One of the greatest obstacles in overcoming the challenges associated with the bioavailability of food peptides, has always been a lack of knowledge or adequate results in studies involving the mechanisms through which bioactive peptides are transported.
With clearer knowledge about the mechanisms involved in the transportation of bioactive peptides, as well as clear insights into the factors that affect their absorption, it becomes relatively easy for scientists to come up with various strategies to enhance the bioavailability of the peptides, and also how to maintain their potency in in vivo. This is because the scientist will have a clearer picture of what they need to overcome in order to make the peptides more bioavailable.
The goal of coming up with such strategies is usually to achieve the following: reduce the harmful effects of food processing on peptide bioactivities, promote positive interactions between peptides and other food matrix components, while at the same time reducing the undesirable interactions, protect bioactive peptides from certain tough gastrointestinal conditions, and the activities of certain enzymes, and improve the transportation of bioactive peptides through the walls of the intestinal epithelium, and the targeted cells.
With the already present evidence, as well as the systems already developed to improve the absorption and the bioavailability of food-derived peptides, below is a brief look at some of the strategies being considered to improve the bioavailability of food peptides:
Application of new food processing techniques
To ensure food preservation and microbial safety, there are certain thermal food processing techniques that are normally used, including evaporation, drying, pasteurization, and sterilization. However, most of these techniques require the use of high temperatures, which in turn, may sometimes provoke certain food components with the results being the damaging of structural components of the peptides, as well as affecting their bioavailability.
Hence, in the past few years, there has been a general shift towards the use of novel non-thermal techniques as a means of mitigating some of the negative effects of high temperatures in processing and also enhancing the bioactivity, bioavailability, and bioaccessibility of food-derived peptides. Some strategies have been found to be very effective in activating microorganisms at near-room temperature, leading to the preservation of the sensory, and the nutritional quality of foods.
Some of these strategies include irradiation, microwave, ultrasound, pulsed electric field, and the application of ultrahigh hydrostatic pressure. However, the data on some of these non-thermal processing techniques is still very limited, and insufficient to be able to draw conclusive results regarding the effects of these techniques on the bioavailability and bioactivity of food peptides. As such, there is still a need for further studies to be conducted.
The modification of peptide structures and peptide properties
Certain actions of digestive enzymes have a way of degrading food-derived peptides, and to protect the peptides from the actions of these peptides, there may be a need to modify the structure of the peptide. This will not only protect the peptides from the actions of the digestive enzymes, but also enhance the intestinal permeability of the peptides, in addition to potentiating the biological activities of the peptides.
Through the changes in the C- and the N-terminals, through processes such as amidation/acetylation, it has been determined that it is possible to protect the peptide from the actions of carboxypeptidases. Another biochemical feature, known to improve the resistance of peptides to the actions of exopeptidases degradation, is cyclization. This feature also enhances the half-life, as well as the stability of the peptides, when they are in the gastrointestinal environment.
Additionally, when modifications are done inside the peptide chain, it may be possible to improve certain biological activities of the peptides. Therefore, processes such as phosphorylation of hydroxyl groups of serine, may hamper the hydrolysis of certain digestive enzymes, improve their rates of absorption, and offer protection to their mineral-binding capacity. In a study conducted by Tanzadehpanah et al., on the effects of two similar peptides, but with different last amino acids, it was observed that the presence of proline enhanced ACE-inhibitory activities of one peptide, while it enhanced the antimicrobial, and antioxidant properties of the other peptide.
Following this, it has also been suggested that changes in the molecular mass, as well as the structure of peptide-based compounds, may impact positively on their permeation across the walls of the small intestines. However, there is still limited data on the influence of these modifications, when it comes to the absorption capacity of food-derived peptides, and further studies are recommended for more definitive conclusions.
The use of protease and peptidase inhibitors
The administration of peptides in conjunction with protease or peptidase inhibitors, may help in stopping or reducing the biodegradation of peptides in the gastrointestinal environment. As such, it is believed that such co-administration may play a role in facilitating intestinal absorption. Over the years, synthetic peptides have been used as a way of protecting peptide-based compounds, however, naturally occurring inhibitors like Kunitz trypsin inhibitors, are currently being considered because they portray low side effects, and they also enjoy good compatibility with most of the food-derived peptides.
Therefore, these naturally occurring inhibitors, have shown that they have the ability to protect soybean peptide lunasin from the actions of certain enzymes found in the gastrointestinal tract, and as such, they can improve the absorption and the bioavailability of food-derived peptides. However, there have been major challenges when it comes to the use of protease inhibitors, and this has been mainly due to their own susceptibility to the degrading actions of the gut enzymes.
As a counter-measure to this, it may be necessary to co-administer high doses of the inhibitors, in a bid to change their metabolic patterns within the gastrointestinal environment. This has consequently led to the inappropriate digestion of nutritive proteins, and with this, comes the possibility of provoking endogenous mechanisms, which may, in turn, stimulate the production of digestive peptidase.
The Use of Absorption Enhancers
Absorption enhancers simply refer to substances that are used to encourage the permeation of bioactive compounds, through the walls of the intestinal epithelium, into systemic circulation so that they may reach their targets, where they will exert their biological activities. Absorption enhancers have a variety of mechanisms through which they work. These include reducing the mucus viscosity of the epithelial walls of the small intestines, interfering with the structural integrity of the epithelial walls, increasing the fluidity of the membranes, and reducing the aperture of the TJs.
Absorption enhancers are also known to be safe, since they are non-toxic, non-irritant, chemically and pharmacologically inert, and also, they are non-allergic. But just like protease inhibitors, absorption enhancers come with the possibility of potential damage to the intestinal membranes, leading to local inflammation if used for the long term. Also, the use of absorption enhancers may lead to the introduction of certain undesirable substances into the bloodstream.
Absorption enhancers, such as chelating agents, cationic & ionic polymers, bile salts, and surfactants, have received a lot of attention for their potential usefulness in enhancing the oral bioavailability of bot peptides and proteins. Although the use of absorption enhancers has been very common in the pharmacological field, where they have been used in enhancing the bioavailability of compounds, such as insulin, their use in the food industry is still at its infancy stage, and is very limited at the moment.
However, there are certain food-grade absorption enhancers, such as chitosan, fatty acids, and citric acids that have shown very promising results, and they are currently being considered in the design and development of bioactive peptide-based functional nutraceuticals and foods.
The use of delivery systems for food bioactive peptides
As it is already known, bioactive peptides are nothing but labile compounds with sensitivity to light, temperature, and oxygen, and they have the capability to interact with other compounds, when they are released into the food matrix. It is also known that bioactive peptides are susceptible to the harsh conditions of the gastrointestinal environment.
Consequently, just like other food bioactives and nutrients, when you incorporate bioactive peptides into carriers, it has been shown that their bioavailability, as well as stability, can be increased. These systems of incorporating bioactive peptides into carriers, use a variety of mechanisms, including mucoadhesion, targeted delivery, the use of the high total surface area, and high affinity to specific intestinal cells.
An effective delivery system must have the ability to protect the bioactive peptide from the tough conditions normally associated with food storage, food processing, and processes, such as gastrointestinal digestion. Additionally, such a system must have the capacity to maintain the stability and activity of the peptide until they have been successfully released at the target site. Also, they should not possess the ability or the activity to modify the organoleptic and physicochemical properties of the food-derived peptides.
Lastly, because “clean label” food products are in such high demand, the development of the systems must adhere to the use of natural and biodegradable ingredients, generally recognized as safe alternatives. Consequently, it has been generally difficult to come up with the right food-based delivery systems that possess all the functional attributes. As such, it must be appreciated that the development of a good delivery system requires in-depth knowledge of the molecular features, as well as the physicochemical properties of the bioactive peptides. Also, significant knowledge of ingredient interactions, digestive conditions, and environmental factors that may negatively impact the structure, as well as the bioactivity of the peptide, is also necessary.
- Ilina P., Partti S., Niklander J., Ruponen M., Lou Y.-R., Yliperttula M. Effect of differentiation on endocytic profiles of endothelial and epithelial cell culture models. Exp. Cell Res. 2015;332:89–101.
- Kim H.J., Huh D., Hamilton G., Ingber D.E. Human gut-on-a-chip inhabited by microbial flora that experiences intestinal peristalsis-like motions and flow. Lab. Chip. 2012;12:2165–2174.
- Kim H.J., Ingber D.E. Gut-on-a-Chip microenvironment induces human intestinal cells to undergo villus differentiation. Integr. Biol. 2013;5:1130–1140
- Karas M. Influence of physiological and chemical factors on the absorption of bioactive peptides. Int. J. Food Sci. Technol. 2019;54:1486–1496.
- Rath E., Zietek T. Intestinal organoids: A model for biomedical and nutritional research. Organoids Mini-Organs. 2018;2018:195–214.
- Zieztek T., Rath E., Haller D., Daniel H. Intestinal organoids for assessing nutrient transport, sensing and incretin secretion. Sci. Rep. 2015;5:16831.
- Bouglé D., Bouhallab S. Dietary bioactive peptides: Human studies. Crit. Rev. Food Sci. Nutr. 2017;57:335–343.
- Cicero A.F.G., Gerocarni B., Laghi L., Borghi C. Blood pressure lowering effect of lactotripeptides assumed as functional foods: A meta-analysis of currentavailable clinical trials. J. Hum. Hypert. 2011;25:425–436.
- Cicero A.F.G., Fogacci F., Colletti A. Potential role of bioactive peptides in prevention and treatment of chronic diseases: A narrative review. Br. J. Pharmacol. 2017;174:1378–1394.
- Moughan P.J., Rutherfurd S.M. Gut luminal endogenous protein: Implications for the determination of ileal amino acid digestibility in humans. Br. J. Nutr. 2012;108(Suppl. S2):S258–S263.
- Moughan P.J., Rutherfurd S.M., Montoya C.A., Dave L.A. Food-derived bioactive peptides—A new paradigm. Nutr. Res. Rev. 2014;27:16–20.
- Dave L.A., Montoya C.A., Rutherfurd S.M., Moughan P.J. Gastrointestinal endogenous proteins as a source of bioactive peptides an in silico study. PLoS ONE. 2014;9:e98922.
- Dave L.A., Hayes M., Mora L., Montoya C.A., Moughan P.J., Rutherfurd S.M. Gastrointestinal endogenous protein-derived bioactive peptides: An in vitro study of their gut modulatory potential. Int. J. Mol. Sci. 2016;17:482.
- Dave L.A., Montoya C.A., Moughan P.J., Rutherfurd S.M. Novel dipeptidyl peptidase IV inhibitory and antioxidant peptides derived from human gastrointestinal endogenous proteins. Int. J. Pept. Res. Ther. 2016;22:355–369.
- Dave L.A., Hayes M., Montoya C.A., Rutherfurd S.M., Moughan P.J. Human gut endogenous proteins as a potential source of angiotensin-I-converting enzyme (ACE-I)-, renin inhibitory and antioxidant peptides. Peptides. 2016;76:30–44.
- Sun X., Acquah C., Aluko R.E., Udenigwe C.C. Considering food matrix and gastrointestinal effects in enhancing bioactive peptide absorption and bioavailability. J. Funct. Foods. 2020;64:103680.
- Pereira R.N., Vicente A.A. Environmental impact of novel thermal and non-thermal technologies in food processing. Food Res. Int. 2010;43:1936–1943
- Piccolomini A.F., Iskandar M.M., Lands L.C., Kubow S. High hydrostatic pressure pre-treatment of whey proteins enhances whey protein hydrolysate inhibition of oxidative stress and IL-8 secretion in intestinal epithelial cells. Food Nutr. Res. 2012;56:17549.
- Wallace R.J. Acetylation of peptides inhibits their degradation by rumen microorganisms. Br. J. Nutr. 1992;68:365–372
- Arnesen T. Towards a functional understanding of protein N-terminal acetylation. PLoS Biol. 2011;9:e1001074.
- Colgrave M.L., Craik D.J. Thermal, chemical, and enzymatic stability of the cyclotide kalata B1: The importance of the cyclic cystine knot. Biochemistry. 2004;43:5965–5975.
- Boutrou R., Jardin J., Blais A., Tomé D., Léonil J. Glycosylations of κ–casein derived caseinomacropeptide reduce its accessibility to endo- but not exointestinal brush border membrane peptidases. J. Agric. Food Chem. 2008;56:8166–8173
- Tanzadehpanah H., Asoodeh A., Saidijam M., Chamani J., Mahaki H. Improving efficiency of an angiotensin converting enzyme inhibitory peptide as multifunctional peptides. J. Biomol. Struct. Dyn. 2017;7:1–16
- Pauletti G.M., Okumu F.W., Borchardt R.T. Effect of size and charge on the passive diffusion of peptides across Caco-2 cell monolayers via the paracellular pathway. Pharm. Res. 1997;14:164–168.
- Knipp G.T., Vander Velde D.G., Siahaan T.J., Borchardt R.T. The effect of beta-turn structure on the passive diffusion of peptides across Caco-2 cell monolayers. Pharm. Res. 1997;14:1332–1340.