'Substance P' in tears—a noninvasive test for diabetes-related nerve damage?

July 5, 2017

Levels of a nerve cell signaling molecule called substance P—measured in tear samples—might be a useful marker of diabetes-related nerve damage (neuropathy), suggests a study in the July issue of Optometry and Vision Science, the official journal of the American Academy of Optometry.

Tear samples from patients with diabetes show elevated levels of substance P, which are related to early damage to the corneal nerves, which may contribute to the development of corneal ulcers and poor wound healing in patients with diabetes, according to the pilot study by Maria Markoulli, PhD, MOptom, FAAO, and colleagues of University of New South Wales, Sydney, Australia. They researchers suggest that substance P measurement could be a new and noninvasive test to assess the risk of diabetic neuropathy.

Substance P in Tears a 'Potential Biomarker of Corneal Nerve Health'

The researchers measured substance P levels in the natural tear film in the eyes of nine adults with diabetes and a control group of 17 nondiabetic subjects. Substance P is a neuropeptide that contributes to wound healing, among other functions. Substance P is also involved in maintenance and nutrition of the cornea—the clear, outermost layer of the eye. The cornea has a rich network of fine nerves, which play critical roles in protecting and healing the surface of the eye.

Unlike nerves elsewhere in the body, the structure of the living corneal nerve can be seen and measured using a technique called confocal microscopy. Studies have shown that corneal nerve fiber density, measured by confocal microscopy, can predict diabetes-related damage to the peripheral nerves, called peripheral neuropathy.

This common diabetes complication causes symptoms including pain and numbness of the hands and feet. Damage to the peripheral nerves can be seen on biopsy samples, but this is an invasive and nonrepeatable procedure. Dr. Markoulli and colleagues sought to determine whether substance P levels in tears reflect damage to the corneal nerves in diabetic patients.

The results showed that patients with diabetes had substantially lower levels of substance P in tear film samples, compared to healthy controls.

On confocal microscopy, the diabetic patients also had a significantly lower corneal nerve fiber density, indicating loss of corneal nerve fibers. Substance P levels were "moderately" correlated with the corneal nerve fiber density measurements.

"The positive correlation between substance P and corneal nerve density indicates that substance P may be a potential biomarker for corneal health," Dr. Markoulli and coauthors write. In the eyes, reduced levels of substance P might contribute to poor wound healing and the development of in patients with diabetes. That's consistent with recent studies reporting that substance P derivatives can promote healing of diabetes-related corneal defects.

In the future, measuring substance P levels in the tear film might become a useful, noninvasive test for assessing the risk of peripheral neuropathy in with . Dr. Markoulli and colleagues emphasize that further research is needed—including studies to confirm whether substance P reflects the presence or absence of peripheral neuropathy.

Explore further: Reduced corneal nerve fiber density in patients with HIV

More information: Maria Markoulli et al. Corneal Nerve Morphology and Tear Film Substance P in Diabetes, Optometry and Vision Science (2017). DOI: 10.1097/OPX.0000000000001096

Related Stories

Reduced corneal nerve fiber density in patients with HIV

June 12, 2017
(HealthDay)—Patients with HIV and HIV-associated sensory neuropathy (HIV-SN) have reduced corneal nerve fiber density, which can be identified using in vivo corneal confocal microscopy (IVCCM), according to a study published ...

Research suggests seal oil could help people with Type 1 diabetes

June 13, 2017
A research team at the Krembil Neuroscience Centre in Toronto has published a paper that suggests seal oil has the potential to help promote nerve regeneration in patients with Type 1 diabetes.

Omega-3 essential fatty acids may protect corneal nerves in dry eye

March 21, 2017
(HealthDay)—Oral, long-chain omega-3 (ω-3) essential fatty acid (EFA) supplementation is neuroprotective to corneal nerves for patients with dry eye disease, according to a study published online March 12 in Ophthalmic ...

New research sets stage for noninvasive monitoring of HIV-induced peripheral neuropathy

May 12, 2014
Corneal nerve fiber assessment has great potential as a tool to diagnose and monitor peripheral neuropathy induced by HIV, say scientists at the Johns Hopkins University School of Medicine. The results of their study are ...

Study provides new understanding of diabetic peripheral neuropathy

April 11, 2016
A research team from Wayne State University recently published a paper in the Journal of Clinical Investigation that provides a paradigm shift in the understanding of cellular and molecular mechanisms underlying diabetic ...

Substances found in cornea activate healing of blinding scar tissue

December 18, 2015
Doctoral student Marta Słoniecka at the Department of Integrative Medical Biology has found that the neuropeptide substance P and the neurotransmitter acetylcholine activate and enhance healing of the cornea. The two substances ...

Recommended for you

Research reveals biological mechanism of a leading cause of childhood blindness

November 16, 2017
Scientists at the Virginia Tech Carilion Research Institute (VTCRI) have revealed the pathology of cells and structures stricken by optic nerve hypoplasia, a leading cause of childhood blindness in developed nations.

Genetic treatment for blindness may soon be reality

November 11, 2017
Patients who had lost their sight to an inherited retinal disease could see well enough to navigate a maze after being treated with a new gene therapy, according to research presented today at AAO 2017, the 121st Annual Meeting ...

Study finds donor corneas can be safely preserved for longer period

November 10, 2017
Results from a large, national clinical trial show that corneal donor tissue can be safely stored for 11 days without negatively impacting the success of transplantation surgery to restore vision in people with diseases of ...

Exploring the genetics of glaucoma and retinal development

November 10, 2017
Guillermo Oliver, PhD, the Thomas D. Spies Professor of Lymphatic Metabolism, recently published two studies related to the eye, one on retinal formation and the other on the genetics behind glaucoma.

Scientists discover potential treatment to stop glaucoma in its tracks

November 6, 2017
Vision scientists at the University of California, Berkeley, and the University of Toronto have discovered that naturally occurring molecules known as lipid mediators have the potential to halt the progression of glaucoma, ...

New focus on correcting refractive vision

October 25, 2017
While doctors take delight in solving the common issue of refractive vision error by prescribing eye glasses, Flinders University researchers have found that many patients are upset with this solution and claim it affects ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.