Incorporation of mevalonate into dolichol and other isoprenoids during estrogen-induced chick oviduct differentiation

Inferring lanosterol functions in the female rabbit reproductive tract based on the immunolocalization of lanosterol 14-demethylase and farnesoid beta-receptor

Female reproductive organs have de novo synthesis of cholesterol. Some sterol molecules, intermediaries in the cholesterol synthesis, have important paracrine/autocrine actions. Lanosterol binds to the farnesoid beta-receptor (FXRβ), a molecule widely expressed in the ovaries, suggesting that it may play a role in reproduction. Up to date, we know little about lanosterol functions across female reproductive organs. We described immunolocalized lanosterol 14-demethylase (LDM or CYP51A1), responsible for catalyzing the conversion of lanosterol in cholesterol, and FXRβ in the ovary, oviduct, uterus, and vagina of virgin and pregnant rabbits. In virgin rats, we found CYP51A1 and FXRβ immunoreactivity was found in all ovarian follicles, epithelial cells, stroma, and Graafian follicles. Also, the epithelium and stroma, as well as the smooth muscle of the oviduct, vagina, and uterus showed CYP51A1 and FXRβ immunoreactivity. In pregnant dams, we observed the presence of CYP51A1 and FXRβ immunoreactivity in the corpora lutea, giant uterine cells, and trophoblastic cells. The presence of CYP51A1 and FXRβ support that lanosterol participates in diverse reproductive processes, including follicular maturation, transport of gametes and zygote, implantation of blastocyst, lubrication, and contraction of the vagina, secretion of female prostate, and control of delivery mediated by pelvic muscles contraction.

Zoledronic acid repolarizes tumour-associated macrophages and inhibits mammary carcinogenesis by targeting the mevalonate pathway

It is unknown whether zoledronic acid (ZA) at clinically relevant doses is active against tumours not located in bone. Mice transgenic for the activated ErbB-2 oncogene were treated with a cumulative number of doses equivalent to that recommended in human beings. A significant increase in tumour-free and overall survival was observed in mice treated with ZA. At clinically compatible concentrations, ZA modulated the mevalonate pathway and affected protein prenylation in both tumour cells and macrophages. A marked reduction in the number of tumour-associated macrophages was paralleled by a significant decrease in tumour vascularization. The local production of vascular endothelial growth factor and interleukin-10 was drastically down-regulated in favour of interferon-γ production. Peritoneal macrophages and tumour-associated macrophages of ZA-treated mice recovered a full M1 antitumoral phenotype, as shown by nuclear translocation of nuclear factor kB, inducible nitric oxide synthase expression and nitric oxide production. These data indicate that clinically achievable doses of ZA inhibit spontaneous mammary cancerogenesis by targeting the local microenvironment, as shown by a decreased tumour vascularization, a reduced number of tumour-associated macrophages and their reverted polarization from M2 to M1 phenotype.

Geranylgeraniol prevents the cytotoxic effects of mevastatin in THP-1 cells, without decreasing the beneficial effects on cholesterol synthesis

BACKGROUND AND PURPOSE

Statins, inhibitors of hydroxymethylglutaryl-CoA reductase, reduce the intracellular synthesis of cholesterol and prevent the onset of atherosclerosis. They also decrease the synthesis of isoprenoid molecules, such as the side chain of ubiquinone and geranylgeranyl pyrophosphate. As a consequence, statins impair mitochondrial metabolism and the activation of small monomeric GTPases (such as Rho and Ras), causing toxic effects. To date, a successful strategy to prevent statin toxicity is lacking.

EXPERIMENTAL APPROACH

In human monocytic THP-1 cells, we measured the synthesis of cholesterol and isoprenoids, mitochondrial electron flow, the activity of RhoA and Rac, cell death and proliferation.

KEY RESULTS

Mevastatin reduced the synthesis of cholesterol, geranylgeranyl pyrophosphate and ubiquinone, mitochondrial electron transport, activity of RhoA and Rac, and cell proliferation, accompanied by increased cell death. Geranylgeraniol, a cell-permeable analogue of geranylgeranyl pyrophosphate, reversed all these effects of mevastatin, without affecting its ability to reduce cholesterol synthesis. Notably, geranylgeraniol was more effective than the addition of exogenous ubiquinone, which rescued mitochondrial respiratory activity and reversed mevastatin cytotoxicity, but did not alter the decrease in cell proliferation. The same results were obtained in human liver HepG2 cells.

CONCLUSIONS AND IMPLICATIONS

Geranylgeraniol had a broader protective effect against the cytotoxicity of statins than exogenous ubiquinone. Therefore, geranylgeraniol may be a more useful and practical means of limiting the toxicities of statins, without reducing their efficacy as cholesterol lowering agents.

Asbestos Induces Nitric Oxide Synthesis in Mesothelioma Cells via Rho Signaling Inhibition

We have observed that in three human malignant mesothelioma cell lines, crocidolite asbestos induced the activation of the transcription factor NF-kappaB and the synthesis of nitric oxide (NO) by inhibiting the RhoA signaling pathway. The incubation with crocidolite decreased the level of GTP-bound RhoA and the activity of Rho-dependent kinase, and induced the activation of Akt/PKB and IkBalpha kinase, leading to the nuclear translocation of NF-kappaB. The effects of crocidolite fibers on NF-kappaB activation and NO synthesis were mimicked by Y27632 (an inhibitor of the Rho-dependent kinases) and toxin B (an inhibitor of RhoA GTPase activity), while they were reverted by mevalonic acid, the product of 3-hydroxy-3-methylglutaryl coenzyme A (HMGCoA) reductase. Furthermore, crocidolite, similarly to mevastatin, inhibited the synthesis of cholesterol and ubiquinone and the prenylation of RhoA: these effects were prevented in the presence of mevalonic acid. This suggests that crocidolite fibers might inhibit the synthesis of isoprenoid molecules at the level of the HMGCoA reductase reaction or of an upstream step, thus impairing the prenylation and subsequent activation of RhoA. Akt can stimulate NO synthesis via a double mechanism: it can activate the inducible NO synthase via the NF-kappaB pathway and the endothelial NO synthase via a direct phosphorylation. Our results suggest that crocidolite increases the NO levels in mesothelioma cells by modulating both NO synthase isoforms.