KPV

In mice with DSS colitis and in CD45RB-high T-cell transfer colitis, KPV-treated animals recovered earlier; DSS mice regained significantly more body weight and had significantly less inflammatory infiltrate on histology and significantly lower colonic myeloperoxidase activity than colitic controls, while the transfer-model histology improved without those quantitative comparators. In MC1Re/e mice carrying a nonfunctional melanocortin-1 receptor, KPV rescued every animal in the treatment group from death during DSS colitis, indicating the effect is at least partly MC1R-independent.¹⁰

In human Caco2-BBE and HT29-Cl.19A intestinal epithelial cells and human Jurkat T cells, nanomolar KPV inhibited cytokine-induced activation of NF-κB and MAP-kinase signalling and reduced proinflammatory cytokine secretion; uptake was via the di/tripeptide transporter PepT1, for which KPV is a relatively high-affinity substrate (Km approximately 160 µmol/L in Caco2-BBE cells).^3,12

In mice given azoxymethane plus DSS to induce colitis-associated cancer, 100 µmol/L KPV in the drinking water reduced tumour number, tumour size and total colonic tumour burden compared with AOM/DSS alone; in PepT1-knockout mice the same regimen left tumour number, size, burden and body weight unchanged, with only a nonsignificant trend toward lower tumour burden.¹²

In mice with DSS colitis, KPV loaded into 400 nm nanoparticles embedded in an alginate-chitosan hydrogel protected against the inflammatory and histological changes seen with DSS alone, and matched the therapeutic efficacy of free KPV solution at a KPV concentration 12,000-fold lower.¹⁵

In immortalised human bronchial epithelial cells (16HBE14o-) stimulated with TNF-α or respiratory syncytial virus, KPV produced a dose-dependent inhibition of NF-κB reporter activity, matrix metalloproteinase-9 activity, and IL-8 and eotaxin secretion; the peptide entered the nucleus, stabilised IκBα and blocked YFP-p65RelA nuclear translocation at the importin-α3 binding site. The MC3R agonist γ-MSH suppressed NF-κB in the same cells but, unlike KPV, required its receptor.⁷

In RAW 264.7 mouse macrophages stimulated with lipopolysaccharide and interferon-γ, α-MSH(11-13) inhibited nitric oxide production and NF-κB nuclear translocation with maximal effect between 1 nM and 1 µM — comparable to full-length α-MSH, which was equal or slightly more potent — yet failed to displace 125I-NDP-MSH from MC1 receptor binding sites at concentrations up to 1 mM and produced no cAMP rise.⁸

In mice with crystal-induced peritonitis, systemic KPV significantly reduced polymorphonuclear leukocyte accumulation in the peritoneal cavity; the effect persisted in recessive yellow e/e mice lacking a functional MC1 receptor and in IL-1β-induced peritonitis, and was not blocked by the MC3/MC4 receptor antagonist SHU9119. Unlike α-MSH and MTII, KPV neither raised macrophage cAMP nor inhibited macrophage KC and IL-1β release.⁹

In cultures of methicillin-sensitive and methicillin-resistant Staphylococcus aureus, α-MSH(11-13) killed more than 90% of cells at micromolar concentrations and about 50% at nanomolar concentrations — comparable to full-length α-MSH, while the N-terminal fragment α-MSH(1-5) was inactive — and depolarised and lysed roughly 70–80% of cells after 2 hours of micromolar exposure, with activity unaffected by NaCl, Ca²⁺ or Mg²⁺.¹¹

In bacterial growth-inhibition assays run under a variety of conditions by an independent group, the capped tripeptide Ac-KPV-NH2 showed no activity, nor did its α- and ε-glycoalkylated analogues — so the antibacterial property attributed to this sequence is not consistently reproducible across laboratories, peptide forms and assay conditions.⁴

In mice with picryl-chloride-induced ear swelling, intraperitoneal Ac-α-MSH(11-13)-NH2 reduced swelling measured at 3 and 6 hours after the irritant. Substituting D-valine at position 13 increased anti-inflammatory activity approximately four-fold over the parent tripeptide, D-lysine at position 11 was equivalent, and D-proline at position 12 abolished activity entirely. The dose-response relations were bell-shaped.¹⁶

In rabbits whose corneal epithelium had been completely denuded by mechanical abrasion, topical KPV left 8 of 8 corneas fully re-epithelialised at 60 hours while none of the phosphate-buffered-saline controls had re-epithelialised (P<0.05); pretreatment with the nitric oxide synthase inhibitor L-NAME inhibited the effect, implicating nitric oxide in the repair.¹⁷

In rats with chemotherapy-induced oral mucositis, a mucoadhesive thermosensitive PLGA-PEG-PLGA hydrogel carrying KPV and applied to the gingival mucosa improved food intake and body-weight recovery, significantly lowered gingival IL-1β and TNF-α, raised IL-10, and repaired the ulcerated tissue morphology with increased CK10 and PCNA expression; the same hydrogel reduced inflammatory-cell infiltration in MRSA-infected gingival ulcers.¹⁸