A Practical Approach, Second Edition=Ronald D. Ho.pdf

PRINCIPLES OF RISK ASSESSMENT — FDA PERSPECTIVE 8872) Sperm Motility — Sperm motility may be assessed either from the vas deferens or the caudaepididymis (rat and mouse) or from an ejaculate (rabbit and dog). In rats and mice, placing the vasor cauda epididymis in an appropriate medium and allowing sperm to swim out is a popular methodfor collecting sperm for analysis. 23 Sperm motion may be captured on videotape or digitallyformatted and analyzed at a later date, either manually or by computer-assisted sperm analysis(CASA) systems.Although there is no standard for the percentage of motile sperm, the general consensus is thatin a control sample the number of “progressively” motile sperm should be at least 70%. 24,25 Visualestimates of counts of moving sperm are straightforward. CASA systems have given us the abilityto quantify a number of sperm motion parameters. For the CASA systems, a variety of parametersmust be defined correctly for accurate image acquisition and analysis. It is important to rememberthat the information obtained from a CASA system is dependent upon the instrument settings. Twodifferent laboratories can use the same instrument but use different settings and obtain differentresults for various motion parameters. Therefore, data obtained by these instruments cannot becompared across laboratories, and all values obtained should be compared to concurrent controls,not historical controls.The use of the CASA system allows for the rapid and efficient collection of motility information,including velocity (straight-line and curvilinear) measurements, beat cross-frequency, and amplitudeof lateral head displacement measurements, on a large number of sperm. Recently, using CASAsystems, compound-induced changes in motility have been detected 26-29 and associated with changesin fertility 30-32 in experimental animals. Preliminary results have suggested that significant reductionsin sperm velocity are associated with reduced fertility, even when the percentage of motile spermis not affected. It is important to distinguish motility from progressive motility. Sperm may bemotile but not demonstrate a directed forward movement. A change in motility may be independentof changes in testicular histopathology because the agent may adversely affect epididymal function.Motility is also influenced by abstinence, the time between obtaining the sample and the evaluationof the sample, medium pH, sample chamber depth, and temperature. The investigator should becareful to avoid artifactual cell death during specimen preparation so that the percentage of motilesperm from control animals is consistently high. A reduction in the velocity or pattern of motilityof treated animals when compared with controls may indicate a need for further testing. Of all thesperm motion parameters, the percent motility is clearly related to fertility. Therefore, any changein the percent motility should be considered an adverse effect, especially if it is dose related.3) Other Selected Endpoints of Male Reproductive Toxicitya) Organ Weights — Other endpoints commonly evaluated are reproductive organ weights andhistopathological effects observed on male secondary sex organs. The male reproductive organsfor which weights may be useful for reproductive risk assessment include the testis, epididymis,pituitary, seminal vesicle with coagulating gland, and the prostate. Reproductive organ weightchanges may occur irrespective of a decrease in body weight; however, it should be rememberedthat changes in other endpoints related to reproductive function (i.e., motility) might be alteredwithout a concomitant change in reproductive organ weight. Organ weights should be reported asabsolute weights or relative weights (weights per gram of body weight; weights per gram of brainweight). 33 Care should be taken to ensure that deleterious reproductive effects are not maskedbecause the organ weight and body weight are both reduced by treatment. Testicular weights arerelatively stable and vary only modestly within a given test species. 34,35 Increases or decreases intestis weight indicate that a compound has significantly altered testis structure but do not help tocharacterize the effect.Depending on the treatment period, not all testicular effects will result in a decrease or anincrease in testicular weight. For example, short treatment periods may produce increased germcell degeneration that may not immediately be reflected in testicular weights. Additionally, blockage© 2006 by Taylor & Francis Group, LLC