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Regular Manuscript

Docosahexaenoic acid and 17-oestradiol co-treatment is more effective than 17-oestradiol alone in maintaining bone post-ovariectomy

¹ Massey University
² Massey Univ

^* To whom correspondence should be addressed. E-mail: M.C.Kruger{at}massey.ac.nz.

	Abstract

Bone-protective effects of combined treatment with long chain polyunsaturated fatty acids (LCPUFAs) and oestrogenic compounds following ovariectomy have previously been reported. Recent evidence suggests the n-3 LCPUFA docosahexaenoic acid (DHA, 22:6n-3) is particularly bone-protective. The aim of this study was to determine whether combined treatment with DHA and oestrogenic compounds has a beneficial effect on bone mass in ovariectomised (OVX) rats. Rats were randomised into 9 groups and either ovariectomised (8 groups) or sham-operated (1 group). Using a 2x4 factorial design approach, OVX animals received either no oestrogenic compound, genistein (20mg/kg body weight/day), daidzein, (20mg/kg body weight/day) or 17-oestradiol (1µg/day) with or without DHA (0.5g/kg body weight/day) for 18 weeks. Bone mineral content (BMC), area (BA) and density (BMD), plasma osteocalcin and IL-6 concentrations and red blood cell (RBC) fatty acid composition were measured. Femur BMC was significantly greater in animals treated with DHA or 17-oestradiol than in ovariectomised controls. Plasma carboxylated osteocalcin was significantly higher in DHA-treated animals and total osteocalcin significantly lower in 17-oestradiol-treated animals compared to ovariectomised controls. There were significant interactions between treatment with oestrogenic compounds and DHA for femur BMC, plasma IL-6 concentration and RBC fatty acid composition. Combined treatment with 17-oestradiol+DHA was more effective than either treatment alone at preserving femur BMC and lowering circulating concentrations of pro-inflammatory Il-6. The percentage of n-3 LCPUFAs in RBCs was significantly greater in animals receiving 17-oestradiol+DHA compared to either treatment alone. There was no beneficial effect of combined DHA and phytoestrogen treatment on bone. Results from this study raise the possibility that co-treatment with 17-estradiol and DHA may allow a lower dose of 17-estradiol to be used to provide the same bone-protective effects as when 17-estradiol is administered alone.

Key Words: Isoflavones, n-3 fat, long chain polyunsaturated fatty acids, estrogen, phytoestrogens