Contribution of adenosine and ATP to the carotid body chemosensory activity in ageing.

KEY POINTS: Adenosine and ATP are excitatory neurotransmitters involved in the carotid body (CB) response to hypoxia. During ageing the CB exhibits a decline in its functionality, demonstrated by decreased hypoxic responses. In aged rats (20-24 months old) there is a decrease in: basal and hypoxic release of adenosine and ATP from the CB; expression of adenosine and ATP receptors in the petrosal ganglion; carotid sinus nerve (CSN) activity in response to hypoxia; and ventilatory responses to ischaemic hypoxia. There is also an increase in SNAP25, ENT1 and CD73 expression. It is concluded that, although CSN activity and ventilatory responses to hypoxia decrease with age, adjustments in purinergic metabolism in the CB in aged animals are present aiming to maintain the contribution of adenosine and ATP. The possible significance of the findings in the context of ageing and in CB-associated pathologies is considered. ABSTRACT: During ageing the carotid body (CB) exhibits a decline in its functionality. Here we investigated the effect of ageing on functional CB characteristics as well as the contribution of adenosine and ATP to CB chemosensory activity. Experiments were performed in 3-month-old and 20- to 24-month-old male Wistar rats. Ageing decreased: the number of tyrosine hydroxylase immune-positive cells, but not type II cells or nestin-positive cells in the CB; the expression of P2X2 and A2A receptors in the petrosal ganglion; and the basal and hypoxic release of adenosine and ATP from the CB. Ageing increased ecto-nucleotidase (CD73) immune-positive cells and the expression of synaptosome associated protein 25 (SNAP25) and equilibrative nucleoside transporter 1 (ENT1) in the CB. Additionally, ageing did not modify basal carotid sinus nerve (CSN) activity or the activity in response to hypercapnia, but decreased CSN activity in hypoxia. The contribution of adenosine and ATP to stimuli-evoked CSN chemosensory activity in aged animals followed the same pattern of 3-month-old animals. Bilateral common carotid occlusions during 5, 10 and 15 s increased ventilation proportionally to the duration of ischaemia, an effect decreased by ageing. ATP contributed around 50% to ischaemic-ventilatory responses in young and aged rats; the contribution of adenosine was dependent on the intensity of ischaemia, being maximal in ischaemias of 5 s (50%) and much smaller in 15 s ischaemias. Our results demonstrate that both ATP and adenosine contribute to CB chemosensory activity in ageing. Though CB responses to hypoxia, but not to hypercapnia, decrease with age, the relative contribution of both ATP and adenosine for CB activity is maintained.

Hypoxic pulmonary vasoconstriction, carotid body function and erythropoietin production in adult rats perinatally exposed to hyperoxia.

KEY POINTS: Adult animals that have been perinatally exposed to oxygen-rich atmospheres (hyperoxia), recalling those used for oxygen therapy in infants, exhibit a loss of hypoxic pulmonary vasoconstriction, whereas vasoconstriction elicited by depolarizing agents is maintained. Loss of pulmonary hypoxic vasoconstriction is not linked to alterations in oxygen-sensitive K(+) currents in pulmonary artery smooth muscle cells. Loss of hypoxic vasoconstriction is associated with early postnatal oxidative damage and corrected by an antioxidant diet. Perinatal hyperoxia damages carotid body chemoreceptor cell function and the antioxidant diet does not reverse it. The hypoxia-elicited increase in erythropoietin plasma levels is not affected by perinatal hyperoxia. The potential clinical significance of the findings in clinical situations such as pneumonia, chronic obstructive pulmonary disease or general anaesthesia is considered. ABSTRACT: Adult mammalians possess three cell systems that are activated by acute bodily hypoxia: pulmonary artery smooth muscle cells (PASMC), carotid body chemoreceptor cells (CBCC) and erythropoietin (EPO)-producing cells. In rats, chronic perinatal hyperoxia causes permanent carotid body (CB) atrophy and functional alterations of surviving CBCC. There are no studies on PASMC or EPO-producing cells. Our aim is to define possible long-lasting functional changes in PASMC or EPO-producing cells (measured as EPO plasma levels) and, further, to analyse CBCC functional alterations. We used 3- to 4-month-old rats born and reared in a normal atmosphere or exposed to perinatal hyperoxia (55-60% O2 for the last 5-6 days of pregnancy and 4 weeks after birth). Perinatal hyperoxia causes an almost complete loss of hypoxic pulmonary vasoconstriction (HPV), which was correlated with lung oxidative status in early postnatal life and prevented by antioxidant supplementation in the diet. O2 -sensitivity of K(+) currents in the PASMC of hyperoxic animals is normal, indicating that their inhibition is not sufficient to trigger HPV. Perinatal hyperoxia also abrogated responses elicited by hypoxia on catecholamine and cAMP metabolism in the CB. An increase in EPO plasma levels elicited by hypoxia was identical in hyperoxic and control animals, implying a normal functioning of EPO-producing cells. The loss of HPV observed in adult rats and caused by perinatal hyperoxia, comparable to oxygen therapy in premature infants, might represent a previously unrecognized complication of such a medical intervention capable of aggravating medical conditions such as regional pneumonias, atelectases or general anaesthesia in adult life.

Disclosing caffeine action on insulin sensitivity: effects on rat skeletal muscle.

Caffeine, a non-selective adenosine antagonist, has distinct effects on insulin sensitivity when applied acutely or chronically. Herein, we investigated the involvement of adenosine receptors on insulin resistance induced by single-dose caffeine administration. Additionally, the mechanism behind adenosine receptor-mediated caffeine effects in skeletal muscle was assessed. The effect of the administration of caffeine, 8-cycle-1,3-dipropylxanthine (DPCPX, A1 antagonist), 2-(2-Furanyl)-7-(2-phenylethyl)-7H-pyrazolo[4,3-e][1,2,4]triazolo[1,5-c]pyrimidin-5-amine (SCH58261, A2A antagonist) and 8-(4-{[(4-cyanophenyl)carbamoylmethyl]-oxy}phenyl)-1,3-di(n-propyl)xanthine (MRS1754, A2B antagonist) on whole-body insulin sensitivity was tested. Skeletal muscle Glut4,5'-AMP activated protein kinase (AMPK) and adenosine receptor protein expression were also assessed. The effect of A1 and A2B adenosine agonists on skeletal muscle glucose uptake was evaluated in vitro. Sodium nitroprussiate (SNP, 10nM), a nitric oxide (NO) donor, was used to evaluate the effect of NO on insulin resistance induced by adenosine antagonists. Acute caffeine decreased insulin sensitivity in a concentration dependent manner (Emax=55.54±5.37%, IC50=11.61nM), an effect that was mediated by A1 and A2B adenosine receptors. Additionally, acute caffeine administration significantly decreased Glut4, but not AMPK expression, in skeletal muscle. We found that A1, but not A2B agonists increased glucose uptake in skeletal muscle. SNP partially reversed DPCPX and MRS1754 induced-insulin resistance. Our results suggest that insulin resistance induced by acute caffeine administration is mediated by A1 and A2B adenosine receptors. Both Glut4 and NO seem to be downstream effectors involved in insulin resistance induced by acute caffeine.

Carotid body, insulin, and metabolic diseases: unraveling the links.

The carotid bodies (CB) are peripheral chemoreceptors that sense changes in arterial blood O2, CO2, and pH levels. Hypoxia, hypercapnia, and acidosis activate the CB, which respond by increasing the action potential frequency in their sensory nerve, the carotid sinus nerve (CSN). CSN activity is integrated in the brain stem to induce a panoply of cardiorespiratory reflexes aimed, primarily, to normalize the altered blood gases, via hyperventilation, and to regulate blood pressure and cardiac performance, via sympathetic nervous system (SNS) activation. Besides its role in the cardiorespiratory control the CB has been proposed as a metabolic sensor implicated in the control of energy homeostasis and, more recently, in the regulation of whole body insulin sensitivity. Hypercaloric diets cause CB overactivation in rats, which seems to be at the origin of the development of insulin resistance and hypertension, core features of metabolic syndrome and type 2 diabetes. Consistent with this notion, CB sensory denervation prevents metabolic and hemodynamic alterations in hypercaloric feed animal. Obstructive sleep apnea (OSA) is another chronic disorder characterized by increased CB activity and intimately related with several metabolic and cardiovascular abnormalities. In this manuscript we review in a concise manner the putative pathways linking CB chemoreceptors deregulation with the pathogenesis of insulin resistance and arterial hypertension. Also, the link between chronic intermittent hypoxia (CIH) and insulin resistance is discussed. Then, a final section is devoted to debate strategies to reduce CB activity and its use for prevention and therapeutics of metabolic diseases with an emphasis on new exciting research in the modulation of bioelectronic signals, likely to be central in the future.

A systems biology approach reveals a link between systemic cytokines and skeletal muscle energy metabolism in a rodent smoking model and human COPD.

BACKGROUND: A relatively large percentage of patients with chronic obstructive pulmonary disease (COPD) develop systemic co-morbidities that affect prognosis, among which muscle wasting is particularly debilitating. Despite significant research effort, the pathophysiology of this important extrapulmonary manifestation is still unclear. A key question that remains unanswered is to what extent systemic inflammatory mediators might play a role in this pathology. Cigarette smoke (CS) is the main risk factor for developing COPD and therefore animal models chronically exposed to CS have been proposed for mechanistic studies and biomarker discovery. Although mice have been successfully used as a pre-clinical in vivo model to study the pulmonary effects of acute and chronic CS exposure, data suggest that they may be inadequate models for studying the effects of CS on peripheral muscle function. In contrast, recent findings indicate that the guinea pig model (Cavia porcellus) may better mimic muscle wasting. METHODS: We have used a systems biology approach to compare the transcriptional profile of hindlimb skeletal muscles from a Guinea pig rodent model exposed to CS and/or chronic hypoxia to COPD patients with muscle wasting. RESULTS: We show that guinea pigs exposed to long-term CS accurately reflect most of the transcriptional changes observed in dysfunctional limb muscle of severe COPD patients when compared to matched controls. Using network inference, we could then show that the expression profile in whole lung of genes encoding for soluble inflammatory mediators is informative of the molecular state of skeletal muscles in the guinea pig smoking model. Finally, we show that CXCL10 and CXCL9, two of the candidate systemic cytokines identified using this pre-clinical model, are indeed detected at significantly higher levels in serum of COPD patients, and that their serum protein level is inversely correlated with the expression of aerobic energy metabolism genes in skeletal muscle. CONCLUSIONS: We conclude that CXCL10 and CXCL9 are promising candidate inflammatory signals linked to the regulation of central metabolism genes in skeletal muscles. On a methodological level, our work also shows that a system level analysis of animal models of diseases can be very effective to generate clinically relevant hypothesis.

Intermittent hypoxia and diet-induced obesity: effects on oxidative status, sympathetic tone, plasma glucose and insulin levels, and arterial pressure.

Obstructive sleep apnea (OSA) consists of sleep-related repetitive obstructions of upper airways that generate episodes of recurrent or intermittent hypoxia (IH). OSA commonly generates cardiovascular and metabolic pathologies defining the obstructive sleep apnea syndrome (OSAS). Literature usually links OSA-associated pathologies to IH episodes that would cause an oxidative status and a carotid body-mediated sympathetic hyperactivity. Because cardiovascular and metabolic pathologies in obese patients and those with OSAS are analogous, we used models (24-wk-old Wistar rats) of IH (applied from weeks 22 to 24) and diet-induced obesity (O; animals fed a high-fat diet from weeks 12 to 24) to define the effect of each individual maneuver and their combination on the oxidative status and sympathetic tone of animals, and to quantify cardiovascular and metabolic parameters and their deviation from normality. We found that IH and O cause an oxidative status (increased lipid peroxides and diminished activities of superoxide dismutases), an inflammatory status (augmented C-reactive protein and nuclear factor kappa-B activation), and sympathetic hyperactivity (augmented plasma and renal artery catecholamine levels and synthesis rate); combined treatments worsened those alterations. IH and O augmented liver lipid content and plasma cholesterol, triglycerides, leptin, glycemia, insulin levels, and HOMA index, and caused hypertension; most of these parameters were aggravated when IH and O were combined. IH diminished ventilatory response to hypoxia, and hypercapnia and O created a restrictive ventilatory pattern; a combination of treatments led to restrictive hypoventilation. Data demonstrate that IH and O cause comparable metabolic and cardiovascular pathologies via misregulation of the redox status and sympathetic hyperactivity.

Fernando de Castro and the discovery of the arterial chemoreceptors.

When de Castro entered the carotid body (CB) field, the organ was considered to be a small autonomic ganglion, a gland, a glomus or glomerulus, or a paraganglion. In his 1928 paper, de Castro concluded: "In sum, the Glomus caroticum is innervated by centripetal fibers, whose trophic centers are located in the sensory ganglia of the glossopharyngeal, and not by centrifugal [efferent] or secretomotor fibers as is the case for glands; these are precisely the facts which lead to suppose that the Glomus caroticum is a sensory organ." A few pages down, de Castro wrote: "The Glomus represents an organ with multiple receptors furnished with specialized receptor cells like those of other sensory organs [taste buds?]…As a plausible hypothesis we propose that the Glomus caroticum represents a sensory organ, at present the only one in its kind, dedicated to capture certain qualitative variations in the composition of blood, a function that, possibly by a reflex mechanism would have an effect on the functional activity of other organs… Therefore, the sensory fiber would not be directly stimulated by blood, but via the intermediation of the epithelial cells of the organ, which, as their structure suggests, possess a secretory function which would participate in the stimulation of the centripetal fibers." In our article we will recreate the experiments that allowed Fernando de Castro to reach this first conclusion. Also, we will scrutinize the natural endowments and the scientific knowledge that drove de Castro to make the triple hypotheses: the CB as chemoreceptor (variations in blood composition), as a secondary sensory receptor which functioning involves a chemical synapse, and as a center, origin of systemic reflexes. After a brief account of the systemic reflex effects resulting from the CB stimulation, we will complete our article with a general view of the cellular-molecular mechanisms currently thought to be involved in the functioning of this arterial chemoreceptor.

The effects of intermittent hypoxia on redox status, NF-κB activation, and plasma lipid levels are dependent on the lowest oxygen saturation.

Obstructive sleep apnea syndrome (OSAS) is described as repetitive obstructions of the upper airways during sleep, causing concomitant episodes of systemic hypoxia and associated cardiovascular and metabolic pathologies. The mechanisms generating these pathologies are controversial. Because recurrent hypoxia is the element of inadequate respiration that leads to the pathology, experimental models of OSAS consist in the exposure of the animals to intermittent hypoxia (IH) by cycling O2 percentages in their habitats. A proposed mechanism linking the IH of OSAS to pathologies is the increased production of reactive oxygen species (ROS). However, it has been argued that many patients seem to lack oxidative stress and that, to augment ROS in IH animals, intense hypoxia, seldom encountered in patients, has to be applied. To solve the controversy, we have exposed rats to two intensities of IH (cycles of 10 or 5% O2, 40s, and then 21% O2, 80s; 8h/day, 15 days). We then measured reduced and oxidized glutathione and lipid peroxide levels, aconitase and fumarase activities, and ROS-disposal enzyme activity in liver, brain, and lung. Liver levels of nuclear NF-κB-p65 and plasma C-reactive protein (CRP), as well as lipid levels, were also assessed. Lowest hemoglobin saturations were 91.7 ± 0.8 and 73.5 ± 1.4%. IH caused tissue-specific oxidative stress related to hypoxic intensity. Nuclear NF-κB-p65 and lipid content in the liver and CRP in the plasma all increased with IH intensity, as did both plasma triglycerides and cholesterol. We conclude that IH, even of moderate intensity, causes oxidative stress probably related to the pathologies encountered in OSAS patients.

Carotid body denervation prevents the development of insulin resistance and hypertension induced by hypercaloric diets.

Increased sympathetic activity is a well-known pathophysiological mechanism in insulin resistance (IR) and hypertension (HT). The carotid bodies (CB) are peripheral chemoreceptors that classically respond to hypoxia by increasing chemosensory activity in the carotid sinus nerve (CSN), causing hyperventilation and activation of the sympathoadrenal system. Besides its role in the control of ventilation, the CB has been proposed as a glucose sensor implicated in the control of energy homeostasis. However, to date no studies have anticipated its role in the development of IR. Herein, we propose that CB overstimulation is involved in the etiology of IR and HT, core metabolic and hemodynamic disturbances of highly prevalent diseases like the metabolic syndrome, type 2 diabetes, and obstructive sleep apnoea. We demonstrate that CB activity is increased in IR animal models and that CSN resection prevents CB overactivation and diet-induced IR and HT. Moreover, we show that insulin triggers CB, highlighting a new role for hyperinsulinemia as a stimulus for CB overactivation. We propose that CB is implicated in the pathogenesis of metabolic and hemodynamic disturbances through sympathoadrenal overactivation and may represent a novel therapeutic target in these diseases.

Cyclic AMP and Epac contribute to the genesis of the positive interaction between hypoxia and hypercapnia in the carotid body.

Carotid body chemoreceptor cells in response to hypoxic and hypercapnic stimulus increase their resting rate of release of neurotransmitters and their action potential frequency in the carotid sinus sensory nerve. When chemoreceptor activity is assessed at the level of the carotid sinus nerve and on ventilation, there exists an interaction between hypoxic and hypercapnic stimulus so that the response to both stimuli combined is additive or more than additive, over a wide range of stimulation. It is not clear if this interaction occurs at chemoreceptor cell or directly acting on the sensory nerve. In the present work we demonstrate for the first time the existence of a positive interaction between hypoxic and hypercapnic-acidotic stimuli at the level of both, membrane potential depolarization and neurotransmitter release in rat and rabbit carotid body. Inhibition of adenylate cyclase (SQ-22536) abolished the positive interaction between stimuli and the Epac (exchange proteins activated by cAMP) activator 8-pCPT-2'-O-Me-cAMP reversed the effect of adenylate cyclase inhibition. These results suggest that this interaction between the two natural stimuli is mediated by cAMP via an Epac-dependent pathway, at least at the level of neurotransmitter release.

Interactions between postnatal sustained hypoxia and intermittent hypoxia in the adulthood to alter brainstem structures and respiratory function.

Neural plasticity is defined as a persistent change in the morphology and/or function based on prior experiences. Plasticity is well evident when the triggering experience occurs early in life, but in the case of respiratory control plasticity, it also can be triggered in adult life. We have combined a 10 days postnatal hypoxic (PH) (0-10 days of age;11% O(2)) and a 15 days intermittent hypoxia (IH) exposures in the adulthood (90-105 days of age; 5% O(2), 40 s/20% O(2), 80 s; 8 h/day) to test if early PH interacts with IH of the adulthood to generate detrimental plastic changes. After recording of ventilatory parameters, the brains were studied immunocytochemically for localization of the organization pattern of non-phosphorylated subunit of neurofilament H (NFH) and tyrosine hydroxylase (TH) expression in the nucleus tractus solitarius (Sol) and caudal (CVL) and rostral ventrolateral reticular (RVL) nuclei, areas related to central cardio-respiratory regulation. In comparison to control, PH male rats (but not females) at 1 month of age hyperventilated at rest, in response to moderate hypoxia (12% O(2)) and 5% CO(2), the effect being due to increased tidal volume. At 3.5 months sex differences in ventilation disappeared and it was indistinguishable between control and PH. IH tended to decrease ventilation in both control (C) and PH animals. PH augmented PENH values in air and in hypoxic conditions when compared with C group. IH in both groups, tended to decrease the PENH value, being statistically different in PH+IH. Results also show an increment of disorganization of NFH-positive labeled structures at the level of Sol and CVL/RVL nuclei in PH, IH and HP+HI groups. PH rats showed differences in the number of TH-positive neurons at the level of CVL/RVL nuclei, which was increased in the PH and PH+IH groups with respect to C one. In conclusion, PH alters the central morpho-physiological organization and the catecholaminergic components of cardio-respiratory nuclei, whose effects were enhanced after a period of IH in the adulthood.

Serotonin dynamics and actions in the rat carotid body: preliminary findings.

Serotonin or 5-HT is a biogenic amine present in the carotid body (CB) of several species as evidenced in many immunocytochemical studies and in a few biochemical measurements. Early literature on 5-HT actions in the CB in all studied species has lead to the conclusion that it does not participate in the setting of conducted action potentials in the sensory nerve of the CB. However, during the last 10 years very important roles in the cellular physiology of the CB have been proposed for this biogenic amine. These roles include a primary role in setting the excitability of chemoreceptor cells via an autocrine or paracrine action, and thereby, the conducted activity in the carotid sinus nerve, and a critical role in the genesis of long term sensory facilitation observed in CBs of animals exposed to intermittent hypoxia. These facts, along with important discrepancies in the endogenous levels of 5-HT in the CB prompted present study conducted in rat CBs. We measured CB endogenous 5-HT content by HPLC with electrochemical detection and found levels of 5-HT in the range of 15-22 pmole/mg tissue in control and chronically hypoxic animals either sustained or intermittent, with no significant differences among them. 5-HT and the 5-HT2A antagonist ketanserin dose-dependently activated chemoreceptor cells as assessed by their capacity to release catecholamines from freshly isolated CB. In preliminary experiments we have observed that intense hypoxia and high extracellular K(+) promote a small release of 5-HT from CB which is not dependent on the presence of extracellular Ca(2+). Further studies are needed to firmly establish the dynamics of 5-HT in the CB of the rat.

Effect of chronic caffeine intake on carotid body catecholamine dynamics in control and chronically hypoxic rats.

Caffeine is the most commonly psychoactive drug, an habitual drink in high altitude sporting, and when acutely taken, it causes profound alterations in carotid body (CB) function and ventilation via adenosine receptors antagonism. In the present work we have investigated the effects of chronic caffeine ingestion in catecholamine (CA) dynamics in the carotid body of control and chronic hypoxic rats. Four groups of animals were used: normoxic (N), caffeine-treated normoxic (1 mg/mL in drinking water 15 days; CafN), chronic hypoxic (CH, 12%O(2), 15 days) and chronically hypoxic-caffeine-treated (CafH).. Caffeine intake in controls rats did not modify CA content, synthesizing, and releasing responses, and the expression of tyrosine hydroxylase. CH increased dopamine content, synthesis, and basal and acute hypoxia-induced release; chronic caffeine ingestion augmented CH effects. Findings indicate that chronic caffeine ingestion in normoxic rats did not modify dopamine dynamics at the CB, but increases dopaminergic system during chronic hypoxia.

Effects of cigarette smoke and chronic hypoxia on ventilation in guinea pigs. Clinical significance.

Ventilatory effects of chronic cigarette smoke (CS) alone or associated to chronic hypoxia (CH), as frequently occurs in chronic obstructive pulmonary disease (COPD), remain unknown. We have addressed this problem using whole-body plethysmography in guinea-pigs, common models to study harmful effects of CS on the respiratory system. Breathing frequencies (Bf) in control (2-5 months old) guinea pigs is 90-100 breaths/min, their tidal volume (TV) increased with age but lagged behind body weight gain and, as consequence, their minute volume (MV)/Kg decreased with age. MV did not change by acutely breathing 10% O(2) but doubled while breathing 5% CO(2) in air. Exposure to chronic sustained hypoxia (15 days, 12% O(2), CH) did not elicit ventilatory acclimatization nor adaptation. These findings confirm the unresponsiveness of the guinea pig CB to hypoxia. Exposure to CS (3 months) increased Bf and MV but association with CH blunted CS effects. We conclude that CS and CH association accelerates CS-induced respiratory system damage leading to a hypoventilation that can worsen the ongoing COPD process.

Some reflections on intermittent hypoxia. Does it constitute the translational niche for carotid body chemoreceptor researchers?

The views presented in this article are the fruit of reflections and discussion with my colleagues at Valladolid and with the members of the Sleep Apnea Hypopnea Syndrome Group of the CIBERES (Spain). We have assembled the article in three sections. In the first one we provide a mechanistic description of obstructive sleep apnea (OSA) and all of its components, including the repetitive episodes of upper airways (UA) obstruction and accompanying hypoxic hypoxia, the respiratory efforts to fight and overcome the obstruction, and the sleep fragmentation due to the hypoxia-triggered arousal reactions, all events occurring during sleep hours with frequencies that might reach up >40-50 episodes/sleep hour. When OSA is accompanied by some of the elements of a big cohort of associated pathologies (vascular, metabolic, and neuropsychiatric) it conforms the obstructive sleep apnea syndrome (OSAS). The high frequency of OSAS in adults (>35 years old) and the costs in every regard of the treatment makes the syndrome a primary importance socio-sanitary problem. In the second section, we describe the experimental models of OSAS, basically the episodic repetitive hypoxic model described by Fletcher and coworkers in 1992, today named in short intermittent hypoxia (IH). From these lines, we want to call for some kind of consensus among researchers to lessen the dispersion of IH protocols. Finally, in the last section we intend to share our optimism with all ISAC members. The optimism is based on the recognition that carotid body (CB) chemoreceptors are critical elements of one of the main pathophysiologic loops in the genesis of OSAS. Therefore, we believe that all of us, as ISAC members, are well qualified to contribute in multidisciplinary research teams with well defined translational interests.

Chronic caffeine intake in adult rat inhibits carotid body sensitization produced by chronic sustained hypoxia but maintains intact chemoreflex output.

Sustained hypoxia produces a carotid body (CB) sensitization, known as acclimatization, which leads to an increase in carotid sinus nerve (CSN) activity and ensuing hyperventilation greater than expected from the prevailing partial pressure of oxygen. Whether sustained hypoxia is physiological (high altitude) or pathological (lung disease), acclimatization has a homeostatic implication because it tends to minimize hypoxia. Caffeine, the most commonly ingested psychoactive drug and a nonselective adenosine receptor antagonist, alters CB function and ventilatory responses when administered acutely. Our aim was to investigate the effect of chronic caffeine intake on CB function and acclimatization using four groups of rats: normoxic, caffeine-treated normoxic, chronically hypoxic (12% O2, 15 days), and caffeine-treated chronically hypoxic rats. Caffeine was administered in drinking water (1 mg/ml). Caffeine ameliorated ventilatory responses to acute hypoxia in normoxic animals without altering the output of the CB (CSN neural activity). Caffeine-treated chronically hypoxic rats exhibited a decrease in the CSN response to acute hypoxia tests but maintained ventilation compared with chronically hypoxic animals. The findings related to CSN neural activity combined with the ventilatory responses indicate that caffeine alters central integration of the CB input to increase the gain of the chemoreflex and that caffeine abolishes CB acclimatization. The putative mechanisms involved in sensitization and its loss were investigated: expression of adenosine receptors in CB (A(2B)) was down-regulated and that in petrosal ganglion (A(2A)) was up-regulated in caffeine-treated chronically hypoxic rats; both adenosine and dopamine release from CB chemoreceptor cells was increased in chronic hypoxia and in caffeine-treated chronic hypoxia groups.

The human carotid body transcriptome with focus on oxygen sensing and inflammation--a comparative analysis.

The carotid body (CB) is the key oxygen sensing organ. While the expression of CB specific genes is relatively well studied in animals, corresponding data for the human CB are missing. In this study we used five surgically removed human CBs to characterize the CB transcriptome with microarray and PCR analyses, and compared the results with mice data. In silico approaches demonstrated a unique gene expression profile of the human and mouse CB transcriptomes and an unexpected upregulation of both human and mouse CB genes involved in the inflammatory response compared to brain and adrenal gland data. Human CBs express most of the genes previously proposed to be involved in oxygen sensing and signalling based on animal studies, including NOX2, AMPK, CSE and oxygen sensitive K+ channels. In the TASK subfamily of K+ channels, TASK-1 is expressed in human CBs, while TASK-3 and TASK-5 are absent, although we demonstrated both TASK-1 and TASK-3 in one of the mouse reference strains. Maxi-K was expressed exclusively as the spliced variant ZERO in the human CB. In summary, the human CB transcriptome shares important features with the mouse CB, but also differs significantly in the expression of a number of CB chemosensory genes. This study provides key information for future functional investigations on the human carotid body.

Determination of lipoic acid, Trolox methyl ether and tocopherols in human plasma by liquid-chromatography and ion-trap tandem mass spectrometry.

A method for the simultaneous determination of lipoic acid and/or Trolox methyl ether, along with α-, γ- and δ-tocopherol was developed using liquid chromatography-tandem mass spectrometry with negative electrospray ionization (HPLC-ESI-MS/MS) in an ion-trap mass spectrometer. Detection and quantification were accomplished by a multiple reaction monitoring method, using specific transitions from precursor ion to product ion for each analyte. Chromatographic separation was achieved in a 12 min run using a C(18) -bonded phase and methanol-aqueous ammonium acetate elution gradient. Linear correlations of the chromatographic peak area (r.u. × s(-1) ) to the injected amount (ng) gave the slope values (r.u. × s(-1) × ng(-1) ) 2.34 × 10(4) for α-tocopherol, 5.05 × 10(4) for γ-tocopherol, 1.27 × 10(5) for δ-tocopherol, 8.86 × 10(5) for lipoic acid and 1.23 × 10(5) for Trolox methyl ether. The lower limit of quantification ranged between 0.02 and 1.22 ng for Trolox methyl ether and lipoic acid. MS(3) experiments of γ- and δ-tocopherol suggest ion-radical reactions and dependence of the tocopherol fragmentation pattern on the phenolic ring methylation degree. The method is shown to be applicable to measurement of these metabolites in human serum after extraction.

Effects of low glucose on carotid body chemoreceptor cell activity studied in cultures of intact organs and in dissociated cells.

The participation of the carotid body (CB) in glucose homeostasis and evidence obtained in simplified cultured CB slices or dissociated cells have led to the proposal that CB chemoreceptor cells are glucoreceptors. However, data generated in intact, freshly excised organs deny CB chemoreceptor cells' glucosensing properties. The physiological significance of the contention has prompted the present study, performed in a newly developed preparation of the intact CB organ in culture that maintains chemoreceptor cells' microenvironment. Chemoreceptor cells of intact CBs in culture retained their capacity to store, synthesize, and secrete catecholamine in response to hypoxia for at least 6 days. Aglycemia did not elicit neurosecretion in dissociated chemoreceptor cells or in intact CB in culture, but potentiated hypoxia-elicited neurosecretion, exclusively, in 1-day-old intact CB cultures and dissociated chemoreceptor cells cultured for 24 h. In fura 2-loaded cells, aglycemia (but not 1 mM) caused a slow Ca(2+)-dependent and nifedipine-insensitive increase in fluorescence at 340- to 380-nm wavelength emission ratio and augmented the fluorescent signal elicited by hypoxia. Association of nifedipine and KBR7943 (a Na(+)/Ca(2+) exchanger inhibitor) completely abolished the aglycemic Ca(2+) response. We conclude that chemoreceptor cells are not sensitive to hypoglycemia. We hypothesize that cultured chemoreceptor cells become transiently more dependent on glycolysis. Consequently, aglycemia would partially inhibit the Na(+)/K(+) pump, causing an increase in intracellular Na(+) concentration, and a reversal of Na(+)/Ca(2+) exchanger. This would slowly increase intracellular Ca(2+) concentration and cause the potentiation of the hypoxic responses. We discuss the nature of the signals detected by chemoreceptor cells for the CB to achieve its glycemic homeostatic role.

Chronic caffeine intake decreases circulating catecholamines and prevents diet-induced insulin resistance and hypertension in rats.

We tested the hypothesis that long-term caffeine intake prevents the development of insulin resistance and hypertension in two pathological animal models: the high-fat (HF) and the high-sucrose (HSu) diet rat. We used six groups of animals: control; caffeine-treated (Caff; 1 g/l in drinking water during 15 d); HF; caffeine-treated HF (HFCaff); HSu; caffeine-treated HSu (HSuCaff). Insulin sensitivity was assessed using the insulin tolerance test. Blood pressure, weight gain, visceral fat, hepatic glutathione, plasma caffeine, insulin and NO, and serum NEFA and catecholamines were measured. Caffeine reversed insulin resistance and hypertension induced by both the HF and HSu diets. In the HF-fed animals caffeine treatment restored fasting insulin levels to control values and reversed increased weight gain and visceral fat mass. In the HSu group, caffeine reversed fasting hyperglycaemia and restored NEFA to control values. There were no changes either in plasma NO or in hepatic glutathione levels. In contrast, caffeine totally prevented the increase in serum catecholamines induced by HF and HSu diets. To test the hypothesis that inhibition of the sympathetic nervous system prevents the development of diet-induced insulin resistance we administered carvedilol, an antagonist of ß1, ß2 and also α1 adrenoceptors, to HF and HSu rats. Carvedilol treatment fully prevented diet-induced insulin resistance and hypertension, mimicking the effect of caffeine. We concluded that long-term caffeine intake prevented the development of insulin resistance and hypertension in HF and HSu models and that this effect was related to a decrease in circulating catecholamines.