Reduced circulating oxidized LDL is associated with hypocholesterolemia and enhanced thiol status in Gilbert syndrome

A protective association between bilirubin and atherosclerosis/ischemic heart disease clearly exists in vivo. However, the relationship between bilirubin and in vivo oxidative stress parameters in a clinical population remains poorly described. The aim of this study was to assess whether persons expressing Gilbert syndrome (GS; i.e., unconjugated hyperbilirubinemia) are protected from thiol oxidation and to determine if this, in addition to their improved lipoprotein profile, could explain reduced oxidized low-density lipoprotein (oxLDL) status in them. Forty-four matched GS and control subjects were recruited and blood was prepared for the analysis of lipid profile and multiple plasma antioxidants and measures of oxidative stress. GS subjects possessed elevated plasma reduced thiol (8.03±1.09 versus 6.75±1.39 nmol/mg protein; P<0.01) and glutathione concentrations (12.7±2.39 versus 9.44±2.45 μM; P<0.001). Oxidative stress status (reduced:oxidized glutathione; GSH:GSSG) was significantly improved in GS (0.49±0.16 versus 0.32±0.12; P<0.001). Protein carbonyl concentrations were negatively associated with bilirubin concentrations and were significantly lower in persons with >40 μM bilirubin versus controls (<17.1 μmol/L; P<0.05). Furthermore, absolute oxLDL concentrations were significantly lower in GS subjects (P<0.05). Forward stepwise regression analysis revealed that bilirubin was associated with increased GSH:GSSG ratio and reduced thiol concentrations, which, in addition to reduced circulating LDL, probably decreased oxLDL concentrations within the cohort. In addition, a marked reduction in total cholesterol concentrations in hyperbilirubinemic Gunn rats is presented (Gunn 0.57±0.09 versus control 1.69±0.40 mmol/L; P<0.001), arguing for a novel role for bilirubin in modulating lipid status in vivo. These findings implicate the physiological importance of bilirubin in protecting from atherosclerosis by reducing thiol and subsequent lipoprotein oxidation, in addition to reducing circulating LDL concentrations.

Peroxynitrite modifies the structure and function of the extracellular matrix proteoglycan perlecan by reaction with both the protein core and the heparan sulfate chains

The heparan sulfate (HS) proteoglycan perlecan is a major component of basement membranes, plays a key role in extracellular matrix (ECM) structure, interacts with growth factors and adhesion molecules, and regulates the adhesion, differentiation and proliferation of vascular cells. Atherosclerosis is characterized by chronic inflammation and the presence of oxidized materials within lesions, with the majority of protein damage present on ECM, rather than cell, proteins. Weakening of ECM structure plays a key role in lesion rupture, the major cause of heart attacks and strokes. In this study peroxynitrite, a putative lesion oxidant, is shown to damage perlecan structurally and functionally. Exposure of human perlecan to peroxynitrite decreases recognition by antibodies raised against both the core protein and heparan sulfate chains; dose-dependent formation of 3-nitrotyrosine was also detected. These effects were modulated by bicarbonate and reaction pH. Oxidant exposure resulted in aggregate formation, consistent with oxidative protein crosslinking. Peroxynitrite treatment modified functional properties of perlecan that are dependent on both the protein core (decreased binding of human coronary artery endothelial cells), and the HS chains (diminished fibroblast growth factor-2 (FGF-2) receptor-mediated proliferation of Baf-32 cells). The latter is consistent with a decrease in FGF-2 binding to the HS chains of modified perlecan. Immunofluorescence of advanced human atherosclerotic lesions provided evidence for the presence of perlecan and extensive formation of 3-nitrotyrosine epitopes within the intimal region; these materials showing marked co-localization. These data indicate that peroxynitrite induces major structural and functional changes to perlecan and that damage to this material occurs within human atherosclerotic lesions.

Weaning-induced expression of a milk-fat globule protein, MFG-E8, in mouse mammary glands, as demonstrated by the analyses of its mRNA, protein and phosphatidylserine-binding activity

A milk membrane glycoprotein, MFG-E8 [milk fat globule-EGF (epidermal growth factor) factor 8], is expressed abundantly in lactating mammary glands in stage- and tissue-specific manners, and has been believed to be secreted in association with milk fat globules. In the present paper, we describe further up-regulation of MFG-E8 in involuting mammary glands, where the glands undergo a substantial increase in the rate of epithelial cell apoptosis, and a possible role of MFG-E8 in mediating recognition and engulfment of apoptotic cells through its specific binding to PS (phosphatidylserine). Immunoblotting and RNA blotting analyses revealed that both MFG-E8 protein and MFG-E8 mRNA were markedly increased in mammary tissue within 3 days of either natural or forced weaning (pup withdrawal) of lactating mice. Using immunohistochemical analysis of the mammary tissue cryosections, the MFG-E8 signal was detected around the epithelium of such involuting mammary glands, but was almost undetectable at early- and mid-lactation stages, although strong signals were obtained for milk fat globules stored in the alveolar lumen. Some signals double positive to a macrophage differentiation marker, CD68, and MFG-E8 were detected in the post-weaning mammary tissue, although such double-positive signals were much smaller in number than the MFG-E8 single-positive ones. Total MFG-E8 in milk was also increased in the post-weaning mammary glands and, furthermore, the free MFG-E8 content in the post-weaning milk, as measured by in vitro PS-binding and apoptotic HC11 cell-binding activities, was much higher than that of lactation. In addition, the post-weaning milk enhanced the binding of apoptotic HC11 cells to J774 macrophages. Sucrose density-gradient ultracentrifugation analyses revealed that such enhanced PS-binding activity of MFG-E8 was present in membrane vesicle fractions (density 1.05-1.13 g/ml), rather than milk fat globule fractions. The weaning-induced MFG-E8 might play an important role in the recognition and engulfment of apoptotic epithelial cells by the neighbouring phagocytic epithelial cells in involuting mammary glands.

Involvement of the Gi/o/cGMP/PKG pathway in the AT2-mediated inhibition of outer cortex proximal tubule Na+-ATPase by Ang-(1-7)

The molecular mechanisms involved in the Ang-(1-7) [angiotensin-(1-7)] effect on sodium renal excretion remain to be determined. In a previous study, we showed that Ang-(1-7) has a biphasic effect on the proximal tubule Na+-ATPase activity, with the stimulatory effect mediated by the AT1 receptor. In the present study, we investigated the molecular mechanisms involved in the inhibition of the Na+-ATPase by Ang-(1-7). All experiments were carried out in the presence of 0.1 nM losartan to block the AT1 receptor-mediated stimulation. In this condition, Ang-(1-7) at 0.1 nM inhibited the Na+-ATPase activity of the proximal tubule by 54%. This effect was reversed by 10 nM PD123319, a specific antagonist of the AT2 receptor, and by 1 muM GDP[beta-S] (guanosine 5'-[beta-thio]diphosphate), an inhibitor of G protein. Ang-(1-7) at 0.1 M induced [35S]GTP[S] (guanosine 5'-[gamma-[35S]thio]triphosphate) binding and 1 mug/ml pertussis toxin, an inhibitor of G(i/o) protein, reversed the Ang-(1-7) effect. Furthermore, it was observed that the inhibitory effect of Ang-(1-7) on the Na+-ATPase activity was completely reversed by 0.1 microM LY83583, an inhibitor of guanylate cyclase, and by 2 muM KT5823, a PKG (protein kinase G) inhibitor, and was mimicked by 10 nM d-cGMP (dibutyryl cGMP). Ang-(1-7) increased the PKG activity by 152% and this effect was abolished by 10 nM PD123319 and 0.1 microM LY83583. Taken together, these data indicate that Ang-(1-7) inhibits the proximal tubule Na+-ATPase by interaction with the AT2 receptor that subsequently activates the G(i/o) protein/cGMP/PKG pathway.

Comparison of the in vitro estrogenic activities of compounds from hops (Humulus lupulus) and red clover (Trifolium pratense)

Because the prevailing form of hormone replacement therapy is associated with the development of cancer in breast and endometrial tissues, alternatives are needed for the management of menopausal symptoms. Formulations of Trifolium pratense L. (red clover) are being used to alleviate menopause-associated hot flashes but have shown mixed results in clinical trials. The strobiles of Humulus lupulusL. (hops) have been reported to contain the prenylflavanone, 8-prenylnaringenin (8-PN), as the most estrogenic constituent, and this was confirmed using an estrogen receptor ligand screening assay utilizing ultrafiltration mass spectrometry. Extracts of hops and red clover and their individual constituents including 8-PN, 6-prenylnaringenin (6-PN), isoxanthohumol (IX), and xanthohumol (XN) from hops and daidzein, formononetin, biochanin A, and genistein from red clover were compared using a variety of in vitro estrogenic assays. The IC50 values for the estrogen receptor alpha and beta binding assays were 15 and 27 microg/mL, respectively, for hops and 18.0 and 2.0 microg/mL, respectively, for the red clover extract. Both of the extracts, genistein, and 8-PN activated the estrogen response element (ERE) in Ishikawa cells while the extracts, biochanin A, genistein, and 8-PN, significantly induced ERE-luciferase expression in MCF-7 cells. Hop and red clover extracts as well as 8-PN up-regulated progesterone receptor (PR) mRNA in the Ishikawa cell line. In the MCF-7 cell line, PR mRNA was significantly up-regulated by the extracts, biochanin A, genistein, 8-PN, and IX. The two extracts had EC50 values of 1.1 and 1.9 microg/mL, respectively, in the alkaline phosphatase induction assay. On the basis of these data, hops and red clover could be attractive for the development as herbal dietary supplements to alleviate menopause-associated symptoms.

Thromboxane A2-induced contraction of rat caudal arterial smooth muscle involves activation of Ca2+ entry and Ca2+ sensitization: Rho-associated kinase-mediated phosphorylation of MYPT1 at Thr-855, but not Thr-697

The signal transduction pathway whereby the TxA2 (thromboxane A2) mimetic U-46619 activates vascular smooth muscle contraction was investigated in de-endothelialized rat caudal artery. U-46619-evoked contraction was inhibited by the TP receptor (TxA2 receptor) antagonist SQ-29548, the ROK (Rho-associated kinase) inhibitors Y-27632 and H-1152, the MLCK (myosin light-chain kinase) inhibitors ML-7, ML-9 and wortmannin, the voltagegated Ca2+-channel blocker nicardipine, and removal of extracellular Ca2+; the protein kinase C inhibitor GF109203x had no effect. U-46619 elicited Ca2+ sensitization in a-toxin-permeabilized tissue. U-46619 induced activation of the small GTPase RhoA, consistent with the involvement of ROK. Two downstream targets of ROK were investigated: CPI-17 [protein kinase C-potentiated inhibitory protein for PP1 (protein phosphatase type 1) of 17 kDa], a myosin light-chain phosphatase inhibitor, was not phosphorylated at the functional site (Thr-38); phosphorylation of MYPT1 (myosin-targeting subunit of myosin light-chain phosphatase) was significantly increased at Thr-855, but not Thr-697. U-46619-evoked contraction correlated with phosphorylation of the 20 kDa light chains of myosin. We conclude that: (i) U-46619 induces contraction via activation of the Ca2+/calmodulin/MLCK pathway and of the RhoA/ROK pathway; (ii) Thr-855 of MYPT1 is phosphorylated by ROK at rest and in response to U-46619 stimulation; (iii) Thr-697 of MYPT1 is phosphorylated by a kinase other than ROK under resting conditions, and is not increased in response to U-46619 treatment; and (iv) neither ROK nor protein kinase C phosphorylates CPI-17 in this vascular smooth muscle in response to U-46619.

Cephalopod vision involves dicarboxylic amino acids: D-aspartate, L-aspartate and L-glutamate

In the present study, we report the finding of high concentrations of D-Asp (D-aspartate) in the retina of the cephalopods Sepia officinalis, Loligo vulgaris and Octopus vulgaris. D-Asp increases in concentration in the retina and optic lobes as the animal develops. In neonatal S. officinalis, the concentration of D-Asp in the retina is 1.8+/-0.2 micromol/g of tissue, and in the optic lobes it is 5.5+/-0.4 micromol/g of tissue. In adult animals, D-Asp is found at a concentration of 3.5+/-0.4 micromol/g in retina and 16.2+/-1.5 micromol/g in optic lobes (1.9-fold increased in the retina, and 2.9-fold increased in the optic lobes). In the retina and optic lobes of S. officinalis, the concentration of D-Asp, L-Asp (L-aspartate) and L-Glu (L-glutamate) is significantly influenced by the light/dark environment. In adult animals left in the dark, these three amino acids fall significantly in concentration in both retina (approx. 25% less) and optic lobes (approx. 20% less) compared with the control animals (animals left in a diurnal/nocturnal physiological cycle). The reduction in concentration is in all cases statistically significant (P=0.01-0.05). Experiments conducted in S. officinalis by using D-[2,3-3H]Asp have shown that D-Asp is synthesized in the optic lobes and is then transported actively into the retina. D-aspartate racemase, an enzyme which converts L-Asp into D-Asp, is also present in these tissues, and it is significantly decreased in concentration in animals left for 5 days in the dark compared with control animals. Our hypothesis is that the dicarboxylic amino acids, D-Asp, L-Asp and L-Glu, play important roles in vision.

Identification of the actin-binding domain of Ins(1,4,5)P3 3-kinase isoform B (IP3K-B)

Dewaste et al. [Dewaste, Moreau, De Smedt, Bex, De Smedt, Wuytaack, Missiaen and Erneux (2003) Biochem. J. 374, 41-49] showed that over-expressed EGFP (enhanced green fluorescent protein) fused to Ins(1,4,5)P3 3-kinase B (IP3K-B) co-localizes with the cytoskeleton, as well as with the endoplasmic reticulum and the plasma membrane. The domains responsible for these subcellular localizations are not yet identified. For the endogenous enzyme, we confirmed both actin and endoplasmic reticulum localization by employing a high affinity antibody against IP3K-B. F-actin targeting is exclusively dependent on the non-catalytic N-terminal region of IP3K-B. By expressing fragments of this N-terminal domain as EGFP-fusion proteins and inspecting transfected cells by confocal microscopy, we characterized a distinct 63-amino-acid domain comprising amino acids 108-170 of the enzyme which is responsible for F-actin targeting. A truncation of this fragment from both sides revealed that the full size of this segment is essential for this function. Deletion of this segment in a full-length over-expressed IP3K-B-EGFP-fusion protein completely abolished F-actin interaction. Direct interaction of this actin-binding segment with only F-actin, but not with G-actin, was observed in vitro using a bacterially expressed, affinity-purified GST (glutathione S-transferase)-Rattus norvegicus IP3K (aa 108-170) fusion protein. Helix-breaking mutations within this isolated segment abolished the F-actin binding properties both in vitro and when over-expressed in cells, indicating that an intact secondary structure is essential for actin targeting. The segment shows sequence similarities to the actin-binding region in IP3K-A, but no similarity to other actin-binding domains.

Quaternary structure of vaccinia virus thymidine kinase

Thymidine kinase enzymes isolated from a variety of sources are generally considered to have a native molecular weight of 80-90 kDa composed of two 40-45 kDa subunits. Although these parameters may accurately describe the atypical deoxypyrimidine kinases expressed by members of the Herpesviridae, the nucleotide sequences of thymidine kinase genes isolated from human, mouse, chicken and variety of poxviruses (vaccinia virus, monkeypox virus, variola virus, fowlpox virus and capripoxvirus) predict molecular weights on the order of 20-25 kDa for the derived primary translation products. To resolve this apparent dilemma, velocity sedimentation centrifugation, gel filtration chromatography and protein cross-linking procedures were employed to provide experimental evidence that enzymatically-active vaccinia virus thymidine kinase is a homotetrameric complex of 20 kDa monomers with a native Mr of 80 kDa.