Plasma creatinine and creatine quantification by capillary electrophoresis diode array detector

Determination of creatinine in urine and blood serum human samples by CZE-UV using on-column internal standard injection

Creatinine is a well-stablished biomarker for kidney malfunctions and for normalization parameter of urinary quantitative information. Recently, metabolic studies have been discovering other functionalities for creatinine tests in human urine and blood serum. In this work we present an enhanced capillary electrophoresis (CE) based protocol for determination of creatinine. CE is a high-throughput separation technique that have been getting attention through the last decades and might be considered to be adopted as an analytical instrumentation for clinical purposes. In the proposed method, we performed a short injection program with on-column addition of internal standard. Additionally, the method allows a simultaneous screening of non-proteinogenic amino acids that could be considered for metabolomics purposes. We design a pilot study that successfully estimated the creatinine value in 100 urine samples with (2.85 ± 1.78) mg dL^-1 LOD; (8.24 ± 5.93) mg dL^-1 LOQ and 82.4% accuracy. Considering that serum creatinine is also included in the clinical laboratory routines for estimated Glomerular Filtration Rate dosage, the method was complementary applied to 10 blood serum samples, which resulted in a model with (0.4 ± 0.2) mg dL^-1 LOD; (2.0 ± 0.6) mg dL^-1 LOQ and 83.8% of accuracy. All results were in agreement with reference values. The proposed method promotes a great analytical frequency and reproducibility with enhanced specificity compared with the ongoing protocol by Jaffe's reaction, thereby proving to be useful as an alternative for creatinine exams that might help complete a diagnosis of a series of health-related issues.

KIM-1-mediated anti-inflammatory activity is preserved by MUC1 induction in the proximal tubule during ischemia-reperfusion injury

Cell-associated kidney injury molecule-1 (KIM-1) exerts an anti-inflammatory role following kidney injury by mediating efferocytosis and downregulating the NF-κB pathway. KIM-1 cleavage blunts its anti-inflammatory activities. We reported that mucin 1 (MUC1) is protective in a mouse model of ischemia-reperfusion injury (IRI). As both KIM-1 and MUC1 are induced in the proximal tubule (PT) during IRI and are a disintegrin and metalloprotease 17 (ADAM17) substrates, we tested the hypothesis that MUC1 protects KIM-1 activity. Muc1 knockout (KO) mice and wild-type (WT) littermates were subjected to IRI. KIM-1, MUC1, and ADAM17 levels (and signaling pathways) were assessed by immunoblot analysis. PT localization was assessed by confocal microscopy and an in situ proximity ligation assay. Findings were extended using human kidneys and urine as well as KIM-1-mediated efferocytosis assays in mouse PT cultures. In response to tubular injury in mouse and human kidneys, we observed induction and coexpression of KIM-1 and MUC1 in the PT. Compared with WT mice, Muc1 KO mice had higher urinary KIM-1 and lower kidney KIM-1. KIM-1 was apical in the PT of WT kidneys but predominately with luminal debris in Muc1 KO mice. Efferocytosis was reduced in Muc1 KO PT cultures compared with WT cultures, whereas inflammation was increased in Muc1 KO kidneys compared with WT kidneys. MUC1 was cleaved by ADAM17 in PT cultures and blocked KIM-1 shedding in Madin-Darby canine kidney cells. We conclude that KIM-1-mediated efferocytosis and thus anti-inflammatory activity during IRI is preserved in the injured kidney by MUC1 inhibition of KIM-1 shedding.NEW & NOTEWORTHY KIM-1 plays a key role in the recovery of the tubule epithelium during renal IRI by mediating efferocytosis and associated signaling that suppresses inflammation. Excessive cleavage of KIM-1 by ADAM17 provides a decoy receptor that aggravates efferocytosis and subsequent signaling. Our data from experiments in mice, patients, and cultured cells show that MUC1 is also induced during IRI and competes with KIM-1 for cleavage by ADAM17. Consequently, MUC1 protects KIM-1 anti-inflammatory activity in the damaged kidney.

Loss of diacylglycerol kinase ε causes thrombotic microangiopathy by impairing endothelial VEGFA signaling

Loss of function of the lipid kinase diacylglycerol kinase ε (DGKε), encoded by the gene DGKE, causes a form of atypical hemolytic uremic syndrome that is not related to abnormalities of the alternative pathway of the complement, by mechanisms that are not understood. By generating a potentially novel endothelial specific Dgke-knockout mouse, we demonstrate that loss of Dgke in the endothelium results in impaired signaling downstream of VEGFR2 due to cellular shortage of phosphatidylinositol 4,5-biphosphate. Mechanistically, we found that, in the absence of DGKε in the endothelium, Akt fails to be activated upon VEGFR2 stimulation, resulting in defective induction of the enzyme cyclooxygenase 2 and production of prostaglandin E₂ (PGE₂). Treating the endothelial specific Dgke-knockout mice with a stable PGE₂ analog was sufficient to reverse the clinical manifestations of thrombotic microangiopathy and proteinuria, possibly by suppressing the expression of matrix metalloproteinase 2 through PGE₂-dependent upregulation of the chemokine receptor CXCR4. Our study reveals a complex array of autocrine signaling events downstream of VEGFR2 that are mediated by PGE₂, that control endothelial activation and thrombogenic state, and that result in abnormalities of the glomerular filtration barrier.

Kidney Biomarkers and Major Adverse Kidney Events in Critically Ill Patients

Background

Several biomarkers of AKI have been examined for their ability to predict AKI before serum creatinine. Few studies have focused on using kidney biomarkers to better predict major adverse kidney events (MAKE), an increasingly used composite outcome in critical care nephrology research.

Methods

Single-center prospective study collecting blood and urine samples from critically ill patients with AKI Kidney Disease Improving Global Outcomes stage 2 or above, and matched controls from a single, tertiary care intensive care unit (ICU). Samples were collected at 24-48 hours after AKI diagnosis (patients) or ICU admission (controls), 5-7 days later, and 4-6 weeks after discharge for patients with AKI. The primary outcome of interest was MAKE at hospital discharge (MAKE-DC), consisting of the composite end point of death, RRT dependence, or a decrease in estimated glomerular filtration to <75% of baseline.

Results

Serum/urinary neutrophil gelatinase-associated lipocalin (NGAL), serum/urinary cystatin C, and urinary kidney injury molecule-1 early in the AKI or ICU course were all significantly higher in patients with MAKE-DC compared with those not experiencing MAKE-DC. Additionally, serum/urinary NGAL and serum cystatin C measurements at the first time point remained significantly associated with MAKE events at 3, 6, and 12 months. Serum cystatin C, and to a lesser extent serum NGAL, significantly improved upon a logistic regression clinical prediction model of MAKE-DC (AUROC 0.94 and 0.87 versus 0.83; P=0.001 and P=0.02, respectively). Patients without MAKE-DC experienced a greater decline in serum NGAL from first to second measurement than those patients experiencing MAKE-DC.

Conclusions

Early measures of kidney biomarkers in patients who are critically ill are associated with MAKE-DC. This relationship appears to be greatest with serum NGAL and cystatin C, which display additive utility to a clinical prediction model. Trending serum NGAL may also have utility in predicting MAKE-DC.

Hierarchically Molecular Imprinted Porous Particles for Biomimetic Kidney Cleaning

Blood purification by adsorption of excessive biomolecules is vital for maintaining human health. Here, inspired by kidney self-purification, which removes a number of biomolecules with different sizes simultaneously, hierarchical molecular-imprinted inverse opal particles integrated with a herringbone microfluidic chip for efficient biomolecules cleaning are presented. The particle possesses combinative porous structure with both surface and interior imprints for the specific recognition of small molecules and biomacromolecules. Additionally, the presence of the herringbone mixer largely improve the adsorption efficiency due to enhanced mixing. Moreover, the inverse opal framework of the particles give rise to optical sensing ability for self-reporting of the adsorption states. These features, together with its reusability, biosafety, and biocompatibility, make the platform highly promising for clinical blood purification and artificial kidney construction.

Improved detection and precise relative quantification of the urinary cancer metabolite biomarkers - Creatine riboside, creatinine riboside, creatine and creatinine by UPLC-ESI-MS/MS: Application to the NCI-Maryland cohort population controls and lung cancer cases

Creatine riboside (CR) is a novel metabolite of cancer metabolism. It is a urinary diagnostic biomarker of lung and liver cancer risk and prognosis. The level of CR is highly positive correlated in tumor and urine indicating that it is derived from human lung and liver cancers. A precise and sensitive ultra-pressure liquid chromatography-tandem mass spectrometry (UPLC-ESI-MS/MS) method was developed and validated for simultaneous quantification of the noninvasive biomarker CR, along with creatinine riboside (CNR), and their precursors creatine and creatinine, utilizing the labeled internal standard creatine riboside-13C,15N2 (CR-13C,15N2). Chromatography was carried out on a hydrophilic interaction chromatography column under a gradient mobile phase condition. MRM transitions were monitored for CR (264.1 > 132.1, m/z), CNR (246.1 > 113.9, m/z), creatine (132.0 > 72.0, m/z), creatinine (114.0 > 85.8, m/z) and CR-13C,15N2 (267.1 > 134.9, m/z) with a 11.0 min run time in the positive mode ionization. The calibration plot of the method was linear over the concentration range of 4.50-10,000 nM. Method validation was performed according to regulatory guidelines established for sensitivity, selectivity, calibration curve, stability at different storage conditions, reinjection reproducibility, ruggedness with acceptable accuracy, and precision. This assay was applied for the quantification of CR along with CNR, creatine and creatinine in a subset of urine and serum samples from the National Cancer Institute - Maryland (NCI-MD) cohort population controls and lung cancer cases. It can be standardized and used in multiple laboratories for cancer diagnosis and determining the efficacy of cancer therapy and monitoring cancer recurrence.

Retinoic Acid Alleviates Cisplatin-Induced Acute Kidney Injury Through Activation of Autophagy

Cisplatin-induced acute kidney injury (CIAKI) is a common complication in patients receiving cisplatin-based chemotherapy. But the effective therapies for CIAKI are not available. Retinoic acid (RA), the main derivative of vitamin A, has the potential to reduce inflammation and fibrosis in renal injury. However, the effect and mechanism of RA on CIAKI are still unclear. The aim of this study is to investigate whether RA can alleviate CIAKI through activation of autophagy. In this study, we evaluated the effect of RA, RA’s effect on autophagy and apoptosis after cisplatin-induced injury on renal tubular epithelial cells (RTECs) by LDH assay, immunoblotting and TUNEL staining. Then we established Atg5^flox/flox:Cagg-Cre mice in which Cagg-Cre is tamoxifen inducible, and Atg5 is conditional deleted after tamoxifen injection. The effect of RA and RA’s effect on autophagy on CIAKI model were evaluated by biochemical assessment, hematoxylin and eosin (HE) staining, and immunoblotting in the control and autophagy deficient mice. In vitro, RA protected RTECs against cisplatin-induced injury, activated autophagy, and inhibited cisplatin-induced apoptosis. In vivo, RA attenuated cisplatin-induced tubular damage, shown by improved renal function, decreased renal cast formation, decreased NGAL expression, and activated autophagy in the control mice. Furthermore, the nephrotoxicity of cisplatin was aggravated, and the protective effect of RA was attenuated in autophagy deficient mice, indicating that RA works in an autophagy-dependent manner on CIAKI. RA activates autophagy and alleviates CIAKI in vivo and in vitro.Thus RA may be a renoprotective adjuvant for cisplatin-based chemotherapy.

High-Phosphate Diet Induces Exercise Intolerance and Impairs Fatty Acid Metabolism in Mice

BACKGROUND

Inorganic phosphate (Pi) is used extensively as a preservative and a flavor enhancer in the Western diet. Physical inactivity, a common feature of Western societies, is associated with increased cardiovascular morbidity and mortality. It is unknown whether dietary Pi excess contributes to exercise intolerance and physical inactivity.

METHODS

To determine an association between Pi excess and physical activity in humans, we assessed the relationship between serum Pi and actigraphy-determined physical activity level, as well as left ventricular function by cardiac magnetic resonance imaging, in DHS-2 (Dallas Heart Study phase 2) participants after adjusting for relevant variables. To determine direct effects of dietary Pi on exercise capacity, oxygen uptake, serum nonesterified fatty acid, and glucose were measured during exercise treadmill test in C57/BL6 mice fed either a high-Pi (2%) or normal-Pi (0.6%) diet for 12 weeks. To determine the direct effect of Pi on muscle metabolism and expression of genes involved in fatty acid metabolism, additional studies in differentiated C2C12 myotubes were conducted after subjecting to media containing 1 to 3 mmol/L Pi (pH 7.0) to simulate in vivo phosphate conditions.

RESULTS

In participants of the DHS-2 (n=1603), higher serum Pi was independently associated with reduced time spent in moderate to vigorous physical activity ( P=0.01) and increased sedentary time ( P=0.004). There was no association between serum Pi and left ventricular ejection fraction or volumes. In animal studies, compared with the control diet, consumption of high-Pi diet for 12 weeks did not alter body weight or left ventricular function but reduced maximal oxygen uptake, treadmill duration, spontaneous locomotor activity, fat oxidation, and fatty acid levels and led to downregulation of genes involved in fatty acid synthesis, release, and oxidation, including Fabp4, Hsl, Fasn, and Pparγ, in muscle. Similar results were recapitulated in vitro by incubating C2C12 myotubes with high-Pi media.

CONCLUSIONS

Our data demonstrate a detrimental effect of dietary Pi excess on skeletal muscle fatty acid metabolism and exercise capacity that is independent of obesity and cardiac contractile function. Dietary Pi may represent a novel and modifiable target to reduce physical inactivity associated with the Western diet.

Creatinine Deiminase: Characterization, Using in Enzymatic Creatinine Assay, and Production of the Enzyme

The goal of the review is description of the main characteristics of creatinine deiminase (CDI), an important bioanalytical tool for creatinine (Crn) assay. Crn is an essential metabolite for diagnostics of kidney disfunction and some other diseases, a biomarker to control the hemodialysis procedure, as well as an important analyte for sport medicine (estimation of general physiological status of athletes). We have described the important sources for CDI isolation, cloning of the corresponding gene, the construction of microbial recombinant strains, overproducing CDI, and characteristics of the enzyme from different microorganisms. There are reviewing also the new bioanalytical methods for quantitative determination of Crn, including enzymatic ones based on using CDI.

Combination of medical and health care based on digital smartphone-powered photochemical dongle for renal function management

Currently, the global healthcare market is increasing at high speed with the impendent global aging issue. Healthcare Industry 4.0 has emerged as an efficient solution towards the aging issue since it was integrated with ubiquitous medical sensors, big health processing platform, high bandwidth, speed technologies, and medical services, etc. It is believed to fulfil the requirement of the tremendously growing health market. The acquisition of medical data acts as the dominant precondition to implement the Healthcare Industry 4.0. In the same way, the widely available smartphone could serve as the best biomedical information collect station. In this study, a smartphone-powered photochemical dongle is demonstrated to precisely estimate blood creatinine from the fingertip blood, which works as a highly compact reflectance spectral analyzer with an enzymatically dry chemical test strip. Comparing with conventional laboratory facility for the evaluation and treatment of chronic kidney disease (CKD), it implemented the platform of point care with agreed accuracy. In order to estimate the efficiency of treatment and recovery of the CKD, the proposed photochemical dongle would provide a flexible and rapid platform for point of care. Furthermore, the proposed measured technology is very promising method for remote CKD management.

Urine Klotho Is Lower in Critically Ill Patients With Versus Without Acute Kidney Injury and Associates With Major Adverse Kidney Events

Supplemental Digital Content is available in the text.

Klotho and fibroblast growth factor-23 were recently postulated as candidate biomarkers and/or therapeutic targets in acute kidney injury. We examined whether urine Klotho and serum intact fibroblast growth factor-23 levels were differentially and independently associated with major adverse kidney events in critically ill patients with and without acute kidney injury.

Loss of Glis2/NPHP7 causes kidney epithelial cell senescence and suppresses cyst growth in the Kif3a mouse model of cystic kidney disease

Enlargement of kidney tubules is a common feature of multiple cystic kidney diseases in humans and mice. However, while some of these pathologies are characterized by cyst expansion and organ enlargement, in others, progressive interstitial fibrosis and kidney atrophy prevail. The Kif3a knockout mouse is an established non-orthologous mouse model of cystic kidney disease. Conditional inactivation of Kif3a in kidney tubular cells results in loss of primary cilia and rapid cyst growth. Conversely, loss of function of the gene GLIS2/NPHP7 causes progressive kidney atrophy, interstitial inflammatory infiltration, and fibrosis. Kif3a null tubular cells have unrestrained proliferation and reduced stabilization of p53 resulting in a loss of cell cycle arrest in the presence of DNA damage. In contrast, loss of Glis2 is associated with activation of checkpoint kinase 1, stabilization of p53, and induction of cell senescence. Interestingly, the cystic phenotype of Kif3a knockout mice is partially rescued by genetic ablation of Glis2 and pharmacological stabilization of p53. Thus, Kif3a is required for cell cycle regulation and the DNA damage response, whereas cell senescence is significantly enhanced in Glis2 null cells. Hence, cell senescence is a central feature in nephronophthisis type 7 and Kif3a is unexpectedly required for efficient DNA damage response and cell cycle arrest.

High dietary phosphate intake induces hypertension and augments exercise pressor reflex function in rats

An increasing number of studies have linked high dietary phosphate (Pi) intake to hypertension. It is well established that the rise in sympathetic nerve activity (SNA) and blood pressure (BP) during physical exertion is exaggerated in many forms of hypertension, which are primarily mediated by an overactive skeletal muscle exercise pressor reflex (EPR). However, it remains unknown whether high dietary Pi intake potentiates the EPR-mediated SNA and BP response to exercise. Accordingly, we measured renal SNA (RSNA) and mean BP (MBP) in normotensive Sprague-Dawley rats fed a normal Pi diet (0.6%, n = 13) or high Pi diet (1.2%, n = 13) for 3 mo. As previously reported, we found that resting BP was significantly increased by 1.2% Pi diet in both conscious and anesthetized animals. Activation of the EPR by electrically induced hindlimb contraction triggered greater increases in ΔRSNA and ΔMBP in the 1.2% compared with 0.6% Pi group (126 ± 25 vs. 42 ± 9%; 44 ± 5 vs. 14 ± 2 mmHg, respectively, P < 0.01). Activation of the muscle mechanoreflex, a component of the EPR, by passively stretching hindlimb muscle also evoked greater increases in ΔRSNA and ΔMBP in the 1.2% compared with 0.6% Pi group (109 ± 27 vs. 24 ± 7%, 38 ± 7 vs. 8 ± 2 mmHg, respectively, P < 0.01). A similar response was produced by hindlimb intra-arterial capsaicin administration to stimulate the metaboreflex arm of the EPR. Thus, our data demonstrate a novel action of dietary Pi loading in augmenting EPR function through overactivation of both the muscle mechanoreflex and metaboreflex.

Loss of diacylglycerol kinase epsilon in mice causes endothelial distress and impairs glomerular Cox-2 and PGE2 production

Thrombotic microangiopathy (TMA) is a disorder characterized by microvascular occlusion that can lead to thrombocytopenia, hemolytic anemia, and glomerular damage. Complement activation is the central event in most cases of TMA. Primary forms of TMA are caused by mutations in genes encoding components of the complement or regulators of the complement cascade. Recently, we and others have described a genetic form of TMA caused by mutations in the gene diacylglycerol kinase-ε (DGKE) that encodes the lipid kinase DGKε (Lemaire M, Fremeaux-Bacchi V, Schaefer F, Choi MR, Tang WH, Le Quintrec M, Fakhouri F, Taque S, Nobili F, Martinez F, Ji WZ, Overton JD, Mane SM, Nurnberg G, Altmuller J, Thiele H, Morin D, Deschenes G, Baudouin V, Llanas B, Collard L, Majid MA, Simkova E, Nurnberg P, Rioux-Leclerc N, Moeckel GW, Gubler MC, Hwa J, Loirat C, Lifton RP. Nat Genet 45: 531-536, 2013; Ozaltin F, Li BH, Rauhauser A, An SW, Soylemezoglu O, Gonul II, Taskiran EZ, Ibsirlioglu T, Korkmaz E, Bilginer Y, Duzova A, Ozen S, Topaloglu R, Besbas N, Ashraf S, Du Y, Liang CY, Chen P, Lu DM, Vadnagara K, Arbuckle S, Lewis D, Wakeland B, Quigg RJ, Ransom RF, Wakeland EK, Topham MK, Bazan NG, Mohan C, Hildebrandt F, Bakkaloglu A, Huang CL, Attanasio M. J Am Soc Nephrol 24: 377-384, 2013). DGKε is unrelated to the complement pathway, which suggests that unidentified pathogenic mechanisms independent of complement dysregulation may result in TMA. Studying Dgke knockout mice may help to understand the pathogenesis of this disease, but no glomerular phenotype has been described in these animals so far. Here we report that Dgke null mice present subclinical microscopic anomalies of the glomerular endothelium and basal membrane that worsen with age and develop glomerular capillary occlusion when exposed to nephrotoxic serum. We found that induction of cyclooxygenase-2 and of the proangiogenic prostaglandin E2 are impaired in Dgke null kidneys and are associated with reduced expression of the antithrombotic cell adhesion molecule platelet endothelial cell adhesion molecule-1/CD31 in the glomerular endothelium. Notably, prostaglandin E2 supplementation was able to rescue motility defects of Dgke knockdown cells in vitro and to restore angiogenesis in a test in vivo. Our results unveil an unexpected role of Dgke in the induction of cyclooxygenase-2 and in the regulation of glomerular prostanoids synthesis under stress.

Improved Gas Chromatographic Determination of Guanidino Compounds Using Isovaleroylacetone and Ethyl Chloroformate as Derivatizing Reagents

An improved GC method in terms of sensitivity and decrease in the analysis time has been developed for the analysis of eight guanidino compounds: guanidine (G), methylguanidine (MG), creatinine (CTN), guanidinoacetic acid (GAA), guanidinobutyric acid (GBA), guanidinopropionic acid (GPA), argenine (Arg), and guanidinosuccinic acid (GSA), using isovaleroylacetone (IVA) and ethyl chloroformate (ECF) as derivatizing reagents. The separation was obtained from column HP-5 (30 m × 0.32 mm i.d.) with film thickness of 0.25 μm within 11 min. The linear calibrations were obtained with 0.5 to 50 μg/mL with coefficient of determination (R(2)) within 0.9969 - 0.9998. Limits of detections (LODs) were within 5 - 140 ng/mL. The derivatization, separation and determination was repeatable (n = 6) with relative standard deviation (RSD) within 1.2 - 3.1%. The guanidino compounds were determined in deproteinized serum of healthy volunteers and uremic patients within below LOD to 8.8 μg/mL and below LOD to 43.99 μg/mL with RSD within 1.4 - 3.6%. The recovery of guanidino compounds calculated by standard addition from serum was within 96.1 - 98.9%, with RSD 1.4 - 3.6%.

Benzylic rearrangement stable isotope labeling for quantitation of guanidino and ureido compounds in thyroid tissues by liquid chromatography-electrospray ionization mass spectrometry

Benzylic rearrangement stable isotope labeling (BRSIL) was explored to quantify the guanidino and ureido compounds (GCs and UCs). This method employed a common reagent, benzil, to label the guanidino and ureido groups through nucleophilic attacking then benzylic migrating. The use of BRSIL was investigated in the analysis of five GCs (creatine, l-arginine, homoarginine, 4-guanidinobutyric acid, and methylguanidine) and two UCs (urea and citrulline). The labeling was found simple and specific. The introduction of bi-phenyl group and the generation of nitrogen heterocyclic ring in the benzil-d0/d5 labeled GCs and UCs improved the retention behaviors in liquid chromatography (LC) and increased the sensitivity of electrospray ionization mass spectrometry (ESI MS) detection. The fragment ion pairs of m/z 182/187 and m/z 210/215 from the benzil-d0/d5 tags facilitated the discovery of potential GCs and UCs candidates residing in biological matrices. The use of BRSIL combined with LC-ESI MS was applied for simultaneously quantitation of GCs and UCs in thyroid tissues. It was demonstrated that nine GCs and UCs were detected, six of which were further quantified based on corresponding standards. It was concluded that five GCs and UCs (l-arginine, homoarginine, 4-guanidinobutyric acid, methylguanidine, and citrulline) were statistically significantly different (p < 0.05) between the para-carcinoma and carcinoma thyroid tissue samples.

Colorimetric Detection of Creatinine Based on Plasmonic Nanoparticles via Synergistic Coordination Chemistry

A simple and portable colorimetric assay for creatinine detection is fabricated based on the synergistic coordination of creatinine and uric acid with Hg(2+) on the surface of gold nanoparticles, which exhibits good selectivity and sensitivity. Point-of-care clinical creatinine monitoring can be supported for monitoring renal function and diagnosing corresponding renal diseases at home.

Green tea polyphenol (-)-epigallocatechin-3-gallate restores Nrf2 activity and ameliorates crescentic glomerulonephritis

Crescentic glomerulonephritis (GN) is the most severe form of GN and is associated with significant morbidity and mortality despite aggressive immunotherapy with steroids, cytotoxic drugs, and plasmapheresis. We examined the therapeutic efficacy of the green tea polyphenol (−)-epigallocatechin-3-gallate (EGCG, 50 mg/kg BW/day x3weeks), a potent anti-inflammatory and anti-oxidant agent, on experimental crescentic GN induced in 129/svJ mice by administration of rabbit anti-mouse glomerular basement membrane sera. Routine histology and key molecules involved in inflammatory and redox signaling were studied. EGCG treatment significantly reduced mortality, decreased proteinuria and serum creatinine, and markedly improved renal histology when compared with vehicle-treated mice. The improvements in renal function and histology were accompanied by the restoration of Nrf2 signaling (which was impaired in vehicle-treated mice) as shown by increased nuclear translocation of Nrf2 and cytoplasmic glutamate cysteine ligase catalytic subunit, glutamate cysteine ligase modifier subunit, and glutathione peroxidase. EGCG-treated mice also showed reduction in p-Akt, p-JNK, p-ERK1/2 and p-P38 as well as restoration of PPARγ and SIRT1 levels. Lower dose of EGCG (25 mg/kg BW/day x2 weeks) treatment also significantly decreased proteinuria and serum creatinine, and markedly improved renal histology when compared with vehicle-treated mice. Thus, our data illustrate the efficacy of EGCG in reversing the progression of crescentic GN in mice by targeting multiple signaling and inflammatory pathways as well as countering oxidative stress.

Effect of collecting duct-specific deletion of both Rh B Glycoprotein (Rhbg) and Rh C Glycoprotein (Rhcg) on renal response to metabolic acidosis

The Rhesus (Rh) glycoproteins, Rh B and Rh C Glycoprotein (Rhbg and Rhcg, respectively), are ammonia-specific transporters expressed in renal distal nephron and collecting duct sites that are necessary for normal rates of ammonia excretion. The purpose of the current studies was to determine the effect of their combined deletion from the renal collecting duct (CD-Rhbg/Rhcg-KO) on basal and acidosis-stimulated acid-base homeostasis. Under basal conditions, urine pH and ammonia excretion and serum HCO3(-) were similar in control (C) and CD-Rhbg/Rhcg-KO mice. After acid-loading for 7 days, CD-Rhbg/Rhcg-KO mice developed significantly more severe metabolic acidosis than did C mice. Acid loading increased ammonia excretion, but ammonia excretion increased more slowly in CD-Rhbg/Rhcg-KO and it was significantly less than in C mice on days 1-5. Urine pH was significantly more acidic in CD-Rhbg/Rhcg-KO mice on days 1, 3, and 5 of acid loading. Metabolic acidosis increased phosphenolpyruvate carboxykinase (PEPCK) and Na(+)/H(+) exchanger NHE-3 and decreased glutamine synthetase (GS) expression in both genotypes, and these changes were significantly greater in CD-Rhbg/Rhcg-KO than in C mice. We conclude that 1) Rhbg and Rhcg are critically important in the renal response to metabolic acidosis; 2) the significantly greater changes in PEPCK, NHE-3, and GS expression in acid-loaded CD-Rhbg/Rhcg-KO compared with acid-loaded C mice cause the role of Rhbg and Rhcg to be underestimated quantitatively; and 3) in mice with intact Rhbg and Rhcg expression, metabolic acidosis does not induce maximal changes in PEPCK, NHE-3, and GS expression despite the presence of persistent metabolic acidosis.

Klotho has dual protective effects on cisplatin-induced acute kidney injury

Klotho protects the kidney from ischemia-reperfusion injury, but its effect on nephrotoxins is unknown. Here we determined whether Klotho protects the kidney from cisplatin toxicity. Cisplatin increased plasma creatinine and induced tubular injury, which were exaggerated in Klotho haplosufficient (Kl/+) and ameliorated in transgenic Klotho overexpressing (Tg-Kl) mice. Neutrophil gelatinase-associated lipocalin and active caspase-3 protein and the number of apoptotic cells in the kidney were higher in Kl/+ and lower in Tg-Kl compared with wild-type mice. Klotho suppressed basolateral uptake of cisplatin by the normal rat kidney cell line (NRK), an effect similar to cimetidine, a known inhibitor of organic cation transport (OCT). A decrease in cell surface and total OCT2 protein and OCT activity by Klotho was mimicked by β-glucuronidase. The Klotho effect was attenuated by β-glucuronidase inhibition. On the other hand, OCT2 mRNA was reduced by Klotho but not by β-glucuronidase. Moreover, cimetidine inhibited OCT activity but not OCT2 expression. Unlike cimetidine, Klotho reduced cisplatin-induced apoptosis from either the basolateral or apical side and even when added after NRK cells were already loaded with cisplatin. Thus, Klotho protects the kidney against cisplatin nephrotoxicity by reduction of basolateral uptake of cisplatin by OCT2 and a direct anti-apoptotic effect independent of cisplatin uptake. Klotho may be a useful agent to prevent and treat cisplatin-induced nephrotoxicity.

Connective tissue growth factor (CTGF) expression modulates response to high glucose

Connective tissue growth factor (CTGF) is an important mediator of fibrosis; emerging evidence link changes in plasma and urinary CTGF levels to diabetic kidney disease. To further ascertain the role of CTGF in responses to high glucose, we assessed the consequence of 4 months of streptozotocin-induced diabetes in wild type (+/+) and CTGF heterozygous (+/−) mice. Subsequently, we studied the influence of glucose on gene expression and protein in mice embryonic fibroblasts (MEF) cells derived from wildtype and heterozygous mice. At study initiation, plasma glucose, creatinine, triglyceride and cholesterol levels were similar between non-diabetic CTGF+/+ and CTGF+/− mice. In the diabetic state, plasma glucose levels were increased in CTGF+/+ and CTGF+/− mice (28.2 3.3 mmol/L vs 27.0 3.1 mmol/L), plasma triglyceride levels were lower in CTGF+/− mice than in CTGF+/+ (0.7 0.2 mmol/L vs 0.5 0.1 mmol/L, p<0.05), but cholesterol was essentially unchanged in both groups. Plasma creatinine was higher in diabetic CTGF+/+ group (11.7±1.2 vs 7.9±0.6 µmol/L p<0.01), while urinary albumin excretion and mesangial expansion were reduced in diabetic CTGF+/− animals. Cortices from diabetic mice (both CTGF +/+ and CTGF +/−) manifested higher expression of CTGF and thrombospondin 1 (TSP1). Expression of nephrin was reduced in CTGF +/+ animals; this reduction was attenuated in CTGF+/− group. In cultured MEF from CTGF+/+ mice, glucose (25 mM) increased expression of pro-collagens 1, IV and XVIII as well as fibronectin and thrombospondin 1 (TSP1). In contrast, activation of these genes by high glucose was attenuated in CTGF+/− MEF. We conclude that induction of Ctgf mediates expression of extracellular matrix proteins in diabetic kidney. Thus, genetic variability in CTGF expression directly modulates the severity of diabetic nephropathy.

Intercalated cell-specific Rh B glycoprotein deletion diminishes renal ammonia excretion response to hypokalemia

The ammonia transporter family member, Rh B Glycoprotein (Rhbg), is an ammonia-specific transporter heavily expressed in the kidney and is necessary for the normal increase in ammonia excretion in response to metabolic acidosis. Hypokalemia is a common clinical condition in which there is increased renal ammonia excretion despite the absence of metabolic acidosis. The purpose of this study was to examine Rhbg's role in this response through the use of mice with intercalated cell-specific Rhbg deletion (IC-Rhbg-KO). Hypokalemia induced by feeding a K(+)-free diet increased urinary ammonia excretion significantly. In mice with intact Rhbg expression, hypokalemia increased Rhbg protein expression in intercalated cells in the cortical collecting duct (CCD) and in the outer medullary collecting duct (OMCD). Deletion of Rhbg from intercalated cells inhibited hypokalemia-induced changes in urinary total ammonia excretion significantly and completely prevented hypokalemia-induced increases in urinary ammonia concentration, but did not alter urinary pH. We conclude that hypokalemia increases Rhbg expression in intercalated cells in the cortex and outer medulla and that intercalated cell Rhbg expression is necessary for the normal increase in renal ammonia excretion in response to hypokalemia.

Renal ammonia excretion in response to hypokalemia: effect of collecting duct-specific Rh C glycoprotein deletion

The Rhesus factor protein, Rh C glycoprotein (Rhcg), is an ammonia transporter whose expression in the collecting duct is necessary for normal ammonia excretion both in basal conditions and in response to metabolic acidosis. Hypokalemia is a common clinical condition associated with increased renal ammonia excretion. In contrast to basal conditions and metabolic acidosis, increased ammonia excretion during hypokalemia can lead to an acid-base disorder, metabolic alkalosis, rather than maintenance of acid-base homeostasis. The purpose of the current studies was to determine Rhcg's role in hypokalemia-stimulated renal ammonia excretion through the use of mice with collecting duct-specific Rhcg deletion (CD-Rhcg-KO). In mice with intact Rhcg expression, a K(+)-free diet increased urinary ammonia excretion and urine alkalinization and concurrently increased Rhcg expression in the collecting duct in the outer medulla. Immunohistochemistry and immunogold electron microscopy showed hypokalemia increased both apical and basolateral Rhcg expression. In CD-Rhcg-KO, a K(+)-free diet increased urinary ammonia excretion and caused urine alkalinization, and the magnitude of these changes did not differ from mice with intact Rhcg expression. In mice on a K(+)-free diet, CD-Rhcg-KO increased phosphate-dependent glutaminase (PDG) expression in the outer medulla. We conclude that hypokalemia increases collecting duct Rhcg expression, that this likely contributes to the hypokalemia-stimulated increase in urinary ammonia excretion, and that adaptive increases in PDG expression can compensate for the absence of collecting duct Rhcg.

Endothelial pentraxin 3 contributes to murine ischemic acute kidney injury

Toll-like receptor 4 (TLR4), a receptor for damage-associated molecular pattern molecules and also the lipopolysaccharide receptor, is required for early endothelial activation leading to maximal inflammation and injury during murine ischemic acute kidney injury. DNA microarray analysis of ischemic kidneys from TLR4-sufficient and -deficient mice showed that pentraxin 3 (PTX3) was upregulated only on the former while transgenic knockout of PTX3 ameliorated acute kidney injury. PTX3 was expressed predominantly on peritubular endothelia of the outer medulla of the kidney in control mice. Acute kidney injury increased PTX3 protein in the kidney and the plasma where it may be a biomarker of the injury. Stimulation by hydrogen peroxide, or the TLR4 ligands recombinant human high-mobility group protein B1 or lipopolysaccharide, induced PTX3 expression in the Mile Sven 1 endothelial cell line and in primary renal endothelial cells, suggesting that endothelial PTX3 was induced by pathways involving TLR4 and reactive oxygen species. This increase was inhibited by conditional endothelial knockout of myeloid differentiation primary response gene 88, a mediator of a TLR4 intracellular signaling pathway. Compared to wild-type mice, PTX3 knockout mice had decreased endothelial expression of cell adhesion molecules at 4 h of reperfusion, possibly contributing to a decreased early maladaptive inflammation in the kidneys of knockout mice. At 24 h of reperfusion, PTX3 knockout increased expression of endothelial adhesion molecules when regulatory and reparative leukocytes enter the kidney. Thus, endothelial PTX3 plays a pivotal role in the pathogenesis of ischemic acute kidney injury.

The green tea polyphenol (-)-epigallocatechin-3-gallate ameliorates experimental immune-mediated glomerulonephritis

The unchecked overproduction of reactive oxygen and nitrogen species by inflammatory cells can cause tissue damage, intensify inflammation, promote apoptosis, and accelerate the progression of immune-mediated glomerulonephritis (GN). Here we tested whether the anti-inflammatory and antioxidant properties of the green tea polyphenol (-)-epigallocatechin-3-gallate (EGCG) favorably affect the development of immune-mediated GN. Pretreatment of 129/svJ mice with EGCG from 2 days before to 2 weeks after the induction of GN led to reduced proteinuria and serum creatinine, and marked improvement in renal histology when compared with vehicle-pretreated diseased mice. This pretreatment reduced oxidative stress, and normalized osteopontin, p65/nuclear factor-κB, inducible nitric oxide synthase, nitric oxide metabolites, p-Akt, phosphorylated extracellular signal-regulated kinases 1 and 2, p47phox, and myeloperoxidase, all of which were elevated in vehicle-pretreated diseased mice. Levels of glutathione peroxidase and peroxisome proliferator-activated receptor-γ (PPARγ), both reduced in the vehicle-pretreated diseased mice, were normalized. This renoprotective effect was reversed by concomitant administration of the PPARγ antagonist GW9662 throughout the EGCG pretreatment period. Importantly, mortality and renal dysfunction were significantly attenuated even when the polyphenol treatment was initiated 1 week after the onset of GN. Thus, EGCG reversed the progression of immune-mediated GN in mice by targeting redox and inflammatory pathways.

Modulation of circulating purines and pyrimidines by physical exercise in the horse

This study was designed to examine the influence of sub-maximal exercise on purine and pyrimidine catabolism in horses. Ten horses were initially trained for 12 weeks at the end of which they underwent a standardized exercise test (SET); venous blood samples were taken at rest, 5 and 30 min after the SET. Six untrained healthy horses, from which a blood withdrawal was taken at rest, were used as the control group. Samples were analyzed by HPLC for the simultaneous determination of uric acid, uridine, β-pseudouridine and creatinine in plasma. Glucose and lactate were measured in blood. Trained horses had basal uridine levels significantly lower than sedentary horses. The SET caused significant increase in plasma uric acid, uridine, β-pseudouridine and creatinine. Following the SET, a significant negative correlation was found between plasma uridine and glucose, whilst a significant positive correlation was observed between plasma uric acid and creatinine. These results indicate that increase in energy demand during exercise in the horse causes not only the degradation of purine but also of pyrimidine compounds, the latter possibly exerting a control on glucose uptake as also demonstrated in human beings.

Sexual dimorphic evolution of metabolic programming in non-genetic non-alimentary mild metabolic syndrome model in mice depends on feed-back mechanisms integrity for pro-opiomelanocortin-derived endogenous substances

Previously, we showed that our post-natal handling model induces pro-opiomelanocortin-derived (POMC) endogenous systems alterations in male mice at weaning. These alterations last up to adult age, and are at the basis of adult hormonal and metabolic conditions similar to mild metabolic syndrome/type-2 diabetes. Here, we evaluate how sex influences post-natal programming in these metabolic conditions. Subjects are adult control (non-handled) female (NHF) and male (NHM) CD-1 mice; adult post-natal handled female (HF) and male (HM) mice. Handling consists of daily maternal separation (10 min) plus sham injection, from birth to weaning (21 days). In adult handled males (90-days old) we find not only POMC-derived hormones alterations (enhanced basal plasma corticosterone (+91%) and ACTH (+109%)) but also overweight (+5.4%), fasting hyperglycemia (+40%), hypertriglyceridemia (+21%), enhanced brain mRNA expression of hydroxysteroid(11-beta)dehydrogenase type-1 (HSD11B1) (+49%), and decreased mRNA-HSD11B2 (-39%). Conversely, uric acid, creatinine, HDL(C), total cholesterol, glucose and insulin incremental area under-the-curve are not affected. In females, post-natal handling does not produce both hormonal and dysmetabolic diabetes-like changes; but handling enhances n3- and n6-poly-unsaturated, and decreases saturated fatty acids content in erythrocyte membrane composition in HF versus NHF. In conclusion, for the first time we show that female sex in mice exerts effective protection against the hypothalamus-pituitary-adrenal homeostasis disruption induced by our post-natal handling model on POMC cleavage products; endocrine disruption is in turn responsible for altered metabolic programming in male mice. The role of sex hormones is still to be elucidated.

Collecting duct-specific Rh C glycoprotein deletion alters basal and acidosis-stimulated renal ammonia excretion

NH3 movement across plasma membranes has traditionally been ascribed to passive, lipid-phase diffusion. However, ammonia-specific transporters, Mep/Amt proteins, are present in primitive organisms and mammals express orthologs of Mep/Amt proteins, the Rh glycoproteins. These findings suggest that the mechanisms of NH3 movement in mammalian tissues should be reexamined. Rh C glycoprotein (Rhcg) is expressed in the collecting duct, where NH3 secretion is necessary for both basal and acidosis-stimulated ammonia transport. To determine whether the collecting duct secretes NH3 via Rhcg or via lipid-phase diffusion, we generated mice with collecting duct-specific Rhcg deletion (CD-KO). CD-KO mice had loxP sites flanking exons 5 and 9 of the Rhcg gene (Rhcg(fl/fl)) and expressed Cre-recombinase under control of the Ksp-cadherin promoter (Ksp-Cre). Control (C) mice were Rhcg(fl/fl) but Ksp-Cre negative. We confirmed kidney-specific genomic recombination using PCR analysis and collecting duct-specific Rhcg deletion using immunohistochemistry. Under basal conditions, urinary ammonia excretion was less in KO vs. C mice; urine pH was unchanged. After acid-loading for 7 days, CD-KO mice developed more severe metabolic acidosis than did C mice. Urinary ammonia excretion did not increase significantly on the first day of acidosis in CD-KO mice, despite an intact ability to increase urine acidification, whereas it increased significantly in C mice. On subsequent days, urinary ammonia excretion slowly increased in CD-KO mice, but was always significantly less than in C mice. We conclude that collecting duct Rhcg expression contributes to both basal and acidosis-stimulated renal ammonia excretion, indicating that collecting duct ammonia secretion is, at least in part, mediated by Rhcg and not solely by lipid diffusion.

High-throughput CZE-UV determination of arginine and dimethylated arginines in human plasma

Experimental studies document that increased asymmetric dimethylarginine (ADMA) blood levels inhibit NOS significantly, reducing NO generation. ADMA measurement often needs sample cleanup by SPE prior to chromatography and precolumn derivatization that cannot be easily employed in a routine clinical setting. We set up a new reliable CE method to measure ADMA, symmetric dimethylarginine (SDMA), and arginine without sample extraction or precolumn derivatization in order to examine their concentrations in human plasma. Sample was concentrated prior to CE injection and analytes were monitored by UV detection. CE analysis was performed in an uncoated fused-silica capillary, 75 microm id and 60.2 cm length (50 cm to the detection window), injecting 1 s water plug (0.5 psi) followed by 10 s of the sample (0.5 psi). Separation was carried out in a 50 mmol/L Tris-phosphate run buffer at pH 2.30, 15 degrees C and 15 kV (75 microA) at normal polarity. Recovery of plasma ADMA was 101-104% and inter-day CV was less than 3%. Assay performance was evaluated measuring the levels of arginine and its dimethyl derivatives in 77 subjects. Passing-Bablok regression and Bland-Altman test for methods comparison suggest that the data obtained by our method and by a reference CE-LIF assay are similar.

Acute variations in homocysteine levels are related to creatine changes induced by physical activity

BACKGROUND & AIMS

Although many studies have focused on the effects of the physical activity on plasma homocysteine (Hcy) levels, the data gathered up to now are contradictory. In fact, it is true that some researches highlighted an exercise-induced fall in Hcy concentrations, but there are many reports proving that the physical exercise does not contribute to depress plasma Hcy levels and/or that in some instances it would even produce an increase. As a result, the question about the nature of the relationship between Hcy and physical activity remains unanswered. In this study, we have investigated whether the modification in Hcy level after a moderate physical activity was explainable in the light of the common connection of physical activity and Hcy to creatine (Cn).

METHODS

In 16 young volunteers aged from 21 to 37, divided into sedentary (n=6) and athletes (n=10) sub-groups, before and after an incremental cycle ergometer stress test, performed every 30 days for 4 months, we measured the plasma levels of guanidino acetic acid (GAA), ornithine (Orn), glycine (Gly), arginine (Arg), methionine (Met) as well as the plasma levels of Cn and of total and reduced form of the homocysteine (tHcy, rHcy). By difference in the total proteins (tProt) amount between the pre- and post-exercise phases also the dehydration degree of the subjects was measured.

RESULTS

After exercise rHcy decreased, tHcy was unchanged while Cn increased. Gly, Arg and Met at the end of exercise remained unaffected whereas, interestingly, GAA decreased in both sub-groups while Orn was significant diminished in athletes and, although not significantly, the same trend was observable in the sedentaries group.

CONCLUSION

These findings support an interesting hypothesis on the key role of the creatine haemoconcentration as an important modality by which physical exercise would affect plasma Hcy levels.

Imprinted polymer-modified hanging mercury drop electrode for differential pulse cathodic stripping voltammetric analysis of creatine

The molecularly imprinted polymer [poly(p-aminobenzoicacid-co-1,2-dichloroethane)] film casting was made on the surface of a hanging mercury drop electrode by drop-coating method for the selective and sensitive evaluation of creatine in water, blood serum and pharmaceutical samples. The molecular recognition of creatine by the imprinted polymer was found to be specific via non-covalent (electrostatic) imprinting. The creatine binding could easily be detected by differential pulse, cathodic stripping voltammetric signal at optimised operational conditions: accumulation potential -0.01 V (versus Ag/AgCl), polymer deposition time 15s, template accumulation time 60s, pH 7.1 (supporting electrolyte< or =5 x 10(-4)M NaOH), scan rate 10 mV s(-1), pulse amplitude 25 mV. The modified sensor in the present study was found to be highly reproducible and selective with detection limit 0.11 ng mL(-1) of creatine. Cross-reactivity studies revealed no response to the addition of urea, creatinine and phenylalanine; however, some insignificant magnitude of current was observed for tryptophan and histidine in the test samples.

Plasma methionine determination by capillary electrophoresis-UV assay: application on patients affected by retinal venous occlusive disease

Methionine is an important amino acid involved in protein synthesis and transmethylation reactions. It is also the precursor of homocysteine and cysteine, two important risk factors for cardiovascular diseases. As homocysteine research has gained impulsion, the evaluation of plasma methionine concentrations has acquired importance. Methionine measurement generally has been performed by HPLC after o-phthalaldehyde derivatization. Its separation from other amino acids is time-consuming. We set up a new specific capillary electrophoresis method in which analyte derivatization was avoided by sample concentration before analysis. Methionine was detected by UV absorbance at 204 nm with a detection limit of 0.5 micromol/L. By a capillary with an effective length of 50 cm filled with 125 mmol/L Tris phosphate buffer at pH 2.3, the separation occurred in less than 14 min. Precision tests indicated a good test repeatability for both migration times (coefficient of variation [CV]<0.3%) and areas (CV<2.0%). Moreover, a good reproducibility of intraassay and interassay tests was obtained (CV<2.9% and CV<3.5%, respectively). The Passing-Bablok regression and the Bland-Altman test for methods comparison suggest that the data obtained by our method and by a reference HPLC assay are similar. Assay performance was evaluated measuring methionine concentrations in retinal venous occlusive disease.

Molecularly imprinted solid-phase extraction combined with molecularly imprinted polymer-sensor: a diagnostic tool applicable to creatine deficiency syndrome

Primary creatine deficiency syndromes (CDS) are a new group of disorders caused by guanidinoacetate methyltransferase (GAMT) deficiency, which affects endogenous creatine biosynthesis with depletion of body creatine. A deficiency in creatine can be corrected by treatment with oral creatine supplementation and this necessitates a simple and sensitive screening method for early detection of creatine in dilute physiologic fluids. In this work an artificial receptor, molecularly imprinted polymer (MIP), for creatine was used both as a material for solid-phase extraction (SPE) and as a sensing element in a voltammetric sensor. Using the combination of molecularly imprinted solid-phase extraction (MISPE) with a complementary MIP sensor, the minimum detectable amount was found to be 0.0015 ng mL(-1) (RSD = 1.3%, S/N = 3). The MISPE-MIP sensor combination provided up to 60-fold preconcentration, which was more than sufficient for achieving the required quantification limit 50 ng mL(-1) (or 0.0025 ng mL(-1) after 2 x 10(4)-fold dilution) for creatine in human blood serum.

Assay for the simultaneous determination of guanidinoacetic acid, creatinine and creatine in plasma and urine by capillary electrophoresis UV-detection

Guanidinoacetic acid (GAA) measurement has recently become of great interest for the diagnosis of creatine (Cn) metabolism disorders, and research calls for rapid and inexpensive methods for its detection in plasma and urine in order to assess a large number of patients. We propose a new assay for the measurement of GAA by a simple CZE UV-detection without previous sample derivatization. Plasma samples were filtered by Microcon-10 microconcentrators and directly injected into the capillary, while for urine specimens a simple water dilution before injection was needed. A baseline separation was obtained in less than 8 min using a 60.2 cm x 75 microm uncoated silica capillary, 75 mmol/L Tris-phosphate buffer pH 2.25 at 15 degrees C. The performance of the developed method was assessed by measuring plasma creatinine and Cn in 32 normal subjects and comparing the data obtained by the new method with those found with the previous CE assay. Our new method seems to be an inexpensive, fast and specific tool to assess a large number of patients both in clinical and in research laboratories.