Effects of dextran sulfate on stabilization of milk lipoprotein lipase and VLDL triglyceride hydrolysis in vitro

Lipoprotein lipase is active as a monomer

Lipoprotein lipase (LPL), the enzyme that hydrolyzes triglycerides in plasma lipoproteins, is assumed to be active only as a homodimer. In support of this idea, several groups have reported that the size of LPL, as measured by density gradient ultracentrifugation, is ∼110 kDa, twice the size of LPL monomers (∼55 kDa). Of note, however, in those studies the LPL had been incubated with heparin, a polyanionic substance that binds and stabilizes LPL. Here we revisited the assumption that LPL is active only as a homodimer. When freshly secreted human LPL (or purified preparations of LPL) was subjected to density gradient ultracentrifugation (in the absence of heparin), LPL mass and activity peaks exhibited the size expected of monomers (near the 66-kDa albumin standard). GPIHBP1-bound LPL also exhibited the size expected for a monomer. In the presence of heparin, LPL size increased, overlapping with a 97.2-kDa standard. We also used density gradient ultracentrifugation to characterize the LPL within the high-salt and low-salt peaks from a heparin-Sepharose column. The catalytically active LPL within the high-salt peak exhibited the size of monomers, whereas most of the inactive LPL in the low-salt peak was at the bottom of the tube (in aggregates). Consistent with those findings, the LPL in the low-salt peak, but not that in the high-salt peak, was easily detectable with single mAb sandwich ELISAs, in which LPL is captured and detected with the same antibody. We conclude that catalytically active LPL can exist in a monomeric state.

Dextran sulfate sodium inhibits amyloid-β oligomer binding to cellular prion protein

Amyloid-β peptide (Aβ), especially its oligomeric form, is believed to play an important role in the pathogenesis of Alzheimer's disease (AD). To this end, the binding of Aβ oligomer to cellular prion protein (PrP(C)) plays an important role in synaptic dysfunction in a mouse model of AD. Here, we have screened for compounds that inhibit Aβ oligomer binding to PrP(C) from medicines already used clinically (Mizushima Approved Medicine Library 1), and identified dextran sulfate sodium (DSS) as a candidate. In a cell-free assay, DSS inhibited Aβ oligomer binding to PrP(C) but not to ephrin receptor B2, another endogenous receptor for Aβ oligomers, suggesting that the drug's action is specific to the binding of Aβ oligomer to PrP(C) . Dextran on the other hand did not affect this binding. DSS also suppressed Aβ oligomer binding to cells expressing PrP(C) but not to control cells. Furthermore, while incubation of mouse hippocampal slices with Aβ oligomers inhibited the induction of long-term potentiation, simultaneous treatment with DSS restored the long-term potentiation. As DSS has already been approved for use in patients with hypertriglyceridemia, and its safety in humans has been confirmed, we propose further analysis of this drug as a candidate for AD treatment. Amyloid-β peptide (Aβ) oligomer-binding to cellular prion protein (PrP(C) ) is important in synaptic dysfunction in Alzheimer's disease (AD). We found here that dextran sulfate sodium (DSS) inhibits Aβ oligomer binding to PrP(C) . Simultaneous treatment of hippocampal slices with DSS restored long-term potentiation (LTP) in the presence of Aβ oligomers. Since DSS has already been approved for clinical use, we propose this drug is a candidate drug for AD treatment.