Selective LOXL2/LOXL3 inhibition by PXS-5153A halts ongoing crosslink maturation in aged mouse aorta, creating an end...

IF PXS-5153A (LOXL2/LOXL3-selective inhibitor, estimated oral dose ~10 mg/kg/day based on PXS-5505 rodent pharmacokinetics) is administered to 18-month-old male C57BL/6J mice for 12 weeks,

THEN the ratio of mature-to-immature aortic collagen crosslinks (PYD/HLNL measured by LC-MS/MS) will decrease by ≥30% relative to vehicle-treated aged controls, pulse wave velocity will improve by ≥10% toward young-mouse reference values, vascular cell senescence burden (p16INK4a+ adventitial and smooth muscle cells) will be reduced, and elastic fiber integrity (aortic desmosine content) will be preserved — unlike pan-LOX inhibition with BAPN,

BECAUSE the following mechanistic chain operates:

1. Aged C57BL/6J aorta accumulates elevated LOXL1 and LOXL3 enzyme activity concurrent with an elevated pool of immature divalent crosslinks (HLNL/HHMD), demonstrating that crosslink maturation is an ongoing, active biochemical process in the aged vasculature — not a historical, completed event (Aging-US 2024, as cited in Research Context).
2. Immature divalent crosslinks (HLNL, HHMD) are reducible, aldimine-based adducts that retain susceptibility to endogenous matrix metalloproteinases (MMP-1, MMP-8, MMP-13) and collagenases, while mature trivalent pyridinoline crosslinks (PYD/DPD) are non-reducible, protease-resistant, and represent the molecular checkpoint of fibrosis irreversibility (Circulation Research 2026, as cited in Research Context). [SPECULATIVE: the quantitative MMP accessibility difference between HLNL-crosslinked and PYD-crosslinked collagen fibrils in vascular tissue specifically has not been directly demonstrated by in vitro fibril degradation assays and requires confirmation.]
3. LOXL2 and LOXL3 — not LOXL1 — are the primary enzymatic drivers of pathological collagen I crosslinking and vascular stiffening; genetic depletion of LOXL2 (Loxl2+/- mice) specifically attenuates passive arterial stiffening and delays onset of hypertension-induced fibrosis in males, while LOXL1 remains required for elastic fiber integrity through its tropoelastin crosslinking role (LOXL2 depletion attenuates passive arterial stiffening in males and protects from progressive arterial stiffening)[https://doi.org/10.1101/2023.12.13.571541].
4. By selectively inhibiting LOXL2/LOXL3 with PXS-5153A (>40-fold selectivity over LOX/LOXL1 per Schilter et al. cited in Research Context), the ongoing enzymatic conversion of HLNL/HHMD to PYD/DPD is halted, preventing further accumulation of irreversible crosslinks. Critically, this simultaneously creates a therapeutic repair window: the existing pool of immature crosslinks — which is still large in aged aorta — can now be degraded by endogenous MMP activity, since these crosslinks remain MMP-accessible, while LOXL1 continues to support elastic fiber maintenance. This is the core repair mechanism: not slowing new crosslink formation in an otherwise clean matrix, but halting the maturation cascade to allow endogenous proteolysis to clear...

SENS category: GlycoSENS

Key references: • doi.org/10.1101/2023.12.13.571541]. • doi.org/10.1111/acel.12155]. • doi.org/10.1074/jbc.ra119.011031]. • doi.org/10.1111/acel.12155], • doi.org/10.1101/2023.12.13.571541],