Low Levels of Substance P in Saliva May Help Predict Swallowing Problems, Study Suggests

Low levels in saliva of a molecule called substance P may help predict the development of swallowing problems in people with Parkinson’s disease, a small pilot study in Germany found.

Since this molecule works as communication signal between nerve cells in the body, this discovery suggests that impaired substance P activity may be an important contributing factor in the  development of this Parkinson’s complication.

The study, “Substance P Saliva Reduction Predicts Pharyngeal Dysphagia in Parkinson’s Disease,” was published in the journal Frontiers in Neurology.

The progression of Parkinson’s disease is associated with the loss of movement control, including control over muscles in the face, mouth, and throat. This can lead to speech problems and swallowing difficulties, which are known medically as dysphagia.

Such swallowing difficulties can severely affect a person’s ability to sustain healthy eating practices without needing additional support.

“Parkinson’s-related dysphagia affects the oral, pharyngeal and the esophageal phase of swallowing and occurs in all stages of the disease,” the researchers said.

However, this complication may remain undetected during early stages of Parkinson’s in many patients, which may prevent early diagnosis and timely care, they said.

Previous studies have shown that levels of the neurotransmitter substance P are reduced among elderly Parkinson’s patients who have aspiration pneumonia. This suggests that substance P may be involved in the underlying mechanism of the normal swallowing and cough reflex in the throat’s inner tissues, called the pharyngeal mucosa.

To learn more, German researchers explored the role of substance P in the progression of pharyngeal dysphagia in people with Parkinson’s.

The study enrolled 20 patients; half showed signs of swallowing difficulties. Researchers collected saliva samples from all patients and analyzed the levels of substance P.

Participants who did not have pharyngeal dysphagia were slightly younger, had Parkinson’s for fewer years, and also showed fewer signs of motor impairments caused by the disease as compared to patients with the complication. However, these differences were minor, and the groups were considered to be at similar disease stages.

The results showed that patients who did not have swallowing problems had 1.8-fold higher levels of substance P than those with dysphagia.

“Our findings could be another indication that, in early stages, loss of substance P containing neurons in the pharyngeal mucosa may lead to pharyngeal hyposensitivity and merely incipient pharyngeal dysphagia,” the researchers said.

Additional studies are warranted to further understand the role of substance P in Parkinson’s disease progression, the researchers said. They also recommended that further studies be done to evaluate substance P’s potential as a biomarker for early dysphagia.

Future research also should address the potential use of capsaicin — an active compound in chili peppers known to stimulate the release of substance P — as strategy to target the sensory system within the swallowing network of nerve cells, they added.