Betidamino acids: versatile and constrained scaffolds for drug discovery

Betidamino acids (a contraction of "beta" position and "amide") are N'-monoacylated (optionally, N'-monoacylated and N-mono- or N,N'-dialkylated) aminoglycine derivatives in which each N'acyl/alkyl group may mimic naturally occurring amino acid side chains or introduce novel functionalities. Betidamino acids are most conveniently generated on solid supports used for the synthesis of peptides by selective acylation of one of the two amino functions of orthogonally protected aminoglycine(s) to generate the side chain either prior to or after the elongation of the main chain. We have used unresolved Nalpha-tert-butyloxycarbonyl-N'alpha-fluorenylmethoxycarbonyl++ + aminoglycine, and Nalpha-(Nalpha-methyl)-tert-butyloxycarbonyl-N'alpha-fluo renylmethoxycarbonyl aminoglycine as the templates for the introduction of betidamino acids in Acyline [Ac-D2Nal-D4Cpa-D3Pal-Ser-4Aph(Ac)-D4Aph(A c)-Leu-Ilys-Pro-DAla-NH2, where 2Nal is 2-naphthylalanine, 4Cpa is 4-chlorophenylalanine, 3Pal is 3-pyridylalanine, Aph is 4-aminophenylalanine, and Ilys is Nepsilon-isopropyllysine], a potent gonadotropin-releasing hormone antagonist, in order to test biocompatibility of these derivatives. Diasteremneric peptides could be separated in most cases by reverse-phase HPLC. Biological results indicated small differences in relative potencies (<5-fold) between the D and L nonalkylated betidamino acid-containing Acyline derivatives. Importantly, most betide diastereomers were equipotent with Acyline. In an attempt to correlate structure and observed potency, Ramachandran-type plots were calculated for a series of betidamino acids and their methylated homologs. According to these calculations, betidamino acids have access to a more limited and distinct number of conformational states (including those associated with alpha-helices, beta-sheets, or turn structures), with deeper minima than those observed for natural amino acids.

Urotensin II in the central nervous system of the frog Rana ridibunda: immunohistochemical localization and biochemical characterization

Urotensin II (UII) is traditionally regarded as a product of the neurosecretory cells in the caudal portion of the spinal cord of jawed fishes. A peptide related to UII has been recently isolated from the frog brain, thereby providing the first evidence that UII is also present in the central nervous system of a tetrapod. In the present study, we have investigated the distribution of UII-immunoreactive elements in the brain and spinal cord of the frog Rana ridibunda by immunofluorescence using an antiserum directed against the conserved cyclic region of the peptide. Two distinct populations of UII-immunoreactive perikarya were visualized. The first group of positive neurons was found in the nucleus hypoglossus of the medulla oblongata, which controls two striated muscles of the tongue. The second population of immunoreactive cell bodies was represented by a subset of motoneurons that were particularly abundant in the caudal region of the cord (34% of the motoneuron population). The telencephalon, diencephalon, mesencephalon, and metencephalon were totally devoid of UII-containing cell bodies but displayed dense networks of UII-immunoreactive fibers, notably in the thalamus, the tectum, the tegmentum, and the granular layer of the cerebellum. In addition, a dense bundle of long varicose processes projecting rostrocaudally was observed coursing along the ventral surface of the brain from the midtelencephalon to the medulla oblongata. Reversed-phase high-performance liquid chromatography analysis of frog brain, medulla oblongata, and spinal cord extracts revealed that, in all three regions, UII-immunoreactive material eluted as a single peak which exhibited the same retention time as synthetic frog UII. Taken together, these data indicate that UII, in addition to its neuroendocrine functions in fish, is a potential regulatory peptide in the central nervous system of amphibians.

Chronic administration of neuropeptide Y into the lateral ventricle inhibits both the pituitary-testicular axis and growth hormone and insulin-like growth factor I secretion in intact adult male rats

Neuropeptide Y (NPY) is known to be involved in the central regulation of appetite, sexual behavior, and reproductive function. Whereas central administration of NPY strongly stimulates feeding in satiated animals, diet restriction or other unfavorable metabolic situations, such as diabetes, produce enhanced NPY gene expression and NPY release in the hypothalamus. Numerous studies have indicated that acute central administration of NPY results in various actions on LH secretion in the rat, either stimulatory or inhibitory. We recently demonstrated that chronic infusion of NPY into the lateral ventricle of adult intact female rats profoundly inhibited both the gonadotropic and somatotropic axes, with disruption of estrous cyclicity. Furthermore, we showed that central chronic infusion of NPY delayed sexual maturation in female rats. To analyze the effects of the same type of chronic NPY treatment on the pituitary-testicular axis, 45-day-old Sprague-Dawley male rats were implanted with stainless steel cannulas in the right lateral ventricle. Ten days later, Alzet osmotic minipumps were filled with different NPY solutions, adjusted to deliver 6, 18, or 36 micrograms/day, connected to the intracerebroventricular (icv) cannula, and sc implanted dorsally. The effects of these treatments were evaluated over 7 days. In one case, rats were castrated 5 days after initiation of NPY treatment, and the effect of castration was evaluated 2 days later. Chronic icv infusion of NPY produced the expected dose-related increases in food intake from 33.0 +/- 0.9 (basal) to 53.4 +/- 3.3 g/day (18 micrograms NPY/day) and body weight gain (5.7 +/- 0.7 to 10.5 +/- 1.2 d/day). As in female rats, this orexigenic action of NPY resulted in a significant dose-related decrease in pituitary weight, from 12.4 +/- 0.7 to 9.9 +/- 0.4 mg. The 7-day NPY infusion produced highly significant decreases in seminal vesicle weight (853 +/- 77 to 230 +/- 31 mg) and testis weight (3.82 +/- 0.09 to 3.18 +/- 0.15 g; P = 0.003). Plasma levels of testosterone (231 +/- 71 to 48 +/- 13 ng/dl), LH (20.7 +/- 3.7 to 9.1 +/- 1.2 ng/ml), and FSH (282 +/- 17 to 190 +/- 18 ng/ml) were markedly decreased at the 18 micrograms/day dosage, as also demonstrated for the 36 micrograms/day dosage. None of these effects was observed if vehicle was infused into the lateral ventricle instead of the NPY solution. When bilateral orchidectomy was performed 5 days after initiation of the NPY infusion (18 micrograms/day), the immediate LH and FSH rises usually seen after castration were seriously blunted.(ABSTRACT TRUNCATED AT 400 WORDS)

Y1 and Y2 receptor selective neuropeptide Y analogues: evidence for a Y1 receptor subclass

Neuropeptide Y (NPY), a 36-residue polypeptide produced abundantly in both nervous and peripheral tissues, appears to play a significant role in the regulation of diverse biological processes, including feeding behavior and cardiovascular and psychotropic functions. The actions of NPY are mediated through effective binding to specific receptors of which two, designated Y1 and Y2, have been well characterized. A shortened cyclic analogue of NPY, des-AA10-17-cyclo-7/21[Cys7,21]NPY, was shown to retain high affinity for both human neuroblastoma SK-N-MC and SK-N-BE2 cell types (expressing Y1 and Y2 receptors, respectively). Increasing the size of the ring (des-AA10-17-cyclo-2/27[Cys2,27]NPY) in the present study produced a high-affinity analogue (Ki = 3.0 vs 0.3 nM for NPY) that bound exclusively to Y2 receptors. Using the feedback from structure-activity relationships, we also describe the optimization of specific substitutions and bridging arrangements leading to the production of other truncated, high-affinity Y1 selective analogues which bind, as does NPY itself, in the low-nanomolar range. Of greatest significance, des-AA10-17-cyclo-7/21[Cys7,21,Pro34]NPY (11) was found to possess agonistic properties with an affinity comparable to that of the native NPY molecule when tested for its ability to inhibit norepinephrine-stimulated cAMP release in SK-N-MC human neuroblastoma cells. Compound 11 also caused an increase in blood pressure in anesthetized rats. However, in two central nervous system models of Y1 receptor function, stimulation of feeding and anxiolytic activity, this analogue was inactive, which suggests the presence of a new subclass of receptors. In summary, the present results demonstrate that residues 10-17 of NPY are not directly involved in either Y1 or Y2 receptor recognition or activation. This suggests that the selectivity of NPY receptors is highly dependent on subtle conformational changes such as the substitution of residue 34 to a proline or the introduction of intramolecular constraints. Additionally, we have produced an analogue of NPY that selectively activates peripheral NPY Y1 receptors.

Gonadotropin-releasing hormone antagonists: novel members of the azaline B family

A series of antagonists of gonadotropin-releasing hormone (GnRH) homologous to azaline B ([Ac-DNal1,DCpa2,DPal3,Aph5(Atz),DAph6+ ++(Atz),ILys8,DAla10]GnRH) was synthesized, characterized, and tested in a rat antiovulatory assay (AOA). Selected analogues were also tested in both an in vitro dispersed rat pituitary cell culture assay for inhibition of GnRH-stimulated luteinizing hormone release and an in vitro histamine release assay. The duration of action of some of the most potent and safest analogues in those assays was also determined in the castrated male rat in order to measure the extent (efficacy and duration of action) of inhibition of luteinizing hormone release. Structurally, this series of analogues has novel substitutions (X and Y) in the structure of the azaline B precursor: [Ac-DNal1,DCpa2,DPal3,-Aph5(X),DAph6(Y),++ +ILys8,DAla10]GnRH. These substitutions were designed to confer increased hydrophilicity as compared to that of azaline B (determined by relative retention times on a C18 reverse phase column using a triethylammonium phosphate buffer at pH 7.3) or to make them more easily accessible synthetically. Some bulky substituents were introduced in order to probe the spatial limitations of the receptor's cavity. These substitutions include acylated 4-aminophenylalanine at positions 5 and/or 6 (29 analogues), N alpha-methylated backbone substitutions (six analogues), N omega-isopropylaminophenylalanine at position 8, and hydrophilic amino acids at position 1. Out of 20 novel analogues tested for long duration of action in this series, only seven ([Ac-DNal1,DCpa2,DPal3,Aph5,DAph6,ILys8 ,DAla10]GnRH, [Ac-DNal1,DCpa2,DPal3,Aph5(For),DAph6(For) ,ILys8,DAla10]GnRH, [Ac-DNal1,DCpa2,DPal3,Aph5(Ac),DAph6(Ac),- ILys8,DAla10]GnRH (acyline), [Ac-DNal1,DCpa2,DPal3,Aph5(Pio),DAph6++ +(Pio),ILys8,DAla10]GnRH, [Ac-DNal1,DCpa2,DPal3,Aph5(Atz),DAph6++ +(Ac),ILys8,DAla10]GnRH, [Ac-DNalDCpa2,DPal3,Aph5(Atz-beta Ala),DAph6(Atz-beta Ala),ILys8, DAla10]GnRH, [Ac-DNal1,DCpa2,DPal3,Aph5(Atz-Gab), DAph6(Atz-Gab),ILys8,DAla10]GnRH) had relative potencies and/or duration of action comparable to those of azaline B. The others were one-half to one-tenth as effective as azaline B. N alpha-Methylated backbone substitutions at position 5 yielded analogues that were significantly more hydrophilic presumably because of the breakage of the NH alpha-Tyr5 to Arg8-CO hydrogen bond reported to stabilize a beta-turn encompassing residues 5-8 and which favored beta-sheet formation as shown earlier by Haviv et al. This substitution resulted, however, in an increased potency in the histamine release assay and in significantly shorter duration of action. Similarly, attempts at replacing isopropyllysine in position 8 by either isopropyl-4-aminophenylalanine or isopropyl-4-(aminomethyl)phenylalanine resulted in loss of potency in the AOA. Changes in chirality at position 1 or 10 resulted in analogues that were one-tenth and one-half as potent, respectively, as acyline.(ABSTRACT TRUNCATED AT 400 WORDS)

Dose effects of the gonadotropin-releasing hormone antagonist, Nal-Glu, combined with testosterone enanthate on gonadotropin levels in normal men

OBJECTIVE

To test the hypothesis that over a 4-week treatment period, Nal-Glu GnRH antagonist ([AcD2Nal1, D4ClPhe2, D3Pal3, Arg5, DGlu6 [AA], DAla10] GnRH) at a dose of 200 micrograms/kg per day SC would suppress levels of immunologically active and biologically active LH and FSH more completely than a dose of 100 micrograms/kg per day.

DESIGN

Placebo controlled clinical study.

SETTING

A university community.

SUBJECTS

Thirty normal male volunteers.

INTERVENTIONS

We administered Nal-Glu at doses of 0, 100, and 200 micrograms/kg body weight per day in combination with T enanthate, 50 mg IM weekly, to separate groups of men (9 or 10 men per group) for 4 weeks.

RESULTS

Serum levels of immunologically active and biologically active gonadotropins were suppressed similarly in both groups of men who received Nal-Glu; this suppression was significantly greater than in the men who received placebo + T. Local side effects were more severe in the Nal-Glu 200 micrograms/kg per day group.

CONCLUSIONS

Administration of Nal-Glu in combination with T suppresses gonadotropins more completely than does T alone, but at doses > 100 micrograms/kg, gonadotropins are not suppressed additionally with larger doses of Nal-Glu. Subjects experienced greater local discomfort and side effects with the higher dosage. These findings suggest that dosages of Nal-Glu of > 100 micrograms/kg per day may have no advantage over the 100-micrograms/kg dose in a male contraceptive regimen.

Primary structure of solitary form of gonadotropin-releasing hormone (GnRH) in cichlid pituitary; three forms of GnRH in brain of cichlid and pumpkinseed fish

GnRH is a decapeptide family with at least nine distinct structures. Vertebrates, except for most placental mammals, have more than one of these GnRH forms within the brain. We report chromatographical and immunological evidence that three forms of GnRH are in the brains of both cichlid (Haplochromis burtoni) and pumpkinseed (Lepomis gibbosus) fishes. We argue that the three forms correspond to those previously described as sea bream GnRH (sbGnRH), chicken GnRH-II and salmon GnRH. In contrast, only one GnRH form was present in the pituitary of the cichlid and is identified as sbGnRH by amino acid sequence. This is the first report in which the primary structure of GnRH is determined from pituitary tissue. The N-terminus was identified by monitoring the digestion of the peptide by pyroglutamate aminopeptidase with matrix assisted laser desorption/ionization (MALDI) mass spectrometry (MS). The amidation of the C-terminus was established using an esterification procedure for monitoring with MALDI-MS. This report supports the idea that three forms of GnRH within one species is widespread in the order Perciformes. The present study establishes sbGnRH as the third GnRH form in H. burtoni and predicts that sbGnRH is synthesized in preoptic neurons, then transported to the pituitary in the preoptic-hypophyseal axons for the release of one or both gonadotropins.

Gonadotropin-releasing activities of the three native forms of gonadotropin-releasing hormone present in the brain of gilthead seabream, Sparus aurata

Three forms of gonadotropin-releasing hormone (GnRH) have been recently identified in the brain of gilthead seabream (Sparus aurata): salmon GnRH (sGnRH), chicken GnRH-II (cGnRH-II), and a novel form, Ser8-mammalian GnRH, named seabream GnRH (sbGnRH). sbGnRH is the most abundant form in the pituitaries of sexually mature seabream during the spawning season. The present study investigated the gonadotropin-releasing activities of the three native forms of GnRH found in seabream brains, as well as of two structural analogs of sbGnRH. All native forms of GnRH stimulated gonadotropin-II (GtH-II) secretion in preovulatory female seabream. cGnRH-II was found to be 7 to 8 times more potent than sbGnRH and 2 times more potent than sGnRH in inducing GtH-II release. sGnRH was found to be 3.5 to 5 times more potent than sbGnRH in inducing GtH-II secretion. These data demonstrate that cGnRH-II, which is not present in pituitaries of sexually mature seabream, is the most potent GtH-II releaser, whereas sbGnRH, 500 times more abundant than sGnRH in the pituitary of maturing fish, is the least potent. The lower potency of sbGnRH may suggest faster enzymatic breakdown, more rapid clearance from the circulation, or a lower binding affinity to the pituitary GnRH receptor. The lower bioactivity of sbGnRH may be compensated for by its high levels in the pituitary. The two analogs of sbGnRH, [D-Nal(2)6,Pro9-NEt]-sbGnRH and [D-Arg6,Pro9-NEt]-sbGnRH, were equipotent to each other and 5 times more potent than sbGnRH in inducing GtH-II release in preovulatory seabream. However, they were 5 to 6 times less active than the analog of mammalian GnRH, [D-Ala6,Pro9-NEt]-mGnRH. Strategies for designing superactive analogs of sbGnRH are discussed.

Rat corticostatin R4: synthesis, disulfide bridge assignment, and in vivo activity

We have synthesized significant amounts of the most potent member of the rat corticostatins that inhibits ACTH-induced corticosteroid and compared its structure to that of the natural hormone. The cystine bridging arrangement that corresponds to that reported for a human defensin (3-31, 5-20, 10-30) was determined. The in vitro corticostatic activity of the synthetic rat corticostatin R4 paralleled that of the natural R4. Biological studies in vivo showed that doses of 8 or 12 mg corticostatin/kg effectively interfered with corticosterone release in stressed rats. We conclude that in the assays that were used, the biological activity of the synthetic and natural molecules was identical. The availability of significant amounts of synthetic material will make possible studies investigating the physiological role played by corticostatins in modulating the activity of the hypothalamic-pituitary-adrenal axis.

Three forms of gonadotropin-releasing hormone characterized from brains of one species

Most vertebrate species have more than one form of gonadotropin-releasing hormone (GnRH) in their brains, but it is not clear whether each form has a distinct function. We report that sea bream (Sparus aurata) brains have three forms of GnRH, one of which is described herein and is called sea bream GnRH (sbGnRH). The primary structures of two forms were determined by Edman degradation and mass spectral analysis. The amino acid sequence of sbGnRH is pGlu-His-Trp-Ser-Tyr-Gly-Leu-Ser-Pro-Gly-NH2. The second peptide is identical to a form originally isolated from chicken brains (cGnRH-II): pGlu-His-Trp-Ser-His-Gly-Trp-Tyr-Pro-Gly-NH2. cGnRH-II is the most ancient form of GnRH identified to date in jawed fish and the most prevalent form throughout the vertebrates. The third form of GnRH has previously been identified as salmon GnRH by cDNA studies and is confirmed here by chromatographic and immunological studies. Phylogenetic distribution of GnRH peptides suggests sbGnRH arose in the perch-like fish as a gene duplication of the existing cGnRH-II or salmon GnRH genes. All three identified GnRH peptides were synthesized and shown to release gonadotropin in vivo in the sea bream. The dominant form of GnRH stored in the pituitary was sbGnRH. Not only was the content of sbGnRH 500-fold greater than that of salmon GnRH but also cGnRH-II was not detected in the pituitary. The latter evidence suggests that sbGnRH is the endogenous releaser of gonadotropin II.

In vivo actions of a gonadotropin-releasing hormone (GnRH) antagonist on gonadotropin-II and growth hormone secretion in goldfish, Carassius auratus

In our previous in vitro studies, [Ac-delta 3-Pro1, 4FD-Phe2, D-Trp3,6]-mGnRH (analog E) suppressed both gonadotropin-II (GTH-II) and growth hormone (GH) release stimulated by sGnRH and cGnRH-II. In the present study analog E significantly inhibited the increases in plasma GTH-II levels stimulated by sGnRH in sexually mature female and sexually recrudescent goldfish. Treatment of goldfish with alpha-methyl-p-tyrosin methyl ester (alpha-MPT) inhibits dopamine synthesis and abolishes the inhibitory actions of dopamine on GTH-II release, resulting in a potentiation of the GTH-II response to sGnRH. Following alpha-MPT pretreatment, analog E significantly reduced basal plasma GTH-II levels, and suppressed both sGnRH and cGnRH-II actions on GTH-II release. Analog E also inhibited the increase in plasma GTH-II levels in sexually mature male goldfish exposed to the female sexual pheromone, 17 alpha, 20 beta-dihydroxy-4-pregnen-3-one (17 alpha 20 beta-P), demonstrating that the increase in plasma GTH-II levels is due to release of endogenous GnRH. Analog E significantly inhibited the increases in plasma GH levels stimulated by treatment with sGnRH. Implantation of estradiol pellets increases basal plasma GH levels and increases the GH responsiveness to sGnRH in sexually recrudescent goldfish; analog E also suppressed the increase in plasma GH levels stimulated by injection of sGnRH in estradiol-treated fish. Analog E suppressed basal GTH-II and GH levels in fish that were unhandled prior to injection; however, analog E was not effective in reducing basal plasma GTH-II or GH levels in experiments in which the fish were blood sampled or subjected to some experimental manipulation prior to injection of analog E. Analog E also suppressed basal levels of GTH-II in alpha-MPT-treated fish, suggesting that stress inhibition of GTH-II release may be mediated by the dopaminergic system. In summary, the results demonstrate that (i) analog E can suppress the actions of exogenous sGnRH and cGnRH-II on GTH-II and GH release in vivo, (ii) the GnRH system mediates, at least in part, the plasma GTH-II response in sexually mature male goldfish following exposure to the female sexual pheromone 17 alpha 20 beta-P, and (iii) endogenous GnRH peptides are important in the regulation of basal plasma levels of GTH-II as well as GH, particularly in low stress conditions.

Receptor binding of gonadotropin-releasing hormone antagonists that inhibit release of gonadotropin-II and growth hormone in goldfish, Carassius auratus

In goldfish, GnRH stimulates gonadotropin-II (GTH-II) and growth hormone (GH) release. The two native forms of GnRH, salmon GnRH (sGnRH) and chicken GnRH-II (cGnRH-II), bind to two classes of GnRH binding sites: high-affinity/low-capacity sites and low-affinity/high-capacity sites. Our previous in vitro perifusion studies of goldfish pituitary fragments showed that [Ac-delta 3-Pro1, 4FD-Phe2, D-Trp3,6]-mGnRH (analog E), [Ac-delta 3-Pro1, 4FD-Phe2, D-Trp3,6]-sGnRH (analog C), and [Ac-D(2)Nal1, 4Cl-D-Phe2, D-(3)Pal3,6]-cGnRH-II (analog N) inhibited both sGnRH- and cGnRH-II-stimulated GTH-II and GH release. Interestingly, analog C stimulated GH release but not GTH-II release. The objectives of the present study were 1) to test the site of action of GnRH antagonists in goldfish, 2) to test the relationship between receptor binding affinity of antagonists and their in vitro inhibitory potencies and apparent duration of action, and 3) to compare the binding characteristics of analog C with its differential action on GTH-II and GH release. As in previous studies, analog E suppressed sGnRH-stimulated GTH-II and GH release from perifused pituitary fragments. Similarly, analog E suppressed both sGnRH- and cGnRH-II-stimulated GTH-II and GH release from perifused dispersed goldfish pituitary cells, indicating the direct action of GnRH antagonists at the pituitary cell level. In the receptor binding studies, analog E displaced 125I-[D-Arg6, Pro9NHEt]-sGnRH (sGnRH-A) from crude goldfish pituitary membrane preparations in a dose-dependent manner.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Metabolic and behavioral effects of high-dose, exogenous testosterone in healthy men

In addition to their use as replacement therapy for hypogonadal males, androgens, particularly testosterone (T), are being explored as potential hormonal male contraceptive agents, alone or in combination with other compounds. Androgens have regulatory effects on a variety of physiological systems in addition to gonadotropin secretion and spermatogenesis. Therefore, as hormonal contraceptive regiments that alter serum T levels are explored, it is important to evaluate their effects on these aspects of normal male physiology. The effects of exogenous T on suppression of spermatogenesis in 19 healthy men were recently compared, using a T dosage of 200 mg im/week for 20 weeks. Before treatment, the men were evaluated during a 3-month pretreatment period, and after treatment, they were followed for 4-6 months or until their sperm counts normalized. Because of the lack of information regarding the effects of exogenous T on nonreproductive physiology, we examined the effects of high-dose T on plasma lipids, calcium metabolism, and sexual behavior in our subjects. Mean serum T and estradiol levels increased significantly during the treatment period. Plasma high-density lipoprotein (HDL) cholesterol levels decreased significantly within the first month and remained suppressed during the duration of T administration. At the end of the treatment period, mean plasma HDL cholesterol had decreased by 13 +/- 2% (P < 0.05); plasma levels of HDL2, HDL3, and apoprotein AI also decreased significantly; mean levels of low density lipoprotein cholesterol and triglycerides were unchanged. After 1 month of the recovery period, plasma HDL levels had returned to the baseline range. Serum calcium levels decreased slightly during treatment; this decrease was statistically significant. Urinary calcium excretion did not change. Mean levels of serum intact PTH increased by 84 +/- 17% (P < 0.05) during T administration; in contrast, 25-hydroxyvitamin D levels decreased by 16 +/- 4% (P < 0.05), and 1,25-dihydroxyvitamin D levels did not change significantly. All markers of calcium metabolism returned to baseline during the posttreatment period. Little change was found in self-reported sexual and aggressive behaviors during the study. There was a trend toward increased arousal and spontaneous erections during T administration, but this did not reach statistical significance. Frequency of sexual intercourse, masturbation, and kissing and fondling did not change, nor was the subjects' satisfaction in their relationships affected by T administration. Mean body weight increased by 4.0 +/- 0.5 kg. Approximately half the men noted mild acne. Body weight and acne symptoms returned to baseline during the recovery period.(ABSTRACT TRUNCATED AT 400 WORDS)

Monitoring protein kinase and phosphatase reactions with matrix-assisted laser desorption/ionization mass spectrometry and capillary zone electrophoresis: comparison of the detection efficiency of peptide-phosphopeptide mixtures

Matrix-assisted laser desorption/ionization mass spectrometry (MALDI MS) and capillary zone electrophoresis (CZE) were evaluated for monitoring protein phosphatase and kinase reactions in vitro. Varying concentrations of peptide C (YIHLEKKYVRRDSG), peptide S (YLIEDNEYTARQGA) and kemptide (LARRSALG) mixed with their corresponding phosphorylated peptides, pC, pS and pkemptide, were analyzed. Comparison between the two techniques indicated that MALDI MS was less quantitative than CZE, showing a bias towards detection of the unphosphorylated peptide S and kemptide. In terms of sensitivity, the MALDI MS and CZE techniques are comparable. Protein kinase A phosphorylation of kemptide was monitored with both MALDI MS and CZE, whereas alkaline phosphatase dephosphorylation of pC could only be monitored with MALDI MS. The absence of inhibition with phosphatase or kinase buffers is a significant advantage of MALDI MS. In contrast to CZE, the MALDI spectra allow identification of the species analyzed by virtue of their mass. The results obtained emphasize the advantage of monitoring enzymatic reactions in buffer solutions using MALDI MS compared with CZE.

Computer simulation of the free energy of peptides with the local states method: analogues of gonadotropin releasing hormone in the random coil and stable states

The Helmholtz free energy F (rather than the energy) is the correct criterion for stability; therefore, calculation of F is important for peptides and proteins that can populate a large number of metastable states. The local states (LS) method proposed by H. Meirovitch [(1977) Chemical Physics Letters, Vol. 45, p. 389] enables one to obtain upper and lower bounds of the conformational free energy, FB (b,l) and FA (b,l), respectively, from molecular dynamics (MD) or Monte Carlo samples. The correlation parameter b is the number of consecutive dihedral or valence angles along the chain that are taken into account explicitly. The continuum angles are approximated by a discretization parameter l; the larger are b and l, the better the approximations; while FA can be estimated efficiently, it is more difficult to estimate FB. The method is further developed here by applying it to MD trajectories of a relatively large molecule (188 atoms), the potent "Asp4-Dpr10" antagonist [cyclo(4/10)-(Ac-delta 3Pro1-D-pFPhe2-D-Trp3-Asp4-Tyr5-D-Nal6-Leu7-Arg8 -Pro9- Dpr10-NH2)] of gonadotropin releasing hormone (GnRH). The molecule was simulated in vacuo at T = 300 K in two conformational states, previously investigated [J. Rizo et al. Journal of the American Chemical Society, (1992) Vol. 114, p. 2860], which differ by the orientation of the N-terminal tail, above (tail up, TU) and below (tail down, TD) the cyclic heptapeptide ring. As in previous applications of the LS method, we have found the following: (1) While FA is a crude approximation for the correct F, results for the difference, delta FA = FA (TD)-FA (TU) converge rapidly to 5.6 (1) kcal/mole as the approximation is improved (i.e., as b and l are increased), which suggests that this is the correct value for delta F; therefore TD is more stable than TU. (The corresponding difference in entropy, T delta SA = 1.3(2) kcal/mole, is equal to the value obtained by the harmonic approximation.) (2) The lowest approximation, which has the minimal number of local states, i.e., based on b = 0 (no correlations) and l = 1 (the angle values are distributed homogeneously), also leads to the correct value of delta F, within the error bars. This is important since the lowest approximation can be applied even to large proteins. (3) The method enables one to define the entropy of a part of the molecule and thus to measure the flexibility of this part.(ABSTRACT TRUNCATED AT 400 WORDS)

Isolation of Lys-conopressin-G from the venom of the worm-hunting snail, Conus imperialis

Vasopressin homologs have previously been isolated from the venom of fish-hunting cone snails. We investigated whether a vasopressin-like peptide is found in the worm-hunter, Conus imperialis. Using i.c. injections in mice, we isolated a peptide from the venom of C. imperialis which induces scratching and grooming behavior characteristic of the conopressins. Biochemical characterization showed that this peptide is identical to Lys-conopressin-G. The results led us to speculate that the vasopressin-like peptides in Conus venoms may be examples of an evolving conversion of endogenous peptides for specialized venom uses.

A nicotinic acetylcholine receptor ligand of unique specificity, alpha-conotoxin ImI

We report the isolation, characterization, and total synthesis of a small peptide ligand for nicotinic acetylcholine receptors (nAChRs). It is highly active against the neuromuscular receptor in frog but not in mice. In contrast, it induces seizures when injected centrally in mice and rats, suggesting that it may target neuronal nAChRs in mammals. Although such receptors may be important in both normal cognition and the pathophysiology of several neuropsychiatric disorders, there are few ligands to discriminate between the multiple receptor subtypes. The new peptide is a highly divergent alpha-conotoxin from the snail Conus imperialis, which preys on polychaete worms. In this article, the purification, structural analysis, synthesis, and preliminary physiological characterization of alpha-conotoxin ImI (alpha-CTx-ImI) are reported. The sequence of the peptide is: Gly-Cys-Cys-Ser-Asp-Pro-Arg-Cys-Ala-Trp-Arg-Cys-NH2. The peptide shows striking sequence differences from all alpha-conotoxins of fish-hunting Conus, but its disulfide-bridging is similar: [2-8; 3-12]. We suggest that cone venoms may provide an array of ligands with selectivity for various neuronal nAChR subtypes.

Differential actions of a mammalian gonadotropin-releasing hormone antagonist on gonadotropin-II and growth hormone release in goldfish, Carassius auratus

In goldfish the two native forms of gonadotropin-releasing hormone (GnRH), salmon GnRH (sGnRH) and chicken GnRH-II (cGnRH-II), stimulate both gonadotropin-II (GTH-II) and growth hormone (GH) release. Modifications of GnRH structure at positions 1, 2, 3, and 6 often result in an antagonist in goldfish, an observation well documented in mammalian studies. In a preliminary study in goldfish, a mammalian GnRH antagonist, [Ac-D(2)Nal1, 4Cl-D-Phe2, D(3)-Pal3,6, Arg5, D-Ala10]-mGnRH (analog L) weakly stimulated GTH-II release, and strongly inhibited GH release. The objectives of the present study were to study the dose-related actions of analog L on GTH-II and GH release in the goldfish, the specificity of inhibition of native GnRH actions, and to test whether analog L can act directly on goldfish pituitary cells. In a goldfish pituitary fragments perifusion system, analog L at different concentrations, given as 2-min pulses or as 30-min prolonged treatments, stimulated GTH-II and inhibited GH release in a dose-dependent manner. Analog L at 2 microM concentration (45 min) significantly suppressed sGnRH- and cGnRH-II-stimulated GTH-II as well as GH release. Analog L specifically inhibited GnRH-stimulated GH release, without having any significant effects on the GH release induced by either SKF38393, a dopamine D1 receptor agonist, or thyrotropin-releasing hormone. The GTH-II stimulatory and GH-inhibitory actions of analog L were significantly suppressed by a 'true' GnRH antagonist (Ac-delta 3-Pro1, 4FD-Phe2, D-Trp3,6)-mGnRH. Further, analog L stimulated GTH-II release and suppressed GH release from the enzymatically dispersed goldfish pituitary cells, indicating the direct actions of analog L at the pituitary cell level. Analog L also displaced 125I-(D-Arg6, Pro9 NHEt)-sGnRH bound to crude goldfish pituitary membrane preparations in a dose-related manner. In conclusion, contrary to its action as a potent GnRH antagonist in mammals, analog L has GTH-II stimulatory action in goldfish. Analog L by acting via GnRH receptors at the pituitary cell level differentially acts on GTH-II and GH release, suggesting functional differences in the properties of the GnRH receptors on GTH and GH cells. Analog L also specifically inhibits sGnRH and cGnRH-II actions on GTH-II and GH release.

Physiological levels of estradiol stimulate plasma high density lipoprotein2 cholesterol levels in normal men

Premenopausal women have a lower risk of coronary artery disease than men or postmenopausal women; estrogens are thought to contribute to this lower risk. Administration of exogenous estrogen to post-menopausal women increases plasma high density lipoprotein (HDL) cholesterol and may reduce mortality from coronary disease in users. Although many investigations have examined the roles of estrogen in the regulation of lipoproteins in women, little attention has been directed to estrogen regulation of lipids in men. We designed a paradigm to study the role of physiological levels of estradiol (E2) on plasma lipoproteins in healthy men. We used a GnRH antagonist, Nal-Glu, to suppress endogenous steroid hormones in healthy men. We then administered testosterone (T) enanthate (100 mg, im, weekly) to restore T levels to the baseline range, and we administered an aromatase inhibitor, testolactone (Teslac), to prevent the normal conversion of T to E2, thereby producing a selective estrogen deficiency state in normal young men. As controls, we administered Nal-Glu and T along with placebo Teslac to a separate group of men; a third group of men received all placebo medications. We found that in men who received Nal-Glu plus T plus Teslac, E2 levels were profoundly suppressed during treatment, whereas T levels remained in the baseline range. Plasma HDL cholesterol, particularly, the HDL2 fraction, decreased significantly in response to the low serum E2 level. Plasma apoprotein-AI levels also decreased significantly. Plasma LDL and triglyceride levels did not change. All hormone and lipoprotein parameters returned to baseline within 4 weeks after treatment ended. In men who received Nal-Glu plus T, plasma HDL and apoprotein-AI decreased, but these decreases did not achieve statistical significance. Only a small decrease in HDL2 cholesterol was seen in these men. There were no hormonal or lipid changes in the placebo group. We conclude that in men, physiological levels of E2 are important in maintaining plasma levels of HDL cholesterol, especially the HDL2 fraction. These observations suggest that estrogen, in the amount normally produced in men, may offer some degree of protection against cardiovascular disease in males, as they do in women.

Effects of endogenous testosterone and estradiol on sexual behavior in normal young men

The importance of androgens in establishing and maintaining sexual function in males of most species is well recognized. Estrogens also stimulate male sexual function in some species. In men, most studies of androgen effects on behavior have used hypogonadal men as an experimental model; much less is known about the role of endogenous testosterone (T) or estradiol (E2) in the regulation of behavior in healthy, eugonadal men. In a randomized, double-blind study, we used a GnRH antagonist, Nal-Glu, without T replacement, to induce acute, profound, reversible gonadal steroid deficiency in 9 normal men for 6 weeks (Nal-Glu alone). We also studied the effects of partial androgen replacement by administering Nal-Glu together with T enanthate, 50 mg im weekly, to 10 other men. A third group of 10 men received Nal-Glu plus T, 100 mg im weekly. We studied the role of endogenous E2 by administering Nal-Glu plus T, 100 mg im weekly, plus an aromatase inhibitor, testolactone (Teslac), 250 mg po qid, to 10 additional men (Nal - Glu + T + Teslac). Nine men received placebo injections and tablets. All subjects completed a behavioral questionnaire during the pretreatment period, at weeks 2, 4, and 6 of treatment, and at 3 weeks posttreatment. Men who received Nal-Glu alone became profoundly hypogonadal within 1 week after treatment began. Serum T levels did not change significantly in the controls and in the men who received full T replacement but decreased to approximately half the baseline level in men who received partial T replacement. E2 levels decreased profoundly in men who received Nal-Glu alone or Nal - Glu + T + Teslac and to a lesser degree in men who received partial T replacement. In men who received Nal-Glu alone, there were clinically and statistically significant decreases in the frequency of sexual desire, sexual fantasies, and intercourse at 4-6 weeks. These men also showed a strong trend (P = 0.55) towards decreased spontaneous erections after 4 and 6 weeks of treatment. A significant decrease in the frequency of masturbation was evident after 6 weeks. All measures returned to normal by posttreatment week 3. There was a trend toward increased aggression in the hypogonadal men, but this did not reach statistical significance. No changes in satisfaction or happiness with their partners were observed.(ABSTRACT TRUNCATED AT 400 WORDS)

Comparative effects of two different delivery systems on gonadotropin-releasing hormone (GnRH) antagonist-induced suppression of gonadotropins and testosterone in man

The Nal-Glu gonadotropin-releasing hormone (GnRH) antagonist, when given in daily subcutaneous (SC) doses of 5 mg or higher, maximally suppresses serum luteinizing hormone (LH) and follicle-stimulating hormone (FSH) levels to near undetectable levels and induces azoospermia in normal men; lower doses (1.5 and 3.0 mg) are less effective. Cost and convenience are important considerations in contraceptive development. Studies with GnRH agonists suggest that constant delivery is more effective in suppressing gonadal function than equal doses by single daily injection. In this study, we examined whether the constant infusion (CI) of a submaximal suppressive dose (1.5 mg) of Nal-Glu would be more effective in suppressing the pituitary-gonadal axis than its repeated single daily injections (SDI). This (1.5 mg) dose was selected because the 5 mg dose given once daily SC for 21 days led to maximal suppression of LH, FSH, and testosterone (T) levels, whereas 1.5 mg once daily for 21 days gave only partial suppression. It was felt that if continuous infusion was considerably more effective than intermittent administration of this submaximal dose, then the development of long-acting sustained release delivery systems for contraceptives based on GnRH antagonist analogs would allow both reduced cost and enhanced convenience. One and a half mg of Nal-Glu was administered SC either as a SDI or CI over 24 hours for 21 days to two groups of five normal men. Three measurements of serum LH, FSH, and T were performed before antagonist injection and 1, 2, 4, 8, 12, 16, and 24 hours after Nal-Glu injection on days 0, 1, 7, 21.(ABSTRACT TRUNCATED AT 250 WORDS)