生育三烯酚的生理功能及合成代谢调控

维生素E是一种重要的脂溶性抗氧化剂。天然维生素E包括α-、β-、γ-和δ-生育酚及α-、β-、γ-和δ-生育三烯酚等8种组分。生育三烯酚具有独特的降低胆固醇、抗癌和神经保护功能,这些功能是生育酚所不具备的。生育三烯酚主要由谷物等单子叶植物合成。虽然生育三烯酚成分占天然维生素E的一半,但有关生育三烯酚的研究仅占维生素E全部文献的1%。可喜的是,近年来这一领域的研究取得了较大的进展。我们就生育三烯酚在人体内的生理功能、来源、生物合成及代谢调控等方面的进展进行概述。     

Selective excretion of yolk-derived tocotrienols into the bile of the chick embryo

The aim of this study was to investigate the possibility of biodiscrimination between different forms of vitamin E during the development of the chick embryo. The vitamin E present in the initial yolk consisted of α-tocopherol (90%), (β+γ)-tocopherol (8%), α-tocotrienol (0.3%) and (β+γ)-tocotrienol (1.3%). In marked contrast, the vitamin E recovered from the bile of the day-16 embryo contained much higher proportions of α-tocotrienol (10%) and especially of (β+γ)-tocotrienol (42%). By the time of hatching, 56% of the vitamin E present in the bile was in the form of (β+γ)-tocotrienol. The residual yolk of the newly-hatched chick contained far greater proportions of α-tocotrienol (2.6%) and (β+γ)-tocotrienol (10%) than were present in the initial yolk. The results suggest that the liver of the embryo may selectively excrete tocotrienols as components of bile, whilst retaining the tocopherols within the hepatocytes. The increased proportions of tocotrienols in the residual yolk may result from the recycling of bile from the gall bladder to the yolk. The liver of the day-old chick contained α-tocopherol as the main form of vitamin E (90%) with only a small proportion (0.2%) of (β+γ)-tocotrienol. The α-tocopherol form was also the main vitamin E component in the brain (85%), heart (79%), lung (82%) and adipose tissue (91%) of the day-old chick. The present study suggests the occurrence of a high degree of biodiscrimination between tocopherols and tocotrienols during the development of the chick embryo.     

Combinatory responses of proinflamamtory cytokines on nitric oxide-mediated function in mouse calvarial osteoblasts

Combinatory responses of proinflamamtory cytokines have been examined on the nitric oxide-mediated function in cultured mouse calvarial osteoblasts. Interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α) induced iNOS gene expression and NO production, although these actions were inhibited by L-NG-monomethylarginine (L-NMMA) and decreased alkaline phosphatase (ALPase) activity. Furthermore, NO donors, sodium nitroprusside (SNP) and NONOate dose-dependently elevated ALPase activity. In contrast, transforming-growth factor-β (TGF-β) decreased NO production stimulated by IL-1β, TNF-α and interferon-γ (IFN-γ). iNOS was expressed by mouse calvarial osteoblast cells after stimulation with IL-1β, TNF-α, and IFN-γ. Incubation of mouse calvarial osteoblast cells with the cytokines inhibited growth and ALPase activity. However, TGF-β-treatment abolished these effects of IL-1β, TNF-α and IFN-γ on growth inhibition and stimulation of ALPase in mouse calvarial osteoblast cells. In contrast, IL-1β, TNF-α, and IFN-γ exerted growth-inhibiting effects on mouse calvarial osteoblast cells which were partly NO-dependent. The results suggest that NO may act predominantly as a modulator of cytokine-induced effects on mouse calvarial osteoblast cells and TGF-β is a negative regulator of the NO production stimulated by IL-1β, TNF-α and IFN-γ.     

Antagonistic regulation of EMT by TIF1γ and Smad4 in mammary epithelial cells

TGF-β is a potent inducer of epithelial-to-mesenchymal transition (EMT), a process involved in tumour invasion. TIF1γ participates in TGF-β signalling. To understand the role of TIF1γ in TGF-β signalling and its requirement for EMT, we analysed the TGF-β1 response of human mammary epithelial cell lines. A strong EMT increase was observed in TIF1γ-silenced cells after TGF-β1 treatment, whereas Smad4 inactivation completely blocked this process. Accordingly, the functions of several TIF1γ target genes can be linked to EMT, as shown by microarray analysis. As a negative regulator of Smad4, TIF1γ could be crucial for the regulation of TGF-β signalling. Furthermore, TIF1γ binds to and represses the plasminogen activator inhibitor 1 promoter, demonstrating a direct role of TIF1γ in TGF-β-dependent gene expression. This study shows the molecular relationship between TIF1γ and Smad4 in TGF-β signalling and EMT.     

Effect of chronic administration of vitamin E on the hemopoietic system in hypercholesterolemia

Hypercholesterolemia induces oxidative stress, which is known to have adverse effects on the integrity of cells. Hence, hypercholesterolemia may have adverse effects on the hemopoietic system. Vitamin E, an antioxidant, is being used by normo- and hypercholesterolemic subjects. It is, however, not known if vitamin E has any beneficial or adverse effects on the hemopoietic system. The objectives of this study are to determine if (i) hypercholesterolemia has any adverse effects on the hemopoietic system [red blood cell (RBC) count, mean corpuscular volume (MCV), red blood cell distribution width (RDW), hematocrit (Hct), hemoglobin (Hb), mean corpuscular hemoglobin (MCH), MCH concentration (MCHC), white blood cell (WBC), and platelet counts, and mean platelet volume (MPV)], and (ii) vitamin E has any effect on the hemopoietic system in hypercholesterolemia. Blood samples were collected before and at various intervals during a high cholesterol diet (0.25% cholesterol) for 2 and 4 months, and while on high cholesterol diet with vitamin E (2 months) following a high cholesterol diet (2 months). Serum cholesterol was measured on an automated Clinical System Analyzer and hemopoietic parameters were measured on an automated Cell-dyn-4000. The results show that hypercholesterolemia decreased RBC count, Hct and Hb, increased MCV, RDW, MCH, and MCHC, and had no effect on WBC and platelet counts, and MPV. Vitamin E did not affect any of the parameters of the hemopoietic system. In conclusion, hypercholesterolemia of short duration has adverse effects on certain elements of the hemopoietic system. Vitamin E does not affect the hemopoietic system during hypercholesterolemia.     

IL-11 expression in retinal and corneal cells is regulated by interferon-γ

Interleukin-11 (IL-11) is an anti-apoptotic, anti-inflammatory cytokine with hematopoietic potential. The expression and protective actions of IL-11 have not been explored in the eye. The expression of IL-11 in primary cultures of human retinal pigment epithelial (HRPE) and human corneal fibroblast (HCRF) cells were evaluated in these studies. Constitutive secretion of IL-11 was not observed in either HRPE or HCRF. TNF-α + IL-1 induced IL-11 secretion and this production was inhibited by NFκB pathway inhibitors. IFN-γ significantly inhibited TNF-α and IL-1 induced IL-11 secretion and inhibitors of JAK-STAT pathway reversed this inhibition. TGF-β induced IL-11 secretion that was blocked by TGF-β receptor 1 inhibitor but not by IFN-γ. RT-PCR analysis confirmed the effects of IL-1, TNF-α, IFN-γ and TGF-β on IL-11 secretion at mRNA levels. Our results demonstrate that IL-11 is dramatically up regulated in retina and cornea cells and that IFN-γ is a physiological inhibitor of IL-11 expression.     

Hypoxia-induced inhibition of lung development is attenuated by the peroxisome proliferator-activated receptor-γ agonist rosiglitazone

Hypoxia enhances transforming growth factor-β (TGF-β) signaling, inhibiting alveolar development and causing abnormal pulmonary arterial remodeling in the newborn lung. We hypothesized that, during chronic hypoxia, reduced peroxisome proliferator-activated receptor-γ (PPAR-γ) signaling may contribute to, or be caused by, excessive TGF-β signaling. To determine whether PPAR-γ was reduced during hypoxia, C57BL/6 mice were exposed to hypoxia from birth to 2 wk and evaluated for PPAR-γ mRNA and protein. To determine whether rosiglitazone (RGZ, a PPAR-γ agonist) supplementation attenuated the effects of hypoxia, mice were exposed to air or hypoxia from birth to 2 wk in combination with either RGZ or vehicle, and measurements of lung histology, function, parameters related to TGF-β signaling, and collagen content were made. To determine whether excessive TGF-β signaling reduced PPAR-γ, mice were exposed to air or hypoxia from birth to 2 wk in combination with either TGF-β-neutralizing antibody or vehicle, and PPAR-γ signaling was evaluated. We observed that hypoxia reduced PPAR-γ mRNA and protein, in association with impaired alveolarization, increased TGF-β signaling, reduced lung compliance, and increased collagen. RGZ increased PPAR-γ signaling, with improved lung development and compliance in association with reduced collagen and TGF-β signaling. However, no reduction was noted in hypoxia-induced pulmonary vascular remodeling. Inhibition of hypoxia-enhanced TGF-β signaling increased PPAR-γ signaling. These results suggest that hypoxia-induced inhibition of lung development is associated with a mutually antagonistic relationship between reduced PPAR-γ and increased TGF-β signaling. PPAR-γ agonists may be of potential therapeutic significance in attenuating TGF-β signaling and improving alveolar development.     

The role of inflammatory and anti-inflammatory cytokines in the pathogenesis of human tegumentary leishmaniasis

In tegumentary leishmaniasis caused by Leishmania braziliensis, there is evidence that increased production of IFN-γ, TNF-α and absence of IL-10 is associated with strong inflammatory reaction and with tissue destruction and development of the lesions observed in cutaneous leishmaniasis (CL) and mucosal leishmaniasis (ML). We evaluate the role of regulatory cytokines and cytokine antagonists in the downregulation of immune response in L. braziliensis infection. Peripheral blood mononuclear cells from CL and ML were stimulated with soluble Leishmania antigen in the presence or absence of regulatory cytokines (IL-10, IL-27 and TGF-β) or antagonists of cytokines (α-TNF-α and α-IFN-γ). Cytokines production (IL-10, IL-17, TNF-α and IFN-γ) was measured by ELISA. IL-10 and TGF-β downmodulate TNF-α and IL-17 production, whereas IL-27 had no effect in the production of TNF-α, IFN-γ and IL-17 in these patients. Neutralization of TNF-α decreased IFN-γ level and the neutralization of IFN-γ decreased TNF-α level and increased IL-10 production. This study demonstrate that IL-10 and TGF-β are cytokines that appear to be more involved in modulation of immune response in CL and ML patients. IL-10 might have a protective role, since the neutralization of IFN-γ decreases the production of TNF-α in an IL-10-dependent manner.     

Curcumin augments lung maturation, preventing neonatal lung injury by inhibiting TGF-β signaling

There is no effective intervention to prevent or treat bronchopulmonary dysplasia (BPD). Curcumin has potent antioxidant and anti-inflammatory properties, and it modulates signaling of peroxisome proliferator-activated receptor-γ (PPARγ), an important molecule in the pathobiology of BPD. However, its role in the prevention of BPD is not known. We determined 1) if curcumin enhances neonatal lung maturation, 2) if curcumin protects against hyperoxia-induced neonatal lung injury, and 3) if this protection is mediated by blocking TGF-β. Embryonic day 19 fetal rat lung fibroblasts were exposed to 21% or 95% O(2) for 24 h following 1 h of treatment with curcumin. Curcumin dose dependently accelerated e19 fibroblast differentiation [increased parathyroid hormone-related protein (PTHrP) receptor, PPARγ, and adipocyte differentiation-related protein (ADRP) levels and triolein uptake] and proliferation (increased thymidine incorporation). Pretreatment with curcumin blocked the hyperoxia-induced decrease (PPARγ and ADRP) and increase (α-smooth muscle actin and fibronectin) in markers of lung injury/repair, as well as the activation of TGF-β signaling. In a separate set of experiments, neonatal Sprague-Dawley rat pups were exposed to 21% or 95% O(2) for 7 days with or without intraperitoneal administration of curcumin. Analysis for markers of lung injury/repair [PTHrP receptor, PPARγ, ADRP, fibronectin, TGF-β receptor (activin receptor-like kinase 5), and Smad3] and lung morphology (radial alveolar count) demonstrated that curcumin effectively blocks TGF-β activation and hyperoxia-induced lung injury. Therefore, curcumin accelerates lung maturation by stimulating key alveolar epithelial-mesenchymal interactions and prevents hyperoxia-induced neonatal lung injury, possibly by blocking TGF-β activation, suggesting that it is a potential intervention against BPD.     

Constitutive Smad signaling and Smad-dependent collagen gene expression in mouse embryonic fibroblasts lacking peroxisome proliferator-activated receptor-gamma

Transforming growth factor-β (TGF-β), a potent inducer of collagen synthesis, is implicated in pathological fibrosis. Peroxisome proliferator-activated receptor-γ (PPAR-γ) is a nuclear hormone receptor that regulates adipogenesis and numerous other biological processes. Here, we demonstrate that collagen gene expression was markedly elevated in mouse embryonic fibroblasts (MEFs) lacking PPAR-γ compared to heterozygous control MEFs. Treatment with the PPAR-γ ligand 15d-PGJ₂ failed to down-regulate collagen gene expression in PPAR-γ null MEFs, whereas reconstitution of these cells with ectopic PPAR-γ resulted in their normalization. Compared to control MEFs, PPAR-γ null MEFs displayed elevated levels of the Type I TGF-β receptor (TβRI), and secreted more TGF-β1 into the media. Furthermore, PPAR-γ null MEFs showed constitutive phosphorylation of cellular Smad2 and Smad3, even in the absence of exogenous TGF-β, which was abrogated by the ALK5 inhibitor SB431542. Constitutive Smad2/3 phosphorylation in PPAR-γ null MEFs was associated with Smad3 binding to its cognate DNA recognition sequences, and interaction with coactivator p300 previously implicated in TGF-β responses. Taken together, these results indicate that loss of PPAR-γ in MEFs is associated with upregulation of collagen synthesis, and activation of intracellular Smad signal transduction, due, at least in part, to autocrine TGF-β stimulation.     

Natural forms of vitamin E: metabolism,antioxidant, and anti-inflammatory activities and their role in disease prevention and therapy

The vitamin E family consists of four tocopherols and four tocotrienols. α-Tocopherol (αT) is the predominant form of vitamin E in tissues and its deficiency leads to ataxia in humans. However, results from many clinical studies do not support a protective role of αT in disease prevention in people with adequate nutrient status. On the other hand, recent mechanistic studies indicate that other forms of vitamin E, such as γ-tocopherol (γT), δ-tocopherol, and γ-tocotrienol, have unique antioxidant and anti-inflammatory properties that are superior to those of αT in prevention and therapy against chronic diseases. These vitamin E forms scavenge reactive nitrogen species, inhibit cyclooxygenase- and 5-lipoxygenase-catalyzed eicosanoids, and suppress proinflammatory signaling such as NF-κB and STAT3/6. Unlike αT, other vitamin E forms are significantly metabolized to carboxychromanols via cytochrome P450-initiated side-chain ω-oxidation. Long-chain carboxychromanols, especially 13′-carboxychromanols, are shown to have stronger anti-inflammatory effects than unmetabolized vitamins and may therefore contribute to the beneficial effects of vitamin E forms in vivo. Consistent with mechanistic findings, animal and human studies show that γT and tocotrienols may be useful against inflammation-associated diseases. This review focuses on non-αT forms of vitamin E with respect to their metabolism, anti-inflammatory effects and mechanisms, and in vivo efficacy in preclinical models as well as human clinical intervention studies.     

Disruption of mouse cytochrome p450 4f14 (Cyp4f14 gene) causes severe perturbations in vitamin E metabolism

Vitamin E is a family of naturally occurring and structurally related lipophilic antioxidants, one of which, α-tocopherol (α-TOH), selectively accumulates in vertebrate tissues. The ω-hydroxylase cytochrome P450-4F2 (CYP4F2) is the only human enzyme shown to metabolize vitamin E. Using cDNA cloning, cell culture expression, and activity assays, we identified Cyp4f14 as a functional murine ortholog of CYP4F2. We then investigated the effect of Cyp4f14 deletion on vitamin E metabolism and status in vivo. Cyp4f14-null mice exhibited substrate-specific reductions in liver microsomal vitamin E-ω-hydroxylase activity ranging from 93% (γ-TOH) to 48% (γ-tocotrienol). In vivo data obtained from metabolic cage studies showed whole-body reductions in metabolism of γ-TOH of 90% and of 68% for δ- and α-TOH. This metabolic deficit in Cyp4f14(-/-) mice was partially offset by increased fecal excretion of nonmetabolized tocopherols and of novel ω-1- and ω-2-hydroxytocopherols. 12'-OH-γ-TOH represented 41% of whole-body production of γ-TOH metabolites in Cyp4f14(-/-) mice fed a soybean oil diet. Despite these counterbalancing mechanisms, Cyp4f14-null mice fed this diet for 6 weeks hyper-accumulated γ-TOH (2-fold increase over wild-type littermates) in all tissues and appeared normal. We conclude that CYP4F14 is the major but not the only vitamin E-ω-hydroxylase in mice. Its disruption significantly impairs whole-body vitamin E metabolism and alters the widely conserved phenotype of preferential tissue deposition of α-TOH. This model animal and its derivatives will be valuable in determining the biological actions of specific tocopherols and tocotrienols in vivo.     

A mechanism by which dietary trans fats cause atherosclerosis

Dietary trans fats (TFs) have been causally linked to atherosclerosis, but the mechanism by which they cause the disease remains elusive. Suppressed transforming growth factor (TGF)-β responsiveness in aortic endothelium has been shown to play an important role in the pathogenesis of atherosclerosis in animals with hypercholesterolemia. We investigated the effects of a high TF diet on TGF-β responsiveness in aortic endothelium and integration of cholesterol in tissues. Here, we show that normal mice fed a high TF diet for 24 weeks exhibit atherosclerotic lesions and suppressed TGF-β responsiveness in aortic endothelium. The suppressed TGF-β responsiveness is evidenced by markedly reduced expression of TGF-β type I and II receptors and profoundly decreased levels of phosphorylated Smad2, an important TGF-β response indicator, in aortic endothelium. These mice exhibit greatly increased integration of cholesterol into tissue plasma membranes. These results suggest that dietary TFs cause atherosclerosis, at least in part, by suppressing TGF-β responsiveness. This effect is presumably mediated by the increased deposition of cholesterol into cellular plasma membranes in vascular tissue, as in hypercholesterolemia.     

IFN-γ、IL-1α、NGF-β和TNF-α在皖西白鹅小脑皮质发育中的表达

用免疫组织化学strept actividin-biotin complex(SABC)法,以干扰素-γ(IFN-γ)、白介素-1α(IL-1α)、神经生长因子-β(NGF-β)和肿瘤坏死因子-α(TNF-α)对胚龄13d、19d、24d、28d(E13、E19、E24、E28)和日龄7d、15d(P7、15)的皖西白鹅(WesternAnhuiwhitegoose)小脑皮质中的阳性细胞进行定位和半定量检测,探讨IFN-γ、IL-1α、NGF-β和TNF-α在小脑皮质发育中的作用。研究表明,外颗粒层细胞在E13、E19、E24、E28、P7有IFN-γ和TNF-α阳性表达;在E13、E19、E24、E28有IL-1α阳性表达;在E13、E19、E24有NGF-β阳性表达;且在所检测的6个时期中,4种细胞因子均在E19表达最强。Purkinje细胞层在E13、E19、E24、E28、P7、P15均有IFN-γ、IL-1α、TNF-α阳性表达;在E13、E19、E24、E28、P7有NGF-β阳性表达;内颗粒层细胞在E13、E19、E24、E28、P7、P15有IFN-γ阳性表达;在E13、E19、E24、E28、P7有IL-1α、TNF-α阳性表达;在E13、E19、E24、E28有NGF-β阳性表达。结果表明,E19可能为小脑皮质发育的"关键期";IFN-γ、IL-1α和TNF-α可能由小脑皮质自身合成;NGF-β可能由投射到Purkinje细胞的区域转运而来,且可能在Purkinje细胞生长发育过程中起营养作用;IFN-γ可能在颗粒细胞迁移过程中起干扰作用。