Replacement of the linoleic tail with a primary ester-containing lipid tail (Lipid 5) provids increased expression and optimal tissue clearance. The metabolite identification studies with Lipid 5 indicated that hydrolysis of the primary ester is the first step in the metabolism of the lipid[1].

Clearance of Lipid 5 and MC3 from multiple mouse tissues is measured after dosing 0.05 mg/kg mRNA on days 1, 8, and 15 in CD-1 female mice. Liver and spleen have the highest levels of Lipid 5, however, significantly lower levels than MC3. Lipid 5 is detected in plasma, lung, and kidney, but not in heart[1].