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Liposome uptake by cultured macrophages mediated by modified low-density lipoproteins
Abstract:
We have investigated effects of native low-density lipoproteins (LDL) and malondialdehyde-treated LDL on the interaction of 5(6)-carboxyfluorescein-labeled liposomes bearing antibodies to LDL with cultured J774 macrophages. It was found that an addition of modified LDL to the incubation medium resulted in 15-20-fold increase of carboxyfluorescein binding to cells, whereas native LDL did not produce such effect. The increase of carboxyfluorescein binding to macrophages in the presence of modified LDL was not due to an enhanced leakage of the label from liposomes. The modified-LDL-mediated binding of carboxyfluorescein to cells was reduced to 20-30% of the initial level in the presence of cell-respiration inhibitors (NaF and antimycin A). Fluorescent microscopy data also indicate the modified-LDL-induced incorporation of liposome contents into cells. The results obtained in this study make it possible to assume that in the presence of malondialdehyde-treated LDL, liposomes with antibodies to LDL may be incorporated into macrophages via the receptor-mediated pathway for modified LDL.
Insights
Modified low-density lipoproteins (LDL) enhance liposome binding to macrophages, suggesting a receptor-mediated pathway for modified LDL uptake. This interaction is energy-dependent and not due to liposome leakage.
Area of Science:
- Cell biology
- Biochemistry
- Immunology
Background:
- Low-density lipoproteins (LDL) play a crucial role in cellular lipid metabolism.
- Modified LDL, such as malondialdehyde-treated LDL, are implicated in atherogenesis.
- Liposomes functionalized with antibodies can be used as targeted delivery vehicles.
Purpose of the Study:
- To investigate the effect of native and modified LDL on the interaction of LDL-antibody-bearing liposomes with macrophages.
- To elucidate the mechanism of liposome-macrophage interaction in the presence of modified LDL.
Main Methods:
- Utilized 5(6)-carboxyfluorescein-labeled liposomes with antibodies to LDL.
- Incubated liposomes with J774 macrophages in the presence of native and malondialdehyde-treated LDL.
- Assessed liposome binding using fluorescence measurements.
- Investigated the role of cellular respiration using inhibitors (NaF, antimycin A).
- Employed fluorescent microscopy to visualize liposome incorporation.
Main Results:
- Malondialdehyde-treated LDL significantly increased liposome binding to macrophages (15-20 fold).
- Native LDL did not enhance liposome binding.
- Increased binding was not attributed to liposome leakage.
- Binding was reduced by cell respiration inhibitors, indicating an energy-dependent process.
- Fluorescent microscopy confirmed modified LDL-induced incorporation of liposome contents into macrophages.
Conclusions:
- Malondialdehyde-treated LDL promotes the uptake of LDL-antibody liposomes by macrophages.
- The mechanism appears to involve a receptor-mediated pathway for modified LDL.
- This interaction is dependent on cellular energy metabolism.