Neutral triglyceride lipase in macrophages.

Abstract

High levels of neutral triglyceride lipase activity have been demonstrated In several types of macrophages (J774 cells, human monocyte/macrophages, rabbit alveolar macrophages, and resident mouse peritoneal macrophages). The pH optima ranged from 6.5 to 7.4 depending upon the buffer and the conditions of incubation. The addition of bovine serum albumin stimulated activity at low concentrations, as expected for a fatty acid-releasing reaction, but strongly inhibited at higher concentrations; maximal activity was observed In the presence of 0.625 mg/ml of bovine serum albumin. The enzyme was remarkably thermostable, showing no apparent loss of activity at 50°C for as long as 6 hours. The lipase was Inhibited 80% by 0.1 M NaCI. Assayed under optimal conditions, the specific activity of the neutral triglyceride lipase from J774 cells was more than 100-fold greater than the activity of llpoproteln lipase or neutral cholesterol esterase from those cells; this activity was 10-fold greater than the levels of hormone- T he lipid that accumulates in eruptive xanthomatosis, mostly triglycerides, is found in histiocytes or foam cells, cells that are probably derived from circulating monocytes.1 In patients with hyperchylomicronemia, these triglyceride-rich cells are found in the spleen and liver as well as in the skin; similar triglyceride-rich cells are seen in severe forms of diabetic-hyperlipemia.2 When the hyperlipemia is brought under control, the eruptive xanthomata may resolve very rapidly, sometimes within a day or two. Serial bfopsy studies by Parker et al. 2 showed that the triglyceride content of the lesions fell much more rapidly than the cholesterol ester content. Electron microscopic studies show that most of the stored lipid in foam cells is contained in cytoplasmic vesicles lacking a limiting membrane.3 A number of lines Received May 12, 1983; revision accepted August 17, 1983. of evidence suggest that these cytoplasmic lipid droplets result from lysosomal degradation of lipids taken up from chylomicrons (and/or very low density lipoproteins) and then are resynthesized in the cytoplasmic compartment from products escaping the lysosome. 4' 5 Mobilization of these lipid stores presumably involves either movement back into the lysosomal compartment for hydrolysis or the action of cytoplasmic hydrolases.Previous studies in this laboratory have demonstrated the presence of a neutral cytoplasmic cholesterol esterase in homogenates of several types of macrophages.6 These cells were also shown to contain and to secrete a lipoprotein lipase similar in most respects to postheparin plasma lipoprotein lipase. 78Being a triglyceride lipase, the latter enzyme might theoretically play a role in the mobilization of stored triglycerides, but lipoprotein lipase in adipose tissue and other tissues functions exclusively in the uptake of plasma lipoprotein triglycerides, not in the mobilization of stored triglycerides. Our initial attempts to demonstrate additional neutral triglyceride lipase activities in macrophages were un...

Mobilization of stored triglycerides from macrophages as free fatty acids.

“…Recent studies from this laboratory have demonstrated the presence in several types of macrophages of a very high level of neutral lipase activity that may be responsible for the observed rapid mobilization of stored glycerides. 20 The pattern is reminiscent of that in adipose tissue, the only tissue in which net release of FAA is a prominent pathway. 21 Ehrlich ascites tumor cells in culture can release FFA in net fashion when albumin containing no FFA is present in the medium, but net release in vivo is unlikely.…”

Enzyme Substrates Protective Encapsulation within Polymeric Microspheres

“…Earlier studies [22,23], related to oil-water interface reaction of porcine pancreatic lipase have shown that the presence of low concentration of BSA is able to protect lipase from denaturation. However, at higher concentrations of BSA (2.75 mg/ml [24]) the reduction of lipase activity was observed and attributed to decreased lipase binding at the interface [22][23][24][25][26].…”

Effects of activation on lipid and lipoprotein metabolism in murine macrophages.

“…Neutral triglyceride lipase was assayed in postnuclear homogenates according to the methods described by Khoo et al 25 Substrate was prepared by drying down 15 mg triolein and 6.4 jtCi glycerol tri-9,10(n)-3 l+oleate under N 2 , dissolving it in 1 ml 100% ethanol, rapidly injecting it into 16 ml distilled water, and vortexing vigorously for 1 minute, followed by the addition of 8 ml of HEPES buffer (0.2 M, pH 6.6) and further vortexing. The cells were harvested and homogenized as described above.…”

“…2223 Finally, the lipids stored within the cell are continuously hydrolyzed by the action of cytoplasmic lipases. 24 - 25 Since macrophages are immunocompetent cells that can exist in vivo within a spectrum of functional states of activation, which range from unstjmulated or resident cells that display low levels of metabolic and phagocytic activities to fully activated cells that display new biochemical features, 2627 it would not be surprising for activation to be associated with changes in lipid homeostatic pathways. Indeed, a number of alterations have been observed to occur in macrophage lipid and lipoprotein metabolism with activation.…”