Vitamin K₂ Monotherapy And Combined Therapy With Calcitriol On Bone And Other Target Organs In Ovariectomized Rats

【Background】Osteoporosis is becoming prevalent with the aging of the world population. Postmenopausal women are at increased risk of osteoporosis and osteoporostic fracture for low peak bone mass and fast bone loss resulting from estrogen deficiency.Estrogen therapy is one of the best treatment protocols for postmenopausal osteoporosis,but it has not been accepted by most menopausal women in China.Although vitamin D(VD) regarded as basal drug is widely used for preventing and curing osteoporosis in the world,it has limited efficacy on protection against osteoporosis.Nowadays,vitamin K' s(VK) effects has extended beyond blood clotting to include a role in bone metabolism and potential protection against osteoporosis.In theory,the efficacy of combined treatment with VK and VD may be greater than alone.Furthermore,it is pointed out that VK₂ may prevent from vessel calcification and decrease the incidence of cardiovascular disease.In addition,few side effects have been observed concerning its coagulatory properties under the dosage for osteoporosis.So it is a fairly safe drug.【Objective】This study is designed to investigate the effects of VK₂(menatetrenone) and combined therapy with VD₃(1,25-dihydroxyvitaminD₃,calcitriol) on ovariectomized rats concerning prevention of osteoporosis as well as vessel calcification,blood lipid metabolism and coagulation.The results will serve as evidences guiding clinical application of VK₂ in postmenopausal osteoporosis.【Methods】Establishment of rats model for postmenopausal osteoporosis:37 SD and SPF female rats of 10 months old were randomized into 5 groups according to weight:sham(8), OVX(8),OVX+VK₂(7),OVX+VD₃(7) and OVX+VK₂+VD₃(7).Gastric infusion of corresponding drugs was performed 2 weeks after operation.VK₂:30mg/kg/d;VD₃: 0.1ug/kg/d;Sham and OVX:purified water 2.5ml/kg/d.Variables were evaluated 14 weeks later including bone density,bone turnover parameters,bone histomorphometry, bone biomechanies,blood lipids,coagulatory parameters and aorta calcification.【Results】Effects on bone:(1) turnover parameters:BALP and uDPYD are much increased in OVX group than those in Sham group,revealing an increased bone turnover rate.VK₂ group presents much higher uDPYD and uCa/uCr compared with OVX group,but the BALP is not statistically different between the two groups.The BALP in VD₃ group is lower than that in OVX group.The three parameters are not significantly changed in VK₂+VD₃ group compared with OVX group.VK2 group presents an apparent increase in uDPYD compared with the Sham group.The interaction between VK2 and VD3 on uDPYD is found.(2)BMD:The lumbar BMD in OVX group is lower than Sham group and other groups with drug treatment,while no difference is observed in drug treatment groups compared with sham group.The significant BMD decrease of both femurs in OVX group is observed compared with sham group.Meanwhile,the significant increase of BMD is found in both femurs of VK2+VD3 group and in left femur of VD3 group compared with OVX group.The BMD of both femurs in group VK2 is similar to that in OVX group and is lower than that in sham group.However,no difference is found in VD3 group and combined treatment group compared with sham group regarding BMD of the femurs.In addition,the BMD of right femurs in VK2 group is markedly lower than that in combined treatment group.But no interaction between VK2 and VD3 is showed on both lumbar BMD and femoral BMD.(3) bone morphometry:All the bone formation parameters and absorption parameters in OVX group are higher than Sham group,among which%L.Pm is statistically different.OVX group presents a decreased trabecular thickness,a larger trabecular separation and a lower trabecular count than sham group but the difference is not significant.Compared with OVX group,all bone formation parameters increase in VD3 group and VK2+VD3 group,among which BFR/BS and MAR are much higher than those in OVX group;%E.Pm,one of bone absorption parameters,decreases in the two groups,but it does not attach statistical significance.All parameters indicating bone mass and bone structure in administered groups are not significantly different from those in OVX group.With MAR and BFR/BS significantly increasing and%E.Pm significantly decreasing in VK2+VD3 group,the combined therapy group shows better efficacy for promoting bone formation and suppressing bone absorption than that in VK2 group.Regarding all parameters mentioned above,no difference is observed between VK2 group and VK2+VD3 group. Concerning BV/TV,Tb.N,Tb.Th and Tb.Sp,no difference is found between OVX group and administered groups.Compared with the sham group,the administered groups present same changes in parameters of bone content and structure including downgrading of BV/TV and Tb.N and upgrading of Tb.Sp.Both BV/TV and Tb.Sp in VK2 group are significantly different from sham group,which suggests lower bone mass in VK2.The formation parameters increase in administered groups,and%L.PM,MAR and BFR/BS significantly upgrade in VD3 group and in VK2+VD3 group compared with sham group.(4) biomechanics:No difference for all parameters is observed between OVX group and Sham group.As for maximum load,maximum strain and Young's modulus, all the administered groups present no difference from the Sham and OVX group. However,for maximum load,VK2 group is significantly lower than VD3 group. (5)serum calcium ion:The level of serum calcium in VD3 group and VK2+VD3 group is higher than that in OVX group and in sham group,while that in VK2 group is not different from that in the two groups.The level of serum calcium shows a marked increase in VK2 group compared with combined treatment group.Effects on other systems:(1) prothrombin time:no difference between the groups. (2)serum lipids:Compared with OVX group,VK2 group presents an significant increase of LDL,VD3 group shows a increase of LDL and TC,and VK2+VD3 group reveals a upgrade of LDL,HDL and TC.The LDL is higher in VK2 group than that in sham group.However,no difference is revealed in VD3 group and VK2+VD3 group compared with sham group.The two drugs' interaction is found on LDL.(3)aorta:Thoracic aorta calcification is observed in one case in sham group,in three cases in OVX group and two cases in VD3 group as well as VK2+VD3 group,respectively.No calcification is found in VK2 group.【Conclusion】(1) Administration of VK2 alone can sustain the lumbar BMD of ovariectomized rats with unidentifying mechanism.A dosage of 30mg/kgBW adds no risk to coagulation function in rats and is beneficial for preventing vessel calcification.VK2 has no advantages on serum lipids.(2) Administration of VD3 alone can sustain the BMD of ovariectomized rats both in lumbar and in femur by promoting bone formation.In addition,it does not show disadvantages to aorta and serum lipid.(3) The combined therapy with VK2 and VD3 presents better efficacy for sustaining BMD ovariectomized rats than that administered group with VK2 alone because of increasing bone formation and suppressing bone absorption.Meanwhile,no apparent side effect is observed on coagulation,serum lipid and aorta.