osteoarthritis ( oa ) is the most common form of arthritis and the leading cause of disability , especially among older adults . the disease process leads to limitation of joint movement , joint deformity , tenderness , inflammation , and severe pain . oa is characterized by progressive loss of cartilage from the articulating surfaces of diarthrodial joints . although the pathophysiologic mechanisms of osteoarthritis remain unresolved , chondrocytes in oa cartilage demonstrated morphologic changes that are characteristic features of apoptosis , which suggests apoptosis plays an important role in the development of oa [ 36 ] . conventional approaches for the treatment of oa range from conservative measures , to surgical intervention , and eventually joint replacement [ 79 ] . currently , there is no curative treatment for the disease . even though total joint replacement surgery is relatively successful for the treatment for oa , the lifespan of artificial joints is limited , and there are still significant problems such as implant loosening and failure , and the expensive cost . non - steroidal anti - inflammatory drugs ( nsaids ) are among the most widely prescribed drugs in the treatment of osteoarthritis ( oa ) to alleviate pain and thereby maintain the ability to perform normal daily physical activities , even in treatment of knee replacement surgery . the clinical efficacy of nsaids is primarily related to the inhibition of cyclooxygenase 2 ( cox-2 ) but not cyclooxygenase 1 . celecoxib , as one of the first selective cox-2 inhibitors , has been shown to be an effective anti - inflammatory and analgesic drug in patients with rheumatoid arthritis and oa , comparable to that of traditional nsaids , such as naproxen , diclofenac and ibuprofen [ 912 ] . a significant reduction of gastrointestinal adverse events with selective cox-2 inhibitors compared to non - selective nsaids has been frequently demonstrated . currently , several in vitro studies have shown celecoxib has a positive effect on human osteoarthritic cartilage , but it remains controversial as to what effects these agents have on the progression of oa . herein , based on surgically - induced osteoarthritis model , we performed a study to determine whether celecoxib could inhibit the apoptosis of chondrocytes and ameliorate type ii collagen synthesis to relieve symptoms of oa . one hundred and thirty wistar rats ( 3~4 months old ) were purchased from the laboratory animal center , chongqing medical university . an oa model in wistar rats was induced using the surgical resection of the left achilles tendon , resulting in a decrease in joint stress , performed as previously described . the left knee was used as the experimental side and the right knee as the control side . the experiments were done with reference to the long - term toxicity test methods in the methodology of pharmacological experiments . animals were randomly divided into 4 groups : celecoxib group ( ce ) , ibprofen group ( ibp ) , indomethacin group ( in ) and normal saline group ( ns ) . the daily drug dosages were : ce 24 mg / kg ( american silver pharmaceutical company ) , ibp 72 mg / kg ( chongqing southwest pharmaceutical co.ltd . ) , in 9 mg / kg ( chongqing kerui pharmacy co.ltd . ) , and ns ( sichuan kelun pharmaceutical co. ltd . ) . if there were more than 50 g in the weight difference between rats , the drug would be administered individually . at the end of the 3 , 6 , and 9 months of treatment after the surgically - induced model the knees were dissected from each animal , then fixed in 4% paraformaldehyde and 70% ethanol , and decalcified with 10% edta . after he staining , chondrocytes , cartilage surface , cartilage matrix and tide line were observed with the microscope . type ii collagen antibody , the sabc kit and dab are purchased from boston corp . the ihc stainings of cartilage matrix and chondrocyte were observed and photographed using an olympus microscope . beijing aviation medical image analysis system was adopted to calculate the average density of positive staining in every field . the apoptosis detection kit was purchased from mannheim company ( germany ) , and the procedure of tunel detection was performed according to the manual . the positive cells presented yellow particles distributed throughout the nuclear material , and the negative cells showed blue staining ( hematoxylin ) . apoptosis proportion was calculated by the formula : the number of positive cells / the total number of cells . five hundred chondrocytes were counted in every slide and per 1000 chondrocytes in different periods of each group . the rats were killed by vertebrae dislocation , the left knees were exposed and the weight loading area of femoral condyle ( 22 mm ) was obtained . the specimens were fixed with 1% osmium tetroxide , decalcified with 10% edta , dehydrated in a graded series of ethanol and acetone , and finally embedded in epoxy resin and semithin section . ultrathin sections were cut using an ultramicrotome , double stained , and examined and photographed with a transmission electron microscope . the quantitative and semi - quantitative data analyses , including the analysis of variance , and q - test , were performed with sas 6.12 software , and the significance level was set at =0.05 . one hundred and thirty wistar rats ( 3~4 months old ) were purchased from the laboratory animal center , chongqing medical university . an oa model in wistar rats was induced using the surgical resection of the left achilles tendon , resulting in a decrease in joint stress , performed as previously described . the left knee was used as the experimental side and the right knee as the control side . the experiments were done with reference to the long - term toxicity test methods in the methodology of pharmacological experiments . animals were randomly divided into 4 groups : celecoxib group ( ce ) , ibprofen group ( ibp ) , indomethacin group ( in ) and normal saline group ( ns ) . the daily drug dosages were : ce 24 mg / kg ( american silver pharmaceutical company ) , ibp 72 mg / kg ( chongqing southwest pharmaceutical co.ltd . ) , in 9 mg / kg ( chongqing kerui pharmacy co.ltd . ) , and ns ( sichuan kelun pharmaceutical co. ltd . ) . if there were more than 50 g in the weight difference between rats , the drug would be administered individually . at the end of the 3 , 6 , and 9 months of treatment after the surgically - induced model , the rats were killed . the knees were dissected from each animal , then fixed in 4% paraformaldehyde and 70% ethanol , and decalcified with 10% edta . after he staining , chondrocytes , cartilage surface , cartilage matrix and tide line were observed with the microscope . type ii collagen antibody , the sabc kit and dab are purchased from boston corp . , the ihc stainings of cartilage matrix and chondrocyte were observed and photographed using an olympus microscope . beijing aviation medical image analysis system was adopted to calculate the average density of positive staining in every field . the apoptosis detection kit was purchased from mannheim company ( germany ) , and the procedure of tunel detection was performed according to the manual . the stainings were observed and photographed using an olympus microscope . the test included a positive and negative control . the positive cells presented yellow particles distributed throughout the nuclear material , and the negative cells showed blue staining ( hematoxylin ) . apoptosis proportion was calculated by the formula : the number of positive cells / the total number of cells . five hundred chondrocytes were counted in every slide and per 1000 chondrocytes in different periods of each group . the rats were killed by vertebrae dislocation , the left knees were exposed and the weight loading area of femoral condyle ( 22 mm ) was obtained . the specimens were fixed with 1% osmium tetroxide , decalcified with 10% edta , dehydrated in a graded series of ethanol and acetone , and finally embedded in epoxy resin and semithin section . ultrathin sections were cut using an ultramicrotome , double stained , and examined and photographed with a transmission electron microscope . the quantitative and semi - quantitative data analyses , including the analysis of variance , and q - test , were performed with sas 6.12 software , and the significance level was set at =0.05 . the surface of articular cartilage became slightly rough , where is the focus of the stress . the toluidine blue staining was mildly uneven . because of death of the rats in the in group , the experiment in the 9th month could not be completed . at the 3 , 6 , 9 months of treatment after surgically induced animal model of oa , the ns group and ce group showed similar in different periods , which was the progressive development of oa . in the 3 month , the surface of the stress concentration area was rough , and double - columnar , nested chondrocyte hyperplasia was observed . in the 6 month , the superficial layer of articular cartilage shed , and there was a large amount of chondrocyte hyperplasia . in the 9 month , the superficial layer of the articular cartilage became rougher . the chondrocytes in the ns group decreased , while the chondrocytes in the ce group slightly decreased . to the in group , in the 3 month the layer of the cartilage became thinner and appeared villous . chondrocytes were arranged in irregular clusters . at the 6 month , the changes as mentioned above further progressed , and chondrocyte necrosis occurred . in the ibp group , in the 9 month , the thickness of the articular cartilage became thin and deteriorated . as shown in table 1 , at the 3 , 6 and 9 months , ibp promoted the expression of type ii collagen , but in inhibited its expression . as shown in table 2 , at the 3 month of treatment , ce suppressed chondrocyte apoptosis , while ibp and in promoted chondrocyte apoptosis , especially in . ibp significantly increased chondrocyte apoptosis , but chondrocyte apoptosis maximized at the 3 month of treatment , and then began to reduce . at the 9 month of treatment , ce still inhibited chondrocyte apoptosis . taken together , ce inhibited chondrocyte apoptosis and retained the degeneration of cartilage , while in and ibp promoted chondrocyte apoptosis and aggravated the degeneration of cartilage . in the ns and ce groups , the chondrocytes of articular cartilage appeared similar . the shape of cells was normal , with integrated nuclear membrane , slight aggregated chromatin and abundant cytoplasm . in the ce group , there were a large number of rough endoplasmic reticulum ( rer ) , mitochondria and glycogen in the chondrocytes . in the ibp group , the perinuclear halo gradually disappeared , cell shape was irregular , chromatin structure was obscure , the number of golgi complex and rough endoplasmic reticulum reduced and they shrank , and the structure of mitochondria was unclear . there are many microfilament and lysosome - related organelles in the cytoplasm . in the in group , the electron density of chondrocytes significantly increased , and many had lytic necrosis . the structure of collagen fiber in the matrix also became unclear ( figure 3 ) . the surface of articular cartilage became slightly rough , where is the focus of the stress . the toluidine blue staining was mildly uneven . because of death of the rats in the in group at the 3 , 6 , 9 months of treatment after surgically induced animal model of oa , the ns group and ce group showed similar in different periods , which was the progressive development of oa . in the 3 month , the surface of the stress concentration area was rough , and double - columnar , nested chondrocyte hyperplasia was observed . in the 6 month , the superficial layer of articular cartilage shed , and there was a large amount of chondrocyte hyperplasia . in the 9 month , the superficial layer of the articular cartilage became rougher . the chondrocytes in the ns group decreased , while the chondrocytes in the ce group slightly decreased . to the in group , in the 3 month the layer of the cartilage became thinner and appeared villous . chondrocytes were arranged in irregular clusters . at the 6 month , the changes as mentioned above further progressed , and chondrocyte necrosis occurred . in the ibp group , in the 9 month , the thickness of the articular cartilage became thin and deteriorated . the expression of type ii collagen was detected using immunohistochemistry ( figure 1 ) . as shown in table 1 , at the 3 , 6 and 9 months , ibp promoted the expression of type ii collagen , but in inhibited its expression . chondrocyte apoptosis was detected by tunel staining ( figure 2 ) . as shown in table 2 , at the 3 month of treatment , ce suppressed chondrocyte apoptosis , while ibp and in promoted chondrocyte apoptosis , especially in . at the 6 month of treatment , ce still inhibited chondrocyte apoptosis . ibp significantly increased chondrocyte apoptosis , but chondrocyte apoptosis maximized at the 3 month of treatment , and then began to reduce . at the 9 month of treatment , ce still inhibited chondrocyte apoptosis . taken together , ce inhibited chondrocyte apoptosis and retained the degeneration of cartilage , while in and ibp promoted chondrocyte apoptosis and aggravated the degeneration of cartilage . the shape of cells was normal , with integrated nuclear membrane , slight aggregated chromatin and abundant cytoplasm . in the ce group , there were a large number of rough endoplasmic reticulum ( rer ) , mitochondria and glycogen in the chondrocytes . in the ibp group , the perinuclear halo gradually disappeared , cell shape was irregular , chromatin structure was obscure , the number of golgi complex and rough endoplasmic reticulum reduced and they shrank , and the structure of mitochondria was unclear . there are many microfilament and lysosome - related organelles in the cytoplasm . in the in group , the electron density of chondrocytes significantly increased , and many had lytic necrosis . the structure of collagen fiber in the matrix also became unclear ( figure 3 ) . the pathological changes and the chemical indicators of cartilage in rat oa models which are noted in human oa have been widely used in the oa research . we adopted the resection of the tendon of the rats , which decreased the cartilage stress of the same side , and induced the instability of the joint and the irregularity of load conduction , resulting in the degeneration of the articular cartilage and then inducing oa . the pathological changes in the 3 , 6 and 9 months were similar to the slow pathological development of human oa . surgically - induced oa , which largely mimics the pathological process of oa , represents an ideal platform to study the early pathological changes associated with the disease , as well as being of use in the study on cartilage metabolism response to the drugs . recent in vitro and in vivo data on celecoxib have shown positive effects on cartilage of oa [ 1821 ] . these studies showed that celecoxib has favorable effects on the turnover of collagen metabolism of oa cartilage . late in oa , the balance between synthesis and degradation of type ii collagen is destroyed and the amount of type ii collagen in the cartilage matrix markedly decreases . in our study , at the 3 , 6 and 9 months of treatment , ce had no effect on the expression of the type ii collagen in oa chondrocytes , which indicates ce possibly does not interfere with the metabolism of type ii collagen in articular cartilage when it plays a role in anti - inflammatory and analgesics . in contrast , ibp promotes the expression of type ii collagen in chondrocytes and increase the synthesis of type ii collagen , which compensates for the loss of type ii collagen during oa . moreover , in inhibits the expression of type ii collagen in chondrocytes , decreases the synthesis of type ii collagen , and restrains the metabolism of type ii collagen in degenerative cartilage . accumulating evidences indicates chondrocyte apoptosis may represent an important component in the pathogenesis of oa [ 36 ] . in our study , a high frequency of chondrocyte apoptosis existed in articular cartilage during oa . chondrocyte apoptosis is positively associated with degree of cartilage matrix damage , which is consistent with previous reports [ 2527 ] . moreover , ce suppressed chondrocyte apoptosis and retained the degeneration of articular cartilage , while in and ibp promoted chondrocyte apoptosis and aggravated the degeneration of articular cartilage . . recently showed a beneficial effect of celecoxib in normal cartilage under the influence of il-1 and tnf- , but no effects in normal healthy cartilage . human articular chondrocytes stimulated with cytokines such as il-1 or tnf produce high levels of no . chondrocytes are the cellular components of cartilage metabolic activity , which is associated with the synthesis and degradation of cartilage matrix . the morphology of chondrocytes is related with metabolic activity and the synthesis of proteoglycan . in our study , ce promoted the number of golgi complex and rough endoplasmic reticulum , and enlarged their size . in the long - term use of nsaids in treatment of oa , ce displays better therapy and toleration , and retained the degeneration of oa cartilage , and may be the ideal choice for treatment of chronic destructive joint disease .