Elimination of macrophages drives LXR-induced regression both in initial and advanced stages of atherosclerotic lesion development.

While numerous studies have aimed to develop strategies to inhibit the development and progression of atherosclerosis, recent attention has focussed on the regression of pre-existing atherosclerotic plaques. As important regulator of total body cholesterol homeostasis, the liver X receptor (LXR) could possibly be an important target to induce regression. Here, we describe the effect of LXR activation by the synthetic agonist T0901317 on lesion regression in different mouse models with early fatty streak lesions or advanced collagen-rich lesions. Although T0901317 caused a dramatic increase in plasma (V)LDL levels in low-density lipoprotein (LDL) receptor knockout mice, no further increase in lesion size was observed, which points to beneficial LXR activity in the vascular wall. In normolipidemic C57BL/6 mice with cholate diet-induced atherosclerotic lesions, T0901317 treatment improved plasma lipoprotein levels and induced lesion regression (-43%, p<0.05). Apolipoprotein E (APOE) reconstitution in APOE knockout mice by means of bone marrow transplantation dramatically improved plasma lipoprotein profiles and resulted in a marked regression of initial (-45%, p<0.001) and advanced lesions (-23%, p<0.01). Atherosclerosis regression was associated with a decrease in the absolute macrophage content (-84%, p<0.001). T0901317 supplementation further decreased the size of early (-71%, p<0.001 vs baseline; -48%, p<0.01 vs chow diet alone) and more advanced atherosclerotic lesions (-36%, p<0.001 and -17%, p=0.06 respectively). In conclusion, our study highlights the potential of LXR agonist T0901317 to stimulate removal of macrophages from atherosclerotic lesions ultimately leading to a highly significant plaque regression of both early and advanced atherosclerotic lesions.

Org 214007-0: a novel non-steroidal selective glucocorticoid receptor modulator with full anti-inflammatory properties and improved therapeutic index.

Glucocorticoids (GCs) such as prednisolone are potent immunosuppressive drugs but suffer from severe adverse effects, including the induction of insulin resistance. Therefore, development of so-called Selective Glucocorticoid Receptor Modulators (SGRM) is highly desirable. Here we describe a non-steroidal Glucocorticoid Receptor (GR)-selective compound (Org 214007-0) with a binding affinity to GR similar to that of prednisolone. Structural modelling of the GR-Org 214007-0 binding site shows disturbance of the loop between helix 11 and helix 12 of GR, confirmed by partial recruitment of the TIF2-3 peptide. Using various cell lines and primary human cells, we show here that Org 214007-0 acts as a partial GC agonist, since it repressed inflammatory genes and was less effective in induction of metabolic genes. More importantly, in vivo studies in mice indicated that Org 214007-0 retained full efficacy in acute inflammation models as well as in a chronic collagen-induced arthritis (CIA) model. Gene expression profiling of muscle tissue derived from arthritic mice showed a partial activity of Org 214007-0 at an equi-efficacious dosage of prednisolone, with an increased ratio in repression versus induction of genes. Finally, in mice Org 214007-0 did not induce elevated fasting glucose nor the shift in glucose/glycogen balance in the liver seen with an equi-efficacious dose of prednisolone. All together, our data demonstrate that Org 214007-0 is a novel SGRMs with an improved therapeutic index compared to prednisolone. This class of SGRMs can contribute to effective anti-inflammatory therapy with a lower risk for metabolic side effects.

Liver receptor homolog-1 is critical for adequate up-regulation of Cyp7a1 gene transcription and bile salt synthesis during bile salt sequestration.

UNLABELLED: Liver receptor homolog-1 (LRH-1) is a nuclear receptor that controls a variety of metabolic pathways. In cultured cells, LRH-1 induces the expression of CYP7A1 and CYP8B1, key enzymes in bile salt synthesis. However, hepatic Cyp7a1 mRNA levels were not reduced upon hepatocyte-specific Lrh-1 deletion in mice. The reason for this apparent paradox has remained elusive. We describe a novel conditional whole-body Lrh-1 knockdown (LRH-1-KD) mouse model to evaluate the dependency of bile salt synthesis and composition on LRH-1. Surprisingly, Cyp7a1 expression was increased rather than decreased under chow-fed conditions in LRH-1-KD mice. This coincided with a significant reduction in expression of intestinal Fgf15, a suppressor of Cyp7a1 expression, and a 58% increase in bile salt synthesis. However, when fecal bile salt loss was stimulated by feeding the bile salt sequestrant colesevelam, Cyp7a1 expression was up-regulated in wildtype mice but not in LRH-1-KD mice (+593% in wildtype versus +9% in LRH-1-KD). This translated into an increase in bile salt synthesis of +272% in wildtype versus +21% in LRH-1-KD mice. CONCLUSION: Our data provide mechanistic insight into a missing link in the maintenance of bile salt homeostasis during enhanced fecal loss and support the view that LRH-1 controls Cyp7a1 expression from two distinct sites, i.e., liver and ileum, in the enterohepatic circulation.

Nonpeptidergic allosteric antagonists differentially bind to the CXCR2 chemokine receptor.

The chemokine receptor CXCR2 is involved in different inflammatory diseases, like chronic obstructive pulmonary disease, psoriasis, rheumatoid arthritis, and ulcerative colitis; therefore, it is considered an attractive drug target. Different classes of small CXCR2 antagonists have been developed. In this study, we selected seven CXCR2 antagonists from the diarylurea, imidazolylpyrimide, and thiazolopyrimidine class and studied their mechanisms of action at human CXCR2. All compounds are able to displace (125)I-CXCL8 and inhibit CXCL8-induced beta-arrestin2 recruitment. Detailed studies with representatives of each class showed that these compounds displace and antagonize CXCL8, most probably via a noncompetitive, allosteric mechanism. In addition, we radiolabeled the high-affinity CXCR2 antagonist SB265610 [1-(2-bromophenyl)-3-(4-cyano-1H-benzo[d] [1,2,3]-triazol-7-yl)urea] and subjected [(3)H]SB265610 to a detailed analysis. The binding of this radioligand was saturable and reversible. Using [(3)H]SB265610, we found that compounds of the different chemical classes bind to distinct binding sites. Hence, the use of a radiolabeled low-molecular weight CXCR2 antagonist serves as a tool to investigate the different binding sites of CXCR2 antagonists in more detail.

A signaling-selective, nanomolar potent allosteric low molecular weight agonist for the human luteinizing hormone receptor.

Luteinizing hormone (LH) and human chorionic gonadotropin (hCG) activate the LH receptor/cyclic AMP (cAMP) signaling pathway to induce ovulation. As an alternative to parenterally administered hCG to treat anovulatory infertility, orally active low molecular weight (LMW) LHR agonists have been developed at Organon. In this paper, we present the mechanism of action of a prototypic, nanomolar potent and almost full LHR agonist, Org 43553. Org 43553 interacts with the endodomain of the LHR, whereas LH acts via the N-terminal exodomain. LH stimulates the cAMP pathway with an EC50 of 35 pM, but this stimulation is not antagonized by simultaneous incubation with Org 43553. At nanomolar concentrations, LH also stimulates phospholipase C (PLC), but Org 43553 is hardly able to do so. In contrast, Org 43553 inhibits LH-induced PLC (IC50 approximately 10 nM). While Org 43553 stimulates dissociation of [125I]hCG from the LHR and reduces [125I]hCG binding, LH reduces specific [3H]Org 43553 binding. We conclude that Org 43553 is a signaling-selective, allosteric LHR agonist. We hypothesize that Org 43553 and LH induce a similar LHR conformation necessary for activating adenylyl cyclase, which initiates most, if not all, physiological responses of LH.

Uniform procedure of (1)H NMR analysis of rat urine and toxicometabonomics Part II: comparison of NMR profiles for classification of hepatotoxicity.

A procedure of nuclear magnetic resonance (NMR) urinalysis using pattern recognition is proposed for early detection of toxicity of investigational compounds in rats. The method is applied to detect toxicity upon administration of 13 toxic reference compounds and one nontoxic control compound (mianserine) in rats. The toxic compounds are expected to induce necrosis (bromobenzene, paracetamol, carbon tetrachloride, iproniazid, isoniazid, thioacetamide), cholestasis (alpha-naphthylisothiocyanate (ANIT), chlorpromazine, ethinylestradiol, methyltestosterone, ibuprofen), or steatosis (phenobarbital, tetracycline). Animals were treated daily for 2 or 4 days except for paracetamol and bromobenzene (1 and 2 days) and carbon tetrachloride (1 day only). Urine was collected 24 h after the first and second treatment. The animals were sacrificed 24 h after the last treatment, and NMR data were compared with liver histopathology as well as blood and urine biochemistry. Pathology and biochemistry showed marked toxicity in the liver at high doses of bromobenzene, paracetamol, carbon tetrachloride, ANIT, and ibuprofen. Thioacetamide and chlorpromazine showed less extensive changes, while the influences of iproniazid, isoniazid, phenobarbital, ethinylestradiol, and tetracycline on the toxic parameters were marginal or for methyltestosterone and mianserine negligible. NMR spectroscopy revealed significant changes upon dosing in 88 NMR biomarker signals preselected with the Procrustus Rotation method on principal component discriminant analysis (PCDA) plots. Further evaluation of the specific changes led to the identification of biomarker patterns for the specific types of liver toxicity. Comparison of our rat NMR PCDA data with histopathological changes reported in humans and/or rats suggests that rat NMR urinalysis can be used to predict hepatotoxicity.

Sensitivity of (1)H NMR analysis of rat urine in relation to toxicometabonomics. Part I: dose-dependent toxic effects of bromobenzene and paracetamol.

(1)H nuclear magnetic resonance (NMR) spectroscopy of rat urine in combination with pattern recognition analysis was evaluated for early noninvasive detection of toxicity of investigational chemical entities. Bromobenzene (B) and paracetamol (P) were administered at five single oral dosages between 2 and 500 mg/kg and between 6 and 1800 mg/kg, respectively. The sensitivity of the proposed method to detect changes in the NMR spectra 24 and 48 h after single dosing was compared with histopathology and biochemical parameters in plasma and urine. Both B and P applied at the highest dosages induced liver necrosis and markedly increased aspartate aminotransferase (AST) and alanine aminotransferase (ALT) plasma levels. At dosages of 125 mg/kg B and 450 mg/kg P, liver necrosis and changes in AST and ALT were less pronounced, while at lower dose levels these effects could not be detected. Changes in kidney pathology or standard urine biochemistry were not observed at any of these dosages. Evaluation of the total NMR dataset showed 80 signals to be sensitive for B and P dosing. Principal component analysis on the reduced dataset revealed that NMR spectra were significantly different at dosages above 8 mg/kg (B) and 110 mg/kg (P) at both sampling times. This implies a 4- to 16-fold increased sensitivity of NMR versus histopathology and clinical chemistry in recognizing early events of liver toxicity.

Unique overlap in the prerequisites for thrombin inhibition and oral bioavailability resulting in potent oral antithrombotics.

Despite intense research over the last 10 years, aided by the availability of X-ray structures of enzyme-inhibitor complexes, only very few truly orally active thrombin inhibitors have been found. We conducted a comprehensive study starting with peptide transition state analogues (TSA). Both hydrophobic nonpeptide analogues as well as hydrophilic peptidic analogues were synthesized. The bioavailability in rats and dogs could be drastically altered depending on the overall charge distribution in the molecule. Compound 27, a tripeptide TSA inhibitor of thrombin, showed an oral bioavailability of 32% in rats and 71% in dogs, elimination half-lives being 58 and 108 min, respectively. The thrombin inhibition constant of compound 27 was 1.1 nM, and in an in vivo arterial flow model, the ED(50) was 5.4 nmol/kg.min, comparable to known non-TSA inhibitors. A molecular design was found that combines antithrombotic efficiency with oral bioavailability at low dosages.

Increased hepatobiliary and fecal cholesterol excretion upon activation of the liver X receptor is independent of ABCA1.

The ATP-binding cassette transporter ABCA1 is essential for high density lipoprotein (HDL) formation and considered rate-controlling for reverse cholesterol transport. Expression of the Abca1 gene is under control of the liver X receptor (LXR). We have evaluated effects of LXR activation by the synthetic agonist T0901317 on hepatic and intestinal cholesterol metabolism in C57BL/6J and DBA/1 wild-type mice and in ABCA1-deficient DBA/1 mice. In wild-type mice, T0901317 increased expression of Abca1 in liver and intestine, which was associated with an approximately 60% rise in HDL. Biliary cholesterol excretion rose 2.7-fold upon treatment, and fecal neutral sterol output was increased by 150-300%. Plasma cholesterol levels also increased in treated Abca1(-/-) mice (+120%), but exclusively in very low density lipoprotein-sized fractions. Despite the absence of HDL, hepatobiliary cholesterol output was stimulated upon LXR activation in Abca1(-/-) mice, leading to a 250% increase in the biliary cholesterol/phospholipid ratio. Most importantly, fecal neutral sterol loss was induced to a similar extent (+300%) by the LXR agonist in DBA/1 wild-type and Abca1(-/-) mice. Expression of Abcg5 and Abcg8, recently implicated in biliary excretion of cholesterol and its intestinal absorption, was induced in T0901317-treated mice. Thus, activation of LXR in mice leads to enhanced hepatobiliary cholesterol secretion and fecal neutral sterol loss independent of (ABCA1-mediated) elevation of HDL and the presence of ABCA1 in liver and intestine.