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Assuntos
Humanos , Masculino , Feminino , Sociedades Médicas/organização & administração , Sociedades Médicas/normas , Técnicas de Laboratório Clínico/história , Técnicas de Laboratório Clínico/tendências , Tecnologia Biomédica/história , Tecnologia BiomédicaRESUMO
Leptin (Ob) is a non-glycosylated peptide hormone that regulates energy homeostasis centrally, but also has systemic effects including the regulation of the immune function. We have reported previously that leptin activates human peripheral blood lymphocytes co-stimulated with phytohaemagglutinin (PHA) (4 microg/ml), which prevented the employment of pharmacological inhibitors of signalling pathways. In the present study, we used Jurkat T cells that responded to leptin with minimal PHA co-stimulation (0.25 microg/ml). The long isoform of leptin receptor is expressed on Jurkat T cells and upon leptin stimulation, the expression of early activation marker CD69 increases in a dose-dependent manner (0.1-10 nM). We have also found that leptin activates receptor-associated kinases of the Janus family-signal transucers and activators of transcription (JAK-STAT), mitogen-activated protein kinase (MAPK) and phosphatidylinositol 3 kinase (PI3K) signalling pathways. Moreover, we sought to study the possible effect of leptin on cell survival and apoptosis of Jurkat T cells by culture in serum-free conditions. We have assayed the early phases of apoptosis by flow cytometric detection of fluorescein isothiocyanate (FITC)-labelled annexin V simultaneously with dye exclusion of propidium iodide (PI). As well, we have assayed the activation level of caspase-3 by inmunoblot with a specific antibody that recognizes active caspase-3. We have found that leptin inhibits the apoptotic process dose-dependently. By using pharmacological inhibitors, we have found that the stimulatory and anti-apoptotic effects of leptin in Jurkat T cells are dependent on MAPK activation, rather than the PI3K pathway, providing new data regarding the mechanism of action of leptin in T cells, which may be useful to understand more clearly the association between nutritional status and the immune function.
Assuntos
Leptina/imunologia , Ativação Linfocitária/imunologia , Proteínas Quinases Ativadas por Mitógeno/metabolismo , Linfócitos T/imunologia , Sobrevivência Celular/imunologia , Relação Dose-Resposta Imunológica , Ativação Enzimática/imunologia , Humanos , Células Jurkat , Sistema de Sinalização das MAP Quinases/imunologia , Proteínas de Neoplasias/metabolismo , Fosfatidilinositol 3-Quinases/metabolismo , Fosforilação , Receptores para Leptina/metabolismo , Proteínas Recombinantes/imunologia , Reação em Cadeia da Polimerase Via Transcriptase Reversa/métodos , Fator de Transcrição STAT3/metabolismo , Tirosina/metabolismoRESUMO
Human immunodeficiency virus (HIV) codes for a protein, Rev, that mediates the viral RNA export from the nucleus to the cytoplasm. Recently, it has been found that Sam68, the substrate of Src associated in mitosis, is a functional homologue of Rev, and a synergistic activator of Rev activity. Thus, it has been suggested that Sam68 may play an important role in the post-transcriptional regulation of HIV. Sam68 contains an RNA binding motif named KH [homology to the nuclear ribonucleoprotein (hnRNP) K]. Tyrosine phosphorylation of Sam68 and binding to SH3 domains have been found to negatively regulate its RNA binding capacity. Besides, tyrosine phosphorylation of Sam68 allows the formation of signalling complexes with other proteins containing SH2 and SH3 domains, suggesting a role in signal transduction of different systems in human lymphocytes, such as the T cell receptor, and leptin receptor, or the insulin receptor in other cell types. In the present work, we have found that Sam68 is tyrosine phosphorylated in peripheral blood mononuclear cells (PBMC) from HIV infected subjects, leading to the formation of signalling complexes with p85 the regulatory subunit of PI3K, GAP and STAT-3, and decreasing its RNA binding capacity. In contrast, PBMC from HIV infected subjects have lower expression levels of Sam68 compared with controls. These results suggest that Sam68 may play some role in the immune function of lymphocytes in HIV infection.
Assuntos
Infecções por HIV/imunologia , Leucócitos Mononucleares/imunologia , Fosfotirosina/metabolismo , Proteínas de Ligação a RNA/metabolismo , Transdução de Sinais/fisiologia , Proteínas Adaptadoras de Transdução de Sinal , Adulto , Western Blotting , Proteínas de Ligação a DNA , Infecções por HIV/metabolismo , Humanos , Immunoblotting/métodos , Imunoprecipitação , Ligação Proteica , RNA/metabolismo , RNA Mensageiro/análise , Proteínas de Ligação a RNA/genética , Reação em Cadeia da Polimerase Via Transcriptase ReversaRESUMO
Leptin, the 16 kDa product of the ob gene, is a an adipocyte-secreted hormone that centrally regulates weight. However, the physiological role of leptin is not limited to the regulation of food intake and energy expenditure, and leptin has a variety of effects in peripheral tissues, such as a regulatory role modulating the immune system. Thus, leptin receptor is expressed in human peripheral blood mononuclear cells, mediating the leptin stimulation of proliferation and activation, the production of proinflammatory cytokines from cultured monocytes, and the prevention of apoptotic death in serum-deprived monocytes. Because leptin can stimulate monocytes and the production of reactive oxygen species (ROS) are the result of monocyte activation, we investigated the effect of leptin on ROS production by human monocytes in vitro. Oxidative burst was measured by oxidation of the redox-sensitive dye 2',7'-dichlorofluorescein diacetate, and analysed by flow cytometry. We have found that stimulation with leptin produces oxygen radical formation by monocytes. This effect is dependent on the dose and maximal response is achieved at 10 nM leptin. Because HIV infection induces the production of ROS, we next investigated the effect of leptin on ROS production in monocytes from HIV-positive (HIV+) subjects. We have also found that monocytes from HIV+ subjects spontaneously produced increased amounts of free radicals. In contrast, leptin stimulation of monocytes from these patients partially inhibited the production of ROS. This effect of leptin was also dependent on the dose and maximal effect was achieved at 10 nM. The effect of leptin stimulating the production of ROS is consistent with the proinflammatory role in the immune system. On the other hand, the inhibitory effect on monocytes from HIV+ subjects may be explained by the attenuation of the oxidative burst by a delayed activation of monocytes in a hyperinflammatory state.
Assuntos
Infecções por HIV/metabolismo , HIV-1 , Leptina/farmacologia , Monócitos/metabolismo , Adulto , Estudos de Casos e Controles , Células Cultivadas , Feminino , Citometria de Fluxo , Infecções por HIV/imunologia , Humanos , Masculino , Pessoa de Meia-Idade , Monócitos/efeitos dos fármacos , Espécies Reativas de Oxigênio/metabolismo , Explosão Respiratória/efeitos dos fármacos , Estimulação QuímicaRESUMO
Leptin is a an adipocyte-secreted hormone that regulates weight centrally. However, the leptin receptor is expressed not only in the central nervous system, but also in peripheral tissues, such as haematopoietic and immune systems. Therefore, the physiological role of leptin should not be limited to the regulation of food intake and energy expenditure. Moreover, the leptin receptor bears homology to members of the class I cytokine family, and recent data have demonstrated that leptin is able to modulate the immune response. Thus, the leptin receptor is expressed in human peripheral blood mononuclear cells, mediating the leptin effect on proliferation and activation. In vitro activation and HIV infection in vivo induce the expression of the long isoform of the leptin receptor in mononuclear cells. Also, leptin stimulates the production of proinflammatory cytokines from cultured monocytes and enhances the production of Th1 type cytokines from stimulated lymphocytes. Moreover, leptin has a trophic effect on monocytes, preventing apoptosis induced by serum deprivation. Leptin stimulation activates JAK-STAT, IRS-1-PI3K and MAPK signalling pathways. Leptin also stimulates Tyr-phosphorylation of the RNA-binding protein Sam68 mediating the dissociation from RNA. In this way, leptin signalling could modulate RNA metabolism. These signal transduction pathways provide possible mechanisms whereby leptin may modulate activation of peripheral blood mononuclear cells. Therefore, these data support the hypothesis regarding leptin as a proinflammatory cytokine with a possible role as a link between the nutritional status and the immune response. Moreover, these immunoregulatory functions of leptin could have some relevance in the pathophysiology of obesity.
Assuntos
Adipócitos/metabolismo , Leptina/imunologia , Leucócitos Mononucleares/imunologia , Receptores de Superfície Celular/metabolismo , Transdução de Sinais/fisiologia , Apoptose , Doenças Autoimunes/imunologia , Células Cultivadas , Citocinas/imunologia , Humanos , Janus Quinase 1 , Leptina/farmacologia , Leucócitos Mononucleares/efeitos dos fármacos , Ativação Linfocitária , Sistema de Sinalização das MAP Quinases , Estado Nutricional , Obesidade/imunologia , Fosfatidilinositol 3-Quinases/metabolismo , Isoformas de Proteínas/metabolismo , Proteínas Tirosina Quinases/metabolismo , Receptores para Leptina , Células Th1/metabolismoRESUMO
Leptin, the Ob gene product, is an adipocyte hormone that centrally regulates weight control. In addition, other effects of leptin in peripheral tissues have been described. Thus, leptin has been found to regulate reproduction, haematopoiesis and immune function. We have found recently that leptin has a stimulatory effect on human peripheral blood mononuclear cells (PBMC). Monocytes are activated by leptin alone whereas T lymphocytes need a suboptimal stimulus of PHA or ConA before further activation by leptin. These effects are mediated by the long isoform of the leptin receptor, which has been shown to trigger signalling in PBMC. In fact, we have found that human leptin stimulates Janus kinase (JAK)-signal transducer and activator of transcription (STAT), phosphatidylinositol 3-kinase (PI3K) and mitogen-activated protein kinase (MAPK) pathways in PBMC. In order to assess possible regulation of the long isoform of the leptin receptor (Ob-R) in mononuclear cells upon activation, we have studied the expression of Ob-R by RT-PCR and Western blotting in PBMC activated in vitro by PHA or ConA and in vivo in HIV-infected patients. We have found that in vitro activation and in vivo HIV infection correlates with an increase in leptin receptor expression in PBMC. Moreover, the leptin receptor is tyrosine phosphorylated in PBMC from HIV-infected patients, suggesting that the leptin receptor is activated. These results are consistent with the suggested role of leptin in modulating the immune response.
Assuntos
Proteínas de Transporte/biossíntese , Regulação da Expressão Gênica , Infecções por HIV/imunologia , Leptina/fisiologia , Ativação Linfocitária/genética , Isoformas de Proteínas/biossíntese , Receptores de Superfície Celular , Linfócitos T/metabolismo , Adolescente , Adulto , Proteínas de Transporte/efeitos dos fármacos , Proteínas de Transporte/genética , Proteínas de Transporte/fisiologia , Células Cultivadas/metabolismo , Criança , Concanavalina A/farmacologia , Feminino , Regulação da Expressão Gênica/efeitos dos fármacos , Infecções por HIV/complicações , Hepatite C/complicações , Hepatite C/imunologia , Humanos , Leptina/farmacologia , Ativação Linfocitária/efeitos dos fármacos , Masculino , Fosforilação , Fito-Hemaglutininas/farmacologia , Isoformas de Proteínas/efeitos dos fármacos , Isoformas de Proteínas/genética , Isoformas de Proteínas/fisiologia , Processamento de Proteína Pós-Traducional , RNA Mensageiro/biossíntese , Receptores para Leptina , Proteínas Recombinantes/farmacologia , Transdução de Sinais/efeitos dos fármacos , Linfócitos T/efeitos dos fármacosRESUMO
Leptin is an adipocyte-secreted hormone that centrally regulates weight control. However, leptin receptor is expressed not only in the central nervous system, but also in other systems such as reproductive and hematopoietic tissues. Human leptin has previously been shown to enhance cytokine production by murine peritoneal macrophages and human circulating monocytes. In this paper we have assessed the presence of leptin receptors in peripheral human T lymphocytes and we have studied their functional role. Both CD4(+) and CD8(+) T lymphocytes express leptin receptors. Moreover, we show that human leptin dose-dependently enhances proliferation and activation of human circulating T lymphocytes when they are costimulated by PHA or Con A. Leptin alone was not able to activate T lymphocytes. To confirm a direct effect of leptin on T lymphocytes, monocytes were extracted by adhesion to culture flasks. The early activation surface marker CD69 was then induced in both CD4(+) and CD8(+) T lymphocytes after 8 h stimulation with PHA or Con A. Leptin dose-dependently enhanced stimulated CD69 expression. Moreover, leptin dose-dependently enhanced the expression of the late activation markers CD25 and CD71 in both CD4(+) and CD8(+) T lymphocytes after 48 h stimulation with PHA or Con A. Finally, we have found that leptin modulates CD4(+) T lymphocyte activation toward Th1 phenotype by stimulating the synthesis of IL-2 and IFN-gamma. These results demonstrate the presence of the leptin receptor in human circulating CD4(+) and CD8(+) T lymphocytes and a functional role of leptin as a modulator (enhancer) of lymphocyte stimulation with a shift toward Th1 cytokine-production profile. This function of leptin may have some relevance in the pathophysiology of immunologic alterations related to obesity.
Assuntos
Leptina/farmacologia , Ativação Linfocitária/efeitos dos fármacos , Receptores de Superfície Celular , Linfócitos T/imunologia , Antígenos CD/metabolismo , Proteínas de Transporte/química , Proteínas de Transporte/genética , Proteínas de Transporte/metabolismo , Divisão Celular/efeitos dos fármacos , Células Cultivadas , Concanavalina A/imunologia , Relação Dose-Resposta a Droga , Citometria de Fluxo , Expressão Gênica/efeitos dos fármacos , Humanos , Interferon gama/biossíntese , Interleucina-2/biossíntese , Ativação Linfocitária/imunologia , Peso Molecular , Monócitos/fisiologia , Obesidade/imunologia , Obesidade/fisiopatologia , Fito-Hemaglutininas/imunologia , Receptores para Leptina , Linfócitos T/citologia , Linfócitos T/efeitos dos fármacos , Linfócitos T/metabolismo , Células Th1/efeitos dos fármacos , Células Th1/imunologia , Células Th1/metabolismoRESUMO
This work evaluates whether physiological concentrations of the pineal secretory product melatonin contribute to the total antioxidant status (TAS) of human serum. Day and nighttime serum samples were collected from healthy volunteers ranging from 2 to 89 years of age and used to measure melatonin and TAS. Results showed that both melatonin and TAS in human serum exhibited 24 hr variations with nocturnal peak values at 01:00 hr. Moreover, exposure of volunteers to light at night resulted in clear decreases of both TAS and melatonin. Furthermore, when melatonin was removed from sera collected at night, the TAS value of the sample was reduced to basal daytime values. In aging studies, it was found that nocturnal serum values of TAS and melatonin exhibited maximal values during the first four decades; thereafter, these values decreased as age advanced. In 60-year-old individuals, day/night differences in serum melatonin and TAS levels were clearly diminished, by more than 80%, with these differences being completely abolished in older individuals. Our results suggest that melatonin contributes to the total antioxidative capability of human serum. This antioxidant contribution of melatonin is reduced as age advances correlating with the age-related reduction of melatonin.
Assuntos
Antioxidantes/metabolismo , Melatonina/sangue , Adolescente , Adulto , Idoso , Idoso de 80 Anos ou mais , Envelhecimento/sangue , Envelhecimento/fisiologia , Criança , Pré-Escolar , Ritmo Circadiano/fisiologia , Escuridão , Humanos , Luz , Melatonina/fisiologia , Pessoa de Meia-Idade , OxirreduçãoRESUMO
The Ob gene product, leptin, is an adipocyte-secreted hormone that centrally regulates weight control. However, leptin receptor is expressed not only in the central nervous system, but also in other systems such as reproductive and hematopoietic tissues. Human leptin has previously been shown to enhance cytokine production by murine peritoneal macrophages. In this paper we show that human leptin stimulates proliferation in a dose-dependent manner and functionally activates human circulating monocytes in vitro, by inducing the production of cytokines such as TNF-alpha and IL-6. Proliferation was assessed both by [3H]thymidine and bromodeoxyuridine incorporation at 48 h. We also checked the leptin stimulated monocyte expression of activation markers by flow cytometry: CD25, HLA-DR, CD38, CD71, CD11b, and CD11c expression increased after 72 h. Moreover, leptin increases the expression of the early activation marker CD69 in monocytes but not in lymphocytes. The stimulation produced by leptin is comparable to that produced by endotoxin [lipopolysaccharide (LPS)]. In addition, leptin can potentiate the stimulatory effect of LPS or PMA. Furthermore, we studied cytokine production (TNF-alpha and IL-6) simultaneously by flow cytometric detection of intracellular cytokines in the activated monocytes. Leptin produced a dose-dependent increase in the number of activated monocytes producing cytokines. These data indicate that leptin is a potent stimulatory hormone on human peripheral blood monocytes and suggest that it may have a role as a proinflammatory cytokine.
Assuntos
Monócitos/efeitos dos fármacos , Proteínas/farmacologia , Antígenos CD/biossíntese , Biomarcadores , Divisão Celular/efeitos dos fármacos , Humanos , Interleucina-6/biossíntese , Leptina , Monócitos/citologia , Monócitos/imunologia , Monócitos/metabolismo , Proteínas Recombinantes/farmacologia , Fator de Necrose Tumoral alfa/biossínteseRESUMO
OBJECTIVE: To investigate plasma pancreastatin (a chromogranin A-derived peptide) and catecholamine levels (counterregulatory hormones) in subjects with gestational diabetes compared with normal pregnant subjects. RESEARCH DESIGN AND METHODS: Fasting blood samples were obtained from 11 normal pregnant and 12 nonobese gestational diabetic subjects at late pregnancy (30+/-1 weeks). Selection criteria were those recommended by the National Diabetes Data Group (modified from O'Sullivan original criteria). Plasma glucose, insulin, glucagon, pancreastatin-like, epinephrine, and norepinephrine were measured. RESULTS: Gestational diabetic subjects had significantly higher insulin levels than control pregnant subjects (18+/-1 vs. 15+/-1 microU/ml), whereas glucose and glucagon levels where comparable in the two groups. However, increased catecholamine levels (epinephrine and norepinephrine) were found in the gestational diabetic group. We also found increased pancreastatin-like levels in these patients compared with the pregnant control group (46+/-2 vs. 30+/-2 pmol/l). Actually, pancreastatin levels positively correlated with both epinephrine (r = 0.34) and norepinephrine (r = 0.80) levels. CONCLUSIONS: Catecholamine and pancreastatin-like levels were found elevated in gestational diabetic subjects. These counterregulatory hormones may play a role in the insulin resistance syndrome of gestational diabetes.
Assuntos
Catecolaminas/sangue , Diabetes Gestacional/sangue , Hormônios Pancreáticos/sangue , Fragmentos de Peptídeos/sangue , Glicemia/análise , Epinefrina/sangue , Jejum , Feminino , Humanos , Insulina/sangue , Norepinefrina/sangue , Gravidez , RadioimunoensaioRESUMO
In this paper, we show for the first time, a nyctohemeral rhythm in serum total antioxidant status (TAS) in rats which parallels the 24-H melatonin cycle. Both TAS and melatonin in rat serum exhibited 24 hr variations with nocturnal peak values at 05.00 hr and low basal values during the day. When rats were maintained under light exposure (>500 lux) from 20.00 h to 05.00 hr, serum TAS was significantly reduced when compared with control rat killed in darkness. Moreover, when animals were maintained under continuous light exposure for 5 days and killed at 05.00 hr, serum TAS exhibited an additional decrease when compared with control rats. Since administering exogenous melatonin also increased TAS in the rat serum, results suggest that melatonin may be relevant in terms of participating in the antioxidative capacity of the rat serum.
Assuntos
Antioxidantes/metabolismo , Ritmo Circadiano , Melatonina/sangue , Animais , Luz , Masculino , Melatonina/farmacologia , Ratos , Ratos WistarRESUMO
Many functional studies show that melatonin plays a fundamental role in neuroimmunomodulation. In this paper, we have extended our studies on the influence of melatonin on IL-2 and IL-6 production by human peripheral blood mononuclear cells (PBMCs) by comparing the effects of the specific membrane receptor agonist S 20098, the RZR/ROR(alpha) receptor agonist CGP 52608, and structurally related thiazolidinediones. Melatonin bound to membranes as well as to nuclei of human PBMCs with about the same affinity (IC50 values around 5 nM). S 20098 bound to PBMC membranes but not to PBMC nuclei, although the affinity was at least 100 times lower than that of melatonin; this compound did not stimulate cytokine production. In contrast, all four CGP compounds did not bind to PBMC membranes, while binding to nuclei exhibited IC50 values comparable to those of melatonin. The thiazolidinediones activating the RZR/ROR(alpha) receptor (CGP 52608, CGP 53079) also increased IL-2 and IL-6 production. CGP 55644 had no effect on cytokine production and antagonized the effects of CGP 52608 on IL-2 and IL-6 production; moreover, CGP 55644 decreased the enhanced IL-2 production caused by melatonin. Results obtained in monocyte cultures resembled closely those shown in PBMCs. The results reported in this paper confirm the involvement of a nuclear mechanism in the melatonin effects on cytokine production in human PBMCs. We have also shown a synergistic effect of S 20098 and CGP 52608, suggesting a possible link between nuclear and membrane melatonin receptors in PBMCs.
Assuntos
Núcleo Celular/metabolismo , Interleucina-2/sangue , Interleucina-6/sangue , Melatonina/metabolismo , Monócitos/metabolismo , Acetamidas/farmacologia , Adulto , Sítios de Ligação/fisiologia , Membrana Celular/metabolismo , Citocinas/biossíntese , Humanos , Melatonina/farmacologia , Pessoa de Meia-Idade , Monócitos/efeitos dos fármacos , Tiazóis/farmacologia , Tiossemicarbazonas/farmacologiaRESUMO
This paper shows that melatonin is able to activate human Th1 lymphocytes by increasing the production of IL-2 and IFN-gamma in vitro. Th2 cells appear not to be affected by melatonin, since IL-4, which is mostly produced by Th2 cells, is not modified by the hormone. Melatonin also enhances IL-6 production by PBMCs. The activation by melatonin of IL-6 production is apparently related to the presence of monocytes, rather than to Th2 cells, in the cell preparation, since PBMCs depleted of monocytes (CD14+ cells) were not activated. Activation of PBMCs by melatonin was dependent on the dose and, measured by cytokine production, was observed only when cells were either not activated or only slightly activated by low concentrations of PHA, or when cell activation was achieved by incubating the cells with previously irradiated cells. Using a different approach to identify what type of cells among the PBMC subsets was activated by melatonin, the expression of CD69, a marker of cell activation, was studied. Melatonin increased the percentage of cells expressing the CD69 Ag in CD4+ but not in CD8+ cells. We have also achieved enhanced production of IL-2 and IL-6 using CGP 52608, a specific ligand of the putative nuclear melatonin receptor RZR/ROR, raising the possibility of direct effects of melatonin on gene regulation in both Th1 cells and monocytes. The results suggest that melatonin may be involved in the regulation of human immune functions by modulating the activity of Th1 cells and monocytes via nuclear receptor-mediated transcriptional control.
Assuntos
Interferon gama/biossíntese , Interleucina-2/biossíntese , Interleucina-6/biossíntese , Ativação Linfocitária/efeitos dos fármacos , Melatonina/farmacologia , Monócitos/imunologia , Receptores Imunológicos/imunologia , Células Th1/imunologia , Antígenos CD4/imunologia , Células Cultivadas , Humanos , Interferon gama/imunologia , Interleucina-2/imunologia , Interleucina-6/imunologia , Células Th1/efeitos dos fármacosRESUMO
Pancreastatin is a regulatory peptide known to inhibit insulin secretion and insulin action with a glycogenolytic effect in the liver. This peptide is present in and secreted by many endocrine and chromaffin cells. Abnormalities of glucose, insulin and lipoprotein metabolism are common in patients with hypertension, as well as their first-degree relatives. We have recently studied a group of non-obese hypertensive subjects in which pancreastatin-like levels were increased compared with controls, and correlated with norepinephrine levels. We hypothesized that pancreastatin alongside the sympathoadrenal system might have a part in the insulin resistance of these patients, and this metabolic syndrome could play a role in the pathogenesis and complications of hypertension. In this article, we studied the normotensive offspring of these nonobese hypertensive patients and looked for metabolic abnormalities as well as plasma pancreastatin, glucagon and catecholamine levels. The subjects were separated into two groups: (1) offspring from non-insulin-resistant patients and (2) offspring from insulin-resistant patients. We found that after an intravenous glucose load, offspring from insulin-resistant patients were already hyperinsulinemic, although glucose clearance was normal, suggesting an early alteration in insulin sensitivity, whereas pancreastatin and catecholamine levels were normal compared with matched controls. However, offspring from non-insulin-resistant patients had no differences with controls. These results suggest that pancreastatin and catecholamines may not play an important role in triggering insulin resistance, although they may be important once the syndrome is established.
Assuntos
Hipertensão/genética , Resistência à Insulina/genética , Insulina/sangue , Hormônios Pancreáticos/sangue , Adulto , Glicemia/metabolismo , Catecolaminas/sangue , HDL-Colesterol/sangue , Cromogranina A , Feminino , Teste de Tolerância a Glucose , Humanos , Hipertensão/sangue , Masculino , Taxa de Depuração Metabólica , Triglicerídeos/sangueRESUMO
Pancreastatin is a 49 amino acid peptide first isolated, purified and characterized from the porcine pancreas, and whose biological activity in different tissues can be assigned to the C-terminal part of the molecule. Pancreastatin has a prohormonal precursor, chromogranin A (CGA), which is a glycoprotein present in neuroendocrine cells, including the endocrine pancreas. Both intracellular and extracellular processing of CGA can yield pancreastatin. This processing is tissue-specific, with the pancreatic islet and antral gastric endocrine cells being the major source of fully processed pancreastatin. Most of the circulating CGA is secreted by chromaffin tissue. Therefore, peripheral processing of CGA is probably the major indirect source of pancreastatin. Pancreastatin seems to have a general modulatory control on endocrine (insulin, glucagon, parathormone) and exocrine (pancreatic, gastric) secretion from tissues close to the source of production. This has led to the assumption that pancreastatin may be a peptide with an autocrine and paracrine function. It has recently been revealed to be a peptide with a metabolic function counter-regulatory to insulin action. This effect, in conjunction with the inhibitory effect on insulin and pancreatic exocrine secretion, points to a role in the physiology of stress. The molecular mechanism of the glycogenolytic effect of pancreastatin is better known, although further work is still needed. In general, more studies should be carried out at the molecular level to investigate the mechanism of action of pancreastatin and thus to clarify its physiological role in the neuroendocrine system.
Assuntos
Hormônios Pancreáticos/fisiologia , Animais , Cromogranina A , Cromograninas/metabolismo , Glândulas Endócrinas/fisiologia , Glândulas Exócrinas/fisiologia , Humanos , Ilhotas Pancreáticas/fisiologia , Sistemas Neurossecretores/fisiologia , Pâncreas/fisiologia , Hormônios Pancreáticos/biossíntese , SuínosRESUMO
Pancreastatin is a 49 amino acid peptide first isolated, purified and characterized from porcine pancreas. Its biological activity in different tissues can be assigned to the C-terminal part of the molecule. Pancreastatin has a prohormonal precursor, chromogranin A, which is a glycoprotein present in neuroendocrine cells, including the endocrine pancreas. We have been interested in pancreastatin action in the liver. We found that pancreastatin has a glycogenolytic effect in the hepatocyte both in vivo and in vitro. We then studied and characterized the specific pancreastatin receptor in the rat liver plasma membrane, as well as the specific signal transduction. This receptor appears to be coupled to two different G proteins. A pertussis toxin-insensitive G proteins leads to the activation of phospholipase C, and therefore mediates the glycogenolytic effect in the liver by increasing cytoplasmic free calcium and stimulating protein kinase C. The role of cyclic GMP in the action of pancreastatin is not known yet, although it seems to regulate negatively the activation of phospholipase C. The precise mechanism by which pancreastatin stimulates guanylate cyclase activity remains to be studied.
Assuntos
Proteínas de Ligação ao GTP/fisiologia , Fígado/fisiologia , Hormônios Pancreáticos/fisiologia , Transdução de Sinais/fisiologia , Animais , Calmodulina/fisiologia , Cromogranina A , Cromograninas/metabolismo , GMP Cíclico/fisiologia , Ativação Enzimática , Glicogênio/biossíntese , Guanilato Ciclase/metabolismo , Humanos , Modelos Biológicos , Fosfatidilinositol Diacilglicerol-Liase , Diester Fosfórico Hidrolases/metabolismo , Precursores de Proteínas/metabolismo , Ratos , Receptores dos Hormônios Gastrointestinais/efeitos dos fármacos , Receptores dos Hormônios Gastrointestinais/fisiologia , Transdução de Sinais/efeitos dos fármacos , SuínosRESUMO
This paper shows the presence of high-affinity binding sites for melatonin in human circulating T lymphocytes, but not in B lymphocytes. The binding of melatonin to T cells was dependent on time, stable, reversible, saturable, specific, and inversely correlated to the production of melatonin, expressed as the nocturnal 12 h production of its urinary metabolite 6-sulfatoxymelatonin. The affinity of these binding sites (Kd = 0.27 nM) suggests that they may recognize the physiological concentrations of melatonin in serum. Moreover, among the lymphocyte subpopulations studied, binding of melatonin was mostly found in CD4+ cells rather than in CD8+ cells. Results suggest that CD4+ cells may be the target of melatonin among the human circulating lymphocytes.
Assuntos
Linfócitos T CD4-Positivos/metabolismo , Melatonina/metabolismo , Adulto , Linfócitos B/metabolismo , Linfócitos T CD8-Positivos/metabolismo , Humanos , Melatonina/análogos & derivados , Melatonina/urinaRESUMO
Pancreastatin (PST), a 49 amino acid peptide originally isolated from porcine pancreas, is derived from chromogranin A (Cg A), an acidic protein co-released with catecholamines from sympathetic nerve terminals and chromaffin cells. Extracellular processing of Cg A yields PST as well as other biological active peptides. Measurement of Cg A and PST-like immunoreactivity (PST-LI) has been used to investigate patients with pheochromocytoma and other neuroendocrine neoplasia. Some studies have found increased plasma norepinephrine (NE) levels in essential hypertension. We therefore measured venous plasma PST-LI and catecholamines in patients with essential hypertension. We employed a radioimmunoassay developed with commercially available reagents for measuring plasma PST-like immunoreactivity, and HPLC with electrochemical detection for measurement of plasma catecholamines. The correlation of PST-LI with epinephrine (E) was very weak. However, its correlation with NE was highly significant. Thus, venous plasma PST-LI immunoreactivity may reflect sympathetic nerve activity in essential hypertension.
Assuntos
Hipertensão/sangue , Norepinefrina/sangue , Hormônios Pancreáticos/imunologia , Adulto , Animais , Cromogranina A , Reações Cruzadas , Relação Dose-Resposta Imunológica , Epinefrina/sangue , Humanos , Pessoa de Meia-Idade , Hormônios Pancreáticos/sangue , Radioimunoensaio , Ratos , SuínosRESUMO
DESIGN: Pancreastatin, a novel peptide, is known to inhibit insulin secretion and to have a glycogenolytic effect, and is present in many endocrine and chromaffin cells. Both the plasma insulin levels and the adrenergic activity accompanying insulin resistance have been shown to be increased in hypertensive subjects. Our working hypothesis was that pancreastatin might play a role in these pathological phenomena. METHODS: We studied the plasma pancreastatin level in non-obese essential hypertensive patients in response to an intravenous glucose load. We further measured the responses to the glucose challenge of insulin, glucagon, catecholamines and free fatty acids, as well as other factors related to insulin resistance (i.e. lipoproteins and apolipoproteins). We separated the hypertensive patients into three groups according to their response to an oral glucose-tolerance test: normoinsulinaemic, hyperinsulinaemic and glucose-intolerant. Matched normotensive control subjects were also studied. RESULTS: Pancreastatin levels did not change in the control group after the glucose challenge. However, all hypertensive patients showed an increase in plasma pancreastatin levels after glucose loading. The normoinsulinaemic hypertensive patients also had elevated basal pancreastatin levels. The increase in pancreastatin levels was in the ranking: normoinsulinaemic > hyperinsulinaemic > glucose-intolerant. The pancreastatin: insulin ratio showed that the secretion of pancreastatin and insulin may be regulated differently. Basal free fatty acid and glucagon levels were found to be elevated both in the hyperinsulinaemic and in the glucose-intolerant group. Fasting triglycerides levels were increased in all of the hypertensive patients. Other risk factors for coronary artery disease were also found to be altered: elevated very low-density lipoprotein-cholesterol and decreased high-density lipoprotein-cholesterol, with ranking: normoinsulinaemic < hyperinsulinaemic < glucose-intolerant. CONCLUSIONS: These results show an increase in pancreastatin levels in hypertensive patients, suggesting that pancreastatin might play a role in the pathophysiology of essential hypertension.