Cross-influence of membrane polyunsaturated fatty acids and hypoxia-reoxygenation on alpha- and beta-adrenergic function of rat cardiomyocytes

Docosahexaenoic Acid (DHA) Induced Morphological Differentiation of Astrocytes Is Associated with Transcriptional Upregulation and Endocytosis of β2-AR

Docosahexaenoic acid (DHA), an important ω-3 fatty acid, is abundantly present in the central nervous system and is important in every step of brain development. Much of this knowledge has been based on studies of the role of DHA in the function of the neurons, and reports on its effect on the glial cells are few and far between. We have previously reported that DHA facilitates astrocyte differentiation in primary culture. We have further explored the signaling mechanism associated with this event. It was observed that a sustained activation of the extracellular signal-regulated kinase (ERK) appeared to be critical for DHA-induced differentiation of the cultured astrocytes. Prior exposure to different endocytic inhibitors blocked both ERK activation and differentiation of the astrocytes during DHA treatment suggesting that the observed induction of ERK-2 was purely endosomal. Unlike the β₁-adrenergic receptor (β₁-AR) antagonist, atenolol, pre-treatment of the cells with the β₂-adrenergic receptor (β₂-AR) antagonist, ICI-118,551 inhibited the DHA-induced differentiation process, indicating a downstream involvement of β₂-AR in the differentiation process. qRT-PCR and western blot analysis demonstrated a significant induction in the mRNA and protein expression of β₂-AR at 18-24 h of DHA treatment, suggesting that the induction of β₂-AR may be due to transcriptional upregulation. Moreover, DHA caused activation of PKA at 6 h, followed by activation of downstream cAMP response element-binding protein, a known transcription factor for β₂-AR. Altogether, the observations suggest that DHA upregulates β₂-AR in astrocytes, which undergo endocytosis and signals for sustained endosomal ERK activation to drive the differentiation process.

Does early-life exposure to organophosphate insecticides lead to prediabetes and obesity?

Human exposures to organophosphate insecticides are ubiquitous. Although regarded as neurotoxicants, increasing evidence points toward lasting metabolic disruption from early-life organophosphate exposures. We gave neonatal rats chlorpyrifos, diazinon or parathion in doses devoid of any acute signs of toxicity, straddling the threshold for barely-detectable cholinesterase inhibition. Organophosphate exposure during a critical developmental window altered the trajectory of hepatic adenylyl cyclase/cyclic AMP signaling, culminating in hyperresponsiveness to gluconeogenic stimuli. Consequently, the animals developed metabolic dysfunction resembling prediabetes. When the organophosphate-exposed animals consumed a high fat diet in adulthood, metabolic defects were exacerbated and animals gained excess weight compared to unexposed rats on the same diet. At the same time, the high fat diet ameliorated many of the central synaptic defects caused by organophosphate exposure, pointing to nonpharmacologic therapeutic interventions to offset neurodevelopmental abnormalities, as well as toward fostering dietary choices favoring high fat intake. These studies show how common insecticides may contribute to the increased worldwide incidence of obesity and diabetes.

Neonatal exposure to parathion alters lipid metabolism in adulthood: Interactions with dietary fat intake and implications for neurodevelopmental deficits

Organophosphates are developmental neurotoxicants but recent evidence also points to metabolic dysfunction. We determined whether neonatal parathion exposure in rats has long-term effects on regulation of adipokines and lipid peroxidation. We also assessed the interaction of these effects with increased fat intake. Rats were given parathion on postnatal days 1-4 using doses (0.1 or 0.2mg/kg/day) that straddle the threshold for barely detectable cholinesterase inhibition and the first signs of systemic toxicity. In adulthood, animals were either maintained on standard chow or switched to a high-fat diet for 7 weeks. We assessed serum leptin and adiponectin, tumor necrosis factor-alpha (TNFalpha) in adipose tissues, and thiobarbituric acid reactive species (TBARS) in peripheral tissues and brain regions. Neonatal parathion exposure uncoupled serum leptin levels from their dependence on body weight, suppressed adiponectin and elevated TNFalpha in white adipose tissue. Some of the effects were offset by a high-fat diet. Parathion reduced TBARS in the adipose tissues, skeletal muscle and temporal/occipital cortex but not in heart, liver, kidney or frontal/parietal cortex; it elevated TBARS in the cerebellum; the high-fat diet again reversed many of the effects. Neonatal parathion exposure disrupts the regulation of adipokines that communicate metabolic status between adipose tissues and the brain, while also evoking an inflammatory adipose response. Our results are consistent with impaired fat utilization and prediabetes, as well as exposing a potential relationship between effects on fat metabolism and on synaptic function in the brain.

Neonatal parathion exposure disrupts serotonin and dopamine synaptic function in rat brain regions: modulation by a high-fat diet in adulthood

The consequences of exposure to developmental neurotoxicants are influenced by environmental factors. In the present study, we examined the role of dietary fat intake. We administered parathion to neonatal rats and then evaluated whether a high-fat diet begun in adulthood could modulate the persistent effects on 5HT and DA systems. Neonatal rats received parathion on postnatal days 1-4 at 0.1 or 0.2 mg/kg/day, straddling the cholinesterase inhibition threshold. In adulthood, half the animals in each exposure group were given a high-fat diet for 8 weeks. We assessed 5HT and DA concentrations and turnover in brain regions containing their respective cell bodies and projections. In addition, we monitored 5HT1A and 5HT2 receptor binding and the concentration of 5HT presynaptic transporters. Neonatal parathion exposure evoked widespread increases in neurotransmitter turnover, indicative of presynaptic hyperactivity, further augmented by 5HT receptor upregulation. In control rats, consumption of a high-fat diet recapitulated many of the changes seen with neonatal parathion exposure; the effects represented convergent mechanisms, since the high-fat diet often obtunded further increases caused by parathion. Neonatal parathion exposure causes lasting hyperactivity of 5HT and DA systems accompanied by 5HT receptor upregulation, consistent with "miswiring" of neuronal projections. A high-fat diet obtunds the effect of parathion, in part by eliciting similar changes itself. Thus, dietary factors may produce similar synaptic changes as do developmental neurotoxicants, potentially contributing to the increasing incidence of neurodevelopmental disorders.

Dietary polyunsaturated fatty acids and adaptation to chronic hypoxia alter acyl composition of serum and heart lipids

The effects of dietary supplementation with fat of different fatty acid profile and chronic intermittent hypoxia (CIH) on the fatty acid composition of serum and heart lipids were analysed. Adult male Wistar rats were fed a standard non-fat diet enriched with 10 % of lard, fish oil (n-3 PUFA) or maize oil (n-6 PUFA) for 10 weeks. After 4 weeks on the diets, each group was divided in two subgroups, either exposed to CIH in a barochamber (7000 m, twenty-five exposures) or kept at normoxia. In normoxic rats, the fish oil diet increased the level of conjugated dienes. The n-6:n-3 PUFA ratio in serum TAG, phospholipids (PL), cholesteryl esters (CE) and heart TAG, PL and diacylglycerols (DAG) followed the ratio in the fed diet (in the sequence maize oil>lard>fish oil). In heart TAG, PL and DAG, 20 : 4n-6 and 18 : 2n-6 were replaced by 22 : 6n-3 in the fish oil group. The main fatty acid in CE was 20 : 4n-6 in the lard and maize oil groups whereas in the fish oil group, half of 20 : 4n-6 was replaced by 20 : 5n-3. CIH further increased 20 : 5n-3 in CE in the fish oil group. CIH decreased the n-6:n-3 PUFA ratio in serum CE, heart TAG, PL and DAG in all dietary groups and stimulated the activity of catalase in the maize and fish oil groups. In conclusion, PUFA diets and CIH, both interventions considered to be cardioprotective, distinctly modified the fatty acid profile in serum and heart lipids with specific effects on conjugated diene production and catalase activity.

Consumption of a high-fat diet in adulthood ameliorates the effects of neonatal parathion exposure on acetylcholine systems in rat brain regions

BACKGROUND

Developmental exposure to a wide variety of developmental neurotoxicants, including organophosphate pesticides, evokes late-emerging and persistent abnormalities in acetylcholine (ACh) systems. We are seeking interventions that can ameliorate or reverse the effects later in life.

OBJECTIVES

We administered parathion to neonatal rats and then evaluated whether a high-fat diet begun in adulthood could reverse the effects on ACh systems.

METHODS

Neonatal rats received parathion on postnatal days 1-4 at 0.1 or 0.2 mg/kg/day, straddling the cholinesterase inhibition threshold. In adulthood, half the animals were switched to a high-fat diet for 8 weeks. We assessed three indices of ACh synaptic function: nicotinic ACh receptor binding, choline acetyltransferase activity, and hemicholinium-3 binding. Determinations were performed in brain regions comprising all the major ACh projections and cell bodies.

RESULTS

Neonatal parathion exposure evoked widespread abnormalities in ACh synaptic markers, encompassing effects in brain regions possessing ACh projections and ACh cell bodies. In general, males were affected more than females. Of 17 regional ACh marker abnormalities (10 male, 7 female), 15 were reversed by the high-fat diet.

CONCLUSIONS

A high-fat diet reverses neurodevelopmental effects of neonatal parathion exposure on ACh systems. This points to the potential for nonpharmacologic interventions to offset the effects of developmental neurotoxicants. Further, cryptic neurodevelopmental deficits evoked by environmental exposures may thus engender a later preference for a high-fat diet to maintain normal ACh function, ultimately contributing to obesity.

Effects of alpha-linolenic acid vs. docosahexaenoic acid supply on the distribution of fatty acids among the rat cardiac subcellular membranes after a short- or long-term dietary exposure

BACKGROUND

Previous work showed that the functional cardiac effect of dietary alpha-linolenic acid (ALA) in rats requires a long feeding period (6 months), although a docosahexaenoic (DHA) acid-supply affects cardiac adrenergic response after 2 months. However, the total cardiac membrane n-3 polyunsaturated fatty acid (PUFA) composition remained unchanged after 2 months. This delay could be due to a specific reorganization of the different subcellular membrane PUFA profiles. This study was designed to investigate the evolution between 2 and 6 months of diet duration of the fatty acid profile in sarcolemmal (SL), mitochondrial (MI), nuclear (NU) and sarcoplasmic reticulum (SR) membrane fractions.

METHODS

Male Wistar rats were randomly assigned to 3 dietary groups (n = 10/diet/period), either n-3 PUFA-free diet (CTL), or ALA or DHA-rich diets. After 2 or 6 months, the subcellular cardiac membrane fractions were separated by differential centrifugations and sucrose gradients. Each membrane profile was analysed by gas chromatography (GC) after lipid extraction.

RESULTS

As expected the n-3 PUFA-rich diets incorporated n-3 PUFA instead of n-6 PUFA in all the subcellular fractions, which also exhibited individual specificities. The diet duration increased SFA and decreased PUFA in SL, whereas NU remained constant. The SR and MI enriched in n-3 PUFA exhibited a decreased DHA level with ageing in the DHA and CTL groups. Conversely, the n-3 PUFA level remained unchanged in the ALA group, due to a significant increase in docosapentaenoic acid (DPA). N-3 PUFA rich diets lead to a better PUFA profile in all the fractions and significantly prevent the profile modifications induced by ageing.

CONCLUSION

With the ALA diet the n-3 PUFA content, particularly in SR and SL kept increasing between 2 and 6 months, which may partly account for the delay to achieve the modification of adrenergic response.

Formation of three-dimensional fetal myocardial tissue cultures from rat for long-term cultivation

Three-dimensional cardiomyocyte cultures offer new possibilities for the analysis of cardiac cell differentiation, spatial cellular arrangement, and time-specific gene expression in a tissue-like environment. We present a new method for generating homogenous and robust cardiomyocyte tissue cultures with good long-term viability. Ventricular heart cells prepared from fetal rats at embryonic day 13 were cultured in a scaffold-free two-step process. To optimize the cell culture model, several digestion protocols and culture conditions were tested. After digestion of fetal cardiac ventricles, the resultant cell suspension of isolated cardiocytes was shaken to initialize cell aggregate formation. In the second step, these three-dimensional cell aggregates were transferred onto a microporous membrane to allow further microstructure formation. Autonomously beating cultures possessed more than 25 cell layers and a homogenous distribution of cardiomyocytes without central necrosis after 8 weeks in vitro. The cardiomyocytes showed contractile elements, desmosomes, and gap junctions analyzed by immunohistochemistry and electron microscopy. The beat frequency could be modulated by adrenergic agonist and antagonist. Adenoviral green fluorescent protein transfer into cardiomyocytes was possible and highly effective. This three-dimensional tissue model proved to be useful for studying cell-cell interactions and cell differentiation processes in a three-dimensional cell arrangement.

Ethanolic extract of Spirulina maxima alters the vasomotor reactivity of aortic rings from obese rats

BACKGROUND

Aortic rings with endothelium excised from fructose-fed obese rats develop more tension in response to phenylephrine and relax less in response to carbachol than corresponding rings from lean rats. This altered vascular reactivity is prevented when Spirulina maxima is added to the fructose-rich diet. In the present study the effects of a raw ethanolic extract of Spirulina maxima on the vasomotor responses of aorta rings from sucrose-fed obese hypertensive rats were analyzed.

METHODS

The experiments were performed on aorta rings from sucrose-fed obese male rats. For each experiment, a pair of rings from the same aorta (one with intact endothelium, the other without a functional endothelium) was used. In this study we analyzed, in vitro, the effects of the ethanolic extract of Spirulina maxima on the reactivity of the aortic rings to phenylephrine and to carbachol.

RESULTS

On rings with endothelium, the extract produced the following effects: a) a concentration-dependent (0.06-1.0 mg/mL) decrease of the contractile response to phenylephrine; b) a rightward shift and a decrease in maximal developed tension, of the concentration-response curve to phenylephrine; c) a concentration-dependent relaxation of phenylephrine-precontracted rings. These effects persisted in the presence of indomethacin but were prevented by L-NAME. The extract had no effect on the concentration-response curve of phenylephrine-precontracted rings to carbachol. On endothelium-denuded rings the extract caused a significant rightward shift of the concentration response curve to phenylephrine without any effect on maximal tension development.

CONCLUSIONS

These results suggest that, in rings from obese rats, the extract, in addition to increasing the synthesis/release of NO, also inhibits the synthesis/release of a cyclooxygenase-dependent vasoconstrictor metabolite of arachidonic acid, which is increased in obesity.

Beta1-adrenergic receptors maintain fetal heart rate and survival

Beta-adrenergic receptor (betaAR) activation has been shown to maintain heart rate during hypoxia and to rescue the fetus from the fetal lethality that occurs in the absence of norepinephrine. This study examines whether the same subtype of betaAR is responsible for survival and heart rate regulation. It also investigates which betaARs are located on the early fetal heart and whether they can be directly activated during hypoxia. Cultured E12.5 mouse fetuses were treated with subtype-specific betaAR antagonists to pharmacologically block betaARs during a hypoxic insult. Hypoxia alone reduced heart rate by 35-40% compared to prehypoxic levels. During hypoxia, heart rate was further reduced by 31% in the presence of a beta(1)AR antagonist, CGP20712A, at 100 nM, but not with a beta2 (ICI118551)- or a beta3 (SR59230A)-specific antagonist at 100 nM. Survival in utero was also mediated by beta1ARs. A beta1 partial agonist, xamoterol, rescued 74% of catecholamine-deficient (tyrosine-hydroxylase-null) pups to birth, a survival rate equivalent to that with a nonspecific betaAR agonist, isoproterenol (87%). Receptor autoradiography showed that beta1ARs were only found on the mouse heart at E12.5, while beta2ARs were localized to the liver and vasculature. To determine if the response to hypoxia was intrinsic to the heart, isolated fetal hearts were incubated under hypoxic conditions in the presence of a betaAR agonist. Heart rate was reduced to 25-30% by hypoxia alone, but was restored to 63% of prehypoxic levels with 100 nM isoproterenol. Restoration was completely prevented if beta1ARs were blocked with CGP20712A at 300 nM, a concentration that blocks beta1ARs, but not beta2- or beta3ARs. Our results demonstrate that beta1ARs are located on the heart of early fetal mice and that beta1AR stimulation maintains fetal heart rate during hypoxia and mediates survival in vivo.

Attenuation of liver ischemia-reperfusion-induced atrial dysfunction by external pacing but not by isoproterenol

Remote ischemia–reperfusion detrimentally affects myocardial function by initially interfering with the rate of contraction. We investigated the usefulness of isoproterenol versus external electrical pacing in attenuating secondary functional damage of isolated Wistar rat atria. Atrial strips (n = 10/group) were bathed within oxygenated Krebs–Henseleit solution that exited from isolated livers that had been either perfused normally (controls) or underwent no flow (ischemia) for 2 h. In addition to one noninterventional ischemia-exposed strip group, a second group was externally paced at a fixed rate (55 pulses·min–1, 6 V) and a third "ischemia" group was treated with isoproterenol (0.1 mM), both interventions commencing upon the strips' exposure to the hepatic effluents. Control strips displayed unaltered contraction rate and systolic-generated tension during the 2-h exposure. Nontreated strips exposed to ischemic reperfusate experienced bradycardia compared with baseline values (7 ± 2 vs. 50 ± 12 beats·min–1, p < 0.05), followed <1-min later by a fall in the generated tension (11 ± 4 vs. 20 ± 6 mmHg, p < 0.05). The paced-ischemic strips displayed unaltered rate and force of contraction, whereas the addition of isoproterenol did not prevent deterioration in the rate and force of contraction (8 ± 3 beats·min–1, 12 ± 4 mmHg, respectively; p < 0.05 vs. baseline control ischemia-paced strips). Thus, external electrical pacing prevented liver ischemia–reperfusion-induced atrial strips' bradycardia and loss of contractility, while isoproterenol did not.Key words: ischemia, reperfusion, liver, atrium, dysfunction, isoproterenol, pacing.

Oxygen-mediated cold-acclimation in cucumber (Cucumis sativus) seedlings

Cold acclimation of etiolated cucumber seedlings, consisting of cooling at 12 degrees C for 48 h followed by a warming period at 25 degrees C, led to tolerance to subsequent chilling at 2 degrees C. Tolerance, as evidenced by freedom from chilling injury and continued growth, developed during the warming period in a time-course manner for 12 h but decreased with prolonged warming. A similar increase and subsequent decrease was also observed in the content of palmitic, linoleic and linolenic acids in total lipid fraction from cucumber hypocotyl tissue. During the warming period supra-ambient oxygen stimulated, whereas subambient oxygen inhibited, the increase in fatty acid content as well as development of chilling tolerance. A strong correlation between oxygen-mediated changes in fatty acid content and associated development of cold tolerance suggests that both these processes are interrelated. Cold acclimation, but not cold stress, led to an increase followed by a decrease in CO2 evolution suggesting that a respiratory upsurge is yet another feature of cold acclimation in cucumbers.