The reactive pyruvate metabolite dimethylglyoxal in experimental disease models and the role of Ilvbl in its generation in the brain

Abstract

Reactive glucose metabolites are involved in neurological complications of diabetes by the generation of advanced glycated end products (AGEs), which are formed by the interaction between α-dicarbonyls and proteins. AGEs induce oxidative stress, inflammation and tissue damage and have been associated with neuropathy, nephropathy and retinopathy. So far, only the α-dicarbonyls 3-deoxyglucosone, glyoxal and methylglyoxal have been recognized as reactive glucose metabolites and associated with complications in diabetes. Only recently, the α-dicarbonyl dimethylglyoxal (DMG) has been categorized as mammal cellular pyruvate metabolite, and its levels were higher in the plasma of type-1 diabetic mice and in the serum of patients with diabetes. In this thesis, I investigated the α-dicarbonyl DMG in mouse models under pathological conditions and its metabolic pathway in mammals using liquid chromatography coupled to tandem mass spectrometry (LC-MS2). Here, plasma DMG concentrations were upregulated in mouse experimental models of type-1 and type-2 diabetes. In contrast, high-fat diet did not influence the serum levels of DMG, suggesting that diabetic conditions – but not obesity itself – are associated with plasma DMG upregulation and accumulation. Moreover, DMG levels were enormously augmented in the ipsilateral side of a mouse model of hyperglycemic stroke compared to sham control. Interestingly, DMG levels were also higher in the contralateral hemisphere of the brain of mice with stroke compared to sham controls, showing that the contralateral hemisphere is also affected by ischemic stroke. Furthermore, the current study confirmed that DMG is a post-glycolytic product in mammals and its levels are increased under hypoxic conditions in vitro. Then, I investigated the role of the gene ilvB acetolactate synthase-like (Ilvbl), the mammal orthologue gene of acetolactate synthase that generates DMG from pyruvate in bacteria, yeast and plants. Importantly, Ilvbl knockout reduced DMG levels in the brain of mice with type-1 diabetes or hyperglycemic stroke, showing that Ilvbl has conserved its role in DMG generation in mammals. Moreover, DMG interacted with lysine, generating the glycated amino acid Nε-3-hydroxy-2-butanonelysine (HBL), confirming that DMG is a reactive compound and can glycate proteins generating AGEs. Thus, DMG induced oxidative stress and neuroinflammation in mouse hippocampal neuronal (HT-22) cells, probably based on protein glycation. In conclusion, this study characterizes the α-dicarbonyl DMG in experimental models under pathological conditions, showing that DMG could play a significant role in diabetic complications and ischemic stroke complications. DMG is the only α-dicarbonyl generated after glycolysis, and the current discovery could explain why cells consuming lactate – such as neurons – are not protected by dicarbonyl stress. Importantly, this study shows that ILVBL plays a significant role in the DMG generation from pyruvate in the brain of acute or chronic hyperglycemic mice. Further investigation on DMG and the attenuation of its concentrations may lead to improvement in diabetic and ischemic stroke complications.