Cardiac metabolic imaging using hyperpolarized [1-13 C]lactate as a substrate

Role of L-lactate as an energy substrate in primary rat podocytes under physiological and glucose deprivation conditions

Lactate has long been acknowledged to be a metabolic waste product, but it has more recently been found as a fuel energy source in mammalian cells. Podocytes are an important component of the glomerular filter, and their role in maintaining the structural integrity of this structure was established. These cells rely on a constant energy supply and reservoir. The utilization of alternative energy substrates to preserve energetic homeostasis is a subject of extensive research, and lactate appears to be one such candidate. Therefore, we investigated the role of lactate as an energy substrate and characterize the lactate transport system in cultured rat podocytes during sufficient and insufficient glucose supplies. The present study, for the first time, demonstrated the presence of lactate transporters in podocytes. Moreover, we observed modified the amount of these transporters in response to limited glucose availability and after l-lactate supplementation. Simultaneously, exposure to l-lactate preserved cell survival during insufficient glucose supply. Interestingly, during glucose deprivation, lactate exposure allowed the steady flow of glycolysis and prevented glycogen reserves depletion. Summarizing, podocytes utilize lactate as an energy substrate and possess a developed system that controls lactate homeostasis, suggesting that it plays an essential role in podocyte metabolism, especially during fluctuations of energy availability.

Labile Photo-Induced Free Radical in α-Ketoglutaric Acid: a Universal Endogenous Polarizing Agent for In Vivo Hyperpolarized 13 C Magnetic Resonance

Hyperpolarized (HP) 13 C magnetic resonance enables non-invasive probing of metabolism in vivo. To date, only 13 C-molecules hyperpolarized with persistent trityl radicals have been injected in humans. We show here that the free radical photo-induced in alpha-ketoglutaric acid (α-KG) can be used to hyperpolarize photo-inactive 13 C-molecules such as [1-13 C]lactate. α-KG is an endogenous molecule with an exceptionally high radical yield under photo-irradiation, up to 50 %, and its breakdown product, succinic acid, is also endogenous. This radical precursor therefore exhibits an excellent safety profile for translation to human studies. The labile nature of the radical means that no filtration is required prior to injection while also offering the opportunity to extend the 13 C relaxation time in frozen HP 13 C-molecules for storage and transport. The potential for in vivo metabolic studies is demonstrated in the rat liver following the injection of a physiological dose of HP [1-13 C]lactate.

Labile Photo-Induced Free Radical in α-Ketoglutaric Acid: a Universal Endogenous Polarizing Agent for In Vivo Hyperpolarized 13C Magnetic Resonance

Hyperpolarized (HP) 13C magnetic resonance enables non-invasive probing of metabolism in vivo. To date, only 13C-molecules hyperpolarized with persistent trityl radicals have been injected in humans. We show here that the free radical photo-induced in alpha-ketoglutaric acid (α-KG) can be used to hyperpolarize photo-inactive 13C-molecules such as [1-13C]lactate. α-KG is an endogenous molecule with an exceptionally high radical yield under photo-irradiation, up to 50 %, and its breakdown product, succinic acid, is also endogenous. This radical precursor therefore exhibits an excellent safety profile for translation to human studies. The labile nature of the radical means that no filtration is required prior to injection while also offering the opportunity to extend the 13C relaxation time in frozen HP 13C-molecules for storage and transport. The potential for in vivo metabolic studies is demonstrated in the rat liver following the injection of a physiological dose of HP [1-13C]lactate.