O6C-20-nor-salvinorin A is a stable and potent KOR agonist

Salvinorin A (SalA) is a potent and selective agonist of the kappa-opioid receptor (KOR), but its instability has frustrated medicinal chemistry efforts. Treatment of SalA with weak bases like DBU leads to C8 epimerization with loss of receptor affinity and signaling potency. Here we show that replacement of C20 with H and replacement of O6 with CH₂ stabilizes the SalA scaffold relative to its C8 epimer, so much so that epimerization is completely supressed. This new compound, O6C-20-nor-SalA, retains high potency for agonism of KOR.     

Long-term results of long-acting luteinizing-hormone-releasing hormone agonist in central precocious puberty.

Thirty children with precocious puberty (24 girls aged 6.5 +/- 2.3 years and 6 boys aged 7 +/- 2.9 years) were treated over 5 years with Decapeptyl. In girls, the menses disappeared, breast enlargement regressed, and uterus and ovary sizes returned to prepubertal values. In boys, a significant decrease of testicular size was observed. Plasma levels of estradiol and testosterone, and basal and post-luteinizing hormone (LH)-releasing hormone (LHRH) LH and follicle-stimulating hormone (FSH) remained in the prepubertal range. Growth velocity decreased after 1 year from 9.7 +/- 3.5 to 5.5 +/- 1.3 cm/year, while the height age/bone age ratio was normalized in both sexes after 3 years. In 15 girls, Decapeptyl was interrupted after 2.3 years. During those 2.3 years, bone age increased from 11.6 +/- 0.8 to 12.5 +/- 0.7 years with a growth velocity of 5.3 +/- 1.8 cm/year. During the year following interruption, height increased from 152.2 +/- 4.9 to 157.7 +/- 4.9 cm (growth velocity 5.5 cm/year) and bone age from 12.5 +/- 0.7 to 13.5 +/- 0.6 years. One year after treatment, plasma levels of estradiol were 106.7 +/- 84.7 pg/ml, of LH, 25.5 +/- 17.6 mIU/ml, and of FSH, 10.8 +/- 5.9 mIU/ml. Menses appeared in 13 girls. Moreover, 18 months after interruption, bone age was 13.9 +/- 0.6 years and height 159.5 +/- 5.2 cm, being significantly superior to the final height of a historical control group: 151.5 +/- 4.8 cm (p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)     

The psoriasis drug monomethylfumarate is a potent nicotinic acid receptor agonist

Nicotinic acid has been used for several decades to treat dyslipidemia. In mice, the lipid-lowing effect of nicotinic acid is mediated by the Gi coupled receptor PUMA-G. In humans, high (GPR109A) and low (GPR109B) affinity nicotinic acid receptors have been characterized. Here we identify monomethylfumarate as a GPR109A agonist. Monomethylfumarate is the active metabolite of the psoriasis drug Fumaderm. We show that monomethylfumarate activates GPR109A in a calcium based aequorin assay, cAMP assay and demonstrate competitive binding with nicotinic acid. We show that GPR109A is highly expressed in neutrophils and epidermal keratinocytes, and that its expression is increased in human psoriatic lesions. Our findings provide evidence that GPR109A is a target for the drug Fumaderm and suggest that niacin should be investigated to treat psoriasis in addition to its role in treating lipid disorders.     

Adenosine: A partial agonist of the growth hormone secretagogue receptor

The growth hormone secretagogue receptor (GHS-R) is involved in the regulation of pulsatile GH release. However, until recently, natural endogenous ligands for the receptor were unknown. We fractionated porcine hypothalamic extracts and assayed fractions for activity on HEK293 cells expressing GHS-R and aequorin. A partial agonist was isolated and identified using microspray tandem mass spectrometry as adenosine. GHS-R activation by adenosine and synthetic adenosine agonists is inhibited by the GHS-R selective antagonists L-765,867, D-Lys(3)-GHRP-6, and by theophylline and XAC. Cross desensitization of the GHS-R occurs with both MK-0677 and adenosine. Ligand binding and site directed mutagenesis studies show that adenosine binds to a binding site that is distinct from the previously characterized MK-0677 and GHRP-6 binding pocket. We propose, that adenosine is a physiologically important endogenous GHS-R ligand and speculate that GHS-R ligands modulate dopamine release from hypothalamic neurons.     

Semirational design of a potent, artificial agonist of fibroblast growth factor receptors

Fibroblast growth factors (FGFs) are being investigated in human clinical trials as treatments for angina, claudication, and stroke. We designed a molecule structurally unrelated to all FGFs, which potently mimicked basic FGF activity, by combining domains that (1) bind FGF receptors (2) bind heparin, and (3) mediate dimerization. A 26-residue peptide identified by phage display specifically bound FGF receptor (FGFR) 1c extracellular domain but had no homology with FGFs. When fused with the c-jun leucine zipper domain, which binds heparin and forms homodimers, the polypeptide specifically reproduced the mitogenic and morphogenic activities of basic FGF with similar potency (EC50 = 240 pM). The polypeptide required interaction with heparin for activity, demonstrating the importance of heparin for FGFR activation even with designed ligands structurally unrelated to FGF. Our results demonstrate the feasibility of engineering potent artificial agonists for the receptor tyrosine kinases, and have important implications for the design of nonpeptidic ligands for FGF receptors. Furthermore, artificial FGFR agonists may be useful alternatives to FGF in the treatment of ischemic vascular disease.     

The erythromycin derivative EM-523 is a potent motilin agonist in man and in rabbit

Erythromycin may stimulate gastrointestinal motor activity via its effect upon motilin receptors. We have studied the ability of the derivative EM-523 [de(N-methyl)-N-ethyl-8,9-anhydroerythromycin A 6,9-hemiacetal] to induce contractions in duodenal smooth muscle strips and to displace labeled motilin bound to antral smooth muscle, in man and in rabbit. In both species EM-523 approached the potency of motilin for inducing contractions. Thus pED50 values were 7.84 +/- 0.11 and 8.69 +/- 0.12 for motilin in, respectively, man and rabbit, against 6.08 +/- 0.13 and 8.19 +/- 0.10 for EM-523. In rabbit the efficacy of both compounds decreased in parallel aborally, the responses to EM-523 could not be blocked by atropine (10(-7) M) or TTX (10(-7) M), and both compounds were unable to further enhance the maximum effect to the other compound. In binding studies the order of potency was the same as in the contraction studies. The pIC50 values were: motilin (8.84 +/- 0.31, 9.17 +/- 0.20) greater than EM-523 (7.89 +/- 0.1, 8.40 +/- 0.10). A Schild plot revealed that EM-523 was a competitive inhibitor of motilin receptor binding in man and in rabbit. We conclude that EM-523 is a potent motilin agonist.     

Inhibition of testicular luteinizing hormone receptor level by treatment with a potent luteinizing hormone-releasing hormone agonist of human chorionic gonadotropin.

Two proteins larger than proinsulin (estimated molecular weight 11,000 and 10,000 daltons), were observed when labeled rat islet proteins were electrophoresed on sodium dodecyl sulfate gels. The proteins are synthesized before proinsulin, turn over more rapidly than proinsulin, their synthesis is stimulated by glucose, and they are specifically bound by anti-insulin antibodies.     

The synthetic peptide Trp-Lys-Tyr-Met-Val-D-Met is a potent chemotactic agonist for mouse formyl peptide receptor

Formyl peptides are potent neutrophil chemoattractants. In humans and rabbits, the formyl peptide receptor (FPR) binds N-formyl-Met-Leu-Phe (fMLF) with high affinity (K(d) approximately 1 nM). The mouse FPR (mFPR) is a low-affinity receptor for fMLF (K(d) approximately 100 nM); therefore, other agonists for this receptor may exist. Using mFPR-transfected rat basophilic leukemia cells, we found that a recently identified synthetic peptide Trp-Lys-Tyr-Met-Val-D-Met (WKYMVm) is a potent agonist for mFPR. WKYMVm induced calcium mobilization with an EC(50) of 1.2-1.5 nM. Optimal chemotaxis was achieved with 1 nM of WKYMVm, but it required 100 nM of fMLF. WKYMVm stimulated rapid and potent phosphorylation of the mitogen-activated protein kinases extracellular signal-related kinases 1 and 2 when used at 50 nM. Pertussis toxin only partially blocked calcium mobilization and production of inositol 1,4,5-trisphosphate in the stimulated mFPR cells, suggesting the possibility that this receptor couples to Galpha proteins other than Gi and Go. Competitive binding and desensitization data suggest that both peptides interact with the same receptor but may use nonoverlapping binding sites because WKYMVm was unable to effectively displace [(3)H]fMLF bound to mFPR. These results provide evidence for the presence of an alternative potent agonist for mFPR, and suggest a potential usage of WKYMVm for probing the ligand-receptor interactions with the murine formyl peptide receptor homologs.     

Equilibrium denaturation of human growth hormone and its cysteine-modified forms

The equilibrium denaturation of human growth hormone (hGH) derived from heterologous gene expression in Escherichia coli was studied. Denaturation was measured by ultraviolet absorbance, intrinsic fluorescence, far ultraviolet circular dichroism, and size exclusion chromatography. The denaturation transitions obtained from each method of detection were coincident, indicating a two-state denaturation mechanism. The denaturation transitions were independent of the concentration of protein. The Gibbs free energy of unfolding is 14.5 +/- 1 kcal/mol. Human growth hormone contains two disulfide bridges between residues 53-165 (large loop) and 182-189 (small loop). The small loop was selectively reduced and cysteines alkylated with iodoacetic acid or iodoacetamide. The tetra-S-carbamidomethylated and tetra-S-carboxymethylated derivatives were also prepared. All S-alkylated hGH forms were indistinguishable from the native conformations in the absence of denaturant by far ultraviolet circular dichroism. The circular dichroism-detected equilibrium denaturation of each derivative was determined and the Gibbs free energy of unfolding of the tetra-S-modified forms was 5.3 +/- 0.5 kcal/mol and of the di-S-alkylated derivatives was 11.2 +/- 0.8 kcal/mol. These results for hGH are different than previously obtained results for bovine, ovine, and rat growth hormones. Stable equilibrium intermediates have been identified for these non-human species of growth hormone. The stable intermediates observed in the denaturation of reduced, alkylated hGH or nonhunam growth hormones are similar and characterized as compact, helical, lacking native-like tertiary structure, and having a tendency to aggregate. The apparent absence of intermediates in the folding of oxidized hGH is due to the relative instability of intermediates compared with their native structures. The hGH conformation is at least 5 kcal/mol more stable than the growth hormones from other species. Reduction and alkylation of the disulfide bridges of hGH diminish the stability differences between the native and intermediate states, such that the denaturation behavior is similar to the nonhuman growth hormones with well-populated intermediates. Most proteins do not demonstrate equilibrium folding intermediates presumably because intermediates are only marginally stable in conditions that disrupt the native state. The folding results with hGH and alkylated hGH substantiate this.     

Hepatocyte growth factor is a potent stimulator of human melanocyte DNA synthesis and growth.

Hepatocyte growth factor (HGF) is a potent mitogen for adult rat hepatocytes in primary culture. HGF stimulates growth and DNA synthesis of normal human epidermal melanocytes in culture. The maximal stimulation of DNA synthesis by 4.0-fold occurred with 10 ng/ml HGF. This stimulatory effect was additive with both acidic and basic fibroblast growth factors, while it was inhibited by transforming growth factor-beta 1. Melanocytes expressed a single class of specific, high-affinity receptors for HGF with a Kd of 22 pM and approximately 120 receptors/cell. Thus, HGF is a potent mitogen for normal human epidermal melanocytes.     

Bad is a BH3 domain-containing protein that forms an inactivating dimer with Bcl-XL.

The Bcl-2 related protein Bad is a promoter of apoptosis and has been shown to dimerize with the anti-apoptotic proteins Bcl-2 and Bcl-XL. Overexpression of Bad in murine FL5.12 cells demonstrated that the protein not only could abrogate the protective capacity of coexpressed Bcl-XL but could accelerate the apoptotic response to a death signal when it was expressed in the absence of exogenous Bcl-XL. Using deletion analysis, we have identified the minimal domain in the murine Bad protein that can dimerize with Bcl-xL. A 26-amino-acid peptide within this domain, which showed significant homology to the alpha-helical BH3 domains of related apoptotic proteins like Bak and Bax, was found to be necessary and sufficient to bind Bcl-xL. To determine the role of dimerization in regulating the death-promoting activity of Bad and the death-inhibiting activity of Bcl-xL, mutations within the hydrophobic BH3-binding pocket in Bcl-xL that eliminated the ability of Bcl-xL to form a heterodimer with Bad were tested for the ability to promote cell survival in the presence of Bad. Several of these mutants retained the ability to impart protection against cell death regardless of the level of coexpressed Bad protein. These results suggest that BH3-containing proteins like Bad promote cell death by binding to antiapoptotic members of the Bcl-2 family and thus inhibiting their survival promoting functions.     

Ascorbic acid is a potent inhibitor of various forms of T cell apoptosis.

This study was designed to examine the effect of ascorbic acid (vitamin C) on various death pathways of mouse T cells. Unlike humans, mice produce their own ascorbic acid and our study tested the effect of additional ascorbic acid on murine T cells. Our data show that three T cell death pathways (growth factor withdrawal-, spontaneous-, and steroid-induced death) were inhibited when T cells were incubated with ascorbic acid. The data show that both activated and resting T cells were responsive to ascorbic acid since both populations were resistant to death stimuli when treated with ascorbic acid. Additionally, effector T cells were more likely to enter S phase if treated with ascorbic acid. Our data implicate ascorbic acid as a potent inhibitor of various forms of T cell death and suggest that vitamin C may function as an immune booster through this mechanism.     

Model for growth hormone receptor activation based on subunit rotation within a receptor dimer

Growth hormone is believed to activate the growth hormone receptor (GHR) by dimerizing two identical receptor subunits, leading to activation of JAK2 kinase associated with the cytoplasmic domain. However, we have reported previously that dimerization alone is insufficient to activate full-length GHR. By comparing the crystal structure of the liganded and unliganded human GHR extracellular domain, we show here that there is no substantial change in its conformation on ligand binding. However, the receptor can be activated by rotation without ligand by inserting a defined number of alanine residues within the transmembrane domain. Fluorescence resonance energy transfer (FRET), bioluminescence resonance energy transfer (BRET) and coimmunoprecipitation studies suggest that receptor subunits undergo specific transmembrane interactions independent of hormone binding. We propose an activation mechanism involving a relative rotation of subunits within a dimeric receptor as a result of asymmetric placement of the receptor-binding sites on the ligand.     

Sargassum fusiforme fraction is a potent and specific inhibitor of HIV-1 fusion and reverse transcriptase

Background

Hepatitis C virus (HCV) circulates in an infected individual as a heterogeneous mixture of closely related viruses called quasispecies. The E1/E2 region of the HCV genome is hypervariable (HVR1) and is targeted by the humoral immune system. Hepatitis C virions are found in two forms: antibody associated or antibody free. The objective of this study was to investigate if separation of Hepatitis C virions into antibody enriched and antibody depleted fractions segregates quasispecies populations into distinctive swarms.

Results

A HCV genotype 4a specimen was fractionated into IgG-depleted and IgG-enriched fractions by use of Albumin/IgG depletion spin column. Clonal analysis of these two fractions was performed and then compared to an unfractionated sample. Following sequence analysis it was evident that the antibody depleted fraction was significantly more heterogeneous than the antibody enriched fraction, revealing a unique quasispecies profile. An in-frame 3 nt insertion was observed in 26% of clones in the unfractionated population and in 64% of clones in the IgG-depleted fraction. In addition, an in-frame 3 nt indel event was observed in 10% of clones in the unfractionated population and in 9% of clones in the IgG-depleted fraction. Neither of these latter events, which are rare occurrences in genotype 4a, was identified in the IgG-enriched fraction.

Conclusion

In conclusion, the homogeneity of the IgG-enriched species is postulated to represent a sequence that was strongly recognised by the humoral immune system at the time the sample was obtained. The heterogeneous nature of the IgG-depleted fraction is discussed in the context of humoral escape.     

Isolation of dimeric forms of human pituitary growth hormone

A procedure is described which for the first time allows the isolation of noncovalently-linked dimeric human pituitary growth hormone. Isomers of this dimeric species were prepared as were also, for the first time, isomers of covalently-linked dimers. Chromatography on DEAE-Sepharose CL-6B revealed the existence of noncovalently-linked dimers composed of monomers of 22K hGH, 20K hGH and 20K1 hGH (the latter is a new form of 20K hGH with a scission in the peptide chain) and covalent dimers containing 22K hGH and 24K hGH (the latter a 22K hGH with a scission). The different dimers all occurred as charge isomers and subsequent HPLC on an anion exchanger followed by zone electrophoresis in agarose suspension made possible the isolation of four noncovalently-linked isomers: one form of (20K-20K)hGH, two forms of (20K-22K)hGH and one form of (22K-22K)hGH; and of three covalently-linked isomers: one form of (22K-22K)hGH and two forms of (22K-24K)hGH.