Spatial Metabolomics Identifies LPC(18:0) and LPA(18:1) in Advanced Atheroma With Translation to Plasma for Cardiovascular Risk Estimation.

BACKGROUND: The metabolic alterations occurring within the arterial architecture during atherosclerosis development remain poorly understood, let alone those particular to each arterial tunica. We aimed first to identify, in a spatially resolved manner, the specific metabolic changes in plaque, media, adventitia, and cardiac tissue between control and atherosclerotic murine aortas. Second, we assessed their translatability to human tissue and plasma for cardiovascular risk estimation. METHODS: In this observational study, mass spectrometry imaging (MSI) was applied to identify region-specific metabolic differences between atherosclerotic (n=11) and control (n=11) aortas from low-density lipoprotein receptor-deficient mice, via histology-guided virtual microdissection. Early and advanced plaques were compared within the same atherosclerotic animals. Progression metabolites were further analyzed by MSI in 9 human atherosclerotic carotids and by targeted mass spectrometry in human plasma from subjects with elective coronary artery bypass grafting (cardiovascular risk group, n=27) and a control group (n=27). RESULTS: MSI identified 362 local metabolic alterations in atherosclerotic mice (log2 fold-change ≥1.5; P≤0.05). The lipid composition of cardiac tissue is altered during atherosclerosis development and presents a generalized accumulation of glycerophospholipids, except for lysolipids. Lysolipids (among other glycerophospholipids) were found at elevated levels in all 3 arterial layers of atherosclerotic aortas. LPC(18:0) (lysophosphatidylcholine; P=0.024) and LPA(18:1) (lysophosphatidic acid; P=0.025) were found to be significantly elevated in advanced plaques as compared with mouse-matched early plaques. Higher levels of both lipid species were also observed in fibrosis-rich areas of advanced- versus early-stage human samples. They were found to be significantly reduced in human plasma from subjects with elective coronary artery bypass grafting (P<0.001 and P=0.031, respectively), with LPC(18:0) showing significant association with cardiovascular risk (odds ratio, 0.479 [95% CI, 0.225-0.883]; P=0.032) and diagnostic potential (area under the curve, 0.778 [95% CI, 0.638-0.917]). CONCLUSIONS: An altered phospholipid metabolism occurs in atherosclerosis, affecting both the aorta and the adjacent heart tissue. Plaque-progression lipids LPC(18:0) and LPA(18:1), as identified by MSI on tissue, reflect cardiovascular risk in human plasma.

Analysis of Vascular Smooth Muscle Cells from Thoracic Aortic Aneurysms Reveals DNA Damage and Cell Cycle Arrest as Hallmarks in Bicuspid Aortic Valve Patients.

Thoracic aortic aneurysm (TAA) is mainly sporadic and with higher incidence in the presence of a bicuspid aortic valve (BAV) for unknown reasons. The lack of drug therapy to delay TAA progression lies in the limited knowledge of pathophysiology. We aimed to identify the molecular hallmarks that differentiate the aortic dilatation associated with BAV and tricuspid aortic valve (TAV). Aortic vascular smooth muscle cells (VSMCs) isolated from sporadic TAA patients with BAV or TAV were analyzed by mass spectrometry. DNA oxidative damage assay and cell cycle profiling were performed in three independent cohorts supporting proteomics data. The alteration of secreted proteins was confirmed in plasma. Stress phenotype, oxidative stress, and enhanced DNA damage response (increased S-phase arrest and apoptosis) were found in BAV-TAA patients. The increased levels of plasma C1QTNF5, LAMA2, THSB3, and FAP confirm the enhanced stress in BAV-TAA. Plasma FAP and BGN point to an increased inflammatory condition in TAV. The arterial wall of BAV patients shows a limited capacity to counteract drivers of sporadic TAA. The molecular pathways identified support the need of differential molecular diagnosis and therapeutic approaches for BAV and TAV patients, showing specific markers in plasma which may serve to monitor therapy efficacy.

Prevention of cardiorenal damage: importance of albuminuria.

Chronic kidney disease (CKD) is projected to become a leading global cause of death by 2040, and its early detection is critical for effective and timely management. The current definition of CKD identifies only advanced stages, when kidney injury has already destroyed >50% of functioning kidney mass as reflected by an estimated glomerular filtration rate <60 mL/min/1.73 m2 or a urinary albumin/creatinine ratio >six-fold higher than physiological levels (i.e. > 30 mg/g). An elevated urinary albumin-excretion rate is a known early predictor of future cardiovascular events. There is thus a 'blind spot' in the detection of CKD, when kidney injury is present but is undetectable by current diagnostic criteria, and no intervention is made before renal and cardiovascular damage occurs. The present review discusses the CKD 'blind spot' concept and how it may facilitate a holistic approach to CKD and cardiovascular disease prevention and implement the call for albuminuria screening implicit in current guidelines. Cardiorenal risk associated with albuminuria in the high-normal range, novel genetic and biochemical markers of elevated cardiorenal risk, and the role of heart and kidney protective drugs evaluated in recent clinical trials are also discussed. As albuminuria is a major risk factor for cardiovascular and renal disease, starting from levels not yet considered in the definition of CKD, the implementation of opportunistic or systematic albuminuria screening and therapy, possibly complemented with novel early biomarkers, has the potential to improve cardiorenal outcomes and mitigate the dismal 2040 projections for CKD and related cardiovascular burden.

Non-syndromic thoracic aortic aneurysm: cellular and molecular insights.

Thoracic aortic aneurysm (TAA) develops silently and asymptomatically and is a major cause of mortality. TAA prevalence is greatly underestimated, it is usually diagnosed incidentally, and its treatment consists mainly of prophylactic surgery based on the aortic diameter. The lack of effective drugs and biological markers to identify and stratify TAAs by risk before visible symptoms results from scant knowledge of its pathophysiological mechanisms. Here we integrate the structural impairment affecting non-syndromic non-familial TAA with the main cellular and molecular changes described so far and consider how these changes are interconnected through specific pathways. The ultimate goal is to define much-needed novel markers of TAA, and so the potential of previously identified molecules to aid in early diagnosis/prognosis is also discussed. © 2021 The Authors. The Journal of Pathology published by John Wiley & Sons, Ltd. on behalf of The Pathological Society of Great Britain and Ireland.

Analysis of urinary exosomal metabolites identifies cardiovascular risk signatures with added value to urine analysis.

BACKGROUND: Subclinical atherosclerosis may result in fatal cardiovascular (CV) events, but the underlying mechanisms and molecular players leading to disease are not entirely understood. Thus, novel approaches capable of identifying the factors involved in pathological progression and providing a better understanding of the subjacent mechanisms are needed. Extracellular vesicles (EVs) have been shown to have numerous biological functions, and their metabolome has recently generated interest as a source of novel biomarkers. The metabolic content of the exosomes has been so far unexplored in cardiovascular disease (CVD), and here, we developed an analytical strategy aimed at probing urinary exosomal metabolite content and its association to CV risk. RESULTS: Direct analysis of the exosomes without metabolite extraction was evaluated by high-resolution magic angle spinning (1H HR-MAS). Other two methodologies for the analysis of exosomal metabolites by 1H NMR were set up, based on methanol or organic solvents sequential extraction. The three methods were compared in terms of the number of detected signals and signal to noise ratio (S/N). The methanol method was applied to identify altered metabolites in the urinary exosomes of subjects with programmed coronary artery by-pass grafting (CABG) versus a control group. Target mass spectrometry (MS) was also performed for differential analysis. The clinical performance of exosomal metabolites of interest in CVD was investigated, and the added value of the exosomes compared to urine analysis was evaluated. Based on S/N ratio, simplicity, reproducibility, and quality of the spectrum, the methanol method was chosen for the study in CVD. A cardiometabolic signature composed by 4-aminohippuric acid, N-1-methylnicotinamide, and citric acid was identified in urinary exosomes. Directly in urine, 4-aminohippuric acid and citric acid do not show variation between groups and changes in N-1-methylnicotinamide are less pronounced, proving the added value of exosomes. CONCLUSIONS: We set up a novel methodology to analyze metabolic alterations in urinary exosomes and identified a cardiometabolic signature in these microvesicles. This study constitutes the first evidence of a role for the exosomal metabolism in CVD and demonstrates the possibility to evaluate the urinary exosomal metabolic content by NMR and MS.

Advances in understanding the role of angiotensin-regulated proteins in kidney diseases.

Introduction: Renin-angiotensin system (RAS) blockers are in clinical use to treat high blood pressure and proteinuric chronic kidney disease. However, RAS blockade is limited by the risk of hyperkalemia, angiotensin receptor blockers are not clinically superior to angiotensin-converting enzyme inhibitors and dual RAS blockade is formally contraindicated. Areas covered: We review the regulation of protein expression and activation by angiotensin II and RAS blockers as it contributes to kidney disease. Specifically excluded are direct renin actions as well as aldosterone actions. The search strategy included the terms angiotensin, protein, proteomics, inflammation, fibrosis, and kidney and was complemented by additional searches based on initial results. Expert commentary: Recent developments include an improved understanding of the structure, function, and signaling of angiotensin G-protein-coupled receptors; identification of ligands that behave as agonists, antagonists, and even reverse agonists on specific signaling and functional pathways of the same receptor; characterization of further signaling pathways by applying proteomics and phosphoproteomics; and systems biology approaches to characterize signatures of adequate RAS blockade or resistance of kidney injury to RAS blockade. These developments will allow optimization of clinical RAS targeting to improve kidney outcomes through precision nephrology strategies that may include combined approaches, along the path marked by clinically successful dual RAS/neprilysin blockade.

Translational science in albuminuria: a new view of de novo albuminuria under chronic RAS suppression.

The development of de novo albuminuria during chronic renin-angiotensin system (RAS) suppression is a clinical entity that remains poorly recognized in the biomedical literature. It represents a clear increment in global cardiovascular (CV) and renal risk that cannot be counteracted by RAS suppression. Although not specifically considered, it is clear that this entity is present in most published and ongoing trials dealing with the different forms of CV and renal disease. In this review, we focus on the mechanisms promoting albuminuria, and the predictors and new markers of de novo albuminuria, as well as the potential treatment options to counteract the excretion of albumin. The increase in risk that accompanies de novo albuminuria supports the search for early markers and predictors that will allow practising physicians to assess and prevent the development of de novo albuminuria in their patients.

Cytoskeleton deregulation and impairment in amino acids and energy metabolism in early atherosclerosis at aortic tissue with reflection in plasma.

BACKGROUND: Cardiovascular disease (CVD) is the leading cause of death globally, being atherosclerosis the main cause. Main risk factors are known and current effort is very much dedicated to improve prevention. However, the asymptomatic and silent course of atherosclerosis hampers an accurate and individualized risk evaluation. OBJECTIVES: Here we investigate subjacent molecular changes taking place in arterial tissue which can be ultimately translated in a measurable fingerprint in plasma. METHODS: First, we applied a combined approach to find out main molecular alterations at protein and metabolite level in response to early atherosclerosis development in a rabbit model. A potential reflection of all these alterations observed in aortic tissue was investigated in rabbit plasma and further analyzed in a translational study in human plasma from 62 individuals. RESULTS: Data link the structural remodeling taking place in atherosclerotic arteries in terms of loss of contractile properties and favored cellular migration, with an up-regulation of integrin linked kinase, tropomyosin isoform 2 and capping protein gelsolin-like, and a down-regulation of vinculin. A molecular response to oxidative stress is evidenced, involving changes in the glucose metabolism enzymes pyruvate kinase (PKM) and phosphoglycerate kinase (PGK), and pyruvate. Up-regulation of aspartate connects different changes observed in amino acid metabolism and, additionally, alterations in the phosphatidylcholine route of the glycerophospholipid metabolism were found. CONCLUSIONS: A specific molecular marker panel composed by PKM, valine and pyruvate is shown here linked to cardiovascular risk.

Molecular histology of arteries: mass spectrometry imaging as a novel ex vivo tool to investigate atherosclerosis.

Atherosclerosis is usually the underlying cause of a fatal event such as myocardial infarction or ictus. The atherome plaque develops silently and asymptomatically within the arterial intima layer. In this context, the possibility to analyze the molecular content of arterial tissue while preserving each molecule's specific localization is of great interest as it may reveal further insights into the physiopathological changes taking place. Mass spectrometry imaging (MSI) enables the spatially resolved molecular analysis of proteins, peptides, metabolites, lipids and drugs directly in tissue, with a resolution sufficient to reveal molecular features specific to distinct arterial structures. MSI represents a novel ex vivo imaging tool still underexplored in cardiovascular diseases. This review focuses on the MSI technique applied to cardiovascular disease and covers the main contributions to date, ongoing efforts, the main challenges and current limitations of MSI.

Urinary alpha-1 antitrypsin and CD59 glycoprotein predict albuminuria development in hypertensive patients under chronic renin-angiotensin system suppression.

BACKGROUND: Hypertension is a multi-factorial disease of increasing prevalence and a major risk factor for cardiovascular mortality even in the presence of adequate treatment. Progression of cardiovascular disease (CVD) occurs frequently during chronic renin-angiotensin-system (RAS) suppression, and albuminuria is a marker of CV risk. High prevalence of albuminuria in treated hypertensive patients has been demonstrated, but there are no available markers able to predict evolution. The aim of this study was the identification of novel indicators of albuminuria progression measurable in urine of diabetic and non-diabetic patients. METHODS: 1143 hypertensive patients under chronic treatment were followed for a minimum period of 3 years. Among them, 105 diabetic and non-diabetic patients were selected and classified in three groups according to albuminuria development during follow-up: (a) patients with persistent normoalbuminuria; (b) patients developing de novo albuminuria; (c) patients with maintained albuminuria. Differential urine analysis was performed by 2D gel electrophoresis (2D-DIGE) and further confirmed by liquid chromatography-mass spectrometry. Non-parametric statistical tests were applied. RESULTS: CD59 glycoprotein and alpha-1 antitrypsin (AAT) resulted already altered in patients developing albuminuria de novo, with a similar response in those with maintained albuminuria. A prospective study in a sub-group of normoalbuminuric patients who were clinically followed up for at least 1 year from urine sampling, revealed CD59 and AAT proteins significantly varied in the urine collected from normoalbuminurics who will negatively progress, serving as predictors of future albuminuria development. CONCLUSIONS: CD59 and AAT proteins are significantly altered in hypertensive patients developing albuminuria. Interestingly, CD59 and AAT are able to predict, in normoalbuminuric individuals, who will develop albuminuria in the future, being potential predictors of vascular damage and CV risk. These findings contribute to early identify patients at risk of developing albuminuria even when this classical predictor is still in the normal range, constituting a novel strategy towards a prompt and more efficient therapeutic intervention with better outcome.

Role of matrix metalloproteinase-9 in chronic kidney disease: a new biomarker of resistant albuminuria.

Resistant albuminuria, developed under adequate chronic blockade of the renin-angiotensin system, is a clinical problem present in a small number of patients with chronic kidney disease (CKD). The mechanism underlying this resistant albuminuria remains unknown. Matrix metalloproteinases (MMPs) are involved in the pathophysiology of cardiovascular and renal diseases. In the present study we tested the role of MMPs in resistant albuminuria. First we evaluated gelatinase MMP-2 and MMP-9 activity by zymography in the Munich Wistar Frömter (MWF) rat, a model of progressive albuminuria, and subsequently in patients with resistant albuminuria. Markers of oxidative stress were observed in the kidneys of MWF rats, together with a significant increase in pro-MMP-2 and active MMP-9 forms. These changes were normalized together with reduced albuminuria in consomic MWF-8(SHR) rats, in which chromosome 8 of MWF was replaced with the respective chromosome from spontaneously hypertensive rats. The MMP-2 and MMP-9 protein levels were similar in patients with normal and resistant albuminuria; however, high circulating levels of collagen IV, a specific biomarker of tissue collagen IV degradation, were observed in patients with resistant albuminuria. These patients showed a significant increase in gelatinase MMP-2 and MMP-9 activity, but only a significant increase in the active MMP-9 form quantified by ELISA, which correlated significantly with the degree of albuminuria. Although the expression of the tissue inhibitor of MMP-9 (TIMP)-1 was similar, a novel AlphaLISA assay demonstrated that the MMP-9-TIMP-1 interaction was reduced in patients with resistant albuminuria. It is of interest that oxidized TIMP-1 expression was higher in patients with resistant albuminuria. Therefore, increased circulating MMP-9 activity is associated with resistant albuminuria and a deleterious oxidative stress environment appears to be the underlying mechanism. These changes might contribute to the progression of CKD in these patients.

Modification of the secretion pattern of proteases, inflammatory mediators, and extracellular matrix proteins by human aortic valve is key in severe aortic stenosis.

One of the major challenges in cardiovascular medicine is to identify candidate biomarker proteins. Secretome analysis is particularly relevant in this search as it focuses on a subset of proteins released by a cell or tissue under certain conditions. The sample can be considered as a plasma subproteome and it provides a more direct approximation to the in vivo situation. Degenerative aortic stenosis is the most common worldwide cause of valve replacement. Using a proteomic analysis of the secretome from aortic stenosis valves we could identify candidate markers related to this pathology, which may facilitate early diagnosis and treatment. For this purpose, we have designed a method to validate the origin of secreted proteins, demonstrating their synthesis and release by the tissue and ruling out blood origin. The nLC-MS/MS analysis showed the labeling of 61 proteins, 82% of which incorporated the label in only one group. Western blot and selective reaction monitoring differential analysis, revealed a notable role of the extracellular matrix. Variation in particular proteins such as PEDF, cystatin and clusterin emphasizes the link between aortic stenosis and atherosclerosis. In particular, certain proteins variation in secretome levels correlates well, not only with label incorporation trend (only labeled in aortic stenosis group) but, more importantly, with alterations found in plasma from an independent cohort of samples, pointing to specific candidate markers to follow up in diagnosis, prognosis, and therapeutic intervention.

Identification of a urine metabolomic signature in patients with advanced-stage chronic kidney disease.

The prevalence of chronic kidney disease (CKD) is increasing and frequently progresses to end-stage renal disease. There is an urgent demand to discover novel markers of disease that allow monitoring disease progression and, eventually, response to treatment. To identify such markers, and as a proof of principle, we determined if a metabolite signature corresponding to CKD can be found in urine. In the discovery stage, we analyzed the urine metabolome by NMR of 15 patients with CKD and compared that with the metabolome of 15 healthy individuals and found a classification pattern clearly indicative of CKD. A validation cohort of urine samples from an additional 16 patients with CKD and 15 controls was then analyzed by (Selected Reaction Monitoring) liquid chromatography-triple quadrupole mass spectrometry and indicated that a group of seven urinary metabolites differed between CKD and non-CKD urine samples. This profile consisted of 5-oxoproline, glutamate, guanidoacetate, α-phenylacetylglutamine, taurine, citrate, and trimethylamine N-oxide. Thus, we identified a panel of urine metabolites differentially present in urine that may help identify and monitor patients with CKD.

Urine 2DE proteome analysis in healthy condition and kidney disease.

Urine is a source of potential markers of disease. In the context of renal disease, urine is particularly important as it may directly reflect kidney injury. Current markers of renal dysfunction lack both optimal specificity and sensitivity, and improved technologies and approaches are needed. There is no clear consensus about the best sample pretreatment procedure for 2DE analysis of the urine proteome. Sample pretreatment conditions spots resolution and detection sensitivity, critically. As a first goal, we exhaustively compared eight different sample cleaning and protein purification methodologies for 2DE analysis of urine from healthy individuals. Oasis® HLB cartridges allowed the detection of the highest number of low molecular weight proteins; while PD10 desalting columns resulted in the highest number of detected spots in the high molecular weight area. Sample pretreatment strategies were also explored in the context of proteinuria, a clinical condition often associated to renal damage. Testing of urine samples from 13 patients with hypertension or kidney disease and different levels of proteinuria identified Oasis® HLB cartridge purification in combination with albumin depletion by ProteoPrep kit as the best option for urine proteome profiling from patients with proteinuric (> 30 mg/L albumin in urine) renal disease.

A proteomic focus on the alterations occurring at the human atherosclerotic coronary intima.

Coronary atherosclerosis still represents the major cause of mortality in western societies. Initiation of atherosclerosis occurs within the intima, where major histological and molecular changes are produced during pathogenesis. So far, proteomic analysis of the atherome plaque has been mainly tackled by the analysis of the entire tissue, which may be a challenging approach because of the great complexity of this sample in terms of layers and cell type composition. Based on this, we aimed to study the intimal proteome from the human atherosclerotic coronary artery. For this purpose, we analyzed the intimal layer from human atherosclerotic coronaries, which were isolated by laser microdissection, and compared with those from preatherosclerotic coronary and radial arteries, using a two-dimensional Differential-In-Gel-Electrophoresis (DIGE) approach. Results have pointed out 13 proteins to be altered (seven up-regulated and six down-regulated), which are implicated in the migrative capacity of vascular smooth muscle cells, extracellular matrix composition, coagulation, apoptosis, heat shock response, and intraplaque hemorrhage deposition. Among these, three proteins (annexin 4, myosin regulatory light 2, smooth muscle isoform, and ferritin light chain) constitute novel atherosclerotic coronary intima proteins, because they were not previously identified at this human coronary layer. For this reason, these novel proteins were validated by immunohistochemistry, together with hemoglobin and vimentin, in an independent cohort of arteries.

Metabolomics Analysis of Urinary Extracellular Vesicles by Nuclear Magnetic Resonance and Liquid Chromatography-Mass Spectrometry.

Extracellular vesicle (EV) release and their content are influenced by diverse clinical conditions. EVs participate in inter-cellular communication and have been postulated as reflectors of the pathophysiology of the cells, tissues, organs or the whole system with which they are in contact. Urinary EVs have been proved to reflect pathophysiology not only of renal system related diseases constituting an additional source of potential biomarkers easily accessible in a non-invasive way. The interest in EVs cargo has been mostly focused on proteins and nucleic acids and more recently it has been extended to metabolites. Metabolites represent the downstream changes in the genome, transcriptome, and proteome as a reflection of processes occurring in living organisms. For their study, nuclear magnetic resonance (NMR) and mass spectrometry in tandem (LC-MS/MS) are widely used. NMR is a reproducible and non-destructive technique and we show here methodological protocols for the metabolomics analysis of urinary EVs by NMR. Additionally, we also describe the workflow for a targeted LC-MS/MS analysis that is extensible to untargeted studies.

Donor liquid biopsy and outcomes in kidney transplantation.

Kidney transplantation is the treatment of choice for patients with kidney failure. Priority on the waiting list and optimal donor-recipient matching are guided by mathematical scores, clinical variables and macroscopic observation of the donated organ. Despite the increasing rates of successful kidney transplantation, maximizing the number of available organs while ensuring the optimum long-term performance of the transplanted kidney remains both key and challenging, and no unequivocal markers are available for clinical decision making. Moreover, the majority of studies performed thus far has focused on the risk of primary non-function and delayed graft function and subsequent survival and have mainly analysed recipients' samples. Given the increasing use of donors with expanded criteria and/or cardiac death, predicting whether grafts will provide sufficient kidney function is increasingly more challenging. Here we compile the available tools for pre-transplant kidney evaluation and summarize the latest molecular data from donors that may predict short-term (immediate or delayed graft function), medium-term (6 months) and long-term (≥12 months) kidney function. The use of liquid biopsy (urine, serum, plasma) to overcome the limitations of the pre-transplant histological evaluation is proposed. Novel molecules and approaches such as the use of urinary extracellular vesicles are also reviewed and discussed, along with directions for future research.

Evidence of chronic kidney injury in patients not meeting KDIGO criteria for chronic kidney disease.

Subjects not meeting KDIGO criteria for chronic kidney disease (CKD), i.e. normoalbuminuric (urinary albumin:creatinine ratio, UACR <30 mg/g) individuals with an estimated glomerular filtration rate >60 mL/min/1.73 m2, are considered at no increased cardiovascular or kidney risk associated with kidney disease, but the incidence of subclinical atherosclerosis, cardiovascular events and CKD progression is already increased in the high-normal UACR range (10-30 mg/g). Earlier intervention in this subclinical pre-CKD stage may diminish cardiorenal risk. However, tools to predict albuminuria development and to identify those subjects who will benefit most from intervention are limited. Recent data have identified urine molecular changes within the normoalbuminuria condition, consisting of an altered urinary peptidome, proteome and metabolome, which represent subclinical organ damage and processes such as inflammation, oxidative stress, tricarboxylic acids cycle deregulation, impaired fatty acids ß-oxidation or defective tubular reabsorption.

Prediction of the early response to spironolactone in resistant hypertension by the combination of matrix metalloproteinase-9 activity and arterial stiffness parameters.

AIMS: The aim of this study was to determine whether arterial stiffness assessed with the biochemical parameter active matrix metalloproteinase (MMP)-9 and the clinical parameters pulse pressure (PP) and pulse wave velocity predicts the response to spironolactone in resistant hypertension (RH). METHODS AND RESULTS: Ambulatory blood pressure (BP) and active MMP-9 (measured by zymography and ELISA) were measured at baseline, and patients were classified as having pseudo-RH or RH. Patients with RH received spironolactone and the response was determined after 8 weeks by ambulatory BP monitoring: those who achieved BP goals were considered controlled (CRH) and those who did not were considered uncontrolled (UCRH). Plasma active MMP-9 was significantly higher in patients with RH than with pseudo-RH, and correlated with 24 h systolic BP and PP. Receiver operating characteristic analysis indicated that active MMP-9 could predict the response to spironolactone, and its combination with 24 h PP and pulse wave velocity significantly improved this prediction. Moreover, plasma of patients with UCRH induced the MMP-9 expression pathway. CONCLUSION: We propose active MMP-9 as a useful biomarker to identify patients with RH who will not respond to spironolactone. Combining MMP-9 activity with classical arterial stiffness parameters improves the prediction of the clinical response to spironolactone and might contribute to guide the most appropriate therapeutic decisions for patients with RH.