Association Between HDL Functions and Atherosclerotic Burden in Healthy Individuals
Condition: Low HDL Cholesterol
Study type: Observational

Summary: 
      This is a study of HDL function in healthy individuals classified in three groups according
      to their HDL-cholesterol levels (Low HDL-C, Intermediate HDl-C and High HDL-C), with the
      purpose of investigating which characteristics of the HDL particle might be associated to
      atherosclerotic burden, characterized by carotid intima-media thickness above 1mm.
    

Detailed description: 
      Selection: Study participants are initially selected trough the evaluation of consecutive
      lipid profiles from individuals who spontaneously seek governmental primary care centers of
      the city of Campinas, Sao Paulo, Brazil. Telephone-based screening interviews are performed,
      followed by in-person clinical evaluation and blood exams.

      Biochemical analyses: Glucose, triglycerides, HDL-C and c-reactive protein (CRP) are measured
      in an automated Modular® Analytics Evo (Roche Diagnostics, Burgess Hill, West Sussex, UK),
      using Roche Diagnostics® reagents (Mannheim, Germany). LDL-cholesterol is calculated by the
      Friedewald formula. Serum insulin levels are measured using ELISA (Millipore, Massachusetts,
      USA). The Homeostasis Model Assessment (HOMA) Calculator version 2.2 (University of Oxford,
      UK) is used to estimate insulin sensitivity. Apolipoproteins A-I and B-100 and lipoprotein
      (a) are determined by nephelometry in an automated system and reagents from Dade-Behring®
      (Marburg, Germany).

      Carotid artery ultrasound: Carotid artery atherosclerosis is estimated by using
      high-resolution B-mode ultrasound, at the posterior wall of the common carotid artery.

      Lipoprotein isolation: HDL from each study participant is isolated from plasma, through
      ultracentrifugation (Beckman Coulter Inc., Palo Alto, USA).

      HDL chemical composition: Using commercially available enzymatic kits, HDL content of total
      proteins, total cholesterol, free cholesterol, phospholipids, triglycerides and
      apolipoprotein A-I are measured. Cholesteryl ester (CE) is calculated as the difference
      between total cholesterol and free cholesterol times 1.67. HDL molar concentration is
      estimated based on particle total mass and molecular weight.

      HDL physical-chemical characterization: HDL particle size is determined using dynamic light
      scattering, and zeta potential using laser Doppler micro-electrophoresis.

      Determination of proteins involved in HDL metabolism: Cholesteryl ester transfer protein,
      phospholipids transfer protein, lipoprotein lipase, hepatic lipase and lecithin:cholesterol
      acyl transferase activities are determined trough radiometric exogenous assays.

      HDL functions: Cholesterol efflux capacity, antioxidant activity, susceptibility to
      oxidation, anti-inflammatory activity and platelet aggregation inhibition are measured using
      straightforward and consolidated methodologies.

      Statistical Analyses: Differences between groups are evaluated using ANOVA or Kruskal-Wallis,
      with Bonferroni's post-hoc multiple comparison analysis, according to variable distribution.
      Chi-Square is used to compare categorical data. Analysis of covariance (ANCOVA) adjusted for
      confounding variables is also used, after checking variables with histograms, normality
      plots, and residual scatter plots that tested for linearity, normality, and variance.
      Pearson's correlation test is used to assess the relationships between variables. A two-sided
      p-value of 0.05 is considered significant.
    

Observational model: Case-Control
Time perspective: Cross-Sectional
Sampling method: Non-Probability Sample
Study population: 
        Individuals who sought governmental primary care centers of the city of Campinas, SP,
        Brazil.
      
Keywords: HDL; Carotid artery intima-media thickness; Cholesterol efflux capacity; Antioxidant effect of HDL; Susceptibility to oxidation of HDL; Anti-inflammatory effect of HDL; Platelet aggregation inhibition by HDL