Inhibition of Astrocytic Histamine N-Methyltransferase as a Possible Target for the Treatment of Alzheimer's Disease.

Alzheimer's disease (AD) represents the principal cause of dementia among the elderly. Great efforts have been established to understand the physiopathology of AD. Changes in neurotransmitter systems in patients with AD, including cholinergic, GABAergic, serotoninergic, noradrenergic, and histaminergic changes have been reported. Interestingly, changes in the histaminergic system have been related to cognitive impairment in AD patients. The principal pathological changes in the brains of AD patients, related to the histaminergic system, are neurofibrillary degeneration of the tuberomammillary nucleus, the main source of histamine in the brain, low histamine levels, and altered signaling of its receptors. The increase of histamine levels can be achieved by inhibiting its degrading enzyme, histamine N-methyltransferase (HNMT), a cytoplasmatic enzyme located in astrocytes. Thus, increasing histamine levels could be employed in AD patients as co-therapy due to their effects on cognitive functions, neuroplasticity, neuronal survival, neurogenesis, and the degradation of amyloid beta (Aß) peptides. In this sense, the evaluation of the impact of HNMT inhibitors on animal models of AD would be interesting, consequently highlighting its relevance.

Central Histamine, the H3-Receptor and Obesity Therapy.

The brain histaminergic system plays a pivotal role in energy homeostasis, through H1- receptor activation, it increases the hypothalamic release of histamine that decreases food intake and reduces body weight. One way to increase the release of hypothalamic histamine is through the use of antagonist/inverse agonist for the H3-receptor. Histamine H3-receptors are auto-receptors and heteroreceptors located on the presynaptic membranes and cell soma of neurons, where they negatively regulate the synthesis and release of histamine and other neurotransmitters in the central nervous system. Although several compounds acting as H3-receptor antagonist/inverse agonists have been developed, conflicting results have been reported and only one has been tested as anti-obesity in humans. Animal studies revealed the opposite effect in food intake, energy expeditor, and body weight, depending on the drug, spice, and route of administration, among others. The present review will explore the state of art on the effects of H3-receptor ligands on appetite and body-weight, going through the following: a brief overview of the circuit involved in the control of food intake and energy homeostasis, the participation of the histaminergic system in food intake and body weight, and the H3-receptor as a potential therapeutic target for obesity.

Intracerebellar microinjection of histaminergic compounds on locomotor and exploratory behaviors in mice.

The neural histaminergic system innervates the cerebellum, with a high density of fibers in the vermis and flocculus. The cerebellum participates in motor functions, but the role of the histaminergic system in this function is unclear. In the present study, we investigated the effects of intracerebellar histamine injections and H1, H2 and H3 receptor antagonist injections (chlorpheniramine, ranitidine, and thioperamide, respectively) and H4 receptor agonist (VUF-8430) on locomotor and exploratory behaviors in mice. The cerebellar vermis of male mice was implanted with guide cannula. After three days of recovery,the animals received microinjections of saline or histamine (experiment1), saline or chlorpheniramine (experiment 2), saline or ranitidine(experiment 3), saline or thioperamide (experiment 4), and saline or VUF-8430 (experiment 5) in different concentrations. Five minutes postinjection,the open field test was performed. The data were analyzed using one-way ANOVA and Duncan's post hoc test. The microinjections of histamine, ranitidine or thioperamide did not lead any behavioral effects at the used doses. In contrast, animals that received chlorpheniramine at the highest dose (0.16 nmol) and VUF-8430 at the highest dose (1.48 nmol)were more active in the open field apparatus, with an increase in the number of crossed quadrants, number of rearings and time spent in the central area of the arena, suggesting that chlorpheniramine and VUF-8430 modulates locomotor and exploratory behaviors in mice.

Hypertensive response to stress: the role of histaminergic H1 and H2 receptors in the medial amygdala.

Different brain areas seem to be involved in the cardiovascular responses to stress. The medial amygdala (MeA) has been shown to participate in cardiovascular control, and acute stress activates the MeA to a greater extent than any of the other amygdaloid structures. It has been demonstrated that the brain histaminergic system may be involved in behavioral, autonomic and neuroendocrine responses to stressful situations. The aim of the present study was to investigate the role of the histaminergic receptors H1 and H2 in cardiovascular responses to acute restraint stress. Wistar rats (280-320g) received bilateral injections of cimetidine, mepyramine or saline into the MeA and were submitted to 45min of restraint stress. Mepyramine microinjections at doses of 200, 100 and 50nmol promoted a dose-dependent blockade of the hypertensive response induced by the restraint stress. Cimetidine (200 and 100nmol) promoted a partial blockade of the hypertensive response to stress only at the highest dose administered. Neither drugs altered the typical stress-evoked tachycardiac responses. Furthermore, mepyramine and cimetidine were unable to modify the mean arterial pressure or heart rate of freely moving rats under basal conditions (non-stressed rats). The data suggest that in the MeA the histaminergic H1 receptors appear to be more important than H2 receptors in the hypertensive response to stress. Furthermore, there appears to be no histaminergic tonus in the MeA controlling blood pressure during non-stress conditions.

Estudo da participação dos receptores histaminérgicos centrais dos tipos H1 e H2 no controle da ingestão de água / Study of participation of central histaminergic types H1 and H2 in the control of water intake

Diferentes grupos de pesquisa têm se dedicado à investigação dos mecanismos cerebrais de controle da sede. O avanço neste campo da Neurociência tem trazido importantes contribuições para a compreensão da regulação da homeostasia hidrossalina, o que pode levar a futuras aplicações clínicas. Desde a década de 1950 tem sido sugerido que a histamina pode atuar como neuromodulador/neurotransmissor no sistema nervoso central, entretanto sua função ainda não é clara, especialmente no que concerne ao controle da homeostasia hidrossalina. Assim o objetivo do presente trabalho foi investigar o papel das vias histaminérgicas centrais no controle da ingestão hídrica e ingestão de água pós-prandial. Foram utilizados quatro modelos de estudo: ingestão hídrica em animais normoidratados, em animais desidratados por privação hídrica e por sobrecarga de sódio e pós-prandial. No primeiro grupo ratos normoidratados receberam microinjeções bilaterais no núcleo ventromedial hipotalâmico (VMH), de HTMT, agonista específico para os receptores histaminérgicos do tipo H1, nas doses de 100 e 200 nmol e dimaprite agonista para os receptores H2 na dose de 100 nmol. No segundo grupo, animais em privação hídrica por 14 horas "overnight" foram injetados no VMH com mepiramine, antagonista dos receptores histaminérgicos H1, e cimetidine, antagonista específico para os receptores H2 nas doses de 100 e 200 nmol. No terceiro grupo foi realizado em animais sob desidratação osmótica induzida por sobrecarga da salina hipertônica (solução salina 9% num volume de 10% do peso corporal). Nesses três grupos o volume ingerido pelos animais foi monitorado a cada 15 minutos durante 2 horas. No quarto grupo as 18:00 horas foram aplicadas microinjeçóes de mepiramine e cimetidine na dose de 200 nmol para a investigação da ingestão hídrica pós-prandial. A ingestão alimentar e o volume hídrico ingeridos deste grupo foram monitorados a cada 30 minutos durante as primeiras 4 horas do período noturno e ao fim deste período (6:00 h)...

Antiinflammatory effects of Tacrolimus in a mouse model of pleurisy.

INTRODUCTION: Tacrolimus is an antibiotic macrolide with immunosuppressant properties isolated from Streptomyces tsukubaensis. OBJECTIVES: This study evaluated whether the acute and systemic administration of Tacrolimus significantly interfered in leukocyte migration, exudation, myeloperoxidase and adenosine-deaminase and nitric oxide levels, as well as Interleukin-1 (IL-1beta) and tumor necrosis factor alpha (TNFalpha) levels in a mouse model of pleurisy in comparison to those obtained with dexamethasone. MATERIALS AND METHODS: Pleurisy was induced by carrageenan (Cg, 1%), bradykinin (BK, 10 nmol), histamine (HIS, 1 micromol) or substance P (PS, 20 nmol) administered by intrapleural route (ipl.) and the inflammatory parameters (cell migration and exudation) were analyzed 4 h after. In the model of pleurisy induced by carrageenan, other markers in the pleural fluid, such as cytokines (TNFalpha and Il-1beta), nitrite/nitrate (NOx), myeloperoxidase (MPO) and adenosine-deaminase (ADA) levels, were also studied. Dexamethaseone (0.5 mg/kg, i.p., 0.5 h before) was also analyzed in all protocols. RESULTS: In the pleurisy induced by carrageenan, Tacrolimus (1 mg/kg, i.p.) and dexamethasone (0.5 mg/kg, i.p.) administered 0.5 h before caused a significant decrease in leukocytes, neutrophils and exudation (P < 0.01). Under the same conditions, Tacrolimus and dexamethasone did not modify the blood's white or red cells (P > 0.05). Tacrolimus showed a long lasting antiinflammatory effect, inhibiting leukocytes and neutrophils for up to 24 h (P < 0.01), whereas the inhibition of exudation was less marked (up to 2 h) (P < 0.01). These drugs caused a marked reduction in MPO activity, as well as IL-1beta and TNFalpha levels (P < 0.01), but only Tacrolimus inhibited ADA activity (P < 0.01). On the other hand, dexamethasone, but not Tacrolimus, inhibited NOx levels (P < 0.01). In the same conditions, Tacrolimus significantly inhibited cell migration induced by either bradykinin, histamine or substance P (P < 0.05). In a similar manner, dexamethasone inhibited leukocyte influx induced by bradykinin and histamine (P < 0.05). Regarding exudation effects, dexamethasone markedly inhibited this parameter induced by BK, HIS or SP, whereas Tacrolimus only inhibited exudation caused by HIS (P < 0.05). CONCLUSIONS: The results of the present work indicate that Tacrolimus showed important antiinflammatory properties against pleurisy in mice that are different from those caused by dexamethasone. The inhibition of proinflammatory cytokine (TNFalpha, IL-1beta), enzyme (myeloperoxidase, adenosine-deaminase) and mediator (bradykinin, histamine, substance P) release and/or action appears to account for Tacrolimus's actions.

Histamine combined with melphalan in isolated limb perfusion for the treatment of locally advanced soft tissue sarcomas: preclinical studies in rats.

PURPOSE: To evaluate the potential benefit of histamine combined with melphalan in the isolated limb perfusion (ILP) as an alternative to TNF-alfa and melphalan combination, for the treatment of irresectable soft tissue sarcomas of the limbs in Brown Norway (BN) rats. METHODS: 20 BN rats had small fragments of syngeneic BN-175 fibrosarcoma inserted on the right hind limb. In 7-10 days the tumor reached a median diameter of 12-15 mm and they were randomly divided in four groups (sham, melphalan, histamine and escalating doses of histamine combined to melphalan) being submitted to experimental ILP for 30 minutes. Tumors were measured daily with a caliper and the volume was calculated. RESULTS: Response curves showed a significant effect of the combination of histamine 200 mg/mL with melphalan, with 66% overall response, including 33% complete responses (p< 0.01). There were no systemic collateral effects and locally only mild temporary edema was observed for some animals treated with histamine. CONCLUSION: Histamine combined with melphalan had a promising effect in the ILP warranting future studies to better explore the mechanism of action as well as its potential use in organ perfusion.

Histamine combined with melphalan in isolated limb perfusion for the treatment of locally advanced soft tissue sarcomas: preclinical studies in rats

OBJETIVO: Avaliar o potencial benéfico da histamina combinada ao melfalano, na perfusão de membro isolado (PMI), como alternativa à combinacão TNF-alfa mais melfalano, no tratamento de sarcomas de partes moles irressecaveis em extremidades, em ratos de linhagem Brown Norway (BN). MÉTODOS: 20 ratos BN foram submetidos a implantacão de fragmentos de fibrosarcoma singênico BN-175 na pata traseira direita. Em cerca de 7-10 dias o tumor atingiu um diâmetro médio de 12-15 mm e foram aleatóriamente divididos em quatro grupos (controle, melfalano,histamina em doses progessivas combinada ao melfalano e histamina) sendo submetidos a PMI experimental por 30 minutos. Os tumores foram então medidos diariamente com o uso de paquímetro e o volume tumoral calculado. RESULTADOS: As curvas de resposta mostram um efeito significativo da combinacão de Histamina na concentracão de 200 mg/mL ao melfalano, com 66% de resposta global incluindo 33% de respostas completas (p < 0.01). Não houve efeitos colaterais sistêmicos e localmente apenas edema leve e transitório nos animais tratados com histamine. CONCLUSAO: A histamina em combinacão com o melfalano apresenta um efeito promissor na PMI garantindo maiores investigacões do seu mecanismo de acão e do seu potencial uso na perfusão de órgãos.

Prescriçöes farmacêuticas em casos de rinite alérgica nas drogarias de Curitiba / Over the counter drugs in allergic rhinitis at Curitiba's drugstores

Com este trabalho os autores demonstraram que pacientes com sintomas de rinite alérgica e sem atendimento médico prévio foram medicados nos balcöes das drogarias de Curitiba excluindo quaisquer critérios ou orientaçöes sobre efeitos colaterais. O estudo mostra ainda quais os medicamentos mais vendidos pelos atendentes para o tratamento dos sintomas à eles relatados: vasoconstritores nasais, descongestionantes orais, anti-histamínicos e corticosteróides. Com isto, alertam para o risco das prescriçöes sem orientaçäo médica, expondo, muitas vezes, os pacientes ao uso inadequado de medicaçöes, piorando a condiçäo clínica destas pessoas