The metabolism and distribution of docosapentaenoic acid (n−6) in rats and rat hepatocytes

Abstract

In this study, a new marine oil that contains 45% docosahexaenoic acid (DHA, 22:6n-3) and 13% docosapentaenoic acid (DPA, 22:5n-6) was administered to rats. The metabolism and distribution of DPA in rats was investigated. In experiment 1, the effects of DHA and n-6 fatty acids (linoleic acid, LA; arachidonic acid, AA; and DPA) on AA contents were investigated in vivo. LA group: LA 25%, DHA 30%; LA-DPA group: LA 15%, DPA 10%, DHA 35%; LA-AA-DPA group: LA 10%, AA 5%, DPA 10%, DHA 35% were administered to rats for 4 wk. In the liver, the AA content in the LA-DPA and LA-AA-DPA groups was significantly higher than in the LA group. The decreased AA contents in the LA group might be caused by DHA administration. Although DHA also was administered in the LA-DPA and LA-AA-DPA groups, the AA contents in these two groups did not decrease. These results suggested that DPA retroconverted to AA, blunting the decrease in AA content caused by DHA administration. To conduct a detailed investigation on DPA metabolism and its relation with AA and DHA, rat hepatocytes were cultured with purified DPA and DHA for 24 h. We discovered the retroconversion of DPA to AA occurred only when AA content was decreased by a high DHA administration; it did not occur when AA content was maintained at a normal level.

Bioconversion of Docosapentaenoic Acid in Human Cell Lines, Caco-2, HepG2, and THP-1

“…Retro-conversion of n-6 DPA was also reported in rat hepatocytes 23 . However, the bioconversion profiles of DPAs have not been compared between several human cell lines established from different tissues and blood.…”

The Metabolism and Distribution of Docosapentaenoic Acid (n-6) in the Liver and Testis of Growing Rats

“…This D6D decline did not stop the increase of 20:4n-6 by 22:5n-6, which implies that the conversion of 22:5n-6 to 20:4n-6 did not involve D6D and supports the retroconversion of 22:5n-6 to 20:4n-6 that had been reported in our previous study. 19) Studies on the retroconversion of 22:5n-6 to 20:4n-6 in rat liver have reported that the retroconversion occured with 22:4n-6 as the intermediate, suggesting that retroconversion took place by direct hydrogenation and subsequent -oxidation. 24) It has been well reported that a 20:4n-6 decline would be caused by 22:6n-3 administration in vivo.…”

“…19) The testis is an organ that consumes C22 PUFA to transport the sperm into the vesiculae seminalis. 34) At homeostasis, 22:5n-6 as the dominant C22 PUFA in the testis is believed to be involved in the function of sperm transportation.…”

“…In our previous in vivo and in vitro study, 22:5n-6 was found to blunt the decrease in 20:4n-6 level, but 18:2n-6 could not prevent the same decline in 20:4n-6 caused by a high 22:6n-3 administration level, implying that the 20:4n-6 level increased by 22:5n-6 supplementation was not affected by 22:6n-3. 19) There has been no previous report on the effect of 22:6n-3 on the 20:4n-6 level from pregnancy; studies on the effect of 22:5n-6 and 18:2n-6 on the biosynthesis of 20:4n-6 conditioned by high 22:6n-3 supplementation are also limited. It would therefore be valuable to compare the effects of 22:5n-6 and 18:2n-6, the two possible sources of 20:4n-6 accumulation, under a high 22:6n-3 administration level on the accumulation of 20:4n-6 in pups from pregnancy to weaning.…”

“…19) Therefore, the testicular 22:5n-6 accumulation was investigated in newborn and weaned rats to clarify the source of 22:5n-6 in the testis during growth.…”