Felix J. Frey

Prophylactic hemodialysis after radiocontrast media in patients with renal insufficiency is potentially harmful.

PURPOSE Acute renal failure induced by contrast media is an important cause of hospital-acquired renal insufficiency. Preexisting renal failure and the dose of contrast media are known risk factors for the development of radiocontrast nephropathy. We performed a randomized trial to test whether radiocontrast nephropathy can be avoided by prophylactic hemodialysis immediately after the administration of contrast media in patients with impaired renal function. SUBJECTS AND METHODS Renal function and other parameters, hemodialysis requirement, and relevant clinical events were recorded before and during the 6 days after administration of contrast media in 113 patients with a baseline serum creatinine level >200 microm/L (>2.3 mg/dL). Patients were randomly assigned to either hemodialysis (n = 55) or nonhemodialysis (n = 58) treatment after parenteral low-osmolality contrast media. RESULTS The characteristics of the patients in the two groups were similar. Compared with baseline levels, the mean [+/- SD] serum creatinine level decreased at day 1 (277 +/- 95 microm/L), peaked at day 4 (353 +/- 126 microm/L), and returned to baseline at day 6 (327 +/- 119 microm/L, P <0.05 by analysis of variance) after administration of contrast media in the hemodialysis group, whereas in the nonhemodialysis group, no significant changes in mean serum creatinine level were observed. Eleven patients required 1 or more hemodialyses (8 in the hemodialysis group and 3 in the nonhemodialysis group, P = 0.12), 6 of whom (4 vs. 2, P = 0.44) required 3 or more hemodialyses. Clinically relevant events included pulmonary edema (1 vs. 4 patients, P = 0.36), myocardial infarction (2 vs. 2), stroke (2 vs. 0, P = 0.24), and death (1 vs. 1). CONCLUSIONS The strategy of performing hemodialysis immediately after the administration of low-osmolality contrast media in all patients with a reduced renal function did not diminish the rate of complications, including radiocontrast nephropathy.

Epigenetic regulation of 11β-hydroxysteroid dehydrogenase type 2 expression

The enzyme 11β-hydroxysteroid dehydrogenase type 2 (11βHSD2) is selectively expressed in aldosterone target tissues, where it confers aldosterone selectivity for the mineralocorticoid receptor by inactivating 11β-hydroxyglucocorticoids. Variable activity of 11βHSD2 is relevant for blood pressure control and hypertension. The present investigation aimed to elucidate whether an epigenetic mechanism, DNA methylation, accounts for the rigorous control of expression of the gene encoding 11βHSD2, HSD11B2. CpG islands covering the promoter and exon 1 of HSD11B2 were found to be densely methylated in tissues and cell lines with low expression but not those with high expression of HSD11B2. Demethylation induced by 5-aza-2′-deoxycytidine and procainamide enhanced the transcription and activity of the 11βHSD2 enzyme in human cells in vitro and in rats in vivo. Methylation of HSD11B2 promoter–luciferase constructs decreased transcriptional activity. Methylation of recognition sequences of transcription factors, including those for Sp1/Sp3, Arnt, and nuclear factor 1 (NF1) diminished their DNA-binding activity. Herein NF1 was identified as a strong HSD11B2 stimulatory factor. The effect of NF1 was dependent on the position of CpGs and the combination of CpGs methylated. A methylated-CpG–binding protein complex 1 transcriptional repression interacted directly with the methylated HSD11B2 promoter. These results indicate a role for DNA methylation in HSD11B2 gene repression and suggest an epigenetic mechanism affecting this gene causally linked with hypertension.

The N-terminal anchor sequences of 11beta-hydroxysteroid dehydrogenases determine their orientation in the endoplasmic reticulum membrane.

11β-Hydroxysteroid dehydrogenase enzymes (11β- HSD) regulate the ratio of active endogenous glucocorticoids to their inactive keto-metabolites, thereby controlling the access of glucocorticoids to their cognate receptors. In this study, the topology and intracellular localization of 11β-HSD1 and 11β-HSD2 have been analyzed by immunohistochemistry and protease protection assays ofin vitro transcription/translation products. 11β-HSD constructs, tagged with the FLAG epitope, were transiently expressed in HEK-293 cells. The enzymatic characteristics of tagged and native enzymes were indistinguishable. Fluorescence microscopy demonstrated the localization of both 11β-HSD1 and 11β-HSD2 exclusively to the endoplasmic reticulum (ER) membrane. To examine the orientation of tagged 11β-HSD enzymes within the ER membrane, we stained selectively permeabilized HEK-293 cells with anti-FLAG antibody. Immunohistochemistry revealed that the N terminus of 11β-HSD1 is cytoplasmic, and the catalytic domain containing the C terminus is protruding into the ER lumen. In contrast, the N terminus of 11β-HSD2 is lumenal, and the catalytic domain is facing the cytoplasm. Chimeric proteins where the N-terminal anchor sequences of 11β-HSD1 and 11β-HSD2 were exchanged adopted inverted orientation in the ER membrane. However, both chimeric proteins were not catalytically active. Furthermore, mutation of a tyrosine motif to alanine in the transmembrane segment of 11β-HSD1 significantly reducedV max. The subcellular localization of 11β-HSD1 was not affected by mutations of the tyrosine motif or of a di-lysine motif in the N terminus. However, residue Lys5, but not Lys6, turned out to be critical for the topology of 11β-HSD1. Mutation of Lys5 to Ser inverted the orientation of 11β-HSD1 in the ER membrane without loss of catalytic activity. Our results emphasize the importance of the N-terminal transmembrane segments of 11β-HSD enzymes for their proper function and demonstrate that they are sufficient to determine their orientation in the ER membrane.

Risk of acute kidney injury in patients with severe aortic valve stenosis undergoing transcatheter valve replacement

BACKGROUND Transcatheter aortic valve implantation (TAVI) for high-risk and inoperable patients with severe aortic stenosis is an emerging procedure in cardiovascular medicine. Little is known of the impact of TAVI on renal function. METHODS We analysed retrospectively renal baseline characteristics and outcome in 58 patients including 2 patients on chronic haemodialysis undergoing TAVI at our institution. Acute kidney injury (AKI) was defined according to the RIFLE classification. RESULTS Fifty-eight patients with severe symptomatic aortic stenosis not considered suitable for conventional surgical valve replacement with a mean age of 83 +/- 5 years underwent TAVI. Two patients died during transfemoral valve implantation and two patients in the first month after TAVI resulting in a 30-day mortality of 6.9%. Vascular access was transfemoral in 46 patients and transapical in 12. Estimated glomerular filtration rate (eGFR) increased in 30 patients (56%). Fifteen patients (28%) developed AKI, of which four patients had to be dialyzed temporarily and one remained on chronic renal replacement therapy. Risk factors for AKI comprised, among others, transapical access, number of blood transfusions, postinterventional thrombocytopaenia and severe inflammatory response syndrome (SIRS). CONCLUSIONS TAVI is feasible in patients with a high burden of comorbidities and in patients with pre-existing end-stage renal disease who would be otherwise not considered as candidates for conventional aortic valve replacement. Although GFR improved in more than half of the patients, this benefit was associated with a risk of postinterventional AKI. Future investigations should define preventive measures of peri-procedural kidney injury.

Clinical Pharmacokinetics of Prednisone and Prednisolone

SummaryThe growth of knowledge in the field of the pharmacokinetics of prednisolone/prednisone has been slow for several reasons. First, convenient and specific methods for measuring these steroids only became available with the development of high performance liquid Chromatographic methods. Secondly, prednisolone is nonlinearly bound to transcortin and albumin: since the unbound concentrations of prednisolone are biologically relevant, it was necessary to determine the free fraction in each plasma sample. Thirdly, due to the short half-life of prednisolone no steady-state is achieved, and therefore area under the concentration-time curve needed to be determined in all studies. Fourthly, prednisolone and prednisone are interconvertible and prednisolone is given intravenously as an ester prodrug, features which created controversies about the correct interpretation of pharmacokinetic results. Finally, the total body clearances of total and (to a lesser degree) of unbound prednisolone increase with increasing concentrations of prednisolone. Therefore, in order to compare pharmacokinetic results between different subjects, standardised doses had to be administered.The investigations performed so far have revealed that: (1) the dose-dependent pharmacokinetics partly explain the clinical observation that an alternate-day regimen with prednisone yields fewer biological effects; (2) the interconversion of prednisone into prednisolone is not a limiting factor, even in patients with severely impaired liver function; (3) hypoproteinaemia per se does not cause increased unbound concentrations of prednisolone in vivo; (4) patients with liver failure, renal failure or a renal transplant, subjects older than 65 years, women on estrogen-containing oral contraceptive steroids or subjects taking ketoconazole have increased unbound concentrations of prednisolone - whereas hyperthyroid patients, some patients with Crohn’s disease, subjects taking microsomal liver enzyme-inducing agents or patients on intravenous prednisolone phthalate (instead of prednisolone phosphate) or on some brands of enteric coated prednisolone tablets have decreased concentrations of prednisolone. The biological relevance of the altered pharmacokinetics is supported in part by altered clinical effects and altered effects on cellular immunofunctions.

Additive antiproteinuric effect of combined Ace inhibition and angiotensin Ii receptor blockade

Background Limitation of systemic and glomerular hypertension reduces urinary protein excretion and prevents renal function deterioration. Objective To investigate whether, in hypertensive patients with glomerulonephritis, a combination of an angiotensin converting enzyme inhibitor (ACEI, fosinopril 20 mg/day) with an angiotensin receptor blocker (ARB, irbesartan 150 mg/day) produces a more profound antiproteinuric effect than either drug alone. Methods Ten non-diabetic patients with glomerulonephritis, normal or slightly reduced but stable renal function (creatinine clearance 40–106 ml/min) without immunosuppression were studied. Clinical evaluations, 24 h blood pressure measurements and laboratory tests were performed as follows: (1) without medication (baseline) and in random sequence; (2) ACEI alone; (3) ARB alone; and (4) combination of ACEI + ARB. Each period lasted for 6 weeks, separated by three washout periods of 4 weeks each without therapy. Results ACEI and ARB alone reduced proteinuria from 7.9 ± 7.1 to 5.3 ± 5.2 and 5.0 ± 4.9 g/24 h (mean ± SD), respectively. The combination of ACEI + ARB induced a more remarkable reduction of proteinuria in every patient (to 3.3 ± 3.7 g/24 h) than either drug alone (P = 0.039 by ANOVA). The enhanced antiproteinuric effect of the combined therapy could not be attributed to a more pronounced reduction of 24 h mean arterial pressure (basal, 106 ± 8; ACEI, 97 ± 5; ARB, 98 ± 5; ACEI + ARB, 95 ± 5 mmHg) or creatinine clearance (basal, 77 ± 27; ACEI, 73 ± 31; ARB 80 ± 30; ACEI + ARB, 73 ± 32 ml/min). Conclusions A combination of ACEI and ARB in patients with glomerulonephritis produces a more profound decrease in proteinuria than either drug alone. This additive antiproteinuric effect is not dependent on changes in blood pressure or creatinine clearance. A long-term controlled study is required to confirm the positive effect of this treatment on the progression of renal function loss.

Hypoxia up-regulates expression of Eph receptors and ephrins in mouse skin

Eph receptor tyrosine kinases and their ligands (ephrins) are key players during the development of the embryonic vasculature; however, their role and regulation in adult angiogenesis remain to be defined. Both receptors and ligands have been shown to be up‐regulated in a variety of tumors. To address the hypothesis that hypoxia is an important regulator of Ephs/ephrins expression, we developed a mouse skin flap model of hypoxia. We demonstrate that our model truly represents segmental skin hypoxia by applying four independent methods: continuous measurement of partial cutaneous oxygen tension, monitoring of tissue lactate/pyruvate ratio, time course of hypoxia‐inducible factor‐1α (HLF‐1α) induction, and localization of stabilized HIF‐1α by immunofluorescence in the hypoxic skin flap. Our experiments indicate that hypoxia up‐regulates not only HIF‐1α and vascular endothelial growth factor (VEGF) expression, but also Ephs and ephrins of both A and B subclasses in the skin. In addition, we show that in Hep3B and PC‐3 cells, the hypoxia‐induced up‐regulation of Ephs and ephrins is abrogated by small interfering RNA‐mediated down‐regulation of HIF‐1α. These novel findings shed light on the role of this versatile receptor/ligand family in adult angiogenesis. Furthermore, our model offers considerable potential for analyzing distinct mechanisms of neovascularization in gene‐targeted mice.

Thigh muscle mass and function in patients treated with glucocorticoids

Abstract. Treatment with glucocorticoids causes wasting of proximal skeletal muscles. There is evidence that physical training improves muscle mass and strength in glucocorticoid‐treated rats. Whether this is also true in humans is unknown. The present investigation was designed to establish in what respect moderate physical training may alter muscle mass and function as assessed quantitatively by computed tomography (CT) and with an isokinetic dynamometer (Cybex® II). Compared with matched controls, both female (n= 17) and male (n= 22) patients treated with prednisone (15±4 ± 6±6 mg die‐1) had a lower mid‐thigh muscle area of 20 and 45% and an increased mid‐thigh fat/muscle ratio of 25 and 100%, respectively. The mean peak torque and the total work output of the thigh muscle were lower by 20–30% (n= 14). Fifty days of isokinetic training in six patients increased the thigh muscle area, decreased the thigh fat area and normalized the mean peak torque and total work output. Thus, glucocorticoid‐induced muscle wasting can be reversed by increasing physical activity.

Glucocorticoid-mediated mineralocorticoid receptor activation and hypertension.

Purpose of reviewTraditionally, the mineralocorticoid receptor was thought to be activated by the mineralocorticoid hormone aldosterone, and to exhibit its main action on epithelia by promoting renal sodium retention, potassium excretion and inducing hypertension upon excessive activation. Recently, evidence appeared that mineralocorticoid receptors are expressed in nonepithelial cells and activated by endogenous glucocorticoids including cortisol. Therefore, the prereceptor regulation of cortisol access to the mineralocorticoid receptors by 11β-hydroxysteroid dehydrogenase enzymes (11β-HSDs), a mechanism absent in most nonepithelial cells, appears to be relevant for disease states with cortisol-induced mineralocorticoid action. The present review focuses on direct and indirect effects attributable to mineralocorticoid receptor activation by glucocorticoids. Recent findingsThe determination of the intracellular topology of 11β-HSD1, facing the endoplasmic reticulum lumen, and 11β-HSD2, facing the cytoplasm, suggests that 11β-HSD1 acts as a prereceptor mechanism in the local activation of glucocorticoid receptors, whereas 11β-HSD2 controls mineralocorticoid receptors by interacting with the receptor in the absence of aldosterone. Downregulation of 11β-HSD2 was observed with various stimuli including hypoxia, shear stress, angiotensin II and tumor necrosis factor α. The corresponding signal transcription pathways and some relevant transcription factors have been identified. Renal sodium retention in liver cirrhosis, nephrotic syndrome and hypoxia have been linked to 11β-HSD2 reduced activity. Overexpression of 11β-HSD1 specifically in adipose tissue in mice caused central obesity, a metabolic syndrome and hypertension due to increased intracellular cortisol concentrations. Peroxisome proliferator-activated receptor γ agonists reduce 11β-HSD1 activity and diminish the intracellular availability of cortisol, an effect accompanied by a decline in blood pressure. Three individuals with loss-of-function mutations of peroxisome proliferator-activated receptor γ developed early hypertension. A potential mechanism might be glucocorticoid dependent mineralocorticoid receptor-mediated downregulation of endothelial nitric oxide synthase. SummaryRecently, mineralocorticoid receptor antagonists have been used in the randomized aldactone evaluation study (RALES) with spironolactone, the eplerenone post-AMI heart failure efficacy and survival study (EPHESUS), and in severe and postmyocardial infarct heart failure, respectively. These investigations cannot be understood on the basis of the present physiological knowledge and underscore the relevance of focusing on mineralocorticoid receptor activation by ligands other than aldosterone.

Sodium thiosulfate prevents vascular calcifications in uremic rats

Accelerated vascular calcification is a severe complication of chronic kidney disease contributing to high morbidity and mortality in patients undergoing renal replacement therapy. Sodium thiosulfate is increasingly used for the treatment of soft tissue calcifications in calciphylaxis. Therefore, we determined whether it also prevents development of vascular calcifications in chronic kidney disease. We found that uremic rats treated by thiosulfate had no histological evidence of calcification in the aortic wall whereas almost three-fourths of untreated uremic rats showed aortic calcification. Urinary calcium excretion was elevated and the calcium content of aortic, heart, and renal tissue was significantly reduced in the thiosulfate-treated compared to non-treated animals. Sodium thiosulfate treatment transiently lowered plasma ionized calcium and induced metabolic acidosis. It also lowered bone strength in the treated animals compared to their normal controls. Hence, sodium thiosulfate prevented vascular calcifications in uremic rats, likely by enhancing acid- and/or chelation-induced urinary calcium loss. The negative impact on rat bone integrity necessitates a careful risk-benefit analysis before sodium thiosulfate can be used in individual human patients.