A study conducted by the University of Maryland School of Medicine in the United States may provide hope for future treatments for millions of patients who suffer for years from a lack of comfort due to a chronic itching condition that accompanies them with no known cause.
The condition, known as chronic pruritus, has an unknown cause and no approved treatment. In the study, published in the journal Scientific Reports on July 29, researchers found lower-than-normal levels of several markers in patients’ blood plasma, which could hint at the cause of their painful symptoms.
Deficiency in a number of amino acids and other substances
“Our study found significant deficiencies in certain metabolic markers, including several important amino acids and other metabolites involved in immune regulation, in patients with chronic idiopathic pruritus compared to healthy controls,” said lead study author Sean Kwatra, Ph.D., chair of the Department of Dermatology at the University of Maryland and chair of the department at the University of Maryland Medical Center. “This is an exciting finding because it provides new insights into the cause of this condition and identifies future therapeutic targets for consideration.”
Chronic pruritus of unknown origin is most common in older adults and causes severe itching that lasts for more than 6 weeks. Current treatments used to help manage symptoms are off-label and have poor efficacy, with many patients experiencing significant impairment in their quality of life.
In the latest study, Dr. Kwatra and colleagues compared blood plasma samples from patients with chronic idiopathic pruritus and matched healthy controls, and found lower levels of 9 amino acids in patients with chronic idiopathic pruritus than in controls, and that lower levels correlated with itch severity.
Itching and experiments on mice
Previous animal studies have linked low levels of these amino acids to itchy symptoms in mice. These amino acids are building blocks of neurotransmitters, or brain chemicals, that play a role in the body’s response to itching and other skin reactions. Giving mice drugs such as antidepressants to increase neurotransmitters, such as serotonin, has been found to reduce itchy symptoms.
“Many of these metabolic markers that we found in low amounts in the blood of patients with chronic pruritus of unknown cause, such as tryptophan and glycine, may contribute to the underlying pathogenesis of this condition, but we certainly need larger studies to investigate this further,” Dr. Kwatra said, according to the EurekAlert website.
Chronic itching and immunity
In addition to affecting neurotransmitters, several biomarkers that are altered in patients with chronic idiopathic pruritus also contribute to immune modulation, suggesting an immune dysfunction in the pathogenesis of chronic idiopathic pruritus. Another mechanism described for tryptophan and serotonin in regulating the itch pathway is by reducing lymphocyte proliferation, as serotonin receptors are found on many immune cells, including mast cells, T cells, natural killer cells, and Langerhans cells. Thus, the function of drugs that affect these metabolites is twofold, affecting both neurotransmission and immune regulation.