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To the Editor:

Increasingly, researchers apparently fail to read broadly about what is known on their subject. Authors poorly introduce their experiments (often without a clear goal or hypothesis unequivocally tested with well-designed experiments) or incompletely discuss their results with pertinent literature. These problems are common and the solution rests with scientists. A truly critical colleague is essential during planning, because more stringent journal review really is too late.

This letter was prompted by Li et al (2010). The authors concluded that human sperm are impacted by “cryodamage” and that including catalase in the medium reduces damage consequent to production of reactive oxygen species. Neither concept is new. Little historic information and no unifying hypothesis were provided; why pick ascorbate, catalase, and studied sperm attributes? Readers were left to dig out, from tertiary citations, information regarding benefit of catalase (or other antioxidants) in maintaining desirable sperm attributes.

Effects of “dead” sperm and catalase on “live” sperm were evidenced ∼40 years ago. Adding dead bull sperm to a suspension damaged living cells therein; catalase reduced this damage (Macmillian, 1970; Shannon and Curson, 1972, 1982). Cryopreservation, among other things, kills sperm and “extracts” molecules into the suspension of “living” sperm; that is, repeating what was done decades ago. Germane literature includes documentation that the degree of benefit from catalase depends on sperm, seminal plasma, and catalase concentrations in the suspension; medium composition; oxygen tension; and temperature and time of/for the reaction (no benefit at 5°C). These factors might account for some unexplained variation in results cited in the letter-prompting paper.

We recognize that sperm differ among individuals and species. In the exampled paper, concentrations of sperm in suspensions frozen were unreported, but were likely >75 × 106/mL (neat samples >100 × 106/mL were diluted 1:1). “Dead” sperm averaged 28% before processing and 41% after thawing. Between “dead” sperm, seminal plasma, and altered “living sperm,” after thawing there was no scarcity of substrates for reactive oxygen species during postthaw manipulations at ∼22°C; catalase should benefit the “living” sperm.

Catalase is beneficial for bull sperm frozen at 100 × 106/mL (Vishwanath et al, 1996). On the other hand, catalase provides little benefit with bull sperm, processed at 5°C including 60- to 150-fold dilution, and cryopreserved at 4 to 40 × 106 sperm/mL. Catalase has been included in media for preserving bull sperm at 15°C to 23°C for >40 years because more pregnancies result. It is estimated that 90 million calves sired by sperm exposed to catalase have been born worldwide (R. Vishwanath, personal communication).

References

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  2. References
  • Li Z., Lin Q., Liu R., Xiao W., Liu W.. Protective effects of ascorbate and catalase on human spermatozoa during cryopreservation. J Androl. 2010; 31: 437444.
  • Macmillian KL. The effect of amylase, catalase, and a decapacitating preparation on fertility of bull semen diluted in ambient temperature extender. Aust J Biol Sci. 1970; 23: 691695.
  • Shannon P., Curson B.. Toxic effect and action of dead sperm on diluted bovine semen. J Dairy Sci. 1972; 55: 614620.
  • Shannon P., Curson B.. Kinetics of the aromatic L-amino acid oxidase from dead bovine spermatozoa and the effect of catalase on fertility of diluted bovine semen stored at 5°C and ambient temperatures. J Reprod Fertil. 1982; 64: 463467.
  • Vishwanath R., Pitt CP, Shannon P.. Sperm numbers, semen age and fertility in fresh and frozen bovine semen. Proc N Z Soc Anim Prod. 1996; 56: 3134.