Carnosine metabolism in diabetes is altered by reactive metabolites

Abstract

Carnosinase 1 (CN1) contributes to diabetic nephropathy by cleaving histidine-dipeptides which scavenge reactive oxygen and carbonyl species and increase nitric oxide (NO) production. In diabetic mice renal CN1 activity is increased, the regulatory mechanisms are unknown. We therefore analysed the in vitro and in vivo regulation of CN1 activity using recombinant and human CN1, and the db/db mouse model of diabetes. Glucose, leptin and insulin did not modify recombinant and human CN1 activity in vitro, glucose did not alter renal CN1 activity of WT or db/db mice ex vivo. Reactive metabolite methylglyoxal and Fenton reagent carbonylated recombinant CN1 and doubled CN1 efficiency. NO S-nitrosylated CN1 and decreased CN1 efficiency for carnosine by 70 % (p < 0.01), but not for anserine. Both CN1 cysteine residues were nitrosylated, the cysteine at position 102 but not at position 229 regulated CN1 activities. In db/db mice, renal CN1 mRNA and protein levels were similar as in non-diabetic controls, CN1 efficiency 1.9 and 1.6 fold higher for carnosine and anserine. Renal carbonyl stress was strongly increased and NO production halved, CN1 highly carbonylated and less S-nitrosylated compared to WT mice. GSH and NO2/3 concentrations were reduced and inversely related with carnosine degradation rate (r = -0.82/-0.85). Thus, reactive metabolites of diabetes upregulate CN1 activity by post-translational modifications, and thus decrease the availability of reactive metabolite-scavenging histidine dipeptides in the kidney in a positive feedback loop. Interference with this vicious circle may represent a new therapeutic target for mitigation of DN.

Carnosine Catalyzes the Formation of the Oligo/Polymeric Products of Methylglyoxal

“…The putative β-alanine transporter TauT is expressed in all renal cells and we previously demonstrated carnosine synthase (CS) expression in podocytes and tubular cells [26]. On the other hand, increased CN1 activity due to MG-induced carbonylation of the enzyme, as described before [27], also did not alter intracellular carnosine levels. Although we only found low carnosine transport into cells, all three cell types only tolerated a certain amount of carnosine or anserine.…”

“…Recent studies have demonstrated the beneficial effects of carnosine on the development of diabetic complications [2, 19, 22, 27] and it is assumed that those effects are, at least partially, due to the MG-scavenging potential of carnosine. The quenching capacity and structure related reactivity of carnosine for reactive species has already been reported [39-41].…”

“…The kidney has an intrinsic carnosine metabolism with carnosine synthase and carnosinase 1 (CN1) being expressed in glomeruli and tubular cells [26]. CN1 activity is increased under diabetic conditions [27]. Carnosine uptake into renal cells occurs by the proton-coupled oligotransporter PEPT2 [16].…”

On the Relationship between Energy Metabolism, Proteostasis, Aging and Parkinson’s Disease: Possible Causative Role of Methylglyoxal and Alleviative Potential of Carnosine

“…Animal studies indicate that carnosine is beneficial towards senescence-accelerated mice [131] and may have therapeutic potential where deleterious aldehydes such as MG appear to be important in age-related pathologies [132] such as diabetes [127,133,134], diabetic kidney disease [134-136], atherosclerosis [137-139] and cataractogenesis [140-144] as well as models of stroke [145-148], Alzheimer’s disease [149-151] and PD [152-154]. …”

FL‐926‐16, a novel bioavailable carnosinase‐resistant carnosine derivative, prevents onset and stops progression of diabetic nephropathy in db/db mice

“…What is more, an experimental study conducted in db / db mice revealed that renal CNDP1 activity is up‐regulated by post‐translational modifications induced by RCS and ROS. In turn, increased CNDP1 activity reduces the availability of histidine‐containing dipeptides in the diabetic kidney, thus establishing a positive feedback loop resulting in increasing renal carbonyl stress (Peters et al, ). Therefore, the search for carnosinase‐resistant carnosine derivatives represents a suitable strategy against carbonyl stress‐dependent disorders.…”