Hepatic Mitochondrial Renin-Angiotensin Systems

Introduction: The circulating renin-angiotensin system (RAS) was originally described as a key endocrine regulator of intravascular homeostasis; however, the existence of a local (tissue) RAS has become increasingly reported in a variety of tissues including liver. RAS components have now also been detected in rat heart, brain and smooth muscle cell mitochondria as well as within intramitochondrial dense bodies of rat adrenal tissue. Further, reduced RAS levels have been associated with improved endurance performance and fatigue resistance in human skeletal muscle, suggesting that low RAS activity is associated with metabolic efficiency, potentially via RAS action upon, or within, mitochondria. However, such investigation has often relied heavily upon qualitative techniques (e.g. Western blotting, immunofluorescence and electron microscopy), which contain inherent limitations in that they completely rely upon the limited specificity of antibodies to demonstrate the existence of intra-mitochondrial RAS components. Methods: The presence of RAS components within the mitochondria of rat hepatic tissue and liver cell-lines was investigated via sub-fractionation of rat liver tissue and cell-lines, followed by Western blotting, as well as via immunofluorescence and confocal microscopy, and electron microscopy. The mitochondrial effects of stimulating or antagonizing hepatic RAS were assessed via functional fluorescence microscopy (for assessment of NADH, calcium and mitochondrial membrane potential) and measurement of oxygen consumption within live cells of a liver cell-line. Results: Western blotting, immunofluorescence and electron microscopy suggested the presence of RAS components within mitochondria; however, there was a lack of results consistency between techniques and the staining patterns were largely non-specific. Western blotting further demonstrated the presence of a prominent 55 kDa band, when immunostaining a mitochondrial fraction with (angiotensin-converting enzyme) ACE Cterminal antibody (usual size 180 kDa). This was further explored via isolation of the 55 kDa molecule and mass spectrometry to yield results consistent with non-specific staining only. Addition of RAS agonists or antagonists to live liver cell-lines demonstrated no consistent results, except at supra-physiological levels, where RAS antagonists improved oxygen consumption. Conclusions: Such data suggest that the previous descriptions of RAS components within mitochondria are likely to be secondary to methodological flaws, particularly the reliance upon single antibodies, which have subsequently been shown to have poor specificity. Thus, the effect of ang II on liver mitochondria is unlikely to be direct and any such action is likely to occur via one of several intracellular pathways, regulation of gene expression or mitochondrial biogenesis

ACE and response to pulmonary rehabilitation in COPD: two observational studies.

INTRODUCTION: Skeletal muscle impairment is an important feature of chronic obstructive pulmonary disease (COPD). Renin-angiotensin system activity influences muscle phenotype, so we wished to investigate whether it affects the response to pulmonary rehabilitation. METHODS: Two studies are described; in the first, the response of 168 COPD patients (mean forced expiratory volume in one second 51.9% predicted) to pulmonary rehabilitation was compared between different ACE insertion/deletion polymorphism genotypes. In a second, independent COPD cohort (n=373), baseline characteristics and response to pulmonary rehabilitation were compared between COPD patients who were or were not taking ACE inhibitors or angiotensin receptor antagonists (ARB). RESULTS: In study 1, the incremental shuttle walk distance improved to a similar extent in all three genotypes; DD/ID/II (n=48/91/29) 69(67)m, 61 (76)m and 78 (78)m, respectively, (p>0.05). In study 2, fat free mass index was higher in those on ACE-I/ARB (n=130) than those who were not (n=243), 17.8 (16.0, 19.8) kg m-2 vs 16.5 (14.9, 18.4) kg/m2 (p<0.001). However change in fat free mass, walking distance or quality of life in response to pulmonary rehabilitation did not differ between groups. CONCLUSIONS: While these data support a positive association of ACE-I/ARB treatment and body composition in COPD, neither treatment to reduce ACE activity nor ACE (I/D) genotype influence response to pulmonary rehabilitation.The study was funded by a Trevor Clay grant from The British Lung Foundation (TC 04/4) and supported by the NIHR Respiratory Biomedical Research Unit at Royal Brompton and Harefield Hospital and Imperial College who part fund MIP’s salary. WD-CM is an NIHR Clinician Scientist and supported by a MRC New Investigator Research Grant. DS was funded by the MRC G0701628. ZP is a NIHR Doctorate Research Fellow. SSCK and CJJ were funded by the MR

Splenic Injury Following Colonoscopy – An Underdiagnosed, But Soon to Increase, Phenomenon?

INTRODUCTION: We present a case of splenic rupture in a 71-year-old woman admitted 6 days following a diagnostic colonoscopy. She underwent an open splenectomy and made a delayed, but complete, recovery. We proceeded to perform a retrospective review of all relevant literature to assess the frequency of similar post-colonoscopy complications. MATERIALS AND METHODS: Using relevant keywords, we identified 63 further PubMed reports of splenic injury associated with colonoscopy that were reported in English. FINDINGS: We have described only the fourth report of splenic injury secondary to colonoscopy from a UK centre. Literature review reveals a mean age of 63 years and a female preponderance for this complication. Most patients present on the day of their colonoscopy with abdominal pain, anaemia, elevated white cell count and Kehr's sign. CT is the investigation of choice and splenectomy the definitive management of choice. Most patients make a routine recovery, with mortality rates of approximately 8%. There is likely to be an under-reporting of this complication from UK-based centres, with the majority of reports originating from Europe and US. This points to a possible under-diagnosis or under-recognition of this potentially fatal complication. The incidence of such post-colonoscopic complications may increase with the forthcoming introduction of the National Bowel Cancer Screening Programme