Neurotrophic Effects of the Glycosaminoglycan C3 on Dendritic Arborization and Spines in the Adult Rat Hippocampus: A Quantitative Golgi Study

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.

Attenuation of glial scar formation in the injured rat brain by heparin oligosaccharides

Injury to the central nervous system causes glial reactions, which eventually lead to the formation of a glial scar and inhibit axonal regeneration. The present study aimed to reduce the extent of glial scar formation in injured cerebral cortex using heparin hexasaccharide (6-mer) and octasaccharide (8-mer). A single injection of 20 microl of heparin 6-mer or heparin 8-mer (10mg/ml), native heparin (10mg/ml), or saline vehicle was given into the wound cavity just after cryo-injury in the cerebral cortex. In saline-injected control rats, strong chondroitin sulfate-A (CS-A) immunoreactivity using 2H6 antibody was observed around the injured site. Double labeling using an antibody against glial fibrillary acidic protein, a glial marker, further demonstrated that CS-A immunoreactivity was mainly expressed on the reactive astrocytes at the glial scar, indicating that CS-A immunohistochemistry is useful for evaluating glial scar formation. Quantitative morphometrical analysis revealed that the area of CS-A immunoreactivity was significantly decreased by 53% in heparin-6-mer-injected animals and 44% in heparin-8-mer-injected ones 6 days after the injury, but native heparin had no effect on CS-A-immunoreactive areas. Both heparin oligosaccharides also attenuated the intensity of CS-A immunoreactivity in the reactive astrocytes and caused astrocytic cellular processes to be less branched. These results demonstrate that a single injection of heparin oligosaccharides attenuates glial scar formation, indicating that heparin oligosaccharides may be applicable to many fibrotic diseases and restore functional integrity.

Glycosaminoglycan C3 protects against AF64A-induced cholinotoxicity in a dose-dependent and time-dependent manner

Several studies revealed that proteoglycans (PGs) and glycosaminoglycans (GAGs) play a pivotal role in the pathogenesis of Alzheimer's disease (AD). PGs have affinity to amyloid beta (Abeta) and protect it against proteolysis, and the consequent aggregation is the cause of neurotoxicity. This effect is believed to be attenuated by GAGs. Moreover, a low-molecular-weight GAG C3 derived from unfractionated heparin has been reported to protect against Abeta-induced tau-2 immunoreactivity and cholinergic damage induced by a cholinotoxin, AF64A, in rat. However, the optimal dose and the timeframe of administration of C3 are still unknown. In our studies, we revealed the concentration-dependent and time-dependent effects of C3 on AF64A-induced cholinergic lesion in rat. C3 was administered orally in 5, 10, and 25 mg/kg/day concentration, 7 days before and/or 7 days after intracerebroventricular (i.c.v.) AF64A administration. Our results have shown that 25 mg/kg/day C3 effectively protects against AF64A-generated cholinotoxicity if administered both 7 days before and 7 days after the AF64A injection. In contrast to these findings, administration of 5 or 10 mg/kg/day C3 or 25 mg/kg/day C3, given 7 days before or 7 days after stereotaxic AF64A injection, did not show cholinoprotective effects. In conclusion, the time-dependent effects of C3 on AF64A-induced cholinergic lesion suggest that C3 may act via the processes of both neuroprotection and neurorepair. Moreover, the effects of C3 depend largely on the administered dose of this low-molecular-weight GAG. The present findings also indicate that C3, administered in the effective concentration and timeframe, may play a pivotal role in the treatment of AD.

Protective effect of the heparin-derived oligosaccharide C3, on AF64A-induced cholinergic lesion in rats

Alzheimer's disease (AD) literature indicates that glycosaminoglycans (GAGs) may prevent proteoglycan-induced amyloid-beta (Abeta) aggregation, decrease Abeta-induced tau-2 immunoreactivity, and increase the axonal growth and arborization of hippocampal neurons. However, there is no information about the impact of GAGs on cholinergic lesions. Here, AF64A was administered stereotaxically into the lateral ventricles of rats, at doses that are selective for cholinotoxicity (1 and 2 nmol). The heparin-derived oligosaccharide (HDO), C3 (25mg/kg), was administered orally, once daily for 7 days before, and 7 days after AF64A administration. Choline acetyltransferase (ChAT) immunohistochemistry revealed that C3 administration reduced AF64A-induced cholinergic damage in the septum and cingulum bundle. Quantitative neuronal cell counts showed that C3 attenuated, by 60%, the decrease in cell number in the medial septum. Enzyme analysis showed that C3 also significantly restored ChAT (30%) and acetylcholinesterase (AChE) enzyme activity (45%), which had been diminished by AF64A. Our data suggest that, in addition to its effects of anti-Abeta aggregation, anti-Abeta-induced tau-2 immunoreactivity, and neurotrophic effects, C3 also effectively reduces AF64A-induced cholinergic damage; hence it may have potential therapeutic value in AD patients.

Low molecular weight glycosaminoglycan blockade of beta-amyloid induced neuropathology

Previous studies have shown different roles for proteoglycans and glycosaminoglycans (GAGs) in Alzheimer's disease (AD) neuropathology. Using a rat model of beta-amyloid induced neuropathology, we tested whether low molecular weight glycosaminoglycans (Certoparin and C6) could be useful as preventative agents and/or as a potential therapeutic treatment for AD. Chronic subcutaneous low molecular weight glycosaminoglycan injections beginning either before or after an intra-amygdaloid beta-amyloid-(25-35) injection blocked abnormal intracellular tau changes and reactive astrocytosis but did not affect beta-amyloid's aggregation state. Also, low molecular weight glycosaminoglycan injections beginning 1 day prior to sacrifice did not block the effects of beta-amyloid nor did injections of a disaccharide, suggesting chronic low molecular weight glycosaminoglycan treatment is needed to block the effects of beta-amyloid. Furthermore, these data indicate that there is a molecular weight range of active low molecular weight glycosaminoglycans in this model; and supports the investigation of low molecular weight glycosaminoglycans as a preventative and/or therapeutic treatment of beta-amyloid induced neuropathology.