The heyday of leeches was in the 18th and 19th centuries when it was believed that bloodletting was a way to cure diseases of various origins. Leeches facilitated this procedure, allowing the removal of “bad” blood that disrupted the balance of the entire body. It was only later discovered that leech saliva contains valuable hirudin compounds for the human body.
Today, leeches are considered living pharmacological laboratories. From the salivary glands of medical leeches come many active ingredients now used to treat diseases such as thromboembolic diseases, atherosclerosis, and arterial hypertension. Among the most well-known are hirudin, which prevents blood clotting, and a specific histamine – a substance that causes the dilation of blood vessels. Leech saliva also contains lipases, esterases, prostaglandins, neurotransmitters, and many other substances. Discover the effects of some active substances from leech saliva on the human body.
The impact of leech saliva secretion on the cardiovascular system
Leeches are applied to patients with atherosclerosis, thromboembolic diseases, hypertension, and plastic surgeries, primarily after plantations, because their saliva contains components exhibiting anticoagulant, fibrinolytic, and anti-aggregatory actions.
Atherosclerosis
Clinical studies involving leeches have shown the beneficial impact of compounds in their saliva on lipid levels. Evidence indicates that after leech therapy, total cholesterol (TCL) and triglycerides (TG) levels normalise, and LDL is reduced. This is all thanks to the leeches secreting cholesterol esterase and lipase, which break down triglycerides. Studies also found that saratin exhibits anti-atherosclerotic effects, causing an antithrombin effect during atherosclerotic plaque formation.
Thromboembolic diseases
Hirudin, an anticoagulant compound secreted by leeches, is a potent thrombin inhibitor. It is suspected that this substance prevents heart attacks and strokes more effectively than aspirin. The saliva of leeches also contains components that limit the formation of clots, such as antistasin and those that dissolve clots and clear vessels, such as hementerin.
Arterial hypertension
Another important factor from leech saliva is PC-LS. It is a typical regulator of blood arterial pressure – it raises too-low pressure and lowers too-high pressure. Histamine, as mentioned earlier, dilates blood vessels and, as a result, reduces arterial pressure. It also plays a significant role in combating arterial hypertension.
Surgical procedures and replantations
Leech therapy is effective in patients after surgical procedures and replantations, as it efficiently prevents thromboembolic complications due to anticoagulant, anti-aggregatory, and fibrinolytic factors released by leeches. These small, unassuming animals restore circulation in the reattached organ. Moreover, substances derived from their saliva, such as bdellins, accelerate wound healing, inhibit inflammatory factors, and reduce swelling.
The impact of leech saliva secretion on the nervous system
In the past, leeches were applied to improve mood and well-being. Over time, it was discovered that endorphins, commonly known as happiness hormones released by leeches, are behind the improvement in mental condition right after their application. Therefore, leech therapy is one of the methods for treating diseases such as neurosis, depression, and nervous tics.
Neurotransmitters – dopamine, histamine, serotonin, and acetylcholine – essential components for the proper functioning of the nervous system—are present in the secretion from leeches’ salivary glands. Compounds stimulating the growth of nerve cells, such as destabilised stabilising and protease inhibitors – bdellin A (bdellastasin), bdellin B, and Eglin—were also isolated from it.
The discovery of components in leech saliva that stimulate the growth of nerve cells gives hope that leech therapy may help treat neurodegenerative diseases, including Parkinson’s and Alzheimer’s.
The impact of leech saliva secretion on the inflammatory process and pain therapy
Leeches secrete substances with anti-inflammatory action, such as Eglin, which is a potent inhibitor of inflammatory factors (e.g., proteases). Protease enzymes play an active role in the pathogenesis of thrombotic disorders, lung diseases, and other inflammatory processes. Therefore, leech therapy is used to support the treatment of lung and bronchial diseases. The previously mentioned bdellins also act as anti-inflammatories.
There is evidence that leeches alleviate pain in osteoarthritis and improve motor activity. Moreover, treatment with their participation brings relief in pain, including radiculitis, sciatica, spinal diseases, rheumatoid arthritis, osteoarthritis, and headaches. Leech therapy also effectively treats liver pain, gallbladder diseases, periodontitis, inflammatory eye conditions, laryngitis, sinusitis, and acute otitis media.
The impact of leech saliva secretion on urogenital system diseases
Leech therapy yields positive effects in female diseases such as vaginal and uterine mucosal inflammations, ovarian and fallopian tube abscesses, ovarian cysticity, and cervical erosions; in men, it reduces prostate enlargement. This is due to bdellastasins–acrosin inhibitors, which likely play a role in the inflammation of individual parts of the urogenital system.
Clinical studies have also shown the effectiveness of leech therapy in treating menstrual disorders and infertility in both women and men. The participation of hormones such as progesterone, estradiol, testosterone, cortisol, and dehydroepiandrosterone in leech saliva is noted.
The impact of leech saliva secretion on infections
During research on leech therapy, it was noticed that leeches live in symbiosis with a microorganism producing an antibacterial substance – chloromycetin. Therefore, their application may be helpful when it should be used, such as in meningococcal septicemia, meningitis, Staphylococcus aureus infection, or tetanus. Moreover, leech saliva contains destabilase, a substance that has antibacterial properties.
The impact of leech saliva secretion on the cancer process
Research on mice involving the implantation of T 241 sarcoma followed by intravenous administration of an extract from leech salivary glands proved that tumour development was halted due to the presence of (presumably) ghilanten in the applied secretion. The antioxidant action of leech mucous secretion was also proven, and it is a fact that antioxidant substances have significant importance in preventing and treating cancer diseases.
The impact of leech saliva secretion on dermatological conditions and its role in cosmetology
In the Middle Ages, it was noticed that applying leeches improves well-being and helps maintain a youthful appearance. After hundreds of years, the validity of using leech therapy in dermatology and cosmetology has been confirmed. Antielastase derived from leech saliva slows the skin ageing process by inhibiting the enzyme that breaks down elastin and slowing the breakdown of the skin’s elastic tissue. Numerous studies have shown that applying leeches supports the treatment of lupus, acne, psoriasis, roseola, cellulite, eczema, scleroderma, spider veins on the lower limbs, boils, abscesses, and hyperpigmentation.
Applying leeches usually helps, but it can also harm. Adverse effects related to it are rare yet very dangerous. Therefore, before using leech therapy, it is necessary to consult with a doctor to evaluate, based on examinations and interviews, whether conducting the procedure will not harm the patient’s life and health.