l -Carnosine supplementation attenuated fasting glucose, triglycerides, advanced glycation end products, and tumor necrosis factor– α levels in patients with type 2 diabetes: a double-blind placebo-controlled randomized clinical trial

The gut microbiota intervenes in glucose tolerance and inflammation by regulating the biosynthesis of taurodeoxycholic acid and carnosine

Objective

This study aims to investigate the pathogenesis of hyperglycemia and its associated vasculopathy using multiomics analyses in diabetes and impaired glucose tolerance, and validate the mechanism using the cell experiments.

Methods

In this study, we conducted a comprehensive analysis of the metagenomic sequencing data of diabetes to explore the key genera related to its occurrence. Subsequently, participants diagnosed with impaired glucose tolerance (IGT), and healthy subjects, were recruited for fecal and blood sample collection. The dysbiosis of the gut microbiota (GM) and its associated metabolites were analyzed using 16S rDNA sequencing and liquid chromatograph mass spectrometry, respectively. The regulation of gene and protein expression was evaluated through mRNA sequencing and data-independent acquisition technology, respectively. The specific mechanism by which GM dysbiosis affects hyperglycemia and its related vasculopathy was investigated using real-time qPCR, Western blotting, and enzyme-linked immunosorbent assay techniques in HepG2 cells and neutrophils.

Results

Based on the published data, the key alterable genera in the GM associated with diabetes were identified as Blautia, Lactobacillus, Bacteroides, Prevotella, Faecalibacterium, Bifidobacterium, Ruminococcus, Clostridium, and Lachnoclostridium. The related metabolic pathways were identified as cholate degradation and L-histidine biosynthesis. Noteworthy, Blautia and Faecalibacterium displayed similar alterations in patients with IGT compared to those observed in patients with diabetes, and the GM metabolites, tauroursodeoxycholic acid (TUDCA) and carnosine (CARN, a downstream metabolite of histidine and alanine) were both found to be decreased, which in turn regulated the expression of proteins in plasma and mRNAs in neutrophils. Subsequent experiments focused on insulin-like growth factor-binding protein 3 and interleukin-6 due to their impact on blood glucose regulation and associated vascular inflammation. Both proteins were found to be suppressed by TUDCA and CARN in HepG2 cells and neutrophils.

Conclusion

Dysbiosis of the GM occurred throughout the entire progression from IGT to diabetes, characterized by an increase in Blautia and a decrease in Faecalibacterium, leading to reduced levels of TUDCA and CARN, which alleviated their inhibition on the expression of insulin-like growth factor-binding protein 3 and interleukin-6, contributing to the development of hyperglycemia and associated vasculopathy.

PEGylation renders carnosine resistant to hydrolysis by serum carnosinase and increases renal carnosine levels

Carnosine's protective effect in rodent models of glycoxidative stress have provided a rational for translation of these findings in therapeutic concepts in patient with diabetic kidney disease. In contrast to rodents however, carnosine is rapidly degraded by the carnosinase-1 enzyme. To overcome this hurdle, we sought to protect hydrolysis of carnosine by conjugation to Methoxypolyethylene glycol amine (mPEG-NH2). PEGylated carnosine (PEG-car) was used to study the hydrolysis of carnosine by human serum as well as to compare the pharmacokinetics of PEG-car and L-carnosine in mice after intravenous (IV) injection. While L-carnosine was rapidly hydrolyzed in human serum, PEG-car was highly resistant to hydrolysis. Addition of unconjugated PEG to carnosine or PEG-car did not influence hydrolysis of carnosine in serum. In mice PEG-car and L-carnosine exhibited similar pharmacokinetics in serum but differed in half-life time (t1/2) in kidney, with PEG-car showing a significantly higher t1/2 compared to L-carnosine. Hence, PEGylation of carnosine is an effective approach to prevent carnosine degradations and to achieve higher renal carnosine levels. However, further studies are warranted to test if the protective properties of carnosine are preserved after PEGylation.

The protective role of carnosine against type 2 diabetes-induced cognitive impairment

The morbidity and mortality associated with type 2 diabetes mellitus (T2DM) have grown exponentially over the last 30 years. Together with its associated complications, the mortality rates have increased. One important complication in those living with T2DM is the acceleration of age-related cognitive decline. T2DM-induced cognitive impairment seriously affects memory, executive function, and quality of life. However, there is a lack of effective treatment for both diabetes and cognitive decline. Thus, finding novel treatments which are cheap, effective in both diabetes and cognitive impairment, are easily accessible, are needed to reduce impact on patients with diabetes and health-care systems. Carnosine, a histidine containing dipeptide, plays a protective role in cognitive diseases due to its antioxidant, anti-inflammation, and anti-glycation properties, all of which may slow the development of neurodegenerative diseases and ischemic injury. Furthermore, carnosine is also involved in regulating glucose and insulin in diabetes. Herein, we discuss the neuroprotective role of carnosine and its mechanisms in T2DM-induced cognitive impairment, which may provide a theoretical basis and evidence base to evaluate whether carnosine has therapeutic effects in alleviating cognitive dysfunction in T2DM patients.

The dynamic roles of advanced glycation end products

Advanced glycation end products (AGEs) are a heterogeneous group of potentially harmful molecules that can form as a result of a non-enzymatic reaction between reducing sugars and proteins, lipids, or nucleic acids. The total body pool of AGEs reflects endogenously produced AGEs as well as exogeneous AGEs that come from sources such as diet and the environment. Engagement of AGEs with their cellular receptor, the receptor for advanced glycation end products (RAGE), which is expressed on the surface of various cell types, converts a brief pulse of cellular activation to sustained cellular dysfunction and tissue destruction. The AGEs/RAGE interaction triggers a cascade of intracellular signaling pathways such as mitogen-activated protein kinase/extracellular signal-regulated kinase, phosphoinositide 3-kinases, transforming growth factor beta, c-Jun N-terminal kinases (JNK), and nuclear factor kappa B, which leads to the production of pro-inflammatory cytokines, chemokines, adhesion molecules, and oxidative stress. All these events contribute to the progression of several chronic diseases. This chapter will provide a comprehensive understanding of the dynamic roles of AGEs in health and disease which is crucial to develop interventions that prevent and mitigate the deleterious effects of AGEs accumulation.

Effects of carnosine supplementation on markers for the pathophysiological development of metabolic dysfunction-associated steatotic liver disease in a diet-induced model

Consumption of diets high in sugar and fat is related to the development of Metabolic dysfunction-associated steatotic liver disease (MASLD). Carnosine (CAR) is a dipeptide with antioxidant and anti-inflammatory action and has been studied for treating diseases. This work aimed to evaluate the effects of CAR on diet-induced MASLD in rats. Male Wistar rats were distributed into 2 groups (17 weeks): normocaloric (Co, n = 12), and hypercaloric diet rich in lipids and simple carbohydrates (MASLD, n = 12). After, the animals were redistributed to begin the treatment with CAR (4 weeks): Co (n = 6), Co + CAR (n = 6), MASLD (n = 6), and MASLD + CAR (n = 6), administered intraperitoneally (250 mg/kg). Evaluations included nutritional, hormonal and metabolic parameters; hepatic steatosis, inflammatory and oxidative markers. MASLD group had a higher adiposity index, systolic blood pressure, glucose, plasma and liver triglycerides and cholesterol, insulin, hepatic steatosis, oxidative markers, and lower PPAR-α (Peroxisome Proliferator-activated receptor α), compared to the Co. CAR attenuated plasma and hepatic triglyceride and cholesterol levels, hepatic steatosis, CD68+ macrophages, and hepatic oxidative markers, in addition to increasing HDL cholesterol levels and PPAR-α, compared to the untreated MASLD group. CAR acts in importants pathophysiological processes of MASLD and may be a therapeutic compound to control the disease.

Effects of in ovo injection of the L-carnosine on physiological indexes of neonatal broiler chicken

The objective of the present investigation was to ascertain the impact of in ovo administration of L-carnosine on physiological indicators in neonatal broiler chickens. A total of 280 viable broiler eggs were allocated to 7 distinct groups: control, Sham in ovo injection of sterile water on d 7 of incubation. Groups 3 and 4 were subjected to in ovo injections of L-carnosine (25 and 50 µg) on d 7 of incubation. Group 5, functioning as a sham in ovo, received an injection of sterile water on d 18 of incubation. Groups 6 and 7 were in ovo injected with L-carnosine (25 and 50 µg) on d 18 of incubation. All eggs were subjected to incubation, and the hatching rate and body weight were measured post-hatch. Subsequently, blood samples were collected, and the levels of biochemical constituents in the serum were determined. Based on the outcomes, the administration of L-carnosine (50 µg) on d 7 of incubation led to a significant increase in post-hatch body weight compared to the control group (P < 0.05). The in ovo injection of L-carnosine (25 and 50 µg) on d 7 and 18 of incubation resulted in a significant decrease in the levels of serum glucose, triglyceride (TG), low-density lipoprotein (LDL), phosphorus (P), alkaline phosphatase (ALP), aspartate aminotransferase (AST), and alanine transaminase (ALT) in the newly hatched chickens (P < 0.05). Furthermore, the in-ovo injection of L-carnosine (25 and 50 µg) on d 7 and 18 of incubation led to a significant increase in the levels of serum high-density lipoprotein (HDL), calcium, and total protein (TP) in the newly hatched chickens (P < 0.05). Nonetheless, L-carnosine did not have a significant effect on the levels of serum IgY and IgA in the newly hatched chickens (P > 0.05). These findings indicate that the in ovo administration of L-carnosine yielded favorable outcomes in neonatal broiler chickens.

Carnosine supplementation improves glucose control in adults with pre-diabetes and type 2 diabetes: A randomised controlled trial

BACKGROUND AND AIMS

Type 2 diabetes (T2DM) is a major cause of morbidity and mortality globally. Carnosine, a naturally occurring dipeptide, has anti-inflammatory, antioxidant, and anti-glycating effects, with preliminary evidence suggesting it may improve important chronic disease risk factors in adults with cardiometabolic conditions.

METHODS AND RESULTS

In this randomised controlled trial, 43 adults (30%F) living with prediabetes or T2DM consumed carnosine (2 g) or a matching placebo daily for 14 weeks to evaluate its effect on glucose metabolism assessed via a 2-h 75 g oral glucose tolerance test. Secondary outcomes included body composition analysis by dual energy x-ray absorptiometry (DEXA), calf muscle density by pQCT, and anthropometry. Carnosine supplementation decreased blood glucose at 90 min (-1.31 mmol/L; p = 0.02) and 120 min (-1.60 mmol/L, p = 0.02) and total glucose area under the curve (-3.30 mmol/L; p = 0.04) following an oral glucose tolerance test. There were no additional changes in secondary outcomes. The carnosine group results remained significant before and after adjustment for age, sex, and change in weight (all>0.05), and in further sensitivity analyses accounting for missing data. There were no significant changes in insulin levels.

CONCLUSION

This study provides preliminary support for larger trials evaluating carnosine as a potential treatment for prediabetes and the initial stages of T2DM. Likely mechanisms may include changes to hepatic glucose output explaining the observed reduction in blood glucose without changes in insulin secretion following carnosine supplementation.

Potential therapeutic implications of histidine catabolism by the gut microbiota in NAFLD patients with morbid obesity

The gut microbiota contributes to the pathophysiology of non-alcoholic fatty liver disease (NAFLD). Histidine is a key energy source for the microbiota, scavenging it from the host. Its role in NAFLD is poorly known. Plasma metabolomics, liver transcriptomics, and fecal metagenomics were performed in three human cohorts coupled with hepatocyte, rodent, and Drosophila models. Machine learning analyses identified plasma histidine as being strongly inversely associated with steatosis and linked to a hepatic transcriptomic signature involved in insulin signaling, inflammation, and trace amine-associated receptor 1. Circulating histidine was inversely associated with Proteobacteria and positively with bacteria lacking the histidine utilization (Hut) system. Histidine supplementation improved NAFLD in different animal models (diet-induced NAFLD in mouse and flies, ob/ob mouse, and ovariectomized rats) and reduced de novo lipogenesis. Fecal microbiota transplantation (FMT) from low-histidine donors and mono-colonization of germ-free flies with Enterobacter cloacae increased triglyceride accumulation and reduced histidine content. The interplay among microbiota, histidine catabolism, and NAFLD opens therapeutic opportunities.

Carnosine and Beta-Alanine Supplementation in Human Medicine: Narrative Review and Critical Assessment

The dipeptide carnosine is a physiologically important molecule in the human body, commonly found in skeletal muscle and brain tissue. Beta-alanine is a limiting precursor of carnosine and is among the most used sports supplements for improving athletic performance. However, carnosine, its metabolite N-acetylcarnosine, and the synthetic derivative zinc-L-carnosine have recently been gaining popularity as supplements in human medicine. These molecules have a wide range of effects—principally with anti-inflammatory, antioxidant, antiglycation, anticarbonylation, calcium-regulatory, immunomodulatory and chelating properties. This review discusses results from recent studies focusing on the impact of this supplementation in several areas of human medicine. We queried PubMed, Web of Science, the National Library of Medicine and the Cochrane Library, employing a search strategy using database-specific keywords. Evidence showed that the supplementation had a beneficial impact in the prevention of sarcopenia, the preservation of cognitive abilities and the improvement of neurodegenerative disorders. Furthermore, the improvement of diabetes mellitus parameters and symptoms of oral mucositis was seen, as well as the regression of esophagitis and taste disorders after chemotherapy, the protection of the gastrointestinal mucosa and the support of Helicobacter pylori eradication treatment. However, in the areas of senile cataracts, cardiovascular disease, schizophrenia and autistic disorders, the results are inconclusive.

Pancreatic β-cell dysfunction in type 2 diabetes: Implications of inflammation and oxidative stress

Insulin resistance and pancreatic β-cell dysfunction are major pathological mechanisms implicated in the development and progression of type 2 diabetes (T2D). Beyond the detrimental effects of insulin resistance, inflammation and oxidative stress have emerged as critical features of T2D that define β-cell dysfunction. Predominant markers of inflammation such as C-reactive protein, tumor necrosis factor alpha, and interleukin-1β are consistently associated with β-cell failure in preclinical models and in people with T2D. Similarly, important markers of oxidative stress, such as increased reactive oxygen species and depleted intracellular antioxidants, are consistent with pancreatic β-cell damage in conditions of T2D. Such effects illustrate a pathological relationship between an abnormal inflammatory response and generation of oxidative stress during the progression of T2D. The current review explores preclinical and clinical research on the patho-logical implications of inflammation and oxidative stress during the development of β-cell dysfunction in T2D. Moreover, important molecular mechanisms and relevant biomarkers involved in this process are discussed to divulge a pathological link between inflammation and oxidative stress during β-cell failure in T2D. Underpinning the clinical relevance of the review, a systematic analysis of evidence from randomized controlled trials is covered, on the potential therapeutic effects of some commonly used antidiabetic agents in modulating inflammatory makers to improve β-cell function.

Carnosine increases insulin-stimulated glucose uptake and reduces methylglyoxal-modified proteins in type-2 diabetic human skeletal muscle cells

Type-2 diabetes (T2D) is characterised by a dysregulation of metabolism, including skeletal muscle insulin resistance, mitochondrial dysfunction, and oxidative stress. Reactive species, such as methylglyoxal (MGO) and 4-hydroxynonenal (4-HNE), positively associate with T2D disease severity and can directly interfere with insulin signalling and glucose uptake in skeletal muscle by modifying cellular proteins. The multifunctional dipeptide carnosine, and its rate-limiting precursor β-alanine, have recently been shown to improve glycaemic control in humans and rodents with diabetes. However, the precise mechanisms are unclear and research in human skeletal muscle is limited. Herein, we present novel findings in primary human T2D and lean healthy control (LHC) skeletal muscle cells. Cells were differentiated to myotubes, and treated with 10 mM carnosine, 10 mM β-alanine, or control for 4-days. T2D cells had reduced ATP-linked and maximal respiration compared with LHC cells (p = 0.016 and p = 0.005). Treatment with 10 mM carnosine significantly increased insulin-stimulated glucose uptake in T2D cells (p = 0.047); with no effect in LHC cells. Insulin-stimulation increased MGO-modified proteins in T2D cells by 47%; treatment with carnosine attenuated this increase to 9.7% (p = 0.011). There was no effect treatment on cell viability or expression of other proteins. These findings suggest that the beneficial effects of carnosine on glycaemic control may be explained by its scavenging actions in human skeletal muscle.

Serum levels of carnosine may be associated with the duration of MDD episodes

BACKGROUND

Major depressive disorder (MDD) is a recurrent disorder that incurs a high societal burden. However, the etiology of MDD remains unclear. The functioning of several systems associated with the etiopathogenesis of MDD, such as inflammatory and stress systems, is partially modulated by the dipeptide carnosine.

METHODS

The study comprised 99 MDD patients and 253 non-depressed controls aged 20-71 years. Fasting serum samples were analyzed using ultra-performance liquid chromatography coupled to mass spectrometry to determine the serum levels of carnosine and its constituent, histidine. We compared these metabolites in three different settings: 1) MDD patients vs. non-depressed controls and 2) remitted vs. non-remitted MDD patients, as well as 3) changes in the metabolite levels during the follow-up period within a) the remitted group and b) the non-remitted group. In addition, we assessed the possible effect of medications on the measured metabolites.

RESULTS

We observed higher serum levels of carnosine in the MDD group compared to the control group at baseline (OR = 1.895, 95%CI = 1.223-2.937, p = 0.004). Elevated serum levels of carnosine were also associated with a longer duration of the depressive episode (Z = 0.406, p = 0.001). However, the use of any antipsychotic medication (n = 36) was associated with lowered carnosine levels (p = 0.010 for use vs. non-use). At the follow-up, remitted and non-remitted participants displayed no significant differences in their carnosine levels (Z = -0.14, p = 0.891) or histidine (Z = -1.39 p = 0.164).

CONCLUSIONS

An increase in circulating carnosine may characterize depressive episodes and may represent a protective homeostatic reaction against MDD-related oxidative stress and inflammation.

L-carnosine Attenuates Bleomycin-Induced Oxidative Stress via NFκB Pathway in the Pathogenesis of Pulmonary Fibrosis

Idiopathic Pulmonary fibrosis (IPF), a chronic interstitial lung disease, has pulmonary manifestations clinically characterized by collagen deposition, epithelial cell injury, and a decline in lung function. L-carnosine, a dipeptide consisting of β-alanine and L-histidine, has demonstrated a therapeutic effect on various diseases because of its pivotal function. Despite the effect of L-carnosine in experimental IPF mice, its anti-oxidative effect and associated intercellular pathway, particularly alveolar epithelial cells, remain unknown. Therefore, we demonstrated the anti-fibrotic and anti-inflammatory effects of L-carnosine via Reactive oxygen species (ROS) regulation in bleomycin (BLM)-induced IPF mice. The mice were intratracheally injected with BLM (3 mg/kg) and L-carnosine (150 mg/kg) was orally administrated for 2 weeks. BLM exposure increased the protein level of Nox2, Nox4, p53, and Caspase-3, whereas L-carnosine treatment suppressed the protein level of Nox2, Nox4, p53, and Caspase-3 cleavage in mice. In addition, the total SOD activity and mRNA level of Sod2, catalase, and Nqo1 increased in mice treated with L-carnosine. At the cellular level, a human fibroblast (MRC-5) and mouse alveolar epithelial cell (MLE-12) were exposed to TGFβ1 following L-carnosine treatment to induce fibrogenesis. Moreover, MLE-12 cells were exposed to cigarette smoke extract (CSE). Consequently, L-carnosine treatment ameliorated fibrogenesis in fibroblasts and alveolar epithelial cells, and inflammation induced by ROS and CSE exposure was ameliorated. These results were associated with the inhibition of the NFκB pathway. Collectively, our data indicate that L-carnosine induces anti-inflammatory and anti-fibrotic effects on alveolar epithelial cells against the pathogenesis of IPF.

Reduction of Obesity and Insulin Resistance through Dual Targeting of VAT and BAT by a Novel Combination of Metabolic Cofactors

Obesity is an epidemic disease worldwide, characterized by excessive fat accumulation associated with several metabolic perturbations, such as metabolic syndrome, insulin resistance, hypertension, and dyslipidemia. To improve this situation, a specific combination of metabolic cofactors (MC) (betaine, N-acetylcysteine, L-carnitine, and nicotinamide riboside) was assessed as a promising treatment in a high-fat diet (HFD) mouse model. Obese animals were distributed into two groups, orally treated with the vehicle (obese + vehicle) or with the combination of metabolic cofactors (obese + MC) for 4 weeks. Body and adipose depots weights; insulin and glucose tolerance tests; indirect calorimetry; and thermography assays were performed at the end of the intervention. Histological analysis of epidydimal white adipose tissue (EWAT) and brown adipose tissue (BAT) was carried out, and the expression of key genes involved in both fat depots was characterized by qPCR. We demonstrated that MC supplementation conferred a moderate reduction of obesity and adiposity, an improvement in serum glucose and lipid metabolic parameters, an important improvement in lipid oxidation, and a decrease in adipocyte hypertrophy. Moreover, MC-treated animals presented increased adipose gene expression in EWAT related to lipolysis and fatty acid oxidation. Furthermore, MC supplementation reduced glucose intolerance and insulin resistance, with an increased expression of the glucose transporter Glut4; and decreased fat accumulation in BAT, raising non-shivering thermogenesis. This treatment based on a specific combination of metabolic cofactors mitigates important pathophysiological characteristics of obesity, representing a promising clinical approach to this metabolic disease.

Oxidative stress and metabolic diseases: Relevance and therapeutic strategies

Metabolic syndrome (MS) is a prominent cause of death worldwide, posing a threat to the global economy and public health. A mechanism that causes the oxidation of low-density lipoproteins (LDL) is associated with metabolic abnormalities. Various processes are involved in oxidative stress (OS) of lipoprotein. Although the concept of the syndrome has been fiercely debated, this confluence of risk factors is associated with a higher chance of acquiring type 2 diabetes mellitus (T2DM) and atherosclerosis. Insulin resistance has been found to play a significant role in the progression of these metabolism-associated conditions. It causes lipid profile abnormalities, including greater sensitivity to lipid peroxidation, contributing to the increased prevalence of T2DM and atherosclerosis. This review aims to cover the most recent scientific developments in dietary OS, the consequence of metabolic disorders, and their most significant clinical manifestations (T2DM and atherosclerosis). It will also emphasize the effects of dietary approaches in alleviating OS in MS.

The Therapeutic Potential of Carnosine as an Antidote against Drug-Induced Cardiotoxicity and Neurotoxicity: Focus on Nrf2 Pathway

Different drug classes such as antineoplastic drugs (anthracyclines, cyclophosphamide, 5-fluorouracil, taxanes, tyrosine kinase inhibitors), antiretroviral drugs, antipsychotic, and immunosuppressant drugs are known to induce cardiotoxic and neurotoxic effects. Recent studies have demonstrated that the impairment of the nuclear factor erythroid 2–related factor 2 (Nrf2) pathway is a primary event in the pathophysiology of drug-induced cardiotoxicity and neurotoxicity. The Nrf2 pathway regulates the expression of different genes whose products are involved in antioxidant and inflammatory responses and the detoxification of toxic species. Cardiotoxic drugs, such as the anthracycline doxorubicin, or neurotoxic drugs, such as paclitaxel, suppress or impair the Nrf2 pathway, whereas the rescue of this pathway counteracts both the oxidative stress and inflammation that are related to drug-induced cardiotoxicity and neurotoxicity. Therefore Nrf2 represents a novel pharmacological target to develop new antidotes in the field of clinical toxicology. Interestingly, carnosine (β-alanyl-l-histidine), an endogenous dipeptide that is characterized by strong antioxidant, anti-inflammatory, and neuroprotective properties is able to rescue/activate the Nrf2 pathway, as demonstrated by different preclinical studies and preliminary clinical evidence. Starting from these new data, in the present review, we examined the evidence on the therapeutic potential of carnosine as an endogenous antidote that is able to rescue the Nrf2 pathway and then counteract drug-induced cardiotoxicity and neurotoxicity.

Association Between Serum Carnosinase Concentration and Activity and Renal Function Impairment in a Type-2 Diabetes Cohort

Introduction: Genetic studies have identified associations of carnosinase 1 (CN1) polymorphisms with diabetic kidney disease (DKD). However, CN1 levels and activities have not been assessed as diagnostic or prognostic markers of DKD in cohorts of patients with type 2 diabetes (T2D).

Methods: We established high-throughput, automated CN1 activity and concentration assays using robotic systems. Using these methods, we determined baseline serum CN1 levels and activity in a T2D cohort with 970 patients with no or only mild renal impairment. The patients were followed for a mean of 1.2 years. Baseline serum CN1 concentration and activity were assessed as predictors of renal function impairment and incident albuminuria during follow up.

Results: CN1 concentration was significantly associated with age, gender and estimated glomerular filtration rate (eGFR) at baseline. CN1 activity was significantly associated with glycated hemoglobin A1c (HbA1c) and eGFR. Serum CN1 at baseline was associated with eGFR decline and predicted renal function impairment and incident albuminuria during the follow-up.

Discussion: Baseline serum CN1 levels were associated with presence and progression of renal function decline in a cohort of T2D patients. Confirmation in larger cohorts with longer follow-up observation periods will be required to fully establish CN1 as a biomarker of DKD.

In Patients with Chronic Kidney Disease Advanced Glycation End-Products Receptors Isoforms (sRAGE and esRAGE) Are Associated with Malnutrition

Background: in patients with chronic kidney disease (CKD), the inflammatory and pro-oxidant milieu may contribute to malnutrition development. In this study, we investigated the relationship between inflammation, advanced glycation end-products (AGEs), and their receptors (RAGEs) with malnutrition in CKD patients. Methods: we evaluated 117 patients. AGEs were quantified by fluorescence intensity using a fluorescence spectrophotometer, soluble RAGEs isoforms, and inflammatory interleukins by ELISA. Malnutrition was assessed by a malnutrition inflammation score. Results: mean age was 80 ± +11 years, eGFR was 25 ± +11 mL/min/1.73 m2 and BMI was 28 ± 5 Kg/m2. Malnourished individuals were older, had lower estimated protein intake (nPCR 0.65 ± 0.2 vs. 0.8 ± 0.2 vs. 0.8 ± 0.3, p = 0.01), higher C reactive protein (CRP 0.6 ± 1 vs. 0.6 ± 0.7 vs. 0.17 ± 0.13, p = 0.02) and tumor necrosis factor α (TNF α 14.7 ± 8.7 vs. 15.6 ± 8 vs. 11.8 ± 5.8, p = 0.029). Malnourished patients had higher sRAGE (2813 ± 1477 vs. 2158 ± 1236 vs. 2314 ± 1115, p = 0.035) and esRAGE (648 [408–1049] vs. 476 [355–680] vs. 545 [380–730] p = 0.033). In the multivariate analysis, only sRAGE maintained its association with malnutrition (p = 0.02) independently of aging and inflammation. Conclusions: in CKD patients, RAGEs isoforms, but not AGEs, are associated with malnutrition, irrespective of systemic inflammation, aging, and renal function.

The Potential Use of Carnosine in Diabetes and Other Afflictions Reported in Long COVID Patients

Carnosine is a dipeptide expressed in both the central nervous system and periphery. Several biological functions have been attributed to carnosine, including as an anti-inflammatory and antioxidant agent, and as a modulator of mitochondrial metabolism. Some of these mechanisms have been implicated in the pathophysiology of coronavirus disease-2019 (COVID-19). COVID-19 is caused by severe acute respiratory syndrome-coronavirus 2 (SARS-CoV-2). The clinical manifestation and recovery time for COVID-19 are variable. Some patients are severely affected by SARS-CoV-2 infection and may experience respiratory failure, thromboembolic disease, neurological symptoms, kidney damage, acute pancreatitis, and even death. COVID-19 patients with comorbidities, including diabetes, are at higher risk of death. Mechanisms underlying the dysfunction of the afflicted organs in COVID-19 patients have been discussed, the most common being the so-called cytokine storm. Given the biological effects attributed to carnosine, adjuvant therapy with this dipeptide could be considered as supportive treatment in patients with either COVID-19 or long COVID.

Unveiling the Hidden Therapeutic Potential of Carnosine, a Molecule with a Multimodal Mechanism of Action: A Position Paper

Carnosine (β-alanyl-L-histidine) is a naturally occurring endogenous dipeptide and an over-the-counter food supplement with a well-demonstrated multimodal mechanism of action that includes the detoxification of reactive oxygen and nitrogen species, the down-regulation of the production of pro-inflammatory mediators, the inhibition of aberrant protein formation, and the modulation of cells in the peripheral (macrophages) and brain (microglia) immune systems. Since its discovery more than 100 years ago, a plethora of in vivo preclinical studies have been carried out; however, there is still substantial heterogeneity regarding the route of administration, the dosage, the duration of the treatment, and the animal model selected, underlining the urgent need for "coordinated/aligned" preclinical studies laying the foundations for well-defined future clinical trials. The main aim of the present position paper is to critically and concisely consider these key points and open a discussion on the possible "alignment" for future studies, with the goal of validating the full therapeutic potential of this intriguing molecule.

The Cost-Effectiveness of Supplemental Carnosine in Type 2 Diabetes

In this paper, we assess the cost-effectiveness of 1 g daily of carnosine (an over the counter supplement) in addition to standard care for the management of type 2 diabetes and compare it to standard care alone. Dynamic multistate life table models were constructed in order to estimate both clinical outcomes and costs of Australians aged 18 years and above with and without type 2 diabetes over a ten-year period, 2020 to 2029. The dynamic nature of the model allowed for population change over time (migration and deaths) and accounted for the development of new cases of diabetes. The three health states were 'Alive without type 2 diabetes', 'Alive with type 2 diabetes' and 'Dead'. Transition probabilities, costs, and utilities were obtained from published sources. The main outcome of interest was the incremental cost-effectiveness ratio (ICER) in terms of cost per year of life saved (YoLS) and cost per quality-adjusted life year (QALY) gained. Over the ten-year period, the addition of carnosine to standard care treatment resulted in ICERs (discounted) of AUD 34,836 per YoLS and AUD 43,270 per QALY gained. Assuming the commonly accepted willingness to pay threshold of AUD 50,000 per QALY gained, supplemental dietary carnosine may be a cost-effective treatment option for people with type 2 diabetes in Australia.

Effect of Carnosine or β-Alanine Supplementation on Markers of Glycemic Control and Insulin Resistance in Humans and Animals: A Systematic Review and Meta-analysis

There is growing evidence that supplementation with carnosine, or its rate-limiting precursor β-alanine, can ameliorate aspects of metabolic dysregulation that occur in diabetes and its related conditions. The purpose of this systematic review and meta-analysis was to evaluate the effect of carnosine or β-alanine supplementation on markers of glycemic control and insulin resistance in humans and animals. We performed a systematic search of 6 electronic databases up to 31 December 2020. Primary outcomes were changes in 1) fasting glucose, 2) glycated hemoglobin (HbA1c), and 3) 2-h glucose following a glucose-tolerance test. A set of additional outcomes included fasting insulin and homeostatic model assessment of β-cell function (HOMA-β) and insulin resistance (HOMA-IR). We assessed risk of bias using the Cochrane risk of bias (RoB) 2.0 (human studies) and the Systematic Review Center for Laboratory Animal Experimentation (SYRCLE) RoB (animal studies) tools; and used the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) approach to assess certainty. We used Bayesian hierarchical random-effects models, with informative priors for human data and noninformative priors for animal data. Inferences were made on posterior samples generated by Hamiltonian Markov Chain Monte Carlo using 90% credible intervals (90% CrI) and calculated probabilities. Twenty studies (n = 4 human, n = 16 rodent) were included, providing data for 2 primary outcomes (fasting glucose and HbA1c) and 3 additional outcomes (fasting insulin, HOMA-β, and HOMA-IR). The model provides evidence that supplementation decreases fasting glucose [humans: mean difference (MD)0.5 = -0.95 mmol · L-1 (90% CrI: -2.1, 0.08); rodent: MD0.5 = -2.26 mmol · L-1 (90% CrI: -4.03, -0.44)], HbA1c [humans: MD0.5 = -0.91% (90% CrI: -1.46, -0.39); rodents: MD0.5 = -1.05% (90% CrI: -1.64, -0.52)], HOMA-IR [humans: standardized mean difference (SMD)0.5 = -0.41 (90% CrI: -0.82, -0.07); rodents: SMD0.5 = -0.63 (90% CrI: -1.98, 0.65)], and fasting insulin [humans: SMD0.5 = -0.41 (90% CrI: -0.77, -0.07)]. GRADE assessment showed our certainty in the effect estimate of each outcome to be moderate (human outcomes) or very low (rodent outcomes). Supplementation with carnosine or β-alanine may reduce fasting glucose, HbA1c, and HOMA-IR in humans and rodents, and fasting insulin in humans; both compounds show potential as therapeutics to improve glycemic control and insulin resistance. This review was registered at PROSPERO as CRD42020191588.

Erythrocytes Prevent Degradation of Carnosine by Human Serum Carnosinase

The naturally occurring dipeptide carnosine (β-alanyl-l-histidine) has beneficial effects in different diseases. It is also frequently used as a food supplement to improve exercise performance and because of its anti-aging effects. Nevertheless, after oral ingestion, the dipeptide is not detectable in human serum because of rapid degradation by serum carnosinase. At the same time, intact carnosine is excreted in urine up to five hours after intake. Therefore, an unknown compartment protecting the dipeptide from degradation has long been hypothesized. Considering that erythrocytes may constitute this compartment, we investigated the uptake and intracellular amounts of carnosine in human erythrocytes cultivated in the presence of the dipeptide and human serum using liquid chromatography–mass spectrometry. In addition, we studied carnosine’s effect on ATP production in red blood cells and on their response to oxidative stress. Our experiments revealed uptake of carnosine into erythrocytes and protection from carnosinase degradation. In addition, no negative effect on ATP production or defense against oxidative stress was observed. In conclusion, our results for the first time demonstrate that erythrocytes can take up carnosine, and, most importantly, thereby prevent its degradation by human serum carnosinase.

Carnosine protects stimulus-secretion coupling through prevention of protein carbonyl adduction events in cells under metabolic stress

Type 2 diabetes is characterised by failure to control glucose homeostasis, with numerous diabetic complications attributable to the resulting exposure of cells and tissues to chronic elevated concentrations of glucose and fatty acids. This, in part, results from formation of advanced glycation and advanced lipidation end-products that are able to modify protein, lipid, or DNA structure, and disrupt normal cellular function. Herein we used mass spectrometry to identify proteins modified by two such adduction events in serum of individuals with obesity, type 2 diabetes, and gestational diabetes, along with similar analyses of human and mouse skeletal muscle cells and mouse pancreatic islets exposed to glucolipotoxic stress. We also report that carnosine, a histidine containing dipeptide, prevented 65-90% of 4-hydroxynonenal and 3-nitrotyrosine adduction events, and that this in turn preserved mitochondrial function and protected stimulus-secretion coupling in cells exposed to metabolic stress. Carnosine therefore offers significant therapeutic potential against metabolic diseases.

2-Oxo-Imidazole-Containing Dipeptides Play a Key Role in the Antioxidant Capacity of Imidazole-Containing Dipeptides

There is substantial evidence for the antioxidant functions of imidazole-containing dipeptides (IDPs), including carnosine and anserine, under physiological and pathological conditions in vivo. However, the detailed mechanism underlying the antioxidant functions is still poorly understood. Recently, we discovered the endogenous production of 2-oxo-imidazole-containing dipeptides (2-oxo-IDPs), such as 2-oxo-carnosine and 2-oxo-anserine, as novel derivatives of IDPs in mouse tissues and revealed that the antioxidant capacity of 2-oxo-carnosine was much greater than that of carnosine. However, the antioxidant capacity of 2-oxo-IDPs still remains unclear. In this study, we evaluated 2-oxo-carnosine and 2-oxo-anserine by multiple in vitro assays, such as 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging, ferric reducing/antioxidant power, and oxygen radical absorbance capacity assays in comparison with the corresponding IDPs, carnosine and anserine. All the assays employed herein demonstrated that 2-oxo-carnosine and 2-oxo-anserine exhibited a greater antioxidant capacity than that of the corresponding IDPs. Quantitative high-performance liquid chromatography tandem mass spectrometry revealed that commercial IDPs standards were contaminated with a certain amount of 2-oxo-IDPs, which was correlated with the antioxidant capacity. DPPH radical scavenging assay revealed that the elimination of contaminated 2-oxo-IDPs from the IDPs standards caused a significant decrease in the antioxidant capacity compared to the original IDPs standards. These results suggest that the main driver of the antioxidant capacity of IDPs is 2-oxo-IDPs; accordingly, the conversion of IDPs to 2-oxo-IDPs may be a critical step in the antioxidant functions.

Novel Relationship Between Plasmalogen Lipid Signatures and Carnosine in Humans

INTRODUCTION

Carnosine is a naturally occurring dipeptide abundant in the skeletal and cardiac muscle and brain, which has been shown to improve glucose metabolism and cardiovascular risk. This study showed that carnosine supplementation had positive changes on plasma lipidome. Here, this study aimed to establish the relationship of muscle carnosine and serum carnosinase-1 with cardiometabolic risk factors and the lipidome.

METHODS AND RESULTS

This study profiles >450 lipid species in 65 overweight/obese nondiabetic individuals. Intensive metabolic testing is conducted using direct gold-standard measures of adiposity, insulin sensitivity and secretion, as well as measurement of serum inflammatory cytokines and adipokines. Muscle carnosine is negatively associated with 2-h glucose concentrations, whereas serum carnosinase-1 levels are negatively associated with insulin sensitivity and positively with IL-18. O-PLS and machine learning analyses reveal a strong association of muscle carnosine with ether lipids, particularly arachidonic acid-containing plasmalogens. Carnosinase-1 levels are positively associated with total phosphatidylethanolamines, but negatively with lysoalkylphosphatidylcholines, trihexosylceramides, and gangliosides. In particular, alkylphosphatidylethanolamine species containing arachidonic acid are positively associated with carnosinase-1.

CONCLUSION

These associations reinforce the role of muscle carnosine and serum carnosinase-1 in the interplay among low-grade chronic inflammation, glucose homeostasis, and insulin sensitivity.

Protective effects of dietary carnosine during in-vitro digestion of pork differing in fat content and cooking conditions

Muscle carnosine represents an important health advantage of meat. Ground pork samples with intrinsic or added carnosine; fat content; and cooked under low or high intensity as a 2 × 2 × 2 factorial were digested in-vitro. Changes in free carnosine and in markers of lipid (hexanal, 4-hydroxynonenal (4-HNE), malondialdehyde (MDA) and protein (protein-carbonyls, thiols) oxidation, and of advanced glycation end-products (AGEs) N^ε -(carboxymethyl)lysine (CML) were determined in the saliva, gastric, and duodenal digests. During digestion, the different markers overall indicated increased oxidation and decreased free carnosine. Increasing pork carnosine level significantly reduced protein carbonyls, loss of thiols, and 4-HNE during in-vitro gastric digestion, irrespective of fat and cooking level of the meat. Increased carnosine also significantly reduced hexanal, MDA and CML up to the duodenum phase in moderately cooked lean pork. Besides substantiating the formation of AGEs during digestion, these results show a potentially important role of dietary carnosine occurring in the gastrointestinal tract. PRACTICAL APPLICATIONS: The ailments epidemiologically associated with red meat consumption could be counteracted by ingesting carnosine into meat. The health advantages of dietary carnosine, however, have never been demonstrated during digestion, a unique and complex oxidative environment compounded by the composition and cooking of the meat. The results obtained substantiated that AGEs formation occurred in-vitro in the GIT. They also showed that increased carnosine had an immediate health beneficial role during pork digestion in reducing the formation of different harmful molecules, including AGEs, modulated by the composition and cooking of the meat. However, in exerting this protective role in the GIT, the remaining free level of carnosine, gradually decreased during digestion. Carnosine, as an important meat compositional factor may, depending on the fat content and cooking conditions, change the image of meat from representing a health risk to a health benefit. Carnosine level may also explain discrepancies observed in the literature.

Carnosine, Small but Mighty-Prospect of Use as Functional Ingredient for Functional Food Formulation

Carnosine is a dipeptide synthesized in the body from β-alanine and L-histidine. It is found in high concentrations in the brain, muscle, and gastrointestinal tissues of humans and is present in all vertebrates. Carnosine has a number of beneficial antioxidant properties. For example, carnosine scavenges reactive oxygen species (ROS) as well as alpha-beta unsaturated aldehydes created by peroxidation of fatty acid cell membranes during oxidative stress. Carnosine can oppose glycation, and it can chelate divalent metal ions. Carnosine alleviates diabetic nephropathy by protecting podocyte and mesangial cells, and can slow down aging. Its component, the amino acid beta-alanine, is particularly interesting as a dietary supplement for athletes because it increases muscle carnosine, and improves effectiveness of exercise and stimulation and contraction in muscles. Carnosine is widely used among athletes in the form of supplements, but rarely in the population of cardiovascular or diabetic patients. Much less is known, if any, about its potential use in enriched food. In the present review, we aimed to provide recent knowledge on carnosine properties and distribution, its metabolism (synthesis and degradation), and analytical methods for carnosine determination, since one of the difficulties is the measurement of carnosine concentration in human samples. Furthermore, the potential mechanisms of carnosine's biological effects in musculature, metabolism and on immunomodulation are discussed. Finally, this review provides a section on carnosine supplementation in the form of functional food and potential health benefits and up to the present, neglected clinical use of carnosine.

Use of carnosine in the prevention of cardiometabolic risk factors in overweight and obese individuals: study protocol for a randomised, double-blind placebo-controlled trial

INTRODUCTION

Carnosine, an over the counter food supplement, has been shown to improve glucose metabolism as well as cardiovascular risk factors in animal and human studies through its anti-inflammatory, antioxidative, antiglycating and chelating properties. The aim of this study is to establish if carnosine supplementation improves obesity, insulin sensitivity, insulin secretion, cardiovascular risk factors including arterial stiffness and endothelial function, and other risk factors related to diabetes and cardiovascular disease in the overweight and obese population.

METHODS AND ANALYSIS

Fifty participants will be recruited to be enrolled in a double-blind randomised controlled trial. Eligible participants with a body mass index (BMI) between 25 and 40 kg/m² will be randomly assigned to the intervention or placebo group. Following a medical review and oral glucose tolerance test to check eligibility, participants will then undergo testing. At baseline, participants will have anthropometric measurements (BMI, dual X-ray absorptiometry and peripheral quantitative CT scan), measurements of glucose metabolism (oral glucose tolerance test, intravenous glucose tolerance test and euglycaemic hyperinsulinaemic clamp), cardiovascular measurements (central blood pressure, endothelial function and arterial stiffness), a muscle and fat biopsy, physical activity measurement, liver fibroscan, cognitive function and questionnaires to assess dietary habits, sleep quality, depression, and quality of life. Following baseline assessments, participants will be randomised to either 2 g carnosine or placebo for 15 weeks. In the 15th week, all assessments will be repeated. The preplanned outcome metric is the change between baseline and follow-up measures.

ETHICS AND DISSEMINATION

This study is approved by the Human Research Ethics Committee of Monash Health and Monash University, Australia.

TRIAL REGISTRATION NUMBER

NCT02686996.

Carnosine and histidine-containing dipeptides improve dyslipidemia: a systematic review and meta-analysis of randomized controlled trials

CONTEXT

Cardiovascular disease is a major public health problem and represents a significant burden of disease globally. Lifestyle interventions have their limitations and an intervention that will effectively address cardiovascular risk factors to help reduce this growing burden of disease is required.

OBJECTIVE

Carnosine and other histidine-containing dipeptides (HCDs) have exerted positive effects on cardiovascular risk factors and diseases in animal and human studies. The authors conducted a systematic review and meta-analysis examining the effects of HCDs on cardiovascular outcomes in line with the PRISMA guidelines.

DATA SOURCES

The Medline, Medline in process, Embase, Cumulative Index of Nursing and Allied Health, and All EBM databases were searched from inception until January 25, 2019, for randomized controlled trials (RCTs) examining the effects of HCDs on cardiovascular outcomes, compared with placebo or controls.

DATA EXTRACTION

Basic characteristics of the study and populations, interventions, and study results were extracted. The grading of recommendations assessment, development, and evaluation approach was used to assess the quality of evidence for each outcome.

DATA ANALYSIS

A total of 21 studies were included. Of these, 18 were pooled for meta-analysis (n = 913). In low risk of bias studies, HCD-supplemented groups had lower total cholesterol (n = 6 RCTs; n = 401; weighted mean difference [WMD], -0.32 mmol/L [95%CI, -0.57 to -0.07], P = 0.01) and triglyceride levels (n = 6 RCTs; n = 401; WMD, -0.14 mmol/L [95%CI, -0.20 to -0.08], P < 0.001) compared with controls. In studies using carnosine, triglycerides levels were also lower in the intervention group vs controls (n = 5 RCTS; n = 309; P < 0.001). There were no significant differences in blood pressure, heart rate, low-density lipoprotein cholesterol, high-density lipoprotein cholesterol (HDL-C) or the total cholesterol to HDL-C ratio between groups.

CONCLUSIONS

Carnosine and other HCDs may have a role in improving lipid profiles. Larger studies with sufficient follow-up are necessary to confirm these findings and explore the use of HCDs in the prevention of cardiovascular diseases.

SYSTEMIC REVIEW REGISTRATION

PROSPERO registration no.: CRD42017075354.

The Therapeutic Potential of Carnosine/Anserine Supplementation against Cognitive Decline: A Systematic Review with Meta-Analysis

Carnosine is a natural occurring endogenous dipeptide that was proposed as an anti-aging agent more than 20 years ago. Carnosine can be found at low millimolar concentrations at brain level and different preclinical studies have demonstrated its antioxidant, anti-inflammatory, and anti-aggregation activity with neuroprotective effects in animal models of Alzheimer’s disease (AD). A selective deficit of carnosine has also been linked to cognitive decline in AD. Different clinical studies have been conducted to evaluate the impact of carnosine supplementation against cognitive decline in elderly and AD subjects. We conducted a systematic review with meta-analysis, in accordance with the PRISMA guidelines coupled to the PICOS approach, to investigate the therapeutic potential of carnosine against cognitive decline and depressive symptoms in elderly subjects. We found five studies matching the selection criteria. Carnosine/anserine was administered for 12 weeks at a dose of 1 g/day and improved global cognitive function, whereas no effects were detected on depressive symptoms. These data suggest a preliminary evidence of clinical efficacy of carnosine against cognitive decline both in elderly subjects and mild cognitive impairment (MCI) patients, although larger and long-term clinical studies are needed in MCI patients (with or without depression) to confirm the therapeutic potential of carnosine.

Hydrogen Sulfide and Carnosine: Modulation of Oxidative Stress and Inflammation in Kidney and Brain Axis

Emerging evidence indicates that the dysregulation of cellular redox homeostasis and chronic inflammatory processes are implicated in the pathogenesis of kidney and brain disorders. In this light, endogenous dipeptide carnosine (β-alanyl-L-histidine) and hydrogen sulfide (H₂S) exert cytoprotective actions through the modulation of redox-dependent resilience pathways during oxidative stress and inflammation. Several recent studies have elucidated a functional crosstalk occurring between kidney and the brain. The pathophysiological link of this crosstalk is represented by oxidative stress and inflammatory processes which contribute to the high prevalence of neuropsychiatric disorders, cognitive impairment, and dementia during the natural history of chronic kidney disease. Herein, we provide an overview of the main pathophysiological mechanisms related to high levels of pro-inflammatory cytokines, including interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), and neurotoxins, which play a critical role in the kidney–brain crosstalk. The present paper also explores the respective role of H₂S and carnosine in the modulation of oxidative stress and inflammation in the kidney–brain axis. It suggests that these activities are likely mediated, at least in part, via hormetic processes, involving Nrf2 (Nuclear factor-like 2), Hsp 70 (heat shock protein 70), SIRT-1 (Sirtuin-1), Trx (Thioredoxin), and the glutathione system. Metabolic interactions at the kidney and brain axis level operate in controlling and reducing oxidant-induced inflammatory damage and therefore, can be a promising potential therapeutic target to reduce the severity of renal and brain injuries in humans.

The effect of carnosine or β-alanine supplementation on markers of glycaemic control and insulin resistance in human and animal studies: a protocol for a systematic review and meta-analysis

BACKGROUND

Diabetes is a major public health issue and there is a need to develop low-cost, novel interventions to prevent or reduce disease progression. Growing evidence shows that supplementation with carnosine, or its rate-limiting precursor β-alanine, can ameliorate aspects of the metabolic dysregulation that occurs in diabetes. There is, however, a need to develop a better understanding of the magnitude of effect and the factors associated with positive outcomes. The purpose of this systematic review and meta-analysis is to evaluate the effect of carnosine or β-alanine supplementation on markers of glycaemic control and insulin resistance in humans and animals.

METHODS

We will perform a systematic search for randomised and non-randomised controlled trials. Studies will be retrieved by searching electronic databases, clinical trial registers, author review, and cross-referencing. Primary outcomes include changes in (i) fasting glucose, (ii) glycated haemoglobin, and (iii) 2-h glucose following a glucose tolerance test. A set of additional outcomes includes other markers of glycaemic control and insulin resistance. Risk of bias (RoB) will be assessed using the Cochrane RoB 2.0 tool (human studies) and the Systematic Review Centre for Laboratory Animal Experimentation (SYRCLE) RoB tool (animal studies). Confidence in the cumulative evidence will be assessed using the Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach. All meta-analyses will be conducted within a Bayesian framework, providing a flexible modelling approach to account for uncertainty in model parameters and underlying structures within the data.

DISCUSSION

By including all available human and animal data, we will provide the most comprehensive overview on the topic to date. The results will have implications for those working in prediabetes, diabetes, and metabolic health in general and may lead to the development of new treatment approaches.

DISSEMINATION

Study results will be presented at a professional conference and published in a peer-reviewed journal.

SYSTEMATIC REVIEW REGISTRATION

CRD42020191588.

Lipopolysaccharide exposure induces oxidative damage in Caenorhabditis elegans: protective effects of carnosine

Background

The present study was designed to investigate the protective effects and mechanisms of carnosine on lipopolysaccharide (LPS)-induced injury in Caenorhabditis elegans.

Methods

C. elegans individuals were stimulated for 24 h with LPS (100 μg/mL), with or without carnosine (0.1, 1, 10 mM). The survival rates and behaviors were determined. The activities of superoxide dismutase (SOD), glutathione reductase (GR), and catalase (CAT) and levels of malondialdehyde (MDA) and glutathione (GSH) were determined using the respective kits. Reverse transcription polymerase chain reaction (RT-PCR) was performed to validate the differential expression of sod-1, sod-2, sod-3, daf-16, ced-3, ced-9, sek-1, and pmk-1. Western blotting was used to determine the levels of SEK1, p38 mitogen-activated protein kinase (MAPK), cleaved caspase3, and Bcl-2. C. elegans sek-1 (km2) mutants and pmk-1 (km25) mutants were used to elucidate the role of the p38 MAPK signaling pathway.

Results

Carnosine improved the survival of LPS-treated C. elegans and rescued behavioral phenotypes. It also restrained oxidative stress by decreasing MDA levels and increasing SOD, GR, CAT, and GSH levels. RT-PCR results showed that carnosine treatment of wild-type C. elegans up-regulated the mRNA expression of the antioxidant-related genes sod-1, sod-2, sod-3, and daf-16. The expression of the anti-apoptosis-related gene ced-9 and apoptosis-related gene ced-3 was reversed by carnosine. In addition, carnosine treatment significantly decreased cleaved caspase3 levels and increased Bcl-2 levels in LPS-treated C. elegans. Apoptosis in the loss-of-function strains of the p38 MAPK signaling pathway was suppressed under LPS stress; however, the apoptotic effects of LPS were blocked in the sek-1 and pmk-1 mutants. The expression levels of sek-1 and pmk-1 mRNAs were up-regulated by LPS and reversed by carnosine. Finally, the expression of p-p38MAPK and SEK1 was significantly increased by LPS, which was reversed by carnosine.

Conclusion

Carnosine treatment protected against LPS injury by decreasing oxidative stress and inhibiting apoptosis through the p38 MAPK pathway.

The Development of Maillard Reaction, and Advanced Glycation End Product (AGE)-Receptor for AGE (RAGE) Signaling Inhibitors as Novel Therapeutic Strategies for Patients with AGE-Related Diseases

Advanced glycation end products (AGEs) are generated by nonenzymatic modifications of macromolecules (proteins, lipids, and nucleic acids) by saccharides (glucose, fructose, and pentose) via Maillard reaction. The formed AGE molecules can be catabolized and cleared by glyoxalase I and II in renal proximal tubular cells. AGE-related diseases include physiological aging, neurodegenerative/neuroinflammatory diseases, diabetes mellitus (DM) and its complications, autoimmune/rheumatic inflammatory diseases, bone-degenerative diseases, and chronic renal diseases. AGEs, by binding to receptors for AGE (RAGEs), alter innate and adaptive immune responses to induce inflammation and immunosuppression via the generation of proinflammatory cytokines, reactive oxygen species (ROS), and reactive nitrogen intermediates (RNI). These pathological molecules cause vascular endothelial/smooth muscular/connective tissue-cell and renal mesangial/endothelial/podocytic-cell damage in AGE-related diseases. In the present review, we first focus on the cellular and molecular bases of AGE–RAGE axis signaling pathways in AGE-related diseases. Then, we discuss in detail the modes of action of newly discovered novel biomolecules and phytochemical compounds, such as Maillard reaction and AGE–RAGE signaling inhibitors. These molecules are expected to become the new therapeutic strategies for patients with AGE-related diseases in addition to the traditional hypoglycemic and anti-hypertensive agents. We particularly emphasize the importance of “metabolic memory”, the “French paradox”, and the pharmacokinetics and therapeutic dosing of the effective natural compounds associated with pharmacogenetics in the treatment of AGE-related diseases. Lastly, we propose prospective investigations for solving the enigmas in AGE-mediated pathological effects.

Synergistic Effects of Regular Walking and Alkaline Electrolyzed Water on Decreasing Inflammation and Oxidative Stress, and Increasing Quality of Life in Individuals with Type 2 Diabetes: A Community Based Randomized Controlled Trial

Alkaline electrolyzed water (AEW) and walking are strongly recommended for ameliorating oxidative stress and inflammation. Nevertheless, there is a lack of information on the combination of both on alleviating inflammation, oxidative stress, and improving the quality of life (QoL). We investigated the synergistic effects of drinking AEW and walking on advanced glycation end products (AGEs), advanced oxidation protein products (AOPPs), malondialdehyde (MDA), white blood cells (WBCs), neutrophil-lymphocyte ratio (NLR) and QoL. In total, 81 eligible patients with type 2 diabetes (T2DM) were randomly allocated via single blind to four groups: consumed 2 L/day of AEW (n = 20), instructed to walk for 150 min/week (n = 20), received a combination of AEW and walking (n = 20), and continue their habitual diet and activity (n = 21). Data were collected and analyzed before and after 8 weeks of intervention. Our results showed a significant interaction between the group and time, with both AEW and walking independently and synergistically ameliorating AGEs, AOPPs, MDA, NLR and WBCs levels. Moreover, the AEW group had a higher physical and total QoL score. The walking group and the combined group had higher scores in physical, mental and total QoL compared to the control group. The synergistic effect of AEW and regular walking are an advisable treatment for patients with T2DM.

Inflammation as the Common Biological Link Between Depression and Cardiovascular Diseases: Can Carnosine Exert a Protective Role?

Several epidemiological studies have clearly shown the high co-morbidity between depression and Cardiovascular Diseases (CVD). Different studies have been conducted to identify the common pathophysiological events of these diseases such as the overactivation of the hypothalamic- pituitary-adrenal axis and, most importantly, the dysregulation of immune system which causes a chronic pro-inflammatory status. The biological link between depression, inflammation, and CVD can be related to high levels of pro-inflammatory cytokines, such as IL-1β, TNF-α, and IL-6, released by macrophages which play a central role in the pathophysiology of both depression and CVD. Pro-inflammatory cytokines interfere with many of the pathophysiological mechanisms relevant to depression by upregulating the rate-limiting enzymes in the metabolic pathway of tryptophan and altering serotonin metabolism. These cytokines also increase the risk to develop CVD, because activation of macrophages under this pro-inflammatory status is closely associated with endothelial dysfunction and oxidative stress, a preamble to atherosclerosis and atherothrombosis. Carnosine (β-alanyl-L-histidine) is an endogenous dipeptide which exerts a strong antiinflammatory activity on macrophages by suppressing reactive species and pro-inflammatory cytokines production and altering pro-inflammatory/anti-inflammatory macrophage polarization. This dipeptide exhibits antioxidant properties scavenging reactive species and preventing oxidative stress-induced pathologies such as CVD. In the present review we will discuss the role of oxidative stress and chronic inflammation as common pathophysiological events both in depression and CVD and the preclinical and clinical evidence on the protective effect of carnosine in both diseases as well as the therapeutic potential of this dipeptide in depressed patients with a high co-morbidity of cardiovascular diseases.

Therapeutic Potential of Carnosine and Its Derivatives in the Treatment of Human Diseases

Despite significant progress in the pathogenesis, diagnosis, treatment, and prevention of cancer and neurodegenerative diseases, their occurrence and mortality are still high around the world. The resistance of cancer cells to the drugs remains a significant problem in oncology today, while in the case of neuro-degenerative diseases, therapies reversing the process are still yet to be found. Furthermore, it is important to seek new chemotherapeutics reversing side effects of currently used drugs or helping them perform their function to inhibit progression of the disease. Carnosine, a dipeptide constisting of β-alanine and l-histidine, has a variety of functions to mention: antioxidant, antiglycation, and reducing the toxicity of metal ions. It has therefore been proposed to act as a therapeutic agent for many pathological states. The aim of this paper was to find if carnosine and its derivatives can be helpful in treating various diseases. Literature search presented in this review includes review and original papers found in SciFinder, PubMed, and Google Scholar. Searches were based on substantial keywords concerning therapeutic usage of carnosine and its derivatives in several diseases including neurodegenerative disorders and cancer. In this paper, we review articles and find that carnosine and its derivatives are potential therapeutic agents in many diseases including cancer, neurodegenerative diseases, diabetes, and schizophrenia. Carnosine and its derivatives can be used in treating neurodegenerative diseases, cancer, diabetes, or schizophrenia, although their usage is limited. Therefore, there's an urge to synthesize and analyze new substances, overcoming the limitation of carnosine itself.

Carnosinase-1 overexpression, but not aerobic exercise training, affects the development of diabetic nephropathy in BTBR ob/ob mice

Manipulation of circulating histidine-containing dipeptides (HCD) has been shown to affect the development of diabetes and early-stage diabetic nephropathy (DN). The aim of the present study was to investigate whether such interventions, which potentially alter levels of circulating HCD, also affect the development of advanced-stage DN. Two interventions, aerobic exercise training and overexpression of the human carnosinase-1 (hCN1) enzyme, were tested. BTBR ob/ob mice were either subjected to aerobic exercise training (20 wk) or genetically manipulated to overexpress hCN1, and different diabetes- and DN-related markers were compared with control ob/ob and healthy (wild-type) mice. An acute exercise study was performed to elucidate the effect of obesity, acute running, and hCN1 overexpression on plasma HCD levels. Chronic aerobic exercise training did not affect the development of diabetes or DN, but hCN1 overexpression accelerated hyperlipidemia and aggravated the development of albuminuria, mesangial matrix expansion, and glomerular hypertrophy of ob/ob mice. In line, plasma, kidney, and muscle HCD were markedly lower in ob/ob versus wild-type mice, and plasma and kidney HCD in particular were lower in ob/ob hCN1 versus ob/ob mice but were unaffected by aerobic exercise. In conclusion, advanced glomerular damage is accelerated in mice overexpressing the hCN1 enzyme but not protected by chronic exercise training. Interestingly, we showed, for the first time, that the development of DN is closely linked to renal HCD availability. Further research will have to elucidate whether the stimulation of renal HCD levels can be a therapeutic strategy to reduce the risk for developing DN.

Important roles of dietary taurine, creatine, carnosine, anserine and 4-hydroxyproline in human nutrition and health

Taurine (a sulfur-containing β-amino acid), creatine (a metabolite of arginine, glycine and methionine), carnosine (a dipeptide; β-alanyl-L-histidine), and 4-hydroxyproline (an imino acid; also often referred to as an amino acid) were discovered in cattle, and the discovery of anserine (a methylated product of carnosine; β-alanyl-1-methyl-L-histidine) also originated with cattle. These five nutrients are highly abundant in beef, and have important physiological roles in anti-oxidative and anti-inflammatory reactions, as well as neurological, muscular, retinal, immunological and cardiovascular function. Of particular note, taurine, carnosine, anserine, and creatine are absent from plants, and hydroxyproline is negligible in many plant-source foods. Consumption of 30 g dry beef can fully meet daily physiological needs of the healthy 70-kg adult human for taurine and carnosine, and can also provide large amounts of creatine, anserine and 4-hydroxyproline to improve human nutrition and health, including metabolic, retinal, immunological, muscular, cartilage, neurological, and cardiovascular health. The present review provides the public with the much-needed knowledge of nutritionally and physiologically significant amino acids, dipeptides and creatine in animal-source foods (including beef). Dietary taurine, creatine, carnosine, anserine and 4-hydroxyproline are beneficial for preventing and treating obesity, cardiovascular dysfunction, and ageing-related disorders, as well as inhibiting tumorigenesis, improving skin and bone health, ameliorating neurological abnormalities, and promoting well being in infants, children and adults. Furthermore, these nutrients may promote the immunological defense of humans against infections by bacteria, fungi, parasites, and viruses (including coronavirus) through enhancing the metabolism and functions of monocytes, macrophages, and other cells of the immune system. Red meat (including beef) is a functional food for optimizing human growth, development and health.

Clinical/Translational Aspects of Advanced Glycation End-Products

Advanced glycation end-products (AGEs) have been implicated in chronic hyperglycemia and age-related diseases. Endogenous AGEs produced by humans generate oxidative stress and activation of inflammatory signaling pathways via AGE-specific receptors. The present review summarizes current knowledge on the pathogenic role of AGEs in chronic noncommunicable diseases. Although correlations exist between glycation and the pathogenesis of these diseases, uncertainties remain in light of recurrent intervention failures of apparently promising animal models to be translated into clinically useful anti-AGE strategies. Future intervention of AGEs or their receptors should embrace more carefully executed clinical trials. Nevertheless, suppressing symptoms via lifetime drug application is unlikely to eliminate the burden of chronic diseases unless deep-rooted lifestyle issues that cause these diseases are simultaneously addressed.

Effect of carnosine supplementation on lipid profile, fasting blood glucose, HbA1C and insulin resistance: A systematic review and meta-analysis of long-term randomized controlled trials

OBJECTIVE

Glucose disorders and dyslipidemia are closely associated with obesity and metabolic disease. The purpose of this study was to investigate the effect of Carnosine supplementation on lipid profile, fasting blood glucose, HbA1C and Insulin resistance.

METHOD

MEDLINE/PubMed, Scopus and Web of sciences were investigated to identify relevant articles up to June 2019. The search strategy combined the Medical Subject Heading and Title and/or abstract keywords. The combined effect sizes were calculated as weight mean difference (WMD) using the random-effects model. Between study heterogeneity was evaluated by the Cochran's Q test and I².

RESULTS

Four RCTs studies investigated Carnosine use versus any control for at least 2 weeks were identified and analyzed. Overall results from the random-effects model on included studies, with 184 participants, indicated that carnosine intervention reduced HbA1C levels in intervention vs control groups (WMD: -0.92 %, 95 % CI: -1.20, -0.63, I²:69 %). Four studies, including a total of 183 participants, reported TG changes as an outcome measure variable, but combined results did not show significant reduction in this outcome (WMD: -14.46 mg/dl, 95 % CI: -29.11, 0.19, I²:94 %). Furthermore, combined results did not show any significant change in HOMA-IR, Cholesterol, fasting blood sugar, or HDL-C.

CONCLUSION

Carnosine supplementation results in a decrease in HbA1C, but elicits no effect on HOMA-IR, Cholesterol, fasting blood sugar, TG and HDL-C. Future studies with a larger sample sizes, varied doses of carnosine, and population-specific sub-groups are warranted to confirm, and enhance, the veracity of our findings.

CNDP1 knockout in zebrafish alters the amino acid metabolism, restrains weight gain, but does not protect from diabetic complications

The gene CNDP1 was associated with the development of diabetic nephropathy. Its enzyme carnosinase 1 (CN1) primarily hydrolyzes the histidine-containing dipeptide carnosine but other organ and metabolic functions are mainly unknown. In our study we generated CNDP1 knockout zebrafish, which showed strongly decreased CN1 activity and increased intracellular carnosine levels. Vasculature and kidneys of CNDP1-/- zebrafish were not affected, except for a transient glomerular alteration. Amino acid profiling showed a decrease of certain amino acids in CNDP1-/- zebrafish, suggesting a specific function for CN1 in the amino acid metabolisms. Indeed, we identified a CN1 activity for Ala-His and Ser-His. Under diabetic conditions increased carnosine levels in CNDP1-/- embryos could not protect from respective organ alterations. Although, weight gain through overfeeding was restrained by CNDP1 loss. Together, zebrafish exhibits CN1 functions, while CNDP1 knockout alters the amino acid metabolism, attenuates weight gain but cannot protect organs from diabetic complications.

The effects of l-Carnosine on development of metabolic syndrome in rats

AIMS

The prevalence of metabolic syndrome (MetS) is increasing in several countries. The MetS is characterized by the occurrence of at least three of the following risk factors: decreased high-density lipoprotein cholesterol, increased blood pressure, raised fasting blood glucose, elevated triglycerides, and abdominal obesity. There is a growing evidence of the role of l-carnosine in improving lipid profile and enhancement of the antioxidant activity. However, the effects of l-carnosine on development of MetS are unknown.

MAIN METHODS

Male Wistar rats were randomly assigned to receive either; conventional diet (control), high-fat high-carbohydrate diet (HFHCD), l-carnosine and conventional diet (L-Car), or l-carnosine and high-fat high-carbohydrate diet (HFHCD and L-Car) for 16 weeks. Central obesity, systolic blood pressure, lipid profile, glucose hemostasis, levels of leptin and adiponectin were evaluated on week 16.

KEY FINDINGS

Rats that received HFHCD for 16 weeks showed MetS phenotype such as central obesity, increased blood pressure and glucose, as well as an altered lipid profile (P < 0.05). l-Carnosine supplementation to MetS rats significantly reduced abdominal obesity, blood pressure and glucose, and normalized total cholesterol and low density lipoprotein cholesterol levels (P < 0.05). Insulin, leptin and adiponectin concentrations were not affected by l-Carnosine (P > 0.05).

SIGNIFICANCE

l-carnosine has beneficial effects on ameliorating the manifestations of MetS in rats.

Relationship Between Oxidative Stress, ER Stress, and Inflammation in Type 2 Diabetes: The Battle Continues

Type 2 diabetes (T2D) is a metabolic disorder characterized by hyperglycemia and insulin resistance in which oxidative stress is thought to be a primary cause. Considering that mitochondria are the main source of ROS, we have set out to provide a general overview on how oxidative stress is generated and related to T2D. Enhanced generation of reactive oxygen species (ROS) and oxidative stress occurs in mitochondria as a consequence of an overload of glucose and oxidative phosphorylation. Endoplasmic reticulum (ER) stress plays an important role in oxidative stress, as it is also a source of ROS. The tight interconnection between both organelles through mitochondrial-associated membranes (MAMs) means that the ROS generated in mitochondria promote ER stress. Therefore, a state of stress and mitochondrial dysfunction are consequences of this vicious cycle. The implication of mitochondria in insulin release and the exposure of pancreatic β-cells to hyperglycemia make them especially susceptible to oxidative stress and mitochondrial dysfunction. In fact, crosstalk between both mechanisms is related with alterations in glucose homeostasis and can lead to the diabetes-associated insulin-resistance status. In the present review, we discuss the current knowledge of the relationship between oxidative stress, mitochondria, ER stress, inflammation, and lipotoxicity in T2D.

Characteristics of Selected Antioxidative and Bioactive Compounds in Meat and Animal Origin Products

Meat and meat products have a high nutritional value. Besides major components, meat is rich in bioactive components, primarily taurine, l-carnitine, choline, alpha-lipoic acid, conjugated linoleic acid, glutathione, creatine, coenzyme Q10 and bioactive peptides. Many studies have reported their antioxidant and health-promoting properties connected with their lipid-lowering, antihypertensive, anti-inflammatory, immunomodulatory activity and protecting the organism against oxidative stress. The antioxidant activity of meat components results, among others, from the capability of scavenging reactive oxygen and nitrogen species, forming complexes with metal ions and protecting cells against damage. This review is focused to gather accurate information about meat components with antioxidant and biological activity.