Accumulation of non-steroidal anti-inflammatory drugs by gingival fibroblasts

Abstract

Non-steroidal anti-inflammatory drugs (NSAIDs) are used to manage pain and inflammatory disorders. We hypothesized that gingival fibroblasts actively accumulate NSAIDs and enhance their levels in gingival connective tissue. Using fluorescence to monitor NSAID transport, we demonstrated that cultured gingival fibroblasts transport naproxen in a saturable, temperature-dependent manner with a K(m) of 127 mug/mL and a V(max) of 1.42 ng/min/mug protein. At steady state, the intracellular/extracellular concentration ratio was 1.9 for naproxen and 7.2 for ibuprofen. Naproxen transport was most efficient at neutral pH and was significantly enhanced upon cell treatment with TNF-alpha. In humans, systemically administered naproxen attained steady-state levels of 61.9 mug/mL in blood and 9.4 mug/g in healthy gingival connective tissue, while ibuprofen attained levels of 2.3 mug/mL and 1.5 mug/g, respectively. Thus, gingival fibroblasts possess transporters for NSAIDs that are up-regulated by an inflammatory mediator, but there is no evidence that they contribute to elevated NSAID levels in healthy gingiva.

Figure 1

Naproxen accumulation by cultured gingival fibroblast monolayers. Cells were pre-incubated in a balanced salt solution at 37°C or 3°C for 10 min prior to the addition of 40 μg/mL naproxen. At the indicated times, the naproxen solution was removed, and extracellular naproxen was rapidly washed away. Where indicated, the cells were pre-treated for 15 min with 100 nM phorbol myristate acetate. Data are expressed as mean ± SEM of 6 experiments.

Figure 2

Characteristics of naproxen transport by cultured gingival fibroblasts. Upper panel: pH dependence of naproxen transport. Data are expressed as mean ± SEM of 5 experiments. At pH 6.3, 6.8, and 8.3, the K_m of transport was significantly higher than at pH 7.3 (P < 0.05, Dunnett’s test). Lower panel: Lineweaver-Burk plot of naproxen transport kinetics, showing competitive inhibition in the presence of 1 mM phenol red. The data are representative of 4 experiments.

Figure 3

Stimulation of fibroblast naproxen accumulation by phorbol myristate acetate and TNF- αUpper panel: Enhancement of fibroblast naproxen and ibuprofen transport by phorbol myristate acetate. Confluent fibroblast cultures were treated for 15 min with the indicated phorbol ester concentrations prior to incubation with naproxen or ibuprofen. The treatment effects of phorbol myristate acetate were significant for both NSAIDs (P < 0.001, analysis of variance, n = 6 experiments). Lower panel: Time- and dose-dependent enhancement of naproxen transport by TNF- α. Confluent fibroblasts were starved for 16 hrs in medium containing 0.5% fetal bovine serum and treated with the indicated concentrations of TNF for 1, 3, or 6 hrs prior to assay of naproxen transport. TNF produced a significant treatment effect at 1, 3, and 6 hrs (P ≤ 0.002, analysis of variance, n = 7 experiments).