The relationship between alkaline phosphatase activity and intracellular lipid accumulation in murine 3T3-L1 cells and human preadipocytes

Alkaline phosphatase (ALP) is expressed in 3T3-L1 preadipocytes, and its activity increases during adipogenesis. The purpose of this study was to determine whether ALP activity Could be used as a measure of intracellular lipid accumulation in human preadipocytes and 3T3-L1 cells and which of the factors that induce adipogenesis are responsible for stimulating ALP activity. Adipogenesis was initiated in 3T3-L1 cells by incubation with differentiation medium containing insulin. dexamethasone. and 3-isobutyl-1methylxanthine. The effect of leaving out each of the differentiation medium components was, studied. Adipogenesis was also assessed in human preadipocytes and 3T3-L1 cells in the presence of the ALP inhibitor histidine. ALP activity was measured Using an automated colorimetric assay and intracellular lipid accumulation was measured using the lipid-specific dye oil red O. Removal of insulin or dexamethasone from the differentiation medium had little effect on either ALP activity or lipid accumulation in 3T3-L1 cells, while removal of IBMX blocked both. Histidine inhibited ALP activity and adipogenesis in human preadipocytes and 3T3-L1 cells. Pearson univariate correlation analysis demonstrated strong correlations between ALP activity and lipid accumulation in human preadipocytes (r = 0.78, n = 69) and in 3T3-L1 cells (r = 0.92, it = 27). These data suggest that ALP and fat storage are tightly linked during preadipocyte maturation and that the measurement of ALP activity my be a novel technique for the quantification of intracellular lipid accumulation that is more sensitive and rapid than currently used methods. (c) 2006 Elsevier Inc. All rights reserved.