Individual dipeptidyl peptidase-4 inhibitors and acute kidney injury in patients with type 2 diabetes: A systematic review and network meta-analysis

This network meta-analysis of randomized controlled trials aimed to determine whether any individual dipeptidyl peptidase-4 (DPP-4) inhibitors increase the risk of acute kidney injury (AKI). The Medical Literature Analysis and Retrieval System Online via PubMed, the Cochrane Central Register of Controlled Trials and ClinicalTrials.gov were systematically searched to identify relevant studies. The primary outcome was AKI. A frequentist network meta-analysis was performed using a random-effects model to account for heterogeneity. Twenty-nine studies involving 56 117 participants were included. There were 918 cases of AKI (1.63%). The risk of bias was generally considered to be low. The only DPP-4 inhibitor that significantly increased the frequency of AKI when compared with placebo was sitagliptin (risk ratio 1.65, 95% confidence interval 1.22-2.23). However, because one study showed significant outliers in the funnel plot, in a highly heterogeneous population composed solely of patients undergoing surgery for coronary artery bypass graft, we conducted a post-hoc sensitivity analysis to exclude this study. The results showed no statistically significant difference in the risk of AKI between sitagliptin and placebo. Individual DPP-4 inhibitors do not appear to increase the risk of AKI. However, sitagliptin may be associated with AKI in patients with underlying severe cardiovascular disease.

Urate-Lowering Drugs and Muscle Injury: A Systematic Review and Network Meta-Analysis

Several urate-lowering drugs have been linked to muscle injury. This study investigated the association of oral urate-lowering drugs with the risk of muscle injury by performing a network meta-analysis of randomized and non-randomized controlled trials. A systematic search of MEDLINE, via PubMed, the ClinicalTrials.gov website, and the Cochrane Central Register of Controlled Trials was conducted to identify relevant studies with a primary outcome of "all muscle injuries." A random-effects model was used to perform a frequentist network meta-analysis to estimate whether there was significant heterogeneity among the studies. In total, 32 studies including 28,327 participants with 2694 (9.5%) "all muscle injuries" were assessed, and the overall risk of bias was judged to be low to moderate. No statistically significant differences were found between placebo and 6 urate-lowering therapies: allopurinol (risk ratio, RR, 1.05; 95% confidence interval, 95%CI, 0.63-1.73), febuxostat (RR 1.10, 95%CI 0.71-1.70), lesinurad (RR 7.00, 95%CI 0.31-160.36), lesinurad concomitant with allopurinol (RR 0.85, 95%CI 0.34-2.11), lesinurad concomitant with febuxostat (RR 1.97, 95%CI 0.55-7.03), and topiroxostat (RR 0.99, 95%CI 0.37-2.65). The findings suggest that there is little need to consider the risk of muscle injury when using urate-lowering drugs in the clinical setting.

Megalin is involved in angiotensinogen-induced, angiotensin II-mediated ERK1/2 signaling to activate Na + -H + exchanger 3 in proximal tubules

BACKGROUND

Kidney angiotensin (Ang) II is produced mainly from liver-derived, glomerular-filtered angiotensinogen (AGT). Podocyte injury has been reported to increase the kidney Ang II content and induce Na + retention depending on the function of megalin, a proximal tubular endocytosis receptor. However, how megalin regulates the renal content and action of Ang II remains elusive.

METHODS

We used a mass spectrometry-based, parallel reaction-monitoring assay to quantitate Ang II in plasma, urine, and kidney homogenate of kidney-specific conditional megalin knockout (MegKO) and control (Ctl) mice. We also evaluated the pathophysiological changes in both mouse genotypes under the basal condition and under the condition of increased glomerular filtration of AGT induced by administration of recombinant mouse AGT (rec-mAGT).

RESULTS

Under the basal condition, plasma and kidney Ang II levels were comparable in the two mouse groups. Ang II was detected abundantly in fresh spot urine in conditional MegKO mice. Megalin was also found to mediate the uptake of intravenously administered fluorescent Ang II by PTECs. Administration of rec-mAGT increased kidney Ang II, exerted renal extracellular signal-regulated kinase 1/2 (ERK1/2) signaling, activated proximal tubular Na + -H + exchanger 3 (NHE3), and decreased urinary Na + excretion in Ctl mice, whereas these changes were suppressed but urinary Ang II was increased in conditional MegKO mice.

CONCLUSION

Increased glomerular filtration of AGT is likely to augment Ang II production in the proximal tubular lumen. Thus, megalin-dependent Ang II uptake should be involved in the ERK1/2 signaling that activates proximal tubular NHE3 in vivo , thereby causing Na + retention.

Sodium Magnetic Resonance Imaging Shows Impairment of the Counter-current Multiplication System in Diabetic Mice Kidney

Key Points

23Na MRI allows us to noninvasively assess sodium distribution. We propose the utility of 23Na MRI for evaluating functional changes in diabetic kidney disease and not as a marker reflecting structural damage. 23Na MRI may be an early marker for structures beyond the glomeruli, enabling prompt intervention with novel efficacious tubule-targeting therapies.

Background

Sodium magnetic resonance imaging can noninvasively assess sodium distribution, specifically sodium concentration in the countercurrent multiplication system in the kidney, which forms a sodium concentration gradient from the cortex to the medulla, enabling efficient water reabsorption. This study aimed to investigate whether sodium magnetic resonance imaging can detect changes in sodium concentrations under normal conditions in mice and in disease models, such as a mouse model with diabetes mellitus.

Methods

We performed sodium and proton nuclear magnetic resonance imaging using a 9.4-T vertical standard-bore superconducting magnet.

Results

A condition of deep anesthesia, with widened breath intervals, or furosemide administration in 6-week-old C57BL/6JJcl mice showed a decrease in both tissue sodium concentrations in the medulla and sodium concentration gradients from the cortex to the medulla. Furthermore, sodium magnetic resonance imaging revealed reductions in the sodium concentration in the medulla and in the gradient from the cortex to the medulla in BKS.Cg-Leprdb+/+ Leprdb/Jcl mice at very early type 2 diabetes mellitus stages compared with corresponding control BKS.Cg-m+/m+/Jcl mice.

Conclusions

The kidneys of BKS.Cg-Leprdb+/+ Leprdb/Jcl mice aged 6 weeks showed impairments in the countercurrent multiplication system. We propose the utility of 23Na MRI for evaluating functional changes in diabetic kidney disease and not as a marker that reflects structural damage. Thus, 23Na MRI may be a potentially very early marker for structures beyond the glomerulus; this may prompt intervention with novel efficacious tubule-targeting therapies.

Assessing fluid volume and determining outcomes of acute heart failure using plasma human atrial natriuretic peptide

BACKGROUND

The post-dialysis plasma level of human atrial natriuretic peptide (hANP) reflects the fluid volume in patients on hemodialysis. The threshold hANP level is reportedly 100 pg/mL; however, the clinical usefulness of the threshold hANP level for volume control has not been sufficiently studied.

METHODS

We conducted a single-center, retrospective, observational study that included 156 hemodialysis patients without atrial fibrillation. First, we examined the usefulness of the threshold hANP level (100 pg/mL) for predicting hypoxemia due to congestion in a short-term observational study from December 30, 2015 to January 5, 2016. Subsequently, we conducted a 5-year follow-up study wherein the outcomes were hospitalization due to acute heart failure (AHF), development of cardiovascular diseases (CVD), and all-cause death. Finally, we collected echocardiography data to investigate the relationship between cardiac function and hANP.

RESULTS

Our short-term observational study showed that patients with an hANP level ≥ 100 pg/mL developed hypoxemia due to congestion (odds ratio, 3.52; 95% confidence interval, 1.06-11.71; P = 0.040). At the 5-year follow-up, patients with an hANP level ≥ 100 pg/mL had significantly higher rates of hospitalization due to AHF, CVD, and all-cause death based on the log-rank test (P = 0.003, P = 0.019, P < 0.001, respectively). Cardiac disfunctions were significantly associated with the high hANP level.

CONCLUSIONS

The hANP level is indicative of both fluid volume and cardiac dysfunction. A threshold hANP level of 100 pg/mL can serve as a predictive marker for AHF and a practical indicator for volume control.

Efficacy of Low-Protein Rice for Dietary Protein Restriction in CKD Patients: A Multicenter, Randomized, Controlled Study

Background

The benefits of dietary protein restriction in CKD remain unclear, largely due to inadequate adherence in most clinical trials. We examined whether low-protein rice (LPR) previously developed to reduce the protein content of rice, a major staple food, would help improve adherence to dietary protein restriction.

Methods

This open-label, multicenter, randomized, controlled trial evaluated the efficacy of LPR use for reducing dietary protein intake (DPI) in patients with CKD stages G3aA2-G4. Participants were randomly assigned in a 1:1 ratio to an LPR or control group and were followed up for 24 weeks. Both groups received regular counseling by dietitians to help achieve a target DPI of 0.7 g/kg ideal body weight (IBW) per day. The amount of protein in LPR is about 4% of that in ordinary rice, and the participants in the LPR group were instructed to consume LPR with at least two meals per day. The primary outcome was estimated dietary protein intake (eDPI) determined using the Maroni formula. The secondary outcomes included creatinine clearance (CCr) and urinary protein on the basis of 24-hour urine collection.

Results

In total, 51 patients were randomized to either the LPR group or the control group. At baseline, mean age was 62.5 years, 70% were men, mean CCr was 52.0 ml/min, and mean eDPI was 0.99 g/kg IBW per day. At 24 weeks, mean eDPI decreased to 0.80 g/kg IBW per day in the LPR group and to 0.91 g/kg IBW per day in the control group, giving a between-group difference of 0.11 g/kg IBW per day (95% confidence interval, 0.03 to 0.19 g/kg IBW per day; P=0.006). There was no significant between-group difference in CCr, but urinary protein was lower at 24 weeks in the LPR group than in the control group.

Conclusions

LPR is a feasible tool for efficiently reducing DPI in patients with CKD.

Clinical Trial registry name and registration number

Randomized, Multicenter, Controlled Study for the Efficacy of Low-Protein Rice Diet in Patients with Chronic Kidney Disease, UMIN000015630.

Urinary A- and C-megalin predict progression of diabetic kidney disease: an exploratory retrospective cohort study

AIMS

Megalin, a proximal tubular endocytosis receptor, is excreted in urine in two forms: ectodomain (A-megalin) and full-length (C-megalin). We explored whether urinary megalin levels can be used as independent prognostic biomarkers in the progression of diabetic kidney disease (DKD).

METHODS

The associations between baseline urinary A-megalin/creatinine (Cr) and/or C-megalin/Cr levels and the subsequent estimated glomerular filtration rate (eGFR) slope were analyzed using a generalized estimating equation. Patients were categorized into higher or lower groups based on the optimal cutoff values, obtained from a receiver operating characteristic curve, of the two forms of urinary megalin.

RESULTS

We retrospectively analyzed 188 patients with type 2 diabetes. The eGFR slopes of the higher A-megalin/Cr and higher C-megalin/Cr groups were - 0.904 and -0.749 ml/min/1.73 m²/year steeper than those of the lower groups, respectively. Moreover, the eGFR slope was -1.888 ml/min/1.73 m²/year steeper in the group with both higher A- and higher C-megalin/Cr than in the other group. These results remained significant when adjusted for known urinary biomarkers (albumin, α₁-microglobulin, β₂-microglobulin, and N-acetyl-β-d-glucosaminidase).

CONCLUSIONS

Urinary A- and C-megalin/Cr levels are likely to be prognostic biomarkers in the progression of DKD independent of other urinary biomarkers.

Association between Anti-Osteoporotic Drugs and Risk of Acute Kidney Injury: A Cross-Sectional Study Using Disproportional Analysis and a Pharmacovigilance Database

The number of fractures related to osteoporosis is expected to increase. Therefore, clarifying the risk of acute kidney injury (AKI) associated with each type of anti-osteoporotic drug may avoid discontinuation of osteoporosis pharmacotherapy due to onset of AKI. This cross-sectional study using disproportional analysis and a pharmacovigilance database assessed the risk of AKI with various anti-osteoporotic drugs by analyzing data entered into the US Food and Drug Administration's Adverse Event Reporting System (FAERS) from April 2014 to March 2021 and the Medical Data Vision (MDV) database in Japan in November 2021. All anti-osteoporotic drugs were investigated, including bisphosphonates, selective estrogen receptor modulators, denosumab, romosozumab, abaloparatide, and teriparatide. In the analysis of FAERS data, disproportionality for decreasing AKI was observed for oral ibandronate [reporting odds ratios (ROR) 0.22, 95% confidence interval (CI) 0.09-0.45, P < 0.01], bazedoxifene (ROR 0.26, 95% CI 0.05-0.77, P = 0.01), and intravenous ibandronate (ROR 0.39, 95% CI 0.14-0.86, P = 0.01). In the analysis of the MDV data, the incidence of AKI was lower in patients taking intravenous ibandronate [odds ratio (OR) 0.22, 95% CI 0.06-0.89, P = 0.03], and the incidence of AKI was higher in patients taking oral alendronate (OR 2.40, 95% CI 2.08-2.77, P < 0.01). Risk of AKI may differ even among oral anti-osteoporotic drugs, and the evidence of this association should be assessed further in future drug safety studies. This article is protected by copyright. All rights reserved.

Association Between the Use of Sodium-Glucose Cotransporter-2 Inhibitors and Drug-Induced Acute Kidney Injury: Analysis of 2 Databases

The association between the use of sodium-glucose cotransporter-2 (SGLT-2) inhibitors and the occurrence of drug-induced kidney injury has not been evaluated. This study assessed whether the use of SGLT-2 inhibitors decreases the risk of drug-induced acute kidney injury (AKI) using the US Food and Drug Administration's Adverse Event Reporting System and the Medical Data Vision database. The occurrence of AKI in SGLT-2 inhibitor users and dipeptidyl peptidase-4 (DPP-4) inhibitor users was compared using both databases. In the US Food and Drug Administration's Adverse Event Reporting System analysis, disproportionality for AKI was observed between DPP-4 inhibitor users and SGLT-2 inhibitor users administered nonsteroidal anti-inflammatory drugs (reporting odds ratio, 0.65; 95%CI, 0.48-0.88; P < .01) and thiazide diuretics (reporting odds ratio, 0.78; 95%CI, 0.67-0.90; P < .01). In Medical Data Vision analysis, SGLT-2 inhibitor users administered nonsteroidal anti-inflammatory drugs (odds ratio [OR], 0.46; 95%CI, 0.41-0.53; P < .01), anti-herpes simplex virus drugs (OR, 0.20; 95%CI, 0.07-0.53; P < .01), thiazide diuretics (OR, 0.50; 95%CI, 0.36-0.71, P < .01), and loop diuretics (OR, 0.71; 95%CI, 0.62-0.83; P < .01) had a lower incidence of AKI compared with DPP-4 inhibitor users receiving the same drugs. No differences were observed in the risk of AKI between SGLT-2 and DPP-4 inhibitor users administered vancomycin and cisplatin in both databases. The use of SGLT-2 inhibitors might reduce the risk of drug-induced AKI caused by some drugs.

Development of an Add-on 23Na-MRI Radiofrequency Platform for a 1H-MRI System Using a Crossband Repeater: Proof-of-concept

²³Na-MRI provides information on Na⁺ content, and its application in the medical field has been highly anticipated. However, for existing clinical ¹H-MRI systems, its implementation requires an additional broadband RF transmitter, dedicated transceivers, and RF coils for Na⁺ imaging. However, a standard medical MRI system cannot often be modified to perform ²³Na imaging. We have developed an add-on crossband RF repeater system that enables ²³Na-MRI simply by inserting it into the magnet bore of an existing ¹H MRI. The three axis gradient fields controlled by the ¹H-MRI system were directly used for ²³Na imaging without any deformation. A crossband repeater is a common technique used for amateur radio. This concept was proven by a saline solution phantom and in vivo mouse experiments. This add-on RF platform is applicable to medical ¹H MRI systems and can enhance the application of ²³Na-MRI in clinical usage.

Association Between Steroid Use and Nephropathy in Patients Who Were Administered a Proton Pump Inhibitor: Analysis of the Japanese Adverse Event Report Database

This study used the Japanese Adverse Drug Event Report database to investigate whether steroid use decreases the risk of nephropathy in patients who were administered a proton pump inhibitor (PPI). Disproportionality of kidney injury was observed between patients who did and those who did not use steroids while taking lansoprazole (reporting odds ratio, 0.78; 95% confidence interval [CI], 0.65-0.93; P = .002) or rabeprazole (reporting odds ratio, 0.69; 95%CI, 0.53-0.89; P = .005). Multiple logistic regression analysis revealed a significantly negative association of kidney injury with steroid use (odds ratio [OR], 0.85; 95%CI, 0.75-0.96; P = .011) and a significantly positive association with the presence of chronic kidney disease (OR, 1.66; 95%CI, 1.44-1.90; P < .001), the presence of comorbidities that relate to nephropathy (OR, 1.43; 95%CI, 1.29-1.59; P < .001), male sex (OR, 1.25; 95%CI, 1.13-1.39; P < .001), and age ≥80 years (OR, 1.21; 95%CI, 1.07-1.37; P = .002). These findings suggest that steroid use may decrease the risk of proton pump inhibitor-induced nephropathy.

Rice Endosperm Protein Improves the Anti-Inflammatory Effects of High-Density Lipoprotein and Produces Lower Atherosclerotic Lesion Accelerated by the Renal Mass Reduction than Casein in a Mouse Model

Chronic kidney disease (CKD) impairs the anti-inflammatory effects of high-density lipoprotein (HDL) and increases cardiovascular mortality. Though the potential role of dietary interventions to manage HDL is well studied, the clinical trials aimed to increase HDL levels have failed to reduce cardiovascular risk, rendering HDL function to be explored as a more relevant clinical parameter. This study investigates the effects of rice endosperm protein (REP), a plant-based protein, on the anti-inflammatory properties of HDL and renal injury-driven atherosclerosis in comparison with casein, an animal protein.

Ten-week-old apolipoprotein E-deficient hyperlipidemic mice underwent uninephrectomy. The mice (n = 6 each) were pair-fed a normal casein-based diet or a REP-based diet (both with 20.0% protein content) for seven weeks. Atherosclerotic lesions were detected by en face Sudan IV staining of the aorta.

The number and sizes of the atherosclerotic lesions were significantly lower in the REP-based diet-fed group than the casein-based diet-fed group (p = 0.038). However, the REP-based diet neither elicited an ameliorative effect on kidney function or histology nor impacted the cholesterol profiles. Furthermore, HDL from the REP-based diet-fed mice significantly suppressed the inflammatory cytokine response of human umbilical vein endothelial cells than that from the casein-based diet-fed mice (MCP-1, p = 0.010; IL-6, p = 0.011; IL-1β, p = 0.028).

The REP-based diet has a higher potential to lessen the atherosclerotic lesions accelerated by renal mass reduction than a casein-based diet, which could be associated with the anti-inflammatory effects of HDL.

Effects of DPP-4 Inhibitors on Blood Glucose Variability in Japanese Patients with Type 2 Diabetes on Maintenance Hemodialysis: A Prospective Observational Exploratory Study

INTRODUCTION

The precise blood glucose (BG) profile of hemodialysis patients is unclear, as is the effectiveness of dipeptidyl peptidase-4 (DPP-4) inhibitors in hemodialysis patients with type 2 diabetes. Here, we used continuous glucose monitoring (CGM) to evaluate BG variability in these patients and to assess the efficacy of DPP-4 inhibitors, particularly during hemodialysis sessions and at nighttime (UMIN000012638).

METHODS

We examined BG profiles using CGM in 31 maintenance hemodialysis patients with type 2 diabetes. Differences between patients with and without DPP-4 inhibitors (n = 15 and 16, respectively) were analyzed using a linear mixed-effects model to assess changes in glucose levels in 5-min intervals.

RESULTS

The model revealed that DPP-4 inhibitor use was significantly associated with suppression of a rapid drop in glucose levels, both with and without adjustment for BG levels at the start of hemodialysis. Moreover, the model revealed that the two groups differed significantly in the pattern of changes in BG levels from 0:00 to 6:55 am. DPP-4 inhibitors suppressed the tendency for subsequent nocturnal hypoglycemia.

CONCLUSIONS

This prospective observational exploratory study showed that DPP-4 inhibitors could suppress BG variability during hemodialysis sessions as well as subsequent nocturnal changes in patients with type 2 diabetes.

TRIAL REGISTRATION

ClinicalTrials.gov identifier, UMIN000012638.

Correlation of prechemotherapy urinary megalin ectodomain (A-megalin) levels with the development of cisplatin-induced nephrotoxicity: a prospective observational study

Background

Cisplatin is a potent chemotherapeutic agent used to treat a variety of solid tumors. One of the major side effects of cisplatin is dose-limiting nephrotoxicity. We recently demonstrated that the renal uptake of cisplatin and resultant cisplatin-induced nephrotoxicity are mediated in part by megalin, an endocytic receptor in proximal tubule epithelial cells (PTECs). We also developed sandwich enzyme-linked immunosorbent assays to measure the megalin ectodomain (A-megalin) and full-length megalin (C-megalin) in urine using monoclonal antibodies against the amino- and carboxyl-termini of megalin, respectively. The present study examined the correlation of urinary megalin level with cisplatin-induced nephrotoxicity and its utility as a biomarker in patients with thoracic cancer.

Methods

This prospective observational study involved 45 chemotherapy-naïve patients scheduled to receive chemotherapy with ≥60 mg/m² cisplatin for histologically diagnosed small cell lung cancer, non-small cell lung cancer, or malignant pleural mesothelioma. Before and after the first course of chemotherapy, we measured urinary A- and C-megalin and other markers of PTEC injury, such as N-acetyl-β-D-glucosaminidase, α₁-microglobulin, β₂-microglobulin, neutrophil gelatinase-associated lipocalin, and liver-type fatty acid-binding protein, and compared the values with the change in the estimated glomerular filtration rate (eGFR) and clinical risk factors for renal impairment.

Results

A negative correlation was found between baseline urinary A-megalin levels and change in eGFR (r = − 0.458, P = 0.002). According to Kaplan–Meier survival curves, eGFR decline was associated with the baseline urinary A-megalin quartile (P = 0.038). In addition, according to the hazard ratios (HRs) for eGFR decline > 10 mL/min/1.73 m² calculated using a Cox proportional hazard model, the highest quartile had a significantly higher risk of eGFR decline compared with the lowest quartile (HR 7.243; 95% confidence interval 1.545–33.962). Other baseline urinary markers showed no correlation with eGFR decline.

Conclusions

This is the first report demonstrating that prechemotherapy urinary A-megalin levels are correlated with the development of cisplatin-induced nephrotoxicity. This finding has clinical implications for the identification of patients at risk for cisplatin-induced nephrotoxicity and the development of possible prophylactic therapies.

Higher estimated net endogenous acid production with lower intake of fruits and vegetables based on a dietary survey is associated with the progression of chronic kidney disease

Background

Dietary acid load has been suggested to mediate the progression of chronic kidney disease (CKD). However, it is unclear what kinds of foods are actually associated with dietary acid load in patients with CKD. The self-administered diet history questionnaire (DHQ), which semi-quantitatively assesses the dietary habits of Japanese individuals through 150 question items, can estimate average daily intake of various foods and nutrients during the previous month. Using the DHQ, we investigated the association of dietary acid load with CKD progression. We also analyzed the kinds of food that significantly affect dietary acid load.

Methods

Subjects were 96 outpatients with CKD (average estimated glomerular filtration rate [eGFR], 53.0 ± 18.1 ml/min/1.73 m²) at Niigata University Hospital, who had completed the DHQ in 2011. We calculated net endogenous acid production (NEAP) from potassium and protein intake evaluated by the DHQ in order to assess dietary acid load. CKD progression was assessed by comparing eGFR between 2008 and 2014.

Results

NEAP was not correlated with protein intake (r = 0.088, p = 0.398), but was negatively correlated with potassium intake (r = − 0.748, p < 0.001). Reduction in eGFR from 2008 to 2014 was estimated to be significantly greater in patients with higher NEAP (NEAP > 50.1 mEq/day, n = 45) than in those with lower NEAP (NEAP ≤50.1 mEq/day, n = 50) by 5.9 (95% confidence interval [95%CI], 0.1 to 11.6) ml/min/1.73 m². According to multiple logistic regression analysis, higher NEAP was significantly associated with lower intake of fruits (odds ratio [OR], 6.454; 95%CI, 2.19 to 19.00), green and yellow vegetables (OR, 5.18; 95%CI, 1.83 to14.66), and other vegetables (OR, 3.87; 95%CI, 1.29 to 11.62).

Conclusions

Elevated NEAP could be a risk factor for CKD progression. Low intake of fruits and vegetables would increase dietary acid load and might affect the progression of renal dysfunction in Japanese CKD patients.

Angiotensin receptor blocker vs ACE inhibitor effects on HDL functionality in patients on maintenance hemodialysis

BACKGROUND AND AIMS

Angiotensin receptor blockers (ARB) and angiotensin converting enzyme inhibitors (ACEI) reduce cardiovascular events in the general population. Maintenance hemodialysis (MHD) patients are at high cardiovascular risk but few studies have directly addressed the comparative efficacy of these drugs. MHD disrupts the normally atheroprotective actions of high density lipoprotein (HDL), therefore, we compared ACEI or ARB treatment on HDL functions in MHD.

METHODS AND RESULTS

HDL was isolated at the starting point (pre) and 3-6 months later (post) in 30 MHD randomly assigned to placebo, ramipril or valsartan. Outcomes included cholesterol efflux, inflammatory cytokine response, effects on Toll-like receptors (TLR), superoxide production, methylarginine and serum amyloid A (SAA) levels. HDL from ARB- or ACEI-treated subjects was more effective in maintaining efflux than HDL of placebo. HDL from ARB- or ACEI-treated subjects but not placebo lessened cellular superoxide production. In contrast, neither ARB nor ACEI improved HDL anti-inflammatory effect. Indeed, HDL of ACEI-treated subjects potentiated the cytokine responses in association with activation of TLR but did not alter the HDL content of methylarginines or SAA.

CONCLUSION

Both ACEI and ARB stabilized HDL cholesterol acceptor function and sustained cellular anti-oxidative effects but not anti-inflammatory effects, and ACEI-treatment instead amplified the HDL inflammatory response. The findings reveal possible utility of antagonizing angiotensin actions in MDH and suggest a possible mechanism for superiority of ARB vs ACEI in the setting of advanced kidney disease.

Kidney morphological parameters measured using noncontrast-enhanced steady-state free precession MRI with spatially selective inversion recovery pulse correlate with eGFR in patients with advanced CKD

BACKGROUND

It is well known that atrophic renal changes are associated with chronic kidney disease (CKD) progression, but conventional diagnostic imaging methods such as noncontrast-enhanced computed tomography and magnetic resonance imaging (MRI) have been insufficient for precisely assessing kidney function because they cannot clearly distinguish between the medulla and cortex. Hence, here we used noncontrast-enhanced steady-state free precession (SSFP) MRI with a spatially selective inversion recovery (IR) pulse to improve visibility for renal corticomedullary differentiation and evaluated the association between morphological parameters and kidney function in patients with CKD.

METHODS

Kidney corticomedullary contrast ratio, cortical and medullary areas, and minimal cortical thickness of 107 patients with CKD G1-G5 were measured using SSFP MRI with a spatially selective IR pulse and the association between these morphological parameters and kidney function were evaluated.

RESULTS

Corticomedullary contrast ratio was significantly improved on SSFP MRI compared with conventional in-phase T1-weighted gradient-echo MRI and positively correlated with estimated glomerular filtration ratio (eGFR), raw eGFR, and 24-h creatinine clearance. The medullary and cortical areas and minimal cortical thickness also positively correlated with those of kidney functional markers and the age. In patients with CKD and diabetes mellitus (DM), the correlation coefficients between raw eGFR and morphological parameters were higher than those in patients without DM, while minimal cortical thickness was larger in CKD patients with DM with a raw eGFR ≥ 45 mL/min.

CONCLUSION

Kidney morphological parameters measured with SSFP MRI were clearly correlated with kidney function in patients with CKD, including those with advanced kidney dysfunction.

Chronic kidney disease alters lipid trafficking and inflammatory responses in macrophages: effects of liver X receptor agonism

BACKGROUND

Our aim was to evaluate lipid trafficking and inflammatory response of macrophages exposed to lipoproteins from subjects with moderate to severe chronic kidney disease (CKD), and to investigate the potential benefits of activating cellular cholesterol transporters via liver X receptor (LXR) agonism.

METHODS

LDL and HDL were isolated by sequential density gradient ultracentrifugation of plasma from patients with stage 3-4 CKD and individuals without kidney disease (HDLCKD and HDLCont, respectively). Uptake of LDL, cholesterol efflux to HDL, and cellular inflammatory responses were assessed in human THP-1 cells. HDL effects on inflammatory markers (MCP-1, TNF-α, IL-1β), Toll-like receptors-2 (TLR-2) and - 4 (TLR-4), ATP-binding cassette class A transporter (ABCA1), NF-κB, extracellular signal regulated protein kinases 1/2 (ERK1/2) were assessed by RT-PCR and western blot before and after in vitro treatment with an LXR agonist.

RESULTS

There was no difference in macrophage uptake of LDL isolated from CKD versus controls. By contrast, HDCKD was significantly less effective than HDLCont in accepting cholesterol from cholesterol-enriched macrophages (median 20.8% [IQR 16.1-23.7] vs control (26.5% [IQR 19.6-28.5]; p = 0.008). LXR agonist upregulated ABCA1 expression and increased cholesterol efflux to HDL of both normal and CKD subjects, although the latter continued to show lower efflux capacity. HDLCKD increased macrophage cytokine response (TNF-α, MCP-1, IL-1β, and NF-κB) versus HDLCont. The heightened cytokine response to HDLCKD was further amplified in cells treated with LXR agonist. The LXR-augmentation of inflammation was associated with increased TLR-2 and TLR-4 and ERK1/2.

CONCLUSIONS

Moderate to severe impairment in kidney function promotes foam cell formation that reflects impairment in cholesterol acceptor function of HDLCKD. Activation of cellular cholesterol transporters by LXR agonism improves but does not normalize efflux to HDLCKD. However, LXR agonism actually increases the pro-inflammatory effects of HDLCKD through activation of TLRs and ERK1/2 pathways.

A Randomized, Double-Blind, Crossover Pilot Trial of Rice Endosperm Protein Supplementation in Maintenance Hemodialysis Patients

In maintenance hemodialysis (MHD) patients, low protein intake is associated with protein-energy wasting, a risk factor that affects outcome. However, increased protein intake may lead to hyperphosphatemia and hyperkalemia, which are also mortality risk factors. Here, we evaluated the safety and effects of purified rice endosperm protein (REP), which contains less phosphorus and potassium than soy and casein proteins, as a supplemental protein source for MHD patients. This randomized, double-blind, placebo-controlled, crossover pilot study of REP supplementation (5 g/day × 4 weeks) was carried out in 50 Japanese adult MHD patients (1 dropped out); the primary outcome was the change in the urea kinetic-based normalized protein catabolic rate (nPCR), an indicator of protein intake in MHD patients. Intention-to-treat analyses of 24 patients in the REP-first group and 25 in the placebo-first group showed that REP supplementation increased nPCR significantly by 0.07 g/kg/day (95% confidence interval, 0.03–0.11), whereas changes in serum phosphorus and potassium concentrations were not different from the placebo. REP supplementation did not show a significant effect on other nutritional or metabolic parameters and no specific complications. In conclusion, purified REP with efficient bioavailability may be safe and useful for dietary supplementation in MHD patients.

The Assessment of the Efficacy of Dipeptidyl Peptidase-4 Inhibitors in Patients with Glucocorticoid-induced Diabetes by Continuous Glucose Monitoring

Objective The administration of glucocorticoids usually causes a mild increase in fasting glucose levels and a greater dose-dependent increase in postprandial values in patients without pre-existing diabetes mellitus. Patients with persistent hyperglycemia due to glucocorticoid therapy sometimes require insulin therapy, which might result in increased weight gain and more episodes of hypoglycemia, some of which are severe. On the other hand, scant evidence is available on the efficacy of oral hypoglycemic agents in treating glucocorticoid-induced diabetes. In this study, we evaluated the efficacy of dipeptidyl peptidase (DPP)-4 inhibitors in patients with glucocorticoid-induced diabetes by continuous glucose monitoring (CGM). Methods We examined the glycemic profiles using CGM at baseline and 1-4 weeks after initiating DPP-4 inhibitor treatment in patients with newly developed glucocorticoid-induced diabetes. Results Eleven patients who had been diagnosed with kidney disease or other diseases with renal involvement were recruited for the present retrospective study. After starting DPP-4 inhibitors, the mean and standard deviation (SD) of the glucose level, and the mean amplitude of glycemic excursion (MAGE) were significantly improved in comparison to baseline. Furthermore, the area over the curve (AOC) for the glucose levels <70 mg/dL was not increased in comparison to baseline after the initiation of DPP-4 inhibitor treatment. The results indicate that the treatment of patients with glucocorticoid-induced diabetes using DPP-4 inhibitors can minimize the risk of hypoglycemia and reduce glucose variability. Conclusion DPP-4 inhibitors are potentially useful for blood glucose control in patients with glucocorticoid-induced diabetes.

Exocytosis-Mediated Urinary Full-Length Megalin Excretion Is Linked With the Pathogenesis of Diabetic Nephropathy

Efficient biomarkers for diabetic nephropathy (DN) have not been established. Using ELISA, we found previously that urinary levels of full-length megalin (C-megalin), a multiligand endocytic receptor in proximal tubules, was positively correlated with DN progression in patients with type 2 diabetes mellitus (T2DM). Here, we found that urinary extracellular vesicle (UEV) excretion and C-megalin content in UEVs or in their exosomal fraction increased along with the progression of the albuminuric stages in patients with T2DM. Cultured immortalized rat proximal tubule cells (IRPTCs) treated with fatty acid-free BSA or advanced glycation end product-modified BSA (AGE-BSA), endocytic ligands of megalin, increased EV excretion, and their C-megalin content. C-megalin excretion from IRPTCs via extracellular vesicles was significantly blocked by an exosome-specific inhibitor, GW4869, indicating that this excretion is mainly exocytosis-mediated. AGE-BSA treatment of IRPTCs caused apparent lysosomal dysfunction, which stimulated multivesicular body formation, resulting in increased exosomal C-megalin excretion. In a high-fat diet-induced, megalin-mediated kidney injury model in mice, urinary C-megalin excretion also increased via UEVs. Collectively, exocytosis-mediated urinary C-megalin excretion is associated with the development and progression of DN in patients with T2DM, particularly due to megalin-mediated lysosomal dysfunction in proximal tubules, and hence it could be a candidate biomarker linked with DN pathogenesis.

Megalin Blockade with Cilastatin Suppresses Drug-Induced Nephrotoxicity

Nephrotoxicity induced by antimicrobial or anticancer drugs is a serious clinical problem. Megalin, an endocytic receptor expressed at the apical membranes of proximal tubules, mediates the nephrotoxicity of aminoglycosides and colistin, key antimicrobials for multidrug-resistant organisms. The mechanisms underlying the nephrotoxicity induced by vancomycin, an antimicrobial for methicillin-resistant Staphylococcus aureus, and cisplatin, an important anticancer drug, are unknown, although the nephrotoxicity of these drugs and gentamicin, an aminoglycoside, is suppressed experimentally with cilastatin. In the clinical setting, cilastatin has been used safely to suppress dehydropeptidase-I-mediated renal metabolism of imipenem, a carbapenem antimicrobial, and thereby limit tubular injury. Here, we tested the hypothesis that cilastatin also blocks megalin-mediated uptake of vancomycin, cisplatin, colistin, and aminoglycosides, thereby limiting the nephrotoxicity of these drugs. Quartz crystal microbalance analysis showed that megalin also binds vancomycin and cisplatin and that cilastatin competes with megalin for binding to gentamicin, colistin, vancomycin, and cisplatin. In kidney-specific mosaic megalin knockout mice treated with colistin, vancomycin, or cisplatin, the megalin-replete proximal tubule epithelial cells exhibited signs of injury, whereas the megalin-deficient cells did not. Furthermore, concomitant cilastatin administration suppressed colistin-induced nephrotoxicity in C57BL/6J mice. Notably, cilastatin did not inhibit the antibacterial activity of gentamicin, colistin, or vancomycin in vitro, just as cilastatin did not affect the anticancer activity of cisplatin in previous studies. In conclusion, megalin blockade with cilastatin efficiently suppresses the nephrotoxicity induced by gentamicin, colistin, vancomycin, or cisplatin. Cilastatin may be a promising agent for inhibiting various forms of drug-induced nephrotoxicity mediated via megalin in the clinical setting.

Megalin-Mediated Tubuloglomerular Alterations in High-Fat Diet-Induced Kidney Disease

Obesity, an important risk factor for metabolic syndrome (MetS) and cardiovascular disease, is often complicated by CKD, which further increases cardiovascular risk and causes ESRD. To elucidate the mechanism underlying this relationship, we investigated the role of the endocytic receptor megalin in proximal tubule epithelial cells (PTECs). We studied a high-fat diet (HFD)-induced obesity/MetS model using kidney-specific mosaic megalin knockout (KO) mice. Compared with control littermates fed a normal-fat diet, control littermates fed an HFD for 12 weeks showed autolysosomal dysfunction with autophagy impairment and increased expression of hypertrophy, lipid peroxidation, and senescence markers in PTECs of the S2 segment, peritubular capillary rarefaction with localized interstitial fibrosis, and glomerular hypertrophy with mesangial expansion. These were ameliorated in HFD-fed megalin KO mice, even though these mice had the same levels of obesity, dyslipidemia, and hyperglycemia as HFD-fed control mice. Intravital renal imaging of HFD-fed wild-type mice also demonstrated the accumulation of autofluorescent lipofuscin-like substances in PTECs of the S2 segment, accompanied by focal narrowing of tubular lumens and peritubular capillaries. In cultured PTECs, fatty acid-rich albumin induced the increased expression of genes encoding PDGF-B and monocyte chemoattractant protein-1 via megalin, with large (auto)lysosome formation, compared with fatty acid-depleted albumin. Collectively, the megalin-mediated endocytic handling of glomerular-filtered (lipo)toxic substances appears to be involved primarily in hypertrophic and senescent PTEC injury with autophagy impairment, causing peritubular capillary damage and retrograde glomerular alterations in HFD-induced kidney disease. Megalin could be a therapeutic target for obesity/MetS-related CKD, independently of weight, dyslipidemia, and hyperglycemia modification.

Dysfunctional high-density lipoproteins in children with chronic kidney disease

OBJECTIVES

Our aim was to determine if chronic kidney disease (CKD) occurring in childhood impairs the normally vasoprotective functions of high-density lipoproteins (HDLs).

MATERIALS AND METHODS

HDLs were isolated from children with end-stage renal disease on dialysis (ESRD), children with moderate CKD and controls with normal kidney function. Macrophage response to HDLs was studied as expression of inflammatory markers (MCP-1, TNF-α, IL-1β) and chemotaxis. Human umbilical vein endothelial cells were used for expression of adhesion molecules (ICAM-1, VCAM-1, E-selectin) and adhesion. Cellular proliferation, apoptosis, and necrosis of endothelial cells were measured by MTS/PMS reagent-based assay, flow cytometry, and ELISA. Cholesterol efflux was assessed by gas chromatographic measurements of cholesterol in macrophages exposed to HDLs.

RESULTS

Compared with HDL(Control), HDL(CKD) and HDL(ESRD) heightened the cytokine response and disrupted macrophage chemotaxis. HDL(Control) reduced endothelial expression of ICAM-1, VCAM-1, E-selectin, whereas HDL(CKD) and HDL(ESRD) were less effective and showed reduced capacity to protect endothelial cells against monocyte adhesion. Compared with a dramatically enhanced endothelial proliferation following injurious stimulus by HDL(Control), neither HDL(CKD) nor HDL(ESRD) caused proliferative effects. HDLs of all three groups were equally protective against apoptosis assessed by flow cytometry and cleaved caspase-3 activity. Compared to HDL(Control), HDL(CKD) and HDL(ESRD) trended toward reduced capacity as cholesterol acceptors.

CONCLUSION

CKD in children impairs HDL function. Even in the absence of long-standing and concomitant risk factors, CKD alters specific HDL functions linked to control of inflammation and endothelial responses.

Dysfunctional high-density lipoprotein in patients on chronic hemodialysis

OBJECTIVES

This study examined the functionality of high-density lipoprotein (HDL) in individuals with end-stage renal disease on dialysis (ESRD-HD).

BACKGROUND

The high rate of cardiovascular disease (CVD) in chronic kidney disease is not explained by standard risk factors, especially in patients with ESRD-HD who appear resistant to benefits of statin therapy. HDL is antiatherogenic because it extracts tissue cholesterol and reduces inflammation.

METHODS

Cellular cholesterol efflux and inflammatory response were assessed in macrophages exposed to HDL of patients with ESRD-HD or controls.

RESULTS

HDL from patients with ESRD-HD was dramatically less effective than normal HDL in accepting cholesterol from macrophages (median 6.9%; interquartile range [IQR]: 1.4% to 10.2%) versus control (median 14.9%; IQR: 9.8% to 17.8%; p < 0.001). The profound efflux impairment was also seen in patients with ESRD-HD and diabetes compared with patients with diabetes without renal disease (median 8.1%; IQR: 3.3% to 12.9%) versus control (median 13.6%; IQR: 11.0% to 15.9%; p = 0.009). In vitro activation of cellular cholesterol transporters increased cholesterol efflux to both normal and uremic HDL. HDL of patients with ESRD-HD had reduced antichemotactic ability and increased macrophage cytokine response (tumor necrosis factor-alpha, interleukin-6, and interleukin-1-beta). HDL of patients with ESRD-HD on statin therapy had reduced inflammatory response while maintaining impaired cholesterol acceptor function. Interestingly, impaired HDL-mediated efflux did not correlate with circulating C-reactive protein levels or cellular inflammatory response.

CONCLUSIONS

These findings suggest that abnormal HDL capacity to mediate cholesterol efflux is a key driver of excess CVD in patients on chronic hemodialysis and may explain why statins have limited effect to decrease CV events. The findings also suggest cellular cholesterol transporters as potential therapeutic targets to decrease CV risk in this population.

Significance of urinary full-length and ectodomain forms of megalin in patients with type 2 diabetes

OBJECTIVE

Megalin, an endocytic receptor in proximal tubule cells, is involved in the mechanisms of albuminuria in diabetic nephropathy (DN). To develop efficient novel biomarkers associated with the pathogenesis of DN, we investigated urinary megalin excretion in type 2 diabetes.

RESEARCH DESIGN AND METHODS

Sandwich enzyme-linked immunosorbent assay systems were established with monoclonal antibodies against the NH(2) (amino [A]-megalin assay) and COOH (C-megalin assay) termini of megalin to analyze urinary forms of megalin in 68 patients with type 2 diabetes.

RESULTS

The A-megalin assay mainly detected a megalin ectodomain form in the soluble urinary fraction, whereas the C-megalin assay identified a full-length form in both soluble and insoluble fractions. Urinary C-megalin levels were significantly high in patients with normoalbuminuria, were elevated in line with increased albuminuria, and showed a better association with estimated glomerular filtration rate (eGFR) (<60 mL/min/1.73 m(2)) than did urinary albumin. In contrast, urinary A-megalin levels were increased in patients with normo- and microalbuminuria but not in those with macroalbuminuria. Urinary C-megalin levels were also positively associated with plasma inorganic phosphate and negatively with hemoglobin levels in those showing no features of bleeding and not taking vitamin D analogs, phosphate binders, or erythropoiesis-stimulating agents.

CONCLUSIONS

Urinary full-length megalin excretion as measured by the C-megalin assay is well associated with reduced eGFR and linked to the severity of DN, phosphate dysregulation, and anemia, whereas urinary excretion of megalin ectodomain as measured by the A-megalin assay may be associated with distinctive mechanisms of earlier DN in type 2 diabetes.

Macrophage polarization by angiotensin II-type 1 receptor aggravates renal injury-acceleration of atherosclerosis

OBJECTIVE

Angiotensin II is a major determinant of atherosclerosis. Although macrophages are the most abundant cells in atherosclerotic plaques and express angiotensin II type 1 receptor (AT1), the pathophysiologic role of macrophage AT1 in atherogenesis remains uncertain. We examined the contribution of macrophage AT1 to accelerated atherosclerosis in an angiotensin II-responsive setting induced by uninephrectomy (UNx).

METHODS AND RESULTS

AT1(-/-) or AT1(+/+) marrow from apolipoprotein E deficient (apoE(-/-)) mice was transplanted into recipient apoE(-/-) mice with subsequent UNx or sham operation: apoE(-/-)/AT1(+/+)→apoE(-/-)+sham; apoE(-/-)/AT1(+/+) →apoE(-/-)+UNx; apoE(-/-)/AT1(-/-)→apoE(-/-)+sham; apoE(-/-)/AT1(-/-)→apoE(-/-)+UNx. No differences in body weight, blood pressure, lipid profile, and serum creatinine were observed between the 2 UNx groups. ApoE(-/-)/AT1(+/+) →apoE(-/-)+UNx had significantly more atherosclerosis (16907±21473 versus 116071±8180 μm(2), P<0.05). By contrast, loss of macrophage AT1 which reduced local AT1 expression, prevented any effect of UNx on atherosclerosis (77174±9947 versus 75714±11333 μm(2), P=NS). Although UNx did not affect total macrophage content in the atheroma, lesions in apoE(-/-)/AT1(-/-)→apoE(-/-)+UNx had fewer classically activated macrophage phenotype (M1) and more alternatively activated phenotype (M2). Further, UNx did not affect plaque necrosis or apoptosis in apoE(-/-)/AT1(-/-)→apoE(-/-) whereas it significantly increased both (by 2- and 6-fold, respectively) in apoE(-/-)/AT1(+/+) →apoE(-/-) mice. Instead, apoE(-/-)/AT1(-/-)→apoE(-/-) had 5-fold-increase in macrophage-associated apoptotic bodies, indicating enhanced efferocytosis. In vitro studies confirmed blunted susceptibility to apoptosis, especially in M2 macrophages, and a more efficient phagocytic function of AT1(-/-) macrophages versus AT1(+/+).

CONCLUSIONS

AT1 receptor of bone marrow-derived macrophages worsens the extent and complexity of renal injury-induced atherosclerosis by shifting the macrophage phenotype to more M1 and less M2 through mechanisms that include increased apoptosis and impaired efferocytosis.

Role of megalin and cubilin in the metabolism of vitamin D(3)

Vitamin D deficiency is associated with various medical conditions including musculoskeletal disorders, infection, metabolic diseases, and cardiovascular disease. Megalin and cubilin, endocytic receptors in proximal tubule cells, are involved in the reabsorption of vitamin D binding protein from glomerular filtrates and the subsequent intracellular conversion of 25-hydroxyvitamin D(3) to biologically active 1α,25-dihydroxyvitamin D(3). Dysfunction of these receptors, which is commonly found in patients with diabetic nephropathy, even at early stages, may explain why vitamin D deficiency is often complicated in these patients. Therapeutic strategies to protect the functions of these receptors from injury could be used to prevent vitamin D deficiency and its related disorders.

Proximal tubule cell hypothesis for cardiorenal syndrome in diabetes

Incidence of cardiovascular disease (CVD) is remarkably high among patients with chronic kidney disease (CKD), even in the early microalbuminuric stages with normal glomerular filtration rates. Proximal tubule cells (PTCs) mediate metabolism and urinary excretion of vasculotoxic substances via apical and basolateral receptors and transporters. These cells also retrieve vasculoprotective substances from circulation or synthesize them for release into the circulation. PTCs are also involved in the uptake of sodium and phosphate, which are critical for hemodynamic regulation and maintaining the mineral balance, respectively. Dysregulation of PTC functions in CKD is likely to be associated with the development of CVD and is linked to the progression to end-stage renal disease. In particular, PTC dysfunction occurs early in diabetic nephropathy, a leading cause of CKD. It is therefore important to elucidate the mechanisms of PTC dysfunction to develop therapeutic strategies for treating cardiorenal syndrome in diabetes.

Regulation of megalin expression in cultured proximal tubule cells by angiotensin II type 1A receptor- and insulin-mediated signaling cross talk

Impairment of proximal tubular endocytosis of glomerular-filtered proteins including albumin results in the development of proteinuria/albuminuria in patients with chronic kidney disease. However, the mechanisms regulating the proximal tubular function are largely unknown. This study aimed to investigate the role of angiotensin II type 1A receptor (AT(1A)R)- and insulin-mediated signaling pathways in regulating the expression of megalin, a multiligand endocytic receptor in proximal tubule cells (PTCs). Opossum kidney PTC-derived OK cells that stably express rat AT(1A)R but are deficient in endogenous angiotensin II receptors (AT(1A)R-OK cells) were used for this study. Treatment of the cells with angiotensin II suppressed mRNA and protein expression of megalin at 3- and 24-h incubation time points, respectively. Cellular uptake and degradation of albumin and receptor-associated protein, megalin's endocytic ligands were suppressed 24 h after angiotensin II treatment. The AT(1A)R-mediated decrease in megalin expression was partially prevented by ERK inhibitors. Insulin competed with the AT(1A)R-mediated ERK activation and decrease in megalin expression. Inhibitors of phosphatidylinositol 3-kinase (PI3K), a major component of insulin signaling, also suppressed megalin expression, and activation of the insulin receptor substrate (IRS)/PI3K system was prevented by angiotensin II. Collectively the AT(1A)R-mediated ERK signaling is involved in suppressing megalin expression in the OK cell line, and insulin competes with this pathway. Conversely, the insulin-IRS/PI3K signaling, with which angiotensin II competes, tends to stimulate megalin expression. In conclusion, there is AT(1A)R- and insulin-mediated competitive signaling cross talk to regulate megalin expression in cultured PTCs.

Megalin-mediated endocytosis of cystatin C in proximal tubule cells

Serum levels of cystatin C, an endogenous cysteine proteinase inhibitor, are often used as an indicator of glomerular filtration rate. Although it is known that cystatin C is filtered by glomeruli and metabolized in proximal tubule cells (PTC), the precise molecular mechanism underlying this process is undetermined. Using quartz-crystal microbalance analyses, we demonstrate that cystatin C binds directly to megalin, an endocytic receptor in PTC, in a Ca(+)-dependent manner. We also find that cystatin C is endocytosed specifically via megalin in rat yolk sac epithelium-derived L2 cells which share a variety of characteristics with PTC. Finally, in vivo studies using kidney-specific megalin knockout mice provide evidence that megalin mediates proximal tubular uptake of cystatin C. We conclude that megalin is an endocytic receptor of cystatin C in PTC.

Significance of Proximal Tubular Metabolism of Advanced Glycation End Products in Kidney Diseases

Advanced glycation end products (AGEs) are formed by the nonenzymatic Maillard reaction between sugars and proteins. Low-molecular weight AGEs are filtered by renal glomeruli and then reabsorbed and metabolized by proximal tubule cells (PTCs). High-molecular weight AGEs are also delivered to PTCs in proteinuric states. In patients with diabetes, AGE generation is increased, and the actions of AGEs on PTCs are likely involved in the pathogenesis of diabetic nephropathy. In patients with chronic renal failure (CRF), reduced renal metabolism of AGEs likely accounts for the accumulation of AGEs in serum, leading to uremic complications including dialysis-related amyloidosis. AGE precursors such as reactive carbonyl compounds also accumulate in the sera of patients with CRF. It is likely that PTCs take up AGEs and AGE precursors via specific endocytotic receptors or transporters. Megalin is a multiligand endocytotic receptor that is abundantly expressed on PTCs. There is evidence that megalin is involved in the cellular uptake and degradation of AGEs. We previously reported a cell therapy model involving implantation of megalin-expressing cells into experimental mice with renal failure for elimination of uremic toxin proteins. Further studies are needed to clarify the molecular mechanisms of the metabolism of AGEs and their precursors to develop a strategy for the treatment of diabetic nephropathy and uremic complications of CRF.

Role of megalin, a proximal tubular endocytic receptor, in the pathogenesis of diabetic and metabolic syndrome-related nephropathies: protein metabolic overload hypothesis

Megalin is an endocytic receptor on the apical membranes of proximal tubule cells (PTC) in the kidney, and is involved in the reabsorption and metabolism of various proteins that have been filtered by glomeruli. Patients with diabetes, especially type 2 diabetes, or metabolic syndrome are likely to have elevated serum levels of advanced glycation end products, liver-type fatty acid binding protein, angiotensin II, insulin and leptin, and renal metabolism of these proteins is potentially overloaded. Some of these proteins are themselves nephrotoxic, while others are carriers of nephrotoxic molecules. Megalin is involved in the proximal tubular uptake of these proteins. We hypothesize that megalin-mediated metabolic overload in PTC leads to compensatory cellular hypertrophy and sustained Na+ reabsorption, causing systemic hypertension and glomerular hyperfiltration via tubuloglomerular feedback, and named this as 'protein metabolic overload hypothesis'. Impaired metabolism of bioactive proteins such as angiotensin II and insulin in PTC may enhance hypertrophy of PTC and/or Na+ reabsorption. Sleep apnoea syndrome, a frequent complication of diabetes and metabolic syndrome, may cause renal hypoxia and result in relative overload of protein metabolism in the kidneys. The development of strategies to identify patients with diabetes or metabolic syndrome who are at high risk for renal metabolic overload would allow intensive treatment of these patients in an effort to prevent the development of nephropathy. Further studies on the intracellular molecular signalling associated with megalin-mediated metabolic pathways may lead to the development of novel strategies for the treatment of nephropathies related to diabetes and metabolic syndrome.

Evidence for megalin-mediated proximal tubular uptake of L-FABP, a carrier of potentially nephrotoxic molecules

Liver-type fatty acid binding protein (L-FABP) binds with high affinity to hydrophobic molecules including free fatty acid, bile acid and bilirubin, which are potentially nephrotoxic, and is involved in their metabolism mainly in hepatocytes. L-FABP is released into the circulation, and patients with liver damage have an elevated plasma L-FABP level. L-FABP is also present in renal tubules; however, the precise localization of L-FABP and its potential role in the renal tubules are not known. In this study, we examined the cellular and subcellular localization of L-FABP in the rat kidney and tried to determine from where the L-FABP in kidney tissues had originated. Immunohistochemical studies of kidney sections localized L-FABP in the lysosomes of proximal tubule cells (PTC). In rats with carbon tetrachloride (CCl4)-induced acute liver injury, we detected high levels of L-FABP in the circulation and in the kidney compared with those in the control rat by immunoblotting, while reverse transcription-polymerase chain reaction showed that the level of L-FABP mRNA expression in the kidney of CCl4-treated rats was low and did not differ from that in the control rat. When 35S-L-FABP was intravenously administered to rats, the kidneys took up 35S-L-FABP more preferentially than the liver and heart, and histoautoradiography of kidney sections revealed that 35S-L-FABP was internalized via the apical domains of PTC. Quartz-crystal microbalance analysis revealed that L-FABP bound to megalin, a multiligand endocytotic receptor on PTC, in a Ca2+-dependent manner. Degradation assays using megalin-expressing rat yolk sac tumor-derived L2 cells demonstrated that megalin mediated the cellular uptake and catabolism of 125I-L-FABP. In conclusion, circulatory L-FABP was found to be filtered by glomeruli and internalized by PTC probably via megalin-mediated endocytosis. These results suggest a novel renal uptake pathway for L-FABP, a carrier of hydrophobic molecules, some of which may exert nephrotoxic effects.

Adult-onset leukoencephalopathy with vanishing white matter with a missense mutation inEIF2B5

We report of a woman aged 52 years born to consanguineous parents and seeking treatment for progressive dementia and delusion. Neurologic examination revealed dementia and emotional instability, indifference, and confabulation. There was also mild spasticity of the bilateral lower limbs. MRI revealed diffuse white matter hyperintensity on T2-weighted images accompanied by hypointense areas on fluid-attenuated inversion recovery images. A homozygous missense mutation was identified in EIF2B5.