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Thyroid hormones induce browning of white fat.
The canonical view about the effect of thyroid hormones (THs) on thermogenesis assumes that the hypothalamus acts merely as a modulator of the sympathetic outflow on brown adipose tissue (BAT). Recent data have challenged that vision by demonstrating that THs act on the ventromedial nucleus of the hypothalamus (VMH) to inhibit AMP-activated protein kinase (AMPK), which regulates the thermogenic program in BAT, leading to increased thermogenesis and weight loss. Current data have shown that in addition to activation of brown fat, the browning of white adipose tissue (WAT) might also be an important thermogenic mechanism. However, the possible central effects of THs on the browning of white fat remain unclear. Here, we show that 3,3',5,5' tetraiodothyroxyne (T4)-induced hyperthyroidism promotes a marked browning of WAT. Of note, central or VMH-specific administration of 3,3',5-triiodothyronine (T3) recapitulates that effect. The specific genetic activation of hypothalamic AMPK in the VMH reversed the central effect of T3 on browning. Finally, we also showed that the expression of browning genes in human WAT correlates with serum T4 Overall, these data indicate that THs induce browning of WAT and that this mechanism is mediated via the central effects of THs on energy balance.
Reduction of Hypothalamic Endoplasmic Reticulum Stress Activates Browning of White Fat and Ameliorates Obesity.
The chaperone GRP78/BiP (glucose-regulated protein 78 kDa/binding immunoglobulin protein) modulates protein folding in reply to cellular insults that lead to endoplasmic reticulum (ER) stress. This study investigated the role of hypothalamic GRP78 on energy balance, with particular interest in thermogenesis and browning of white adipose tissue (WAT). For this purpose, we used diet-induced obese rats and rats administered thapsigargin, and by combining metabolic, histologic, physiologic, pharmacologic, thermographic, and molecular techniques, we studied the effect of genetic manipulation of hypothalamic GRP78. Our data showed that rats fed a high-fat diet or that were centrally administered thapsigargin displayed hypothalamic ER stress, whereas genetic overexpression of GRP78 specifically in the ventromedial nucleus of the hypothalamus was sufficient to alleviate ER stress and to revert the obese and metabolic phenotype. Those effects were independent of feeding and leptin but were related to increased thermogenic activation of brown adipose tissue and induction of browning in WAT and could be reversed by antagonism of β3 adrenergic receptors. This evidence indicates that modulation of hypothalamic GRP78 activity may be a potential strategy against obesity and associated comorbidities.
Hypothalamic mTOR: the rookie energy sensor.
Optimal cellular function and therefore organism's survival is determined by the sensitive and accurate convergence of energy and nutrient abundance to cell growth and division. Among other factors, this integration is coupled by the target of rapamycin (TOR) pathway, which is able to sense nutrient, energy and oxygen availability and also growth factor signaling. Indeed, TOR signaling regulates cell energy homeostasis by coordinating anabolic and catabolic processes for survival. TOR, named mTOR in mammals, is a conserved serine/threonine kinase that exists in two different complexes, mTORC1 and mTORC2. Recently, studies are suggesting that alterations of those complexes promote disease and disrupted phenotypes, such as aging, obesity and related disorders and even cancer. The evidences linking mTOR to energy and metabolic homeostasis included the following. At central level mTOR regulates food intake and body weight being involved in the mechanism by which signals such as leptin and ghrelin exert its effects. At peripheral level it influences adipogenesis and lipogenesis in different tissues including the liver. Noteworthy chronic nutritional activation of mTOR signaling has been implicated in the development of beta cell mass expansion and on insulin resistance. Understanding of mTOR and other molecular switches, such as AMP-activated protein kinase (AMPK), as well as their interrelationship is crucial to know how organisms maintain optimal homeostasis. This review summarizes the role of hypothalamic TOR complex in cellular energy sensing, evidenced in the last years, focusing on the metabolic pathways where it is involved and the importance of this metabolic sensor in cellular and whole body energy management. Understanding the exact role of hypothalamic mTOR may provide new cues for therapeutic intervention in diseases.
Site-dependent differences in both prelamin A and adipogenic genes in subcutaneous adipose tissue of patients with type 2 familial partial lipodystrophy.
BACKGROUND: Type 2 familial partial lipodystrophy (FPLD2) is characterised by loss of fat in the limbs and buttocks and results from mutations in the LMNA gene. AIM: To evaluate the role of several genes involved in adipogenesis in order to better understand the underlying mechanisms of regional loss of subcutaneous adipose tissue (scAT) in patients with FPLD2. METHODS: In total, 7 patients with FPLD2 and 10 healthy control participants were studied. A minimal model was used to calculate the insulin sensitivity (IS). scAT was obtained from abdomen and thigh by biopsy. Relative gene expression was quantified by real-time reverse transcription PCR in a thermal cycler. Prelamin A western blot analysis was carried out on scAT and prelamin A nuclear localisation was determined using immunofluorescence. Adipocyte nuclei were examined by electron microscopy. RESULTS: Patients with FPLD2 were found to have significantly lower IS. The expression of LMNA was similar in both groups. The expression of PPARG2, RB1, CCND3 and LPL in thigh but not in abdomen scAT was significantly reduced (67%, 25%, 38% and 66% respectively) in patients with FPLD2. Significantly higher levels of prelamin A were found in peripheral scAT of patients with FPLD2. Defects in the peripheral heterochromatin and a nuclear fibrous dense lamina were present in the adipocytes of patients with FPLD2. CONCLUSIONS: In FPLD2 participants, prelamin A accumulation in peripheral scAT is associated with a reduced expression of several genes involved in adipogenesis, which could perturb the balance between proliferation and differentiation in adipocytes, leading to less efficient tissue regeneration.
Lipopolysaccharide (LPS)-induced septic shock causes profound changes in myocardial energy metabolites in pigs.
INTRODUCTION: Energy deficiency is a cause for myocardial dysfunction during septic shock. In rodents, septic shock decreases the oxidation of long-chain fatty acids and glucose in the myocardium causing energy deficiency. However, the effect of septic shock on myocardial energy metabolites in large animals and human is unknown. OBJECTIVES: Investigate the effects of septic shock on myocardial energy metabolites in domestic pigs. METHODS: Seventeen female pigs divided into control and lipopolysaccharide (LPS)-induced septic shock groups. Myocardial metabolites were analyzed ex vivo by 1H nuclear magnetic resonance spectroscopy and liquid chromatography-tandem mass spectrometry. Gene and protein expression analysis were analyzed by real-time PCR and western blot. RESULTS: Septic shock was associated with an increase in myocardial levels of short- and medium-chain acylcarnitines, lactate, alanine, and pyruvate dehydrogenase kinase 4 gene expression. COX-2 and prostaglandin E4 receptor gene expression also increased in the septic myocardium, although the only elevated eicosanoid in the septic animals was thromboxane B2. Myocardial levels of niacin, taurine, glutamate, glutamine, and glutathione were higher, and hypoxanthine levels lower in septic pigs than controls. CONCLUSIONS: In pigs, septic shock induced by LPS caused myocardial changes directed to decrease the oxidation of medium- and short-chain fatty acid without an effect on long-chain fatty acid oxidation. The increase in myocardial levels of lactate, alanine, and pyruvate dehydrogenase kinase 4 gene expression suggest that septic shock decreases pyruvate dehydrogenase complex activity and glucose oxidation. Homeostasis of niacin, taurine, glutamate, glutamine, glutathione, hypoxanthine and thromboxane B2 is also affected in the septic myocardium.
A Functional Link between AMPK and Orexin Mediates the Effect of BMP8B on Energy Balance.
AMP-activated protein kinase (AMPK) in the ventromedial nucleus of the hypothalamus (VMH) and orexin (OX) in the lateral hypothalamic area (LHA) modulate brown adipose tissue (BAT) thermogenesis. However, whether these two molecular mechanisms act jointly or independently is unclear. Here, we show that the thermogenic effect of bone morphogenetic protein 8B (BMP8B) is mediated by the inhibition of AMPK in the VMH and the subsequent increase in OX signaling via the OX receptor 1 (OX1R). Accordingly, the thermogenic effect of BMP8B is totally absent in ox-null mice. BMP8B also induces browning of white adipose tissue (WAT), its thermogenic effect is sexually dimorphic (only observed in females), and its impact on OX expression and thermogenesis is abolished by the knockdown of glutamate vesicular transporter 2 (VGLUT2), implicating glutamatergic signaling. Overall, our data uncover a central network controlling energy homeostasis that may be of considerable relevance for obesity and metabolic disorders.
Hyperthyroidism differentially regulates neuropeptide S system in the rat brain.
Thyroid hormones play an important role in the regulation of energy balance, sleep and emotional behaviors. Neuropeptide S (NPS) is a recently discovered neuropeptide, regulating feeding, sleep and anxiety. Here, we examined the effect of hyperthyroidism on the gene and protein expression of neuropeptide S and its receptor (NPS-R) in the hypothalamus, brainstem and amygdala of rats. Our results showed that the expression of NPS and NPS-R was differentially modulated by hyperthyroidism in the rat brain. NPS and NPS-R mRNA and protein levels were decreased in the hypothalamus of hyperthyroid rats. Conversely NPS-R expression was highly increased in the brainstem and NPS and NPS-R expression were unchanged in the amygdala of these rats. These data suggest that changes in anxiety and food intake patterns observed in hyperthyroidism could be associated with changes in the expression of NPS and NPS-R. Thus, the NPS/NPS-R system may be involved in several hyperthyroidism-associated comorbidities.
Genetic Targeting of GRP78 in the VMH Improves Obesity Independently of Food Intake.
Recent data have demonstrated that the hypothalamic GRP78/BiP (glucose regulated protein 78 kDa/binding immunoglobulin protein) modulates brown adipose tissue (BAT) thermogenesis by acting downstream on AMP-activated protein kinase (AMPK). Herein, we aimed to investigate whether genetic over-expression of GRP78 in the ventromedial nucleus of the hypothalamus (VMH: a key site regulating thermogenesis) could ameliorate very high fat diet (vHFD)-induced obesity. Our data showed that stereotaxic treatment with adenoviruses harboring GRP78 in the VMH reduced hypothalamic endoplasmic reticulum ER stress and reversed vHFD-induced obesity. Herein, we also demonstrated that this body weight decrease was more likely associated with an increased BAT thermogenesis and browning of white adipose tissue (WAT) than to anorexia. Overall, these results indicate that the modulation of GRP78 in the VMH may be a target against obesity.
Incendiary Leptin.
Leptin is a hormone released by adipose tissue that plays a key role in the control of energy homeostasis through its binding to leptin receptors (LepR), mainly expressed in the hypothalamus. Most scientific evidence points to leptin's satiating effect being due to its dual capacity to promote the expression of anorexigenic neuropeptides and to reduce orexigenic expression in the hypothalamus. However, it has also been demonstrated that leptin can stimulate (i) thermogenesis in brown adipose tissue (BAT) and (ii) the browning of white adipose tissue (WAT). Since the demonstration of the importance of BAT in humans 10 years ago, its study has aroused great interest, mainly in the improvement of obesity-associated metabolic disorders through the induction of thermogenesis. Consequently, several strategies targeting BAT activation (mainly in rodent models) have demonstrated great potential to improve hyperlipidemias, hepatic steatosis, insulin resistance and weight gain, leading to an overall healthier metabolic profile. Here, we review the potential therapeutic ability of leptin to correct obesity and other metabolic disorders, not only through its satiating effect, but by also utilizing its thermogenic properties.
Central ceramide-induced hypothalamic lipotoxicity and ER stress regulate energy balance.
Hypothalamic endoplasmic reticulum (ER) stress is a key mechanism leading to obesity. Here, we demonstrate that ceramides induce lipotoxicity and hypothalamic ER stress, leading to sympathetic inhibition, reduced brown adipose tissue (BAT) thermogenesis, and weight gain. Genetic overexpression of the chaperone GRP78/BiP (glucose-regulated protein 78 kDa/binding immunoglobulin protein) in the ventromedial nucleus of the hypothalamus (VMH) abolishes ceramide action by reducing hypothalamic ER stress and increasing BAT thermogenesis, which leads to weight loss and improved glucose homeostasis. The pathophysiological relevance of this mechanism is demonstrated in obese Zucker rats, which show increased hypothalamic ceramide levels and ER stress. Overexpression of GRP78 in the VMH of these animals reduced body weight by increasing BAT thermogenesis as well as decreasing leptin and insulin resistance and hepatic steatosis. Overall, these data identify a triangulated signaling network involving central ceramides, hypothalamic lipotoxicity/ER stress, and BAT thermogenesis as a pathophysiological mechanism of obesity.
Metabolic regulation of female puberty via hypothalamic AMPK-kisspeptin signaling.
Conditions of metabolic distress, from malnutrition to obesity, impact, via as yet ill-defined mechanisms, the timing of puberty, whose alterations can hamper later cardiometabolic health and even life expectancy. AMP-activated protein kinase (AMPK), the master cellular energy sensor activated in conditions of energy insufficiency, has a major central role in whole-body energy homeostasis. However, whether brain AMPK metabolically modulates puberty onset remains unknown. We report here that central AMPK interplays with the puberty-activating gene, Kiss1, to control puberty onset. Pubertal subnutrition, which delayed puberty, enhanced hypothalamic pAMPK levels, while activation of brain AMPK in immature female rats substantially deferred puberty. Virogenetic overexpression of a constitutively active form of AMPK, selectively in the hypothalamic arcuate nucleus (ARC), which holds a key population of Kiss1 neurons, partially delayed puberty onset and reduced luteinizing hormone levels. ARC Kiss1 neurons were found to express pAMPK, and activation of AMPK reduced ARC Kiss1 expression. The physiological relevance of this pathway was attested by conditional ablation of the AMPKα1 subunit in Kiss1 cells, which largely prevented the delay in puberty onset caused by chronic subnutrition. Our data demonstrate that hypothalamic AMPK signaling plays a key role in the metabolic control of puberty, acting via a repressive modulation of ARC Kiss1 neurons in conditions of negative energy balance.
Hypothalamic AMPK-ER Stress-JNK1 Axis Mediates the Central Actions of Thyroid Hormones on Energy Balance.
Thyroid hormones (THs) act in the brain to modulate energy balance. We show that central triiodothyronine (T3) regulates de novo lipogenesis in liver and lipid oxidation in brown adipose tissue (BAT) through the parasympathetic (PSNS) and sympathetic nervous system (SNS), respectively. Central T3 promotes hepatic lipogenesis with parallel stimulation of the thermogenic program in BAT. The action of T3 depends on AMP-activated protein kinase (AMPK)-induced regulation of two signaling pathways in the ventromedial nucleus of the hypothalamus (VMH): decreased ceramide-induced endoplasmic reticulum (ER) stress, which promotes BAT thermogenesis, and increased c-Jun N-terminal kinase (JNK) activation, which controls hepatic lipid metabolism. Of note, ablation of AMPKα1 in steroidogenic factor 1 (SF1) neurons of the VMH fully recapitulated the effect of central T3, pointing to this population in mediating the effect of central THs on metabolism. Overall, these findings uncover the underlying pathways through which central T3 modulates peripheral metabolism.
Estradiol regulates brown adipose tissue thermogenesis via hypothalamic AMPK.
Estrogens play a major role in the modulation of energy balance through central and peripheral actions. Here, we demonstrate that central action of estradiol (E2) inhibits AMP-activated protein kinase (AMPK) through estrogen receptor alpha (ERα) selectively in the ventromedial nucleus of the hypothalamus (VMH), leading to activation of thermogenesis in brown adipose tissue (BAT) through the sympathetic nervous system (SNS) in a feeding-independent manner. Genetic activation of AMPK in the VMH prevented E2-induced increase in BAT-mediated thermogenesis and weight loss. Notably, fluctuations in E2 levels during estrous cycle also modulate this integrated physiological network. Together, these findings demonstrate that E2 regulation of the VMH AMPK-SNS-BAT axis is an important determinant of energy balance and suggest that dysregulation in this axis may account for the common changes in energy homeostasis and obesity linked to dysfunction of the female gonadal axis.
3-Iodothyronamine Induces Tail Vasodilation Through Central Action in Male Mice.
3-Iodothyronamine (3-T1AM) is an endogenous thyroid hormone (TH)-derived metabolite that induces severe hypothermia in mice after systemic administration; however, the underlying mechanisms have remained enigmatic. We show here that the rapid 3-T1AM-induced loss in body temperature is a consequence of peripheral vasodilation and subsequent heat loss (e.g., over the tail surface). The condition is subsequently intensified by hypomotility and a lack of brown adipose tissue activation. Although the possible 3-T1AM targets trace amine-associated receptor 1 or α2a-adrenergic receptor were detected in tail artery and aorta respectively, myograph studies did not show any direct effect of 3-T1AM on vasodilation, suggesting that its actions are likely indirect. Intracerebroventricular application of 3-T1AM, however, replicated the phenotype of tail vasodilation and body temperature decline and led to neuronal activation in the hypothalamus, suggesting that the metabolite causes tail vasodilation through a hypothalamic signaling pathway. Consequently, the 3-T1AM response constitutes anapyrexia rather than hypothermia and closely resembles the heat-stress response mediated by hypothalamic temperature-sensitive neurons. Our results thus underline the well-known role of the hypothalamus as the body's thermostat and suggest an additional molecular link between TH signaling and the central control of body temperature.
Investigation of the Antiarrhythmic Mechanism of the Multi-herbal Medicine Xing Su Ning
Introduction. Xing Su Ning (XSN) is a multi-herbal Chinese medicine produced by Momentum Pharmaceutical Co. Ltd., which is sold in China since 2005 for treating cardiac ventricular arrhythmia, especially arrhythmias induced by cardiac ischemia and viral myocarditis. Aims. To discover the cellular electrophysiological mechanism of the actions of XSN in treating cardiac arrhythmia. Methods. Whole-cell patch-clamp techniques (1) were used to record action potentials and whole cell current in isolated adult rat ventricular myocytes. The myocytes were continuously perfused with physiological solution without or with XSN. Results. XSN at 2mg/ml significantly prolonged the action potential Duration (APD) as shown in the Figure: control was 45.4ms±4.9 and with XSN 2mg/ml was 52.2ms±4.5 (P<0.01, n=7). At this concentration XSN did not have significant effect on the resting potential or the amplitude of the action potential. The effect of XSN is reversible upon the washout of the medicine. Discussion. XSN Prolongs APD, an action that increases the effective refractory period which suppress tachyarrhythmias caused by reentry mechanisms. XSN displays the property of Class III antiarrhythmic drugs, such as amiodarone, without adverse reactions. Further studies on the effect of XSN at various concentrations on action potential and ionic channels, i.e. potassium channels, will be carried out. (1) Ma Y-L et al (2006) European Journal of Pharmacology. 545:87-92 2 4 6 8 10 46 48 50 52 54 b a&c a-Control b-XSN 2mg/ml c-Recovery 20mV 20ms XSN 2mg/ml Action Potential Duration (ms) Time (Min)
Ion Channel Targeted Mechanisms of Anti-arrhythmic Chinese Herbal Medicine Xin Su Ning.
Xin Su Ning (XSN) is a China patented and certified herbal medicine used to treat premature ventricular contractions (PVCs) since 2005. A recent completed clinical trial of 861 patients showed that XSN had similar PVC inhibition rate to the class I antiarrhythmic drug mexiletine, at 65.85% for XSN and 63.10% for mexiletine. We have previously reported that XSN prolongs action potential duration (APD) and suppresses action potential amplitude (APA) of the cardiac ventricular myocytes. In this report we aim to reveal the effect of XSN on the ionic channels that govern APD and APA, which would help to explain the cellular electrophysiological mechanism of XSN. Our main findings are: (1) On ECG recorded in isolated rat, in the presence of XSN the amplitude of R wave was significantly decreased and the amplitude of T wave was increased significantly; (2) XSN blocked hNaV1.5 channel stably transfected cell line in a dose-dependent manner with an IC50 of 0.18 ± 0.02 g/L; and (3) XSN suppresses hERG channels in a dose-dependent manner with an IC50 of 0.34 ± 0.01 g/L. In conclusion, the clinical antiarrhythmic efficacy of XSN is based on its class I and Class III antiarrhythmic properties by suppression hNaV1.5 channel and hERG channels, which are directly responsible for XSN's effect on APA suppression and APD prolongation.
Investigation on the cardio-protective effect of Xin Su Ning on ischemia-reperfusion induced injury in isolated heart.
Introduction: We previously reported that Xin Su Ning (XSN) prolongs action potential duration (APD) of isolated cardiac myocytes1,2. In this study we aimed to identify the cardio-protective effect of XSN in Ischemia-reperfusion (I/R) induced injury in isolated heart. Methods: CHL cell line stably transfected human NaV1.5 channel were used for electrophysiological assay using Axopatch 200B patch clamp system with external and internal solutions prepared as previously described3. For isolated hearts study, male Sprague-Dawley rats (280 ∼ 320g) were divided into control, I/R, XSN 0.05 g/L and 0.1 g/L groups. The hearts were isolated and perfused in retrograde mode at constant pressure of 60 mmHg at 37°C as previously reported3. The extracts of XSN in the form of frozen dried power were administrated by dissolving in the perfusing solution. The measurements used to evaluate XSN’s effects were: Left ventricular developed pressure (LVDP), the rate of pressure development and rate of relaxation (max/min dP/dt), and heart rate (HR). Rate pressure product (RPP) was calculated by multiplying LVDP by HR. The differences between control and other groups were tested using Student’s t-test. Results: XSN blocks human NaV1.5 channel in a dose dependent manner with an IC50 = 0.184±0.017 g/L. XSN at 0.1 g/L produced the significant recovery of LVDP during 60 min reperfusion as shown in Figure 1. Max dP/dt, min dP/dt and HR after 60 min perfusion with vehicle and difference concentrations of XSN were shown in Table 1. Fig. 1 (A) Dose response curve of XSN on human NaV1.5 channel (n=5); (B) Experimental protocol of contractile function of I/R perfused rat heart; (C) percent rate of LVDP of rat hearts with/without XSN treatment after reperfusion 0, 5, 10, 20, 30, 40, 60 min (n=5). The data were presented as mean±SEM. * p<0.05, ** p<0.01, ** p<0.001 vs. I/R group. Table 1 Myocardial contractile function measured ex vivo in a rat I/R heart (mean±SEM, n=5). %pre-ischemia LVDP max dP/dt min dP/dt HR RPP I/R 48.11±2.18 56.82±4.91 48.06±3.67 97.61±5.80 46.82±3.06 XSN 0.05 g/L 61.28±6.08 57.50±7.82 58.07±6.05* 79.15±4.34 48.85±6.43 XSN 0.1 g/L 87.36±4.34*** 93.39±4.53** 90.27±4.25*** 75.56±3.94* 70.57±5.38** * p<0.05, ** p<0.01, ** p<0.001 vs. I/R group. Conclusions: XSN blocked NaV1.5 channel dose dependently, and together with the APD prolongation which could be the cellular electrophysiological mechanisms of the anti-tachyarrhythmic effect of XSN. XSN improved cardiac systolic function on ischemia-reperfusion injured rat heart by increasing LVDP, RPP, max dP/dt and min dP/dt, the protective effect may contribute to the anti-arrhythmic effect of XSN on ischemic heart.
Assessing Oxidative Stress in Tumors by Measuring the Rate of Hyperpolarized [1-13C]Dehydroascorbic Acid Reduction Using 13C Magnetic Resonance Spectroscopy.
Rapid cancer cell proliferation promotes the production of reducing equivalents, which counteract the effects of relatively high levels of reactive oxygen species. Reactive oxygen species levels increase in response to chemotherapy and cell death, whereas an increase in antioxidant capacity can confer resistance to chemotherapy and is associated with an aggressive tumor phenotype. The pentose phosphate pathway is a major site of NADPH production in the cell, which is used to maintain the main intracellular antioxidant, glutathione, in its reduced state. Previous studies have shown that the rate of hyperpolarized [1-13C]dehydroascorbic acid (DHA) reduction, which can be measured in vivo using non-invasive 13C magnetic resonance spectroscopic imaging, is increased in tumors and that this is correlated with the levels of reduced glutathione. We show here that the rate of hyperpolarized [1-13C]DHA reduction is increased in tumors that have been oxidatively prestressed by depleting the glutathione pool by buthionine sulfoximine treatment. This increase was associated with a corresponding increase in pentose phosphate pathway flux, assessed using 13C-labeled glucose, and an increase in glutaredoxin activity, which catalyzes the glutathione-dependent reduction of DHA. These results show that the rate of DHA reduction depends not only on the level of reduced glutathione, but also on the rate of NADPH production, contradicting the conclusions of some previous studies. Hyperpolarized [1-13C]DHA can be used, therefore, to assess the capacity of tumor cells to resist oxidative stress in vivo However, DHA administration resulted in transient respiratory arrest and cardiac depression, which may prevent translation to the clinic.