Amino acid linked to asthma, obesity combo

U. PITTSBURGH (US) — An imbalance in the metabolism of arginine could cause respiratory trouble and asthma issues in obese people, especially those who develop asthma later in life.

The relationship between asthma and obesity is in many ways a conundrum, says the study’s lead author, Fernando Holguin, associate professor in the Division of Pulmonary, Allergy and Critical Care Medicine at University of Pittsburgh School of Medicine, and co-director of the Asthma Institute.

A person who has severe asthma may require frequent steroid treatments and limit his or her activity, resulting in weight gain; in others, obesity seems to aggravate or even initiate asthma symptoms.

“Obese asthma patients tend to have worse symptoms, more frequent episodes of breathing difficulty, and don’t respond as readily to conventional treatments,” says Holguin, whose findings appear in the American Journal of Respiratory and Critical Care Medicine.

“Our study supports the premise that asthma is a multifactorial condition that can be triggered by a variety of underlying problems.” Interventions to improve clinically meaningful outcomes may need to be personalized to the type of asthmatic condition that patient has.

Patients who are obese and develop asthma as adults tend to exhale lower levels of nitric oxide (NO), a compound that relaxes blood vessels and is thought to play a similar role in airways.

The researchers collected blood samples from 155 adults, nearly half of whom had severe asthma and half of whom were obese. The team found that compared to early-onset asthma patients, late-onset obese asthma patients had lower plasma levels of the amino acid arginine and higher levels of an arginine metabolite called ADMA, which interferes with NO production.

“In healthy people, a balance is maintained between arginine and ADMA ensuring normal levels of airway NO,” Holguin says.

“But in obese, adult-onset asthma, the lower arginine and higher ADMA reduces airway NO levels. This finding is promising because it suggests that increasing arginine could restore NO levels and its positive effect on airways.” This might translate into patients having less wheezing and shortness of breath.

Arginine is readily available over the counter as a dietary supplement, but it is rapidly metabolized by the body and reduces its practicality as a treatment, he says. Another supplement called citrulline is known to enhance arginine production, and can be taken in high doses without ill effects.

“We will soon begin a small pilot study to see whether citrulline supplements can help alleviate symptoms in patients who fit this profile of late-onset asthma, obesity and decreased exhaled NO,” says Holguin.

Co-authors of the paper include researchers from the University of Pittsburgh School of Medicine, as well as from the Cleveland Clinic, Wake Forest University, University of Wisconsin, University of Texas, Washington University, Emory University, University of Virginia, Harvard University, and Imperial College London.

The National Institutes of Health funded the study.

Source: University of Pittsburgh