Is Low Molecular Weight Heparin a Neuroprotectant?

Abstract

This communication reports the results of investigations on the effect of low molecular weight heparin (LMWH) on intraneuronal calcium release, and considers its possible relevance to the treatment of ischemic stroke. It previously was shown that intraneuronal injection of conventional heparin (MW 12,000) in vitro prevents glutamate-induced calcium release from intracellular stores through its blocking action on IP3 (inositol-1,4,5-triphosphate) receptors, and thus interferes with events occurring in the ischemic cascade. In the experiments reported herein, a LMWH of MW 4500 was shown to have these same effects when injected into a Purkinje cell in an in vitro cerebellar slice preparation, and also when administered externally (bath application). By contrast, conventional heparin works only when injected into the cell; bath application has no effect. The results are interpreted to mean that the larger conventional heparin molecule cannot pass through the cell membrane, while the smaller LMWH molecule does indeed enter the cell. In a clinical trial, LMWH begun within 48 hours of ischemic stroke onset in humans improved outcome at 6 months; conventional heparin given in a similar trial was without benefit. That one anticoagulant was beneficial while another failed suggests the possibility that the difference was independent of effect on the clotting system. The experimental data herein reported support the view that LMWH may benefit stroke victims by an action directly cytoprotective against the consequences of neuronal ischemia.

The Phospholipase C-IP3 Pathway is Involved in Muscarinic Antinociception

“…Some evidence indicates that the low molecular weight heparin (6000 Da) used in this study is membrane permeable. Perfusion of low molecular weight heparin over a nonpermeabilized cerebellar slice preparation attenuated glutamate-stimulated increases in free intracellular Ca 2+ (Jonas et al, 1997). IP 3 , through the interaction with specific receptors located on the endoplasmic reticulum, causes release of Ca 2+ from intracellular stores into the cytoplasm (Mignery and Sudhof, 1990;Ferris et al, 1992).…”

“…Furthermore, a shift to the right of the dose-response curve of physostigmine was produced by pretreatment with low molecular weight heparin. Heparin is a potent and selective IP 3 receptor antagonist (Jonas et al, 1997). This compound must be injected into cells or perfused onto permeabilized cells because of its high molecular weight (12 000-13 000 Da) and lack of membrane permeability.…”

2-Aminoethoxydiphenyl borate (2-APB) antagonises inositol 1,4,5-trisphosphate-induced calcium release, inhibits calcium pumps and has a use-dependent and slowly reversible action on store-operated calcium entry channels

“…This compound is limited because it has multiple actions including uncoupling G-protein signalling and activating ryanodine receptors (RyRs) (for reviews see [4,5]). Furthermore, heparin is not membrane permeant, and therefore has to be injected or infused into cells from micropipettes, although it has been suggested that low molecular weight heparin species may cross the plasma membrane and thus inhibit InsP 3 Rs within intact cells [6]. Xestospongins, which were first described as relatively specific membrane-permeant InsP 3 R antagonists by Pessah and colleagues [7], have been employed many times to prove whether InsP 3 Rs are involved in particular responses.…”

Role of intracellular calcium in acute thermal pain perception

“…Some evidence indicates that the low molecular weight heparin (6000 Da) used in this study is membrane permeable. Perfusion of low molecular weight heparin over a nonpermeabilized cerebellar slice preparation attenuated glutamate-stimulated increases in free intracellular Ca ++ (Jonas et al, 1997). Conversely, the i.c.v injection of d-myo inositol, compound which generates InsP 3 , produced an increase of the mouse pain threshold that was prevented by non-hyperalgesic doses of heparin.…”

“…The i.c.v. administration of heparin, a potent InsP 3 -receptor antagonist (Jonas et al, 1997), produced a dose-dependent hyperalgesic effect indicating the importance of InsP 3 R in the modulation of pain perception. This hypothesis is supported by data indicating that the blockade of InsP 3 R by heparin, as well as the inhibition of InsP 3 production by LiCl, prevented the analgesic effect of cholinomimetic drugs (Galeotti et al, 2003) and delta opioid agonists (Narita et al, 2000).…”