This was the conclusion of a recent model study that NIFES carried out in collaboration with the University of Nijmegen in the Netherlands. Experiments on zebrafish suggest that excessive amounts of omega-6 fatty acids may disturb the delicate balance between the formation and breakdown of bone that is essential to the development of a healthy skeleton. Both processes take place continuously, and both are necessary for the skeleton to grow normally and optimally.
“We see that a high intake of omega-6 largely activates the mechanisms that break down bone, but to a much lesser extent those that build it up,” says NIFES scientists Kai Kristoffer Lie.
These findings are extremely relevant to the aquaculture industry, which to an even greater extent is utilising plant raw materials replacing marine oils and fish meal. Marine raw materials are rich in the omega-3 fatty acids EPA and DHA. Plant raw materials lack these fatty acids, but contain omega-6.
Breaks down bone
In this study, the scientists used zebrafish scales. Although these are located on the skin of the fish, they are formed in the same way as the skeleton.
In one experiment, zebrafish scales were collected and kept alive in the laboratory in various concentrations of omega-6. The scientists observed a rise in the level of activity of the enzyme that breaks down bone, in line with the rise in omega-6 concentrations. Also the genes that regulate bone breakdown were up-regulated.
In another experiment they removed scales from the zebrafish and analysed the scales that grew out to replace them. They looked at the ratio of calcium to phosphorus, which is a measure of the strength of both bone and scales. The fish had been given feed containing various levels of omega-6. Fish fed high levels of omega-6 had lower concentrations of phosphorus.
“All in all, we can see quite clearly that high levels of omega-6 change the pattern of activity in a way that can lead to the development of weaker structures. We also see that omega-6 has little effect on cells that are involved in the formation of bone,” says Lie.
This is the first time that zebrafish scales have been used to study how nutrients affect bone formation.
Model with wide range of applications
Since scales were affected by fat, both directly and via feed, the scientists have demonstrated that fish-scales are a useful model that gives rapid results. Scales also consists of relatively few different types of cells compared to a whole organism. This means that scientists have a the possibility to identify which molecular and biological systems are influenced by particular nutrients.
“The model helps us to explain how different fatty acids affect bone development. We believe that this model could also be useful in studies of contaminants and of how other nutrients affect bone metabolism. We have already planned our next series of experiments,” says Lie.