The Biological Effect Of Angiotensin-converting Enzyme Inhibitor Captopril On Bones In Normal And Orchidectomised Male Mice

Background:The main effector peptide Ang II in RAS is formed from angiotensin I by the action of ACE,a key molecule in this system.Patients treated with an ACE inhibitor?ACEI?showed an increased bone mineral density?BMD?and a reduced fracture risk.However,recent clinical data indicated that the use of ACEI did not have beneficial effects on bones,and even led to bone loss in older American men,Chinese women and Japanese.This study was performed to investigate the effect of angiotensin-converting enzyme inhibitor,captopril,on bone metabolism and mechanism in normal and orchidectomised male mice.Part one:Objective:This study was performed to investigate the effect of angiotensin converting enzyme inhibitor?ACEI?,captopril,on bone metabolism and histology in normal male mice.Methods:The mice were orally administered with captopril(10 mg/kg·^-1)for 4weeks and 8 weeks with vehicle-treated mice as normal control.The biomarkers in serum and urine were measured,and tibias were taken for the measurement on gene expression.The histology of trabecular bone at distal femoral end was determined by Hematoxylin&Eosin,Safranin O and Masson-Trichrome staining.Results:The mice after treatment with captopril showed decreased level of testosterone?P<0.05?and procollagen type I N-terminal propeptide?P<0.05?in serum as compared to those in control group.The serum level of tartrate-resistant acid phosphatase?TRAP?,one of bone resorption markers,was not changed between groups.Captopril has detrimental effects on trabecular bone as demonstrated by the loss of cancellous bone mass and network connections as well as the changes of chondrocytes zone.Conclusions:The present study demonstrated that the treatment with ACEI captopril has detrimental effects on trabecular bone of normal mice.The potential underlying mechanism for the damages of captopril on bone may be attributed to the inhibition of bone formation.Part twoObjective:This study was performed to investigate the involvement of skeletal renin-angiotensin system?RAS?of mice in response to the treatment with ACEI captopril.Methods:Modle establishion is the same way with part one.And tibias were taken for the measurement on RAS components gene and protein expression.Results:The treatment of captopril significantly increased the mRNA expression of renin receptor?P<0.01?,but did not change the mRNA expression of AGT or chymase.The mRNA expression of ACE upon to captopril treatment for 4 weeks and 8 weeks was increased by 38%?P<0.05?and 21%,respectively,as compared to those of control group.The mice after treatment with captopril showed higher expression of Ang II?P<0.05?and B2R?P<0.05?than those of mice without treatment.In addition,the captopril treatment did not alter the protein expression of renin and B1R.Conclusions:The potential underlying mechanism for the damages of captopril on bone may be attributed to the increased activity of local bone RAS and the activation of bradykinin receptor upon to captopril treatment.Part threeObjective:This study was performed to investigate the effect of ACEI captopril on bone histology in orchidectomised male mice.Methods:Twenty-four ICR normal male mice aged 10 weeks old were divided into four groups of sham-operated?Sham?,orchidectomised control?ORX?,orchidectomised+low captopril(OL,10mg/kg·d^-1),orchidectomised+high captopril(OH,50mg/kg·d^-1).The mice were orally administered captopril for 6 weeks with vehicle-treated mice as normal control.The biomarkers in serum and urine were measured,and the histology of tibias,femurs and the 4_th lumbar vertebras was determined by Hematoxylin&Eosin,Safranin O and Masson-Trichrome staining.Results:Compared with Sham group,serum calcium of the ORX group significantly decreased?P<0.05?,urinary calcium decreased slightly,and trabecular thickness was significantly decreased?P<0.05?,thickness of cortical and growth plate also decreased in varying degrees.Conclusions:The treatment of Captopril increased thickness of trabecular,cortical and growth plate,and also increased bone densityand and improved bone tissue microstructure effectively in orchidectomised male mice.Summary:?1?The present study demonstrated that the treatment with ACEI captopril has detrimental effects on bone of normal mice.?2?The potential underlying mechanism for the damages of captopril on bone may be attributed to the increased activity of local bone RAS and the activation of bradykinin receptor upon to captopril treatment.?3?The ACEI captopril improves the microstructure of bone tissue and reduce the risk of osteoporosis in orchidectomised male mice.