Incubation of porcine high-density lipoprotein with the apical surface of LLC-PK1 renal tubular cells sustains the properties of orientated monolayers.
BACKGROUND
HDL is present in the urine of patients with the nephrotic syndrome. The amount of HDL is directly related to the protein selectivity and therefore to the renal prognosis. Urinary HDL may therefore be involved in the pathogenesis of progressive renal impairment in proteinuric renal disease.


METHODS
LLC-PK1 cells were grown as orientated monolayers on filters. Uptake of HDL and permeability to inulin were measured. The influence of HDL in the growth medium on monolayer resistance, protein content, and sodium dependent glucose transport was studied. The effects of tetranitromethane (TNM) nitrosylation of HDL and of albumin, mevalonate, or simvastatin were investigated.


RESULTS
Confluent LLC-PK1 monolayers took up fluorescently labelled HDL from either epithelial surface and formed a significant diffusion barrier to inulin. Monolayers incubated in 300 micrograms/ml HDL achieved a protein content and plateau of resistance equal to those in 10% fetal calf serum (FCS); 30-1000 micrograms/ml HDL applied to the apical surface of confluent monolayers maintained a plateau of resistance as well as 10% FCS and significantly better than serum-free medium. Sodium-dependent glucose transport was preserved in monolayers exposed to HDL. Simvastatin completely, and nitrosylation partially, removed the stimulatory properties of HDL. These were partly reproduced by albumin or mevalonate.


CONCLUSIONS
HDL can enter renal epithelial cells from the apical surface. HDL added to this surface at confluence, reproducing the conditions found in the nephrotic syndrome, had a measurable positive effect on monolayer resistance. Results with nitrosylated HDL and HMG-CoA blockade suggest that these effects may be mediated via receptors and this enzyme system.
Streather
C P
CP
Department of Medicine, King's College School of Medicine and Dentistry, London, UK.
Owen
J S
JS
Hendry
B M
BM
Scoble
J E
JE
D000418:Albumins / Q000494:pharmacology; D000818:Animals; D002462:Cell Membrane / Q000187:drug effects; D002463:Cell Membrane Permeability / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured; D000960:Hypolipidemic Agents / Q000494:pharmacology; D007444:Inulin / Q000378:metabolism; D007687:Kidney Tubules, Proximal / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D018374:LLC-PK1 Cells / Q000187:drug effects / Q000378:metabolism*; D008075:Lipoproteins, HDL / Q000494:pharmacology*; D008148:Lovastatin / Q000031:analogs & derivatives / Q000494:pharmacology; D008798:Mevalonic Acid / Q000494:pharmacology; D009004:Monosaccharide Transport Proteins / Q000187:drug effects / Q000502:physiology*; D009404:Nephrotic Syndrome / Q000378:metabolism; D019821:Simvastatin; D013552:Swine
D000418:Albumins; D000960:Hypolipidemic Agents; D008075:Lipoproteins, HDL; D009004:Monosaccharide Transport Proteins; D007444:Inulin; D008148:Lovastatin; D019821:Simvastatin; D008798:Mevalonic Acid