GLOW and KLOW: what is in the blends

What the blends are

GLOW and KLOW are names used in the research-peptide trade for two fixed combinations of short peptides supplied in a single vial. GLOW contains GHK-Cu, BPC-157 and TB-500. KLOW contains the same three and adds KPV. The names are trade shorthand rather than anything from the scientific literature.

Each component has its own identity, its own published record and, for three of the four, its own monograph on this site. The combinations do not. That is the central fact about these products: there is no published peer-reviewed study of GLOW, of KLOW, or of these three- or four-way combinations as such. What exists is literature on the individual peptides, which this guide summarises component by component before explaining what putting them in one vial does and does not change.

Both blends are supplied by BuyUK Peptides as research chemicals for in-vitro laboratory use under the Terms of Sale. They are not medicines and not for human or veterinary administration, and nothing here is dosing or administration guidance. The product pages are at GLOW blend and KLOW blend.

The components

GHK-Cu

GHK-Cu is the copper(II) complex of the tripeptide glycyl-L-histidyl-L-lysine, first isolated from human plasma in 1973 [1]. A single copper ion is held by three nitrogen donors in a stable 1:1 complex, which is blue [2]. Its literature is the oldest and broadest of the four: collagen synthesis in cultured human fibroblasts at nanomolar concentrations [3], animal wound-healing studies and gene-expression comparisons, much of it reviewed by Pickart and colleagues [4]. The human evidence is small and cosmetic, with no controlled trials. The full account is in the GHK-Cu monograph. GHK-Cu brings a metal into the blend: its copper is why a GLOW or KLOW vial is blue, and why buffer choice for the blend has to avoid strong chelators such as EDTA and citrate and high phosphate.

BPC-157

BPC-157 is a 15-residue peptide described by the Zagreb group of Predrag Sikirić as a fragment of a protein from human gastric juice [5]. The literature is large by count but almost entirely from rodent models and largely from one laboratory; the independent 2019 review by Gwyer, Wragg and Wilson notes that efficacy in humans has not been confirmed [6]. The best mechanistic paper from outside Zagreb reports increased tendon fibroblast outgrowth and migration with FAK and paxillin phosphorylation [7]. There is no controlled human trial, and the compound has been on the World Anti-Doping Agency's Prohibited List since 2022. The full account is in the BPC-157 monograph.

TB-500

TB-500 is the N-acetylated heptapeptide Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln, residues 17 to 23 of thymosin β4, containing the parent protein's actin-binding motif [8, 9]. It is not thymosin β4, a 43-residue protein, and most of what is written about TB-500 online quotes data generated with the full protein. The fragment's own record is small: it reproduced the parent's effect in endothelial migration and sprouting assays [10] and its inhibition of hepatic stellate cell activation [11]. There are no controlled human trials of the fragment, and thymosin β4 and its derivatives, TB-500 named explicitly, are on the WADA Prohibited List. The full account is in the TB-500 monograph.

KPV

KPV is the tripeptide Lys-Pro-Val, the C-terminal fragment of α-melanocyte-stimulating hormone, α-MSH(11-13), studied since the late 1980s as the part of the parent hormone that carries its anti-inflammatory activity. Its molecular weight calculated from the sequence is about 342 g/mol. There is no KPV monograph on this site yet; the summary below is drawn from three primary papers we have verified directly.

Hiltz and Lipton reported in 1989 that α-MSH(11-13), given to mice at graded doses, inhibited picryl chloride-induced ear swelling in a dose-related fashion [12].

Dalmasso and colleagues, in Gastroenterology in 2008, reported that in human intestinal epithelial cell lines (Caco2-BBE and HT29-Cl.19A) and Jurkat T cells stimulated with pro-inflammatory cytokines, KPV at nanomolar concentrations inhibited NF-κB and MAP kinase signalling and reduced cytokine secretion. Uptake and effect depended on PepT1, a di- and tripeptide transporter induced in the colon during inflammatory bowel disease. In mice, oral KPV in drinking water reduced the incidence of DSS- and TNBS-induced colitis [13].

Kannengiesser and colleagues, in Inflammatory Bowel Diseases the same year, tested KPV in dextran sodium sulfate colitis, CD45RB-high T-cell transfer colitis, and DSS colitis in mice lacking a functional melanocortin-1 receptor. In the first two, KPV led to earlier recovery, greater weight regain and less colonic inflammation by histology and myeloperoxidase activity; in the third it protected all treated animals from death, which the authors took to mean the effect is at least partly independent of MC1R [14].

That is the verified KPV record relevant here: one mouse ear-swelling study, one combined cell and mouse colitis study, and one mouse colitis study. There are no published human trials of KPV, and nothing in these papers concerns skin, wound healing or the readouts for which the other three components are usually studied.

What co-lyophilisation means

A blend of this kind is made by dissolving the component peptides together in one solution at the intended ratio, filling that solution into vials and freeze-drying it. The result is a single lyophilised cake with all the components distributed through it, rather than separate powders mixed in the vial. That is what "co-lyophilised" means.

The consequence is that the ratio is fixed at manufacture. Reconstituting the vial gives a solution in which every component is present at a concentration set by that ratio and the volume of solvent added. The blend is sold as a single vial for the same reason: it is one preparation with one fill mass and, ideally, one certificate. Where a programme needs a different ratio, or needs to vary one component while holding the others constant, the single-component products are the right starting material; a blend cannot be un-mixed.

Co-lyophilisation also means the components share a handling regime, which has to satisfy the most demanding of them. For GLOW and KLOW that is GHK-Cu: the buffer rules for copper peptides apply to the whole vial, and a solution that fades from blue has lost copper regardless of what the other components are doing. The storage and stability guide sets out the general principles.

The certificate complication

A certificate for a single peptide reports one main HPLC peak, its area as a percentage of all peaks, and one mass that should match the theoretical value. Our guide to reading a certificate of analysis goes through that process line by line.

A blend breaks the pattern. Reversed-phase HPLC of a GLOW vial shows three main peaks at three retention times, and a KLOW vial four. The single number a single-peptide certificate reports as "purity" has no straightforward meaning for a chromatogram with several intended main peaks, and a certificate quoting one purity figure for a blend without explaining how it was calculated should prompt questions.

A sound blend certificate instead treats each component as a separate identity and purity question. For each main peak it should report the retention time, the area and the mass observed by LC-MS, and the mass should match the component assigned to it: about 341 for protonated GHK (with the copper-bound doublet if the complex has survived the column), about 1420 for singly protonated BPC-157 or 711 for the doubly charged ion, about 889 for protonated TB-500, and about 343 for protonated KPV. Identity has to be confirmed per component, because the right number of peaks is not evidence that the right peptides are in them. Copper content should be reported separately, as for GHK-Cu alone, and ideally the certificate gives the ratio of components as found, for comparison with the label.

Small peaks between the main peaks are harder to interpret in a blend, because an impurity of one component can co-elute with another component or its impurities. That is a limitation of the format rather than a defect of a batch, and a further reason to prefer single-component products where analytical certainty matters.

What is not known

The gaps deserve to be explicit, because the blends are often marketed as though the combination were itself an established entity.

There is no published literature on GLOW or KLOW, or on the combination of GHK-Cu, BPC-157 and TB-500, with or without KPV, as a mixture; we have not found a peer-reviewed study of these peptides together in any system. The rationale for combining them is empirical: the three GLOW components have each been studied in wound and tissue-repair models and KPV has an anti-inflammatory literature, so they have been put together on the assumption that the effects are complementary. That assumption has not been tested, and no mechanism is shared: GHK-Cu is proposed to act through copper delivery and gene expression, BPC-157 has no identified receptor, TB-500 acts through an actin-binding motif, and KPV through PepT1-dependent uptake and NF-κB signalling. Whether they interact at all, and whether any interaction is additive, synergistic or antagonistic, is unknown.

There is also no stability literature for the mixture. GHK-Cu can lose copper to chelators, BPC-157 acetate degrades substantially in acidic solution according to patent data, and TB-500's C-terminal glutamine is liable to deamidation. A reconstituted blend is subject to all of these at once.

The blends are therefore a convenience preparation, useful where a programme has already decided to study the components together and wants a fixed-ratio starting material, and a poor choice where the question is what any one component does. In the second case the single-component products, each with its own monograph and an unambiguous certificate, are the right material, and can be combined at the bench at whatever ratio the experiment requires.

References

1. Pickart L, Thaler MM. Tripeptide in human serum which prolongs survival of normal liver cells and stimulates growth in neoplastic liver. Nature New Biology. 1973;243(124):85–87. PMID 4349963.
2. Lau SJ, Sarkar B. The interaction of copper(II) and glycyl-L-histidyl-L-lysine, a growth-modulating tripeptide from plasma. Biochemical Journal. 1981;199(3):649–656. doi:10.1042/bj1990649. PMID 7340824.
3. Maquart FX, Pickart L, Laurent M, Gillery P, Monboisse JC, Borel JP. Stimulation of collagen synthesis in fibroblast cultures by the tripeptide-copper complex glycyl-L-histidyl-L-lysine-Cu²⁺. FEBS Letters. 1988;238(2):343–346. doi:10.1016/0014-5793(88)80509-X. PMID 3169264.
4. Pickart L, Margolina A. Regenerative and protective actions of the GHK-Cu peptide in the light of the new gene data. International Journal of Molecular Sciences. 2018;19(7):1987. doi:10.3390/ijms19071987. PMID 29986520.
5. Sikiric P, Seiwerth S, Rucman R, et al. Stable gastric pentadecapeptide BPC 157: novel therapy in gastrointestinal tract. Current Pharmaceutical Design. 2011;17(16):1612–1632. doi:10.2174/138161211796196954. PMID 21548867.
6. Gwyer D, Wragg NM, Wilson SL. Gastric pentadecapeptide body protection compound BPC 157 and its role in accelerating musculoskeletal soft tissue healing. Cell and Tissue Research. 2019;377(2):153–159. doi:10.1007/s00441-019-03016-8. PMID 30915550.
7. Chang CH, Tsai WC, Lin MS, Hsu YH, Pang JHS. The promoting effect of pentadecapeptide BPC 157 on tendon healing involves tendon outgrowth, cell survival, and cell migration. Journal of Applied Physiology. 2011;110(3):774–780. doi:10.1152/japplphysiol.00945.2010. PMID 21030672.
8. Van Troys M, Dewitte D, Goethals M, Carlier MF, Vandekerckhove J, Ampe C. The actin binding site of thymosin β4 mapped by mutational analysis. EMBO Journal. 1996;15(2):201–210. doi:10.1002/j.1460-2075.1996.tb00350.x. PMID 8617195.
9. Esposito S, Deventer K, Goeman J, Van der Eycken J, Van Eenoo P. Synthesis and characterization of the N-terminal acetylated 17–23 fragment of thymosin beta 4 identified in TB-500, a product suspected to possess doping potential. Drug Testing and Analysis. 2012;4(9):733–738. doi:10.1002/dta.1402. PMID 22962027.
10. Philp D, Huff T, Gho YS, Hannappel E, Kleinman HK. The actin binding site on thymosin β4 promotes angiogenesis. FASEB Journal. 2003;17(14):2103–2105. doi:10.1096/fj.03-0121fje. PMID 14500546.
11. Shah R, Reyes-Gordillo K, Rojkind M. Thymosin β4 inhibits PDGF-BB induced activation, proliferation, and migration of human hepatic stellate cells via its actin-binding domain. Expert Opinion on Biological Therapy. 2018;18(sup1):177–184. doi:10.1080/14712598.2018.1478961. PMID 30063851.
12. Hiltz ME, Lipton JM. Antiinflammatory activity of a COOH-terminal fragment of the neuropeptide alpha-MSH. FASEB Journal. 1989;3(11):2282–2284. PMID 2550304.
13. Dalmasso G, Charrier-Hisamuddin L, Nguyen HTT, et al. PepT1-mediated tripeptide KPV uptake reduces intestinal inflammation. Gastroenterology. 2008;134(1):166–178. doi:10.1053/j.gastro.2007.10.026. PMID 18061177.
14. Kannengiesser K, Maaser C, Heidemann J, et al. Melanocortin-derived tripeptide KPV has anti-inflammatory potential in murine models of inflammatory bowel disease. Inflammatory Bowel Diseases. 2008;14(3):324–331. doi:10.1002/ibd.20334. PMID 18092346.

This monograph summarises the published literature for laboratory researchers. It is not medical advice, and nothing on this site is for human or veterinary use.