Milk protein hydrolysates activate 5-HT2C serotonin receptors: influence of the starting substrate and isolation of bioactive fractions

Abstract

Milk protein hydrolysates generated with different starting substrates, including sodium caseinate (NaCN), acid casein (Acid CN), skim milk powder (SMP) and glycomacropeptide (GMP) were demonstrated to behave as serotonin 2C (5-HT 2c ) receptor agonists. The 5-HT 2c receptor activating potential of NaCN hydrolysates correlated with an increased protein hydrolysis, most likely due to 10 enhanced release of bioactive peptides over the time course of hydrolysis. In its unhydrolysed form, GMP was the only starting substrate showing 5-HT 2c serotonin receptor agonist activity. The 5-HT 2c serotonin receptor agonist activity of its corresponding hydrolysate (GMPH-240 min) was significantly higher (P < 0.05). Fractionation of the 240 min NaCNH using ultrafiltration (UF), solid-phase extraction (SPE), semipreparative reverse-phase high performance liquid chromatography (RP-HPLC) and isoelectric focusing 15 (IEF) was carried out. Characterisation of the fractions obtained shows that the bioactive peptides had a relatively low molecular mass (< 1 kDa), were hydrophobic in nature and had a pI between 8.6 and 13.2. These different physicochemical characteristics together with the stability of NaCNH-240 min to simulated intestinal digestion, allow prediction of a favourable outcome regarding the bioavailability of the bioactive peptides therein. These results reinforce the potential of milk-derived bioactive peptides to 20 be developed into functional foods targeted at 5-HT 2c receptor modulation.

In vitrotransport and satiety of a beta-lactoglobulin dipeptide and beta-casomorphin-7 and its metabolites

“…[44][45][46] Furthermore, an in vitro study involving HEK293A human embryonic kidney cells transfected with two isoforms of the 5-HT 2C (serotonin) receptors, demonstrated receptor agonist activity in response to casein hydrolysate fractions suggesting casein peptides, including β-casomorphins, may be involved in the regulation of food intake and the suppression of appetite through serotonin receptors. 47 Conversely, radioreceptor analysis indicated that both human and bovine β-CM7 act as 5-HT 2C antagonists, 48 suggesting a stimulatory role for these peptides. The effect of β-Lg on satiety is also unclear, however many studies report the satiating effect of whey protein 49,50 with one recent study implicating a role for β-Lg 51 in satiety.…”

Gastric Emptying and Gastrointestinal Transit Compared among Native and Hydrolyzed Whey and Casein Milk Proteins in an Aged Rat Model

“…In addition, milk proteins are digested during the various stages of human GI tract digestion to give rise to an array of peptides that can elicit a variety of physiologic effects that affect the rate of digestion and transit for casein and whey proteins [ 2 , 22 , 25 , 26 ]. Some of these peptides modulate opioid [ 26 , 27 , 28 , 29 ] or serotonin receptors [ 30 ]. Whey supplementation may confer benefits for modulation of GI motility in the elderly.…”

Milk proteins as a source of tryptophan-containing bioactive peptides

“…Consumption of -La has been shown to increase plasma W in rats 45 and in humans 50,129 , which may result in higher hypothalamic serotonin concentrations 50 . Different milk protein 60 (whey and CN-derived) hydrolysates have been shown to act as serotonin 5-HT 2C receptor agonist in embryonic kidney cell lines (HEK 293A) 131,132 . While no effect was seen in vivo with the 1 kDa permeate of a whey protein hydrolysate, the 1 kDa permeate of a CN hydrolysate was show to yield a significant reduction in 5 cumulative food intake when administered intraperiteonally (500 mg kg −1 body weight) to mice 131 .…”