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Biomedical subjects

Hans Lee

Publications and source records attributed to Hans Lee.

11 recordsLinked to original sources
PubMed2006

FXR, a multipurpose nuclear receptor.

The farnesoid X receptor (FXR) is a ligand-activated transcription factor and a member of the nuclear receptor superfamily. In the past six years, remarkable inroads have been made into determining the functional importance of FXR. This receptor has been shown to have crucial roles in controlling bile acid homeostasis, lipoprotein and glucose metabolism, hepatic regeneration, intestinal bacterial growth and the response to hepatotoxins. Thus, the development of FXR agonists might prove useful for the treatment of diabetes, cholesterol gallstones, and hepatic and intestinal toxicity.

Animals↗
PubMed2006

FXR deficiency causes reduced atherosclerosis in Ldlr-/- mice.

OBJECTIVE: Based on the observation that Fxr-/- mice exhibit a proatherogenic lipoprotein profile, we investigated the role of FXR in the development of atherosclerosis. METHODS AND RESULTS: Administration of a western diet to Fxr-/- mice or wild-type mice does not result in the development of significant atherosclerotic lesions. Consequently we generated Fxr-/- Ldlr-/- (DKO) mice and compared lesion development with Ldlr-/- mice. After 16 weeks on a Western diet, en face analysis of the aorta indicated that the male DKO mice had reduced atherosclerotic lesions as compared with Ldlr-/- mice. Plasma low-density lipoprotein cholesterol and high-density lipoprotein cholesterol levels were reduced by 40% to 50%, whereas triglyceride levels increased 4-fold in the male DKO mice. Finally, peritoneal macrophages freshly isolated from male DKO mice had reduced expression of CD36 mRNA and decreased neutral lipid accumulation, as compared with Ldlr-/- mice. CONCLUSIONS: FXR deficiency in male, but not female, Ldlr-/- mice results in a reduction in the size of atherosclerotic lesions in the aorta. The reduction in atherosclerosis may result from a decrease in plasma low-density lipoprotein cholesterol, coupled with reduced expression of CD36 in macrophages of DKO mice.

Animals↗
PubMed2006

Specific monocyte adhesion to endothelial cells induced by oxidized phospholipids involves activation of cPLA2 and lipoxygenase.

Oxidized phospholipids stimulate endothelial cells to bind monocytes, but not neutrophils, an initiating event in atherogenesis. Here, we investigate intracellular signaling events induced by oxidized phospholipids in human umbilical vein endothelial cells (HUVECs) that lead to specific monocyte adhesion. In a static adhesion assay, oxidized 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphorylcholine and one of its components, 1-palmitoyl-2-oxovaleroyl-sn-glycero-3-phosphorylcholine, stimulated HUVECs to bind U937 cells and human peripheral blood monocytes but not HL-60 cells or blood neutrophils. Monocyte adhesion was dependent on protein kinases A and C, extracellular signal-regulated kinase 1/2, p38 mitogen activated protein kinases (MAPKs), and cytosolic phospholipase A(2) (cPLA(2)). Inhibition of 12-lipoxygenase (12-LOX), but not cyclooxygenases, blocked monocyte adhesion, and addition of 12-hydroxyeicosatetraenoic acid (12-HETE) mimicked the effects of oxidized phospholipids. Peroxisome proliferator-activated receptor alpha (PPARalpha) was excluded as a possible target for 12-HETE, because monocyte adhesion was still induced in endothelial cells from PPARalpha null mice. Together, our results suggest that oxidized phospholipids stimulate HUVECs to specifically bind monocytes involving MAPK pathways, which lead to the activation of cPLA(2) and 12-LOX. Further analysis of signaling pathways induced by oxidized phospholipids that lead to specific monocyte adhesion should ultimately lead to the development of novel therapeutic approaches against chronic inflammatory diseases.

Animals↗
PubMed2006

Activation of the nuclear receptor FXR improves hyperglycemia and hyperlipidemia in diabetic mice.

Farnesoid X receptor (FXR) plays an important role in maintaining bile acid and cholesterol homeostasis. Here we demonstrate that FXR also regulates glucose metabolism. Activation of FXR by the synthetic agonist GW4064 or hepatic overexpression of constitutively active FXR by adenovirus-mediated gene transfer significantly lowered blood glucose levels in both diabetic db/db and wild-type mice. Consistent with these data, FXR null mice exhibited glucose intolerance and insulin insensitivity. We further demonstrate that activation of FXR in db/db mice repressed hepatic gluconeogenic genes and increased hepatic glycogen synthesis and glycogen content by a mechanism that involves enhanced insulin sensitivity. In view of its central roles in coordinating regulation of both glucose and lipid metabolism, we propose that FXR agonists are promising therapeutic agents for treatment of diabetes mellitus.

3-Hydroxybutyric Acid↗
PubMed2005

FXR regulates organic solute transporters alpha and beta in the adrenal gland, kidney, and intestine.

Expression of the farnesoid X receptor (FXR; NR1H4) is limited to the liver, intestine, kidney, and adrenal gland. However, the role of FXR in the latter two organs is unknown. In the current study, we performed microarray analysis using RNA from H295R cells infected with constitutively active FXR. Several putative FXR target genes were identified, including the organic solute transporters alpha and beta (OSTalpha and OSTbeta). Electromobility shift assays and promoter-reporter studies identified functional farnesoid X receptor response elements (FXREs) in the promoters of both human genes. These FXREs are conserved in both mouse genes. Treatment of wild-type mice with 3-(2,6-dichlorophenyl)-4-(3'-carboxy-2-chloro-stilben-4-yl)-oxymethyl-5-isopropyl-isoxazole (GW4064), a synthetic FXR agonist, induced OSTalpha and OSTbeta mRNAs in the intestine and kidney. Both mRNAs were also induced when wild-type, but not FXR-deficient (FXR-/-), adrenals were cultured in the presence of GW4064. OSTalpha and OSTbeta mRNA levels were also induced in the adrenals and kidneys of wild-type, but not FXR-/-, mice after the increase of plasma bile acids in response to the hepatotoxin alpha-naphthylisothiocyanate. Finally, overexpression of human OSTalpha and OSTbeta facilitated the uptake of conjugated chenodeoxycholate and the activation of FXR target genes. These results demonstrate that OSTalpha and OSTbeta are novel FXR target genes that are expressed in the adrenal gland, kidney, and intestine.

Adrenal Glands↗
PubMed2005

Analysis of guanidine in high salt and protein matrices by cation-exchange chromatography and UV detection.

A simple and sensitive HPLC method for quantitative determination of guanidine in high salt and protein matrices was developed. The HPLC system consisted of an Agilent 1100 pump with an online degasser, a UV detector, an autosampler, and Dionex CS 14 cation-exchange guard (4 mm x 50 mm) and analytical (4 mm x 250 mm) columns. The mobile phase was 3.75 mM methanesulfonic acid (MSA) with a flow rate of 1 mL/min. The other analysis parameters were: 50 microL injection volume, 195 nm UV detection, and 21 min runtime. The limit of quantitation (LOQ) for guanidine HCl was determined to be 0.25 mg/L and the standard curve ranged from 0.25 mg/L to 10 mg/L. Sample preparation was required for the samples containing high protein concentrations. Proteins were removed by centrifuging a sample in a 30 K NanoSep centrifugal filter at 15,300 x g for 20 min. The method could determine guanidine accurately in sample matrices containing up to 200 mM sodium ion or up to 50 mM potassium ion. The method can be used for clearance testing of guanidine in biopharmaceutical products.

Cation Exchange Resins↗
PubMed2004

Activation of the nuclear receptor FXR induces fibrinogen expression: a new role for bile acid signaling.

Three genes, fibrinogen-alpha (FBGalpha), -beta, and -gamma, encode proteins that make up the mature FBG protein complex. This complex is secreted from the liver and plays a key role in coagulation in response to vascular disruption. We identified all three FBG genes in a screen designed to isolate genes that are regulated by the farnesoid X receptor (FXR; NR1H4). Treatment of human hepatoma cells with either naturally occurring or synthetic [3-(2,6-dichlorophenyl)-4-(3'-carboxy-2-chloro-stilben-4-yl)-oxymethyl-5-isopropyl-isoxazole] FXR ligands resulted in the induction of transcripts for all three genes. The induction of FBGbeta mRNA in response to activated FXR appears to be a primary transcriptional response, as it is blocked by actinomycin D but not by cycloheximide. Four FXR isoforms were recently identified that differ either at their N termini and/or by the presence of four amino acids in the hinge region. Interestingly, the activities of the human FBGbeta promoter-reporter constructs were highly induced by FXR isoforms that lack the four amino acid insert. The observation that all three FBG subunits are induced by specific FXR isoforms, in response to FXR ligands, suggests that bile acids and FXR modulate fibrinolytic activity.

Bile Acids and Salts↗
PubMed2003

The synthesis of carboacycles derived from B,B'-bis(aryl) derivatives of icosahedral ortho-carborane.

Reactions of both closo-9,12-I2-1,2-C2B10H10 and closo-9,10-I2-1,7-C2B10H10 with an excess of aryl magnesium bromide in the presence of [PdCl2(PPh3)2] afford the corresponding closo-9,12-(4-R-C6H4)2-1,2-C2B10H10 [R=H (1), Me (2), OMe (3), SMe (4), N(CH3)2 (5), Cl (6)] and closo-9,10-(4-R-C6H4)2-1,7-C2B10H10 [R'=Me (7), OMe (8), N(CH3)2 (9), Cl (10), and -C[(OCH2)2]CH3 (11)] compounds in high yields. The anisole derivatives 3 and 8 were deprotected to yield the corresponding bis-phenols 12 and 13, respectively. Structural analyses of compounds 1, 3, 6, and 12 are reported. Re-etherification of compound 12 by using gamma-bromotriethyleneglycol methyl ether provided 14 (R=(CH2CH2O)3CH3). Oxidation of 4 with ceric(IV) ammonium nitrate (CAN) generated the bis-sulfoxide 15 (R=S(O)Me). Deprotection of compound 11 led to the corresponding acetyl derivative 18 (R'=C(O)Me). Bis-anisole 3 was tethered with 1,3-dibromopropane, 1,6-dibromohexane, 1,8-dibromooctane, 4,4'-bis(iodomethyl)-1,1'-biphenyl, and alpha,alpha'-dibromo-2,6-lutidine to afford the dimers 20b, 21b, 22b, 23b, and 24b, respectively. The tetrameric carboracycles 27a and 30a, as well as the dimeric 29c were obtained through repetitive coupling of the dimeric compounds 20b, 24b, and 22b with 1,3-dibromopropane, alpha,alpha'-dibromo-2,6-lutidine, and 1,8-dibromooctane, respectively. The tetrameric carboracycle 28a was obtained upon consecutive reactions of 1 with 1,4-dibromobutane. Hexameric carboracycle 28b was identified as a byproduct. Exhaustive ether cleavage of 27a generated octaphenol 31a. Re-etherification of 31a with trimethylenesultone provided the octasulfonate 32a, the first example of a water-soluble carboracycle. Linkage of dimer 23b with alpha,alpha'-dibromolutidine yielded the cyclic tetrameric tetrapyridyl derivative 30a in low yield. The structures of the carboracycles 27a, 28a, 28b, and 30a have been confirmed by Xray crystallography. In addition, the compounds 28a,b are the first reported carboracycles that interact with solvent molecules in a host-guest fashion.

Journal Article↗
PubMed2001

Epoxyisoprostane and epoxycyclopentenone phospholipids regulate monocyte chemotactic protein-1 and interleukin-8 synthesis. Formation of these oxidized phospholipids in response to interleukin-1beta.

Monocyte recruitment to the vessel wall, mediated by monocyte chemotactic protein-1 (MCP-1) and interleukin-8 (IL-8), plays an important role in atherogenesis. We have shown previously that minimally oxidized low density lipoprotein, oxidized 1-palmitoyl-2-arachidonyl-sn-glycero-3-phosphorylcholine (Ox-PAPC), activates endothelial cells to produce MCP-1 and IL-8. By using liquid chromatography/mass spectrometry methods coupled with bioassay, we report a family of epoxyisoprostane (PEIPC) and epoxycyclopentenone (PECPC) phospholipids that are the components of Ox-PAPC responsible for the majority of this activity. Ox-PAPC contains five chromatographically distinguishable active PEIPC components (m/z 825.5) and four PECPC components (m/z 810.5). All nine components induced endothelial cell synthesis of IL-8 and MCP-1 in a dose-dependent fashion between 0.1 and 5 microm concentrations. The five PEIPC components had identical functional groups and all underwent dehydration to produce m/z 810.5. We present evidence that these phospholipids are regioisomers with epoxide groups at the 5,6-, 8,9-, 11,12-, or 14,15-positions of the sn-2 fatty acid and their epoxide groups is important for biological activity. We have shown previously that peroxisome proliferator-activated receptor alpha is involved in MCP-1 synthesis in response to Ox-PAPC. We now show that PEIPC and PECPC isomers are potent activators of peroxisome proliferator-activated receptor alpha. PEIPC and PECPC isomers are strongly recognized by specific circulating murine natural autoantibodies (EO6) and accumulate in cells treated with IL-1beta. These studies demonstrate that PEIPC and PECPC isomers are potent activators of endothelial cells increasing synthesis of IL-8 and MCP-1. Their accumulation in cells exposed to cytokines and in atherosclerotic lesions suggests that these lipids may play a role in a number of chronic disease processes.

Binding, Competitive↗