OBJECTIVETo investigate the effects of atorvastatin on C-reactive protein (CRP) induced Toll-Like receptor 4 (TLR4)expression on CD14+ monocyte, and the production of proinflammatory cytokines tumor necrosis factor alpha (TNFalpha), interleukin-6 (IL-6), matrix metalloproteinases-9 (MMP-9), and to study the anti-inflammatory mechanisms of statins.

METHODSThe monocytes were isolated from blood of healthy volunteers by the Ficoll density gradient and stimulated by CRP with different doses (5, 25, 50, 100 microg/ml) and different exposure time (6, 12, 24, 48 h). Cells were also incubated with atorvastatin of different doses (1.0, 2.5, 5.0, 7.5, 10.0 micromol/L) in the presence of CRP 50 microg/ml. The protein expression of TLR4 was measured by flow cytometry, mRNA expression of TLR4 and of myeloid differentiation protein (MD2)was detected by quantitative PCR. TNFalpha, IL-6, MMP-9 concentrations in supernatants of cultured medium were measured by ELISA.

RESULTS(1) Compared with the un-stimulated control group, enhanced TLR4 protein expression was already detected at a concentration of 5 microg/ml of CRP and increased in a dose-dependent manner (32.22 +/- 2.80)%, (49.94 +/- 5.58)%, (74.82 +/- 3.24)% and (90.82 +/-2.88)% at 5, 25, 50 and 100 microg/ml CRP. (2) TLR4 protein expression on 50 microg/ml CRP stimulated cells also increased in a time-dependent manner (29.80 +/- 2.70)%, (47.44 +/- 4.41)%, (81.71 +/- 2.92)% and (50.57 +/- 3.34)% after 6 h, 12 h, 24 h, 48 h. (3) When monocytes were incubated with CRP 50 microg/ml and atorvastatin (1.0, 2.5, 5.0, 7.5, 10.0 micromol/L), protein expression [(68.17 +/- 1.71)%, (52.43 +/- 1.38)%, (27.72 +/- 4.55)%, (17.46 +/- 3.20)%, (9.99 +/- 2.81)%] and mRNA expression (82.72%, 67.34%, 48.16%, 30.88%, 13.85%) of TLR4 as well as mRNA expression of MD2 (81.78%, 71.04%, 47.85%, 27.06%, 18.30%) were reduced in a dose-dependent manner. (4) Level of TNFalpha, IL-6 and MMP-9 in supernatants was significantly reduced by atorvastatin (2.5 micromol/L) compared with control group (P < 0.01). When monocyte incubated with CRP 50 microg/ml and atorvastatin 10.0 micromol/L, the level of TNFalpha, IL-6, MMP-9 decreased to (25.8 +/- 2.5) microg/ml, (128.2 +/- 14.7) pg/ml, (65.2 +/- 12.3) ng/ml, respectively.

CONCLUSIONCRP increased the protein expression of TLR4 on CD14+ monocyte in a dose-dependent and time-dependent manner. Atorvastatin can inhibit the signal transduction of TLR4 and reduce proinflammatory cytokines release induced by CRP on CD14 monocyte, and this might be one of the anti-inflammatory mechanisms of atorvastatin.