In Vivo Clearance and Elimination of Nine Marker Substances during Hemofiltration with Different Membranes

The handling of low, middle and high molecular weight markers was examined in seven stable dialysis patients during hemofiltration with different membranes. Four membranes were examined in a randomized, crossover order (polysulfone, polyamide, AN69 polyacrylonitrile, Asahi polyacrylonitrile) by measuring plasma and dialysate concentrations of phosphate, creatinine, vitamin B12, β2-microglobulin, furanic acid, hippuric acid, retinolbinding protein, alpha-1-antitrypsin, and albumin. Sieving coefficients and plasma clearances of β-microglobulin or retinol-binding protein were markedly or slightly lower during hemofiltration with the Asahi polyacrylonitrile membrane than with the other membranes (highest removal with polysulfone/AN69 polyacrylonitrile membranes). No differences of obvious clinical relevance could be seen between the four membranes. A high β2-microglobulin removal rate might be important to prevent dialysis-associated amyloidosis.

Associations between metabolomic compounds and incident heart failure among African Americans: the ARIC Study

Heart failure is more prevalent among African Americans than in the general population. Metabolomic studies among African Americans may efficiently identify novel biomarkers of heart failure. We used untargeted methods to measure 204 stable serum metabolites and evaluated their associations with incident heart failure hospitalization (n = 276) after a median follow-up of 20 years (1987-2008) by using Cox regression in data from 1,744 African Americans aged 45-64 years without heart failure at baseline from the Jackson, Mississippi, field center of the Atherosclerosis Risk in Communities (ARIC) Study. After adjustment for established risk factors, we found that 16 metabolites (6 named with known structural identities and 10 unnamed with unknown structural identities, the latter denoted by using the format X-12345) were associated with incident heart failure (P < 0.0004 based on a modified Bonferroni procedure). Of the 6 named metabolites, 4 are involved in amino acid metabolism, 1 (prolylhydroxyproline) is a dipeptide, and 1 (erythritol) is a sugar alcohol. After additional adjustment for kidney function, 2 metabolites remained associated with incident heart failure (for metabolite X-11308, hazard ratio = 0.75, 95% confidence interval: 0.65, 0.86; for metabolite X-11787, hazard ratio = 1.23, 95% confidence interval: 1.10, 1.37). Further structural analysis revealed X-11308 to be a dihydroxy docosatrienoic acid and X-11787 to be an isoform of either hydroxyleucine or hydroxyisoleucine. Our metabolomic analysis revealed novel biomarkers associated with incident heart failure independent of traditional risk factors.

Multivariate statistical interpretation of laboratory clinical data

Laboratory aids are extensively used in the diagnosis of diseases, in preventive medicine, and as management tools. Reference values of clinically healthy people serve as a guide to the clinician in evaluating biochemical parameters. Determination of 21 biochemical parameters of healthy persons using standard methods of analysis. Cluster analysis and principal components analysis were applied on the above 21 biochemical parameters data. The application of a typical classification approach as cluster analysis proved that four major groups of similarity between all 21 clinical parameters are formed, which correspond to the authors assumption of the existence of several summarizing pattern of clinical parameters such as “enzyme,” “major component excretion”, “general health state,” and “blood specific” pattern. These patterns appear also in the subsets obtained by separation of the general dataset into “male”, “female”, “young”, and “adult” healthy groups. The results obtained from principal components analysis have additionally proved the validity of a similar assumption. The intelligent data analysis on the clinical parameter dataset has shown that when a complex system is considered as a multivariate one, the information about the system substantially increases. All these results support an idea that probably a general health indicator could be constructed taking into account the existing classification groups in the list of clinical parameters.

Determination of urinary hippuric acid by micellar electrokinetic capillary chromatography

We propose a method for the simultaneous determination of hippuric acid (HA) and creatinine based on capillary micellar electrokinetic chromatography. Experimental conditions were 20 mM sodium phosphate, pH 7.20, 25 mM sodium dodecyl sulfate, 5% (v/v) acetonitrile. Electropherograms evidenced HA and creatinine peaks in less than 12 min. The method showed good linearity for both analytes and satisfactory within-day precision. The present method, which is accurate, sensitive, rapid and simple, may be applied to single-spot urine samples.

Hippurate participates in the correction of metabolic acidosis

Hippurate (Hip), an endogenous conjugate, belongs to the group of uremic toxins. Hip stimulates P-independent glutaminase (PIG) localized at the proximal luminal membrane, desamidating glutamine with the formation of ammonia, a dominant and adaptive elimination product of H+. This appears to be important because metabolic acidosis (MAC) does not stimulate PIG. Moreover, Hip inhibits ammonia production by P-dependent mitochondrial glutaminase (PDG) that is primarily stimulated by MAC. By this mechanism, it shifts the ammonia production from mitochondria to proximal tubular lumen. MAC stimulates Hip synthesis in the liver and kidney and increases Hip plasma concentration and even fractional excretion by the kidney, which creates an effective regulatory loop of ammoniagenesis. Thus, it appears that Hip by its participation in the correction of MAC possesses the modulatory function.

Capillary electrophoresis as a clinical tool. Determination of organic anions in normal and uremic serum using photodiode-array detection

We report the use of free solution capillary electrophoresis to identify and quantify low-molecular-mass compounds found in normal and uremic serum as well as in hemodialysate fluid. The method reported provides a multicomponent analysis, allowing a single-step screening for more than 19 metabolites in less than 16 min. Serum samples from healthy individuals and from patients who have been diagnosed with chronic renal failure are analyzed using a borate buffer system at pH 9.0, and an extended light path capillary. Several ionic sample constituents are identified by electrophoretic mobility, UV spectra, and spiking with authentic standards. An analysis of the relative concentration of several metabolites, including hypoxanthine, pseudouridine, hippuric acid, and uric acid is presented. Each of these four metabolites is found in both normal and uremic serum samples (limits of detection 1 to 6 microM). Moreover, each of these metabolites is present at significantly elevated levels in uremic patients. The method reported is shown to have promising clinical utility for profiling serum sample constituents, and for quantitative determination of a few important metabolites.

Subfractions in uremic plasma ultrafiltrate inhibit calcitriol metabolism

Previous study from our laboratory has demonstrated that uremic plasma ultrafiltrate suppresses both the production rate (PR) and metabolic clearance rate (MCR) of calcitriol in normal rats. To characterize the the substances responsible for the suppression of the synthesis and degradation of calcitriol, we fractionated 20 ml uremic plasma ultrafiltrates into 13 fractions using high-performance liquid chromatography (HPLC) and studied the effect of each fraction on calcitriol metabolism. We measured the MCR and PR of calcitriol in normal rats after they were infused for 20 hours with each fraction dissolved in 20 ml normal saline. Using a UV absorption and fluorescence emission technique, several known uremic compounds were identified as individual peaks corresponding to the fractions. We found that fractions 4, and 6 to 13 markedly reduced the MCR of calcitriol. The patterns of the MCR suppression by the HPLC fractions suggest that there were at least two groups of chemically distinguishable compounds. Infusion of a solution containing all 13 fractions of the uremic ultrafiltrate also inhibited the calcitriol synthesis. One of the 13 fractions (fraction 4, containing uric acid, xanthine, and hypoxanthine) was further fractionated into eight subfractions. Infusion of subfractions 4 to 7 markedly reduced both the PR and MCR of calcitriol. We conclude that uremic plasma ultrafiltrate contains factors that inhibit calcitriol synthesis and degradation. These substances have molecular weight less than 2,000 Daltons.

Defects in platelet adhesion and aggregate formation in uremic bleeding disorder can be attributed to factors in plasma

Uremia is associated with bleeding diathesis. Platelet adhesion to the subendothelium is inhibited by a factor in uremic plasma that may play a role in the disturbed hemostasis of uremic patients. In the formation of the hemostatic plug, platelet adherence is followed by stimulus-induced platelet aggregation and reinforcement by thrombin-generated fibrin. To study these processes in uremic blood, a newly developed thrombosis model was used. Perfusates anticoagulated with low-molecular-weight heparin were circulated over a matrix of stimulated cultured endothelial cells. By stimulation of the endothelial cells, tissue factor was synthesized and deposited in the matrix. When this tissue factor rich-matrix was exposed to flowing blood, local thrombin was formed via activation of the extrinsic coagulation pathway. With this system, platelet adhesion, thrombin-dependent platelet activation, and fibrin formation can all be studied at the same surface. In addition to an adhesion defect, decreased aggregate formation was also found in uremic perfusates. Normal platelets in uremic plasma showed similar results, which indicates that a factor in uremic plasma caused this adhesion and aggregation defect. Platelet aggregation in the system was dependent on endogenously formed thrombin. Fibrinopeptide A generation, however, was normal in uremic perfusates; therefore, uremic plasma has a normal capacity to form thrombin. Resuspension of washed uremic platelets in control plasma did not reverse the aggregation defect in perfusions. In contrast, aggregometer studies with isolated uremic platelets could not detect an abnormal response to threshold concentrations of exogenous thrombin. Thus, uremic toxin(s) cause defective aggregate formation in flow, but not necessarily in the aggregometer. This apparent discrepancy may be due to the higher shear forces in the flow system, which may prevent aggregate formation that is allowed in the aggregometer. Another explanation, that uremic platelets are less responsive to locally formed thrombin than they are to exogenously added thrombin, seems less likely.

Isolation, identification, and analysis of 4-acetylaminophenol-glucuronide in body fluids of dialyzed renal patients; a molecular mass marker for peritoneal diffusive transport

A noncharacteristic solute, appearing in gradient elution liquid chromatography (HPLC) profiles of body fluids of dialyzed renal patients, was isolated and identified by preparative HPLC, beta-glucuronidase induced enzymatic peak shift, and mass spectrometry. The compound was shown to be p-acetylaminophenol ('paracetamol')-glucuronide (PG). Serum and peritoneal dialysate PG concentrations were determined in a number of patients. Cuprophan in vivo dialyzer clearances were calculated. Peritoneal membrane mass transfer coefficients (MTC) of PG were calculated and compared with those of molecular mass markers for peritoneal diffusive mass transport studies (urea, creatinine, uric acid, and inulin). By extrapolation of an MTC versus molecular mass calibration line for urea, creatinine, and uric acid it is shown that PG behaves as expected from its molecular mass. We suggest that PG (Mr = 327) is suitable as a molecular mass marker for the molecular mass range between Mr 200 and 500. It may also be used as a marker for diffusive solute transport in hemodialysis treatment. The HPLC gradient elution technique used here appears to be suitable for the simultaneous analysis of the molecular mass markers creatinine, uric acid, and paracetamolglucuronide.

Hippuric acid and 3-carboxy-4-methyl-5-propyl-2-furanpropionic acid in serum and urine. Analytical approaches and clinical relevance in kidney diseases

Hippuric acid (HA) and 3-carboxy-4-methyl-5-propyl-2-furanpropionic acid (FA) were determined in serum, plasma, ultrafiltrate and urine by gas chromatography (GC), high-performance liquid chromatography and GC with mass-selective detection, and the methods were compared. As determined by affinity chromatography and analysis of serum and ultrafiltrate, 0.5% of FA in serum occurs free and 99.5% is bound to albumin. In haemodialysed patients with chronic renal failure, the plasma levels of HA and FA are elevated in comparison with normal controls and hospital patients without kidney diseases: HA, 11.1 +/- 5.7 mg/dl (n = 86); FA, 1.9 +/- 1.2 mg/dl (n = 86). Gradual increases in HA in serum, depending on the creatinine concentrations, are found in non-dialysed patients with chronic renal failure. By haemodialysis and haemofiltration the HA levels are lowered (53-66 and 30-36%, respectively), whereas FA is not dialysable.

Biochemical and neurophysiological parameters in hemodialyzed patients with chronic renal failure

Serum concentrations of accumulated solutes, standard clinical biochemistry, and parameters of clinical neuropathy, were determined in hemodialyzed patients with chronic renal failure. Analyses by high-performance liquid chromatography included creatinine, pseudouridine, urate, p-hydroxyhippuric acid, hippuric acid, indoxylsulfate, tryptophan, tyrosine, 3-indoleacetic acid, and a number of as-yet unidentified solutes. Standard biochemical parameters were measured; aluminium, parathyroid hormone, serum electrolytes and enzymes, hemoglobin, bilirubin, phosphate and urea. Measures of clinical neuropathy were: maximal motor nerve conduction velocities, and Hoffmann reflex latency. Several solutes had higher concentrations when nerve function was impaired. Serum total LDH, and total calcium levels correlated positively with values of the Hoffmann reflex, as did serum hippuric acid concentrations. Concentrations of p-hydroxyhippuric acid and two fluorescent compounds correlated negatively with motor nerve conduction velocities. In principal component analysis a number of 'organic acid-like' substances, like hippuric acid and p-hydroxyhippuric acid, were shown to associate multivariately with the neurophysiological variables while urea, creatinine, urate and phosphate were not.

Determination of hippuric acid and furanic acid in serum of dialysis patients and control persons by high-performance liquid chromatography

A high-performance liquid chromatographic method for the determination of 3-carboxy-4-methyl-5-propyl-2-furanpropionic acid (furanic acid) and hippuric acid in human serum is described. Quantitative data were obtained from 20 blood donors, 26 non-dialysis patients and 41 dialysis patients. In healthy persons hippuric acid ranged from 0.2 to 0.6 mg/dl, furanic acid from 0.13 to 0.53 mg/dl. In dialysis patients the mean concentration of hippuric acid was elevated to 17.2 mg/dl (range 1.7-50.8 mg/dl) and the mean concentration of furanic acid was elevated to 1.89 mg/dl (range 0.17-6.45 mg/dl). In patients without renal insufficiency the concentrations were not elevated. These data are in accordance with previous data obtained by gas chromatographic methods. Preliminary results indicate that hippuric acid and furanic acid may be more specific parameters than other uremic retention products, and better indicators for the need for dialysis treatment than urea or creatinine.