Effects of conjugated linoleic acid on tissue lipid composition and bone remodeling in an ovariectomized aged rat model

Abstract

[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT REQUEST OF AUTHOR.] Dietary fat is known to alter certain characteristics of bone metabolism in rats. CLA has been shown to decrease arachidonic acid and PGE2, thus improving bone density. The objective of this study were to determine if varied sources of 0.6% CLA altered body fat content, specific organ weights, whole body BMC and BMD, rat tissue fatty acid compositions, femur bone mineral content (BMC), femur BMD, spine BMC, spine BMD, and osteoclast activity in aged ovariectomized female rats. Retired breeder (365 [plus or minus] 28 d of age and 4.5 [plus or minus] 0.5 parity), Sprague Dawley, female rats (n=86) were randomly assigned to ovariectomy (OVX) or sham (SHAM) surgeries. Rats were fed 4% soy oil (CON) for 14 d. For an additional 70 d, within surgery groups, rats were randomly allotted to dietary treatments: CON, 0.6% CLA + 3% soy oil (CLA), 0.6% CLA from cheddar cheese powder + 3% soy oil (CC), or 0.3% CLA + 0.3% CLA from cheddar cheese powder + 3% soy oil (CCCLA). Feed intake and body weight were measured weekly. Total fatty acids from liver, peritoneal fat, thigh muscle, and femoral bone marrow were extracted by chloroform:methanol and detected by gas chromatography. Whole body DEXA scans were performed to measure body fat content and bone composition prior to dietary treatments and post mortem. Additionally, BMC and BMD of femora and spines (L1-L4) were measured by high resolution DEXA scans. Activity of rat serum band 5 tartrate-resistant acid phosphatase (TRAcP5b), an osteoclast activity indicator, was detected by ELISA. Additionally, serum estradiol concentrations were measured by RIA. Dual-energy X-ray absorptiometry (DEXA) scans were performed to measure fat content and bone composition prior to dietary treatments and post-mortem. At the end of the feeding period rats were sacrificed and livers, thigh muscles, peritoneal fat, femurs, and tibias were removed and weighed. Fat content (P < 0.01), ADG (P < 0.01), and ADFI (P < 0.05) increased in OVX rats. Compared to SHAM, rats that were OVX had lower whole body BMD (P < 0.01) and femur weights (P < 0.01), thus resulting in less dense bones. There were no significant effects of treatment on whole body bone mineral content (BMC, g), bone mineral density (BMD, g/cm2), or body fat content (%). There were no differences for treatment or surgery effects on femur BMC, spine BMC, or spine BMD. However rats fed CC and CCCLA tended to have less dense femurs (P=0.08) when compared to CON- and CLA-fed rats. The fatty acid composition of liver was not significantly altered by the dietary treatments. When given CLA, the percentage of 20:4n6 (P<0.01) and total n3 (P<0.01) decreased in rat peritoneal fat. In thigh muscle, rats given CLA decreased total PUFA (P<0.01), PUFA:SFA (P<0.01), total n6 (P=0.01), total n3 (P<0.01), and 20:4n6 (P<0.01). Rats that were given CLA had lower amounts of 18:2n6c (P<0.05), total PUFA (P<0.01), PUFA:SFA (P<0.01), total n3 (P<0.01), and total n6 (P<0.05) in rat femoral bone marrow, therefore indicating a possible reduction in PGE2. TRAcP5b and estradiol were not affected by treatment, surgery, or the treatment by surgery interaction. Therefore, 0.6% CLA inclusion in aged rats may not be enough CLA for this enhanced anti-inflammatory response. In conclusion, the geriatric postmenopausal model that we created may be beneficial in future osteoporosis research.