On the neurotrophic action of melanocortins

Peripheral nerve regeneration following transection injury to rat sciatic nerve by local application of adrenocorticotropic hormone

The objective of this study was to assess local effect of adrenocorticotropic hormone (ACTH) on the functional recovery of the sciatic nerve in a transection model. Sixty male healthy white Wistar rats were randomized into four experimental groups of 15 animals each: In the sham-operated group (SHAM), the sciatic nerve was exposed and manipulated. In the transected group (TC), the left sciatic nerve was transected and the cut nerve ends were fixed in the adjacent muscle. In the silicone graft group (SIL) a 10-mm defect was made and bridged using a silicone tube. The graft was filled with phosphated-buffer saline alone. In the treatment group a silicone tube (SIL/ACTH) was filled with 10 μL ACTH (0.1 mg/mL). Each group was subdivided into three subgroups of five animals each and regenerated nerve fibres were studied at 4, 8 and 12 weeks post operation. Behavioral testing, functional, gastrocnemius muscle mass and morphometric indices showed earlier regeneration of axons in SIL/ACTH than in SIL group (p < 0.05). Immunohistochemistry clearly showed more positive location of reactions to S-100 in SIL/ACTH than in SIL group. ACTH improved functional recovery and morphometric indices of sciatic nerve. This finding supports role of ACTH after peripheral nerve repair and may have clinical implications for the surgical management of patients after nerve transection.

Sciatic nerve regeneration in mice and rats: recovery of sensory innervation is followed by a slowly retreating neuropathic pain-like syndrome

Peripheral nerve regeneration has been studied extensively in the sciatic nerve crush model, at the level of both function and gene expression. The crush injury allows full recovery of sensory and motor function in about 3 weeks as assessed by the foot reflex withdrawal test and De Medinacelli walking patterns. We used the recently developed CatWalk paradigm to study walking patterns in more detail in mice and rats. We found that, following the recovery of sensory function, the animals developed a state of mechanical allodynia, which retreated slowly over time. The motor function, although fully recovered with the conventional methods, was revealed to be still impaired because the animals did not put weight on their previously injured paw. The development of neuropathic pain following successful sensory recovery has not been described before in crush-lesioned animals and may provide an important new parameter to assess full sensory recovery.

The potent melanocortin receptor agonist melanotan-II promotes peripheral nerve regeneration and has neuroprotective properties in the rat

The neurotrophic and neuroprotective potential of the alpha-melanocyte-stimulating hormone (alpha-MSH) analog cyclo-[Ac-Nle(4),Asp(5),D-Phe(7),Lys(10)]alpha-MSH-(4-10) amide (melanotan-II), a potent melanocortin receptor agonist, was investigated. The sciatic nerve crush model was used as a paradigm to investigate the neurotrophic properties of melanotan-II. Melanotan-II significantly enhanced the recovery of sensory function following a crush lesion of the sciatic nerve in the rat at a dose of 20 microg kg(-1) per 48 h, s.c., but not at a dose of 2 or 50 microg kg(-1). In addition, we observed that melanotan-II also possesses neuroprotective properties, as it partially protected the nerve from a toxic neuropathy induced by cisplatin. Thus, the present data for the first time demonstrate the effectiveness of the potent alpha-MSH analog melanotan-II in nerve regeneration and neuroprotection.

Behavioral pharmacology of neuropeptides related to melanocortins and the neurohypophyseal hormones

Neuropeptides are peptides which affect the nervous system. They are derived from large precursor molecules. These are converted to neurohormones, neuropeptides of the "first generation", which can be further converted to neuropeptides of the "second generation". This review is a brief survey of the nervous system effects of neuropeptides derived from pro-opiomelanocortin (POMC) and the neurohypophyseal hormones. Processing of these molecules results in neuropeptides of the first and second generation which have similar, different, more selective or even opposite effects. Among those are effects on learning and memory processes, grooming, stretching and yawning, social, sexual and rewarded behavior, aging and nerve regeneration, thermoregulation, pain, sensitivity to seizures, and cardiovascular control. Results of animal studies as well as those of clinical studies suggest that these neuropeptides may be beneficial in aging, neuropathy, memory disturbances and schizophrenia. Most of these nervous system effects in animal studies were found before receptors in the nervous system for the various neuropeptides were detected. G-protein-coupled receptors for the neuropeptides of the "first generation", i.e., melanocortin receptors, opioid receptors, and neurohypophyseal hormone receptors have been found, in contrast to the receptors for neuropeptides of the "second generation", although there are indications that G-protein coupled receptors for these may be present in the brain.

Trophic effects of melanotropin-potentiating factor (MPF) on cultures of cells of the central nervous system

MPF is a tetrapeptide (structure Lys-Lys-Gly-Glu) that elicits a variety of neurotrophic effects in vivo consistent with a role in neuronal regeneration. In support of this role, we now show that MPF stimulates the proliferation of cultured astrocytes and neurite outgrowth from cultures of neocortical cholinergic and mesenchephalic dopaminergic neurons. The dose-response relationships are biphasic ("bell shaped"), maximal responses being obtained with 10(-6) M concentrations of MPF. MPF and nerve growth factor seem to act on different receptors, because their effects on cholinergic neurons are synergistic.

The neurotrophic effects of ebiratide, an analog of ACTH4-9, on cultured septal cells and aged rats

The neurotrophic effects of ebiratide, an ACTH4-9 analog, have been examined using both fetal rat septal cultures and aged rats. The 5-day treatment with ebiratide (10-100 pmol/ml) partially prevented neuronal degeneration that occurred in the cultures in which cells were sparsely plated. Ebiratide (10 pmol/ ml) increased choline acetyltransferase (ChAT) and acetylcholinesterase (AChE) activities up to 1.5 and 1.2 times the respective control values in the sub-confluent cultures. AChE cytochemistry of the cultures has shown that ebiratide increased the stained area per cell. Ebiratide subcutaneously administered by constant infusion (10 nmol/body/hr) for 4 weeks elevated ChAT activities in the septum (35% over control), neocortex (79%) and hippocampus (89%) of aged rats. Thus, the present study indicates that ebiratide shares neurotrophic properties which may prove beneficial in the therapy for CNS degenerative disorders, especially Alzheimer's disease.

Alpha-MSH and MCH are functional antagonists in a CNS auditory gating paradigm

The peptides alpha-melanocyte stimulating hormone (alpha-MSH) and melanin concentrating hormone (MCH; rat and salmon sequence) were administered to anesthetized rats by intracerebroventricular infusion. Depth recordings were carried out in the dorsal hippocampus, and auditory gating was assessed. Auditory gating in this paradigm refers to the decrease in amplitude of the second of two tone-evoked CNS potentials that can be measured when pairs of identical tones are presented 500 ms apart. Alpha-MSH increases auditory gating, whereas MCH has the opposite effect. When MCH was administered prior to alpha-MSH, the ability of alpha-MSH to increase auditory gating was blocked. Thus, the two peptides appear to be functional antagonists.

ACTH/MSH(4-10) analog BIM 22015 aids regeneration via neurotrophic and myotrophic attributes

Structural differences between noncorticotropic ACTH peptides result in marked differences in their effects on regenerating nerve and muscle in rats. The ACTH/MSH(4-10) analog BIM 22015 was administered IP in dosages from 0.1 to 40 micrograms/kg/48 h for 5, 7, or 11 days after peroneal nerve crush, and characteristics of extensor digitorum longus (EDL) muscle were studied and compared with ACTH/MSH(4-10). Eleven days postcrush 40 micrograms/kg BIM 22015 increases rate of development of tetanic tension and amplitude of contraction of indirectly stimulated EDL. In a 21-day study, reinnervated BIM 22015-treated muscles retain tetanic strength, whereas ACTH/MSH(4-10)-treated muscles are significantly weakened. Both peptides show neurotrophic characteristics in their stimulation of endplate nerve terminal branching. However, in contrast to ACTH/MSH(4-10), BIM 22015 also prevents denervation atrophy of the EDL. This dual neurotrophic and myotrophic role for BIM 22015 accords it a clinical potential for degenerative myopathies of either pure or mixed origin, such as muscular dystrophy, infantile spinal atrophy, and hypotonia.

An ACTH/MSH(4-9) analog counteracts the behavioral effects of a mineralocorticoid receptor antagonist

The ACTH/MSH(4-9) analog Org2766 has been demonstrated to counteract age-related behavioral and morphological parameters especially those related to hippocampal functioning. Hippocampal mineralocorticoid receptors (MRs) are known to decline in the senescent rat. This decrease can be also counteracted by a chronic treatment with an ACTH(4-9) analog. The apparent effect of the peptide on hippocampal functioning prompted us to study a possible interaction between ACTH and MRs at a behavioral level. A chronic treatment with the ACTH(4-9) analog prevented the behavioral alteration induced by a specific MR antagonist (RU28318; 100 ng/microliters, ICV) in the Morris water maze and a step-through avoidance task. A possible role for neuronal excitation, involving MR activation, in peptide-facilitated behavioral recovery as seen in lesion studies and aging is discussed.

Effects of the ACTH4-9 analog Org2766 on brain plasticity: modulation of excitatory neurotransmission?

ACTH-like neuropeptides have been investigated in various paradigms such as cognition, neuronal damage and neuronal excitation. All their effects may be collectively described as modulation of neural plasticity. However, the mechanism of action accounting for these effects remains to be demonstrated. This report is an overview of the data and has incorporated some additional findings of the influence of the ACTH4-9 analog, Org2766, on neuronal excitation, especially in the hippocampus. An interaction with NMDA receptors may account for the various aspects of plasticity. Based on recent findings demonstrating that the ACTH4-9 analog counteracts both the NMDA antagonist, AP5, and NMDA-induced explosive running behavior, the hypothesis is put forward that glutamatergic neurotransmission is involved in behavioral changes induced by the ACTH4-9 analog.

An ACTH4-9 analog enhances social attention in aging rats: a longitudinal study

Effect of chronic treatment of the ACTH4-9 analog, Org2766, on social attention was studied longitudinally in aging rats. A 6-week treatment temporarily enhanced specific combinations of behaviors of two interacting animals. During a 6-month treatment social attention of treated animals remained at the same level, whereas control animals showed a gradual decrease. Two months after the treatment was ceased this effect on social attention was still present; moreover, the peptide-treated animals performed better in a spatial water maze task three months after the last injection. In addition, the nerve conduction velocity of the major caudal nerves and the sciatic nerve were measured; aged, peptide-treated animals preserved their conduction velocity. The present study shows beneficial long-lasting effects of the ACTH4-9 analog in aging rats on complex behavioral indices and on a physiological measure.

Capillary electrophoresis of peptides. Analysis of adrenocorticotropic hormone-related fragments

Capillary electrophoresis can be used successfully to analyse small peptides to give additional information to that obtained using high-performance liquid chromatography (HPLC). The separation of a modified adrenocorticotropic hormone (4-9) fragment (Org 2766) and several of its fragments was investigated using capillary zone electrophoresis. Prediction of migration in aqueous systems using pKa-related data and the migration behaviour using sodium dodecyl sulphate in the buffer are discussed, as is the choice of buffer systems. The electrophoretic patterns are compared with the HPLC separation.

Cellular distribution of cis-diamminedichloroplatinum(II)-DNA binding in rat dorsal root spinal ganglia: effect of the neuroprotecting peptide ORG.2766

The in situ binding of the anticancer drug cis-diamminedichloroplatinum(II) (cisDDP) to DNA was studied in the rat dorsal root spinal ganglion (DRG), using an antiserum against cisDDP-modified calf thymus DNA in a quantitative immunocytochemical assay. Rats received a dose of cisDDP (1 mg/kg), two times a week, up to a cumulative dose of 15 mg/kg (group I) or 34 mg/kg (group II). Rats of group III were given a single dose of 15 mg/kg. Rats were killed 48 hr (groups I and II) or 6 hr (group III) after the last injection. In groups I and II cisDDP-induced neurological damage was assessed by measuring both motor and sensory nerve conduction velocities (MNCV and SNCV). Whereas the MNCV was not influenced by the treatment with cisDDP, the SNCV decreased significantly. The level of cis-DDP-DNA binding in DRG satellite cells equalled that in liver cells, but binding could not be shown in DRG neuron nuclei. The level of cisDDP-DNA binding in spinal cord and brain was very low. The neuroprotecting peptide ORG.2766, an ACTH4-9 analog, was given sc (10 micrograms/rat) four times a week concomitantly with cisDDP to some rats of groups I and II. ORG.2766 prevented the decrease of the SNCV, but did not change the extent of cisDDP-DNA binding in satellite or liver cells. It is concluded that the amelioration of cisDDP toxicity by ORG.2766 is not directly related to the cisDDP-DNA binding in satellite cells.

Efficacy of the neuropeptide ORG.2766 in the prevention and treatment of cisplatin-induced neurotoxicity in rats

In rats chronic systemic treatment with cisplatin results in a sensory neuropathy as evidenced by a reduction in the sensory conduction velocity in the sciatic nerve. Concomitant administration of the neurotrophic ACTH4-9 analog, ORG.2766, prevents the occurrence of the neuropathy. In addition, treatment with ORG.2766 stops further deterioration and improves recovery of an already established cisplatin-induced neuropathy. Furthermore, concomitant administration of ORG.2766 during a first cisplatin treatment period results in a better resistance against neurotoxicity in a second exposure period. Finally, ORG.2766 was shown not to hamper the anti-tumor effect of cisplatin in mice, carrying implanted tumor cells from a FMa human tumor line. These data are discussed in view of the potential clinical use of ORG.2766 in prevention and treatment of cisplatin-induced neuropathy.