Miguel Chaves

Anti-inflammatory effect of α, β-Amyrin, a pentacyclic triterpene from Protium heptaphyllum in rat model of acute periodontitis

Abstract.This study was aimed to evaluate the anti-inflammatory potential of triterpene α, β-amyrin in rats on acute phase periodontitis. Periodontitis was induced by ligature placement around the maxillary right second molar tooth. Rats (n = 8/group) were pretreated with α, β-amyrin (5 and 10 mg/kg, p. o.), two hours before the induction of periodontal inflammation. Sham-operated and positive controls (lumiracoxib and dexamethasone) were included. Six hours later, plasma levels of TNF-alpha were analysed. Rats were sacrificed at 24 h, and the gingival tissue analysed for myeloperoxidase (MPO) and thiobarbituric acid-reactive substances (TBARS), as measures of neutrophil influx and lipid-peroxidation, respectively α, β-Amyrin as well as dexamethasone significantly inhibited the periodontitis-associated increases of TNF-alpha, and the gingival MPO and TBARS. α, β-Amyrin effect was more prominent at 5 mg/kg. Lumiracoxib manifested varied influence on the studied parameters. These results provide evidence to show that α, β-Amyrin retards acute inflammation in rat model of periodontitis and warrant further study on its efficacy to prevent chronic periodontitis-associated bone loss.

Antinoceptive effect of triterpenoid α, β-amyrin in rats on orofacial pain induced by formalin and capsaicin

The effects of alpha,beta-amyrin, a pentacyclic triterpene isolated from Protium heptaphylum was investigated on rat model of orofacial pain induced by formalin or capsaicin. Rats were pretreated with alpha,beta-amyrin (10, 30, and 100mg/kg, i.p.), morphine (5mg/kg, s.c.) or vehicle (3% Tween 80), before formalin (20 microl, 1.5%) or capsaicin (20 microl, 1.5 microg) injection into the right vibrissa. In vehicle-treated controls, formalin induced a biphasic nociceptive face-rubbing behavioral response with an early first phase (0-5 min) and a late second phase (10-20 min) appearance, whereas capsaicin produced an immediate face-rubbing (grooming) behavior that was maximal at 10-20 min. Treatment with alpha,beta-amyrin or morphine significantly inhibited the face-rubbing response in both test models. While morphine produced significant antinociception in both phases of formalin test, alpha,beta-amyrin inhibited only the second phase response, more prominently at 30 mg/kg, in a naloxone-sensitive manner. In contrast, alpha,beta-amyrin produced much greater antinociceptive effect at 100mg/kg in the capsaicin test, which was also naloxone-sensitive. These results provide first time evidence to show that alpha,beta-amyrin attenuates orofacial pain at least, in part, through a peripheral opioid mechanism but warrants further detailed study for its utility in painful orofacial pathologies.

On the problem of balancing the DC capacitor voltage divider in back-to-back multilevel converters

This paper presents a new generalized solution for DC bus capacitors voltage balancing in back-to-back m level diode-clamped multilevel converters connecting AC networks. The solution is based on the DC bus average power flow and exploits the switching configuration redundancies. The proposed balancing solution is particularized for the back-to-back multilevel structure with m = 5 levels. This back-to-back converter is studied working with bidirectional power flow, connecting an induction machine to the power grid.

Generalized State-Space Modeling for m Level Diode-Clamped Multilevel Converters

Multilevel power converter structures have been introduced as the solutions for high power high voltage applications and also for grid interface connection of renewable energy sources systems, where they have several advantages, namely low distortion voltages and currents, low switching losses resulting in higher efficiency. As a consequence of the increasing interest on multilevel converter applications, accurate models of these power converters are essential for computer simulation studies. This paper presents a systematic modeling approach suitable to obtain generalized state-space models for m level diode-clamped multilevel converters supplying AC loads. In particular, for m = 5, the proposed model is compared to the corresponding model using general purpose Simulink blocks and SimPowerSystems toolbox.