State‐dependent blocking mechanism of Kv1.3 channels by the antimycobacterial drug clofazimine

Background and Purpose

K_v1.3 potassium channels are promising pharmaceutical targets for treating immune diseases as they modulate Ca²⁺ signalling in T cells by regulating the membrane potential and with it the driving force for Ca²⁺ influx. The antimycobacterial drug clofazimine has been demonstrated to attenuate antigen‐induced Ca²⁺ oscillations, suppress cytokine release and prevent skin graft rejection by inhibiting K_v1.3 channels with high potency and selectivity.

Experimental Approach

We used patch‐clamp methodology to investigate clofazimine''s mechanism of action in K_v1.3 channels expressed in HEK293 cells.

Key Results

Clofazimine blocked K_v1.3 channels by involving two discrete mechanisms, both of which contribute to effective suppression of channels: (i) a use‐dependent open‐channel block during long depolarizations, resulting in accelerated K⁺ current inactivation and (ii) a block of closed deactivated channels after channels were opened by brief depolarizations. Both modes of block were use‐dependent and state‐dependent in that they clearly required prior channel opening. The clofazimine‐sensitive closed‐deactivated state of the channel was distinct from the resting closed state because channels at hyperpolarized voltages were not inhibited by clofazimine. Neither were channels in the C‐type inactivated state significantly affected. K_v1.3 channels carrying the H399T mutation and lacking C‐type inactivation were insensitive to clofazimine block of the closed‐deactivated state, but retained their susceptibility to open‐channel block.

Conclusions and Implications

Given the prominent role of K_v1.3 in shaping Ca²⁺ oscillations, the use‐dependent and state‐dependent block of K_v1.3 channels by clofazimine offers therapeutic potential for selective immunosuppression in the context of autoimmune diseases in which K_v1.3‐expressing T cells play a significant role.

Abbreviations

CLF

clofazimine

FDA

Food and Drug Administration

IPI

interpulse intervals

WT

wild type

     

Effect of nizatidine 300 mg at night and omeprazole 20 mg in the morning on 24-hour intragastric pH and bacterial overgrowth in patients with acute duodenal ulcer

The study investigated the effect of either nocturnal acid suppression by the H₂ antagonist nizatidine 300 mg at night or prolonged acid suppression by the proton-pump inhibitor omeprazole 20 mg in the morning, during four weeks, on intragastric pH profile, occurrence of bacterial growth in gastric fluid and biopsies, and healing rate in 23 patients with an acute duodenal ulcer. The endoscopic healing rate did not differ significantly between the two treatment modalities. The 24-hr acid secretion was significantly more reduced by omeprazole than nizatidine (P<0.002). After treatment by nizatidine and omeprazole, respectively, median 24-hr intragastric pH increased from 1.5 to 1.8 (P<0.01) and from 1.5 to 6.1 (P<0.01), respectively. Nighttime acid inhibition did not differ significantly. The difference in gastric bacterial colonization after either omeprazole or nizatidine did not reach significance. However, median 24-hr pH and the fraction of the day with pH<3 and pH<4 were significantly correlated to bacterial colonization of the gastric fluid (P<0.05).This study was supported by Eli Lilly Nederland B.V.     

New European initiatives in colorectal cancer screening: Budapest Declaration. Official appeal during the Hungarian Presidency of the Council of the European Union under the Auspices of the United European Gastroenterology Federation, the European Association for Gastroenterology and Endoscopy and the Hungarian Society of Gastroenterology

Colorectal cancer (CRC) is the second most common newly diagnosed cancer and the second most common cause of death in the European Union (EU). CRC is an enormous health and economic burden. Early detection and prevention have the possibility of reducing this burden significantly. Many cancer-associated deaths can be avoided through early detection by high-quality colorectal screening programs followed by appropriate treatment. Under the auspices of the United European Gastroenterology Federation (UEGF), the European Association for Gastroenterology and Endoscopy, the Hungarian Society of Gastroenterology and the Hungarian College of Gastroenterology, the 'Budapest Declaration' (2011) was an accepted official scientific program during the Hungarian Presidency of the Council of the European Union. The Budapest Declaration follows the Munich Declaration (2001), the Brussels Declaration (2007), the Transatlantic Declaration (2009), the Barcelona Declaration (2010), the written declaration of CRC screening, a joint initiative with European Parliamentarians coordinated by the UEGF, and finally, the 'European Guidelines for Quality Assurance in Colorectal Cancer Screening and Diagnosis'. The 'Budapest Declaration' together with previous declarations aims to urge the national and supranational healthcare decision makers to launch new Europe-wide initiatives to establish high-quality CRC programs to achieve optimal efficiency in CRC screening. In case of implementation of the proposals, actions and conditions recommended, we can achieve that one of the basic principles of the EU - the chance of equal access - be realized in member states with respect to the prevention of CRC and reduction of cancer-related mortality. To better achieve this goal, we propose to establish an UEGF joint committee, with one participant representing each EU member state to coordinate and supervise the implementation of CRC screening.     

NKG2C deletion is a risk factor of HIV infection

NK cell function is important in the immune response to HIV infection. NKG2C and NKG2A are activating and inhibitory NK cell receptors, respectively, and their only known ligand, HLA-E, demonstrates increased expression in HIV infection and presents at least one HIV-derived peptide. A variation in chromosome 12 exists in which the 16-kb section of DNA encompassing the nkg2c gene is completely absent. DNA samples of 433 HIV-1-infected patients and 280 controls were genotyped by PCR, and revealed an association of the absence variation with a higher risk of HIV infection, as well as faster progression and higher pretreatment viral loads (p<0.05, respectively). Surface NKG2C expression, analyzed by FACS, on the freshly isolated lymphocytes of 20 control and 19 HIV-infected donors revealed that NKG2C expression is genotype dependent in both populations: no NKG2C expression in the -/- groups, intermediate expression in the +/- groups, and highest expression in the +/+ groups. The comparison of NKG2C and NKG2A expression in HIV and control groups (+/- and +/+ included) indicates an increased NKG2C expression on HIV patient NK cells (p<0.05) and decreased inhibitory NKG2A expression on CD8 T cells (p<0.001), and both these effects are more striking in the +/+ genotype (p<0.005). Furthermore, a positive correlation was found between HIV viral load and the proportion of NKG2C(+) NK cells. The increased expression of NKG2C in HIV patients, in combination with the genetic association of the absence variation with an increased susceptibility to HIV infection, higher HIV viral set point, and a faster progression, indicate that NKG2C is important in the defense against HIV infection and progression.     

Dichotomous effects of C-C chemokines in HIV-1 pathogenesis

Whilst many physiological functions of nitric oxide (NO) have been revealed so far, recent evidence proposes an essential role for NO in T lymphocyte activation and signal transduction. NO acts as a second messenger, activating soluble guanyl cyclase and participating in signal transduction pathways involving cyclic GMP. NO modulates mitochondrial events that are involved in apoptosis and regulates mitochondrial biogenesis in many cell types, including lymphocytes. Several studies undertaken on patients with RA and SLE have documented increased endogenous NO synthesis, although the effects of NO may be distinct. Here, we discuss recent evidence that NO contributes to T cell dysfunction in both SLE and RA by altering multiple signaling pathways in T cells. Although NO may play a physiological role in lymphocyte cell signaling, its overproduction may perturb T cell activation, differentiation and effector responses, each of which may contribute in different ways to the pathogenesis of autoimmunity.     

Die Einwilligung in die medizinische Behandlung minderjähriger Patienten und die Neuregelung der Patientenverfügung

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