Iridoids are basically a group of secondary or lesser important metabolites that are present in an assortment of plants as well as in a number of animals. Iridoids are monoterpenes (a unit of isoprene forming a terpene) that are synthesized biologically from isoprene and often they act in the form of agents in alkaloid biosynthesis. From the chemical point of view, iridoids generally comprise a cyclopentane ring combined with an oxygen heterocycle having six units.
Iridomyrmecin perfectly demonstrates the chemical makeup of iridoids. Iridomyrmecin is actually a protective chemical that is made by ants belonging to the Iridomyrmex genus and this gives iridoids their name. A split in a link in the cyclopentane ring results in the production of a sub-class called seco-iridoids, for instance, armarogentin. Typically, iridoids are present in plants in the form of glycosides, very frequently linked to glucose.
It has been found that the secondary metabolite iridoids are present in several remedial plants and they are likely to be accountable for a number of pharmaceutical activities of these plants. When iridoids are isolated and decontaminated, they demonstrate an assortment of bioactivities, counting analgesic, cardiovascular, anti-mutagenic, anti-inflammatory, antiviral, anti-tumor, anti-hepatotoxic, hypoglycemic, choleretic, and purgative, immunomodulator as well as anti-spasmodic activities.
The plants mainly produce iridoids to defend them against invasions by herbivorous animals or to protect them against infections by pathogenic microbes. Humans as well as most other mammals find the flavor of iridoids to be distinctly bitter.
Where do we find iridoids?
Iridoids are found in the plants belonging to the heather family, including blueberry, cranberry, lingonberry and huckleberry. All these plants enclose a blend of simple as well as complex iridoids. In fact, the juice extracted from cranberry has been traditionally used in folk medicine to treat infections of the urinary tract. Cranberry juice as well as the jam prepared with it is consumed to improve night vision.
In addition to the plants mentioned above, iridoids are also present in the herb eyebright, which is reputed for possessing wonderful anti-inflammatory attributes. For several centuries, herbalists have been employing poultices prepared with flowers of eyebright for treating inflamed (swelling and redness) eyes. Even to this day, eyebright is used in the form of a natural substitute to antibiotics for treating conjunctivitis. In addition, the herb valerian, which possesses sedative properties and is very well liked by people suffering from problems in falling asleep, also has a rich content of iridoids.
Iridoids are divided into two classes - simple and complex, depending on their respective chemical composition. The arrangement of iridoid molecules is actually responsible for their bioactive attributes.
Sources of simple iridoids
Simple iridoids are found in a number of plants, including actinidia (also called the silver vine), boobialla (also called figwort), broomrape, catnip, cat thyme and Noni (botanical name Morinda citrifolia).
While the broomrape is basically a weed having attractive purple hued flowers akin to those of foxglove and is usually found growing among aubergine, potato and tomato plants in Europe, boobialla is actually a cluster of shrubs that flower perennially and is indigenous to Australia. On the other hand, the herb cat thyme is a spiky plant that grows perennially and possesses an aroma that has resemblance to the scent produced by thyme.
Sources of complex iridoids
Complex iridoids are also present in a number of herbs, which include:
Sources of iridoid glycosides
In addition to the simple and complex iridoids, a third variety of iridoid exists. In this type of iridoid, the real molecule is fastened to a sugar form that provides them with a specific chemical arrangement and also particular attributes - different from those of the simple and complex iridoids. This variety of iridoids is known as iridoid glycosides.
This particular type of iridoid is present in a number of plants, which include catalpa vine, chasteberry, gardenia, glandiflora, Morinda citrifolia (Noni), snapdragon (also known as dragon flower), plantago and verbena.
It is worth mentioning here that the majority of plants enclose either one or two iridoids, while there are some plants that even enclose all the three types of iridoids, for instance, Morinda citrifolia (Noni). In fact, the Morinda citrifolia plant is the sole exception and its fruit, commonly called 'noni', contains as many as 12 dissimilar types of iridoids, which includes glycoside iridoid, non-glycoside iridoid, simple iridoid as well as complex iridoid.
Benefits of iridoids
Iridoids are known to offer a great variety of health benefits, including providing us support against a vast assortment of physical, biological as well as chemical stressors. Iridoids also have a stabilizing consequence on the human body targeting imbalances, but not having any adverse effect on the normal functioning of our bodily systems. Most importantly, iridoids perform all these tasks without causing any toxic side effects. Some of the specific health benefits offered by iridoids are listed below.
- It is worth mentioning that science has just begun to comprehend enormous bioactive potentials of the iridoid amalgams. Iridoids possess anti-allergic attributes and these appear to be a result of their ability to hold back the release of histamine. This particular attribute makes iridoids a natural option for treating allergies and inflammations. Besides, iridoids also possess the ability to diminish inflammation that usually accompanies allergies, making them the perfect medication for people who are susceptible to various types of allergies.
- Anti-cancer and anti-tumour
- Iridoids are known to possess anti-cancer properties. It has been reported that asperulosidic acid obtained from dehydrated fruits of Morinda citrifolia (noni) works to slow down melanoma or skin cancer cell formation. An iridoid that has been discovered recently and called aucubin demonstrates notable anti-tumour actions on cultures of cells related to various forms of cancers, including those of the breast, colon, skin, throat, lung, nose, and also leukemia.
- Till recent times, people considered the seeds of noni to be useless and discarded them when the noni fruits were processed for extracting their juice or the noni oil. However, a latest study undertaken by scientists in Japan hints that the noni seeds contain an iridoid called americanin and it may be used as an effective constituent of cosmetics meant for skincare, such as those that are used for whitening the skin or preventing wrinkles, as this iridoid possesses the aptitude to augment elastin production. It may be noted here that elastin is among the vital skin proteins that help the skin to remain moist and youthful.
- It has been found that many types of iridoids possess potent anti-inflammatory attributes. These properties are effective when iridoids are taken by mouth or applied externally on the affected areas.
- Iridoids possess potent antioxidant attributes, which is thought to be much more powerful compared to those of the more conventional antioxidants found in plants, for instance, polyphenols or flavonoids that are obtained from green tea and citrus plants. It has been found that plants belonging to the gentian family have one of the highest iridoid concentrations. In addition, it has been found that the fruit of the noni (morinda citrifolia) plant is among the most excellent sources of both simple as well as complex iridoids.
- Different iridoids present in the plants belonging to the gentian family have such potent natural antibacterial effects that they can be easily compared with antibiotic medications.
- Many scientific studies have documented that iridoids possess antiviral properties. In fact, they have a distinct antiviral activity against viruses that are responsible for encephalitis. In addition, iridoids are also effective in providing protection against herpes simplex type 1 viruses.
- Blood sugar control
- It appears that iridoids also have the aptitude to safeguard the pancreas and this attribute is beneficial for people with diabetes. In addition, it has been found that iridoids that have been isolated from dissimilar plants possess attributes that regulate the blood sugar levels and their effectiveness can be compared to those of the anti-diabetic medicaments.
- Cardiovascular protection
- It has been found that
olive oil contains two iridoids known as oleuropein and oleacein, which possess potent cardio-protective attributes. People who consume olive oil are inclined to have fewer deposits of fat in their abdominal and hepatic regions. In addition, they also have much less fat accumulation in their heart as well as liver tissues and suffer from much less cardiac stiffness. It has also been found that people consuming olive oil also have an augmented resistance against stress and are inclined to suffer less due to problems related to cholesterol and high blood pressure (hypertension). The types of iridoids present in olive oil are known to safeguard the heart as well as the arteries from the harmful consequences of toxicity caused by stress.
- Liver protection
- It is interesting to note that iridoids have been prescribed to patients to help them recuperate from damaged liver owing to drug abuse and excessive consumption of alcohol. These iridoids are so effective in protecting the liver that their actions can be compared with those of the milk thistle plant.
- It has been found that many different types of iridoids shield our nervous system from numerous environmental as well as chemical stressors, including pesticides and heavy metals present in substances such as amalgam tooth fillings. In addition, many studies have discovered that iridoids also possess properties that help to enhance our memory.
- Protection of the arteries
- Findings of a research carried in the European Journal of Pharmacology have shown that iridoids are effective in putting off the arteries from furrying up (have a white coating) due to cholesterol deposits. Iridoids are very effective in lowering the blood cholesterol levels and this attribute of these compounds is equivalent to that of the statins (atorvastatin).