Angiogenesis & cytoprotection

What actually decides this outcome, in order of size

The pathway's premise is that blood supply is the rate-limiting step in tendon repair. It is a serious hypothesis, and 3 of the 4 things that sit above it are not molecules.

1. Mechanical load, the only variable with randomized evidence in this tissue, over 12 weeks. In 58 patients with chronic midportion Achilles tendinopathy, twelve weeks of heavy slow resistance and twelve weeks of eccentric training both produced significant improvement (P<.0001), and the heavy slow resistance arm differed mainly in adherence, 92% against 78% (P<.005) Beyer 2015. Tendon cells respond to strain by upregulating collagen synthesis through the prolyl hydroxylase step; that is the signal the tissue is built to answer.
2. Which tissue this actually is. Muscle is richly vascular and heals in 2 to 6 weeks. Tendon midsubstance is hypovascular and heals over 3 to 12 months. Ligament sits between them, and cartilage does not heal at all. Applying a tendon strategy to a muscle strain buys nothing, because the muscle was never blood-limited.
3. Whether the problem is inflammation or degeneration, which the histology answers. Chronic tendinopathy is not tendinitis: histology shows disorganized collagen, increased ground substance and a scarcity of inflammatory cells. That changes what an anti-inflammatory is for, and it is the reason Inflammation resolution (not suppression) is a separate pathway.
4. A tension inside the premise, stated as a tension rather than as a finding. Chronic tendinopathy already shows neovascularization, and the new vessels arrive accompanied by nerve ingrowth, which is one of the leading explanations for why a degenerative tendon hurts. Treatments have been trialed that ablate those vessels rather than adding to them. So driving further angiogenesis into a tendon that is already neovascularized is an extrapolation from acute wound healing, and it is not what the chronic histology obviously predicts. That is a reason to test the idea, not a reason to dismiss it, and it should be read as an open question rather than as evidence.
5. Metabolic background, which changes the ceiling over decades of glycation. Glycation of long-lived collagen cross-links stiffens tendon and impairs repair, and diabetes is an established risk factor for tendinopathy and for rupture. HbA1c (Hemoglobin A1c) is a tendon test that nobody thinks of as one.

The order to run these in, and what has to be true first

Load first, because it is the only step with randomized support in this tissue, then the compounds in order of how much human data each one has for anything.

1. Get the loading program right and give it 12 weeks. Both protocols in the trial worked and the difference between them was adherence Beyer 2015, which means the practical question is which one gets done rather than which one is theoretically superior. Nothing below has been shown to substitute for those 12 weeks.
2. BPC-157 (inj/oral) is the pathway's lead compound, and 0 randomized human tendon trials is the thing to be clear about. It is a stable gastric pentadecapeptide with a broad preclinical record across tendon, muscle, nerve and gastrointestinal tissue, including effects on the nitric oxide system and on VEGF-driven vessel formation Staresinic 2022. That record is almost entirely rodent, across studies running 7 to 21 days. There is no published randomized controlled trial in human tendinopathy, and the honest description is a strong mechanistic case with no clinical end point behind it.
3. TB-500 and Wolverine Blend share that position, one of them as a blend that cannot be titrated. Thymosin beta-4 is an actin-sequestering peptide with cell-migration and angiogenic effects in models; the blend is a combination product, which means it cannot be titrated and a response cannot be attributed to a component.
4. GHK-Cu (inj/oral) has the best-characterized molecular biology on the list, modulating gene transcription, and the least relevant end points. The copper tripeptide modulates a large number of genes in the direction of repair and remodeling Pickart 2018, and the human work sits in skin rather than in tendon. Collagen synthesis & dermal matrix is where its own evidence lives.
5. Actovegin and ARA-290 each have 1 real randomized trial, in a different condition. Actovegin's largest controlled trial is in post-stroke cognitive outcome Guekht 2017; ARA 290 is a non-erythropoietic peptide derived from erythropoietin acting at the innate repair receptor, with a randomized trial in sarcoidosis-associated small-fiber neuropathy Brines 2015. Both are evidence that the molecule does something in a person, and neither is evidence about a tendon.
6. Pentosan Polysulfate carries a specific and permanent risk after years of exposure. Long-term exposure is associated with a pigmentary maculopathy in a US cohort study Jain 2020, which is a retinal outcome rather than a nuisance side effect, and it belongs in the decision before the mechanism does.
7. GLP-2 is on the wrong page for most readers, because its receptor is in the small intestine. It is intestinotrophic, acting on the crypt compartment of the small intestine, which makes it a Gut lining & mucosal repair compound listed here because its mechanism is cytoprotective rather than because a tendon will notice it.

What gets bought for this that cannot move it

Platelet-rich plasma is the cautionary trial for this entire premise. It was the most plausible way to deliver growth factors directly into a hypovascular tendon, and in 54 randomized patients the VISA-A score improved 21.7 points (95% CI 13.0 to 30.5) with PRP against 20.5 points (11.6 to 29.4) with saline at 24 weeks, a difference that was not significant de Vos 2010. Both arms did an eccentric program for 24 weeks. The program worked and the injection added nothing measurable.

Passive treatment is the category that fails structurally here, because strain is the input the cell transduces. Anything that asks a tendon to remodel without giving it a mechanical signal is missing the input the tissue actually uses. That is the common feature of the injections, the modalities and most of the shelf, and it is why the loading program is step one rather than an adjunct.

Injecting or dosing to get back to sport 6 weeks sooner is the specific harm. A tendon that feels better under a molecule is not a tendon that has remodeled, and the interval between symptom resolution and mechanical competence is where ruptures happen. Pain is a poor proxy for tensile strength in this tissue, and an actively misleading one across the 12 weeks of treatment.

And if the injury is a muscle tear or a bone, this is the wrong page by months. Muscle has its own blood supply and its own satellite cell population and heals on a different clock, which is Satellite cells & local repair. Bone regenerates rather than scars and has drugs with fracture end points, which is Bone & fracture healing. The substrate half of tendon repair, which is the part with a genuinely evidence-based timing trick, is Collagen & matrix synthesis.

How you would know it was working, on a real read-out and a real timescale

Tendon has no blood marker, so the honest read-out is functional with a small blood panel behind it. The prediction this page makes is the one nobody has tested: if angiogenesis is the rate-limiting step, a compound acting on it should shorten time to load tolerance relative to the same loading program alone. That trial does not exist, and until it does everything here is a mechanism rather than a result.

• Load tolerance, measured the same way at 0, 6 and 12 weeks. Single-leg heel raises to failure for an Achilles, pain during and 24 hours after a standardized loading test, and the VISA-A questionnaire, which is the instrument both randomized trials above used Beyer 2015 de Vos 2010. Expect meaningful change over 12 weeks, not 3.
• HbA1c (Hemoglobin A1c) once, because it changes the prognosis for the next 12 months. Glycation of tendon collagen is cumulative and impairs remodeling, so a raised HbA1c reframes a slow-healing tendon as a metabolic finding rather than a stubborn one.
• hs-CRP (High-Sensitivity C-Reactive Protein) once, expected normal. Chronic tendinopathy is not an inflammatory disease, so a raised CRP with tendon pain at multiple sites points toward a spondyloarthropathy or another systemic process, and that is a diagnosis rather than a loading problem.
• Vitamin D (25-Hydroxy) and Ferritin once each, and both are correctable inside 12 weeks. Both are on this list for the same reason: they are common, cheap, correctable, and each one produces a plausible reason for a repair process to be running slowly.
• Comprehensive Metabolic Panel (CMP) if a peptide is being used for 3 months or more. The compounds on this page have no human safety database of the kind that would make a baseline unnecessary, and a baseline is only useful if it was drawn before rather than after.

What will fool you. Tendinopathy fluctuates over 4 to 8 weeks and regresses toward the mean after a flare, so anything started at the worst point will look effective. Both arms of a good trial improve by twenty points de Vos 2010, which is what an untreated loading program does on its own. And a tendon that has stopped hurting under an analgesic effect is a tendon whose loading has just been un-limited without its structure having changed.

Sources read for these sections

• Beyer R. Heavy Slow Resistance Versus Eccentric Training as Treatment for Achilles Tendinopathy: A Randomized Controlled Trial. American Journal of Sports Medicine 2015;43(7):1704-11 · PMID 26018970
• de Vos RJ. Platelet-rich plasma injection for chronic Achilles tendinopathy: a randomized controlled trial. JAMA 2010;303(2):144-9 · PMID 20068208
• Staresinic M, et al. Stable Gastric Pentadecapeptide BPC 157 and Striated, Smooth, and Heart Muscle. Biomedicines 2022 · PMID 36551977
• Brines M, et al. ARA 290, a nonerythropoietic peptide engineered from erythropoietin, improves metabolic control and neuropathic symptoms in patients with type 2 diabetes. Molecular Medicine 2015 · PMID 25387363
• Pickart L, et al. Regenerative and Protective Actions of the GHK-Cu Peptide in the Light of the New Gene Data. International Journal of Molecular Sciences 2018 · PMID 29986520
• Guekht A, Skoog I, Edmundson S, Zakharov V, Korczyn AD. ARTEMIDA Trial (A Randomized Trial of Efficacy, 12 Months International Double-Blind Actovegin): A Randomized Controlled Trial to Assess the Efficacy of Actovegin in Poststroke Cognitive Impairment. Stroke 2017;48(5):1262-1270 · PMID 28432265
• Jain N. Association of macular disease with long-term use of pentosan polysulfate sodium: findings from a US cohort.. Br J Ophthalmol 2020 · PMID 31694837