BIBP 3226, the first selective neuropeptide Y1 receptor antagonist: a review of its pharmacological properties

Based on the assumption that the pharmacophoric groups interacting with the Y1 receptor are located in the C-terminal part of neuropeptide Y, low molecular weight compounds with high affinity and selectivity for the Y1 receptor were designed and synthesized. The prototype BIBP 3226 possesses affinity for the Y1 receptor in the nanomolar range. In addition, this compound is selective displaying rather low affinity for Y2, Y3, Y4 and a set of 60 other receptors. Both biochemical and pharmacological studies showed that BIBP 3226 behaves as a competitive antagonist. Using BIBP 3226 it was possible to investigate the role of NPY and/or Y1 receptors in blood pressure regulation. The interesting observation was that antagonism to Y1 receptors had no major influence on the basal blood pressure but attenuated stress induced hypertension. This strongly supports the hypothesis that NPY is mainly released during stress involving intense sympathetic nervous system activation. Moreover, BIBP 3226 can be used to characterize NPY receptor subtypes. For instance, we were able to show that presynaptic NPY receptors mediating catecholamine release do not solely belong to the Y2 subtype, but that presynaptic Y1 receptors also exist. In conclusion, BIBP 3226 has been shown to be an important tool for the elucidation of the physiological role of Y1 receptors in the cardiovascular system.

Neuropeptide Y and the nonpeptide antagonist BIBP 3226 share an overlapping binding site at the human Y1 receptor

Neuropeptide Y (NPY) is a 36-amino acid peptide that exhibits actions on the cardiovascular system and the central nervous system. NPY can regulate blood pressure, psychomotor function, anxiety, food intake, and endocrine secretions. BIBP 3226, the first potent and selective nonpeptide antagonist at the NPY Y1 receptor, was designed by mimicking the carboxyl-terminal structure of NPY. We investigated the interaction of NPY and BIBP 3226 with the human Y1 receptor at the molecular level. Alanine mutants at positions Y100, D104, W288, and H298 of the human Y1 receptor showed no or significantly reduced binding for NPY but were not affected in their ability to bind BIBP 3226. Receptors with alanine mutations at positions W163, F173, Q219, N283, F286, and D287 showed reduced binding for both NPY and BIBP 3226. Mutations at other positions were tested (H105, S170, L174, V178, D200, D205, S206, H207, S210, T212, T280, T284, N289, H290, and Q291) and did not affect the binding of NPY or BIBP 3226. The human Y1 receptor mutant Y211A showed no affinity for BIBP 3226 but retained wild-type affinity for NPY. Based on these experimental results, a detailed model for the interaction of BIBP 3226 with the human Y1 receptor was developed using a Y1 receptor model and a three-dimensional model of BIBP 3226. The experimental results, supported by modeling studies, clearly suggest that the native ligand (NPY) and the antagonist (BIBP 3226) share an overlapping binding site.

Subtype selectivity and antagonistic profile of the nonpeptide Y1 receptor antagonist BIBP 3226

In the present study, the subtype specificity and species selectivity of the nonpeptide BIBP 3226, as well as its in vitro antagonism of neuropeptide Y (NPY)-mediated second messengers have been investigated. Radiolabeled NPY is potently displaced by BIBP 3226 [(R)-N2-(diphenylacetyl)-N-[(4-hydroxyphenylmethyl]-D- arginine amide] on human Y1 receptor expressing Chinese hamster ovary-K1 cells (Ki = 0.47 +/- 0.07 nM). SK-N-MC human neuroblastoma cells (Ki = 5.1 +/- 0.5 nM) and the rat parietal cortex membranes (Ki = 6.8 +/- 0.7 nM). The interaction of BIBP 3226 with the Y1 receptor is stereoselective, because the (S)-enantiomer of the (R)-configured BIBP 3226 displays almost no affinity (Ki > 10,000 nM). In contrast, concentrations up to 10 microM BIBP 3226 do not displace [125I]NPY from the human Y2 receptor (neuroblastoma cell line SMS-KAN), the rabbit Y2 receptor (kidney) and the rat Y2 receptor (hippocampus). Functional antagonism could be shown for the human Y1 receptor: 0.1 microM BIBP 3226 antagonizes the NPY induced Ca++ mobilization (pKb = 7.5 +/- 0.17) as well as the NPY-mediated inhibition of cyclic AMP synthesis (pKb = 8.2 +/- 0.24) in SK-N-MC cells. In contrast, none of the formerly described putative antagonists PYX-2, [D-Trp32]NPY and benextramine could be characterized as high affinity Y1 receptor antagonists. The 18 amino acid NPY analog EXBP 68 Ile-Glu-Pro-Orn-Tyr-Arg-Leu-Arg-Tyr-NH2, cyclic (2,4'), (2',4')-diamide] displayed Y1-selective affinity with in vitro antagonistic properties (Ki = 0.33 +/- 0.04 nM and pKb = 8.4 +/- 0.07) in SK-N-MC cells. Therefore, BIBP 3226 is the first potent and subtype-selective nonpeptide Y1 receptor antagonist.

Pharmacological characterization of the selective nonpeptide neuropeptide Y Y1 receptor antagonist BIBP 3226

The present study was undertaken to investigate the in vitro and in vivo pharmacological profile of the novel, nonpeptide neuropeptide Y (NPY) Y1-selective antagonist, BIBP 3226 [(R)-N2-(diphenylacetyl)-N-[(4-hydroxyphenyl)methyl]-D-arginine-am ide], and a recently described peptidic structure [Ile-Glu-Pro-Orn-Tyr-Arg-Leu-Arg-Tyr-NH2, cyclic (2,4'), (2',4)-diamide]. BIBP 3226 antagonized the NPY Y1 receptor-mediated decrease in the twitch response in the rabbit vas deferens preparation with a pKb value of 6.98 +/- 0.06 (n = 16). It showed no affinity (EC50 > 1 microM) for NPY Y2 receptors in the rat vas deferens. NPY-induced increases in perfusion pressure in the isolated perfused rat kidney and rabbit ear preparations were antagonized with IC50 values of 26.8 +/- 4.5 (n = 4) and 214 +/- 30 nM (n = 4), respectively. The NPY-mediated potentiation of the noradrenaline elicited increase in perfusion pressure in the rat mesenteric bed was antagonized with an IC50 value of 976 (542-1760) nM. The NPY-induced increase in blood pressure in the pithed rat was inhibited by BIBP 3226 dose-dependently (ED50 = 0.11 +/- 0.03 mg/kg i.v.), whereas no effect of BIBP 3226 (1 mg/kg i.v.) was observed for the noradrenaline-, angiotensin-, endothelin- or vasopressin-induced pressor response. The data presented demonstrate that BIBP 3226 is a competitive and NPY Y1-selective antagonist. The peptidic compound proved to possess high potency for NPY Y1 receptors, but showed both agonistic as well as antagonistic properties.(ABSTRACT TRUNCATED AT 250 WORDS)

[Regression of functional cysts: high dosage ovulation inhibitor and gestagen therapy has no added effect]

To investigate the need for hormonal treatment in patients with functional ovarian cysts (FOC), the efficacy of this treatment was evaluated in a retrospective and also in a randomised prospective study. By retrospective analyses the resolution of FOC with a mean diameter larger than 2.0 cm at the beginning of a cycle was determined in 113 patients (31.6 +/- 4.6 years). Fifty-seven women received an oral contraceptive (ethinylestradiol 50 micrograms/d for 7 days, ethinylestradiol 50 micrograms and desogestrel 125 micrograms/d for 15 days), the others had no therapy. In a second study 59 patients (32.3 +/- 4.6 years) were randomised to receive a combination of ethinylestradiol 50 micrograms and levonorgestrel 250 micrograms/d for 21 days (Group 1, n = 24), or lynestrenol 10 mg/d continuously (Group 2, n = 14) or a third group (Group 3, n = 21) without treatment. In both studies no differences were found between those patients who had hormonal treatment and those who had not. The prospective study revealed that spontaneously appearing FOC and FOC evolving after ovulation induction during the cycle prior to study enrolment, resolved equally well within 12 weeks independent of contraceptive or gestagen treatment. FOC persisted in only one woman (group 2) who had a surgically proven endometrioma. In conclusion, hormonal treatment does not produce regression of FOC in women of reproductive age.

Labeling of neuropeptide Y receptors in SK-N-MC cells using the novel, nonpeptide Y1 receptor-selective antagonist [3H]BIBP3226

The binding of tritium-labelled BIBP3226, N2-(diphenylacetyl)-N-[(4-hydroxy-phenyl)methyl]-D-arginine amide, to human neuroblastoma SK-N-MC cells was investigated. [3H]BIBP3226 reversibly binds to neuropeptide Y receptors of the Y1 subtype expressed in SK-N-MC cells with a KD of 2.1 +/- 0.3 nM (mean +/- S.E.M., n = 3) and a Bmax of 58,400 +/- 1100 sites/cell. Non-specific binding did not exceed 30% of the total radioactivity bound at KD. In competition experiments [3H]BIBP3226 is concentration-dependently displaced by neuropeptide Y and its peptide analogues with an affinity pattern neuropeptide Y = [Leu31, Pro34]neuropeptide Y >> neuropeptide Y-(18-36). This rank order of potencies is consistent with the interaction of [3H]BIBP3226 with neuropeptide Y receptors of the Y1 subtype. Therefore, [3H]BIBP3226 can be used as selective ligand to study neuropeptide Y Y1 receptors.

The first highly potent and selective non-peptide neuropeptide Y Y1 receptor antagonist: BIBP3226

The design and subsequent in vitro and in vivo biological characterisation of the first potent and selective non-peptide neuropeptide Y Y1 receptor antagonist, BIBP3226 ((R)-N2-(diphenylacetyl)-N-[(4-hydroxyphenyl)methyl]-argininami de) is reported. BIBP3226 displaced 125I-labelled neuropeptide Y with high affinity (Ki = 7 nM) from the human neuropeptide Y Y1 receptor and proved to be highly selective. BIBP3226 displayed potent antagonistic properties both in in vitro and in vivo models and thus represents the first selective non-peptide neuropeptide Y Y1 receptor antagonist.

Complete L-alanine scan of neuropeptide Y reveals ligands binding to Y1 and Y2 receptors with distinguished conformations

The synthesis of more than fifty 36-residue oligopeptide analogs of neuropeptide Y (NPY) and their affinity to human Y1 and Y2 receptors is described. Each amino acid of the natural sequence was replaced by L-alanine, the four alanine residues at position 12, 14, 18 and 23 were replaced by glycine. Additional residues were exchanged to closely related ones in order to characterize the prerequisites for binding. A combination of automated single and multiple peptide synthesis using fluoren-9-ylmethoxycarbonyl/tert-butoxy strategy was applied. The purified peptides were characterized by electrospray mass spectrometry, analytical HPLC and amino acid analysis. Binding was investigated by displacement of 125I-labelled neuropeptide Y from human neuroblastoma cell lines SK-N-MC and SMS-KAN. Whereas Pro2 and the integrity of the neuropeptide Y loop is important for the binding to the Y1 receptor, exchanges within the C-terminal helix affect the affinity to the Y2 receptor. The C-terminal pentapeptide amide is important for both receptors and probably represents the binding site. However, Arg33 and Arg35 may not be exchanged by L-alanine in the Y1 system, whereas Arg35 and Tyr36 are the most susceptible residues in the Y2 system. In order to distinguish between conformational effects and direct hormone/receptor interaction via the side chains of neuropeptide Y, circular dichroic studies of the alanine-containing peptides were performed and structure affinity relationships are discussed. Comparing the affinities of the neuropeptide Y analogs to Y1 and Y2 receptors significant differences were found for the two binding sites, which suggests a different active conformation of neuropeptide Y at the two subtypes of receptors. Using molecular dynamics calculations, two distinct conformations were identified which are in good agreement with the data obtained by structure/affinity investigations.

[Contraception in the premenopause]

Reproduction continues in the perimenopause. To prevent unintended pregnancies, the use of a highly effective reversible contraceptive is necessary. The most effective methods of contraception are hormonal contraceptive methods and the intrauterine device (IUD). Barrier contraceptives can have a high-use effective rate in motivated users, too. Hormonal contraception has both risks and benefits, but can be used safely for healthy women without risk factors during the time of perimenopause. To prevent the metabolic side effects of synthetic estrogen-ethinyl-estradiol in the contraceptive pill in perimenopause, the use of natural estrogen (estradiol) in combination with a progestagen for contraception is effective, too. A major problem of IUDs has been the increased incidence of bleeding or dysmenorrhea. For these women, Progestin-releasing IUDs are recommended because of their ability to reduce the amount of uterine bleeding associated with menstruation.

Characterization of BIBN 99: a lipophilic and selective muscarinic M2 receptor antagonist

The present study was designed to characterize the receptor selectivity profile of the novel muscarinic M2 receptor antagonist BIBN 99 (5,11-dihydro-8-chloro-11-[[4-[3-[(2,2-dimethyl-1- oxopentyl)ethylamino]propyl]-1-piperidinyl]acetyl]-6H- pyrido[2,3-b][1,4]benzodiazepin-6-one). In radioligand binding studies BIBN 99 showed high affinity for m2/M2 sites (pKi = 7.52/7.57), intermediate affinity for m4 sites (pKi = 6.76) and low affinity for m1/M1 (pKi = 5.97/6.17), m3/M3 (pKi = 6.11/6.04) and m5 sites (pKi = 5.84). Functional studies in vitro showed BIBN 99 to be a competitive antagonist and to have an 11- to 25-fold higher affinity for M2 receptors than for putative M1 receptors in the rabbit vas deferens or M3 receptors in guinea-pig trachea. In vivo studies revealed that BIBN 99 is able to cross the blood-brain barrier, and although showing an approximately 3-fold higher affinity for M2 binding sites BIBN 99 appeared to be 7- to 18-fold less potent than AF-DX 116 in inhibiting muscarinic agonist or vagally induced bradycardia in rats and guinea-pigs. The results show that BIBN 99 is the first lipophilic muscarinic M2 receptor antagonist to have remarkable M2 versus M1 selectivity (30-fold). In addition, BIBN 99 possesses central nervous system activity and only minor peripheral cardiac effects.

Laparoscopic electrocoagulation of the ovarian surface in infertile patients with polycystic ovarian disease

OBJECTIVE

To assess the endocrinologic and clinical outcome after laparoscopic ovarian electrocautery because of polycystic reaction to ovarian stimulation in anovulatory infertility patients.

DESIGN

Between 1986 and 1989, 133 patients with polycystic ovarian disease underwent laparoscopic electrocoagulation of the ovarian surface in an outpatient clinic after conventional ovarian stimulation had led to polycystic reaction.

SETTING

All patients were referred to our outpatient clinic affiliated with the university hospital.

RESULTS

The reduction of androgen levels and normalization of cycle length were highly significant. The overall pregnancy rate was 70% (73 of 104), ranging from 27% in smokers to 94% in nonsmoking couples. In 26 second-look operations de novo adhesions were found in 26.9% of the patients.

CONCLUSION

Laparoscopic coagulation of the ovarian surface is an effective tool to reduce elevated androgen levels and to improve the intraovarian mechanism of selecting a dominant follicle. A postoperative complication may be adhesion formation.

Therapeutic potential of CNS-active M2 antagonists: novel structures and pharmacology

Clinical trials with muscarinic agonists or acetylcholine esterase inhibitors for the treatment of Alzheimer's dementia have shown disappointing or equivocal results. An alternative treatment of this disease is the development of drugs which enhance the release of acetylcholine. It is believed, that of the five muscarinic receptor subtypes so far identified in the brain, M2 receptors are located presynaptically in the cortex and hippocampus and upon stimulation inhibit the release of acetylcholine. Based on this hypothesis, we initiated a drug discovery program with the aim of identifying selective and centrally active M2 antagonists which are capable of enhancing cholinergic transmission. These efforts resulted in the successful design and synthesis of novel muscarinic antagonists able to cross the blood brain barrier. Moreover, these compounds show few peripheral effects and possess a superior M2 versus M1 selectivity. The prototype of this novel class of M2 selective compounds, BIBN 99, could be a valuable tool to test the hypothesis that lipophilic M2 antagonists show beneficial effects in the treatment of cognitive disorders.

Structure-activity relationships and pharmacological profile of selective tricyclic antimuscarinics

The discovery of the M1-selective receptor antagonist pirenzepine was the impetus for a research project directed towards the development of selective muscarinic antagonists. In the pursuit of this objective, compounds with different selectivity profiles have been found. AF-DX 116 was the first cardioselective antagonist synthesized. Subsequently novel M2 receptor antagonists have been discovered with higher potency and selectivity. Moreover, a pirenzepine-type compound UH-AH 37 has been identified that, in contrast to pirenzepine, shows a higher affinity for ileal than for atrial muscarinic receptors. Among tricyclic muscarinic receptor antagonists three different selectivity profiles have been identified, namely: M1 greater than M3 greater than M2, Msm for pirenzepine; M2 greater than M1 greater than M3, Msm for AF-DX 116, AF-DX 384, AQ-RA 741; and Msm congruent to M1 greater than M2, M3 for UH-AH 37 and its (+) enantiomer.

[Behavior of the basal and stimulated serum level of thyroid stimulating hormone and determination of thyroxine, thyroxine- binding capacity and free thyroxine index in females with chronic uremia]

In 11 female patients with chronic uraemia at the age of 20 to 47 years (average age 33.1 years) the basal and the thyrotropin releasing hormone-(TRH-) stimulated thyroid gland stimulating hormone-(SH-) secretion were investigated, in addition to this the parameters of the thyroid gland total thyroxin (T4), thyroxin binding capacity (TBC) as well as the free thyroxin-index (FT4-I). In 2 women the investigations were repeated after kidney transplantation. The determination of TSH and T4 was carried out radioimmunologically, TBC was determined according to the principle of the test tube analysis, whereas FT4-I was established by computation. In 9 of the 11 female patients with chronic uraemia a physiological TSH-response behaviour is existing, whereas for T4 deviations from the reference area are to be stated in 7 female patients and for FT4-I in 6 female patients.

[Behavior of basal and stimulated serum levels of prolactin, growth hormone and gonadotropins in females with chronic uremia]

In 11 female patients with chronic uraemia at the age of 20 to 47 years (average age: 33.1 years) the behaviour of basal and stimulated serum levels of prolactin (PRL), growth hormone (HGH) and gonadotropins (LH, FSH) was investigated. For stimulation of the hormone secretion a sequential test with arginine hydrochloride, gonadotropin releasing hormone (GnRH) and thyrotropin releasing hormone (TRH) was used. In 2 women the investigations were repeated after kidney transplantation. The determination of LH, FSH, PRL and HGH was performed radioimmunologically. The investigations show that in women with chronic uraemia the basal LH-levels in general lie clearly above of those ones of women with biphasic cycles, whereas the FSH-levels are not increased. The LH-response after administration of 25 micrograms GnRH is adequate in 6 women and is absent in 5 women. After kidney transplantation a clear reduction of the basal LH-levels in comparison to the preliminary values is to be established. The increased basal LH-levels are causally made responsible for the disturbances of the menstrual cycle in women with chronic uraemia. For PRL hyper- and normoprolactinaemic as well as hypoprolactinaemic basal levels are found. A connection between the height of the PRL and creatinine levels cannot be proved. Apart from a adequate PRL response to the stimulation with TRH in the individual case this response is inadequate or is absent. The basal HGH-levels are in the area of reference. In all women HGH can adequately be stimulated, whereby the case in question is presumably a so-called paradoxical TRH-effect.

Coincidence of gonadal dysgenesis and hyperprolactinemia

It is reported about 4 female patients aged from 3 to 31 years (average age 18 years) with gonadal dysgenesis and hyperprolactinemia. Beside one all these females were not treated with synthetic sexual steroids. In 3 of the 4 patients both hyperprolactinemic and hypergonadotropic serum levels were observed. In one case the gonadotropic serum levels were normal. A stimulation test with GnRH-TRH or arginine-GnRH-TRH, respectively, was performed. In patients with gonadal dysgenesis a change on the area of hypothalamo-hypophyseal axis is supposed to cause the hyperprolactinemia.

The effect of a single midcycle administration of 0.5 or 2.0 mg dienogest (17 alpha-cyanomethyl-17 beta-hydroxy-estra-4,9-dien-3-one) on pituitary and ovarian function--investigation for the use as a postcoital contraceptive

Estradiol-17 beta, progesterone, LH and FSH levels in plasma were measured simultaneously by radioimmunoassay and BBT was recorded in order to investigate the effect of a single midcycle oral dose of 0.5 or 2.0 mg dienogest (17 alpha-cyanomethyl-17 beta-hydroxy-estra-4,9-dien-3-one, VEB Jenapharm, Jena/GDR) on pituitary and ovarian function in 18 healthy fertile females. After application of 0.5 mg dienogest in the follicular phase the cycles appeared to be anovulatory. Administration of 2.0 mg two days prior to the expected LH-surge produced a delay of the LH-peak combined with an absence of ovulation as well as the absence of the normal subsequent increase of progesterone. With 0.5 mg the delay of the LH-surge was followed by an ovulation with normal corpus luteum function. The application of 0.5 or 2.0 mg one day before or during the rising LH-peak lowered the LH-surge but ovulation and luteal phase were not altered. Administration of both dosages during the LH-peak could neither prevent ovulation nor disturb corpus luteum function. Postovulatory ingestion of 0.5 or 2.0 mg dienogest during the BBT-rise produced no alteration of the further cycle. These results demonstrate that dienogest in a single-dose-administration in midcycle can alter pituitary and ovarian function depending on the time interval between application and the day of LH-surge.

[Behavior of the hypothalamo-hypophyseal axis in a patient with asymmetric mixed gonadal dysgenesis (chromosome pattern 45,XO/46,XY) before and after gonad excision after with arginine, GRH and TRH stimulation]

In a 12 years old patient with asymmetric mixed gonadal dysgenesis (karyotype 45, XO/46,XY) a stimulation test with arginine, gonadotropin-releasing hormone (GRH) and thyreotropin-releasing hormone (TRH) was performed before and after exstirpation of the gonads as well as after application of sex steroids. FSH, LH, PRL, HGH, TSH, testosterone and oestradiol were determined by radioimmunoassay. The results show an intact hypothalamo-pituitary axis which reacts with a normal negative feedback with respect to the secretion of gonadotropins after application of sex steroids.

Thyrotropin, total thyroxine, thyroxine binding capacity and free thyroxine index in patients with gonadal dysgenesis (karyotype 45/XO)

In 9 patients with gonadal dysgenesis (karyotype 45/XO), the responsiveness of thyreotropic cells of the pituitary was investigated by stimulation with thyreotropin-releasing hormone (TRH). Both after hormone substitution in the form of sequential therapy (mestranol/mestranol-chlormadinone acetate) and after the end of therapy the investigations were repeated. TSH was determined by RIA, total thyroxine and binding capacity of thyroxine binding globuline (TBC-index) by protein binding assay. The free thyroxine index (FT4-index) was calculated. The results show that the hypothalamic-pituitary unit in patients with gonadal dysgenesis reacts in a similar manner as in normal female subjects.

[Stimulation test of the adenohypophysis with arginine, gonadotropin-releasing hormone (GRH), and thyrotropin-releasing hormone (TRH) in 45, XO patients with Turner's syndrome (author's transl)]

Pituitary stimulation tests with arginine, gonadotropin-releasing hormone (GRH) and thyrotropin-releasing hormone (TRH) were performed in five 45, XO patients with Turner's syndrome. Their ages ranged from 12--17 years. Serum levels of LH, FSH, PRL, HGH, and TSH were measured by RIA. The hypothalamo-pituitary system appeared normal in the patients with Turner's syndrome.