IF recombinant bacterial heparinase III (HepIII, EC 4.2.2.8; estimated dose range 0.5–2.5 U/kg, intravenous, administered as a priming dose on days 1 and 3) is administered to aged C57BL/6 mice (18–24 months, both sexes, with established spontaneous AA amyloid deposits confirmed by Congo red birefringence in spleen and kidney) followed five days later by passive immunotherapy with a murine anti-SAA monoclonal antibody (anti-SAA IgG, 10 mg/kg i.v., three doses over two weeks),

THEN splenic and renal AA amyloid burden (quantified by Congo red morphometry, thioflavin S fluorescence, and anti-SAA ELISA on tissue homogenates) will be reduced by ≥40% relative to either monotherapy arm (HepIII alone or antibody alone) at the 6-week primary endpoint, with a parallel ≥2-fold increase in macrophage infiltration density (F4/80⁺ cells per amyloid plaque area, immunohistochemistry) and measurable anti-SAA IgG co-localization within the amyloid core (confirmed by immunofluorescence co-staining with thioflavin S),

BECAUSE the following sequential mechanistic chain operates:

1. Perlecan and agrin co-localize with AA amyloid fibrils in splenic perifollicular zones and renal glomeruli from the earliest stages of deposition, forming an electrostatically stabilizing scaffold of highly sulfated heparan sulfate (HS) chains around the cross-β fibril core that physically occludes the amyloid surface from immune surveillance. (Snow et al., Am J Pathol 1988; Lab Invest 1991 — as cited in Evidence Set)

2. The integrated HS scaffold creates a dual barrier: (a) a steric obstruction limiting diffusion of IgG molecules (hydrodynamic radius ~5 nm) into the dense proteoglycan matrix surrounding fibrils, and (b) electrostatic repulsion between anionic HS chains and the Fc regions of therapeutic antibodies, collectively preventing opsonization of fibril-bound SAA epitopes. (van der Westhuizen et al., Am J Pathol — as cited in Evidence Set)

3. Bacterial HepIII selectively cleaves β-1,4 glycosidic linkages within heparan sulfate (not heparin), enzymatically liberating the HS side chains from perlecan and agrin core proteins embedded within the amyloid matrix. This substrate specificity is mechanistically critical because it targets the amyloid-associated HS pool while sparing heparin-class GAGs that modulate antithrombin III-mediated coagulation, defining a therapeutic window between amyloid destabilization and systemic anticoagulant toxicity. (HepIII substrate specificity and coagulation safety — Evidence Set, Safety Profile section)

4. Enzymatic stripping of HS chains from the amyloid matrix destabilizes the fibril scaffold, rendering previously protected SAA epitopes accessible. Evidence from transgenic mammalian heparanase-1 overexpression models demonstrates that HS removal from amyloid deposits is sufficient to reduce splenic and renal amyloid load without requiring concurrent immunotherapy, establishing proof-of-concept that HS is load-bearing with...

SENS category: GlycoSENS