Glomerular cell death and inflammation with high-protein diet and diabetes

Nephrol Dial Transplant. 2013 Jul;28(7):1711-20. doi: 10.1093/ndt/gfs579. Epub 2013 Jan 12.

Abstract

Background: Overfeeding amino acids (AAs) increases cellular exposure to advanced glycation end-products (AGEs), a mechanism for protein intake to worsen diabetic kidney disease (DKD). This study assessed receptor for AGE (RAGE)-mediated apoptosis and inflammation in glomerular cells exposed to metabolic stressors characteristic of high-protein diets and/or diabetes in vitro with proof-of-concept appraisal in vivo.

Methods: Mouse podocytes and mesangial cells were cultured under control and metabolic stressor conditions: (i) no addition; (ii) increased AAs (4-6-fold>control); (iii) high glucose (HG, 30.5 mM); (iv) AA/HG combination; (v) AGE-bovine serum albumin (AGE-BSA, 300 µg/mL); (vi) BSA (300 µg/mL). RAGE was inhibited by blocking antibody. Diabetic (streptozotocin) and nondiabetic mice (C57BL/6J) consumed diets with protein calories of 20 or 40% (high) for 20 weeks. People with DKD and controls provided 24-h urine samples.

Results: In podocytes and mesangial cells, apoptosis (caspase 3/7 activity and TUNEL) increased in all metabolic stressor conditions. Both inflammatory mediator expression (real-time reverse transcriptase-polymerase chain reaction: serum amyloid A, caspase-4, inducible nitric oxide synthase, and monocyte chemotactic protein-1) and RAGE (immunostaining) also increased. RAGE inhibition prevented apoptosis and inflammation in podocytes. Among mice fed high protein, podocyte number (WT-1 immunostaining) decreased in the diabetic group, and only these diabetic mice developed albuminuria. Protein intake (urea nitrogen) correlated with AGE excretion (carboxymethyllysine) in people with DKD and controls.

Conclusions: High-protein diet and/or diabetes-like conditions increased glomerular cell death and inflammation, responses mediated by RAGEs in podocytes. The concept that high-protein diets exacerbate early indicators of DKD is supported by data from mice and people.

Keywords: apoptosis; high-protein diet; mesangial cells; podocytes; receptor for advanced glycation end-products.

Publication types

  • Comparative Study
  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Apoptosis*
  • Blotting, Western
  • Case-Control Studies
  • Cells, Cultured
  • Diabetes Mellitus, Experimental / complications
  • Diabetes Mellitus, Experimental / pathology*
  • Diabetes Mellitus, Type 2 / metabolism
  • Diabetes Mellitus, Type 2 / pathology*
  • Diabetic Nephropathies / etiology*
  • Diabetic Nephropathies / metabolism
  • Diabetic Nephropathies / pathology
  • Diet*
  • Dietary Proteins / pharmacology*
  • Glycation End Products, Advanced / genetics
  • Glycation End Products, Advanced / metabolism
  • Humans
  • Inflammation / etiology*
  • Inflammation / metabolism
  • Inflammation / pathology
  • Inflammation Mediators / metabolism
  • Male
  • Mesangial Cells / metabolism
  • Mesangial Cells / pathology
  • Mice
  • Mice, Inbred C57BL
  • Podocytes / metabolism
  • Podocytes / pathology
  • RNA, Messenger / genetics
  • Real-Time Polymerase Chain Reaction
  • Receptor for Advanced Glycation End Products
  • Receptors, Immunologic / genetics
  • Receptors, Immunologic / metabolism
  • Reverse Transcriptase Polymerase Chain Reaction

Substances

  • Dietary Proteins
  • Glycation End Products, Advanced
  • Inflammation Mediators
  • RNA, Messenger
  • Receptor for Advanced Glycation End Products
  • Receptors, Immunologic