Background Researches showed that platelet-derived growth factor (PDGF) modulate the expression of matrix metalloproteinase/tissue inhibitor of metalloproteinase (MMP/TIMP) in cells,but the association of expression of MMP/TIMP in retinal pigment epithelial (RPE) cells and the dose and active time of PDGF is unclear.Objective This study was to observe the effects of PDGF on the expressions of MMP-2,MMP-9 and TIMP-1 in cultured RPE cells in vitro.Methods RPE cell line,ARPE-19,was calculated in vitro,and the cells were divided into 5 groups when they reached 70％-80％ confluence.Different concentrations (0,0.1,1,10,50 mg/L) of PDGF was added into the medium respectively for 36 hours,and the expressing levels of mRNA and protein of MMP-2,MMP-9 and TIMP-1 were detected by reverse transcription PCR (RT-PCR) and Western blot assay.In addition,RPE cells in PDGF group were treated with 10 mg/L PDGF for 24,36,48 hours respectively to detect the expressions of mRNA and protein of MMP-2,MMP-9 and TIMP-1 in the cells and to compare with the control group without PDGF.Results PDGF stimulated proliferation of RPE cells in a dose-and time-dependent manner.As the increase of the PDGF concentrations,the expression values of MMP-2 mRNA and MMP-9 mRNA in RPE cells were gradually elevated,with a statistically significant difference among various groups (MMP-2 mRNA:F=79.304,P=0.000;MMP-9 mRNA:F =8.465,P=0.003),and the expressions of MMP-2 mRNA and MMP-9 mRNA were significantly higher in the 1,10,50 mg/L PDGF groups compared with 0 mg/L PDGF normal control group (all at P＜0.05).Also,the expression values of MMP-2 and MMP-9 proteins in RPE cells were gradually elevated with the increase of PDGF concentrations,showing statistically differences among the groups (MMP-2:F=26.550,P=0.000;MMP-9:F=80.993,P=0.000).Compared with the 0 mg/L PDGF group,MMP-2 and MMP-9 expression levels in the 1,10,50 mg/L PDGF groups were significantly up-regulated (all at P＜ 0.05).However,the expression levels of TIMP-1 mRNA and protein group in the cells were not significantly different among various groups (mRNA:F =0.143,P =0.962 ; protein:F =1.955,P =0.178).The expression levels of M MP-2 mRNA,M MP-9 mRNA in the cells were increased in the PDGF group compared with the control group at different time points (MMP-2 mRNA:Ftime =83.250,P=0.002 ; MMP-9 mRNA:Ftime =6.785,P =0.019).Also,the expression values of MMP-2 and MMP-9proteins in RPE cells were increased in the PDGF group compared with the control group at different time points (MMP-2:Ftime =1 l.185,P =0.041 ; MMP-9:Ftime =968.413,P =0.000).The expression levels of MMP-2 and MMP-9 mRNAs and proteins were significant between the two groups at different time points (all at Pgroup =0.000;all at Ptime＜0.05).While the expression changes of TIMP-1 werc not significant between the two groups and among various time points (all at P＞0.05) Conclusions PDGF up-regulates MMP-2 and MMP-9 expressions in RPE cells in a dose-and time-dependent manner.But,PDGF dose not alter the expression of TIMP-1.These results indicate that PDGF disrupt the balance of MMP/TIMP,which may damage the extracellular matrix and therefore facilitate the migration of RPE cells in the pathogenesis of proliferative vitreoretinopathy.

Objective To provide scientific information for comprehending the progress of asthma research, speculating asthma research trends and selecting the reserach topics and promoting thorough asthma research by studying the speciality distribution of asthma papers.Date and Methods MEDLINE search was conducted to retrieve the papers published between the years 1983-1996 under the main headings of asthma. Nationalities, languages, journals, authors and headings frequency of 24 276 papers were analysed with bibliometrics.Results 24 276 papers on asthma research between the years 1983-1996 were found in MEDLINE. They came from 74 nations and regions, in 27 languages and 451 journals. 91.36% came from America and 14 other nations, while 59 other nations made up less than 9%. Six nations publishing papers more than others were America 8778 (36.4%), England 4143 (17.07%), Denmark 1465 (6.03%), Japan 1288 (5.31%), Germany 1079 (4.44%) and Switzerland 1075 (4.43%). 74.21% were in English and 26 other languages were only 25.8%. The source journals of papers showed the distribution of the Bradford's law. Less than 1% journals carried more than 20% of all papers. 5 journals that carried more papers than others were Am J Respir Crit Care Med 1212 (5%), JAllergy Clin Immunol 1124 (4.63%), Chest 960 (3.96%), Eur Respir J 825 (3.40%), and Ann Allergy Asthma Immunol 800 (3.30%). There were 15 authors who each presented more than 30 papers in first position, among whom, Barnes PJ (English) produced 70 papers, Tanizaki Y (Japanese) 53 papers, Mole JL (Canadian) 48 papers, Sears MR (New Zealander) 47 papers, and Holgate ST (English) 43 papers. The variety of subject heading frequency reflected the hot topics and the developing direction of the research. Heading frequency on asthma research focused on therapeutics 27.20% (including drug therapy 20.07%, comprehensive therapy 7.01%, diet therapy 0.09%, and radiotherapy 0.03%); physiopathology 18.10%; immunology 8.03%; diagnosis 7.88% and etiology 7.82%. It is worth noticing that little has been done before on epidemiology, economics, microbiology and virology of asthma, but literature on these aspects has increased obviously in recent years. Conclusion Asthma literature mainly came from America and 5 other nations. English was the major language. The source journals of the papers showed the distribution of the Bradford's law. Am J Respir Crit Care Med and 4 other journals were core journals of asthma research. Barnes PJ and 14 other authors were the most active and the most important researchers in this field. Treatment, physiopathology, immunology, diagnosis and etiology were the emphasis and hot topics on asthma research. Great attention has been paid to the research on epidemiology, economics, microbiology and virology of asthma year after year.