Disapearance and excretion of labeled alpha-MSH in man

Radiochemical and radiopharmacological characterization of a 64 Cu-labeled α-MSH analog conjugated with different chelators

Radiolabeled α-melanocyte-stimulating hormone (α-MSH) derivatives have a high potential for diagnosis and treatment of melanoma, because of high specificity and binding affinity to the melanocortin-1 receptor (MC1R). Hence, the α-MSH-derived peptide NAP-NS1 with a β-Ala linker (ε-Ahx-β-Ala-Nle-Asp-His-D-Phe-Arg-Trp-Gly-NH₂ ) was conjugated to different chelators: either to NOTA (p-SCN-Bn-1,4,7-triazacyclononane-1,4,7-triacetic acid), to a hexadentate bispidine carbonate derivative (dimethyl-9-(((4-nitrophenoxy)carbonyl)oxy)-2,4-di(pyridin-2-yl)-3,7-bis(pyridin-2-ylmethyl)-3,7-diazabicyclo[3.3.1]nonane-1,5-dicarboxylate), or to DMPTACN (p-SCN-Ph-bis(2-pyridyl-methyl)-1,4,7-triaza-cyclononane), labeled with ⁶⁴ Cu, and investigated in terms of radiochemical and radiopharmacological properties. For the three ⁶⁴ Cu-labeled conjugates negligible transchelation, suitable buffer and serum stability, as well as appropriate water solubility, was determined. The three conjugates exhibited high binding affinity (low nanomolar range) in murine B16F10, human MeWo, and human TXM13 cells. The B_max values of [⁶⁴ Cu]Cu-bispidine-NAP-NS1 ([⁶⁴ Cu]Cu-2) and [⁶⁴ Cu]Cu-DMPTACN-NAP-NS1 ([⁶⁴ Cu]Cu-3) were higher than those of [⁶⁴ Cu]Cu-NOTA-NAP-NS1 ([⁶⁴ Cu]Cu-1), implying that different charged chelate units might have an impact on binding capacity. Preliminary in vivo biodistribution studies suggested the main excretion pathway of [⁶⁴ Cu]Cu-1 and [⁶⁴ Cu]Cu-3 to be renal, while that of [⁶⁴ Cu]Cu-2 seemed to be both renal and hepatobiliary. An initial moderate uptake in the kidney decreased clearly after 60 minutes. All three ⁶⁴ Cu-labeled conjugates should be considered for further in vivo investigations using a suitable xenograft mouse model.

Two-level delivery systems for oral administration of peptides and proteins based on spore capsules of Lycopodium clavatum

Two-level delivery systems for oral administration of therapeutic proteins and peptides were developed.

α-MSH: a potential neuroprotective and immunomodulatory agent for the treatment of stroke

Alpha-melanocyte-stimulating hormone (MSH) is a neuropeptide with profound immunomodulatory properties; we evaluated the effects of α-MSH on stroke outcome and its ability to modulate the postischemic immune response. In Lewis rats subjected to 3 hours of middle cerebral artery occlusion (MCAO), plasma concentrations of α-MSH rapidly decreased and returned to baseline over the course of days. Exogenous administration of α-MSH (100 or 500 μg/kg) improved 24 hour outcome in animals subjected to 2 hours MCAO; α-MSH 500 μg/kg also decreased infarct volume at this time point. Both doses of α-MSH were ineffective in improving outcome or decreasing infarct volume in animals subjected to 3 hours MCAO. The splenocyte response to phytohemagglutin in animals treated with α-MSH was attenuated at 24 hours after MCAO. At 1 month after MCAO, treatment with α-MSH 500 μg/kg at the time of stoke was associated with a decrease in TH1 response to myelin basic protein (MBP) in animals subjected to 2 hours MCAO, although treatment was not associated with improved outcome at this time point. Given the early benefits of α-MSH treatment and its effect on immunologic outcome, further studies to evaluate the utility of α-MSH for the treatment of cerebral ischemia are warranted.

Alpha-melanocyte-stimulating hormone protects against renal injury after ischemia in mice and rats

Reperfusion after ischemia induces cytokines, chemoattractant chemokines, adhesion molecules, and nitric oxide (NO). The resultant neutrophil adherence and NO potentiates renal injury. alpha-Melanocyte-stimulating hormone (alpha-MSH) is a potent anti-inflammatory agent that inhibits neutrophil migration and production of neutrophil chemokines and NO. Since neutrophils and NO promote renal ischemic injury, we sought to determine if alpha-MSH inhibits renal injury in a model of bilateral renal ischemia. alpha-MSH significantly reduced ischemia-induced renal damage, measured by changes in renal histology and plasma blood urea nitrogen and creatinine in mice. alpha-MSH significantly decreased tubule necrosis, neutrophil plugging, and capillary congestion. Delay of alpha-MSH treatment for 6 h after ischemia also significantly inhibited renal damage. alpha-MSH also significantly inhibited ischemic damage in rats. To begin to determine the mechanism of action of alpha-MSH, we measured its effects on mediators of neutrophil trafficking and induction of the inducible isoform of NO synthase-II. alpha-MSH inhibited ischemia-induced increases in mRNA for the murine neutrophil chemokine KC/IL-8. alpha-MSH also inhibited induction of mRNA for the adhesion molecule ICAM-1, which is known to be critical in renal ischemic injury. alpha-MSH inhibited nitration of kidney proteins and induction of NO synthase-II. We conclude: (a) alpha-MSH protects against renal ischemia/reperfusion injury; and (b) it may act, in part, by inhibiting the maladaptive activation of genes that cause neutrophil activation and adhesion, and induction of NO synthase.

On the stimulatory nature of the control of MSH secretion in ducks

Though birds lack the pars intermedia of the hypophysis, their pituitary glands do secrete MSH. This hormone and ACTH are elaborated in special cells of the pars distalis called corticomelanotrops. The present study was designed to ascertain whether the release of MSH in aves is under either stimulatory or inhibitory hypothalamic control. Extracts of median eminence were injected in ducks and plasma MSH was observed to rise after the injections: on the other hand, when pituitaries were ectopically grafted, significant changes in the levels of circulating MSH were not detected. Twenty days after grafting, the transplants were extirpated and incubated in media containing median eminence extracts. The extracts stimulated the release of MSH not only from grafts but also from pieces of normotopic glands. The grafts showed cells which contained ACTH but not MSH; however, they contained small amounts of MSH, detectable by RIA. The administration of ergocryptine brought about the inhibition of MSH secretion in vivo, and it is suggested that this drug acted on hypothalamic structures rather than directly on the corticomelanotrops. On the basis of the preceding results, it is concluded for the first time that in ducks the release of MSH has stimulatory control from the hypothalamus, contrarily to that occurring in almost all the animals so far investigated.

Synthesis of tritium labeled Ac-[Nle4, D-Phe7]-alpha-MSH4-11-NH2: a superpotent melanotropin with prolonged biological activity

Ac-[Nle4, D-Phe7]-alpha-MSH4-11-NH2 an octapeptide, is a melanotropin analogue (Ac-Nle-Glu-His-D-Phe-Arg-Trp-Gly-Lys-NH2), which is a superpotent agonist of frog and lizard skin melanocytes and mouse S 91 (Cloudman) melanoma cells. This melanotropin possesses ultraprolonged activity on melanocytes, both in vitro and in vivo, and the peptide is resistant to inactivation by serum enzymes. The tritium-labeled congener was prepared by direct incorporation of [3H]-labeled norleucine into the peptide. The melanotropic activity of the labeled peptide is identical to the unlabeled analogue. This labeled peptide should be useful for studies on the localization and characterization of melanotropin receptors.

Misleading concepts in the field of brain peptides

Peptide research, like all of science, requires a careful balance between building upon previously accumulated knowledge and exploring perspectives that are in conflict with prevailing views. Many of the concepts discussed here originally stimulated certain lines of research. The downfall of most of these concepts, and thus their misleading nature, lies in the limitation of possible modes by which peptides are perceived to affect the functioning of the central nervous system (CNS).

Absorption of alpha-MSH from subcutaneous and intraperitoneal sites in the rat

Pentobarbitone anesthetized rats were injected with 30 nmol (50 micrograms) alpha-MSH administered intraperitoneally (IP) and subcutaneously (SC) in an acid-saline vehicle, or SC in a zinc phosphate vehicle. Concentrations of alpha-MSH in plasma were measured by radioimmunoassay. The pharmacokinetic parameters for the three modes of administration were determined by fitting a one-compartment open model to the plasma level data. The t1/2 for absorption using the saline vehicle was 7.3 and 5.6 min from the IP and SC sites, respectively. The t1/2 for absorption from the zinc phosphate complex of 17.7 min was significantly longer. Five percent of the IP dose was absorbed into the systemic circulation giving a peak plasma level of 14.1 nmol/l. The absorption of 2-3 percent was significantly lower following SC administration; peak plasma levels were 8.3 and 4.8 nmol/l for the saline and zinc phosphate vehicles, respectively. The low percentage absorption values indicated a high degree of metabolism of the peptide by peripheral tissues on its passage from the injection sites into the circulation.

Limitations to effect of alpha-MSH on permeability of blood-brain barrier to IV 99mTc-pertechnetate

The effects of several variables on the permeability of the blood-brain barrier (BBB) to 99mTc-labeled sodium pertechnetate after IV administration of alpha-MSH were investigated. Doses of alpha-MSH of about 200 micrograms/kg were generally more effective in increasing the brain:blood ratio of radioactivity than the smaller doses that had previously been shown to affect behavior and the EEG. Pulsatile administration of a total of 200 micrograms/kg alpha-MSH over 90 min did not change the permeability of the BBB to the pertechnetate anion. Infusion of the same dose over 90 min significantly increased the brain:blood ratio of radioactivity in one of two experiments: no significant effects were seen with infusion for shorter times, lower concentrations, or with a 4-9 analog (Org 2766). In another experiment, bolus injection of 200 micrograms/kg alpha-MSH resulted in a significantly increased ratio 90 min later as compared with controls. Although the effects of a peptide on the permeability of the BBB to other compounds remains intriguing, limitations appear to exist in experiments with 99mTc-pertechnetate.

Evidence for homologous actions of pro-opiocortin products

alpha-Melanocyte-stimulating hormone (alpha-MSH), a modified fragment of adrenocorticotropic hormone, derives from the same biosynthetic route as beta-endorphin and is stored by the same arcuate neurons. Microinjection of alpha-melanocyte-stimulating hormone and several related peptides into the periaqueductal gray matter significantly reduced responsiveness to pain and had a behavioral profile similar to that produced by beta-endorphin.