Lipid accumulation and alkaline phosphatase activity in human preadipocytes isolated from different body fat depots

Abstract

BACKGROUND: Alkaline phosphatase (ALP) controls intracellular lipid accumulation in human preadipocytes, but it is not known whether ALP is expressed in all body fat depots, or whether it has a similar role at all sites. DESIGN: Cross-sectional. SETTING AND SUBJECTS: Subjects undergoing breast reduction and abdominal fat biopsies operations at Charlotte Maxeke Johannesburg Academic Hospital. OUTCOME MEASURES: This study compared intracellular lipid accumulation and ALP activity in the presence and absence of ALP inhibitors in preadipocytes that were obtained from different adipose depots. Abdominal and mammary gland preadipocytes were isolated from women and induced to differentiate in culture. ALP activity and intracellular lipid levels were measured at baseline and after 12 days of differentiation in the presence and absence of the ALP inhibitors, histidine and levamisole. RESULTS: ALP activity was detected in nondifferentiated abdominal (134 ± 7.5 mU/mg protein) and mammary gland (136 ± 9.6 mU/mg protein) preadipocytes. Its activity had increased significantly (p-value < 0.0005 for both) by day 12 of differentiation (388 ± 55 for abdominal and 278 ± 28 mU/mg protein for mammary). Preadipocytes treated with histidine had lower fat accumulation (p-value < 0.0005) and ALP activity (p-value < 0.005) than nontreated cells on day 12, while those treated with levamisole had lower fat accumulation (p-value < 0.005), but elevated ALP activity (p-value < 0.05), compared to nontreated cells. Lipid accumulation (p-value < 0.005) and ALP activity (p-value < 0.05) were higher in abdominal than mammary gland preadipocytes by day 12. CONCLUSION: ALP is involved in the control of intracellular lipid accumulation in human preadipocytes that are isolated from both adipose depots. The ability of levamisole to inhibit this process while activating ALP, suggests that this molecule acts via an ALP-independent pathway, while histidine attenuates both lipid deposition and ALP activity.