Synthesis and biological activity of novel thiazolidinediones

Novel compounds having a dual pharmacophore were synthesised and evaluated for their insulin sensitiser and anti-inflammatory properties in different animal models.

Deletion mapping of endocrine tumors localizes a second tumor suppressor gene on chromosome band 11q13

Multiple endocrine neoplasia type 1 syndrome (MEN1, MIM 131100), an autosomal dominant disease, is characterized by parathyroid hyperplasia, pancreatic endocrine tumors, and pituitary adenomas. These tumors also occur sporadically. Both the familial (MEN1) and the sporadic tumors reveal loss of heterozygosity (LOH) for chromosome band 11q13 sequences. Based on prior linkage and LOH analyses, the MEN1 gene was localized between PYGM and D11S460. Recently, the MEN1 gene (menin) has been cloned from sequences 30-kb distal to PYGM. We performed deletion mapping on 25 endocrine tumors (5 MEN1 and 20 sporadic) by using 21 polymorphic markers on chromosome band 11q13. Of these, two (137C7A, 137C7B) were derived from PYGM-containing BAC (bacterial artificial chromosome-137C7) sequences, one from INT2-containing cosmid sequences and the marker D11S4748, a (CA)20 repeat marker that was developed by us. The LOH analysis shows that the markers close to the MEN1 (menin) gene were not deleted in three of the tumors. These tumors, however, showed LOH for distal markers. Thus, the data suggest the existence of a second tumor suppressor gene on chromosome band 11q13.

Transcriptional regulation of the rat glutamine synthetase gene by tumor necrosis factor-alpha

The expression of glutamine synthetase (GS) is induced in rat skeletal muscle cells (L-6) in response to treatment with the inflammatory cytokine tumor necrosis factor alpha (TNF-alpha). This paper reports the regulation of GS expression in rat skeletal muscle which expresses high levels of GS. TNF-alpha treatment leads to a 3-4-fold increase in GS activity in a dose-dependent and time-dependent manner. Northern-blot analysis of GS mRNA revealed an increased mRNA concentration, reaching a peak at 12 h in response to TNF-alpha treatment. To monitor transcriptional activation of GS by TNF-alpha, and to identify a TNF-alpha-responsive element in the GS promoter, L6 cells were treated with TNF-alpha following transfection of GS-chloramphenicol-acetyltransferase (CAT) constructs. The first 251-bp fragment at the GS upstream sequence showed basal promoter activity, but failed to show any TNF-alpha-inducible activity. However, a 2.5-3-fold induction was noted in constructs extending up to 1.1 kb. This data demonstrates that the rat GS gene is transcriptionally regulated by TNF-alpha and identifies a TNF-alpha-responsive region at the 5' flanking sequence of the GS gene.

Novel euglycemic and hypolipidemic agents. 1

A series of [[(heterocyclyl)ethoxy]benzyl]-2,4-thiazolidinediones have been synthesized by the condensation of corresponding aldehyde 1 and 2,4-thiazolidinedione followed by hydrogenation. Both unsaturated thiazolidinedione 2 and its saturated counterpart 3 have shown antihyperglycemic activity. Many of these compounds have shown superior euglycemic and hypolipidemic activity compared to troglitazone (CS 045). The indole analogue DRF-2189 (3g) was found to be a very potent insulin sensitizer, comparable to BRL-49653 in genetically obese C57BL/6J-ob/ob and 57BL/KsJ-db/db mice. Pharmacokinetic and tissue distribution studies conducted on BRL-49653 and DRF-2189 (3g) indicate that these drugs are well-distributed in target tissues. On the basis of euglycemic activity as well as enhanced selectivity against reduction of triglycerides in plasma, DRF-2189 (3g) has been selected for further evaluation.

Novel euglycemic and hypolipidemic agents: Part-2. Antioxidant moiety as structural motif

Several thiazolidinediones having antioxidant moities in their structural motif have been synthesised and evaluated for their euglycemic and hypolipidemic activities. A few of them have been found to be superior to troglitazone.

Characterization of glutamine synthetase transcript, protein, and enzyme activity in the human placenta

This study characterizes the molecular mechanisms necessary for glutamine synthesis in the human placenta. RNA hybridization and protein immunoblotting were used to verify the presence of glutamine synthetase (GS) transcripts and protein, respectively. Additionally, the presence of GS was determined by immunohistochemistry. RNA hybridization demonstrated the presence of 1.8- and 2.8-kB transcripts and protein immunoblotting yielded a single 49-kDa band, characteristics of GS transcripts and protein, respectively. The mean (+/- s.d.) specific activity of placental GS, expressed as mumol gamma-glutamyl hydroxamic acid/mg protein/h was 1.80 +/- 0.59, which is comparable to other organs which are net glutamine producers. Immunohistochemical analysis indicated the presence of GS within the cytotrophoblast and mesenchyme layers of placental villi, but not in the syncytiotrophoblast. Although these results suggest that the human placenta is capable of synthesizing glutamine, the fate of glutamine produced by this organ remains speculative.

Deletion analysis of the p16/CDKN2 gene in head and neck squamous cell carcinoma using quantitative polymerase chain reaction method

BACKGROUND

Recently, the p16/CDKN2/MTS1 gene in the 9p21-22 region has been offered as a candidate tumor suppressor gene. We examined the frequency of hemizygous and homozygous deletions of p16/CDKN2 in head and neck squamous cell carcinoma (HNSCC) using a quantitative polymerase chain reaction (PCR) method.

DESIGN

Twenty-one HNSCC and 12 corresponding normal DNA samples were examined for deletion of p16/ CDKN2 using PCR amplification and fluorescent quantification of DNA. All tumor and normal DNA samples were also amplified with fluorescein-labeled primers for a control DNA marker on chromosome 8p (D8S265). The ratios of the observed fluorescence of the p16/CDKN2 and 8p PCR products were compared.

SETTING AND PARTICIPANTS

Patients with HNSCC scheduled to undergo surgical resection of their tumors were recruited. After the specimen was removed, a portion of the tissue was snap frozen for further DNA extraction.

RESULTS

Eight tumors (38%) had p16/CDKN2-D8S265 ratios of greater than 0.75; 8 tumors (38%), from 0.25 to 0.75; and 5 tumors (24%), of less than 0.25, the average ratio in this last group being 0.06.

CONCLUSIONS

These ratios suggest a higher rate of homozygous deletion than previously reported and significant probable hemizygous deletion of the p16/CDKN2 gene in HNSCC.

A transcript map encompassing the multiple endocrine neoplasia type-1 (MEN1) locus on chromosome 11q13

A transcription map of a 1200-kb region encompassing the MEN1 locus was constructed by direct cDNA selection and mapping ESTs. A total of 29 genes were mapped. Ten transcripts were identified by cDNA selection of a focused 300-kb genomic region telomeric to the MEN1 consensus region. Since many of the sequences cloned by cDNA selection also identified ESTs from the region, 19 additional RH-mapped ESTs were mapped to the entire contig region by PCR amplification of genomic clones. Nine known genes, 2 putative human homologues to mouse genes, and 18 novel transcripts map to the region. Transcripts that map to the MEN1 interval PYGM-D11S449 include SGC35223, IB1256, AA147620, ZFM1, FAU, and CAPN1. The latter 3 known genes have already been excluded as candidate MEN1 genes. The 2 putative human homologues of mouse genes Ltbp2 and Spa-1 may be candidate tumor suppressor genes, but they map telomeric to D11S449. Although both of these genes map outside the MEN1 consensus region they may play a role in sporadic endocrine tumors independent of the MEN1 gene or in other tumors, such as breast cancer, that have loss of heterozygosity within this region.

Alteration of platelet-activating factor-induced signal transduction in macrophages by n-3 fatty acids

Diets rich in polyunsaturated n-3 fatty acids can alter various macrophage functions. One possible mechanism by which this occurs is through modulation of the physicochemical properties of the cell membrane and the signal transduction pathways associated with macrophage activation. In this study, we investigated how n-3 fatty acids altered the signaling pathway of the lipid-based mediator platelet-activating factor (PAF). Macrophages from mice fed a diet containing n-3 fatty acids showed a greater increase in PAF-induced intracellular Ca2+ mobilization than macrophages from mice fed an n-6 fatty acid-rich diet. Macrophages treated in vitro with the n-3 fatty acids docosahexaenoic and eicosapentaenoic also showed higher intracellular Ca2+ mobilization than untreated or n-6 fatty acid-treated macrophages. Scatchard analysis of PAF binding showed the presence of one type of PAF receptor; their number and affinities were not altered by dietary fat. Mastoparan, which can activate G-protein-linked phosphoinositide (PI)-signaling pathway through the activation of G proteins, stimulated a higher Ca2+ mobilization in macrophages from mice fed n-3 compared to n-6 fatty acids. In addition, the response of macrophages from n-3-fed mice to PAF was less sensitive to phospholipase C inhibition than that of macrophages from those fed n-6 diets. The activity of phospholipase C in macrophages from mice fed n-3 diets was significantly higher than that of macrophages from mice fed diets containing n-6 fatty acids. Collectively, these results showed that n-3 fatty acids can enhance the PAF-signaling pathway in macrophages by increasing the activation potential of phospholipase C, without affecting PAF receptor number and affinity.

A 1.5-megabase physical map encompassing the multiple endocrine neoplasia type-1 (MEN1) locus on chromosome 11q13

Linkage analysis and loss of heterozygosity studies have shown that the gene responsible for the multiple endocrine neoplasia type-1 (MEN1) syndrome localizes to a small interval between D11S427 and D11S460 on chromosome 11q13. As an initial step to clone this tumor suppressor gene, our group is the first to map the MEN1 region physically using yeast artificial chromosome, bacterial artificial chromosome (BAC), and cosmid contigs. The 1.5-Mb high-resolution, contiguous map extends from PYGM to 300 kb telomeric of D11S460. Of this, the 1.2-Mb interval between PYGM and D11S460 is isolated in cosmids and BACs and will be useful for the development of genomic sequences and transcription maps of this important region. Nine new sequence-tagged sites (STS) are also characterized from this region. The physical map and the STSs will be valuable tools for the cloning of the MEN1 gene.

Dielectric analysis of phosphorylcholine head group mobility in egg lecithin liposomes

PURPOSE

A knowledge of the interfacial properties of lecithin underpins our understanding of many of the physicochemical characteristics of drug delivery systems such as liposomes and lecithin stabilized microemulsions. In order to further this understanding, a high frequency dielectric study of the interfacial properties of egg lecithin liposomes was undertaken.

METHODS

The effect of temperature, lecithin concentration and probe sonication on the interfacial dielectric properties of liposomal suspensions was investigated by high frequency dielectric relaxation spectroscopy between 0.2-6 GHz.

RESULTS

The frequency dependent permittivity of each suspension exhibited a dielectric dispersion centred around 100 MHz, corresponding to the relaxation of zwitterionic head groups. The activation energy for head group reorientation was estimated as delta H = 6.3 kJ mol-1. There was an increase in extent of inter-head group interactions on increasing the liposome volume fraction, whereas the effect of probe sonication showed that: (i) head groups in both the outer and inner lamellae contribute to the dielectric response; (ii) the head groups may be less restricted in liposomes of high surface curvature with few lamellae; (iii) the high frequency permittivity of the suspension increased on sonication, as a result of a reduction in the amount of (depolarized) interlamellar water following a reduction in the number of lamellae per liposome.

CONCLUSIONS

Dielectric analysis of the zwitterionic head groups of lecithin therefore provides a means for investigating the surface of lecithin liposomes, and may be used to investigate the effect of drugs and other solutes on membranes.

Glutamine nutrition and metabolism: where do we go from here ?

Glutamine, a "nonessential" amino acid, is attracting widespread attention because of its relevance to numerous metabolic processes and its potential role in the treatment and prevention of critical illness. In this paper we review some key concepts of glutamine biochemistry, metabolism, and nutrition. We then discuss several studies in the area of glutamine metabolism and nutrition that are primed for further investigation.

Ontogeny of glutamine synthetase in rat small intestine

Glutamine synthetase (GS) is a key enzyme involved in the endogenous biosynthesis of glutamine, an amino acid known to be essential for small intestinal metabolism and function. This study describes the ontogeny of rat small intestinal GS from fetal life through adulthood with enzyme activities, protein immunoblotting, and steady state levels of GS mRNA by RNA gel blots and dot blots. Enzyme activities progressively increased from 21 d of fetal life to 32 d postnatally, then decreased in adulthood. The amount of GS immunoreactive protein in the small intestine increased from fetal life to 10-day-old infants and persisted into adulthood. GS mRNA, as quantified by dot blots was highest at 19 d postnatally. The ontogenic changes in rat small intestinal GS appear to correspond temporally with rapid growth and weaning. The steady increase in GS enzyme activity up to 32 d of age with a subsequent drop in adulthood is not paralleled by an increase in GS mRNA or protein. These findings suggest an apparent complex regulation of the enzyme activity at a transcriptional or translational levels.

Tyrosine kinase but not phospholipid/Ca2+ signaling pathway is involved in interferon-gamma stimulation of Ia expression in macrophages

The specific signal transduction pathway(s) involved in the induction of the expression of the MHC class II molecule, Ia, on macrophages by interferon-gamma (IFN-gamma) is unclear. In this paper, we assessed the role of several signal transduction pathways including calcium mobilization, phospholipase C, protein kinase C and cyclic nucleotide-dependent protein kinase, and the tyrosine kinase pathways. IFN-gamma was unable to mobilize intracellular calcium, unlike platelet-activating factor, which stimulated a threefold increase in cytosolic Ca2+ concentration in macrophages. Inhibition of the phospholipase C pathway by U73122 or ET-180CH3 and of phosphatidic acid phosphohydrolase by propranolol did not suppress IFN-gamma-induced Ia expression. In addition, inhibition of protein kinase C by calphostin C or cyclic nucleotide-dependent protein kinase by HA1004 did not suppress Ia expression. However, IFN-gamma-induced Ia expression was significantly suppressed when the tyrosine kinase pathway was inhibited with herbimycin A and genestein. In addition, those two inhibitors suppressed tyrosine phosphorylation of several proteins in macrophages that may or may not be involved in the induction of Ia expression. Thus, IFN-gamma used only the tyrosine kinase signaling pathway, but not the phospholipid/Ca2+ signaling pathways, to induce Ia expression in macrophages.

T cell receptor-mediated Ca2+ signaling: release and influx are independent events linked to different Ca2+ entry pathways in the plasma membrane

In this study, we showed that cross-linking CD3 molecules on the T cell surface resulted in Ca2+ release from the intracellular stores followed by a sustained Ca2+ influx. Inhibition of release with TMB-8 did not block the influx. However, inhibition of phospholipase C activity suppressed both Ca2+ release and influx. Once activated, the influx pathway remained open in the absence of further hydrolysis of PIP2. Thapsigargin, a microsomal Ca(2+)-ATPase inhibitor, stimulated Ca2+ entry into the cells by a mechanism other than emptying Ca2+ stores. In addition, Ca2+ entry into the Ca(2+)-depleted cells was stimulated by low basal level of cytosolic Ca2+, not by the emptying of intracellular Ca2+ stores. Both the Ca2+ release and influx were dependent on high and low concentrations of extracellular Ca2+. At low concentrations, Mn2+ entered the cell through the Ca2+ influx pathway and quenched the sustained phase of fluorescence; whereas, at higher Mn2+ concentration both the transient and the sustained phases of fluorescence were quenched. Moreover, Ca2+ release was inhibited by low concentrations of Ni2+, La3+, and EGTA, while Ca2+ influx was inhibited by high concentrations. Thus, in T cells Ca2+ influx occurs independently of IP3-dependent Ca2+ release. However, some other PIP2 hydrolysis-dependent event was involved in prolonged activation of Ca2+ influx. Extracellular Ca2+ influenced Ca2+ release and influx through the action of two plasma membrane Ca2+ entry pathways with different pharmacological and biochemical properties.

Modulation of signal transduction in macrophages by dietary fatty acids

Tumor growth can be altered by the amount and type of fat in the diet. Although there are several possible mechanisms for this, recent work suggests that alterations in the immune system by dietary fat may affect tumorigenesis. The focus of recent studies has been on dietary fat modulation of macrophage function because that cell plays a pivotal role in many immune responses, including anti-tumor activity. One possible mechanism of dietary fat effects on macrophages is altered signal transduction, which, in turn, could alter gene regulation and macrophage function. Initial studies tested the effects of dietary fat on kinase activity after stimulation with interferon-gamma. Macrophages from mice fed menhaden fish oil (MFO) had slightly decreased protein kinase C activity compared with macrophages from mice fed safflower oil (SAF). No differences among the diets were observed when the activity of protein kinase A and G were tested. When calcium mobilization was tested, we found that macrophages from mice fed MFO had an increased response compared with macrophages from mice fed SAF. Dietary fat also modified the response of macrophages to platelet-activating factor with respect to the induction of Ia expression. In studies to identify genes involved in dietary fat effects on macrophage function, we screened a cDNA library of macrophages treated with prostaglandin E2 (PGE2), a lipid-based mediator that can modulate macrophage function and be altered by dietary fat. The cloned gene, BTG1, was enhanced in macrophages treated with PGE2, but the relationship with dietary fat remains to be determined.(ABSTRACT TRUNCATED AT 250 WORDS)

Localization of rat small intestine glutamine synthetase using immunofluorescence and in situ hybridization

Glutamine is an important energy source for small intestinal epithelial enterocytes and serves as a key precursor for de novo synthesis of purines and pyrimidines in these rapidly dividing cells. Although glutamine synthetase (GS) is known to be the major enzyme of glutamine biosynthesis, the precise localization of this enzyme in the small intestine is not known. Because glutamine is an important precursor for nucleic acids biosynthesis, we hypothesized that GS is preferentially expressed in the crypt region, which contains the rapidly proliferating cells in the small intestine. Accordingly, immunofluorescence with a specific polyclonal antibody and in situ hybridization using a riboprobe were performed to localize GS protein and mRNA, respectively, in adult rats. Both GS protein and GS mRNA were detected primarily in the crypt region. This finding suggests that GS is located in the region with the highest nucleotide synthesis and cell proliferation. This finding is in support of the use of parenteral glutamine in patients with severe mucosal injury affecting the crypts.

Detection of a functional promoter/enhancer in an intron-less human gene encoding a glutamine synthetase-like enzyme

A human genomic clone, psi GS, containing an intron-less glutamine synthetase (GS)-encoding pseudogene, was isolated by screening a human library. A sequence of 3004 bp, containing the GS coding region and both the 5' and 3' flanking sequences, was identified that exhibits all the characteristics of a processed pseudogene. The coding region shows 93% identity with the human GS cDNA (hGS) sequence and contains two frame-shifts and two termination codons. The coding sequence is flanked by a 9-bp AT repeat and a putative polyadenylation site, AATAAA, at the 3' end. Primer extension analysis and S1 nuclease mapping showed a transcription start point (tsp) 62 bp upstream from the start codon indicating a shorter untranslated region than hGS. Transfection of HeLa cells with cat constructs containing portions of the 5' flanking sequence showed the presence of a functional promoter/enhancer within 200 bp of the tsp, independent of its orientation.

A double leucine within the GLUT4 glucose transporter COOH-terminal domain functions as an endocytosis signal

The unique COOH-terminal 30-amino acid region of the adipocyte/skeletal muscle glucose transporter (GLUT4) appears to be a major structural determinant of this protein's perinuclear localization, from where it is redistributed to the cell surface in response to insulin. To test whether an underlying mechanism of this domain's function involves glucose transporter endocytosis rates, transfected cells were generated expressing exofacial hemagglutinin epitope (HA)-tagged erythrocyte/brain glucose transporter (GLUT1) or a chimera containing the COOH-terminal 30 amino acids of GLUT4 substituted onto this GLUT1 construct. Incubation of COS-7 or CHO cells expressing the HA-tagged chimera with anti-HA antibody at 37 degrees resulted in an increased rate of antibody internalization compared to cells expressing similar levels of HA-tagged GLUT1, which displays a cell surface disposition. Colocalization of the internalized anti-HA antibody in vesicular structures with internalized transferrin and with total transporters was established by digital imaging microscopy, suggesting the total cellular pool of transporters are continuously recycling through the coated pit endocytosis pathway. Mutation of the unique double leucines 489 and 490 in the rat GLUT4 COOH-terminal domain to alanines caused the HA-tagged chimera to revert to the slow endocytosis rate and steady-state cell surface display characteristic of GLUT1. These results support the hypothesis that the double leucine motif in the GLUT4 COOH terminus operates as a rapid endocytosis and retention signal in the GLUT4 transporter, causing its localization to intracellular compartments in the absence of insulin.

Cytokines decrease glutaminase expression in human fibroblasts

BACKGROUND

Glutamine metabolism in fibroblasts is essential for energy production, nucleotide biosynthesis, and growth during wound healing. Because cytokines can impair fibroblast proliferation, we tested the hypothesis that cytokines impair glutamine metabolism. We studied the influence of several cytokines on the expression of glutaminase, the major enzyme of intracellular glutamine metabolism in fibroblasts.

METHODS

Human foreskin fibroblasts were incubated for 6 and 12 hours with varying doses (10, 100, or 1000 units/ml) of interleukin (IL)-1, IL-6, tumor necrosis factor-alpha, or gamma-interferon. Cell lysates were assayed for glutaminase-specific activity, and glutaminase protein content was measured by Western blotting with a polyclonal antibody. Total cellular RNA was extracted, and relative glutaminase messenger RNA levels were determined by Northern blotting with a 32P-labeled glutaminase complement DNA-derived probe. These mRNA levels were normalized by blotting with a beta-actin cDNA-derived probe as control. Cell nuclei were isolated, and nuclear run-ons were used to determine relative glutaminase mRNA transcription rates.

RESULTS

IL-1, IL-6, tumor necrosis factor-alpha, and gamma-interferon decreased glutaminase activity and protein concentration after a 12-hour incubation in a dose-independent fashion. No difference was noted at 6 hours. Western blot analysis showed a 30% to 60% reduction in glutaminase protein in treated cells. These cytokines also decreased glutaminase mRNA levels, consistent with transcriptional regulation. This was confirmed by nuclear run-on assays that showed a decrease in the number of glutaminase transcripts.

CONCLUSIONS

A variety of different pro-inflammatory cytokines decrease glutaminase expression in cultured human fibroblasts. This cytokine-mediated inhibition of glutamine metabolism may limit the availability of key glutamine-derived intermediates and impair fibroblast proliferation in certain patients.

Insulin-sensitive association of GLUT-4 with endocytic clathrin-coated vesicles revealed with the use of brefeldin A

The interaction of the adipocyte/skeletal muscle glucose transporter (GLUT-4) with clathrin lattices may be important in maintaining its intracellular distribution. To better understand the role of clathrin lattices in the sorting of GLUT-4, we have attempted to determine the cellular origin of clathrin-coated vesicles (CCVs) that contain this transporter. The fungal toxin brefeldin A (BFA) causes the selective disassembly of clathrin lattices at the trans-Golgi network (TGN), but not at the plasma membrane (PM), thus providing a way of estimating the proportion of GLUT-4 in PM- versus TGN-derived clathrin lattices. Exposure of 3T3-L1 adipocytes to BFA resulted in a rapid disassembly of clathrin lattices at the TGN, observed by optical sectioning microscopy, and to a pronounced decrease in the yield of CCVs purified from these cells. Thus, CCVs isolated from BFA-treated cells are likely to be derived from the PM. Immunoblotting experiments revealed the presence of GLUT-4 in such CCVs, suggesting that under basal conditions the transporter is continually retrieved from the PM through the CCV pathway. Exposure of both BFA-treated or non-treated cells to insulin resulted in a 4-6-fold increase in the concentration of GLUT-4 at the PM. In parallel, the concentration of GLUT-4 in PM-derived CCVs decreased by 60%. These results suggest (a) that the effect of insulin to increase the cell surface concentration of GLUT-4 is not inhibited by BFA, and (b) that a decreased association of GLUT-4 with endocytic CCVs may be important in facilitating its increased cell surface concentration in response to the hormone.