Regilane M. Silva

Anti-inflammatory effect of kaurenoic acid, a diterpene from Copaifera langsdorffii on acetic acid-induced colitis in rats

Kaurenoic acid, a diterpene from Copaifera langsdorffii (Leguminaceae), was evaluated on rat colitis induced by acetic acid. Rats were pretreated orally (15 and 2 h before) or rectally 2 h before induction of colitis with kaurenoic acid (50 and 100 mg/kg) or vehicle (1 ml, 3% DMSO). Colitis was induced by intracolonic instillation of a 2 ml of 4% (v/v) acetic acid solution and, 24 h later, the colonic mucosal damage was analysed macroscopically for the severity of mucosal damage, the myeloperoxidase (MPO) activity and the malondialdehyde (MDA) levels in the colon segments. A marked reduction in gross damage score (52% and 42%) and wet weight of damaged colon tissue (39% and 32%) were observed in rats that received 100 mg/kg kaurenoic acid, respectively, by rectal and oral routes. This effect was confirmed biochemically by a two- to three-fold reduction of colitis associated increase in MPO activity, the marker of neutrophilic infiltration and by a marked decrease in MDA level, an indicator of lipoperoxidation in colon tissue. Furthermore, light microscopy revealed the marked diminution of inflammatory cell infiltration and submucosal edema formation in the colon segments of rats treated with the test compound. These findings indicate the anti-inflammatory potential of kaurenoic acid in acetic acid-induced colitis.

Gastroprotective and ulcer-healing mechanisms of ellagic acid in experimental rats.

Ellagic acid (EA), a plant-derived polyphenol, exhibits antioxidant, anti-inflammatory, and gastroprotective effects. Its gastroprotective mechanisms have not been fully elucidated nor have its effects on chronic ulcer previously been described. Toward these ends, the antiulcer activities of EA were evaluated in acute (ethanol and indomethacin) and chronic (acetic acid) ulcer models in Wistar rats. In this study, oral administration of EA significantly prevented the gastric ulceration caused by ethanol, indomethacin, and acetic acid treatments. Its gastroprotective mechanism in ethanol-induced ulcer were partly due to intensification in the endogenous production of nitric oxide, an antioxidant effect by replenishing depletion of endogenous nonprotein sulfhydryls and attenuation of tumor necrosis factor-α increase, whereas in indomethacin ulcer, it is partly due to a reduction in the plasma level of leukotriene B(4). In acetic acid ulcer, promotion of ulcer-healing effects was partly due to attenuation of the elevated levels of the inflammatory cytokines TNF-α, interferon-γ, and interleukins-4 and -6. These findings suggest that ellagic acid exerts its antiulcer activity by strengthening the defensive factors and attenuating the offensive factors.

Pentacyclic triterpenoids, α,β-amyrins, suppress the scratching behavior in a mouse model of pruritus

In the search for natural compounds useful against pruritus, α,β-amyrins, the pentacyclic triterpenes isolated from the resin of popular medicinal plant Protium heptaphyllum were examined on scratching behavior induced by dextran T40 and compound 48/80 in mice. The animals were pretreated orally with α,β-amyrins (50, 100 and 200 mg/kg) or cyproheptadine (10 mg/kg), an antagonist of histamine and serotonin receptors and 2 h later, they were given subcutaneous injections of dextran T40 (75 mg/kg) or compound 48/80 (3 mg/kg) into the rostral back, and scratching was quantified for 20 min. The scratching behavior induced by dextran T40 and compound 48/80 was significantly inhibited in mice pretreated with α,β-amyrins (100 and 200 mg/kg) or cyproheptadine (10 mg/kg), In addition, the compound 48/80-elicited degranulation of rat peritoneal mast cells (ex vivo) was also markedly reduced in animals pretreated with α,β-amyrins (100 mg/kg) or ketotifen (1 mg/kg), a known mast cell stabilizer. In the open-field test, α,β-amyrins (100 and 200 mg/kg)-pretreated mice showed no impairment of spontaneous locomotion, suggesting that these triterpenoids possess no sedative activity that could account for suppression of scratching behavior. These results clearly indicate the antipruritic effect of α,β-amyrins and suggest that this effect may be related to a stabilizing action on mast cell membrane.

1,8‐Cineole protects against liver failure in an in‐vivo murine model of endotoxemic shock

The effects of 1,8‐cineole on d‐galactosamine/lipopolysaccharide (GalN/LPS)‐induced shock model of liver injury was investigated in mice. The co‐administration of GalN (700 mg kg−1, i.p.) and LPS (5 μg kg−1, i.p.) greatly elevated serum concentrations of tumour necrosis factor‐α (TNF‐α), alanine aminotransferase and aspartate aminotransferase, and induced massive hepatic necrosis and lethality in 100% of control mice. Pretreatment with 1,8‐cineole (400 mg kg−1, p.o.) and dexamethasone (1 mg kg−1, s.c.),60 min before GalN/LPS, offered complete protection (100%) against the lethal shock and acute elevation in serum TNF‐α and serum transaminases. Hepatic necrosis induced by GalN/LPS was also greatly reduced by both 1,8‐cineole and dexamethasone treatment. The results indicate that 1,8‐cineole protects mice against GalN/LPS‐induced liver injury through the inhibition of TNF‐α production, and suggest that 1,8‐cineole may be a promising agent to combat septic‐shock‐associated pathologies.

Effects of nitric oxide synthase inhibitors and melatonin on the hyperglycemic response to streptozotocin in rats

Recent studies evidence that peroxynitrite is spontaneously formed when nitric oxide (NO) and superoxide coexist and suggest that it is likely to be involved in the destruction of the pancreatic beta cells. We examined whether drugs that inhibit nitric oxide synthase (NOS) or scavenge peroxynitrite could abrogate STZ-induced hyperglycemia in rats. Blood glucose levels were measured before (0 h) and 24, 48, and 72 h following intraperitoneal administration of 60 mg/kg streptozotocin (STZ). The levels of blood sugar in STZ-treated control animals were significantly elevated at all time points of observation with a peak increase at 48 h. The hyperglycemic response of STZ was found to be significantly reduced in animals pretreated with aminoguanidine (50 mg/kg i.p.), an inducible isoform-selective NOS (iNOS) inhibitor with antioxidant property, and by melatonin (6 mg/kg i.p.), an antioxidant that also prevents peroxynitrite formation but not by Nw-nitro-L-arginine methyl ester (L-NAME, 10 mg/kg i.p.), and 7-nitroindazole (7-NI, 50 mg/kg i.p.), the constitutive inhibitors of endothelial and neuronal NOS, respectively. These findings indicate the possible participation of iNOS-derived NO as well as oxygen free radicals in STZ-induced pancreatic beta cell destruction and compounds that act as scavengers of peroxynitrite may offer protection against such a damage.

Blood glucose‐ and triglyceride‐lowering effect of trans‐dehydrocrotonin, a diterpene from Croton cajucara Benth., in rats

Aim: The objective of this study was to assess in rats the antidiabetic effects (i.e. reduction of hyperglycaemia and hypertriglyceridaemia) of trans‐dehydrocrotonin (t‐DCTN), a bioactive diterpene isolated from the popular medicinal plant Croton cajucara.

The lipid-lowering effect of trans-dehydrocrotonin, a clerodane diterpene from Croton cajucara Benth. in mice fed on high-fat diet

The clerodane diterpene trans‐dehydrocrotonin extracted and isolated from the stem bark of Croton cajucara Benth. was investigated for its lipid‐lowering effect in mice fed on a high‐fat diet. Mice fed on a high‐fat diet for a two‐week period demonstrated significantly increased blood levels of total cholesterol and triglycerides, compared with normal controls. Oral treatment with trans‐dehydrocrotonin at a dose of 25 or 50 mg kg−1 daily markedly suppressed the high‐fat‐diet associated rise in total cholesterol and triglyceride levels. The hypocholesterolaemic effect of trans‐dehydrocrotonin was more prominent at the dose of 50 mg kg−1 with significant decreases in high‐density lipoprotein, very‐low‐density lipoprotein and low‐density lipoprotein cholesterol levels. The lower atherogenic index of the trans‐dehydrocrotonin‐treated groups suggests the hypolipidaemic potential of this plant‐based drug. These results indicate that orally administered trans‐dehydrocrotonin is effective in suppressing high‐fat‐diet‐induced hyperlipidaemia in mice and suggest its likely beneficial use as anti‐atherogenic agent.

Effects of acute and repeated dose administration of caffeine and pentoxifylline on diazepam-induced mouse behavior in the hole-board test

Rationale: The behavioral effects of methyl xanthines and their interactions with benzodiazepines have not been clearly established in animal models of anxiety. Objective: The present study extended the previous studies to determine the effects of acute and repeated administration of caffeine, a non-specific phosphodiesterase (PDE) inhibitor and pentoxyfylline, a specific type-4 phosphodiesterase (PDE4) inhibitor on (1) baseline anxiety-like behavior and (2) the response to an acute challenge with diazepam on anxiety-like behavior in the hole-board test. Methods: Mice were observed for the number of head-dips they made into the holes of the hole-board apparatus during a 5-min period, starting 30 min after acute (20 mg/kg) and repeated oral dose (20 mg/kg, twice a day for 4 days) administration of caffeine and pentoxifylline. In separate experiments, the response to an acute challenge with graded doses of diazepam (0.375–3 mg/kg, SC) was observed in naive mice or mice on acute and repeated dose regimen with methyl xanthines. Results: Mice on acute but not after repeated dose regimen demonstrated a significantly increased number of hole-dips, indicating an anxiolytic-like effect of methylxanthines. Diazepam at the lower doses (0.375 and 0.75 mg/kg) but not at the highest doses (1.5 and 3 mg/kg) examined produced a significant anxiolytic-like effect. After an acute dose exposure of mice to caffeine and pentoxifylline, a rightward shift in the dose-response curve of diazepam was observed and particularly at 1.5 mg/kg dose, the net effect of diazepam was significantly enhanced which was, however, impaired upon repeated administration, more so with caffeine than with pentoxifylline. Conclusions: It is concluded that the xanthine drugs exert anxiolytic-like activity similar to diazepam in the hole-board test. In addition, they seem to modulate the anxiolytic effects of diazepam after both acute and repeated administration, probably as a result of an endogenous adenosinergic mechanism which may have therapeutic significance.