دكتوراه
الطب والخدمات الصحية
University of Birmingham
مجال التميز | تميز دراسي وبحثي |
البحوث المنشورة |
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البحث (1): | |
عنوان البحث: | β-Adrenoceptor blockade prevents carotid body hyperactivity and elevated vascular sympathetic nerve density induced by chronic intermittent hypoxia |
رابط إلى البحث: | https://link.springer.com/article/10.1007/s00424-020-02492-0 |
تاريخ النشر: | 19/11/2020 |
موجز عن البحث: | Carotid body (CB) hyperactivity promotes hypertension in response to chronic intermittent hypoxia (CIH). The plasma concen- tration of adrenaline is reported to be elevated in CIH and our previous work suggests that adrenaline directly activates the CB. However, a role for chronic adrenergic stimulation in mediating CB hyperactivity is currently unknown. This study evaluated whether beta-blocker treatment with propranolol (Prop) prevented the development of CB hyperactivity, vascular sympathetic nerve growth and hypertension caused by CIH. Adult male Wistar rats were assigned into 1 of 4 groups: Control (N), N + Prop, CIH and CIH + Prop. The CIH paradigm consisted of 8 cycles h−1, 8 h day−1, for 3 weeks. Propranolol was administered via drinking water to achieve a dose of 40 mg kg−1 day−1. Immunohistochemistry revealed the presence of both β1 and β2-adrenoceptor subtypes on the CB type I cell. CIH caused a 2–3-fold elevation in basal CB single-fibre chemoafferent activity and this was prevented by chronic propranolol treatment. Chemoafferent responses to hypoxia and mitochondrial inhibitors were attenuated by propranolol, an effect that was greater in CIH animals. Propranolol decreased respiratory frequency in normoxia and hypoxia in N and CIH. Propranolol also abolished the CIH mediated increase in vascular sympathetic nerve density. Arterial blood pressure was reduced in propranolol groups during hypoxia. Propranolol exaggerated the fall in blood pressure in most (6/7) CIH animals during hypoxia, suggestive of reduced sympathetic tone. These findings therefore identify new roles for β-adrenergic stimulation in evoking CB hyperactivity, sympathetic vascular hyperinnervation and altered blood pressure control in response to CIH. |
البحث (2): | |
عنوان البحث: | G-Protein-Coupled Receptor (GPCR) Signaling in the Carotid Body: Roles in Hypoxia and Cardiovascular and Respiratory Disease |
رابط إلى البحث: | https://pubmed.ncbi.nlm.nih.gov/32825527/ |
تاريخ النشر: | 20/08/2020 |
موجز عن البحث: | The carotid body (CB) is an important organ located at the carotid bifurcation that constantly monitors the blood supplying the brain. During hypoxia, the CB immediately triggers an alarm in the form of nerve impulses sent to the brain. This activates protective reflexes including hyperventilation, tachycardia and vasoconstriction, to ensure blood and oxygen delivery to the brain and vital organs. However, in certain conditions, including obstructive sleep apnea, heart failure and essential/spontaneous hypertension, the CB becomes hyperactive, promoting neurogenic hypertension and arrhythmia. G-protein-coupled receptors (GPCRs) are very highly expressed in the CB and have key roles in mediating baseline CB activity and hypoxic sensitivity. Here, we provide a brief overview of the numerous GPCRs that are expressed in the CB, their mechanism of action and downstream effects. Furthermore, we will address how these GPCRs and signaling pathways may contribute to CB hyperactivity and cardiovascular and respiratory disease. GPCRs are a major target for drug discovery development. This information highlights specific GPCRs that could be targeted by novel or existing drugs to enable more personalized treatment of CB-mediated cardiovascular and respiratory disease. |
البحث (3): | |
عنوان البحث: | Mitochondrial Succinate Metabolism and Reactive Oxygen Species Are Important but Not Essential for Eliciting Carotid Body and Ventilatory Responses to Hypoxia in the Rat |
رابط إلى البحث: | https://doi.org/10.3390/antiox10060840 |
تاريخ النشر: | 25/05/2021 |
موجز عن البحث: | Reflex increases in breathing in response to acute hypoxia are dependent on activation of the carotid body (CB)—A specialised peripheral chemoreceptor. Central to CB O2-sensing is their unique mitochondria but the link between mitochondrial inhibition and cellular stimulation is unresolved. The objective of this study was to evaluate if ex vivo intact CB nerve activity and in vivo whole body ventilatory responses to hypoxia were modified by alterations in succinate metabolism and mitochondrial ROS (mitoROS) generation in the rat. Application of diethyl succinate (DESucc) caused concentration-dependent increases in chemoafferent frequency measuring approximately 10–30% of that induced by severe hypoxia. Inhibition of mitochondrial succinate metabolism by dimethyl malonate (DMM) evoked basal excitation and attenuated the rise in chemoafferent activity in hypoxia. However, approximately 50% of the response to hypoxia was preserved. MitoTEMPO (MitoT) and 10-(6′-plastoquinonyl) decyltriphenylphosphonium (SKQ1) (mitochondrial antioxidants) decreased chemoafferent activity in hypoxia by approximately 20–50%. In awake animals, MitoT and SKQ1 attenuated the rise in respiratory frequency during hypoxia, and SKQ1 also significantly blunted the overall hypoxic ventilatory response (HVR) by approximately 20%. Thus, whilst the data support a role for succinate and mitoROS in CB and whole body O2-sensing in the rat, they are not the sole mediators. Treatment of the CB with mitochondrial selective antioxidants may offer a new approach for treating CB-related cardiovascular–respiratory disorders. |
المؤتمرات العلمية |
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المؤتمر (1): | |
عنوان المؤتمر: | Annual conference physiology 2021 |
تاريخ الإنعقاد: | 12/07/2021 |
مكان الإنعقاد: | UK |
طبيعة المشاركة: | Poster |
عنوان المشاركة: | Chronic intermittent hypoxia in utero depresses basal carotid body activity and hypoxic sensitivity in adult offspring |
ملخص المشاركة: | Introduction: Chronic intermittent hypoxia (CIH) is a common feature of obstructive sleep apnoea (OSA) and is prevalent in pregnancy thus exposing the fetus to CIH [1]. In adults exposed to CIH, neurogenic hypertension develops as a consequence of carotid body (CB) hyperactivity. Evidence in animal models suggests that CIH in utero (CIHU) may cause subsequent hypertension in the adult [2]. Any role of the CBs in promoting hypertension development in adult offspring following CIHU programming is undefined. We aimed to identify whether CIHU alters basal CB activity and the hypoxic sensitivity in adult offspring, and if this is associated with alterations in cardiovascular and respiratory function. Methods: All animal procedures were approved by the Home Office (UK) (PPL number PF4C074AD) and University of Birmingham. 12 female Wistar rats (Charles River, UK) arrived on day 6 of pregnancy and were housed in individually ventilated cages with free access to food and water (n= 1 animal per cage). On day 10 of pregnancy, animals were randomly assigned to 3 different groups: normoxia (N; n= 4), mild maternal CIH (8 cycles/hour, 8 hours per day; CIHU 8; n=4), and severe maternal CIH (15 cycles/hour, 8 hours per day, CIHU 15; n=4). Following birth, male offspring were matured to adults (10-20W) without further exposure to hypoxia. The in vitro CB chemoafferent activity was assessed on freshly isolated CBs, in normoxic conditions (superfusate PO2 ca 300mmHg) and during hypoxia (PO2 ca 100mmHg). Respiratory measurements were collected on awake animals using whole body plethysmography and cardiovascular reflex responses to hypoxia were performed under terminal anaesthesia (alfaxan i.v 17 – 20 mg kg-1 h-1), as described [3]. Results: Basal chemoafferent activity was significantly decreased in adult offspring exposed to severe but not mild CIHU (N 1.±0.2 vs. CIHU 15 0.2±0.04 Hz, P<0.05, Fig.1a). Similarly, the CB response to hypoxia was depressed in the animals exposed to severe CIHU, when measured at fixed, defined superfusate PO2s. E.g. At a superfusate PO2 of 100mmHg: N 4±1 vs. CIHU 15 0.5±0.15 Hz, P<0.0005 (Fig. 1c). Absolute peak chemoafferent responses were consistent between groups but occurred at lower PO2’s in the CIHU animals, consistent with a reduced CB O2 sensitivity. Interestingly, both mild and severe CIHU did not alter the mean arterial blood pressure in normoxia or hypoxia. Furthermore, baseline ventilation and the hypoxic ventilatory response were unaltered by CIHU. Conclusion: These results suggest that prenatal CIH leads to attenuation of CB function in the adult without completely abolishing it. However, this change did not alter the basal cardiovascular and respiratory measurements or attenuate reflex responses to hypoxia. The inconsistency of the current findings with the evidence that showed CIH in utero causes hypertension may be due to the lower CIH frequency and the duration used in this study compared to other studies. Further adaptations in the chemoreflex may also act to counter this reduction in the CB activity, preventing systemic cardiorespiratory dysfunction. |
المؤتمر (2): | |
عنوان المؤتمر: | Annual conference physiology 2019 |
تاريخ الإنعقاد: | 08/07/2019 |
مكان الإنعقاد: | UK |
طبيعة المشاركة: | Poster |
عنوان المشاركة: | Effects of beta-blocker treatment on ventilation in conscious rats before and after exposure to chronic intermittent hypoxia |
ملخص المشاركة: | Introduction: Obstructive sleep apnoea (OSA) patients have increased risk of cardiovascular and respiratory disease including hypertension, arrhythmia and breathing instability. A key feature of OSA is exposure to chronic intermittent hypoxia (CIH). Carotid body (CB) hyperactivity caused by CIH is central to the development of pathology. However, the mechanisms underpinning CB hyperactivity in response to CIH remain incompletely characterised. We hypothesise that the rise in serum catecholamines in response to CIH could be a key driver of CB hyperactivity. This study examined the effect of chronic administration of a beta blocker (propranolol) on baseline and hypoxic ventilation, before and after exposure to CIH. Methods: A total of 33 male Wistar rats (11-13 weeks) were split into four groups (Control (N) n=10, Propranolol (PN) n=8, Chronic Intermittent Hypoxia (CIH) n=7, CIH + Propranolol (CIHP) n=8). The CIH paradigm consisted of 8 cycles hr-1, 8 hours day-1, 5% O2 nadir, for 3 weeks. Propranolol was added to the drinking water (40 mg/kg body weight/day). Ventilation was recorded using whole body plethysmography on conscious rats. The protocol consisted of 5 min baseline ventilation followed by 5 min hypoxia (10% O2). Results: Propranolol modified the breathing pattern in normoxia and hypoxia by significantly increasing tidal volume (21% O2: N 4.3±0.2 vs PN 5.3±0.2 ml/kg, P<0.05; 10% O2: N 5.8±0.1 vs PN 7.0±0.3 ml/kg P<0.05) and reducing respiratory frequency (21% O2: N 96±2 vs PN 80±3 bpm, P<0.05; 10% O2: N 146±6 vs PN 128±5 bpm P=0.1), without altering overall minute ventilation. Propranolol did not significantly impact on the elevation in tidal volume, respiratory frequency or minute ventilation induced by hypoxia. Following CIH, there was an approximately 20% increase in minute ventilation in normoxia (P<0.05) and a trend towards an increase in hypoxia (P=0.09). CIH also significantly increased the inspiratory duty cycle and the Inspiratory:Expiratory time ratio. A similar effect of propranolol on breathing pattern was observed after CIH, as evidenced by a 30% increase in tidal volume and a 10% reduction in respiratory frequency without an overall change in minute ventilation. Following CIH, propranolol did not significantly impact on the elevation in tidal volume, respiratory frequency or minute ventilation induced by hypoxia. Conclusion: These results suggest that propranolol induces a change in the pattern of ventilation before and after CIH, characterised by a switch towards slower and deeper breathing. This change in pattern is predicted to cause an increase in alveolar ventilation. A role for the CB in mediating these effects is questionable as the hypoxic ventilatory response was not significantly modified by propranolol before or after CIH. Future experiments are required to directly measure CB activity following propranolol treatment before and after CIH. |
المؤتمر (3): | |
عنوان المؤتمر: | Annual conference physiology 2021 |
تاريخ الإنعقاد: | 12/07/2021 |
مكان الإنعقاد: | UK |
طبيعة المشاركة: | Poster |
عنوان المشاركة: | Angiotensin I receptor clustering and hypoxic remodelling in O2 sensitive cells |
ملخص المشاركة: | Introduction: The carotid body (CB) contains specialised O2 sensitive cells located at the carotid bifurcation that monitor the blood PaO2 supplying the brain to initiate corrective cardiovascular respiratory reflexes. O2 sensitivity of the CB is modulated by G-protein-coupled-receptor signalling (1). The angiotensin 1 receptor (AT1R) is expressed in the CB and angiotensin II causes chemoexcitation. In pathology, changes in AT1R signalling promote CB hyperactivity. However, little is known about the single molecule distribution of AT1R in CB type I cells or PC12 cells- a closely associated cell line, which may underpin signalling microdomains. Furthermore, it is not clear if AT1R membrane expression can be altered by exposure to hypoxia. This study aimed to reveal if membrane AT1R are clustered and if expression is altered by chronic hypoxia. Methods: AT1R expression was assessed in PC12 cells (an O2 sensitive cell line used to model the CB type I cell). PC12 cells (passage number 10-30) were plated onto human placental collagen and were incubated in media equilibrated with either 1% O2 or 20% O2 for 4, 12 and 24 hours. At each time point, cells were fixed and stained with primary antibodies (1:500 anti-AT1R and 1:500 anti-tyrosine hydroxylase-TH). Cells were stained with secondary F(ab) fragment antibodies conjugated with Alexa fluor 647 (1:1000) and 488 (1:1000). Cytosolic TH and membrane AT1R expression were assessed by confocal microscopy. Membrane AT1R clustering was visualised using direct STochastic Optical Reconstruction Microscopy (dSTORM). Data was expressed as mean ± S.E.M and significance determined with two-way repeated measures ANOVA and taken as P<0.05. Results: Exposure of PC12 cells to hypoxia (1% O2), caused a significant increase in cell area after 12 hours (normoxia 142.8±5.8μm2 (n=93), hypoxia 164.9±6.8μm2 (n=81), P<0.05) and 24 hours (normoxia 143.3±6.2μm2 (n=72), hypoxia 183.1±8.5μm2 (n=92), P<0.05). Confocal imaging demonstrated that cytosolic TH fluorescence levels were significantly elevated after 12 (normoxia 1333.6±93.5AU, hypoxia 1903.8±135.4AU, P<0.05) and 24 hours (normoxia 1175.8±61.3AU, hypoxia 1765.8±116.0AU, P<0.05). Furthermore, AT1R fluorescence was also significantly increased after 12 hours (normoxia 1315.8±35.1AU, hypoxia 1547.3±53.4AU, P<0.05) and 24 hours (normoxia 1286.6±33.5AU, hypoxia 1592.3±46.6AU, P<0.05) of hypoxia. Preliminary reconstructed images using dSTORM indicated the presence of distinct AT1R clusters on the PC12 cell surface membrane (Figure 1). The presence of clusters was consistent in all 5 cells imaged to date using dSTORM. Discussion: This preliminary data suggests that in O2 sensitive PC12 cells, AT1R are present in distinct clusters or ‘hotspots’ in the cell membrane, raising the potential of AT1R signalling microdomains. More experiments are required to validate this finding and quantify specific cluster parameters. In addition, this data shows that AT1R expression is increased in response to hypoxia along with an elevation in TH and cell area. A key next step will be to assess changes in AT1R expression and clustering specifically in primary CB type I cells as a further move towards the generation of potential novel therapies for cardiorespiratory diseases associated with chronic hypoxia. |