RESUMEN
Supplements containing pharmacological concentrations of biotin are commercially available. The mechanisms by which biotin at pharmacological concentrations exerts its action have been the subject of multiple investigations, particularly for biotin's medicinal potential and wide use for cosmetic purposes. Several studies have reported that biotin supplementation increases cell proliferation; however, the mechanisms involved in this effect have not yet been characterized. In a previous study, we found that a biotin-supplemented diet increased spermatogonia proliferation. The present study was focused on investigating the molecular mechanisms involved in biotin-induced testis cell proliferation. Male BALB/cAnNHsd mice were fed a control or a biotin-supplemented diet (1.76 or 97.7 mg biotin/kg diet) for eight weeks. Compared with the control group, the biotin-supplemented mice presented augmented protein abundance of the c-kit-receptor and pERK1/2Tyr204 and pAKTSer473, the active forms of ERK/AKT proliferation signaling pathways. No changes were observed in the testis expression of the stem cell factor and in the serum levels of the follicle-stimulating hormone. Analysis of mRNA abundance found an increase in cyclins Ccnd3, Ccne1, Ccna2; Kinases Cdk4, Cdk2; and E2F; and Sp1 & Sp3 transcription factors. Decreased expression of cyclin-dependent kinase inhibitor 1a (p21) was observed but not of Cdkn2a inhibitor (p16). The results of the present study identifies, for the first time, the mechanisms associated with biotin supplementation-induced cell proliferation, which raises concerns about the effects of biotin on male reproductive health because of its capacity to cause hyperplasia, especially because this vitamin is available in large amounts without regulation.
Asunto(s)
Biotina/toxicidad , Proliferación Celular/efectos de los fármacos , Suplementos Dietéticos/toxicidad , Hormona Folículo Estimulante/sangre , Espermatogonias/efectos de los fármacos , Factor de Células Madre/metabolismo , Testículo/efectos de los fármacos , Animales , Proteínas de Ciclo Celular/genética , Proteínas de Ciclo Celular/metabolismo , Masculino , Ratones Endogámicos BALB C , Proteínas Quinasas Activadas por Mitógenos/metabolismo , Fosforilación , Proteínas Proto-Oncogénicas c-akt/metabolismo , Proteínas Proto-Oncogénicas c-kit/genética , Proteínas Proto-Oncogénicas c-kit/metabolismo , Transducción de Señal , Factor de Transcripción Sp1/genética , Factor de Transcripción Sp1/metabolismo , Factor de Transcripción Sp3/genética , Factor de Transcripción Sp3/metabolismo , Espermatogonias/metabolismo , Espermatogonias/patología , Testículo/metabolismo , Testículo/patologíaRESUMEN
Supplements containing pharmacological concentrations of biotin are commercially available over the counter. Classical toxicity studies have considered biotin administration as harmless; however, recent investigations have shown that biotin supplementation modifies tissue morphology without changes in toxicity markers, raising concerns about the consequences of morphological changes on tissues' functions and the safety of pharmacological concentrations of the vitamin. Testes are very sensitive to toxicants, and testicular histology is a reliable method to study its function. In this work, we investigated the effects of dietary biotin supplementation on testis morphology and spermatogenesis function using an experimental model, in which we have not observed unfavorable effects on other tissue functions or toxicity markers. Male BALB/cAnNHsd mice were fed a control or a biotin-supplemented diet (1.76 or 97.7 mg biotin/kg diet) for 8 weeks. Compared to the control group, the biotin-supplemented mice presented remarkable testis morphology changes, including increased spermatogonia layers; the cellular mechanism involved is related to increased proliferation. Sperm count and serum testosterone levels were not affected, but spermatozoa motility and morphology were significantly impaired in the biotin-supplemented mice. These results caution against the use of supplements with high concentrations of biotin and indicate that biotin's pharmacological effects on morphology need to be considered in toxicological studies.