Presence of Heme B in Sputum Linked to Worse Lung Function in CF Patients, Study Shows

Presence of Heme B in Sputum Linked to Worse Lung Function in CF Patients, Study Shows
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The presence of heme B — a component of red blood cells — in the lungs is linked to worse lung function in people with cystic fibrosis (CF).

That finding was described in the study “Refinement of metabolite detection in cystic fibrosis sputum reveals heme correlates with lung function decline,” published in the journal PLOS ONE.

Lung infections with the bacteria Pseudomonas aeruginosa are one of the main causes of disease worsening and mortality in people with CF. P. aeruginosa produces chemical compounds called phenazines as a result of its microbial processes. Phenazines are known to be virulence factors —  molecules that allow the bacteria to proliferate and spread within the host. 

The research team that lead the new study previously published a report of a negative relationship between the amount of phenazines in sputum (mix of saliva and mucus coughed up from the lungs) of people with CF, and their lung function, as measured by percent predicted forced expiratory volume in one second (ppFEV1).

In their initial study, researchers used a technique called high-performance liquid chromatography to identify and quantify phenazines. However, this type of technology has evolved considerably since the team’s initial study in 2012, and a more specific and sensitive technique called liquid chromatography mass spectrometry (LC-MS) is now available.

So, researchers tried to reproduce the results of their previous study by using LC-MS in 71 new sputum samples provided by CF patients to the Mountain West CF Consortium (MWCFC) SputumBiomarker Study. All patients were older than 12 and were clinically stable.

The team was surprised to find that the new technique was not able to pick up the phenazines reported in the previous study — namely pyocyanin, phenazine-1-carboxylic acid, phenazine-1-carboxamide, and 1-hydroxyphenazine — suggesting that these, if present in the samples, were below the detection limits of the instrument.

Instead, researchers identified a new compound in the samples called ferriprotoporphyrin IX, also known as heme B, a molecule that contains iron and is commonly found in red blood cells.

A careful analysis showed that the compound identified in the previous study as phenazine-1-carboxylic acid was instead heme B. This result suggested that the relationship found in the previous study is actually between heme B and lung function (measured by ppFEV1), rather than with phenazines like phenazine-1-carboxylic acid.

To confirm this possibility, the team quantified the concentration of ferriprotoporphyrin IX/heme B in their MWCFC samples, and found a statistically significant correlation between sputum heme B levels and ppFEV1.

Taken together, the data show that the greater the heme B concentration, the lower the ppFEV1 is in CF patients, and a sign of worse lung function.

The presence of heme B in sputum samples, according to the researchers,  probably results from the presence of blood. In fact, “consistent with this assumption, hemoptysis, or coughing up blood, is observed in up to 60% of CF patients,” the researchers stated.

Overall, the team concluded that “given that hemoptysis is strongly associated with airway inflammation, pulmonary exacerbations, and impaired lung function, these new data suggest that heme B may be a useful biomarker of CF pathophysiology.”

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