Dopamine stimulates the degradation of gonadotropin releasing hormone by rat synaptosomes

Surface Modification of Bacteria to Optimize Immunomodulation for Advanced Immunotherapy

Bacteria have been widely exploited as therapeutic agents for immunotherapy due to their native immunogenicity, living characteristic, and genetic manipulability. However, conventional bacteria-based immunotherapy often suffers from dose-dependent safety issues and poor treatment efficacy. Harnessing surface modification of bacteria to carry additional immune modulators has emerged as a promising strategy to reduce bacterial dose and synergistically enhance the activation of immune responses. In this paper, bacteria-mediated immunomodulation and the underlying mechanisms are introduced, followed by a summarization on the concept of using surface-modification approaches including physical encapsulation, chemical conjugation, and metabolic labelling to combine diverse immune functions. The applications of modified bacteria as therapeutics for immunotherapy toward cancer and inflammatory bowel disease have been expounded further. Both challenges and future perspectives regarding the utilization of surface-modified bacteria for immunomodulation are also proposed. This work offers unique insights into developing safe yet potent bacteria-based therapeutics for advanced immunotherapy.

Polydopamine Nanoparticle-Mediated Dopaminergic Immunoregulation in Colitis

Despite immunosuppression is critical for reducing immune overactivation, existing immunosuppressive agents are largely restricted by low inhibition efficiencies and unpredictable off-target toxicities. Here, the use of the dopaminergic system is reported to suppress hyperactive immune responses in local inflamed tissues. A polydopamine nanoparticular immunosuppressant (PDNI) is synthesized to stimulate regulatory T (Treg) cells and directly inhibit T helper 1 (Th1), Th2, and Th17 cells. Moreover, PDNI can inhibit the activation of dendritic cells to upregulate the ratio of Treg/Th17, which assists the reversion of inflammatory responses. The application of dopaminergic immunoregulation is further disclosed by combining with gut microbiota modulation for treating inflammations. The combination is implemented by coating living beneficial bacteria with PDNI. Following oral delivery, coated bacteria not only suppress the hyperactive immune responses but also positively modulate the gut microbiome in mice characterized with colitis. Strikingly, the combination demonstrates enhanced treatment efficacies in comparison with clinical aminosalicylic acid in two murine models of colitis. The use of the dopaminergic system opens a window to intervene immune responses and provides a versatile platform for the development of new therapeutics for treating inflammatory diseases.

Effect of chronic L-dopa administration on serum luteinizing hormone levels in male rats

We examined whether the repeated oral administration with a high dose of L-3-(3,4-dihydroxyphenyl)-alanine (L-DOPA) in 0.5% carboxymethyl cellulose increases serum luteinizing hormone (LH) levels in male rats. Serum LH levels were increased 4 h after a single administration of 1000 mg/kg L-DOPA to male rats, and returned to control levels within 8 h after administration. Four hours after a single administration, serum LH levels were significantly increased by L-DOPA at 1000 mg/kg, but not at 20, 100 or 200 mg/kg. Decreases in body weight and relative weight of the prostate were observed after 7 and 14 days of administration of 1000 mg/kg per day L-DOPA, but no changes were observed in weight of the testis, epididymis or seminal vesicle. The administration of L-DOPA at 500 or 1000 mg/kg per day for 7 or 14 days resulted in increased basal serum LH levels and decreased basal serum prolactin levels 24 h after the last administration. Serum testosterone levels tended to be higher in treated than in control rats. The levels of two metabolites of dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), in rats treated with 500 mg/kg per day tended to be slightly higher than those in control rats after 7 days of administration. Levels of DA, DOPAC and HVA were significantly increased after 7 and 14 days of administration of 1000 mg/kg per day and after 14 days of administration of 5000 mg/kg per day. The level of norepinephrine, but not its metabolite 3-methoxy-4-hydroxyphenylglycol, was significantly increased after only 7 days of administration of 1000 mg/kg per day. No significant changes were observed in levels of 5-hydroxytryptamine or its metabolite 5-hydroxyindole-3-acetic acid with administration of 500 or 1000 mg/kg per day. These findings suggest that a prolonged treatment with a high dose of L-DOPA in male rats induces release of LH from the pituitary, resulting in sustained elevation of LH levels in peripheral circulation.

Antidopaminergic-induced hypothalamic LHRH release and pituitary gonadotrophin secretion in 12 day-old female and male rats

In previous studies we have shown that the developing rat provides an interesting physiologic model in which the dopaminergic control of both LH and FSH is well defined in contrast to the controversial results obtained in adult rats. We wished to establish the role of testosterone in antidopaminergic induced gonadotrophins release in 12 day-old male and female rats, and evaluate the effect of antidopaminergic drugs at the hypothalamic level during this developmental stage. Haloperidol, an antidopaminergic drug, increased both LH and FSH in female 12 day-old rats but not in male littermates. The effect was blocked by bromocriptine and not by phentolamine indicating that haloperidol acted on the dopaminergic receptor, and that unspecific stimulation of the noradrenergic system was not involved. Haloperidol was ineffective when female rats were previously ovariectomized and injected with testosterone propionate at 9 days of age. If females were treated on the day of birth with testosterone propionate, haloperidol-induced FSH and LH release was also abolished. In control males haloperidol had no effect on the release of LH or FSH. But if males were orchidectomized at birth or at 9 days of age, haloperidol released both LH and FSH during the infantile period. In an attempt to establish the site of action of antidopaminergic drugs on gonadotrophin release, hypothalami (mediobasal and preoptic-suprachiasmatic area) from 12 day-old infant female rats were perifused with either haloperidol or domperidone (2*10(-6) M). Both drugs increased LHRH release into the perifusate. Besides haloperidol did not modify the release of LH or FSH from adenohypophyseal cells incubated in vitro. We therefore conclude that antidopaminergic-induced gonadotrophins release is modulated by serum testosterone concentrations, and that the site of action is probably the LHRH-secreting neuron of the hypothalamus.

Behavioral effects of centrally administered LH-RH agonist in rats

The neuropharmacological actions of the agonist analog D-Trp-6-LH-RH were investigated in several tests after intracerebroventricular (ICV) administrations to male rats. The doses applied were 10, 100 and 1000 ng/animal. In the open field the 1000 ng ICV dose of the peptide D-Trp-6-LH-RH suppressed the ambulation, rearing and grooming. In a combined catalepsy test, the 10 ng and 1000 ng dose of D-Trp-6-LH-RH increased the total duration of immobility. The LH-RH agonist inhibited stereotyped behavior induced by both apomorphine and amphetamine, and the effects of 100 and 1000 ng D-Trp-6-LH-RH were significant. Naloxone in a dose of 0.5 mg/kg IP totally abolished the inhibition of apomorphine-induced stereotypy by 1000 ng D-Trp-6-LH-RH, but the opiate antagonist did not influence amphetamine-induced stereotypy but significantly potentiated the inhibitory effect of 100 ng D-Trp-6-LH-RH. In the tail-flick test the latencies were significantly increased after D-Trp-6-LH-RH ICV, both 20 or 40 min after the injections. The peptide-induced analgesia was totally naloxone reversible. The results indicate that the agonist analog of LH-RH exert potent actions on the central nervous system, and the mechanism of effects may involve dopaminergic transmission and/or endogenous opiates.

Neuropharmacological actions of the superactive agonist analog D-TRP-6-LH-RH after peripheral injection into mice

The neuropharmacological actions of the agonist analog D-Trp-6-LH-RH were investigated in several tests after subcutaneous administrations to male mice. The doses applied were in the range 1-1000 micrograms/kg. D-Trp-6-LH-RH doses of 10 micrograms/kg and higher induced significant analgesic effects in the hot-plate and tail-flick tests, and decreased the open-field parameters (ambulation, rearing, grooming). The 100 and 1000 micrograms/kg doses increased the latencies of picrotoxin-induced seizures, significantly inhibited apomorphine-induced cage climbing and also exerted a cataleptogenic effect. The results indicate that this agonist analog of LH-RH has an inhibitory effect on the central nervous system, and the mechanism of its action may involve dopaminergic transmission and/or endogenous opiates.

Degradation of gonadotropin-releasing hormones in the gilthead seabream, Sparus aurata. I. Cleavage of native salmon GnRH and mammalian LHRH in the pituitary

The pattern and kinetics of degradation of native salmon gonadotropin-releasing hormone (sGnRH) and mammalian leuteinizing hormone-releasing hormone (LHRH) by pituitary bound enzymes were studied in the gilthead seabream, Sparus aurata. sGnRH and LHRH were incubated for different periods of time with membrane or cytosolic fractions of pituitary homogenates. At the end of the incubation, the degradation mixture was fractionated on reverse-phase high-pressure liquid chromatography. The degradation products were identified by comparing their retention times to those of synthesized GnRH fragments and by analyzing their amino acid composition. The main GnRH degradative activity resides in the cytosolic fraction of the pituitary homogenate. Both sGnRH and LHRH are rapidly degraded by pituitary cytosol, with 78.3 and 87.7% of the peptides, respectively, cleaved after 3 hr of incubation. Maximal degradation of sGnRH occurred at a pH range of 7 to 8. The main initial products of degradation of sGnRH and LHRH are the 1-5, 6-10, and 1-9 fragments. This suggests the involvement of two site-specific peptidases, a Tyr5-Gly6 endopeptidase and a Pro9-Gly10NH2 peptidase or postproline cleaving enzyme. While the 1-6 and 1-9 fragments undergo rapid secondary degradation, the 1-5 is relatively stable. Competition experiments suggest that the endopeptidase cleaving the sGnRH at the Tyr5-Gly6 bond is not specific to the neuropeptide and is probably a general proteolitic enzyme. However, the cleavage at the 9-10 bond has a high degree of specificity to the Pro9-Gly10NH2 sequence found in sGnRH. The two proposed pituitary peptidases of S. aurata have some characteristics similar to those of rat hypophyseal and hypothalamic GnRH cleaving enzymes. No differences are found in hypophyseal GnRH degradative activity between females with occytes undergoing previtellogenesis or advanced stages of vitellogenesis.

Dopamine decreases release of luteinizing hormone releasing hormone from superfused rat mediobasal hypothalamus

The effects of dopamine hydrochloride (DA) on the releases of LHRH and LH were examined in a serial sequential double chamber perifusion system by perifusing the mediobasal hypothalamus including the preoptic area and/or pituitaries excised from diestrus female rats. DA, perifused at a dose of 4.2 X 10(-4) M, significantly (p less than 0.05) lowered LH secretion from the pituitary in series with the hypothalamus 40-80% below the preinfusion level, but it had no effect on LH efflux from the pituitary perifused alone. DA also significantly (p less than 0.05) reduced the LHRH level 20-40% below the initial level. Perifusion with the DA receptor blocker haloperidol at a concentration of 10(-6) M abolished the suppressive effect of DA on LH secretion. These findings indicate that DA suppressed hypothalamic LHRH release, resulting in decrease in LH secretion from the pituitary in diestrus rats.

GnRH secreting cultured fetal rat hypothalamic cells do not degrade GnRH

The possible degradation of GnRH in the hypothalamus was investigated. Rat fetal hypothalamic cells were kept in culture for two weeks and basal and stimulated GnRH release was measured by highly sensitive RIA. These intact hypothalamic cells did not degrade GnRH during 4 hours of incubation, but a 50% degradation occurred after 24 hours incubation followed by HPLC using specifically tritium labeled GnRH or RIA. The rate of degradation or the kinetic of degradation did not change by increasing GnRH concentration in the medium or by mechanical instead of enzymatic dispersion of the cells. For comparison GnRH degradation in homogenized hypothalamic tissue and in synaptosomal preparation was measured and rapid degradation was found. Our results suggest that intact hypothalamic cells under physiological circumstances do not degrade extracellular GnRH.

Enzymic inactivation of hypothalamic regulatory hormones

The considerable expansion in studies on the enzymic inactivation of thyrotrophin-releasing hormone, luteinizing hormone-releasing hormone and somatostatin (growth hormone release-inhibiting hormone) has necessitated a re-evaluation of the peptidase enzymes responsible. Through the use of new methods such as high-performance liquid chromatography and the development of artificial enzyme substrates, it has been possible to clarify the mechanisms of enzyme cleavage of these hypothalamic regulatory hormones and to attempt purification of the peptidases. This has brought about a renewed interest in the physiological significance of the enzymes, as well as their role in biotransformation of the hypothalamic hormones. From such studies, the information gained may be used in the design of agonist and antagonist analogues, as well as providing details of the mechanisms of action of such analogues through their increased stability to enzymic degradation. The characterization of corticotrophin-releasing factor and growth hormone-releasing factor will provide a new field for the application of peptidase inactivation to analogue design. Similarly, future examination of the peptidases inactivating the hypothalamic hormones in certain clinical conditions may give new insight into the significance of the enzymes in pathological conditions. Identification of these enzymes, investigation of their localization, properties and functions and assessment of their contribution to the control of hormone action may yield valuable insight into the physiology and pathology of the hypothalamic regulatory hormones.

Thyrotropin-releasing hormone in the pancreas and brain of the rat is regulated by central noradrenergic and dopaminergic pathways

These studies have been undertaken to evaluate the role of the brain noradrenergic and dopaminergic pathways in the regulation of the secretion of thyrotropin-releasing hormone (TRH) in the central nervous system (CNS) and pancreas of the neonatal rat. When CNS stores of norepinephrine (NE) were selectively reduced by the subcutaneous administration of the dopamine-beta-hydroxylase inhibitor FLA-63, TRH concentrations were significantly reduced throughout the brain. However, when CNS stores of both NE and dopamine (DA) were depleted by the subcutaneous administration of the tyrosine hydroxylase inhibitor alpha-methyl-rho-tyrosine (alpha-MT), TRH concentrations in the brain were not significantly altered.FLA-63 and alpha-MT did not significantly reduce pancreatic catecholamine concentrations, indicating that in the basal state, these agents predominantly deplete central catecholamine stores. Nevertheless, pancreatic TRH concentrations were markedly reduced by FLA-63, and this effect was significantly attenuated by the simultaneous intracerebroventricular (icv) administration of NE. In contrast to the effects of FLA-63, alpha-MT caused a significant increase in pancreatic TRH concentrations, and this effect was significantly lessened by icv DA. To determine whether the sympathetic nervous system might be one route by which these central effects are mediated, a chemical sympathectomy was induced with guanethidine. This treatment selectively reduced pancreatic concentrations of NE, and caused a marked increase in pancreatic TRH concentrations. FROM THESE OBSERVATIONS, WE CONCLUDE THE FOLLOWING: (a) within the central nervous system, both NE and DA are involved in regulating brain TRH secretion or biosynthesis, and the direction of action of these two neurotransmitters appears to be opposite; (b) pancreatic TRH secretion or biosynthesis is also controlled by the brain noradrenergic and dopaminergic systems, and the net effects of each of these pathways appears to be opposite; (c) at least one route by which impulses from the brain may travel and modulate pancreatic TRH secretion or biosynthesis is by the sympathetic nervous system.

A method for studying synaptosomal release of neurotransmitter candidates, as evaluated by studies on cortical cholecystokinin octapeptide release

A method for perfusing rat cortical synaptosomes for studying the regulation of cholecystokinin octapeptide (CCK-8) release has been developed and was found to have advantages over the static incubation system. Synaptosomes isolated from rat cortex were suspended in Biogel P2 columns and perfused with Krebs Ringer Bicarbonate buffer. One hundred mM KCl and 75 microM veratine stimulated CCK-8 release, which was Ca++-dependent. The synaptosomes were functionally viable for at least 135 min of incubation as indicated by multiple 100 mM KCl depolarizations and uptake of (3H)-norepinephrine and (14C)-choline. Dopamine and acetylcholine (10(-6)M) stimulated CCK-8 release while serotonin and norepinephrine were without effect. Approximately 20% of total occluded CCK-8 was released from synaptosomes by 100 mM KCl and degradation of CCK-8 was less than 10%. Perfusion of synaptosomes has several advantages over static incubation systems and allows systematic studies on the role of neurotransmitter in the regulation of neuropeptide secretion.

Degradation of luteinizing hormone-releasing hormone by serum and plasma in vitro

Luteinizing hormone-releasing hormone (LH-RH) is degraded in vitro by serum and plasma from several species (human, rat, guinea-pig and cattle). Separation of the degradation products by high-performance liquid chromatography (HPLC) followed by amino acid analysis and radioimmunoassay showed that the main sites of cleavage are the Trp3-Ser4 and Tyr5-Gly6 bonds. Two peptidases are responsible since the cleavage at Trp3-Ser4 can be selectively inhibited by EDTA. In human plasma, the peptidase responsible for Trp3-Ser4 hydrolysis has a Km of 2.9 . 10(-4) M and V of 30 nmol/h per ml plasma. The half-life in vitro of LH-RH in serum and plasma from various species ranges from 3 h (guinea-pig) to 9.8 h (human). The peptidase cleaving LH-RH at Tyr5-Gly6 is present as an impurity in some commercial bovine serum and plasma albumins. Such contamination may have important practical implications for work involving peptide assays where albumins are used as carrier proteins.

Characterization and determination of neuropeptides by high-performance liquid chromatography and radioimmunoassay

A method is described for the separation and analysis of a variety of neuropeptides using reversed-phase high-performance liquid chromatography coupled with radioimmunoassay. The solvent system (an acetonitrile gradient containing 0.08% trifluoroacetic acid) allows UV detection at 206 nm, gives good resolution and, by being volatile, is readily compatible with radioimmunoassay. Three applications of the method are described: (a) thyrotropin releasing hormone immunoreactivity in the rat brain has been characterized; (b) ACTH immunoreactivity in the rat pituitary pars intermedia has been resolved into its component peptides; (c) degradation of luteinizing hormone releasing hormone in vitro has been followed.

Peptidase regulation of gonadotropin-releasing hormone levels during in vitro incubations of the rat hypothalamus

The fate of gonadotropin-releasing hormone (GnRH) was examined by a GnRH radioimmunoassay during in vitro incubations of the rat medial basal hypothalamus (MBH). There was a progressive disappearance of exogenous GnRH during MBH incubations. The GnRH degradation could be explained by the release of peptidases from the MBH into the incubation medium. The cytoplasmic marker lactic dehydrogenase (LDH) was also released into the incubation medium. The peptide antibiotic bacitracin produced a dose-dependent inhibition of GnRH degradation during MBH incubations; 1 mM-bacitracin completely inhibited exogenous GnRH degradation during 4-h incubations. Bacitracin also produced dose-dependent increases in the recovery of endogenous GnRH released from the MBH under basal conditions or when stimulated with the depolarizing agent veratrine. Veratrine also was found to decrease the GnRH peptidase activity significantly but not the LDH activity during MBH incubations. The present results indicate that peptidase activity can be an important regulator of endogenous GnRH released from the hypothalamus during in vitro incubations.