ARA-290 (Cibinetide): Innate Repair Receptor Pharmacology and Research Findings

ARA-290 is an 11-residue linear peptide whose sequence reproduces the solvent-exposed surface of helix B of human erythropoietin. Brines and colleagues reported in 2008 that helix B spans residues 58 to 82 of the parent glycoprotein, that its aqueous face consists of the residues QEQLERAL, and that three further residues from the neighbouring BC loop complete the peptide.

The finished sequence is QEQLERALNSS. In the isolated molecule the N-terminal glutamine cyclizes spontaneously to pyroglutamate, which is why the same compound appears in the literature as pyroglutamate helix B surface peptide, abbreviated pHBSP, alongside the designations ARA 290 and cibinetide. PubChem records the molecule under CID 91810664 with CAS registry number 1208243-50-8 and UNII 9W5677JKDA.

Chemically the peptide is unremarkable except in its polarity. PubChem computes the formula C51H84N16O21, an average molecular weight of 1257.3 g/mol and a monoisotopic mass of 1256.5997 Da, with no net formal charge, 20 hydrogen-bond donors, 22 acceptors, 42 rotatable bonds and a topological polar surface area of 623 Ų. The computed XLogP of −7.7 places it far into the hydrophilic range, consistent with a short, unstructured, freely water-soluble sequence rather than a membrane-partitioning molecule.

ARA-290 engages a heteromeric receptor built from the erythropoietin receptor (EPOR) and CD131, the β-common receptor shared with the interleukin-3, interleukin-5 and GM-CSF receptor systems. Brines and colleagues named this complex the innate repair receptor and reported that it, rather than the EPOR homodimer, carries the tissue-protective arm of erythropoietin signalling.

The two receptor assemblies differ sharply in how readily they respond. Review literature describes the EPOR/CD131 heteromer as having much lower affinity for erythropoietin than the homodimeric receptor, so concentrations far above those needed for red cell production are required before the protective arm engages. The engineering logic behind ARA-290 follows from that asymmetry: a fragment that retains contact with the heteromer while losing the surface that assembles the homodimer separates the two activities.

Loss-of-function work supports that assignment rather than leaving it as inference. In a 2024 mouse middle cerebral artery occlusion study, intracerebroventricular small interfering RNA against the β-common receptor suppressed receptor expression by day one after surgery and significantly reduced the protection otherwise seen with ARA290. A 2026 sepsis-associated encephalopathy report found the same: β-common receptor knockdown abolished the effect of the peptide, as did the TLR9 agonist ODN1826, implicating a TLR9/MyD88/NF-κB branch downstream.

Localization data complement the genetic evidence. Wu and colleagues tracked iridium-labelled HBSP in 2023 and reported that it settled mainly in the tubular epithelia of mouse kidney 17 hours after ischaemia-reperfusion, and that it anchored to cultured mouse kidney epithelial cells exposed to hydrogen peroxide, where both EPOR and the EPOR/β-common receptor pair were significantly upregulated by the oxidative challenge.

ARA-290 does not stimulate red blood cell production in the systems where it has been measured. The 2008 report introducing the peptide stated that neither helix B nor the 11-residue fragment is erythropoietic in vitro or in vivo, a design goal rather than an incidental finding, since the homodimer-assembling surface of erythropoietin is absent.

Head-to-head rodent comparisons make the separation concrete. In the 2024 cerebral ischaemia work, red blood cell count, haemoglobin and haematocrit were unchanged in ARA290 groups relative to sham, while erythropoietin significantly raised all three (p < 0.05) and produced splenomegaly (p < 0.001). ARA290 caused no change in spleen weight or length in the same experiment.

Human study records point the same way. The 2013 sarcoidosis study reported no medically significant deviations in general blood chemistry or haematology, and the 2015 diabetes study reported no clinically significant changes from baseline in haematology or clinical chemistry at any sampling point. A 2021 mouse bone study likewise found haemoglobin unaffected by cibinetide while erythropoietin co-exposure retained its own erythropoietic response.

Cibinetide has been examined in several randomized placebo-controlled studies, most running 28 days and most built around a 4 mg daily regimen. Sarcoidosis-associated small nerve fibre loss was the setting for two of them, type 2 diabetes with neuropathic symptoms for a third, and diabetic macular oedema for a fourth, open-label pilot that returned a negative primary result.

Dahan and colleagues enrolled 38 adults with documented small nerve fibre loss in 2013, assigning 21 to ARA 290 and 17 to placebo for 28 days. Quantitative sensory testing separated the groups on cold pain threshold (p = 0.027), heat pain threshold (p = 0.032) and thermal sensory limen (p = 0.008). Six-minute walk distance rose 18.7 m in the peptide group against a 15.1 m decline on placebo (p = 0.049), and corneal confocal microscopy showed a median nerve fibre area increase of 14.5% over baseline, an absolute median gain of 185 µm² (p = 0.022), against a non-significant 5.3% decline on placebo.

Culver and colleagues ran the larger phase 2b follow-up in 64 participants, published in 2017, comparing 1, 4 and 8 mg per day against placebo over 28 days with corneal nerve fibre area as the primary endpoint. The 4 mg arm produced the clearest signal: a placebo-corrected mean change from baseline of 697 µm²/mm² at day 28, with a 95% confidence interval of 159 to 1236 (P = 0.012), together with an increase in regenerating fibres.

The 2015 type 2 diabetes study enrolled 49 adults and analysed 48 across a 28-day exposure plus a further month of observation. Glycated haemoglobin fell 0.16 ± 0.07 percentage points by day 28 and 0.21 ± 0.09 by day 56 in the peptide group, against a 0.21 ± 0.08 rise on placebo (p = 0.002). The cholesterol to HDL ratio (p = 0.039) and triglycerides (p = 0.043) separated as well. PainDetect scores improved 4.2 points by day 56 versus 0.74 on placebo (p = 0.037), and in the subgroup whose corneal nerve fibre density started more than one standard deviation below normal, density rose 2.6 ± 1.0 fibres/mm² against 0.7 ± 1.3 (p = 0.02).

The diabetic macular oedema study published in 2020 is the clearest null result in the set and is worth stating plainly. Nine adults with central retinal thickness above 400 µm entered a 12-week open-label protocol at 4 mg per day, and eight completed. Mean change in best-corrected visual acuity was −2.9 ± 5.0 letters, mean change in central retinal thickness was 10 ± 94.6 µm, and central retinal sensitivity moved −0.53 ± 1.9 dB. No participant gained 10 or more ETDRS letters. Three of nine eyes showed a thickness reduction beyond test-retest variability, and no serious adverse events or anti-peptide antibodies were recorded.

ARA-290 and its uncyclized counterpart HBSP recur through recent kidney, brain and peripheral nerve work, generally at 24 nmol/kg or 30 to 100 µg/kg in rodents and in the nanomolar to low microgram-per-millilitre range in culture. Recent readouts concentrate on inflammasome assembly, pyroptosis, macrophage polarization and apoptotic signalling rather than on any haematological endpoint.

Ghassemi-Barghi and colleagues reported the cell-line end of that range in 2023, exposing HEK-293 and ACHN cells to ARA290 at 50 to 400 nM ahead of 2.5 µM cisplatin. Comet-assay DNA damage parameters and micronucleus frequency both fell, malondialdehyde and reactive oxygen species declined while antioxidant enzyme levels rose, and gene and protein levels of TNF-α, IL-1β, IL-6, caspase-3 and Bax decreased while Bcl-2 increased relative to cisplatin alone.

Huang and colleagues published the kidney counterpart in 2024, giving 8 to 10 week old C57BL/6 mice 20 mg/kg lipopolysaccharide followed immediately by 24 nmol/kg HBSP. Flow cytometry at 24 hours showed F4/80+CD86+ M1 macrophages at 61.50 ± 2.63% after lipopolysaccharide alone against 30.43 ± 1.67% with the peptide, while F4/80+CD206+ M2 macrophages moved from 0.75 ± 0.09% to 1.60 ± 0.13%. Gasdermin-D N-terminal fragment, cleaved IL-1β and IL-18 all fell. Parallel TCMK-1 cultures used 5 µg/mL lipopolysaccharide with HBSP across 5 to 80 ng/mL.

Wang and colleagues examined 22 to 25 g male C57BL/6J mice after middle cerebral artery occlusion in 2024, comparing 30 µg/kg twice daily against 30 and 100 µg/kg once daily starting at reperfusion. The twice-daily schedule reduced infarct volume at seven days (p < 0.005) and brain tissue loss at 14 days (p < 0.05), lowered Longa and mNSS neurological scores across the 1 to 14 day window (p < 0.001), reduced TNF-α, IL-1β and IL-6 at day seven (p < 0.05), and lowered TUNEL-positive NeuN-labelled cell counts (p < 0.05).

Liu and colleagues moved the mechanism into peripheral nerve in 2025, using rat sciatic nerve crush injury. Both erythropoietin and ARA290 suppressed the early inflammatory response and supported functional restoration, and the reported route was inhibition of NLRP3 inflammasome activation inside Schwann cells through reduced NF-κB phosphorylation and lower reactive oxygen species production.

Two 2026 reports set boundaries on the picture. The sepsis-associated encephalopathy study combined a retrospective analysis of 150 adults with sepsis, where elevated serum erythropoietin was an independent risk factor for delirium, with septic rat work in which a lower amount of erythropoietin or HBSP raised β-common receptor and TLR9 expression and shifted microglia from M1 toward M2 polarization. Separately, a touchscreen operant study in male db/db mice found that ARA 290 improved insulin sensitivity and altered circulating monocyte proportions yet did not rescue the reversal-learning deficits that defined the model, a dissociation the authors state explicitly.

ARA-290 differs from erythropoietin in size, persistence and receptor selectivity. Erythropoietin is a 165-residue glycoprotein; ARA-290 is an 11-residue peptide reported to clear from rat and rabbit plasma with a half-life of roughly two minutes. Despite that brevity, the 2008 report measured protection of motoneurons against kainic acid at 1.8 nM peptide, against 3.3 nM for erythropoietin itself.

Whole-animal comparisons in the same 2008 work used single systemic exposures in the nanomole-per-kilogram range. A 1.5 nmol/kg exposure in a rat stroke model reduced infarct volume measured by tetrazolium salt staining 24 hours after reperfusion, with pHBSP giving 225 ± 20 mm³ against 291 ± 23 mm³ for saline, and a sciatic nerve crush model responded on a molar basis comparable to erythropoietin and to non-erythropoietic chemical derivatives of it.

Other laboratories have used far higher concentrations in cell-free and marrow-derived systems, so the working range is model-specific rather than fixed. A 2021 study of osteoclast formation cultured bone marrow-derived macrophages with M-CSF at 20 ng/mL and RANKL at 50 ng/mL alongside cibinetide at 3, 30, 150 and 300 µM, reporting suppression of TRAP-positive multinucleated cell formation without cytotoxicity by MTT assay, and downregulation of CTSK, OSCAR, OC-STAMP, DC-STAMP and NFATC1. In female C57BL/6J mice at 120 µg/kg three times weekly for four weeks, cortical tissue mineral density rose 5.8% and trabecular tissue mineral density 5.2% (both p < 0.05), with osteoprotegerin expression up 52.4% and RANKL unchanged.

Long-horizon rodent work sets a useful limit on interpretation. Fischer 344 × Brown Norway rats given 100 µg/kg three times weekly from 18 to 33 months of age scored significantly lower on an overall frailty index at 33 months (P < 0.001) and showed lower CD45, CD38 and Mac-1 staining areas in heart tissue, yet median lifespan and overall survival did not differ from saline controls (P = 0.182). Together with the null macular oedema result and the null cognitive-flexibility result, the record describes a molecule with a well-supported receptor mechanism and an outcome literature that remains uneven across model systems.

ARA-290 is supplied as a lyophilized powder, and its computed profile matches that presentation: a topological polar surface area of 623 Ų, 20 hydrogen-bond donors and an XLogP of −7.7 describe a strongly hydrophilic solid with no lipophilic character. Published methods sections reconstitute it in aqueous buffer, saline or culture medium rather than in organic solvent.

Working concentrations vary by an enormous factor across model systems, so the source protocol matters more than any single figure. Kidney and renal-carcinoma cell lines have been run at 50 to 400 nM, mouse kidney epithelial cultures at 5 to 80 ng/mL, and bone marrow-derived macrophage cultures at 3 to 300 µM. Rodent work clusters much lower on a molar basis, at 0.3 to 24 nmol/kg in the founding 2008 experiments and at 30 to 120 µg/kg in the 2021 to 2024 studies described above.

Identity confirmation follows ordinary peptide practice. Electrospray mass spectrometry is checked against a monoisotopic mass of 1256.5997 Da, which for the doubly protonated species falls near m/z 629.3, and purity is reported by reversed-phase HPLC on the lot certificate of analysis. One point deserves specific attention on this sequence: cyclization of the N-terminal glutamine to pyroglutamate releases ammonia and shifts the mass by about 17 Da, so an analytical method should distinguish the cyclized peptide from its uncyclized counterpart rather than reporting them together.

Lyophilized peptide is normally held frozen, protected from light and moisture, with reconstituted stocks aliquoted so that repeated freeze-thaw cycles are avoided. This material is offered for laboratory research use only. It is not a drug, not a food, and not intended for human or veterinary use.