Mod GRF 1-29 vs CJC-1295 DAC – Comparison in terms of Structure, Stability, and GH Stimulation

Mod GRF 1-29 and CJC-1295 DAC are synthetic research peptides investigated for their potential interactions with the growth hormone-releasing hormone (GHRH) receptors in pituitary cells and possibly stimulating growth hormone (GH) release. These two peptides have identical peptide structures based on the truncated version of endogenous GHRH, but one major difference is the attachment of the DAC (Drug Affinity Complex) to CJC-1295.

This key modification may allow CJC-1295 DAC to resist breakdown and possess a considerably more extended half-life and prolonged receptor action compared to Mod GRF. Below, we compare the two across their shared architecture, their stability, signaling route, and the secretion patterns reported in mammalian research models.

 

What Does Research Show About Mod GRF 1-29 vs CJC-1295 DAC?

How Do Mod GRF 1-29 and CJC-1295 DAC Compare in Molecular Architecture?

According to research, both peptides have the same amino acid sequence, consisting of 29 amino acids. These are the first 29 amino acids of endogenous GHRH, and research such as the study by Grossman et al. suggests that the sequence is sufficient to induce a similar GHRH-receptor activation as full-length GHRH.⁽¹⁾ Thus, the first 29 amino acids are regarded as the shortest fragment of GHRH that still holds full affinity for the receptor.

Furthermore, the sequence of Mod GRF 1-29 vs CJC-1295 DAC carries four amino acid substitutions that may support the stability and affinity of the molecule. Namely, research by Jetté et al. reveals that the modifications include D-Ala at position 2, Lys at position 8, D-Phe at position 15, and Sar at position 27, and they are supposed to have the following potential:⁽²⁾

• At positions 2, 15, and 27, the substitutions might help the peptide become more resistant to breakdown by enzymes such as DPP-4, and this may extend its half-life.
• At position 8, asparagine appears to be replaced with lysine, which might support the peptide’s affinity towards the GHRH receptors.

While the two peptides may have identical amino acid structure, CJC-1295 DAC also possesses a C-terminal lysine residue joined to a molecule called Drug Affinity Complex (DAC). DAC appears to be a molecule called N-epsilon-3-maleimidopropionamide, which has high affinity for protein molecules like albumin. As CJC-1295 DAC may bind to proteins like albumin, this may considerably improve its resistance to breakdown, compared to Mod GRF 1-29.

How Do Mod GRF 1-29 and CJC-1295 DAC Compare in Pharmacokinetics and Pharmacodynamics?

While both peptides appear to exert extended stability compared to the unmodified fragment called GRF 1-29, CJC-1295 DAC is still considered to be much more stable than Mod GRF 1-29. Specifically, unmodified GHRH 1-29 appears to have a half-life of about 10 minutes, while the four amino acid substitutions of Mod GRF 1-29 may extend this to 0.5 hours. However, the addition of a DAC to CJC-1295 DAC allows for binding to proteins like albumin, thanks to the maleimide group. This is reported by researchers such as Teichman et al. to extend the half-life of the peptide to roughly 140-190 hours.⁽³⁾

Despite the differences in pharmacokinetics, both peptides appear to act through the same signaling pathway, which involves the growth hormone-releasing hormone receptor on pituitary somatotroph cells. Therefore, they appear to have identical pharmacodynamics, which involve interactions with the GHRH receptor.

The GHRH receptor belongs to the Class II G-protein-coupled receptor family, as described by the research of Zhou et al.⁽⁴⁾ When it is engaged, it is thought to trigger G-protein activation at the inner face of the membrane. This may activate downstream pathways which may lead to the production of secondary messengers such as cyclic adenosine monophosphate (cAMP) and inositol triphosphate (IP3). Those in turn may stimulate the adenylyl cyclase pathway, which converts ATP into cyclic AMP. The rising cyclic AMP activates protein kinase A, which phosphorylates membrane calcium channels. The resulting influx of calcium ions is posited to drive the fusion of growth-hormone-containing vesicles and their release.

How Do Mod GRF 1-29 and CJC-1295 DAC Compare in Anabolic Potential?

Mod GRF 1-29 vs CJC-1295 DAC appear to engage with the GHRH receptors, which may promote the synthesis of anabolic mediators such as growth hormone (GH) and insulin-like growth factor-1 (IGF-1). However, due to their different pharmacokinetics, the peptides also appear to induce significant differences in their anabolic potential.

Currently, there is a lack of research on the full potential of Mod GRF 1-29, but work by Khorram et al. examined a closely related modified GHRH 1-29 analog and reported an apparent transient rise in growth hormone across a 12-hour window.⁽⁵⁾ That surge was described as roughly 70% to 107% higher than 12-hour control experiments with placebo, and it apparently led to a mean increase in insulin-like growth factor-1 of about 27%.

Due to the short half-life, Mod GRF 1-29 appears to induce only a short-term peak in the first couple of hours after initiating an experiment, which then quickly subsides. Nevertheless, this appeared to still be sufficient to also noticeably increase average 12-hour synthesis.

On the other hand, the previously mentioned research by Teichman et al., who studied the potential of CJC-1295, suggests the peptide may induce a sustained 2- to 10-fold rise in mean growth hormone levels when monitoring the total synthesis over 140+ hours.⁽³⁾ Consequently, the researchers also noted a significant and lasting increase in IGF-1 levels, which was estimated to reach 1.5- to 3-fold above control experiments, and the elevations continued for as long as 28 days after repeated experimentation.

Other experiments, such as those by Ionescu et al., also suggest that CJC-1295 DAC may possess significant anabolic potential.⁽⁶⁾ The researchers observed that during pituitary cell experiments with the peptide, it appeared that “basal (trough) GH levels were markedly increased (7.5-fold) and contributed to an overall increase in GH secretion (mean GH levels, 46%) and IGF-I levels (45%).”

Which of the Two Peptides May Promote Somatotroph Cell Proliferation?

While research on short-acting GHRH-analog peptides such as Mod GRF 1-29 is limited to their potential for stimulating GH release and anabolic signaling, there is data that CJC-1295 DAC may also work at the level of the pituitary cells themselves. Specifically, some researchers have posited that sustained engagement of the GHRH receptor is thought to raise transcriptional activity within somatotrophs. Research by Alba et al. gave CJC-1295 DAC on a repeated schedule to GHRH knockout models and tracked the pituitary response.⁽⁷⁾

The peptide apparently raised total pituitary RNA and growth hormone mRNA. The authors read that shift as a sign of somatotroph proliferation. Specifically, they posited that CJC-1295 DAC may have “caused an increase in total pituitary RNA and GH mRNA [in mammalian models], suggesting that proliferation of somatotroph cells had occurred, as confirmed by immunohistochemistry images.”

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References:

1. Grossman A, Savage MO, Lytras N, Preece MA, Sueiras-Diaz J, Coy DH, Rees LH, Besser GM. Responses to analogs of growth hormone-releasing hormone in normal subjects, and in growth-hormone deficient children and young adults. Clin Endocrinol (Oxf). 1984 Sep;21(3):321-30. doi: 10.1111/j.1365-2265.1984.tb03477.x. PMID: 6236914.
2. Jetté L, Léger R, Thibaudeau K, Benquet C, Robitaille M, Pellerin I, Paradis V, van Wyk P, Pham K, Bridon DP. Human growth hormone-releasing factor (hGRF)1-29-albumin bioconjugates activate the GRF receptor on the anterior pituitary in rats: identification of CJC-1295 as a long-lasting GRF analog. Endocrinology. 2005 Jul;146(7):3052-8. doi: 10.1210/en.2004-1286. PMID: 15817669.
3. Teichman SL, Neale A, Lawrence B, Gagnon C, Castaigne JP, Frohman LA. 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 Mar;91(3):799-805. doi: 10.1210/jc.2005-1536. PMID: 16352683.
4. Zhou F, Zhang H, Cong Z, Zhao LH, Zhou Q, Mao C, Cheng X, Shen DD, Cai X, Ma C, Wang Y, Dai A, Zhou Y, Sun W, Zhao F, Zhao S, Jiang H, Jiang Y, Yang D, Eric Xu H, Zhang Y, Wang MW. Structural basis for activation of the growth hormone-releasing hormone receptor. Nat Commun. 2020 Oct 15;11(1):5205. doi: 10.1038/s41467-020-18945-0. PMID: 33060564.
5. Khorram O, Laughlin GA, Yen SS. Endocrine and metabolic effects of long-term administration of [Nle27]growth hormone-releasing hormone-(1-29)-NH2 in age-advanced men and women. J Clin Endocrinol Metab. 1997 May;82(5):1472-9. doi: 10.1210/jcem.82.5.3943. PMID: 9141536.
6. Ionescu M, Frohman LA. 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 Dec;91(12):4792-7. doi: 10.1210/jc.2006-1702. PMID: 17018654.
7. Alba M, Fintini D, Sagazio A, Lawrence B, Castaigne JP, Frohman LA, Salvatori R. Once-daily administration of CJC-1295, a long-acting growth hormone-releasing hormone (GHRH) analog, normalizes growth in the GHRH knockout mouse. Am J Physiol Endocrinol Metab. 2006 Dec;291(6):E1290-4. doi: 10.1152/ajpendo.00201.2006. PMID: 16822960.