Possible Induction of Cholinesterase in Epileptic Patients Treated With Anticonvulsant Drugs: Relationship With Lipoprotein Levels

The effect of enzyme-inducing anticonvulsant drugs on the serum concentrations of lipoproteins has been widely studied. However, there is little agreement between the results with regard to the possible development of a lipoprotein profile related to an increased or decreased cardiovascular risk. It has been suggested that cholinesterase (ChE) could be induced by these drugs, something of undeniable interest as ChE appears to have a relation to the metabolism of lipoproteins. The serum activity of ChE was determined in a group of 90 adult epileptic patients (56 male and 34 female) treated with phenobarbital, phenytoin, and carbamazepine. The liver enzyme induction produced by these drugs was then evaluated by determining serum gamma-glutamyltranspherase activity and urinary excretion of D-glucaric acid. A significant increase of serum ChE (p < 0.005) was found in the group of patients compared to a control group (n = 49) with a similar distribution for age and sex. A significant correlation was found for both male and female patients between ChE and concentrations of triglycerides, phospholipids, cholesterol, low-density lipoprotein (LDL) phospholipids, LDL-cholesterol, and apolipoprotein B (p < 0.01). Similarly, in female patients, ChE had a significant correlation with the total cholesterol/high-density lipoprotein (HDL) cholesterol and LDL-cholesterol/HDL-cholesterol ratios (p < 0.01). The ChE/HDL-cholesterol relationship, which has been proposed as a marker for cardiovascular risk, presented significant correlations with the total cholesterol/HDL-cholesterol and LDL-cholesterol/HDL-cholesterol ratios in patients of both sexes (p < 0.001). In the case of epileptic patients treated with enzyme-inducing anticonvulsant drugs, there may be an association between the possible induction of ChE and the metabolism of lipoproteins containing apolipoprotein B.

Impact of creatinine production on the agreement between glomerular filtration rate estimates using cystatin C-derived, and 4- and 6-variable Modification of Diet in Renal Disease (MDRD), and Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equations

BACKGROUND

It has recently been reported that patient selection has a strong impact on the agreement between glomerular filtration rate (GFR) estimates from serum cystatin C and creatinine. The aim of our study was to evaluate the effect of creatinine production rate (CPR) on this subject.

MATERIAL AND METHODS

GFR was estimated from serum cystatin C and from creatinine using the 4- and 6-variable Modification of Diet in Renal Disease (MDRD), and Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equations in 50 healthy subjects, 43 patients with renal failure, 794 kidney and 104 liver transplant recipients, 61 patients with heart failure, 59 patients with biliary obstruction, and 113 critically ill patients.

RESULTS

In the 295 patients with impaired CPR (< 900 mg/24 h/1.73 m(2)), discordances of more than 40% between GFR(MDRD4) and GFR(cystatinC) were observed in 38% of cases, between GFR(MDRD6) and GFR(cystatinC) in 22%, and between GFR(CKD-EPI) and GFR(cystatinC) in 27% (in all cases due to GFR overestimation from creatinine). In the 929 patients with maintained CPR (> 900 mg/24 h/1.73 m(2)), greater discordances than 40% between GFR(MDRD4) and GFR(cystatinC) were observed in 8% of cases, between GFR(MDRD6) and GFR(cystatinC) in 9%, and between GFR(CKD-EPI) and GFR(cystatinC) in 7% (in the major part of cases due to GFR overestimation from cystatin C).

CONCLUSION

The main source of differences of more than 40% between GFR estimates from serum creatinine and cystatin C is a GFR overestimation in patients with low CPR and GFR underestimation in patients with high CPR by the creatinine-derived equations.

Apparent clearance of valproic acid in elderly epileptic patients: estimation of the confounding effect of albumin concentration

BACKGROUND

Valproic acid (VPA) apparent clearance (CL) estimated from total serum concentrations is analogous in elderly and non-elderly adult patients. As drug-protein binding decreases in old age, the aim of our study was to evaluate the confounding effect of the serum albumin concentration on the VPA apparent CL in elderly patients.

METHODS

In 102 epileptic out-patients treated with VPA in monotherapy, serum total steady-state trough concentrations (Css) were determined. Css concentrations were normalized for a 42 g/L albumin concentration (Css(N)), and the apparent CL and normalized apparent CL(N) were calculated.

RESULTS

A poor concordance of 53% was found in the classification of Css and Css(N) levels of VPA as subtherapeutic, therapeutic, or supratherapeutic dose. In the elderly (≥65 years) and non-elderly adult patients, the VPA apparent CL was similar; however, normalized apparent CL(N) was significantly lower in older patients (P < 0.01), with a 40% median decrease.

CONCLUSIONS

Total VPA concentrations should be interpreted with caution, mainly in older patients, in which determination of unbound or normalized total drug concentrations may be clinically useful. Normalization of total concentrations permits an estimation of the masking effect of serum albumin concentrations on the VPA apparent CL in elderly patients.

Investigation of possible interference by digoxin-like immunoreactive substances on the Architect iDigoxin CMIA in serum samples from pregnant women, and patients with liver disease, renal insufficiency, critical illness, and kidney and liver transplant

BACKGROUND

Although the possible interference of digoxin-like immunoreactive substances (DLIS) on the Architect iDigoxin chemiluminiscent microparticle immunoassay (CMIA) has been emphasized by the manufacturer, a specific study about this subject has still not been carried out.

METHODS

Apparent serum digoxin concentrations were determined using the Architect iDigoxin CMIA from Abbott Laboratories in digoxin-free pregnant women (n = 50), and patients with liver disease (n = 50), renal insufficiency (n = 50), kidney (n = 25) or liver (n = 25) transplant, and critical illness (n = 50).

RESULTS

In all of the patients included in this study, apparent serum digoxin concentrations were lower than the correspondent quantification limit (< 0.30 microg/L).

CONCLUSIONS

The Architect iDigoxin CMIA assay would be relatively free from endogenous DLIS positive interferences.

A preliminary investigation on the possible association between diminished copper availability and non-alcoholic fatty liver disease in epileptic patients treated with valproic acid

BACKGROUND

Patients treated with valproic acid (VPA) present a high incidence of non-alcoholic fatty liver disease (NAFLD) (around 61%). Several recent studies suggest that low copper stores could be associated with NAFLD, and a significant decrease of copper availability in VPA-treated patients has been described.

DESIGN AND METHODS

In 101 adult epileptic patients treated with valproic acid in monotherapy (n = 75) and polytherapy (n = 26) the copper availability was evaluated using the specific oxidase activity of ceruloplasmin (activity per unit mass of enzyme protein) and the copper/ceruloplasmin ratio. Copper deficiency was supposed in the cases in which this biochemical variable was smaller than the lower reference limit (333 U/g).

RESULTS

The differences between the groups of patients with ceruloplasmin oxidase activity smaller or greater than 333 U/g for the serum levels of aminotransferases, gamma-glutamyltransferase, butyrylcholinesterase, cholesterol, triglycerides, and C-reactive protein, and the APRI and FIB-4 liver fibrosis scores were not statistically significant. Most patients (93%) had low APRI and FIB-4 scores, suggesting absence of significant liver fibrosis.

CONCLUSIONS

The results obtained do not confirm the hypothesis of an association between diminished copper availability and NAFLD in patients treated with valproic acid.

A limited sampling strategy for estimation of the area under the curve (0 to 8 hours) of mycophenolic acid administered three times daily to liver transplant recipients

OBJECTIVES

Gastrointestinal side-effects caused by mycophenolic acid (MPA) are frequent in liver transplant recipients, and in these cases a switch from two to three daily doses is usually recommended. However, a limited sampling strategy for the estimation of MPA area under the curve from 0 to 8 hours (AUC(0-8h)) has not been made.

DESIGN AND METHODS

In 22 liver transplant patients who were administered MPA three times daily, the trapezoidal extrapolated MPA AUC(0-8h) values using a sampling time from 0 to 2 hours were calculated.

RESULTS

A tentative therapeutic range for MPA AUC(0-8h) of about 20-40 μg.h/mL is proposed, and in the 13 patients with supratherapeutic values the total leukocyte blood count was significantly lower than in the 9 patients with AUC(0-8h) ≤ 40 μg.h/mL (P < 0.001). Significant negative correlations were found between the total leukocyte blood count and the MPA trough levels (r = -0.458; P < 0.05), AUC(0-8h) (r = -0.479; P < 0.05), and AUC(0-2h) (r = -0.437; P < 0.05). A significant correlation was found between the trapezoidal extrapolated AUC(0-8h) and trapezoidal AUC(0-2h) results (r = 0.850; P < 0.001).

CONCLUSIONS

The trapezoidal extrapolated AUC(0-8h), and possibly trapezoidal AUC(0-2h), may be useful for routine therapeutic MPA monitoring in liver transplant recipients in which the dosing frequency is increased from twice to three times a day.

Macromolecular complexes of cystatin C with circulating liver plasma membrane fragments and determination of serum cystatin C using the particle enhanced nephelometric immunoassay (PENIA) in kidney and liver transplantation and biliary obstruction

BACKGROUND

In a patient with biliary obstruction, a macromolecular complex of cystatin C with liver plasma membrane fragments, which also contain several membrane-bound enzymes, which may be removed by butanol extraction, has recently been characterised. This could lead to an underestimation of the glomerular filtration rate (GFR) from serum cystatin C concentration.

METHODS

Using the particle enhanced nephelometric immunoassay (PENIA), serum cystatin C concentration was determined in 50 healthy controls, 43 patients with renal insufficiency, 68 kidney and 88 liver transplant recipients, and 60 patients with biliary obstruction. Residual cystatin C concentrations and gamma-glutamyltransferase (GGT) activities after butanol extraction were also determined.

RESULTS

In the controls and patients with renal insufficiency the residual concentrations of cystatin C after butanol extraction were always > or = 80%. However, in 2 renal and 7 liver transplant recipients and in 11 patients with biliary obstruction this biochemical variable was < 80%. A significant correlation between the residual cystatin C concentrations and residual GGT activities was obtained (r = 0.386, p < 0.001). In the relationship between estimated GFR from serum cystatin C and creatinine concentrations in the liver transplant recipients and patients with biliary obstruction, the 18 cases with residual cystatin C concentrations < 80% were included in the distribution of the total population data with no particular tendency.

CONCLUSIONS

These results suggest that in the cases with residual cystatin C concentrations < 80% after butanol extraction, presumably due to the presence of circulating macromolecular cystatin C, the serum levels of cystatin C obtained using the PENIA assay do not lead to a systematic GFR underestimation.

Determination of blood everolimus concentrations in kidney and liver transplant recipients using the sirolimus antibody conjugated magnetic immunoassay (ACMIA)

BACKGROUND

The aim of our study was to evaluate the possible determination of everolimus concentrations using the newly-introduced sirolimus antibody conjugated magnetic immunoassay (ACMIA).

METHODS

Everolimus concentrations were determined in 100 blood samples from kidney (n = 47) and liver (n = 53) transplant recipients using the IMx sirolimus microparticle enzyme immunoassay (MEIA) from Abbott as previously described (Clin Biochem 2007;40:132-36) and sirolimus ACMIA from Siemens Healthcare Diagnostics Ltd.

RESULTS

The ACMIA everolimus values were significantly higher than those of MEIA (p < 0.001). Analogous slope and intercept values were obtained in the linear regression between the ACMIA and MEIA results when compared to the Seradyn Certican everolimus controls or the blood samples from transplant recipients. Correction of the ACMIA values using the regression equation obtained for the control material (ACMIAcorrected = 0.55 ACMIA + 1.14) led to a satisfactory relationship with the results provided by the MEIA for the patients' samples (MEIA = 1.00 ACMIAcorrected + 0.30, r = 0.905, p < 0.001).

CONCLUSIONS

The sirolimus ACMIA on the Dimension platform, which does not require manual pre-treatment of the blood samples, may be an acceptable option for therapeutic everolimus monitoring, significantly reducing technician time in comparison to other widely-used immunoassays.

Sirolimus and everolimus clearance in maintenance kidney and liver transplant recipients: diagnostic efficiency of the concentration/dose ratio for the prediction of trough steady-state concentrations

OBJECTIVES

Therapeutic monitoring of sirolimus and everolimus is necessary in order to minimize adverse side-effects and to ensure effective immunosuppression. A sirolimus-dosing model using the concentration/dose ratio has been previously proposed for kidney transplant patients, and the aim of our study was the evaluation of this single model for the prediction of trough sirolimus and everolimus concentrations.

METHODS

Trough steady-state sirolimus concentrations were determined in several blood samples from each of 7 kidney and 9 liver maintenance transplant recipients, and everolimus concentrations from 20 kidney, 17 liver, and 3 kidney/liver maintenance transplant recipients. Predicted sirolimus and everolimus concentrations (Css), corresponding to the doses (D), were calculated using the measured concentrations (Css(0)) and corresponding doses (D(0)) on starting the study: Css = (Css(0))(D)/D(0).

RESULTS

The diagnostic efficiency of the predicting model for the correct classification as subtherapeutic, therapeutic, and supratherapeutic values with respect to the experimentally obtained concentrations was 91.3% for sirolimus and 81.4% for everolimus in the kidney transplant patients. In the liver transplant patients the efficiency was 69.2% for sirolimus and 72.6% for everolimus, and in the kidney/liver transplant recipients the efficiency for everolimus was 67.9%.

CONCLUSIONS

The model has an acceptable diagnostic efficiency (>80%) for the prediction of sirolimus and everolimus concentrations in kidney transplant recipients, but not in liver transplant recipients. However, considering the wide ranges found for the prediction error of sirolimus and everolimus concentrations, the clinical relevance of this dosing model is weak.

Determination of blood sirolimus concentrations in liver and kidney transplant recipients using the Innofluor fluorescence polarization immunoassay: comparison with the microparticle enzyme immunoassay and high-performance liquid chromatography-ultraviolet method

BACKGROUND

Although high-performance liquid chromatography (HPLC) is the method of choice for blood sirolimus determination, the microparticle enzyme immunoassay (MEIA) run on the IMx analyser is widely used in therapeutic monitoring of this immunosuppressant agent. The aim of our study was to evaluate the possible determination of sirolimus using the fluorescence polarization immunoassay (FPIA) commercialized for everolimus quantification.

METHODS

Sirolimus concentrations were determined in whole-blood samples from liver and kidney transplant recipients using the Innofluor Certican FPIA (Seradyn Inc.) run on a TDx analyser (Abbott Laboratories), Sirolimus MEIA run on an IMx analyser (Abbott Laboratories), and HPLC (UV detection) methods.

RESULTS

The Innofluor FPIA has a similar cross-reactivity with everolimus and sirolimus, and the within- and between-run coefficients of variation obtained for sirolimus determination were 2.7%-13.3%. In analysing different blood samples from liver and kidney transplant patients the linear regressions obtained were: FPIA = 1.12 HPLC + 0.43 (n=104, r=0.874), MEIA = 1.14 HPLC (n=146, r=0.892), and FPIA = 1.00 MEIA + 0.29 (n=106, r=0.941). Better correlation coefficients were obtained between the methods in the liver transplant samples (r>or=0.900) than in the kidney transplant samples (r>or=0.849). No significant effect was found for sirolimus clearance or the blood hematocrit on the relationship between the results produced by both immunoassays and HPLC.

CONCLUSION

The Innofluor FPIA is a valid alternative with an analogous performance to the MEIA for the therapeutic monitoring of sirolimus.

Glomerular filtration rate estimation using the Cockcroft-Gault and modification of diet in renal disease formulas for digoxin dose adjustment in patients with heart failure

OBJECTIVE

The aim of this study was to compare the estimated glomerular filtration rate (GFR) using the Cockcroft-Gault and the 4-, 5-, and 6-variable Modification of Diet in Renal Disease (MDRD) formulas for digoxin dose adjustment.

METHODS

Steady-state serum digoxin concentrations were determined in 100 patients with heart failure and normal to severely impaired renal function. Total clearance (CL) and predicted average concentrations of digoxin were calculated using general pharmacokinetic principles.

RESULTS

The mean+/-SEM (median) estimated GFR values were 48.9+/-2.8 (46.5) mL/min/1.73 m(2) using the Cockcroft-Gault formula, 61.4+/-3.6 (56.4) mL/min/1.73 m(2) using the MDRD4 formula, 56.8+/-3.3 (52.1) mL/min/1.73 m(2) using the MDRD5 formula, and 53.3+/-3.0 (48.7) mL/min/1.73 m(2) using the MDRD6 formula, with high correlation coefficients between the estimates (r > or = 0.928, P < 0.001). Significant correlations were found between the digoxin total CL and estimated GFR by the Cockcroft-Gault (r = 0.649, P < 0.001), MDRD4 (r = 0.634, P <0.001), MDRD5 (r = 0.635, P < 0.001), and MDRD6 (r = 0.652, P < 0.001) formulas. A significant negative correlation of the digoxin total CL/GFR ratio with estimated GFR was obtained (r = -0.356, P < 0.001), with a high variability for this ratio for GFR lower than 60 mL/min. Analogous correlation coefficients were found between the obtained and predicted digoxin concentrations calculated using the estimated GFR by the Cockcroft-Gault (r = 0.628, P < 0.001), MDRD4 (r = 0.642, P < 0.001), MDRD5 (r = 0.650, P < 0.001), and MDRD6 (r = 0.665, P < 0.001) formulas, with a wide dispersion between the values in all cases.

CONCLUSION

For GFR lower than 60 mL/min, the high interindividual variation of the digoxin total CL found among patients with similar renal function is an important limiting factor in the prediction of digoxin dosage regimens.

Relative proportions of serum carbamazepine and its pharmacologically active 10,11-epoxy derivative: effect of polytherapy and renal insufficiency

BACKGROUND

The proposed action mechanism and pharmacological activity of carbamazepine (CBZ) and its major metabolite, carbamazepine-10,11-epoxide (CBZE), are the same. The aim of our study was the investigation of the effect of concomitant antiepileptic treatment and renal insufficiency on the relative proportions of serum CBZ and CBZE.

METHODS

Serum trough steady-state CBZ and CBZE concentrations were determined by high-performance liquid chromatography (HPLC) in 140 epileptic patients treated with CBZ in monotherapy (n=100) and polytherapy with phenytoin, phenobarbital and valproate (n=40). The levels of CBZ were also determined using the Dade Behring enzyme multiplied immunoassay technique (EMIT). The glomerular filtration rate (GFR) was estimated from serum cystatin C using the Dade Behring nephelometric immunoassay.

RESULTS

The CBZE/CBZ and CBZ+CBZE/CBZEMIT ratios were significantly increased in 7 cases (3 in monotherapy and 4 in polytherapy) with GFR<60 mL/min/1.73m2 in relation to the patients treated in monotherapy or polytherapy having normal or mildly decreased renal function (p<0.001).

CONCLUSIONS

In patients with moderate to severe renal insufficiency the relative proportion of CBZE with respect to the parent drug is significantly increased. In these cases, the CBZ concentrations obtained using the EMIT, or other immunoassays having low CBZE cross-reactivity, may have an inadequate diagnostic efficiency.

Comparison of blood tacrolimus concentrations in liver and kidney transplant recipients using ACMIA and MEIA immunoassays

BACKGROUND

Published data on the performance of the new Dade Behring antibody conjugated magnetic immunoassay (ACMIA) for tacrolimus determination are scarce. The aim of this study was to compare the results obtained using the ACMIA and Abbott microparticle enzyme immunoassay (MEIA), which is the most widely used method for therapeutic tacrolimus monitoring.

METHODS

Trough tacrolimus concentrations were determined in 305 blood samples from kidney (n=138) and liver (n=167) transplant recipients using the ACMIA and MEIA immunoassays. The MEIA results were corrected for hematocrit values lesser than 30% and higher than 40% (Hermida et al. Clin Lab 2005; 51: 43-45).

RESULTS

The obtained ACMIA within- and between-run variation coefficients (<10.8%) were acceptable. In the comparison between ACMIA and MEIA results in the blood samples studied, the regression equation was: ACMIA=1.02MEIA+0.29 (r=0.912, p<0.001), with an acceptable difference between the means (8.13+/-0.53 ng/mL vs. 7.62+/-0.50 ng/mL). However, in accordance with the well-established interference of the hematocrit on the MEIA results, a highly significant negative correlation between the MEIA/ACMIA ratio and the hematocrit values was obtained (r=-0.585, p<0.001). When the MEIA results were corrected according to the hematocrit (MEIAHtC), the regression with ACMIA levels was: ACMIA=1.08MEIAHtC-0.09 (r=0.926, p<0.001). This equation was analogous to that obtained between ACMIA and MEIA tacrolimus concentrations in the 164 blood samples with hematocrit of 30-40%.

CONCLUSIONS

ACMIA is an acceptable option for therapeutic tacrolimus monitoring, with an important decrease in technician time in relation to the widely used MEIA.

Phenytoin immunoassay measurements in serum samples from patients with renal insufficiency: comparison with high-performance liquid chromatography

The debate continues regarding the possible interference of phenytoin metabolites in phenytoin immunoassays, and its clinical importance for patients with renal failure. The aim of this study was to compare the results obtained using the Abbott fluorescence polarization immunoassay (FPIA), Dade enzyme-multiplied immunoassay technique (EMIT), and high-performance liquid chromatography (HPLC) to establish the significance of the differences in conditions of renal failure. Thirty-six adult patients who had been treated with phenytoin and whose renal function ranged from normal to severely impaired were chosen for this study. In accordance with previously established validation criteria for analytical methods for the determination of drugs, a 15% bias from the HPLC phenytoin values was considered an acceptable limit. The mean (+/-SEM) glomerular filtration rate (GFR) of the patients was 37.5+/-4.6 mL/min (range = 10-102 mL/min). The mean values found using FPIA (10.8+/-1.2 microg/mL) and EMIT (10.8+/-1.3 microg/mL) presented acceptable deviations with respect to HPLC (10.5+/-1.2 microg/mL), and a high correlation was found among the results (N = 36) of the different methods (r > or = 0.987, P < 0.001). An FPIA deviation above the 15% bias limit with respect to HPLC was found only in two cases with very low serum phenytoin concentrations and low GFR values (< 20 mL/min), although it does not appear to be important in terms of adjusting drug dosage. According to our data, FPIA and EMIT gave accurate results for total phenytoin in serum samples from patients with renal failure.

Determination of everolimus in whole blood using the Abbott IMx® sirolimus microparticle enzyme immunoassay

OBJECTIVES

Everolimus (Certican) is a new immunosuppressant derived from sirolimus (Rapamune) with a 2-hydroxyethyl chain at position 40 of the macrolide ring. The aim of our study was to evaluate the possible determination of everolimus in whole blood using a commercialized microparticle enzyme immunoassay for sirolimus determination.

DESIGN AND METHODS

Everolimus concentrations were determined in blood samples from 11 kidney transplant patients (n=51) and different control materials (n=35) using the Seradyn Innofluor Certican fluorescence polarization immunoassay (FPIA) and the Abbott IMx sirolimus microparticle enzyme immunoassay (MEIA).

RESULTS

The MEIA gave a concentration-dependent cross-reactivity with the everolimus, with a linear regression between the assigned values (y) for the Innofluor Certican calibrators and those obtained (x) using this immunoassay: y=0.96x+0.67 (ma68=0.21 microg/L, r=0.974, p<0.001). The within- and between-run coefficients of variation using the MEIA were <or=7.3%. In analyzing the different blood samples from patients and control materials using the MEIA and FPIA, a linear regression was found: MEIA=0.99FPIA-0.46 (ma68=0.32 microg/L, r=0.967, p<0.001). Correcting the MEIA results by means of the linear regression equation found between the assigned values for the Innofluor Certican calibrators and those obtained using this immunoassay led to a reduction in the deviation with respect to the FPIA values. The possible effect of the hematocrit on the results is analogous for both immunoassays.

CONCLUSIONS

The Abbott IMx sirolimus MEIA permits the simple and precise determination of everolimus in whole blood, making it a valid alternative for the therapeutic monitoring of this immunosuppressant agent.

Renal tubular dysfunction in schizophrenic patients treated with antipsychotic drugs

Several factors have been considered in relation to the free radical formation in schizophrenia, such as the disease itself, drug treatment and smoking. Several chemicals and drugs may cause damage to the renal tubules by different subcellular mechanisms including oxidative stress, and the aim of our study was the investigation of tubular dysfunction in schizophrenic patients. The urinary excretion of beta-N-acetylhexosaminidase (Hex) and its isoenzymes Hex A and Hex B, alpha1-microglobulin, albumin, total proteins and fractionated porphyrins were determined in 45 schizophrenic patients treated with first- and second-generation antipsychotics. In 7 patients, an increase in proteinuria of tubular origin was found, and in one as a result of mixed glomerular/tubular origin. The group of patients had a significantly higher level of excretion than the control group (n = 54) of total Hex (p < 0.001), Hex A (p < 0.05), Hex B (p < 0.001) and the relative proportion of this isoenzyme (p < 0.001). In some cases with normal levels of total Hex and urinary alpha1-microglobulin, the proportion of Hex B was already increased. Significant correlations were found for total Hex and its isoenzymes with alpha1-microglobulin (p < 0.001). Also, the porphyrins had significant correlations with total Hex (p < 0.001), Hex A (p < 0.05), Hex B (p < 0.005) and alpha1-microglobulin (p < 0.001). In the group of patients studied, it was possible to reveal early tubular cell damage (affected structural integrity) with increased excretion of Hex B, possibly mediated by free radicals, previous to the decrease in tubular reabsorption of proteins with low molecular mass filtered by the glomerulus (affected functional integrity).

Chitotriosidase activity in pleural effusions

Chitotriosidase (ChT) is mainly secreted by monocyte-derived macrophages, and is considered a useful marker of macrophage activation. Macrophages represent the first line of defence against Mycobacterium tuberculosis, and consequently the study of ChT activity in pleural effusions (PE) would be of clinical value in the laboratory characterization of tuberculous pleurisy. ChT and adenosine deaminase (ADA) activities were determined in 12 tuberculous PE, 26 non-tuberculous lymphocytic PE and 25 neutrophilic PE. The enzyme heterogeneity study for ChT was made by thermal inactivation at 60 degrees C according to Wajner et al. (Clin Biochem 2004;37:893). ChT activity was significantly higher in the group of tuberculous PE than in the non-tuberculous lymphocytic PE group (p < 0.01), although no significant difference was found with respect to neutrophilic PE. The correlation between ChT and ADA was statistically significant, although in the partial correlation keeping the protein concentration constant, statistical significance was only achieved in tuberculous and non-tuberculous lymphocytic PE (r = 0.358, p < 0.05). In lymphocytic PE, a ChT activity greater than 40 mmol/h/mL has a sensitivity of 92%, specificity of 72%, and efficiency of 78% for the biochemical characterization of tuberculous pleurisy. Residual activities obtained for ChT by heat inactivation did not make it possible to differentiate the enzyme isoforms in PE presumably secreted by macrophages and polymorphonuclear leukocytes.

Effect of the hematocrit and its correction on the relationship between blood tacrolimus concentrations obtained using the microparticle enzyme immunoassay (MEIA) and enzyme multiplied immunoassay technique (EMIT)

The Abbott microparticle enzyme immunoassay (MEIA) and the Dade Behring enzyme multiplied immunoassay technique (EMIT) are the most frequently used methods in the therapeutic drug monitoring of tacrolimus; however, a hematocrit-dependent interference for the MEIA has been described. In 244 whole blood samples from patients with liver (n=152) and kidney (n=92) transplants, the MEIA/EMIT ratio presented a highly significant negative correlation with the hematocrit (r = -0.482, p < 0.001). On distributing the samples into three groups with a hematocrit of less than 30%, 30-40%, and higher than 40%, different regression equations were found between the results of MEIA and EMIT and demonstrate the different effect of the hematocrit on both immunoassays. Correcting the MEIA results by calculation for a hematocrit of less than 30% and higher than 40% (Hermida et al. Clin Lab 2005; 51: 43-45) led to a regression with EMIT that was similar to that found between MEIA and EMIT for the group of samples with a hematocrit of 30-40%. Furthermore, the corrected MEIA/EMIT ratio had a poor correlation with the hematocrit (r = 0.149, p < 0.05). In 95 samples with a hematocrit of less than 25% (n=73) and higher than 40% (n=22) we also determined the tacrolimus levels using the modified MEIA method to correct hematocrit interference, as proposed by Tomita et al. (Ther Drug Monit 2005; 27: 94-97). In the samples with a hematocrit of less than 25%, correcting the MEIA results by calculation produced results that were similar and had a high correlation coefficient (r = 0.954, p < 0.001) to those of the modified MEIA method, whose application as a routine practice is more expensive and laborious. Calculation of the corrected MEIA values in anemic patients may be useful for the therapeutic monitoring of tacrolimus.

Serum cystatin C for the prediction of glomerular filtration rate with regard to the dose adjustment of amikacin, gentamicin, tobramycin, and vancomycin

Dosage regimes of aminoglycosides and vancomycin are modified according to the glomerular filtration rate (GFR). In 130 hospitalized patients who were administered amikacin, gentamicin, tobramycin, and vancomycin by intermittent intravenous infusion, we compared the predicted GFR values from the serum concentrations of creatinine (Cockcroft and Gault. Nephron. 1976;16:31-41) and cystatin C (Larsson et al. Scand J Clin Lab Invest. 2004;64:25-30) with respect to their relevance for proper dosage. In 83% and 67% of the cases, respectively, the serum levels of albumin and cholinesterase were below the corresponding lower limit of the reference range. The ratio of creatinine/cystatin C concentrations presented significant correlations with the predicted rate of creatinine production (r=0.762, P<0.001), serum albumin concentration (r=0.205, P<0.05), and catalytic serum concentrations of cholinesterase (r=0.207, P<0.05), gamma glutamyltransferase (r=-0.273, P<0.01), and alkaline phosphatase (r=-0.289, P<0.01). The GFR (mean+/-SD; median) predicted by the serum creatinine (84.0+/-35.1 mL/min/1.73 m; 82.6 mL/min/1.73 m) was significantly higher (P<0.001) than that predicted by the serum cystatin C (53.1+/-30.2 mL/min/1.73 m; 44.9 mL/min/1.73 m). The ratio between the GFR values predicted by creatinine and cystatin C had a highly significant negative correlation with the rate of creatinine production (r=-0.912, P<0.001). Furthermore, significant differences were found for the peak concentrations and clearances of amikacin and vancomycin estimated by means of the Abbottbase Pharmacokinetic Systems program, and using the GFR values predicted by the serum creatinine and cystatin C (P<0.005). In patients with hepatic dysfunction, the clearance of creatinine predicted by the Cockcroft-Gault formula leads to a significant overestimation of the GFR. Cystatin C seems to be a valid alternative as a GFR marker with regard to drug dose adjustment in these cases.

Comparison of estimated glomerular filtration rates from serum creatinine and cystatin C in patients with impaired creatinine production

Determination of the glomerular filtration rate (GFR) is important for the drug dosage adjustment and clinical management of patients. The aim of our study was the comparison of estimated GFR values from serum creatinine (eGFRcreatinine) and cystatin C (eGFRcystatin C) in patients with impaired creatinine production. A total of 564 serum samples from patients with kidney disease (n=179), liver (n=71) and kidney (n=182) transplants, critically ill patients (n=82) and healthy subjects (n=50) were analyzed for serum creatinine and cystatin C. The creatinine production rate (CPR) was significantly lower in the different groups of patients than in the control group (p<0.001). A negative correlation was found between the eGFRcreatinine/eGFRcystatin C ratio and CPR (r= -0.964, p<0.001). For CPR higher than 800 mg/24h both procedures for estimating the GFR classified values higher and lower than 60 mL/min with an acceptable agreement; however, for CPR less than 800 mg/24h the eGFRcreatinine led to false negatives in a high number of cases with eGFRcystatin C <60 mL/min.

β-Hexosaminidase isoenzyme profiles in serum, plasma, platelets and mononuclear, polymorphonuclear and unfractionated total leukocytes

OBJECTIVES

The relative proportion in percentage of the isoenzyme A of beta-hexosaminidase (Hex) is the single discriminatory function most frequently used for the biochemical screening of heterozygote Tay-Sachs disease carriers. It has been suggested that the assay of the Hex isoenzymes in homogeneous cell preparations is preferable to that in mixed total leukocytes which present greater interindividual variation. The major aim of our study was the evaluation of this hypothesis.

DESIGN AND METHODS

Total Hex and its Hex A and Hex B isoenzymes were determined in different samples of serum and plasma (n = 81) as well as in lysates of platelets (n = 75), and mononuclear (n = 81), polymorphonuclear (n = 81) and mixed total leukocytes (n = 33).

RESULTS

The interindividual variations found for % Hex A in the different biological samples were: plasma (CV = 23.4%), platelets (CV = 10.2%), mononuclear (CV = 5.7%), polymorphonuclear (CV = 5.3%) and total leukocytes (CV = 7.1%). Although the relative proportion of Hex A was significantly greater in polymorphonuclear than in mononuclear leukocytes (P < 0.001), a statistical significance was not attained for the correlation between the relative proportions of blood polymorphonuclear cells and Hex A in mixed total leukocytes (r = 0.220).

CONCLUSIONS

The use of total leukocyte lysates does not appear to introduce a significant increase for the interindividual variation of the Hex A isoenzyme relative proportion in relation to the use of homogeneous cell preparations.

A comparative study of three kidney biomarker tests in autosomal-dominant polycystic kidney disease

BACKGROUND

The relationship between the progress of tubular damage and renal insufficiency in autosomal-dominant polycystic kidney disease (ADPKD) is a subject of doubtless interest, and is the object of this present work.

METHODS

A total of 92 adult ADPKD patients of both genders were studied, none of which presented end-stage renal disease (ESRD), and classified according to an ultrasound score based on kidney size and number of cysts. Urinary albumin and beta-N-acetylhexosaminidase (Hex) and its isoenzymes were determined, together with serum glutathione peroxidase, cystatin C, creatinine, and urea.

RESULTS

A frequent elevation of the urinary Hex was found and an alteration of its isoenzymatic profile, with 31% of the normotensive patients with normoalbuminuria already presenting an increased proportion of Hex B isoenzyme. Keeping age constant, a partial significant correlation was found between the ultrasound score and the proportion of Hex B (r = 0.352, P < 0.05), but not with albuminuria or cystatin C. In 42 patients the different biochemical variables were again determined after 1 year, finding that in the 13 normotensive patients with normoalbuminuria there had been a significant decrease in the concentration of cystatin C (P < 0.05), and a significant increase in the urinary excretion of albumin and Hex B isoenzyme (P < 0.05). By the other hand, in the other 29 patients with micro- or macroalbuminuria and hypertension, no significant differences were found.

CONCLUSION

The results point toward an important participation of tubular damage in the pathogenesis of this disease. It may also be suggested that in normotensive and normoalbuminuric ADPKD patients, a gradual increase of glomerular filtration would be produced. After the start of hypertension and microalbuminuria, the glomerular filtration rate (GFR) would decrease progressively, although more slowly.

Thermodynamic study of beta-N-acetylhexosaminidase enzyme heterogeneity in human seminal plasma

BACKGROUND

It has been suggested that the activity of beta-N-acetylhexosaminidase (Hex) in seminal plasma may be used as a biochemical marker of azoospermia. The purpose of our study was to evaluate this hypothesis using a thermodynamic procedure developed to determine total Hex activity and that of its isoenzymes in this biological fluid.

METHODS

Using the substrate 3,3'-dichlorophenolsulphoftaleinil N-acetyl-beta-D-glucosaminide, a highly significant difference (p<0.001) is found between the activation energy of Hex A (41.5 kJ/mol) and of Hex B (72.3 kJ/mol), making it possible to determine the activity of these isoenzymes from the apparent activation energy of the total Hex in seminal plasma.

RESULTS

A significant difference between the normozoospermic and azoospermic groups was only found for Hex A isoenzyme activity (p<0.05), although with considerable overlapping between the values of both groups. Significant partial correlations were found for the total Hex, Hex A and Hex B activities with the immobile spermatozoa count (p<0.01) and for total Hex and Hex B with the dead spermatozoa count (p<0.05). In turn, Hex A had a significant partial correlation with the live spermatozoa count (p<0.05); however, Hex activity in seminal plasma of acromosomal origin appears to be of little importance in quantitative terms.

CONCLUSIONS

It was not possible to confirm that total Hex activity in seminal plasma, or even of its isoenzymes Hex A and Hex B, is a suitable biochemical marker of azoospermia (efficiency< or =67%). The thermodynamic procedure described may be a useful alternative for the study of the Hex enzyme heterogeneity in spermatozoa.

A Theoretical Method for Normalizing Total Serum Valproic Acid Concentration in Hypoalbuminemic Patients

In patients with hypoalbuminemia, the total serum concentration of valproic acid may offer poor clinical information; however, very few clinical laboratories routinely analyze the free concentration of the drug. The aim of this study was to design a procedure to normalize the total concentration of valproic acid according to the level of serum albumin and using previously published free fraction values. In 121 adult patients, with albumin levels of 18 - 41 g/L, the total concentration of valproic acid was normalized using the derived equation: C(N) = alpha(H)C(H)/6.5, where alpha(H) is the free fraction of the drug corresponding to the patient's particular albuminemia and C(H) is the total concentration of valproic acid. The value of 6.5 corresponds to the free fraction of the drug for a serum albumin of 42 g/L (percentile 50 of the reference range). For total concentrations lower than 75 mg/L, the predicted normalized valproic acid concentrations were reasonably concordant with the observed normalized concentrations calculated using the data from a protein-binding study. In a significant number of cases, subtherapeutic concentrations of the drug became therapeutic and even supratherapeutic when corrected according to the albumin levels. Furthermore, cases with therapeutic drug concentrations frequently became supratherapeutic when normalized. The limitations and clinical applications of the proposed formula for normalizing the total concentration of valproic acid are presented. It is concluded that it may be useful for the posological management of hypoalbuminemic patients when the free concentration of the drug is not available, and decisions have to be made based on the total serum concentration.

Effect of Antiepileptic Drugs on the Urinary Excretion of Porphyrins in Non-porphyric Subjects

The action of some anticonvulsant drugs as the causal agents of attacks of acute porphyria has been widely documented in the literature. However, little attention has been paid to the effect of these drugs on the urinary excretion of porphyrins in non-porphyric subjects. In a sample of 82 epileptic patients treated with phenobarbital (n = 54), phenytoin (n = 64), carbamazepine (n = 33), and valproate (n = 8), the daily doses were expressed according to a drug score that would reflect the capacity of these drugs as enzymatic inducers when administered in polytherapy. A significantly increased urinary excretion of D-glucaric acid (DGA) and porphyrins was found in this group of patients (P<0.001), with coproporphyrin being the major fraction in all cases (>60%). Urinary DGA had a highly significant correlation with the drug score (r = 0.783, P<0.001); however, no significant correlations were found between the urinary porphyrins and DGA (r = 0.005) or the drug score (r = 0.053). Neither was any significant relationship found between the urinary porphyrins and the serum activity of 5'-nucleotidase (r = 0.066) or the presence of a cholestasis objectivized through the presence of the isoform of gamma-glutamyltransferase with beta-globulins electrophoretic mobility. However, in a group of 10 patients a significant correlation was found between the urinary excretion of porphyrins and beta-N-acetylhexosaminidase (r = 0.790, P<0.01). Therefore, it does not appear that the liver enzyme induction, or even a subclinical cholestasis, produced by the antiepileptic drugs administered to these patients may serve to explain the increase in the urinary excretion of porphyrins. A possible renal origin is proposed for the increase of urinary porphyrins in these cases.

Clinical significance of hematocrit interference in the tacrolimus II microparticle enzyme immunoassay: a tentative approach

Recently, the possible interference of hematocrit on the results of the Abbott Tacrolimus II microparticle enzyme immunoassay (MEIA) has been described, although its significance in clinical practice has not been established as yet. The aim of our study was the evaluation of the significance of this analytical interference in therapeutic tacrolimus monitoring. In 1121 cases selected at random over a 9-month period from kidney (n=379) and liver (n=742) transplant patients, an estimation was made of errors caused by the hematocrit in the results provided by the Tacrolimus II MEIA. In accordance with the available data, it was assumed that an error may be produced beyond the range of hematocrit values from 30% to 40%, either positive or negative respectively, of 3% per unit of hematocrit. The acceptance criterion for accuracy was no more than 15% of deviation (error) with respect to the experimental concentration of tacrolimus. In 160 cases (14.3%) the results of the Tacrolimus II MEIA would not be acceptable due to hematocrit-dependent errors, both with positive (hematocrit <25%) in 108 cases (9.7%) and negative values (hematocrit >45%) in 52 cases (4.6%). The obtained results demonstrate the practical interest of the subject, although additional studies are required in order to validate our approach to the clinical significance of this hematocrit-dependent interference in the Tacrolimus MEIA.

Activation of serum aminotransferases by pyridoxal-5′-phosphate in epileptic patients treated with anticonvulsant drugs

OBJECTIVES

Significant decreases in the serum concentration of pyridoxal-5' -phosphate (PLP) have been described in epileptic patients treated with anticonvulsant drugs. This would be expected to lead to a decrease in the sensitivity of aspartate aminotransferase (AST) and alanine aminotransferase (ALT) for the detection of hepatocellular damage in these patients if optimized methods with coenzyme supplementation are not used. The aim of our study was to evaluate this hypothesis.

DESIGN AND METHODS

The serum activities of AST and ALT (with and without the addition of PLP) were determined in a group of 90 adult epileptic patients (56 male, 34 female) undergoing chronic treatment polytherapy with phenobarbital, phenytoin, carbamazepine, and valproic acid. As a control group, 49 clinically healthy individuals were studied with a similar distribution for age and sex.

RESULTS

Supplementation with PLP produced an activation of AST and ALT in both the control and patient groups with a highly significant correlation between the enzyme activities with and without the addition of PLP (r > or = 0.956, P < 0.001). The differences between the control and patient groups for the PLP activation of both aminotransferases were not clinically significant. The increases in AST (9%) and ALT (28%) in the patient group compared to the control group were lower than those found for alcohol dehydrogenase (ADH, 82%) and alpha-glutathione S-transferase (alphaGST, 76%).

CONCLUSIONS

It does not appear that in the epileptic patients studied the in vitro addition of PLP increased the diagnostic sensitivity of AST and ALT for hepatocellular injury. The lower responses of both aminotransferases to the action of anticonvulsant drugs in relation to other cytosolic enzymes may be due to the preferred periportal localization of AST and ALT in the hepatic lobe.

Chitotriosidase activity in plasma and mononuclear and polymorphonuclear leukocyte populations

In the general population, about 5% of individuals are homozygotic and 35% are heterozygotic carriers for chitotriosidase (ChT) deficiency. Activated macrophages are considered to be the main source of plasma ChT activity, which permits the biochemical characterization of homozygote deficients. However, in the case of detecting heterozygotic carriers, the results are often inconclusive. The activities of ChT in plasma and mononuclear (MN) and polymorphonuclear (PMN) leukocytes were determined in 169 control subjects (72 males and 97 females) with a mean age (+/- SD) of 47.5+/-9.7 years (range 18-96 years). The specific enzyme activity was in PMN leukocytes >MN leukocytes >plasma, with a highly significant partial correlation being found between the activities of ChT in plasma and PMN leukocytes (r=0.578, P<0.001). A significant correlation was found between the age of the patients studied and plasma ChT activity (r=0.568, P<0.001). No significant correlation was found for enzyme activities in MN (r=0.105) or in PMN leukocytes (r=0.043). The results obtained suggest that, in normal physiological conditions, PMN leukocytes may secrete ChT to the plasma. Although the activities of ChT in MN and PMN leukocytes are not affected by demographic factors, it is not possible to use them for the biochemical detection of ChT-deficient heterozygotic carriers.

Biochemical characterization of the GM2 gangliosidosis B1 variant

The deficiency of the A isoenzyme of beta-hexosaminidase (Hex) produced by different mutations of the gene that codes for the alpha subunit (Tay-Sachs disease) has two variants with enzymological differences: the B variant consists of the absence of Hex A isoenzyme and the B1 variant produces an inactive Hex A isoenzyme for the hydrolysis of the GM2 ganglioside and synthetic substrates with negative charge. In contrast to the early childhood form of the B variant, the B1 variant appears at a later clinical stage (3 to 7 years of age) with neurodegenerative symptoms leading to the death of the patient in the second decade of life. The most frequent mutation responsible for the GM2 gangliosidosis B1 variant is R178H, which has a widespread geographic and ethnic distribution. The highest incidence has been described in Portugal, which has been suggested as the point of origin of this mutation. Biochemical characterization of this lysosomal disease is carried out using negatively charged synthetic alpha subunit-specific sulfated substrates, since Hex A isoenzyme heat-inactivation assays are not applicable. However, the determination of the apparent activation energy of Hex using the neutral substrate 3,3'-dichlorophenolsulfonphthaleinyl N-acetyl-beta-D-glucosaminide, may offer a valid alternative. The presence of an alpha subunit in the alphabeta heterodimer Hex A means that its activation energy (41.8 kJ/mol) is significantly lower than that of the betabeta homodimer Hex B (75.1 kJ/mol); however, as mutation inactivates the alpha subunit, the Hex A of the B1 variant presents an activation energy that is similar to that of the Hex B isoenzyme.

Effect of analytical inaccuracy on dose adjustment for gentamicin using the Abbottbase Pharmacokinetic Systems

We studied the effect of analytical inaccuracy on the determination of gentamicin for estimation of the recommended dose regime (RDR) using the Abbottbase Pharmacokinetic System programme (PKS). The study was carried out in a group of 26 adult patients, determining their serum levels of gentamicin (Cmin and one hour after completing infusion, C1h) and these concentrations were processed using the PKS in order to establish the RDR (dose, posologic interval and infusion time) for each patient. Various simulations were made for each patient, adding and subtracting the clinically acceptable error (CAE) once, twice and three times to the experimentally determined Cmin and the estimated Cmax. The simulated dose regime (SDR) was calculated for each patient. The number of cases in which the SDR differed from the RDR were determined, and also the percentage of variation of the SDR with respect to the RDR. A highly significant correlation was found between C1h and the estimated Cmax (r = 0.941, p < 0.001). A statistically significant difference (p < 0.05) and a clinically significant difference were found between both populations of concentrations, and so the simulations were carried out using the estimated Cmax. A frequency of change of 29.87% was recorded in the RDR, and inaccuracies of +/- CAE in the Cmin and Cmax led to changes of the RDR in 21.2% of the cases studied. A higher frequency of change in the RDR was observed in additive-type simulations for Cmax, with this change mainly affecting the dose, and in subtractive-type simulations for Cmin, with this change affecting both the dose and the posologic interval. An inaccuracy of the order of +/- CAE in the serum concentrations of gentamicin (both for Cmin and Cmax) frequently led to changes in the RDR, thus requiring precise and accurate concentration results, particularly in the case of Cmin. For this reason, we would suggest the convenience of using a previous moment in the time concentration level in the monitoring of gentamicin instead of Cmin, which would be determined with greater imprecision and inaccuracy.

Serum markers of monocyte/macrophage activation in patients with Alzheimer's disease and other types of dementia

OBJECTIVES

Recently an increase in serum neopterin has been described in patients with Alzheimer's disease (AD) that would be associated with an increased cell-mediated immune response. We have studied the serum levels of several monocyte/macrophage activation markers in patients with AD and other types of dementia.

DESIGN AND METHODS

Serum neopterin concentration, and the chitotriosidase (ChT), angiotensin-converting enzyme (ACE) and adenosine deaminase (ADA) activities were determined in 30 patients with AD, in 19 patients with other types of dementia, and in 24 nonaffected controls.

RESULTS

Neopterin concentration was significantly higher in the subgroup of AD patients with a global deterioration scale higher than in the other patients with AD, patients with other types of dementia and in the control group (p < 0.005). However, the activities of ChT, ACE and ADA, despite having a significant correlation with neopterin, did not present any statistically significant differences among the groups studied.

CONCLUSION

In the most advanced clinical stages of AD, as well as an increased immune activation, an impaired formation of tetrahydrobiopterin from dehydroneopterin triphosphate would contribute to an increase in the serum concentration of neopterin. However, the large overlap between the groups, limits the possible clinical value of serum neopterin in AD patients.

Assessment of copper status in epileptic patients treated with anticonvulsant drugs by measuring the specific oxidase activity of ceruloplasmin

Significant increases in serum levels and decreases in hair copper levels have been previously described in epileptic patients treated with anticonvulsant drugs. A condition not directly related to copper nutriture, such as chronic treatment with these drugs, could increase the serum concentrations of copper and ceruloplasmin and would mask a possible copper deficiency produced by drug-increased biliary copper excretion. Serum immunoreactive ceruloplasmin concentration and its oxidase activity were determined in 90 adult epileptic patients treated with phenobarbital (n=60), phenytoin (n=70), carbamazepine (n=33) and valproic acid (n=8). The levels of ceruloplasmin and oxidase activity were significantly higher (P<0.001) than in an age and gender-matched control group (n=49). The significant correlations (P<0.01) between ceruloplasmin and the urinary excretion of D-glucaric acid, serum gamma-glutamyltransferase (GGT) and drug score in the patients group, would suggest that phenobarbital-type enzyme-inducing agents may increase the hepatic synthesis of ceruloplasmin. In 11 patients with a beta-globulin migrating GGT isoform (GGT3), a sensitive marker of cholestasis, the levels of ceruloplasmin, oxidase activity and total GGT activity were significantly higher (P<0.05) than in the group of 79 patients without the GGT3 isoform; consequently, in some cases a drug-induced cholestasis may also contribute to the increase of serum copper and ceruloplasmin. The values obtained for the specific oxidase activity of ceruloplasmin (activity per unit mass of enzyme protein) suggest that in the most of the cases, chronic administration of phenobarbital, phenytoin, carbamazepine or valproic acid, does not produce marginal or moderate copper deficiency.

Relationship between changes in drug score, D-glucaric acid excretion, and gamma-glutamyltransferase and beta-glucuronidase serum activities during anticonvulsant treatment

The purpose of this study was to investigate the relationship of changes in the enzyme-inducing anticonvulsant daily dosage (drug score) to variations in urinary D-glucaric acid excretion and gamma-glutamyltransferase and beta-glucuronidase serum activities. These biochemical determinations were carried out before and after a mean period of 5.0 years in 16 adult epileptic patients (8 men and 8 women) treated with phenobarbital, phenytoin and/or carbamazepine and with a good therapeutic compliance. A significant correlation between D-glucaric acid excretion and drug score was obtained (r=0.508, p<0.001). When the interindividual variation was diminished by assessing the changes of these variables in the same subjects, the correlation was better (r=0.836, p<0.001). However, a statistical significance was not attained between the gamma-glutamyltransferase or beta-glucuronidase and drug score changes. Therefore the urinary excretion of D-glucaric acid appears to be more sensitive to changes in anticonvulsant drug score than serum gamma-glutamyltransferase and beta-glucuronidase.

How suitable are currently used carbamazepine immunoassays for quantifying carbamazepine-10,11-epoxide in serum samples?

The pharmacologic activity of the metabolite carbamazepine-10,11-epoxide (CBZ-E) is similar to that of carbamazepine (CBZ). As a result, determining the CBZ + CBZ-E concentration would offer a better correlation with therapeutic or toxic effects than measurement of the parent drug alone. However, the most upto-date CBZ immunoassays are not able to quantitatively measure CBZ-E. Trough serum concentrations of CBZ were measured in 116 patients either in monotherapy (n = 66) or in polytherapy with other antiepileptic drugs (n = 50) using the Dade Dimension and Roche Cobas Integra immunoassays. The results were compared with those obtained for CBZ + CBZ-E by high-performance liquid chromatography (HPLC). The Dade Dimension immunoassay gave a concentration-dependent CBZ-E cross-reactivity for the metabolite levels present in the samples studied (mean, 1.41 mg/L; range, 0.0-7.6 mg/L), whereas the Roche Cobas Integra gave a negligible cross-reactivity. The results provided by the Dade Dimension immunoassay only presented a clinically significant difference with regard to the CBZ + CBZ-E value in the group of patients comedicated with valproic acid. The results of this immunoassay revealed a high correlation and small standard error of the estimate for the total group of patients with the composite results of parent drug + metabolite obtained by HPLC (r = 0.993, ma68 = 0.22 mg/L), with a regression line CBZ + CBZ-E = 1.09 CBZ(Dade Dimension) + 0.07. By using the Dade Dimension immunoassay, it is possible to make a clinically valid estimate of the CBZ + CBZ-E concentrations in patients treated with CBZ in monotherapy and polytherapy. However, other immunoassays with a lower CBZ-E cross-reactivity are not suitable for this estimate to be made at increased metabolite levels.

Thermodynamic determination of plasma and leukocyte beta-hexosaminidase isoenzymes in homozygote and heterozygote carriers for the GM2 gangliosidosis B1 variant

In the GM2 gangliosidosis B1 variant, the mutated isoenzyme A of beta-hexosaminidase (Hex) is incapable of hydrolyzing ganglioside GM2 and negatively charged substrates. Biochemical characterization of this lysosomal disease is carried out using synthetic alpha-subunit-specific sulfated substrates, as heat-inactivation assays are not applicable. The apparent enzyme activation energy of Hex using the chromogenic substrate 3,3'-dichlorophenolsulfonphthaleinyl N-acetyl-beta-D-glucosaminide is related directly to the relative proportions of Hex A and Hex B isoenzymes. This thermodynamic variable was used for the study of Hex enzyme heterogeneity in 3 patients with the GM2 gangliosidosis B1 variant and 6 heterozygote carriers. Hex activity was determined at 25 degrees C, 30 degrees C, 35 degrees C, and 37 degrees C in a Cobas Bio analyzer (Roche Diagnostics, Basel, Switzerland), and Arrhenius plot slopes and apparent activation energies were calculated in plasma samples and mononuclear and polymorphonuclear leukocyte lysates. The determination of the Hex isoenzymes in plasma presented a high discrimination power for B1 variant patients but not for heterozygote carriers, in whom false-negative results may be obtained. However, thermodynamic evaluation of the isoenzyme composition of Hex in leukocyte lysates permits the biochemical identification of patients with the GM2 gangliosidosis B1 variant and of heterozygote carriers.

Effect of partial proteolysis on the activation energy of beta-n-acetylhexosaminidase precursor and mature forms

Using 3,3'-diclorophenolsulfoftaleinil N-acetyl-beta-D-glucosaminide as a substrate, the apparent activation energy of beta-N-acetylhexosaminidase (Hex) was determined in samples of plasma and urine, as well as in leukocyte and platelet lysates. Incubation with papain produced an increase in this thermodynamic variable for plasma Hex (precursor forms with high molecular mass) that would be caused by the proteolytic action of papain on the Hex A isoenzyme. However, digestion with papain did not significantly modify the activation energy of Hex in leukocyte and platelet lysates (mature enzymatic forms). In 11 healthy subjects and 28 patients with different renal diseases, no statistically significant differences were found with regard to the values obtained in cellular lysates for variations in the activation energy of urinary Hex, regardless of whether they presented normoalbuminuria, microalbuminuria or macroalbuminuria. These results support the hypothesis that even in patients with proteinuria, no significant amounts of plasma Hex precursor forms are found in urine samples, and the source of the enzyme activity is the kidney itself.

Thermodynamic determination of beta-hexosaminidase isoenzymes in mononuclear and polymorphonuclear leukocyte populations

Isoenzymes of beta-hexosaminidase (Hex) were determined in mononuclear (MN) and polymorphonuclear (PMN) leukocytes, with a thermodynamic method using the chromogenic substrate sodio-3,3'-dichlorophenolsulfonphthaleinyl N-acetyl-beta-D-glucosaminide. Imprecision was very satisfactory, and the results are very much in agreement with those obtained using the fluorogenic substrates 4-methylumbelliferyl N-acetyl-beta-D-glucosaminide and 4-methylumbelliferyl N-acetyl-beta-D-glucosaminide 6-sulfate. In 163 healthy individuals we found, for the proportion as a percentage of the Hex A isoenzyme, significantly higher values (P < 0.001) in PMN than in MN cells (71.56 +/- 0.30% vs. 54.28 +/- 0.24%), meaning that it would not appear advisable to use total leukocyte lysates for evaluating this variable. The method is fast, precise, and highly suitable for the biochemical diagnosis and heterozygote screening of GM2 gangliosidoses, and would be applicable in cases of thermolabile Hex B and for detecting the B1 variant.

More on the reliability of the microparticle enzyme immunoassay (MEIA) for therapeutic tacrolimus monitoring

Recently, the validity of determining tacrolimus concentrations in blood samples using Abbott's microparticle enzyme immunoassay (MEIA) has been seriously questioned. This communication presents the results obtained in our laboratory using the MEIA for 31 pooled blood samples from kidney and liver transplant patients (Tacrolimus International Proficiency Testing Scheme). A good correlation was found with regard to the average of the MEIA method (r=0.950) without reaching clinical significance for the difference between the means (9.54 ng/ml vs 9.74 ng/ml), although the standard error of the estimate (Syx=0.66 ng/ml) was clinically significant. With regard to the average values for HPLC-methods, a lower correlation coefficient was found (r=0.819), with a difference between the means (9.54 ng/ml vs 8.91 ng/ml) slightly greater than the clinically acceptable value, and a clinically significant standard error of the estimate (Syx=1.22 ng/ml). In the case of the correlation between the average values for the MEIA and HPLC methods, a higher correlation coefficient was found (r=0.918), with a difference between the means (9.74 ng/ml vs 8.91 ng/ml) and a standard error of the estimate (Syx=0.75 ng/ml) being clinically significant. However, these differences were lesser than 15% of HPLC results in accordance with the American Association of Pharmaceutical Scientists acceptance criteria for analytical methods employed for quantification of drugs and their metabolites.

Relationship between cyclosporine concentrations obtained using the Roche Cobas Integra and Abbott TDx monoclonal immunoassays in pre-dose and two hour post-dose blood samples from kidney transplant recipients

Current evidence suggests that cyclosporine (CsA) concentration in blood samples taken 2 hours after Neoral microemulsion (Novartis Pharmaceuticals; East Hanover, NJ) administration (C2) predicts clinical events in transplant patients better than the pre-dose (trough) concentration (C0). Similarly, previous findings have shown that the metabolites/CsA ratio is substantially lower in C2 than in C0 samples; however the between-monoclonal immunoassay differences for C2 samples have received little attention in the literature. In 56 C samples and 60 C samples from renal transplant patients, CsA levels were determined using the monoclonal fluorescence polarization immunoassay (mFPIA) from Abbott (Abbott Park, IL) and the homogeneous enzyme immunoassay technique (HEIT) from Roche Diagnostics (Basel, Switzerland). In both cases a high correlation coefficient between the results was obtained (r > or = 0.971), with a linear regression for C0 samples: mFPIA = 1.47 HEIT + 22.0 and for C2 samples: mFPIA = 1.11 HEIT + 71.96. The difference between the linear regression slopes was statistically significant (P < 0.001), and the mFPIA/HEIT ratio was significantly higher for C than for C samples (P < 0.001).

Effect of analytical inaccuracy on dose adjustment for vancomycin, amikacin, and tobramycin using the Abbottbase Pharmacokinetic Systems

The authors studied the inaccuracy effect in the determination of C(min) and C(1h) post-infusion serum concentrations of vancomycin, amikacin, and tobramycin on the recommended dose regimen (RDR) using the Abbottbase Pharmacokinetic Systems (PKS) program (Abbott; Abbott Park, IL). According to previously established criteria, the clinically acceptable error (CAE) was defined as 1/8 of the therapeutic range. For a total of 647 simulations, in most cases (94.3%) an inaccuracy of up to three times the CAE did not lead to changes in the RDR. However, and particularly for amikacin and tobramycin, in some cases an inaccuracy in the order of the CAE in C(min) lead to important differences in the RDR, which could have important consequences in clinical practice. For therapeutic monitoring of these antibiotics, it is suggested that a serum concentration from a previous moment in time, which may be determined with greater precision and accuracy, could be used instead of C(min).

Plasma and peripheral leukocyte beta-N-acetylhexosaminidase isoenzymes and disease activity in rheumatoid arthritis

OBJECTIVES

Recently it has been suggested that serum beta-N-acetylhexosaminidase (Hex) could be a joint destruction marker in rheumatoid arthritis (RA) patients. However, a large amount of serum Hex activity has its source from platelets, and the blood platelet-count is often increased in RA, which may have masked the significance of the results. The purpose of this study was to investigate the relationship between plasma activity of Hex and disease activity or severity.

DESIGN AND METHODS

In 51 patients with RA, with an evolution period for the illness of 10.9 +/- 1.2 yr (range 1-40 yr), we determined the total Hex activity together with its Hex A and B isoenzymes in plasma and in mononuclear (MN) and polymorphonuclear (PMN) leukocytes.

RESULTS

The plasma activity of total Hex and Hex B isoenzyme was slightly higher in the group of patients studied (p < 0.01), together with the specific activity of total Hex, Hex A and B in PMN leukocytes (p < 0.001) than in the control group. No significant correlation was found between plasma or leukocyte Hex and the radiologic evaluation of the disease (Sharp's modified method), or the patient's functional capacity (modified Health Assessment Questionnaire). Likewise, a significant correlation between Hex activity and laboratory inflammation markers (C reactive protein, sialic acid, erythrocyte sedimentation rate) or the evolution time of the disease was not found.

CONCLUSIONS

The plasma activity of total Hex, or even of its isoenzymes Hex A and Hex B, does not appear to be a reliable marker of erosion and cartilage degradation in RA patients. Liver function appears to be the major determinant for the plasma Hex activity in these patients.