Besides its classical biological effects on calcium and phosphorus homeostasis, calcitriol, the active vitamin D metabolite, has a broad variety of actions including anticancer effects that are mediated either transcriptionally and/or via non-genomic pathways. In the context of cancer, calcitriol regulates the cell cycle, induces apoptosis, promotes cell differentiation and acts as anti-inflammatory factor within the tumor microenvironment. In this review, we address the different mechanisms of action involved in the antineoplastic effects of calcitriol.

The human placenta synthesizes 1,25-dihydroxyvitamin D(3) and expresses the vitamin D receptor. Because preeclampsia (PE) is associated with low circulating levels of maternal 1,25-dihydroxyvitamin D(3) and IGF-I, it is possible that alterations in calcium metabolism seen in PE could occur at the level of the fetoplacental unit. In this study, the patterns of gene expression and enzyme activity of 25-hydroxyvitamin D-1 alpha-hydroxylase (1 alpha-hydroxylase) and the abundance of IGF-I mRNA in placentas from normal (NT) and PE-complicated pregnancies were investigated. Cultured syncytiotrophoblast cells from preeclamptic placentas had only one tenth the activity of 1 alpha-hydroxylase and did not respond to IGF-I, when compared with NT cultures. Similarly, the levels of 1 alpha-hydroxylase mRNA in syncytiotrophoblast cells from PE placentas under basal and IGF-I-stimulated conditions were significantly reduced. In contrast, IGF-I mRNA levels were found to increase during the differentiation process, with no differences between NT and PE cultures. These results support the role of placenta as a contributor to the abnormalities observed in calcium metabolism in PE.

Although accumulating data show that placenta is able to synthesize 1,25-dihydroxyvitamin D3, the presence of cytochrome P(450) enzyme capable of converting 25-hydroxyvitamin D3 (250HD(3)) to the biologically active form of vitamin D in this tissue, has not been yet clearly established. In this study, we have investigated the presence of 25-hydroxyvitamin D3 1alpha-hydroxylase (1alpha-(OH)ase) gene expression products in cultured human syncytiotrophoblast. Total RNA was isolated from cultured placental cells and subjected to Northern blots or RT-PCR by using 1alpha-(OH)ase-specific primers. The amplified complementary DNA fragments were analyzed by gel electrophoresis and nucleotide sequencing. Total RNA from kidney HEK 293 cells was subjected to reverse transcriptase reaction, and a 298-bp complementary DNA 1alpha-(OH)ase probe was generated by PCR. Primary cultures of human syncytiotrophoblasts exhibited 1alpha-(OH)ase activity, and a transcript for this gene could be demonstrated in these cells. Northern blot analysis revealed the presence of a 2.5-kb product, similar in size to that previously reported in kidney. RT-PCR analysis demonstrated the presence of a single transcript with nucleotide sequence identical to that previously reported for human 1alpha-(OH)ase complementary DNA clones. In addition, data are presented which suggest that differentiation of cytotrophoblast to the syncytial state was not necessary for this gene to be expressed, which may indicate a role of this enzyme all through pregnancy. The overall results of this study provide evidence for the presence of 1alpha-(OH)ase in the human placenta, suggesting that conversion of 25OHD(3) to 1,25-dihydroxyvitamin D3 in the trophoblast is most probably attributed to an enzymatic 1alpha-hydroxylation reaction.

In the last century, progress in the knowledge of human diseases, their diagnosis and treatment have grown exponentially, due in large part to the introduction and use of laboratory animals. Along with this important progress, the need to provide training and guidance to the scientific community in all aspects related to the proper use of experimental animals has been indispensable. Animal research committees play a primary role in evaluating experimental research protocols, from their feasibility to the rational use of animals, but above all in seeking animal welfare. The Institutional Committee for the Care and Use of Animals (IACUC) has endeavored to share several relevant aspects in conducting research with laboratory animals. Here, we present and discuss the topics that we consider of utmost importance to take in the account during the design of any experimental research protocol, so we invite researchers, technicians, and undergraduate and graduate students to dive into the fascinating subject of proper animal care and use for experimentation. The main intention of these contributions is to sensitize users of laboratory animals for the proper and rational use of them in experimental research, as well as to disseminate the permitted and unpermitted procedures in laboratory animals. In the first part, the significance of experimental research, the main functions of IACUC, and the principle of the three R's (replacement, reduction, and refinement) are addressed.

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