Assessment of the in vitro and in vivo biological activities of the human follicle-stimulating isohormones

Antinociceptive structure-activity studies with enkephalin-based opioid glycopeptides

Development of opioid peptides as therapeutic agents has historically been limited due to pharmacokinetic issues including stability and blood-brain barrier (BBB) permeability. Glycosylation of opioid peptides can increase peptide serum stability and BBB penetration. To further define the requirements for optimizing in vivo antinociceptive potency following intravenous administration, we synthesized a series of enkephalin-based glycopeptides using solid phase 9-fluorenylmethyloxy carbamate methods. The compounds differed in the sixth and subsequent amino acid residues (Ser or Thr) and in the attached carbohydrate moiety. In vitro binding and functional smooth muscle bioassays indicated that the addition of mono- or disaccharides did not significantly affect the opioid receptor affinity or agonist activity of the glycopeptides compared with their unglycosylated parent peptides. All of the glycopeptides tested produced potent antinociceptive effects in male ICR mice following intracerebroventricular injection in the 55 degrees C tail-flick test. The calculated A(50) values for the Ser/Thr and monosaccharide combinations were all very similar with values ranging from 0.02 to 0.09 nmol. Selected compounds were administered to mice intravenously and tested for antinociception to indirectly assess serum stability and BBB penetration. All compounds tested produced full antinociceptive effects with calculated A (50) values ranging from 2.2 to 46.4 micromol/kg with the disaccharides having potencies that equaled or exceeded that of morphine on a micromoles per kilogram basis. Substitution of a trisaccharide or bis- and tris-monosaccharides resulted in a decrease in antinociceptive potency. These results provide additional support for the utility of glycosylation to increase central nervous system bioavailability of small peptides and compliment our ongoing stability and blood-brain barrier penetration studies.

Effect of Thyroid Hormone on CYP19 Expression in Ovarian Granulosa Cells From Gonadotropin-Treated Immature Rats

The present study was designed to determine the mechanisms by which serum estradiol levels are enhanced during gonadotropin-induced ovarian development in hypothyroid immature rats. Thyroidectomized (Tx)-immature rats receiving thyroidectomy on day 22 were treated with 8 IU equine chorionic gonadotropin (eCG) at 26 days of age to induce follicular development in ovaries. Ovaries or ovarian granulosa cells were collected on the first proestrus (day 28). Enhanced expression of aromatase (CYP19) mRNA induced by eCG treatment was inhibited by injection of thyroxine (T(4): 5 microg x 6 times) in Tx rats. Ovarian granulosa cells harvested from Tx rats were cultured for 24 h in chemically defined serum-free medium containing gonadotropin in the presence of 3,5,3'-triidothyronine (T(3)). Addition of low doses of T(3) (10(-8), 10(-7) M) to the medium significantly decreased 17beta-estradiol (E(2)) levels, whereas high doses of T(3) (10(-6), 10(-5) M) did not inhibit the levels. Similar effects of T(3) on CYP19 mRNA expression were observed. These results indicate that augmentation of E(2) production in hypothyroid animals may be mediated, in part, via the stimulation of CYP19 mRNA expression in granulosa cells, which is suppressed by thyroid hormone.

Effect of dihydrotestosterone on pituitary follicle-stimulating hormone isoforms in adult male rats treated with a gonadotropin-releasing hormone antagonist

The effect of androgens on the oligosaccharide structure of follicle-stimulating hormone (FSH) isoforms was studied in adult male rats treated with a potent gonadotropin-releasing hormone (GnRH) antagonist. Animals were castrated (Cx), and 24 h later were treated with physiological doses of either testosterone propionate (T) or dihydrotestosterone propionate (DHT) (0.25 mg/rat in corn oil, daily, s.c.) for 7 days. The antiandrogen flutamide (F; 5 mg/day/rat, twice a day, s.c.) was administered to either Cx-T or Cx-DHT rats to block androgen action. The GnRH antagonist Org 30276 (Ant; 1 mg/kg/day, s.c.) was injected to both Cx- and Cx-DHT treated rats. FSH serum levels reached normal values in Cx rats treated with either T or DHT, whereas those treated with F retained Cx conditions. Both Cx-Ant and Cx-Ant-DHT treated animals presented normal serum FSH levels. Concanavalin A affinity chromatography was used to isolate pituitary FSH isoforms according to their carbohydrate inner structure. An increased proportion of FSH isoforms bearing complex-type oligosaccharides was observed in Cx rats treated with T or DHT, whereas the proportion of these isoforms was reduced in Cx and Cx-T-F or Cx-DHT-F rats. These results demonstrate that functional androgens are needed to complete the oligosaccharide processing of FSH. In addition, the proportion of the different pituitary FSH isoforms after DHT replacement was equivalent to that found when GnRH action was blocked, indicating that androgens are involved in the regulation of carbohydrate incorporation to the FSH molecule by acting mainly at the pituitary level, independently of GnRH action.

Impact of carbohydrate heterogeneity in function of follicle-stimulating hormone: studies derived from in vitro and in vivo models

Carbohydrates attached to the protein core of glycoprotein hormones influence a number of intracellular and extracellular processes. As with other members of the glycoprotein hormone family, FSH is produced and released as an array of isoforms that differ from each other in the structure of their oligosaccharide attachments. In this review, we discuss how carbohydrate heterogeneity can impact on FSH action in different in vitro and in vivo systems. We present evidence for diverse effects of distinct charge isoforms at the target cell level, including differential and unique effects on various end responses, and discuss how the use of multiple cell-type assays has allowed identification of some specific effects of FSH isoforms on different cell populations and follicle compartments as well as oocyte maturation. Finally, we discuss recent information on the ability of naturally occurring and laboratory manufactured FSH isoforms to evoke particular effects on granulosa cell function and ovarian follicular maturation in vivo. Such studies have provided evidence that the type(s) of FSH signal delivered may in fact regulate distinct biological outcomes irrespective or in addition to outcomes dictated solely by clearance rate differences.

Glycosylation of an N-terminal extension prolongs the half-life and increases the in vivo activity of follicle stimulating hormone

FSH is a key component in assisted reproductive technologies. Because of rapid clearance of the hormone, patients have to be treated with daily injections. To address this problem, a long-acting FSH mutein was created by introduction of additional N-linked glycosylation into the molecule. New glycosylation sites were introduced by two different approaches: structure-aided, site-directed introduction of sites within the FSH molecule and addition of N-terminal extensions. A mutein with the extension sequence ANITVNITV at the N terminus of the alpha-chain (FSH1208) was efficiently glycosylated at both new sites. This resulted in a molecule with increased size and charge, factors known to reduce renal clearance of proteins. FSH1208 was found to have a 3- to 4-fold increased serum half-life, compared with wild-type recombinant FSH. Furthermore, in spite of a lower in vitro activity, FSH1208 had a markedly increased in vivo potency, as shown by increased ability to augment the ovarian weight and stimulate the serum estradiol levels in rats. These characteristics make FSH1208 a possible candidate for improved infertility treatment.

Intact follicle culture: what it can tell us about the roles of FSH glycoforms during follicle development

An important limiting factor in assisted reproduction treatment success rates is oocyte quality. In spite of improved results through several important innovations, the pregnancy rate per collected oocyte remains far too low. In order to improve this situation, it is necessary to learn more about fundamental factors modulating follicular development patterns. FSH is known to be the driving force for follicle development, but it is not yet understood how its multifarious functions are controlled and modulated. Evidence is accumulating that FSH glycoforms may be the key to this mystery. Intact follicle culture is a useful tool for the clarification of the actions of the different isoforms because the follicle unit is maintained and allowed to develop through several critical stages. Additionally important is the availability of the oocyte for functional evaluation. Because of these features, relationships can be uncovered that are not revealed with single cell test systems. The results so far obtained with this system suggest that follicle development pattern and oocyte quality is strongly influenced by FSH glycoform range, and that the requirements of the follicle may shift during progress through different stages of development. More studies are required, but these findings already suggest that the physiological shifts of circulating FSH glycoforms may indeed be important, and that attention should be paid to the glycoform distribution of exogenously applied FSH.

Effect of FSH and its different isoforms on maturation of oocytes from pre-ovulatory follicles

FSH exists as a family of isohormones exhibiting distinct oligosaccharide structures, and the released FSH isoform mixtures change during the follicular phase of the menstrual cycle. In addition, the pulsatile release of gonadotrophins seems to expose follicles to bursts of more less-acidic FSH isoforms and the follicle is likely to be exposed to an almost ever changing composition of FSH isoforms. The different isoforms causes a number of different and divergent biological effects. FSH promotes oocyte maturation, and 5-10 IU/l of less-acidic FSH isoforms are sufficient to induce oocyte maturation in vitro. Exposure of cumulus-oocyte complexes to less-acidic FSH isoforms in a pulse-like fashion results in a rapid pattern of cAMP accumulation exceeding that seen with acidic isoforms, which appear to sustain lower but more constant cAMP production. The presence of particularly less-acidic isoforms for a period exceeding 30 min causes an attenuated cAMP response. In conclusion, it appears that pulsatile and intermittent release of less-acidic/short-living FSH isoforms is sufficient to induce biological responses, while allowing the granulosa cells to regain responsiveness to further FSH stimulation. Together with the interpulse release of more acidic isoforms, overall FSH secretion seems to ensure proper follicular maturation resulting in the release of developmentally competent oocytes.