IGF-1 DES

Des(1-3)IGF-I is human IGF-1 without its first three residues, Gly-Pro-Glu. It was not invented so much as found: it has been isolated from bovine colostrum, human brain and porcine uterus, and appears to be a post-translational product of IGF-1 rather than a separate gene product [1]. An acid protease present in serum will make it from intact IGF-1 in the test tube, working best around pH 5.5 and acting only on free IGF-1, not on the binding-protein complexes [2]. The practical reading is that the acidic microenvironment around damaged or metabolically active tissue may generate it locally.

Why it is more potent. The glutamate at position 3 is one of the contacts the IGF binding proteins need. Without it, the molecule is roughly ten times more potent than IGF-1 at driving hypertrophy and proliferation in cultured cells [1], and none of the binding-protein forms secreted by one human colon carcinoma line would bind it at all, while its affinity at the IGF-1 receptor was identical to IGF-1's [6]. The potency is availability, not receptor affinity.

What it does in animals. The rodent work is more coherent than for most peptides in this group, and it is about catabolism rather than muscle building. In rats after removal of 80% of the small bowel, seven days of infusion at 0.96 mg/kg/day produced 20.8 g of weight gain over the last three days against 14.0 g on vehicle, and nitrogen balance of 217 against 153 mg/day [5]. In rats with subtotal nephrectomy, 0.9 mg/kg/day improved weight gain and nitrogen balance, with reduced 3-methylhistidine excretion pointing to slower muscle protein breakdown — an effect the authors singled out as particularly clear for the truncated analogue [4]. In growth-hormone-deficient lit/lit mice, 3 µg/day of des(1-3) raised kidney and heart weights where the same dose of IGF-1 did nothing, confirming that the cell-culture potency advantage carries over into a living animal [7].

Human evidence. None. The 1996 review that summarised the field said clinical opportunities had not yet been evaluated but could apply in catabolic states and inflammatory bowel disease [1]; three decades later, no trial has been published. A 2026 review of the peptides people self-administer against the GH–IGF-1 axis puts it in the same category as the rest — used far ahead of the evidence [8]. The only human-facing literature is antidoping: it is a prohibited substance, sold on the black market for bodybuilding, and a validated serum assay detects it [9].

IGF-1 circulates almost entirely bound — mostly in 150 kDa ternary complexes with IGFBP-3 and the acid-labile subunit — and it is the small free fraction that reaches the IGF-1 receptor and drives PI3K/Akt and MAPK signalling [10]. Truncating the N terminus removes the binding-protein contact and leaves the receptor contact intact [6].

The consequence, measured directly in rats, is a molecule that behaves quite differently in the body from IGF-1. Labelled des(1-3)IGF-I stayed almost entirely free in plasma, was cleared about four times faster, had a steady-state volume of distribution of 461 ml/kg against 167 for IGF-I, and appeared in adrenals, brain, skin, stomach and gut in greater amounts than IGF-I did. The authors' inference was that the binding proteins act as a brake on delivery to tissue, and that analogues cleared quickly from blood may be more potent in vivo, not less [3].

That is a real mechanistic insight, and it is also the reason the pharmacology is awkward. The same property that gets it into tissue gets it out of the circulation, so a bolus injection is a brief, intense, poorly buffered IGF-1 signal rather than the sustained one an infusion gives — and every efficacy result in the literature came from a week-long minipump infusion [4][5].

The molecule is the 67 C-terminal residues of human IGF-1, with the same three disulfide bridges. It has been produced recombinantly in Chinese hamster ovary cells, purified to homogeneity and shown to retain the biological potency of authentic des(1-3)IGF-I [11]; commercial research material is generally made in E. coli.

It is not orally usable in any form that has been demonstrated, and the whole published efficacy literature used continuous subcutaneous infusion. Because it does not bind IGFBP-3, it also does not form the long-lived ternary complex that keeps injected IGF-1 in circulation — there is no depot effect to fall back on [3].

No human safety data exist. Three things in the animal and epidemiological record are worth stating plainly.

The tumour signal. Transgenic mice engineered to overexpress des(1-3)hIGF-I in mammary tissue developed hyperplastic mammary lesions and, by 23 months, mammary adenocarcinomas in 53% of animals — two to three times the rate in non-transgenic controls. Crossing them with a mutant p53 line did not raise incidence further but cut tumour latency by eight months [13]. Lifelong tissue-specific overexpression in a transgenic mouse is a long way from intermittent injection in a person, and it should not be read as a measured risk. It is, however, the most direct experiment anyone has done on what sustained des(1-3)IGF-I signalling does to a tissue, and the answer was tumours.

That sits alongside the epidemiology of IGF-1 itself: higher circulating IGF-1 is associated with modestly raised risk of prostate and premenopausal breast cancer [14], with an odds ratio of 1.29 for prostate cancer between the top and bottom fifth in a pooled analysis of individual data from 19 studies [15]. In one cancer cell line des(1-3)IGF-I actually pushed cells toward differentiation and slightly inhibited proliferation [6], so the cell-level picture is not uniform.

Hypoglycaemia. IGF-1 receptor activation lowers blood glucose, and hypoglycaemia is the dose-limiting adverse effect of licensed recombinant IGF-1: 80 of 306 children in the European Increlex registry had at least one event, 0.11 events per patient per treatment year [16][17]. A fragment that the binding proteins cannot buffer delivers that signal with less restraint.

Product quality. There is no pharmaceutical supply. Antidoping analysis of black-market IGF-1 analogue material found abundant oxidised and lower-quality peptide forms [9].

No human interaction data exist. Mechanistically the concern is additive IGF-1 receptor activity: insulin, recombinant IGF-1 and anything that raises endogenous IGF-1 all push in the same direction as des(1-3)IGF-I on blood glucose, and hypoglycaemia is the documented dose-limiting effect of IGF-1 in people [16].

One laboratory observation is worth carrying: IGFBP-3 inhibits Des(1-3)IGF-I-induced receptor phosphorylation in cells over the same concentration range as it inhibits IGF-I, by sequestration [18]. The escape from the binding proteins is large but not absolute.