Effect of chain length on absorption of biologically active peptides from the gastrointestinal tract

Bioavailability of angiotensin I converting enzyme inhibitory peptides

Hypertension or high blood pressure is a significant health problem worldwide. Bioactive peptides that inhibit angiotensin I converting enzyme (ACE) in the cardiovascular system can contribute to the prevention and treatment of hypertension. These ACE inhibitory peptides are derived from many food proteins, especially milk proteins. An ACE inhibitory activity in vitro does not always imply an antihypertensive effect in vivo. Even if it does, it is very difficult to establish a direct relationship between in vitro and in vivo activity. This is mainly due to the bioavailability of the ACE inhibitory peptides after oral administration and the fact that peptides may influence blood pressure by mechanisms other than ACE inhibition. To exert an antihypertensive effect after oral ingestion, ACE inhibitory peptides have to reach the cardiovascular system in an active form. Therefore, they need to remain active during digestion by human proteases and be transported through the intestinal wall into the blood. The bioavailability of some ACE inhibitory peptides has been studied. It is also known that (hydroxy)proline-containing peptides are generally resistant to degradation by digestive enzymes. Peptides can be absorbed intact through the intestine by paracellular and transcellular routes, but the potency of the bioactivity after absorption is inversely correlated to chain length. In addition, some strategies are proposed to increase the bioavailability of ACE inhibitory peptides. Further research into the bioavailability of ACE inhibitory peptides will lead to the development of more effective ACE inhibitory peptides and foods.

Structural modulation of calmodulin and calmodulin-dependent protein kinase II by pea protein hydrolysates

The effects of two fractions of pea protein hydrolysate with high levels of positively charged amino acids on the structural conformations of calmodulin (CaM) and CaM-dependent protein kinase II (CaMKII) were determined using fluorescence and circular dichroism methods. In the presence of Ca2 + , addition of the protein hydrolysates to CaM and CaM/CaMKII complex led to increased exposure of aromatic groups as measured by intrinsic and extrinsic fluorescence spectroscopy. Near-UV circular dichroism data revealed an increase in the tertiary structure of CaM in the presence of pea protein hydrolysates. Effect of the protein hydrolysates on the CaM structure was greater with the fraction that contained higher contents of arginine and lysine when compared with the fraction with lower levels of these two amino acids. We concluded that the presence of the pea protein hydrolysates led to rearrangement of the native protein structure and exposure of buried hydrophobic groups of CaM and/or CaMKII.

Kinetics of the inhibition of calcium/calmodulin-dependent protein kinase II by pea protein-derived peptides

Calcium/calmodulin-dependent protein kinase II (CaMKII) catalyzes the phosphorylation of various cellular proteins and excessive activities have been implicated in the pathogenesis of various chronic diseases. We hypothesized that positively charged peptides can be produced through enzymatic hydrolysis of pea proteins; such peptides could then bind to negatively charged calmodulin (CaM) at a physiological pH level and inhibit CaMKII activity. Pea protein isolate was hydrolyzed with an alkaline protease (alcalase) and filtered through a 1000-mol wt cutoff membrane. The permeate, which contained low-molecular weight peptides, was used to isolate cationic peptides on an SP-Sepharose column by ion exchange chromatography. Separation of the permeate on the SP-Sepharose column yielded two fractions with net positive charges that were subsequently used for enzyme inhibition studies. Fraction I eluted earlier from the column and contained lower contents of lysine and arginine than Fraction II, which eluted later. Results show that both peptide fractions inhibited CaMKII activity mostly in a competitive manner, although kinetic data suggested that inhibition by Fraction II may be of the mixed type. Kinetic analysis (K(m) and K(i)) showed that affinity of peptides in Fraction II for CaM was more than that in Fraction I, which was directly correlated with the higher inhibitory properties of Fraction II against CaMKII. The results suggest that it may be possible to use pea protein-derived cationic peptides to modulate CaMKII activities.

Identification of angiotensin-I-converting enzyme inhibitory peptides derived from sodium caseinate hydrolysates produced by Lactobacillus helveticus NCC 2765

Angiotensin-I-converting enzyme (ACE) inhibitory activity was identified in milk proteins fermented with Lactobacillus (Lb.) helveticus NCC 2765 (Nestle Culture Collection, Vers-chez-les-Blanc, Switzerland). Hydrolyzing sodium caseinate for 1 and 2 h inhibited ACE activity, as measured by an in vitro ACE inhibition test. The hydrolysates with the highest ACE inhibitory potential were fractionated by gel permeation chromatography and their low molecular weight fractions collected. These fractions were subsequently subfractionated by reverse-phase high-pressure liquid chromatography. Several hydrophobic subfractions showed high ACE inhibitory potential, and their peptide composition was determined using an ion trap mass spectrometer equipped with an elctrospray ionization source. Analysis of the low molecular weight fraction identified 14 peptides with known antihypertensive activity and 1 with previously described opioid activity. On the basis of the peptide composition of active subfractions, two potentially active novel sequences were defined, and the following synthetic peptides were synthesized: FVAPFPEVFG (alphaS1 39-48), ENLLRFFVAPFPEVFG (alphaS1 33-48), NENLLRFFVAPFPEVFG (alphaS1 32-48), LNENLLRFFVAPFPEVFG (alphaS1 31-48), NLHLPLPLL (beta 147-155), ENLHLPLPLL (beta 146-155), and VENLHLPLPLL (beta 145-155). The ACE inhibitory potential of these synthetic peptides was assessed, and IC50 values were determined. NLHLPLPLL (beta 147-155), which was the only synthetic peptide also present in the sodium caseinate hydrolysates, and NENLLRFFVAPFPEVFG (alphaS1 32-48) showed the highest inhibition of ACE activity, with IC50 values of 15 and 55 microM, respectively. Furthermore, the stability of all synthetic peptides was assessed using an in vitro model simulating gastric digestion. The beta-casein-derived peptides remained intact following the successive hydrolysis by pepsin and pancreatin, whereas alphaS1-casein-derived peptides were degraded by pepsin.

Responding to the challenge of novel technology: an industrial hygiene and safety program for antibody production in maize

The production of pharmaceutical proteins in plants, particularly in maize (corn), offers solutions to the limited production capacity and flexibility of current cell culture technologies. Implementation of this technology presents unique challenges to industrial hygiene, safety, and occupational medicine, including the handling of pharmaceuticals in the context of agricultural production and the processing of grain for extraction. Protein-related challenges include: (1) widely varying potential for hazard depending upon the activity of the protein and nature and location of the target molecule; (2) limited data related to industrial routes of exposure; and (3) the inability to obtain relevant animal data because of high species-specificity. These challenges necessitate the development of novel approaches to industrial hygiene and safety. Realizing that much remains to be learned, our approach uses conservative assumptions to assure protection of employee health.

Absorption of the cholic acid-conjugated peptide hormone cholylsecretin from the rat ileum in vivo

AIMS

Previously, we demonstrated that gastrin peptides as long as 34 amino acids were absorbed from the ileum of rat after conjugation to the C24 position of cholic acid and that these peptides retained full biological activity. As absorption was specific to the ileum, it was inferred that the conjugated hormone was taken up by the bile salt transporters. We have now extended these experiments to a member of a different family of hormones, viz. secretin, a 27-amino acid hormone that stimulates serous secretions from the exocrine pancreas.

METHODS

After conjugation to cholic acid, the degree of cholylsecretin absorption from the ileum of anaesthetized rats was assessed from the increase in pancreatic secretions.

RESULTS

A complication to the study was that intra-ileal infusion of native secretin caused a transient increase in the levels of pancreatic secretions. This was in contrast to the effects of intra-ileal infusion of cholylsecretin which did not cause this transient increase but, instead, gave rise to a delayed increase in pancreatic secretions which was sustained over several hours during which cholylsecretin was detected in plasma in high concentration by mass spectrometry. The pancreatic response to cholylsecretin was abolished by co-infusion of 50 mm taurocholate, employed to compete with the bile salt transporters, although a transient increase in pancreatic secretions similar to that caused by secretin was now generated. This was shown to arise from an action of taurocholate per se causing the release of endogenous secretin which is present in rat ileum.

CONCLUSIONS

We, therefore, concluded that cholylsecretin had been absorbed from the rat ileum by uptake by bile salt transporters.

A quantitative in silico analysis calculates the angiotensin I converting enzyme (ACE) inhibitory activity in pea and whey protein digests

Angiotensin I converting enzyme (ACE) inhibitory peptides can induce antihypertensive effects after oral administration. By means of an ACE inhibitory peptide database, containing about 500 reported sequences and their IC(50) values, the different proteins in pea and whey were quantitatively evaluated as precursors for ACE inhibitory peptides. This analysis was combined with experimental data from the evolution in ACE inhibitory activity and protein degradation during in vitro gastrointestinal digestion. Pea proteins produced similar in silico scores and were degraded early in the in vitro digestion. High ACE inhibitory activity was observed after the simulated stomach phase and augmented slightly in the simulated small intestine phase. The major whey protein beta-lactoglobulin obtained the highest in silico scores, which corresponded with the fact that degradation of this protein in vitro only occurred from the simulated small intestine phase on and resulted in a 10-fold increase in the ACE inhibitory activity. Whey protein obtained total in silico scores of about 124 ml/mg, compared to 46 ml/mg for pea protein, indicating that whey protein would be a richer source of ACE inhibitory peptides than pea protein. Although beta-lactoglobulin is only partially digested, a higher ACE inhibitory activity was indeed found in the whey (IC(50) = 0.048 mg/ml) compared to the pea digest (IC(50) = 0.076 mg/ml). In silico gastrointestinal digestion of the highest scoring proteins in pea and whey, vicilin and albumin PA2, and beta-lactoglobulin, respectively, directly released a number of potent ACE inhibitory peptides. Several other ACE inhibitory sequences resisted in silico digestion by gastrointestinal proteases. Briefly, the quantitative in silico analysis will facilitate the study of precursor proteins on a large scale and the specific release of bioactive peptides.

Pressure/temperature combined treatments of precursors yield hormone-like peptides with pyroglutamate at the N terminus

Peptides containing the cyclic product of glutamine at the N terminus are usually biologically active. If the cyclization of glutamine was associated with a volume reduction, pressure should displace the equilibrium in the direction of the lower volume. Here, results in model solutions and in whey are discussed, showing that the theorized cyclization of glutamine in Gln-His-ProNH(2) or Gln-Leu-ProNH(2) is significantly accelerated during the application of heat and even more strongly when elevated temperature and pressure combinations are used. The reaction rate depended on the intensity of the pressure treatment, the pH, and the nature of the amino acids adjacent to glutamine. The products of the reaction were identified as thyrotropin-releasing hormone (TRH) and [Leu(2)]TRH. The reported reactions could affect the naturally balanced concentration of short-chain peptides in foods and therefore induce unpredictable biological effects.

Absorption of biologically active peptide hormones from the small intestine of rat

Absorption of the 4, 10 and 34 amino acid forms of gastrin from the small intestine has been investigated in anaesthetized rats. The method of assessment of successful absorption of the hormone into the systemic circulation was when the amount of acid secreted by the stomach over consecutive 15-min periods was increased. When the natural hormones were infused into the ileum in a relatively high dose, there was no increase in gastric acid secretion, indicating that they had not been absorbed. Each of the forms of gastrin was conjugated at the free amino terminus to the carboxyl group of cholic acid. Subsequent infusion of the conjugated form of gastrin into the ileum, this time in relatively low doses, resulted in substantial and prolonged increases in gastric acid secretion, indicating that these hormones had been successfully absorbed. In addition, conjugation of the 10 and 34 amino acid forms of gastrin with cholic acid was shown to increase markedly the potency in evoking an increase in gastric acid secretion in response to intravenous injection of the hormone. Absorption of the gastrin conjugates was specific to the ileum thus indicating that they had been absorbed through the bile salt transporters.

Intestinal transport of the lactokinin Ala-Leu-Pro-Met-His-Ile-Arg through a Caco-2 Bbe monolayer

ACE inhibitory peptides are biologically active peptides that play a role in blood pressure regulation. When derived from food proteins during food processing or gastrointestinal digestion, these peptides could function as efficient agents in treating and preventing hypertension. However, in order to exert an antihypertensive effect by inhibition of the ACE enzyme, they have to reach the bloodstream intact. The aim of this research was to assess if the known ACE inhibitory peptide Ala-Leu-Pro-Met-His-Ile-Arg, derived from a tryptic digest of beta-lactoglobulin, could be absorbed through a Caco-2 Bbe cell monolayer in an Ussing chamber and reach the serosal side undegraded. Samples of the mucosal compartment showed high ACE inhibitory activity. No or only little ACE inhibitory activity was detected in the serosal compartment. However, when the serosal sample was concentrated three-fold, a substantial ACE inhibitory activity was registered. Concomitantly, HPLC and MS clearly showed the presence of Ala-Leu-Pro-Met-His-Ile-Arg in the mucosal compartment, whereas in the serosal compartment only MS was able to detect the heptapeptide. In conclusion. under the observed experimental conditions, the ACE inhibitory peptide Ala-Leu-Pro-Met-His-Ile-Arg was transported intact through the Caco-2 Bbe monolayer, but in concentrations too low to exert an ACE inhibitory activity.

Val-Tyr as a natural antihypertensive dipeptide can be absorbed into the human circulatory blood system

1. Intact absorption of the bioactive dipeptide Val-Tyr (VY), with in vivo antihypertensive ability in normotensive human subjects, was investigated. 2. As a result of a single oral administration of VY, the VY absorption curve occurred maximally over the second hour postprandially; a greater than 10-fold higher increment of VY following a dose of 12 mg was observed in the plasma at 2 h compared with the baseline concentration of VY at 0 h (1934 +/- 145 vs 159 +/- 11 fmol/mL plasma, respectively). 3. Plasma VY levels increased with dose administered (3, 6 and 12 mg), suggesting that exogenous VY could be absorbed intact into the human blood depending on the dose. The elimination half time (t1/2) of VY was estimated to be 3.1 h. The area under the curve for the 12 mg VY dose was 9185 +/- 688 fmol small middle doth/mL plasma.

Gastrointestinal enzyme production of bioactive peptides from royal jelly protein and their antihypertensive ability in SHR

In order to clarify the potential physiological function of royal jelly (RJ), we report here the gastrointestinal enzyme production of antihypertensive peptides from RJ. Intact RJ and its protein fraction did not retard the action of angiotensin I-converting enzyme (ACE) activity at all. However, development of ACE inhibition power of RJ was newly observed by pepsin hydrolysis (IC(50)=0.358 mg protein/mL), and the subsequent trypsin and chymotrypsin hydrolyses (IC(50)=0.099 mg protein/mL). Single oral administration of this gastrointestinal RJ hydrolysate (1 g/kg dose) in 10-week spontaneously hypertensive rat resulted in a significant reduction of systolic blood pressure of 22.7 plus minus 3.6 mmHg at 2 hr (P<0.05 vs. 0 hr by one-way ANOVA, n=7). Then, the RJ hydrolysate was fractionated with gel permeation chromatography to obtain the di- and tri-peptides (DTP) fraction. As a result of isolation from the DTP fraction by reversed phase-high performance liquid chromatography, eleven ACE inhibitory peptides were isolated from the DTP-RJ hydrolysate. Some of the ACE inhibitors were derived from the RJ-glycoprotein; eight peptides with the IC(50) value of <10 &mgr;M were identified from natural resources for the first time. Consequently, RJ protein was thought to be a good resource of ACE inhibitory peptides produced by the gastrointestinal enzyme hydrolyses.

Non-invasive treatments of luteinizing hormone-releasing hormone for inducing spermiation in American (Bufo americanus) and Gulf Coast (Bufo valliceps) toads

As many as 20% of all assessed amphibian species are threatened with extinction, and captive breeding programs are becoming important components of conservation strategies for this taxon. For some species, exogenous hormone administration has been integrated into breeding protocols to improve propagation. However, most treatments are administered by an intraperitoneal injection that can be associated with some risks. The general goal of this study was to identify a non-invasive method of applying luteinizing hormone-releasing hormone (LHRH), which reliably induces sperm release in toads. Specific objectives were to 1) test the spermiation response after topical application of different LHRH doses to the abdominal seat region, 2) evaluate the effects of adding the absorption enhancers dimethyl sulfoxide (DMSO), acetone, and glyceryl monocaprylate (GMC) to the LHRH, 3) assess the spermiation response after oral delivery of LHRH in a mealworm vehicle, and 4) compare sperm characteristics and spermiation responses to treatments in two different toad species. Male American (n = 9) and Gulf Coast (n = 7) toads were rotated systematically through a series of treatments. Urine was collected and evaluated for the presence of sperm at 0, 3, 7, 12, and 24 hours post-treatment. There were no statistical differences in spermiation induction or sperm characteristics between American and Gulf Coast toads after the treatments. Oral administration of 100 &mgr;g LHRH was occasionally successful in inducing spermiation, but results appeared largely unreliable. Ventral dermal application of 100 or 10 &mgr;g LHRH in 40% DMSO were more effective (P < 0.05) at inducing spermiation compared with the other treatments tested, eliciting sperm release in more than 70% of toads tested. In breeding programs for rare and/or fragile anurans, these non-invasive methods of exogenous hormone administration might be preferred over intraperitoneal injections. Zoo Biol 20:63-74, 2001. Copyright 2001 Wiley-Liss, Inc.

Turnover of 125I-labelled tissue kallikrein following intraduodenal or intravenous administration

Tissue kallikrein is released in the body both physiologically and in many inflammatory disorders. Little is, however, known about the turnover of released tissue kallikrein in humans. Approximately 1 mg of tissue kallikrein (mol wt 43,000 Da) was purified from 85 L human urine by: (1) ultracentrifugation, (2) filtration through an aprotinin-coupled Sepharose 4B column, followed by (3) gel filtration over a Sephadex G-75 column. The elimination, after intraduodenal or intravenous administration of purified tissue kallikrein radiolabelled with 125I, was followed by collecting serial samples of plasma, urine and faeces from three volunteers. Within 72 h, about 96% of the intraduodenally administered radioactivity had been excreted in urine, and approximately 5.4% in faeces, mainly as 125I. No intact 125I-tissue kallikrein was found in plasma, urine or faeces after the intraduodenal instillation of the protein. The plasma half-life of 125I-tissue kallikrein up to 3 h after intravenous injection was 9 min and, thereafter, 20 h. The 125I-tissue kallikrein was quickly bound to a plasma protein with a mol wt of about 67 kDa, but some of the radioiodinated tissue kallikrein was still unbound 15 min after injection, judged by gel filtration on Sephadex G-200 columns. Most of the radioactivity was excreted in the urine as 125I, but about 4-6% was recovered as free 125I-tissue kallikrein.

CONCLUSION

The use of tissue kallikrein as an oral drug appears, therefore, to be useless. Tissue kallikrein released into plasma seems to be quickly bound to a protein with a mol wt of 67 kDa, probably kallistatin or Protein C inhibitor, but some tissue kallikrein seems to be unbound and may have some physiological or pathophysiological action. The unbound tissue kallikrein is, at least partly, cleared from the circulation by the kidneys, and tissue kallikrein in the urine may partly be derived from plasma.

Vasodilatory actions of the dietary peptide carnosine

The objective of this study was to test the hypothesis that the dietary dipeptide carnosine (beta-alanine-L-histidine) causes direct decreases in arterial tone. Isolated descending thoracic aortic rings from male Sprague-Dawley rats were used for all studies. Preconstriction of vessels was accomplished with phenylephrine. Carnosine (0.625-20 mM) produced dose-dependent vascular relaxation (P < 0.05) that was independent of endothelium. The constituent amino acid L-histidine did not produce any significant relaxation over the same dose range, whereas beta-alanine actually produced dose-dependent vasoconstriction (P < 0.05). The soluble guanylate cyclase inhibitor methylene blue (10(-5) M) significantly decreased the relaxation produced by carnosine (P < 0.05). Measurement of cyclic GMP in the presence and absence of methylene blue after carnosine and phenylephrine exposure was also done. Methylene blue 10(-5) M resulted in a decrease in cyclic GMP levels from 65.3 +/- 15.6 fmol/mg protein to 8.6 +/- 0.9 fmol/mg of protein (P = 0.001). We conclude that carnosine produces relaxation of isolated rat aorta independent of endothelium. The effect of carnosine is at least in part mediated via cyclic GMP production and is not reproduced by its constituent amino acids, L-histidine and beta-alanine.