs were performed to understand their biological functions. Results: A total of 185 DEGs were screened in this study. The main biological function of the 111 upregulated genes in AV fistula primarily concentrated on cell proliferation and vascular remodeling, and the 74 downregulated genes in AV fistula were enriched in the biological function mainly relevant to inflammation. GSEA found four signaling pathways crucial for intimal hyperplasia, namely, MAPK, NOD-like, Cell Cycle, and TGF-beta signaling pathway. A total of 10 hub genes were identified, namely, EGR1, EGR2, EGR3, NR4A1, NR4A2, DUSP1, CXCR4, ATF3, CCL4, and CYR61. Particularly, DUSP1 and NR4A1 were identified as core genes that potentially participate in the MAPK signaling pathway. In AV fistula, the biological processes and pathways were primarily involved with MAPK signaling pathway and MAPK-mediated pathway with the high expression of DUSP1 and were highly relevant to cell proliferation and inflammation with the low expression of DUSP1. Besides, the biological processes and pathways in AV fistula with the high expression of NR4A1 similarly included the MAPK signaling pathway and the pathway mediated by MAPK signaling, and it was mainly involved with inflammation in AV fistula with the low expression of NR4A1. Conclusion: We screened four potential signaling pathways relevant to intimal hyperplasia and identified 10 hub genes, including two core genes (i.e., DUSP1 and NR4A1). Two core genes potentially participate in the MAPK signaling pathway and might serve as the therapeutic targets of intimal hyperplasia to prevent stenosis after AV fistula creation.

The renal microcirculation in chronic kidney disease: novel diagnostic methods and therapeutic perspectives

Chronic kidney disease (CKD) affects 8–16% of the population worldwide and is characterized by fibrotic processes. Understanding the cellular and molecular mechanisms underpinning renal fibrosis is critical to the development of new therapeutics. Microvascular injury is considered an important contributor to renal progressive diseases. Vascular endothelium plays a significant role in responding to physical and chemical signals by generating factors that help maintain normal vascular tone, inhibit leukocyte adhesion and platelet aggregation, and suppress smooth muscle cell proliferation. Loss of the rich capillary network results in endothelial dysfunction, hypoxia, and inflammatory and oxidative effects and further leads to the imbalance of pro- and antiangiogenic factors, endothelial cell apoptosis and endothelial-mesenchymal transition. New techniques, including both invasive and noninvasive techniques, offer multiple methods to observe and monitor renal microcirculation and guide targeted therapeutic strategies. A better understanding of the role of endothelium in CKD will help in the development of effective interventions for renal microcirculation improvement. This review focuses on the role of microvascular injury in CKD, the methods to detect microvessels and the novel treatments to ameliorate renal fibrosis.

LRG1 Mitigates Renal Interstitial Fibrosis through Alleviating Capillary Rarefaction and Inhibiting Inflammatory and Pro-Fibrotic Cytokines

INTRODUCTION

Increasing evidence has demonstrated that loss of peritubular capillaries plays a critical role in renal interstitial fibrosis. Leucine-rich α2-glycoprotein-1 (LRG1) has been observed promoting angiogenesis in the ocular disease mouse model and myocardial infarction model. We aimed to explore the role of LRG1 in renal interstitial fibrosis.

METHODS

We analyzed the expression of LRG1 in the plasma and kidney of CKD patients by ELISA and immunohistochemistry. Relationships between the expression of LRG1 in plasma and kidney and renal fibrosis and inflammation were analyzed. Tube formation assay was used to detect the angiogenesis in the human umbilical vein endothelial cell lines (HUVECs). And real-time PCR was used to detect the mRNA expression of LRG1, inflammatory factors, renal tubular injury indicators, pro-fibrotic cytokines, and CD31. We examined the effects of genetic ablation of LRG1 on renal fibrosis induced by unilateral ureteral obstruction (UUO) mice model at day 7.

RESULTS

We demonstrated that the expression of LRG1 in renal tissues and plasma samples was upregulated in CKD patients. And the expression of LRG1 was elevated in human renal tubular epithelial cell line (HK-2) cells in response to the stimulation of TNF-α in vitro, and in kidney after UUO in vivo. The deficiency of the LRG1 gene aggravated renal fibrosis, inflammatory cells infiltration, and capillary rarefaction after UUO. In vitro, LRG1 promoted the tube formation of HUVEC cells. LRG1 inhibits fibronectin secretion induced by TGF-β1 in HK-2 and overexpression of LRG1 in HK-2 cells decreased fibronectin secretion.

CONCLUSION

LRG1 may prevent renal fibrosis by inhibiting the secretion of inflammatory and pro-fibrotic cytokines and promoting angiogenesis.

Enhanced renoprotective effect of GDNF-modified adipose-derived mesenchymal stem cells on renal interstitial fibrosis

Background

The therapeutic effect of mesenchymal stem cells (MSCs) from human adipose tissue on renal interstitial fibrosis has been demonstrated by several groups. However, the way to enhance the renoprotective effect of adipose-derived mesenchymal stem cells (AMSCs) and the possible mechanisms are still unclear. The present study aimed to determine whether glial cell line-derived neurotrophic factor (GDNF)-modified AMSCs hold an enhanced protective effect on renal fibrosis.

Methods

AMSCs were isolated and purified for culture. The gene GDNF has been constructed to transfect into AMSCs. The ability of GFP-AMSCs and GDNF-AMSCs supernatants to promote tube formation of endothelial cells, repair damaged endothelial cell junctions, and improve endothelial cell function was compared by using tube formation assay, immunofluorescence techniques, and vascular ring assay, respectively. Furthermore, HE and Masson staining were used to observe the histological morphology of the kidney in vivo. Peritubular capillary changes were detected and analyzed by fluorescence microangiography (FMA). Meanwhile, the hypoxia, oxidative stress, fibrotic markers, and PI3K/Akt pathway proteins were measured by western blot or qRT-PCR technics.

Results

Compared with GFP-AMSCs only, GDNF-AMSCs could enhance the repair of injured endothelial cells and promote angiogenesis through secreting more growth factors in the supernatant of GDNF-AMSC culture media demonstrated in vitro studies. Studies in vivo, unilateral ureteral obstruction (UUO)-induced mice were injected with transfected AMSCs through their tail veins. We showed that enhanced homing of AMSCs was observed in the GDNF-AMSC group compared with the GFP-AMSC group. The animals treated with GDNF-AMSCs exhibited an improvement of capillary rarefaction and fibrosis induced by obstructed kidney compared with the GFP-AMSC group. Furthermore, we reported that GDNF-AMSCs protect renal tissues against microvascular injuries via activation of the PI3K/Akt signaling pathway. Therefore, GDNF-AMSCs further ameliorated the tissue hypoxia, suppressed oxidative stress, and finally inhibited endothelial to mesenchymal transition noting by decreased coexpression of endothelial cell (CD31) and myofibroblast (a-SMA) markers.

Conclusion

Collectively, our data indicated that the GDNF gene enhances the ability of AMSCs in improving renal microcirculation through PI3K/Akt/eNOS signaling pathway and afterward inhibit the EndMT process and kidney fibrogenesis, which should have a vast of implications in designing future remedies for chronic kidney disease (CKD) treatment.

Microrheology, microcirculation and structural compensatory mechanisms of a chronic kidney disease rat model. A preliminary study

BACKGROUND

Chronic kidney disease (CKD) models are known to study pathophysiology and various treatment methods. Renal dysfunction could influence erythrocytes through several pathways. However, hemorheological and microcirculatory relation of CKD models are not completely studied yet.

OBJECTIVE

To evaluate erythrocyte micro-rheology, microcirculatory and structural compensatory mechanisms in a rat model of CKD.

METHODS

Female Sprague-Dawley rats were subjected to nephrectomy group (NG, n = 6) or sham-operated group (SG, n = 6). NG rats were subjected to 5/6 nephrectomy in two stages. In SG no intervention was made on kidneys. Hemorheological and hematological measurements were carried out after each stage, and 5 weeks after the last operation. Histological and microcirculatory studies were done on the remaining kidney and compared with sham rats.

RESULTS

Serum creatinine increased in NG (p = 0.008), accompanied with decrease of red blood cell count (p = 0.028) and hemoglobin (p = 0.015). Erythrocyte aggregation parameters slightly increased in NG, while the elongation index didn't show significant changes. Microcirculation was intact in the remnant kidney of NG. However, in comparison with SG, the diameter of glomeruli increased significantly (p < 0.01).

CONCLUSIONS

Erythrocyte mass was influenced more than micro-rheological properties in this model. The main compensation mechanism was rather structural than at microcirculatory level.

Platelet inhibition by ticagrelor is protective against diabetic nephropathy in mice

Diabetic nephropathy (DN) is a major complication of diabetes and is associated with high risk for cardiovascular mortality, which is partially related to elevated platelet activity. Platelets are also active players in inflammation and fibrosis. In this study, we examine the effect of ticagrelor-induced platelet inhibition on the development of DN. DN was induced by unilateral nephrectomy followed by streptozotocin injections for 5 days. Mice received ticagrelor (300 mg/kg) or vehicle every other day, for 16 weeks. Experimental groups: non-diabetic control, diabetic control, non-diabetic ticagrelor, and diabetic ticagrelor. Ticagrelor treatment in diabetic mice lowered urinary albumin excretion, it prevented diabetes-induced mesangial matrix expansion, podocyte effacement, and glomerular endothelial cell injury, which includes loss of endothelial fenestrations, ICAM-1 expression, and PECAM expression. In addition, ticagrelor treatment prevented collagen IV deposition and macrophage infiltration in the tubulointerstitium and these diabetic mice showed lower systemic and tubular inflammation and tubular apoptosis. This tubular protection is likely to be a result of protection to the glomerular endothelium by ticagrelor, which reduces albuminuria and albumin toxicity to the tubules and reduced tubular and interstitial inflammation and fibrosis. In conclusion, ticagrelor-induced platelet inhibition protects against renal injury in diabetic mice, likely by protecting the glomerular endothelial cells.

Exosomes derived from GDNF-modified human adipose mesenchymal stem cells ameliorate peritubular capillary loss in tubulointerstitial fibrosis by activating the SIRT1/eNOS signaling pathway

Mesenchymal stem cells (MSCs) have emerged as ideal cell-based therapeutic candidates for the structural and functional restoration of the diseased kidney. Glial cell line-derived neurotrophic factor (GDNF) has been demonstrated to promote the therapeutic effect of MSCs on ameliorating renal injury. The mechanism may involve the transfer of endogenous molecules via paracrine factors to salvage injured cells, but these factors remain unknown.

Methods: GDNF was transfected into human adipose mesenchymal stem cells via a lentiviral transfection system, and exosomes were isolated (GDNF-AMSC-exos). Using the unilateral ureteral obstruction (UUO) mouse model and human umbilical vein endothelial cells (HUVECs) against hypoxia/serum deprivation (H/SD) injury models, we investigated whether GDNF-AMSC-exos ameliorate peritubular capillary (PTC) loss in tubulointerstitial fibrosis and whether this effect is mediated by the Sirtuin 1 (SIRT1) signaling pathway. Additionally, by using SIRT1 activators or siRNAs, the roles of the candidate mRNA and its downstream gene in GDNF-AMSC-exo-induced regulation of endothelial cell function were assessed. PTC characteristics were detected by fluorescent microangiography (FMA) and analyzed by the MATLAB software.

Results: The green fluorescent PKH67-labeled exosomes were visualized in the UUO kidneys and colocalized with CD81. GDNF-AMSC-exos significantly decreased PTC rarefaction and renal fibrosis scores in mice with UUO. In vitro studies revealed that GDNF-AMSC-exos exerted cytoprotective effects on HUVECs against H/SD injury by stimulating migration and angiogenesis as well as conferring apoptosis resistance. Mechanistically, GDNF-AMSC-exos enhanced SIRT1 signaling, which was accompanied by increased levels of phosphorylated endothelial nitric oxide synthase (p-eNOS). We also confirmed the SIRT1-eNOS interaction in HUVECs by immunoprecipitation. Furthermore, we observed a correlation of the PTC number with the SIRT1 expression level in the kidney in vivo.

Conclusion: Our study unveiled a mechanism by which exosomes ameliorate renal fibrosis: GDNF-AMSC-exos may activate an angiogenesis program in surviving PTCs after injury by activating the SIRT1/eNOS signaling pathway.

Perioperative acute kidney injury: Stratification and risk reduction strategies

Perioperative acute kidney injury (AKI) is associated with increased morbidity and mortality. Patient comorbidities, the type of surgery, timing of surgery, and exposure to nephrotoxins are important contributors for developing acute kidney injury. Urgent or emergent surgery, cardiac, and organ transplantation procedures are associated with a higher risk of acute kidney injury. Nephrotoxic drugs, contrast dye, and diuretics can worsen preexisting kidney dysfunction or act as an additive and/or synergistic insult to perioperative injury. A history of preoperative chronic kidney disease is the main risk factor for developing AKI, conferring as much as a 10-fold risk. However, beyond the preoperative renal function, the development of AKI is a complex phenomenon that involves a combination of patient-related and surgery-related factors.

Higher levels of daily physical activity are associated with better skin microvascular function in type 2 diabetes-The Maastricht Study

Objective

Physical activity may provide a means for the prevention of cardiovascular disease via improving microvascular function. Therefore, this study investigated whether physical activity is associated with skin and retinal microvascular function.

Methods

In The Maastricht Study, a population‐based cohort study enriched with type 2 diabetes (n = 1298, 47.3% women, aged 60.2 ± 8.1 years, 29.5% type 2 diabetes), we studied whether accelerometer‐assessed physical activity and sedentary time associate with skin and retinal microvascular function. Associations were studied by linear regression and adjusted for major cardiovascular risk factors. In addition, we investigated whether associations were stronger in type 2 diabetes.

Results

In individuals with type 2 diabetes, total physical activity and higher‐intensity physical activity were independently associated with greater heat‐induced skin hyperemia (regression coefficients per hour), respectively, 10 (95% CI: 1; 18) and 36 perfusion units (14; 58). In individuals without type 2 diabetes, total physical activity and higher‐intensity physical activity were not associated with heat‐induced skin hyperemia. No associations with retinal arteriolar %‐dilation were identified.

Conclusion

Higher levels of total and higher‐intensity physical activity were associated with greater skin microvascular vasodilation in individuals with, but not in those without, type 2 diabetes.

Perioperative Acute Kidney Injury

Perioperative organ injury is among the leading causes of morbidity and mortality of surgical patients. Among different types of perioperative organ injury, acute kidney injury occurs particularly frequently and has an exceptionally detrimental effect on surgical outcomes. Currently, acute kidney injury is most commonly diagnosed by assessing increases in serum creatinine concentration or decreased urine output. Recently, novel biomarkers have become a focus of translational research for improving timely detection and prognosis for acute kidney injury. However, specificity and timing of biomarker release continue to present challenges to their integration into existing diagnostic regimens. Despite many clinical trials using various pharmacologic or nonpharmacologic interventions, reliable means to prevent or reverse acute kidney injury are still lacking. Nevertheless, several recent randomized multicenter trials provide new insights into renal replacement strategies, composition of intravenous fluid replacement, goal-directed fluid therapy, or remote ischemic preconditioning in their impact on perioperative acute kidney injury. This review provides an update on the latest progress toward the understanding of disease mechanism, diagnosis, and managing perioperative acute kidney injury, as well as highlights areas of ongoing research efforts for preventing and treating acute kidney injury in surgical patients.

Microcirculation: Physiology, Pathophysiology, and Clinical Application

This paper briefly reviews the physiological components of the microcirculation, focusing on its function in homeostasis and its central function in the realization of oxygen transport to tissue cells. Its pivotal role in the understanding of circulatory compromise in states of shock and renal compromise is discussed. Our introduction of hand-held vital microscopes (HVM) to clinical medicine has revealed the importance of the microcirculation as a central target organ in states of critical illness and inadequate response to therapy. Technical and methodological developments have been made in hardware and in software including our recent introduction and validation of automatic analysis software called MicroTools, which now allows point-of-care use of HVM imaging at the bedside for instant availability of functional microcirculatory parameters needed for microcirculatory targeted resuscitation procedures to be a reality.

Dynamic Contrast-Enhanced Ultrasound Identifies Microcirculatory Alterations in Sepsis-Induced Acute Kidney Injury

OBJECTIVES

We developed quantitative methods to analyze microbubble kinetics based on renal contrast-enhanced ultrasound imaging combined with measurements of sublingual microcirculation on a fixed area to quantify early microvascular alterations in sepsis-induced acute kidney injury.

DESIGN

Prospective controlled animal experiment study.

SETTING

Hospital-affiliated animal research institution.

SUBJECTS

Fifteen female pigs.

INTERVENTIONS

The animals were instrumented with a renal artery flow probe after surgically exposing the kidney. Nine animals were given IV infusion of lipopolysaccharide to induce septic shock, and six were used as controls.

MEASUREMENTS AND MAIN RESULTS

Contrast-enhanced ultrasound imaging was performed on the kidney before, during, and after having induced shock. Sublingual microcirculation was measured continuously using the Cytocam on the same spot. Contrast-enhanced ultrasound effectively allowed us to develop new analytical methods to measure dynamic variations in renal microvascular perfusion during shock and resuscitation. Renal microvascular hypoperfusion was quantified by decreased peak enhancement and an increased ratio of the final plateau intensity to peak enhancement. Reduced intrarenal blood flow could be estimated by measuring the microbubble transit times between the interlobar arteries and capillary vessels in the renal cortex. Sublingual microcirculation measured using the Cytocam in a fixed area showed decreased functional capillary density associated with plugged sublingual capillary vessels that persisted during and after fluid resuscitation.

CONCLUSIONS

In our lipopolysaccharide model, with resuscitation targeted at blood pressure, contrast-enhanced ultrasound imaging can identify renal microvascular alterations by showing prolonged contrast enhancement in microcirculation during shock, worsened by resuscitation with fluids. Concomitant analysis of sublingual microcirculation mirrored those observed in the renal microcirculation.

Intrarenal Renin–Angiotensin System Involvement in the Pathogenesis of Chronic Progressive Nephropathy—Bridging the Informational Gap Between Disciplines

Chronic progressive nephropathy (CPN) is the most commonly encountered spontaneous background finding in laboratory rodents. Various theories on its pathogenesis have been proposed, but there is a paucity of data regarding specific mechanisms or physiologic pathways involved in early CPN development. The current CPN mechanism of action for tumorigenesis is largely based on its associated increase in tubular cell proliferation without regard to preceding subcellular degenerative changes. Combing through the published literature from multiple biology disciplines provided insight into the preceding cellular events. Mechanistic pathways involved in the progressive age-related decline in rodent kidney function and several key inflexion points have been identified. These critical pathway factors were then connected using data from renal models from multiple rodent strains, other species, and mechanistic work in humans to form a cohesive picture of pathways and protein interactions. Abundant data linked similar renal pathologies to local events involving hypoxia (hypoxia-inducible factor 1α), altered intrarenal renin–angiotensin system (RAS), oxidative stress (nitric oxide), and pro-inflammatory pathways (transforming growth factor β), with positive feedback loops and downstream effectors amplifying the injury and promoting scarring. Intrarenal RAS alterations seem to be central to all these events and may be critical to CPN development and progression.

Vitamin K-Dependent Matrix Gla Protein as Multifaceted Protector of Vascular and Tissue Integrity

Supplemental Digital Content is available in the text.

Fibroblast growth factor 23, endothelium biomarkers and acute kidney injury in critically-ill patients

BACKGROUND

Fibroblast growth factor 23 (FGF23) and endothelium-related biomarkers have been related to AKI in critically-ill patients. Also, FGF23 is associated with endothelial dysfunction. In this study, we investigated if elevated FGF23 association with severe AKI is mediated by several endothelial/glycocalyx-related biomarkers.

METHODS

Prospective cohort study with critically-ill patients. Blood samples were collected within the first 24 h after ICU admission. Severe AKI (defined according to KDIGO stage 2/3) was the analyzed outcome.

RESULTS

265 patients were enrolled and 82 (30.9%) developed severe AKI-defined according to KDIGO stage 2/3. Blood samples to biomarkers measurement were collected within the first 24 h after ICU admission. After adjustment for several variables, FGF23, vascular cell adhesion protein 1 (VCAM-1), angiopoietin 2 (AGPT2), syndecan-1 and intercellular adhesion molecule-1 (ICAM-1) were associated with severe AKI. The individual indirect effects of VCAM-1, AGPT2 and syndecan-1 explained 23%, 31%, and 32% of the total observed effect of FGF23 on severe AKI, respectively. ICAM-1 showed no statistically significant mediation. When all three endothelium-related biomarkers were included in a directed acyclic graph (DAG), the Bayesian network learning suggested the following causal association pathway FGF-23 → syndecan-1 → VCAM-1 → AGPT2 → severe AKI.

CONCLUSIONS

The association between FGF23 and AKI are mediated by endothelium-related biomarkers, mainly VCAM-1, AGPT2 and syndecan-1. Moreover, the statistical models show that syndecan-1, a biomarker of endothelial glycocalyx dysfunction, seems to be the initial mediator between FGF23 and severe AKI.

Impaired Retinal Vessel Dilation Predicts Mortality in End-Stage Renal Disease

RATIONALE

Patients with end-stage renal disease (ESRD) are characterized by increased cardiovascular (CV) and all-cause mortality due to advanced remodeling of the macro- and microvascular beds.

OBJECTIVE

The aim of this study was to determine whether retinal microvascular function can predict all-cause and CV mortality in patients with ESRD.

METHODS AND RESULTS

In the multicenter prospective observational ISAR (Risk Stratification in End-Stage Renal Disease) study, data on dynamic retinal vessel analysis (DVA) was available in a sub-cohort of 214 dialysis patients (mean age 62.6{plus minus}15.0; 32% female). Microvascular dysfunction was quantified by measuring maximum arteriolar (aMax) and venular dilation (vMax) of retinal vessels in response to flicker light stimulation. During a mean follow-up of 44 months, 55 patients died, including 25 CV and 30 non-CV fatal events. vMax emerged as a strong independent predictor for all-cause mortality. In the Kaplan-Meier analysis, individuals within the lowest tertile of vMax showed significantly shorter three-year survival rates than those within the highest tertile (66.9{plus minus}5.8% vs 92.4{plus minus}3.3%). Uni- and multivariate hazard ratios for all-cause mortality per SD increase of vMax were 0.62 [0.47;0.82] and 0.65[0.47;0.91], respectively. aMax and vMax were able to significantly predict nonfatal and fatal CV events (HR 0.74[0.57;0.97] and 0.78[0.61;0.99], respectively).

CONCLUSIONS

Our results provide the first evidence that impaired retinal venular dilation is a strong and independent predictor of all-cause mortality in hemodialyzed ESRD patients. DVA provides added value for prediction of all-cause mortality and may be a novel diagnostic tool to optimize CV risk stratification in ESRD and other high-risk CV cohorts.

CLINICAL TRIAL REGISTRATION

NCT01152892.

Beraprost sodium mitigates renal interstitial fibrosis through repairing renal microvessels

Beraprost sodium (BPS), as a prostacyclin analog, plays a significant role in various diseases based on its antiplatelet and vasodilation functions. However, its regulation and role in chronic kidney disease (CKD) still remain elusive. Here, we determined whether BPS could alleviate renal interstitial fibrosis, and improve the renal function and its therapeutic mechanism. In vitro, BPS increased angiogenesis in the HUVECs incubated with BPS detected by tube formation assay and repair damaged endothelial cell-cell junctions induced by hypoxia. In vivo, mice were randomly assigned to a sham-operation group (sham), a unilateral ureteral obstruction group (UUO), and a BPS intragastrical administration group (BPS), and sacrificed at days 3 and 7 post-surgery (six in each group). In UUO model, tissue hypoxia, renal inflammation, oxidative stress, and fibrotic lesions were detected by q-PCR and Western blot techniques and peritubular capillaries (PTCs) injury was detected by a novel technique of fluorescent microangiography (FMA) and analyzed by MATLAB software. Meanwhile, we identified cells undergoing endothelial cell-to-myofibroblast transition by the coexpression of endothelial cell (CD31) and myofibroblast (a-SMA) markers in the obstructed kidney. In contrast, BPS protected against interstitial fibrosis and substantially reduced the number of endothelial cell-to-myofibroblast transition cells. In conclusion, our data indicate the potent therapeutic of BPS in mitigating fibrosis through repairing renal microvessels and suppressing endothelial-mesenchymal transition (EndMT) progression after inhibiting inflammatory and oxidative stress effects. KEY MESSAGES: BPS could improve renal recovery through anti-inflammatory and anti-oxidative pathways. BPS could mitigate fibrosis through repairing renal microvessels and suppressing endothelial-mesenchymal transition (EndMT).

Angiopoietin-2 as a predictor of acute kidney injury in critically ill patients and association with ARDS

BACKGROUND AND OBJECTIVE

Angiopoietin-2 (AGPT2) has been proposed as a key mediator of organ dysfunction, mainly in acute respiratory distress syndrome (ARDS). It has also been associated with acute kidney injury (AKI). We aimed to investigate the role of AGPT2 in patients with and without ARDS.

METHODS

In a cohort study with critically ill patients, AGPT1 and AGPT2 were assayed in plasma collected within the first 24 h after admission to intensive care unit (ICU). Severe AKI and the need for dialysis were outcome measures from comparative analysis with clinical characteristics useful for AKI risk stratification.

RESULTS

Among 283 patients (50.2% males), 109 (38.5%) had ARDS. AGPT2 levels at admission were higher in patients with ARDS. Although overall AGPT2 and AGPT2/AGPT1 levels were associated with severe AKI, this association was not significant in patients without ARDS; however, it remained strongly significant in ARDS patients. In patients without ARDS, AGPT2 showed only a weak discriminatory capacity to predict severe AKI (area under the curve (AUC): 0.64 vs 0.81 in the ARDS group). The continuous net reclassification improvement (NRI) in the ARDS group resulting from AGPT2 inclusion was 64.1% (P < 0.001) and the integrated discrimination improvement (IDI) index was 0.057 (P = 0.003). There was no significant difference in NRI in the no-ARDS group.

CONCLUSION

AGPT2 and AGPT2/AGPT1 ratio are associated with severe AKI and there was only a need of renal replacement therapy (RRT) in patients with or at risk of ARDS, not in other critically ill patients. Adding AGPT2 to a clinical model resulted in a significant improvement in the capacity to predict severe AKI specifically in ARDS patients.

Insuffisances rénales aiguës : actes du 5e Séminaire de recherche translationnelle de la Société de réanimation de langue française (Paris, 4 décembre 2018)

Le séminaire annuel de la commission de recherche translationnelle de la SRLF a eu lieu à Paris le 4 décembre 2018. Ce séminaire a pour but de réunir des cliniciens et scientifiques autour de grandes thématiques de recherche en médecine intensive et réanimation. La cinquième édition a porté sur l’insuffisance rénale aiguë, problématique quotidienne importante des réanimateurs. Les interventions se sont intéressées à la physiopathologie des diverses formes d’insuffisance rénale aiguë, à la récupération rénale, aux modèles expérimentaux, à l’hémodynamique régionale ou encore aux innovations technologiques en épuration extrarénale.

Microvascular rarefaction and hypertension in the impaired recovery and progression of kidney disease following AKI in preexisting CKD states

Acute kidney injury (AKI) is a major complication in hospitalized patients and is associated with elevated mortality rates. Numerous recent studies indicate that AKI also significantly increases the risk of chronic kidney disease (CKD), end-stage renal disease (ESRD), hypertension, cardiovascular disease, and mortality in those patients who survive AKI. Moreover, the risk of ESRD and mortality after AKI is substantially higher in patients with preexisting CKD. However, the underlying mechanisms by which AKI and CKD interact to promote ESRD remain poorly understood. The recently developed models that superimpose AKI on rodents with preexisting CKD have provided new insights into the pathogenic mechanisms mediating the deleterious interactions between AKI and CKD. These studies show that preexisting CKD impairs recovery from AKI and promotes the development of mechanisms of CKD progression. Specifically, preexisting CKD exacerbates microvascular rarefaction, failed tubular redifferentiation, disruption of cell cycle regulation, hypertension, and proteinuria after AKI. The purpose of this review is to discuss the potential mechanisms by which microvascular rarefaction and hypertension contribute to impaired recovery from AKI and the subsequent progression of renal disease in preexisting CKD states.

Urine electrolyte measurement as a "window" into renal microcirculatory stress assessment in critically ill patients

Urine electrolyte assessment has long been used in order to understand electrolyte concentration disturbances in blood and as an easy tool for monitoring renal perfusion and structural tubular damage. In the last few years, great improvement in the pathophysiology of acute kidney injury (AKI) has occurred, and the correlation between urine biochemistry (UB) behavior and renal perfusion was frequently questioned. Many authors have suggested abandoning UB monitoring due to its unclear role in AKI monitoring. Our group has been working in this field in the critically ill population, and we believe that, although UB is indeed very useful, a different point of view regarding the interpretation of the data should be used. The aim of this review is to explain the rationale of these new concepts and make suggestions for their adequate use in daily ICU practice, especially in low-income countries where more sophisticated and expensive AKI biomarker assessments are not available.

The renal blood flow reserve in healthy humans and patients with atherosclerotic renovascular disease measured by positron emission tomography using [15O]H2O

BACKGROUND

Microvascular function plays an important role in ARVD (atherosclerotic renovascular disease). RFR (renal flow reserve), the capacity of renal vasculature to dilate, is known to reflect renal microvascular function. In this pilot study, we assessed PET (positron emission tomography)-based RFR values of healthy persons and renal artery stenosis patients. Seventeen patients with ARVD and eight healthy subjects were included in the study. Intravenous enalapril 1 mg was used as a vasodilatant, and the maximum response (blood pressure and RFR) to it was measured at 40 min. Renal perfusion was measured by means of oxygen-15-labeled water PET. RFR was calculated as a difference of stress flow and basal flow and was expressed as percent [(stress blood flow - basal blood flow)/basal blood flow] × 100%.

RESULTS

RFR of the healthy was 22%. RFR of the stenosed kidneys of bilateral stenosis patients (27%) was higher than that of the stenosed kidneys of unilateral stenosis patients (15%). RFR of the contralateral kidneys of unilateral stenosis patients was 21%. There was no difference of statistical significance between RFR values of ARVD subgroups or between ARVD subgroups and the healthy. In the stenosed kidneys of unilateral ARVD patients, stenosis grade of the renal artery correlated negatively with basal (p = 0.04) and stress flow (p = 0.02). Dispersion of RFR values was high.

CONCLUSIONS

This study is the first to report [15O]H2O PET-based RFR values of healthy subjects and ARVD patients in humans. The difference between RFR values of ARVD patients and the healthy did not reach statistical significance perhaps because of high dispersion of RFR values. [15O]H2O PET is a valuable non-invasive and quantitative method to evaluate renal blood flow though high dispersion makes imaging challenging. Larger studies are needed to get more information about [15O]H2O PET method in evaluation of renal blood flow.

Update on perioperative acute kidney injury

PURPOSE OF REVIEW

In this review, we discuss the latest updates on perioperative acute kidney injury (AKI) and the specific considerations that are relevant to different surgeries and patient populations.

RECENT FINDINGS

AKI diagnosis is constantly evolving. New biomarkers detect AKI early and shed a light on the possible cause of AKI. Hypotension, even for a short duration, is associated with perioperative AKI. The debate on the deleterious effects of chloride-rich solutions is still far from conclusion. Remote ischemic preconditioning is showing promising results in the possible prevention of perioperative AKI. No definite data show a beneficiary effect of statins, fenoldepam, or sodium bicarbonate in preventing AKI.

SUMMARY

Perioperative AKI is prevalent and associated with significant morbidity and mortality. Considering the lack of effective preventive or therapeutic interventions, this review focuses on perioperative AKI: measures for early diagnosis, defining risks and possible mechanisms, and summarizing current knowledge for intraoperative fluid and hemodynamic management to reduce risk of AKI.

Glucagon-Like Peptide-1 Mediates the Protective Effect of the Dipeptidyl Peptidase IV Inhibitor on Renal Fibrosis via Reducing the Phenotypic Conversion of Renal Microvascular Cells in Monocrotaline-Treated Rats

Chronic kidney diseases are characterized by renal fibrosis with excessive matrix deposition, leading to a progressive loss of functional renal parenchyma and, eventually, renal failure. Renal microcirculation lesions, including the phenotypic conversion of vascular cells, contribute to renal fibrosis. Here, renal microcirculation lesions were established with monocrotaline (MCT, 60 mg/kg). Sitagliptin (40 mg/kg/d), a classical dipeptidyl peptidase-4 (DPP-4) inhibitor, attenuated the renal microcirculation lesions by inhibiting glomerular tuft hypertrophy, glomerular mesangial expansion, and microvascular thrombosis. These effects of sitagliptin were mediated by glucagon-like peptide-1 receptor (GLP-1R), since they were blocked by the GLP-1R antagonist exendin-3 (Ex-3, 40 ug/kg/d). The GLP-1R agonist liraglutide showed a similar renal protective effect in a dose-independent manner. In addition, sitagliptin, as well as liraglutide, alleviated the MCT-induced apoptosis of renal cells by increasing the expression of survival factor glucose-regulated protein 78 (GRP78), which was abolished by the GLP-1R antagonist Ex-3. Sitagliptin and liraglutide also effectively ameliorated the conversion of vascular smooth muscle cells (SMCs) from a synthetic phenotype to contractile phenotype. Moreover, sitagliptin and liraglutide inhibited endothelial-mesenchymal transition (EndMT) via downregulating transforming growth factor-β1 (TGF-β1). Collectively, these findings suggest that DPP-4 inhibition can reduce microcirculation lesion-induced renal fibrosis in a GLP-1-dependent manner.

Cardiovascular risk factors as determinants of retinal and skin microvascular function: The Maastricht Study

Objective

Microvascular dysfunction is an important underlying mechanism of microvascular diseases. Determinants (age, sex, hypertension, dyslipidemia, hyperglycemia, obesity, and smoking) of macrovascular diseases affect large-artery endothelial function. These risk factors also associate with microvascular diseases. We hypothesized that they are also determinants of microvascular (endothelial) function.

Methods

In The Maastricht Study, a type 2 diabetes-enriched population-based cohort study (n = 1991, 51% men, aged 59.7±8.2 years), we determined microvascular function as flicker light-induced retinal arteriolar %-dilation and heat-induced skin %-hyperemia. Multiple linear regression analyses were used to assess the associations of cardiovascular risk factors (age, sex, waist circumference, total-to-high-density lipoprotein (HDL) cholesterol ratio, fasting plasma glucose (FPG), 24-h systolic blood pressure, and cigarette smoking) with retinal and skin microvascular function.

Results

In multivariate analyses, age and FPG were inversely associated with retinal and skin microvascular function (regression coefficients per standard deviation (SD) were -0.11SD (95%CI: -0.15;-0.06) and -0.12SD (-0.17;-0.07) for retinal arteriolar %-dilation and -0.10SD (-0.16;-0.05) and -0.11SD (-0.17;-0.06) for skin %-hyperemia, respectively. Men and current smokers had -0.43SD (-0.58;-0.27) and -0.32SD (-0.49;-0.15) lower skin %-hyperemia, respectively. 24-h systolic blood pressure, waist circumference, and total-to-HDL cholesterol ratio were not statistically significantly associated with these microvascular functions.

Conclusions

Associations between cardiovascular risk factors and retinal and skin microvascular function show a pattern that is partly similar to the associations between cardiovascular risk factors and macrovascular function. Impairment of microvascular function may constitute a pathway through which an adverse cardiovascular risk factor pattern may increase risk of diseases that are partly or wholly of microvascular origin.