Biomedical subjects

Jan Fleckner

Publications and source records attributed to Jan Fleckner.

17 recordsLinked to original sources

PubMed2006

Proteome profiling in the rat Harderian gland.

The Harderian gland is an orbital gland located behind the ocular bulb in most terrestrial vertebrates probably functioning for production of lipid secretion to protect the eye. We herein present a protein reference database of the rat Harderian gland that may serve as analytical tool for future proteomic work, report lipid and porphyrin handling cascades, address sequence conflicts and report structures that have not been so far described by proteomics methods.

Amino Acid Sequence↗

PubMed2006

Selective PPAR agonists for the treatment of type 2 diabetes.

Type 2 diabetes is a metabolic disease characterized by increased plasma glucose and insulin as well as dyslipidemia. If left untreated, chronic diseases will develop that are associated with neuropathic damage and higher mortality risk. Using a rational drug design, novel compounds have been developed that selectively activate the human PPAR receptors, leading to lessening of hyperglycemia and hyperinsulinemia as well as reduction of lipid levels in conjunction with an increase of the beneficial HDL-cholesterol. These PPAR agonists showed increased potency and efficacy compared to previously marketed insulin sensitizers. Lead compounds with desirable pharmacokinetic properties were chosen for further testing in several animal models. The in vivo activity of some synthetic ligands, capable of activating two or all three members of peroxisome proliferator-activated receptors (PPAR) family of receptors, suggested that they may have improved efficacy in type 2 diabetes therapy. Here, we briefly summarize the development of some novel PPAR agonists identified by our group in recent years.

Animals↗

PubMed2006

The effect of neurogenin3 deficiency on pancreatic gene expression in embryonic mice.

To understand the molecular mechanisms regulating pancreatic endocrine development and function, pancreatic gene expression was compared between Ngn3-deficient mice and littermate controls on embryonic days 13 and 15. Microarray analysis identified 504 genes with significant differences in expression. Fifty-two of these showed at least twofold reduction in Ngn3 knockouts compared to controls. Many of them were previously described to be involved in endocrine development and function. Among the genes not previously characterized were Rhomboid veinlet-like 4, genes involved in tetrahydrobiopterin biosynthesis and the Iroquois-type homeobox gene Irx1, the latter was selected for further investigation. In situ hybridisation demonstrated that two Iroquois genes, Irx1 and Irx2, were expressed in pancreatic endoderm of wild-type, but not Ngn3 mutant embryos. Furthermore, ectopic Ngn3 induced prominent Irx2 expression in chicken endoderm. Co-labelling established that Irx1 and Irx2 mRNA is located to glucagon-, but not insulin- or somatostatin-producing cells in mice and chicken. These data suggest that Irx1 and Irx2 serve an evolutionary conserved role in the regulation of alpha-cell-specific gene expression.

Animals↗

PubMed2005

Structure-activity relationships of dimeric PPAR agonists.

A series of dimeric PPAR agonists were designed and tested for PPAR activity in vitro. The SAR showed that dimeric ligands with a common group or full dimeric ligands had retained or even increased PPARgamma potency. The dimeric agonist concept can be used to fine tune the subtype selectivity of PPAR agonists. The PPARgamma potency could, at least partly, be explained using molecular modeling.

Dimerization↗

PubMed2005

Peroxisome proliferator-activated receptor expression and activation in normal human colonic epithelial cells and tubular adenomas.

OBJECTIVE: Peroxisome proliferator-activated receptor (PPAR) ligands, widely used in type 2 diabetes treatment, have variably been shown to promote or prevent colon tumor formation in animal models and cell lines, but their role in normal human colon is unknown. The aim of this study was to determine PPAR expression and function in normal human colonic epithelial cells and tubular adenomas. MATERIAL AND METHODS: Short-term cultures of normal human colonic epithelial cells were established from biopsies obtained in 42 patients with normal colonoscopy. PPAR and adipophilin mRNA expression was assessed by real-time RT-PCR. PPARs were activated by ligands for PPAR alpha (Wy-14643), PPAR delta (GW-501516) and PPAR gamma (rosiglitazone or troglitazone). Cell viability was measured using the methyltetrazoleum assay, proliferation by thymidine incorporation, and DNA profiles by flow cytometry. PPAR mRNA levels in tubular adenomas or metaplastic polyps (n=12) were compared with those in controls. RESULTS: PPAR alpha and gamma were consistently expressed in normal colonocytes while no PPAR delta expression could be detected. PPAR gamma activation induced a 7.5-fold increase in adipophilin expression (a PPAR-activated gene). PPAR gamma activation had no effect on viability or DNA profiles, but led to a 25% significant decrease in cell proliferation. Finally, a selective and significant 2.5-fold decrease in PPAR alpha expression was observed in tubular adenomas, but not in metaplastic polyps, compared to controls. CONCLUSIONS: Our findings support the view that PPAR gamma ligands act as anti-proliferative agents rather than as promoters of tumorigenesis in normal human colon. Moreover, they raise interest in investigation of PPAR alpha as a therapeutic target to prevent adenoma formation.

Adenoma↗

PubMed2005

Sensory nerve inactivation by resiniferatoxin improves insulin sensitivity in male obese Zucker rats.

Recent studies have suggested that sensory nerves may influence insulin secretion and action. The present study investigated the effects of resiniferatoxin (RTX) inactivation of sensory nerves (desensitization) on oral glucose tolerance, insulin secretion and whole body insulin sensitivity in the glucose intolerant, hyperinsulinemic, and insulin-resistant obese Zucker rat. After RTX treatment (0.05 mg/kg RTX sc given at ages 8, 10, and 12 wk), fasting plasma insulin was reduced (P < 0.0005), and oral glucose tolerance was improved (P < 0.005). Pancreas perfusion showed that baseline insulin secretion (7 mM glucose) was lower in RTX-treated rats (P = 0.01). Insulin secretory responsiveness to 20 mM glucose was enhanced in the perfused pancreas of RTX-treated rats (P < 0.005) but unaffected in stimulated, isolated pancreatic islets. At the peak of spontaneous insulin resistance in the obese Zucker rat, insulin sensitivity was substantially improved after RTX treatment, as evidenced by higher glucose infusion rates (GIR) required to maintain euglycemia during a hyperinsulinemic euglycemic (5 mU.kg(-1).min(-1)) clamp (GIR(60-120min): 5.97 +/- 0.62 vs. 11.65 +/- 0.83 mg.kg(-1).min(-1) in RTX-treated rats, P = 0.003). In conclusion, RTX treatment and, hence, sensory nerve desensitization of adult male obese Zucker rats improved oral glucose tolerance by enhancing insulin secretion, and, in particular, by improving insulin sensitivity.

Animals↗

PubMed2004

Array-A-Lizer: a serial DNA microarray quality analyzer.

BACKGROUND: The proliferate nature of DNA microarray results have made it necessary to implement a uniform and quick quality control of experimental results to ensure the consistency of data across multiple experiments prior to actual data analysis. RESULTS: Array-A-Lizer is a small and convenient stand-alone tool providing the necessary initial analysis of hybridization quality of an unlimited number of microarray experiments. The experiments are analyzed for even hybridization across the slide and between fluorescent dyes in two-color experiments in spotted DNA microarrays. CONCLUSIONS: Array-A-Lizer allows the expedient determination of the quality of multiple DNA microarray experiments allowing for a rapid initial screening of results before progressing to further data analysis. Array-A-Lizer is directed towards speed and ease-of-use allowing both the expert and non-expert microarray researcher to rapidly assess the quality of multiple microarray hybridizations. Array-A-Lizer is available from the Internet as both source code and as a binary installation package.

Computer Graphics↗

PubMed2004

Prediction of PPAR-alpha ligand-mediated physiological changes using gene expression profiles.

Peroxisome proliferator-activated receptor (PPAR)-alpha controls the transcription of a variety of genes involved in lipid metabolism and is the target receptor for the hypolipidemic drug class of fibrates. In the present study, the molecular and physiological effects of seven different PPAR-activating drugs have been examined in a rodent model of dyslipidemia. The drugs examined were selected to display varying potencies and efficacies toward PPAR-alpha. To help elucidate the link between the gene regulation elicited by PPAR-alpha ligands and the concomitant physiological changes, we have used cDNA microarray analysis to identify smaller gene sets that are predictive of the function of these ligands. A number of genes showed strong correlations to the relative PPAR-alpha efficacy of the drugs. Furthermore, using multivariate analysis, a strong relationship between the drug-induced triglyceride lowering and the transcriptional profiles of the different drugs could be found.

Animals↗

PubMed2004

Artifactual insulin release from differentiated embryonic stem cells.

Several recent reports claim the generation of insulin-producing cells from embryonic stem cells via the differentiation of progenitors that express nestin. Here, we investigate further the properties of these insulin-containing cells. We find that although differentiated cells contain immunoreactive insulin, they do not contain proinsulin-derived C-peptide. Furthermore, we find variable insulin release from these cells upon glucose addition, but C-peptide release is never detected. In addition, many of the insulin-immunoreactive cells are undergoing apoptosis or necrosis. We further show that cells cultured in the presence of a phosphoinositide 3-kinase inhibitor, which previously was reported to facilitate the differentiation of insulin(+) cells, are not C-peptide immunoreactive but take up fluorescein isothiocyanate-labeled insulin from the culture medium. Together, these data suggest that nestin(+) progenitor cells give rise to a population of cells that contain insulin, not as a result of biosynthesis but from the uptake of exogenous insulin. We conclude that C-peptide biosynthesis and secretion should be demonstrated to claim insulin production from embryonic stem cell progeny.

Animals↗

PubMed2003

Large dimeric ligands with favorable pharmacokinetic properties and peroxisome proliferator-activated receptor agonist activity in vitro and in vivo.

Two potent nonselective, but PPARalpha-preferring, PPAR agonists 5 and 6 were designed and synthesized in high yields. The concept of dimeric ligands in transcription factors was investigated by synthesizing and testing the corresponding dimers 7, 8a, and 8b in PPAR transactivation assays. The three dimeric ligands all showed agonist activity on all three PPAR receptor subtypes, but with different profiles compared to the monomers 5 and 6. Despite breaking all the "rule of five" criteria, the dimers had excellent oral bioavailability and pharmacokinetic properties, resulting in good in vivo efficacy in db/db mice. X-ray crystal structure and modeling experiments suggested that the dimers interacted with the AF-2 helix as well as with amino acid residues in the lipophilic pocket close to the receptor surface.

Alkenes↗

PubMed2003

Synthesis and biological and structural characterization of the dual-acting peroxisome proliferator-activated receptor alpha/gamma agonist ragaglitazar.

A new and improved synthesis of the peroxisome proliferator-activated receptor (PPAR) agonist ragaglitazar applicable for large-scale preparation has been developed. The convergent synthetic procedure was based on a novel enzymatic kinetic resolution step. The conformation of ragaglitazar bound to the hPPARgamma receptor was quite different compared to the single-crystal structures of the l-arginine salt of ragaglitazar. In particular, the phenoxazine ring system had varying orientations. Ragaglitazar had high affinity for the hPPARalpha and -gamma receptors with IC(50) values of 0.98 and 0.092 microM, respectively. The lack of hPPARdelta activity could be explained by the absence of binding in the tail-up pocket in the hPPARdelta receptor, in contrast to the hPPARdelta agonist GW2433, which was able to bind in both the tail-up and tail-down pockets of the receptor.

Binding Sites↗

PubMed2003

Design and synthesis of novel PPARalpha/gamma/delta triple activators using a known PPARalpha/gamma dual activator as structural template.

Using a known dual PPARalpha/gamma activator (5) as a structural template, SAR evaluations led to the identification of triple PPARalpha/gamma/delta activators (18-20) with equal potency and efficacy on all three receptors. These compounds could become useful tools for studying the combined biological effects of PPARalpha/gamma/delta activation.

Animals↗

PubMed2003

Mutational analysis of the UCP2 core promoter and relationships of variants with obesity.

OBJECTIVE: To identify polymorphisms in the human uncoupling protein 2 gene (UCP2) promoter and to investigate whether these were associated with obesity or weight gain. RESEARCH METHODS AND PROCEDURES: The human UCP2 promoter was characterized by reporter gene analysis in cell lines derived from skeletal muscle, white adipose tissue, and embryonic tissue. We analyzed the core promoter for polymorphisms in 60 obese subjects. A prevalent polymorphism, the -866 G/A variant, was investigated for association with obesity in 749 men obese as young adults and 816 men of the same age representing the background population. Genotype-phenotype interaction studies were performed in two other population-based samples: one group of middle-aged-to-elderly Danish subjects (mean age, 53 years; range, 30 to 88 years) and one group of 60-year-old Danish subjects. RESULTS: The region up to -1202 bp relative to the UCP2 transcription initiation site gave rise to the highest promoter activity. Eight mutations in this region were identified comprising -866 G/A, -850 G/A, -337 G/C, -41 G/T, -28 insertion T, -5 insertion (cactgcgaagccc), +45 C/T, and +53 G/C, but none of these was associated with consistent alterations in BMI, body fat content, weight gain, or fasting levels of plasma glucose and serum insulin. DISCUSSION: Variation of the UCP2 promoter including the single common variant (-866 A/G) is not associated with obesity or obesity-related intermediary phenotypes in Danish subjects.

Adipose Tissue↗

PubMed2002

Dual PPARalpha /gamma activation provides enhanced improvement of insulin sensitivity and glycemic control in ZDF rats.

Improvement of insulin sensitivity and lipid and glucose metabolism by coactivation of both nuclear peroxisome proliferator-activated receptor (PPAR)gamma and PPARalpha potentially provides beneficial effects over existing PPARgamma and alpha preferential drugs, respectively, in treatment of type 2 diabetes. We examined the effects of the dual PPARalpha/gamma agonist ragaglitazar on hyperglycemia and whole body insulin sensitivity in early and late diabetes stages in Zucker diabetic fatty (ZDF) rats and compared them with treatment with the PPARgamma preferential agonist rosiglitazone. Despite normalization of hyperglycemia and Hb A(1c) and reduction of plasma triglycerides by both compounds in both prevention and early intervention studies, ragaglitazar treatment resulted in overall reduced circulating insulin and improved insulin sensitivity to a greater extent than after treatment with rosiglitazone. In late-intervention therapy, ragaglitazar reduced Hb A(1c) by 2.3% compared with 1.1% by rosiglitazone. Improvement of insulin sensitivity caused by the dual PPARalpha/gamma agonist ragaglitazar seemed to have beneficial impact over that of the PPARgamma-preferential activator rosiglitazone on glycemic control in frankly diabetic ZDF rats.

Animals↗

PubMed2002

The gene encoding the Acyl-CoA-binding protein is activated by peroxisome proliferator-activated receptor gamma through an intronic response element functionally conserved between humans and rodents.

The acyl-CoA-binding protein (ACBP) is a 10-kDa intracellular protein that specifically binds acyl-CoA esters with high affinity and is structurally and functionally conserved from yeast to mammals. In vitro studies indicate that ACBP may regulate the availability of acyl-CoA esters for various metabolic and regulatory purposes. The protein is particularly abundant in cells with a high level of lipogenesis and de novo fatty acid synthesis and is significantly induced during adipocyte differentiation. However, the molecular mechanisms underlying the regulation of ACBP expression in mammalian cells have remained largely unknown. Here we report that ACBP is a novel peroxisome proliferator-activated receptor (PPAR)gamma target gene. The rat ACBP gene is directly activated by PPARgamma/retinoid X receptor alpha (RXRalpha) and PPARalpha/RXRalpha, but not by PPARdelta/RXRalpha, through a PPAR-response element in intron 1, which is functionally conserved in the human ACBP gene. The intronic PPAR-response element (PPRE) mediates induction by endogenous PPARgamma in murine adipocytes and confers responsiveness to the PPARgamma-selective ligand BRL49653. Finally, we have used chromatin immunoprecipitation to demonstrate that the intronic PPRE efficiently binds PPARgamma/RXR in its natural chromatin context in adipocytes. Thus, the PPRE in intron 1 of the ACBP gene is a bona fide PPARgamma-response element.

3T3 Cells↗

PubMed2002

Novel tricyclic-alpha-alkyloxyphenylpropionic acids: dual PPARalpha/gamma agonists with hypolipidemic and antidiabetic activity.

Synthesis and structure-activity relationships of tricyclic alpha-ethoxy-phenylpropionic acid derivatives guided by in vitro PPARalpha and PPARgamma transactivation data and computer modeling led to the identification of the novel carbazole analogue, 3q, with dual PPARalpha (EC(50) = 0.36 microM) and PPARgamma (EC(50) = 0.17 microM) activity in vitro. Ten days treatment of db/db mice with 3q improved the insulin sensitivity, as measured by OGTT, better than that seen with both pioglitazone and rosiglitazone treatment, suggesting in vivo PPARgamma activity. Likewise, 3q lowered plasma triglycerides and cholesterol in high cholesterol fed rats after 4 days treatment, indicating in vivo PPARalpha activity. Investigations of the pharmacokinetics of selected compounds suggested that extended drug exposure improved the in vivo activity of in vitro active compounds.

Animals↗

PubMed2002

Novel genes regulated by the insulin sensitizer rosiglitazone during adipocyte differentiation.

Thiazolidinediones (TZDs) are a new class of compounds that improve insulin sensitivity in type 2 diabetic patients as well as in rodent models of this disease. These compounds act as ligands for a member of the nuclear hormone receptor superfamily, peroxisome proliferator-activated receptor-gamma (PPAR-gamma), which is highly expressed in adipose tissue and, moreover, has been shown to play an important role in adipocyte differentiation. The strong correlation between the antidiabetic activity of TZDs and their ability to activate PPAR-gamma suggests that PPAR-gamma, through downstream-regulated genes, mediates the effects of TZDs. In this report, we present the isolation and characterization of 81 genes, encoding proteins of known function, differentially expressed during TZD-stimulated differentiation of 3T3-L1 cells. By the use of different reverse- Northern blot techniques, the differential expression of 50 of these genes could be verified, and 21 genes were specifically regulated by a potent TZD during the course of adipocyte differentiation, whereas no effect of a PPAR-gamma antagonist could be observed in mature adipocytes. The differential expression of a large fraction of the isolated genes was also shown to occur in white adipose tissue of ob/ob mice treated with rosiglitazone; combined, our results suggest that an important effect of rosiglitazone in adipose tissue is based on activation of PPAR-gamma in preexisting preadipocytes found among the mature adipocytes, resulting in subsequent adipocyte differentiation.

3T3 Cells↗