title: Recurrent exposure to subclinical lipopolysaccharide increases mortality and induces cardiac fibrosis in mice.
abstract: BACKGROUND
  Circulating subclinical lipopolysaccharide (LPS) occurs in health and disease. Ingesting high fatty meals increases LPS that cause metabolic endotoxemia. Subclinical LPS in periodontal disease may impair endothelial function. The heart may be targeted as cardiac cells express TLR4, the LPS receptor. It was hypothesized that recurrent exposure to subclinical LPS increases mortality and causes cardiac fibrosis.
  
  
  METHODS
  C57Bl/6 mice were injected with intraperitoneal saline (control), low dose LPS (0.1 or 1 mg/kg), or moderate dose LPS (10 or 20 mg/kg), once a week for 3 months. Left ventricular (LV) function (echocardiography), hemodynamics (tail cuff pressure) and electrocardiograms (telemetry) were measured. Cardiac fibrosis was assessed by picrosirius red staining and LV expression of fibrosis related genes (QRT-PCR). Adult cardiac fibroblasts were isolated and exposed to LPS.
  
  
  RESULTS
  LPS injections transiently increased heart rate and blood pressure (<6 hours) and mildly decreased LV function with full recovery by 24 hours. Mice tolerated weekly LPS for 2-3 months with no change in activity, appearance, appetite, weight, blood pressure, LV function, oximetry, or blood chemistries. Mortality increased after 60-90 days with moderate, but not low dose LPS. Arrhythmias occurred a few hours before death. LV collagen fraction area increased dose-dependently from 3.0±0.5% (SEM) in the saline control group, to 5.6±0.5% with low dose LPS and 9.7±0.9% with moderate dose LPS (P<0.05 moderate vs low dose LPS, and each LPS dose vs control). LPS increased LV expression of collagen Iα1, collagen IIIα1, MMP2, MMP9, TIMP1, periostin and IL-6 (P<0.05 moderate vs low dose LPS and vs control). LPS increased α-SMA immunostaining of myofibroblasts. LPS dose-dependently increased IL-6 in isolated adult cardiac fibroblasts.
  
  
  CONCLUSIONS
  Recurrent exposure to subclinical LPS increases mortality and induces cardiac fibrosis.
authors.affiliation: Cardiology Section, Department of Medicine and Research Service, Veterans Administration San Diego Healthcare System, and University of California San Diego, San Diego, California, United States of America.
authors.forename: Wilbur Y W
authors.initials: WY
authors.lastname: Lew
authors.forename: Evelyn
authors.initials: E
authors.lastname: Bayna
authors.forename: Erminia Dalle
authors.initials: ED
authors.lastname: Molle
authors.forename: Nancy D
authors.initials: ND
authors.lastname: Dalton
authors.forename: N Chin
authors.initials: NC
authors.lastname: Lai
authors.forename: Valmik
authors.initials: V
authors.lastname: Bhargava
authors.forename: Vincent
authors.initials: V
authors.lastname: Mendiola
authors.forename: Paul
authors.initials: P
authors.lastname: Clopton
authors.forename: Tong
authors.initials: T
authors.lastname: Tang
mesh_terms: D000818:Animals; D015415:Biomarkers / Q000378:metabolism; D001794:Blood Pressure / Q000187:drug effects; D002478:Cells, Cultured; D003094:Collagen / Q000235:genetics / Q000378:metabolism; D017364:Collagenases / Q000235:genetics / Q000378:metabolism; D005347:Fibroblasts / Q000187:drug effects / Q000473:pathology; D005355:Fibrosis / Q000139:chemically induced / Q000401:mortality / Q000473:pathology; D006339:Heart Rate / Q000187:drug effects; D006439:Hemodynamics / Q000187:drug effects; D015850:Interleukin-6 / Q000235:genetics / Q000378:metabolism; D008070:Lipopolysaccharides / Q000494:pharmacology*; D051379:Mice; D008810:Mice, Inbred C57BL; D009206:Myocardium / Q000473:pathology*; D016019:Survival Analysis; D019715:Tissue Inhibitor of Metalloproteinase-1 / Q000235:genetics / Q000378:metabolism; D016277:Ventricular Function, Left / Q000187:drug effects
chemical_list: D015415:Biomarkers; D015850:Interleukin-6; D008070:Lipopolysaccharides; C560825:Timp1 protein, mouse; D019715:Tissue Inhibitor of Metalloproteinase-1; D003094:Collagen; D017364:Collagenases