Patients with scleroderma and pulmonary arterial hypertension (PAH) have increased levels of two serum proteins, midkine (MDK) and follistatin-like 3 (FSTL3), according to a new study. The finding indicates that combined measurement of these biomarkers could quicken diagnosis.
The research, “Serum biomarker for diagnostic evaluation of pulmonary arterial hypertension in systemic sclerosis,” was published in the journal Arthritis Research and Therapy.
Current estimates indicate that scleroderma-associated PAH (SSc-PAH) affects 12 percent of scleroderma patients. The diagnosis of PAH is currently done through right heart catheterization (RHC), an invasive technique not suitable for routine screening.
Because patients with SSc-PAH have shown better outcomes when diagnosed and treated earlier with PAH medications, identifying a diagnostic biomarker could increase survival, as well as provide an additional screening option and potentially lower the need for RHC, researchers say.
A cardiac assessment called transthoracic echocardiography is the most commonly accepted screening strategy to diagnose SSc-PAH. PAH biomarkers such as brain natriuretic peptide (BNP) and a fragment of pro-BNP (NT-proBNP), both produced in response to changes in pressure inside the heart, have similar diagnostic accuracy as an echocardiogram.
Levels of these markers correlate with blood flow measurements and predict disease prognosis in PAH patients. However, they lack sensitivity for SSc-PAH. Other biomarkers — such as the pro-inflammatory molecules interleukin-1 and TNF-alpha — have been evaluated and shown promise in preliminary studies, but these findings still need to be replicated.
As prior research showed specific gene expression patterns related to PAH development, the team hypothesized that a proteomic (a large-scale study of proteins) serum analysis would identify a diagnostic biomarker of SSc-PAH.
Their study included 13 untreated SSc-PAH patients (mean age 65 years), whose diagnosis was made by RHC. Sixteen patients with scleroderma, but not PAH (mean age 50 years), were enrolled as controls. Both patients and controls had limited localized scleroderma, and had serum samples collected at the time of diagnosis at Boston University. A total of 1,129 proteins were analyzed simultaneously.
The results showed that 82 proteins had altered levels (32 increased, 50 decreased) in SSc-PAH patients compared to the controls. Then, scientists found that 16 of these proteins had been reported previously as having changed levels (in publicly available data) of skin and lung tissue of SSc-PAH patients, including immune markers and proteins related to the extracellular matrix, which provides structural and biochemical support to cells.
When further examining which of the proteins with elevated levels could be used to discriminate between SSc-PAH and scleroderma only, the growth factor MDK — previously implicated in hypertension, kidney disease, and pulmonary fibrosis — and FSTL3, which acts on cardiac muscle cells, showed high specificity and sensitivity.
As they did not correlate with each other or with BNP, the researchers suggested that “in combination these proteins would give additional information to the currently measured BNP.”
The team tested the diagnostic accuracy of the two proteins in two independent groups of patients, with 34 SSc-PAH patients and 30 control participants. Consistent increases in FSTL3 and MDK protein concentrations in SSc-PAH patients were seen compared to those with scleroderma only.
“In sum, we demonstrated that the combination of FSTL3 and MDK are highly associated with [localized SSc-PAH],” the investigators wrote. They also said that the validation in patients receiving PAH treatments “suggests that this is a robust diagnostic biomarker.”
“These results suggest that serum assays in patients with PAH could be dramatically improved with identification of these serum biomarkers and, thus, aid in the earlier diagnosis of SSc-PAH,” the team concluded.