Objective: Carnosine is a naturally present dipeptide in humans and an over-the counter food additive. Evidence from animal studies supports the role for carnosine in the prevention and treatment of diabetes and cardiovascular disease, yet there is limited human data. This study investigated whether carnosine supplementation in individuals with overweight or obesity improves diabetes and cardiovascular risk factors. Methods: In a double-blind randomized pilot trial in nondiabetic individuals with overweight and obesity (age 43 6 8 years; body mass index 31 6 4 kg/m 2 ), 15 individuals were randomly assigned to 2 g carnosine daily and 15 individuals to placebo for 12 weeks. Insulin sensitivity and secretion, glucose tolerance (oral glucose tolerance test), blood pressure, plasma lipid profile, skeletal muscle ( 1 H-MRS), and urinary carnosine levels were measured. Results: Carnosine concentrations increased in urine after supplementation (P < 0.05). An increase in fasting insulin and insulin resistance was hampered in individuals receiving carnosine compared to placebo, and this remained significant after adjustment for age, sex, and change in body weight (P 5 0.02, P 5 0.04, respectively). Two-hour glucose and insulin were both lower after carnosine supplementation compared to placebo in individuals with impaired glucose tolerance (P < 0.05). Conclusions: These pilot intervention data suggest that carnosine supplementation may be an effective strategy for prevention of type 2 diabetes.

Key pointsr Using recombinant DNA technology, the present study provides the first strong and direct evidence indicating that β-alanine is an efficient substrate for the mammalian transaminating enzymes 4-aminobutyrate-2-oxoglutarate transaminase and alanine-glyoxylate transaminase.r The concentration of carnosine and anserine in murine skeletal and heart muscle depends on circulating availability of β-alanine, which is in turn controlled by degradation of β-alanine in liver and kidney.r Chronic oral β-alanine supplementation is a popular ergogenic strategy in sports because it can increase the intracellular carnosine concentration and subsequently improve the performance of high-intensity exercises. The present study can partly explain why the β-alanine supplementation protocol is so inefficient, by demonstrating that exogenous β-alanine can be effectively routed toward oxidation.Abstract The metabolic fate of orally ingested β-alanine is largely unknown. Chronic β-alanine supplementation is becoming increasingly popular for improving high-intensity exercise performance because it is the rate-limiting precursor of the dipeptide carnosine (β-alanyl-L-histidine) in muscle. However, only a small fraction (3-6%) of the ingested β-alanine is used for carnosine synthesis. Thus, the present study aimed to investigate the putative contribution of two β-alanine transamination enzymes, namely 4-aminobutyrate-2-oxoglutarate transaminase (GABA-T) and alanine-glyoxylate transaminase (AGXT2), to the homeostasis of carnosine and its methylated analogue anserine. We found that, when transfected into HEK293T cells, recombinant mouse and human GABA-T and AGXT2 are able to transaminate β-alanine efficiently. The reaction catalysed by GABA-T is inhibited by vigabatrin, whereas both GABA-T and AGXT2 activity is inhibited by aminooxyacetic acid (AOA). Both GABA-T and AGXT2 are highly expressed in the mouse liver and kidney and the administration of the inhibitors effectively reduced their enzyme activity in liver (GABA-T for vigabatrin; GABA-T and AGXT2 for AOA). In vivo, injection of AOA in C57BL/6 mice placed on β-alanine (0.1% w/v in drinking water) for 2 weeks lead to a 3-fold increase in circulating β-alanine levels and to significantly higher levels of carnosine and anserine in skeletal muscle and heart. By contrast, specific inhibition of GABA-T by vigabatrin did not affect carnosine and anserine levels in either tissue. Collectively, these data demonstrate that homeostasis of carnosine and anserine in mammalian skeletal muscle and heart is controlled by circulating β-alanine levels, which are suppressed by hepatic and renal β-alanine transamination upon oral β-alanine intake.

Carnosine (beta-alanyl-L-histidine) and its methylated analogue anserine are present in relevant concentrations in the omnivore human diet. Several studies reported promising therapeutic potential for carnosine in various rodent models of oxidative stress and inflammation-related chronic diseases.Nevertheless, the poor serum stability of carnosine in humans makes the translation of rodent models hard. Even though anserine and carnosine have similar biochemical properties, anserine has better serum stability. Despite this interesting profile, the research on anserine is scarce.The aim of this study was to explore the bioavailability and stability of synthesized anserine by 1) performing in vitro stability experiments in human plasma and molecular modelling studies and by 2) evaluating the plasma and urinary pharmacokinetic profile in healthy volunteers following different doses of anserine (4-10-20 mg/kg body weight). A bio-analytical method for measuring anserine levels was developed and validated using liquid chromatography-electrospray mass spectrometry.

In this study, we aimed to determine the exercise intensities eliciting the highest (FAT max ) and the lowest (FAT min ) fat oxidation rate in male cyclists and to compare these intensities with their individual aerobic (AeT) and anaerobic (AnT) thresholds, respectively. Twenty-two moderately trained male cyclists performed a 2-min stage graded exercise test until exhaustion using breath-by-breath gas analysis to determine maximal oxygen consumption (VO 2max ). The fat oxidation rate was calculated using a stoichiometric equation, with metabolic thresholds being determined by ventilatory gas analysis. In the present group of subjects, FAT max was found at a 21.34 ± 3.64 ml•kg −1 •min −1 corresponding to 45.05 ± 7.68% VO 2max . AeT occurred at an exercise intensity of 22.15 ± 4.84 ml•kg −1 •min −1 , matching 46.76 ± 10.24% VO 2max . AnT and FAT min were located at intensities equivalent to 32.56 ± 5.52 ml•kg −1 •min −1 and 32.30 ± 5.35 ml•kg −1 •min −1 which corresponded to 68. 74 ± 11.65 and 68.19 ± 11.29% VO 2max , respectively. The correlation between FAT max and AeT was strong (r = 0.80, p < 0.05). No statistical difference was observed between FAT min and AnT (r = 0.99, p < 0.05). The strong relationship between observed indices can be used to provide a more tailored exercise approach.

Classic in vitro experiments (Severin's phenomenon) demonstrated that acute carnosine supplementation may potentiate muscle contractility. However, upon oral ingestion, carnosine is readily degraded in human plasma by the highly active serum carnosinase-1 (CN1). We developed a novel strategy to circumvent CN1 by pre-exercise ingestion of combined carnosine (CARN) and anserine (ANS), the methylated analog with similar biochemical properties but more resistant to CN1. First, in vitro hydrolysis was tested by adding carnosine and anserine to human plasma, alone or in combination. Secondly, 5 subjects were supplemented with 25mg/kg anserine or 25mg/kg of each anserine and carnosine to test in vivo bioavailability. Thirdly, two double-blind, placebo-controlled, crossover studies investigated the effect of pre-exercise ANS+CARN (20mg/kg BW of each) supplementation on performance during a single all-out Wingate test following 6-minute high-intensity cycling (study A) or 3 repeated Wingate tests (study B). In vitro experiments demonstrated slower degradation of anserine vs carnosine, which was further slowed by simultaneously adding carnosine. In vivo bioavailability of plasma anserine was more prominent (2.5-fold increased AUC) when ANS+CARN vs ANS was ingested. Study A showed significantly higher (+6±11%; p=0.04) power in the first 5s of the Wingate test following ANS+CARN (12.8±2.4W/kg) vs placebo (12.1±2.2W/kg). Study B demonstrated increased peak power (+3%) throughout 3 consecutive Wingate tests (ANS+CARN 10.5±0.6W/kg vs placebo 10.2±9.9W/kg). These experiments reveal a novel acute nutritional method to effectively raise plasma anserine and carnosine by high-dose combined supplementation. This approach led to improved initial cycling power, revealing a new nutritional strategy to increase exercise performance.