Melanostatin DM

Also known as: H-His-D-Arg-Ala-Trp-D-Phe-Lys-NH2, HrAWfK-NH2

Evidence: Preclinical

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Overview

Synthetic hexapeptide (His-D-Arg-Ala-Trp-D-Phe-Lys-NH2), an MSH and GHRP hybrid that blocked alpha-MSH skin darkening in frogs and lizards; it was inactive in mouse melanoma cells.

The name suggests the hypothalamic peptide melanostatin (MIF-1, Pro-Leu-Gly-NH2), but this product is a different molecule: a hexapeptide hybrid of a growth hormone-releasing peptide analog and alpha-MSH(6-11) from Sawyer, Castrucci and Hadley (Sawyer et al., 1989). Injected into lizards it halved or abolished alpha-MSH skin darkening (Castrucci et al., 1994). It also blocked alpha-MSH in frog and anole skin, but had no agonist or antagonist activity in mouse melanoma cells or in a fish species (Castrucci et al., 1997), so effects on mammalian pigment cells are unproven. No topical study in any species and no human study has been published.

Benefits

Blocks alpha-MSH skin darkening (lizard in vivo, frog and lizard skin in vitro); no mammalian or human data

Dosing reference

Research dose: Topical by vendor framing only; no study in any species has applied it to skin, and no published formulation concentration exists. Lizard studies injected 1 to 10 nmol per 5 g body weight.

Sold as a topical peptide. All published work used injection in lizards or isolated frog and lizard skin; no topical concentration has been studied.

Mechanism

Proposed competitive alpha-MSH antagonism at the MC1-type receptor of amphibian and reptile melanophores. MSH and GHRP hybrids with a D-Arg-Ala pair inhibited alpha-MSH on frog and anole skin with pA2 of about 5 to 6 (Sawyer et al., 1989), and the compound blocked alpha-MSH darkening in live lizards (Castrucci et al., 1994). It was inactive in murine melanoma cells, which the authors attribute to species differences in MC1 receptors (Castrucci et al., 1997). Effects on human MC1R, cAMP or tyrosinase have not been tested.

Evidence

Preclinical: animal or in vitro data only

MSH and GHRP hybrid analogs with D-Arg-Ala substitutions inhibited alpha-MSH on frog and anole lizard skin in vitro (Sawyer et al., 1989)
Injected into white-adapted lizards, 1 nmol per 5 g abolished alpha-MSH darkening in U. ornatus and 10 nmol halved it in S. jarrovii (Castrucci et al., 1994)
Antagonist in Anolis lizard skin but inactive in a teleost fish and in murine melanoma cells (Castrucci et al., 1997)
Human-trial status: no human, topical or mammalian in vivo study; all data are from one group's amphibian and reptile assays

References

Side effects

No safety data in any species. The design is based on a growth hormone-releasing peptide analog, and whether it keeps any GH-releasing activity has not been reported. Commonly reported (anecdotal): none documented.

Storage

Storage: Room temperature, away from light
Lyophilized: 2 years at room temp
Reconstituted: N/A (ready to use)

Pharmacology

Half-life: No published pharmacokinetic data in any species
Bioavailability: Not measured; skin penetration has never been studied
Molecular weight: 843.01 Da
Sequence: His-[D-Arg]-Ala-Trp-[D-Phe]-Lys-NH2