Background: Metabolic effects of free fatty acids (FFAs) frequently are tested using combined infusion of triglycerides and heparin, which stimulates lipolysis in vivo. Ongoing in vitro lipolysis, however, probably produces falsely high plasma FFA concentrations under these conditions. Therefore, this study aims to assess the efficacy of tetrahydrolipstatin (THL) in inhibiting plasma lipolytic activity and to improve plasma FFA determination.
Methods: Plasma concentrations of FFAs and glycerol were measured in five healthy subjects in the presence and absence of THL. Blood was drawn at baseline, during infusion of a triglyceride emulsion (1.5 mL/min), and during infusion of triglycerides plus heparin (0.2 IU. kg(-1). min(-1)). In addition, the effects of storage temperature of the samples were analyzed.
Results: In samples frozen immediately after collection, plasma FFAs were 28% lower in the presence of THL than in its absence (P = 0.008). When THL-free plasma was incubated for 3 h on ice or at room temperature, plasma FFAs were 22% (P = 0.02) and 91% (P = 0.0004) higher, respectively, than in samples frozen immediately. The addition of THL blunted temperature-dependent in vitro lipolysis by 88% (P<0.01) and 89% (P <0.001) after incubation on ice and at room temperature, respectively. Changes in plasma glycerol concentrations exhibited similar behavior.
Conclusions: THL, which is safe and easy to handle, is a potent inhibitor of in vitro lipolysis and could, therefore, be added to blood samples drawn during triglyceride/heparin infusions to allow more accurate determination of plasma FFA concentrations.