The ACTH/MSH(4-9) analogue ORG 2766 stimulates microtubule formation in axons of central neurons of the snail Lymnaea stagnalis

In vivo modulation of vincristine-induced neurotoxicity in Lymnaea stagnalis, by the ACTH(4-9) analogue Org 2766

The use of the cytostatic agent vincristine (VCR) is limited by the occurrence of peripheral neuropathy. This side-effect is probably caused by interference with axonal microtubules. VCR depolymerizes microtubules and reacts with tubulin to form paracrystals. The potential of a neurotrophic ACTH(4-9) analogue, Org 2766, to counteract peripheral neuropathy caused by cytostatic agents is being investigated. In the present ultrastructural study, modulatory effects of Org 2766 on VCR-induced neurotoxicity were studied in vivo in neurons of the pond snail Lymnaea stagnalis, which has been shown previously to be a suitable test system to investigate neurotoxic side-effects of cytostatic agents. 24 h after treatment with VCR (25 microM), 68.4 +/- 34.7 paracrystals were counted per cross-section of the cerebral commissure and the number of microtubules in the axons had been lowered to 46% of the control level. After a survival period of two weeks all paracrystals had disappeared. By that time, no recovery of the axonal microtubular system could be observed. However, post-treatment with Org 2766 (10(-6) M) on day 6 after VCR treatment had induced a significant increase in the number of microtubules (+55%) on day 7. This beneficial effect lasted for the rest of the experimental period (14 days). These results suggest that post-treatment with Org 2766, i.e. after VCR clearance, can induce long-lasting beneficial effects on VCR-induced neurotoxicity in vivo.

Hormones and the cytoskeleton of animals and plants

It is often overlooked that a cell can exert its specific functions only after it has acquired a specific morphology: function follows form. The cytoskeleton plays an important role in establishing this form, and a variety of hormones can influence it. The cytoskeletal framework has also been shown to function in a variety of cellular processes, such as cell motility (important for behavior), migration (important for the interrelationship between the endocrine and immune systems, e.g., chemotaxis), intracellular transport of particles, mitosis and meiosis, maintenance of cellular morphology, spatial distribution of cell organelles (e.g., nucleus and Golgi system), cellular responses to membrane events (e.g., endocytosis and exocytosis), intracellular communication including conductance of electrical signals, localization of mRNA, protein synthesis, and--more specifically in plants--ordered cell wall deposition, cytoplasmic streaming, and spindle function followed by phragmoplast function. All classes of hormones seem to make use of the cytoskeleton, either during their synthesis, transport, secretion, degradation, or when influencing their target cells. In this review special attention is paid to cytoskeleton-mediated effects of selected hormones related to growth, transepithelial transport, steroidogenesis, thyroid and parathyroid functioning, motility, oocyte maturation, and cell elongation in plants.

Effect of cisplatin and ACTH4-9 on neural transport in cisplatin induced neurotoxicity

Cisplatin causes a dose limiting peripheral neuropathy, however, the biological mechanism by which this occurs is unknown. Murine N1E.115 neuroblastoma cells and neural crest derived pigment cells have similar transport mechanisms to human neural cells and were used to study the effect of cisplatin on cellular transport. Cisplatin reduced both the number and velocity of organelles moving in the anterograde and retrograde direction, compared to control cells. Cisplatin induced inhibition of transport was prevented by the simultaneous administration of ACTH4-9. This analog alone had no effect on N1E.115 organelle, or erythrophore granule, movement. In both N1E.115 and pigment cells cisplatin inhibited transport within 1 h of exposure to the drug. The degree of inhibition did not increase insignificantly if pigment cells were incubated in cisplatin for 48 h compared to acute exposure. Microtubules in both pigment cells and N1E.115 neurites retained their structural integrity suggesting that factors other than changes in gross microtubule morphology are responsible for cisplatin neurotoxicity. Cisplatin reduces N1E.115 neurite growth after 48 h incubation but this can be prevented by simultaneous use of ACTH4-9. This study demonstrates for the first time that cisplatin and ACTH4-9 affect fast axonal transport by specific mechanisms which appear related to their observed neurotoxic and neuroprotective roles, respectively.

ACTH-related peptides: receptors and signal transduction systems involved in their neurotrophic and neuroprotective actions

ACTH-related peptides are promising neurotrophic and neuroprotective agents, as demonstrated in many in vivo and in vitro studies. They accelerate nerve repair after injury, improving both sensor and motor function. Furthermore, ACTH-related peptides have neuroprotective properties against cisplatin- and taxol-induced neurotoxicity, they improve neuronal function in animals with neuropathy due to experimental diabetes, and they prevent degeneration of myelinated axons in rats suffering from experimental allergic neuritis, a model of peripheral demyelinating neuropathy. Studies in neuronal cultures have corroborated these clinical observations and serve to investigate the mechanism of action of the ACTH-related peptide effects. This paper reviews both in vitro and in vivo effects and emphasizes the mechanism of action. Recent data on melanotrophic receptors and signal transduction systems will be discussed in this context.

Ultrastructural neuropathologic effects of Taxol on neurons of the freshwater snail Lymnaea stagnalis

Cerebral ganglia of the freshwater snail Lymnaea stagnalis were incubated in vitro in 10 microM Taxol for 8 and 24 h. Cremophor EL (0.1%) was used as a diluant. The tissue was processed for electron microscopy. Various ultrastructural parameters were assessed quantitatively. Cremophor EL appeared to seriously affect the cell somata of the multipeptidergic caudodorsal cells. In the Cremophor-controls the mean area of Golgi zones, the percentage dense material (neuropeptides) in these zones, the number of large electron dense granules (these are involved in neuropeptide processing) and the mean nuclear heterochromatin clump size, were significantly smaller than in the Ringer-controls, whereas the number of lipid droplets was higher. All these parameters, except for the lipid droplets, were not different in the Cremophor-controls and the Taxol-treated specimens. After 24 h treatment, but not after 8 h, Cremophor EL furthermore induced an increase in the number of axonal microtubules. It is argued that the results might signify activation of the neurons by Cremophor EL. Taxol induced a significant increase in the number of microtubules in axons and cell somata. Furthermore an increase in the number of Golgi zones was observed, suggesting activated neuropeptide synthesis. In all groups immunostaining with antibodies to neuropeptides produced by the caudodorsal cells was normal. Release of neuropeptide (exocytosis) from axon endings was elevated after Taxol treatment, and exceptionally high in specimens cotreated with Taxol and Org 2766 (incubation time 22 h). The effect of Org 2766 and Taxol on the number of microtubules was cumulative.(ABSTRACT TRUNCATED AT 250 WORDS)

Protection by an ACTH4-9 analogue against the toxic effects of cisplatin and taxol on sensory neurons and glial cells in vitro

Sensory neuropathy is a serious side effect of anti-tumour drugs such as cisplatin and taxol. There are indications that an analogue of the adrenocorticotrophic hormone 4-9 fragment (ACTH4-9: Met(O2)-Glu-His-Phe-D-Lys-Phe) can prevent these neurotoxic effects. We studied the potential protective effects of this analogue in cultures of chick dorsal root ganglia and rat Schwann cells treated with cisplatin or taxol to gain insight into the mode of action and characteristics of this neuroprotection. Neurite outgrowth of sensory neurons in vitro was dose-dependently inhibited by cisplatin and taxol; after 48 hr, 10 micrograms/ml cisplatin reduced outgrowth from 431 +/- 17 microns to 220 +/- 6 microns and 0.01 micrograms/ml taxol from 344 +/- 3 microns to 200 +/- 43 microns. Co-treatment of 10 micrograms/ml cisplatin with the ACTH4-9 analogue (0.1 nM-1 nM) resulted in about 35% more outgrowth than cisplatin alone. In contrast, the analogue could not prevent taxol neurotoxicity. Migration of neurons and satellite cells from the DRG-body is completely inhibited by 10 micrograms/ml cisplatin. Taxol had no effect on the migration of these cells. In addition, cisplatin was more toxic to Schwann cells than taxol; 3-10 micrograms/ml cisplatin significantly reduced their laminin content, total protein, 2',3'-cyclic nucleotide 3'-phosphodiesterase activity, and cell division. The ACTH4-9 analogue (0.01 nM-100 nM) had no effect on the migration of cells out of the DRGs and could not prevent the toxic effect on the Schwann cells. These data support our hypothesis that the neuroprotective effect of ACTH4-9 analogue is brought about by a direct action on neurons, possibly by replacing a Schwann-/satellite-cell derived trophic factor.

Effects of the ACTH(4-9) analogue, ORG 2766, on vincristine cytotoxicity in two human lymphoma cell lines, U937 and U715

The use of cytotoxic drug vincristine (VCR) is limited by the occurrence of peripheral neuropathy. A neurotrophic ACTH(4-9) analogue, ORG 2766, is being studied for its protective effect. Possible modulatory effects of ORG 2766 on tumour cell growth and interference with the cytotoxic efficacy of VCR were studied in two human lymphoma cell lines, U937 and U715. The effects of ORG 2766 on cell growth and survival and on VCR-mediated cytotoxicity were investigated using two MTT-based assays to study direct cytotoxic effects and to assess residual growth after pretreatment. Treatment with ORG 2766 alone had no effect on cell growth and survival. Neither did this drug affect VCR cytotoxicity. However, after 96 h pretreatment with ORG 2766 and a culture period of 7 days, a reduction in residual growth and a potentiation of VCR-induced inhibition of growth capacity was observed in U715 cells, and to some extent also in U937 cells. It is concluded that ORG 2766 has no stimulatory effects on tumour growth and does not negatively interfere with VCR-mediated cytotoxicity. Rather it enhances the cytostatic effect of VCR. It is suggested that ORG 2766 can safely be used in clinical trials investigating the ability of ORG 2766 to counteract VCR-induced neurotoxicity.

Differential trophic effects of ORG 2766, an ACTH(4-9)/MSH(4-9) analogue, on peptidergic neurons and glial cells in the snail Lymnaea stagnalis

Cerebral ganglia of the pond snail Lymnaea stagnalis were incubated in vitro in 10(-6) M ORG 2766 for 10 and 20 h, with or without regular refreshment of the medium. Quantitative ultrastructural study of cross sections of the cerebral commissure showed that the number of microtubules in large axons of all ORG 2766-treated groups had increased after 10 h by approximately 40%. In a separate experiment, central nervous systems were incubated in ORG 2766 for only 15 min and then kept in Ringer's for 9 h and 45 min. Maximal stimulation (40% increase of microtubules) in these specimens was also observed. The results would seem to support the hypothesis that ORG 2766 binds to a receptor and initiates a long-lasting effect. It is argued that ORG 2766 stimulates novel synthesis of tubulin rather than being involved in the assembly of microtubules. Also, glial cells were found to be activated by ORG 2766. This was concluded from the fact that the number of heterochromatin clumps and the size of the clumps in these cells had decreased and the amount of glial tissue surrounding the axons had increased (approximately 50%). In contrast to the activating effects of ORG 2766 on glial tissue, this drug did not affect nucleoli, number, and size of the heterochromatin clumps and the Golgi apparatus in the neuropeptidergic caudodorsal cells. The data indicate that ORG 2766 exerts differential trophic effects.

Binding of a biotinylated neurotrophic ACTH(4-9) analogue, Org 2766, to neurofilament-positive cells in primary or cell line cultures

To study the putative binding sites of the neurotrophic peptide Org 2766, an analogue of ACTH(4-9) [H-Met(O2)-Glu-His-Phe-D-Lys-Phe-OH], biotinylated forms of the peptide were used. After fixation, cultures of rat spinal cord and dorsal root ganglia were incubated with 4-10 microM of biotinyl-Org 2766 (b-Org 2766). Binding of both N- and C-terminally biotinylated Org 2766 was seen to phase-bright, round cells with thin processes, but not to flat, orthogonal-shaped cells with tapering processes. The b-Org 2766 binding was displaceable by an excess of nonbiotinylated Org 2766. Light and electron microscopy showed that the biotinylated peptide binds to a cytoplasmatic component as well as to the cell membrane. Double-labeling experiments with b-Org 2766 and an antibody (RT-97) to a high molecular weight neurofilament protein in dorsal root ganglion cultures showed, using fluorescence and confocal scanning laser microscopy, that all b-Org 2766 binding cells were neurofilament positive. Biotinylated Org 2766 did also bind to the neuronally differentiated cells in cultures of the human neuroblastoma cell line SK-N-SH, but not to those differentiated into epithelial cells. The present data suggest that the neurotrophic peptide Org 2766 binds specifically to cell types with neuronal characteristics.

The influences of fragments and analogs of ACTH/MSH upon recovery from nervous system injury

Post-injury treatment with some fragments and analogs of the adrenocorticotropic hormone (ACTH) can influence recovery after nervous system injury. This review considers both the successful and unsuccessful attempts to facilitate neural and behavioral recovery from nervous system damage via post-injury administration of these compounds. To date no single unifying explanation for the mixed results observed in animals prepared with forebrain injuries has been achieved. Several possible explanations for the variety of observations reported and several potentially productive avenues for future research are suggested.