Avoiding falsely low creatinine concentrations measured in patients treated with N-acetylcysteine for acetaminophen intoxication using enzymo-amperometric method - An in vitro and in vivo study

BACKGROUND

Circulating creatinine is a biomarker of paramount importance in clinical practice. In cases of acetaminophen (APAP) intoxication, the antidote, N-acetylcysteine (NAC), interferes with commonly used creatininase-peroxidase methods. This study aimed to assess whether creatininase-amperometric methods were affected in this context.

METHODS

This study includes in vitro interference tests, involving four creatinine assays using NAC-spiked plasma pools and an in vivo retrospective study comparing creatininase-peroxidase and creatininase-amperometric measurements in patients presenting with NAC-treated APAP poisoning.

RESULTS

Creatininase-peroxidase method was impacted by NAC interference in a clinically-significant manner at therapeutic NAC levels (basal value recovery of 80 % and 70 % for 500 and 1000 mg.L-1 of NAC, respectively), surpassing the desirable Reference Change Value (RCV%). Enzymo-amperometric methods were not impacted. Among patients, a mean bias of -45.2 ± 28.0 % was observed for the peroxidase detection method compared to the amperometric in those who received NAC prior plasma sampling and -2.7 ± 5.4 % in those who did not.

CONCLUSIONS

Our findings indicate that enzymo-amperometric creatinine assays remain unaffected by NAC interference due to the absence of the peroxidase step in the analytical process. Therefore, these methods are suitable to prevent spurious hypocreatininemia in APAP intoxicated patients undergoing NAC therapy.

Heterologous expression of recombinant urate oxidase using the intein-mediated protein purification in Pichia pastoris

The potential of urate oxidase (uricase) for clinical use has been highlighted because of its role in lowering the blood uric acid levels for the treatment of tumor lysis syndrome. In the present study, the codon-optimized synthetic gene of Aspergillus flavus uricase was fused to the Mxe GyrA intein and chitin-binding domain. The construct was inserted into pPICZA and pPICZαA vectors and electroporated into Pichia pastoris GS115 for the cytosolic and secretory expression. Transformants were screened on gradients of Zeocin up to 2000 μg/ml to find multi-copy integrants. For both constructs, colonies with more resistance were screened for the highest uricase producers by enzyme assay. PCR analysis confirmed successful cassettes insertion into the genome and Mut + phenotype. The gene copy index was determined to be two and five for cytosolic and secretory strains, respectively. Productivity of the cytosolic and secretory strains was found to be 0.74 and 0.001 U/ml culture media in order while the cytosolic recombinant enzyme accounted for about 6% of total proteins. One-step purification of the expressed uricase was done with the aid of the chitin affinity column, followed by DTT induction for intein on-column cleavage. The yield of 40.8 mg/L and K m of 0.22 mM was obtained for intracellular expression. It seems that the intracellular production of uricase can indeed serve as an effective alternative to secretory expression. Moreover, this is the first report considering cytosolic production of uricase using the intein-mediated protein purification in the methylotrophic yeast, P. pastoris.

Engineering of Bifunctional Enzymes with Uricase and Peroxidase Activities for Simple and Rapid Quantification of Uric Acid in Biological Samples

Serum uric acid (SUA) is an important biomarker for prognosis and management of gout and other diseases. The development of a low-cost, simple, rapid and reliable assay for SUA detection is of great importance. In the present study, to save the cost of enzyme production and to shorten the reaction time for uric acid quantification, bifunctional proteins with uricase and peroxidase activities were engineered. In-frame fusion of Candida utilis uricase (CUOX) and Vitreoscilla hemoglobin (VHb) resulted in two versions of the bifunctional protein, CUOX-VHb (CV) and VHb-CUOX (VC). To our knowledge, this is the first report to describe the production of proteins with uricase and peroxidase activities. Based on the measurement of the initial rates of the coupled reaction (between uricase and peroxidase), CV was proven to be the most efficient enzyme followed by VC and native enzymes (CUOX+VHb), respectively. CV was further applied for the development of an assay for colorimetric detection of SUA, which was based on VHb-catalyzed oxidation of Amplex Red in the presence of hydrogen peroxide (H2O2). Under the optimized conditions, the assay exhibited a linear relationship between the absorbance and UA concentration over the range of 2.5 to 50 μM, with a detection limit of 1 μM. In addition, the assay can be performed at a single pH (8.0) so adjustment of the pH for peroxidase activity was not required. This advantage helped to further reduce costs and time. The developed assay was also successfully applied to detect UA in pooled human serum with the recoveries over 94.8%. These results suggest that the proposed assay holds great potential for clinical application.

Cloning and expression of Aspergillus flavus urate oxidase in Pichia pastoris

Urate oxidase is an important enzyme with therapeutic and diagnostic applications. Rasburicase is a recombinant urate oxidase enzyme approved by FDA to use in the treatment of hyperuricemia conditions. Various hosts such as Saccharomyces cerevisiae, Hansenula polymorpha and Escherichia coli have been used to express the enzyme. Today, Pichia pastoris is considered as an important host for heterologous protein expression since it has beneficial characteristics such as strong promoters, simple scale up, post translational modifications, high cell density cultivation and simple genetic manipulation. In this study, Aspergillus flavus urate oxidase gene was cloned in pPICZαA expression vector and expressed in P. pastoris. The recombinant urate oxidase was expressed in secretory form and was confirmed through RT-PCR, SDS-PAGE analysis and western blotting. The enzyme activity was determined using a colorimetric assay. A production yield of 0.43 U/ml of culture supernatant was obtained.

Uricase production by a recombinant Hansenula polymorpha strain harboring Candida utilis uricase gene

Uricase is an important medical enzyme which can be used to determine urate in clinical analysis, to therapy gout, hyperuricemia, and tumor lysis syndrome. Uricase of Candida utilis was successfully expressed in Hansenula polymorpha under the control of methanol oxidase promoter using Saccharomyces cerevisiae alpha-factor signal peptide as the secretory sequence. Recombinant H. polymorpha MU200 with the highest extracellular uricase production was characterized with three copies of expression cassette and selected for process optimization for the production of recombinant enzyme. Among the parameters investigated in shaking flask cultures, the pH value of medium and inoculum size had great influence on the recombinant uricase production. The maximum extracellular uricase yield of 2.6 U/ml was obtained in shaking flask culture. The yield of recombinant uricase was significantly improved by the combined use of a high cell-density cultivation technique and a pH control strategy of switching culture pH from 5.5 to 6.5 in the induction phase. After induction for 58 h, the production of recombinant uricase reached 52.3 U/ml (about 2.1 g/l of protein) extracellularly and 60.3 U/ml (about 2.4 g/l) intracellularly in fed-batch fermentation, which are much higher than those expressed in other expression systems. To our knowledge, this is the first report about the heterologous expression of uricase in H. polymorpha.

Alterations in plasma antioxidants during reperfusion of the ischemic small intestine in rats

The aim of this study was to evaluate the contribution of three plasma antioxidants (albumin, uric acid, SH groups) to the plasma total peroxyl radical-trapping antioxidant capacity (TRAP) in 2 and 4 h of intestinal reperfusion in rats. TRAP increased significantly both after 2 and 4 h of reperfusion. Neither albumin nor SH groups contributed significantly to this increase. TRAP was strongly influenced by the increase in uric acid concentration and also probably by the cell destruction caused by oxidative stress. Since the TRAP increase was accompanied by an increase in the level of thiobarbituric acid reactive substances (TBARS, a marker of lipid peroxidation), we can conclude that even such a large increase in TRAP is not sufficient to prevent the progression of lipid peroxidation and oxidative stress.

Influence of nonspecific reaction on determination of H2O2 using Trinder reagents

BACKGROUND

We examined two enzymatic reagents for cholesterol measurement that contained cholesterol oxidase. One of the reagents gave higher values by up to 11 mg/dl in samples of 109 out of 3119 patients examined. We found that the positive errors were caused by a nonspecific reaction that has not previously been recognized in the determination of H(2)O(2) using Trinder reagents, and we further discovered its mechanism.

METHODS

We compared the total cholesterol concentration in 3119 patients between the 2 reagents. By examining the characteristics of the interferrent-susceptible reagent and affected patients' samples, we identified the cause and mechanism of the influence of the nonspecific reaction.

RESULTS

The existence of potassium ferrocyanide in the reagent gave rise to positive errors when the concentration of unsaturated iron binding capacity (UIBC) in the patients' sample was <70 microg/dl. Moreover, ceruloplasmin in the patients' sample was found to cause a nonspecific reaction and its influence was proportional to the serum copper concentration. The two types of reagents compared in the present study included buffers with different metal chelating capacities; the one with the lower capacity gave an erroneous measurement. The buffer in the reagent without influence had been acting as a chelating agent. Therefore, the influence of the interferrent-susceptible reagent could be prevented by addition of a chelating agent (e.g. EDTA).

CONCLUSIONS

Trinder reagents containing potassium ferrocyanide have been widely used for clinical diagnostic tests such as creatinine, uric acid and so on. These reagents would have similar problems. Some test items might have a greater influence than cholesterol reagent. Physicians should be aware of the risks of diagnostic mistakes due to these errors of measurement.

A new colorimetric assay for purine nucleoside phosphorylase

A new colorimetric procedure for the determination of purine nucleoside phosphorylase (PNP, E.C. 2.4.2.1) activity is described. In this procedure, the hydrogen peroxide formed in the PNP-xanthine oxidase reaction is used to oxidize the chromogenic reagents--3,5-dichloro-2-hydroxybenzenesulfonic acid/4-aminophenazone using the enzyme peroxidase. The rate of enzyme reaction is followed at 520 nm. This procedure correlated well with the UV method (290 nm), with a correlation coefficient of 0.98 (P less than 0.005). Within-run and between-run precision (CV) were less than 2.8% and 3.7%, respectively. Here we also describe an optimized NAD-dependent method (340 nm) for PNP determination. The colorimetric method is superior to both the 340 nm and the UV methods in terms of both sensitivity and precision. The mean erythrocyte PNP activity for 17 healthy subjects was 11.88 U/mL packed cells for the NAD-dependent method and 13.22 U/mL packed cells for the colorimetric method.

Evaluation of the enzymatic assay of serum uric acid with 2,2'-azino-di(3-ethylbenzthiazoline-6-sulphonate) (ABTS) as chromogen

A spectrophotometric method for the determination of serum uric acid based on the oxidation of 2,2'-azino-di(3-ethylbenzthiazoline-6-sulphonate) by use of uricase and peroxidase has already been reported. The method is very precise (CV less than 4.7%). The standard curve is linear up to 4640 mumol/L. Comparison with other enzymatic methods gave good correlation. The method gave results 9% lower than the phosphotungstate method. The effects of bilirubin, haemoglobin, glucose, ascorbic acid, anticoagulants and purine compounds were studied. The reference values for this method are 140.8-407.8 mumol/L for female subjects and 145.6-514.7 mumol/L for male subjects.

Clofibrate and tiadenol treatment in hyperlipoproteinemias. A comparative trial of drugs affecting lipoprotein catabolism and biosynthesis

Changes in plasma lipoprotein levels and platelet reactivity were evaluated during sequential treatments with clofibrate and tiadenol, two hypolipidemic agents with apparently different mechanisms, in 27 hyperlipoproteinemic patients. The objective of the study was to determine the pattern of plasma lipoprotein variations, induced by a drug mainly affecting lipoprotein catabolism (clofibrate) and by a drug affecting biosynthesis (tiadenol), and to single out-patients specifically responding to either treatment. Both drugs proved significantly active in type IIA and IV hyperlipoproteinemias, not in type IIB. Clofibrate significantly lowered very low density lipoprotein (VLDL) associated cholesterol in all three hyperlipoproteinemia phenotypes, and it also lowered VLDL triglycerides in type IV, while increasing high density lipoprotein (HDL) cholesterol in type IIA patients. Low density lipoprotein (LDL) cholesterol levels were minimally reduced by clofibrate in type IIA (-4%), and increased in types IIB (+ 14.2%) and IV (+ 6.1%) patients. Conversely, tiadenol lowered VLDL cholesterol and triglycerides to a lesser extent, but it did significantly reduce LDL cholesterolemia in type IIA (-17.6%), while increasing HDL cholesterol in type IIB. Statistical evaluation of the results did not permit identification of parameters associated with the response to either drug, although individuals specifically responding to one or the other agent, or to both, were detected in all three phenotypes. The sensitivity to the major platelet aggregating factors, ADP, adrenaline and collagen, was not significantly altered after drug treatments. Evaluation of the hypolipidemic response to agents with different mechanisms may be of help in selecting the best treatment for individual patients.

The binding of urate to plasma proteins determined by four different techniques

Venous occlusion in healthy individuals showed no binding of urate under conditions when the expected increased levels of known bound species was demonstrated. Ultrafiltration of serum from 10 healthy controls and five gouty individuals also showed the absence of binding in all cases, as did electrophoretic and chromatographic studies.

The application of a sensitive uricase-peroxidase couple reaction to a centrifugal fast analyser for the determination of uric acid

A uricase-peroxidase coupled system, for the determination of uric acid, applied to a CentrifiChem-500 centrifugal fast analyser is described. Relatively large amounts of ascorbic acid, due to the inclusion of an ascorbate oxidase urine diluent, and hemoglobin appear not to interfere with the procedure while the incorporation of potassium ferrocyanide into the reagents has led to the near-total elimination of bilirubin interference. The incubation period is relatively short compared with other similar procedures and the one reagent system has made the procedure simple to perform. The use of sodium 2-hydroxy-3,5-dichlorobenzenesulfonate and 4-aminoantipyrene in the oxidative coupling reaction has incorporated the advantages of increased sensitivity, over phenol-4-aminoantipyrene systems, as well as the amenability of the reagent towards lyophilization or "dry-fill".

Development and improvement of a commercial uric acid enzymatic determination kit on a centrifugal fast analyzer

The performance of a uric acid determination kit has been evaluated for five months, under routine conditions, in a General Hospital Biochemical Laboratory. An anomalous increment in fresh serum blanks was noted in the kit when first introduced. This interference, probably due to alcohol dehydrogenase contamination, was corrected by addition of 50 mmol/l (NH4)2SO4 to the reagent. Results obtained with this modified reagent correlate perfectly with those obtained with modified kits by Smith Kline Instruments (SKI), and with many other determination methods. Correlations are discussed and explanations for differences in statistical data are offered. Within run and between run precision data are presented. The kit fits perfectly with the needs of centrifugal fast analyzers and discrete micro analyzers, on account of its speed, reliability and precision.