A metabolic brake on the scleroderma fibroblast

Design

In vitro study in human fibroblasts with an in vivo bleomycin mouse model

Population

TGF-beta-stimulated healthy and systemic sclerosis skin fibroblasts; bleomycin-treated mice

Primary outcome

Myofibroblast differentiation, profibrotic gene and matrix expression, dermal thickness and collagen

Effect

II559 suppressed myofibroblast differentiation and matrix secretion; reduced dermal thickening and collagen in mice with preserved dermal white adipose tissue

Skin fibrosis in systemic sclerosis is the part of the disease we treat worst. Immunosuppression helps some patients somewhat; nothing reliably reverses established dermal thickening. This work targets the fibroblast's metabolism rather than the immune system upstream of it.

Nicotinamide N-methyltransferase (NNMT) sits at the junction of NAD metabolism and cellular methylation. The bisubstrate inhibitor II559 suppressed TGF-beta-induced myofibroblast differentiation in healthy fibroblasts and reduced constitutive profibrotic gene expression and matrix secretion in fibroblasts taken from patients with SSc. The proposed mechanism is coherent: NNMT inhibition lowered 1-methylnicotinamide, restored methylation potential and increased repressive H3K27me3 marks. In bleomycin-treated mice it reduced dermal thickening and collagen while preserving dermal white adipose tissue, which is lost in scleroderma and in most fibrosis models.

This is research-stage. There is no NNMT inhibitor in clinical use and none near it, and the bleomycin mouse has flattered a long list of compounds that failed in patients. What makes it worth a rheumatology-facing dermatologist's attention is the target class: a small-molecule metabolic intervention acting directly on the fibroblast would sit alongside immunosuppression rather than competing with it.

• Nothing to prescribe — there is no NNMT inhibitor available.
• Keep screening SSc patients for interstitial lung disease and pulmonary hypertension, where treatment does exist.
• Record modified Rodnan skin score consistently; it is still how fibrosis progression is judged.
• Do not offer nicotinamide or NAD supplements on the basis of this — the intervention is inhibition of a methyltransferase, not a vitamin.

Why it matters

It puts a metabolic, fibroblast-directed lever in a disease where we mostly aim at the immune system.

Don't overread it

Cell and mouse work only; no human has received this compound.

The statistics, in plain English

No effect size is reported in patients because no patient was treated. The readouts are gene expression, matrix secretion and dermal thickness in cells and mice. The reason to be cautious about the mouse result specifically is that bleomycin-induced fibrosis is an inducible, largely reversible model, whereas human systemic sclerosis is chronic and self-sustaining — preventing fibrosis in the model is much easier than reversing it in a patient.

Read the rest in the app

You have read your two free briefings this month. The app carries all 27 specialties, every morning, free — and this finding is waiting in it.

Get Daily Doctor — free

Scan to keep reading on your phone. No account needed to start.