Activity Of Lecithin Research Articles

Effect of Silybum marianum (L. Gaerthn) on C-reactive protein, Lactate Dehydrogenase and Reverse Cholesterol Transport in Rats Prematurely Exposed to a High-Fat, High-Sugar Diet

The milk thistle (Silybum marianum (Sm)) is a medicinal plant used for a long time in the Algerian traditional medicine. its cardioprotective and preventive effects against the development of obesity complications have been very little investigated. The aim of this study was to see if milk thistle seed can slow down the onset of cardio-metabolic disorders in rats prematurely exposed to a High Lipid/High Sugar (HL/HS) diet. Thirty male Wistar rats are divided into three homogeneous groups. The first Control group (C) receives a normocaloric diet; the second consumes the HL/HS diet (untreated group) and the third treated group was exposed to the HL/HS diet supplemented with 10 g/day of Sm seeds (HL/HS-Sm group). After 1 month of experimentation, a reduction in body weight (-14%), enzymatic activities of aspartate aminotransferase (-37%) and alanine aminotransferase (-33%), total lipids, total cholesterol (-58%), unesterified cholesterol (-56%) and cholesteryl esters (-38%) was noted in HL/HS-Sm group compared to HL/HS. Sm seed also reduces blood glucose (1.3-fold), HbA1c (2-fold) as well as CRP, albumin and lactate dehydrogenase (LDH) activity (-32%, -20%, -24 %). In contrast, the cholesterol content of anti-atherogenic lipoproteins, the activity of lecithin: cholesterol acyltransferase and the antioxidant capacity (CAox) were high (+36%; +42%; +10%). In conclusion, Sm seeds in an HL/HS diet have a hypolipidemic effect by improving the antiatherogenic pathway, reduce liver disorders and decrease inflammation and lipoperoxidation by strengthening CAox preventing the development of obesity and the progression of fatty liver disease and its complications.

Highly conserved amino acid residues in apolipoprotein A1 discordantly induce high density lipoprotein assembly in vitro and in vivo

ObjectiveApolipoprotein A1 (APOA1) is essential to reverse cholesterol transport, a physiologically important process that protects against atherosclerotic cardiovascular disease. APOA1 is a 28 kDa protein comprising multiple lipid-binding amphiphatic helices initialized by proline residues, which are conserved across multiple species. We tested the hypothesis that the evolutionarily conserved residues are essential to high density lipoprotein (HDL) function. ApproachWe used biophysical and physiological assays of the function of APOA1P➔A variants, i.e., rHDL formation via dimyristoylphosphatidylcholine (DMPC) microsolubilization, activation of lecithin: cholesterol acyltransferase, cholesterol efflux from human monocyte-derived macrophages (THP-1) to each variant, and comparison of the size and composition of HDL from APOA1−/− mice receiving adeno-associated virus delivery of each human variant. ResultsDifferences in microsolubilization were profound and showed that conserved prolines, especially those in the C-terminus of APOA1, are essential to efficient rHDL formation. In contrast, P➔A substitutions produced small changes (−25 to +25%) in rates of cholesterol efflux and no differences in the rates of LCAT activation. The HDL particles formed following ectopic expression of each variant in APOA1−/− mice were smaller and more heterogeneous than those from control animals. ConclusionStudies of DMPC microsolubilization show that proline residues are essential to the optimal interaction of APOA1 with membranes, the initial step in cholesterol efflux and HDL production. In contrast, P➔A substitutions modestly reduce the cholesterol efflux capacity of APOA1, have no effect on LCAT activation, but according to the profound reduction in the size of HDL formed in vivo, P➔A substitutions alter HDL biogenesis, thereby implicating other cellular and in vivo processes as determinants of HDL metabolism and function.

Study of LCAT and some biochemical parameters in cardiovascular patient

The Clinical study included individuals (m23ales and females aged 25-75y) with cardiovascular disease. The activity of Lecithin: cholesterol acyl transferase (LCAT) and glutathione peroxidase(GPx) was estimated, in addition to the level of apolipoprotein AI (apo AI), apolipoprotein B100 (apoB100), total cholesterol (TC), triglyceride (TG), high density lipoprotein-cholesterol (HDL-c), low density lipoprotein-cholesterol (LDL-c), glutathione (GSH), peroxy nitrate (PN), malondialdehyde (MDA), glucose and certain elements (Zn, Cu, Mg and Co) in blood serum. The results showed that there was a significant decrease in the activity of LCAT and GPx, and the level of apoAI, HDL-c, GSH, Zn and Mg. on the other hand, it was shown that there was a significant increase in the level of apoB100, TC, TG, LDL-c, PN, Glu, Cu and Co but on unsignificant change in the level of MDA for both male and females.

Hypertension, lipoprotein subclasses and lipid transfer proteins in obese children and adolescents

Background: Obesity-related childhood hypertension is associated with disturbances of serum lipids, but less is known about distribution of lipoprotein subclasses and activities of proteins involved in reverse cholesterol transport in hypertensive obese children. Our objective was to determine low-density lipoprotein (LDL) and high-density lipoprotein (HDL) subclasses distribution and activities of lecithin:cholesterol acyltransferase (LCAT) and cholesteryl ester transfer protein (CETP) in hypertensive and non-hypertensive obese children.Methods: A total of 40 hypertensive and 25 non-hypertensive obese children were enrolled. Lipoprotein subclasses were assessed by polyacrylamide gradient gel electrophoresis. LCAT and CETP activities were determined as a rate of formation and a rate of transfer of cholesteryl esters.Results: Despite of comparable values of serum lipid parameters, a shift toward smaller LDL and HDL subclasses was observed in hypertensive compared to normotensive obese children. Activities of LCAT were similar, but proatherogenic CETP activities were significantly higher in the hypertensive group (p = 0.036). LCAT/net CETP ratio inversely correlated with relative proportion of small, dense LDL particles (ρ = −0.423; p = 0.025) in the group with hypertension.Conclusions: The results of our study demonstrated a tendency toward altered distribution of lipoprotein subclasses in favor of more proatherogenic particles in childhood hypertension. Also, hypertensive obese children had increased proatherogenic CETP activity.

Influence of Casein–Phospholipid Combinations as Emulsifier on the Physical and Oxidative Stability of Fish Oil-in-Water Emulsions

The objective of this study was to investigate the influence of casein (0.3% w/w) and phospholipid (0.5% w/w) emulsifier combinations on the physical and oxidative stability of 10% fish oil-in-water emulsions at pH 7. For that purpose, three phospholipids were evaluated, namely, lecithin (LC), phosphatidylcholine (PC), and phosphatidylethanolamine (PE). The emulsion stabilized with LC showed the best physical stability having the most negative zeta potential and the lowest mean droplet size. In addition, this emulsion was also the least oxidized in terms of peroxide value and concentration of the volatile oxidation product 1-penten-3-ol. This finding is not explained by the antioxidant activity of LC because it showed similar DPPH scavenging activity and lower metal chelating activity than the other phospholipids. Therefore, these results suggested that other factors such as the combination of casein and lecithin, which could result in a favorable structure and thickness of the interfacial layer, prevented lipid oxidation in this emulsion.

Antihyperlipidemic and antiatherogenic activity of simvastatin may involve modulation of the expression of lecithin:cholesterol acyl transferase.

The statin-induced effects on high density lipoprotein (HDL) are relatively small compared with those of low density lipoprotein (LDL) and, as a result, most clinical trials of statins are underpowered with respect to HDL parameters. This study experimentally investigated, the effects of statin on serum lipids, atherogenic index and examined the possibility of a relationship amongst serum concentrations of HDL-C, atherogenic index and activity of lecithin:cholesterol acyl transferase. Thirty albino rats equally divided into 2 groups were used for the study. Group 1 was given 0.05mg/g of statin daily for 28 days, while group 2 served as control. HDL concentration was determined as a measure of HDL-C. Total cholesterol (TC), triglyceride (TG) and HDL-C were determined spectrophotometrically while LDL-C was calculated using the Frieldwald formula. Effect on the activity of lecithin:cholesterol acyl transferase was determined by the difference between the amount of free cholesterol converted to cholesteryl ester in the two experimental groups. Effects on body and relative organs weights were also determined. The administration of statin caused a significant increase in serum concentration of HDL-C, while levels of LDL-C, triglyceride and total cholesterol were reduced. Simvastatin caused a significant reduction in the atherogenic index (TC/HDL-C; LDLC/HDL-C). The administration of statin significantly induced the activity of lecithin:cholesterol acyl transferase (LCAT) as evident by reduced serum concentration of free cholesterol when compared with control. The administration of statin caused reduced body and relative organs weights. The study showed that serum antihyperlipidemic and antiatherogenic activity of statin may involve the induction of LCAT.

Conservation of Apolipoprotein A-I’s Central Domain Structural Elements upon Lipid Association on Different High-Density Lipoprotein Subclasses

The antiatherogenic properties of apolipoprotein A-I (apoA-I) are derived, in part, from lipidation-state-dependent structural elements that manifest at different stages of apoA-I's progression from lipid-free protein to spherical high-density lipoprotein (HDL). Previously, we reported the structure of apoA-I's N-terminus on reconstituted HDLs (rHDLs) of different sizes. We have now investigated at the single-residue level the conformational adaptations of three regions in the central domain of apoA-I (residues 119-124, 139-144, and 164-170) upon apoA-I lipid binding and HDL formation. An important function associated with these residues of apoA-I is the activation of lecithin:cholesterol acyltransferase (LCAT), the enzyme responsible for catalyzing HDL maturation. Structural examination was performed by site-directed tryptophan fluorescence and spin-label electron paramagnetic resonance spectroscopies for both the lipid-free protein and rHDL particles 7.8, 8.4, and 9.6 nm in diameter. The two methods provide complementary information about residue side chain mobility and molecular accessibility, as well as the polarity of the local environment at the targeted positions. The modulation of these biophysical parameters yielded new insight into the importance of structural elements in the central domain of apoA-I. In particular, we determined that the loosely lipid-associated structure of residues 134-145 is conserved in all rHDL particles. Truncation of this region completely abolished LCAT activation but did not significantly affect rHDL size, reaffirming the important role of this structural element in HDL function.

Effects of Lagenaria sicessaria fruit juice on lipid profile and glycoprotein contents in cardiotoxicity induced by isoproterenol in rats

This study investigated antihyperlipidemic effects of Lagenaria siceraria fruit juice (LSFJ) in isoproterenol (ISO)induced cardiotoxicity in rats. Rats treated with ISO (200 mg/kg, s.c.) showed a significant increase in the levels of triglycerides, cholesterol, and free fatty acids, in both serum and heart tissue. An increase in the levels of phospholipids, low-density lipoprotein, and very low-density lipoprotein-cholesterol, and decrease in high-density lipoprotein-cholesterol in serum and phospholipid levels in the heart were observed. ISO intoxicated rats also showed a significant decrease in the activities of lecithin: cholesterol acyl transferase, whereas lipoprotein lipase was found to be increased. Administration of LSFJ (400 mg/kg, p.o.) for 30 consecutive days and challenged with ISO on day 29th and 30th significantly attenuated these alterations and restored the levels of serum and heart lipids along with lipid metabolizing enzymes. Histopathological observations were also in correlation with the biochemical parameters. These findings indicate the protective effect of LSFJ during ISO-induced cardiotoxicity in rats.

ApoA-I deficiency in mice is associated with redistribution of apoA-II and aggravated AApoAII amyloidosis

Apolipoprotein A-II (apoA-II) is the second major apolipoprotein following apolipoprotein A-I (apoA-I) in HDL. ApoA-II has multiple physiological functions and can form senile amyloid fibrils (AApoAII) in mice. Most circulating apoA-II is present in lipoprotein A-I/A-II. To study the influence of apoA-I on apoA-II and AApoAII amyloidosis, apoA-I-deficient (C57BL/6J.Apoa1⁻/⁻) mice were used. Apoa1⁻/⁻ mice showed the expected significant reduction in total cholesterol (TC), HDL cholesterol (HDL-C), and triglyceride (TG) plasma levels. Unexpectedly, we found that apoA-I deficiency led to redistribution of apoA-II in HDL and an age-related increase in apoA-II levels, accompanied by larger HDL particle size and an age-related increase in TC, HDL-C, and TG. Aggravated AApoAII amyloidosis was induced in Apoa1⁻/⁻ mice systemically, especially in the heart. These results indicate that apoA-I plays key roles in maintaining apoA-II distribution and HDL particle size. Furthermore, apoA-II redistribution may be the main reason for aggravated AApoAII amyloidosis in Apoa1⁻/⁻ mice. These results may shed new light on the relationship between apoA-I and apoA-II as well as provide new information concerning amyloidosis mechanism and therapy.

Surface interaction of lecithin and lysolecithin.

Abstract The lowering of the surface tension of water by lysolecithin in the presence of a small constant amount of lecithin has been investigated to examine the changes in the boundary tension during the formation of a primary phosphatide membrane. In the higher concentration range of lysolecithin (above 0.05 per cent w/v corresponding to a weight fraction of 0.4) the surface activity was not affected by the presence of lecithin. Below 0.05 per cent w/v lysolecithin the surface activity was reduced but in the very dilute region of the critical micelle concentration it was restored. The presence of calcium chloride reduced the surface activity to a greater extent above the critical micelle concentration region of lysolecithin than below. The effects of potassium chloride differed from calcium chloride for different regions of the lysolecithin concentration range. Ageing effects due to the salts affected the surface acitivity, probably by reason of the removal of lecithin from the interface. The results were complex and only a qualitative interpretation of the behaviour was attempted. The surface tension: concentration relation for aqueous lecithin sols at four different temperatures, a precursor to the main work, showed a lowering of the surface tension of water to less than 41 dyne/cm. by 0.5 per cent w/v lecithin at 25°; reducing the concentration to 0.05 per cent w/v the surface activity of lecithin steadily diminished to zero.

Sex Dimorphism in Serum Lecithin: Cholesterol Acyltransferase and Lipoprotein Lipase Activities in Adult Sickle Cell Anaemia Patients with Proteinuria

Proteinuria in subjects with sickle cell anaemia (SCA) is an indication of an ongoing renal insufficiency and it's prevalence varies between sexes. We evaluated sex differences in the activities of Lecithin: cholesterol acyltransferase (LCAT), Lipoprotein lipase (LPL) and the levels of lipoproteins in SCA patients with proteinuria. Fifty SCA patients (30 males aged: 26.4±7.3years and 20 females, aged 25.4±2.6years) and 50 age and sex matched control SCA patients were recruited for the study. Random urine specimens were collected and tested for the presence of albumin by urine dipstick technique. A 24h urinary protein was quantitated using sulphosalicylic acid technique. Fasting serum total cholesterol, triglyceride, urea and creatinine were determined using enzymes catalyzed colorimetric methods. HDL cholesterol was determined in the supernatant after precipitation with manganese chloride-phosphotungstic acid solution. LCAT was measured using the Anasolv LCAT assay with proteoliposome as substrate. LPL was determined by incubating the serum in glyceryl trioleate substrate, the glycerol liberated was measured in an aliquot of the incubating mixture. In male SCA controls there was 18.2 and 6.9% increase in the activities of LPL and LCAT respectively when compared with females but in SCA patients with proteinuria there was 8.4 and 5.2% decreases in the male SCA patients compared with females. The concentration of 24h urine protein in the SCA male subjects with proteinuria was significantly higher (0.25g/day; P<0.001) compared with the SCA female patients with proteinuria (0.09g/day). There are sex differences in the activities of LCAT and LPL in SCA patients with proteinuria. Metabolism of these lipolytic enzymes may be modulated differently in SCA patients with proteinuria.

Ground Beef Fatty Acid Composition Alters HDL Functionality

High dense lipoprotein (HDL), also referred to as the “good cholesterol” has various atheroprotective functions. In this study, the functionality change of HDL induced by beef consumption, with a focus on the capability to promote reverse cholesterol transport was assessed. Human serum and plasma samples used for the assays were collected from 28 individuals that successfully completed the beef feeding trial, in which hamburger patties containing low and high monounsaturated fatty acid (MUFA): saturated fatty acid (SFA) ratios were consumed. Each subject completed a three 5‐week diet in a random order with a 4‐week wash period between the diets. The activities of lecithin:cholesterol acyltransferase (LCAT) and cholesterol ester transfer protein (CETP) were measured by commercially available kits from Roar Biomedical, Inc. Lipoprotein Profiling was achieved by ultracentrifugal density gradient separation in CsBiEDTA. Sphingosine 1phosphate, an important component of HDL, was extracted by a two step liquid‐liquid extraction and quantified by HPLC. The concentrations of serum and HDL3 apoproteins including Apo A‐I, A‐II, B, E were measured by fluorescent microsphere immunoassay. The results of the lipid profiling indicated that the consumption of high MUFA:SFA and low MUFA:SFA diets significantly increased the blood level of both HDL and HDL3. This work is supported by the National Cattlemen's Beef Association.

Activation of lecithin:cholesterol acyltransferase by HDL ApoA-I central helices.

Lecithin:cholesterol acyltransferase (LCAT) is an enzyme that first hydrolyzes the sn-2 position of phospholipids, preferentially a diacylphosphocholine, and then transfers the fatty acid to cholesterol to yield a cholesteryl ester. HDL ApoA-I is the principal catalytic activator for LCAT. Activity of LCAT on nascent or lipid-poor HDL particles composed of phospholipid, cholesterol and ApoA-I allows the maturation of HDL particles into lipid-rich spherical particles that contain a core of cholesteryl ester surrounded by phospholipid and ApoA-I on the surface. This article reviews the recent progress in elucidating structural aspects of the interaction between LCAT and ApoA-I. In the last decade, there has been considerable progress in understanding the structure of ApoA-I and the central helices 5, 6, and 7 that are known to activate LCAT. However, much less information has been forthcoming describing the 3D structure and conformation of LCAT required to catalyze two separate reactions within a single monomeric peptide.

ApoA-I cleaved by transthyretin has reduced ability to promote cholesterol efflux and increased amyloidogenicity

A fraction of plasma transthyretin (TTR) circulates in HDL through binding to apolipoprotein A-I (apoA-I). Moreover, TTR is able to cleave the C terminus of lipid-free apoA-I. In this study, we addressed the relevance of apoA-I cleavage by TTR in lipoprotein metabolism and in the formation of apoA-I amyloid fibrils. We determined that TTR may also cleave lipidated apoA-I, with cleavage being more effective in the lipid-poor prebeta-HDL subpopulation. Upon TTR cleavage, discoidal HDL particles displayed a reduced capacity to promote cholesterol efflux from cholesterol-loaded THP-1 macrophages. In similar assays, TTR-containing HDL from mice expressing human TTR in a TTR knockout background had a decreased ability to perform reverse cholesterol transport compared with similar particles from TTR knockout mice, reinforcing the notion that cleavage by TTR reduces the ability of apoA-I to promote cholesterol efflux. As amyloid deposits composed of N-terminal apoA-I fragments are common in the atherosclerotic intima, we assessed the impact of TTR cleavage on apoA-I aggregation and fibrillar growth. We determined that TTR-cleaved apoA-I has a high propensity to form aggregated particles and that it formed fibrils faster than full-length apoA-I, as assessed by electron microscopy. Our results show that apoA-I cleavage by TTR may affect HDL biology and the development of atherosclerosis by reducing cholesterol efflux and increasing the apoA-I amyloidogenic potential.

Effects of atorvastatin on high‐density lipoprotein apolipoprotein A‐I metabolism in dogs

The mechanisms involved in the decline of high-density lipoprotein (HDL) levels at a higher dose of atorvastatin have not yet been elucidated. We investigated the effects of atorvastatin on HDL-apolipoprotein (apo) A-I metabolism in dogs, a species lacking cholesteryl ester transfer protein activity. Seven ovariectomized normolipidaemic female Beagle dogs underwent a primed constant infusion of [5,5,5-(2)H(3)] leucine to determine HDL-apo A-I kinetics before and after atorvastatin treatment (5 mg kg(-1) d(-1) for 6 weeks). Plasma lipoprotein profiles, activity of HDL-modifying enzymes involved in reverse cholesterol transport and hepatic scavenger receptor class B type I (SR-BI) expression were also studied. Atorvastatin treatment decreased HDL-cholesterol levels (3.56 +/- 0.24 vs. 2.64 +/- 0.15 mmol L(-1), P < 0.05). HDL-triglycerides were not affected. HDL-phospholipids levels were decreased (4.28 +/- 0.13 vs. 3.29 +/- 0.13 mmol L(-1), P < 0.05), as well as phospholipids transfer protein (PLTP) activity (0.83 +/- 0.05 vs. 0.60 +/- 0.05 pmol microL(-1) min(-1), P < 0.05). Activity of lecithin: cholesterol acyl transferase (LCAT), hepatic lipase (HL) and SR-BI expression did not change. HDL-apo A-I absolute production rate (APR) was higher after treatment (twofold, P < 0.05) as well as fractional catabolic rate (FCR) (threefold, P < 0.05). This resulted in lower HDL-apo A-I levels (2.36 +/- 0.03 vs. 1.55 +/- 0.04 g l(-1), P < 0.05). Plasma lipoprotein profiles showed a decrease in large HDL(1) levels, with lower apo A-I and higher apo E levels in this subfraction. Although a high dose of atorvastatin up-regulated HDL-apo A-I production, this drug also increased HDL-apo A-I FCR in dogs. This effect could be explained by a higher uptake of apo E-enriched HDL(1) by hepatic lipoprotein receptors.

Endothelial lipase releases saturated and unsaturated fatty acids of high density lipoprotein phosphatidylcholine

We assessed the ability of endothelial lipase (EL) to hydrolyze the sn-1 and sn-2 fatty acids (FAs) from HDL phosphatidylcholine. For this purpose, reconstituted discoidal HDLs (rHDLs) that contained free cholesterol, apolipoprotein A-I, and either 1-palmitoyl-2-oleoylphosphatidylcholine, 1-palmitoyl-2-linoleoylphosphatidylcholine, or 1-palmitoyl-2-arachidonylphosphatidylcholine were incubated with EL- and control (LacZ)-conditioned media. Gas chromatography analysis of the reaction mixtures revealed that both the sn-1 (16:0) and sn-2 (18:1, 18:2, and 20:4) FAs were liberated by EL. The higher rate of sn-1 FA cleavage compared with sn-2 FA release generated corresponding sn-2 acyl lyso-species as determined by MS analysis. EL failed to release sn-2 FA from rHDLs containing 1-O-1'-hexadecenyl-2-arachidonoylphosphatidylcholine, whose sn-1 position contained a nonhydrolyzable alkyl ether linkage. The lack of phospholipase A(2) activity of EL and its ability to liberate [(14)C]FA from [(14)C]lysophosphatidylcholine (lyso-PC) led us to conclude that EL-mediated deacylation of phosphatidylcholine (PC) is initiated at the sn-1 position, followed by the release of the remaining FA from the lyso-PC intermediate. Thin-layer chromatography analysis of cellular lipids obtained from EL-overexpressing cells revealed a pronounced accumulation of [(14)C]phospholipid and [(14)C]triglyceride upon incubation with 1-palmitoyl-2-[1-(14)C]linoleoyl-PC-labeled HDL(3), indicating the ability of EL to supply cells with unsaturated FAs.

Decreased activity of lecithin:cholesterol acyltransferase and hepatic lipase in chronic hypothyroid rats: implications for reverse cholesterol transport.

Chronic hypothyroidism is frequently associated with atherosclerosis due to increased cholesterol plasma levels; nevertheless, the contribution of impaired reverse cholesterol transport (RCT) in this process has not been completely elucidated. The aim of this study was to evaluate the effect of thyroidectomy (Htx) upon the main stages of RCT in rats. Plasma lipid alterations induced by thyroidectomy showed a slight, but significant, reduction of total plasma triglycerides, a 300% increase of LDL-cholesterol and a 25% decrease in HDL-cholesterol compared to control rats. We evaluated the first stage of RCT determining 3H-cholesterol efflux in Fu5AH cells. The capacity of HDL obtained from Htx rats to promote cholesterol efflux was similar to that of controls. Lecithin:cholesterol acyltransferase (LCAT) activity, the second stage and the driving force of RCT was 30% lower in Htx animals compared to controls, as determined by reconstituted HDL used as an external substrate. Lipoproteins are remodeled by hepatic lipase; the mean activity of this enzyme in postheparin plasma of Htx animals was reduced by 30% compared to controls, thus suggesting an impaired HDL remodeling by this enzyme in the hypothyroid status. In contrast, lipoprotein lipase activity in the Htx group was unchanged. In summary, this study demonstrates that chronic hypothyroidism in the rat induced an impaired RCT mainly at the cholesterol esterification, and HDL remodeling mediated by hepatic lipase. The latter probably results in an abnormal HDL structure, i.e. phospholipid enrichment, which contributes to decrease HDL-apo AI fractional catabolic rates.

Optimized bacterial expression of human apolipoprotein A-I

Apolipoprotein A-I (apoA-I) serves critical functions in plasma lipoprotein metabolism as a structural component of high density lipoprotein, activator of lecithin:cholesterol acyltransferase, and acceptor of cellular cholesterol as part of the reverse cholesterol transport pathway. In an effort to facilitate structure:function studies of human apoA-I, we have optimized a plasmid vector for production of recombinant wild type (WT) and mutant apoA-I in bacteria. To facilitate mutagenesis studies, subcloning, and DNA manipulation, numerous silent mutations have been introduced into the apoA-I cDNA, generating 13 unique restriction endonuclease sites. The coding sequence for human apoA-I has been modified by the introduction of additional silent mutations that eliminate 18 separate codons that employ tRNAs that are of low or moderate abundance in Escherichia coli. Yields of recombinant apoA-I achieved using the optimized cDNA were 100±20 mg/L bacterial culture, more than fivefold greater than yields routinely obtained with the original cDNA. Site-directed mutagenesis of the apoA-I cDNA was performed to generate a Glu2Asp mutation in the N-terminal sequence of apoA-I. This modification, which creates an acid labile Asp–Pro peptide bond between amino acids 2 and 3, permits specific chemical cleavage of an N-terminal His-Tag fusion peptide used for rapid protein purification. The product protein’s primary structure is identical to WT apoA-I in all other respects. Together, these changes in apoA-I cDNA and bacterial expression protocol significantly improve the yield of apoA-I protein without compromising the relative ease of purification.

Relevance of apolipoproteins in the development of fatty liver and fatty liver-related peripartum diseases in dairy cows.

Most metabolic diseases in dairy cows occur during the peripartum period and are suggested to be derived from fatty liver initially developed during the nonlactating stage. Fatty liver is induced by hepatic uptake of nonesterified fatty acids that are released in excess by adipose tissues attributable to negative energy balance. The fatty accumulation leads to impairment of lipoprotein metabolism in the liver, and the impairment in turn influences other metabolic pathways in extrahepatic tissues such as the steroid hormone production by the corpus luteum. Detailed understanding of the impaired lipoprotein metabolism is crucial for elucidation of the mechanistic bases of the development of fatty liver and fatty liver-related peripartum diseases. This review summarizes results on evaluation of lipoprotein lipid and protein concentrations and enzyme activity in cows with fatty liver and those with ketosis, left displacement of the abomasum, milk fever, downer syndrome and retained placenta. Obtained data strongly suggest that decreases in serum concentrations of apolipoprotein B-100, apolipoprotein A-I and apolipoprotein C-III, a reduction in activity of lecithin:cholesterol acyltransferase and induction of haptoglobin and serum amyloid A are intimately related to the development of fatty liver and fatty liver-related diseases. Moreover, determination of the apolipoprotein concentrations and enzyme activity during the peripartum period is useful for early diagnoses of these diseases.

Role of individual amino acids of apolipoprotein A-I in the activation of lecithin:cholesterol acyltransferase and in HDL rearrangements

The central region of apolipoprotein A-I (apoA-I), spanning residues 143–165, has been implicated in lecithin:cholesterol acyltransferase (LCAT) activation and also in high density lipoprotein (HDL) structural rearrangements. To examine the role of individual amino acids in these functions, we constructed, overexpressed, and purified two additional point mutants of apoA-I (P143R and R160L) and compared them with the previously studied V156E mutant. These mutants have been reported to occur naturally and to affect HDL cholesterol levels and cholesterol esterification in plasma. The P143R and R160L mutants were effectively expressed in Escherichia coli as fusion proteins and were isolated in at least 95% purity. In the lipid-free state, the mutants self-associated similarly to wild-type protein. All the mutants, including V156E, were able to lyse dimyristoylphosphatidylcholine liposomes. In the lipid-bound state, the major reconstituted HDL (rHDL) of the mutants had diameters similar to wild type (96–98 Å). Circular dichroism and fluorescence methods revealed no major differences among the structures of the lipid-free or lipid-bound mutants and wild type. In contrast, the V156E mutant had exhibited significant structural, stability, and self-association differences compared with wild-type apoA-I in the lipid-free state, and formed rHDL particles with larger diameters. In this study, limited proteolytic digestion with chymotrypsin showed that the V156E mutant, in lipid-free form, has a distinct digestion pattern and surface exposure of the central region, compared with wild type and the other mutants. Reactivity of rHDL with LCAT was highest for wild type (100%), followed by P143R (39%) and R160L (0.6%). Tested for their ability to rearrange into 78-Å particles, the rHDL of the two mutants (P143R and R160L) behaved normally, compared with the rHDL of V156E, which showed no rearrangement after the 24-h incubation with low density lipoprotein (LDL). Similarly, the rHDL of V156E was resistant to rearrangement in the presence of apoA-I or apoA-II. These results indicate that structural changes are absent or modest for the P143R and R160L mutants, especially in rHDL form; that these mutants have normal conformational adaptability; and that LCAT activation is obliterated for R160L. Thus, individual amino acid changes may have markedly different structural and functional consequences in the 143–165 region of apoA-I. The R160L mutation appears to have a direct effect in LCAT activation, while the P143R mutation results in only minor structural and functional effects. Also, the processes for LCAT activation and hinge mobility appear to be distinct even if the same region of apoA-I is involved. —Cho, K-H., D. M. Durbin, and A. Jonas. Role of individual amino acids of apolipoprotein A-I in the activation of lecithin:cholesterol acyltransferase and in HDL rearrangements.