Low Low-Density Lipoprotein Levels Are Associated With, But Do Not Causally Contribute to, Increased Mortality in Sepsis*

OBJECTIVES: Low low-density lipoprotein levels are associated with increased mortality in sepsis. Whether low low-density lipoprotein levels contribute causally to adverse sepsis outcome is unknown. DESIGN: Retrospective analysis of two sepsis patient cohorts using a Mendelian Randomization strategy. SETTING: Sepsis patients enrolled into clinical research cohorts at tertiary care teaching hospitals. PATIENTS: The first cohort included 200 sepsis patients enrolled in an observational study in a hospital Emergency Department. The second cohort included genotyped patients enrolled in the Vasopressin and Septic Shock Trial. INTERVENTIONS: Retrospective analysis of these patient datasets. In 632 patients enrolled in Vasopressin and Septic Shock Trial, Proprotein Convertase Subtilisin/Kexin type 9, and 3-Hydroxy-3-Methylglutaryl-CoA Reductase single nucleotide polymorphisms known to be associated with low-density lipoprotein levels were genotyped, and a genetic score related to low-density lipoprotein levels was calculated. MEASUREMENTS AND MAIN RESULTS: In the first cohort, we replicated the finding that low low-density lipoprotein levels are associated with increased 28-day mortality. In genotyped patients in the Vasopressin and Septic Shock Trial trial, we found that the 3-Hydroxy-3-Methylglutaryl-CoA Reductase genetic score, known to be directly related to low low-density lipoprotein levels, was not associated with increased mortality. Surprisingly the Proprotein Convertase Subtilisin/Kexin type 9 genetic score, known to be directly related to low low-density lipoprotein levels, was associated with decreased (not increased) mortality. CONCLUSIONS: Both 3-Hydroxy-3-Methylglutaryl-CoA Reductase and Proprotein Convertase Subtilisin/Kexin type 9 genetic scores should have been associated with increased mortality if low low-density lipoprotein levels contributed causally to sepsis mortality. But this was not the case, and the opposite was observed for the Proprotein Convertase Subtilisin/Kexin type 9 genetic score. This suggests that low-density lipoprotein levels, per se, do not contribute causally to adverse sepsis outcomes. The Proprotein Convertase Subtilisin/Kexin type 9 genetic score finding raises the possibility that increased low-density lipoprotein clearance (the effect of these Proprotein Convertase Subtilisin/Kexin type 9 genotypes) may contribute to improved sepsis outcomes.