Lysozyme enhances renal excretion of advanced glycation endproducts in vivo and suppresses adverse age-mediated cellular effects in vitro: a potential AGE sequestration therapy for diabetic nephropathy?

BACKGROUND: Lysozyme (LZ), a host-defense protein, contains an 18 amino-acid domain with high affinity binding for sugar-derived proteins or lipids, called advanced glycation endproducts (AGE), that are implicated in diabetes- and age-dependent complications (DC).
MATERIALS AND METHODS: A) The effects of LZ on AGE- removal were tested in vivo. LZ was injected (200 ug/day, i.p., X2 weeks) in non-obese diabetic (NOD), db/db (+/+) mice, and non-diabetic, AGE-infused Sprague-Dawley rats. B) LZ: AGE interactions with macrophage-like T1B-183 cells (Mf) and mesangial cells (MC) were tested in vitro.
RESULTS: A) In NOD mice, LZ reduced the elevated basal serum AGE (sAGE) (p < 0.05), enhanced urinary AGE (uAGE) excretion by approximately 2-fold (p < 0.01), while it reduced albuminuria (UA), p < 0.005. In db/db mice, LZ infusion also reduced the elevated sAGE (p < 0.05), doubled uAGE excretion (p < 0.05), and decreased UA (p < 0.01). In addition, LZ maintained normal sAGE in normal rats infused with AGE-BSA, as it doubled the urinary AGE (uAGE) clearance (p < 0.01). B) LZ stimulated the uptake and degradation of (125) I-labeled AGE-BSA and (25) I-human serum AGE by Mf, while suppressing AGE-induced TNFalpha and IGF-I production. In MC, LZ suppressed the AGE-promoted PDGF-B, alpha1 type IV collagen, and tenascin mRNA levels, and restored the AGE-suppressed expression and activity of MMP-9, but not MMP-2.
CONCLUSION: LZ may act to: a) accelerate renal in-vivo AGE clearance, b) suppress macrophage and mesangial cell- specific gene activation in vitro, and c) improve albuminuria due to diabetes. These data suggest that LZ by sequestering AGEs may protect against diabetic renal damage.