Characterization of glycosaminoglycans in tubular epithelial cells: calcium oxalate and oxalate ions effects.
BACKGROUND
The interaction between tubular epithelial cells and calcium oxalate crystals or oxalate ions is a very precarious event in the lithogenesis. Urine contains ions, glycoproteins and glycosaminoglycans that inhibit the crystallization process and may protect the kidney against lithogenesis. We examined the effect of oxalate ions and calcium oxalate crystals upon the synthesis of glycosaminoglycans in distal [Madin-Darby canine kidney (MDCK)] and proximal (LLC-PK1) tubular cell lines.


METHODS
Glycosaminoglycan synthesis was analyzed by metabolic labeling with (35)S-sulfate and enzymatic digestion with specific mucopolysaccharidases. Cell death was assessed by fluorescent dyes and crystal endocytosis was analised by flow cytometry.


RESULTS
The main glycosaminoglycans synthesized by both cells were chondroitin sulfate and heparan sulfate most of them secreted to the culture medium or present at cellular surface. Exposition of MDCK cells to oxalate ions increased apoptosis rate and the incorporation of (35)S-sulfate in chondroitin sulfate and heparan sulfate, while calcium oxalate crystals were endocyted by LLC-PK1, induced necrotic cell death, and increased (35)S-sulfate incorporation in glycosaminoglycans. These effects seem to be specific and due to increased biosynthesis, since hydroxyapatite and other carboxylic acid did not induced cellular death or glycosaminoglycan synthesis and no changes in sulfation degree or molecular weight of glycosaminoglycans could be detected. Thapsigargin inhibited the glycosaminoglycan synthesis induced by calcium oxalate in LLC-PK1, suggesting that this effect was sensitive to the increase in cytosolic calcium.


CONCLUSIONS
Tubular cells may increase the synthesis of glycosaminoglycans to protect from the toxic insult of calcium oxalate crystals and oxalate ions, what could partially limit the lithogenesis.
Borges
Fernanda T
FT
Departamento de Medicina, Disciplina de Nefrologia, Universidade Federal de São Paulo (UNIFESP), São Paulo, Brasil.
Michelacci
Yara M
YM
Aguiar
Jair A K
JA
Dalboni
Maria A
MA
Garófalo
Andrezza S
AS
Schor
Nestor
N
D000818:Animals; D002118:Calcium / Q000378:metabolism; D002129:Calcium Oxalate / Q000737:chemistry / Q000633:toxicity*; D016923:Cell Death / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D003460:Crystallization; D004285:Dogs; D017886:Durapatite / Q000737:chemistry / Q000633:toxicity; D004705:Endocytosis; D005561:Formates / Q000737:chemistry / Q000633:toxicity; D006025:Glycosaminoglycans / Q000096:biosynthesis / Q000378:metabolism*; D007476:Ionophores / Q000494:pharmacology; D007477:Ions / Q000633:toxicity; D007686:Kidney Tubules, Distal / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D007687:Kidney Tubules, Proximal / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D018374:LLC-PK1 Cells; D009336:Necrosis; D010070:Oxalates / Q000737:chemistry / Q000633:toxicity; D013431:Sulfates / Q000493:pharmacokinetics; D013462:Sulfur Radioisotopes; D013552:Swine; D019284:Thapsigargin / Q000494:pharmacology; D014545:Urinary Calculi / Q000737:chemistry / Q000378:metabolism* / Q000473:pathology
D005561:Formates; D006025:Glycosaminoglycans; D007476:Ionophores; D007477:Ions; D010070:Oxalates; D013431:Sulfates; D013462:Sulfur Radioisotopes; C030544:formic acid; D002129:Calcium Oxalate; D019284:Thapsigargin; D017886:Durapatite; D002118:Calcium