Effects Of Warm Exposure On Bone Mineral Density And Bone Metabolic Indexes In SAMP6 Mice

Purpose Several studies have shown that the lower the ambient temperature,the higher the risk of osteoporosis-related fractures in humans.Compared with people at low latitudes,people at high latitudes with long-term exposure to cold usually show lower bone mineral density and accelerated rate of bone loss.Animal experiments also show that placing mice in a warm environment at 30-34℃ can improves bone mass at birth,in adulthood and in ovariectomized mice(postmenopausal osteoporosis model),but studies on bone mass in aged mice are lacking.Therefore,we used Senescence accelerated mouse prone 6(SAMP6)mice(senescence osteoporosis model)as the experimental object to analyze whether warm exposure can affect and consistently affect the bone mineral density,bone microstructure and bone metabolism of senile mice.Materials and methods Twenty 3-month-old SAMP6 male mice were randomly divided into two groups:warm group(32±1)℃ and room temperature group(22±1)℃(temperature controlled by an infant incubator)after 7 days of acclimatization feeding,and fed continuously for 6 months at different temperatures in the two groups.Using dual-energy X-ray absorptiometry(DXA)for in vivo whole-body bone mineral density(BMD)measurement before the start of the experiment and at the end of 1,3 and 6 month of the experiment.At the end of 3 month,five mice from each group were randomly selected for eye removal and blood collection.The concentration of serum type I collagen carboxy-terminal peptide(CTX-I)and alkaline phosphatase(ALP)was detected by ELISA,then the right femur was taken for Micro-CT to detect and analyze the general bone parameters(bone mineral density,bone volume fraction,bone surface area/tissue volume ratio)and trabecular parameters(trabecular number,trabecular thickness,trabecular separation,trabecular pattern factor,trabecular connection density,anisotropy degree,structural pattern index).At the end of month 6,the remaining mice were treated with the same steps as above.Result1.Effect of ambient temperature on body weight and food intake of miceThe food intake of mice in the warm group was lower than that in the room temperature group(P<0.01),but there was no difference in body weight between the two groups(P>0.05).2.Effect of ambient temperature on whole-body BMDThere was no difference in the initial whole-body BMD between the two groups of mice(P>0.05);compared with the room-temperature group,at the end of 1 month,the BMD levels were relatively the same in the warm group(P>0.05),and at the end of 3 month,the BMD of mice in the warm group was significantly higher than that of the room-temperature group(P=0.0002),and at the end of 6 month,there was no significant difference in the BMD levels between the two groups(P>0.05).3.Effects of ambient temperature on bone microstructure(1)Results of bone general parameters:compared with the room temperature group,the warm group mice had an increase in bone volume/tissue volume(BV/TV)and bone surface area tissue volume(BS/TV)in the warm group at the end of 3 month,the difference was statistically significant(P<0.05),and the bone mineral density(F-BMD)of femur had some increase,but the difference was not statistically significant(P>0.05);the warm group had an increase in BV/TV,F-BMD,and BS/TV were increased in the warm group at the end of 6 month,but the difference was not statistically significant(P>0.05).(2)Results of bone trabecular analysis parameters:compared with the room temperature group,the number of trabeculae(Tb.N),thickness of trabeculae(Tb.Th),and density of trabecular junctions(Conn.D)increased and the separation of trabeculae(Tb.Sp)and structural pattern index(SMI)decreased in the warm group at the end of 3 month,and the differences were statistically significant(P<0.05),and the trabecular pattern factor(Tb.Pf),and degree of anisotropy(DA)were reduced but not statistically significant(P>0.05),and Tb.N,Tb.Th,and Conn.D were increased in the warm group at the end of 6 month,and Tb.Sp,Tb.Pf,DA,and SMI were reduced but not statistically significant(P>0.05).4.Effect of ambient temperature on serum bone metabolic indexesCompared with the room temperature group,the level of ALP in the warm group increased(P<0.05)and the level of CTX-1 decreased(P>0.05)at the end of 3 month.At the end of 6 month,the level of ALP in the warm group increased and the level of CTX-1 decreased,but there was no statistical difference(P>0.05).Compared with the end of 3 month,the ALP of the two groups decreased and the CTX-1 increased in both groups of mice at the end of 6 month,and the difference was statistically significant(P<0.05).Conclusions Warm exposure reduced food intake in mice,but had no effect on body weight.Intervention of ambient temperature could delay the decrease of BMD and increase the level of ALP in SAMP6 mice in the early stage of aging,but the above effects could not be sustained in the later stage of aging.Therefore,warm exposure intervention in the early stage of senile osteoporosis can delay the process to some extent and may provide a novel choice for the prevent of senile osteoporosis.