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Bioactive Proteins and Peptides

Proteins provide nutritional benefit as essential components of a healthy diet. The body metabolizes proteins to make hormones, antibodies, enzymes and various tissue/organ components including muscle. Proteins consist of long chains of amino acids – building blocks linked together with peptide bonds. In their natural form, proteins are not easily absorbed from the digestive tract into the blood stream. Digestive enzymes in the stomach and intestine must first break apart the peptide bonds. The process of digestion breaks proteins into shorter chains of amino acids called peptides, which the body can easily absorb. Nutritional efficiency (the percent-age of protein in our diet that is used for nutritional benefit by the body) depends on the ability of our digestive enzymes to split peptide bonds and release peptides.

Peptides released during protein digestion may also serve a therapeutic purpose (1). For example, reactive oxygen species (ROS) are toxic compounds that are produced during periods of metabolic or environmental stress. Peptides carry free electrons that neutralize ROS, which require an extra electron to become unreactive. The toxic side effects of ROS include damage to DNA (cancer-causing effects) or damage to structural components of the brain (neurodegenerative effects, e.g. Alzheimer’s disease). By accepting free electrons from peptides, the ROS are neutralized and their toxic side effects may be prevented (an effect referred to as scavenging).

Due to their therapeutic effects, some peptides are deemed to be ‘bioactive’ and could serve as tools to prevent or treat various human diseases (1). However, bioactive peptides in the diet are usually not concentrated enough to be absorbed into the blood stream at sufficiently high levels in order to produce their bioactive effects. To address this issue, bioactive peptides are made in concentrated form through a process called in vitro digestion. In vitro digestion uses digestive enzymes to break apart (digest) proteins, forming specific types of bioactive peptides. This method can be customized with the use of microbial enzymes that are more efficient than the digestive enzymes normally present in our digestive tract.

Pea Protein Hydrolysate (PPH)

In my research program, we have taken advantage of in vitro digestion to convert yellow field pea protein into bioactive peptides, referred to as pea protein hydrolysate (PPH). Yellow field peas are a legume crop grown for human and animal consumption. Yellow field pea proteins are subjected to in vitro digestion and, after three hours of digestion with microbial enzymes, any undigested proteins are separated from the bioactive peptides. In the final step of the process the isolated bioactive peptides are dried to form PPH (2).

Animal and human trials have demonstrated that PPH has blood pressure lowering (anti-hypertensive) effects (2).We have tested PPH as an inhibitor of the renin-angiotensin system (RAS). The RAS is the main metabolic pathway that regulates human blood pressure (Figure 1). Under in vitro conditions, we found that PPH was able block the function of (inhibit) the two main enzymes that operate the RAS: renin and angiotensin-converting enzyme (ACE). Spontaneously hypertensive rats (which closely model hypertension [high blood pressure] in humans) were fed PPH over acute (24-hour) and long-term (five-week) periods. Over the acute and long-term feeding periods, spontaneously hypertensive rats fed PPH had reduced systolic blood pressure (SBP) (2,3).

The so called Han:SPRD-cy rat is an animal model of human chronic kidney disease (CKD) which was also used for testing PPH as an anti-hypertensive agent. The kidneys of Han:SPRD-cy rats contain large numbers of cysts, which are known to activate the RAS and contribute to hypertension. Hypertension is known to increase the risk of cardiovascular disease. We indeed found that PPH was effective at reducing SBP in Han:SPRD-cy rats. During an eight-week feeding experiment, PPH was added to the feed of Han:SPRD-cy rats and caused a reduction in SBP by 29 mmHg and a reduction in diastolic blood pressure (DPB) by 25 mmHg (3). PPH also significantly increased urine production when compared to Han:SPRD-cy rats not fed PPH. In addition to anti-hypertensive effects, our data suggested that PPH may also improve kidney function and enhance urine production under conditions of CKD.

These animal experiments provided the rationale for testing PPH as an anti-hypertensive agent in human volunteers. PPH was added to orange juice that was consumed by mildly hypertensive human volunteers with normal kidney function. During a three-week feeding test, there was a significant decrease in the SBP of human volunteers who consumed PPH when compared to a placebo (orange juice only). Another potential health benefit of PPH was demonstrated as an immune-modulating agent. For example, activated immune cells (macrophages exposed to lipopolysaccharides) produced 80% less pro-inflammatory agents when treated with PPH (4). When PPH was orally administered to mice, there was increased activity of their peritoneal macrophages in addition to enhanced stimulation of the immune response in the gut mucosa. The technology for PPH production has been licensed to AOR Inc. to make PPH available to consumers.

Hemp Seed Protein Hydrolysate (HPH)

My research program has also investigated the anti-hypertensive effects of peptides produced from the enzymatic digestion of hemp seed proteins (HPH) (5). We have found that when provided to young systemic hypertensive rats, HPH prevented the development of hypertension. Young systemic hypertensive rats fed HPH maintained normal systolic blood pressure (120 mmHg) during the eight-week experiment (6). In comparison, young systemic hypertensive rats not fed HPH (control diet) developed hypertension with systolic blood pressure of 158 mmHg.

In adult systemic hypertensive rats with full-blown hypertension, incorporation of HPH into the feed led to significant reductions in SBP. Plasma analysis confirmed HPH reduced blood levels of renin and ACE, which underpinned the observed reduction in SBP. Therefore, the HPH had both preventive and therapeutic effects in the systemic hypertensive rat.

In addition to these anti-hypertensive effects, HPH had anti-oxidant properties, including the ability to neutralize highly reactive species (free radicals and metal ions) and inhibit the production of peroxyl radicals (peroxidation of unsaturated fatty acids) (7). HPH also significantly decreased plasma lipid peroxides and boosted levels of anti-oxidant enzymes (8). Together, these results suggested that HPH acted as a multifunctional agent with the ability to simultaneously reduce blood pressure, plasma lipid peroxides, and toxic free radicals.


Figure 1: Effect of PPH and HPH on the Renin-Angiotensin SystemOn sensing reduction in blood pressure, the kidneys release renin which converts angioten-sinogen (secreted by the liv-er) to angiotensin I. ACE (angiotensin-converting enzyme), released by the lungs, converts angiotensin I to angiotensin II. Angiotensin II acts on blood vessels, stimulating vasoconstriction (narrowing) which increases blood pressure. Angiotensin II also stimulates the adrenal gland to secrete aldoster-one, which stimu-lates the kidneys to reabsorb salt and water. PPH (pea protein hydrolysate) and HPH (hemp seed protein hydro-lysate) are able to normalize high blood pressure (hypertension) by reducing the levels of renin and ACE, thus blocking the conversion of angiotensinogen into angiotensin II.

Key Terms

HPHHemp seed protein hydrolysate (HPH) is the term for bioactive peptides produced from hemp seed (of the Cannabis sativa plant species) using the process of in vitro digestion. HPH has been found to have anti-hypertensive and anti-oxidant effects

Bioactive Proteins

Iron-deficiency anemia (IDA) is a global problem that afflicts close to one quarter of the world’s population. IDA contributes to the development of several conditions, including an abnormally fast heartbeat (tachycardia), heart failure and, in the female population, a higher risk of complications before or after childbirth. Current approaches to treatment involve the use of inorganic iron salts, which are consumed orally at very high doses. Very high doses of inorganic iron are used because inorganic iron has relatively poor solubility within, and low absorption from the gastrointestinal tract. The problem is that there are always high amounts of unabsorbed iron, which can cause negative side effects such as constipation and other gastrointestinal ailments.

My research program has focused on developing a protein alternative to inorganic iron as a treatment for IDA. Phytoferritins consist of an iron core enclosed within a protein cage. These organic forms of iron are soluble and readily broken down in the gastrointestinal tract to release their iron payload. Therefore, ferritins could serve as a more efficient iron source for the treatment of IDA when compared to inorganic iron supplements currently in use.

To achieve this goal, we have developed a method for producing a phytoferritin concentrate from legume seeds. The extraction process is wholly aqueous-based and produces phytoferritin concentrates

providing up to 50 mg of iron per 100 g. We estimate that an adult dose of only 300 mg of phytoferritin concentrate per day (which could be supplied in a single capsule) would provide sufficient iron to meet the daily iron requirement and prevent or treat IDA. Plans are underway to test the efficacy of this phytoferritin in a suitable animal model of IDA before moving on to human intervention trials. This phytoferritin project was partially funded by a research grant from AOR Inc.

Conclusion

The market for natural therapeutic products continues to grow rapidly due to strong demand from increasingly health conscious consumers. This demand is driven by the reduced risk of negative side effects associated with natural therapies. Within the natural products market, the use of proteins and peptides has gained significant interest due to their ease of production and the safety of the products. Whole proteins can be used to provide bioactive effects, but prior digestion into smaller sized peptides seems to be the optimal route for developing naturally therapeutic products. In general, peptides produced from hydrolyzed proteins are more readily absorbed and provide beneficial effects on the human body. Such health benefits include the reduction of high blood pressure, the neutralization of oxidative stress, and the support of the normal function of the immune system. While these health benefits have been demonstrated in animals, there is a drive for human intervention trials to support the market adoption of bioactive proteins and peptides as effective and safe therapeutic agents.

References

1. Udenigwe CC, Aluko RE. Food protein-derived bioactive peptides: production, processing and potential health benefits. J. Food Sci. 2012;71:R11-R24.

2. Li H, et al. Blood pressure lowering effect of a pea protein hydrolysate in hypertensive rats and humans. J. Agric. Food Chem. 2011;59:9854-9860.

3. Girgih AT, et al. Antihypertensive properties of a pea protein hydrolysate during short and long term oral administration to spontaneously hypertensive rats. J. Food Sci. 2016;81:H1281-H1287.

4. Ndiaye F, et al. Anti-oxidant, anti-inflammatory and immunomodulating properties of an enzymatic protein hydrolysate from yellow field pea seeds. Eur. J. Nutr. 2012;51:29-37.

4. Girgih AT, et al. Kinetics of enzyme inhibition and antihypertensive effects of hemp seed (Cannabis sativa L.) protein hydrolysates. J. Am. Oil Chem. Soc. 2011;88:1767-1774.

5. Girgih AT, et al. Preventive and treatment effects of hemp seed (Cannabis sativa L.) meal protein hydrolysate against high blood pressure in spontaneously hypertensive rats. Eur. J. Nutr. 2014;53:1237–1246.

6. Girgih AT, et al. In vitro antioxidant properties of hempseed (Cannabis sativa L.) protein hydrolysate fractions. J. Am. Oil Chem. Soc. 2011;88:381-389.

7. Girgih AT, et al. A novel hemp seed meal protein hydrolysate reduces oxidative stress factors in spontaneously hypertensive rats. Nutrients. 2014;6:5652-5666.

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