Growth factors: potential therapeutic applications in neurology

Expression of nerve growth factor and brain-derived neurotrophic factor in astrocytomas

Neurotrophic factors (NTFs) are well known to serve critical functions in neural survival, neurite growth and cell differentiation in vivo and in vitro. Previous progress has indicated that nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF), two NTF family members, may be involved in the process of tumor progression. In the present study, the expression of NGF and BDNF was detected using immunohistochemistry on 70 adult astrocytoma samples collected from distinct locations as well as of various pathological grades, with an additional 15 samples being collected from normal adult brain tissue to be used as controls. NGF and BDNF were identified to be expressed in all samples, and their positive cell expression rates in astrocytomas demonstrated a significant increase compared with that in the normal controls (P<0.05), particularly in grade III (P<0.05). In addition, the expression of NGF and BDNF exhibited a gradual decrease ranging from the temporal lobe, parietal lobe and cerebellum to the frontal lobe (P<0.05). The results of the present study suggest that the expression of NGF and BDNF is increased in astrocytomas, which is associated with the pathological grade and the astrocytoma location.

Hyperbaric oxygenation in peripheral nerve repair and regeneration

Peripheral nerves are essential connections between the central nervous system and muscles, autonomic structures and sensory organs. Their injury is one of the major causes for severe and longstanding impairment in limb function. Acute peripheral nerve lesion has an important inflammatory component and is considered as ischemia-reperfusion (IR) injury. Surgical repair has been the standard of care in peripheral nerve lesion. It has reached optimal technical development but the end results still remain unpredictable and complete functional recovery is rare. Nevertheless, nerve repair is not primarily a mechanical problem and microsurgery is not the only key to success. Lately, there have been efforts to develop alternatives to nerve graft. Work has been carried out in basal lamina scaffolds, biologic and non-biologic structures in combination with neurotrophic factors and/or Schwann cells, tissues, immunosuppressive agents, growth factors, cell transplantation, principles of artificial sensory function, gene technology, gangliosides, implantation of microchips, hormones, electromagnetic fields and hyperbaric oxygenation (HBO). HBO appears to be a beneficial adjunctive treatment for surgical repair in the acute peripheral nerve lesion, when used at lower pressures and in a timely fashion (<6 hours).

Neurotrophic factor expression in childhood low-grade astrocytomas and ependymomas

BACKGROUND

Neurotrophic factors (nerve growth factor [NGF], brain-derived neurotrophic factor [BDNF] and glial-derived neurotrophic factor [GDNF]) are growth factors implicated in the growth and differentiation of brain nerve cells. An involvement of these factors in the biology and progression of some specific tumours has been suggested. In accordance with the role of neurotrophic factors in tumour behaviour the aim of the present study was to investigate their expression in two childhood brain neoplasms, namely low-grade astrocytomas and ependymomas.

MATERIALS AND METHODS

We investigated the NGF, BDNF, GDNF and NGF receptors (TrkA and p75) expression in the tumour tissues, cerebrospinal fluid (CSF) and plasma of ten children affected by low-grade astrocytomas and ependymomas. Control tissue samples (together with CSF and plasma samples) were obtained from patients who underwent surgery for cerebral vascular or epileptogenic lesions.

RESULTS

The expression of NGF decreases both in tumour samples and in the CSF of affected children compared with controls. BDNF instead increases in CSF, while the expression of GDNF remains unchanged both in tissues and in CSF. No differences were found in neurotrophic factor plasma levels in patients or in controls. Gene expression of NGF and its high-affinity receptor (TrkA) are reduced in tumour tissues, whereas the number of cells immunopositive to the low-affinity NGF receptor (p75) is increased.

CONCLUSION

Reduced expression of NGF and TrkA has been shown in low-grade astrocytomas and ependymomas. These findings may be related to the role of this neurotrophin in cell differentiation and apoptosis. The different expression of NGF, BDNF, and GDNF in low-grade astrocytomas and ependymomas suggests that a different degree of redundancy exists among members of the neurotrophic factor family and that their expression may be correlated with the biology and the behaviour of these tumours.

Postnatal changes in nerve growth factor and brain derived neurotrophic factor levels in the retina, visual cortex, and geniculate nucleus in rats with retinitis pigmentosa

Royal College of Surgeons (RCS) rats are a well established animal model of inherited retinitis pigmentosa (RP). Using RCS rats we examined the distribution of nerve growth factor (NGF) and brain derived neurotrophic factor (BDNF) in the visual cortex, geniculate nucleus and retina at three different postnatal ages. It was found that the retina of rats with RP expresses low amounts of NGF and BDNF in young and adult life. Altered levels of these factors were found in the visual cortex and in the geniculate nucleus. Our findings indicate that NGF and BDNF are differentially affected in the visual system of developing and adult RCS rats, suggesting that neurotrophins may be implicated in the pathogenesis of inherited RP.

Stress and nerve growth factor: findings in animal models and humans

Stress is elicited by environmental, social or pathological conditions occurring during the life of animals and humans that determine changes in the nervous, endocrine and immune systems. In the present review, we present data supporting the hypothesis that stress-related events both in animal models and humans are characterized by modifications of endogenous nerve growth factor (NGF) synthesis and/or utilization. Stress inducing alteration in NGF synthesis and/or utilization appears to be more severe during neurogenesis and in early postnatal life. However, NGF endogenously released during stress may promote remodeling of damaged tissues following acute and/or chronic stressful events.

Molecular mechanisms regulating motor neuron development and degeneration

Motor neurons are a well-defined, although heterogeneous group of cells responsible for transmitting information from the central nervous system to the locomotor system. Spinal motor neurons are specified by soluble factors produced by structures adjacent to the primordial spinal cord, signaling through homeodomain proteins. Axonal pathfinding is regulated by cell-surface receptors that interact with extracellular ligands and once synaptic connections have formed, the survival of the somatic motor neuron is dependent on the provision of target-derived growth factors, although nontarget-derived factors, produced by either astrocytes or Schwann cells, are also potentially implicated. Somatic motor neuron degeneration leads to profound disability, and multiple pathogenetic mechanisms including aberrant growth factor signaling, abnormal neurofilament accumulation, excitotoxicity, and autoimmunity have been postulated to be responsible. Even when specific deficits have been identified, for example, mutations of the superoxide dismutase-1 gene in familial amyotrophic sclerosis and polyglutamine expansion of the androgen receptor in spinal and bulbar muscular atrophy, the mechanisms by which somatic motor neuronal degeneration occurs remain unclear. In order to treat motor system degeneration effectively, we will need to understand these mechanisms more thoroughly.

Song behavior, NGF level and NPY distribution in the brain of adult male zebra finches

The aim of the present study was to investigate the role of nerve growth factor (NGF) and neuropeptide Y (NPY) in the higher vocal center (HVC) on singing behavior of adult male zebra finches. The results of our studies show: (a) that NGF is present in the brain of these birds and it is higher in the HVC than in the other neostriatal tissues; (b) that exogenous administration of NGF or NGF-antibody had no discernible effect on singing behavior; and (c) that NGF enhances the NPY immunoreactivity in neurons and fibers localized in HVC and other areas of the neostriatum and hippocampus whereas anti-NGF decreased NPY stained cells in the hippocampus. These studies indicate that NGF is produced in the brain of zebra finch and that it plays a role in the regulation of NPY.

The role of neuronal growth factors in neurodegenerative disorders of the human brain

Recent evidence suggests that neurotrophic factors that promote the survival or differentiation of developing neurons may also protect mature neurons from neuronal atrophy in the degenerating human brain. Furthermore, it has been proposed that the pathogenesis of human neurodegenerative disorders may be due to an alteration in neurotrophic factor and/or trk receptor levels. The use of neurotrophic factors as therapeutic agents is a novel approach aimed at restoring and maintaining neuronal function in the central nervous system (CNS). Research is currently being undertaken to determine potential mechanisms to deliver neurotrophic factors to selectively vulnerable regions of the CNS. However, while there is widespread interest in the use of neurotrophic factors to prevent and/or reduce the neuronal cell loss and atrophy observed in neurodegenerative disorders, little research has been performed examining the expression and functional role of these factors in the normal and diseased human brain. This review will discuss recent studies and examine the role members of the nerve growth factor family (NGF, BDNF and NT-3) and trk receptors as well as additional growth factors (GDNF, TGF-alpha and IGF-I) may play in neurodegenerative disorders of the human brain.

Overstimulation of nerve growth factors in postinfectious and autoimmune diseases

Nerve growth factor (NGF) in cerebrospinal fluid was measured by ELISA in ten children with postinfectious diseases and in five children with diseases suggested to be of autoimmune etiology. Three groups of patients were studied: (1) those with moderately elevated concentrations (50.67 +/- 17.02 pg/mL, mean and SEM), (2) those with high concentrations (mean 424.25 +/- 125.41 pg/mL, mean and SEM), and (3) those with enormously high concentrations (mean 2,745 +/- 1,819.46 pg/mL, mean and SEM). We suggest that CSF-NGF could be used as an immunologic marker of an ongoing CNS process. Uncontrolled signaling of NGF receptors may lead to long-term inflammatory and autoimmune responses, which in turn can lead to disease.

Neurological monitoring of neurotoxicity induced by paclitaxel/cisplatin chemotherapy

To evaluate the neurotoxicity of paclitaxel/cisplatin chemotherapy, we studied neurological and electrophysiological functions in 14 patients who had been treated with 1-7 courses of paclitaxel/cisplatin. The cumulative paclitaxel and cisplatin doses ranged from 175 to 1225 mg/m2 and 100-700 mg/m2, respectively. Neurological examinations as well as motor nerve conduction studies of the peroneal nerve were performed and summarised by means of a peripheral neuropathy score. Neurotoxicity with onset usually after the second treatment cycle occurred in 13 patients. 12 patients complained about sensory symptoms, 13 patients had impaired vibration sense and 8 patients developed additional muscle weakness, predominantly of the legs. Dysfunction of peroneal motor nerve conduction occurred in 13 patients. Reduction of amplitudes as well as slowing of conduction velocities were seen in 13 patients and prolonged distal latencies in 10 patients. The peripheral neuropathy score was elevated in 13 patients. Neurological symptoms, impairment of both vibration sense and tendon reflexes, and the peripheral neuropathy score increased with the cumulative doses of paclitaxel/cisplatin. Serial analysis among selected patients also revealed an increase in neurotoxicity with increasing cumulative drug doses. These data indicate the development of neurotoxicity in most patients treated with paclitaxel/cisplatin and also suggest that early signs of neurotoxicity can be detected by clinical examination with emphasis on symptoms as well as vibration sense and can be well documented by electrophysiological investigations.