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

Acute Effect of Selective Chemical Inactivation of Sympathetic or Parasympathetic Atrial Ganglionated Plexus Structures on Atrial Fibrillation Inducibility in Pigs

We studied the role of both parts of the autonomic intracardiac nervous system in the pathogenesis of atrial fibrillation (AF). In 12 pigs weighing 39±3 kg, AF was induced by burst stimulation. Chemical inactivation of intrinsic cardiac neurons within the right atria was performed by transendocardial injections of liposomal neuromodulators into the dorsal part of the right atrial wall. Sympathetic and parasympathetic terminals were inactivated with 6-hydroxydopamine (6-OHDA, n=6) and ethylcholine aziridinium ion (AF64A, n=6), respectively. Neuromodulators were encapsulated in liposomes (LS) with diameters of 310±50 nm for OHDA and 290±50 nm for AF64A. LS-6-OHDA and LS-AF64A were injected into the ganglionated plexuses after measuring the baseline effective refractory period and assessing myocardial resistance to AF. These measurements were repeated 90 min after the injections. The optimal doses were 0.2 mg/kg for LS-6-OHDA and 0.4 mg/kg for LS-AF64A (in 4 ml of suspension). Immediately after injections of liposomal neuromodulators, almost all pigs showed an increase in HR, and a short-term BP elevation was observed in the LS-AF64A group. At the end of the experiment, similar decrease in the effective refractory period and similar increase in the resistance to AF were observed in all animals. Thus, selective chemical inactivation of cholinergic and adrenergic terminals of the intracardiac nervous system with liposomal neuromodulators increased the resistance to AF in an acute experiment. However, the short observation period does not allow making a definite conclusion about the role of the autonomic nervous system in the pathogenesis of AF, which requires verification of the obtained data in a chronic experiment.

Protective Effects of a synthetic glycosaminoglycan mimetic (OTR4132) in a rat immunotoxic lesion model of septohippocampal cholinergic degeneration

Using a partial hippocampal cholinergic denervation model, we assessed the effects of the RGTA^® named OTR4132, a synthetic heparan-mimetic biopolymer with neuroprotective/neurotrophic properties. Long-Evans male rats were injected with the cholinergic immunotoxin 192 IgG-saporin into the medial septum/diagonal band of Broca (0.37 µg); vehicle injections served as controls. Immediately after surgery, OTR4132 was injected into the lateral ventricles (0.25 µg/5 µl/rat) or intramuscularly (1.5 mg/kg). To determine whether OTR4132 reached the lesion site, some rats received intracerebroventricular (ICV) or intramuscular (I.M.) injections of fluorescent OTR4132. Rats were sacrificed at 4, 10, 20, or 60 days post-lesion (DPL). Fluorescein-labeled OTR4132 injected ICV or I.M. was found in the lesion from 4 to 20 DPL. Rats with partial hippocampal cholinergic denervation showed decreases in hippocampal acetylcholinesterase reaction products and in choline acetyltransferase-positive neurons in the medial septum. These lesions were the largest at 10 DPL and then remained stable until 60 DPL. Both hippocampal acetylcholinesterase reaction products and choline acetyltransferase-positive neurons in the medial septum effects were significantly attenuated in OTR4132-treated rats. These effects were not related to competition between OTR4132 and 192 IgG-saporin for the neurotrophin receptor P75 (p75^NTR), as OTR4132 treatment did not alter the internalization of Cy3-labelled 192 IgG. OTR4132 was more efficient at reducing the acetylcholinesterase reaction products and choline acetyltransferase-positive neurons than a comparable heparin dose used as a comparator. Using the slice superfusion technique, we found that the lesion-induced decrease in muscarinic autoreceptor sensitivity was abolished by intramuscular OTR4132. After partial cholinergic damage, OTR4132 was able to concentrate at the brain lesion site possibly due to the disruption of the blood-brain barrier and to exert structural and functional effects that hold promises for neuroprotection/neurotrophism.

Sugar glues for broken neurons

Proteoglycans (PGs) regulate diverse functions in the central nervous system (CNS) by interacting with a number of growth factors, matrix proteins, and cell surface molecules. Heparan sulfate (HS) and chondroitin sulfate (CS) are two major glycosaminoglycans present in the PGs of the CNS. The functionality of these PGs is to a large extent dictated by the fine sulfation patterns present on their glycosaminoglycan (GAG) chains. In the past 15 years, there has been a significant expansion in our knowledge on the role of HS and CS chains in various neurological processes, such as neuronal growth, regeneration, plasticity, and pathfinding. However, defining the relation between distinct sulfation patterns of the GAGs and their functionality has thus far been difficult. With the emergence of novel tools for the synthesis of defined GAG structures, and techniques for their characterization, we are now in a better position to explore the structure-function relation of GAGs in the context of their sulfation patterns. In this review, we discuss the importance of GAGs on CNS development, injury, and disorders with an emphasis on their sulfation patterns. Finally, we outline several GAG-based therapeutic strategies to exploit GAG chains for ameliorating various CNS disorders.

Proteoglycans in the central nervous system: role in development, neural repair, and Alzheimer's disease

Proteoglycans (PGs) are major components of the cell surface and extracellular matrix and play critical roles in development and maintenance of the central nervous system (CNS). PGs are a family of proteins, all of which contain a core protein to which glycosaminoglycan side chains are covalently attached. PGs possess diverse physiological roles, particularly in neural development, and are also implicated in the pathogenesis of neurodegenerative diseases such as Alzheimer's disease (AD). The main functions of PGs in the CNS are reviewed as are the roles of PGs in brain injury and in the development or treatment of AD.

Glycosaminoglycans and neuroprotection

Glycosaminoglycans (GAGs) are basic building blocks of the ground substance of the extracellular matrix and present at the cellular level as an important component of the glycocalyx covering the cell membrane. In addition to the general role of GAGs in maintaining the integrity of the cell and extracellular matrix by retaining water, certain GAGs exhibit anticoagulant and neuroprotective properties and serve as cell-surface receptors for various molecules. Although heparin, a highly sulfated GAG, has been used as a drug for more than 70 years due to its anticoagulant attributes, the neuroprotective properties of GAGs came into focus only in recent years. The discovery of some of the roles GAGs play in the pathomechanism of numerous neurodegenerative disorders as well as shedding light on the neuroprotective properties of these compounds in animal studies raised the possibility that GAGs may provide an entirely new avenue in the treatment of neurodegenerative diseases. Indeed, some GAGs were successfully used to improve the cognitive function of patients with various neurodegenerative conditions (Ban et al. (1991, 1992); Conti et al. (1989a, b); Passeri and Cucinotta, (1989); Santini (1989). Although the mechanism by which the GAGs exhibit neuroprotective properties is not entirely clear, there is a general consensus that the major factors of the neuroprotective attributes of GAGs include the impact of GAGs on amyloidogenesis and the regulatory action of GAGs in the apoptotic pathway.

Effects of heparin and enoxaparin on APP processing and Aβ production in primary cortical neurons from Tg2576 mice

BACKGROUND

Alzheimer's disease (AD) is caused by accumulation of Aβ, which is produced through sequential cleavage of β-amyloid precursor protein (APP) by the β-site APP cleaving enzyme (BACE1) and γ-secretase. Enoxaparin, a low molecular weight form of the glycosaminoglycan (GAG) heparin, has been reported to lower Aβ plaque deposition and improve cognitive function in AD transgenic mice.

METHODOLOGY/PRINCIPAL FINDINGS

We examined whether heparin and enoxaparin influence APP processing and inhibit Aβ production in primary cortical cell cultures. Heparin and enoxaparin were incubated with primary cortical cells derived from Tg2576 mice, and the level of APP and proteolytic products of APP (sAPPα, C99, C83 and Aβ) was measured by western blotting. Treatment of the cells with heparin or enoxaparin had no significant effect on the level of total APP. However, both GAGs decreased the level of C99 and C83, and inhibited sAPPα and Aβ secretion. Heparin also decreased the level of β-secretase (BACE1) and α-secretase (ADAM10). In contrast, heparin had no effect on the level of ADAM17.

CONCLUSIONS/SIGNIFICANCE

The data indicate that heparin and enoxaparin decrease APP processing via both α- and β-secretase pathways. The possibility that GAGs may be beneficial for the treatment of AD needs further study.

Neuroprotective properties of glycosaminoglycans: potential treatment for neurodegenerative disorders

Previous studies suggest that proteoglycans and glycosaminoglycans (GAGs) may play an important role in the pathogenesis and/or alleviation of neurodegenerative disorders, including Alzheimer's disease (AD). Proteoglycans increase the formation of neurofibrillary tangles, and stimulate the aggregation of beta-amyloid (Abeta). This effect, on the other hand, is believed to be competitively inhibited by certain GAGs. Over the past few years, we have examined the neuroprotective properties of Neuroparin (C3), a low-molecular-weight GAG (approx. 2.1 kDa), in animal models of lesions characteristic of AD. Neuroparin is composed of 4-10 oligosaccharides, and it is derived from heparin involving depolymerization of heparin by gamma irradiation. In our experiments, Neuroparin protected against cholinergic lesions induced by intracerebroventricular injection of a specific cholinotoxin, AF64A, in rats. Administration of Neuroparin attenuated AF64A-stimulated, low-affinity nerve growth factor receptor-immunoreactive axonal varicosities in the rat septum, and increased arborization of hippocampal CA1 neurons. Neuroparin also reduced the septal caspase 3 immunoreactivity induced by AF64A treatment. Moreover, Neuroparin reduced tau 2 immunoreactivity in the rat hippocampus, stimulated by intra-amygdaloid injection of Abeta(25-35). These findings are in good agreement with our previous data indicating a neuroprotective role of GAGs. These results, plus others, all suggest that Neuroparin may possess neuroprotective properties against many of the characteristic neural lesions in AD. Since our pharmacokinetic studies revealed that Neuroparin is capable of crossing the blood-brain barrier, Neuroparin may, conceivably, open an entirely new avenue in the treatment of neurodegenerative disorders. Phase I studies have been completed, and have proven to be extremely supportive in that regard.

Heparin accelerates gelsolin amyloidogenesis

The chemical environment of the extracellular matrix may influence the tissue-selective deposition observed there in gelsolin amyloid disease. Previously, we have identified the proteases that generate the amyloidogenic fragments from the full-length gelsolin variants and demonstrated that heparin is capable of accelerating gelsolin amyloidogenesis. Herein, we identify the structural features of heparin that promote the 8 kDa disease-associated gelsolin fragments (residues 173-243) generated at the cell surface to form amyloid. In conjunction with electron microscopy analyses, our kinetic studies demonstrate that heparin efficiently accelerates the formation of gelsolin amyloid by enabling intermolecular beta-sheet formation. The use of heparin analogues reveals that sulfation is important in accelerating amyloidogenesis and that the extent of acceleration is proportional to the molecular weight of heparin. In addition, heparin accelerated aggregation at both early and late stages of amyloidogenesis. Dynamic light scattering coupled to size exclusion chromatography showed that heparin promotes the formation of soluble aggregates. Collectively, these data reveal that heparin templates fibril formation and affords solubility to the aggregating peptides through its sulfated structure. By extension, the biochemical results herein suggest that tissue-selective deposition characteristic of the gelsolin amyloidoses is likely influenced by the extracellular localization of distinct glycosaminoglycans.

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.