Emerging pharmacology of nerve growth factor

Delivery of nerve growth factor to brain via intranasal administration and enhancement of brain uptake

The main objective of the study was to investigate the efficacy of chitosan to facilitate brain bioavailability of intranasally administered nerve growth factor (NGF). In vitro permeability studies and electrical resistance studies were carried out across the bovine olfactory epithelium using Franz diffusion cells. The bioavailability of intranasally administered NGF in rat hippocampus was determined by carrying out brain microdialysis in Sprague-Dawley rats. The in vitro permeation flux across the olfactory epithelium of NGF solution without chitosan (control) was found to be 0.37 +/- 0.06 ng/cm(2)/h. In presence of increasing concentration of chitosan (0.1%, 0.25%, and 0.5%, w/v) the permeation flux of NGF was found to be 2.01 +/- 0.12, 3.88 +/- 0.19, and 4.12 +/- 0.21 ng/cm(2)/h respectively. Trans-olfactory epithelial electrical resistance decreased approximately 34.50 +/- 4.06% in presence of 0.25% (w/v) chitosan. The C(max) in rats administered with 0.25% (w/v) chitosan and NGF was 1008.62 +/- 130.02 pg/mL, which was significantly higher than that for rats administered with NGF only 97.38 +/- 10.66 pg/mL. There was approximately 14-fold increase in the bioavailability of intranasally administered NGF with chitosan than without chitosan. Chitosan can enhance the brain bioavailability of intranasally administered NGF.

Low molecular weight glycosaminoglycan C3 attenuates AF64A-stimulated, low-affinity nerve growth factor receptor-immunoreactive axonal varicosities in the rat septum

Glycosaminoglycans (GAGs) play a pivotal role in the pathogenesis of Alzheimer's disease (AD). Although, as we have shown earlier, a low molecular weight GAG, C3, protects against ethylcholine aziridinium (AF64A)-induced cholinergic damage, and against A(beta)-induced tau-2-immunoreactivity (IR), the mechanism of the neuroprotective effect of GAGs is not yet known. Several clues exist. Previous studies in rats revealed that continuous NGF infusion (icv) after AF64A injection increases septal ChAT and AChE activities. Moreover, C3 increases axonal outgrowth in the rat hippocampus, raising the possibility of a NGF-receptor mediated neuroprotection. Furthermore, it has been reported that NGF expression is increased in the septum following AF64A administration. To study the question regarding the mechanism of neuroprotective action of GAGs, AF64A, a selective cholinotoxin, was administered stereotaxically, bilaterally, into the lateral ventricles of Fischer albino male rats (1 nmol/2 microl/side). In order to establish the effect of C3 on the expression of the NGF receptor-IR elements, C3 was administered orally (25 mg/kg, once a day), by gavage, 7 days before, and 7 days after the AF64A injection. NGF receptor immunohistochemistry revealed that AF64A induced the appearance of NGF-receptor-IR axonal varicosities in the rat medial septum. These varicose fibers were attenuated by 14 days' administration of C3. The possible explanation of our data may be that C3 increases NGF synthesis in the lateral septum. The increased level of NGF could suppress the increased, AF64A-induced NGF receptor expression in the medial septal nucleus. These results further accentuate our earlier observations that C3 may have potential as a therapeutic agent in AD and other neurodegenerative disorders.

Neurotrophic activities and therapeutic experience with a brain derived peptide preparation

In spite that the use of naturally occurring neurotrophic factors like NGF, BDNF, CNTF, GDNF and others for treatment of neurodegenerative disorders seems promising because of their pharmacological properties, until now no large scale clinical trials have been published. One of the reasons is that these molecules are unable to penetrate through the blood brain barrier, making invasive application strategies like intracerebroventricular infusion necessary. Another one is the fact that in first clinical studies, several undesirable side-effects like hyperalgesia or weight loss have been reported. Major efforts are now put into development of improved application procedures and in treatment protocols for avoiding the known side-effects. Already 7 years ago it has been demonstrated that Cerebrolysin, a peptidergic drug, produced from purified brain proteins by standardized enzymatic breakdown, containing biologically active peptides, is exerting nerve growth factor like activity on neurons from dorsal root ganglia. Still ongoing investigations are showing growth promoting efficacy of this drug in different neuronal populations from peripheral and central nervous system. The current findings are in accordance with several older publications, enabling now a more clear interpretation of these findings. In addition to the direct neurotrophic effect, the drug also shows clear neuroprotective properties after different types of lesion in vitro and in vivo, resembling the pharmacological activities of naturally occurring nerve growth factors. Neurotrophic and neuroprotective efficacy has been shown with a broad variety of methods in different models and it is remarkable that all biochemical and morphological drug dependent alterations are resulting in improvements of learning and memory. Because of these experimental results, clinical trials using cerebrolysin in Alzheimer's patients have been performed, demonstrating a quick improvement in the overall state of the patients, particularly enhancing the cognitive performance. It is remarkable that these effects are long lasting after cessation of the active treatment procedure. Even 6 months after stop of drug application improvements in AD-patients are detectable. Therefore it is concluded that cerebrolysin is able to induce repair phenomena, resulting in long term stabilization. In contrast to the naturally occurring growth factors, tolerability of this drug is extremely high, without any reports about serious side-effects in these clinical studies.

Nerve growth factor affects passive avoidance learning and retention in developing mice

The present studies investigate the effects of early nerve growth factor (NGF) administration on the ontogenetic profile of learning and retention capacities in mice. The learning paradigm used required the animals to withhold an escape response from a vibrating platform to avoid a punishment (step-down passive avoidance). In Experiment 1, acquisition of step-down passive avoidance was essentially the same in 11- and 15-day-old mice whereas only the latter showed significant retention after 24 h. In younger animals, data pointed to a facilitating effect of familiarization with the test environment. In Experiment 2 ICV NGF treatment on postnatal day 9 increased step-down latencies in both reinforced and nonreinforced pups on day 11. Moreover, NGF mice exposed in nonreinforcement condition on day 11 failed to acquire the avoidance response 24 h later, suggesting that the treatment anticipated the appearance of latent inhibition. Results of Experiment 3, investigating the effects of different durations of preexposure to the test apparatus on passive avoidance acquisition 24 h later, supported the specificity of NGF effects on the emergence of latent inhibition. These findings suggest that neural populations responsive to NGF trophic effect are involved in the maturation of early learning and retention capacities in rodents.

Cholinergic differentiation factor/leukemia inhibitory factor enhances functional effects of adrenal medulla grafts after hippocampal lesions in rats

We recently found that adrenal medulla grafts implanted into the hippocampus of rats survived for several months and significantly decreased the deficits produced by hippocampal lesions in the radial maze test [Jousselin-Hossaja et al. (1994) Neuroscience 59, 275-284]. These grafts contained choline acetyltransferase immunopositive chromaffin cells and received cholinergic innervation. In the experiments reported here, adrenal medulla grafts implanted in lesioned hippocampus were treated with cholinergic differentiation factor/leukemia inhibitory factor. In the presence of this factor, the number of chromaffin cells with cholinergic phenotypes increased as well as the beneficial effects of the grafts on the performances of rats in the radial maze. These results suggest that the functional effects of adrenal medulla grafted into the hippocampus set into play cholinergic mechanisms. The cholinergic differentiation factor/leukemia inhibitory factor may also have facilitated the survival and recovery of cholinergic neurons in the host tissue. However, due to the large range of action of this cytokine and the richness of the adrenal medulla contents, non cholinergic factors are also probably involved. Our results may help to elucidate the functions of the cholinergic differentiation factor/leukemia inhibitory factor since they provide the first indication that its intracerebral injection may have behavioral effects. Moreover, our data confirm the possibility of improving the efficiency of adrenal medulla implants in the central nervous system by appropriate treatments, not only by facilitating survival but also by selectively amplifying some potential factors of the graft. This might greatly enlarge the field of this grafting technique for analysing the normal functioning of the brain and for repairing it.

Effects of chronic basic fibroblast growth factor administration to rats with partial fimbrial transections on presynaptic cholinergic parameters and muscarinic receptors in the hippocampus: comparison with nerve growth factor

The present study compares the effects of chronic administration of basic fibroblast growth factor (bFGF) and nerve growth factor (NGF) on various hippocampal cholinergic parameters in rats with partial unilateral fimbrial transections. Lesions resulted in marked reductions of several presynaptic cholinergic parameters: choline acetyltransferase (ChAT) activity (by 50%), [3H]-acetylcholine ([3H]ACh) synthesis (by 59%), basal and veratridine (1 microM)-evoked [3H]ACh release (by 44 and 57%, respectively), and [3H]vesamicol binding site densities (by 35%). In addition, [3H]AF-DX 116/muscarinic M2 binding site densities were also modestly decreased (by 23%). In contrast, [3H]pirenzepine/muscarinic M1 and [3H]AF-DX 384/muscarinic M2/M4 binding site densities were not altered by the lesions, nor were they affected by any of the treatments. Intracerebroventricular administration of bFGF (10 ng, every other day, for 21 days) partially prevented the lesion-induced deficit in hippocampal ChAT activity, an effect that was not markedly different from that measured in the NGF-treated (1 microgram, intracerebroventricularly, every other day, for 21 days) rats. In rats treated with a combination of bFGF and NGF, ChAT activity was not different from that in rats treated with the individual factors alone. In contrast, the lesion-induced deficits in the other cholinergic parameters were not attenuated by bFGF treatment, although they were at least partially prevented by NGF administration. To determine whether higher concentrations of bFGF are necessary to affect cholinergic parameters other than hippocampal ChAT activity, rats were treated with 1 microgram (every other day, 21 days) of the growth factor. In this group of rats, detrimental effects of bFGF, manifested by an increased death rate (46%), and marked reductions in body weight of the survivors, were observed. In addition, this concentration of bFGF appeared to exacerbate the lesion-induced reduction in [3H]ACh synthesis by hippocampal slices; [3H]ACh synthesis in lesioned hippocampi represented 36 and 52% of that in contralateral unlesioned hippocampi for the bFGF-treated and control groups, respectively. In conclusion, although bFGF administration attenuates the deficit in hippocampal ChAT activity induced by partial fimbrial transections, this does not appear to translate into enhanced functional capacity of the cholinergic terminals. This is clearly in contrast to NGF, which enhances not only hippocampal ChAT activity, but also other parameters indicative of increased function in the cholinergic terminals.

Pharmacological stimulation reveals recombinant human nerve growth factor-induced increases of in vivo hippocampal cholinergic function measured in rats with partial fimbrial transections

The present study determined the effects of chronic recombinant human nerve growth factor administration [1 microgram given intracerebroventricularly q.i.d. (every other day) for three weeks] on in vivo hippocampal cholinergic function in adult rats with unilateral partial fimbrial transections. Partial fimbrial transections did not significantly alter the levels of endogenous acetylcholine or [2H4]acetylcholine in the hippocampus due to functional compensation by surviving cholinergic terminals. In animals chronically treated with nerve growth factor, the levels of endogenous choline, endogenous acetylcholine, [2H4]choline and [2H4]acetylcholine accumulated in the hippocampus on the lesioned side were not significantly different from those on the contralateral unlesioned side or from values measured in animals treated with cytochrome c, a control protein. However, changes in cholinergic parameters induced by the partial lesions or recombinant human nerve growth factor treatment became manifest when animals were challenged using pharmacological agents such as pentylenetetrazole or pilocarpine given after lithium chloride pretreatment. First, in nerve growth factor-treated animals administered the general stimulant pentylenetetrazole (10 mg/kg) 2 min prior to measuring in vivo cholinergic parameters, we observed a significant increase in the hippocampal content of [2H4]choline in both lesioned and unlesioned hippocampi. The magnitude of the increase was significantly higher on the lesioned compared to the unlesioned side. Although chronic recombinant human nerve growth factor treatment induced increases of hippocampal [2H4]choline levels, there were no concomitant increases in the level of [2H4]acetylcholine. Second, in nerve growth factor-treated animals administered lithium chloride (3 mmol/kg) 20 h prior to pilocarpine (30 mg/kg), we observed a significant enhancement of the content of endogenous acetylcholine in the hippocampus of the lesioned side. Partial fimbrial transections also reduced in vitro cholinergic parameters reflecting endogenous acetylcholine levels in hippocampal slices. The content of endogenous acetylcholine in the slices was decreased by approximately 50% and chronic nerve growth factor treatment significantly elevated this value to approximately non-lesioned control values. Similarly, reductions in spontaneous and veratridine-evoked release of endogenous acetylcholine induced by partial fimbrial transections were counteracted by recombinant human nerve growth factor treatment. These findings demonstrate that chronic recombinant human nerve growth factor treatment effectively enhances the in vivo and in vitro synthesis, storage and release of endogenous acetylcholine. The results from the in vivo studies suggest that recombinant human nerve growth factor-induced differences in functional performance of hippocampal neurons may only be manifest during behavioral and/or pharmacological stimulation.