A Study to Evaluate the Effect of Lipid Infusion on Toll Like Receptor 4 (TLR4) Signaling

The investigators plan to examine the effect of a lipid infusion on TLR4 expression and insulin sensitivity. A group of 30 subjects aged 18-60 years old, lean (BMI < 26 kg/m2) normal glucose tolerant subjects without a family history of type 2 diabetes will receive a lipid or saline infusion. The subjects will be randomly assigned to first receive either a 48 hour long lipid or saline infusion. Approximately 4-6 weeks later subjects will return to undergo another study (if, in the first study they received lipid, on the second study they will receive saline, and vice versa). A near-equal number of women and men will be included in each group.

Inclusion criteria

• Subjects must have the following laboratory values: Hematocrit ≥ 35%, serum creatinine ≤ 1.5 mg/dl, aspartate aminotransferase (AST) < 2 X upper limit of normal, Alanine aminotransferase (ALT) < 2 X upper limit of normal, alkaline phosphatase < 2 X upper limit of normal, normal urinalysis [no glucose, trace protein, trace ketones, lipase < 50 IU/L, no bacteria, up to 1-3 white blood cells (WBC) and red blood cells (RBC) per hpf], and normal platelets, prothrombin time (PT) and partial thromboplastin time (PTT).
• Female subjects must be non-lactating. Female patients are eligible only if they have a negative pregnancy test throughout the study period (or postmenopausal). Postmenopausal women taking hormone replacement will be included if they have been on a stable dose for ≥6 months.
• Subjects whose body weight has been stable (within 2%) for at least three months.

Exclusion criteria

• Subjects with impaired glucose tolerance based on American Diabetes Association criteria.
• Subjects taking drugs known to affect glucose and lipid homeostasis will be excluded. Statins will be permitted if the subject has been on a stable dose for at least three months. Subjects who have taken for more than a week non-steroidal anti inflammatory drugs (NSAIDS) within two months or systemic steroids, anabolic steroids, growth hormone or immunosuppressants within 12 months will be excluded. Subjects taking low-dose (81 mg/day or less) aspirin will be allowed.
• Patients with a history of clinically significant heart disease (New York Heart Classification greater than grade II; more than non-specific ST-T wave changes on the EKG), peripheral vascular disease (history of claudication), or pulmonary disease (dyspnea on exertion of one flight or less; abnormal breath sounds on auscultation) will not be studied.
• Recent systemic or pulmonary embolus, impaired renal function, poorly controlled blood pressure (systolic BP>170, diastolic BP>95), resting heart rate >100, electrolyte abnormalities, neuromuscular or musculoskeletal disease.
• Subjects who smoke.
• Subjects who engage in a regular exercise program (zero or one exercise sessions per week are allowed).
• Any subject who has donated blood in the previous two months.
• Any subject with a hematocrit of less than 35.
• Subjects who are claustrophobic.
• Women taking oral contraceptives.
• alcohol consumption greater than 30 grams daily.
• baseline plasma triglyceride levels over 200 mg/dl