Cardiovascular calcification in patients with end-stage renal disease

Implementation of Proteomics Biomarkers in Nephrology: From Animal Models to Human Application?

Preclinical animal models are extensively used in nephrology. In this review, the utility of performing proteome analysis of kidney tissue or urine in such models and transfer of the results to human application has been assessed. Analysis of the literature identified 68 relevant publications. Pathway analysis of the reported proteins clearly indicated links with known biological processes in kidney disease providing validation of the observed changes in the preclinical models. However, although most studies focused on the identification of early markers of kidney disease or prediction of its progression, none of the identified makers has made it to substantial validation in the clinic or at least in human samples. Especially in renal disease where urine is an abundant source of biomarkers of diseases of the kidney and the urinary tract, it therefore appears that the focus should be on human material based discovery studies. In contrast, the most valid information of proteome analysis of preclinical models in nephrology for translation in human disease resides in studies focusing on drug evaluation, both efficacy for translation to the clinic and for mechanistic insight.

Cellular mechanosensitivity to substrate stiffness decreases with increasing dissimilarity to cell stiffness

Computational modelling has received increasing attention to investigate multi-scale coupled problems in micro-heterogeneous biological structures such as cells. In the current study, we investigated for a single cell the effects of (1) different cell-substrate attachment (2) and different substrate modulus [Formula: see text] on intracellular deformations. A fibroblast was geometrically reconstructed from confocal micrographs. Finite element models of the cell on a planar substrate were developed. Intracellular deformations due to substrate stretch of [Formula: see text], were assessed for: (1) cell-substrate attachment implemented as full basal contact (FC) and 124 focal adhesions (FA), respectively, and [Formula: see text]140 KPa and (2) [Formula: see text], 140, 1000, and 10,000 KPa, respectively, and FA attachment. The largest strains in cytosol, nucleus and cell membrane were higher for FC (1.35[Formula: see text], 0.235[Formula: see text] and 0.6[Formula: see text]) than for FA attachment (0.0952[Formula: see text], 0.0472[Formula: see text] and 0.05[Formula: see text]). For increasing [Formula: see text], the largest maximum principal strain was 4.4[Formula: see text], 5[Formula: see text], 5.3[Formula: see text] and 5.3[Formula: see text] in the membrane, 9.5[Formula: see text], 1.1[Formula: see text], 1.2[Formula: see text] and 1.2[Formula: see text] in the cytosol, and 4.5[Formula: see text], 5.3[Formula: see text], 5.7[Formula: see text] and 5.7[Formula: see text] in the nucleus. The results show (1) the importance of representing FA in cell models and (2) higher cellular mechanical sensitivity for substrate stiffness changes in the range of cell stiffness. The latter indicates that matching substrate stiffness to cell stiffness, and moderate variation of the former is very effective for controlled variation of cell deformation. The developed methodology is useful for parametric studies on cellular mechanics to obtain quantitative data of subcellular strains and stresses that cannot easily be measured experimentally.

Hemodialysis immediately after cardiac catheterization is a risk factor for intradialytic hypotension

Many hemodialysis clinicians have noticed that patients frequently develop intradialytic hypotension (IDH) immediately after cardiac catheterization (CC). However, precise data about the incidence of IDH immediately after CC are scarce. This study involved a single-center, retrospective, cross-sectional design. We reviewed the medical records of all HD patients who underwent CC between January 2009 and March 2012 at Hiroshima Prefectural Hospital. IDH was defined as a fall of systolic blood pressure of more than 20 mm Hg or a fall of mean blood pressure of more than 10 mm Hg, with symptoms according to the K/DOQI criteria. Data on a total of 112 patients were obtained: 64 patients commenced HD immediately after CC (IA group) and 48 patients underwent HD on the day after CC (ND group). The overall incidence of IDH was 34% (38/112). The incidence of IDH was significantly higher in the IA group than in the ND group (27/64, 42% vs. 11/48, 23%; P < 0.05). Multivariate logistic regression analysis showed that IA (odds ratio, 5.39; 95% confidence interval, 1.76 to 16.49; P < 0.01), coronary stenosis (odds ratio, 4.16; 95% confidence interval, 1.49 to 11.64; P < 0.05) were independently associated with IDH. This study revealed that HD immediately after CC is associated with a higher incidence of IDH. Clinicians should consider that HD following CC be scheduled for the next day, especially in patients with coronary stenosis.

Identification of nestin as a urinary biomarker for acute kidney injury

OBJECTIVES

Acute kidney injury (AKI) is a common complication in hospitalized patients and the incidence of AKI is rapidly increasing. Despite the advances in treatment of AKI, many patients still progress to end-stage renal disease and depend on dialysis. Therefore, early diagnosis and adequate treatment of AKI could improve prognosis.

METHODS

We established rat models of AKI induced by cisplatin nephrotoxicity and renal ischemia-reperfusion (I/R). Urine samples were collected, labeled with isobaric tags for relative and absolute quantification agents, and then subjected to nano-LC-MS/MS-based proteomic analysis. Results of the proteomic study were confirmed by Western blot. We also performed RNAi to silence nestin and investigate its role in renal I/R injury. We then validated its clinical application by studying urine nestin levels in AKI patients with cardiovascular surgeries.

RESULTS

Our proteomic analysis showed that fetuin-A, nestin, hamartin and T-kininogen were differentially expressed in the urine samples of rats after cisplatin or I/R treatment. Western blot confirmed the differential expression of these proteins in animal models and ELISA confirmed the differential expression of nestin in human urine samples. To explore the expression of nestin in the development of AKI, our results showed that nestin was primarily detected in the glomeruli and barely detected in tubular cells but increased in tubular cells during I/R- and cisplatin-induced AKI. The urine nestin-to-creatinine ratio increased earlier than serum creatinine in AKI patients with postcardiovascular surgeries. The role of nestin in AKI might be related to the p53 signaling pathway.

CONCLUSIONS

Thus, our results demonstrated that urinary nestin could be a urinary biomarker for patients with AKI and its role in AKI might be related to the p53 signaling pathway.

Trichostatin A, an HDAC class I/II inhibitor, promotes Pi-induced vascular calcification via up-regulation of the expression of alkaline phosphatase

AIM

Vascular calcification, a major complication of chronic kidney disease (CKD), refers to the mineralization of vascular smooth muscle cells (VSMCs), resulting from a phenotypic change towards osteoblast-like cells. Histone deacetylase inhibitors (HDIs), potential therapeutic agents for CKD, are known to promote the differentiation and mineralization of osteoblasts. In this study, we aimed to determine the effects of an HDI on the phenotypic change of VSMCs and the development of vascular calcification.

METHODS

The effect of trichostatin A (TSA), an HDI, on human aortic smooth muscle cells (HASMCs) was determined. The mineralization of HASMCs was induced by inorganic phosphorus (Pi), and was confirmed by quantitation of Ca levels and by von Kossa staining. Furthermore, we examined the effect of alkaline phosphatase (ALP) suppression using siRNA on Pi-induced vascular calcification in the presence or absence of TSA.

RESULTS

TSA increased the expression and activity of ALP in HASMCs at a concentration which showed an inhibitory effect of histone deacetylase (HDAC) activity but not on cell viability. Moreover, TSA promoted the Pi-induced mineralization of HASMCs. In addition, both phosphonoformic acid (PFA), which is a sodium-dependent phosphate transporter inhibitor, and suppression of ALP expression by siRNA markedly inhibited the TSA-promoted mineralization of HASMCs.

CONCLUSION

These data show that inhibition of HDAC activity promotes Pi-induced vascular calcification via the up-regulation of ALP expression. Taken together, HDIs may increase the risk of vascular calcification in CKD patients.

Finite-element modeling of viscoelastic cells during high-frequency cyclic strain

Mechanotransduction refers to the mechanisms by which cells sense and respond to local loads and forces. The process of mechanotransduction plays an important role both in maintaining tissue viability and in remodeling to repair damage; moreover, it may be involved in the initiation and progression of diseases such as osteoarthritis and osteoporosis. An understanding of the mechanisms by which cells respond to surrounding tissue matrices or artificial biomaterials is crucial in regenerative medicine and in influencing cellular differentiation. Recent studies have shown that some cells may be most sensitive to low-amplitude, high-frequency (i.e., 1-100 Hz) mechanical stimulation. Advances in finite-element modeling have made it possible to simulate high-frequency mechanical loading of cells. We have developed a viscoelastic finite-element model of an osteoblastic cell (including cytoskeletal actin stress fibers), attached to an elastomeric membrane undergoing cyclic isotropic radial strain with a peak value of 1,000 µstrain. The results indicate that cells experience significant stress and strain amplification when undergoing high-frequency strain, with peak values of cytoplasmic strain five times higher at 45 Hz than at 1 Hz, and peak Von Mises stress in the nucleus increased by a factor of two. Focal stress and strain amplification in cells undergoing high-frequency mechanical stimulation may play an important role in mechanotransduction.

Phenylacetic acid stimulates reactive oxygen species generation and tumor necrosis factor-α secretion in vascular endothelial cells

Tumor necrosis factor (TNF)-α and oxidative stress are considered to play crucial roles in atherosclerosis and vascular calcification. "Uremic toxins" detected in patients with chronic kidney disease (CKD) could cause impaired signal transduction and dysfunction in many organs. Since phenylacetic acid (PAA), identified as one of the uremic toxins, has an inhibiting property of monocytes as well as osteoblastic cells, we examined the effects of PAA on TNF-α secretion and oxidative stress in vascular endothelial cells. In human aortic endothelial cells, TNF-α secretion was assessed after treatment with PAA using an ELISA kit and following the manufacturer's instructions. For determination of reactive oxygen species (ROS), 8-hydroxydeoxyguanosine (8-OHdG) in the culture medium was measured in the presence or absence of PAA. Treatment with PAA in aortic endothelial cells for 24 h significantly stimulated TNF-α secretion in a dose-dependent manner ranging between 0.5 and 5 mM. On the other hand, the 8-OHdG level in the culture medium was significantly increased in the cells incubated with 1 mM PAA for 12 h. To determine if PAA-induced TNF-α secretion is mediated by ROS production, the effect of free radical scavenger 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPOL) was examined. It was found that PAA-induced TNF-α secretion was significantly inhibited by TEMPOL. Our findings indicate that PAA stimulates TNF-α secretion at least in part through ROS production in aortic endothelial cells. The plasma PAA level was reported to be approximately 3.5 mM in end-stage CKD patients, whereas it was <5 µM in healthy subjects; thus, PAA could be involved in the pathological changes of the vasculature in CKD.

Elastin degradation accelerates phosphate-induced mineralization of vascular smooth muscle cells

Medial layer vascular calcification is common in patients with end-stage kidney disease. Inorganic phosphate has been shown to accelerate the transformation of vascular smooth muscle cells (VSMCs) into osteoblast-like cells, which is thought to be a major process of medial layer calcification. Although elastin degradation is associated with medial layer calcification, the linkage between elastin degradation and the transformation of VSMCs remains to be clarified. We investigated the involvement of elastin degradation in the transformation of VSMCs. Rat VSMCs were isolated and cultured with a normal- (NP, 1.0 mM) or high- (HP, 2.5 mM) phosphate medium. An elastin-derived peptide, alpha-elastin (500 microg/ml), was also added to the normal- (NP + E) or high- (HP + E) phosphate medium. After a culture period of 2 weeks, von Kossa staining revealed mineralization in the HP group, which was accelerated by alpha-elastin, whereas alpha-elastin did not affect the mineralization at a normal phosphate concentration. The gene expression of osteoblastic differentiation factors, i.e., Runx2 or osteocalcin (OC), in VSMCs was significantly increased in the HP (Runx2 P < 0.05, OC P < 0.05) and HP + E (OC P < 0.05) groups compared with the NP and NP + E groups. Both gene and protein expressions of tissue-nonspecific alkaline phosphatase (TNAP) were significantly increased in the HP group compared with the NP and NP + E groups (P < 0.01, respectively). This increment was augmented in the HP + E group (P < 0.01). These results suggest that elastin degradation would accelerate or stabilize the process of VSMC transformation, which is induced by high phosphate through the upregulation of TNAP.

Superoxide production: a procalcifying cell signalling event in osteoblastic differentiation of vascular smooth muscle cells exposed to calcification media

Recent studies showed that hydrogen peroxide (H(2)O(2)) enhanced bone markers expression in vascular smooth muscle cells (VSMCs) implicated in osteoblastic differentiation. This study aimed at investigating the role of NAD(P)H oxidase in vascular calcification processes. A7r5 rat VSMCs were incubated with beta-glycerophosphate (10 mm) or uremic serum to induce a diffuse mineralization. H(2)O(2) production by VSMCs was determinated by chemiluminescence. NAD(P)H oxidase sub-unit (p22(phox)), Cbfa-1, ERK phosphorylation and bone alkaline phosphatase (ALP) expressions were measured by Western blotting. VSMCs exhibited higher production of H(2)O(2) and early expression of p22(phox) with beta-glycerophosphate or uremic serum within 24 h of treatment. beta-glycerophosphate-induced oxidative stress was associated with Cbfa-1 expression followed by ALP expression and activity, meanwhile the VSMCs expressing ALP diffusely calcified their extracellular matrix. Interestingly, diphenyleneiodonium partly prevented the osteoblastic differentiation. Results from this model strongly suggest a major implication of vascular NAD(P)H oxidase in vascular calcification supported by VSMCs osteoblastic differentiation.

Serum fetuin--a concentrations are inversely related to cytokine concentrations in patients with chronic renal failure

BACKGROUND/AIMS

A close relationship exists between inflammation and vascular calcification. Although fetuin-A is known to be an inhibitor of calcification, studies correlating levels of this glycoprotein to markers of inflammation are limited. To understand these relationships, we investigated the relationship between serum fetuin-A and proinflammatory cytokine levels in patients with chronic renal failure (CRF).

METHODS

Thirty-two patients on haemodialysis (HD), 32 conservatively managed chronic kidney disease (CKD) patients and a control group of 25 subjects with normal renal function were enrolled in this study. Serum fetuin-A, IL-1beta, IL-6 and TNF-alpha levels were measured by ELISA. Correlations between serum fetuin-A and IL-1beta, IL-6 and TNF-alpha concentrations were investigated by the Spearman correlation test.

RESULTS

In 64 CRF patients (on HD and with CKD), serum fetuin-A was significantly and inversely related to IL-1beta (P<0.001), IL-6 (P=0.025) and TNF-alpha levels (P=0.007), respectively. The serum fetuin-A levels of the control subjects were not significantly correlated to levels of the inflammatory markers IL-1beta, IL-6 and TNF-alpha (P=0.551, 0.985 and 0.984, respectively).

CONCLUSION

The negative correlation between serum fetuin-A and cytokine concentrations in CRF patients supports the hypothesis of inflammation-dependent down-regulation of fetuin-A expression.

Exosomal Fetuin-A identified by proteomics: a novel urinary biomarker for detecting acute kidney injury

Urinary exosomes containing apical membrane and intracellular fluid are normally secreted into the urine from all nephron segments, and may carry protein markers of renal dysfunction and structural injury. We aimed to discover biomarkers in urinary exosomes to detect acute kidney injury (AKI), which has a high mortality and morbidity. Animals were injected with cisplatin. Urinary exosomes were isolated by differential centrifugation. Protein changes were evaluated by two-dimensional difference in gel electrophoresis and changed proteins were identified by mass spectrometry. The identified candidate biomarkers were validated by Western blotting in individual urine samples from rats subjected to cisplatin injection; bilateral ischemia and reperfusion (I/R); volume depletion; and intensive care unit (ICU) patients with and without AKI. We identified 18 proteins that were increased and nine proteins that were decreased 8 h after cisplatin injection. Most of the candidates could not be validated by Western blotting. However, exosomal Fetuin-A increased 52.5-fold at day 2 (1 day before serum creatinine increase and tubule damage) and remained elevated 51.5-fold at day 5 (peak renal injury) after cisplatin injection. By immunoelectron microscopy and elution studies, Fetuin-A was located inside urinary exosomes. Urinary Fetuin-A was increased 31.6-fold in the early phase (2-8 h) of I/R, but not in prerenal azotemia. Urinary exosomal Fetuin-A also increased in three ICU patients with AKI compared to the patients without AKI. We conclude that (1) proteomic analysis of urinary exosomes can provide biomarker candidates for the diagnosis of AKI and (2) urinary Fetuin-A might be a predictive biomarker of structural renal injury.