High Potassium Intake Enhances the Inhibitory Effect of 11,12-EET on ENaC

High dietary potassium stimulates the renal expression of cytochrome P450 (CYP) epoxygenase 2C23, which metabolizes arachidonic acid (AA). Because the AA metabolite 11,12-epoxyeicosatrienoic acid (11,12-EET) can inhibit the epithelial sodium channel (ENaC) in the cortical collecting duct, we tested whether dietary potassium modulates ENaC function. High dietary potassium increased 11,12-EET in the isolated cortical collecting duct, an effect mimicked by inhibiting the angiotensin II type I receptor with valsartan. In patch-clamp experiments, a high potassium intake or treatment with valsartan enhanced AA-induced inhibition of ENaC, an effect mediated by a CYP-epoxygenase–dependent pathway. Moreover, high dietary potassium and valsartan each augmented the inhibitory effect of 11,12-EET on ENaC. Liquid chromatography/mass spectrometry showed that the rate of EET conversion to dihydroxyeicosatrienoic acids (DHET) was lower in renal tissue obtained from rats on a high-potassium diet than from those on a control diet, but this was not a result of altered expression of soluble epoxide hydrolase (sEH). Instead, suppression of sEH activity seemed to be responsible for the 11,12-EET–mediated enhanced inhibition of ENaC in animals on a high-potassium diet. Patch-clamp experiments demonstrated that 11,12-DHET was a weak inhibitor of ENaC compared with 11,12-EET, whereas 8,9- and 14,15-DHET were not. Furthermore, inhibition of sEH enhanced the 11,12-EET–induced inhibition of ENaC similar to high dietary potassium. In conclusion, high dietary potassium enhances the inhibitory effect of AA and 11,12-EET on ENaC by increasing CYP epoxygenase activity and decreasing sEH activity, respectively.We previously demonstrated that cytochrome P450 (CYP) epoxygenase-dependent arachidonic acid (AA) metabolism inhibited epithelial sodium channel (ENaC) in the cortical collecting duct (CCD) and that 11,12-epoxyeicosatrienoic acid (11,12-EET) was responsible for mediating the effect of AA on ENaC.¹ Furthermore, the observation that AA failed to inhibit ENaC in the CCD of the mice with a low expression of CYP2C44 suggests that CYP2C44 and its orthologs may be responsible for mediating the inhibitory effect of AA.² The expression of CYP2C44 or its orthologs has been shown to be regulated by dietary Na intake: A high Na intake stimulates² whereas a low, Na intake suppresses the expression of CYP2C44 homologue.³ A large body of evidence has suggested that EET plays a role in the regulation of renal Na transport and salt-sensitive hypertension.^1,2,4,5 Inhibition of CYP epoxygenase-dependent AA metabolism results in the development of salt-sensitive hypertension^5,6; however, the BP returned to normal after the removal of the epoxygenase inhibitor, even when the animals were still kept on a high-Na diet. The high Na intake–induced increase in EET formation was defective in CYP4A10(−/−) mice.² Although CYP4A10 is not the enzyme responsible for generating EET, deleting the CYP4A10 gene impairs the expression of CYP epoxygenases, CYP2C44 in particular. Consequently, CYP4A10(−/−) mice had developed a salt-sensitive hypertension that was prevented by amiloride, suggesting that defective regulation of ENaC by CYP epoxygenase-dependent AA metabolism was responsible for the salt-sensitive hypertension in CYP4A(−/−) mice.² The expression of CYP2C44 or its ortholog is stimulated not only by high Na but also by high potassium (HK) intake.⁷ Because CYP2C44 is highly expressed in the connecting tubule and the CCD,¹ it is conceivable that a high expression of CYP2C44 should enhance the AA-induced inhibition of ENaC; therefore, the aim of this study was to examine whether HK intake enhances the CYP-epoxygenase–dependent inhibitory effect of AA on ENaC.     

Morphology of the medial collateral ligament of the knee

Background  

Quantitative knowledge on the anatomy of the medial collateral ligament (MCL) is important for treatment of MCL injury and for MCL release during total knee arthroplasty (TKA). The objective of this study was to quantitatively determine the morphology of the MCL of human knees.     

Direct comparison of enoxaparin and nadroparin in a rabbit model of arterial thrombosis prevention

Introduction

The aim of the study was to evaluate and compare the efficacy of standard unfractionated heparin (UFH) and low-molecular weight heparins (LMWH's).

Materials and Methods

We modified a previously published rabbit model of arterial thrombosis prevention [1,2] to compare unfractionated heparin and two different doses of two low-molecular weight heparin fragments - nadroparin and enoxaparin. Thrombosis in the distal aorta was triggered by vessel wall injury and critical stenosis. Blood flow in the damaged arterial segment was monitored by a flow probe placed distal to the constrictor. The primary endpoints of the study were: (1) cumulative flow, (2) time to occlusion and (3) residual clot weight. Thirty six animals were split into 6 groups with six animals in each group. Control groups were given saline or heparin and four more groups were used to compare LMWH's at 2 different doses.

Results

In our study, all treatments were superior to the saline control group (α ≤ 0,01). Standard heparin was inferior (α ≤ 0,05) to both low molecular weight heparins for all primary endpoints (cumulative flow, time to occlusion and residual clot weight). There were no differences between the LMWH's except for cumulative flow at high doses.

Conclusions

This study revealed no relevant differences between nadroparin and enoxaparin for the primary endpoints of our model. Clinical use of each drug remains a personal preference.     

Isolation,structure elucidation and biological activity of angucycline antibiotics from an epiphytic yew streptomycete

In the course of study of epiphytic microorganisms occurring on the surface of roots of Taxus baccata L. a new strain Streptomyces sp. AC113 was isolated. According to 16S ribosomal DNA‐based identification the new strain is 99% identical with Streptomyces flavidofuscus. This strain cultivated in an arginine glycerol medium produced three major metabolites identified as (–)‐8‐O ‐methyltetrangomycin ( 1 ), 8‐O ‐methyltetrangulol ( 2 ) and 8‐O ‐methyl‐7‐deoxo‐7‐hydroxytetrangomycin ( 3 ). The chemical structures of these angucyclines were elucidated by 1D and 2D NMR as well as by mass spectrometry. Isolated angucycline metabolites showed significant antimicrobial activity against Bacillus cereus and Listeria mocytogenes. Cytotoxic activities of compounds 1 , 2 and 3 against four cell lines (B16, HT‐29 and non – tumor V79, L929) were evaluated. Compound 3 was the most potent anticancer agents with IC₅₀ 0.054 μg/ml against cell line B16. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Optical system based on time-gated, intensified charge-coupled device camera for brain imaging studies

An imaging system for brain oxygenation based on a time-gated, intensified charge-coupled device camera was developed. It allows one to image diffusely reflected light from an investigated medium at defined time windows delayed with respect to the laser pulse. Applying a fast optomechanical switch to deliver the light at a wavelength of 780 nm to nine source fibers allowed one to acquire images in times as short as 4 s. Thus, the system can be applied in in vivo studies. The system was validated in phantom experiments, in which absorbing inclusions were localized at different depths and different lateral positions. Then, the decrease in absorption of the brain tissue related to increase in oxygenation was visualized in the motor cortex area during finger tapping by a healthy volunteer.