María Enciso

A two-tailed Comet assay for assessing DNA damage in spermatozoa

DNA fragmentation is considered an important parameter of semen quality, and of significant value as a predictor of male fertility. Poor quality chromatin is closely associated with, and highly indicative of, some fertility problems. Many methodologies to assess DNA fragmentation in spermatozoa are available, but they are all unable to differentiate between single-stranded DNA breaks (SSB) and double-stranded DNA breaks (DSB) in the same sperm cell. The two-tailed Comet assay (2T-Comet) protocol overcomes this limitation. A modification of the original Comet assay was developed for the simultaneous evaluation of DNA SSB and DSB in human spermatozoa. The 2T-Comet assay is a fast, sensitive, and reliable procedure for the quantification and characterization of DNA damage in spermatozoa. It is an innovative method for assessing sperm DNA integrity, which has important implications for human fertility and andrological pathology.

The ability of sperm selection techniques to remove single- or double-strand DNA damage

A wide variety of techniques for the preparation of sperm are currently available, of which the most commonly employed are density-gradient centrifugation (DGC) and swim-up (SUP). To date, these methods appear to be effective in selecting functional sperm for assisted reproduction techniques (ART), but they may have negative effects on sperm DNA. In this study, the ability of these semen processing techniques to eliminate spermatozoa containing single- and double-strand DNA damage was assessed by the two-tailed comet assay and the sperm chromatin dispersion test in 157 semen samples from patients seeking assisted reproduction treatment. Our results indicated that SUP and DGC are equally efficient in eliminating spermatozoa containing double-strand DNA damage and sperm with highly damaged (degraded) DNA, as characterized by the presence of both single- and double-strand DNA breaks. However, DGC is more efficient than SUP in selecting spermatozoa that are free from single-strand DNA damage. Future studies should characterise the importance of the various types of DNA damage and examine the sperm processing protocols used in each laboratory to determine their ability to eliminate DNA damage and hence, prevent the potential transmission of genetic mutations via ART.

Differential resistance of mammalian sperm chromatin to oxidative stress as assessed by a two-tailed comet assay

Protamines of eutherian species are cysteine-rich molecules that become cross-linked by disulfide bonds during epididymal transit, whereas the protamines of most marsupial species lack cysteine residuals. The present study made use of the differences in protamine structure between eutherian and metatherian mammal spermatozoa to examine the comparative resistance of sperm DNA to oxidative damage in three eutherian species (Mus musculus, Homo sapiens, Sus domesticus) and three metatherian species (Vombatus ursinus, Phascolarctos cinereus, Macropus giganteus). Sperm DNA fragmentation of samples exposed to increasing concentrations of hydrogen peroxide was assessed by means of the two-tailed comet assay. The sperm DNA of the marsupial species studied were significantly more sensitive to oxidative stress than the spermatozoa of eutherian species. Such susceptibility is consistent with the lack of disulfide cross-linking in marsupial sperm chromatin and suggests that the oxidation of thiols to disulfides for chromatin condensation during epididymal transit in eutherian mammals is likely to be important in order to provide stability and protect these cells from the genotoxic effects of adverse environments.

Han sido el IBEX35 y el IPC definiciones financieramente eficientes del portafolio de mercado

En este trabajo se presenta un estudio inicial que cuestiona la eficiencia financiera de las aproximaciones del portafolio de mercado mas empleadas en Espana y Mexico (IBEX35 e IPC); se observa que podrian no considerarse como tales, con lo que se pone en duda su uso como “referencias neutrales”, segun lo proponen Black y Litterman (1992), para la gestion de los mismos. Con el objeto de probar la eficiencia financiera en estos dos indices, se desarrollaron dos simulaciones de eventos discretos empleando el modelo Markowitz-Tobin-Sharpe-Lintner (Markowitz, 1987) con datos de frecuencia mensual —a partir de febrero de 2001 a diciembre de 2010— de sus acciones miembro en una ventana temporal. Los resultados fueron comparados a traves del ratio de Sharpe (1966) y demostraron que, en el corto plazo, los supuestos de equilibrio no se mantienen y las aproximaciones del portafolio de mercado estudiadas resultan ineficientes en relacion con otros portafolios optimos derivados de manera simultanea.