The Journal of Bone and Joint Surgery 83:201 (2001)
© 2001 The Journal of Bone and Joint Surgery, Inc.
The Effects of Particulate Wear Debris, Cytokines, and Growth Factors on the Functions of MG-63 Osteoblasts
Csaba Vermes, MD,
Raman Chandrasekaran, PhD,
Joshua J. Jacobs, MD,
Jorge O. Galante, MD, DMSc,
Kenneth A. Roebuck, PhD and
Tibor T. Glant, MD, PhD
Investigation performed at Rush-Presbyterian-St. Luke's Medical
Center, Chicago, Illinois
Csaba Vermes, MD Raman Chandrasekaran, PhD Joshua J. Jacobs,
MD Jorge O. Galante, MD, DMSc Tibor T. Glant, MD, PhD Department
of Orthopedic Surgery, Rush University, Rush-Presbyterian-St. Luke's
Medical Center, 1653 West Congress Parkway, Chicago, IL 60612. E-mail
address for T.T. Glant: tglant{at}rush.edu
Kenneth A. Roebuck, PhD Department of Immunology/Microbiology,
Rush University, Rush-Presbyterian-St. Luke's Medical Center, 1653
West Congress Parkway, Chicago, IL 60612
Although none of the authors has received or will receive benefits
for personal or professional use from a commercial party related
directly or indirectly to the subject of this article, benefits
have been or will be received but are directed solely to a research
fund, foundation, educational institution, or other nonprofit organization
with which one or more of the authors is associated. Funds were received
in total or partial support of the research or clinical study presented
in this article. The funding sources were the National Institutes
of Health, Zimmer, and the Musculoskeletal Research Foundation.
Background: Particle-challenged cells release
cytokines, chemokines, and eicosanoids, which contribute to periprosthetic
osteolysis. The particle-induced activation of macrophages and monocytes
has been extensively studied, but only limited information is available
on the response of osteoblasts to particulate wear debris. This
study examines the effects of particulate wear debris, proinflammatory
cytokines, and growth factors on osteoblast functions.
Methods: MG-63 osteoblasts were treated with metal
particles (titanium, titanium alloy, and chromium orthophosphate)
or polymeric particles (polyethylene and polystyrene) of phagocytosable
sizes or were treated with exogenous cytokines and growth factors.
The kinetics of particle phagocytosis and the number of engulfed
particles were assessed with use of fluoresceinated particles. Cell
proliferation was determined according to [3H]-thymidine
incorporation, and cell viability was determined by either fluorescein
diacetate uptake or trypan blue exclusion. Expressions of osteoblast-specific
genes were quantified with Northern blot hybridization, and the
secretions of osteoblast-specific proteins and cytokines were analyzed
by enzyme-linked immunosorbent assays.
Results: MG-63 osteoblasts phagocytosed particles
and became saturated after twenty-four hours. A maximum of forty
to sixty particles per cell were phagocytosed. Each type of particle
significantly suppressed procollagen a1[I] gene expression (p < 0.05),
whereas other osteoblast-specific genes (osteonectin, osteocalcin,
and alkaline phosphatase) did not show significant changes. Particle-stimulated
osteoblasts released interleukin-6 (p < 0.05) and a smaller
amount of transforming growth factor-b1. Particles reduced cell
proliferation in a dose-dependent manner without affecting cell
viability (p < 0.05). Exogenous tumor necrosis factor-a also
enhanced the release of interleukin-6 (p < 0.01) and transforming
growth factor-b1 (p < 0.05), whereas the secretion of transforming
growth factor-b1 was increased by insulin-like growth factor-I and
prostaglandin E2 as well. Insulin-like growth factor-I and transforming
growth factor-b1 significantly increased procollagen a1[I] gene
expression in osteoblasts (p < 0.05), while tumor necrosis factor-a
and prostaglandin E2 significantly suppressed procollagen a1[I]
gene expression (p < 0.01). In contrast, neither exogenous nor
endogenous interleukin-6 had any effect on other cytokine secretion, on
proliferation, or on procollagen a1[I] gene expression. The transcription
inhibitor actinomycin D reduced both procollagen a1[I] transcription
and interleukin-6 production. Inhibitors of protein synthesis (cyclohexamide)
and intracellular protein transport (brefeldin A and monensin) blocked
the release of interleukin-6, but none of these compounds influenced
the suppressive effect of titanium on procollagen a1[I] gene expression.
Conclusions: MG-63 osteoblasts phagocytose particulate
wear debris, and this process induces interleukin-6 production and
suppresses type-I collagen synthesis. Osteoblast-derived interleukin-6
may induce osteoclast differentiation and/or activation, but the resorbed
bone cannot be replaced by new bone because of diminished osteoblast
function (reduced type-I collagen synthesis). Exogenous cytokines (tumor
necrosis factor-a and interleukin-1b), growth factors (insulin-like
growth factor-I and transforming growth factor-b1), and prostaglandin E2
can modify particulate-induced alterations of osteoblast functions.
Clinical Relevance: Altered osteoblast functions
probably contribute to the progression of periprosthetic osteolysis.
Suppressed osteoblast functions, however, could be compensated for
by certain growth factors, such as insulin-like growth factor-I
or transforming growth factor-b1. These growth factors, if delivered
locally, may have therapeutic potential to prevent or reverse periprosthetic
osteolysis.

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