The effects of gossypol on nuclear protein in rat testes. II. The synthesis of histones and testis-specific proteins after gossypol treatment

Gossypol-induced apoptotic DNA fragmentation correlates with inhibited protein kinase C activity in spermatocytes

After exposure of cultured rat spermatocytes to gossypol acetic acid for five hours, DNA fragmentation in a ladder pattern was found in the medium and supernatants of cell lysates. The concentrations of gossypol used for the induction of apoptosis ranged from 100 microM to 300 microM. Within this dose range, gossypol was also found to be effective at inhibiting protein kinase C (PKC) activity. This inhibitory effect was demonstrated by measuring the PKC residing in cytosolic and particulate fractions. However, the gossypol-induced inhibition of PKC activity was protected by phorbol 12,13-dibutyrate (PDBu), an activator of PKC. Furthermore, the presence of PDBu prevented gossypol-induced DNA fragmentation. These results suggest that spermatocyte apoptosis induced by gossypol is correlated with the reduction of PKC activity, and that maintenance of PKC basal activity is essential for protecting the spermatocyte from apoptosis.

Biological activity in the repopulating rat spermatocyte after the withdrawal of gossypol treatment. VI. Alteration in nuclear factors for interaction with histone gene promoter

This article reports the effects of gossypol at the genomic level in rat spermatogenic cells. After gossypol treatment for various times (8, 12, and 19 weeks), the spermatogonial cells were allowed to rest for 2 to 4 weeks. The function of histone H4 gene promoter (H4GP) in the repopulating pachytene spermatocytes (RPS) was investigated. The sequences of the oligonucleotides for the H4GP binding sites 1 and 2 were synthesized by an ABI-392 DNA synthesizer. RPS and the control pachytene spermatocytes (CPS) were obtained by centrifugal elutriation and subsequently they were used for the preparation of nuclear protein extracts (NPE). The NPE interaction with the DNA fragment of site 1 or 2 was studied by an electrophoresis mobility shift assay (EMSA). EMSA with NPE-CPS revealed ten major gel shift bands for site 1 and 2. The presence of extra unlabelled DNA fragments competed with 6 of the bands. After 2 to 4 weeks recovery from 8, 12, and 19 weeks of gossypol treatment, NPE-RPS failed to shift four bands (b through e) in site 1. These results suggested that gossypol treatment affected the transcription factors for interaction with site 1. On the contrary, no effect was demonstrated in NPE that interacted with site 2. Furthermore, gossypol treatment did not change the nucleotide sequence in the H4GP site 1 and 2.

Genetic toxicity studies of gossypol

Gossypol, a polyphenolic compound extracted from cotton plants, shows promise for use as a male contraceptive, as well as a treatment for gynecological disorders, cancer, and certain microbial diseases. Before gossypol can be considered safe for widespread human use, particularly by healthy people of childbearing age, its effect on normal genetic processes should be understood. Characterization of gossypol's genotoxic potential has not been approached systematically, although numerous clinical and laboratory studies have addressed issues relating to genetic effects of gossypol. This review summarizes results of relevant studies and offers recommendations for the emphasis of future efforts to understand gossypol's genotoxicity potential. Evidence suggesting that gossypol has any genotoxic effects in mammals under normal physiologic conditions so far is weak, at best. However, several unresolved issues that are important for establishing long-term genetic safety of gossypol were uncovered by this analysis. These include the need for a better understanding of the significance of weak increases in SCE frequency seen in a number of laboratory exposure studies, and more definitive, comprehensive animal tumor bioassay data.

Biological activity in the repopulating rat spermatocyte after the withdrawal of gossypol treatment. IV. The activity for the modification of core histones

Mature male rats were treated with gossypol for 8 weeks. Afterwards, treatment was halted to allow the arrested spermatogonia to revive. Fifteen days after the withdrawal of the drug treatment, the repopulating pachytene spermatocyte (RPS) had a lower level of core histone H3 and H4 acetylation (40 and 55% reduction, respectively) than that of the control pachytene spermatocyte (CPS). The reduction in core histone acetylation was found in histone H3 and H4 but not in H2A and H2B. Forty-five days after the withdrawal of the drug treatment, the inhibitory effect on core histone acetylation was recovered. Both dot-blot and standard liquid assays were used to detect the nuclear histone acetylase activity in RPS and CPS. Fifteen days after the withdrawal of gossypol treatment, the acetylase type A activity in RPS was reduced by 42% when compared to CPS. It has been concluded that after gossypol treatment, the activity for nucleosomal core histones acetylation was selectively inhibited. This effect is related to an inhibitory effect on the histone acetylase activity.

Biological activity in the repopulating rat spermatocyte after the withdrawal of gossypol treatment: III. The activity for the transcription of messenger RNA

Mature male rats were treated with gossypol for 8 weeks after which the treatment was stopped to allow the arrested spermatogonia to revive. The arrested spermatogonia in the testes were allowed to develop for 15, 30, and 45 days. The amount of histone H2b, H4 and actin messenger RNA (mRNA) in the repopulated pachytene spermatocyte (RPS) and the control pachytene spermatocyte (CPS) was detected by the dot-blot hybridization technique. Histone H2b mRNA in total testicular RNA is higher than that detected in CPS and RPS. The amount of histone H2b mRNA in 5 micrograms to 10 micrograms of poly (A)+ RNA isolated from CPS is 235% higher than that detected in the RPS. The H2b mRNA content in the resting spermatocytes (15, 30, and 45 days after the withdrawal of gossypol treatment) was inhibited by 68, 72, and 45%, respectively. Histone H2b mRNA transcription in the resting spermatocyte of these 3 time periods was inhibited by 26, 40, and 0%, respectively. Fifteen days after the withdrawal of gossypol treatment, the amount of actin mRNA in RPS was inhibited by 47%. The inhibitory effect of gossypol was rapidly recovered within 30 days after the withdrawal of the drug treatment. It was concluded that after the withdrawal of gossypol treatment, the production of H2b, H4, and actin mRNA in RPS was inhibited. However, the inhibitory effect on the mRNAs' production is reversible. The recovery rate for the mRNAs follows the following order: Actin mRNA greater than H4 mRNA greater than H2b mRNA.

Effects of gossypol on the motility of mammalian sperm

The effects of the male contraceptive gossypol on the motility of mammalian spermatozoa are reviewed. The role of sperm motility in the processes of fertilization and the effect of the drug on these processes determine its effectiveness as a contraceptive. The promising male contraceptive potential of gossypol is discussed in the context of the serious adverse effects of the agent.

Biological activity in the repopulating rat spermatocyte after the withdrawal of gossypol treatment: II. The activity for the synthesis of cellular and nuclear basic proteins

The synthesis of cellular and nuclear basic proteins in the first generation of the repopulated pachytene spermatocyte (RPS) and the control pachytene spermatocyte (CPS) was studied by the incorporation of 3H-arginine into proteins. After pretreatment with gossypol for various lengths of time, the synthetic activity for cellular protein in the RPS was slightly inhibited. In comparison to CPS, on the other hand, the inhibition ranged from 12% to 26% (for gossypol pretreatment from 3 to 12 weeks, respectively). However, the synthetic activity for nuclear basic protein in the RPS was drastically reduced in comparison to that of the CPS. The reduction ranged from 46% to 61% in RPS after receiving gossypol pretreatment for 3 to 12 weeks, respectively. Gel electrophoretic separation of the basic protein extracted from the pachytene cell indicated that the major basic proteins are nucleosomal linker and core proteins, i.e., histone H1, H2A,B, H3, and H4, and with a lesser amount of sperm-specific BP and X1 proteins. After gossypol treatment in the RPS, the synthesis of sperm-specific proteins (BP and X1) and core histones (H2A and H4) became drastically reduced. Finally, the effect of gossypol on the ratio of nuclear basic protein to DNA in RPS and the direct correlation of this ratio to nucleosomal spacing and chromatin structure are discussed.

Biological activity in the repopulating rat spermatocyte after the withdrawal of gossypol treatment: I. The activity for DNA synthesis

Mature male rats were treated with gossypol for various lengths of time after which the treatment was stopped to allow the arrested spermatogonia to revive. Fifteen days after withdrawal of the drug treatment, the arrested spermatogonia entered into the meiotic division and then reached the pachytene stage. The meiotic cells derived from the arrested spermatogonia were the first generation of the differentiated germ cells after long-term gossypol treatment. Centrifugal elutriation technique was used to isolate the repopulating pachytene spermatocytes (RPS) or the control pachytene spermatocytes (CPS) from the rat testis with or without receiving gossypol pretreatment. In vitro culture condition for RPS and CPS was established for the synthesis of DNA by the measurement of 3H-thymidine incorporation. The activity for DNA synthesis in RPS was studied and compared to that of the CPS. It was concluded that after gossypol treatment for various times, the incorporation of 3H-thymidine into the cellular thymidine pool of RPS was not affected. However, the activity for DNA synthesis in RPS was significantly lower than that in the CPS. The synthetic activity for DNA was reduced by 14%, 26%, 42%, 40%, and 40% in the RPS for the gossypol pretreatment of 3, 4, 6, 7, and 8 weeks, respectively.