The effect of long term supplementation D with different dietary omega 6 to omega 3 ratios on mineral content and ex vivo prostaglandin E2 release in bone of growing rabbits

The aim of this research was to study the different long term effects of consumption of dietary oil sources with varying omega 6 per omega 3 polyunsaturated fatty acids (PUFAs) ratios on bone marrow fatty acid level, ex vivo prostaglandin E2 (PGE2) release, and mineral content of bone in rabbits. For this purpose, weaning and female New Zealand white rabbits were purchased and randomly divided into five groups and offered ad libitum diets containing 70 g per kg of added oil for 100 days. The dietary lipid treatments were formulated to provide the following ratios of omega 6 per omega 3 fatty acids: 8.68 soy bean oil (SBO control), 21.75 sesame oil (SO), 0.39 fish oil (FO), 0.63 algae oil (DHA), and 0.68 algae oils (DHA per ARA). DHA and ARA are two types of marine microalgae of the genus Crypthecodinium cohnii. The dietary treatments had significant effects on the bone marrow fatty acids of rabbits. Rabbits fed the FO diet, containing the highest omega 3 PUFA concentration, and those fed the SBO diet showed the highest omega 6 PUFA. On the other hand, a positive correlation was observed between Ex vivo PGE2 level and the omega 6 to omega 3 dietary ratio. Significant effects of dietary treatment on femur Ca, P, Mg, and Zn contents were observed in both genders. Findings of the current study clearly demonstrated that dietary PUFA, particularly omega 6 omega 3 and ARA to EPA ratios are important factors in determining bone marrow fatty acid profile, and this in turn determines the capacity of bone for synthesis of PGE2, thereby reducing bone resorption and improving bone mass during growth. (Authors abstract)

During growth, addition of omega 3 LCPUFA (eicosapentaenoic acid EPA and docosahexaenoic acid DHA) enhances the bone formation rate, the mechanism of which has largely been attributed to reduced synthesis of prostaglandin E2 (PGE2) in bone. PGE2 is a potent stimulator of both bone formation and bone resorption. The effect of PGE2 on bone is based on its amount in bone, which follows a concentration dependent pattern, with moderate concentrations encouraging bone formation, and high concentrations causing elevated bone resorption. The omega 3 LCPUFA are precursors to PGE3, which is equally as potent as PGE2, in bone. However, conversion is less effective than for PGE2 from omega 6 LCPUFA (arachidonic acid ARA), resulting in a decrease in total PGE2. Reduction in the concentration of PGE2 may result in reduction of bone resorption, and enhancement of bone formation. The relationships among dietary fat, calcium metabolism, and bone development are still not clear. Dietary lipids, depending on the type and amount ingested, may impair bone growth or have no effect. In addition, dietary lipids modify the fatty acid composition of cartilage and bone. Alteration in the dietary ratio of omega 6 to omega 3 and supplementation with specific LCPUFA (ARA, EPA, and DHA) in the diet is known to increase Ca transport across the mucosal membrane, Ca absorption, bone Ca content and bone mass. The purpose of this study was to investigate different long term effects of consumption of dietary oil sources with varying omega 6 to omega 3 polyunsaturated fatty acids (PUFAs) ratios on the bone marrow fatty acids level, ex vivo prostaglandin E2 (PGE2) release, and mineral content of bone in rabbits, and to determine the role of gender to respond similarly or differently to this variation, and finally, to determine correlation between bone marrow omega 6 per omega 3 ratio and mineral content in bone. There was a main effect of different dietary omega 6 to omega 3 ratios on bone marrow EPA, total omega 3, omega 6 to omega 3, and ARA to EPA levels.  As the dietary ratio of omega 6 to omega 3 declined from 21.8 to 0.4, the concentrations of EPA and total omega 3 rose; and, as the dietary omega 6 to omega 3 ratio declined, so did the omega 6 to omega 3 and ARA to EPA ratios.  This study confirmed that different dietary oil sources varying in their omega 6 per omega 3 ratios caused significant alteration of the fatty acid profile of bone marrow. Rabbits fed the FO diet maintained a higher concentration of total omega 3 PUFA and lower omega 6 to omega 3 ratio compared to those fed the SBO control diet with a higher omega 6 PUFA content. Those fed the SO diet maintained a higher omega 6 to omega 3 ratio compared to those fed the control SBO diet. In addition, results of this study showed that bone marrow fatty acid profile in different groups reflected the effects of different dietary treatments. In conclusion, the current study clearly demonstrated that dietary PUFA, particularly omega 6 to omega 3 and ARA to EPA ratios are important factors in determining bone marrow fatty acid profile, and this in turn determines the capacity of bone for synthesis of PGE2, thereby reducing bone resorption and improving bone mass during growth. The reduction in the omega 6  to omega 3 ratio resulted in a significant increase in femur Ca, P, and Mg contents in both genders, although low dietary intake of these minerals suggests an important role of LCPUFA in mineral metabolism and bone mineralization. In addition, the reduction in the omega 6 to omega 3 ratio using fish oil or marine algae oils as sources of ARA, EPA, and DHA supports femur Ca, P, Mg, and Zn contents depending on the dietary amount of these fatty acids and, more importantly, their ratio. In addition, the significant elevation in mineral content and the maintenance of optimal Ca per P ratio in bones of DHA to ARA and DHA fed groups has proven that marine algae oils may be promising dietary sources for promotion of bone mineralization during the growing stage. (Editors comments)