PURPOSE: Apolipoprotein M (apoM) retards atherosclerosis development in murine 
models, and may be regulated by pathways involved in LDL metabolism. Proprotein 
convertase subtilisin-kexin type 9 (PCSK9) plays a key role in LDL receptor 
processing. We determined the extent to which plasma apoM is related to PCSK9 
levels in subjects with varying degrees of obesity.
METHODS: We sought correlations between plasma apoM and PCSK9, measured using 
recently developed ELISAs, in 79 non-diabetic subjects.
RESULTS: ApoM and PCSK9 levels were both correlated positively with total 
cholesterol, non-HDL cholesterol, LDL cholesterol and apoB (P < 0.05 to P < 
0.001). ApoM correlated positively with PCSK9 in lean individuals (n = 37, r = 
0.337, P = 0.041), but not in overweight subjects (n = 32, r = 0.125, P = 0.50) 
and in obese subjects (n = 10, r = -0.055, P = 0.88).
CONCLUSIONS: The PCSK9 pathway may contribute to plasma apoM regulation in 
humans. The influence of PCSK9 on circulating apoM appears to be modified by 
adiposity.