Leuprolide -a GnRH agonist prevents restraint stress-induced immunosuppression via sex steroid-independent peripheral mechanism in mice

Sex steroid ablation: an immunoregenerative strategy for immunocompromised patients

Age-related decline in thymic function is a well-described process that results in reduced T-cell development and thymic output of new naïve T cells. Thymic involution leads to reduced response to vaccines and new pathogens in otherwise healthy individuals; however, reduced thymic function is particularly detrimental in clinical scenarios where the immune system is profoundly depleted such as after chemotherapy, radiotherapy, infection and shock. Poor thymic function and restoration of immune competence has been correlated with an increased risk of opportunistic infections, tumor relapse and autoimmunity. Apart from their primary role in sex dimorphism, sex steroid levels profoundly affect the immune system in general and, in fact, age-related thymic involution has been at least partially attributed to the increase in sex steroids at puberty. Subsequently it has been demonstrated that the removal of sex steroids, or sex steroid ablation (SSA), triggers physiologic changes that ultimately lead to thymic re-growth and improved T-cell reconstitution in settings of hematopoietic stem cell transplant (HSCT). Although the cellular and molecular process underlying these regenerative effects are still poorly understood, SSA clearly represents an attractive therapeutic approach to enhance thymic function and restore immune competence in immunodeficient individuals.

Hypothalamic neurohormones and immune responses

The aim of this review is to provide a comprehensive examination of the current literature describing the neural-immune interactions, with emphasis on the most recent findings of the effects of neurohormones on immune system. Particularly, the role of hypothalamic hormones such as Thyrotropin-releasing hormone (TRH), Corticotropin-releasing hormone (CRH) and Gonadotropin-releasing hormone (GnRH). In the past few years, interest has been raised in extrapituitary actions of these neurohormones due to their receptors have been found in many non-pituitary tissues. Also, the receptors are present in immune cells, suggesting an autocrine or paracrine role within the immune system. In general, these neurohormones have been reported to exert immunomodulatory effects on cell proliferation, immune mediators release and cell function. The implications of these findings in understanding the network of hypothalamic neuropeptides and immune system are discussed.

Immunomodulatory effects of anti-estrogenic drugs

There are substantial experimental, epidemiological and clinical evidences that show that breast cancer pathology is influenced by endogenous estrogens. This knowledge is the foundation upon which endocrine deprivation therapy has been developed as a major modality for the management of breast cancer. Tamoxifen, which functions as a competitive partial agonist-inhibitor of estrogen at its receptor, has been widely used for more than three decades for adjuvant endocrine treatment in breast cancer. Currently, other effective drugs for endocrine therapy include raloxifene, different aromatase inhibitors (particularly third-generation agents) and luteinizing hormone-releasing hormone agonists. In recent years, a growing body of evidence suggests that these drugs can also act as immune modulators by altering the function of various leukocytes and the release of different cytokines. Moreover, there is evidence that anti-estrogens may prove to be beneficial in the treatment or prevention of some autoimmune diseases due to their effects on immune function. However, their immunopharmacological aspects in the present state of knowledge are not precisely comprehensible. Only a clear pathophysiological understanding could lead to an efficient strategy for breast cancer prevention and decrease in the mortality due to this disease.

Acquisition, expression, and reinstatement of ethanol-induced conditioned place preference in mice: effects of exposure to stress and modulation by mecamylamine

Nicotinic acetylcholine receptors mediate some of the rewarding and motivational effects of ethanol, including relapses. Relapses are common in drug addicts during abstinence when exposure to any stressor ensues. However, the role of nicotinic acetylcholine receptors in the ethanol- and stress-induced reinstatement of ethanol-induced conditioned place preference has not yet been explored. Therefore, the present study investigated the influence of mecamylamine, a nicotinic acetylcholine receptors antagonist on acquisition, expression, and reinstatement of ethanol-induced conditioned place preference in adult male Swiss mice. The results revealed that mecamylamine (0.1-10 µg/mouse, intracerebroventricularly) dose dependently prevented the development, expression, and reinstatement of ethanol-induced conditioned place preference. Further, acute treatment with mecamylamine blocked the restraint stress and forced swim stress-induced reinstatement of ethanol-induced conditioned place preference. All of these treatments had no influence on the locomotor activity. Therefore, it is concluded that mecamylamine blocks the acquisition, expression and reinstatement of conditioned reinforcing effects of ethanol without per se reinforcing or aversive influence. This ability of mecamylamine might be a potential advantage in the treatment of alcoholism.

Luteinizing hormone receptor deficiency increases the susceptibility to alkylating agent-induced lymphomagenesis in mice

Previous studies have revealed a close link between luteinizing hormone (LH)/human chorionic gonadotropin (hCG) signaling and oncogenesis in gonadal and nongonadal tissues. To investigate whether genetic ablation of LH receptor (Lhr) affects the animal's oncogenic susceptibility, adult female wild-type (wt), heterozygous, and homozygous Lhr knockout (LhrKO) mice were intraperitoneally injected with an alkylating agent, N-methyl-N-nitrosourea (MNU, 50 mg/kg of body weight). The mice were sacrificed when they were short of breath or 10 months after the injection. The results showed that MNU induced non-Hodgkin's thymic and lymphonodus lymphomas in 70.6% and 100% of heterozygous and homozygous animals, respectively, compared with 35.7% in wt siblings. The tumor development was rapid; they were more aggressive and metastasized to the spleen, liver, and kidney in Lhr-deficient mice compared to wt siblings. All tumors were immunostained-positive for a T-cell specific marker, CD3, but not for a B-cell marker, CD22, suggesting that all the lymphomas arose from T-cells, which are known to be LH/hCG receptor-positive. There was no rearrangement of the Lhr gene locus or differences in thymic cell proliferation among the genotypes. However, apoptosis was lower in the Lhr-deficient thymuses. The thymic Bcl-2 levels were elevated and caspase-3 activation was reduced in Lhr heterozygous and homozygous animals. In conclusion, MNU induced a higher incidence and an earlier onset of aggressive lymphomas in LhrKO animals, which may be associated with a reduction in apoptosis of thymocytes.

Reversal by quercetin of corticotrophin releasing factor induced anxiety- and depression-like effect in mice

Quercetin is a bioflavonoid reported to produce variety of behavioral effects like anxiolytic, antidepressant, etc. Recent gathering evidences indicated that quercetin attenuates stress-induced behavioral and biochemical effects. It also decreases CRF expression in the brain. As CRF is commonly implicated in the high-anxiety and depression, we hypothesized that quercetin may involve CRF in its anxiolytic- and antidepressant-like effects. To support such possibility, we investigated the influence of quercetin on CRF or CRF antagonist (antalarmin) induced changes in social interaction time in social interaction test, and immobility time in forced swim test. Results indicated that quercetin (20-40 mg/kg, p.o.) or antalarmin (2-4 microg/mouse, i.c.v.) dose dependently increased social interaction time and decreased immobility time indicating anxiolytic- and antidepressant-like effect. These effects were comparable with the traditional anxiolytic (diazepam, 1-2mg/kg, i.p.) and antidepressant (fluoxetine, 10-20mg/kg, i.p.) agents. Administration of CRF (0.1 and 0.3 nmol/mouse, i.c.v.) produced just opposite effects to that of quercetin on these parameters. Further, it was seen that pretreatment with quercetin (20 or 40 mg/kg, p.o.) dose dependently antagonized the effects of CRF (0.1 or 0.3 nmol/mouse, i.c.v.) in social interaction and forced swim test. The sub-effective dose of antalarmin (1 microg/mouse) when administered along with the sub-effective dose of quercetin (10mg/kg) produced significant anxiolytic-and antidepressant-like effect. These observations suggest reciprocating role of quercetin on the CRF-induced anxiogenic and depressant-like effects.

Autism: an emerging 'neuroimmune disorder' in search of therapy

BACKGROUND

Autism spectrum disorders (ASDs) are neurodevelopmental disorders characterized by difficulties in communication and by repetitive and stereotypic behaviors, as well as by social impairment, attention, cognitive, and learning defects. ASDs present in early childhood and their prevalence has increased significantly to 1/150 children. Despite a number of theories, the actual reasons for this increase are still not clear. There is no reliable screening test, and no definite pathogenesis or curative therapy. Consequently, there is a major gap hampering development of effective treatments.

OBJECTIVE

To review recent publications on ASDs pathogenesis and treatment with emphasis on neuroimmune processes and new therapeutic approaches.

METHODS

Mostly original papers (450) on epidemiology, possible pathogenesis or treatment of ASDs in Medline from 1990 to May 2009 were reviewed. All authors contributed to this review.

RESULTS/CONCLUSION

Increased oxidative stress and immune dysregulation are present in ASDs. Mast-cell activation may contribute to gut-blood-brain barrier disruption and brain inflammation. No effective treatments have emerged. Well-designed clinical trials with nonpsychotropic drugs were few and ASD characteristics varied considerably, making conclusions difficult. Psychotropic drugs are often used for stereotypic and aggressive behaviors. Unique combinations with antioxidant and anti-inflammatory flavonoids hold promise. New potential translational research areas and possible treatments are suggested.

Neurosteroids modulate compulsive and persistent behavior in rodents: implications for obsessive-compulsive disorder

Neurosteroids are reported to modulate GABAergic and glutamatergic pathways that then influence serotonin and dopamine, the neurotransmitters implicated in pathophysiology of obsessive-compulsive disorder (OCD). Fluoxetine, a selective serotonin reuptake inhibitor clinically used in OCD is reported to increase the levels of neurosteroids like allopregnanolone, whereas OCD patients exhibit higher plasma levels of dehydroepiandrosterone 3-sulphate (DHEAS), a neuroactive steroid having opposite effects to that of allopregnanolone. Hence, it was contemplated that neurosteroids may influence obsessive-compulsive behavior. To test this possibility we studied the influence of various neurosteroids on two behavioral models of OCD, namely marble-burying behavior in mice and 8-OH-DPAT induced disruption of spontaneous alternation behavior (SAB) in rats. The results revealed that allopregnanolone (1 microg/mouse, i.c.v) and progesterone (20mg/kg, s.c.) reduced the marble-burying behavior in mice, whereas dehydroisoandrosterone 3-sulphate (DHAS) (5mg/kg, i.p.) exacerbated the same. The effects of allopregnanolone were comparable to that of fluoxetine (10mg/kg, i.p.). In view of the report that restraint stress increases the levels of allopregnanolone and isolation stress decreases the same, we studied the effect of these stressors on marble-burying behavior; wherein it was found to be less in restraint stress exposed mice, and higher in socially isolated mice. Restrain stress-induced attenuation of marble-burying behavior was blocked by finasteride, a neurosteroid biosynthesis blocker. In rat model of SAB disruption, acute and chronic treatment with allopregnanolone (1 microg/mouse, i.c.v.) reduced 8-OH-DPAT-induced persistent behavior, whereas treatment with DHAS (5mg/kg, i.p.) had an opposite effect. In conclusion, the studies indicate that neurosteroids can modulate obsessive-compulsive behavior in a bidirectional manner, and could serve as an effective target in the management of OCD.

Effects of central administration of gonadotropin-releasing hormone agonists and antagonist on elevated plus-maze and social interaction behavior in rats

The correlation between neuronal mechanism of anxiety and neuroanatomic expression/neuromodulatory role of gonadotropin-releasing hormone (GnRH), points to a role of GnRH in the modulation of anxiety. Therefore, we investigated the influence of GnRH agonists and antagonist on the anxiety-like behavior of rats in the elevated plus-maze and social interaction tests. GnRH agonists, leuprolide [100 or 200 ng/rat, intracerebroventricularly (i.c.v.)] or 6-D-tryptophan luteinizing hormone-releasing hormone (400 ng/rat, i.c.v.), significantly increased percentage of open arms entries, time spent in open arms, and time spent in social interaction. The observed anxiolytic effect of these agents was comparable with diazepam (0.5-1.0 mg/kg, intraperitoneally). Treatment with a GnRH antagonist [pGlu-D-Phe-Trp-Ser-Tyr-D-Ala-Leu-Arg-Pro-Gly-NH2, (100 ng/rat, i.c.v.)], significantly reduced percentage of open arm indices and decreased time spent in social interaction, indicating an anxiogenic-like effect. Further, castrated rats exhibited anxiogenic-like behavior in these tests, which was significantly attenuated by leuprolide (200 ng/rat, i.c.v.) or 6-D-tryptophan luteinizing hormone-releasing hormone (400 ng/rat, i.c.v.), indicating the noninvolvement of peripheral sex hormone in their anxiolytic-like effect, at least in castrated rats. In conclusion, this study indicated a putative role of GnRH in the control of anxiety, and further adds to the importance of investigating the possible role of the hypothalamus-pituitary-gonadal axis in regulating the anxiety-related disorders arising out of hypothalamus-pituitary-adrenal axis dysregulation.

Gonadotropin-releasing hormone agonist blocks anxiogenic-like and depressant-like effect of corticotrophin-releasing hormone in mice

Corticotrophin-releasing factor (CRF) is reported to inhibit the release of gonadotropin-releasing hormone (GnRH). In addition to the endocrine effects, GnRH is reported to influence the behavior via its neuronal interactions. We therefore, hypothesized that anxiety and depression produced by CRF could be also subsequent to the decrease in GnRH. To support such possibility, we investigated the influence of GnRH agonists on CRF or CRF antagonist induced changes in social interaction time in social interaction test, and immobility time in forced swim test in mice, as the indices for anxiety and depression, respectively. Results indicated that GnRH agonists [leuprolide (20-80 ng/mouse, i.c.v.), or d-Trp-6-LHRH (40-160 ng/mouse, i.c.v.)] dose dependently increased social interaction time and decreased immobility time indicating anxiolytic- and antidepressant-like effect, respectively. Such effects of GnRH agonists were even evident in castrated mice, which suggest that these effects were unrelated to their endocrine influence. Administration of CRF (0.1 and 0.3 nmol/mouse, i.c.v.) produced just opposite effects as that of GnRH agonist on these parameters. Further, it was seen that pretreatment with leuprolide (10 or 20 ng/mouse, i.c.v.) or d-Trp-6-LHRH (20 or 40 ng/mouse, i.c.v.) dose dependently antagonized the effects of CRF (0.3 nmol/mouse, i.c.v.) in social interaction and forced swim test. CRF antagonist [alpha-Helical CRF (9-41), (1 or 10 nmol/mouse, i.c.v.)] was found to exhibit anxiolytic- and antidepressant-like effect, and its sub-effective dose (0.1 nmol/mouse, i.c.v.) when administered along with sub-threshold dose of leuprolide (10 ng/mouse, i.c.v.), or d-Trp-6-LHRH (20 ng/mouse, i.c.v.) also produced significant anxiolytic- and antidepressant-like effect. These observations suggest reciprocating role of GnRH in modulating the CRF induced anxiogenic- and depressant-like effects.

Leuprolide: a luteinizing hormone releasing hormone agonist attenuates ethanol withdrawal syndrome and ethanol-induced locomotor sensitization in mice

Ethanol inhibits the synthesis, content and release of hypothalamic luteinizing hormone releasing hormone (LHRH), and LHRH modulates the activity of several neurotransmitters that experience adaptive changes on chronic exposure to ethanol, and also implicate in ethanol dependence. Hence, it was contemplated that LHRH agonist such as leuprolide may influence the behavioral consequences of withdrawing ethanol in dependent state. In the present study, ethanol dependence was produced in mice by providing ethanol liquid diet for 10 days; and its withdrawal on day 11 led to physical signs of hyperexcitability with its peak at 6th h. Acute treatment with leuprolide (20 ng/mouse, i.c.v.), 10 min prior to peak, significantly attenuated hyperexcitability. Such effect of leuprolide was evident even in castrated mice, and castration significantly increased the hyperexcitability in ethanol withdrawal state. Chronic treatment with leuprolide (10 ng/mouse, twice daily, i.c.v.) till day 10 significantly reduced the signs of hyperexcitability in ethanol withdrawal state. In another set of experiment, ethanol (2.4 g/kg, i.p.) was administered on day 1, 4, 7, 10 and 15, which caused gradual increase in locomotor activity indicating ethanol-induced sensitization. Leuprolide (20 ng/mouse, i.c.v.), 10 min prior to the challenge dose of ethanol (2.4 g/kg, i.p.) on day 15 significantly attenuated the expression of sensitization to hyperlocomotor effect of ethanol. Similarly, administration of leuprolide (20 ng/mouse, i.c.v.), 10 min prior to ethanol on day 1, 4, 7 and 10 not only reduced the gradual increase in locomotor activity but also attenuated the sensitized locomotor response on day 15, indicated attenuation of development of sensitization. Leuprolide per se did not affect physical signs and locomotor activity in control group. In conclusion, the present study demonstrated that leuprolide treatment attenuates expression and development of ethanol dependence and sensitization in mice.