Soybean Bioactive Peptides and Their Functional Properties.

Soy consumption has been associated with many potential health benefits in reducing chronic diseases such as obesity, cardiovascular disease, insulin-resistance/type II diabetes, certain type of cancers, and immune disorders. These physiological functions have been attributed to soy proteins either as intact soy protein or more commonly as functional or bioactive peptides derived from soybean processing. These findings have led to the approval of a health claim in the USA regarding the ability of soy proteins in reducing the risk for coronary heart disease and the acceptance of a health claim in Canada that soy protein can help lower cholesterol levels.

The α' subunit of β-conglycinin and various glycinin subunits of soy are not required to modulate hepatic lipid metabolism in rats.

Purpose: This study examined the effect of soy proteins with depletion of different subunits of the two major storage proteins, β-conglycinin and glycinin, on hepatic lipids and proteins involved in lipid metabolism in rats, since the bioactive component of soy responsible for lipid-lowering is unclear.

Methods: Weanling Sprague Dawley rats were fed diets containing either 20% casein protein in the absence (casein) or presence (casein + ISF) of isoflavones or 20% alcohol-washed soy protein isolate (SPI) or 20% soy protein concentrates derived from a conventional (Haro) or 2 soybean lines lacking the α' subunit of β-conglycinin and the A1-3 (1TF) or A1-5 (1a) subunits of glycinin. After 8 weeks, the rats were necropsied and liver proteins and lipids were extracted and analysed.

P2X receptors regulate adenosine diphosphate release from hepatic cells.

Extracellular nucleotides act as paracrine regulators of cellular signaling and metabolic pathways. Adenosine polyphosphate (adenosine triphosphate (ATP) and adenosine diphosphate (ADP)) release and metabolism by human hepatic carcinoma cells was therefore evaluated. Hepatic cells maintain static nanomolar concentrations of extracellular ATP and ADP levels until stress or nutrient deprivation stimulates a rapid burst of nucleotide release.

Hepatic lipase release is inhibited by a purinergic induction of autophagy.

Background/aims: We have shown that extracellular adenosine diphosphate (ADP) affects lipoprotein secretion from liver cells by stimulating cellular autophagic degradation. In this study, we investigated the effect of ADP and cellular autophagy on hepatic lipase (HL) release from human liver cells.

Methods/results: Depletion of media serum stimulates an autophagic response in liver cells, which parallels an 8-fold increase in the release of ADP into the media and a complete inhibition of HL release.

Purinergic signaling, dyslipidemia and inflammatory disease.

Metabolic syndrome is a compound obesity disorder, wherein the abnormal metabolism of glucose and lipid is associated with the development of chronic inflammatory diseases. The prevalence of this disease is increasing in the developed world, but the causative linkage between these metabolic disorders has remained obscure. Metabolic disease may be associated with chronic nucleotide secretion, purinergic signaling and activation of inflammatory pathways.

Extracellular nucleotides inhibit insulin receptor signaling, stimulate autophagy and control lipoprotein secretion.

Hyperglycemia is associated with abnormal plasma lipoprotein metabolism and with an elevation in circulating nucleotide levels. We evaluated how extracellular nucleotides may act to perturb hepatic lipoprotein secretion. Adenosine diphosphate (ADP) (>10 µM) acts like a proteasomal inhibitor to stimulate apoB100 secretion and inhibit apoA-I secretion from human liver cells at 4 h and 24 h.

Hepatic lipase, high density lipoproteins, and hypertriglyceridemia.

Hepatic lipase (HL) is a lipolytic enzyme that contributes to the regulation of plasma triglyceride (TG) levels. Elevated TG levels may increase the risk of developing coronary heart disease, and studies suggest that mutations in the HL gene may be associated with elevated TG levels and increased risk of coronary heart disease. Hepatic lipase facilitates the clearance of TG from the very low density lipoprotein (VLDL) pool, and this function is governed by the composition and quality of high density lipoprotein (HDL) particles.

HDL-ApoE content regulates the displacement of hepatic lipase from cell surface proteoglycans.

Human hepatic lipase (HL) is an interfacial enzyme that must be liberated from cell surface proteoglycans to hydrolyze lipoprotein triglyceride. Both high-density lipoprotein (HDL) and apolipoprotein (apo)A-I can displace HL from cell surface proteoglycans, much like heparin. HL displacement is inhibited by HDL-apoE content.

Hepatic high-density lipoprotein secretion regulates the mobilization of cell-surface hepatic lipase.

HDL acts much like heparin to liberate hepatic lipase (HL) from cell surface proteoglycans and stimulate triglyceride clearance. Experiments were undertaken to evaluate the effects of factors that stimulate the secretion of HDL from the liver on the release of HL. Treatment of HepG2 cells with linoleic acid phospholipids (LAPL) (12 muM) promotes a similar increase in the accumulation of both HDL and HL in the cell media.

HDL composition regulates displacement of cell surface-bound hepatic lipase.

HDL is able to displace cell surface-bound hepatic lipase (HL) and stimulate vascular triglyceride (TG) hydrolysis, much like heparin. Displacement appears to be a result of a high-affinity association of HL and apoA-I. HDL varies in its ability to displace HL, and therefore experiments were undertaken to evaluate the impact of HDL composition and structure on HL displacement from cell surface proteoglycans.

Lipoprotein charge and vascular lipid metabolism.

Lipoproteins play a central role in transporting hydrophobic molecules through the bloodstream and between specific tissues. Lipoprotein molecules have a distinctive electrical charge and changes in electrostatic properties directly affect the metabolism of the lipoprotein. Lipoprotein charge controls interfacial interactions and determines the ability of the lipoprotein to interact with intravascular enzymes and cell surface proteins.