CJC-1295 With DAC vs Without DAC: What DAC Means

DAC stands for drug affinity complex: a reactive group attached to CJC-1295 that forms a covalent bond with serum albumin once the peptide is in circulation. Adding it changes the peptide’s behaviour completely. Without DAC, the modified GHRH(1-29) core acts briefly. With DAC, it rides on albumin, with an estimated half-life of 5.8–8.1 days in healthy adults (Teichman et al., 2006).

For laboratory research use only. The compounds discussed are not approved for human or veterinary use and are not drugs, foods or cosmetics. This article summarises published research and is not medical advice.

Key points

Same modified GHRH(1-29) core; the difference is the albumin-binding DAC group.
With DAC: sustained GH and IGF-I elevation; half-life about a week.
Without DAC (Mod GRF 1-29): short-acting, pulse-like GH responses.
Pulsatile GH secretion persisted even with the DAC form.
MS distinguishes the forms easily (~280 Da difference).

Side-by-side

	Without DAC	With DAC
Other names	Mod GRF 1-29, tetrasubstituted GRF(1-29)	CJC-1295 DAC
Molecular weight	~3367.9 g/mol	~3647.2 g/mol
Albumin binding	No	Covalent, via maleimide–cysteine reaction
Half-life	Short	5.8–8.1 days
GH response profile	Brief rise after each exposure	Sustained rise in trough GH for days
IGF-I response	Modest, transient	1.5- to 3-fold for 9–11 days after one dose
Research use	Modelling pulsatile stimulation; combination with GH secretagogues	Modelling continuous GHRH receptor stimulation

Our CJC-1295 without DAC and CJC-1295 with DAC are listed separately, each with MS confirmation of the form.

How DAC works

The DAC group contains a maleimide, which reacts selectively with free thiol groups. Human serum albumin has one free cysteine (Cys34), so after administration the peptide becomes covalently linked to albumin. Albumin circulates for weeks and is too large for renal filtration, so the attached peptide is protected from clearance and many proteases. The GHRH portion remains free to activate pituitary receptors. A study describing CJC-1295 with DAC states that it binds permanently to endogenous albumin after injection, with a half-life of about 8 days (Ionescu et al., 2006).

Effects on GH secretion patterns

A concern with long-acting GHRH analogues is that constant stimulation might flatten the natural pulsatile pattern of GH release. Ionescu and colleagues tested this directly with overnight sampling every 20 minutes. One week after a single dose of CJC-1295 with DAC, GH pulse frequency and magnitude were unchanged, while trough GH increased 7.5-fold. Mean GH rose 46% and IGF-I 45% (Ionescu et al., 2006). The DAC form therefore raises the baseline GH level while pulses continue.

The no-DAC form behaves differently: each exposure produces a short-lived GH response, more like native GHRH. That is why it is often studied alongside short-acting GH secretagogues such as ipamorelin, which itself has a terminal half-life of about 2 hours in humans (Gobburu et al., 1999). See CJC-1295 + ipamorelin.

Analytical distinction

Because the names are used loosely by suppliers, identity testing matters. The two forms differ by roughly 280 Da, easily resolved by MS. An anti-doping study characterised in vitro metabolites of both forms (as well as sermorelin and tesamorelin) and developed an LC-MS/MS method with detection limits at or below 1 ng/mL (Memdouh et al., 2021). In solution before administration, the DAC maleimide is reactive. Avoid thiol-containing buffers or additives (DTT, cysteine, mercaptoethanol), which can consume the reactive group.

Handling in the lab

Both forms: lyophilized powder, −20 °C, sealed and dark.
Reconstitute with bacteriostatic or sterile water; swirl gently (method).
DAC form: avoid thiol-containing solutions; use promptly after reconstitution.
Concentrations: peptide reconstitution calculator.

Choosing between the forms for an experiment

The choice follows from the question. To mimic the natural, episodic release of GHRH, or to pair GHRH-receptor stimulation with a short-acting GH secretagogue, the no-DAC form fits better. To study what happens when the GHRH receptor is stimulated continuously for days, including effects on trough GH and IGF-I, the DAC form is the relevant tool.

Open questions

How stable is the DAC maleimide group in reconstituted research solutions over days at 2–8 °C? Hydrolysis of maleimides in water is known in general chemistry, but no peptide-specific data have been published.
What are the human pharmacokinetics of the no-DAC form? Most clinical data cover the DAC form.

Related research

Frequently asked questions

What does DAC mean in peptides?

DAC stands for ‘drug affinity complex’. It is a reactive chemical group, attached through a lysine linker, that forms a covalent bond with a cysteine on serum albumin after administration. The peptide then circulates attached to albumin.

What is the difference between CJC-1295 with DAC and without DAC?

Both share the same modified GHRH(1-29) core. Without DAC, the peptide is short-acting and produces brief GH responses. With DAC, it binds albumin and has an estimated half-life of 5.8–8.1 days, producing a sustained rise in GH and IGF-I.

Is Mod GRF 1-29 CJC-1295 with or without DAC?

Mod GRF 1-29 is CJC-1295 without DAC.

Which is better, CJC-1295 with or without DAC?

Neither is better in general; they answer different research questions. The DAC form models sustained GHRH receptor stimulation; the no-DAC form models short pulses closer to native GHRH.

How can you tell the two apart?

By mass spectrometry. The no-DAC form is about 3368 g/mol and the DAC form about 3647 g/mol, a difference of roughly 280 Da.

References

Teichman SL, et al. Prolonged stimulation of growth hormone (GH) and insulin-like growth factor I secretion by CJC-1295, a long-acting analog of GH-releasing hormone, in healthy adults. J Clin Endocrinol Metab. 2006. PMID: 16352683 https://pubmed.ncbi.nlm.nih.gov/16352683/
Ionescu M, et al. Pulsatile secretion of growth hormone (GH) persists during continuous stimulation by CJC-1295, a long-acting GH-releasing hormone analog. J Clin Endocrinol Metab. 2006. PMID: 17018654 https://pubmed.ncbi.nlm.nih.gov/17018654/
Memdouh S, et al. Advances in the detection of growth hormone releasing hormone synthetic analogs. Drug Test Anal. 2021. PMID: 34665524 https://pubmed.ncbi.nlm.nih.gov/34665524/
PubChem Compound Summary for CID 91971820, CJC-1295. National Center for Biotechnology Information. https://pubchem.ncbi.nlm.nih.gov/compound/91971820
Gobburu JV, et al. Pharmacokinetic-pharmacodynamic modeling of ipamorelin, a growth hormone releasing peptide, in human volunteers. Pharm Res. 1999. PMID: 10496658 https://pubmed.ncbi.nlm.nih.gov/10496658/