Lipid transfer particle-catalyzed transfer of lipoprotein-associated diacylglycerol and long chain aliphatic hydrocarbons

Emerging risk biomarkers in cardiovascular diseases and disorders

Present review article highlights various cardiovascular risk prediction biomarkers by incorporating both traditional risk factors to be used as diagnostic markers and recent technologically generated diagnostic and therapeutic markers. This paper explains traditional biomarkers such as lipid profile, glucose, and hormone level and physiological biomarkers based on measurement of levels of important biomolecules such as serum ferritin, triglyceride to HDLp (high density lipoproteins) ratio, lipophorin-cholesterol ratio, lipid-lipophorin ratio, LDL cholesterol level, HDLp and apolipoprotein levels, lipophorins and LTPs ratio, sphingolipids, Omega-3 Index, and ST2 level. In addition, immunohistochemical, oxidative stress, inflammatory, anatomical, imaging, genetic, and therapeutic biomarkers have been explained in detail with their investigational specifications. Many of these biomarkers, alone or in combination, can play important role in prediction of risks, its types, and status of morbidity. As emerging risks are found to be affiliated with minor and microlevel factors and its diagnosis at an earlier stage could find CVD, hence, there is an urgent need of new more authentic, appropriate, and reliable diagnostic and therapeutic markers to confirm disease well in time to start the clinical aid to the patients. Present review aims to discuss new emerging biomarkers that could facilitate more authentic and fast diagnosis of CVDs, HF (heart failures), and various lipid abnormalities and disorders in the future.

Lipid transport biochemistry and its role in energy production

Recent advances on the biochemistry of flight-related lipid mobilization, transport, and metabolism are reviewed. The synthesis and release of adipokinetic hormones and their function in activation of fat body triacylglycerol lipase to produce diacylglycerol is discussed. The dynamics of reversible lipoprotein conversions and the structural properties and role of the exchangeable apolipoprotein, apolipophorin III, in this process is presented. The nature and structure of hemolymph lipid transfer particle and the potential role of a recently discovered lipoprotein receptor of the low-density lipoprotein receptor family, in lipophorin metabolism and lipid transport is reviewed.

Lipid transfer particle catalyzes transfer of carotenoids between lipophorins of Bombyx mori

The yellow color of Bombyx mori hemolymph is due to the presence of carotenoids, which are primarily associated with lipophorin particles. Carotenoids were extracted from high density lipophorin (HDLp) of B. mori and analyzed by HPLC. HDLp contained 33 micrograms of carotenoids per mg protein. Over 90% of carotenoids were lutein while alpha-carotene and beta-carotene were minor components. When larval hemolymph was subjected to density gradient ultracentrifugation, a second minor yellow band was present, which was identified as B. mori lipid transfer particle (LTP). During other life stages examined however, this second band was not visible. To determine if coloration of LTP may fluctuate during development, we determined its concentration in hemolymph and compared it to that of lipophorin. Both proteins were present during all life stages and their concentrations gradually increased. The ratio of lipophorin: LTP was 10-15:1 during the fourth and fifth instar larval stages, and 20-30:1 during the pupal and adult stages. Thus, there was no correlation between the yellow color attributed to LTP and its hemolymph concentration. It is possible that yellow coloration of the LTP fraction corresponds to developmental stages when the particle is active in carotene transport. To determine if LTP is capable of facilitating carotene transfer, we took advantage of a white hemolymph B. mori strain which, when fed artificial diet containing a low carotene content, gives rise to a lipophorin that is nearly colorless. A spectrophotometric, carotene specific, transfer assay was developed which employed wild type, carotene-rich HDLp as donor particle and colorless low density lipophorin, derived from the white hemolymph strain animals, as acceptor particle. In incubations lacking LTP carotenes remained associated with HDLp while inclusion of LTP induced a redistribution of carotenes between the donor and acceptor in a time and concentration dependent manner. Time course studies suggested the rate of LTP-mediated carotene transfer was relatively slow, requiring up to 4 h to reach equilibrium. By contrast, studies employing 3H-diacylglycerol labeled HDLp as donor particle in lipid transfer assays revealed a rapid equilibration of label between the particles. Thus, it is plausible that the slower rate of LTP-mediated carotene transfer is due to its probable sequestration in the core of HDLp.

Merck Frosst award lecture 1995. La conference Merck Frosst 1995. Structural studies of lipoproteins and their apolipoprotein components

Lipid transport processes via the circulatory system of animals are a vital function that utilizes highly specialized lipoprotein complexes. These complexes of protein and lipid impart solubility to otherwise insoluble lipids. The apoprotein components of lipoprotein complexes serve to stabilize the lipid components and modulate particle metabolism and function as ligands for receptor-mediated endocytosis of lipoproteins. We have used an insect (Manduca sexta) model system for studies of lipid transport. In this system, flight activity elicits a dramatic increase in the demand for glycerolipid fuel molecules by flight muscle tissue. These lipids are mobilized from a storage organ and transported through the hemolymph (blood) to the flight muscle by the lipoprotein, lipophorin. This system possesses the unique property that lipids are loaded onto pre-existing high density lipophorin through the action of a lipid transfer particle (LTP). LTP is a high molecular weight hemolymph component that facilitates net vectorial lipid transfer from fat body tissue to lipophorin. The increase in lipid content of the lipoprotein induces association of a low molecular weight amphipathic exchangeable apolipoprotein, apolipophorin III (apoLp-III). ApoLp-III is a 18 kDa protein that normally exists as a water-soluble monomeric hemolymph protein. The structural properties of apoLp-III have been investigated by X-ray crystallography. ApoLp-III from Locusta migratoria adopts a five helix bundle conformation wherein each of the amphipathic helices orients with its hydrophobic face directed toward the interior of the bundle. It has been hypothesized that lipid association requires a dramatic conformational change wherein the helix bundle opens about putative hinge domains located in the loops between helices. The data accumulated support the concept that apoLp-III is a member of the broad class of exchangeable apolipoproteins and structural information learned from this system is directly applicable to analogous proteins in higher organisms.

Manduca sexta lipid transfer particle: synthesis by fat body and occurrence in hemolymph

Lipid transfer particle (LTP) is present in hemolymph of the tobacco hornworm Manduca sexta. Biosynthesis of LTP, occurrence in hemolymph, and the role of LTP-apoproteins in the lipid transfer reaction were investigated using antibodies specific for LTP or for each of the apoproteins. In vitro protein synthesis followed by immunoprecipitation demonstrated that LTP is synthesized by the fat body and secreted into the medium. In contrast to apolipophorin III, an exchangeable apoprotein of lipophorin (the major lipid transport protein in hemolymph), apoLTP-III could not be detected free in hemolymph. LTP concentrations in the hemolymph were measured by a sandwich ELISA using a mouse monoclonal antibody against apoLTP-III as capturing antibody and rabbit polyclonal antibody against apoLTP-I as detecting antibody. LTP concentration increased during the late fifth instar larval stage, followed by a decrease in the wandering stage. Subsequently, LTP concentrations were strongly increased in hemolymph of adult moths. The role of the three apoproteins of LTP in the lipid transfer reaction was analyzed using apoprotein-specific antibodies. All three, apoLTP-I, -II, and -III, appeared to be important for lipid transfer activity, as shown by inhibition of lipid transfer by antibodies specific for each of the three apoproteins.

A turbidimetric assay of lipid transfer activity

A novel method to assay insect plasma lipid transfer particle (LTP) activity has been developed that employs insect high density lipophorin (HDLp) and human low density lipoprotein (LDL) as donor/acceptor substrate particles. At a 3:1 or greater HDLp:LDL protein ratio, LTP-mediated net vectorial transfer of diacylglycerol from lipophorin to LDL produces destabilized LDL particles that aggregate, causing sample turbidity. Turbidity was measured spectrophotometrically as a function of absorbance at 340 nm. After an initial lag phase, lipoprotein sample turbidity increased as a function of reaction time and LTP concentration. Saturation was observed at longer times or higher LTP concentrations, indicating that a reaction end point had been reached. As the substrate HDLp concentration was increased relative to LDL, a saturable increase in LTP-induced lipoprotein sample turbidity was observed. When the LDL concentration was increased relative to HDLp, however, there was an initial production of turbidity but at higher concentrations the sample did not develop turbidity. Reaction progress was also dependent on temperature over the range 0-37 degrees C. Taken together the results are consistent with the concept that LTP-mediated diacylglycerol transfer from HDLp to LDL creates unstable product LDL particles that aggregate. The assay method is advantageous because it employs relatively abundant, natural lipoprotein substrates, does not require prelabeling of donor lipid particles with radioactive or fluorescent lipids, and does not require separation of donor and acceptor after incubation. This is the first description of a lipid transfer assay that can be measured spectrophotometrically.