Chronic beta-adrenoceptor blockade and human atrial cell electrophysiology: evidence of pharmacological remodelling

OBJECTIVE: Chronic beta-adrenoceptor antagonist (beta-blocker) treatment reduces the incidence of reversion to AF in patients, possibly via an adaptive myocardial response. However, the underlying electrophysiological mechanisms are presently unclear. We aimed to investigate electrophysiological changes in human atrial cells associated with chronic treatment with beta-blockers and other cardiovascular-acting drugs. METHODS: Myocytes were isolated enzymatically from the right atrial appendage of 40 consenting patients who were in sinus rhythm. The cellular action potential duration (APD), effective refractory period (ERP), L-type Ca(2+) current (I(CaL)), transient (I(TO)) and sustained (I(KSUS)) outward K(+) currents, and input resistance (R(i)) were recorded using the whole cell patch clamp. Drug treatments and clinical characteristics were compared with electrophysiological measurements using simple and multiple regression analyses. P<0.05 was taken as statistically significant. RESULTS: In atrial cells from patients treated chronically with beta-blockers, the APD(90) and ERP (75 beats/min stimulation) were significantly longer, at 213+/-11 and 233+/-11 ms, respectively (n=15 patients), than in cells from non-beta-blocked patients, at 176+/-12 and 184+/-12 ms (n=11). These cells also displayed a significantly reduced action potential phase 1 velocity (22+/-3 vs. 34+/-3 V/s). Chronic beta-blockade was also associated with a significant reduction in the heart rate (58+/-3 vs. 69+/-5 beats/min) and in the density of I(TO) (8.7+/-1.3 vs. 13.7+/-2.1 pA/pF), an increase in the R(i) (214+/-24 vs. 132+/-14 MOmega), but no significant change in I(CaL) or I(KSUS). The I(TO) blocker 4-aminopyridine largely mimicked the changes in phase 1 and ERP associated with chronic beta-blockade, in cells from non-beta-blocked patients. Chronic treatment of patients with calcium channel blockers or angiotensin converting enzyme inhibitors (n=11-13 patients) was not associated with any significant changes in atrial cell electrophysiology. CONCLUSION: The observed atrial cellular electrophysiological changes associated with chronic beta-blockade are consistent with a long-term adaptive response, a type of 'pharmacological remodelling', and provide mechanistic evidence supportive of the anti-arrhythmic actions of beta-blockade.     

Central memory self/tumor-reactive CD8+ T cells confer superior antitumor immunity compared with effector memory T cells

Central memory CD8+ T cells (T(CM)) and effector memory CD8+ T cells (T(EM)) are found in humans and mice; however, their relative contributions to host immunity have only recently been examined in vivo. Further, the ability of T(CM) to treat an established tumor or infection has yet to be evaluated. To address the therapeutic potential of different tumor-reactive CD8+ T cell memory subsets, we used an established model for the in vitro generation of T(CM) and T(EM) by using IL-15 and IL-2, respectively. Adoptively transferred T(CM) exhibited a potent in vivo recall response when combined with tumor-antigen vaccination and exogenous IL-2, leading to the eradication of large established tumors. By contrast, T(EM) were far less effective on a per-cell basis. Microarray analysis revealed that the signature of highly in vivo effective antitumor T cells included the overexpression of genes responsible for trafficking to secondary lymphoid tissues. This gene expression profile correctly predicted the in vitro and in vivo lymphoid-homing attributes of tumor-reactive T cells. Furthermore, we found that homing to secondary lymphoid tissue is required for optimal tumor treatment. Our findings indicated that highly in vivo effective antitumor T cells were those that initially targeted secondary lymphoid tissue, rather than tumor sites, as had previously been postulated. Thus, tumor-reactive CD8+ T cell populations with the phenotypic and functional attributes of T(CM) may be superior to T(EM)/effector T cells for adoptive immunotherapies using concomitant tumor-antigen vaccination.     

Coronary artery stenting for acute closure complicating primary angioplasty for acute myocardial infarction

We report a case of progressive right coronary artery dissection complicating direct angioplasty for an acute inferior myocardial infarct, with successful bail-out stenting of the affected vessel.     

Colchicine for large pericardial effusion

On the basis of our reported experience with colchicine for recurrent pericarditis, we administered colchicine to two patients with large pericardial effusions complicating idiopathic pericarditis. The first was a 26-year-old male who showed clinical deterioration following emergency pericardiocentesis and aspirin (3 g/day) for 10 days; the second was a 2-year-old girl who was unsuccessfully treated with aspirin (100 mg/kg/day) for 2 weeks, followed by corti-costeroids for 7 months. Administration of colchicine (1 mg/ day) instead of aspirin in the first case, and with a rapid tapering-off of the corticosteroids in the second case, led to complete regression of the pericardial effusion on echocardiography within 1 week and 1 month, respectively. Colchicine was discontinued after 1 month in the first patient and was continued for 6 months in the child. Neither has had a recurrence at 24 and 6 months of follow-up, respectively. No side effects of colchicine were observed. We conclude that colchicine may be effective in the treatment of large pericardial effusion when therapy with nonsteroidal anti-inflammatory drugs and/or corticosteroids fails.     

Development of extended multidrug resistance in HL60 promyelocytic leukaemia cells

Summary. In an attempt to mimic clinical conditions for the treatment of leukaemia, the HL60 promyelocytic cell line was treated for 18 h with low, clinically relevant, levels of the anthracycline epirubicin and the Vinca alkaloid vinblastine. The resulting drug-resistant sublines not only expressed P-glycoprotein and the MDR phenotype but were also cross-resistant to chlorambucil, methotrexate but were also cross-resistant to chlorambucil, methotrexate and cisplatinum, and had increased resistance to radiation. Development of resistance was associatted with an aberrant differentiation phenotype with decreased expression of myeloid antigens and expression of glycophorin A. an antigen normally associated with erythroid differentiation. The ability of HL60 cells to terminally differentiate in response to all- trans -retinoic acid (vitamin A acid) was lost in the sublines. These results suggest that either a single novel mechanism is responsible for multiple drug resistance or the initial response to drug treatment is the co-induction of multiple mechanisms. These cells and the method by which they were generated therefore provide a clinically relevant model for the study of the initial events in the development of not only multidrug resistance but also the extended multiple drug resistance usually encountered in the treatment of leukaemia.     

Ternary complex formation of AFN‐1252 with Acinetobacter baumannii FabI and NADH: Crystallographic and biochemical studies

Acinetobacter baumannii is an opportunistic Gram‐negative bacterial pathogen, associated mostly with hospital‐acquired infections. The emergence of drug resistance strains made it necessary to explore new pathways for the development of more effective antibiotics. Enoyl CoA reductase (FabI), a key enzyme in the fatty acid biosynthesis (FAS) pathway, has emerged as a potential target for antibacterial drug development. Earlier reports show that the lead SaFabI inhibitor AFN‐1252 can inhibit FabI from other organisms including Escherichia coli and Burkholderia pseudomallei, but with differential potency. In the present work, we show that AFN‐1252 is a moderate inhibitor of AbFabI with an IC₅₀ of 216 nM. AFN‐1252 stabilized AbFabI with a 4.2°C increase in the melting temperature (T_m) and, interestingly, the stabilization effect was significantly increased in presence of the cofactor NADH (?T_m = 17°C), suggesting the formation of a ternary complex AbFabI: AFN‐1252: NADH. X‐ray crystallography studies of AbFabI co‐crystalized with AFN‐1252 and NADH confirmed the ternary complex formation. The critical interactions of AFN‐1252 with AbFabI and NADH identified from the co‐crystal structure may facilitate the design and development of new drugs against A. baumannii infections by targeting the FAS pathway.