pH-Dependent Protein Binding Properties of Uremic Toxins In Vitro

Protein-bound uremic toxins (PBUTs) are difficult to remove using conventional dialysis treatment owing to their high protein-binding affinity. As pH changes the conformation of proteins, it may be associated with the binding of uremic toxins. Albumin conformation at pH 2 to 13 was analyzed using circular dichroism. The protein binding behavior between indoxyl sulfate (IS) and albumin was examined using isothermal titration calorimetry. Albumin with IS, and serum with IS, p-cresyl sulfate, indole acetic acid or phenyl sulfate, as well as serum from hemodialysis patients, were adjusted pH of 3 to 11, and the concentration of the free PBUTs was measured using mass spectrometry. Albumin was unfolded at pH < 4 or >12, and weakened interaction with IS occurred at pH < 5 or >10. The concentration of free IS in the albumin solution was increased at pH 4.0 and pH 11.0. Addition of human serum to each toxin resulted in increased free forms at acidic and alkaline pH. The pH values of serums from patients undergoing hemodialysis adjusted to 3.4 and 11.3 resulted in increased concentrations of the free forms of PBUTs. In conclusion, acidic and alkaline pH conditions changed the albumin conformation and weakened the protein binding property of PBUTs in vitro.

Untargeted Metabonomics of Genetically Modified Cows Expressing Lactoferrin Based on Serum and Milk

Metabolites of serum and milk from genetically modified (GM) cows and contrast check (CK) cows were comparatively investigated. Serum and milk were collected from genetically modified (GM) cows and contrast check (CK) cows, and then, they were analyzed using ultraperformance liquid chromatography-mass spectrometry (UPLC-MS) and gas chromatography-mass spectrometry (GC-MS). Although the level of some blood biochemical indexes for GM cows was shifted up or down, they were generally in normal physiological condition. Serum samples from lactoferrin GM cows exhibited reduced levels of amino acids and elevated levels of indoleacetate, α-keto acids, long-chain fatty acids, etc. GM milk possessed elevated levels of pentose and amino sugar metabolites, including arabitol, xylulose, glucuronate, and N-acetylgalactosamine. Interestingly, some essential nutrients, such as certain unsaturated fatty acids (e.g., eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), and docosapentaenoic acid (DPA)), and some necessary rare sugars were significantly upregulated. Compared to the CK group, a Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis was conducted based on the increased or decreased metabolites identified in the serum and milk samples of the GM group. The results showed that the GM cows were in healthy condition and their milk has improved benefits for customers. The milk from genetically modified cows was found to be a promising milk source for producing recombinant human lactoferrin (rhLF) for human beings.

Selective Transport of Protein-Bound Uremic Toxins in Erythrocytes

To better understand the kinetics of protein-bound uremic toxins (PBUTs) during hemodialysis (HD), we investigated the distribution of hippuric acid (HA), indole-3-acetic acid (IAA), indoxyl sulfate (IS), and p-cresyl sulfate (pCS) in erythrocytes of HD patients. Their transport across the erythrocyte membrane was explored in the absence of plasma proteins in vitro in a series of loading and unloading experiments of erythrocytes from healthy subjects and HD patients, respectively. Furthermore, the impact of three inhibitors of active transport proteins in erythrocytes was studied. The four PBUTs accumulated in erythrocytes from HD patients. From loading and unloading experiments, it was found that (i) the rate of transport was dependent on the studied PBUT and increased in the following sequence: HA < IS < pCS < IAA and (ii) the solute partition of intra- to extra-cellular concentrations was uneven at equilibrium. Finally, inhibiting especially Band 3 proteins affected the transport of HA (both in loading and unloading), and of IS and pCS (loading). By exploring erythrocyte transmembrane transport of PBUTs, their kinetics can be better understood, and new strategies to improve their dialytic removal can be developed.

The Effect of Sevelamer on Serum Levels of Gut-Derived Uremic Toxins: Results from In Vitro Experiments and A Multicenter, Double-Blind, Placebo-Controlled, Randomized Clinical Trial

High serum levels of gut-derived uremic toxins, especially p-cresyl sulfate (pCS), indoxyl sulfate (IS) and indole acetic acid (IAA), have been linked to adverse outcomes in patients with chronic kidney disease (CKD). Sevelamer carbonate could represent an interesting option to limit the elevation of gut-derived uremic toxins. The aim of the present study was to evaluate the adsorptive effect of sevelamer carbonate on different gut-derived protein-bound uremic toxins or their precursors in vitro, and its impact on the serum levels of pCS, IS and IAA in patients with CKD stage 3b/4. For the in vitro experiments, IAA, p-cresol (precursor of pCS) and indole (precursor of IS), each at a final concentration of 1 or 10 µg/mL, were incubated in centrifugal 30 kDa filter devices with 3 or 15 mg/mL sevelamer carbonate in phosphate-buffered saline at a pH adjusted to 6 or 8. Then, samples were centrifuged and free uremic toxins in the filtrates were analyzed. As a control experiment, the adsorption of phosphate was also evaluated. Additionally, patients with stage 3b/4 CKD (defined as an eGFR between 15 and 45 mL/min per 1.73 m²) were included in a multicenter, double-blind, placebo-controlled, randomized clinical trial. The participants received either placebo or sevelamer carbonate (4.8 g) three times a day for 12 weeks. The concentrations of the toxins and their precursors were measured using a validated high-performance liquid chromatography method with a diode array detector. In vitro, regardless of the pH and concentration tested, sevelamer carbonate did not show adsorption of indole and p-cresol. Conversely, with 10 µg/mL IAA, use of a high concentration of sevelamer carbonate (15 mg/mL) resulted in a significant toxin adsorption both at pH 8 (mean reduction: 26.3 ± 3.4%) and pH 6 (mean reduction: 38.7 ± 1.7%). In patients with CKD stage 3b/4, a 12-week course of treatment with sevelamer carbonate was not associated with significant decreases in serum pCS, IS and IAA levels (median difference to baseline levels: −0.12, 0.26 and −0.06 µg/mL in the sevelamer group vs. 1.97, 0.38 and 0.05 µg/mL in the placebo group, respectively). Finally, in vitro, sevelamer carbonate was capable of chelating a gut-derived uremic toxin IAA but not p-cresol and indole, the precursors of pCS and IS in the gut. In a well-designed clinical study of patients with stage 3b/4 CKD, a 12-week course of treatment with sevelamer carbonate was not associated with significant changes in the serum concentrations of pCS, IS and IAA.

Association between Protein-Bound Uremic Toxins and Asymptomatic Cardiac Dysfunction in Patients with Chronic Kidney Disease

Although the relationship between protein-bound uremic toxins (PBUTs) and cardiac structure and cardiac mortality in chronic kidney disease (CKD) has been studied in the past, the association between cardiac dysfunction and PBUTs has not yet been studied. We therefore evaluated the association between impaired peak cardiac performance and the serum free and total concentrations of potentially cardiotoxic PBUTs. In a cross-sectional study of 56 male CKD patients (stages 2–5 (pre-dialysis)) who were asymptomatic with no known cardiac diseases or diabetes we measured peak cardiac power (CPO_max), aerobic exercise capacity (VO_2max), and echocardiographic parameters of cardiac morphology and evaluated their association with PBUTs. The serum total and free concentrations of indoxyl sulfate (IXS), p-cresyl sulfate (PCS), p-cresyl glucuronide, indole acetic acid, and hippuric acid showed significant negative correlation with CPO_max and VO_2max. IXS and PCS were independently associated with CPO_max and VO_2max even after controlling for eGFR. No correlation between left ventricular mass index (LVMI) and PBUTs was seen. The present study for the first time has demonstrated the association between subclinical cardiac dysfunction in CKD and serum levels of a panel of PBUTs. Further studies are required to evaluate the mechanism of cardiotoxicity of the individual uremic toxins.

The Impact of Uremic Toxicity Induced Inflammatory Response on the Cardiovascular Burden in Chronic Kidney Disease

Uremic toxin (UT) retention in chronic kidney disease (CKD) affects biological systems. We aimed to identify the associations between UT, inflammatory biomarkers and biomarkers of the uremic cardiovascular response (BUCVR) and their impact on cardiovascular status as well as their roles as predictors of outcome in CKD patients. CKD patients stages 3, 4 and 5 (n = 67) were recruited and UT (indoxyl sulfate/IS, p-cresil sulfate/pCS and indole-3-acetic acid/IAA); inflammatory biomarkers [Interleukin-6 (IL-6), high sensitivity C reactive protein (hsCRP), monocyte chemoattractant protein-1 (MCP-1), soluble vascular adhesion molecule-1 (sVCAM-1), soluble intercellular adhesion molecule-1 (sICAM-1) and soluble Fas (sFas)] and BUCVRs [soluble CD36 (sCD36), soluble receptor for advanced glycation end products (sRAGE), fractalkine] was measured. Patients were followed for 5.2 years and all causes of death was used as the primary outcome. Artery segments collected at the moment of transplantation were used for the immunohistochemistry analysis in a separate cohort. Estimated glomerular filtration rate (eGFR), circulating UT, plasma biomarkers of systemic and vascular inflammation and BUCVR were strongly interrelated. Patients with plaque presented higher signs of UT-induced inflammation and arteries from CKD patients presented higher fractalkine receptor (CX3CR1) tissue expression. Circulating IS (p = 0.03), pCS (p = 0.007), IL-6 (p = 0.026), sFas (p = 0.001), sCD36 (p = 0.01) and fractalkine (p = 0.02) were independent predictors of total mortality risk in CKD patients. Our results reinforce the important role of uremic toxicity in the pathogenesis of cardiovascular disease (CVD) in CKD patients through an inflammatory pathway.

Does the adequacy parameter Kt/V(urea) reflect uremic toxin concentrations in hemodialysis patients?

Hemodialysis aims at removing uremic toxins thus decreasing their concentrations. The present study investigated whether Kt/V_urea, used as marker of dialysis adequacy, is correlated with these concentrations. Predialysis blood samples were taken before a midweek session in 71 chronic HD patients. Samples were analyzed by colorimetry, HPLC, or ELISA for a broad range of uremic solutes. Solute concentrations were divided into four groups according to quartiles of Kt/V_urea, and also of different other parameters with potential impact, such as age, body weight (BW), Protein equivalent of Nitrogen Appearance (PNA), Residual Renal Function (RRF), and dialysis vintage. Dichotomic concentration comparisons were performed for gender and Diabetes Mellitus (DM). Analysis of Variance in quartiles of Kt/V_urea did not show significant differences for any of the solute concentrations. For PNA, however, concentrations showed significant differences for urea (P<0.001), uric acid (UA), p-cresylsulfate (PCS), and free PCS (all P<0.01), and for creatinine (Crea) and hippuric acid (HA) (both P<0.05). For RRF, concentrations varied for β₂-microglobulin (P<0.001), HA, free HA, free indoxyl sulfate, and free indole acetic acid (all P<0.01), and for p-cresylglucuronide (PCG), 3-carboxy-4-methyl-5-propyl-2-furanpropionic acid (CMPF), free PCS, and free PCG (all P<0.05). Gender and body weight only showed differences for Crea and UA, while age, vintage, and diabetes mellitus only showed differences for one solute concentration (UA, UA, and free PCS, respectively). Multifactor analyses indicated a predominant association of concentration with protein intake and residual renal function. In conclusion, predialysis concentrations of uremic toxins seem to be dependent on protein equivalent of nitrogen appearance and residual renal function, and not on dialysis adequacy as assessed by Kt/V_urea. Efforts to control intestinal load of uremic toxin precursors by dietary or other interventions, and preserving RRF seem important approaches to decrease uremic solute concentration and by extension their toxicity.

Pharmacological separation between peripheral and central functions of cyclooxygenase-2 with CIAA, a novel cyclooxygenase-2 inhibitor

There are many reports concerning the physiological and pathological involvement of cyclooxygenase (COX)-2 in the central nervous system and peripheral tissue cells. Selective COX-2 inhibitors that mainly distribute peripherally have not been reported thus far. Therefore central and peripheral roles of COX-2 remain classified pharmacologically. In this study, in vivo pharmacological profiles of CIAA ([6-chloro-2-(4-chlorobenzoyl)-1H-indol-3-yl]acetic acid), a novel selective COX-2 inhibitor which distributes at higher concentrations in plasma than in brain, were compared with those of well-known selective COX-2 inhibitors, celecoxib and rofecoxib. Additionally, the possibility of pharmacological separation between peripheral and central actions of COX-2 with the inhibitors was investigated. CIAA selectively inhibited COX-2 activity compared with COX-1 in in vitro assays with rat whole blood. The compound exhibited lower brain penetration and higher plasma concentration (the brain/plasma concentration ratio was approximately 0.02) than celecoxib and rofecoxib after oral administration. Therefore, CIAA is mainly expected to act peripherally. Edema and prostaglandin E2 (PGE2) production in Carrageenan-injected rat paws, and pyrexia and PGE2 production in the brain in lipopolysaccharide (LPS)-injected rats were measured in in vivo experiments. CIAA exhibited lower ratios of anti-pyretic/anti-edematous activities and of inhibitory activities of PGE2 production in brain/paw than those of celecoxib and rofecoxib, and these ratios well-reflected brain/plasma concentration ratios. In conclusion, we discovered a novel selective COX-2 inhibitor, CIAA, which distributes at higher concentrations in plasma than in brain, which would make possible the pharmacological separation of the peripheral and central functions of COX-2.

Involvement of organic anion transporters in the efflux of uremic toxins across the blood-brain barrier

Renal failure causes multiple physiological changes involving CNS dysfunction. In cases of uremia, there is close correlation between plasma levels of uremic toxins [e.g. 3-carboxy-4-methyl-5-propyl-2-furanpropionate (CMPF), hippurate (HA) and indoleacetate (IA)] and the degree of uremic encephalopathy, suggesting that uremic toxins are involved in uremic encephalopathy. In order to evaluate the relevance of uremic toxins to CNS dysfunction, we investigated directional transport of uremic toxins across the blood-brain barrier (BBB) using in vivo integration plot analysis and the brain efflux index method. We observed saturable efflux transport of [(3)H]CMPF, [(14)C]HA and [(3)H]IA, which was inhibited by probenecid. For all uremic toxins evaluated, apparent efflux clearance across the BBB was greater than apparent influx clearance, suggesting that these toxins are predominantly transported from the brain to blood across the BBB. Saturable efflux transport of [(3)H]CMPF, [(14)C]HA and [(3)H]IA was completely inhibited by benzylpenicillin, which is a substrate of rat organic anion transporter 3 (rOat3). Taurocholate and digoxin, which are common substrates of rat organic anion transporting polypeptide (rOatp), partially inhibited the efflux of [(3)H]CMPF. Transport experiments using a Xenopus laevis oocyte expression system revealed that CMPF, HA and IA are substrates of rOat3, and that CMPF (but not HA or IA) is a substrate of rOap2. These results suggest that rOat3 mediates brain-to-blood transport of uremic toxins, and that rOatp2 is involved in efflux of CMPF. Thus, conditions typical of uremia can cause inhibition of brain-to-blood transport involving rOat3 and/or rOatp2, leading to accumulation of endogenous metabolites and drugs in the brain.

Behavior of non-protein-bound and protein-bound uremic solutes during daily hemodialysis

BACKGROUND

In the last few years, renewed interest in daily short hemodialysis (DHD; six 2-hour sessions per week) has become apparent as a consequence of the better clinical outcome of patients treated by this schedule. Uremic syndrome is characterized by the retention of a large number of toxins with different molecular masses and chemical properties. Some toxins are water soluble and non-protein bound, whereas others are partially lipophilic and protein bound. There is increased evidence that protein-bound toxins are responsible for the biochemical and functional alterations present in uremic syndrome, and the kinetics of urea is not applicable to these substances for their removal. The aim of this study is to investigate whether DHD is accompanied by increased removal of non-protein-bound and protein-bound toxins and a decrease in their prehemodialysis (pre-HD) serum levels.

PATIENTS AND METHODS

We studied 14 patients with end-stage renal disease treated by standard HD (SHD; three 4-hour sessions per week) for at least 6 months and randomly assigned them to a two-period crossover study (SHD to DHD and DHD to SHD). Patients maintained the same dialyzer, dialysate, and Kt/V during the entire study. At the end of 6 months of SHD and 6 months of DHD, we evaluated hemoglobin levels, hematocrits, recombinant human erythropoietin doses, and pre-HD and post-HD concentrations of serum urea, creatinine, uric acid, and the following protein-bound toxins: 3-carboxy-4-methyl-5-propyl-2-furanpropionic acid, p-cresol, indole-3-acetic acid, indoxyl sulfate, and hippuric acid.

RESULTS

Values for hemoglobin, hematocrit, and recombinant human erythropoietin dose did not change during the two study periods. Pre-HD concentrations of creatinine, urea, and uric acid decreased on DHD (creatinine, from 8.7 +/- 1.9 to 7.8 +/- 1.6 mg/dL; P < 0.05; urea, from 149.4 +/- 28.8 to 132.7 +/- 40 mg/dL; P = 0.05; uric acid, from 9.14 +/- 1.49 to 8.16 +/- 1.98 mg/dL; P = 0.06). Concerning protein-bound toxins, lower pre-HD levels during DHD were reported for indole-3-acetic acid (SHD, 0.16 +/- 0.04 mg/dL; DHD, 0.13 +/- 0.03 mg/dL; P = 0.01), indoxyl sulfate (SHD, 3.35 +/- 1.68 mg/dL; DHD, 2.85 +/- 1.08 mg/dL; P = 0.02), and p-cresol at the borderline of significance (SHD, 0.96 +/- 0.59 mg/dL; DHD, 0.78 +/- 0.33 mg/dL; P = 0.07).

CONCLUSION

Such non-protein-bound compounds as uric acid, creatinine, and urea were removed significantly better by DHD, and pre-HD serum levels were reduced. Furthermore, pre-HD concentrations of some protein-bound solutes, such as indole-3-acetic acid, indoxyl sulfate, and p-cresol, also were lower during DHD.

Serum substances that interfere with thyroid hormone assays in patients with chronic renal failure

OBJECTIVE

Serum thyroid hormone concentrations in patients with chronic renal failure are usually low, despite normal serum TSH levels. We investigated the effect on thyroid hormone assays of serum dialysable organic acids that are elevated in uraemic patients.

PATIENTS

Serum samples from 42 patients with chronic renal failure who were receiving haemodialysis and 37 sex- and age-matched healthy subjects were examined.

DESIGN AND MEASUREMENTS

Serum thyroid hormone concentrations were measured with an analogue radioimmunoassay (RIA), a labelled antibody assay, and an equilibrium dialysis/RIA method. Serum concentrations of organic acids were determined with high performance liquid chromatography.

RESULTS

Serum thyroid hormone levels determined by an analogue RIA and a labelled antibody assay in uraemic patients increased, and serum concentrations of organic acids decreased following haemodialysis. A significant association existed between serum free T3 (FT3) levels determined by an analogue RIA and serum concentrations of indoxyl sulphate (IS) prior to dialysis. There was also a significant association between serum free T4 (FT4) levels determined by an analogue RIA and serum concentration of IS and hippuric acid (HA) prior to dialysis. There was a significant association between the changes of serum concentrations of indole acetic acid (IAA) and FT4 concentrations prior to and following haemodialysis when determined by an analogue RIA. Serum FT3 and FT4 levels significantly decreased after the addition of IS to serum from healthy subjects when determined by an analogue RIA but not by a labelled antibody assay. Serum FT4 levels, but not FT3 levels, decreased after addition of IAA when determined by an analogue RIA. Serum FT4 concentrations determined by an equilibrium dialysis/RIA were significantly higher than those determined by the other two methods. The addition of IS, IAA, and HA to serum samples from healthy subjects significantly increased FT4 concentrations when determined by an equilibrium dialysis/RIA method.

CONCLUSIONS

Increased serum levels of indoxyl sulphate, indole acetic acid and hippuric acid in sera of uraemic patients may interfere with thyroid hormone measurements when an analogue radioimmunoassay is used. In contrast, there was little Interference with a labelled antibody assay. Dialysable organic acids may also interfere with thyroid hormone assays determined by an equilibrium dialysis/radioimmunoassay method.

Determination of indomethacin, its metabolites and their glucuronides in human plasma and urine by means of direct gradient high-performance liquid chromatographic analysis. Preliminary pharmacokinetics and effect of probenecid

Indomethacin is metabolized in humans by O-demethylation, and by acyl glucuronidation to the 1-O-glucuronide. Indomethacin, its metabolite O-desmethylindomethacin (DMI) and their conjugates can be measured directly by gradient high-performance liquid chromatographic analysis without enzymic deglucuronidation. The glucuronide conjugates were isolated by preparative HPLC from human urine samples. In plasma only indomethacin was present. No isoglucuronides were present in acidic urine of the volunteer. The possible metabolite deschlorobenzoylindomethacin (DBI) was not detectable in urine. Calibration curves were constructed by enzymic deconjugation of samples containing different concentrations of isolated indomethacin acyl glucuronide, DMI acyl glucuronide and DMI ether glucuronide. The limit of quantitation of indomethacin in plasma is 0.060 microgram/ml. The limits of quantitation in urine are: indomethacin 0.053 microgram/ml, DMI 0.065 microgram/ml, DMI acyl glucuronide 0.065 microgram/ml and DMI ether glucuronide 0.254 microgram/ml. A pharmacokinetic profile of indomethacin is shown, and some preliminary pharmacokinetic parameters of indomethacin obtained from one human volunteer are given. Probenecid inhibits the formation of both the ether and the acyl glucuronide of DMI.

Stereoselective disposition of etodolac enantiomers in synovial fluid

The synovial fluid (SF) uptake of the chiral nonsteroidal anti-inflammatory drug, etodolac, was studied in six arthritic patients, 2 hours (n = 1) or 12 hours (n = 5) after a single 200 mg dose of racemate. Marked stereoselectivity was seen in both SF and plasma; concentrations of pharmacologically inactive R-etodolac were up to 10-fold greater than active S-etodolac. Concentrations of S-etodolac were greater in SF than in plasma (SF:plasma ratio = 1.98 +/- 0.8): No such difference was seen for R-etodolac (SF:plasma = 0.91 +/- 0.3). Considerable concentrations of conjugated enantiomers were present in SF. In vitro equilibrium dialysis studies in drug-spiked samples showed that the unbound fraction of both enantiomers in SF was greater than in plasma; both fluids bound R more extensively than S etodolac. Therapeutically active S-etodolac has greater concentrations in synovial fluid than plasma during the post-distributive phase, which may be of possible clinical relevance.

The effect of renal transplantation on a major endogenous ligand retained in uremic serum

The effects of renal transplantation on serum concentrations of 3-carboxy-4-methyl-5-propyl-2-furanpropanoic acid (CMPF) and indole-3-acetic acid (IAA), which are endogenous ligands retained in uremic serum, and on phenytoin binding to serum protein were investigated. IAA, a weakly bound ligand, was rapidly excreted by the transplanted kidney during the first one to three days after renal transplantation, but CMPF, a strongly bound ligand, was slowly excreted. The binding defect of phenytoin was partially corrected by transplantation during the period of study. The results suggested that the prolonged drug binding defect observed despite successful renal transplantation is caused by a slower decrease of strongly bound ligands such as CMPF retained in uremic serum; hypoalbuminemia, usually observed after transplantation, may also contribute to this phenomenon.

Application of a stereospecific high-performance liquid chromatography assay to a pharmacokinetic study of etodolac enantiomers in humans

An HPLC assay suitable for pharmacokinetic analysis of enantiomers of etodolac [(+/-)-1,8-diethyl-1,3,4,9-tetrahydropyrano[3,4-b] indole-1-acetic acid] was developed. Following addition of internal standard (IS), (+/-)-2-(4-benzoylphenyl)butyric acid, the constituents were extracted from the specimen into a mixture of isooctane:isopropanol (95:5). The organic layer was evaporated and the drug and IS were sequentially derivatized with ethyl chloroformate and iota(-)-alpha-phenylethylamine. The diastereoisomers thus formed were extracted and chromatographed on a normal-phase column, with a mobile phase consisting of hexane:ethyl acetate:isopropanol (85:15:0.2) at a flow rate of 2 mL/min. The etodolac diastereoisomers were separated with a resolution factor of 6.4 and detected at a wavelength of 280 nm. Excellent linear relationships were found between the peak area ratios (etodolac:IS) and the plasma and urine concentrations (0.2-20 mg/L), with intra- and interday variations of less than 10.1%. The assay was applied to a preliminary pharmacokinetic study following seven repeated oral administrations of 200 mg/12 h of racemic etodolac to two healthy subjects. The plasma concentrations of the active S-(+)-enantiomer were considerably less than those of the inactive antipode (AUC S:R, 2.5:30.9 mg.L-1.h-1) due to a greater volume of distribution of the latter (S, 101 and 135 L versus R, 24 and 17 L). Considerable concentrations of conjugated enantiomers were also found in plasma (AUC conjugated: intact: S, 1.1; R, 0.23).

Sensitive determination of deuterated and non-deuterated indole-3-acetic acid and 5-hydroxyindole-3-acetic acid by combined capillary gas chromatography-negative-ion chemical ionization mass spectrometry

Sensitive methods for the determination of deuterated and non-deuterated indole-3-acetic acid and 5-hydroxyindole-3-acetic acid by combined capillary gas chromatography-negative-ion chemical ionization mass spectrometry were developed. Indole-3-acetic and 5-hydroxyindole-3-acetic acids were converted into pentafluorobenzyl and trifluoroacetylmethyl derivatives, respectively, after pre-purification by high-performance liquid chromatography. These derivatives were separated by gas chromatography and determined by selected ion monitoring. In the determinations, indole-3-acetic-2,2,2',4',5',6',7'-d7 acid and 5-hydroxyindole-3-acetic-3,3-d2 acid were used as internal standards. The methods developed in this work were used for the determination of deuterated and non-deuterated indole-3-acetic acid and 5-hydroxyindole-3-acetic acid in human urine samples collected before and after administration of L-tryptophan-3,3-d2.

Are the classical markers sufficient to describe uremic solute accumulation in dialyzed patients? Hippurates reconsidered

Interdependencies of accumulated solutes, analyzed by liquid chromatography in dialyzed and non-dialyzed patients, were studied by multivariate statistical analysis. In principal component analysis, three principal components (PC1-PC3) were retained from the data on 22 accumulated compounds in dialyzed patients, whereas only one principal component was retained from analogous data of a non-dialyzed patient group. PC1 in the dialyzed patient group comprises concentrations of hippuric acid, p-hydroxyhippuric acid, tryptophan, and five unidentified fluorescent solutes in serum. Concentrations of the classical markers urea, uric acid, creatinine, and phosphate were closely related to PC2 in these patients. Indoleacetic acid and two unidentified fluorescent compounds constitute PC3. The compounds associated with the groups found by principal component analysis may be characterized by chemical structure and by the mechanism of their excretion via the remaining nephrons of dialyzed patients. In the non-dialyzed group, most of the solutes could be described by a single PC. This PC and PC1 from the dialyzed group correlated significantly with residual renal function, and with total ultraviolet absorbance and total fluorescence emission. The data suggest that it is of value to introduce a marker of uremic solute retention in addition to urea, to account for renal-function-related "organic-acid-like" compounds that are excreted by renal tubular secretion in dialyzed patients. The hippurates may serve this purpose.

Plasma pharmacokinetics of cinmetacin following oral administration in healthy volunteers

The pharmacokinetics of a single 600 mg oral dose of 1-cinnamoyl-2-methyl-5-methoxy-3-indolylacetic acid (cinmetacin, Cindomet) was studied in 8 healthy volunteers of both sexes. Plasma levels of the drug were assayed by using an HPLC technique ad hoc devised. Following administration, the Cmax was reached at the 2nd h in 7 out of 8 subjects with an average value of 18.19 micrograms/ml; 12 h after the dose (last sampling time) appreciable plasma levels of cinmetacin were measured, corresponding to 17.2% of the maximum average concentration. The mean values +/- S.E. concerning the elimination half-life, the total volume of distribution, the total plasma clearance and the total area under the curve were 3.80 +/- 0.21 h, 0.28 +/- 0.03 l/kg, 0.051 +/- 0.005 l/kg/h, and 125.64 +/- 15.97 micrograms.h/ml, respectively. The plasma decay of cinmetacin was monophasic and the data were interpreted according to a one-compartment open model. Overall results indicate that cinmetacin is well and rapidly absorbed orally and widely distributed in body fluids.

Pharmacokinetics and metabolism of [14C]-proglumetacin after oral administration in the rat

The pharmacokinetics and metabolism of 1H-indole-3-acetic acid, 1-(4-chlorobenzoyl)-5-methoxy-2-methyl 2-[4-[3-[[4-(benzoylamino)-5-(dipropylamino)-1, 5-dioxopentyl]oxy]propyl]-1-piperazinyl]ethyl ester (+/-) (proglumetacin, CR 604), 14C-labelled in position C-2 of the indolic moiety, was studied in male and female rats after oral administration. The radioactivity is slowly absorbed from the gastrointestinal tract and reaches the peak in plasma 6 h after administration. Afterwards the radioactivity is eliminated from plasma according to a bi-exponential equation, with an initial elimination rate having a t1/2 of 4.5 h and a terminal elimination rate having a t1/2 of 16 h. The elimination rate is probably dependent on the slow absorption rate (flip-flop system) and on an entero-hepatic recirculation of the radioactivity. The radioactivity is excreted with the feces (60.8%) and with the urines (33.5%). No radioactivity is eliminated with the expired air. About 13% of the fecal radioactivity is represented by proglumetacin. This fraction or radioactivity (ca. 8% of the administered) represents probably the non-absorbed amount of substance. The parent proglumetacin is not found in blood, urine and organs. Conversely several indolic metabolites are found, with a predomination of indometacin. Proglumetacin is therefore a pro-drug of indometacin and of other indolic metabolites, which are responsible for the antiinflammatory activity of proglumetacin. The radioactivity is distributed in all tissues. The maximum radioactivity is found in liver and kidneys, however, always in a smaller concentration than in plasma. No "deep compartment" was found.

Plasma levels of proglumetacin and its metabolites after intravenous or oral administration in the dog

The absolute bioavailability of 1H-indole-3-acetic acid, 1-(4-chlorobenzoyl)-5-methoxy-2-methyl 2-[4-[4-[[4-(benzoylamino)-1,5-dioxopentyl]oxy]propyl]-1- piperazinyl]-ethyl ester (+/-) (proglumetacin, CR 604) was studied in 12 dogs, in a triple cross-over experiment with single doses of i.v. proglumetacin diphosphate, oral proglumetacin diphosphate or oral proglumetacin dimaleate. Determined were proglumetacin, 2'-[4-(3-hydroxypropyl)-piperazin-1-yl]-ethyl-(1-p- chlorobenzoyl-5-methoxy-2-methylindol-3-yl)-acetic acid (CR 1015), indometacin and proglumide in plasma. Proglumetacin and CR 1015 were found in plasma only after the i.v. administration. Conversely indometacin and proglumide were found after all administration routes. The areas under the curve of indometacin and of proglumide did not differ significantly after the three treatments, as shown by the analysis of variance.

On the binding of cinmetacin and indomethacin to human serum albumin

The binding of two non-steroidal anti-inflammatory drugs, indomethacin and cinmetacin, to human serum albumin was studied by dynamic dialysis at 37 degrees C and pH 7.4. Cinmetacin is bound more than indomethacin. The affinity constant for the primary binding site is 4.28 X 10(6) M-1 for cinmetacin and 1.4 X 10(6) M-1 for indomethacin. The protein binding of indomethacin is decreased in the presence of cinmetacin.

Profiling of endogenous ligand solutes that bind to serum proteins in sera of patients with uremia

The profiling of endogenous ligand solutes in sera of patients with uremia was performed by using an ultrafiltration device and high-performance liquid chromatography. Seventeen endogenous ligand solutes, which are ultraviolet-absorbing substances, were detected in a sample volume of 40 microliters, and four ligand solutes were tentatively identified as indoxylsulfate, hippuric acid, 2-hydroxybenzoylglycine, and 3-indoleacetic acid. One of these ligand solutes designated as peak P was thought to be a candidate for a major drug-binding inhibitor in uremia.

Serum indole-3-acetic acid in control subjects and newly abstinent alcoholics after an oral loading with L-tryptophan: a preliminary study using liquid chromatography with amperometric detection

Described in this paper is a rapid, isocratic assay for serum indole-3-acetic acid (IAA). The sample preparation involves only protein precipitation using sulfosalicylic acid, and the sensitivity of amperometric detection is in the picogram range. The chromatographic analysis time is approximately 4 min. The devised method was used for a longitudinal study of IAA levels in serum samples from control subjects and newly abstinent alcoholics. Dietary variations were eliminated by administering a 2.0-g loading dose of L-Trp to all subjects investigated. The results are presented in the form of cumulative frequency polygons. Preliminary data indicate no differences in IAA levels between newly abstinent alcoholics and control subjects.

Binding of clometacin to human serum albumin. Interactions with clofibrate, indomethacin, salicylic acid and warfarin

The binding of clometacin to human serum albumin (HSA) was studied in vitro by equilibrium dialysis. Our results show that binding to HSA is 99% at therapeutic levels. Binding is characterized by several numbers of binding sites (n = 8) with a moderate association constant (K = 2.7 X 10(4) M-1) and by another non-saturable phenomenon (nK = 4200 M-1). Moreover, interactions were studied with many drugs. Clometacin binding was altered by indomethacin, warfarin, chlorophenoxyisobutyrate (CPIB) and salicylic acid (SA). Conversely, clometacin inhibited the binding of these drugs. Finally, all these results were compared with those previously obtained with indomethacin, a positional isomer of clometacin.

Liquid-chromatographic determination of indole-3-acetic acid and 5-hydroxyindole-3-acetic acid in human plasma

We describe a "high-performance" reversed-phase liquid-chromatographic method for determination of indole-3-acetic acid (I) and 5-hydroxyindole-3-acetic acid (II) in human plasma. I is eluted at 1.0 mL/min with a mixture of 1-pentanesulfonic acid (pH 3.1), methanol, and water. It is detected by fluorometry. A mixture of citric acid/sodium phosphate solution (pH 4.8) and methanol, at 1.5 mL/min, is used to elute II, which is detected with an electrochemical cell. Platelet-poor plasma samples were pretreated with HCl, perchloric acid, and trichloroacetic acid for protein precipitation. Best results were obtained with the last (protein precipitation is incomplete with HCl, while recoveries of I are concentration dependent with perchloric acid). Analytical recoveries were 58% (SD 3.1%, CV 5.3%, n = 12) and 79% (SD 3.3%, CV 5.3%, n = 9) for I and II, respectively. Concentrations of I and II in plasma ranged from 0.61 to 3.32 (mean 1.54, SD 0.59, n = 15) mumol/L and from 33.0 to 102.6 (mean 51.8, SD 20.1, n = 16) nmol/L, respectively.

Determination of tryptophan and several of its metabolites in physiological samples by reversed-phase liquid chromatography with electrochemical detection

A new method for the concurrent assay of three tryptophan metabolites at the picomole level is described. The method has been developed for blood, urine, cerebrospinal fluid, and tissue samples such as whole brain, brain parts, and endocrine glands. Tryptophan itself, serotonin, and 5-hydroxyindoleacetic acid are isolated initially on extraction columns, eluted with a suitable solvent, and injected onto a liquid chromatograph with an amperometric detector. This general approach may be applicable to a variety of other tryptophan metabolites and should be useful in both research and clinical investigations.

[Point of micropreparative high pressure liquid chromatography and thin-layer chromatography for the identification of indole compounds in human plasma (author's transl)]

Results are presented on the analysis of indolic metabolites of tryptophan in human plasma, using high-pressure liquid chromatography and thin-layer chromatography. Dichloromethane/ethanol extracts of denaturated plasma were analysed. Thin-layer chromatography proved to be more advantageous for the analysis of this class compounds because it is possible to use a specific staining reagent (4-dimethylaminobenzaldehyde). The advantage of high-pressure liquid chromatography lies in the rapid isolation and purification of unknown compounds for identification in an off-line method. This application is demonstrated with the isolation of N-acetyltryptophan from human plasma. Preliminary results are presented on the plasma concentration of indole-3-lactic acid, indole-3-acetic acid and N-acetyltryptophan in healthy persons, phenylketonurics, and uremic patients.

Studies with uraemic serum on the renal transport of hippurates and tetraethylammonium in the rabbit and rat: effects of oral neomycin

1. The depression of p-aminohippurate and o-iodohippurate transport induced by uraemic serum in rabbit and rat renal cortex in vitro was confirmed. At the same time no change in oxygen consumption was observed.

2. The transport of the tetraethylammonium ion was unimpaired by uraemic serum from man or rat.

3. When sera from neomycin-treated uraemic rats were incubated with rabbit renal cortex, the uptakes of p-aminohippurate and of o-iodohippurate were 50% higher than when sera from untreated uraemic rats were used.

4. In rat uraemic serum, the levels of hippuric and indole acetic acids are markedly elevated. Administration of neomycin causes a substantial reduction in these levels.

5. The implications of these observations upon the impaired renal transport of hippurates produced by uraemic serum is discussed.