Paricalcitol attenuates 4-hydroxy-2-hexenal-induced inflammation and epithelial-mesenchymal transition in human renal proximal tubular epithelial cells

Vitamin D and chronic kidney disease: Insights on lipid metabolism of tubular epithelial cell and macrophages in tubulointerstitial fibrosis

Chronic kidney disease (CKD) has been recognized as a significant global health problem due to being an important contributor to morbidity and mortality. Inflammation is the critical event that leads to CKD development orchestrated by a complex interaction between renal parenchyma and immune cells. Particularly, the crosstalk between tubular epithelial cells (TECs) and macrophages is an example of the critical cell communication in the kidney that drives kidney fibrosis, a pathological feature in CKD. Metabolism dysregulation of TECs and macrophages can be a bridge that connects inflammation and fibrogenesis. Currently, some evidence has reported how cellular lipid disturbances can affect kidney disease and cause tubulointerstitial fibrosis highlighting the importance of investigating potential molecules that can restore metabolic parameters. Vitamin D (VitD) is a hormone naturally produced by mammalian cells in a coordinated manner by the skin, liver, and kidneys. VitD deficiency or insufficiency is prevalent in patients with CKD, and serum levels of VitD are inversely correlated with the degree of kidney inflammation and renal function. Proximal TECs and macrophages produce the active form of VitD, and both express the VitD receptor (VDR) that evidence the importance of this nutrient in regulating their functions. However, whether VitD signaling drives physiological and metabolism improvement of TECs and macrophages during kidney injury is an open issue to be debated. In this review, we brought to light VitD as an important metabolic modulator of lipid metabolism in TECs and macrophages. New scientific approaches targeting VitD e VDR signaling at the cellular metabolic level can provide a better comprehension of its role in renal physiology and CKD progression.

Vitamin D/VDR in Acute Kidney Injury: A Potential Therapeutic Target

Despite many strategies and parameters used in clinical practice, the incidence and mortality of acute kidney injury (AKI) are still high with poor prognosis. With the development of molecular biology, the role of vitamin D and vitamin D receptor (VDR) in AKI is drawing increasing attention. Accumulated researches have suggested that Vitamin D deficiency is a risk factor of both clinical and experimental AKI, and vitamin D/VDR could be a promising therapeutic target against AKI. However, more qualitative clinical researches are needed to provide stronger evidence for the clinical application of vitamin D and VDR agonists in the future. Issues like the route and dosage of administration also await more attention. The present review aims to summarize the current works on the role of vitamin D/VDR in AKI and provides some new insight on its therapeutic potential.

The effects of vitamin D3 supplementation on TGF-β and IL-17 serum levels in migraineurs: post hoc analysis of a randomized clinical trial

BACKGROUND

Although the exact mechanism involved in migraine pathogenesis remained uncertain, and different researches have been developed to address the role of neuroinflammation and immune dysfunction. Therefore, considering the immune protective functions of vitamin D3, we aimed to investigate the effects of daily administration of 2000 IU D3 supplements on serum status of immune markers in migraine patients.

METHODS AND MATERIALS

Eighty episodic migraineurs who randomly assigned into two equal groups to receive either vitamin D3 2000 IU/d or placebo for 12-week were enrolled in this placebo-controlled double-blind trial included. Serum concentrations of transforming growth factor-beta (TGF-β) and interleukin (IL)-17 were evaluated at baseline and after the trial via the ELISA method.

RESULTS

Applying ANCOVA adjusted for baseline levels and confounding variables, it was found that the serum level of TGF-β was significantly higher in vitamin D group (adjusted mean:1665.50 ng/L) than the placebo group (1361.90 ng/L) after the experiment (P-value = 0.012); on the other hand, vitamin D prevented the increment in IL-17 serum level in the intervention group after the trial (adjusted mean:37.84 ng/L) comparing to the controls (adjusted mean:70.09 ng/L; P-value = 0.039). The Pearson correlation analysis revealed a significant positive correlation between changes in serum 25-hydroxy-vitamin D (25(OH)D) and TGF-β (r = - 0.306, P-value = 0.008). In contrast, no significant correlations were noted between serum 25(OH) D and IL-17 changes throughout the study.

CONCLUSION

Based on the results of this study, it was revealed that 12-week vitamin D3 supplementation (2000 IU/day) could enhance the Th17/Treg related cytokines balance in episodic migraineurs. Although these findings are promising, it is needed to be extended.

TRIAL REGISTRATION

The trial is registered in the Iranian registry of clinical trials (IRCT) at 11 July 2018, with IRCT code: IRCT20151128025267N6 ( https://www.irct.ir/trial/31246 ).

Protective Role of Vitamin D in Renal Tubulopathies

Vitamin D is tightly linked with renal tubular homeostasis: the mitochondria of proximal convoluted tubule cells are the production site of 1α,25-dihydroxyvitamin D3. Patients with renal impairment or tubular injury often suffer from chronic inflammation. This alteration comes from oxidative stress, acidosis, decreased clearance of inflammatory cytokines and stimulation of inflammatory factors. The challenge is to find the right formula for each patient to correctly modulate the landscape of treatment and preserve the essential functions of the organism without perturbating its homeostasis. The complexity of the counter-regulation mechanisms and the different axis involved in the Vitamin D equilibrium pose a major issue on Vitamin D as a potential effective anti-inflammatory drug. The therapeutic use of this compound should be able to inhibit the development of inflammation without interfering with normal homeostasis. Megalin-Cubilin-Amnionless and the FGF23-Klotho axis represent two Vitamin D-linked mechanisms that could modulate and ameliorate the damage response at the renal tubular level, balancing Vitamin D therapy with an effect potent enough to contrast the inflammatory cascades, but which avoids potential severe side effects.

RON Receptor Tyrosine Kinase Regulates Epithelial Mesenchymal Transition and the Expression of Pro-Fibrotic Markers via Src/Smad Signaling in HK-2 and NRK49F Cells

Receptor tyrosine kinases (RTKs) play important roles in the pathogenic processes of kidney fibrosis. However, the pathophysiological roles of recepteur d’origine nantais (RON), one of the receptor tyrosine kinases, have not yet been defined. We investigated whether the activation or sequence-specific small interfering RNA (siRNA) suppression of RON could regulate epithelial mesenchymal transition (EMT) and the expression of pro-fibrotic markers, and its underlying molecular mechanisms. Stable cell lines and transient transfection for RON and the transfected cells of siRNA for RON were developed to investigate the molecular mechanisms in human kidney proximal tubular epithelial (HK-2) and interstitial fibroblasts (NRK49F) cells. RON overexpression induced EMT and increased expression of fibrosis-related proteins such as N-cadherin, vimentin, transforming growth factor-β (TGFβ), αSMA, and fibronectin in HK-2 and NRK49F cells. RON overexpression increased various RTKs and the phosphorylation of Src (Y416) and Smad, while inhibition of RON by siRNA attenuated the expression of EMT- and fibrosis-related proteins and decreased RTKs such as insulin-like growth factor receptor (IGFR), fibroblast growth factor receptor 1 (FGFR1), vascular endothelial growth factor receptor (VEGFR), and platelet-derived growth factor receptor (PDGFR), as well as the phosphorylation of Src and Smad pathways. siRNA silencing of Src also attenuated the expression of IGFR, FGFR1, VEGFR, and PDGFR. Inhibition of RON can exert an anti-fibrotic effect by the inhibition of EMT and other RTKs through control of Src and Smad pathways in HK-2 and NRK49F cells.

Alpha-lipoic acid attenuates p-cresyl sulfate-induced renal tubular injury through suppression of apoptosis and autophagy in human proximal tubular epithelial cells

The p-cresyl sulfate accumulates in kidney disease and may be involved in renal injury. α-Lipoic acid (α-LA) acts as an antioxidant in cell injury. We investigated the effects of α-LA treatment on p-cresyl sulfate-induced renal tubular injury. p-Cresyl sulfate induced cell death, and increased Bax/Bcl-2, cleaved caspase-3, Beclin-1, and LC3BII/LC3BI in human renal proximal tubular epithelial (HK-2) cells, which was counteracted by α-LA treatment. p-Cresyl sulfate-induced apoptosis was reduced by autophagy inhibitor 3-methyladenine, and p-cresyl sulfate induced autophagy was reduced by pan-caspase inhibitor Z-VAD-FMK. Moreover, p-cresyl sulfate treatment increased the expression of ER stress proteins and decreased the expression of baculoviral IAP repeat-containing proteins 6; these effects were prevented by α-LA treatment. Apoptosis and autophagy were associated with the phosphorylation of mitogen-activated protein kinase and nuclear translocation of the nuclear factor-κB p65 subunit. Pretreatment inhibitors of p38 and JNK, and knockdown of ATF4 gene reduced apoptosis- and autophagy-related protein expressions in p-cresyl sulfate treated HK-2 cells. These results demonstrate that α-lipoic acid attenuated p-cresyl sulfate-induced cell death by suppression of apoptosis and autophagy via regulation of ER stress in HK-2 cells.

Paricalcitol attenuates indoxyl sulfate-induced apoptosis through the inhibition of MAPK, Akt, and NF-kB activation in HK-2 cells

BACKGROUND/AIMS

Indoxyl sulfate (IS) is a uremic toxin and an important causative factor in the progression of chronic kidney disease. Recently, paricalcitol (19-nor-1,25-dihydroxyvitamin D2) was shown to exhibit protective effects in kidney injury. Here, we investigated the effects of paricalcitol treatment on IS-induced renal tubular injury.

METHODS

The fluorescent dye 2',7'-dichlorofluorescein diacetate was used to measure intracellular reactive oxygen species (ROS) following IS administration in human renal proximal tubular epithelial (HK-2) cells. The effects of IS on cell viability were determined using MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assays and levels of apoptosis-related proteins (Bcl-2-associated protein X [Bax] and B-cell lymphoma 2 [Bcl-2]), nuclear factor-κB (NF- κB) p65, and phosphorylation of mitogen-activated protein kinase (MAPK) and protein kinase B (Akt) were determined by semiquantitative immunoblotting. The promoter activity of NF-κB was measured by luciferase assays and apoptosis was determined by f low cytometry of cells stained with f luorescein isothiocyanate-conjugated Annexin V protein.

RESULTS

IS treatment increased ROS production, decreased cell viability and induced apoptosis in HK-2 cells. IS treatment increased the expression of apoptosis-related protein Bax, decreased Bcl-2 expression, and activated phosphorylation of MAPK, NF-κB p65, and Akt. In contrast, paricalcitol treatment decreased Bax expression, increased Bcl-2 expression, and inhibited phosphorylation of MAPK, NF-κB p65, and Akt in HK-2 cells. NF-κB promoter activity was increased following IS, administration and was counteracted by pretreatment with paricalcitol. Additionally, flow cytometry analysis revealed that IS-induced apoptosis was attenuated by paricalcitol treatment, which resulted in decreased numbers of fluorescein isothiocyanate-conjugated Annexin V positive cells.

CONCLUSION

Treatment with paricalcitol inhibited IS-induced apoptosis by regulating MAPK, NF-κB, and Akt signaling pathway in HK-2 cells.

Tumor necrosis factor α-converting enzyme inhibitor attenuates lipopolysaccharide-induced reactive oxygen species and mitogen-activated protein kinase expression in human renal proximal tubule epithelial cells

Tumor necrosis factor-α (TNFα) and the angiotensin system are involved in inflammatory diseases and may contribute to acute kidney injury. We investigated the mechanisms by which TNFα-converting enzyme (TACE) contributes to lipopolysaccharide (LPS)-induced renal inflammation and the effect of TACE inhibitor treatment on LPS-induced cellular injury in human renal proximal tubule epithelial (HK-2) cells. Mice were treated with LPS (10 mg/kg, i.p.) and HK-2 cells were cultured with or without LPS (10 µg/ml) in the presence or absence of a type 1 TACE inhibitor (1 µM) or type 2 TACE inhibitor (10 µM). LPS treatment induced increased serum creatinine, TNFα, and urinary neutrophil gelatinase-associated lipocalin. Angiotensin II type 1 receptor, mitogen activated protein kinase (MAPK), and TACE increased, while angiotensin-converting enzyme-2 (ACE2) expression decreased in LPS-induced acute kidney injury and LPS-treated HK-2 cells. LPS induced reactive oxygen species and the down-regulation of ACE2, and these responses were prevented by TACE inhibitors in HK-2 cells. TACE inhibitors increased cell viability in LPS-treated HK-2 cells and attenuated oxidative stress and inflammatory cytokines. Our findings indicate that LPS activates renin angiotensin system components via the activation of TACE. Furthermore, inhibitors of TACE are potential therapeutic agents for kidney injury.

Vitamin D Receptor: A Novel Therapeutic Target for Kidney Diseases

BACKGROUND

Kidney disease is a serious problem that adversely affects human health, but critical knowledge is lacking on how to effectively treat established chronic kidney disease. Mounting evidence from animal and clinical studies has suggested that Vitamin D Receptor (VDR) activation has beneficial effects on various renal diseases.

METHODS

A structured search of published research literature regarding VDR structure and function, VDR in various renal diseases (e.g., IgA nephropathy, idiopathic nephrotic syndrome, renal cell carcinoma, diabetic nephropathy, lupus nephritis) and therapies targeting VDR was performed for several databases.

RESULT

Included in this study are the results from 177 published research articles. Evidence from these papers indicates that VDR activation is involved in the protection against renal injury in kidney diseases by a variety of mechanisms, including suppression of RAS activation, anti-inflammation, inhibiting renal fibrogenesis, restoring mitochondrial function, suppression of autoimmunity and renal cell apoptosis.

CONCLUSION

VDR offers an attractive druggable target for renal diseases. Increasing our understanding of VDR in the kidney is a fertile area of research and may provide effective weapons in the fight against kidney diseases.

1,25(OH)2D3 treatment attenuates high glucose‑induced peritoneal epithelial to mesenchymal transition in mice

It has been previously demonstrated that 1,25(OH)2D3 prevents the progression of epithelial to mesenchymal transition (EMT). However, it remains unclear whether 1,25(OH)2D3 has a role in peritoneal EMT stimulated by high glucose (HG) peritoneal dialysis fluid (PDF). The present study was performed to investigate the role of 1,25(OH)2D3 in the progression of EMT in the peritoneal mesothelium. A total of 35 male Kunming mice were randomly assigned into seven groups. In the control group, no diasylate or saline was infused. In the saline group, the mice were intraperitoneally injected with saline every day for 4 weeks. In the vitamin D group, the mice were subjected to intraperitoneal injections of 1 or 5 µg/kg of 1,25(OH)2D3 once weekly (every Monday) for 4 weeks. The peritoneal dialysis (PD) group were intraperitoneally injected with a conventional 4.25% PDF daily for 4 weeks. The vitamin D+PD group were intraperitoneally injected with 4.25% PDF daily and co‑treated with 1 µg/kg or 5 µg/kg 1,25(OH)2D3 once weekly, for 4 weeks. The peritoneal morphology and thickness were assessed by hematoxylin and eosin and Masson's trichrome staining. The peritoneal protein level of EMT markers (α‑smooth muscle actin, fibronectin and E‑cadherin), vitamin D receptor (VDR), B cell lymphoma‑2 (Bcl‑2), Bcl‑2‑associated X protein, transforming growth factor (TGF)‑β and Smad3 were evaluated by western blot analysis or immunohistochemical staining. Furthermore, apoptosis was assessed using a Caspase‑3 activity assay. The results demonstrated that after 4 weeks of intraperitoneal injections in mice, HG‑PDF decreased the expression of VDR, promoted EMT and apoptosis, and increased the thickness of the peritoneal membrane. However, 1,25(OH)2D3 treatment attenuated HG‑induced EMT and apoptosis, and decreased peritoneal thickness, which may partially occur through inhibition of transforming growth factor TGF‑β/Smad pathways via 1,25(OH)2D3 binding to VDR. The present study demonstrated that 1,25(OH)2D3 attenuated HG‑induced EMT and apoptosis in the peritoneal mesothelium through TGF‑β/Smad pathways. 1,25(OH)2D3 treatment in conjunction with HG dialysate may provide an improved solution to the peritoneal injury in the process of PD.

Anti-inflammatory profile of paricalcitol in kidney transplant recipients

BACKGROUND AND OBJECTIVES

Paricalcitol, a selective vitamin D receptor activator, is used to treat secondary hyperparathyroidism in kidney transplant patients. Experimental and clinical studies in non-transplant kidney disease patients have found this molecule to have anti-inflammatory properties. In this exploratory study, we evaluated the anti-inflammatory profile of paricalcitol in kidney-transplant recipients.

METHODS

Thirty one kidney transplant recipients with secondary hyperparathyroidism completed 3 months of treatment with oral paricalcitol (1μg/day). Serum concentrations and gene expression levels of inflammatory cytokines in peripheral blood mononuclear cells were analysed at the beginning and end of the study.

RESULTS

Paricalcitol significantly decreased parathyroid hormone levels with no changes in calcium and phosphorous. It also reduced serum concentrations of interleukin (IL)-6 and tumour necrosis factor-alpha (TNF-α) by 29% (P<0.05) and 9.5% (P<0.05) compared to baseline, respectively. Furthermore, gene expression levels of IL-6 and TNF-α in peripheral blood mononuclear cells decreased by 14.1% (P<0.001) and 34.1% (P<0.001), respectively. The ratios between pro-inflammatory cytokines (TNF-α and IL-6) and anti-inflammatory cytokines (IL-10), both regarding serum concentrations and gene expression, also experienced a significant reduction.

CONCLUSIONS

Paricalcitol administration to kidney transplant recipients has been found to have beneficial effects on inflammation, which may be associated with potential clinical benefits.

1,25-(OH)2D3 and its analogue BXL-628 inhibit high glucose-induced activation of RhoA/ROCK pathway in HK-2 cells

It has previously been reported that 1,25-(OH)₂D₃ inhibits high glucose-induced epithelial-to-mesenchymal transition (EMT) in HK-2 cells. However, the mechanism of this renoprotective action remains unclear. Elocalcitol (BXL-628), a vitamin D analog, has been suggested to be effective on the RhoA/Rho associated protein kinase (ROCK) pathway, which serves a crucial role in high glucose-induced EMT. The aim of the present study was to investigate the effect of 1,25-(OH)₂D₃ and its analogue BXL-628 on high glucose-induced activation of the RhoA/ROCK pathway in human renal proximal tubular cells. HK-2 cells were co-treated with high glucose and either 1,25-(OH)2D3 or BXL-628. The RhoA expression levels and ROCK activity of the membrane were assessed via western blot analysis or immunofluorescence. α-smooth muscle actin (α-SMA) and epithelial (E)-cadherin were detected using western blotting and reverse transcription-quantitative polymerase chain reaction (RT-qPCR), whereas collagen I and fibronectin levels were measured by ELISA and RT-qPCR. The results demonstrated that 1,25-(OH)₂D₃ and BXL-628 both significantly downregulated the expression of active RhoA and ROCK activity induced by high glucose (P<0.05). Furthermore, the expressions of α-SMA, collagen I, and fibronectin were significantly downregulated at both protein and mRNA (P<0.05) levels, whereas the expression of E-cadherin was significantly increased (P<0.05) by 1,25-(OH)₂D₃ or BXL-628 treatment. In conclusion, the vitamin D receptor agonist 1,25-(OH)₂D₃ and its analogue BXL-628 were both able to attenuate high glucose-induced EMT and extracellular matrix accumulation of HK-2 cells by suppressing the RhoA/ROCK signaling pathway in vitro.

1,25(OH)2D3/VDR attenuates high glucose‑induced epithelial‑mesenchymal transition in human peritoneal mesothelial cells via the TGFβ/Smad3 pathway

Epithelial-mesenchymal transition (EMT) has been recognized to accelerate peritoneal membrane dysfunction. 1,25(OH)2D3/vitamin D receptor (VDR) is important for preventing various types of EMT in vivo. However, its function on EMT and inflammation of human peritoneal mesothelial cells (HPMCs) remains to be elucidated. Therefore, the present study investigated the effects of 1,25(OH)2D3/VDR on high glucose (HG)‑induced EMT and inflammation in HPMCs and the underlying molecular mechanism. It was determined that HG reduced VDR expression, increased inflammatory cytokine expression, including transforming growth factor β (TGFβ) and interleukin‑6 (IL‑6) and phosphorylated‑SMAD family member 3 (p‑Smad3) expression. EMT was promoted as the expression level of the epithelial marker E‑cadherin was reduced, whereas expression levels of the mesenchymal markers α‑SMA and FN were increased. 1,25(OH)2D3 pretreatment inhibited the expression of inflammatory cytokines in HPMCs and attenuated HG‑induced EMT, possibly through inhibition of the TGFβ/Smad pathway by binding to its receptor VDR.

Evolutionary Origin of the Interferon-Immune Metabolic Axis: The Sterol-Vitamin D Link

In vertebrate animals, the sterol metabolic network is emerging as a central player in immunity and inflammation. Upon infection, flux in the network is acutely moderated by the interferon (IFN) response through direct molecular and bi-directional communications. How sterol metabolism became linked to IFN control and for what purpose is not obvious. Here, we deliberate on the origins of these connections based on a systematic review of the literature. A narrative synthesis of publications that met eligibility criteria allowed us to trace an evolutionary path and functional connections between cholesterol metabolism and immunity. The synthesis supports an ancestral link between toxic levels of cholesterol-like products and the vitamin D receptor (VDR). VDR is an ancient nuclear hormone receptor that was originally involved in the recognition and detoxification of xenobiotic marine biotoxins exhibiting planar sterol ring scaffolds present in aquatic environments. Coadaptation of this receptor with the acquisition of sterol biosynthesis and IFNs in vertebrate animals set a stage for repurposing and linking a preexisting host-protection mechanism of harmful xenobiotics to become an important regulator in three key interlinked biological processes: bone development, immunity, and calcium homeostasis. We put forward the hypothesis that sterol metabolites, especially oxysterols, have acted as evolutionary drivers in immunity and may represent the first example of small-molecule metabolites linked to the adaptive coevolution and diversification of host metabolic and immune regulatory pathways.

A double-blind, randomized, placebo-controlled trial of combined calcitriol and ergocalciferol versus ergocalciferol alone in chronic kidney disease with proteinuria

Background

KDOQI guideline suggests that nutritional vitamin D should be supplemented in chronic kidney disease (CKD) patients who have vitamin D insufficiency/deficiency. However, there are scarce data regarding the additional benefit of active vitamin D supplement in CKD patients who were receiving nutritional vitamin D supplement. This study was conducted to explore the effect of adding active vitamin D to nutritional vitamin D supplement on proteinuria and kidney function in CKD with vitamin D insufficiency/deficiency.

Methods

This double-blind, randomized placebo-controlled trial was performed to answer the above question. Sixty-eight patients with CKD stage 3–4, urine protein to creatinine ratio (UPCR) > 1 g/g, and serum 25OH-D level < 30 ng/mL were enrolled. Patients were randomly assigned to receive 12-week treatment with oral ergocalciferol plus placebo (n = 36) or oral ergocalciferol plus calcitriol (n = 32).

Results

The mean baseline values of UPCR of both groups were comparable (3.6 ± 3.8 g/g in combined group and 3.5 ± 3.0 g/g in ergocalciferol group). Following 12-week treatment, there were significant reductions in UPCR from baseline in both groups (2.3 ± 2.1 g/g in combined group and 2.4 ± 2.0 g/g in ergocalciferol group). The percentage reductions in UPCR of both groups were not significantly different. The mean eGFR and blood pressure did not differ between baseline and 12-week follow-up and between both groups. No severe hypercalcemia or serious side effects were noted in both groups.

Conclusions

The proteinuria lowering effect of ergocalciferol in CKD patients with vitamin D deficiency was demonstrated. Additional calcitriol supplement did not have more effects on proteinuria.

Trial registration

(Thai Clinical Trials Registry (TCTR) 20140929002). Date of registration: September 27, 2014.

Nicotine-Induced Apoptosis in Human Renal Proximal Tubular Epithelial Cells

Background

Nicotine is, to a large extent, responsible for smoking-mediated renal dysfunction. This study investigated nicotine’s effects on renal tubular epithelial cell apoptosis in vitro and it explored the mechanisms underlying its effects.

Methods

Human proximal tubular epithelial (HK-2) cells were treated with nicotine. Cell viability was examined by using the WST-1 assay. Intracellular levels of reactive oxygen species (ROS) and the expression of mitogen-activated protein kinase (MAPK) and nuclear factor-κB (NF-κB) proteins were determined. The messenger ribonucleic acid and the protein expression associated with the nicotine acetylcholine receptors (nAChRs) in HK-2 cells was examined, and apoptosis was detected using flow cytometry, cell cycle analysis, and immunoblot analysis.

Results

The HK-2 cells were endowed with nAChRs. Nicotine treatment reduced cell viability dose dependently, increased ROS levels, and increased extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and p38 MAPK expression. Nicotine increased NF-κB activation, which was attenuated by N-acetyl-L-cysteine, and ERK and JNK inhibitors, but was not affected by a p38 MAPK inhibitor. Nicotine increased the Bax/Bcl-2 ratio, which was attenuated by N-acetyl-L-cysteine, the NF-κB inhibitor, Bay 11–7082, and hexamethonium, a non-specific nAChR blocker. Flow cytometry revealed nicotine-induced G2/M phase arrest. While nicotine treatment increased the expression of phosphorylated cdc2 and histone H3, a marker of G2/M phase arrest, hexamethonium and Bay 11–7082 pretreatment reduced their expression.

Conclusions

Nicotine caused apoptosis in HK-2 cells by inducing ROS generation that activated the NF-κB signaling pathway via the MAPK pathway and it arrested the cell cycle at the G2/M phase. Nicotine-induced apoptosis in HK-2 cells involves the nAChRs.

Hydrogen Sulfide Inhibits Transforming Growth Factor-β1-Induced EMT via Wnt/Catenin Pathway

Hydrogen sulfide (H2S) has anti-fibrotic potential in lung, kidney and other organs. The exogenous H2S is released from sodium hydrosulfide (NaHS) and can influence the renal fibrosis by blocking the differentiation of quiescent renal fibroblasts to myofibroblasts. But whether H2S affects renal epithelial-to-mesenchymal transition (EMT) and the underlying mechanisms remain unknown. Our study is aimed at investigating the in vitro effects of H2S on transforming growth factor-β1 (TGF-β1)-induced EMT in renal tubular epithelial cells (HK-2 cells) and the associated mechanisms. The induced EMT is assessed by Western blotting analysis on the expressions of α-SMA, E-cadherin and fibronectin. HK-2 cells were treated with NaHS before incubating with TGF-β1 to investigate its effect on EMT and the related molecular mechanism. Results demonstrated that NaHS decreased the expression of α-SMA and fibronectin, and increased the expression of E-cadherin. NaHS reduced the expression of TGF-β receptor type I (TβR I) and TGF-β receptor type II (TβR II). In addition, NaHS attenuated TGF-β1-induced increase of β-catenin expression and ERK phosphorylation. Moreover, it inhibited the TGF-β1-induced nuclear translocation of ββ-catenin. These effects of NaHS on fibronectin, E-cadherin and TβR I were abolished by the ERK inhibitor U0126 or β-catenin inhibitor XAV939, or β-catenin siRNA interference. We get the conclusion that NaHS attenuated TGF-β1-induced EMT in HK-2 cells through both ERK-dependent and β-catenin-dependent pathways.

Vitamin D and the Epithelial to Mesenchymal Transition

Several studies support reciprocal regulation between the active vitamin D derivative 1α,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃) and the epithelial to mesenchymal transition (EMT). Thus, 1,25(OH)₂D₃ inhibits EMT via the induction of a variety of target genes that encode cell adhesion and polarity proteins responsible for the epithelial phenotype and through the repression of key EMT inducers. Both direct and indirect regulatory mechanisms mediate these effects. Conversely, certain master EMT inducers inhibit 1,25(OH)₂D₃ action by repressing the transcription of VDR gene encoding the high affinity vitamin D receptor that mediates 1,25(OH)₂D₃ effects. Consequently, the balance between the strength of 1,25(OH)₂D₃ signaling and the induction of EMT defines the cellular phenotype in each context. Here we review the current understanding of the genes and mechanisms involved in the interplay between 1,25(OH)₂D₃ and EMT.

Angiotensin-(1-7) Attenuates Kidney Injury Due to Obstructive Nephropathy in Rats

Background

Angiotensin-(1–7) [Ang-(1–7)] counteracts many actions of the renin-angiotensin-aldosterone system. Despite its renoprotective effects, extensive controversy exists regarding the role of Ang-(1–7) in obstructive nephropathy, which is characterized by renal tubulointerstitial fibrosis and apoptosis.

Methods

To examine the effects of Ang-(1–7) in unilateral ureteral obstruction (UUO), male Sprague-Dawley rats were divided into three groups: control, UUO, and Ang-(1–7)-treated UUO rats. Ang-(1–7) was continuously infused (24 μg/[kg·h]) using osmotic pumps. We also treated NRK-52E cells in vitro with Ang II (1 μM) in the presence or absence of Ang-(1–7) (1 μM), Mas receptor antagonist A779 (1 μM), and Mas receptor siRNA (50 nM) to examine the effects of Ang-(1–7) treatment on Ang II-stimulated renal injury via Mas receptor.

Results

Angiotensin II (Ang II) and angiotensin type 1 receptor (AT₁R) protein expression was higher in UUO kidneys than in controls. Ang-(1–7) treatment also decreased proapoptotic protein expression in UUO kidneys. Ang-(1–7) also significantly ameliorated TUNEL positive cells in UUO kidneys. Additionally, Ang-(1–7) reduced profibrotic protein expression and decreased the increased tumor growth factor (TGF)-β1/Smad signaling present in UUO kidneys. In NRK-52E cells, Ang II induced the expression of TGF-β1/Smad signaling effectors and proapoptotic and fibrotic proteins, as well as cell cycle arrest, which were attenuated by Ang-(1–7) pretreatment. However, treatment with A779 and Mas receptor siRNA enhanced Ang II-induced apoptosis and fibrosis. Moreover, Ang II increased tumor necrosis factor-α converting enzyme (TACE) and decreased angiotensin-converting enzyme 2 (ACE2) expression in NRK-52E cells, while pretreatment with Ang-(1–7) or A779 significantly inhibited or enhanced these effects, respectively.

Conclusion

Ang-(1–7) prevents obstructive nephropathy by suppressing renal apoptosis and fibrosis, possibly by regulating TGF-β1/Smad signaling and cell cycle arrest via suppression of AT₁R expression. In addition, Ang-(1–7) increased and decreased ACE2 and TACE expression, respectively, which could potentially mediate a positive feedback mechanism via the Mas receptor.

Paeoniflorin exerts a nephroprotective effect on concanavalin A-induced damage through inhibition of macrophage infiltration

BACKGROUND

It is well established that macrophage infiltration is involved in concanavalin A (conA)-induced liver injury. However, the role of macrophages in conA-induced renal injury remains unknown. The aims of this study were to investigate macrophage infiltration in conA-induced renal injury and determine whether paeoniflorin (PF) could inhibit macrophage infiltration into the kidney.

METHODS

BALB/C mice were pre-treated with or without PF 2 h (h) before conA injection. At 8 h after con A injection, all the mice were sacrificed; The liver and kidney histology were studied. The renal CD68 expression was detected by immunohistochemical and real-time PCR analysis. The level of expression of C-X-C chemokine receptor type 3 (CXCR3) was analyzed by western blot, immunohistochemical and real-time PCR. The pathophysiological involvement of CXCR3 in macrophage infiltration were investigated using dual-colour immunofluorescence microscopy.

RESULTS

PF administration significantly reduced the elevated serum levels of alanine transaminase (ALT), blood urea nitrogen (BUN), creatinine (Cr) and the severity of liver and renal damage compared with that in the conA-vehicle group. PF administration inhibited the increase in renal IL1β mRNA expression and concentration. Furthermore, immunohistochemical analysis showed that macrophages secreted CXCR3 in the kidneys of the conA-vehicle mice. Immunofluorescence microscopy demonstrated CXCR3 bound tightly to C-X-C motif ligand 11 (CXCL11) in the kidneys of the conA-vehicle mice and showed that PF treatment could suppress CXCR3/CXCL11 over-activation.

CONCLUSIONS

Macrophage infiltration was a notable pathological change in the kidneys of conA-treated mice. PF administration attenuated conA-induced renal damage, at least in part, by inhibiting the over-activated CXCR3/CXCL11 signal axis.

Stem cell conditioned culture media attenuated albumin-induced epithelial-mesenchymal transition in renal tubular cells

Background

Proteinuria-induced epithelial-mesenchymal transition (EMT) plays an important role in progressive renal tubulointerstitial fibrosis in chronic renal disease. Stem cell therapy has been used for different diseases. Stem cell conditioned culture media (SCM) exhibits similar beneficial effects as stem cell therapy. The present study tested the hypothesis that SCM inhibits albumin-induced EMT in cultured renal tubular cells.

Methods

Rat renal tubular cells were treated with/without albumin (20 μmg/ml) plus SCM or control cell media (CCM). EMT markers and inflammatory factors were measured by Western blot and fluorescent images.

Results

Albumin induced EMT as shown by significant decreases in levels of epithelial marker E-cadherin, increases in mesenchymal markers fibroblast-specific protein 1 and α-smooth muscle actin, and elevations in collagen I. SCM inhibited all these changes. Meanwhile, albumin induced NF-κB translocation from cytosol into nucleus and that SCM blocked the nuclear translocation of NF-κB. Albumin also increased the levels of pro-inflammatory factor monocyte chemoattractant protein-1 (MCP)-1 by nearly 30 fold compared with control. SCM almost abolished albumin-induced increase of MCP-1.

Conclusion

These results suggest that SCM attenuated albumin-induced EMT in renal tubular cells via inhibiting activation of inflammatory factors, which may serve as a new therapeutic approach for chronic kidney diseases.

Wnt/β-catenin signaling and kidney fibrosis

Wnt/β-catenin signaling is an evolutionarily conserved, highly complex, key developmental pathway that regulates cell fate, organ development, tissue homeostasis, as well as injury and repair. Although relatively silent in normal adult kidney, Wnt/β-catenin signaling is re-activated after renal injury in a wide variety of animal models and in human kidney disorders. Whereas some data point to a protective role of this signaling in healing and repair after acute kidney injury, increasing evidence suggests that sustained activation of Wnt/β-catenin is associated with the development and progression of renal fibrotic lesions. In kidney cells, Wnt/β-catenin promotes the expression of numerous fibrosis-related genes such as Snail1, plasminogen activator inhibitor-1, and matrix metalloproteinase-7. Recent studies also indicate that multiple components of the renin-angiotensin system are the direct downstream targets of Wnt/β-catenin. Consistently, inhibition of Wnt/β-catenin signaling by an assortment of strategies ameliorates kidney injury and mitigates renal fibrotic lesions in various models of chronic kidney disease, suggesting that targeting this signaling could be a plausible strategy for therapeutic intervention. In this mini review, we will briefly discuss the regulation, downstream targets, and mechanisms of Wnt/β-catenin signaling in the pathogenesis of kidney fibrosis.

Encapsulating peritoneal sclerosis in children

Encapsulating peritoneal sclerosis (EPS) is a rare but extremely serious complication of peritoneal dialysis (PD). While EPS has been well recognized in adults on long-term PD, and children can spend many years on PD before a transplant becomes available, only a small number of children with EPS have been described. Two European pediatric registries have recently reported on the prevalence, potential risk factors and outcomes of EPS in children. Although the prevalence of EPS is comparable to that published in adult registries, the outcome of pediatric EPS is significantly better and carries a lower mortality. All studies have shown a greater risk of EPS with a longer dialysis vintage, but it is not known why some individuals are susceptible to EPS development. In this review we discuss current views on the epidemiology, pathogenesis and management strategies for EPS. The hope of the authors is that this review will alert pediatric nephrologists to this rare but extremely serious complication of chronic PD. In the future, collaborative research and the establishment of a pediatric EPS registry may be of importance in helping pediatric nephrologists to recognize the early warning signs of EPS development and thereby to develop strategies for its prevention and optimal management.

Paricalcitol protects against TGF-β1-induced fibrotic responses in hypoxia and stabilises HIF-α in renal epithelia

Epithelial injury and tubulointerstitial fibrosis (TIF) within a hypoxic microenvironment are associated with progressive loss of renal function in chronic kidney disease [CKD]. Transforming growth factor beta-1 (TGF-β1) is an important mediator of renal fibrosis. Growing evidence suggests that Vitamin D [1,25-(OH)2D] and its analogues may have a renoprotective effect in CKD. Here we examined the protective effect of the vitamin D analogue paricalcitol [PC; 19-nor-1α,3β,25-trihydroxy-9,10-secoergosta-5(Z),7(E) 22(E)-triene] on the responses of human renal epithelial cells to TGF-β1. PC attenuated TGF-β1-induced Smad 2 phosphorylation and upregulation of the Notch ligand Jagged-1, α-smooth muscle actin and thrombospondin-1 and prevented the TGF-β1-mediated loss of E-Cadherin. To mimic the hypoxic milieu of CKD we cultured renal epithelial cells in hypoxia [1% O2] and observed similar attenuation by PC of TGF-β1-induced fibrotic responses. Furthermore, in cells cultured in normoxia [21% O2], PC induced an accumulation of hypoxia-inducible transcription factors (HIF) 1α and HIF-2α in a time and concentration [1 µM-2 µM] dependent manner. Here, PC-induced HIF stabilisation was dependent on activation of the PI-3Kinase pathway. This is the first study to demonstrate regulation of the HIF pathway by PC which may have importance in the mechanism underlying renoprotection by PC.

Vitamin D in inflammatory diseases

Changes in vitamin D serum levels have been associated with inflammatory diseases, such as inflammatory bowel disease (IBD), rheumatoid arthritis, systemic lupus erythematosus, multiple sclerosis (MS), atherosclerosis, or asthma. Genome- and transcriptome-wide studies indicate that vitamin D signaling modulates many inflammatory responses on several levels. This includes (i) the regulation of the expression of genes which generate pro-inflammatory mediators, such as cyclooxygenases or 5-lipoxygenase, (ii) the interference with transcription factors, such as NF-κB, which regulate the expression of inflammatory genes and (iii) the activation of signaling cascades, such as MAP kinases which mediate inflammatory responses. Vitamin D targets various tissues and cell types, a number of which belong to the immune system, such as monocytes/macrophages, dendritic cells (DCs) as well as B- and T cells, leading to individual responses of each cell type. One hallmark of these specific vitamin D effects is the cell-type specific regulation of genes involved in the regulation of inflammatory processes and the interplay between vitamin D signaling and other signaling cascades involved in inflammation. An important task in the near future will be the elucidation of the regulatory mechanisms that are involved in the regulation of inflammatory responses by vitamin D on the molecular level by the use of techniques such as chromatin immunoprecipitation (ChIP), ChIP-seq, and FAIRE-seq.

Vitamin D and chronic kidney disease

Chronic kidney disease (CKD) has been recognized as a significant global health problem because of the increased risk of total and cardiovascular morbidity and mortality. Vitamin D deficiency or insufficiency is common in patients with CKD, and serum levels of vitamin D appear to have an inverse correlation with kidney function. Growing evidence has indicated that vitamin D deficiency may contribute to deteriorating renal function, as well as increased morbidity and mortality in patients with CKD. Recent studies have suggested that treatment with active vitamin D or its analogues can ameliorate renal injury by reducing fibrosis, apoptosis, and inflammation in animal models; this treatment also decreases proteinuria and mortality in patients with CKD. These renoprotective effects of vitamin D treatment are far beyond its classical role in the maintenance of bone and mineral metabolism, in addition to its pleiotropic effects on extra-mineral metabolism. In this review, we discuss the altered metabolism of vitamin D in kidney disease, and the potential renoprotective mechanisms of vitamin D in experimental and clinical studies. In addition, issues regarding the effects of vitamin D treatment on clinical outcomes are discussed.

The role of heredity in pterygium development

Several risk factors, which include heredity, ultra-violet (UV) light and chronic inflammation, contribute to pterygium development. However, there is no report integrating these factors in the pathogenesis of pterygium. The aim of this review is to describe the connection between heredity, UV, and inflammation in pterygium development. Existing reports indicate that sunlight exposure is the main factor in pterygium occurrence by inducing growth factor production or chronic inflammation or DNA damage. Heredity may be a factor. Our studies on factors in pterygium occurrence and recurrence identify that heredity is crucial for pterygium to develop, and that sunlight is only a trigger, and that chronic inflammation promotes pterygium enlargement. We propose that genetic factors may interfere with the control of fibrovascular proliferation while UV light or (sunlight) most likely only triggers pterygium development by inducing growth factors which promote vibrant fibrovascular proliferation in predisposed individuals. It also just triggers inflammation and collagenolysis, which may be promoters of the enlargement of the fibrovascular mass. Pterygium probably occurs in the presence of exuberant collagen production and profuse neovascularisation.

Paricalcitol ameliorates epithelial-to-mesenchymal transition in the peritoneal mesothelium

BACKGROUND

The purpose of the present study was to examine the effectiveness of paricalcitol for the prevention of epithelial-to-mesenchymal transition (EMT).

MATERIALS AND METHODS

Human peritoneal mesothelial cells (HPMCs) were cultured in media containing transforming growth factor β1 (TGF-β1) with or without paricalcitol. Forty-two male Sprague-Dawley rats were divided into three groups. In the control group, the catheter was inserted but no dialysate was infused. The peritoneal dialysis (PD) group was infused with a conventional 4.25% dialysis solution. The paricalcitol group was infused with 4.25% dialysis solution and cotreated with paricalcitol.

RESULTS

Exposure of HPMCs to TGF-β1 decreased the protein level of the epithelial cell marker and increased the expression levels of the mesenchymal markers. Cotreatment with paricalcitol increased the protein levels of the epithelial cell marker and decreased those of mesenchymal markers compared with their levels in cells treated with TGF-β1 alone. Exposure of HPMCs to TGF-β1 significantly increased the phosphorylation of Smad2 and Smad3. Cotreatment with paricalcitol significantly decreased the phosphorylation of Smad2 and Smad3 compared with that of cells treated with TGF-β1 alone. After 8 weeks of experimental PD in rats, the thickness of the peritoneal membrane in the PD group was significantly increased compared with that of the control group. Cotreatment with paricalcitol decreased peritoneal thickness.

CONCLUSION

The present study showed that paricalcitol attenuates the TGF-β1-induced EMT in peritoneal mesothelial cells. We suggest that paricalcitol may preserve peritoneal mesothelial cells during PD and could thus be of value for the success of long-term PD.

Selective vitamin D receptor activation as anti-inflammatory target in chronic kidney disease

Paricalcitol, a selective vitamin D receptor (VDR) activator used for treatment of secondary hyperparathyroidism in chronic kidney disease (CKD), has been associated with survival advantages, suggesting that this drug, beyond its ability to suppress parathyroid hormone, may have additional beneficial actions. In this prospective, nonrandomised, open-label, proof-of-concept study, we evaluated the hypothesis that selective vitamin D receptor activation with paricalcitol is an effective target to modulate inflammation in CKD patients. Eight patients with an estimated glomerular filtration rate between 15 and 44 mL/min/1.73 m² and an intact parathyroid hormone (PTH) level higher than 110 pg/mL received oral paricalcitol (1 μg/48 hours) as therapy for secondary hyperparathyroidism. Nine patients matched by age, sex, and stage of CKD, but a PTH level <110 pg/mL, were enrolled as a control group. Our results show that five months of paricalcitol administration were associated with a reduction in serum concentrations of hs-CRP (13.9%, P < 0.01), TNF-α (11.9%, P = 0.01), and IL-6 (7%, P < 0.05), with a nonsignificant increase of IL-10 by 16%. In addition, mRNA expression levels of the TNFα and IL-6 genes in peripheral blood mononuclear cells decreased significantly by 30.8% (P = 0.01) and 35.4% (P = 0.01), respectively. In conclusion, selective VDR activation is an effective target to modulate inflammation in CKD.