2) reduced incubation time 3) small semen sample volume
Transcription
2) reduced incubation time 3) small semen sample volume
EPISCREEN PLUS™ - -GLUCOSIDASE ASSAY (25 TESTS ) 2) reduced incubation time 3) small semen sample volume Update: 12/03/2012, Document ref.: FP09 I87 R01 A.2 4) inclusion of a standard curve ABBREVIATIONS 5) semen plasma background correction. CLSI CV IU LOD LOQ NAG OD PNP PNPG WHO Clinical and Laboratory Standards Institute Coefficient of variation International unit Limit of detection Limit of quantification Neutral -glucosidase Optical density Para (4)-nitrophenol Para (4)-nitrophenyl-α-D-glucopyranoside World Health Organization Table 1 shows a comparison between Episcreen™, EpiScreen PlusTM, and the WHO method7. Table 1: Comparison of Episcreen™ , EpiScreen Plus™ and the WHO assay for the determination of -glucosidase activity in semen. Enzyme activity Total (neutral + acid) EpiScreen TM Plus Neutral (epididymisspecific) Incubation period 4h 2h 2h The enzymatic activity of at least 25 samples (including sample background correction) can be assessed with one EpiScreen Plus TM kit. Standard curve - Yes (PNP) Yes (PNP) Kit contents: Reagent 1 (5 ml): reaction buffer (pH 6.8), supplemented with 1% SDS Background correction - Glucose Castanospermine Sample volume 125 µL 20 µL 15 µL KIT COMPOSITION Parameter TM EpiScreen WHO Neutral (epididymisspecific) Reagent 2 (0.15ml): 50 X substrate solution (PNPG in DMSO) Reagent 3 (5ml): inhibitor solution (reaction buffer containing glucose) Reagent 4 (60ml): stopping buffer (0.02M NaOH) Reagent 5 (1ml): standard stock solution (5 mM PNP) Reagent 6 (60ml): standard dilution buffer (0.02M NaOH + 0.1% SDS) MATERIAL NOT INCLUDED WITH THE TEST Spectrophotometer with 405 nm filter Warm water bath /reaction tube thermoshaker Plasticware (96-well microtiter plates, pipette tips, 1.5 ml eppendorf tubes) BACKGROUND The bulk of -glucosidase activity in semen, and more particularly that of its neutral iso-enzyme, depends on secretion by the epididymis1. In patients with azoospermia and normal androgen levels in peripheral blood, NAG activity in semen plasma is a reliable marker of the epididymal contribution to the ejaculate. Azoospermic males with bilateral obstruction between the epididymis and the ejaculatory duct have very low -glucosidase activity in their seminal plasma2. In contrast, if azoospermia is due to an arrest of sperm maturation, or obstruction situated between the epididymis and the rete testis, or in the rete testis itself, -glucosidase activity is normal. Hence, NAG assessment in seminal plasma of normally virilized men with azoospermia can differentiate between the major causes of this condition3, 4. Low NAG activity in seminal plasma of patients with oligozoospermia may reflect partial obstruction of the epididymides, associated with infections or inflammatory disease2, 5. Enzyme activity in patients with normal sperm concentration is correlated with the result of the Shorrstain of midpiece and tail, reflecting changes The EpiScreen Plus TM assay may assist in the diagnosis and the management of male infertility. ASSAY PRINCIPLE Under specified conditions (pH=6.8; T=37°C), -glucosidase will catalyze the conversion of the substrate 4-nitrophenyl-α-Dglucopyranoside (PNPG) to α-D-glucopyranoside and 4-nitrophenol, as shown below. The yellow colour of the latter product is measured spectrophotometrically at 405 nm. EpiScreen PlusTM and the WHO method, have been tested in parallel on 144 semen plasma samples, obtained from 94 patients / donors and 50 vasectomized men (negative control), respectively. Method comparison demonstrated that both assays yield identical results 8. The EpiScreen PlusTM method differs slightly from the WHO method: a) reaction buffer (pH 6.8) composition, and b) the use of glucose instead of castanospermine as inhibitor for blank correction. Inhibition of -glucosidase by glucose, a process called product inhibition, is a pH-dependent phenomenon and can be explained by glucose binding to the monosaccharide binding site of -glucosidase9. Our experimental data have shown a dose-dependent reduction of enzyme activity. The glucose concentration in EpiScreen PlusTM was optimized to yield identical inhibition as castanospermine. The WHO advises to apply only two internal quality control samples for blank correction. Our experiments have demonstrated that the background variance of semen samples is quite large (+/- 20%). Therefore, we recommend preparing a negative control for each semen plasma sample in order to allow correct and reproducible background correction. ASSAY PERFORMANCE All validation parameters have been calculated based on the latest CLSI guidelines10, 11. Measuring range: 2.32-144 mU/ml Sensitivity: 96.0 % (vasectomized/normozoospermic) Specificity: 93.6 % (vasectomized/normozoospermic) Within-device Precision: Low pool: 0.96 mIU/ml High pool: 3.70 mIU/ml Intra-assay CV: 3.08 % Inter-assay CV: 10.52% Cutoff: 6.35 mIU/ml 19.98 mIU/ejaculate (if corrected for ejaculate volume) STORAGE AND SHELF LIFE PNPG + α-glucosidase α-D-glucopyranoside + PNP (yellow) As the reaction buffer contains SDS, the acid form of -glucosidase (originating from the prostate), is selectively inhibited. This allows specific determination of neutral enzyme activity6. ENZYME ACTIVITY DEFINITION Alpha-glucosidase activity is expressed as IU per liter (or mIU per ml). One unit is able to liberate 1 µmolar of PNP from PNPG per minute under specified conditions (pH=6.8; T=37°C)7. ASSAY CHARACTERISTICS EpiScreen PlusTM has been designed to assess neutral enzyme activity. The main advantages of the new kit are: 1) assessment of neutral activity EpiScreen PlusTM must be stored at 2-8°C, protected from (sun)light, and remains stable for 24 months. PRE-USE CHECKS Do not use the product if seal of the container is opened or defect when the product is delivered. When stored at 4°C, precipitation may occur in reagent 1 but disappears by prewarming to 37°C. SPECIMEN TYPE The assay can be performed on fresh or frozen/thawed semen and semen plasma samples. METHOD Before use, allow reagents 1, 2, and 3 to warm up to 37°C for 30min. We recommend a thermoregulated hot water bath or reaction tube thermoshaker for optimal heating of the samples. DO NOT incubate in an air incubator as this may impair assay outcome. Perform the following steps: 1. For each sample to be analyzed: - make reaction solution: 3µl of reagent 2 in 147µl of reagent 1 - make inhibitor solution: 3µl of reagent 2 in 147µl of reagent 3 2. Pipette 20µl of each sample into two 1.5ml Eppendorf tubes 3. Add 130µl reaction solution to one reaction vessel and 130µl inhibitor solution to the other. 4. Vortex and incubate for exactly 2h at 37°C 5. During incubation, prepare the standard curve. Make the highest standard (200 µM) by dissolving 100 µl of reagent 5 in 2400µl of reagent 6. Use this solution to prepare the other standards, as indicated in table 2. Reagent 6 alone serves as 0 standard (blank). Table 2: Standard curve of PNP 200 µM Standard (µl) Reagent 6 (µl) Final concentration (µM) 375 125 150 250 250 100 125 375 50 25 475 10 0 500 0 6. After 2h, stop incubation by adding 1ml of reagent 4 and vortex. 7. Pipette 200 µl of all standards / samples into a microtitre plate. 8. Read the absorbance at 405nm. DATA INTEGRATION STANDARD CURVE Subtract the blank OD value (0-standard) from the standard OD values (delta OD). Plot the delta OD values (Y-axis) against the standard concentrations (X-axis) and perform a linear regression to calculate the slope. Coefficient of determination (R2) should be at least 0.99. An example is shown below. Standard curve PNP y = 0.0097x R² = 0.9999 2.500 OD 405 nm 2.000 1.500 1.000 0.500 0.000 0 50 100 150 200 250 PNP Concentration (µM) UNKNOWN ENZYME ACTIVITY Subtract the blank OD value (0-standard) from the OD value of each sample and its corresponding background (glucose) control. Next, subtract the background delta OD from the sample delta OD. Calculate the corresponding PNP concentration by dividing the backgroundcorrected OD value with the slope of the standard curve. Finally, enzyme activity (mIU/ml) is obtained by multiplying the PNP value with 0.479 (see below). Example: 1. Assay data: ODsample = 0.845; OD sample + glucose = 0.06; standard curve slope = 0.0097 2. Semen plasma background correction = 0.845 – 0.06 = 0.785 3. Concentration PNP = 0.785 / 0.0097 = 80.93 µM 4. Enzyme activity = 80.93 x 0.479 = 38.76 mIU/ml Calculated enzyme activity can be multiplied with ejaculate volume, to evaluate enzyme activity in the whole ejaculate. Note: The standard curve consists of distinct points between 0-200 µM, as most semen samples lie within this range. Based on our experimental data, linearity is guaranteed up to 300 µM. If desired, the operator can alter the curve by starting at 300 µM, corresponding to an enzyme activity of 144 mIU/ml. If unknown samples have higher activity, we advise to dilute and retest to confirm experimental outcome. CORRECTION FACTOR This factor is obtained by taking into account sample dilution and incubation time (120 min). In this assay, one starts with 20 µL of semen sample, which is finally diluted to 1150 µL (20 µL semen sample + 130 µL reaction buffer + 1000 µL stop buffer). This results in a dilution factor of 57.5. An enzyme unit is defined as the formation of PNP per minute. Therefore, one has to divide the end result with 120 in order to implement time factor. PRECAUTIONS This test is an aid in the diagnosis and, as for other biological tests; interpretation of the results must be performed within the framework of clinical findings and data of history taking. Other causes of insufficient epididymal secretion must be excluded, such as hypo-androgenism or severe testicular atrophy. The material safety datasheet (MSDS) is available on our website. BIBLIOGRAPHY 1. Cooper TG, Yeung CH, Nashan D, Jöckenhovel F, and Nieschlag E. (1990) Improvement in the assessment of human epididymal function by the use of inhibitors in the assay of alpha-glucosidase in seminal plasma. Int. J. Androl., 13: 297-305. 2. Guerin JF, Ben Ali H, Rollet J, Souchier C, and Czyba JC. (1986) Alpha-glucosidase as a specific epididymal enzyme marker. Its validity for the etiologic diagnosis of azoospermia. J. Androl., 7: 156-162. 3. Casano R, Orlando C, Caldini AL, Barni T, Natali A, and Serio M. (1987) Simultaneous measurement of seminal L-carnitine, alpha 14-glucosidase and glycerylphosphorylcholine in azoospermic and oligospermic patients. Fertil. Steril., 47: 324-328. 4. Cooper TG, Yeung CH, Nashan D, and Nieschlag E. (1988) Epididymal markers in human infertility. J. Androl., 9: 91-101. 5. Haidl G, Badura B, Hinsch KD, Ghyczy M, Gareiss J, Schill WB. (1993) Disturbances of sperm flagelle due to failure of epididymal maturation and their possible relationship to phospholipids. Hum. Reprod., 7: 1070-1073. 6. Paquin R, Chapdelaine P, Dubé JY, Tremblay RR (1984) Similar biochemical properties of human seminal plasma and epididymal alpha-1,4-glucosidase. J. Androl., 5: 227-282. 7. WHO laboratory manual for the examination and processing of human semen, 5th edition. Measurement of neutral alphaglucosidase in seminal plasma. pp. 134-136. 8. Eertmans F (2012) White paper: EpiScreen PlusTM for assessment of neutral -glucosidase activity in semen: an update. FertiPro NV. 9. Yao X, Mauldin R, Byers L. (2003) Multiple sugar binding sites in αglucosidase. Biochim. Biophys. Acta, 1645: 22-29. 10. Shrivastava A, Vipin B Gupta VB (2011) Methods for the determination of limit of detection and limit of quantitation of the analytical methods. Chron. Young Sci. 2: 21-25. 11. Chesher D. (2008) Evaluating Assay Precision. Clin Biochem. Rev., 29: S23-S TECHNICAL SUPPORT FERTIPRO NV Industriepark Noord 32, 8730 Beernem, Belgium http://www.fertipro.com - E-mail: [email protected] EPI_PLUS