PPARγ-Independent Side Effects of Thiazolidinediones on Mitochondrial Redox State in Rat Isolated Hearts

The effect of anti-diabetic thiazolidinediones (TZDs) on contributing to heart failure and cardiac ischemia/reperfusion (IR) injury is controversial. In this study we investigated the effect of select TZDs on myocardial and mitochondrial function in Brown Norway rat isolated hearts. In a first set of experiments, the TZD rosiglitazone was given acutely before global myocardial IR, and pre- and post-IR function and infarct size were assessed. In a second set of experiments, different concentrations of rosiglitazone and pioglitazone were administered in the presence or absence of the specific PPARγ antagonist GW9662, and their effects on the mitochondrial redox state were measured by online NADH and FAD autofluorescence. The administration of rosiglitazone did not significantly affect myocardial function except for transiently increasing coronary flow, but it increased IR injury compared to the control hearts. Both TZDs resulted in dose-dependent, reversible increases in mitochondrial oxidation which was not attenuated by GW9662. Taken together, these data suggest that TZDs cause excessive mitochondrial uncoupling by a PPARγ-independent mechanism. Acute rosiglitazone administration before IR was associated with enhanced cardiac injury. If translated clinically, susceptible patients on PPARγ agonists may experience enhanced myocardial IR injury by mitochondrial dysfunction.

Prevalence, management and ethnobotanical investigation of hypertension in two Guinean urban districts

ETHNOPHARMACOLOGICAL RELEVANCE

Hypertension is an important public health challenge in low- and middle-income countries, and in many African countries including Guinea medicinal plants are still widely used for its treatment.

MATERIALS AND METHODS

The objective of this study was to determine the prevalence of hypertension in two Guinean urban districts (Pounthioun and Dowsare), to describe its management and to collect information on traditional herbal remedies. A total of 316 participants entered the study, 28.2% (89/316) men and 71.8% (227/316) women. Of these, 181 were from Dowsare (50 men and 131 women) and 135 from Pounthioun (39 men and 96 women). The mean age of subjects was 40.8 ± 14.0 years (range18 - 88years), while the majority of subjects (63.3% or 200/316) were 45-74 years old.

RESULTS

The overall prevalence of hypertension was 44.9% (142/316): 46.4% (84/181) from Dowsare and 43.0% (58/135) from Pounthioun. Ethnobotanical investigations among hypertensive patients led to the collection of 15 plant species, among which Hymenocardia acida leaves and Uapaca togoensis stem bark were the most cited. Phytochemical investigation of these two plant species led to the isolation and identification of isovitexin and isoorientin from H. acida, and betulinic acid and lupeol from U. togoensis.

CONCLUSION

The presence of these constituents in Hymenocardia acida leaves and Uapaca togoensis stem bark may at least in part support their traditional use against hypertension in Guinea.

[Input of a laboratory in the management of patients with Ebola virus disease and in the training of health personnel: experience of the Forecariah Ebola treatment centre (Guinea) in 2015]

Ebola virus disease (EVD) is associated with a high lethality rate even when the afflicted are provided with good support in an Ebola treatment center (ETC). Basic laboratory tests can help to better understand the pathophysiology of the disease, to guide treatment and to establish simple protocols and procedures tailored to the practice of medicine in the context of such precarious environment for caregivers. Based on a few clinical cases of patients treated in the ETC of Forecariah, Guinea, run by the French Red Cross, this article describes the difficult conditions associated with the provision of medical practice in this challenging environment, aiming to minimize the casualties in the EVD patient and to train the health staff.

Mitochondrial handling of excess Ca2+ is substrate-dependent with implications for reactive oxygen species generation

The mitochondrial electron transport chain is the major source of reactive oxygen species (ROS) during cardiac ischemia. Several mechanisms modulate ROS production; one is mitochondrial Ca(2+) uptake. Here we sought to elucidate the effects of extramitochondrial Ca(2+) (e[Ca(2+)]) on ROS production (measured as H(2)O(2) release) from complexes I and III. Mitochondria isolated from guinea pig hearts were preincubated with increasing concentrations of CaCl(2) and then energized with the complex I substrate Na(+) pyruvate or the complex II substrate Na(+) succinate. Mitochondrial H(2)O(2) release rates were assessed after giving either rotenone or antimycin A to inhibit complex I or III, respectively. After pyruvate, mitochondria maintained a fully polarized membrane potential (ΔΨ; assessed using rhodamine 123) and were able to generate NADH (assessed using autofluorescence) even with excess e[Ca(2+)] (assessed using CaGreen-5N), whereas they remained partially depolarized and did not generate NADH after succinate. This partial ΔΨ depolarization with succinate was accompanied by a large release in H(2)O(2) (assessed using Amplex red/horseradish peroxidase) with later addition of antimycin A. In the presence of excess e[Ca(2+)], adding cyclosporin A to inhibit mitochondrial permeability transition pore opening restored ΔΨ and significantly decreased antimycin A-induced H(2)O(2) release. Succinate accumulates during ischemia to become the major substrate utilized by cardiac mitochondria. The inability of mitochondria to maintain a fully polarized ΔΨ under excess e[Ca(2+)] when succinate, but not pyruvate, is the substrate may indicate a permeabilization of the mitochondrial membrane, which enhances H(2)O(2) emission from complex III during ischemia.

Differential modulation of the cardiac L- and T-type calcium channel currents by isoflurane

BACKGROUND

Volatile anesthetics exert their negative chronotropic and inotropic effects, in part by depressing the L- and T-type calcium channels. This study examines and compares the dose-dependent effects of isoflurane on atrial L- and T-type calcium currents (I(Ca,L) and I(Ca,T)) and ventricular I(Ca,L).

METHODS

Whole cell I(Ca) was recorded from enzymatically isolated guinea pig cardiomyocytes. Current-voltage relations for atrial and ventricular I(Ca,L) was obtained from holding potentials of -90 and -50 mV to test a potential of +60 mV in 10-mV increments. Atrial I(Ca,T) was determined by subtraction of currents obtained from holding potentials of -50 and -90 mV. Steady state inactivation was determined using standard two-pulse protocols, and data were fitted with the Boltzmann equation.

RESULTS

Isoflurane depressed I(Ca) in a dose-dependent manner, with Kd values of 0.23+/-0.03, 0.34+/-0.03, and 0.71+/-0.02 mM of anesthetic for atrial I(Ca,T) and I(Ca,L) and ventricular (ICa,L), respectively, and caused a significant (P < 0.05) hyperpolarizing shift in steady state inactivation. At 1.2 and 1.6 mm, isoflurane caused a significant (P < 0.05) depolarizing shift in the steady state activation in ventricular I(Ca,L) but not in atrial I(Ca,L) or I(Ca,T). In addition to the depression of I(Ca,L), isoflurane also induced a hyperpolarizing shift in the reversal potential of I(Ca) for both atrial and ventricular L-type calcium channels.

CONCLUSION

The results show that atrial I(Ca,T) is more sensitive to isoflurane than atrial I(Ca,L), and ventricular I(Ca,L) was the least responsive to the anesthetic. These differential sensitivities of the calcium channels in the atrial and ventricular chambers might reflect phenotypic differences in the calcium channels or differences in modulation by the anesthetic.

Interactions of halothane with isoproterenol and epinephrine on canine epicardial conduction velocity at normal and elevated potassium levels

BACKGROUND

Halothane is known to potentiate catecholamine-induced depression of conduction velocity in Purkinje fibers but not endocardial muscle fibers. The purpose of this study was to examine the interactions of halothane with epinephrine and isoproterenol on canine epicardial conduction velocity at moderately elevated extracellular potassium concentration ([K]0).

METHODS

Epicardial muscle strips (10x10x2 mm) were superfused with Tyrode's solution containing 4 or 8 mM [K]0 in the presence of 5 microM epinephrine or 1 microM isoproterenol with or without 0.8 mM halothane. Conduction velocity in the longitudinal and transverse directions relative to epicardial fiber orientation was recorded during alternate stimulation in each direction.

RESULTS

In the presence of halothane, a change from 4 to 8 mM [K]0 decreased (P< or =0.05) longitudinal and transverse conduction velocities by 26% and 21%, respectively. Isoproterenol alone at 4 and 8 mM [K]0 depressed (P<0.05) both longitudinal and transverse conduction velocities. However, the depression of longitudinal conduction velocity by isoproterenol at 4 mM [K]0 was attenuated by halothane. Epinephrine with or without halothane depressed (P<0.05) both longitudinal and transverse conduction velocities at 8 but not at 4 mM [K]0.

CONCLUSION

The results do not support a synergistic interaction between halothane and epinephrine on myocardial conduction but do demonstrate depression of conduction by epinephrine at 8 mM [K+]0, a potassium ion concentration comparable to those reported following epinephrine infusions.

Central AT1 and AT2 receptors mediate chronic intracerebroventricular angiotensin II-induced drinking in rats fed high sodium chloride diet from weaning

Intracerebroventricular (ICV) angiotensin (AIl) administration stimulates central AII receptors to induce water consumption in rats. The aim of this study was to determine the role of brain AT1 and AT2 receptors in mediating chronic ICV AII-induced drinking in rats raised on normal or high sodium chloride diets from weaning. Rats were weaned at 21 days of age and placed on normal or high sodium chloride diet for 10-12 weeks. At adulthood, the animals were instrumented with brain lateral ventricular cannulas and femoral arterial catheters. Low dose chronic central AII infusion (20 ng min(-1)) significantly (P < 0.05) increased water intake in both groups of rats when compared with their respective controls of 24 h artificial cerebrospinal fluid infusions. In a separate group of high sodium fed rats, coinfusion of AII with the AT1 receptor antagonist, losartan (0.25 microg min(-1)) or the AT2 receptor blocker, PD 123319 (0.50 microg min(-1)) blocked chronic ICV AII-induced drinking. Upon reinfusion of AII water intake increased above control. Following the cessation of AII infusions, water intake returned to values not significantly different from control (P > 0.05). In contrast, in the normal sodium fed rats losartan, but not PD 123319, blocked the AII-mediated water intake. The data demonstrate that in high sodium chloride fed rats AII stimulates both central AT1 and AT2 receptors to induce drinking, while in the normal sodium chloride fed rats the peptide activates the drinking response primarily by stimulation of central AT1 receptors.

Alpha-adrenergic systems mediate chronic central AII hypertension in rats fed high sodium chloride diet from weaning

Hypertension is elicited by chronic, low dose intracerebroventricular (ICV) angiotensin II (AII) infusion in rats raised from weaning on relatively high sodium chloride diet (250 mEq kg(-1) food). This experimental model of hypertension is dependent upon renal innervation and associated with neurogenic sodium retention. The present study determined whether this neurogenic ICV AII hypertension is mediated by central alpha-adrenoceptors. Rats were weaned at 21 days of age and fed a 1.5% (250 mg kg(-1) food) sodium chloride diet for 10-12 weeks. At adulthood, animals were instrumented with central nervous system (CNS) lateral ventricular cannulas, femoral artery and vein catheters and housed in metabolic pens for chronic study. Low dose ICV AII infusion (20 ng min(-1)) increased mean arterial pressure (MAP) from 121 +/- 4 to 140 +/- 6 mm Hg on the day of ICV infusion. This increase in arterial pressure was associated with 3 consecutive days of decreased urinary sodium excretion. Subsequent ICV alpha-adrenoceptor blockade with phentolamine (AII + phentolamine) abolished the pressor and antinatriuretic responses to low dose chronic ICV AII infusion. Resumption of ICV AII infusion alone increased in MAP toward pre-alpha-adrenergic blockade values (133 +/- 5 mm Hg) on day 8. Following cessation of ICV AII infusion, arterial pressure and sodium excretion returned to values not significantly different from control. This model of hypertension was not dependent on circulating plasma renin activity (PRA), since PRA decreased during ICV AII infusion. These data confirm that low dose ICV AII causes hypertension and sodium retention in rats raised from weaning on moderately elevated sodium intake. We conclude that AII mediated neurogenic hypertension and antinatriuresis is elicited by stimulation of AT1 receptors on neurons which interact with noradrenergic cell bodies in cardiovascular and autonomic centers that may modulate renal sympathetic outflow via alpha-adrenoceptors.

AT1 receptors mediate chronic central nervous system AII hypertension in rats fed high sodium chloride diet from weaning

CNS angiotensin II (AII) hypertension is induced by chronic, low dose intracerebroventricular (ICV) AII infusion only in rats raised on a relatively high sodium chloride diet (250 meq kg(-1)food) from weaning. This experimental model of hypertension is dependent upon renal sympathetic innervation and associated with neurogenic sodium retention. This study determined whether AT1 and/or AT2 receptor subtypes in the CNS mediate this neurogenic ICV AII hypertension. Rats were weaned at 21 days of age and fed a 1.5% sodium chloride diet for 10-12 weeks. At adulthood, animals were instrumented with CNS lateral ventricular cannulas, femoral arterial and vein catheters and housed in metabolic pens for chronic study. Low dose ICV AII infusion (20 ng min(-1) )increased mean arterial pressure by 12+/-2 mm Hg and decreased urinary sodium excretion for three consecutive days. Subsequent ICV AT1 blockade with losartan abolished both the pressor and antinatriuretic responses to low dose ICV AII. In contrast, ICV AT2 receptor blockade with PD 123319 did not affect either angiotensin induced pressor or antinatriuretic responses. Following cessation of ICV AII infusion, arterial pressure and sodium excretion returned to values not significantly different from control in both groups of rats. These data confirm that low dose ICV AII causes hypertension and sodium retention in rats raised from early age on moderately elevated sodium intakes. This AII mediated neurogenic hypertension and antinatriuresis is transduced by activation of CNS AT1 receptors and not by activation of central AT2 receptors.

Renal neurogenic mediation of intracerebroventricular angiotensin II hypertension in rats raised on high sodium chloride diet

Chronic elevation of sodium intake may affect the sensitivity of the central nervous system to intracerebroventricular (I.C.V.) angiotensin II (Ang II) infusion. Experiments were conducted to determine the influence of raising Sprague-Dawley rats from 2 to 3 weeks of age on low (5.0 mmol/L per kg food), normal (50 mmol/L per kg food), or high (250 mmol/L per kg food) NaCl diets on renal and cardiovascular responses to low-dose I.C.V. Ang II infusion. At 12 weeks of age, Sprague-Dawley rats were instrumented for chronic study, including brain lateral ventricular cannulation. Artificial cerebrospinal fluid was infused (0.25 microL/min I.C.V.) during control and recovery, whereas Ang II (20 ng/min) was infused for 5 days. During the experiment, respective sodium intakes were infused intravenously over 24 hours. In rats fed high sodium, control mean arterial pressure was 115+/-2 mm Hg and increased to 132+/-4 mm Hg by day 5 of I.C.V. Ang II infusion. This increase in arterial pressure was associated with significant (P<.05) decreases in sodium excretion, leading to the retention of 5.4+/-0.6 mmol/L total sodium over the 5 days of Ang II infusion. In rats raised on low and normal sodium intakes from weaning and in 10-week-old rats exposed to a high sodium diet for only 2 weeks, arterial pressure was not increased and sodium was not retained during I.C.V. Ang II infusion at 20 ng/min. In rats raised on the high sodium diet, bilateral renal denervation abolished the arterial hypertension and reduced the sodium retention over 5 days of I.C.V. Ang II infusion. Thus, chronic elevation of sodium intake increases the hypertensive response to low-dose I.C.V. Ang II infusion, which is dependent on intact renal nerves. We conclude that elevated postnatal NaCl intake enhances the pressor sensitivity of the brain to Ang II.