Thymalin, sometimes referred to as Thymalin Alpha-1, is the synthetic variant of the endogenous Thymulin, which was first isolated from the thymus in 1977. The endogenously produced Thymalin has been researched for its potential in a wide landscape of research areas, with its influence speculated to extend to regulatory action on inflammation, mitigation of pain perception, neuroprotective action, and immune function support. Early studies have suggested that Thymalin and other thymus and pineal gland secretions may also support cell longevity.

Sermorelin is among the growth hormone-releasing hormone (GHRH) analogs. It is classified as a GHRH as researchers have suggested that the peptide acts to induce the endogenous production and release of growth hormone (hGH). Growth hormone has been associated with numerous physiological activities, making Sermorelin and other GHRH analogs, potentially relevant in growth hormone-related research. Examples of studies employing GHRH analogs include research in the context of tissue scarring following cardiac dysfunction, as well as those examining bone density, renal function, dementia and seizure activity.

TB-500, or synthetic Thymosin Beta-4, also known as synthetic Tβ4, is a synthetic analog of the endogenous Thymosin Beta-4 protein, which is considered to be ubiquitously present in cells. The peptide belongs to a widespread family of 16 related molecules observed to exhibit a high degree of sequence conservation and localization in most tissues and circulating cells. TB-500 was developed to sequester and block actin polymerization in eukaryotic cells.

Selank is a small peptide studied for its potential nootropic and behavior-modifying functions in experimental models. It is a synthetic analog of naturally occurring Tuftsin. This immunomodulatory peptide is a short fragment from the immunoglobulin G (IgG), a natural tetrapeptide involved in certain functions that may regulate the immune system. Selank is also posited to possess additional potential for regulating immune cells, IL-6, a wide range of neurotransmitter systems, and brain-derived neurotrophic factor (BDNF).

Selank differs in structure from the endogenous Tuftsin by an additional three amino acids in its chain, which have been supposed to enhance the metabolic stability and half-life of the synthetic peptide. Specifically, that is the Pro-Gly-Pro segment at the C-terminus of Selank, which might enhance its ability to move through various models, including the blood-brain barrier (BBB). The BBB is a highly selective and semi-permeable barrier that separates circulating blood from the tissues and extracellular fluid of the central nervous system, playing a vital role in regulating substance passage.

The inclusion of Pro-Gly-Pro may possibly increase BBB permeability by affecting the peptide’s hydrophilicity or lipophilicity, which may enhance its affinity for the BBB’s lipid-rich environment. Furthermore, the Pro-Gly-Pro sequence might interact with specific transport mechanisms or receptors at the BBB, possibly initiating facilitated transport or receptor-mediated endocytosis. These processes may enable Selank to circumvent the tight junctions that are said to typically restrict larger molecules.

PT-141, also known as Bremelanotide, was derived from a synthetic melanocortin analog known as Melanotan 2 (MT-2). A melanocortin analog, such as PT-141 and MT-2, is considered to be any synthetic compound designed to mimic or influence the functions of natural melanocortin peptides. These peptides, such as the alpha-melanocyte stimulating hormone (α-MSH), may be involved in a range of physiological processes including appetite regulation, energy homeostasis, immune responses, and skin cell pigmentation. PT-141 is a melanocortin analog that was developed to interact with Melanocortin-4 Receptor (MC-4R). It has been studied for a variety of potential characteristics and bioactivities through its interaction with this receptor. Apart from MC-4R, there are other melanocortin receptors like MC-1R, MC-2R, MC-3R, and MC-5R, each associated with different potential functions. For instance, MC-1R may be primarily involved in skin cell and hair follicle pigmentation, MC-2R appears to play a crucial role in the adrenal axis and stress response, MC-3R is implicated in the regulation of energy homeostasis, and MC-5R has been linked to exocrine function and thus impacts processes such as sweating and sebum production.

Pegylated Mechano-growth factor (PEG-MGF) is a peptide that originates from the IGF-I (main anabolic mediator of growth hormone) gene sequence, which undergoes a process called alternative splicing.^[1] This process allows for the synthesis of additional segments, which form new functional molecules. During stress or injury, it has been suggested that muscles produce an alternative peptide called IGF-IEc, which contains extra “exons” or domains. This is thought to result in an additional segment at the C-terminus of IGF-I, known as the Ec-peptide, which comprises 40 amino acids.^[2]

MGF, or mechano-growth factor, is a synthetic peptide that represents the last 24 amino acids from the naturally occurring IGF-IEc molecule (the Ec-peptide). This 24 amino acid fragment is also called the E-domain or MGF-E and is thought to mediate the beneficial actions of IGF-IEc on muscle recovery and cell proliferation.^[5]. It appears to stimulate myoblast (muscle cell) proliferation and differentiation. It has further been researched for its potential to increase endurance, stimulate the function of the immune system, and possible applications that may decrease cholesterol. PEG-MGF may also hasten wound healing via immune function regulation. The up-regulation of IGF-IEc, sometimes referred to as full-length MGF, during periods of stress or injury has been correlated by researchers with the proliferation of satellite cells and muscle cells. This suggests a potential role in muscle tissue repair and regeneration.^[3][4]

The attachment of a polyethylene glycol moiety to another chemical compound is termed “Pegylation.” Pegylation appears to increase the plasma stability of a compound like MGF by decreasing its clearance and potentially masking its immunogenicity. Pegylation may be considered a common and typically advantageous modification. MGF appears to have a shorter half-life than other peptides. With this in mind, the pegylation of the peptide may overcome any rapid clearance.

Modified GRF (1-29), or Mod GRF (1-29), is a synthetic peptide analog of growth hormone-releasing hormone (GHRH). It was first developed in the 1980s when studies indicated that the first 29 amino acids of GHRH may possess all of the biological roles associated with the full-length 44 residue protein.^[1] The initially designed peptide, known as GRF (1-29), is the shortest segment of GHRH, and appears to possess all the properties of the full-length hormone. A truncated synthetic form of GHRH known as Sermorelin, or GRF 1-29, also has 29 amino acids. Modified GRF (1-29) undergoes alteration to include four substituted amino groups in its chain.^[2] The intention behind these amino modifications is to protect the peptide from both oxidation and degradation during manufacture. The modification also appears to increase the binding affinity to GHRH receptors. Modified GRF (1-29) is also known as Mod GRF, or Tetra-substituted GRF (1-29). The latter name clarifies that the modified peptide differs from GRF (1-29) as a result of changes in four of its amino acids. Modified GRF (1-29) is structurally identical to CJC-1295 without DAC.

Modified GRF (1-29), or Mod GRF (1-29), is a synthetic peptide that is a modified fragment of the endogenously occurring growth hormone-releasing hormone (GHRH). It was first developed in the 1980s when studies indicated that the first 29 amino acids of GHRH may possess all of the biological potential associated with the full-length 44 GHRH molecule.^[1]

This discovery led to the development of a truncated version called GRF (1-29), also referred to as Sermorelin by researchers. Mod GRF (1-29) introduces specific modifications to support the peptide’s stability and efficacy. Four amino acids in the sequence are substituted at positions 2, 8, 15, and 27.^[2] Here is what some researchers believe about these modifications:
– Position 2: The amino acid alanine is replaced with its mirror image, D-alanine. This substitution aims to increase resistance to enzymatic degradation, thereby improving the peptide’s stability.
– Position 8: Asparagine is substituted with lysine, an amino acid with a positively charged side chain. This change may support the peptide’s binding affinity to GHRH receptors, potentially increasing its biological activity.
– Position 15: Histidine is replaced with D-phenylalanine, another D-amino acid. This modification is intended to protect the peptide from further enzymatic breakdown.
– Position 27: Cysteine is substituted with N-methylglycine, also referred to as sarcosine. This alteration may extend the peptide’s half-life by mitigating enzymatic cleavage.

These modifications collectively aim to produce a peptide with increased stability, a longer half-life, and better-supported interaction with GHRH receptors compared to the original GRF (1-29). Modified GRF (1-29) is structurally identical to CJC-1295 without DAC. The DAC in CJC-1295 serves to modify its pharmacokinetic properties.

Semax is a synthetic analog of adrenocorticotropic hormone (ACTH) comprising the amino acids 4 through 10 of ACTH. Semax has primarily been implicated in research on cognitive impairment and stroke. The peptide has also been studied closely within the context of dementia and certain inflammations of the optic nerve. Researchers posit that the peptide may exert neurotrophic action, suggesting that the peptide may act to increase the production of brain-derived neurotrophic factor (BDNF) in the central nervous system, with potential consequences in serotonin and dopamine release. Some researchers also suggest that Semax may interact with serotonin and enkephalin levels in the central nervous system.