Pharmacologic and Genetic Downregulation of Proprotein Convertase Subtilisin/Kexin Type 9 and Survival From Sepsis

Abstract

Objectives: Treatments that prevent sepsis complications are needed. Circulating lipid and protein assemblies-lipoproteins play critical roles in clearing pathogens from the bloodstream. We investigated whether early inhibition of proprotein convertase subtilisin/kexin type 9 (PCSK9) may accelerate bloodstream clearance of immunogenic bacterial lipids and improve sepsis outcomes.

Design: Genetic and clinical epidemiology, and experimental models.

Setting: Human genetics cohorts, secondary analysis of a phase 3 randomized clinical trial enrolling patients with cardiovascular disease (Evaluation of Cardiovascular Outcomes After an Acute Coronary Syndrome During Treatment With Alirocumab [ODYSSEY OUTCOMES]; NCT01663402), and experimental murine models of sepsis.

Patients or subjects: Nine human cohorts with sepsis (total n = 12,514) were assessed for an association between sepsis mortality and PCSK9 loss-of-function (LOF) variants. Incident or fatal sepsis rates were evaluated among 18,884 participants in a post hoc analysis of ODYSSEY OUTCOMES. C57BI/6J mice were used in Pseudomonas aeruginosa and Staphylococcus aureus bacteremia sepsis models, and in lipopolysaccharide-induced animal models.

Interventions: Observational human cohort studies used genetic PCSK9 LOF variants as instrumental variables. ODYSSEY OUTCOMES participants were randomized to alirocumab or placebo. Mice were administered alirocumab, a PCSK9 inhibitor, at 5 mg/kg or 25 mg/kg subcutaneously, or isotype-matched control, 48 hours prior to the induction of bacterial sepsis. Mice did not receive other treatments for sepsis.

Measurements and main results: Across human cohort studies, the effect estimate for 28-day mortality after sepsis diagnosis associated with genetic PCSK9 LOF was odds ratio = 0.86 (95% CI, 0.67-1.10; p = 0.24). A significant association was present in antibiotic-treated patients. In ODYSSEY OUTCOMES, sepsis frequency and mortality were infrequent and did not significantly differ by group, although both were numerically lower with alirocumab vs. placebo (relative risk of death from sepsis for alirocumab vs. placebo, 0.62; 95% CI, 0.32-1.20; p = 0.15). Mice treated with alirocumab had lower endotoxin levels and improved survival.

Conclusions: PCSK9 inhibition may improve clinical outcomes in sepsis in preventive, pretreatment settings.

Keywords: endotoxins; lipid regulating agents; proprotein convertase subtilisin/kexin type 9; sepsis; septic shock.

Figure 1.

Meta-analysis of the association between the proprotein convertase subtilisin/kexin type 9 (PCSK9) loss-of-function variant rs11591147 (R46L) and 28-d mortality in all cohorts of patients with sepsis. AA = Alternate/Alternate, AAF = alternate allele fraction, GEN-SEP = GENetics of SEPsis, GHS = Geisinger Health System, HUNT = Trøndelag Health Study, KP GERA = Kaiser Permanente Resource for Genetic Epidemiology Research on Adult Health and Aging, META = meta-analysis, OR = odds ratio, RA = Reference/Alternate, RR = Reference/Reference, SPH = St. Paul’s Hospital, UKB = U.K. Biobank, VASST = Vasopressin and Septic Shock Trial.

Figure 2.

Relationship between sepsis mortality in an additive genetic model incorporating proprotein convertase subtilisin/kexin type 9 (PCSK9) loss-of-function (rs11591147) and low-density lipoprotein (LDL) receptor (LDLR) gain-of-function (rs6511720) variants; both of which would be expected to increase LDLR availability to remove bacterial endotoxin from the bloodstream. Data are from 2731 participants in the U.K. Biobank. A dose-dependent reduction in sepsis mortality was observed. AA = Alternate/Alternate, OR = odds ratio, PRS = polygenic risk score, RA = Reference/Alternate, RR = Reference/Reference, SNP = single nucleotide polymorphism.

Figure 3.

Effects of anti-proprotein convertase subtilisin/kexin type 9 (PCSK9) monoclonal antibody (mAb) on lipopolysaccharide (LPS) levels and survival in a live bacteria-induced sepsis model due to Pseudomonas aeruginosa. C57Bl/6J mice were given a single subcutaneous injection of the indicated doses of human immunoglobulin G1 (hIgG1) Regeneron (REGN) monoclonal antibodies (mAbs) 48 hr before intraperitoneal injection of live P. aeruginosa (Pa) strains PAK (at 1.5 × 10⁷–2.5 × 10⁷ colony-forming units [CFUs]/mouse; n = 60), PA14 (at 5 × 10⁷–7 × 10⁷ CFU/mouse; n = 30), or 6077 (at 2.5 × 10⁶–7 × 10⁶ CFU/mouse; n = 40), in phosphate-buffered saline (PBS). LPS was measured in serum 16 hr after infection in mice (n = 5 per group), and survival was monitored for up to 96 hr. LPS was lower at 16 hr among mice receiving anti-PCSK9 mAb in strain 6077. *p < 0.001 by unpaired t test; **p < 0.0001 by unpaired t test. mAb to cat allergen, Fel d 1 is used as a control in this experiment, PA14 = P. aeruginosa strain 14, PAK = P. aeruginosa strain K.

Figure 4.

Effects of anti-proprotein convertase subtilisin/kexin type 9 (PCSK9) monoclonal antibody (mAb) on survival in live bacteria-induced sepsis models due to Staphylococcus aureus infection lipopolysaccharide administration. In the S. aureus infection sepsis mode, C57Bl/6J mice (n = 17/group) were given a single subcutaneous injection of the indicated doses of human immunoglobulin G1 (hIgG1) Regeneron (REGN) monoclonal antibodies (mAbs) 48 hr before intraperitoneal injection of live S. aureus 8325-4 strain bacteria (approximately 8 × 10⁷ colony-forming units /mouse) in phosphate-buffered saline (PBS). Mice were monitored for survival and clinical signs for 96 hr and outcomes were compared by log-rank (Mantel-Cox) test. *p = 0.0328. mAb to cat allergen, Fel d 1 is used as a control in this experiment.