Should we depend on reference intervals from manufacturer package inserts? Comparing TSH and FT4 reference intervals from four manufacturers with results from modern indirect methods and the direct method

OBJECTIVES

Correct interpretation of thyroid function tests relies on correct reference intervals (RIs) for thyroid-stimulating hormone (TSH) and free thyroxine (FT4). ISO15189 mandates periodic verification of RIs, but laboratories struggle with cost-effective approaches. We investigated whether indirect methods (utilizing historical laboratory data) could replace the direct approach (utilizing healthy reference individuals) and compared results with manufacturer-provided RIs for TSH and FT4.

METHODS

We collected historical data (2008-2022) from 13 Dutch laboratories to re-establish RIs by employing indirect methods, TMC (for TSH) and refineR (for FT4). Laboratories used common automated platforms (Roche, Abbott, Beckman or Siemens). Indirect RIs (IRIs) were determined per laboratory per year and clustered per manufacturer (>1.000.000 data points per manufacturer). Direct RIs (DRIs) were established in 125 healthy individuals per platform.

RESULTS

TSH IRIs remained robust over the years for all manufacturers. FT4 IRIs proved robust for three manufacturers (Roche, Beckman and Siemens), but the IRI upper reference limit (URL) of Abbott showed a decrease of 2 pmol/L from 2015. Comparison of the IRIs and DRIs for TSH and FT4 showed close agreement using adequate age-stratification. Manufacturer-provided RIs, notably Abbott, Roche and Beckman exhibited inappropriate URLs (overall difference of 0.5-1.0 µIU/mL) for TSH. For FT4, the URLs provided by Roche, Abbott and Siemens were overestimated by 1.5-3.5 pmol/L.

CONCLUSIONS

These results underscore the importance of RI verification as manufacturer-provided RIs are often incorrect and RIs may not be robust. Indirect methods offer cost-effective alternatives for laboratory-specific or platform-specific verification of RIs.

Point-of-care high-sensitivity troponin-I analysis in capillary blood for acute coronary syndrome diagnostics point-of-care troponin-I for ACS diagnostics

OBJECTIVES

Patients with acute coronary syndrome (ACS) should be referred promptly to the hospital to reduce mortality and morbidity. Differentiating between low-risk and high-risk patients remains a diagnostic challenge. Point-of-care testing can contribute to earlier disposition decisions for patients excluded from ACS. This study describes the validation of the Atellica^® VTLi. Patient-side Immunoassay Analyzer for high-sensitivity troponin point-of-care (POC) analysis. (The Atellica VTLi is not available for sale in the USA. The products/features (mentioned herein) are not commercially available in all countries. Their future availability cannot be guaranteed).

METHODS

A total of 152 patients with acute chest pain admitted at the cardiac emergency department (ED) were included in the study. Capillary blood was compared with a whole blood and plasma sample obtained by venipuncture. All samples were analyzed using the Atellica VTLi Patient-side Immunoassay Analyzer; in addition, plasma was analyzed by a central lab immunoassay analyzer.

RESULTS

No significant difference was observed between venous whole blood vs. plasma analyzed by the Atellica VTLi Patient-side Immunoassay Analyzer. The difference between capillary blood and venous blood showed a constant bias of 7.1%, for which a correction factor has been implemented. No clinically relevant differences were observed for the capillary POC results compared to plasma analyzed with a standard immunoassay analyzer.

CONCLUSIONS

The Atellica VTLi Patient-side Immunoassay Analyzer for high-sensitivity troponin analysis shows equivalent results for all sample types, including capillary blood. No clinically relevant discordances were observed between capillary POC and central laboratory results. With additional studies, this could pave the way towards rapid testing of high-sensitivity troponin in the ambulance or the general practitioner's office without the need for hospitalization of patients with acute chest pain.

URGENT 1.5: diagnostic accuracy of the modified HEART score, with fingerstick point-of-care troponin testing, in ruling out acute coronary syndrome

Background

The HEART score is a validated risk stratification tool for chest pain patients presenting to the emergency department and was recently investigated for implementation in a pre-hospital setting. Fingerstick (capillary blood) point-of-care (POC) troponin testing enables quick measurements outside the hospital and seems easier to implement than the current venous blood sampling techniques. This study investigates the diagnostic accuracy of the modified HEART score, integrating fingerstick POC troponin testing, in ruling out acute coronary syndrome (ACS).

Methods

The data of 96 patients with chest pain, included in a study investigating a novel POC troponin device under development at the cardiac emergency department, were analysed retrospectively. Based on the patients’ admission data and capillary POC high-sensitivity troponin I (hs-cTnI) results, the modified HEART score was determined. The outcome measure, for evaluating the diagnostic accuracy of the modified HEART score, was the occurrence of ACS.

Results

Of the total study population, 33 patients (34%) were diagnosed with ACS. Seventeen patients (18%) were classified as low risk (0–3 points) and one patient (6%) in this group was diagnosed with ACS. The sensitivity and negative predictive value of the modified HEART score was 97.0 and 97.6%, respectively.

Conclusion

The modified HEART score, integrating capillary POC hs-cTnI results, is a promising tool for ruling out ACS in patients with chest pain presenting to the cardiac emergency department. These results encourage prospective investigation into the integration of fingerstick POC troponin testing in the modified HEART score in a pre-hospital setting.

Supplementary Information

The online version of this article (10.1007/s12471-021-01646-8) contains supplementary material, which is available to authorized users.

Non-steroidal anti-inflammatory drugs increase urinary neutrophil gelatinase-associated lipocalin in recreational runners

Objectives

To study the effects of running with/without the use of pain killers on urinary neutrophil gelatinase‐associated lipocalin (uNGAL) and other parameters of kidney function in recreational runners.

Methods

Participants of the 10‐ and 21.1‐km Weir Venloop race were enrolled and their urine samples collected before and after the run. Urine dipstick and other conventional tests used to assess kidney function were performed. The presence of ibuprofen, diclofenac, naproxen, and/or paracetamol was assessed by LC‐MS/MS. uNGAL was measured with a two‐step chemiluminescent immunoassay.

Results

NSAIDs/analgesics were detected in urine of 5 (14.4%) 10‐km runners and 13 (28.9%) 21.1‐km runners. Only half‐marathon participants showed significant increases in uNGAL (pre: 11.7 [7.1‐34.3] ng/mL; post: 33.4 [17.4‐50.4] ng/mL; P = .0038). There was a significant effect of NSAID/analgesic use on uNGAL increase (F_{2, 76} = 4.210, P = .004). Post hoc tests revealed that uNGAL increased significantly in runners who tested positive for ibuprofen/naproxen compared to runners who did not use any medications (P = .045) or those who tested positive for paracetamol (P = .033). Running distance had a significant influence on the increase in uNGAL (F_{1, 53} = 4.741, P < .05), specific gravity (F_{1, 60} = 9.231, P < .01), urinary creatinine (F_{1, 61} = 10.574, P < .01), albumin (F_{1, 59} = 4.888, P < .05), and development of hematuria (χ²(4) = 18.44, P = .001).

Conclusions

Running distance and use of ibuprofen/naproxen were identified as risk factors for uNGAL increase in recreational runners.

Effects of Monomeric and Oligomeric Flavanols on Kidney Function, Inflammation and Oxidative Stress in Runners: A Randomized Double-Blind Pilot Study

Nonsteroidal anti-inflammatory drugs are frequently used by athletes in order to prevent musculoskeletal pain and improve performance. In combination with strenuous exercise, they can contribute to a reduction of renal blood flow and promote development of kidney damage. We aimed to investigate whether monomeric and oligomeric flavanols (MOF) could reduce the severity of kidney injuries associated with the intake of 400-mg ibuprofen followed by the completion of a half-marathon in recreational athletes. In this double-blind, randomized study, the original MOF blend of extracts from grape seeds (Vitis vinifera L.) and pine bark (Pinus pinaster L.) or placebo were taken for 14 days preceding the ibuprofen/half-marathon. Urine samples were collected before and after the ibuprofen/half-marathon, and biomarkers of kidney injury, inflammation and oxidative stress were assessed. Intake of MOF significantly reduced the incidence of post-race hematuria (p = 0.0004) and lowered concentrations of interleukin (IL)-6 in the urine (p = 0.032). Urinary neutrophil-associated lipocalin, creatine, albumin, IL-8 and malondialdehyde tended to decrease. The supplementation with MOF in recreational runners appears to safely preserve kidney function, reduce inflammation and promote antioxidant defense during strenuous exercise and intake of a single dose of ibuprofen.

Normocalcemia but still elevated parathyroid hormone levels after parathyroidectomy

Even when laboratory results at first match with clinical assessment, assay interference should still be on a clinician's mind when later results no longer fit with the patient.

Comparison of 7 Published LC-MS/MS Methods for the Simultaneous Measurement of Testosterone, Androstenedione, and Dehydroepiandrosterone in Serum

BACKGROUND

Recently, LC-MS/MS was stated to be the method of choice to measure sex steroids. Because information on the mutual agreement of LC-MS/MS methods is scarce, we compared 7 published LC-MS/MS methods for the simultaneous measurement of testosterone, androstenedione, and dehydroepiandrosterone (DHEA).

METHODS

We used 7 published LC-MS/MS methods to analyze in duplicate 55 random samples from both men and women. We performed Passing-Bablok regression analysis and calculated Pearson correlation coefficients to assess the agreement of the methods investigated with the median concentration measured by all methods, and we calculated the intraassay CV of each method derived from duplicate results and the CVs between the methods.

RESULTS

Median concentrations of testosterone were 0.22-1.36 nmol/L for women and 8.27-27.98 nmol/L for men. Androstenedione and DHEA concentrations were 0.05-5.53 and 0.58-18.04 nmol/L, respectively. Intraassay CVs were 2.9%-10%, 1.2%-8.8%, 2.7%-13%, and 4.3%-16% for testosterone in women, testosterone in men, androstenedione, and DHEA. Slopes of the regression lines calculated by Passing-Bablok regression analysis were 0.92-1.08, 0.92-1.08, 0.90-1.13, and 0.91-1.41 for all testosterone values, testosterone in women, androstenedione, and DHEA. Intermethod CVs were 14%, 8%, 30%, and 22% for testosterone in women, testosterone in men, androstenedione, and DHEA.

CONCLUSIONS

In general, the LC-MS/MS methods investigated show reasonable agreement. However, some of the assays show differences in standardization, and others show high variation.

Evaluation of a next generation direct whole blood enzymatic assay for hemoglobin A1c on the ARCHITECT c8000 chemistry system

BACKGROUND

The utility of HbA1c for the diagnosis of type 2 diabetes requires an accurate, precise and robust test measurement system. Currently, immunoassay and HPLC are the most popular methods for HbA1c quantification, noting however the limitations associated with some platforms, such as imprecision or interference from common hemoglobin variants. Abbott Diagnostics has introduced a fully automated direct enzymatic method for the quantification of HbA1c from whole blood on the ARCHITECT chemistry system.

METHODS

Here we completed a method evaluation of the ARCHITECT HbA1c enzymatic assay for imprecision, accuracy, method comparison, interference from hemoglobin variants and specimen stability. This was completed at three independent clinical laboratories in North America and Europe.

RESULTS

The total imprecision ranged from 0.5% to 2.2% CV with low and high level control materials. Around the diagnostic cut-off of 48 mmol/mol, the total imprecision was 0.6% CV. Mean bias using reference samples from IFCC and CAP ranged from -1.1 to 1.0 mmol/mol. The enzymatic assay also showed excellent agreement with HPLC methods, with slopes of 1.01 and correlation coefficients ranging from 0.984 to 0.996 compared to Menarini Adams HA-8160, Bio-Rad Variant II and Variant II Turbo instruments. Finally, no significant effect was observed for erythrocyte sedimentation or interference from common hemoglobin variants in patient samples containing heterozygous HbS, HbC, HbD, HbE, and up to 10% HbF.

CONCLUSIONS

The ARCHITECT enzymatic assay for HbA1c is a robust and fully automated method that meets the performance requirements to support the diagnosis of type 2 diabetes.

Suboptimal effect of different vitamin D3 supplementations and doses adapted to baseline serum 25(OH)D on achieved 25(OH)D levels in patients with a recent fracture: a prospective observational study

OBJECTIVE

Guidelines on the need for dose adaptation of vitamin D3 supplementation according to baseline serum 25(OH)D are inconclusive. The effects of increasing doses of vitamin D3 at lower baseline serum 25(OH)D values on the serum 25(OH)D after 4.2 and 11 months were determined in an observational study.

DESIGN

A prospective observational study.

METHODS

Out of 1481 consecutive women and men with a recent clinical fracture, 707 had a baseline 25(OH)D level <50 nmol/l and were supplemented with increasing doses of vitamin D3 (400, 800, 1700, and ≥3500 IU/day) according to the lower baseline 25(OH)D. Final analysis was restricted to the 221 participants who had full follow-up data available for 11 months.

RESULTS

Serum 25(OH)D ≥50 nmol/l was achieved in 57-76% of patients after 4.2 months and in 73-79% after 11 months. These percentages were similar for all doses (P=0.06 and P=0.91 respectively). The mean achieved 25(OH)D was similar for all dose groups (56.1-64.0 nmol/l after 4.2 months and 60.2-76.3 nmol/l after 11 months). With multivariate analysis, the increase in 25(OH)D (17±32.0 after 4.2 months and 24.3±34.0 nmol/l after 11 months) was dependent on the baseline 25(OH)D (P<0.001), not on supplementation dose, season, age, BMI, or gender.

CONCLUSIONS

The increase in serum 25(OH)D was significantly larger with higher vitamin D3 supplementation doses. However, this dose-effect response was mainly explained by the baseline 25(OH)D, not the supplementation dose, with a greater magnitude of response at lower baseline 25(OH)D concentrations. In 21-27% of patients, serum 25(OH)D3 levels did not reach 50 nmol/l after 11 months, at any dose. Further studies are needed to identify possible causes of suboptimal response such as non-compliance, undiagnosed malabsorption syndromes, or variability in cholecalciferol content of the vitamin D supplements.

Comparing tolerability and efficacy of generic versus brand alendronate: a randomized clinical study in postmenopausal women with a recent fracture

Introduction

An increasing number of generic alendronate formulations have become available. Although expected to have the same tolerability and efficacy, head-to head comparison of generic and brand alendronate was never performed. Therefore, we compared the tolerability and efficacy of generic and brand alendronate.

Methods

In a randomized double-blinded single centre cross-over study in 37 postmenopausal women (mean age 65.4±6.4 years) with osteoporosis were treated with generic and branded alendronate during 24 (2x12) weeks. Tolerance was evaluated by the Gastro intestinal Symptom Rating Scale (GSRS) and self-reported side effects. Efficacy was assessed by serum bone turnover markers, carboxy terminal telopeptide (CTX) and procollagen type I N-terminal propeptide (PINP). No wash out period was allowed (ethical reasons). Because of possible carry over effect only data of the first 12 weeks were analyzed using linear mixed models.

Results

There were no significant differences in overall tolerance (GSRS) between treatment groups. However, for subscale abdominal pain, patients using generic had a significantly higher mean GSRS score at week 4 (estimated mean difference (B): 0.40; 95%CI: 0.05 to 0.74, p = 0.024). The level of bone turnover markers significantly decreased over 12 weeks of follow-up for generic and branded alendronate (p < 0.001). Mean level of CTX was significantly lower with branded at week 4 (B: 121.3; 95%CI: 52.0 to 190.5), but not at week 12 (B: 53.6; 95%CI:-3.7 to 110.9). No significant differences were found for PINP at week 4 or 12.

Conclusions

Bone turnover markers were significantly reduced with branded and generic alendronate. With branded, CTX was significantly lower at 4 weeks. Generic caused significantly higher abdominal pain scores in the first 4 weeks of treatment. Therefore, generic alendronate may not have the same tolerability and efficacy as branded alendronate in the first weeks after starting treatment in patients with a recent fracture.

Trial Registration

Dutch Trial Register NTR number 1867 http://www.trialregister.nl/trialreg/admin/rctview.asp?TC=1867

Multicenter comparison study of current methods to measure 25-hydroxyvitamin D in serum

OBJECTIVES

Measurement of serum 25-hydroxyvitamin D [25(OH)D] is generally considered to be a reliable indicator of vitamin D status. The recent increase in diversity of 25(OH)D assays prompted us to evaluate the performance of chromatographic methods (two in-house ID-LC-MS/MS and HPLC (ClinRep, Recipe)), a protein binding method (Cobas-25(OH)D-total, Roche) and immunochemical methods (Liaison and RIA (Diasorin), iSYS (IDS), ADVIA Centaur (Siemens), and Architect i1000 and i2000 (Abbott)).

METHODS

Blood was drawn from randomly selected outpatients (N=60) at one site after informed consent. DEQAS and SRM 972 samples were obtained from the scheme organizer and NIST, respectively. Serum aliquots were prepared, frozen and transported to participating centers. Method comparison was performed according to CLSI-EP9 specifications.

RESULTS

With these patient samples, and in comparison with ID-LC-MS/MS, Deming regression parameters slope, intercept and R were found to be within the ranges [0.57-1.07], [-1.7 to 6.9 nmol/L] and [0.88-0.98], respectively. 25(OH)D2 in DEQAS and SRM samples was fully recognized by chromatographic methods, but only partially by protein binding and immunochemical methods. Chromatographic methods, and to a lesser extent the protein binding assay, showed cross-reactivity with 3-epi-25(OH)D3. Agreement of 25(OH)D assays to ID-LC-MS/MS in sorting patients into distinct 25(OH)D categories varied between 53% and 88%.

CONCLUSIONS

Significant bias exists between ID-LC-MS/MS and many, but not all, other 25(OH)D assays. The variable response among different assays for 25(OH)D metabolites impedes the use of uniform cut-off values for defining vitamin D status. Our results indicate the need towards further standardizing assays for 25(OH)D measurement.

[Diagnostic approach to hypocalcaemia and hypercalcaemia]

A 49-year-old woman was examined for osteoporosis and metabolic bone disease after a low-trauma wrist fracture. Laboratory and additional radiological investigations revealed parathyroid hormone (PTH)-mediated hypercalcaemia caused by a parathyroid adenoma. A second patient, a 65-year-old woman with a history of abdominal complaints and tetany, appeared to have hypocalcaemia. Severe vitamin D deficiency and secondary hyperparathyroidism were detected and the patient was finally diagnosed with coeliac disease. Based on these case studies, we highlight the calcium homeostasis and the role of laboratory evaluation of serum calcium, inorganic phosphate, intact PTH, 25-OH vitamin D, magnesium and 24-hour urinary calcium excretion in the diagnostic work-up for hypocalcaemia and hypercalcaemia.

Contributors to secondary osteoporosis and metabolic bone diseases in patients presenting with a clinical fracture

BACKGROUND

Previously undetected contributors to secondary osteoporosis and metabolic bone diseases (SECOB) are frequently found in patients with osteoporosis, but the prevalence in patients at the time they present with a clinical fracture is unknown.

METHODS

All consecutive patients with a recent clinical vertebral or nonvertebral fracture, who were able and willing to be investigated (n = 626: 482 women, 144 men, age range 50-97 yr) had bone mineral density and laboratory investigations (serum calcium, inorganic phosphate, 25-hydroxyvitamin D, creatinine, intact PTH, TSH, free T(4), serum and urine protein electrophoresis, and in men also serum testosterone).

RESULTS

Known SECOB contributors were present in 23.0% of patients and newly diagnosed SECOB contributors in 26.5%: monoclonal proteinemia (14 of 626), renal insufficiency grade III or greater (54 of 626), primary (17 of 626) and secondary (64 of 626) hyperparathyroidism, hyperthyroidism (39 of 626), and hypogonadism in men (12 of 144). Newly diagnosed SECOBs, serum 25-hydroxyvitamin D less than 50 nmol/liter (in 63.9%), and dietary calcium intake less than 1200 mg/d (in 90.6%) were found at any age, in both sexes, after any fracture (except SECOB in men with finger and toe fractures) and at any level of bone mineral density.

CONCLUSION

At presentation with a fracture, 26.5% of patients have previously unknown contributors to SECOB, which are treatable or need follow-up, and more than 90% of patients have an inadequate vitamin D status and/or calcium intake. Systematic screening of patients with a recent fracture identifies those in whom potentially reversible contributors to SECOB and calcium and vitamin D deficiency are present.

False positive troponin result caused by a true macrotroponin

BACKGROUND

A 35-year-old female presented with complaints of tiredness, shortness of breath and recent onset of chest pain. The cardiac troponin I (cTnI) concentration was elevated at 6.4 μg/L (Abbott Architect reference value: <0.03 μg/L) with a normal ECG. Physical examination, radiological imaging and routine laboratory investigations did not provide an explanation for the elevated cTnI concentration.

METHODS

Use of different troponin assays, dilutions with assay diluent, addition of mouse serum, polyethylene glycol (PEG) precipitation and gel filtration chromatography (GFC) were used to investigate possible interference.

RESULTS

Troponin concentrations were below the level of detection when measured using all other troponin immunoassays. Serial dilutions of sample and addition of mouse serum did not alter the results. However, PEG precipitation and GFC showed the presence of a high molecular weight immunoreactive protein. Using GFC and protein-A IgG precipitation, the interference could be identified as a macrocomplex containing IgG and (fragments of) cTnI.

CONCLUSIONS

We report a false positive cTnI result caused by a true macrotroponin, containing IgG and (fragments of) cTnI. This macrotroponin was only immunoreactive in the Abbott Architect cTnI immunoassay. Clinicians should be aware of analytical interference when troponin results are constantly elevated in the absence of (non)coronary causes of an increased troponin.

Accuracy of the Precision® point-of-care ketone test examined by liquid chromatography tandem-mass spectrometry (LC-MS/MS) in the same fingerstick sample

BACKGROUND

The Precision(®) (Abbott Diabetes Care) point-of-care biosensor test strips are widely used by patients with diabetes and clinical laboratories for measurement of plasma β-hydroxybutyrate (β-HB) concentrations in capillary blood samples obtained by fingerstick. In the literature, this procedure has been validated only against the enzymatic determination of β-HB in venous plasma, i.e., the method to which the Precision(®) has been calibrated.

METHODS

In this study, the Precision(®) Xceed was compared to a methodologically different and superior procedure: determination of β-HB by liquid chromatography tandem-mass spectrometry (LC-MS/MS) in capillary blood spots. Blood spots were obtained from the same fingerstick sample from out of which Precision(®) measurements were performed. Linearity was tested by adding varying amounts of standard to an EDTA venous whole blood matrix.

RESULTS

The Precision(®) was in good agreement with LC-MS/MS within the measuring range of 0.0-6.0 mmol/L (Passing and Bablok regression: slope=1.20 and no significant intercept, R=0.97, n=59). Surprisingly, the Precision(®) showed non-linearity and full saturation at concentrations above 6.0 mmol/L, which were confirmed by a standard addition experiment. Results obtained at the saturation level varied between 3.0 and 6.5 mmol/L.

CONCLUSIONS

The Precision(®) β-HB test strips demonstrate good comparison with LC-MS/MS. Inter-individual variation around the saturation level, however, is large. Therefore, we advise reporting readings above 3.0 as >3.0 mmol/L. The test is valid for use in the clinically relevant range of 0.0-3.0 mmol/L.

Validation study of Axis-Shield carbohydrate-deficient transferrin (CDT) on ARCHITECT chemistry analyzer

BACKGROUND

Carbohydrate-deficient transferrin (CDT) is a biochemical marker used for identifying chronic alcohol intake. We developed and validated an ARCHITECT c8000 (Abbott) instrument application for the Axis-Shield %CDT immunoassay.

METHODS

Standard CLSI (Clinical and Laboratory Standards Institute) evaluation protocols were performed.

RESULTS

The Axis-Shield %CDT ARCHITECT method was standardized against the Axis-Shield %CDT microtiter test by linear regression analysis (n=50 mean of duplicate, R=0.996). Method comparison by Deming regression revealed a slope of 1.01 and an intercept of -0.03 with Axis-Shield %CDT microtiter test (n=50 in duplicate, R=0.995), and a slope of 0.82 and an intercept of 1.09 with HPLC method (n=47 in duplicate, R=0.990) as the candidate IFCC (International Federation of Clinical Chemistry and Laboratory Medicine) reference method. The predicted medical decision points (MDPs) are both 2.6% and equal the MDP that is generally used for the Axis-Shield %CDT tests. Precision derived from pooled patient sera (low level) and commercially available control material (high level) was excellent. Total variation was 3.2% and 1.8%, respectively.

CONCLUSIONS

The Axis-Shield %CDT ARCHITECT method, as one of the first Axis-Shield applications on a large-scale analyzer, is a reliable test for routine %CDT analysis providing precise and well-standardized %CDT results.

Kinetic and structural properties of disulfide engineered phospholipase A2: insight into the role of disulfide bonding patterns

The family of secreted 14 kDa phospholipase A(2) (PLA2) enzymes have a common motif for the catalytic site but differ in their disulfide architecture. The functional significance of such structural changes has been analyzed by comparing the kinetic and spectroscopic properties of a series of disulfide mutants engineered into the sequence of pig pancreatic IB PLA2 to resemble the mammalian paralogues of the PLA2 family [Janssen et al. (1999) Eur. J. Biochem. 261, 197-207, 1999]. We report a detailed comparison of the functional parameters of pig iso-PLA2, as well as several of the human homologues, with these disulfide engineered mutants of pig IB PLA2. The crystal structure of the ligand free and the active site inhibitor-MJ33 bound forms of PLA2 engineered to have the disulfide bonding pattern of group-X (eng-X) are also reported and compared with the structure of group-IB and human group-X PLA2. The engineered mutants show noticeable functional differences that are rationalized in terms of spectroscopic properties and the differences detected in the crystal structure of eng-X. A major difference between the eng-mutants is in the calcium binding to the enzyme in the aqueous phase, which also influences the binding of the active site directed ligands. We suggest that the disulfide architecture of the PLA2 paralogues has a marginal influence on interface binding. In this comparison, the modest differences observed in the interfacial kinetics are attributed to the changes in the side chain residues. This in turn influences the coupling of the catalytic cycle to the calcium binding and the interfacial binding event.

Potentiation of tumor necrosis factor alpha-induced secreted phospholipase A2 (sPLA2)-IIA expression in mesangial cells by an autocrine loop involving sPLA2 and peroxisome proliferator-activated receptor alpha activation

In rat mesangial cells, exogenously added secreted phospholipases A2 (sPLA2s) potentiate the expression of pro-inflammatory sPLA2-IIA first induced by cytokines like tumor necrosis factor-alpha (TNFalpha) and interleukin-1 beta. The transcriptional pathway mediating this effect is, however, unknown. Because products of PLA2 activity are endogenous activators of peroxisome proliferator-activated receptor alpha (PPAR alpha, we postulated that sPLA2s mediate their effects on sPLA2-IIA expression via sPLA2 activity and subsequent PPAR alpha activation. This study shows that various sPLA2s, including venom enzymes, human sPLA2-IIA, and wild-type and catalytically inactive H48Q mutant of porcine pancreatic sPLA2-IB, enhance the TNF alpha-induced sPLA2-IIA expression at the mRNA and protein levels. In cells transfected with luciferase sPLA2-IIA promoter constructs, sPLA2s are active only when the promoter contains a functional PPRE-1 site. The effect of exogenous sPLA2s is also blocked by the PPAR alpha inhibitor MK886. Interestingly, the expression of sPLA2-IIA induced by TNF alpha alone is also attenuated by MK886, by the sPLA2-IIA inhibitor LY311727, by heparinase, which prevents the binding of sPLA2-IIA to heparan sulfate proteoglycans, and by the specific cPLA2-alpha inhibitor pyrrolidine-1. Together, these data indicate that sPLA2-IIA released from mesangial cells by TNF alpha stimulates its own expression via an autocrine loop involving cPLA2 and PPAR alpha. This signaling pathway is also used by exogenously added sPLA2s including pancreatic sPLA2-IB and is distinct from that used by TNF alpha.