Transport of angiotensin peptides across the Caco-2 monolayer

The effect of iron absorption in ferrous gluconate form from enriched rice flour using an in vitro digestion model and a Caco-2 cell model

Iron deficiency can cause serious diseases in infants and young children such as indigestion, anemia, and nervous system dysplasia. Consumption of high-iron rice flour can prevent iron deficiency. The objective of this study was to evaluate the potential application of ferrous gluconate as an iron source in high-iron rice flour used as a type of accessory food for infants and young children. In this study, the differences in iron absorption ability between ferrous gluconate and ferrous fumarate in rice flour with the same ingredients in both high and low phytic acid systems were evaluated. The results showed that there was no significant difference in the bioaccessibility/bioavailability between ferrous gluconate and ferrous fumarate at both low and high phytic acid contents. In low phytic acid and high phytic acid systems, the iron absorption rate of ferrous gluconate is 11.53% and 13.45% higher than that of ferrous fumarate, respectively (p < 0.05). In summary, the iron absorption rate of ferrous gluconate was higher than that of ferrous fumarate in the rice flour system. Additionally, the low phytic acid environment is more conducive to iron uptake and utilization. Therefore, ferrous gluconate can be used as an alternative source of iron in accessory foods for infants and young children.

A critical review of a typical research system for food-derived metal-chelating peptides: Production, characterization, identification, digestion, and absorption

In the past decade, food-derived metal-chelating peptides (MCPs) have attracted significant attention from researchers working towards the prevention of metal (viz., iron, zinc, and calcium) deficiency phenomenon by primarily inhibiting the precipitation of metals caused by the gastrointestinal environment and exogenous substances (including phytic and oxalic acids). However, for the improvement of limits of current knowledge foundations and future investigation directions of MCP or their derivatives, several review categories should be improved and emphasized. The species' uniqueness and differences in MCP productions highly contribute to the different values of chelating ability with particular metal ions, whereas comprehensive reviews of chelation characterization determined by various kinds of technique support different horizons for explaining the chelation and offer options for the selection of characterization methods. The reviews of chelation mechanism clearly demonstrate the involvement of potential groups and atoms in chelating metal ions. The discussions of digestive stability and absorption in various kinds of absorption model in vitro and in vivo as well as the theory of involved cellular absorption channels and pathways are systematically reviewed and highlighted compared with previous reports as well. Meanwhile, the chelation mechanism on the molecular docking level, the binding mechanism in amino acid identification level, the utilizations of everted rat gut sac model for absorption, and the involvement of cellular absorption channels and pathway are strongly recommended as novelty in this review. This review makes a novel contribution to the literature by the comprehensive prospects for the research and development of food-derived mineral supplements.

Potential of Food Protein-Derived Bioactive Peptides against Sarcopenia: A Comprehensive Review

Sarcopenia is an age-related progressive muscle disorder characterized by accelerated loss of muscle mass, strength, and function, which are important causes of physiological dysfunctions in the elderly. At present, the main alleviating method includes protein supplements to stimulate synthesis of muscle proteins. Food protein-derived peptides containing abundant branched-chain amino acids have a remarkable effect on the improvement of sarcopenia. Understanding the underlying molecular mechanism and clarifying the structure-activity relationship is essential for the mitigation of sarcopenia. This present review recaps the epidemiology, pathogenesis, diagnosis, and treatment of sarcopenia, which facilitates a comprehensive understanding of sarcopenia. Moreover, the latest research progress on food-derived antisarcopenic peptides is reviewed, including their antisarcopenic activity, molecular mechanism as well as structural characteristics. Food-derived bioactive peptides can indeed alleviate/mitigate sarcopenia. These antisarcopenic peptides play a pivotal role mainly by activating the PI3K/Akt/mTOR and MAPK pathways and inhibiting the ubiquitin-proteasome system and AMPK pathway, thus promoting the synthesis of muscle proteins and inhibiting their degradation. Antisarcopenic peptides alleviate sarcopenia via specific peptides, which may be absorbed into the circulation and exhibit their bioactivity in intact forms. The present review provides a theoretical reference for mitigation and prevention of sarcopenia by food protein-derived bioactive peptides.

Digestion, absorption, and transport properties of soy-fermented douchi hypoglycemic peptides VY and SFLLR under simulated gastrointestinal digestion and Caco-2 cell monolayers

Two novel hypoglycemic peptides VY and SFLLR were identified from douchi as the major peptides responsible for the glucose uptake activity. The present work aimed to elucidate their digestion, absorption and transport properties using simulated digestion and Caco-2 cell monolayers transport models. Besides, the effects of digestion and absorption on the structure and activity were also studied. The results showed that VY was resistant to gastrointestinal tract digestion and could cross Caco-2 cell monolayers intactly via both TJs-mediated passive paracellular pathway and PepT1-mediated active route. In comparison, SFLLR was partially degraded into small fragments of SFLL, SFL, and SF by the digestive system, leading to increased glucose uptake activity. Notably, SFLLR, SFLL, and SFL were partly hydrolyzed by aminopeptidase N or dipeptidyl peptidase IV during transport, but they were transported intact. SFL was transported via both paracellular diffusion and PepT1-mediated routes, while SFLLR and SFLL were via paracellular route only.

Enzymatic hydrolysis and microbial fermentation: The most favorable biotechnological methods for the release of bioactive peptides

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Peptide release methods influence its bioactivity by generating different sequences.

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The absorption, toxicity and taste of peptides is influenced by the production method.

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The most used methods are enzymatic hydrolysis and microbial fermentation.

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The most used methods are biotechnological and differ in their process.

Bioactive peptides are biomolecules derived from proteins. They contain anywhere from 2 to 20 amino acids and have different bioactivities. For example, they have antihypertensive activity, antioxidant activity, antimicrobial activity, etc. However, bioactive peptides are encrypted and inactive in the parental protein, so it is necessary to release them to show their bioactivity. For this, there are different methods, where biotechnological methods are highly favorable, highlighting enzymatic hydrolysis and microbial fermentation.

The choice of the method to be used depends on different factors, which is why it is essential to know about the process, its principle, and its advantages and disadvantages. The process of peptide release is critical to generate various peptide sequences, which will produce different biological effects in the hydrolysate. This review focuses on providing extensive information on the enzymatic method and microbial fermentation to facilitate selecting the method that provides the most benefits.

Pharmacokinetics and Transport of an Osteogenic Dodecapeptide

A dodecapeptide with the amino acid sequence of IEELEEELEAER (PIE), identified from Mytilus edulis proteolysis hydrolysates, has shown good bone-forming activity in previous studies. The pharmacokinetics and transport of the PIE peptide in vivo or in vitro were investigated in this study. The results showed that the PIE peptide can be transported into monolayer Caco-2 cells, and the PIE peptide was identified in the serum after the mice reached the highest value of 173.60 ± 60.30 ng/mL, in which it was quantified by an optimized mass spectrometry method. In addition, the PIE peptide has a promoting effect on the bone morphogenetic protein pathway at the gene and protein levels. According to the distribution of PIE-FITC in ovariectomized mice after orally administrated PIE-FITC, it was confirmed that it can enter the gastrointestinal tract and serum, and reach the bones. Taken together, the PIE peptide can be absorbed well both in vitro and in vivo, and it could promote pre-osteoblast differentiation factors.

Hydrolysis and Transport of Egg White-Derived Peptides in Caco-2 Cell Monolayers and Everted Rat Sacs

The objective of this paper was to investigate the hydrolysis and transepithelial transport of egg white peptides in Caco-2 cell monolayers and everted rat sacs. Results showed that egg white peptides had higher permeability but lower degradation in Caco-2 cell monolayers than found for everted rat sacs. Peptides LGAKDSTRT, DGSRQPVDN, VNDLQGKTS, and GKKDPVLKD were identified from not only the basolateral (BL) side of Caco-2 cell monolayers but also the serous side of everted rat sacs, suggesting that these four peptides could be transported intact in both model systems. In addition, there were 24 peptides identified from the apical (AP) side of Caco-2 cell monolayers and the mucosal side of everted rat sacs, indicating potential resistance to hydrolysis by brush border membrane peptidases. Among these, peptides IRDLLER, YAEERYP, and IRNVLQPS were demonstrated as having dipeptidyl peptidase IV (DPP-IV) inhibitory activities with IC₅₀ values of 186.23 ± 15.25, 340.62 ± 4.73, and 598.28 ± 15.12 μM ( P < 0.05), respectively. Furthermore, molecular docking revealed that the DPP-IV inhibitory peptides were predicted to form hydrogen-bonds, π-π bonds, and charge interactions with the activity sites, especially the amino acid residues located in the S2 pocket of DPP-IV, potentially contributing to their DPP-IV inhibitory activities.

Molecular interactions, bioavailability, and cellular mechanisms of angiotensin-converting enzyme inhibitory peptides

Food-derived angiotensin-converting enzyme inhibitory (ACEi) peptides have gained substantial interest as potential alternatives to synthetic drugs in the management of hypertension. Peptide size and sequence are two critical factors that determine their potency, bioavailability, and cellular mechanisms. Molecular interaction studies between ACE and ACEi peptides support that potent ACEi peptides are generally composed of hydrophobic, positively charged, and aromatic or cyclic amino acid residues at the third, second, and first position from the C-terminus, respectively. Small peptides containing N-terminal Tyr and/or C-terminal Pro could improve their stability against enterocyte peptidases, thus their bioavailability. Different ACEi peptides can reduce aberrant cellular proliferation, excessive inflammation, and oxidative stress but through different mechanisms. Further understanding the structure-activity-bioavailability relationships will help design novel potent ACEi peptides with improved bioavailability and in vivo efficacy. PRACTICAL APPLICATIONS: ACEi peptides have the potential for uses as functional food ingredients against hypertension.

Transepithelial transport of milk-derived angiotensin I-converting enzyme inhibitory peptide with the RLSFNP sequence

BACKGROUND

To exert an antihypertensive effect after oral administration, angiotensin I-converting enzyme (ACE)-inhibitory peptides must remain active after intestinal transport. The purpose of this article is to elucidate the transport permeability and route of ACE-inhibitory peptide Arg-Leu-Ser-Phe-Asn-Pro (RLSFNP) across the intestinal epithelium using Caco-2 cell monolayers.

RESULTS

Intact RLSFNP and RLSFNP breakdown fragments F, FNP, SFNP and RLSF were found in RLSFNP transport solution across Caco-2 cell monolayers using ultra-performance liquid chromatography-tandem mass spectrometry. RLSFNP fragments FNP, SFNP and RLSF also contributed to ACE inhibitory effects. Protease inhibitors (bacitracin and leupeptin) and absorption enhancers (sodium glycocholate hydrate, sodium deoxycholate and Na₂ EDTA) improved the transport flux of RLSFNP. A transport inhibitor experiment showed that intact RLSFNP may be transported via the paracellular route.

CONCLUSION

Intact RLSFNP can be transported across the Caco-2 cell monolayers via the paracellular route. Extensive hydrolysis was the chief reason for the low permeability of RLSFNP. © 2017 Society of Chemical Industry.

Hydrolysis and transepithelial transport of two corn gluten derived bioactive peptides in human Caco-2 cell monolayers

The objective of this paper was to investigate the transepithelial transport of two novel corn gluten-derived antioxidant peptides, YFCLT and GLLLPH, using Caco-2 cell monolayers. Results showed that both of YFCLT and GLLLPH could transport in intact form across Caco-2 cell monolayers with apparent permeability coefficient (P_app) values of (1.10±0.16)×10^-7cm/s and (1.98±0.23)×10^-7cm/s, respectively. However, it was found that the two peptides were susceptible and easily hydrolyzed by brush border membrane peptidases. In the presence of diprotin A, an inhibitor of dipeptidyl peptidase IV (DPPIV), the hydrolysis of YFCLT and GLLLPH decreased and their permeabilities increased significantly compared to control group (P<0.05). The results of transport routes revealed that Gly-Sar, a peptide transporter 1 (PepT1) substrate, had little effects on the transepithelial permeability (P>0.05), suggesting that the transport of YFCLT and GLLLPH across Caco-2 cell monolayers was not mediated by PepT1. However, it was found that cytochalasin d, a tight junctions (TJs) disruptor, increased the permeability significantly (P<0.05). While wortmannin, a transcytosis inhibitor, and sodium azide, an ATP synthesis inhibitor, both decreased the permeability significantly (P<0.05). It indicated that the TJs-mediated paracellular pathway and energy-dependent transcytosis were involved in the transport of YFCLT and GLLLPH across Caco-2 cell monolayers.

Bioavailability of Orally Administered Des-Aspartate-Angiotensin I in Human Subjects

In an earlier single-dose escalation study to evaluate the safety and pharmacokinetics of orally administered des-aspartate-angiotensin I (DAA-I) in healthy subjects, the plasma level of DAA-I could not be determined because DAA-I is rapidly degraded in the circulation. The present study investigated the oral bioavailability of DAA-I by measuring the prostaglandin E₂ metabolite (PGEM) in the plasma samples of the same trial. PGEM is a stable derivative of PGE₂, which has been shown to be a biomarker of DAA-I. The data show that plasma from two of the three subjects who were orally administered the efficacious preclinical dose of 0.70 mg/kg DAA-I exhibited a significant PGEM peak at 5–6 h postdose. Plasma of subjects who were administered 0.08 and 1.5 mg/kg DAA-I, the subefficacious and two-times efficacious dose, respectively, did not exhibit a similar PGEM peak. This observation is concordant with the known in vivo actions of DAA-I, especially its hypoglycemic action where maximum efficacy occurred at a dose of 0.7 mg/kg, and decreased to nil at the two-times efficacious dose. The onset of the PGEM peak at 5–6 h postdose was closed to the 4-h onset of absorption of [C¹⁴]DAA-I seen in preclinical rat studies, albeit the absorption kinetics between rodents and humans are not identical. The occurrence of polymorphism of enzymes involved in the formation and degradation of PGE₂ is common, and this has been attributed to contributing to the variation in response, onset and peak PGEM observed among the three subjects who were administered the efficacious dose.

Importance of Terminal Amino Acid Residues to the Transport of Oligopeptides across the Caco-2 Cell Monolayer

The objective of this paper was to investigate the effects of terminal amino acids on the transport of oligopeptides across the Caco-2 cell monolayer. Ala-based tetra- and pentapeptides were designed, and the N- or C-terminal amino acid residues were replaced by different amino acids. The results showed that the oligopeptides had a wide range of transport permeability across the Caco-2 cell monolayer and could be divided into four categories: non-/poor permeability, low permeability, intermediate permeability, and good permeability. Tetrapeptides with N-terminal Leu, Pro, Ile, Cys, Met, and Val or C-terminal Val showed the highest permeability, with apparent permeability coefficient (P_app) values over 10 × 10^-6 cm/s (p < 0.05), suggesting that nonpolar hydrophobic aliphatic amino acids or polar sulfur-containing amino acids were the best for the transport of tetrapeptides. Pentapeptides with N- or C-terminal Tyr also showed high permeability levels, with P_app values of about 10 × 10^-6 cm/s. The amino acids Glu, Asn, and Thr at the N terminus or Lys, Asp, and Arg at the C terminus were also beneficial for the transport of tetra- and pentapeptides, with P_app values ranging from 1 × 10^-6 to 10 × 10^-6 cm/s. In addition, peptides with amino acids replaced at the N terminus generally showed higher permeability than those with amino acids replaced at the C terminus (p < 0.05), suggesting that N-terminal amino acids were more important for the transport of oligopeptides across the Caco-2 cell monolayer.

Transport Study of Egg-Derived Antihypertensive Peptides (LKP and IQW) Using Caco-2 and HT29 Coculture Monolayers

The objective of this study was to investigate the mechanisms of the transport of antihypertensive tripeptides LKP (Leu-Lys-Pro) and IQW (Ile-Gln-Trp) derived from egg white using a coculture system of Caco-2 and HT29 cell monolayers. The results revealed that LKP and IQW have no cytotoxicity to the cell viability after 2 h incubation, could be transported intact across coculture monolayers (apparent permeability coefficient: (18.11 ± 1.57) × 10^-8 and (13.21 ± 1.12) × 10^-8 cm/s, respectively), and were resistant to peptidase secreted by enterocytes. In addition, the transports were significantly inhibited by dipeptide Gly-Pro (P < 0.05), a competitive substance of peptide transporter 1 (PepT1). The transports from apical to basolateral side were significantly higher than that of the reverse direction (P < 0.05). These results suggest that PepT1 is involved in LKP and IQW transports. The transports were also significantly decreased by theaflavin-3'-O-gallate (P < 0.05), an enhancer of tight junction (TJ) and increased by cytochalasin D (P < 0.05), a disruptor of TJ but not influenced by wortamanin, a transcytosis inhibitor, suggesting that passive paracellular route via TJs is also involved in LKP and IQW transports but not transcytosis. In addition, siRNA was also used to knockdown the expression of PepT1 and significantly inhibited the transport (P < 0.05), confirming that PepT1 is involved in transport process. Therefore, both passive paracellular route via TJ and active route via PepT1 coexist in the transport of antihypertensive LKP and IQW across Caco-2/HT29 coculture monolayers.

A Single Dose-Escalation Study to Evaluate the Safety and Pharmacokinetics of Orally Administered Des-Aspartate Angiotensin I in Healthy Subjects

Des-aspartate-angiotensin I (DAA-I) is an endogenous angiotensin peptide and a prototype angiotensin receptor agonist (ARA). It acts on the angiotensin AT₁ receptor and antagonises the deleterious actions of angiotensin II. DAA-I attenuates animal models of human disease in which angiotensin II has been implicated, such as cardiac hypertrophy, neointima formation, arteriosclerosis, renal failure, post-infarction injuries, diabetes, viral infection, chemical-induced inflammation, heat stroke, cancer, and gamma radiation lethality. DAA-I crosses Caco-2 cells and is effective at sub-nanomolar concentrations. These two properties are responsible for its oral efficacy. A single dose-escalation study was conducted to evaluate the safety, tolerability and pharmacokinetics of orally administered DAA-I in 18 healthy subjects. DAA-I was safe and well tolerated by the subjects, who were administered either 0.08, 0.70 or 1.50 mg/kg of the compound. The heart rate and systolic and diastolic blood pressures determined at each post-dose measurement remained within the clinically acceptable range. Across all cohorts, DAA-I had no substantial effect on blood pressures compared with placebo. Electrocardiographs (ECGs) were normal, and none of the subjects complained of chest discomfort. All clinical laboratory tests obtained before and after DAA-I and placebo treatment were normal. Pharmacokinetic analysis over a 12-h period following DAA-I administration did not show any increase of its level beyond basal concentration. This is in line with studies showing that intravenously administered DAA-I is rapidly metabolized and has a short half-life. We postulate that, during its short systemic sojourn, DAA-I exerts its actions via biased agonism on the angiotensin AT₁ receptor.

The ClinicalTrial.gov assignment number for this study is NCT02666196.

Transport of Antihypertensive Peptide RVPSL, Ovotransferrin 328-332, in Human Intestinal Caco-2 Cell Monolayers

The objective of this study was to investigate the transepithelial transport of RVPSL (Arg-Val-Pro-Ser-Leu), an egg-white-derived peptide with angiotensin I-converting enzyme (ACE) inhibitory and antihypertensive activity, in human intestinal Caco-2 cell monolayers. Results revealed that RVPSL could be passively transported across Caco-2 cell monolayers. However, during the process of transport, 36.31% ± 1.22% of the initial RVPSL added to the apical side was degraded, but this degradation decreased to 23.49% ± 0.68% when the Caco-2 cell monolayers were preincubated with diprotin A (P < 0.001), suggesting that RVPSL had a low resistance to various brush border membrane peptidases. When transport from the apical side to the basolateral side was investigated, the apparent permeability coefficient (Papp) was (6.97 ± 1.11) × 10(-6) cm/s. The transport route of RVPSL appears to be the paracellular pathway via tight junctions, as only cytochalasin D, a disruptor of tight junctions (TJs), significantly increased the transport rate (P < 0.001). In addition, the relationship between the structure of RVPSL and transport across Caco-2 cell monolayers was studied by mutation of RVPSL. It was found that N-terminal Pro residues were more beneficial for transport of pentapeptides across Caco-2 cell monolayers than Arg and Val. Furthermore, RVPSL could be more easily transported as smaller peptides, especially in the form of dipeptides and tripeptides.

Des-aspartate-angiotensin I, a novel angiotensin AT(1) receptor drug

The review describes DAA-I (des-aspartate-angiotensin-I) as a prototype of a novel class of drugs that acts as agonists on the angiotensin AT1 receptor or ARAs (angiotensin receptor agonists). DAA-I is a component of the renin angiotensin system. Earlier studies showed that it was rapidly metabolized to angiotensin III. However, when administered at doses below the Km of enzymes, DAA-I produces specific actions that antagonize the deleterious actions of angiotensin II. DAA-I exerts protective actions in animal models of eight human pathologies in which angiotensin II is implicated. The pathologies include cardiac hypertrophy, neointima growth and cardiovascular hypertrophy, myocardial-ischemia reperfusion injury, hyperglycemia and insulin resistance, chemical induced inflammation, and exercise-induced skeletal muscle inflammation. Binding of DAA-I to the angiotensin AT1 receptors releases prostaglandins, which could either function as autocrines/paracrines or second messengers and attenuate the deleterious actions of angiotensin II. It is possible that in in vivo DAA-I functions as a physiological antagonist to angiotensin II, and exogenous DAA-I is a novel class of angiotensin receptor drug that could rival the angiotensin receptor blockers.

Transport of Egg White ACE-Inhibitory Peptide, Gln-Ile-Gly-Leu-Phe, in Human Intestinal Caco-2 Cell Monolayers with Cytoprotective Effect

The purpose of this study was to investigate the transepithelial transport and cytoprotective effect of Gln-Ile-Gly-Leu-Phe (QIGLF), an ACE-inhibitory peptide derived from egg white ovalbumin, in human intestinal Caco-2 cell monolayers. The results showed that QIGLF could be absorbed intact through Caco-2 cell monolayers with a P_app value of (9.11 ± 0.19) × 10^-7 cm/s (transport kinetic parameters: K_m, 32.37 ± 12.59 mM; V_max, 1.23 ± 0.49 μM/min cm²). The transport was not significantly decreased by sodium azide and Gly-Pro, an ATP synthesis inhibitor and a peptide transporter 1 (PepT1) substrate, respectively, suggesting that transport of QIGLF was not energy-dependent and carrier-mediated. In addition, wortmannin, a transcytosis inhibitor, had little effect on the transport, suggesting that endocytosis was not involved in the transport of QIGLF. However, the transport of QIGLF was increased significantly in the presence of cytochalasin D, a tight junction disruptor, suggesting that paracellular transport via tight junctions was the major transport mechanism for intact QIGLF across Caco-2 cell monolayers. Moreover, QIGLF was added to Caco-2 cells followed by addition of H₂O₂, and exhibited significant cytoprotective effect in Caco-2 cells against oxidative stress induced by H₂O₂.

Transmembrane transport of the Gαq protein carboxyl terminus imitation polypeptide GCIP-27

The Gαq protein carboxyl terminus imitation polypeptide (GCIP)-27 has been shown to affect cardiac hypertrophy and vascular remodeling in various models both in vitro and in vivo. Transport across the plasma membrane is a critical step in regulating the action of this peptide drug. This study was designed to explore the mechanisms underlying the transmembrane transport of GCIP-27. The peptide drug was labeled with fluorescein isothiocyanate (FITC), and measured in a time- and concentration-dependent manner using laser confocal microscopy. Various transport inhibitors, including energy and endocytosis inhibitors, were used to identify the factors that regulate its transmembrane transport. GCIP-27 transport was examined in cardiomyocytes, cardiac fibroblasts, vascular endothelial cells, vascular smooth muscle cells (VSMCs) and hepatocytes. Atomic force microscopy and scanning electron microscopy were used to determine the ultrastructure of the cardiomyocyte membranes. The results showed that GCIP-27 was transported through the plasmalemma in a time- and concentration-dependent manner. The rate of uptake and the level of GCIP-27 in the cells decreased significantly after treatment with energy inhibitors, methyl-ß-cyclodextrin chlorpromazine or heparin. GCIP-27 levels in VSMCs and cardiomyocytes were significantly greater than the levels observed in hepatocytes, cardiac fibroblasts and vascular endothelial cells. Treatment with GCIP-27 led to a marked increase in the surface roughness of the cellular membrane. In conclusion, the transmembrane transport of GCIP-27 is mediated by endocytosis, which requires energy, and GCIP-27 preferentially enters myocardial cells and VSMCs.

Central administration of angiotensin IV rapidly enhances novel object recognition among mice

Angiotensin IV (Val(1)-Tyr(2)-Ile(3)-His(4)-Pro(5)-Phe(6)) has demonstrated potential cognitive-enhancing effects. The present investigation assessed and characterized: (1) dose-dependency of angiotensin IV's cognitive enhancement in a C57BL/6J mouse model of novel object recognition, (2) the time-course for these effects, (3) the identity of residues in the hexapeptide important to these effects and (4) the necessity of actions at angiotensin IV receptors for procognitive activity. Assessment of C57BL/6J mice in a novel object recognition task demonstrated that prior administration of angiotensin IV (0.1, 1.0, or 10.0, but not 0.01 nmol, i.c.v.) significantly enhanced novel object recognition in a dose-dependent manner. These effects were time dependent, with improved novel object recognition observed when angiotensin IV (0.1 nmol, i.c.v.) was administered 10 or 20, but not 30 min prior to the onset of the novel object recognition testing. An alanine scan of the angiotensin IV peptide revealed that replacement of the Val(1), Ile(3), His(4), or Phe(6) residues with Ala attenuated peptide-induced improvements in novel object recognition, whereas Tyr(2) or Pro(5) replacement did not significantly affect performance. Administration of the angiotensin IV receptor antagonist, divalinal-Ang IV (20 nmol, i.c.v.), reduced (but did not abolish) novel object recognition; however, this antagonist completely blocked the procognitive effects of angiotensin IV (0.1 nmol, i.c.v.) in this task. Rotorod testing demonstrated no locomotor effects with any angiotensin IV or divalinal-Ang IV dose tested. These data demonstrate that angiotensin IV produces a rapid enhancement of associative learning and memory performance in a mouse model that was dependent on the angiotensin IV receptor.

Identification and characterization of a functional mitochondrial angiotensin system

The renin-angiotensin (Ang) system regulates multiple physiological functions through Ang II type 1 and type 2 receptors. Prior studies suggest an intracellular pool of Ang II that may be released in an autocrine manner upon stretch to activate surface membrane Ang receptors. Alternatively, an intracellular renin-Ang system has been proposed, with a primary focus on nuclear Ang receptors. A mitochondrial Ang system has not been previously described. Here we report that functional Ang II type 2 receptors are present on mitochondrial inner membranes and are colocalized with endogenous Ang. We demonstrate that activation of the mitochondrial Ang system is coupled to mitochondrial nitric oxide production and can modulate respiration. In addition, we present evidence of age-related changes in mitochondrial Ang receptor expression, i.e., increased mitochondrial Ang II type 1 receptor and decreased type 2 receptor density that is reversed by chronic treatment with the Ang II type 1 receptor blocker losartan. The presence of a functional Ang system in human mitochondria provides a foundation for understanding the interaction between mitochondria and chronic disease states and reveals potential therapeutic targets for optimizing mitochondrial function and decreasing chronic disease burden with aging.

Transport of Val-Leu-Pro-Val-Pro in human intestinal epithelial (Caco-2) cell monolayers

Angiotensin converting enzyme (ACE) inhibitory peptides are biologically active peptides that play a very important role in blood pressure regulation. In previous experiments, we obtained an ACE inhibitory peptide Val-Leu-Pro-Val-Pro (VLPVP) by DNA recombinant technology. The purpose of this study was to examine the bidirectional transport of VLPVP by using the human intestinal Caco-2 monolayers. The permeability coefficient ( P app) values of VLPVP over 4-8 mmol/L ranged from 7.44 x 10(-8) to 1.35 x 10(-6) cm/s for apical (AP) to basolateral (BL) transport, while the P app values for BL to AP flux were significantly lower than those for the AP to BL flux, with efflux ratio values of 0.74-0.13 over 4-8 mM. Preincubation of the paracellular transport enhancer (sodium deoxycholate), the inhibitor of multidrug resistant protein (MK-571), or sodium azide stimulated efflux of VLPVP significantly ( p < 0.01); these results indicate that the transport of VLPVP across Caco-2 monolayers was involved in paracellular diffusion and MRP2 transport.

Des-aspartate-angiotensin I exerts hypoglycemic action via glucose transporter-4 translocation in type 2 diabetic KKAy mice and GK rats

The present study investigated the hypoglycemic action of des-aspartate-angiotensin I (DAA-I), a metabolite of angiotensin I, in two animal models of type 2 diabetes. The rationale was based on our earlier studies demonstrating that DAA-I acts on the angiotensin AT(1) receptor and exerts responses opposing those of angiotensin II and on recent reports that curtailment of angiotensin II formation by angiotensin converting enzyme inhibitors and blockade of the AT(1) receptor attenuate hyperglycemia in type 2 diabetics and diabetic animals. Diabetic KKAy mice and GK rats were administered orally (by gavage) one of the following doses of DAA-I: 400, 600, or 800 nmol/kg.d for 4 and 6 wk, respectively. Control diabetic animals were similarly administered water. Blood glucose of each animal was determined fortnightly by oral glucose tolerance test and blood insulin on the last day of treatment. Animals were killed, and the levels of plasma membrane glucose transporter-4 and cytosolic tyrosine-phosphorylated insulin receptor substrate-1 in hind limb skeletal muscles were determined by Western blot in insulin-challenged and nonchallenged animals. Orally administered DAA-I had no effect on blood insulin level but exerted dose-dependent hypoglycemic action in KKAy mice and GK rats after 4 and 6 wk of treatment, respectively. At the maximal effective dose of 600 nmol/kg, insulin induced a significant increase in plasma membrane glucose transporter-4 and cytosolic tyrosine-phosphorylated insulin receptor substrate-1. These findings show that DAA-I is not an insulin secretagogue and exerts hypoglycemic action by attenuating insulin resistance, the first such demonstration indicating that the nonapeptide is involved in glycemic regulation.