Effect of genistein on voltage-gated potassium channels in guinea pig proximal colon smooth muscle cells

Flavonoids containing Vitex negundo extract displayed calcium channels blocking property underlying its anti-diarrheal and anti-spasmodic activities

Diarrhea is a major health problem and despite of interventions, it remains a substantial cause of mortality and morbidity. In this study, a flavonoids-rich Vitex negundo extract was mechanistically evaluated for its effectiveness in diarrheal diseases. The Vitex negundo ethanolic extract was subjected to extraction for isolation of total flavonoids and qualitative phytochemical analysis. The acute toxicity of flavonoids-extract was done in mice to assess its safety and tolerability. The anti-diarrhoeal activity was determined using the castor oil induced diarrhea mouse model at doses of 10, 30 and 100 mg/kg in relation to loperamide (10 mg/kg, oral). The antispasmodic profile was determined by using cut pieces of rabbit’s jejunum in Tyrode’s solutions, employing acetylcholine (0.03μM) as a tissue stabilizer and verapamil, as a calcium channel blocker. The preliminary qualitative analysis of extract revealed different phytochemicals, in addition to flavonoids. The acute toxicity profile showed that the flavonoids-extract is safe and tolerable (LD50 = 1678 mg/kg). In the tissue experiments, the total flavonoids exhibited an EC50 of 1.52 mg/mL and showed maximum relaxation of spontaneous contractions at 5.0 mg/mL and against high-K + induced contractions at 3 mg/mL (EC50 = 0.43 mg/mL). The spasmolytic activity of total flavonoids was comparable to verapamil which suggests that the activity might be due to the blockade of calcium channels. The flavonoids extract (0.1, 0.3 and 1.0 mg/mL) produced an adequate right shift in the calcium concentration response curve as compared to the control (EC50 value = –2.67 mg/mL), which confirmed that the extract has calcium channel blocking activity.

Therapeutic potential of natural plant products and their metabolites in preventing radiation enteropathy resulting from abdominal or pelvic irradiation

Radiation-induced gastrointestinal injury or radiation enteropathy is an imminent risk during radiation therapy of abdominal or pelvic tumors. Despite remarkable technological advancements in image-guided radiation delivery techniques, the risk of intestinal injury after radiotherapy for abdominal or pelvic cancers has not been completely eliminated. The irradiated intestine undergoes varying degrees of adverse structural and functional changes, which can result in transient or long-term complications. The risk of development of enteropathy depends on dose, fractionation, and quality of radiation. Moreover, the patients' medical condition, age, inter-individual sensitivity to radiation and size of the treatment area are also risk factors of radiation enteropathy. Therefore, strategies are needed to prevent radiotherapy-induced undesirable alteration in the gastrointestinal tract. Many natural plant products, by virtue of their plethora of biological activities, alleviate the adverse effects of radiation-induced injury. The current review discusses potential roles and possible mechanisms of natural plant products in suppressing radiation enteropathy. Natural plant products have the potential to suppress intestinal radiation toxicity.

Effect of tyrphostin AG879 on Kv 4.2 and Kv 4.3 potassium channels

BACKGROUND AND PURPOSE

A-type potassium channels (IA) are important proteins for modulating neuronal membrane excitability. The expression and activity of Kv 4.2 channels are critical for neurological functions and pharmacological inhibitors of Kv 4.2 channels may have therapeutic potential for Fragile X syndrome. While screening various compounds, we identified tyrphostin AG879, a tyrosine kinase inhibitor, as a Kv 4.2 inhibitor from. In the present study we characterized the effect of AG879 on cloned Kv 4.2/Kv channel-interacting protein 2 (KChIP2) channels.

EXPERIMENTAL APPROACH

To screen the library of pharmacologically active compounds, the thallium flux assay was performed on HEK-293 cells transiently-transfected with Kv 4.2 cDNA using the Maxcyte transfection system. The effects of AG879 were further examined on CHO-K1 cells expressing Kv 4.2/KChIP2 channels using a whole-cell patch-clamp technique.

KEY RESULTS

Tyrphostin AG879 selectively and dose-dependently inhibited Kv 4.2 and Kv 4.3 channels. In Kv 4.2/KChIP2 channels, AG879 induced prominent acceleration of the inactivation rate, use-dependent block and slowed the recovery from inactivation. AG879 induced a hyperpolarizing shift in the voltage-dependence of the steady-state inactivation of Kv 4.2 channels without apparent effect on the V1/2 of the voltage-dependent activation. The blocking effect of AG879 was enhanced as channel inactivation increased. Furthermore, AG879 significantly inhibited the A-type potassium currents in the cultured hippocampus neurons.

CONCLUSION AND IMPLICATIONS

AG879 was identified as a selective and potent inhibitor the Kv 4.2 channel. AG879 inhibited Kv 4.2 channels by preferentially interacting with the open state and further accelerating their inactivation.

Cardiovascular ion channels as a molecular target of flavonoids

Flavonoids are a class of naturally occurring polyphenols abundant in edibles and beverages of plant origin. Epidemiological studies consistently associate high flavonoid intake with a reduced risk for the development of cardiovascular diseases. So far these beneficial effects have been mainly attributed to nonspecific antioxidant and antiinflammatory properties. However, there is an increasing body of evidence that flavonoids specifically target molecular structures including cardiovascular ion channels. Playing a pivotal role in the regulation of vascular tone and cardiac electric activity, ion channels represent a major target for the induction of antihypertensive and cardioprotective effects. Thus, pharmacological properties of flavonoids on cardiovascular ion channels, ion currents and tissue preparations are being increasingly addressed in experimental studies. Whereas it has become clear that cardiovascular ion channels represent an important molecular target of flavonoids, the published data have not yet been systematically reviewed.

Cellular effects of gastric electrical stimulation on antral smooth muscle cells in rats

The cellular effects of gastric electrical stimulation (GES), which has recently been introduced as a potential therapy for the treatment of gastroparesis and obesity, were investigated in rat antrum smooth muscle cells (SMCs). Effects on cell membrane potentials of single electrical current pulses (pulse width from 0.1 ms to 200 ms) and 2-s pulse train stimuli with different pulse widths (0.1–4 ms), different frequencies (20–200 Hz), and different intensities were studied: 1) the stimulus amplitude had an exponential relationship to the pulse width from 2 ms to 200 ms, along with a rapidly rising strength-duration curve at pulse widths less than 5 ms, and a relatively flat curve at pulse widths greater than 50 ms; 2) when the pulse frequency was at 80 Hz or above, pulse train electrical stimulation, with a pulse width of 2 ms or above but not ≤1 ms, was able to depolarize cell membrane potentials to above −30 mV and/or generate action potentials. Electrical stimulation with a single long pulse and a width of 50 ms or greater is effective in depolarizing cell membrane potentials of SMCs with low amplitude. Pulse train electrical stimulation with a pulse width of ≤1 ms fails to generate action potentials in SMCs, whereas pulse train electrical stimulation with a pulse width of 2–4 ms and a sufficiently high pulse frequency is able to generate action potentials. These cellular findings may be useful in optimizing stimulation parameters of GES.

Relaxant effects of flavonoids on the mouse isolated stomach: structure-activity relationships

Flavonoids are a large heterogeneous group of benzo-gamma-pyrone derivatives, which are abundantly present in our diet. In this study we investigated the effects of six flavonoids (apigenin, genistein, quercetin, rutin, naringenin and catechin) on the gastric tone in mouse isolated stomach. The mechanical activity was recorded as changes of intraluminal pressure. All flavonoids tested produced a concentration-dependent relaxation, which was reversible after washout. The relative order of potency of the flavonoids was apigenin> or =genistein>quercetin>naringenin> or =rutin>catechin. Analysis of the chemical structure showed that the relaxant activity was progressively diminished by the presence of hydroxyl group at C-3, saturation of the C-2, C-3 double bound, saturation of the C-2, C-3 double bound coupled with lack of the C-4 carbonyl and glycosylation. The flavonoid-induced relaxations were not modified in the presence of tetrodotoxin, a voltage-dependent Na(+)-channel blocker, N(omega)-nitro-L-arginine methyl ester (L-NAME), an inhibitor of nitric oxide synthase, indomethacin, an inhibitor of cycloxygenase or tetraethylammonium, a non-selective blocker of potassium channels. In conclusion, this study provides the first experimental evidence for gastric relaxant activity of flavonoids. This action is influenced to a great extent by the structure of the molecules and it seems not to be dependent on neural action potentials, NO/prostaglandin production or activation of K(+) channels.