Serum Carnosinase Research Articles

Exploring Secondary Amine Carnosine Derivatives: Design, Synthesis, and Properties

Carnosine is a naturally occurring dipeptide that has been advocated by some authors as an interesting scaffold for the development of potential therapeutic agents in view of the positive outcomes of its supplementation in animal models of human diseases. Its mode of action seems to depend on the quenching of toxic electrophiles, such as 4–hydroxynonenal (HNE). However, carnosine’s bioavailability in humans is lower than that in other mammals. The main reason for such an unfavorable pharmacokinetic profile is the activity of the enzyme human serum carnosinase (E.C. 3.4.13.20), which rapidly hydrolyzes carnosine upon absorption. Therefore, some studies have focused on the design of carnosinase-resistant derivatives that retain binding activity toward toxic electrophiles. Nevertheless, the structural modification of the N-terminus amino group of carnosine has rarely been considered, possibly because of its key role in the electrophile scavenging mechanism. This was proven, since some carnosine N-terminus modification generated inactive compounds, despite some derivatives retaining oral bioavailability and gaining resistance to carnosinase hydrolysis. Herein, we therefore report a study aimed at exploring whether the amino group of carnosine can be conveniently modified to develop carnosinase-resistant derivatives retaining the dipeptide activity toward toxic electrophiles.

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.

State of the Art in the Development of Human Serum Carnosinase Inhibitors.

Human serum carnosinase is an enzyme that operates the preferential hydrolysis of dipeptides with a C-terminus histidine. Only higher primates excrete such an enzyme in serum and cerebrospinal fluid. In humans, the serum hydrolytic rate has high interindividual variability owing to gene polymorphism, although age, gender, diet, and also diseases and surgical interventions can modify serum activity. Human genetic diseases with altered carnosinase activity have been identified and associated with neurological disorders and age-related cognitive decline. On the contrary, low peripheral carnosinase activity has been associated with kidney protection, especially in diabetic nephropathy. Therefore, serum carnosinase is a druggable target for the development of selective inhibitors. However, only one molecule (i.e., carnostatine) has been discovered with the purpose of developing serum carnosinase inhibitors. Bestatin is the only inhibitor reported other than carnostatine, although its activity is not selective towards serum carnosinase. Herein, we present a review of the most critical findings on human serum carnosinase, including enzyme expression, localization and substrate selectivity, along with factors affecting the hydrolytic activity, its implication in human diseases and the properties of known inhibitors of the enzyme.

Dual Effect of Carnosine on ROS Formation in Rat Cultured Cortical Astrocytes.

Carnosine is composed of β-alanine and L-histidine and is considered to be an important neuroprotective agent with antioxidant, metal chelating, and antisenescence properties. However, children with serum carnosinase deficiency present increased circulating carnosine and severe neurological symptoms. We here investigated the in vitro effects of carnosine on redox and mitochondrial parameters in cultured cortical astrocytes from neonatal rats. Carnosine did not alter mitochondrial content or mitochondrial membrane potential. On the other hand, carnosine increased mitochondrial superoxide anion formation, levels of thiobarbituric acid reactive substances and oxidation of 2',7'-dichlorofluorescin diacetate (DCF-DA), indicating that carnosine per se acts as a pro-oxidant agent. Nonetheless, carnosine prevented DCF-DA oxidation induced by H2O2 in cultured cortical astrocytes. Since alterations on mitochondrial membrane potential are not likely to be involved in these effects of carnosine, the involvement of N-Methyl-D-aspartate (NMDA) receptors in the pro-oxidant actions of carnosine was investigated. MK-801, an antagonist of NMDA receptors, prevented DCF-DA oxidation induced by carnosine in cultured cortical astrocytes. Astrocyte reactivity induced by carnosine was also prevented by the coincubation with MK-801. The present study shows for the very first time the pro-oxidant effects of carnosine per se in astrocytes. The data raise awareness on the importance of a better understanding of the biological actions of carnosine, a nutraceutical otherwise widely reported as devoid of side effects.

Binding Modes of Carnostatine, Homocarnosine, and Ophidine to Human Carnosinase 1.

Carnosine (CAR), anserine (ANS), homocarnosine (H-CAR), and ophidine (OPH) are histidine-containing dipeptides that show a wide range of therapeutic properties. With their potential physiological effects, these bioactive dipeptides are considered as bioactive food components. However, such dipeptides display low stability due to their rapid degradation by human serum carnosinase 1 (CN1). A dimeric CN1 hydrolyzes such histidine-containing compounds with different degrees of reactivities. A selective CN inhibitor, carnostatine (CARN), was reported to effectively inhibit CN's activity. To date, the binding mechanisms of CAR and ANS have been recently reported, while no clear information about H-CAR, OPH, and CARN binding is available. Thus, in this work, molecular dynamics simulations were employed to elucidate the binding mechanism of H-CAR, OPH, and CARN. Among all, the amine end and imidazole ring are the main players for trapping all of the ligands in a pocket. OPH shows the poorest binding affinity, while CARN displays the tightest binding. Such firm binding is due to the longer amine chain and the additional hydroxyl (-OH) group of CARN. H-CAR and CARN are analogous, but the absence of the -OH moiety in H-CAR significantly enhances its mobility, resulting in the reduction in binding affinity. For OPH which is an ANS analogue, the methylated imidazole ring destroys the OPH-CN1 interaction network at this region, consequentially leading to the poor binding ability. An insight into how CN recognizes and binds its substrates obtained here will be useful for designing an effective strategy to prolong the lifetime of CAR and its analogues after ingestion.

A Green and Cost-Effective Chromatographic Method for the Measurement of the Activity of Human Serum Carnosinase

Carnosinase (i.e., CN1; E.C. 3.4.13.20) is an enzyme found in the sera of higher primates. CN1 preferentially catalyzes the hydrolysis of natural, orally adsorbed histidine dipeptides like carnosine (i.e., β-alanyl-L-histidine). This is the reason why carnosine has a limited use as a human food supplement or pharmacological agent, despite the promising results obtained in experiments on animal models of human diseases. Herein, an assay is reported for the measurement of serum CN1 activity. The method is intended for the screening of CN1 inhibitors able to enhance carnosine bioavailability in humans. The method was developed to monitor serum hydrolytic activity via the quantitation of one of the products of carnosine hydrolysis (i.e., histidine). Separation was achieved without using organic solvents by means of ion chromatography (IC), whereas detection was provided by UV spectroscopy. The assay herein reported is a green and cost-effective alternative to a recently published method based on hydrophilic interaction liquid chromatography (HILIC) and mass spectrometry (MS). The results show that such a method produces reliable measurements of serum hydrolytic activity and can be used for the screening of CN1 inhibitors.

Molecular insights into the binding of carnosine and anserine to human serum carnosinase 1 (CN1)

Carnosine (CAR) and anserine (ANS) are histidine-containing dipeptides that show the therapeutic properties and protective abilities against diabetes and cognitive deficit. Both dipeptides are rich in meat products and have been used as a supplement. However, in humans, both compounds have a short half-life due to the rapid degradation by dizinc carnosinase 1 (CN1) which is a hurdle for its therapeutic application. To date, a comparative study of carnosine- and anserine-CN1 complexes is limited. Thus, in this work, molecular dynamics (MD) simulations were performed to explore the binding of carnosine and anserine to CN1. CN1 comprises 2 chains (Chains A and B). Both monomers are found to work independently and alternatingly. The displacement of Zn2+ pair is found to disrupt the substrate binding. CN1 employs residues from the neighbour chain (H235, T335, and T337) to form the active site. This highlights the importance of a dimer for enzymatic activity. Anserine is more resistant to CN 1 than carnosine because of its bulky and dehydrated imidazole moiety. Although both dipeptides can direct the peptide oxygen to the active Zn2+ which can facilitate the catalytic reaction, the bulky methylated imidazole on anserine promotes various poses that can retard the hydrolytic activity in contrast to carnosine. Anserine is likely to be the temporary competitive inhibitor by retarding the carnosine catabolism.

Cyclo(His-Pro) Exerts Protective Carbonyl Quenching Effects through Its Open Histidine Containing Dipeptides.

Cyclo(His-Pro) (CHP) is a cyclic dipeptide which is endowed with favorable pharmacokinetic properties combined with a variety of biological activities. CHP is found in a number of protein-rich foods and dietary supplements. While being stable at physiological pH, CHP can open yielding two symmetric dipeptides (His-Pro, Pro-His), the formation of which might be particularly relevant from dietary CHP due to the gastric acidic environment. The antioxidant and protective CHP properties were repeatedly reported although the non-enzymatic mechanisms were scantly investigated. The CHP detoxifying activity towards α,β unsaturated carbonyls was never investigated in detail, although its open dipeptides might be effective as already observed for histidine containing dipeptides. Hence, this study investigated the scavenging properties of TRH, CHP and its open derivatives towards 4-hydroxy-2-nonenal. The obtained results revealed that Pro-His possesses a marked activity and is more reactive than l-carnosine. As investigated by DFT calculations, the enhanced reactivity can be ascribed to the greater electrophilicity of the involved iminium intermediate. These findings emphasize that the primary amine (as seen in l-carnosine) can be replaced by secondary amines with beneficial effects on the quenching mechanisms. Serum stability of the tested peptides was also evaluated, showing that Pro-His is characterized by a greater stability than l-carnosine. Docking simulations suggested that its hydrolysis can be catalyzed by serum carnosinase. Altogether, the reported results evidence that the antioxidant CHP properties can be also due to the detoxifying activity of its open dipeptides, which might be thus responsible for the beneficial effects induced by CHP containing food.

IDF21-0406 Genetic variants in the Carnosine-Carnosinase system and their impact on diabetic nephropathy

Background: The role of carnosine-carnosinase system in diabetic nephropathy has been established through various studies in animal models. It has been proven that low carnosinase secretion promotes high circulating carnosine levels which acts as a protective factor against adverse effects of hyperglycemia on renal cells. While genetic variants in the carnosinase gene (CNDP1) could influence carnosinase concentration, variants in the carnosine synthase gene (CARNS1) which synthesizes carnosine and variants in the SLC15A4 and SLC15A2 genes which are involved in the renal transport of carnosine could influence carnosine concentration thereby causing nephropathy. Aim: To study the association of genetic variants in the carnosine-carnosinase system (CARNS1, CNDP1, SLC15A4 and SLC15A2) with nephropathy and their influence on carnosinase levels in south Indian population. Method: Study Participants: 580 type 2 diabetes individuals without nephropathy (DM) and 597 type 2 diabetes individuals with nephropathy (DN) from Dr. Mohan’s Diabetes Specialities Centre, Chennai, India. Methodology: Genomic DNA was extracted from blood samples using phenol chloroform method. A total of 27 SNPs from the four genes were genotyped using MassARRAY. The levels of carnosinase in serum was measured in 116 DM and 93 DN participants using commercially available ELISA kit. Results: The D18S880 repeat polymorphism (5-8 repeats of Leucine) in CNDP1 gene and rs1626067 SNP of CARNS1 gene showed significant association with DN. The odds ratio for DN after adjusting for potential confounders such as age, sex, BMI, HbA1c, duration of diabetes and systolic blood pressure for the 6L/XL genotype of D18S880 and the GA genotype of rs1626067 as compared to their respective homozygous normal genotypes was 0.67 (95%CI: 0.48-0.94, p=0.022) and 0.68 (95% CI:0.49-0.93, p=0.016) respectively. The levels of carnosinase (mean±SE in picogram/mL) was significantly higher in DN (3.07±0.19) compared to DM group (2.48±0.13, p=0.038). Discussion: This study gains significance as the role of genetic variants in the carnosine-carnosinase system in DN remains largely unexplored. Most of the studies so far have focussed only on the CNDP1 gene. The association of D18S880 Leucine repeat with DN is significant as it is present in the signal peptide region of CNDP1 gene and may play a role in the secretion of carnosinase. The association of rs1626067 SNP in CARNS1 with DN has not been reported so far. This SNP is positioned in the 3́UTR region of CARNS1 and hence could alter the binding of transcription factors and have a regulatory effect. The significant difference in serum carnosinase levels between DM and DN groups was an interesting finding. When the groups were further stratified based on the genotypes, the sample size was less than 50 in each group and was not sufficiently powered to study the correlation of enzyme levels and genotypes. Measuring the levels and activity of carnosinase in larger number of samples will help identify whether the genetic variations influence the enzyme levels. If found, targeted dietary intervention studies giving carnosine supplements to those carrying the susceptible alleles can be undertaken to alleviate the burden of nephropathy.

A computational insight into how human serum carnosinase 1 recognises carnosine and anserine

Carnosine (-alanyl-L-histidine) and anserine (-alanyl-3-methylhistidine) are rich in black-boned chicken. Both are bioactive dipeptides that have an excellent role in preventing brain aging-related conditions such as Alzheimer’s disease and fighting against cancer and diabetes. Thus, carnosine- and anserine- rich black-boned chicken is commonly consumed as Chinese medicinal diet. However, both carnosine and anserine are degraded by serum carnosinase 1 (CN1) before the utilization. Protecting the loss of carnosine and anserine can maximize the nutritional benefits.

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.

Correlation between serum carnosinase concentration and renal damage in diabetic nephropathy patients

Diabetic nephropathy (DN) is one of the major complications of diabetes and contributes significantly towards end-stage renal disease. Previous studies have identified the gene encoding carnosinase (CN-1) as a predisposing factor for DN. Despite this fact, the relationship of the level of serum CN-1 and the progression of DN remains uninvestigated. Thus, the proposed study focused on clarifying the relationship among serum CN-1, indicators of renal function and tissue injury, and the progression of DN. A total of 14 patients with minimal changes disease (MCD) and 37 patients with DN were enrolled in the study. Additionally, 20 healthy volunteers were recruited as control. Further, DN patients were classified according to urinary albumin excretion rate into two groups: DN with microalbuminuria (n = 11) and DN with macroalbuminuria (n = 26). Clinical indicators including urinary protein components, serum carnosine concentration, serum CN-1 concentration and activity, and renal biopsy tissue injury indexes were included for analyzation. The serum CN-1 concentration and activity were observed to be the highest, but the serum carnosine concentration was the lowest in DN macroalbuminuria group. Moreover, within DN group, the concentration of serum CN-1 was positively correlated with uric acid (UA, r = 0.376, p = 0.026) and serum creatinine (SCr, r = 0.399, p = 0.018) and negatively correlated with serum albumin (Alb, r = − 0.348, p = 0.041) and estimated glomerular filtration rate (eGRF, r = − 0.432, p = 0.010). Furthermore, the concentration of serum CN-1 was discovered to be positively correlated with indicators including 24-h urinary protein–creatinine ratio (24 h-U-PRO/CRE, r = 0.528, p = 0.001), urinary albumin-to-creatinine ratio (Alb/CRE, r = 0.671, p = 0.000), urinary transferrin (TRF, r = 0.658, p = 0.000), retinol-binding protein (RBP, r = 0.523, p = 0.001), N-acetyl-glycosaminidase (NAG, r = 0.381, p = 0.024), immunoglobulin G (IgG, r = 0.522, p = 0.001), cystatin C (Cys-C, r = 0.539, p = 0.001), beta-2-microglobulin (β2-MG, r = 0.437, p = 0.009), and alpha-1-macroglobulin (α1-MG, r = 0.480, p = 0.004). Besides, in DN with macroalbuminuria group, serum CN-1 also showed a positive correlation with indicators of fibrosis, oxidative stress, and renal tubular injury. Taken together, our data suggested that the level of CN-1 was increased as clinical DN progressed. Thus, the level of serum CN-1 might be an important character during the occurrence and progression of DN. Our study will contribute significantly to future studies focused on dissecting the underlying mechanism of DN.

Human carnosinase 1 overexpression aggravates diabetes and renal impairment in BTBROb/Ob mice

ObjectiveTo assess the influence of serum carnosinase (CN1) on the course of diabetic kidney disease (DKD).MethodshCN1 transgenic (TG) mice were generated in a BTBROb/Ob genetic background to allow the spontaneous development of DKD in the presence of serum carnosinase. The influence of serum CN1 expression on obesity, hyperglycemia, and renal impairment was assessed. We also studied if aggravation of renal impairment in hCN1 TG BTBROb/Ob mice leads to changes in the renal transcriptome as compared with wild-type BTBROb/Ob mice.ResultshCN1 was detected in the serum and urine of mice from two different hCN1 TG lines. The transgene was expressed in the liver but not in the kidney. High CN1 expression was associated with low plasma and renal carnosine concentrations, even after oral carnosine supplementation. Obese hCN1 transgenic BTBROb/Ob mice displayed significantly higher levels of glycated hemoglobin, glycosuria, proteinuria, and increased albumin-creatinine ratios (1104 ± 696 vs 492.1 ± 282.2 μg/mg) accompanied by an increased glomerular tuft area and renal corpuscle size. Gene-expression profiling of renal tissue disclosed hierarchical clustering between BTBROb/Wt, BTBROb/Ob, and hCN1 BTBROb/Ob mice. Along with aggravation of the DKD phenotype, 26 altered genes have been found in obese hCN1 transgenic mice; among them claudin-1, thrombospondin-1, nephronectin, and peroxisome proliferator–activated receptor-alpha have been reported to play essential roles in DKD.ConclusionsOur data support a role for serum carnosinase 1 in the progression of DKD. Whether this is mainly attributed to the changes in renal carnosine concentrations warrants further studies.Key messagesIncreased carnosinase 1 (CN1) is associated with diabetic kidney disease (DKD).BTBROb/Ob mice with human CN1 develop a more aggravated DKD phenotype.Microarray revealed alterations by CN1 which are not altered by hyperglycemia.These genes have been described to play essential roles in DKD.Inhibiting CN1 could be beneficial in DKD.

ASSOCIATION BETWEEN POLYMORPHISMS IN THE CARNOSINASE GENES AND THE PERSONAL BEST TIME OF BRAZILIAN SPRINTERS

Naturally found in some meats, carnosine is a physico-chemical buffering agent that has been shown to have positive effects on high intensity exercises. Because carnosine is readily degraded by highly active carnosinase enzymes, it has been postulated that only individuals with a low carnosinase activity and protein content could show the presence of carnosine in plasma (carnosinemia), which may be beneficial for athletes engaged in high intensity activities. Of note, two carnosinases have been identified: the serum carnosinase (CNDP1) and the tissue carnosinase (CNDP2). PURPOSE: Explore whether the presence of polymorphisms in the CNDP1 and CNDP2 genes is associated with the performance of short (100 m), medium (200 m) and long (400 m) running sprints. METHODS: A cohort of top-level Brazilian sprinters (men) had their genotypes determined for the CNDP1 rs2887 and CNDP2 rs3764509 polymorphisms, and the personal best times for the 100 m (n = 31), 200 m (n = 35) and 400 m (n = 39) compared between genotypes. Based on previous studies, the A/A genotype instead of G/G and G/A genotypes (CNDP1 rs2887) and the G/G genotype instead of C/C and C/G genotypes (CNDP2 rs3764509) were considered optimal for power performance. Athlete’s personal records were acquired using the International Association of Athletics Federations database, available online at https://www.iaaf.org/. Genotyping of both polymorphisms was conducted using a pre-designed specific TaqMan® SNP Genotyping Assay according to the manufacturer's instructions. Student’s t-test was used to compare the personal best times between genotypes. The significance level was established at P < 0.05. RESULTS: No differences were found between polymorphisms and personal best times for the 100 m (overall mean ± SD: 10.66 ± 0.38 s, P > 0.930). However, athletes with the CNDP1 A/A genotype (21.12 ± 0.41 s versus 21.78 ± 0.72 s, P = 0.027) or CNDP2 G/G genotype (21.19 ± 0.80 s versus. 21.78 ± 0.67 s, P = 0.044) had faster personal times for the 200 m. In addition, athletes with the CNDP2 G/G genotype showed a trend of faster personal times for the 400 m (47.19 ± 1.29 s versus 48.39 ± 1.55 s, P = 0.051). CONCLUSION: The homozygous genotype for the mutant allele in both polymorphisms (CNDP1 rs2887 and CNDP2 rs3764509) was associated with 200m sprinting performance in elite athletes.

Development of a direct LC-ESI-MS method for the measurement of human serum carnosinase activity

Carnosine (β-alanyl-L-histidine) is a natural peptide that have been described as a potential pharmacological agent owing to some positive outcomes from several pharmacological tests in animal models of human diseases. However, carnosine has limited activity in humans since the peptide upon absorption is rapidly hydrolyzed in the serum by the enzyme carnosinase (i.e. CN1; E.C. 3.4.13.20). Over the years the main approaches aimed at limiting carnosine hydrolysis have been focused on obtaining CN1-stable derivatives with an increased bioavailability and unmodified or enhanced activity. Only recently the hypothesis of co-administration of carnosine and selective inhibitors of CN1 have been proposed. Such an approach requires reliable methods for screening the effect on carnosine hydrolysis rate operated by CN1 in a throughput scale allowing to test from few compounds up to whole compound libraries. The only assay with such features available in literature relies on ortho-phtalaldehyde (OPA) derivatization of the hydrolysis product (i.e. histidine), followed by a fluorimetric read. Herein, we propose an alternative method based on a direct measurement of the residual substrate by liquid chromatography-mass spectrometry (LC–MS). The assay demonstrated to be reliable since gave results comparable to literature data concerning the hydrolysis rate of carnosine as determined into human serum. Moreover, the method was quite flexible and easily adaptable to a substrate change, as demonstrated by the measurement of the hydrolysis rate of all the natural analogs of carnosine. In this context the data collected for anserine suggest that our method looked more reliable and substrate change can undergo an underestimation of hydrolytic activity in OPA -based assays.

L-carnosine and its Derivatives as New Therapeutic Agents for the Prevention and Treatment of Vascular Complications of Diabetes.

Vascular complications are among the most serious manifestations of diabetes. Atherosclerosis is the main cause of reduced life quality and expectancy in diabetics, whereas diabetic nephropathy and retinopathy are the most common causes of end-stage renal disease and blindness. An effective therapeutic approach to prevent vascular complications should counteract the mechanisms of injury. Among them, the toxic effects of Advanced Glycation (AGEs) and Lipoxidation (ALEs) end-products are well-recognized contributors to these sequelae. L-carnosine (β-alanyl-Lhistidine) acts as a quencher of the AGE/ALE precursors Reactive Carbonyl Species (RCS), which are highly reactive aldehydes derived from oxidative and non-oxidative modifications of sugars and lipids. Consistently, L-carnosine was found to be effective in several disease models in which glyco/lipoxidation plays a central pathogenic role. Unfortunately, in humans, L-carnosine is rapidly inactivated by serum carnosinase. Therefore, the search for carnosinase-resistant derivatives of Lcarnosine represents a suitable strategy against carbonyl stress-dependent disorders, particularly diabetic vascular complications. In this review, we present and discuss available data on the efficacy of L-carnosine and its derivatives in preventing vascular complications in rodent models of diabetes and metabolic syndrome. We also discuss genetic findings providing evidence for the involvement of the carnosinase/L-carnosine system in the risk of developing diabetic nephropathy and for preferring the use of carnosinase-resistant compounds in human disease. The availability of therapeutic strategies capable to prevent both long-term glucose toxicity, resulting from insufficient glucoselowering therapy, and lipotoxicity may help reduce the clinical and economic burden of vascular complications of diabetes and related metabolic disorders.

Carnosine and Kidney Diseases: What We Currently Know?

Carnosine (beta-alanyl-L-histidine) is an endogenously synthesised dipeptide which is present in different human tissues e.g. in the kidney. Carnosine is degraded by enzyme serum carnosinase, encoding by CNDP1 gene. Carnosine is engaged in different metabolic pathways in the kidney. It reduces the level of proinflammatory and profibrotic cytokines, inhibits advanced glycation end products' formation, moreover, it also decreases the mesangial cell proliferation. Carnosine may also serve as a scavenger of peroxyl and hydroxyl radicals and a natural angiotensin-converting enzyme inhibitor. This review summarizes the results of experimental and human studies concerning the role of carnosine in kidney diseases, particularly in chronic kidney disease, ischemia/reperfusion-induced acute renal failure, diabetic nephropathy and also drug-induced nephrotoxicity. The interplay between serum carnosine concentration and serum carnosinase activity and polymorphism in the CNDP1 gene is discussed. Carnosine has renoprotective properties. It has a promising potential for the treatment and prevention of different kidney diseases, particularly chronic kidney disease which is a global public health issue. Further studies of the role of carnosine in the kidney may offer innovative and effective strategies for the management of kidney diseases.

A new derivative of acetylsalicylic acid and carnosine: synthesis, physical and chemical properties, biological activity.

The aim of this study was to create and assess biological activity of a new compound based on carnosine and acetylsalicylic acid (ASA) that will comprise antioxidant effect with antiplatelet activity, while simultaneously preventing side effects on the gastrointestinal tract. Salicyl-carnosine (SC) was synthesized by condensation of ASA and carnosine. Antioxidant activity was determined by spectrophotometric and chemiluminescence methods. Antiplatelet activity was carried out by the light transmission-aggregometry method using the inductor ADP. Chronic gastric ulcer in rats was modeled using glacial acetic acid. Using SOD-like activity, iron-induced chemiluminescence, BaSO4-activated respiratory burst, and evaluation of red blood cell structure stabilization during oxidative damage induced by sodium hypochlorite, it was shown that SC possesses antioxidant activity analogous, or better, than that of carnosine. Antiplatelet activity of SC was evaluated in the blood of healthy individuals, and was also shown to be comparable to, or exceeding that of ASA. Also SC demonstrates high resistance to hydrolysis by tissue and serum carnosinases. Most importantly, it was shown that SC has protected the gastric mucosa against the formation of stomach ulcerative lesions and promoted their epithelization, therefore overcoming the undesirable inherent side effects of ASA. SC preserves pharmacologically significant properties of ASA and carnosine while retaining an anti-ulcer activity and resistance to the carnosinase hydrolysis at the same time. These properties are particularly promising for the potential development of new anti-inflammatory and antithrombotic drugs. Graphical abstract .

COVID-19 and Senotherapeutics: Any Role for the Naturally-occurring Dipeptide Carnosine?

It is suggested that the non-toxic dipeptide carnosine (beta-alanyl-L-histidine) should be examined as a potential protective agent against COVID-19 infection and inflammatory consequences especially in the elderly. Carnosine is an effective anti-inflammatory agent which can also inhibit CD26 and ACE2 activity. It is also suggested that nasal administration would direct the peptide directly to the lungs and escape the attention of serum carnosinase.

The role of carbonyl stress in the development of diabetic complications

The relationship between the potentially developing complications of the 451 million people affected by diabetes and hyperglycaemia can be based on the enhanced generation of advanced glycation endproducts and the more intensive oxidative and carbonyl stress. Advanced glycation endproducts generated partly due to carbonyl stress play an important role in the pathogenesis of diabetic complications such as elevated arterial thickness, vascular permeability, enhanced angiogenesis or the more rigid vessels induced nephropathy, neuropathy, retinopathy. Furthermore, the elevated thrombocyte aggregation, the reduced fibrinolysis induced elevated coagulation, and the atherosclerosis or the mitochondrial dysfunction are important as well. The most potent target of both the non-oxidative and oxidative generation of advanced glycation endproducts can be the scavenging of α,β-unsaturated aldehydes. Although, aminoguanidine, the prototype of scavenger molecules, showed protection in different animal models, it failed in the human clinical studies. Finally, the clinical studies were terminated almost 20 years ago. The endogen dipeptide L-carnosine was also expected to mitigate the complications due to carbonyl stress. However, its clinical significance was limited by the serum carnosinases and by the consequent low serum stability and bioavailability. The carnosinase resistance of the molecule can be achieved by the change of the carboxyl group of the molecule to hydroxyl group. At the same time, the biosafety and the carbonyl stress scavenging activity of the molecule could be preserved. Although clinical studies could not be performed in the last six months, on the basis of the in vitro and in vivo results, carnosinole seems to be a promising compound to mitigate and prevent the diabetic complications. Thus it is worth to the attention of the clinicians. Orv Hetil. 2019; 160(40): 1567-1573.