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Published on: October 12, 2017
Determination of lipid transfer inhibitor protein activity in human lipoprotein-deficient plasma
1Department of Cell Biology, Cleveland Clinic Foundation, OH 44195.
Insights
Lipid transfer inhibitor protein (LTIP) activity varies significantly among individuals. Higher LTIP levels correlate with reduced lipid transfer between very-low-density and low-density lipoproteins.
Area of Science:
- Biochemistry
- Lipid Metabolism
- Cardiovascular Research
Background:
- Lipid transfer protein (LTP) activity is crucial for lipoprotein metabolism.
- LTIP is a plasma protein that modulates LTP activity.
- Understanding LTIP's role is vital for lipid disorder research.
Purpose of the Study:
- To develop a reliable assay for quantifying LTIP activity.
- To investigate LTIP's influence on lipid transfer rates in plasma.
- To explore variations in LTIP activity among individuals.
Main Methods:
- Developed a heat inactivation assay (56°C for 60 min) to measure LTIP activity.
- Quantified LTP activity in lipoprotein-deficient plasma before and after heat treatment.
- Utilized radiolabeled lipoproteins to assess lipid transfer rates between major lipoprotein classes.
- Employed antibodies against LTP to confirm transfer activity.
Main Results:
- The heat protocol effectively inactivated over 90% of LTIP activity, with unique responses per sample.
- LTIP inactivation led to a 230-600% increase in LTP activity in normolipidemic donors.
- Plasma lipid transfer rates generally showed a negative correlation with LTIP activity.
- Lipid transfer between VLDL and LDL was disproportionately reduced (2.4-5.1 fold) with higher LTIP activity.
- HDL2 molecular weight was negatively correlated with LTIP activity.
Conclusions:
- LTIP activity exhibits significant inter-individual variability.
- Higher LTIP activity is associated with reduced VLDL-LDL and LDL-VLDL lipid transfer.
- The developed assay allows for the quantification of LTIP activity in plasma.
- LTIP plays a significant role in regulating specific lipid transfer pathways.
Abstract:
Lipid transfer protein (LTP) activity is modulated by a distinct plasma protein termed lipid transfer inhibitor protein (LTIP). The objective of this study was to establish an assay for LTIP that could be used to quantify its activity in lipoprotein-deficient plasma. A straightforward heating protocol (56 degrees C for 60 minutes) was found to inactivate more than 90% of LTIP activity. The responses of individual lipoprotein-deficient plasma samples to this heating procedure were unique. Among normolipidemic donors, inactivation of LTIP caused a 230% to 600% increase in LTP activity. Essentially all measurable transfer activity in native and heated samples was inhibited by an antibody to LTP. Whole-plasma samples from these donors were spiked with radiolabeled lipoproteins to measure the rates of lipid transfer among the major lipoprotein classes. In general, plasma lipid transfer rates were negatively correlated with LTIP activity in these samples. However, the decrease in lipid transfers from very-low-density lipoprotein (VLDL) to low-density lipoprotein (LDL) and from LDL to VLDL was from 2.4- to 5.1-fold greater than in the transfers from VLDL to high-density lipoprotein (HDL) or from HDL to VLDL. In these samples, the molecular weight of HDL2 was negatively correlated with LTIP activity. Thus, LTIP activities among normolipidemic individuals were observed to vary severalfold; compared with other lipoprotein transfers, higher LTIP activities were associated with a relative reduction in LDL-VLDL lipid transfer events.
