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Leptin, secreted by adipose tissue, indirectly stimulates the activity of GnRH-producing neurons in the hypothalamus and thus regulates the functional activity of the hypothalamic–pituitary–testicular (HPT) axis. Obesity is known to be accompanied by a systemic hyperleptinemia and impaired leptin transport in the central nervous system, which limits the use of full-length leptin as a drug. It was previously shown that the intranasally administered (i.n.) leptin fragment MA-[D-Leu4]-OB3 (LF) enhances the steroidogenic effect of human chorionic gonadotropin (hCG) in rats fed a standard diet. An even more urgent task is to assess its effect on testicular steroidogenesis in obesity that reduces reproductive functions in men. This work was aimed to study the ability of LF (200 µg/kg, i.n., for 3 days) to modulate the effect of hCG (10 IU/rat, s.c., once) on testicular steroidogenesis in male Wistar rats with obesity induced by a 20-week high-fat/high-carb diet (HFHCD), as well as to evaluate the impact of the GnRH receptor antagonist Cetrorelix (ANT, 75 µg/kg, s.c., for 3 days) on the effects of LF in these animals. Obese rats demonstrated reduced testicular levels of the luteinizing hormone receptor (LHR) and a compensatorily upregulated expression of the Cyp11a1 gene encoding the steroidogenic enzyme cytochrome P450scc. LF administration enhanced hCG effects on blood testosterone levels and testicular expression of the Star gene encoding the cholesterol transporter protein StAR, which suggests the ability of LF to positively modulate HPT axis activity under obesity. ANT and LF co-administration, by contrast, reduced the stimulatory effect of hCG on blood testosterone levels and testicular Star gene expression, which may be due to the testicular effects of LF. Our data indicate the ability of LF to influence different components of the male gonadal axis under conditions of diet-induced obesity. [ABSTRACT FROM AUTHOR]

Autoimmune hyperthyroidism (Graves' disease), which is caused by stimulating autoantibodies to the thyroid-stimulating hormone receptor (TSHR), and thyroid tumors, caused by a constitutively increased activity of this receptor, are widespread and have a poor prognosis. The drugs used to treat them are low effective and have many side effects. One of the therapeutic approaches to these thyroid diseases may be the use of TSH receptor allosteric regulators with an activity of inverse agonists. This work was aimed to study the effects of the compound TP48, previously synthesized in our laboratory, and a newly synthesized compound TPY5, with both of them referring to thieno[2,3-d]-pyrimidines, on basal and thyrotropin-releasing hormone (TRH)-stimulated levels of thyroid hormones (THs) in the rat blood and on the expression of genes responsible for TH synthesis in the rat thyroid gland. TP48 and TPY5 effectiveness was studied upon both intraperitoneal (20 mg/kg) and peroral (40 mg/kg) administration. Using ELISA, blood levels of free (fT4) and total (tT4) thyroxine, as well as free (fT3) and total (tT3) triiodothyronine, were assessed, including during stimulation with intranasal TRH (300 µg/kg). Gene expression for thyroid peroxidase (Tpo), thyroglobulin (Tg), Na+/I– symporter (Nis), type 2 deiodinase (Dio2), and TSH receptor (Tshr) in the thyroid gland was assessed by PCR. TPY5, administered via both routes, reduced both basal and TRH-stimulated plasma TH levels, while TP48 suppressed TH production only after intraperitoneal administration. Peroral TPY5 significantly reduced basal Tpo expression, as well as TRH-stimulated Tg and Dio2 expression. Intraperitoneal TP48 reduced only TRH-stimulated Tg and Dio2 expression. Quite surprisingly, peroral TPY5 and intraperitoneal TP48 reduced basal Tshr expression but did not prevent its inhibition by TRH. Thus, the novel compound TPY5 exhibits the activity of a TSH receptor inverse agonist and is effective when administered perorally, which is more in demand in medicine; it can be considered as a prototype of drugs to treat autoimmune hyperthyroidism and thyroid tumors. [ABSTRACT FROM AUTHOR]

Men with obesity demonstrate not only various metabolic disorders and insulin resistance, but also reduced testosterone levels and reproductive system dysfunctions. Although one of the ways for pharmacological correction of these abnormalities may be the use of luteinizing hormone receptor (LHR) agonists and antidiabetic drugs (specifically, metformin, MF), the mechanisms of their effects on the hypothalamic–pituitary–gonadal axis have not been sufficiently investigated. The aim of this work was to study the effects of long-term MF therapy (5 weeks, 120 mg/kg) and five-day treatment with LHR agonists, such as human chorionic gonadotropin (hCG, 20 IU/rat/day, s.c.) and allosteric agonist TP03 (15 mg/kg/day, i.p.), on blood testosterone levels and the expression of testicular and pituitary genes in male Wistar rats with long-term diet-induced obesity (DIO). TP03 moderately stimulated testosterone production in male rats with DIO without having an inhibitory effect on testicular LHR expression and only insignificantly reducing the pituitary expression of the LH β-subunit gene. After a single TP03 administration to DIO rats, its steroidogenic effect was comparable to that in the control group, but after a five-day administration, it was significantly inferior to it. In DIO rats, the steroidogenic effect of hCG after a single administration was lower than that in the control but comparable to that after a five-day administration, significantly exceeding the corresponding effects of TP03. Unlike TP03, hCG significantly reduced testicular LHR expression and more pronouncedly inhibited pituitary LH expression. MF treatment restored the androgenic status without significantly affecting the testicular expression of steroidogenic genes. In MF-treated groups, there was no increase in the steroidogenic effects of both LHR agonists. The results suggest the prospects for the use of TP03 and hCG to stimulate testicular steroidogenesis and increase the effectiveness of MF therapy in order to normalize testosterone production in DIO, which can be used to correct reproductive disorders in obesity. At the same time, a co-administration of MF and LHR agonists in DIO appears to be inappropriate. [ABSTRACT FROM AUTHOR]

The adipokine leptin plays an important role in the regulation of the reproductive system. It stimulates the activity of the hypothalamic–pituitary–gonadal axis by indirectly affecting gonadoliberin (GnRH)-secreting neurons and modulates testicular steroidogenesis via binding to leptin receptors in Leydig cells. The leptin fragment (LF) 116–122, which includes the main receptor-binding determinants of this adipokine, normalizes metabolic parameters in animals with a diet-induced obesity. However, its ability to influence the testicular steroidogenic function, including through interaction with hypothalamic GnRH neurons, has not been studied. The aim of this work was to study the effects of a single and 3-day intranasal LF administration (200 µg/rat) on blood testosterone levels and expression of steroidogenic genes in the testes of mature male Wistar rats, as well as to evaluate the steroidogenic activity of LF upon testosterone synthesis stimulation by human chorionic gonadotropin (hCG, 15 IU/rat, s.c.) and inhibition by the GnRH receptor antagonist Cetrorelix (75 µg/kg, s.c.). It was shown that a single LF administration increases blood testosterone levels, while a 3-day administration enhances the steroidogenic effect of hCG. LF and hCG increased the expression of the Star gene that encodes the key regulatory protein of steroidogenesis StAR. Cetrorelix administration reduced blood testosterone levels and Star expression, while compensatory increasing gene expression of the luteinizing hormone receptor. The potentiating effect of LF on hCG-induced stimulation of testosterone synthesis and Star expression was not detected after Cetrorelix treatment. Thus, LF is able to stimulate testicular steroidogenesis in rats by itself and potentiate the steroidogenic effects of hCG. Since its effects are suppressed in the presence of a GnRH antagonist, there are grounds to assume that they are implemented via stimulation of hypothalamic GnRH neurons. [ABSTRACT FROM AUTHOR]

In clinical practice, ovarian steroidogenesis is stimulated and ovulation is induced using such gonadotropin preparations as human chorionic gonadotropin (hCG) and luteinizing hormone (LH) which, however, have a number of side effects, including a reduction in ovarian sensitivity to endogenous LH and ovarian hyperstimulation syndrome. An alternative to hCG and LH could be allosteric LH/hCG receptor agonists, including the thieno[2,3-d]-pyrimidine derivative TP03 developed in our laboratory. This work was aimed to study the effect of TP03 (40 µg/kg, i.p.) versus hCG (30 IU/rat, s.c.) on ovarian steroidogenesis in mature female rats in the late proestrus phase, including those treated with the gonadotropin releasing hormone (GnRH) antagonist Orgalutran (100 µg/kg, s.c., 3 h before TP03 or hCG administration). Estradiol, progesterone and LH levels were measured in the blood, while expression levels of the steroidogenesis-related genes Star, Cyp11a1, Hsd3b, Cyp17a1, Hsd17b, Cyp19a1 and LH/hCG receptor gene Lhcgr were assessed in the ovaries. Three hours after administration, TP03 and hCG increased blood progesterone levels and stimulated the expression of genes encoding the cholesterol-transporting protein StAR, cytochrome P450c17, and aromatase (cytochrome P450c19), with these effects detected both in control rats with normal LH levels and in Orgalutran-treated rats with reduced LH levels. The effects of TP03 were comparable to those of hCG, but in contrast to hCG, TP03 did not reduce the activity of the hypothalamic–pituitary–gonadal axis, as indicated by the lack of its influence on blood LH levels and ovarian expression of LH/hCG receptors. Our data suggest the ability of TP03 to effectively stimulate ovarian steroidogenesis, as well as good prospects for the development of TP03-based drugs for controlled ovulation induction. [ABSTRACT FROM AUTHOR]

The functional restoration of the male reproductive system in type 2 diabetes mellitus (DM2) is one of the urgent global challenges in modern endocrinology. This problem can be solved through the application of both the drugs that improve glucose homeostasis and insulin sensitivity, primarily metformin, and the activators of luteinizing hormone receptor (LHR), such as human chorionic gonadotropin (hCG) and low-molecular-weight allosteric LHR agonists. The aim of the work was to study the effect of metformin therapy (4 weeks, 120 mg/kg/day) on steroidogenesis- and spermatogenesis-stimulating effects induced by the 5-day administration of 5-amino-N-tert-butyl-2-(methylsulfanyl)-4-(3-(nicotinamido)phenyl)thieno[2,3-d]pyrimidine-6-carboxamide (TP03), an allosteric LHR agonist (15 mg/kg/day), and hCG (20 IU/rat/day) to male Wistar rats with DM2. The DM2 was induced by a high-fat diet and a low-dose streptozotocin (25 mg/kg). Metformin therapy partially restored testosterone levels and normalized spermatogenesis in DM2 rats. On the first day, metformin treatment enhanced the steroidogenic effects of TP03 and hCG, however, in the following days its potentiating effect was not detected. After five days of treatment of diabetic rats with TP03 and hCG, epididymal sperm count was restored, including the spermatozoa with progressive motility, and the percentage of abnormal sperm was decreased. Spermatogenesis indices when treating with metformin or LHR agonists separately were comparable to those resulted from their co-administration. Thus, metformin therapy enhances TP03- and hCG-induced testosterone production on the first day of treatment with these drugs, however, later on, steroidogenic and spermatogenic effects of LHR agonists in the groups of diabetic rats treated and untreated with metformin did not differ significantly. [ABSTRACT FROM AUTHOR]