Prevention of in vitro lipolysis by tetrahydrolipstatin

Background: Metabolic effects of free fatty acids (FFAs) frequently are tes ted using combined infusion of triglycerides and heparin, which stimulates lipolysis in vivo. Ongoing in vitro lipolysis, however, probably produces f alsely high plasma FFA concentrations under these conditions. Therefore, th is study aims to assess the efficacy of tetrahydrolipstatin (THL) in inhibi ting plasma lipolytic activity and to improve plasma FFA determination. Methods: Plasma concentrations of FFAs and glycerol were measured in five h ealthy subjects in the presence and absence of THL. Blood was drawn at base line, during infusion of a triglyceride emulsion (1.5 mL/min), and during i nfusion of triglycerides plus heparin (0.2 IU . kg(-1) . min(-1)). In addit ion, the effects of storage temperature of the samples were analyzed. Results: In samples frozen immediately after collection, plasma FFAs were 2 8% lower in the presence of THL than in its absence (P = 0.008). When THL-f ree 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 sam ples 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 conc entrations exhibited similar behavior. Conclusions: THL, which is safe and easy to handle, is a potent inhibitor o f 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. (C) 2000 American Association for Clinical Ch emistry.