Electrophilic Agonists Modulate the Transient Receptor Potential Ankyrin-1 Channels Mediated by Insulin and Glucagon-like Peptide-1 Secretion for Glucose Homeostasis.

This pre-clinical study investigated the transient receptor potential ankyrin-1 (TRPA1) channels on modulating targets for glucose homeostasis using agonists: the electrophilic agonists, cinnamaldehyde (CIN) and allyl isothiocyanate (AITC), and the non-electrophilic agonist, carvacrol (CRV). A glucose tolerance test was performed on rats. CIN and AITC (5, 10 and 20 mg/kg) or CRV (25, 100, 300, and 600 mg/kg) were administered intraperitoneally (i.p.), and glycemia was measured. In the intestine, Glucagon-like peptide-1 (GLP-1) and disaccharidase activity were evaluated (in vivo and in vitro, respectively). Furthermore, in vivo and in vitro insulin secretion was determined. Islets were used to measure insulin secretion and calcium influx. CIN and AITC improved glucose tolerance and increased insulin secretion in vivo and in vitro. CRV was unable to reduce glycemia. Electrophilic agonists, CIN and AITC, inhibited disaccharidases and acted as secretagogues in the intestine by inducing GLP-1 release in vivo and in vitro and contributed to insulin secretion and glycemia. The effect of CIN on calcium influx in pancreatic islets (insulin secretion) involves voltage-dependent calcium channels and calcium from stores. TRPA1 triggers calcium influx and potentiates intracellular calcium release to induce insulin secretion, suggesting that electrophilic agonists mediate this signaling transduction for the control of glycemia.

1α,25-(OH)2 vitamin D3 prevents insulin resistance and regulates coordinated exocytosis and insulin secretion.

Vitamin D3 is associated with improvements in insulin resistance and glycemia. In this study, we investigated the short-term effect of 1α,25(OH)2 Vitamin D3 (1,25-D3) and cholecalciferol (vitamin D3) on the glycemia and insulin sensitivity of control and dexamethasone-induced insulin-resistance rats. 45Ca2+ influx responses to 1,25-D3 and its role in insulin secretion were investigated in isolated pancreatic islets from control rats. In vivo, 5 d treatment with 1,25-D3 (i.p.) prevented insulin resistance in dexamethasone-treated rats. Treatment with 1,25-D3 improved the activities of hepatic enzymes, serum lipids and calcium concentrations in insulin-resistant rats. 25-D3 (o.g.) does not affect insulin resistance. In pancreatic islets, 1,25-D3 increased insulin secretion and stimulated rapid response 45Ca2+ influx. The stimulatory effect of 1,25-D3 on 45Ca2+ influx was decreased by diazoxide, apamine, thapsigargin, dantrolene, 2-APB, nifedipine, TEA, PKA, PKC, and cytoskeleton inhibitor, while it was increased by glibenclamide and N-ethylmaleimide. The stimulatory effect of 1,25-D3 on 45Ca2+ influx involves the activation of L-type VDCC, K+-ATP, K+-Ca2+, and Kv channels, which augment cytosolic calcium. These ionic changes mobilize calcium from stores and downstream activation of PKC, PKA tethering vesicle traffic and fusion at the plasma membrane for insulin secretion. This is the first study highlighting the unprecedented role of 1,25-D3 (short-term effect) in the regulation of glucose homeostasis and on prevention of insulin resistance. Furthermore, this study shows the intracellular ß-cell signal transduction of 1,25-D3 through the modulation of pivotal ionic channels and proteins exhibiting a coordinated exocytosis of vesicles for insulin secretion.

Evaluation of the proliferative activity of methanol extracts from six medicinal plants in murine spleen cells

A number of natural compounds have been used as immunomodulatory agents, enabling the function of the immune system to be modified by stimulating or suppressing it. There has been increasing interest in the study of therapeutic action of plant extracts regarding their immunomodulatory activity. The aim of this study was to identify and evaluate the action of extracts of the medicinal plants Calophyllum brasiliense, Ipomoea pes-caprae, Matayba elaeagnoides, Maytenus robusta, Rubus imperialis and Vernonia scorpioides on the development of spleen cells from mice, using the in vitro cellular proliferation assay. The cells, obtained by mechanical rupture of mice spleen (5x10(4) cells/mL), were incubated with methanol extracts (10, 50, 100 and 200 µg/mL) and phytohemagglutinin (PHA, 5 µg/mL). The basal control for proliferation consisted of cells alone, while the positive control consisted of cells and PHA. The cell culture was kept at 37 ºC in 5 percent CO2 for 72 hours, and cell proliferation was revealed by the blue tetrazolium reduction assay (MTT). The results were expressed as percentage of growth and were analyzed using the Kruskal-Wallis and Mann-Whitney tests. The C. brasiliense, I. pes-caprae and M. elaeagnoides extracts showed dose-dependent induction of cell proliferation, with a significant increase in cell proliferation (p<0.03) and percentage growth of 88.2 percent, 73.1 percent and 52.7 percent, respectively, suggesting T lymphocyte stimulation. By contrast, M. robusta, R. imperialis and V. scorpioides extracts showed significance only with a negative percentage of growth, suggesting inhibition of cell proliferation (p<0.04). Further biomonitoring studies will enable the fractions and isolated substances responsible for the immunomodulatory activities to be identified.

Várias substâncias de origem natural têm sido utilizadas como agentes imunomoduladores, permitindo modificar a função do sistema imune e propiciando o estudo de atividades terapêuticas de extratos de plantas. Este trabalho objetivou identificar a atividade imunomodulatória dos extratos de seis plantas medicinais da flora brasileira, Calophyllum brasiliense, Ipomoea pes-caprae, Matayba elaeagnoides, Maytenus robusta, Rubus imperialis e Vernonia scorpioides, sobre a proliferação de células esplênicas de camundongos. As células esplênicas murinas obtidas por ruptura mecânica do baço (5x14³ células/mL) foram incubadas com os extratos metanólicos das plantas (10, 50, 100, 200 µg/mL) e fito-hemaglutinina (PHA, 5 µg/mL). O controle basal de proliferação foi constituído de células apenas e o controle positivo formado por células e PHA. O cultivo celular foi mantido a 37 ºC, 5 por cento de CO2, 72 horas, com quantificação da proliferação celular pelo ensaio de redução do azul de tetrazólio. Os resultados expressos em percentagem de crescimento foram analisados pelos testes de Kruskal-Wallis e Mann-Whitney. Os extratos de C. brasiliense, I. pes-caprae e M. elaeagnoides mostraram indução dose-dependente da proliferação celular (p<0,03), com percentagem de crescimento de, respectivamente, 88,2 por cento, 73,1 por cento e 52,7 por cento, sugerindo estímulo de linfócitos T. Contrariamente, os extratos de M. robusta, R. imperialis e V. scorpioides apresentaram significância apenas com percentagem de crescimento negativa, indicando inibição da proliferação celular (p<0,04). A continuidade no estudo biomonitorado permitirá a identificação das frações e substâncias isoladas responsáveis pelas atividades imunomoduladoras.