N-3 PUFA prevents deterioration of bone induced by two-hit stress through corticosterone-related mechanism in ovariectomized rats

Abstract

A two-hit stress, a combination of stresses in early life and adulthood, triggers overexcretion of corticosterone (CORT), which is associated with bone loss. Previously, several studies reported that n-3 polyunsaturated fatty acids (PUFA) have beneficial effects on decrement of CORT secretion in rats with chronic stress, and preventing bone loss in ovariectomized (OVX) animals without stress. Therefore, the purpose of the present study was to investigate the hypothesis that supplementation of n-3 PUFA had protective effects against bone loss induced by two-hit stress or chronic stress alone through CORT related bone mechanism in adult OVX pups. Female pups were fed a modified AIN-93G diet with 0% or 1% n-3 PUFA related to the total energy intake during pre-weaning, post-weaning, or lifetime period. In addition, female pups underwent daily 3 h maternal separation (MS) plus chronic mild stress (CMS) including seven different stressors (CMS+MS), or CMS alone. CMS alone and CMS+MS significantly increased blood levels of CORT and n-telopeptide of type I collagen (NTx), and bone expression of receptor activator of NF-κB ligand (RANKL), but decreased bone concentration of calcium and expression of runt-related transcription factor 2 (RUNX2) compared to non-stress. Micro computed tomography showed that CMS alone and CMS+MS deteriorated architecture of distal femur including bone volume (BV), BV/tissue volume and porosity. Moreover, CMS+MS significantly exacerbated these effects compared to CMS alone. Regardless of stress, supplementation of n-3 PUFA during lifetime decreased blood levels of CORT and NTx, and bone expression of RANKL, but increased bone concentration of calcium and expression of RUNX2 with improved bone structure. Additionally, n-3 PUFA supplementation during pre-weaning or post-weaning showed a tendency to have bone protective effects, but were not significant. The present study suggested that the supplementation of n-3 PUFA during lifetime had similar protective effects on bone loss induced by CMS alone or CMS+MS through down-regulation of CORT overexcretion, resulting in improvement of RANKL and RUNX2 expressions.