Amphotericin B both inhibits and enhances T-cell proliferation: inhibitory effect is mediated through H(2)O(2) production via cyclooxygenase pathway by macrophages

Amphotericin B (AmB) has been shown to have both immunosuppressive and -enhancing effects, making its precise nature of action enigmatic. In the present study, we found that AmB inhibited concanavalin A (Con A)-induced T cell proliferation if added within first 30 min of stimulation, after which inhibition began to diminish rapidly. However, AmB did not inhibit T-cell proliferation induced by a combination of PMA and ionomycin. AmB inhibition of Con A-induced proliferation was completely overcome by cyclooxygenase inhibitor ibuprofen ([alpha-methyl-4-(isobutyl)phenylacetic acid]) and H(2)O(2) scavenger catalase. In fact, in the presence of ibuprofen and catalase, AmB enhanced, instead of suppressing, Con A-induced proliferation in a dose-dependent way. The effect of catalase was limited to the removal of extracellular H(2)O(2) only, as the enzyme did not enter the cells. AmB stimulated H(2)O(2) production by macrophages, but not by a lymphocyte population, which was inhibited by ibuprofen. Our T-cell preparation contained about 3% macrophages, and AmB inhibition of proliferation was further pronounced by increasing the macrophage number by as little as 1%. Finally, AmB inhibition of Con A-induced T-cell proliferation was completely overcome by 2-mercaptoethanol. On the basis of these results, we suggest that AmB stimulates H(2)O(2) production by macrophages through the activation of the cyclooxygenase pathway of arachidonate metabolism. H(2)O(2) then inhibits Con A-induced T-cell proliferation by interfering with an early step of the T-cell receptor signaling pathway through the oxidative modification of some signaling proteins. Our results also show that AmB enhances T-cell proliferation, which can be seen only after blocking its inhibitory effect.

PfPK6, a novel cyclin-dependent kinase/mitogen-activated protein kinase-related protein kinase from Plasmodium falciparum

We have isolated a novel protein kinase cDNA, PfPK6, by differential display RT-PCR (DDRT-PCR) of mRNA obtained from different asexual erythrocytic stages of Plasmodium falciparum, which shows sequence similarity to both cyclin-dependent kinase (CDK) and mitogen-activated protein kinase (MAPK) family members. The 915 bp open reading frame (ORF) is interrupted by seven introns and encodes a 305-residue polypeptide with a predicted molecular mass of 35848 Da. Several cDNA clones with some of the intron sequences were isolated, indicating alternate or defective splicing of PfPK6 transcripts because the gene seems to be a single copy located on chromosome 13. The similarity of the catalytic domain of PfPK6 to those of CDK2 and MAPK is 57.3% and 49.6%, respectively. The signature PSTAIRE (single-letter amino acid codes) CDK motif is changed to SKCILRE in PfPK6. The TXY residues that are phosphorylated in MAPKs for their activation are T(173)PT in PfPK6. Three size classes of PfPK6 transcripts of 6.5, 2.0 and 1.1 kb are up-regulated during the transition of P. falciparum from ring to trophozoite. Western blot analysis suggested the expression of a 35 kDa polypeptide in trophozoites and schizonts. Immunofluorescence studies indicated both nuclear and cytoplasmic localization of PfPK6 in trophozoite, schizont and segmenter stages. In vitro, recombinant PfPK6 phosphorylated itself and also exogenous substrates, histone and the small subunit of the malarial ribonucleotide reductase (R2). The kinase activity of PfPK6 is sensitive to CDK inhibitors such as olomoucine and roscovitine. PfPK6 showed a preference for Mn(2+) over Mg(2+) ions as a cofactor. The Lys(38)-->Arg mutant is severely defective in its interaction with ATP and bivalent cations and somewhat defective in catalytic rate for R2 phosphorylation.

Stimulant-free preculture in heterologous serum-supplemented medium induces unresponsiveness of T cells to subsequent mitogenic stimulation

Quite often freshly isolated lymphocytes are kept in culture before experimentation for 1 or more days without any stimulus. Most of the time, culture is supplemented with fetal bovine serum (FBS) which is heterologous to all species except bovine. In the present study, we found that freshly isolated murine T cells show a good proliferative response to concanavalin A (Con A) and phorbol ester (PMA)/ionomycin in FBS medium, without any detectable background proliferation. However, the cells kept in the same culture without any stimulus for prolonged period of time (referred to as preculture in this report) showed reduced response to Con A and PMA/ionomycin in a time-dependent manner. Almost a complete loss of response to Con A was observed within 1 day of preculture. However, loss of response to PMA/ionomycin was observed only after 2 days of preculture. Interestingly, similar preculture in autologous mouse serum-supplemented media did not cause any loss of the response to these mitogens. The loss of responsiveness of T cells during preculture in heterologous serum was irreversible. The heterologous serum-induced unresponsiveness of T cells to these mitogens was also prevented by adding Calphostin C, a specific protein kinase C (PKC) inhibitor, during preculture in heterologous serum. These results showed that prolonged stimulant-free preculture in heterologous serum induces irreversible unresponsiveness of T cells to mitogens through the down regulation of T cell receptor signaling pathway, which can be prevented by autologous serum or a PKC inhibitor.

GSH transport in human cerebrovascular endothelial cells and human astrocytes: evidence for luminal localization of Na+-dependent GSH transport in HCEC

The purpose of the present study was to identify and localize glutathione (GSH) transport in an in vitro tissue culture model of blood-brain barrier (BBB). The localization of Na+-dependent GSH transport in an immortalized cell line of human cerebrovascular endothelial cells (HCEC) and asymmetry of transport in Transwell studies were investigated. Initial studies with cultured HCEC established a significant (45%) Na+-dependency for GSH uptake in cultured HCEC pretreated with acivicin, an inhibitor of gamma-glutamyltranspeptidase (GGT). Transendothelial electrical resistance (TEER) and uptake of [35S]GSH from luminal and abluminal fluids of HCEC were measured in Na+-containing and Na+-free (choline chloride) buffers using cells grown on gelatin-coated membrane filters. TEER of HCEC monolayers in regular medium was 40.1 +/- 8.0 ohms cm2. Human astrocyte-conditioned medium (ACM) caused no change in TEER, but increased GGT activity approximately threefold when measured in cell lysates. Luminal and abluminal GSH uptake increased in a time-dependent fashion and were not affected by inhibition of GGT activity with acivicin. Sodium dependency was only observed for luminal uptake (Na+-containing 2.41 +/- 0.15 vs. Na+-free 0.96 +/- 0.03 pmol/30 min/million cells, p < 0.001) but not for abluminal uptake (1.02 +/- 0.13 vs. 1.11 +/- 09, p > 0.05). Apparent efflux via the luminal membrane was lower in the presence of sodium as compared to that without sodium, further suggesting that a Na+-dependent uptake process for GSH is operative at this membrane. GSH uptake and efflux were also demonstrated in neonatal rat and fetal human astrocytes, both exhibiting partial Na+-dependency of uptake. In conclusion, our results show for the first time, that HCEC and astrocytes take up GSH by both Na+-dependent and -independent mechanisms. The Na+-dependent GSH transport process in HCEC appears to be localized to luminal plasma membranes of HCEC.

[8-(Diethylamino)octyl-3,4,5-trimethoxybenzoate, HCl], the inhibitor of intracellular calcium mobilization, blocked mitogen-induced T cell proliferation by interfering with the sustained phase of protein kinase C activation

The physiological role of IP(3)-dependent Ca(2+) release in T cell activation was in question due to the contradictory findings that [8-(Diethylamino)octyl-3,4,5-trimethoxybenzoate, HCl] (TMB-8), an inhibitor of intracellular Ca(2+) mobilization, blocked T cell proliferation, curtailing specifically the level of released Ca(2+) did not affect T cell activation and T cell line lacking IP(3) receptor was defective in IL-2 production in response to TCR/CD3 ligand. In the present study we found that TMB-8 inhibited Concanavalin A (Con A)- but not PMA/Ionomycin-induced T cell proliferation in a reversible and dose-dependent manner. The kinetic study revealed that TMB-8 exerted the inhibitory effect at a very early step of T cell activation. The Ca(2+) ionophore ionomycin augmented instead of overcoming the inhibitory effect of TMB-8, although the same doses of ionomycin alone had no effect on Con A-induced T cell proliferation. PMA the metabolically stable, but not diacylglycerol (DAG) the metabolically labile, activator of protein Kinase C (PKC) completely overcome the antiproliferative effect of TMB-8. A specific DAG lipase inhibitor RHC80267 also overcome the effect of TMB-8. Taken together, these results showed that the process of Ca(2+) release through IP(3) receptor, not the released Ca(2+), is essential for the sustained phase of PKC activation during T cell proliferation.

Relative roles of T-cell receptor ligands and interleukin-2 in driving T-cell proliferation

Stimulation of T cells by the T-cell receptor (TCR)/CD3 complex results in interleukin-2 (IL-2) synthesis and surface expression of the IL-2 receptor (IL-2R), which in turn drive T-cell proliferation. However, the significance of the requirement of IL-2 in driving T-cell proliferation, when TCR stimulation itself delivers potential mitogenic signals, is unclear. We show that blocking of IL-2 synthesis by Cyclosporin A (CsA) suppressed both the Concanavalin A (Con A)- and phorbol myristate acetate (PMA)/ionomycin-induced proliferation of T cells. The latter is also inhibited by anti-IL-2R. Kinetic studies showed that T-cell proliferation begins to become resistant to CsA inhibition by about 12 h and became largely resistant by 18 h of stimulation. PMA, the protein kinase C activator, enhanced Con A-induced T-cell proliferation if added only within first 12 h of stimulation, and not after that. Given the fact that, in the present study, TCR is downregulated within 2 h of Con A stimulation and T cells entered the S phase of cell cycle by about 18 h of stimulation, the above results suggest that TCR stimulation provides the initial trigger to the resting T cells, which allows the cells to traverse the first two third portions of G1 phase of cell cycle and become proliferation competent. IL-2 action begins afterward, delivering the actual proliferation signal(s), allowing the cells to traverse the rest of G1 phase and enter the S phase of the cell cycle.

Studies on the euglycemic and hypolipidemic potentials of the novel indole analogue of thiazolidinedione, DRF 2189

Euglycemic and hypolipidemic activities of a novel indole analogue of thiazolidinedione, DRF 2189 (CAS 172647-53-9), have been evaluated in different animal models. Compared to troglitazone (CAS 97322-87-7), DRF 2189 exhibited interesting plasma glucose and triglyceride lowering activity in genetically diabetic and obese db/db mice. It also produced a significant reduction in plasma glucose, triglyceride, total cholesterol levels and improvement in oral glucose tolerance in another genetic mouse model, the ob/ob mice. In high-fat diet fed Sprague-Dawley rats, DRF 2189 treatment showed improvement in plasma lipid parameters. Like other thiazolidinediones, this compound also possesses peroxisome proliferator activated receptor gamma (PPAR gamma) transactivation potential. In anaesthetized rat experiment, DRF 2189 produced a transient fall in blood pressure without any change in the ECG pattern. It showed non-specific smooth muscle relaxant activity against acetylcholine, histamine and potassium chloride induced contractions in isolated guinea pig ileum. A twenty-eight-day toxicity study in Wistar rats did not show any signs of treatment related adverse effects. The overall antidiabetic and hypolipidemic activities of DRF 2189 are comparable with rosiglitazone (CAS 155141-29-0) and superior to troglitazone. In conclusion, results from these preclinical studies indicate that DRF 2189, a novel thiazolidinedione, has a marked potential for the management of type-2 diabetes.

Novel euglycemic and hypolipidemic agents. 4. Pyridyl- and quinolinyl-containing thiazolidinediones

A series of substituted pyridyl- and quinolinyl-containing 2, 4-thiazolidinediones having interesting cyclic amine as a linker have been synthesized. Both unsaturated thiazolidinediones 5 and saturated thiazolidinediones 6 and their various salts were evaluated in db/db mice for euglycemic and hypolipidemic effects and compared with BRL compound 11 and BRL-49653, respectively. Some of the potent compounds were converted to various salts in order to obtain improved activities. Among all the salts evaluated, the maleate salt of unsaturated TZD 5a was found to be a very potent euglycemic and hypolipidemic compound. Some of the more interesting compounds have also been evaluated in ob/ob mice and compared with rosiglitazone (maleate salt of BRL-49653). Oral glucose tolerance tests were performed in both db/db and ob/ob mice. Pharmacokinetic studies of 5a maleate are also reported. Receptor binding studies of PPARgamma by 5a/5a maleate did not show any significant transactivation of PPARalpha or PPARgamma.

Novel antidiabetic and hypolipidemic agents. 3. Benzofuran-containing thiazolidinediones

Several thiazolidinedione derivatives having 5-hydroxy-2,3-dihydro-2, 2,4,6,7-pentamethylbenzofuran moieties and their 5-benzyloxy derivatives and 5-hydroxy-2,4,6,7-tetramethylbenzofuran moieties were synthesized and evaluated in db/db mice. Insertion of an N-Me group into the linker between thiazolidinedione and substituted benzofuran pharmacophores showed considerable improvement in their euglycemic activity. Further improvement has been observed when a pyrrolidine moiety is introduced in the structure to give 5-[4-[N-[3(R/S)-5-benzyloxy-2,3-dihydro-2,2,4,6, 7-pentamethylbenzofuran-3-ylmethyl]-(2S)-pyrrolidin-2- ylmethoxy]pheny lene]thiazolidine-2,4-dione (21a). At a 100 mg/kg/day dose of the maleate salt, compound 21a reduced the plasma glucose and triglyceride to the level of lean littermate, i.e. 8 +/- 1 mM, and is the most potent and efficacious compound reported in this series.

Comparison of growth factor expression in fetal and adult fibroblasts: a preliminary report

BACKGROUND

Fetal wounds can heal without any histological evidence of scarring. Fetal wounds lack the inflammatory infiltrate characteristic of adult wounds, and the fetal environment is not necessary for scarless healing to occur. Recent evidence suggests that fibroblasts are the main effector of scarless healing in fetal tissue. What has not been shown is what profile of growth factors the fibroblast uses to influence wound repair.

OBJECTIVE

To determine the expression of growth factors (transforming growth factors beta1, beta2, and beta3; acidic and basic fibroblast growth factors; keratinocyte growth factor; and platelet-derived growth factor AA, BB, and AB) of fetal and adult fibroblasts in vitro.

DESIGN

Adult and fetal fibroblasts were grown in culture, and messenger RNA was extracted by standard techniques. Northern hybridization was used to identify messenger RNA transcripts for the aforementioned growth factors. Densitometry was used to compare growth factor messenger RNA expression with that of a ubiquitously expressed control, glyceraldehyde phosphate dehydrogenase.

RESULTS

The data suggest that fetal and adult fibroblasts express acidic and basic fibroblast growth factor and transforming growth factor beta1. Adult fibroblasts show twice the relative expression of these growth factors compared with fetal fibroblasts.

CONCLUSIONS

The adult fibroblasts demonstrate a relative excess production of cytokines compared with fetal fibroblasts. This is thought to contribute to suboptimal wound healing in adult wounds compared with the scarless healing of fetal wounds.

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.