ARA-290 (Cibinetide)

ARA-290, non-proprietary name cibinetide, is an 11-residue linear peptide whose sequence corresponds to a solvent-exposed region of the erythropoietin molecule rather than to the surface that binds the classical erythropoietin receptor homodimer. The PubChem entry lists C51H84N16O21, 1257.3 g/mol, consistent with the pyroglutamate-capped form [7]. It was engineered specifically to separate the tissue-protective actions attributed to erythropoietin from its haematopoietic action.

The innate repair receptor concept

Brines and colleagues reported in PNAS in 2008 that erythropoietin signals through two distinct entities: the EPO receptor homodimer, which drives red-cell production, and a heterocomplex of the EPO receptor with the common beta receptor CD131, which mediates tissue protection. That paper delimited the tissue-protective domain to short peptide sequences and described peptides based on them, ARA-290 among the derivatives of this work [1]. The heterocomplex is usually called the innate repair receptor. Because the peptide does not engage the homodimer, it is not expected to raise haemoglobin — the property that makes erythropoietin itself unattractive as a neuroprotective agent.

Sarcoidosis-associated small-fibre neuropathy

The most developed clinical dataset is in sarcoidosis patients with small-fibre neuropathy. Heij and colleagues published a randomised, double-blind pilot study in Molecular Medicine in 2012 with 22 patients, comparing four weeks of intravenous dosing three times weekly against placebo and reporting a reduction in the small-fibre neuropathy screening list score in the treated group [2]. Dahan and colleagues followed with a phase 2 randomised controlled trial in 36 patients with confirmed small-fibre neuropathy, reported in Molecular Medicine in 2013, which described changes in cold and heat pain thresholds, exercise capacity and an increase in corneal small-nerve-fibre density measured by corneal confocal microscopy after 28 days of daily subcutaneous dosing [3]. A further report in Investigative Ophthalmology & Visual Science in 2017 examined corneal nerve fibre abundance in this population in more detail [4], and a separate registered study of corneal nerve fibre density and neuropathic symptoms in sarcoidosis is listed on ClinicalTrials.gov [6].

Why small-fibre neuropathy was chosen as the test case

The choice of indication is itself informative about how the compound is studied. Small unmyelinated C and A-delta fibres are the population most readily quantified without biopsy, because corneal confocal microscopy images the sub-basal nerve plexus directly and yields a numerical fibre density. That gives a repeatable structural readout over a four-week study in a small cohort, which a trial powered on pain scores alone could not provide. The same reasoning connects the sarcoidosis and diabetes programmes: both are conditions in which small-fibre loss is common, both allow the same imaging endpoint, and both permit within-subject comparison against baseline. The trade-off is that a structural change in the cornea is a proxy, and its relationship to symptom burden or to function elsewhere in the body is an assumption rather than a demonstrated link [3][4].

Type 2 diabetes phase 2

A phase 2 double-blind placebo-controlled trial reported by Brines and colleagues in Molecular Medicine in 2015 studied 28 days of daily self-administered subcutaneous dosing in patients with type 2 diabetes. The published results describe differences in HbA1c, in the PainDetect neuropathic symptom score, in the cholesterol-to-HDL ratio and in triglycerides, together with an increase in corneal nerve fibre density in the treated arm, with no safety signals identified in that trial [5]. Sample size and duration were both small, and these are exploratory endpoints.

What the research does not establish

All of the human data come from small phase 2 studies of roughly one month, largely from a small number of related investigator groups, and use surrogate endpoints — corneal nerve fibre density, symptom questionnaires, thermal thresholds — rather than hard clinical outcomes. No phase 3 programme has reported, and cibinetide is not approved by the FDA or the EMA for any indication. There is no controlled evidence for use in healthy individuals, in exercise recovery, in chronic pain of other aetiologies, or in autoimmune conditions generally, and the durability of any effect after dosing stops has not been established. Claims that the peptide lacks any effect on erythropoiesis rest on the receptor-selectivity model and on short trials rather than on long-term human haematology data.

Format. Supplied as a lyophilised powder in a sealed vial. Net peptide content and purity are stated on the certificate of analysis; vial mass includes counter-ion and residual water.

Reconstitution. This short, acidic peptide dissolves readily in aqueous diluent. Add the diluent slowly down the wall of the vial and swirl gently until the solution is clear; avoid vigorous shaking. Diluent volumes for a target working concentration can be calculated with the reconstitution calculator.

Storage. Keep the sealed lyophilised vial at −20°C, protected from light and moisture, and allow it to reach room temperature before opening to prevent condensation. Refrigerate reconstituted material and dispense single-use aliquots rather than repeatedly freezing and thawing a single stock.

Handling. Work aseptically, use a fresh needle for each withdrawal, and label aliquots with lot number and reconstitution date. For in-vitro laboratory research only — not for human or veterinary use.