Urinary Plasminogen Activator Inhibitor-1: A Biomarker of Acute Tubular Injury.

INTRODUCTION: Acute kidney injury (AKI) is a threatening, multiaetiological syndrome encompassing a variety of forms and damage patterns. AKI lacks sufficiently specific diagnostic tools to evaluate the distinct combination of pathophysiological events underlying each case, which limits personalized and optimized handling. Therefore, a pathophysiological diagnosis based on new urinary biomarkers is sought for practical (readiness and noninvasiveness) and conceptual reasons, as the urine is a direct product of the kidneys. However, biomarkers found in the urine may also have extrarenal origin, thus conveying pathophysiological information from other organs or tissues. Urinary plasminogen activator inhibitor-1 (PAI-1) has been associated to AKI, although its origin and traffic to the urine are not known. METHODS: Herein, we studied the blood or renal origin of urinary PAI-1 (uPAI-1) in experimental AKI in Wistar rats, by means of the in situ renal perfusion method. For this purpose, urine was collected while the kidneys of rats with AKI showing increased uPAI-1 excretion, and controls, were in situ perfused with a saline solution. RESULTS: Our results show that during perfusion, PAI-1 remained in the urine of AKI rats, suggesting that renal cells shed this protein directly to the urine. PAI-1 is also significantly increased in the urine of AKI patients. Its low correlation with other urinary markers such as NGAL or NAG suggests that PAI-1 provides complementary and distinct phenotypical information. CONCLUSION: In conclusion, uPAI-1 is a biomarker produced by damaged kidneys following AKI, whose precise pathophysiological meaning in AKI needs to be further investigated.

Combined use of GM2AP and TCP1-eta urinary levels predicts recovery from intrinsic acute kidney injury.

Deficient recovery from acute kidney injury (AKI) has immediate and long-term health, clinical and economic consequences. Pre-emptive recovery estimation may improve nephrology referral, optimize decision making, enrollment in trials, and provide key information for subsequent clinical handling and follow-up. For this purpose, new biomarkers are needed that predict outcome during the AKI episode. We hypothesized that damage pattern-specific biomarkers are expected to more closely associate to outcome within distinct subpopulations (i.e. those affected by specific pathological processes determining a specific outcome), as biomarker pleiotropy (i.e. associated to phenomena unrelated to AKI) introduced by unselected, heterogeneous populations may blur statistics. A panel of urinary biomarkers was measured in patients with AKI and their capacity to associate to normal or abnormal recovery was studied in the whole cohort or after sub-classification by AKI etiology, namely pre-renal and intrinsic AKI. A combination of urinary GM2AP and TCP1-eta best associates with recovery from AKI, specifically within the sub-population of renal AKI patients. This two-step strategy generates a multidimensional space in which patients with specific characteristics (i.e. renal AKI patients with good or bad prognosis) can be identified based on a collection of biomarkers working serially, applying pathophysiology-driven criteria to estimate AKI recovery, to facilitate pre-emptive and personalized handling.

Impaired Tubular Reabsorption Is the Main Mechanism Explaining Increases in Urinary NGAL Excretion Following Acute Kidney Injury in Rats.

Neutrophil gelatinase-associated lipocalin (NGAL) is a secreted low-molecular weight iron-siderophore-binding protein. NGAL overexpression in injured tubular epithelia partly explains its utility as a sensitive and early urinary biomarker of acute kidney injury (AKI). Herein, we extend mechanistic insights into the source and kinetics of urinary NGAL excretion in experimental AKI. Three models of experimental AKI were undertaken in adult male Wistar rats; renal ischemia-reperfusion injury (IRI) and gentamicin (G) and cisplatin (Cisp) nephrotoxicity. Alongside standard histological and biochemical assessment of AKI, urinary NGAL excretion rate, plasma NGAL concentration, and renal NGAL mRNA/protein expression were assessed. In situ renal perfusion studies were undertaken to discriminate direct shedding of NGAL to the urine from addition of NGAL to the urine secondary to alterations in the tubular handling of glomerular filtrate-derived protein. Renal NGAL expression and urinary excretion increased in experimental AKI. In acute studies in both the IRI and G models, direct renal perfusion with Kreb's buffer eliminated urinary NGAL excretion. Addition of exogenous NGAL to the Kreb's buffer circuit, reestablishment of perfusion with systemic blood or reperfusion with renal vein effluent restored high levels of urinary NGAL excretion. Urinary NGAL excretion in AKI arises in large proportion from reduced reabsorption from the glomerular filtrate. Hence, subclinical cellular dysfunction could increase urinary NGAL, particularly in concert with elevations in circulating prerenal NGAL and/or pharmacological inhibition of tubular reabsorption. More granular interpretation of urinary NGAL measurements could optimize the scope of its clinical utility as a biomarker of AKI.

Preventive Effect of Cardiotrophin-1 Administration before DSS-Induced Ulcerative Colitis in Mice.

Ulcerative colitis is a relatively frequent, chronic disease that impacts significantly the patient's quality of life. Although many therapeutic options are available, additional approaches are needed because many patients either do not respond to current therapies or show significant side effects. Cardiotrophin-1 (CT-1) is a cytokine with potent cytoprotective, anti-inflammatory, and antiapoptotic properties. The purpose of this study was to assess if the administration of CT-1 could reduce colon damage in mice with experimental colitis was induced with 5% dextran sulfate sodium (DSS) in the drinking water. Half of the mice received an i.v. dose of CT-1 (200 µg/kg) 2 h before and 2 and 4 days after DSS administration. Animals were followed during 7 days after DSS administration. The severity of colitis was measured by standard scores. Colon damage was assessed by histology and immunohistochemistry. Inflammatory mediators were measured by Western blot and PCR. CT-1 administration to DSS-treated mice ameliorated both the clinical course (disease activity index), histological damage, inflammation (colon expression of TNF-α, IL-17, IL-10, INF IFN-γ, and iNOS), and apoptosis. Our results suggest that CT-1 administration before induction of colitis improves the clinical course, tissue damage, and inflammation in DSS-induced colitis in mice.

Cardiotrophin-1 attenuates experimental colitis in mice.

Cardiotrophin-1 (CT-1) holds potent anti-inflammatory, cytoprotective, and anti-apoptotic effects in the liver, kidneys, and heart. In the present study, the role of endogenous CT-1 and the effect of exogenous CT-1 were evaluated in experimental ulcerative colitis. Colitis was induced in CT-1 knockout and wild-type (WT) mice by administration of dextran sulphate sodium (DSS) in the drinking water during 7 days. CT-1 knockout mice showed higher colon damage and disease severity than WT mice. In addition, CT-1 (200 µg/kg/day, iv) or vehicle (as control) was administered during 3 days to WT, colitic mice, starting on day 4 after initiation of DSS. Disease activity index (DAI), inflammatory markers (tumor necrosis factor α (TNF-α), INFγ, IL-17, IL-10, inducible nitric oxide synthase (iNOS)), colon damage, apoptosis (cleaved caspase 3), nuclear factor κB (NFκB) and STAT-3 activation, and bacterial translocation were measured. Compared with mice treated with DSS, mice also treated with exogenous CT-1 showed lower colon damage, DAI, plasma levels of TNFα, colon expression of TNF-α, INFγ, IL-17, iNOS and cleaved caspase 3, higher NFκB and signal transducer and activator of transcription 3 (STAT3) pathways activation, and absence of bacterial translocation. We conclude that endogenous CT-1 plays a role in the defense and repair response of the colon against ulcerative lesions through an anti-inflammatory and anti-apoptotic effect. Supplementation with exogenous CT-1 ameliorates disease symptoms, which opens a potentially new therapeutic strategy for ulcerative colitis.

Cardiotrophin-1 therapy prevents gentamicin-induced nephrotoxicity in rats.

Aminoglycosides are very effective antibiotics for the treatment of severe infections, but they rank among the most frequent causes of drug-induced nephrotoxicity. Thus, prevention of aminoglycoside nephrotoxicity is an unmet therapeutic objective. Cardiotrophin-1 (CT-1), a member of the IL-6 family of cytokines, has been reported to protect the kidney against toxic and ischemic acute kidney injury (AKI). We have assessed the effect of rat CT-1 in the severity of gentamicin (G)-induced AKI. Groups of male Wistar rats received the following for 6 consecutive days: i) isotonic saline solution (group CONT), ii) G, 150mg/kg/day, i.p. (group G), iii) CT-1, 100µg/kg/day i.v. (group CT-1), or iv) G and CT-1 at the doses described above. The G group showed a manifest AKI characterized by low creatinine clearance, high plasma creatinine and urea levels, increased urinary excretion of proteins, glucose and AKI markers such as N-acetyl-glucosaminidase, neutrophil gelatinase-associated lipocalin, kidney-injury molecule-1 and T-gelsolin, increased kidney levels of CD-68, iNOS, IL-1ß and TNF-α, and markedly higher histological renal damage and leukocyte infiltration than the CONT and CT-1 groups. Administration of CT-1 together with G reduced almost all of the above-described manifestations of G-induced AKI. The results of this study have potential clinical application, as CT-1 is near to being used as a drug for organ protection.

Increased Klk9 Urinary Excretion Is Associated to Hypertension-Induced Cardiovascular Damage and Renal Alterations.

Early detection of hypertensive end-organ damage and secondary diseases are key determinants of cardiovascular prognosis in patients suffering from arterial hypertension. Presently, there are no biomarkers for the detection of hypertensive target organ damage, most outstandingly including blood vessels, the heart, and the kidneys.We aimed to validate the usefulness of the urinary excretion of the serine protease kallikrein-related peptidase 9 (KLK9) as a biomarker of hypertension-induced target organ damage.Urinary, plasma, and renal tissue levels of KLK9 were measured by the Western blot in different rat models of hypertension, including angiotensin-II infusion, DOCA-salt, L-NAME administration, and spontaneous hypertension. Urinary levels were associated to cardiovascular and renal injury, assessed by histopathology. The origin of urinary KLK9 was investigated through in situ renal perfusion experiments.The urinary excretion of KLK9 is increased in different experimental models of hypertension in rats. The ACE inhibitor trandolapril significantly reduced arterial pressure and the urinary level of KLK9. Hypertension did not increase kidney, heart, liver, lung, or plasma KLK9 levels. Hypertension-induced increased urinary excretion of KLK9 results from specific alterations in its tubular reabsorption, even in the absence of overt nephropathy. KLK9 urinary excretion strongly correlates with cardiac hypertrophy and aortic wall thickening.KLK9 appears in the urine in the presence of hypertension as a result of subtle renal handling alterations. Urinary KLK9 might be potentially used as an indicator of hypertensive cardiac and vascular damage.

Hypertension and hyperglycemia synergize to cause incipient renal tubular alterations resulting in increased NGAL urinary excretion in rats.

BACKGROUND: Hypertension and diabetes are the two leading causes of chronic kidney disease (CKD) eventually leading to end stage renal disease (ESRD) and the need of renal replacement therapy. Mortality among CKD and ESRD patients is high, mostly due to cardiovascular events. New early markers of risk are necessary to better anticipate the course of the disease, to detect the renal affection of additive risk factors, and to appropriately handle patients in a pre-emptive and personalized manner. METHODS: Renal function and NGAL urinary excretion was monitored in rats with spontaneous (SHR) or L-NAME induced hypertension rendered hyperglycemic (or not as controls). RESULTS: Combination of hypertension and hyperglycemia (but not each of these factors independently) causes an increased urinary excretion of neutrophil gelatinase-associated lipocalin (NGAL) in the rat, in the absence of signs of renal damage. Increased NGAL excretion is observed in diabetic animals with two independent models of hypertension. Elevated urinary NGAL results from a specific alteration in its tubular handling, rather than from an increase in its renal expression. In fact, when kidneys of hyperglycaemic-hypertensive rats are perfused in situ with Krebs-dextran solution containing exogenous NGAL, they excrete more NGAL in the urine than hypertensive rats. We also show that albuminuria is not capable of detecting the additive effect posed by the coexistence of these two risk factors. CONCLUSIONS: Our results suggest that accumulation of hypertension and hyperglycemia induces an incipient and quite specific alteration in the tubular handling of NGAL resulting in its increased urinary excretion.

Unveiling the rat urinary proteome with three complementary proteomics approaches.

Urine is a suitable biological fluid to look for markers of physiological and pathological processes, including renal and nonrenal diseases. In addition, it is an optimal body sample for diagnosis, because it is easily obtained without invasive procedures and can be sampled in large quantities at almost any time. Rats are frequently used as a model to study human diseases, and rat urine has been analyzed to search for disease biomarkers. The normal human urinary proteome has been studied extensively, but the normal rat urinary proteome has not been studied in such depth. In light of this, we were prompted to analyze the normal rat urinary proteome using three complementary proteomics platforms: SDS-PAGE separation, followed by LC-ESI-MS/MS; 2DE, followed by MALDI-TOF-TOF and 2D-liquid chromatography-chromatofocusing, followed by LC-ESI-Q-TOF. A total of 366 unique proteins were identified, of which only 5.2% of unique proteins were identified jointly by the three proteomics platforms used. This suggests that simultaneous proteomics techniques provide complementary and nonredundant information. Our analysis affords the most extensive rat urinary protein database currently available and this may be useful in the study of renal physiology and in the search for biomarkers related to renal and nonrenal diseases.

Cardiotrophin-1 administration prevents the renal toxicity of iodinated contrast media in rats.

Although generally reversible, contrast media toxicity often induces contrast-induced nephropathy (CIN), which is associated with longer hospitalization time, the need for dialysis, and higher incidence of later cardiovascular events and higher mortality. Preventive cotreatments have been assayed at the preclinical and clinical levels, but recent meta-analysis has not demonstrated a beneficial effect, which supports the search for new nephroprotective strategies. We have assessed if the administration of cardiotrophin-1 (CT-1), an endogenous cytokine with protective properties on the heart and liver, might mitigate CIN in rats. We have developed a model of CIN induced by the administration of the contrast medium gastrographin iv (3.7mg/kg) in rats sensitized by previous administration of subnephrotoxic doses of gentamicin (50mg/kg/day, ip) for 6 days. The severity of CIN was assessed by the measurement of renal function; renal histological damage; urinary excretion of markers of tubular damage, including N-acetyl beta glucosaminidase (NAG), kidney injury molecule 1 (KIM-1), and plasminogen activator inhibitor 1; lipid peroxidation; and renal apoptosis. Treatment with CT-1 almost completely prevented the renal tissue damage, as evidenced by almost total prevention of tubular desepithelization and tubular obstruction, reduced caspase activation, and cell proliferation. Besides, CT-1 also prevented the increment in renal tissue levels of renal tissue injury markers NAG, KIM-1, and neutrophil gelatinase-associated lipocalin. Oxidative stress, a hallmark of CIN, was also prevented by CT-1. Administration of CT-1 also prevented the derangement in kidney function induced by CIN. Renal hemodynamics, also impaired by the contrast medium, was normal in rats cotreated with CT-1. CT-1 administration significantly prevents the alterations in renal function and structure observed in a rat model of CIN.

An integrative overview on the mechanisms underlying the renal tubular cytotoxicity of gentamicin.

Gentamicin is an aminoglycoside antibiotic widely used against infections by Gram-negative microorganisms. Nephrotoxicity is the main limitation to its therapeutic efficacy. Gentamicin nephrotoxicity occurs in 10-20% of therapeutic regimes. A central aspect of gentamicin nephrotoxicity is its tubular effect, which may range from a mere loss of the brush border in epithelial cells to an overt tubular necrosis. Tubular cytotoxicity is the consequence of many interconnected actions, triggered by drug accumulation in epithelial tubular cells. Accumulation results from the presence of the endocytic receptor complex formed by megalin and cubulin, which transports proteins and organic cations inside the cells. Gentamicin then accesses and accumulates in the endosomal compartment, the Golgi and endoplasmic reticulum (ER), causes ER stress, and unleashes the unfolded protein response. An excessive concentration of the drug over an undetermined threshold destabilizes intracellular membranes and the drug redistributes through the cytosol. It then acts on mitochondria to unleash the intrinsic pathway of apoptosis. In addition, lysosomal cathepsins lose confinement and, depending on their new cytosolic concentration, they contribute to the activation of apoptosis or produce a massive proteolysis. However, other effects of gentamicin have also been linked to cell death, such as phospholipidosis, oxidative stress, extracellular calcium-sensing receptor stimulation, and energetic catastrophe. Besides, indirect effects of gentamicin, such as reduced renal blood flow and inflammation, may also contribute or amplify its cytotoxicity. The purpose of this review was to critically integrate all these effects and discuss their relative contribution to tubular cell death.

New insights into the mechanism of aminoglycoside nephrotoxicity: an integrative point of view.

Nephrotoxicity is one of the most important side effects and therapeutical limitations of aminoglycoside antibiotics, especially gentamicin. Despite rigorous patient monitoring, nephrotoxicity appears in 10-25% of therapeutic courses. Traditionally, aminoglycoside nephrotoxicity has been considered to result mainly from tubular damage. Both lethal and sub-lethal alterations in tubular cells handicap reabsorption and, in severe cases, may lead to a significant tubular obstruction. However, a reduced glomerular filtration is necessary to explain the symptoms of the disease. Reduced filtration is not solely the result of tubular obstruction and tubular malfunction, resulting in tubuloglomerular feedback activation; renal vasoconstriction and mesangial contraction are also crucial to fully explain aminoglycoside nephrotoxicity. This review critically presents an integrative view on the interactions of tubular, glomerular, and vascular effects of gentamicin, in the context of the most recent information available. Moreover, it discusses therapeutic perspectives for prevention of aminoglycoside nephrotoxicity derived from the pathophysiological knowledge.

Urinary levels of regenerating islet-derived protein III ß and gelsolin differentiate gentamicin from cisplatin-induced acute kidney injury in rats.

A key aspect for the clinical handling of acute kidney injury is an early diagnosis, for which a new generation of urine biomarkers is currently under development including kidney injury molecule 1 and neutrophil gelatinase-associated lipocalin. A further diagnostic refinement is needed where one specific cause among several potentially nephrotoxic insults can be identified during the administration of multidrug therapies. In this study we identified increases in regenerating islet-derived protein III beta (reg IIIb) and gelsolin as potential differential urinary markers of gentamicin's nephrotoxicity. Indeed, urinary levels of both reg IIIb and gelsolin distinguish between the nephrotoxicity caused by gentamicin from that caused by cisplatin where these markers were not increased by the latter. Reg IIIb was found to be overexpressed in the kidneys of gentamicin-treated rats and excreted into the urine, whereas urinary gelsolin originated from the blood by glomerular filtration. Our results illustrate an etiological diagnosis of acute kidney injury through analysis of urine. Thus, our results raise the possibility of identifying the actual nephrotoxin in critically ill patients who are often treated with several nephrotoxic agents at the same time, thereby providing the potential for tailoring therapy to an individual patient, which is the aim of personalized medicine.

Sub-nephrotoxic doses of gentamicin predispose animals to developing acute kidney injury and to excrete ganglioside M2 activator protein.

We studied whether nephrotoxic drug administration sensitizes to acute renal failure (ARF) by administering a sub-nephrotoxic dose of gentamicin. This pre-treatment sensitized animals with no sign of renal injury to develop ARF when exposed to a second potential nephrotoxic drug, also given at sub-nephrotoxic doses that would be otherwise harmless to non-sensitized animals. We identified urinary ganglioside M2 activator protein (GM2AP) as a biomarker of an enhanced sensitivity to suffer ARF following sub-nephrotoxic treatment with gentamicin. Sub-nephrotoxic gentamicin did not alter renal GM2AP gene expression or protein levels, determined by reverse transcriptase-PCR, western blot, and immunostaining, nor was its serum level modified. The origin of increased GM2AP in the urine is thought to be a defective tubular handling of this protein as a consequence of gentamicin action. Hence, markers of acquired sensitivity may improve the prevention of ARF by enhancing our capacity to monitor for this condition, in a preemptive manner.

Nephrotoxicity of uranium: pathophysiological, diagnostic and therapeutic perspectives.

As in the case of other heavy metals, a considerable body of evidence suggests that overexposure to uranium may cause pathological alterations to the kidneys in both humans and animals. In the present work, our aim was to analyze the available data from a critical perspective that should provide a view of the real danger of the nephrotoxicity of this metal for human beings. A further aim was to elaborate a comparative compilation of the renal pathophysiological data obtained in humans and experimental animals with a view to gaining more insight into our knowledge of the mechanisms of action and renal damage. Finally, we address the existing perspectives for the improvement of diagnostic methods and the treatment of intoxications by uranium, performing an integrated analysis of all these aspects.