Background:
ApoC-III is an important regulator of triglyceride metabolism and was associated with cardiovascular risk in several cohorts. ApoC-III is present in 4 major proteoforms, a native peptide (C-III
0a
), and glycosylated proteoforms with zero (C-III
0b
), 1 (C-III
1
, most abundant), or 2 (C-III
2
) sialic acids, which may differentially modify lipoprotein metabolism. We studied the relationships of these proteoforms with plasma lipids and cardiovascular risk.
Methods:
ApoC-III proteoforms were measured by mass spectrometry immunoassay in baseline plasma samples of 5791 participants of Multi-Ethnic Study of Atherosclerosis, an observational community-based cohort. Standard plasma lipids were collected for up to 16 years and cardiovascular events (myocardial infarction, resuscitated cardiac arrest, or stroke) were adjudicated for up to 17 years.
Results:
ApoC-III proteoform composition differed by age, gender, race and ethnicity, body mass index, and fasting glucose. Notably, C-III
1
was lower in older participants, men and Blacks and Chinese (versus Whites), and higher in obesity and diabetes. In contrast, C-III
2
was higher in older participants, men, Blacks, and Chinese, and lower in Hispanics and obesity. Higher C-III
2
to C-III
1
ratio (C-III
2
/III
1
) was associated with lower triglycerides and higher HDL (high-density lipoprotein) in cross-sectional and longitudinal models, independently of clinical and demographic risk factors and total apoC-III. The associations of C-III
0a
/III
1
and C-III
0b
/III
1
with plasma lipids were weaker and varied through cross-sectional and longitudinal analyses. Total apoC-III and C-III
2
/III
1
were positively associated with cardiovascular disease risk (n=669 events, hazard ratios, 1.14 [95% CI, 1.04–1.25] and 1.21 [1.11–1.31], respectively); however, the associations were attenuated after adjustment for clinical and demographic characteristics (1.07 [0.98–1.16]; 1.07 [0.97–1.17]). In contrast, C-III
0b
/III
1
was inversely associated with cardiovascular disease risk even after full adjustment including plasma lipids (0.86 [0.79–0.93]).
Conclusions:
Our data indicate differences in clinical and demographic relationships of apoC-III proteoforms, and highlight the importance of apoC-III proteoform composition in predicting future lipid patterns and cardiovascular disease risk.