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Background Does minor head impact without signs of structural brain damage cause short-term changes in vasogenic edema as measured by an increase apparent diffusion coefficient (ADC) using diffusion weighted imaging? If so, could the increase in vasogenic edema be treated with a vasopressin V1a receptor antagonist? We hypothesized that SRX251, a highly selective V1a antagonist, would reduce vasogenic edema in response to a single minor head impact. Methods Lightly anesthetized male rats were subjected to a sham procedure or a single hit to the forehead using a closed skull, momentum exchange model. Animals recovered in five min and were injected with saline vehicle (n = 8) or SRX251 (n = 8) at 15 min post head impact and again 7−8 hrs later. At 2 h, 6 h, and 24 h post injury, rats were anesthetized and scanned for increases in ADC, a neurological measure of vasogenic edema. Sham rats (n = 6) were exposed to anesthesia and scanned at all time points but were not hit or treated. Images were registered to and analyzed using a 3D MRI rat atlas providing site-specific data on 150 different brain areas. These brain areas were parsed into 11 major brain regions. Results Untreated rats with brain injury showed a significant increase in global brain vasogenic edema as compared to sham and SRX251 treated rats. Edema peaked at 6 h in injured, untreated rats in three brain regions where changes in ADC were observed, but returned to sham levels by 24 h. There were regional variations in the time course of vasogenic edema and drug efficacy. Edema was significantly reduced in cerebellum and thalamus with SRX251 treatment while the basal ganglia did not show a response to treatment. Conclusion A single minor impact to the forehead causes regional increases in vasogenic edema that peak at 6 h but return to baseline within a day in a subset of brain regions. Treatment with a selective V1a receptor antagonist can reduce much of the edema.

SRX246 is a potent, highly selective, orally bioavailable vasopressin 1a receptor antagonist that represents a novel mechanism of action for the treatment of mood disorders. The compound previously showed efficacy in animal models of mood disorders and excellent safety and tolerability in healthy volunteers in phase I clinical trials. In this study, SRX246 was further characterized in rats and dogs. In vitro determinations of permeability, protein binding, hepatocyte metabolism, and cytochrome P450 enzyme inhibition and in vivo assessments of pharmacokinetics were conducted. In parallel artificial membrane permeability assay (PAMPA) and PAMPA-blood-brain barrier models, SRX246 was comparable to highly permeable, orally active pharmaceuticals. SRX246 hydrochloride salt was 95.5 ± 1.7%, 95.9 ± 1.3%, and 98.6 ± 0.4% bound to rat, dog, and human serum proteins, respectively, and was stable in serum after a 4h incubation at 37°C. P450 enzyme inhibition results showed a very low potential for drug-drug interactions. Metabolism in primary hepatocytes demonstrated that SRX246 was stable in humans and moderately metabolized in dogs and rats. Plasma pharmacokinetics findings showed a half-life ( T 1/2 ) of 2 and 6h in rat and dog, respectively. Rat brain levels following a single oral dose were approximately 20% of plasma values with a T 1/2 of 6 h. The observed profile for SRX246 supports further development. © 2013 Wiley Periodicals, Inc. and the American Pharmacists Association J Pharm Sci 102:2033–2043, 2013

A compelling case for the potential utility of vasopressin (AVP) antagonists as a novel therapeutic class for the treatment of stress-related affective illness has emerged based on observations in depressed individuals, findings in animal models of anxiety and depression, and an understanding of changes in hypothalamic-pituitary-adrenal (HPA) axis regulation under chronic stress. The scientific bases for vasopressin antagonists as a pharmacotherapy for anxiety and depression include: 1) the neuroadaptation and dysregulation of HPA function that accompanies chronic stress in affected humans and in animal models of anxiety and depression, 2) recognition that AVP, not corticotrophin releasing factor (CRF), drives HPA function associated with chronic psychological stress, 3) the CNS localization of vasopressin V1a and V1b receptors in limbic system regions involved in HPA regulation and control of social behaviors, and 4) preclinical data showing efficacy in animal models employed as screens for anxiolytic and antidepressant activity. The public health need for new pharmaceutical treatments for stress-related affective illness is well documented. In the United States alone, anxiety and depression affect some 40 million people each year and carry a conservatively estimated annual total economic burden of at least $125 billion. Existing pharmacotherapies for both indications are not uniformly effective and frequently have undesirable side effects. These limitations demonstrate that a new treatment approach through vasopressin receptor antagonism in the CNS may offer significant opportunities for improved outcomes. In this review, the development of compounds in this class since 2005 is considered. The most advanced clinical candidates and newer compounds described in recent patents are presented.

The mechanism of action of dehydroepiandrosterone (DHEA) and dehydroepiandrosterone sulfate (DHEA-S), two interconvertable neurosteroids, has not been fully characterized in the central nervous system (CNS). Previous studies demonstrated that DHEA was intrinsically androgenic, suggesting that it may act through a genomic pathway. However, it is not known whether DHEA-S also produces androgenic effects, an important question given that the concentration of DHEA-S in brain is some 7-12 times that of DHEA. The current study compared the potential androgenic effects of DHEA-S with DHEA by examining their capacity to induce two characteristic effects of an androgenic compound. These included the ability to (1) up-regulate neural androgen receptor (AR) protein level in mouse brain and immortalized GT1-7 hypothalamic cells and (2) assess their effect on reporter gene expression through AR in CV-1 cells cotransfected with pSG5-AR and pMMTV-ARE-CAT reporter. Semi-quantitative Western blot analysis showed that DHEA treatment significantly augmented AR in mouse brain and GT1-7 cells in a dose-dependent manner and that these effects were not blocked by trilostane (TRIL), a known 3beta-hydroxysteroid dehydrogenase inhibitor. DHEA also promoted AR-mediated reporter gene expression as a function of dose and the effect was comparable with or without the addition of TRIL. In contrast, DHEA-S treatment failed to increase AR level in the mouse brain or GT1-7 cells and modestly induced AR-mediated reporter gene expression only at substantially elevated concentrations compared to DHEA. The findings demonstrate that DHEA is capable of exerting androgenic effects through AR while the androgenicity of DHEA-S is negligible. The implications of the results for models of the mechanism of action of DHEA and its sulfate ester, DHEA-S, in the brain are considered.

Androgens exert profound effects on the organization and function of the central nervous system. These effects are mediated by the androgen receptor (AR), a ligand-dependent transcription factor. The mechanisms of AR regulation in neural tissue, however, remain to be fully elucidated. Characterizing this process can provide important information regarding receptor function and AR gene regulation in the brain. Previously, it was shown that testosterone (T) up-regulated neural AR in a dose-dependent manner in both male and female mice. In the present study, whether AR was differentially regulated by the natural agonists T and dihydrotestosterone (DHT) or the nonsteroidal antagonist flutamide (FLU) was assessed. Males were gonadectomized and AR levels were allowed to decline to baseline 3 days after surgery. Changes in AR protein content produced by the various treatments were measured by semiquantitative Western blot of limbic system extracts. Treatment with T or DHT significantly augmented AR 3 and 7 h after hormone administration, but only DHT sustained this increase for 21 h. This difference also was observed when males were given T plus finasteride (FIN, a 5alpha reductase inhibitor). The findings demonstrate that the two endogenous ligands have differential time course effects on neural AR. The antiandrogen FLU failed to up-regulate AR at doses up to 100 times higher than T or DHT. When administered concomitantly with T or DHT, it effectively inhibited the augmentation of AR normally seen 3 h after androgen treatment. While immunohistochemical studies showed that FLU was able to promote nuclear translocation of AR, Western analysis revealed that FLU, in contrast to T and DHT, failed to maintain the integrity of AR. The results demonstrate that (a) the endogenous androgens T and DHT regulate AR differently, suggesting a potential cellular mechanism that may contribute to the difference in neural target gene sensitivity to these androgens; (b) up-regulation of AR occurs only in the presence of agonists; (c) the mechanism of action of FLU in the brain involves inhibition of AR protein up-regulation normally seen in response to androgen; and (d) FLU promotes AR nuclear translocation but not augmentation of cellular AR populations. These findings demonstrate that in vivo AR regulation in the brain basically parallels mechanisms proposed from results obtained with transfected cells and cell lines.

Our understanding of the neurochemical and neuroendocrine systems' regulating the display of offensive intermale aggression has progressed substantially over the past twenty years. Pharmacological studies have shown that serotonin, via its action at 5HT1A and/or 5HT1B receptor sites, modulates the display of intermale aggressive behavior and that its effects serve to decrease behavioral expression. Neuroendocrine investigations, in turn, have demonstrated that male-typical aggression is testosterone-dependent and studies of genetic effects, metabolic function and steroid receptor binding have shown that facilitation of behavioral displays can occur via independent androgen-sensitive or estrogen-sensitive pathways. Remarkably, there have been virtually no studies that examined the interrelationship between these facilitative and inhibitory systems. As an initial step toward characterizing the interaction between the systems, studies were conducted that assessed hormonal modulation of serotonin function at 5HT1A and 5HT1B receptor sites. They demonstrated: (1) that the androgenic and estrogenic metabolites of testosterone differentially modulate the ability of systemically administered 8-OH-DPAT (a 5HT1A agonist) and CGS12066B (a 5HT1B agonist) to decrease offensive aggression; and (2) when microinjected into the lateral septum (LS) or medial preoptic area (MPO), the aggression-attenuating effects of 1A and 1B agonists differ regionally and vary with the steroidal milieu. In general, the results suggest that estrogens establish a restrictive environment for attenuation of T-dependent aggression by 8-OH-DPAT and CGS 12066B, while androgens either do not inhibit, or perhaps even facilitate, the ability of 5HT1A and 5HT1B agonists to reduce aggression. Potential mechanisms involved in the production of these steroidal effects are discussed and emerging issues that may impact on efforts to develop an integrative neurobiological model of offensive, intermale aggression are considered.

There are multiple pathways involved in the regulation of male typical aggression by T, and the functional pathway is determined by genotype. Target-tissue sensitivity to the aggression-promoting properties of T and its estrogenic and androgenic metabolites is determined by a complex sequence of events in which steroid receptors play a critical role. To date, it appears that the relative density of AR may be an important factor in the biobehavioral effects of androgens. Regarding sensitivity to estrogens, characterization of ER-NM interactions, and understanding of the contribution of the two activating functions within ER, appears to be necessary to comprehensively describe the cellular basis for responsiveness to the aggression-promoting effect of this T metabolite. In broader terms, these observations indicate that understanding the relationship between T and the expression of aggression in humans will require models that incorporate cellular aspects of steroid hormone action, including metabolism, receptor function, and gene regulation. Language: en

Publisher Summary Offensive aggression between conspecific males and conspecific females can serve as model systems to exemplify our understanding of androgenic effects on aggressive behavior. This form of aggression between same-sex conspecifics is a productive behavior because it determines dominance status and access to resources. The use of offensive aggression in males as a model is based on its widely documented dependence on testosterone (T), the principal testicular androgen. Including females as a representative system for exemplifying androgenic effects on aggression seem unusual, given the numerous failures to identify a positive relationship between T and this behavior in female mammals. However, several studies clearly demonstrated that females housed in small groups displayed aggression toward other females, juvenile males, or gonadectomized adult males. Studies also showed that dehydroepiandrosterone (DHEA), an androgenic neurosteroid synthesized in the brains of humans and other mammals, played an important role in regulating the aggressive behavior. Research with animal models demonstrates the complex nature of hormonal modulation and the need for increasingly refined regulatory models of offensive aggression. The complexity and extent of interactions also indicates that focusing on a single genetic or physiological marker, as a cause of aggression is a difficult proposition with limited utility.

Arginine vasopressin functions as a neurochemical signal in the brain to affect social behavior. There is an expanding literature from animal and human studies showing that vasopressin, through the vasopressin 1A receptor (V1A), can stimulate aggressive behavior. Using a novel monocylic beta lactam platform, a series of orally active vasopressin V1a antagonists was developed with high affinity for the human receptor. SRX251 was chosen from this series of V1a antagonists to screen for effects on serenic activity in a resident-intruder model of offensive aggression. Resident, male Syrian golden hamsters were given oral doses of SRX251 or intraperitoneal Manning compound, a selective V1a receptor antagonist with reduced brain penetrance, at doses of 0.2 microg, 20 microg, 2 mg/kg or vehicle. When tested 90-120 min later, SRX251, but not Manning compound, caused a significant dose-dependent reduction in offensive aggression toward intruders as measured by latency to bite and number of bites. The reduction in aggression persisted for over 6 h and was no longer present 12 h post treatment. SRX251 did not alter the amount of time the resident investigated the intruder, olfactory communication, general motor activity, or sexual motivation. These data corroborate previous studies showing a role for vasopressin neurotransmission in aggression and suggest that V1a receptor antagonists may be used to treat interpersonal violence co-occurring with such illness as ADHD, autism, bipolar disorder, and substance abuse.

This chapter utilizes conspecific, offensive aggression in males and females as model systems to exemplify androgenic influences on aggressive behavior. This form of aggression is a productive behavior exhibited between same-sex conspecifics; its effects are reflected in dominance status and access to resources.

The mechanism of action of dehydroepiandrosterone (DHEA), a neuroactive neurosteroid synthesized in the brains of humans and other mammals, has not been fully characterized in the adult brain. Although well known for modulatory effects on GABA(A), NMDA, and sigma(1) receptors, studies in both CNS and peripheral target cells suggest that DHEA also may exert genomic effects via the androgen receptor (AR). The current study tested the hypothesis that DHEA was capable of producing androgenic effects in the CNS by assaying its ability to induce three characteristic effects of an androgenic compound. These included the ability to upregulate neural AR protein level in mouse brain and immortalized GT1-7 hypothalamic cells, the capacity to induce transcriptional activity through AR in CV-1 cells transfected with an MMTV-ARE-CAT reporter, and competition for recombinant AR binding in a radioligand binding assay. The results showed that DHEA treatment significantly augmented AR both in vivo and in vitro, and that this effect was not blocked by trilostane (TRIL), a known 3beta-hydroxysteroid dehydrogenase (3beta-HSD) inhibitor. DHEA also promoted AR-mediated CAT reporter expression and competed with dihydrotestosterone (DHT) for binding to recombinant AR in a cell-free system. These data indicate that DHEA possesses intrinsic androgenic activity that is potentially independent of metabolic conversion to other androgens, and that it can affect gene function through the AR. In combination with its modulation of neurotransmitter receptors at the cell membrane level, the findings suggest that the mechanism of action of DHEA in the brain can involve a "crosstalk" cellular signaling system that involves both nongenomic and genomic components.

Characterization of the hormonal processes that mediate the development and expression of sexual dimorphisms in regulatory systems for conspecific, maletypical aggression has provided a model for elaborating the cellular processes that underlie these sex differences. The ability to pursue these relationships, however, is more than simply the product of methodological advances. While the development of receptor assays, highly specific antibodies, and gene probes have vastly expanded the capabilities of neuroscientists, the systematic description of steroidal effects on aggression represents an essential prerequisite if a functional role is to be ascribed to particular molecular events. Our studies on the regulation of aggression in mice have evolved along these lines over the past fifteen years. They have focused on defining active neuroendocrine pathways in adult males and females from various genotypes. Descriptions of similarities and differences between sexes and among strains provided the basis for developmental investigations that sought to define both the specific roles of the androgenic and estrogenic metabolites of testosterone in the differentiation of these regulatory systems and the precise time frame during the perinatal period when they were established. These data, in turn, generated models for evaluating specific aspects of steroid receptor function in the brain that were potentially linked to observed differences in behavioral sensitivity/insensitivity to the aggression-promoting property of gonadal steroids.