Proteins of white lupin seed, a naturally isoflavone-poor legume, reduce cholesterolemia in rats and increase LDL receptor activity in HepG2 cells

White lupin (Lupinus albus, L.), a widely cultivated crop that has been consumed for many years in Western Europe, may provide a useful alternative for individuals wishing to substitute animal with plant proteins for cardiovascular disease prevention. Lupin seeds have a very low content of isoflavones, and lupin protein isolates are essentially isoflavone free. In rats fed a casein-based cholesterol + cholic acid diet, a relatively low daily intake (50 mg/d by gavage for 2 wk) of total lupin protein extract reduced plasma total and VLDL + LDL cholesterol concentrations by 21 and 30%, respectively (both P<0.001). In an attempt to elucidate the lipid-lowering mechanism, LDL receptor activity was evaluated in a human hepatoma cell line (HepG2). In this model, the lupin total protein extract was essentially inactive, whereas one purified minor protein component, conglutin gamma, had a remarkable upregulatory effect, with maximal increases of 53 and 21% (both P<0.05) for LDL uptake and degradation, respectively. This initial study indicates that lupin, although isoflavone free, has hypocholesterolemic activity similar to that of other leguminous proteins in an established animal model. Further, the cholesterol reduction appears to be associated with stimulation of LDL receptors by a well-defined protein component of the lupin seeds as demonstrated by in vitro studies

Lupin protein isolate versus casein modifies cholesterol excretion and mRNA expression of intestinal sterol transporters in a pig model

Abstract Background Lupin proteins exert hypocholesterolemic effects in man and animals, although the underlying mechanism remains uncertain. Herein we investigated whether lupin proteins compared to casein modulate sterol excretion and mRNA expression of intestinal sterol transporters by use of pigs as an animal model with similar lipid metabolism as humans, and cellular cholesterol-uptake by Caco-2 cells. Methods Two groups of pigs were fed cholesterol-containing diets with either 230 g/kg of lupin protein isolate from L. angustifolius or 230 g/kg casein, for 4 weeks. Faeces were collected quantitatively over a 5 d period for analysis of neutral sterols and bile acids by gas chromatographically methods. The mRNA abundances of intestinal lipid transporters were analysed by real-time RT-PCR. Cholesterol-uptake studies were performed with Caco-2 cells that were incubated with lupin conglutin \u3b3, phytate, ezetimibe or albumin in the presence of labelled [4-14C]-cholesterol. Results Pigs fed the lupin protein isolate revealed lower cholesterol concentrations in total plasma, LDL and HDL than pigs fed casein (P < 0.05). Analysis of faeces revealed a higher output of cholesterol in pigs that were fed lupin protein isolate compared to pigs that received casein (+57.1%; P < 0.05). Relative mRNA concentrations of intestinal sterol transporters involved in cholesterol absorption (Niemann-Pick C1-like 1, scavenger receptor class B, type 1) were lower in pigs fed lupin protein isolate than in those who received casein (P < 0.05). In vitro data showed that phytate was capable of reducing the uptake of labelled [4-14C]-cholesterol into the Caco-2 cells to the same extend as ezetimibe when compared to control ( 1220.5% vs. 1221.1%; P < 0.05). Conclusions Data reveal that the cholesterol-lowering effect of lupin protein isolate is attributable to an increased faecal output of cholesterol and a reduced intestinal uptake of cholesterol. The findings indicate phytate as a possible biofunctional ingredient of lupin protein isolate.Background: Lupin proteins exert hypocholesterolemic effects in man and animals, although the underlying mechanism remains uncertain. Herein we investigated whether lupin proteins compared to casein modulate sterol excretion and mRNA expression of intestinal sterol transporters by use of pigs as an animal model with similar lipid metabolism as humans, and cellular cholesterol-uptake by Caco-2 cells. Methods. Two groups of pigs were fed cholesterol-containing diets with either 230 g/kg of lupin protein isolate from L. angustifolius or 230 g/kg casein, for 4 weeks. Faeces were collected quantitatively over a 5 d period for analysis of neutral sterols and bile acids by gas chromatographically methods. The mRNA abundances of intestinal lipid transporters were analysed by real-time RT-PCR. Cholesterol-uptake studies were performed with Caco-2 cells that were incubated with lupin conglutin \u3b3, phytate, ezetimibe or albumin in the presence of labelled [4- 14C]-cholesterol. Results: Pigs fed the lupin protein isolate revealed lower cholesterol concentrations in total plasma, LDL and HDL than pigs fed casein (P < 0.05). Analysis of faeces revealed a higher output of cholesterol in pigs that were fed lupin protein isolate compared to pigs that received casein (+57.1%; P < 0.05). Relative mRNA concentrations of intestinal sterol transporters involved in cholesterol absorption (Niemann-Pick C1-like 1, scavenger receptor class B, type 1) were lower in pigs fed lupin protein isolate than in those who received casein (P < 0.05). In vitro data showed that phytate was capable of reducing the uptake of labelled [4- 14C]-cholesterol into the Caco-2 cells to the same extend as ezetimibe when compared to control (-20.5% vs. -21.1%; P < 0.05). Conclusions: Data reveal that the cholesterol-lowering effect of lupin protein isolate is attributable to an increased faecal output of cholesterol and a reduced intestinal uptake of cholesterol. The findings indicate phytate as a possible biofunctional ingredient of lupin protein isolate

Molecular nutraceutics as a mean to investigate the positive effects of legume seed proteins on human health

Leguminous seeds are a valuable source of food proteins. A reappraisal of the beneficial effects of legume seed dietary intake, which are the basis for various health claims, is currently taking place. Proteins and peptides concur in the observed biological/functional activities of legume seeds. However, the molecular determinants of these beneficial activities in most cases are far from being understood. A multidisciplinary research work, including the characterisation at molecular level of these molecules and the evaluation of their biological activities, is crucial to unveil food protein nutri-functional properties and optimise their exploitation. These are the approaches of the molecular nutraceutics

Industrial process proteomics : traceability and safety of protein components in lupin-based pasta product

Two-dimensional (2D) IEF/SDS-PAGE is a powerful tool to get molecular \u201cpictures\u201d of a food proteome and to monitor the processing effect of a given food item on its protein profile. In this work 2D electrophoresis has been used to monitor each step of lupin-based gluten-free pasta production. To this purpose various samples at each critical production step, including seeds, raw materials, half-processed products and dry pasta, were used to generate the corresponding 2-D electrophoretic maps. Some differences in the protein profiles between the raw materials, i.e. lupin flour and lupin protein concentrate, were attributed to the different varieties which they arose from. On the other hand, the electrophoretic analyses of half-processed products and dry pasta showed only minor differences among the samples during the industrial processing. These results, despite the intrinsic heterogeneity and complexity of lupin protein samples, indicate that the pasta making process have had no detectable effect on the covalent continuity of the main polypeptide backbones, suggesting that the polypeptides remained intact during the production process. The disulphide pattern did not change during the process, as well, and the constancy of the glycosylation pattern, as measured by the lectin Concanavalin A on the blotted maps, indicated that this molecular feature was not affected by the process too. In conclusion, this work shows that taking 2-D electrophoretic \u201cpictures\u201d of the polypeptides at each relevant step of a food production process can be very useful to both production and quality control strategies. In addition, the traceability of specific protein components is made it possible in force of the technique high resolution also in complex food matrices. In this respect, the additional use of specific antibodies or other approaches, including mass spectrometry identification of specific spots, can be extremely valuable. Moreover, the importance of monitoring the presence/modification of biologically active protein components, such is the case of lupin g-conglutin or specific allergens, by this analytical approach is self evident

Cloning, yeast expression, purification and biological activity of a truncated form of the soybean 7S globulin alpha' subunit involved in Hep G2 cell cholesterol homeostasis

A truncated form of alpha' chain (talpha'), the soybean 7S globulin subunit previously demonstrated to be active in controlling the cholesterol and triglyceride homeostasis in in vitro and in vivo models, was cloned and expressed in the yeast Pichia pastoris. The recombinant polypeptide spanned 216 amino acid residues from the N-terminal side and included the N-terminal extension region of the soybean subunit. The talpha' polypeptide was purified by conventional biochemical techniques, and its potential to modulate the activity of low-density lipoprotein (LDL) receptor was evaluated in a human hepatoma cell line (Hep G2) by monitoring the uptake and degradation of labeled LDL. The LDL uptake (+192%) and degradation (+143%) by cells tested at the highest talpha' dose (8 microM) were similar to those found in cells incubated with 1 microM simvastatin, a potent inhibitor of cholesterol biosynthesis. The cell response to talpha' was found to be dose dependent. The use of a recombinant polypeptide ruled out the involvement of any other soybean component. These findings open new prospects in the studies aimed at identifying soybean regulatory (poly)peptide(s) and the mechanism involved in this biological response, as a gateway to their utilization for the management of human health

Combined 2-D electrophoretic approaches for the study of white lupin mature seed storage proteome

Seed proteome analysis by 2D IEF/SDS\u2013PAGE techniques is challenging for the intrinsic difficulties related to quantitative disparity of the seed proteins, i.e. storage and non-storage proteins, their polymorphic nature, the extensive post-translational modifications and the paucity of deposited primary structures available. Conversely, 2D maps of seed proteomes can be extremely useful for a number of fundamental and applied investigations. In this work, we have used a combination of two experimental approaches to identify the main protein components of an emerging protein-rich legume seed, that is white lupin seed (Lupinus albus, L.). One is the canonical proteomic approach including 2D electrophoretic separation and mass spectrometry of selected trypsin-digested polypeptides; the other approach is a group comparative 2D electrophoretic analysis of cotyledonary protein families. To this second purpose, the three main families of lupin seed proteins, namely \u3b1-conglutins, the 11S globulin fraction, \u3b2-conglutins, the 7S globulin fraction, and \u3b3-conglutin, a basic 7S protein, were isolated by conventional biochemical techniques and their 2D reference maps were compared with the total protein map. With the first approach 37 out of 40 spots, making up about 35% of total spot volumes in the 2D map, were found to belong to the main seed protein families. Thanks to cDNA-deduced lupin storage protein sequences, determined on purpose and deposited, most of the identification statistical parameters were very good. Moreover, it was possible to identify several endogenously proteolysed subunits in the map. The second comparative approach, beside confirming these attributions, allowed to allocate 124 polypeptides within the three main lupin protein families. These two approaches proved to be mutually validating and their combined use was effective for the establishment of a seed proteome map even in the case of sequence and protein post-translational processing lack of information. The results obtained also extend our knowledge of the seed storage protein polymorphism of white lupin

Conglutin gamma, a lupin seed protein, binds insulin in vitro and reduces plasma glucose levels of hyperglycemic rats

This work describes the in vitro interaction between a lupin seed protein, namely, conglutin gamma, and insulin. The binding to an insulin-immobilized matrix occurs in the pH range from 7.5 to 4.2 and is strongly affected by ionic strength, suggesting that it is driven primarily by electrostatic interactions. The quantitative parameters of the binding were determined by surface plasmon resonance. On the basis of the conditions required for the interaction to take place and the quantitative binding parameters, it appeared that the interaction is specific, despite the fact that the origin of the two protein molecules is completely different. The effect of the oral administration of conglutin gamma on the glycemic levels of rats subjected to glucose overloading was a statistically significant reduction in glycemia comparable to that of metformin, a well-known glucose lowering drug. These findings represent the first molecular evidence of the possible use of a legume protein in the control of glycemia

Inhibitory properties and solution structure of a potent Bowman-Birk protease inhibitor from lentil (Lens culinaris, L.) seeds

Bowman-Birk serine protease inhibitors are a family of small plant proteins, whose physiological role has not been ascertained as yet, while chemopreventive anticarcinogenic properties have repeatedly been claimed. In this work we present data on the isolation of a lentil (Lens culinaris, L., var. Macrosperma) seed trypsin inhibitor (LCTI) and its functional and structural characterization. LCTI is a 7448 Da double-headed trypsin/chymotrypsin inhibitor with dissociation constants equal to 0.54 nM and 7.25 nM for the two proteases, respectively. The inhibitor is, however, hydrolysed by trypsin in a few minutes timescale, leading to a dramatic loss of its affinity for the enzyme. This is due to a substantial difference in the kon and k*on values (1.1 microM-1.s-1 vs. 0.002 microM-1.s-1), respectively, for the intact and modified inhibitor. A similar behaviour was not observed with chymotrypsin. The twenty best NMR structures concurrently showed a canonical Bowman-Birk inhibitor (BBI) conformation with two antipodal beta-hairpins containing the inhibitory domains. The tertiary structure is stabilized by ion pairs and hydrogen bonds involving the side chain and backbone of Asp10-Asp26-Arg28 and Asp36-Asp52 residues. At physiological pH, the final structure results in an asymmetric distribution of opposite charges with a negative electrostatic potential, centred on the C-terminus, and a highly positive potential, surrounding the antitryptic domain. The segment 53-55 lacks the anchoring capacity found in analogous BBIs, thus rendering the protein susceptible to hydrolysis. The inhibitory properties of LCTI, related to the simultaneous presence of two key amino acids (Gln18 and His54), render the molecule unusual within the natural Bowman-Birk inhibitor family

Hypoglycemic effect of lupin seed \u3b3-conglutin in experimental animals and healthy human subjects

A lupin seed \u3b3-conglutin-enriched preparation was tested in a glucose overload trial with both murine models and adult healthy volunteers. The results with rats showed a dose-dependent significant decrease of blood glucose concentration, which confirmed previous findings obtained with the purified protein. Moreover, three test-product doses equivalent to 630, 315, and 157.5 mg \u3b3-conglutin, orally administered 30 min before the carbohydrate supply, showed a relevant hypoglycemic effect in human trials. Insulin concentrations were not significantly affected. The general hematic parameters did not change at all. This is the first report on the glucose-lowering effect of lupin \u3b3-conglutin in human subjects