Effect of particle size on hydroxyapatite crystal-induced tumor necrosis factor alpha secretion by macrophages.
Macrophages may promote a vicious cycle of inflammation and calcification in the vessel wall by ingesting neointimal calcific deposits (predominantly hydroxyapatite) and secreting tumor necrosis factor (TNF)alpha, itself a vascular calcifying agent. Here we have investigated whether particle size affects the proinflammatory potential of hydroxyapatite crystals in vitro and whether the nuclear factor (NF)-kappaB pathway plays a role in the macrophage TNFalpha response. The particle size and nano-topography of nine different crystal preparations was analyzed by X-ray diffraction, Raman spectroscopy, scanning electron microscopy and gas sorbtion analysis. Macrophage TNFalpha secretion was inversely related to hydroxyapatite particle size (P=0.011, Spearman rank correlation test) and surface pore size (P=0.014). A necessary role for the NF-kappaB pathway was demonstrated by time-dependent I kappaB alpha degradation and sensitivity to inhibitors of I kappaB alpha degradation. To test whether smaller particles were intrinsically more bioactive, their mitogenic activity on fibroblast proliferation was examined. This showed close correlation between TNFalpha secretion and crystal-induced fibroblast proliferation (P=0.007). In conclusion, the ability of hydroxyapatite crystals to stimulate macrophage TNFalpha secretion depends on NF-kappaB activation and is inversely related to particle and pore size, with crystals of 1-2 microm diameter and pore size of 10-50 A the most bioactive. Microscopic calcific deposits in early stages of atherosclerosis may therefore pose a greater inflammatory risk to the plaque than macroscopically or radiologically visible deposits in more advanced lesions.
Nadra
Imad
I
British Heart Foundation Cardiovascular Medicine Unit, Eric Bywaters Centre for Vascular Inflammation, Faculty of Medicine, Imperial College London, Hammersmith Hospital, Du Cane Road, London W12 ONN, UK.
Boccaccini
Aldo R
AR
Department of Materials, Imperial College London, Prince Consort Road, London SW7 2BP, UK.
Philippidis
Pandelis
P
British Heart Foundation Cardiovascular Medicine Unit, Eric Bywaters Centre for Vascular Inflammation, Faculty of Medicine, Imperial College London, Hammersmith Hospital, Du Cane Road, London W12 ONN, UK.
Whelan
Linda C
LC
Department of Clinical Pharmacology, The Royal College of Surgeons and Mater Misericordiae University Hospital, Dublin, Ireland.
McCarthy
Geraldine M
GM
Department of Clinical Pharmacology, The Royal College of Surgeons and Mater Misericordiae University Hospital, Dublin, Ireland.
Haskard
Dorian O
DO
British Heart Foundation Cardiovascular Medicine Unit, Eric Bywaters Centre for Vascular Inflammation, Faculty of Medicine, Imperial College London, Hammersmith Hospital, Du Cane Road, London W12 ONN, UK.
Landis
R Clive
RC
British Heart Foundation Cardiovascular Medicine Unit, Eric Bywaters Centre for Vascular Inflammation, Faculty of Medicine, Imperial College London, Hammersmith Hospital, Du Cane Road, London W12 ONN, UK. Electronic address: r.landis@imperial.ac.uk.
D050197:Atherosclerosis / Q000503:physiopathology; D001672:Biocompatible Materials / Q000737:chemistry / Q000494:pharmacology*; D002114:Calcinosis / Q000503:physiopathology; D002478:Cells, Cultured; D017886:Durapatite / Q000737:chemistry / Q000494:pharmacology*; D005347:Fibroblasts / Q000378:metabolism; D052816:Foreskin / Q000166:cytology; D006801:Humans; D008264:Macrophages / Q000378:metabolism*; D008297:Male; D016328:NF-kappa B / Q000378:metabolism; D010316:Particle Size; D014409:Tumor Necrosis Factor-alpha / Q000276:immunology / Q000378:metabolism*
D001672:Biocompatible Materials; D016328:NF-kappa B; D014409:Tumor Necrosis Factor-alpha; D017886:Durapatite