Cationic uremic toxins affect human renal proximal tubule cell functioning through interaction with the organic cation transporter

Several organic cations, such as guanidino compounds and polyamines, have been found to accumulate in plasma of patients with kidney failure due to inadequate renal clearance. Here, we studied the interaction of cationic uremic toxins with renal organic cation transport in a conditionally immortalized human proximal tubule epithelial cell line (ciPTEC). Transporter activity was measured and validated in cell suspensions by studying uptake of the fluorescent substrate 4-(4-(dimethylamino)styryl)-N-methylpyridinium-iodide (ASP⁺). Subsequently, the inhibitory potencies of the cationic uremic toxins, cadaverine, putrescine, spermine and spermidine (polyamines), acrolein (polyamine breakdown product), guanidine, and methylguanidine (guanidino compounds) were determined. Concentration-dependent inhibition of ASP⁺ uptake by TPA, cimetidine, quinidine, and metformin confirmed functional endogenous organic cation transporter 2 (OCT2) expression in ciPTEC. All uremic toxins tested inhibited ASP⁺ uptake, of which acrolein required the lowest concentration to provoke a half-maximal inhibition (IC₅₀?=?44?±?2 μM). A Dixon plot was constructed for acrolein using three independent inhibition curves with 10, 20, or 30 μM ASP⁺, which demonstrated competitive or mixed type of interaction (K _i?=?93 ± 16 μM). Exposing the cells to a mixture of cationic uremic toxins resulted in a more potent and biphasic inhibitory response curve, indicating complex interactions between the toxins and ASP⁺ uptake. In conclusion, ciPTEC proves a suitable model to study cationic xenobiotic interactions. Inhibition of cellular uptake transport was demonstrated for several uremic toxins, which might indicate a possible role in kidney disease progression during uremia.     

Mesenchymal stem cell-conditioned medium accelerates regeneration of human renal proximal tubule epithelial cells after gentamicin toxicity

Bone marrow-derived mesenchymal stem cells (MSCs) have the capacity to regenerate renal tubule epithelia and repair renal function without fusing with resident tubular cells. The goal of the present project was to investigate the role of MSCs secreted cytokines on tubule cell viability and regeneration after a toxic insult, using a conditionally immortalized human proximal tubule epithelial cell (ciPTEC) line. Gentamicin was used to induce nephrotoxicity, and cell viability and migration were studied in absence and presence of human MSC-conditioned medium (hMSC-CM) i.e. medium containing soluble factors produced and secreted by MSCs. Exposure of ciPTEC to 0–3000 μg/ml gentamicin for 24 h caused a significant dose-dependent increase in cell death. We further demonstrated that the nephrotoxic effect of 2000 μg/ml gentamicin was recovered partially by exposing cells to hMSC-CM. Moreover, exposure of ciPTEC to gentamicin (1500–3000 μg/ml) for 7 days completely attenuated the migratory capacity of the cells. In addition, following scrape-wounding, cell migration of both untreated and gentamicin-exposed cells was increased in the presence of hMSC-CM, as compared to exposures to normal medium, indicating improved cell recovery. Our data suggest that cytokines secreted by MSCs stimulate renal tubule cell regeneration after nephrotoxicity.     

Autosomal Recessive Spinocerebellar Ataxia 7 (SCAR7) is Caused by Variants in TPP1, The Gene Involved in Classic Late‐Infantile Neuronal Ceroid Lipofuscinosis 2 Disease (CLN2 Disease)

Spinocerebellar ataxias are phenotypically, neuropathologically, and genetically heterogeneous. The locus of autosomal recessive spinocerebellar ataxia type 7 (SCAR7) was previously linked to chromosome band 11p15. We have identified TPP1 as the causative gene for SCAR7 by exome sequencing. A missense and a splice site variant in TPP1, cosegregating with the disease, were found in a previously described SCAR7 family and also in another patient with a SCAR7 phenotype. TPP1, encoding the tripeptidyl‐peptidase 1 enzyme, is known as the causative gene for late infantile neuronal ceroid lipofuscinosis disease 2 (CLN2 disease). CLN2 disease is characterized by epilepsy, loss of vision, ataxia, and a rapidly progressive course, leading to early death. SCAR7 patients showed ataxia and low activity of tripeptidyl‐peptidase 1, but no ophthalmologic abnormalities or epilepsy. Also, the slowly progressive evolution of the disease until old age and absence of ultra structural curvilinear profiles is different from the known CLN2 phenotypes. Our findings now expand the phenotypes related to TPP1‐variants to SCAR7. In spite of the limited sample size and measurements, a putative genotype–phenotype correlation may be drawn: we hypothesize that loss of function variants abolishing TPP1 enzyme activity lead to CLN2 disease, whereas variants that diminish TPP1 enzyme activity lead to SCAR7.     

Photochromic organic solar cells based on diarylethenes

Photovoltaic devices that switch color depending on illumination conditions may find application in future smart window applications. Here a photochromic diarylethene molecule is used as sensitizer in a ternary bulk heterojunction blend, employing poly(4-butylphenyldiphenylamine) (poly-TPD) and [6,6]-phenyl-C₆₁-butyric acid methyl ester (PC₆₁BM) for the transport of holes and electrons, respectively. Sandwiched between two electrodes, the blend creates a photochromic photovoltaic device that changes color, light absorption, and photon-to-electron conversion efficiency in the visible spectral range after having been illuminated with UV light.

A diarylethene dye that reversibly changes color upon illumination is used in a switchable photochromic organic solar cell.     

Hematopoietic growth factor expression and ATRA sensitivity in acute promyelocytic blast cells

Acute promyelocytic leukemia (APL) is a homogeneous subgroup of acute myeloid leukemias (AMLs) characterized by the presence of the t(15,17) translocation and the resulting promyelocytic myeloid leukemia/retinoic acid receptor alpha (PML/RAR alpha) fusion proteins. To date APL is the only AML that is sufficiently sensitive to all-trans retinoic acid's (ATRA) differentiating effect. In vivo ATRA alone achieves complete remission in most APL patients. However, failure or partial responses are observed and the molecular basis of the absence of ATRA response in these patients has not been determined. To gain insights in the cell growth and differentiation of APL cells, expression of hematopoietic growth factors (HGF) shown to be produced by leukemic cells (interleukin-1 beta [IL-1 beta], IL-6, tumor necrosis factor alpha (TNF alpha), granulocyte colony-stimulating factor [G-CSF], granulocyte- macrophage colony-stimulating factor [GM-CSF], and IL-3) was studied in 16 APL samples. Twelve APL cases expressed IL-1 beta, IL-6, and TNF alpha, but not G-CSF, GM-CSF, and IL-3. These cases achieved complete remission with ATRA therapy. The four remaining patients (either TNF alpha negative or G-CSF, GM-CSF or IL-3 positive) did not achieve complete remission with ATRA. In all cases, in vivo response to ATRA therapy was correlated to the in vitro differentiation effect of all- trans retinoic acid 10(-6) mol/L. Thus, ATRA differentiation induction was strongly correlated to the HGF expression (P < .0001). These results suggest that the presence or absence of HGF's expression by APL cells may contribute to the therapeutic effect of ATRA in this disease.     

Validation of Prosthetic Mitral Regurgitation Quantification Using Novel Angiographic Platform by Mock Circulation

ObjectivesThis study aimed to validate a dedicated software for quantitative videodensitometric angiographic assessment of mitral regurgitation (QMR).BackgroundQuantitative videodensitometric aortography of aortic regurgitation using the time-density principle is a well-documented technique, but the angiographic assessment of mitral regurgitation (MR) remains at best semi-quantitative and operator dependent.MethodsFourteen sheep underwent surgical mitral valve replacement using 2 different prostheses. Pre-sacrifice left ventriculograms were used to assess MR fraction (MRF) using QMR and MR volume (MRV). In an independent core lab, the CAAS QMR 0.1 was used for QMR analysis. In vitro MRF and MRV were assessed in a mock circulation at a comparable cardiac output to the in vivo one by thermodilution. The correlations and agreements of in vitro and in vivo MRF, MRV, and interobserver reproducibility for QMR analysis were assessed using the averaged cardiac cycles (CCs).ResultsIn vivo derived MRF by QMR strongly correlated with in vitro derived MRF, regardless of the number of the CCs analyzed (best correlation: 3 CCs y = 0.446 + 0.994x; R = 0.784; p =0.002). The mean absolute difference between in vitro derived MRF and in vivo derived MRF from 3 CCs was 0.01 ± 4.2% on Bland-Altman analysis. In vitro MRV and in vivo MRV from 3 CCs were very strongly correlated (y = 0.196 + 1.255x; R = 0.839; p < 0.001). The mean absolute difference between in vitro MRV and in vivo MRV from 3 CCs was –1.4 ± 1.9 ml. There were very strong correlations of in vivo MRF between 2 independent analysts, regardless of the number of the CCs.ConclusionsIn vivo MRF using the novel software is feasible, accurate, and highly reproducible. These promising results have led us to initiate the first human feasibility study comprising patients undergoing percutaneous mitral valve edge-to-edge repair.