Several studies in recent years have linked supplementation with the amino acid beta-alanine to a better performance in high intensity physical exercises. The effect would be due to the increase in intramuscular carnosine concentrations, which can act as a cellular buffer, maintaining the cytosolic pH and contraction force.

However, scientists from the Center for Research of Redox Processes in Biomedicine (RIDC Redoxoma), led by Professor Marisa H.G. Medeiros at the Instituto de Química of Universidade de São Paulo (USP), investigate another role of carnosine, which would bring even more beneficial effects to the body: the detoxification of reactive aldehydes. In 2016 the team published an article describing the structure of a compound resulting from the reaction between carnosine and aldehyde acrolein found in urine samples of non-smokers adults (https://doi.org/10.1038/srep19348). The work already demonstrated the role of carnosine in cellular detoxification, but did not provide information on where adducts had been formed.

Now the team detected carnosine-acrolein adducts in muscle tissue samples from cyclists supplemented with beta-alanine after intense exercise, demonstrating that carnosine plays an acrolein-scavenger role in skeletal muscle.

"Our results reveal one of the physiological roles of muscle carnosine, especially during intermittent high-intensity exercise, and may explain its ergogenic and therapeutic effects. This research is important because it reveals a specific mechanisms of reactive aldehyde detoxification in samples of human tissue”, said Medeiros.

The study, published in July in the journal Redox Biology, was conducted in collaboration with Professors Guilherme Giannini Artioli and Bruno Gualano at the Escola de Educação Física e Esporte (EEFE) of USP.

Physical exercise and oxidative stress

Exercise has been shown to increase lipid peroxidation and the activity of antioxidant enzymes superoxide dismutase (SOD) and glutathione peroxidase (GPX). This means that intense physical exercise causes oxidative stress.

Lipid peroxidation consists of a cascade of reactions resulting from lipid oxidation of cell membranes. It occurs both during normal physiological and pathological processes, and generates a complex mixture of oxidized phospholipid products, including hydroperoxides, which then decompose to form reactive electrophilic aldehydes. By increasing lipid peroxidation, exercise leads to increased production of aldehydes such as acrolein (ACR), malondialdehyde (MDA), 4-hydroxy-2-hexenal (HHE) and 4-hydroxy-2-nonenal (HNE) among others.

Many of these aldehydes have mutagenic and carcinogenic properties. They are capable of reacting with DNA and proteins, potentially compromising the structure and function of these biomolecules. Therefore, reducing aldehyde concentration is essential for normal cell function.

To deal with these toxic molecules, living organisms have developed defense and detoxification mechanisms. The main endogenous detoxification pathways are the conjugation of aldehydes with glutathione (GSH) and reduction or oxidation reactions catalyzed by alcohol dehydrogenase, aldo-keto reductase and aldehyde dehydrogenase. In addition, histidine-containing dipeptides, such as carnosine, homocarnosine and anserine, may also form adducts with aldehydes and assist in the elimination of such compounds.

Carnosine is a dipeptide formed by the amino acids β-alanine and L-histidine. It is found in several tissues, and is present in high concentrations in the skeletal muscles and brain. In addition to the intake of meat in the diet, the most effective way to increase carnosine levels in the tissues is supplementation with the amino acid beta-alanine, one of its precursors.

Studies have shown that carnosine acts as a cellular buffer in the skeletal muscles, contributing to the improvement of athletes' physical performance. It also has anti-glycation properties, with possible action in type 2 diabetes and diabetic nephropathy, and antioxidant properties, such as metal quenching and reactive aldehydes detoxification. For these reasons, carnosine has long been considered to have a number of relevant physiological roles, such as healthy ageing and disease prevention.

According to Medeiros, the ability to scavenge aldehydes is a likely hypothesis to explain many of the effects attributed to carnosine. In order to test this hypothesis, her team developed an ultra-sensitive and highly specific methodology capable of quantifying carnosine and corresponding adducts in human tissues and biological fluids, based on high performance liquid chromatography (HPLC) coupled to tandem mass spectroscopy (MS/MS). "Although carnosine has been known to scientists for a long time, to unravel the mechanisms by which it acts and to know its biological targets we need techniques that allow to measure what is happening in the tissues," she said.

The study

With this methodology, the researchers analyzed samples of the vastus lateralis muscle of 14 cyclists after intermittent high-intensity cycling tests before and after 28 days of beta-alanine supplementation. They quantified carnosine-acrolein (CAR-ACR), carnosine-4-hydroxy-2-hexenal (CAR-HHE) and carnosine-4-hydroxy-2-nonenal (CAR-HNE) adducts.

The study revealed that supplementation with beta-alanine increased muscle carnosine content by about 50% compared to pre-supplementation. It also showed a significant increase in post-exercise carnosine-acrolein adduct levels following beta-alanine supplementation. Interestingly, neither exercise alone nor supplementation alone increased the formation of adducts. These results show that carnosine acts as an acrolein scavenger in skeletal muscle, which is important for the detoxification of aldehydes generated during exercise.

According to the researchers, these new findings may not only directly benefit athletes who engage in intensive training, but also allow scientists to explore the role of muscle carnosine in detoxifying reactive aldehydes in diseases characterized by abnormal oxidative stress.

The next step of the team will be to investigate the effects of beta-alanine supplementation in a group of elderly people. "With the aging of the population, it is important to have resources that contribute to improve muscular strength of the elderly. In addition, carnosine may also be effective in combating chronic pain associated with accumulation of aldehydes", said Medeiros.

The article Exercise and β-alanine supplementation on carnosine-acrolein adduct in skeletal muscle, by Victor H. Carvalho, Ana H.S. Oliveira, Luana F. de Oliveira, Rafael P. da Silva, Paolo Di Mascio, Bruno Gualano, Guilherme G. Artioli and Marisa H.G. Medeiros, can be read at https://www.sciencedirect.com/science/article/pii/S2213231718305408