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Biomedical subjects

J J Nestor

Publications and source records attributed to J J Nestor.

At least 19 recordsLinked to original sources
PubMed1994

A new gonadotropin-releasing hormone (GnRH) superagonist in goldfish: influence of dialkyl-D-homoarginine at position 6 on gonadotropin-II and growth hormone release.

The two native forms of gonadotropin-releasing hormones (GnRH) present in goldfish, salmon GnRH (sGnRH) and chicken GnRH-II (cGnRH-II), stimulate gonadotropin-II (GTH-II) and growth hormone (GH) release both in vivo and in vitro. In our previous study using perifused goldfish pituitary fragments, many mammalian GnRH antagonists, especially those with D-Arg6, showed weak to strong stimulation of GTH-II and GH release. In the present study, the dose-related stimulation of GTH-II and GH release by [Ac-D(2)-Nal1, 4Cl-D-Phe2, D-Trp3, D-Arg6, Trp7, D-Ala10] mGnRH (analog J) and [Ac-D(2)-Nal1, 4Cl-D-Phe2, D-Trp3, D-hArg(Et2)6, D-Ala10] mGnRH (analog K) was demonstrated; the stimulatory potency of both analogs was significantly lower than that of native sGnRH. In the presence of analogs J and K, cGnRH-II stimulated GTH-II release was significantly suppressed. Further, GTH-II and GH stimulation by 2 microM of analog K was significantly suppressed by a 'true' GnRH antagonist, [Ac-delta 3-Pro1, 4FD-Phe2, D-Trp3,6] mGnRH (analog E). These results indicate that analogs J and K increase GTH-II and GH release in goldfish by acting on GnRH receptors on gonadotrophs and somatotrophs. Since analog K, having [D-hArg(Et2)6], strongly stimulated GTH-II release, the potency of [D-hArg(Et2)6] or [D-hArg(CH2CF3)2(6)] substituted analogs to stimulate GTH-II and GH release from the perifused goldfish pituitary fragments was tested. Among the peptides tested, [D-hArg(Et2)6, Pro9-NHEt] sGnRH had a higher potency in stimulating GTH-II release than any other analog tested in the present or in previous studies. For stimulation of GH release, [D-hArg(Et2)6, Pro9-NHEt] sGnRH and [D-Arg6, Pro9-NHEt] sGnRH were the most potent analogs tested; analogs of mGnRH were less potent than sGnRH, indicating the importance of Trp7, Leu8 residues in the native peptide. These results suggest the importance of [D-Arg6] or alkylated [D-Arg6] in determining the intrinsic activity and potency of GnRH peptides in goldfish.

Amino Acid Sequence↗
PubMed1993

Therapeutic effects of a synthetic peptide of C-reactive protein in pre-clinical tumor models.

Previous studies have shown that multilamellar vesicles (MLV) or other carriers containing purified human C-reactive protein (CRP) have therapeutic activity in preclinical tumor models. Here we evaluated the therapeutic effects of MLV containing novel synthetic peptides, derived from the structure of CRP, on the extent of (a) established lung metastases of fibrosarcoma T241 in C57Bl/6 mice, (b) survival of C57Bl/6 mice bearing established liver metastases of colon carcinoma MCA-38, and (c) primary tumor growth of Renca renal carcinoma in Balb/c mice. In all cases, a single synthetic CRP peptide, RS-83277, demonstrated significant antitumor effects comparable to that seen with intact CRP. Two other synthetic CRP peptides, RS-83287 and RS-83147, showed no therapeutic activity and were comparable to control MLV containing only buffer. None of the peptides contained sequences homologous with that of the phagocyte stimulant, tuftsin. Activity of MLV-encapsulated RS-83277 was dose-dependent, and a comparable dose of the soluble peptide, given either alone or following injection of buffer-MLV, was ineffective. These results demonstrate immunotherapeutic potential for a novel synthetic peptide derived from CRP, and endogenous acute-phase protein.

Adenocarcinoma↗
PubMed1992

Potent gonadotropin releasing hormone antagonists with low histamine-releasing activity.

The incorporation of Arg residues into position 6 of gonadotropin releasing hormone antagonists had resulted in compounds with increased in vivo potency but also made these analogues potent mast cell degranulators. We have focused on the substitution of position 8 by hArg(R)2 (NG,NG'-dialkylhomoarginine) substitutions, based on the hypotheses that the Arg-Pro sequence is of major importance for this side effect and that shielding of the charge may be an effective way to block degranulation. Analogues in four series were evaluated: (A) [N-Ac-D-Nal(2)1,D-pCl-Phe2,D-Pal-(3)3,6,Arg5,hArg(R)2(8),D-+ ++Ala10]GnRH, (B) [N-Ac-D-Nal(2)1,D-pCl-Phe2,D-Pal(3)3,6,hArg(R)2(5,8),D-Ala10 ]-GnRH, (C) [N-Ac-D-Nal(2)1,D-pCl-Phe2,D-Pal(3)3,6,hArg(R)2(8),D-Ala10]G nRH, (D) [N-Ac-D-Nal(2)1,D-pCl-Phe2,D-Pal(3)3,D-hArg(R)2(6),hArg(R)2( 8),D-Ala10]GnRH. Although substitution by hArg(Et)2, hArg(Bu), hArg(CH2)3, and hArg(CH2CF3)2 was tested, in each series the hArg(Et)2 residue was superior. Two compounds were considered for clinical evaluation: [N-Ac-D-Nal(2)1,D-pCl-Phe2,D-Pal(3)3,6,hArg(Et)2(8),D-Ala10] GnRH and [N-Ac-D-Nal(2)1,D-pCl-Phe2,D-Pal(3)3,D-hArg(Et)2(6),hArg(Et) 2(8),D- Ala10]GnRH (ganirelix acetate). These compounds had high potency for ovulation suppression and low histamine-releasing potency in vitro (ED50 = 0.6, 0.29 microgram/rat and EC50 = 196, 13 micrograms/mL, respectively). Ganirelix is currently in Phase II clinical trials and appears to be the most potent GnRH antagonist tested in humans (based upon ED50 for 24-h suppression of testosterone levels).

Amino Acid Sequence↗
PubMed1990

Characterization of beta-amyloid precursor proteins with or without the protease-inhibitor domain using anti-peptide antibodies.

Alternative splicing of the transcript encoding the beta-amyloid precursor protein (BAPP) of Alzheimer's disease produces multiple mRNA species. Translation of these mRNAs predicts protein products of 770, 751, and 695 amino acids. The difference arises from the inclusion in BAPP-770/751 of a 56-residue insert region which is homologous to Kunitz-type protease inhibitors. We have prepared and affinity-purified anti-peptide antibodies that react specifically with either BAPP-770/751 (insert-specific) or BAPP-695 (junction-specific). A detectable level of the mRNA corresponding to the BAPP-770/751 protein was found in all cell lines tested. Immunoprecipitation of 35S-labeled proteins from these cell lines showed them to contain one or two Mr 105,000 bands reactive with the insert-specific serum, i-291. In contrast, only cos-7 cells and the human neuroblastoma cell line, IMR-32, contained mRNA species that encode the BAPP-695 protein, as shown by Northern analysis with a junction-spanning oligonucleotide probe. A band of Mr 95,000 was immunoprecipitated specifically from these two cell lines using the junction-specific serum, J-284. Indirect immunofluorescence labeling of cells corroborated these findings. All cells reacted with the insert-specific antibodies, i-291 and i-324. Only cos-7 and IMR-32 cells reacted with the junction-specific antibody, J-284. These results demonstrate the usefulness of anti-peptide antibodies for the differential detection of the BAPP-695 and BAPP-770/751 proteins.

Alzheimer Disease↗
PubMed1989

Comparative studies on the hypotensive effect of LHRH antagonists in anesthetized rats.

Certain neuropeptides are known to cause a hypotensive response, thought to be due to mast cell degranulation. The effects of five antagonists of luteinizing hormone-releasing hormone on blood pressure and heart rate were compared in the anesthetized rat. When given intravenously, all five compounds induced hypotensive and bradycardiac effects. The order of potency for these effects was Nal-Arg Antagonist approximately detirelix [( N-Ac-D-Nal(2)1, D-pCl-Phe2,D-Trp3,D-hArg(Et2)6,D-Ala10]LHRH) greater than [N-Ac-D-Nal(2)1, D-pCl-Phe2,D-Pal(3)3,D-hArg(Et2)6,L-hArg (Et2)8,D-Ala10]LHRH (RS-26306) approximately antide greater than [N-Ac-D-Nal(2)1, D-pCl-Phe2,D-Pal(3)3,6, L-hArg(Et2)8,D-Ala10]LHRH (RS-15378) and did not parallel the order of antiovulatory potencies of these compounds. The hypotensive activity of LHRH antagonists, therefore, appeared dissociable from their antiovulatory activity. RS-26306 and RS-15378 appeared to have the greatest therapeutic ratios.

Animals↗
PubMed1988

Studies of the biological activity of LHRH analogs in the rainbow trout, landlocked salmon, and the winter flounder.

Studies of gonadotropic hormone (GtH) release bioactivity by mammalian and submammalian varieties of LHRH and LHRH analog were primarily conducted in vivo in testosterone-primed yearling (TPY) rainbow trout, a convenient test animal for LHRH bioassays in fish. Validation of these results, using sexually mature fish, was accomplished by examining LHRH agonist activities on release of GtH in vivo in spermiating landlocked salmon and by studying LHRH peptide hormone binding affinities using a flounder pituitary LHRH radioreceptor assay. Our surveys of LHRH analog bioactivity in vivo in TPY trout and salmon demonstrated that all types of fish, bird, and mammalian LHRH agonists possess superactive properties on the fish pituitary. The most active group of LHRH analogs, based upon both LHRH receptor binding affinity and in vivo release of gonadotropin, was judged to include [D-Nal(2)6,Pro9-NHEt]LHRH, [D-Nal(2)6-AzaGly10]LHRH, [D-Ala6,Pro9-NHEt]-LHRH, and the fish LHRH analogs, [D-Arg6,Trp7,Leu8,Pro9-NHEt]LHRH, [D-hArg(Et2(6),Trp7,Leu8,Pro9-NHEt]LHRH.

Animals↗
PubMed1988

Potent, long-acting luteinizing hormone-releasing hormone antagonists containing new synthetic amino acids: N,N'-dialkyl-D-homoarginines.

A new series of unnatural amino acids has been prepared and incorporated into antagonistic analogues of luteinizing hormone-releasing hormone (LH-RH), on the basis of the hypothesis that stabilization of a proposed phospholipid membrane interaction might yield analogues with high potency and a prolonged duration of action. Thus a series of NG,NG'-dialkyl-D-homoarginine analogues [H-D-hArg(R2)-OH; R = Me, Et, Pr, i-Pr, Bu, hexyl, cyclohexyl, (Et, Me2NPr)] was conveniently prepared by semisynthesis from D-Lys using the appropriate dialkylcarbodiimide. A number of the analogues that were prepared by using these new amino acid analogues exhibited very high potency and a prolonged duration of action. One of the most potent members of the series, [N-Ac-D-Nal(2)1,D-pCl-Phe2,D-Trp3,D-hArg(Et2)6,D-Ala10 ]LH-RH (detirelix), had an ED50 of 0.7 microgram in the rat antiovulatory assay when administered at noon on proestrus and only 2.5 micrograms when administered 24 h earlier, at noon on diestrus II. This antagonist is undergoing detailed biological and clinical evaluation.

Alkylation↗
PubMed1988

"DAKLI": a multipurpose ligand with high affinity and selectivity for dynorphin (kappa opioid) binding sites.

We describe a synthetic ligand, "DAKLI" (Dynorphin A-analogue Kappa LIgand), related to the opioid peptide dynorphin A. A single reactive amino group at the extended carboxyl terminus permits various reporter groups to be attached, such as 125I-labeled Bolton-Hunter reagent, fluorescein isothiocyanate, or biotin. These derivatives have high affinity and selectivity for the dynorphin (kappa opioid) receptor. An incidental finding is that untreated guinea pig brain membranes have saturable avidin binding sites.

Animals↗
PubMed1987

Phosphorylation substrates for protein kinase C in intact pituitary cells: characterization of a receptor-mediated event using novel gonadotropin-releasing hormone analogues.

The involvement of protein kinase C in the signal transduction of gonadotropin-releasing hormone (GnRH) action was investigated with a GnRH superagonist, partial agonists, and antagonists in intact rat pituitary cells. Exposure of 32P-labeled cells to GnRH or to the superagonist [D-Nal(2)6]GnRH (200 times GnRH potency in vivo) induced the enhanced phosphorylation of 42-, 34-, 11-, and 10-kDa proteins and the dephosphorylation of a 15-kDa protein as assessed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis/autoradiography. This effect was blocked in a dose-dependent manner by potent GnRH antagonists. At its maximally effective concentration of 10(-9) M, [D-Nal(2)6]GnRH induced an up to 2 times more pronounced phosphorylation of endogenous substrates than GnRH at 10(-7) M. This was in accord with its ability to cause an 8-fold increase in the translocation of protein kinase C to the particulate fraction vs. 3.4-fold for GnRH. This effect correlated with potency for a series of GnRH agonists ( [D-Nal(2)6]GnRH greater than GnRH greater than [Gly2]LH-RH) and was prevented by GnRH antagonists, as assessed by a novel phorbol ester receptor binding assay and by a standard kinase assay. Downregulation of protein kinase C by prolonged incubation of the pituitary cells with high concentrations of active phorbol esters abolished protein kinase C activity and also prevented the phosphorylation induced by GnRH, or [D-Nal(2)6]GnRH. The same effect was obtained by preincubating the cells with the protein kinase C inhibitor H-7. In this study we identify for the first time physiological substrates for protein kinase C in intact pituitary cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Immuno-enhancing activity of the amino-terminal domain of human prealbumin: isolation, characterization and synthesis.

A decapeptide isolated from highly purified preparations of human prealbumin was able to restore azathioprine (Az) sensitivity, a property of a sub-class of T-lymphocytes, to the spleen rosette-forming cells (RFC) of adult thymectomized (ATx) mice in vitro. The peptide was sequenced by the Edman method and shown to correspond to the ten amino-terminal residues of prealbumin, Gly-Pro-Thr-Gly-Thr-Gly-Glu-Ser-Lys-Cys. Synthesis of this peptide by solid phase methodology confirmed its activity both in vitro and in vivo. Synthesis of a number of structural analogues indicated that the amino-terminal deca, undeca and dodecapeptides of prealbumin as well as some of their derivatives were also able to restore Az sensitivity to RFC in vitro and in vivo. The Cys10 residue and the Glu7 residues both contributed significantly to potency in vitro. Removal of up to three amino acids from the N-terminus of the decapeptide led to a progressive loss of activity. The data indicates that the ability of human prealbumin to restore the Az sensitivity to the RFC of adult Tx mice is intrinsic to the protein and resides in the amino-terminal domain of the molecule.

Amino Acid Sequence↗
PubMed1987

Suppression of luteal function by a luteinizing hormone-releasing hormone antagonist during the early luteal phase in the stumptailed macaque monkey and the effects of subsequent administration of human chorionic gonadotropin.

In previous studies a single sc injection of the LHRH antagonist [N-Ac-D-Nal(2)1,D-pCl-Phe2,D-Trp3,D-hArg(Et2)6,D-Ala10 ]LHRH during the luteal phase of the stumptailed macaque menstrual cycle caused a transient suppression of serum LH and progesterone concentrations. To investigate whether a more prolonged suppression of LH release during the early luteal phase could result in a sustained suppression of progesterone, 10 monkeys were treated with 3 consecutive daily injections of 300 micrograms LHRH antagonist/kg beginning on days 0 (n = 2), 1 (n = 1), 2 (n = 1), 3 (n = 2), 4 (n = 2), and 5 (n = 2) after the LH surge. When the antagonist was administered on the day of the LH surge, serum concentrations of bioactive LH were still elevated on the following day, but then fell to low levels. Serum progesterone concentrations were subnormal in these monkeys for the next 10 days, but recovered toward the late luteal phase. In the 8 monkeys receiving antagonist starting between days 1-5 after the LH surge, serum concentrations of bioactive LH were suppressed to near the detection limit of the assay for 4 days after the first injection. Seven of the 8 monkeys demonstrated a progressive decline in serum progesterone concentrations to undetectable values which remained for the duration of the luteal phase. In the remaining monkey the decline in progesterone was less marked; this animal presented a normal progesterone profile 3 days after the last antagonist injection. Premature menses occurred in all 8 monkeys; the next ovulation occurred 18.9 +/- 0.3 days after the last antagonist injection. To test luteal function after antagonist treatment during the early luteal phase and to mimic the rescue of the corpus luteum during a fertile cycle and assess the contraceptive effects of antagonist, hCG in daily doses of 30, 60, 90, 180, and 360 IU was administered starting on day 7 of the luteal phase to monkeys previously treated with three daily injections of 300 micrograms antagonist/kg during the early luteal phase. Control monkeys received hCG injections alone. In the controls, hCG administration elevated serum progesterone concentrations to 15-20 ng/ml. In three monkeys in which antagonist administration did not commence until day 5 or 6, hCG overcame the suppressive effect of the antagonist. However, in seven monkeys in which antagonist administration began on days 1-4, hCG caused only a small progesterone rise (maximal range, 1.8-4.9 ng/ml), about 20% of that observed in control monkeys receiving hCG.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1986

Differential inhibition of human placental prostaglandin release in vitro by a GnRH antagonist.

Previously, we have demonstrated that the production of prostaglandins by human placental tissue varied with gestational age. In addition, we have shown that placental prostaglandin release was affected by GnRH, and that its response was also dependent on the gestational age of the placenta. Thus, we have studied the effect of a GnRH antagonist ([N-Ac-Pro1,D-p-Cl-Phe2,D-Nal(2)3,6-LHRH, Syntex Research, Palo Alto, CA) on basal prostaglandin release from placentas of 6 to 15 weeks' gestation and found that this antagonist (1 microgram/ml) effects an inhibition of the release of prostaglandin E, prostaglandin F, and 13,14-dihydro-15-keto-prostaglandin from placentas of 13 and 15 weeks of gestation. This effect was not overridden by GnRH at 10 times the antagonist concentration in the 13-week placental cultures, but was totally reversed by GnRH (10 micrograms/ml) in the 15-week placental cultures. These data demonstrate that this GnRH antagonist can affect human placental prostaglandin production at 13 to 15 weeks of gestation and indicate that endogenous placental GnRH-like activity may exert a control over placental prostaglandin release at this gestational stage.

Culture Techniques↗