What Is a Peptide?

A peptide is a short chain made up of two or more amino acids. The amino acids are linked by a chemical bond called a peptide bond. When organized in complex structures (typically consisting of 50 or more amino acids), peptides then become proteins. Peptides have several functions in the body. They are also the basis of various medications.

Types

Peptides are mainly categorized in three different ways:

• According to how many amino acids make up the chain: Oligopeptides have few amino acids, while polypeptides are longer chains—typically between 20 to 50 amino acids. Dipeptides, tripeptides, and tetrapeptides have two, three, and four amino acids respectively. 
• According to their source, whether plant or animal
• According to their functions in the human body

Functions in the Body

Peptides play many roles in the human body. Some peptides and their functions include:

Vasopressin (antidiuretic hormone): This is a peptide hormone that secreted in the hypothalamus— a small portion of the brain that’s located at the base of the brain. Vasopressin has a couple of functions.

It is responsible for regulating the amount of water present in the fluid space around cells (extracellular fluid) It does this by causing the kidneys to absorb water. In high quantities, vasopressin is also a vasoconstrictor, which means that it causes blood vessels to narrow, and as a consequence, blood pressure rises.

Vasopressin is inhibited by alcohol consumption, which causes people to urinate more than usual.

Oxytocin: This peptide hormone is produced by the pituitary gland (located in the brain) and is made up of nine amino acids. It causes the uterus to contract during childbirth. Oxytocin also plays a pivotal role in the milk ejection reflex ("let down") during breastfeeding. Oxytocin is sometimes known as the "cuddle hormone" or the "love hormone" because it is released when people snuggle up together or bond socially.

Defensins: These peptides are mostly active in the immune system and are thought to be antimicrobial, hence promoting the wound healing process.  

Angiotensins: These peptide hormones are part of the renin-angiotensin system. They help to regulate blood pressure and also stimulate the release of aldosterone from the adrenal cortex to promote sodium retention by the kidneys.

Medical Uses

Peptides possess antioxidant, antimicrobial, and antithrombotic (anti-clotting) effects, among others. As of 2017, more than 60 peptide drugs have been approved in the U.S and other markets around the world. Peptides used in medicines are either naturally occurring, or synthetic.

• Peptides like vasopressin are used to treat diabetes insipidus. They're also used to manage antidiuretic hormone deficiency. 
• Carnosine is a dipeptide and natural antioxidant that’s found in the heart, kidneys, gut, skin, brain, and muscles. Studies show that it might be useful in the treatment of conditions like Alzheimer’s disease, brain ischemia, autism, Down syndrome, Parkinson’s disease, schistosomiasis, and epilepsy. It might also be helpful in preventing the formation of cataracts in the eyes.
• Defensins are peptides with broad-spectrum antimicrobial effects. Synthetic defensins are currently being studied as possible therapeutics for HIV-1.
• Hepcidin is a peptide hormone involved in controlling the body’s iron absorption. The measurement of its levels in the body helps with the diagnosis of anemia.
• Chromofungin, a peptide, could potentially help treat inflammatory bowel disease (IBD).
• Many antimicrobial peptides are in use to treat conditions like hepatitis C, pneumonia, HIV, and some bacterial infections. These peptides are either administered topically, orally, or via intravenous (IV) injections.

Cancer Treatment

Many peptides are currently being studied for use in treating different kinds of cancers. Research shows that atrial natriuretic peptide (ANP), for instance, can be potentially effective in treating colorectal cancer.

In fact, some peptide-based cancer treatments have already been approved and are being used to treat patients. Luteinizing hormone releasing hormone (LH-RH) agonist drugs (also called GnRH agonist drugs), for example, are used to treat ovarian and prostate cancer.

Peptide-Based Vaccines

Peptides play a special role in vaccines. Peptide-based vaccines mimic proteins that are naturally present in pathogens (germs that cause disease), allowing for certain responses to be replicated with what is usually a synthetic vaccine.

In addition to providing immunity against specific pathogens, peptide-based vaccines are also used in cancer treatment; an anti-tumor T cell response is produced by vaccinating a patient with peptides from their tumor antigens.

Peptide-based vaccines hold plenty of potential, however, they aren’t without their limitations. While the medical and scientific communities hope to develop an effective Alzheimer’s vaccine in the future, the difference between vaccines based on inactive or weakened pathogens and peptide-based vaccines is significant.

Pathogen-based vaccines tend to cause a greater immune response which often leads to better protection.

Dietary Supplements

Many health supplements contain peptides because of their potential health benefits. 

Antiaging: Collagen is one of the substances that form skin, bone, and cartilage. Collagen peptides are simply small pieces of collagen. Some studies suggest that collagen peptide supplements can help increase skin elasticity and hydration. These supplements may also be able to increase collagen density in the dermis.

Improved wound healing: Collagen is used in various wound treatments, including wound dressings for burn injury scaffolds. Collagen-boosting peptides are able to rebuild and restore the skin while promoting the production of the extracellular matrix (ECM), a three-dimensional network of collagen, enzymes, and other macromolecules (large molecules that are vital for the body).

Antimicrobial peptides have the ability to serve both roles, regenerating skin while providing antimicrobial protection. Peptide wound healing support is especially valuable for people with disrupted healing functions, such as a segment of the diabetic community that suffers from non-healing injuries and wounds.

Cosmetics

Due to their potential anti-aging benefits, many topical creams and skin care formulations contain peptides. Some studies have shown that topical application of some peptides may have positive effects on aged and photodamaged skin.

A Word From Verywell

Peptides are compounds that carry out many important functions in the human body. They’re also used and being studied extensively, for the treatment and management of medical conditions and health issues. 

If you’re planning to use nutritional supplements that contain peptides, remember to consult your healthcare provider first, as you should with any kind of supplements.