A review of odd-chain fatty acid metabolism and the role of pentadecanoic Acid (c15:0) and heptadecanoic Acid (c17:0) in health and disease

Abstract

The role of C17:0 and C15:0 in human health has recently been reinforced following a number of important biological and nutritional observations. Historically, odd chain saturated fatty acids (OCS-FAs) were used as internal standards in GC-MS methods of total fatty acids and LC-MS methods of intact lipids, as it was thought their concentrations were insignificant in humans. However, it has been thought that increased consumption of dairy products has an association with an increase in blood plasma OCS-FAs. However, there is currently no direct evidence but rather a casual association through epidemiology studies. Furthermore, a number of studies on cardiometabolic diseases have shown that plasma concentrations of OCS-FAs are associated with lower disease risk, although the mechanism responsible for this is debated. One possible mechanism for the endogenous production of OCS-FAs is α-oxidation, involving the activation, then hydroxylation of the α-carbon, followed by the removal of the terminal carboxyl group. Differentiation human adipocytes showed a distinct increase in the concentration of OCS-FAs, which was possibly caused through α-oxidation. Further evidence for an endogenous pathway, is in human plasma, where the ratio of C15:0 to C17:0 is approximately 1:2 which is contradictory to the expected levels of C15:0 to C17:0 roughly 2:1 as detected in dairy fat. We review the literature on the dietary consumption of OCS-FAs and their potential endogenous metabolism.

Figure 1

(A) On the left—the bacteria bio-synthesis pathway for the production of the fatty acids, C16:0 and C18:0 through the repeated condensation of malonyl CoA with acetyl CoA [19]. (B) On the right—the fundamental processes of α-oxidation where the removal of one carbon produces an odd chain fatty acid [18].

Figure 2

Cyclic β-oxidation process and the production of the acetyl CoA molecules [76]. This diagram shows the substrates and products of each reaction in the β-oxidation pathway.

Figure 3

The α-oxidation process on the β-branched chain fatty acid (phytanic acid) to produce an α-branched chain fatty acid (pristanic acid) which then can be activated and enter the β-oxidation pathway [77].

Figure 4

The comparison between the C15:0 and C17:0 fatty acids within dairy products [4] and the comparative concentration within in plasma [59].