Fabrizio Grosjean

Effects of Sevelamer on HbA1c, Inflammation, and Advanced Glycation End Products in Diabetic Kidney Disease

BACKGROUND AND OBJECTIVES Increased inflammation and oxidative stress may be caused by proteins and lipids modified by cytotoxic advanced glycation end products (AGEs) in food. Restricting food containing elevated AGEs improves these risk factors in diabetic CKD. Because diet adherence can be problematic, this study aimed to remove cytotoxic AGEs from food already ingested and to determine whether sevelamer carbonate sequesters cytotoxic AGEs in the gut, preventing their uptake and thereby reducing AGE-induced abnormalities. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS This single-center, randomized, 2-month, open-label, intention-to-treat, crossover study compared sevelamer carbonate with calcium carbonate treatment in stage 2-4 diabetic CKD. Participants received 2 months of treatment with one drug, had a 1-week washout, and then received the opposite drug for 2 months. RESULTS Sevelamer carbonate reduced HbA1c, serum methylglyoxal, serum (ε)N-carboxymethyl-lysine, triglycerides, and 8-isoprostanes. Total cholesterol and fibroblast growth factor 23 were reduced by sevelamer carbonate, relative to calcium carbonate. AGE receptor 1 and sirtuin 1 mRNA were increased and PMNC TNFα levels were decreased by sevelamer carbonate, but not calcium carbonate. Medications and caloric and AGE intake remained unchanged. Sevelamer carbonate reversibly bound AGE-BSA at intestinal, but not stomach, pH. CONCLUSIONS Sevelamer carbonate significantly reduces HbA1c, fibroblast growth factor 23, lipids, and markers of inflammation and oxidative stress, and markedly increases antioxidant markers, independently of phosphorus in patients with diabetes and early kidney disease. These novel actions of sevelamer carbonate on metabolic and inflammatory abnormalities in type 2 diabetes mellitus may affect progression of early diabetic CKD.

Oral glycotoxins are a modifiable cause of dementia and the metabolic syndrome in mice and humans.

Significance Suppression of NAD+-dependent sirtuin 1 (SIRT1) is linked to dementia or Alzheimer’s disease (AD) and the metabolic syndrome (MS). Because advanced glycation end products (AGEs) promote MS and neurotoxicity, we conducted studies of C57BL6 mice fed isocaloric diets containing defined AGEs [methyl-glyoxal derivatives (MG)] to determine whether food AGEs promote AD and MS. MG+-fed, but not MG−-fed, mice developed brain SIRT1 deficiency, amyloid-β deposits, cognitive and motor deficits, and MS. These findings were validated in older healthy humans with high baseline circulating MG levels by a time-dependent decline in cognition and insulin sensitivity. The data suggest that food-derived AGEs, an environmental factor, contribute to both AD and MS by causing chronic SIRT1 suppression. Importantly, reduction of food-derived AGEs is feasible and may provide an effective treatment strategy for both these epidemics. Age-associated dementia and Alzheimer’s disease (AD) are currently epidemic. Neither their cause nor connection to the metabolic syndrome (MS) is clear. Suppression of deacetylase survival factor sirtuin 1 (SIRT1), a key host defense, is a central feature of AD. Age-related MS and diabetes are also causally associated with suppressed SIRT1 partly due to oxidant glycotoxins [advanced glycation end products (AGEs)]. Changes in the modern diet include excessive nutrient-bound AGEs, such as neurotoxic methyl-glyoxal derivatives (MG). To determine whether dietary AGEs promote AD, we evaluated WT mice pair-fed three diets throughout life: low-AGE (MG−), MG-supplemented low-AGE (MG+), and regular (Reg) chow. Older MG+-fed mice, similar to old Reg controls, developed MS, increased brain amyloid-β42, deposits of AGEs, gliosis, and cognitive deficits, accompanied by suppressed SIRT1, nicotinamide phosphoribosyltransferase, AGE receptor 1, and PPARγ. These changes were not due to aging or caloric intake, as neither these changes nor the MS were present in age-matched, pair-fed MG− mice. The mouse data were enhanced by significant temporal correlations between high circulating AGEs and impaired cognition, as well as insulin sensitivity in older humans, in whom dietary and serum MG levels strongly and inversely associated with SIRT1 gene expression. The data identify a specific AGE (MG) as a modifiable risk factor for AD and MS, possibly acting via suppressed SIRT1 and other host defenses, to promote chronic oxidant stress and inflammation. Because SIRT1 deficiency in humans is both preventable and reversible by AGE reduction, a therapeutic strategy that includes AGE reduction may offer a new strategy to combat the epidemics of AD and MS.

Combined Anti-Inflammatory and Anti-AGE Drug Treatments Have a Protective Effect on Intervertebral Discs in Mice with Diabetes

Objective Diabetes and low back pain are debilitating diseases and modern epidemics. Diabetes and obesity are also highly correlated with intervertebral disc (IVD) degeneration and back pain. Advanced-glycation-end-products (AGEs) increase reactive-oxygen-species (ROS) and inflammation, and are one cause for early development of diabetes mellitus. We hypothesize that diabetes results in accumulation of AGEs in spines and associated spinal pathology via increased catabolism. We present a mouse model showing that: 1) diabetes induces pathological changes to structure and composition of IVDs and vertebrae; 2) diabetes is associated with accumulation of AGEs, TNFα, and increased catabolism spinal structures; and 3) oral-treatments with a combination of anti-inflammatory and anti-AGE drugs mitigate these diabetes-induced degenerative changes to the spine. Methods Three age-matched groups of ROP-Os mice were compared: non-diabetic, diabetic (streptozotocin (STZ)-induced), or diabetic mice treated with pentosan-polysulfate (anti-inflammatory) and pyridoxamine (AGE-inhibitor). Mice were euthanized and vertebra-IVD segments were analyzed by μCT, histology and Immunohistochemistry. Results Diabetic mice exhibited several pathological changes including loss in IVD height, decreased vertebral bone mass, decreased glycosaminoglycan content and morphologically altered IVDs with focal deposition of tissues highly expressing TNFα, MMP-13 and ADAMTS-5. Accumulation of larger amounts of methylglyoxal suggested that AGE accumulation was associated with these diabetic degenerative changes. However, treatment prevented or reduced these pathological effects on vertebrae and IVD. Conclusion This is the first study to demonstrate specific degenerative changes to nucleus pulposus (NP) morphology and their association with AGE accumulation in a diabetic mouse model. Furthermore, this is the first study to demonstrate that oral-treatments can inhibit AGE-induced ROS and inflammation in spinal structures and provide a potential treatment to slow progression of degenerative spine changes in diabetes. Since diabetes, IVD degeneration, and accumulation of AGEs are frequent consequences of aging, early treatments to reduce AGE-induced ROS and Inflammation may have broad public-health implications.

Low-protein diet supplemented with ketoacids reduces the severity of renal disease in 5/6 nephrectomized rats: a role for KLF15

Dietary protein restriction is an important treatment for chronic kidney disease. Herein, we tested the effect of low-protein or low-protein plus ketoacids (KA) diet in a remnant kidney model. Rats with a remnant kidney were randomized to receive normal protein diet (22%), low-protein (6%) diet (LPD), or low-protein (5%) plus KA (1%) diet for 6 months. Protein restriction prevented proteinuria, decreased blood urea nitrogen levels, and renal lesions; however, the LPD retarded growth and decreased serum albumin levels. Supplementation with KA corrected these abnormalities and provided superior renal protection compared with protein restriction alone. The levels of Kruppel-like factor-15 (KLF15), a transcription factor shown to reduce cardiac fibrosis, were decreased in remnant kidneys. Protein restriction, which increased KLF15 levels in the normal kidney, partially recovered the levels of KLF15 in remnant kidney. The expression of KLF15 in mesangial cells was repressed by oxidative stress, transforming growth factor-β, and tumor necrosis factor (TNF)-α. The suppressive effect of TNF-α on KLF15 expression was mediated by TNF receptor-1 and nuclear factor-κB. Overexpression of KLF15 in mesangial and HEK293 cells significantly decreased fibronectin and type IV collagen mRNA levels. Furthermore, KLF15 knockout mice developed glomerulosclerosis following uninephrectomy. Thus, KLF15 may be an antifibrotic factor in the kidney, and its decreased expression may contribute to the progression of kidney disease.

Reversal of Diabetic Nephropathy by a Ketogenic Diet

Intensive insulin therapy and protein restriction delay the development of nephropathy in a variety of conditions, but few interventions are known to reverse nephropathy. Having recently observed that the ketone 3-beta-hydroxybutyric acid (3-OHB) reduces molecular responses to glucose, we hypothesized that a ketogenic diet, which produces prolonged elevation of 3-OHB, may reverse pathological processes caused by diabetes. To address this hypothesis, we assessed if prolonged maintenance on a ketogenic diet would reverse nephropathy produced by diabetes. In mouse models for both Type 1 (Akita) and Type 2 (db/db) diabetes, diabetic nephropathy (as indicated by albuminuria) was allowed to develop, then half the mice were switched to a ketogenic diet. After 8 weeks on the diet, mice were sacrificed to assess gene expression and histology. Diabetic nephropathy, as indicated by albumin/creatinine ratios as well as expression of stress-induced genes, was completely reversed by 2 months maintenance on a ketogenic diet. However, histological evidence of nephropathy was only partly reversed. These studies demonstrate that diabetic nephropathy can be reversed by a relatively simple dietary intervention. Whether reduced glucose metabolism mediates the protective effects of the ketogenic diet remains to be determined.

Inhibition of inflammation by pentosan polysulfate impedes the development and progression of severe diabetic nephropathy in aging C57B6 mice

Inflammation has a key role in diabetic nephropathy (DN) progression. Pentosan polysulfate (PPS) has been shown to decreases interstitial inflammation and glomerulosclerosis in 5/6 nephrectomized rats. Since PPS has an excellent long-term safety profile in interstitial cystitis treatment, and we recently found that old diabetic C57B6 mice develop DN characterized by extensive tubulointerstitial inflammatory lesions that mimics human DN, we examined the effect of PPS on old diabetic mice. We also examined the anti-inflammatory properties of PPS in renal cells in vitro. Diabetes was induced with streptozotocin in 18 months female (early aging) C57B6 mice. Mice were then randomized to receive oral PPS (25 mg/kg/day) or water for 4 months. The effect of PPS on NF-κB activation and on TNFα, high glucose or advanced glycation end products (AGEs) stimulated proinflammatory gene expression in renal cells was examined. We found that PPS treatment preserved renal function, significantly reduced albuminuria, and markedly decreased the severity of renal lesions, including tubulointerstitial inflammation. PPS also reduced upregulation of TNFα and proinflammatory genes in aging diabetic kidneys. Furthermore, PPS suppressed NF-κB, decreased the proinflammatory actions of TNFα, and decreased high glucose and AGEs stimulated MCP-1 production in vitro. Finally, PPS decreased TNFα-induced increase in albumin permeability in podocyte monolayers. In conclusion, PPS treatment largely prevents the development/progression of nephropathy in aging diabetic mice. As this may be mediated by suppression of TNFα, high glucose, and AGE-stimulated NF-κB activation and inflammation in vitro, the in vivo blockade of DN may be due to the anti-inflammatory properties of PPS.

CHOP deficiency results in elevated lipopolysaccharide-induced inflammation and kidney injury

C/EBP homologous protein (CHOP) is an important mediator of endoplasmic reticulum (ER) stress-induced cell and organ injury. Here we show that lipopolysaccharide (LPS)-induced acute kidney injury (AKI) is associated with ER stress and elevated CHOP. We postulated that CHOP(-/-) mice would be protected against LPS-induced-AKI. Unexpectedly, while Toll-like receptor 4 (TLR4) expression levels were comparable in kidneys of CHOP(-/-) and wild-type (WT) mice, CHOP(-/-) mice developed more severe AKI after LPS injection. Furthermore, the severe kidney injury in CHOP(-/-) mice was associated with an exaggerated inflammatory response. Serum TNF-α levels were more elevated in LPS-treated CHOP(-/-) mice. There was a 3.5-fold higher amount of renal neutrophil infiltrates in LPS-treated CHOP(-/-) than in WT mice. Additionally, the kidneys of LPS-treated CHOP(-/-) mice had a more prominent increase in NF-κB activation and further upregulation of proinflammatory genes, i.e., c-x-c motif ligand 1 (CXCL-1), macrophage inflammatory protein-2 (MIP-2), and IL-6. Finally, proximal tubules, glomeruli, and podocytes isolated from CHOP(-/-) mice also had an exaggerated proinflammatory response to LPS. Since LPS directly increased CHOP in glomeruli and podocytes of WT mice, together these data suggest that the LPS-induced increase of CHOP in kidneys may inhibit inflammatory response in renal cells and provide protection against AKI.

Risk Factors for Chronic Renal Dysfunction in Lung Transplant Recipients

Several factors predispose to renal dysfunction (RD), a common complication of solid organ transplants. We evaluated the impact of clinical and laboratory parameters on the decline of renal function in lung and heart-lung transplant recipients. We enrolled 45 patients who survived more than 6 months after transplantation, had normal renal function and urinalysis before the surgery. The prognostic value of variables for the occurrence of RD was calculated by univariate analysis. Thirty patients developed RD, defined as doubling of serum creatinine or creatinine steadily >1.5 mg/dL after a median time of 12 months. Serum creatinine above 0.9 mg/dL during the month preceding lung transplant, systolic blood pressure above 130 mmHg, and pretransplant idiopathic pulmonary hypertension were significantly associated with the development of RD. Our findings indicate that increased systolic blood pressure, reduced glomerular filtration rate, and idiopathic pulmonary hypertension are risk factors for chronic RD in lung transplant recipients.

The antifibrogenic effect of hepatocyte growth factor (HGF) on renal tubular (HK-2) cells is dependent on cell growth

Although several reports suggest an antifibrogenic effect of hepatocyte growth factor (HGF), an increased deposition of matrix induced by HGF has also been reported. These conflicting effects could result from a diverse proliferative state of the target cells. Aim of the present study was to evaluate HGF effects on growth arrested (quiescent) and actively proliferating renal tubular epithelial (HK-2) cells. HK-2 cells were cultured in RPMI medium either on agarose gel or on plastic surface in order to inhibit or to allow cell proliferation. Cells were incubated with RPMI containing HGF (50 ng/ml) for 24 h at 37°C. Untreated HK-2 were used as control. After 24 h of incubation, cells were counted by Coulter counter. (α2)IV collagen, transforming growth factor-β (TGF-β), Tissue inhibitor of metalloproteases (TIMP1 and 2) mRNA levels were determined by RT-PCR. The production of type IV collagen, c-met, proliferating cell nuclear antigen (PCNA), and SnoN, a transcriptional Smad corepressor and thus a TGF-β inhibitor, was evaluated by ELISA or western blotting. MMP-9 and 2 gelatinolytic activity was studied by zymography. Treatment with HGF did not increase HK-2 cell number and PCNA synthesis when the cells were grown on agarose as it did for cells grown on plastic surface. HGF increased (α2)IV collagen in proliferating cells whereas it reduced (α2)IV collagen and c-met synthesis in growth arrested cells. HGF treatment increased TGF-β and TIMP-2 in proliferating cells while reduced TIMP-1 mRNA levels of quiescent cells. Furthermore, production of the co repressor SnoN was significantly decreased by HGF in proliferating cells. Quiescent and proliferating HK-2 showed a different pattern of metalloproteases activity with a prevalence of MMP2 in quiescent and MMP9 in proliferating cells. In summary, HGF showed opposite effects on growth arrested and proliferating HK-2 cells favouring matrix deposition in the latter with increasing expression of collagen, TIMP-1 and TGF-β. Our results demonstrate that the proliferative state of target cells may influence the effects of HGF on extracellular matrix turnover in HK-2 cells.

Increased susceptibility to acute kidney injury due to endoplasmic reticulum stress in mice lacking tumor necrosis factor-α and its receptor 1

Endoplasmic reticulum (ER) stress is actively involved in acute organ injury. Since tumor necrosis factor α (TNFα) plays a role in acute kidney injury, and induces ER stress and cell death in vitro, we examined the contribution of TNFα to acute kidney ER stress induced by tunicamycin. Contrary to expectation, tunicamycin caused much more severe kidney injury in TNFα-/- than in wild-type mice. The major site of kidney injury in TNFα-/- mice was proximal tubules, which showed extensive cell vacuolation, lipid accumulation, and apoptosis. Reconstitution of TNFα-/- mice with TNFα 24 h before tunicamycin injection reversed the susceptibility. When TNFα-receptor-deficient mice were treated with tunicamycin, severe renal injury developed in TNFR1-/- but not TNFR2-/- mice, suggesting this aspect of TNFα action was through TNF receptor-1 (TNFR1). In response to tunicamycin-induced acute ER stress, kidneys from neither TNFα-/- nor TNFR1-/- mice showed a significant increase in phosphorylated eukaryotic translation initiation factor 2α (eIF2α), a key step in ER stress regulation. Moreover, proximal tubular cells from TNFR1-/- mice did not show increased eIF2α phosphorylation in response to tunicamycin and were susceptible to ER stress-induced cell death. Finally, treatment of proximal tubule cells isolated from TNFR1-/- mice with an inhibitor of eIF2α phosphatase increased the levels of phosphorylated eIF2α and substantially reduced tunicamycin-induced cell death. Thus, disruption of TNFR1 signaling leads to dysregulation of eIF2α and increased susceptibility to acute ER stress injury in the kidney.