Uremic Toxins and their Relation to Dialysis Efficacy.

Toxin retention is felt to be a major contributor to the development of uremia in patients with advanced chronic kidney disease and end-stage renal disease (ESRD). Uremic retention compounds are classically divided into 3 categories: small solutes, middle molecules, and protein-bound toxins. Compounds comprising the first category, for which the upper molecular weight limit is generally considered to be 500 Da, possess a high degree of water solubility and minimal or absent protein binding. The second category of middle molecules has largely evolved now to be synonymous with peptides and proteins that accumulate in uremia. Although not precisely defined, low-molecular weight proteins as a class have a molecular weight spectrum ranging from approximately 500 to 60,000 daltons. The final category of uremic retention compounds is protein-bound uremic toxins (PBUTs). As opposed to the above small, highly water-soluble toxins, which are largely by-products of protein metabolism, PBUTs have diverse origins and possess chemical characteristics that preclude the possibility of circulation in an unbound form despite being of low molecular weight. This review is the first in a series of papers designed to provide the current state of the art for extracorporeal treatment of ESRD. Subsequent papers in this series will address membranes, mass transfer mechanisms, and future directions. For small solutes and middle molecules, particular emphasis is placed on the important clinical trials that comprise the evidence base regarding the influence of dialytic solute removal on outcome. Because such trials do not exist for PBUTs, the discussion here is instead focused on solute characteristics and renal elimination mechanisms.

Zirconia--a stationary phase capable of the separation of polar markers of myocardial metabolism in hydrophilic interaction chromatography.

Creatine, phosphocreatine, and adenine nucleotides are highly polar markers of myocardial metabolism that are poorly retained on RP silica sorbents. Zirconia represents an alternative material to silica with high promise to be used in hydrophilic interaction chromatography (HILIC). This study describes a first systematic investigation of the ability of ZrO2 to separate creatine, phosphocreatine, adenosine 5'-monophosphate, adenosine 5'-diphosphate, and adenosine 5'-triphosphate and compares the results with those obtained on TiO2 . All analytes showed a HILIC-like retention pattern when mobile phases of different strengths were tested. Stronger retention and better column performance were achieved in organic-rich mobile phases as compared to aqueous conditions, where poor retention and insufficient column performance were observed. The effect of mobile phase pH and ionic strength was evaluated as well. The analysis of myocardial tissue demonstrated that all compounds were separated in a relevant biological material and thus proved ZrO2 as a promising phase for HILIC of biological samples that deserves further investigation.

A simple screening method using ion chromatography for the diagnosis of cerebral creatine deficiency syndromes.

Cerebral creatine deficiency syndromes (CCDS) are caused by genetic defects in L-arginine:glycine amidinotransferase, guanidinoacetate methyltransferase or creatine transporter 1. CCDS are characterized by abnormal concentrations of urinary creatine (CR), guanidinoacetic acid (GA), or creatinine (CN). In this study, we describe a simple HPLC method to determine the concentrations of CR, GA, and CN using a weak-acid ion chromatography column with a UV detector without any derivatization. CR, GA, and CN were separated clearly with the retention times (mean ± SD, n = 3) of 5.54 ± 0.0035 min for CR, 6.41 ± 0.0079 min for GA, and 13.53 ± 0.046 min for CN. This new method should provide a simple screening test for the diagnosis of CCDS.

Hydrophilic chromatographic determination of carnosine, anserine, balenine, creatine, and creatinine.

A new HPLC procedure based on hydrophilic interaction chromatography (HILIC) has been developed for the simultaneous determination of carnosine, anserine, balenine, creatine, and creatinine in meat. This is the first time that HILIC has been directly applied to the study of meat components, having the advantage of not requiring complex cleanup and/or sample derivatization procedures. The chromatographic separation has been developed using a silica column (4.6 x 150 mm, 3 microm), and the proposed methodology is simple, reliable, and fast (<13 min per sample). The method has been validated in terms of linearity, repeatability, reproducibility, and recovery and represents an interesting alternative to methods currently in use for determining the mentioned compounds and other polar substances. The detection limits are 5.64, 8.23, 3.66, 3.99, and 0.06 microg/mL for carnosine, anserine, balenine, creatine, and creatinine, respectively.

Separation methods applicable to urinary creatine and creatinine.

Urinary creatinine has been analyzed for many years as an indicator of glomerular filtration rate. More recently, interest in studying the uptake of creatine as a result of creatine supplementation, a practice increasingly common among bodybuilders and athletes, has lead to a need to measure urinary creatine concentrations. Creatine levels are of the same order of magnitude as creatinine levels when subjects have recently ingested creatine, while somewhat elevated urinary creatine concentrations in non-supplementing subjects can be an indication of a degenerative disease of the muscle. Urinary creatine and creatinine can be analyzed by HPLC using a variety of columns. Detection methods include absorption, fluorescence after post-column derivatization, and mass spectrometry, and some methods have been automated. Capillary zone electrophoresis and micellar electrokinetic capillary chromatography have also been used to analyze urinary creatine and creatinine. Creatine and creatinine have also been analyzed in serum and tissue using HPLC and CE, and many of these separations could also be applicable to urinary analysis.

Separation of urea, uric acid, creatine, and creatinine by micellar electrokinetic capillary chromatography with sodium cholate.

The capillary electrophoretic separation of the four nonprotein nitrogenous compounds (NPNs; urea, uric acid, creatine, and creatinine) typically employed in clinical and medical settings for the monitoring of renal function is described. Successful resolution of these compounds is achieved with the use of a bile salt micelle system composed of sodium cholate at phosphate buffer pH 7.4. The elution patterns of four NPNs are obtained within 30 min with a voltage of 30 kV. The effect of varying the applied voltage, temperature, and the mole ratio of phosphate buffer with bile salt surfactant on the migration behavior is also examined.

High-performance capillary electrophoresis-pure creatine monohydrate reduces blood lipids in men and women.

1. A randomized, double-blind, placebo-controlled trial utilizing creatine as a potential lipid-lowering agent was conducted to determine plasma lipid, lipoprotein, glucose, urea nitrogen and creatinine profiles in men and women ranging in age from 32 to 70 years. 2. Thirty-four subjects (18 men and 16 women) with total cholesterol concentrations exceeding 200 mg/dl received either a creatine supplement (5 g of creatine plus 1 g of glucose) or a glucose placebo (6 g of glucose) for 56 days. Creatine and placebo were taken orally four times a day for 5 days and then twice a day for 51 days. Plasma analyses were measured at baseline, 4 and 8 weeks of treatment, and at 4 weeks after cessation of treatment (week 12). 3. Significant reductions in plasma total cholesterol, triacylglycerols and very-low-density lipoprotein-C occurred within the creatine monohydrate group. Minor reductions in plasma total cholesterol from baseline (233 +/- 9 mg/dl) of 6% and 5% occurred at weeks 4 and 8, respectively, before returning to baseline at week 12. Baseline triacylglycerols (194 +/- 21 mg/dl) and very-low-density lipoprotein-C (39 +/- 4 mg/dl) were reduced by 23% and 22% at weeks 4 and 8, respectively, and remained attenuated by 26% at week 12. These results remained consistent when data were separated and analysed by gender. Finally, a small, but statistically significant increase in urea nitrogen was observed in women between baseline (11.8 +/- 0.7 mg/dl) and week 8 (13.8 +/- 0.7 mg/dl, P < 0.05). No significant differences were noted for low-density lipoprotein-C, high-density lipoprotein-C, total cholesterol/high-density lipoprotein ratio, glucose, creatinine, body mass, body mass index or physical activity within or between the experimental and placebo groups. However, a trend towards reduced blood glucose levels was present in males given creatine monohydrate (P = 0.051). 4. These preliminary data suggest that creatine monohydrate may modulate lipid metabolism in certain individuals. These observations may demonstrate practical efficacy to the hyperlipidaemic patient as well as providing possible new mechanistic insights into the cellular regulation of blood lipid concentrations.

Simultaneous determination of creatine compounds and adenine nucleotides in myocardial tissue by high-performance liquid chromatography.

A rapid high-performance liquid chromatography method was developed for the determination of creatine phosphate, creatine, adenine nucleotides, and related compounds in myocardial tissue. Analysis was performed by reversed-phase chromatography on a C18 column containing 3-microns particles, employing gradient elution and uv detection at 210 nm. Separation was achieved in less than 5 min. Total analysis time, including equilibration of the column after return of the gradient to starting conditions, was 8 min. The high reproducibility and short analysis time make this method suitable for the routine analysis of large series of samples.

Rapid separation of creatine, phosphocreatine and adenosine metabolites by ion-pair reversed-phase high-performance liquid chromatography in plasma and cardiac tissue.

A rapid ion-pair reversed-phase high-performance liquid chromatographic method has been developed for the simultaneous detection of creatine, phosphocreatine, hypoxanthine, inosine, adenosine, AMP, ADP, ATP, 8-azaguanine, 2-chloroadenosine, and 2'-O-methyladenosine. This method has proven useful for measuring changes in nucleotide concentrations in both heart tissue and plasma samples. Separation of the compounds of interest is achieved in less than 8 min with re-equilibration in 7 min, making the total run time 15 min. Separation is performed on a 3-microns Ultrasphere ODS column employing tetrabutylammonium phosphate as the ion-pair agent and dipotassium hydrogenphosphate as the counter ion. The accuracy, rapid separation, and re-equilibration time make this method particularly useful for the routine analysis of a large number of samples.

Separation of creatine from arginine in biological fluids by thin-layer chromatography.

Creatine in biological fluids was estimated using a modified Sakaguchi procedure. Interference by arginine was eliminated by thin-layer chromatography.