494

` Asian-Aust. J. Anim. Sci. Vol. 21, No. 4 : 494 - 498

April 2008

www.ajas.info

Evaluation of Boar Sperm Viability by MTT Reduction in Beltsville Thawing Solution Extender*

J. W. Byuna, S. H. Choo1, a, H. H. Kim, Y. J. Kim, Y. J. Hwang and D. Y. Kim** Division of Biological Science, Gachon University of Medicine and Science, Incheon, 406-799, Korea

ABSTRACT : MTT (3-(4, 5-dimethyl thiazol-2-yl)-2, 5-diphenyl tetrazolium bromide) reduction assay is a method that validates the viability of an active . Dehydrogenase in mitochondria converts yellow colored insoluble tetrazolium salt to purple colored water- soluble formazan. Sperm also have mitochondria in the midpiece, therefore sperm viability could be evaluated by MTT reduction assay. Several studies have already demonstrated the capability of application of the MTT reduction assay to sperm of several species in Hepes-BSA buffer. Because most liquid semen was diluted in extender like BTS (Beltsville Thawing Solution), Modena or Androhep when it is used or transferred, semen needed another dilution in Hepes-BSA buffer to assess sperm viability. In this study, we evaluated boar sperm viability especially in BTS extended semen and compared the efficiency of this test with eosin-nigrosin staining. We used the fresh BTS extended semen from a local A.I center. Semen sample was diluted to 3.0×107 sperms/ml in BTS. The rates of formazan production were measured in 96-well microtiter plates immediately and 1h after incubation at 17°C using a spectrophotometer at wave length 560 nm. Simultaneously, split samples of the same semen were tested, using eosin-nigrosin staining to compare the efficiency of the MTT assay of sperm viability in BTS. The correlation between the results of these tests was calculated using Student-t test and ANOVA. The results revealed a strong correlation between the results of MTT reduction rate and the results that were simultaneously determined by eosin-nigrosin staining at 1 h. In conclusion, the MTT reduction test was an effective and simple method to validate sperm viability and it could be used as a simple tool to evaluate sperm viability in the local A.I center and laboratory. (Key Words : MTT Reduction Assay, Sperm Viability, Eosin-nigrosin Staining, BTS Extender)

INTRODUCTION is a technology that allows a single cell to be measured for a variety of characteristics. It is different There are several methods for evaluating sperm viability. technical applications takes many advantages for the Visual estimation of viable sperm using microscope is analysis of sperm quality. Because flow cytometry evaluates commonly used for it. Eosin-nigrosin method and HOST individual cell with rapid speed, it is objective and accurate (Hypo-Osmotic Swelling Test) are simple and inexpensive; method (Cordelli et al., 2005). however the result can be influenced by experience of MTT (3-(4, 5-dimethylthiazol-2-y1)-2, 5-diphenyl- analyst (McNiven et al., 1992; Nasr-Esfahani et al., 2002; tetrazolium bromide) is a yellow water-soluble tetrazolium Jang et al., 2006). By contrast, CASA (Computer Assisted salt. Succinate dehydrogenase system of active Sperm Analysis) and flow cytometry are the more objective mitochondria converts this dye to water-insoluble purple method. CASA measure the speed of sperm and formazan on the reductive cleavage of its tetrazolium ring abnormality of shape. It uses the computer and camera to (Slater et al., 1963). Thus, the amount of formazan formed measure these characters of sperm (Arman et al., 2006). can be determined spectrophotometrically and serves as an * This work was supported by a grant (No.20070301-034-040- estimate of the number of mitochondria and hence the 007-03-00) from BioGreen 21 Program, Rural Development number of living cells in the sample (Denizot and Lang, Administration, Korea. 1986; Song et al., 2007). In many studies, MTT assay was ** Corresponding Author: D. Y. Kim. Tel: +82-32-820-4544, used which were related to viability of different cells Fax: +82-32-821-2734, E-mail: [email protected] (Mosmann, 1983; Levitz and Diamone, 1985; Carmichael et 1 Graduate School of Medicine, Gachon University of Medicine al., 1987; Campling et al., 1988; Freimoser et al., 1999). and Science, Incheon, 406-799, Korea. Therefore, this method can be used to assess sperm viability a These two authors contribute equally to this work. and MTT reduction assay already have successfully applied Received August 25, 2007; Accepted November 23, 2007

Byun et al. (2008) Asian-Aust. J. Anim. Sci. 21(4):494-498 495

1.200 wells of the 96-well microplate were used. One hundred 100 60 20 microliters of semen sample plus 10 μl of MTT stock 80 40 0 1.000 solution (5 mg of MTT/ml of PBS) were placed in each

0.800 well. The optical density of samples were measured immediately and after 1 h of incubation at 17°C using a 0.600 spectrophotometer (μ QuantTM Microplate Spectrophotometer, Bio-Tek instruments, USA) at a wave length of 560 nm. 0.400 MTT reduction rate (optical density) for each sample was calculated by concuring the difference between the first and

Absorbance at 560 nm 0.200 second reading of the spectrophotometer. 0.000 The freeze-killed procedure was used, in order to obtain 01234the standard curve and the relationship between the MTT reduction rate and sperm viability. Liquid semen samples of Incubation time (h) Duroc with good quality (about 80% viable sperms) were used. After the dilution of Semen with BTS, 6 ml of the Figure 1. MTT reduction rates of the semen samples containing different portion of live and dead sperms. The optical density of diluted semen divided in two fractions; one fraction was samples were measured immediately and after 1h of incubation at maintained at 17°C, while the sperms in the other fraction 17°C using a spectrophotometer (μQuantTM Microplate Spectro- were killed by two cycles of plunging into liquid nitrogen photometer, Bio-Tek instruments, USA) at a wave length of 560 and thawing at 37°C. Samples for analysis were made by nm. combining aliquots of viable and freeze-killed sperms at ratios of 10:0, 8:2, 6:4, 4:6, 2:8 and 0:10 v/v, respectively. to check sperm viability in many species (Capkova et al., The prepared samples were analyzed by (1) MTT and 2000; Park et al., 2002, 2004; Aziz et al., 2005; Hu et al., spectrophotometer, and (2) Eosin-nigrosin stain. MTT 2006). In case of boar semen, no research has been studied. reduction rates were determined immediately and each hour Fresh boar semen sample is diluted in BTS (Beltsville up to 4h incubation at 17°C. Thawing Solution) extender. BTS extender is commonly The MTT test was applied to evaluate the sperm used to dilution the fresh boar semen for transfer and viability in liquid semen of Duroc. After the dilution of storage (Joshi et al., 2006). semen samples in BTS, samples and MTT stock solution In this study, we evaluated the boar sperm viability were distributed in the wells of the 96-wll microplate. The especially in BTS extender using simple and less costly rates of MTT reduction were taken immediately, 1 and 4 h MTT reduction assay and compare the efficiency with eosin-nigrosin staining. after incubation at 17°C. Simultaneously split samples of the same semen were tested using eosin-nigrosin stain MATERIALS AND METHODS method to evaluate the efficiency of MTT reduction assay in assess the sperm viability.

Semen samples and analysis Statistic analysis Liquid semen which was diluted in BTS (at 30×106 Regression analysis was used to evaluate the efficiency sperm/ml) were used in this study from Local A.I center. To of the MTT test for the assessment of sperm viability of evaluate sperm viability, 1% eosin-nigrosin stain method boar semen. Data was analyzed using KCjunior (Bio-Tek was performed according to Björndahl’s method (2003). autoreader control Version 1.41.8), and p<0.05 was The staining solution for the one-step eosin-nigrosin considered as statistically significant. staining contained 0.67 g eosin Y, 0.9 g sodium chloride and

10 g of nigrosin. Aliquots of each 6 samples (50 μl) mixed RESULTS AND DISCUSSION with same amount of solution in micro tube. The suspension was incubated for 30 s at room temperature. Then, a 12 μl Analysis of the results droplet was transferred into slide where it was smeared by Initial results showed MTT reduction rates of the semen sliding a cover slip. After smear the samples, dried few sample groups which contained different proportions of second and examine directly 250 sperm were assessed three viable sperm in Figure 1. The rate of MTT reduction assay times at a magnification 400× in each samples. increased gradually with incubation time, in all groups. Increasing the volume of viable sperm cells in semen MTT reduction assay and experiments samples resulted in a proportional and significant increase The MTT assay was performed by routine methods in the rate of MTT reduction. At each time of measurement, (Mosmann, 1983; Aziz et al., 2005). For each sample, 6 the MTT reduction rate correlated (p<0.001, r>0.915)

496 Byun et al. (2008) Asian-Aust. J. Anim. Sci. 21(4):494-498

80 70 60 50 40 30 y = 1.7545x-0.1684 R2 = 0.9011

% of viable sperm viable of % 20 10 0 0 0.1 0.2 0.3 0.4 0.5 0.6 MTT reduction rate

Figure 3. Linear regression between the MTT reduction rate at 1 h of incubation time and the percentage of viable sperm, which was evaluated by eosin-nigrosin staining. Data was analyzed using Figure 2. MTT purple green formazan dye formation in sperm KCjunior (Bio-Tek autoreader control Version 1.41.8), and p< midpiece (400×). 0.05 was considered as statistically significant. positively with proportion of freeze-killed dead sperms. The color changes of MTT from yellow to purple was 80 very clear after 1 h of the incubation time and up to 4 h, 70 especially in midpiece are shown Figure 2. Two standard 60 curves (at 1 h, y = 1.7545x-0.1684 and 4 h, y = 0.8268x- 50 0.0804) for the relationship between the MTT reduction rate 40 and the percentage of viable sperms were acquired (Figures 30 y = 0.8268x-0.0804 R2 = 0.9147 3 and 4). These two standard curves were applied later to 20 % of viable sperm acquire the percentage of viable sperm cells in each sample 10 in accordance with the MTT reduction rate. 0 The results of MTT reduction rate and that of eosin- 0 0.2 0.4 0.6 0.8 1 1.2 nigrosin stain are shown in Table 1. The results showed a MTT reduction rate high correlation (p<0.001) between the results of MTT test at 1 and 4 h of incubation time and the results of eosin- Figure 4. Linear regression between the MTT reduction rate at 4 h nigrosin stain which evaluated the sperm viability. The of incubation time and the percentage of viable sperm, which was MTT reduction rate was significantly (p<0.001) correlated evaluated by eosin-nigrosin staining. Data was analyzed using with the results that simultaneously determined by eosin- KCjunior (Bio-Tek autoreader control Version 1.41.8), and p< 0.05 was considered as statistically significant. nigrosin staining, yielding correlation coefficients of r = 0.9493 for 1 h and r = 0.9564 for 4 h. investigated by comparison of other method which is already believed reliable, that is, eosin-nigrosin staining Discussion and further study especially in BTS extended semen (Zhou et al., 2004). The MTT assay was used in many studies to evaluate In contrast to the procedure that was published the viability of different cells. This test depends on the previously, the MTT reduction rate was taken successfully ability of viable cells to convert the MTT to purple after 1 h of incubation time. This is expected because formazan. In this study, the diagnostic value of the MTT spermatozoa are very active cells and rich in mitochondria; reduction assay to evaluate the boar sperm viability was therefore, the reduction of MTT by spermatozoa is faster

Table 1. Analysis of the liquid semen samples using MTT test and eosin-nigrosin staining for evaluating viability MTT reduction assay Eosin-nigrosin staining Live:dead MTT absorbance rate at 560 nm % of viable sperm No. of sperm Viability (%) 1 h 4 h 1 h 4 h Live Dead 10:0 0.528 1.014 75.80 75.80 175 81 68 8:2 0.440 0.834 60.36 60.92 181 114 61 6:4 0.367 0.671 47.55 47.44 138 93 59 4:6 0.319 0.545 39.13 37.02 90 131 41 2:8 0.220 0.416 21.76 26.35 62 183 25 0:10 0.178 0.236 14.39 11.47 12 226 5

Byun et al. (2008) Asian-Aust. J. Anim. Sci. 21(4):494-498 497 than other cells. A similar observation was reported in other colorimetric assay: assessment of radiosensitivity. Cancer Res. previous study in equine and bovine (Aziz et al., 2005; Aziz, 47:943-946. 2006). Because other studies have already revealed that Cordelli, E., P. Eleuteri, G. Leter, M. Rescia and M. Spano. 2005. sperm viability is positively related to sperm quality Flow cytometry applications in the evaluation of sperm parameters like acrosome integrity, mitochondrial activity quality: semen analysis, sperm function and DNA integrity Contraception. 72(4):273-279. and even these parameters also correlate positively with Denizot, F. and R. Lang. 1986. Rapid colorimetric assay for cell fertility (Garner et al., 1997), these findings is useful in growth and survival. J. Immunol. Methods 89:271-277. evaluating liquid boar semen quality. Furthermore, we Freimoser, F. M., C. A. Jakob, M. Aebi and U. Tuor. 1999. The observed similar results with other experiments in BTS MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium extended semen, so liquid semen wouldn’t need any other bromide) assay is a fast and reliable method for colorimetric treat which can affect sperm viability. determination of fungal cell densities. Appl. Environ. The advantages of the MTT test are that it is feasible Microbiol. 65:3727-3729. and reproducible (Ciapetti et al., 1992). Additionally, results Garner, D. L., C. A. Thomas, H. W. Joerg, J. M. DeJarnette and C. from this study suggest other advantages of this test in E. Marshall. 1997. Fluorometric assessments of mitochondrial evaluating the bovine semen. Firstly, this test is fast (1 h); function and viability in cryopreserved bovine spermatozoa. Biol. Reprod. 57:1401-1406. secondly, many samples (up to 10) can be examined at the Ciapetti, G., E. Cenni, L. Pratelli and A. Pizzoferrato. 1993. In same time; these test wouldn’t need any other treat. When vitro evaluation of cell/biomaterial interaction by MTT assay. we would apply this method to assess sperm viability in Biomaterials, 14(5):359-364. laboratory or local A.I center, some problems seems to have Hu, J. H., Q. W. Li, G. Li, X. Y. Chen, H. Yang, S. S. Zhang and L. to be solved. Firstly, we have to plate same number of Q. Wang. 2006. The cryoprotective effect on frozen-thawed sperm in testing well; secondly, identify whether the boar semen of egg yolk low density lipoproteins. Asian-Aust. J. formazan affect sperm viability or DNA. The MTT Anim. Sci. 19(4):486-494. reduction test was effective and simple method to validate Jang, H. Y., H. S. Kong, C. K. Park, J. D. Oh, S. G. Lee, H. T. sperm viability and it would be used simple tool to evaluate Cheong, J. T. Kim, S. J. Lee, B. K. Yang and H. K. Lee. 2006. Effects of taurine on sperm characteristics during in vitro sperm viability in local A.I center and laboratory. storage of boar semen. Asian-Aust. J. Anim. Sci. 19(11):1561- 1565. ACKNOWLEDGMENTS Joshi, A., A. K. Mathur, S. M. K. Naqvi and J. P. Mittal. 2006. Influence of osmolality of complete semen extender on motion We would like to acknowledge the other members of characteristics of frozen-thawed ram spermatozoa. Asian-Aust. our laboratory for helpful discussion. The study was J. Anim. Sci. 19(12):1716-1721. supported by grants from the Rural Development Levitz, S. M. and R. D. Diamone. 1985. A rapid colorimetric assay Administration (20070301-034-040-007-03-00). of fungal viability with the tetrazolium salt MTT. J. Infect. Dis. 152:938-945. McNiven, M. A., R.K. Gallant and G. F. Richardson. 1992. In vitro REFERENCES methods of assessing the viability of trout spermatozoa. Theriogenol. 38:679-686. Arman, C., P. I. Quintana Casares, L. G. Sanchez-Partida and B. P. Mosmann, T. 1983. Rapid colorimetric assay for cellular growth Setchell. 2006. Ram sperm motility after intermittent scrotal and survival: application to proliferation and insulation evaluated by manual and computer-assisted methods. assays. J. Immunol. Methods. 65:55-63. Asian J. Androl. 8(4):411-418. Nasr-Esfahani, M. H., R. Aboutorabi, E. Esfandiari and M. Aziz, D. M., L. Ahlswede and E. Enbergs. 2005. Application of Mardani. 2002. Sperm MTT viability assay: A new method for MTT reduction assay to evaluate equine spermviability. evaluation of human sperm viability. J. Assist. Reprod. Genet. Theriogenol. 64:1350-1356. 19(10):477-482. Aziz, D. M. 2006. Assessment of bovine sperm viability by MTT Park, C. S., M. Y. Kim, Y. J. Yi, Y. J. Chang, S. H. Lee, J. J. Lee, reduction assay. Anim. Reprod. Sci. March pp. 1-8. M. C. Kim and D. I. Jin. 2004. Liquid boar sperm quality Björndahl, L., I. Söderlund and U. Kvist. 2003. Evaluation of the during storage and in vitro fertilization and culture of pig one-step eosin-nigrosin staining technique for human sperm oocytes. Asian-Aust. J. Anim. Sci. 17(10):1369-1373. vitality assessment. Hum. Reprod. 18(4):813-816. Campling, B. G., J. Pym, P. R. Galbraith and S. P. Cole. 1988. Use Slater, T. F., B. Swyer and U. Str¨auli. 1963. Studies on succinate- of the MTT assay for rapid determination of chemosensitivity tetrazolium reductase systems. III. Points of coupling of four of human leukemic blast cells. Leuk. Res. 12:823-831. different tetrazolium salts. Biochim. Biophys. Acta 77:383-393. Capkova, J., G. Geussova and J. Peknicova. 2000. Monoclonal Song, X. X., C. K. Park, Y. J. Piao and K. Niwa. 2007. Effect of antibody to human sperm acrosomal protein. Folia Biol. 46:55- monosaccharide L-fucose and polysaccharide fucoidan on 57. sperm L-fucosidase activity and relation to sperm-oocyte Carmichael, J., W. G. DeGraff, A. F. Gazdar, J. D. Minna and J. B. interaction in pig. Asian-Aust. J. Anim. Sci. 20(3):351-358. Mitchell. 1987. Evaluation of a tetrazolium-based semiautomated Yi, Y. J., Y. A. Kwon, H. J. Ko and C. S. Park. 2002. Effects of

498 Byun et al. (2008) Asian-Aust. J. Anim. Sci. 21(4):494-498

diluent component, freezing rate, thawing time and thawing Zhou, J. B., K. Z. Yue, M. J. Luo, Z. L. Chang, H. Liang, Z. Y. temperature on acrosome morphology and motility of frozen- Wang and J. H. Tan. 2004. Effect of extenders and thawed boar sperm. Asian-Aust. J. Anim. Sci. 15(11):1553- temperatures on sperm viability and fertilizing capacity of 1558. Harbin White boar semen during long-term liquid storage. Asian-Aust. J. Anim. Sci. 17(11):1501-1508.