Studies on the protective effects of caffeic acid and quercetin on chemical-induced hepatotoxicity in rodents.

Caffeic acid and quercetin, the well-known phenolic compounds widely present in the plant kingdom, were investigated for their possible protective effects against paracetamol and CCl4-induced hepatic damage. Paracetamol at the oral dose of 1 g/kg produced 100% mortality in mice while pretreatment of separate groups of animals with caffeic acid (6 mg/kg) and quercetin (10 mg/kg) reduced the death rate to 20% and 30%, respectively. Oral administration of sub-lethal dose of paracetamol (640 mg/kg) produced liver damage in rats as manifested by the significant (P<0.01) rise in serum levels of aminotransferases (aspartate transaminase (AST) and alanine transaminase (ALT)) compared to respective control values. The serum enzyme values were significantly (P<0.01) lowered on pretreatment of rats with either caffeic acid (6 mg/kg) or quercetin (10 mg/kg). Similarly, the hepatotoxic dose of CCl4 (1.5 ml/kg; orally) also raised significantly (P<0.05) the serum AST and ALT levels as compared to control values. The same dose of the caffeic acid and quercetin was able to prevent CCl4-induced rise in serum enzymes. Caffeic acid and quercetin also prevented the CCl4-induced prolongation in pentobarbital sleeping time confirming their hepatoprotectivity. These results indicate that caffeic acid and quercetin exhibited hepatoprotective activity possibly through multiple mechanisms.

Hypotensive action of coumarin glycosides from Daucus carota.

Daucus carota (carrot) has been used in traditional medicine to treat hypertension. Activity-directed fractionation of aerial parts of D. carota resulted in the isolation of two cumarin glycosides coded as DC-2 and DC-3. Intravenous administration of these compounds caused a dose-dependent (1-10 mg/kg) fall in arterial blood pressure in normotensive anaesthetised rats. In the in vitro studies, both compounds caused a dose-dependent (10-200 microg/ml) inhibitory effect on spontaneously beating guinea pig atria as well as on the K+ -induced contractions of rabbit aorta at similar concentrations. These results indicate that DC-2 and DC-3 may be acting through blockade of calcium channels and this effect may be responsible for the blood pressure lowering effect of the compounds observed in the in vivo studies.

Paan without tobacco: an independent risk factor for oral cancer.

Oral cancer is the second most common cancer in women and the third most common in men in Pakistan. Tobacco is smoked and chewed extensively in Pakistan. Paan is a quid of piper betel leaf that contains areca nut, lime, condiment, sweeteners, and sometimes tobacco, which is also used extensively. We did this study to clarify the independent association of paan and oral cancer. Between July 1996 and March 1998, we recruited biopsy-proven, primary cases of oral squamous-cell carcinoma, from 3 tertiary teaching centers in Karachi, Pakistan, and controls pair-matched for age, gender, hospital and time of occurrence, excluding persons with a past or present history of any malignancy. There were 79 cases and 149 controls. Approximately 68% of the cases were men, 49 years old on average, the youngest being 22 years old and the eldest 80. People with oral submucous fibrosis were 19.1 times more likely to develop oral cancer than those without it, after adjusting for other risk factors. People using paan without tobacco were 9.9 times, those using paan with tobacco 8.4 times, more likely to develop oral cancer as compared with non-users, after adjustment for other covariates. This study identifies an independent effect of paan without tobacco in the causation of oral cancer. Its findings may be of significance in South Asian communities where paan is used, and among health-care providers who treat persons from South Asia.

Inhibitory effect of curcumin, a food spice from turmeric, on platelet-activating factor- and arachidonic acid-mediated platelet aggregation through inhibition of thromboxane formation and Ca2+ signaling.

Curcumin, a dietary spice from turmeric, is known to be anti-inflammatory, anticarcinogenic, and antithrombotic. Here, we studied the mechanism of the antiplatelet action of curcumin. We show that curcumin inhibited platelet aggregation mediated by the platelet agonists epinephrine (200 microM), ADP (4 microM), platelet-activating factor (PAF; 800 nM), collagen (20 microg/mL), and arachidonic acid (AA: 0.75 mM). Curcumin preferentially inhibited PAF- and AA-induced aggregation (IC50; 25-20 microM), whereas much higher concentrations of curcumin were required to inhibit aggregation induced by other platelet agonists. Pretreatment of platelets with curcumin resulted in inhibition of platelet aggregation induced by calcium ionophore A-23187 (IC50; 100 microM), but curcumin up to 250 microM had no inhibitory effect on aggregation induced by the protein kinase C (PKC) activator phorbol myrsitate acetate (1 microM). Curcumin (100 microM) inhibited the A-23187-induced mobilization of intracellular Ca2+ as determined by using fura-2 acetoxymethyl ester. Curcumin also inhibited the formation of thromboxane A2 (TXA2) by platelets (IC50; 70 microM). These results suggest that the curcumin-mediated preferential inhibition of PAF- and AA-induced platelet aggregation involves inhibitory effects on TXA2 synthesis and Ca2+ signaling, but without the involvement of PKC.

Muscarinic regulation of intracellular signaling and neurosecretion in gonadotropin-releasing hormone neurons.

Agonist activation of cholinergic receptors expressed in perifused hypothalamic and immortalized GnRH-producing (GT1-7) cells induced prominent peaks in GnRH release, each followed by a rapid decrease, a transient plateau, and a decline to below basal levels. The complex profile of GnRH release suggested that acetylcholine (ACh) acts through different cholinergic receptor subtypes to exert stimulatory and inhibitory effects on GnRH release. Whereas activation of nicotinic receptors caused a transient increase in GnRH release, activation of muscarinic receptors inhibited basal GnRH release. Nanomolar concentrations of ACh caused dose-dependent inhibition of cAMP production that was prevented by pertussis toxin (PTX), consistent with the activation of a plasma-membrane Gi protein. Micromolar concentrations of ACh also caused an increase in phosphoinositide hydrolysis that was inhibited by the M1 receptor antagonist, pirenzepine. In ACh-treated cells, immunoblot analysis revealed that membrane-associated G(alpha q/11) immunoreactivity was decreased after 5 min but was restored at later times. In contrast, immunoreactive G(alpha i3) was decreased for up to 120 min after ACh treatment. The agonist-induced changes in G protein alpha-subunits liberated during activation of muscarinic receptors were correlated with regulation of their respective transduction pathways. These results indicate that ACh modulates GnRH release from hypothalamic neurons through both M1 and M2 muscarinic receptors. These receptor subtypes are coupled to Gq and Gi proteins that respectively influence the activities of PLC and adenylyl cyclase/ion channels, with consequent effects on neurosecretion.

Seasonal affective disorders.

Seasonal affective disorder is a pattern of major depressive episodes that occur and remit with changes in seasons. It may be seen in major depressive or bipolar disorders, as described in the Diagnostic and Statistical. Manual of Mental Disorders (DSM-IV). The most recognized form of seasonal affective disorder, "winter depression," is characterized by recurrent episodes of depression, hypersomnia, augmented appetite with carbohydrate craving, and weight gain that begin in the autumn and continue through the winter months. Physicians have many options for treating seasonal affective disorder. While questions regarding the validity of seasonal affective disorder as a syndrome and the mechanism of action of light therapy continue to be investigated, the established effectiveness of light therapy in patients with winter depression supports the usefulness of assessment for this seasonal pattern and consideration of light therapy as an option in addition to existing treatment choices.

The antiplatelet aggregatory activity of Acacia nilotica is due to blockade of calcium influx through membrane calcium channels.

1. The extract of Acacia nilotica (A. nilotica) blocked platelet aggregation mediated by platelet agonists, arachidonic acid (0.75 mM), ADP (4.3 microM), platelet activating factor (800 nM) and collagen (638 nM) in a dose-dependent manner. 2. The extract (0.21-1.4 mg/ml) blocked the platelet aggregation induced by Ca2+ ionophore, A-23187 (6 microM), in a dose-dependent manner, indicating that the Ca2+ influx is involved in aggregation. 3. The plant extract also inhibited aggregation in platelets pretreated with phorbol, 12-myristate, 13-acetate (196 nM) alone or in combination with ADP (4.3 microM), indicating an effect on protein kinase C. 4. These results indicate that the antiplatelet aggregatory activity of the extract of A. nilotica is mainly due to blockade of Ca2+ channels, although evidence also suggests the involvement of protein kinase C.

Eugenol: a dual inhibitor of platelet-activating factor and arachidonic acid metabolism.

Eugenol is an active principal and responsible for several pharmacological activities of clove oil. We studied the effects of eugenol on human platelet aggregation, arachidonic acid (AA) and platelet-activating factor (PAF) metabolism and in vivo effects on AA and PAF-induced shock in rabbits. Eugenol strongly inhibited PAF-induced platelet aggregation with lesser effect against AA and collegen. The IC(50) values were against AA: 31 ± 0.5; collagen: 64 ± 0.7 and PAF 7 ± 0.2 µM (n=9) respectively. In addition, eugenol stimulated PAF-acetylhydrolase activity suggesting that inhibition of PAF could be due to its inactivation to lyso-PAF. Pretreatment of rabbits with eugenol (50-100 mg/kg) prevented the lethal effects of intravenous PAF (11 µgg/kg) or AA (2 mg/kg) in a dose-dependent fashion. The protective effects of eugenol in the rabbits, however, were more pronounced against PAF-induced mortality (100% protection). In addition, eugenol also inhibited AA metabolism via cyclooxygenase and lipoxygenase pathways in human platelets. Both the production of thromboxane-A(2) and 12-hydroxy-eicosatetraenoic acid was inhibited by eugenol in a concentration-related manner (30-120 µM). In vivo, eugenol (50-100 mg/kg; i.p.) inhibited carrageenan-induced rat paw oedema (P < 0.001). In this test, eugenol was 5 times more potent than aspirin. These results provide evidence that eugenol acts as a dual antagonist of AA and PAF.

Inhibition of adrenaline-induced aggregation of human platelets by Pakistani medicinal plants.

The effects of extracts of Pakistani plants claiming medicinal value were observed on adrenaline-induced aggregation of human platelets according to the method of Born (1962). The extracts manifested significant inhibitory activity in doses of 0.625 mgm(-1) to 2.5 mgml(-1) in this in vitro model. The potency of the plant extracts in inhibiting platelet aggregation induced by adrenaline is in the following order: Sida pakistanica, IC50 = 0.90 mgml(-1) > Tribulus terrestris, IC50 = 0.97 mgml(-1) > Solanum surattense, IC50 = 1.34 mgml(-1) Tephrosia subtriflora, IC50 = 1.40 mgml(-1) > Glycyrrhiza glabra (butanolic extract), IC50 = 1.66 mgml(-1) > Urtica dioica IC50 = 2.17 mgml(-1). Further studies are proposed to find out whether the inhibition of adrenaline-induced platelet aggregation is mediated through alpha-adrenoceptor blockade or suppressed synthesis of prostaglandin endoperoxides.