Natural Fat-like Molecules Treat Established Lung Fibrosis in Mice

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by Steve Bryson, PhD |

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Lab-made versions of naturally occurring forms of nitro oleic acid effectively treated established pulmonary fibrosis (PF) in a mouse model, a study reports.

These findings support the further development of these agents for reversing fibrosis, or tissue scarring, in the lungs and other organs, its scientists noted.

The study, “Fatty acid nitroalkene reversal of established lung fibrosis,” was published in the journal Redox Biology.

PF is characterized by progressive scarring — or fibrosis — of the lungs, leading to shortness of breath. Although approved treatments slow this process, there are no therapies capable of halting or reversing fibrosis.

Nitro oleic acids (NO2-OAs), also known as nitroalkenes, are naturally occurring fat-like molecules found in humans and animals, as well as in plant-derived oils. Lab-made analogs of two NO2-OAs — called 9- and 10-nitro-octadec-9(E)-enoic acid —have been shown to limit fibrotic responses in multiple animal models.

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Studies have successfully tested these NO2-OAs during the development of fibrotic diseases, but no models have investigated whether these molecules can reverse established fibrosis in lung tissues.

Researchers at the University of Pittsburgh induced PF in a group of healthy mice, and then treated diseased lung tissues with these NO2-OAs to evaluate their impact on established fibrosis.

Mice were exposed to bleomycin to induce PF or to a saline solution as controls. After 14 days, they were euthanized and their lung tissues examined. Researchers then treated precision-cut lung slices with a 1-to-1 mixture of 9- and 10-NO2-OA or a control solution for four days before the analysis.

Results revealed that bleomycin-induced injury led to a 130% increase in the levels of the fibrotic marker hydroxyproline, which rose from 12.24 to 28.14 g/mg of dry tissue. Four days of NO2-OA treatment significantly decreased hydroxyproline content from 28.14 to 15.48 g/mg, “returning PCLS [lung-slice] hydroxyproline levels close to those measured” in slices from control mice without PF, the researchers wrote.

The underlying process of fibrosis is the excessive buildup of collagen and other components of the extracellular matrix (ECM) — the network of molecules surrounding and supporting cells. NO2-OA treatment stopped the buildup of this matrix as driven by bleomycin, and it promoted collagen degradation.

Cells that line the tiny air sacs in the lungs, called AT1 and AT2 cells, are particularly vulnerable to fibrosis. NO2-OA treatment induced a mean increase in both AT1 and AT2 cell populations in healthy tissue, but not to a statistically significant extent.

In contrast, NO2-OA significantly increased the growth of both AT1 (by 88%) and AT2 cells (by 212%) in lung samples from PF mice. Consistently, NO2-OA also significantly suppressed the appearance of a pro-fibrotic cell population of myofibroblasts.

“The observation that NO2-OA restores both AT1 and AT2 cell numbers following bleomycin-induced loss lays the first pillar of fibrosis resolution,” the researchers noted.

In bleomycin-injured lung tissue, NO2-OA treatment also induced the expression, or activity, of the Pparg gene, which is known to limit fibrosis by suppressing pro-fibrotic and pro-inflammatory pathways.

As a result, NO2-OA significantly blocked the expression of multiple pro-fibrotic markers, including the key ECM proteins collagen-1a1, collagen-3a1, fibronectin-1, and connective tissue growth factor.

NO2-OA also suppressed the production of the pro-inflammatory signaling protein TNF-alpha, and lowered the release of pro-fibrotic interleukin-13 and MCP-1.

“NO2-OA significantly limited indices of established fibrosis within 4 days of ex vivo PCLS culture,” meaning a lab culture of sliced lung tissue, the researchers wrote. “Thus, small molecule nitroalkenes may be useful agents for reversing pathogenic [disease-related] fibrosis of lung and other organs.”