Allosteric inhibition of carnosinase (CN1) by inducing a conformational shift

Serum carnosinase 1, an early indicator for incident microalbuminuria in type 1 diabetes

Aims

Carnosinase (CN1) polymorphisms have been linked to diabetic kidney disease (DKD), as CN1 degrades dipeptides which scavenge oxidative metabolites and prevent the formation of advanced glycation end-products. In this work, we studied the association between serum CN1, the systemic redox status and long-term renal outcome in type 1 diabetes.

Methods

Serum CN1 was measured in a prospective type 1 diabetes cohort (n = 218) with a 16-year follow-up. A total of 218 patients treated at the Diabetes Outpatient Clinic of the Weezenlanden Hospital (nowadays Isala Hospital, Zwolle, The Netherlands) were included in this analysis. We assessed whether serum CN1 was associated with renal function and development of DKD as well as other diabetic complications.

Results

At baseline, age, systemic redox status and N-terminal pro brain-natriuretic peptide (NT-proBNP) were associated with serum CN1 concentration (p < 0.05). During follow-up, CN1 concentration in the middle tertile was associated with less incident microalbuminuria (odds ratio = 0.194, 95% C.I.: 0.049-0.772, p = 0.02) after adjustment for age, systemic redox status, NT-proBNP and sex.

Discussion

Serum CN1 could predict incident microalbuminuria and may be used as a novel parameter to identify patients at risk for DKD.

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.

Knock-out of dipeptidase CN2 in human proximal tubular cells disrupts dipeptide and amino acid homeostasis and para- and transcellular solute transport

AIM

Although of potential biomedical relevance, dipeptide metabolism has hardly been studied. We found the dipeptidase carnosinase-2 (CN2) to be abundant in human proximal tubules, which regulate water and solute homeostasis. We therefore hypothesized, that CN2 has a key metabolic role, impacting proximal tubular transport function.

METHODS

A knockout of the CN2 gene (CNDP2-KO) was generated in human proximal tubule cells and characterized by metabolomics, RNA-seq analysis, paracellular permeability analysis and ion transport.

RESULTS

CNDP2-KO in human proximal tubule cells resulted in the accumulation of cellular dipeptides, reduction of amino acids and imbalance of related metabolic pathways, and of energy supply. RNA-seq analyses indicated altered protein metabolism and ion transport. Detailed functional studies demonstrated lower CNDP2-KO cell viability and proliferation, and altered ion and macromolecule transport via trans- and paracellular pathways. Regulatory and transport protein abundance was disturbed, either as a consequence of the metabolic imbalance or the resulting functional disequilibrium.

CONCLUSION

CN2 function has a major impact on intracellular amino acid and dipeptide metabolism and is essential for key metabolic and regulatory functions of proximal tubular cells. These findings deserve in vivo analysis of the relevance of CN2 for nephron function and regulation of body homeostasis.

Human carnosinases: A brief history, medicinal relevance, and in silico analyses

Carnosine, an endogenous dipeptide, has been found to have a plethora of medicinal properties, such as antioxidant, antiageing, and chelating effects, but with one downside: a short half-life. Carnosinases and two hydrolytic enzymes, which remain enigmatic, are responsible for these features. Hence, here we emphasize why research is valuable for better understanding crucial concepts like ageing, neurodegradation, and cancerogenesis, given that inhibition of carnosinases might significantly prolong carnosine bioavailability and allow its further use in medicine. Herein, we explore the literature regarding carnosinases and present a short in silico analysis aimed at elucidating the possible recognition pattern between CN1 and its ligands.

The Therapeutic Potential of Novel Carnosine Formulations: Perspectives for Drug Development

Carnosine (beta-alanyl-L-histidine) is an endogenous dipeptide synthesized via the activity of the ATP-dependent enzyme carnosine synthetase 1 and can be found at a very high concentration in tissues with a high metabolic rate, including muscles (up to 20 mM) and brain (up to 5 mM). Because of its well-demonstrated multimodal pharmacodynamic profile, which includes anti-aggregant, antioxidant, and anti-inflammatory activities, as well as its ability to modulate the energy metabolism status in immune cells, this dipeptide has been investigated in numerous experimental models of diseases, including Alzheimer's disease, and at a clinical level. The main limit for the therapeutic use of carnosine is related to its rapid hydrolysis exerted by carnosinases, especially at the plasma level, reason why the development of new strategies, including the chemical modification of carnosine or its vehiculation into innovative drug delivery systems (DDS), aiming at increasing its bioavailability and/or at facilitating the site-specific transport to different tissues, is of utmost importance. In the present review, after a description of carnosine structure, biological activities, administration routes, and metabolism, we focused on different DDS, including vesicular systems and metallic nanoparticles, as well as on possible chemical derivatization strategies related to carnosine. In particular, a basic description of the DDS employed or the derivatization/conjugation applied to obtain carnosine formulations, followed by the possible mechanism of action, is given. To the best of our knowledge, this is the first review that includes all the new formulations of carnosine (DDS and derivatives), allowing a decrease or complete prevention of the hydrolysis of this dipeptide exerted by carnosinases, the simultaneous blood-brain barrier crossing, the maintenance or enhancement of carnosine biological activity, and the site-specific transport to different tissues, which then offers perspectives for the development of new drugs.

Mechanistic insights on anserine hydrolyzing activities of human carnosinases

Anserine and carnosine represent histidine-containing dipeptides that exert a pluripotent protective effect on human physiology. Anserine is known to protect against oxidative stress in diabetes and cardiovascular diseases. Human carnosinases (CN1 and CN2) are dipeptidases involved in the homeostasis of carnosine. In poikilothermic vertebrates, the anserinase enzyme is responsible for hydrolyzing anserine. However, there is no specific anserine hydrolyzing enzyme present in humans. In this study, we have systematically investigated the anserine hydrolyzing activity of human CN1 and CN2. A targeted multiple reaction monitoring (MRM) based approach was employed for studying the enzyme kinetics of CN1 and CN2 using carnosine and anserine as substrates. Surprisingly, both CN1 and CN2 can hydrolyze anserine effectively. The observed catalytic turnover rate (V_max/[E]_t) was 21.6 s^-1 and 2.8 s^-1 for CN1 and CN2, respectively. CN1 is almost eight-fold more efficient in hydrolyzing anserine compared to CN2, which is comparable to the efficiency of the carnosine hydrolyzing activity of CN2. The Michaelis constant (K_m) value for CN1 (1.96 mM) is almost three-fold lower compared to CN2 (6.33 mM), representing higher substrate affinity for anserine-CN1 interactions. Molecular docking studies showed that anserine binds at the catalytic site of the carnosinases with an affinity similar to carnosine. Overall, the present study elucidated the inherent promiscuity of human carnosinases in hydrolyzing anserine using a sensitive LC-MS/MS approach.

Exploring the structural and dynamic differences between human carnosinase I (CN1) and II (CN2)

Human carnosinases (CNs) are dimeric dipeptidases in the metallopeptidase M20 family. Two isoforms of carnosinases (Zn²⁺ -containing carnosinase 1 (CN1) found in serum and Mn²⁺ -carnosinase 2 (CN2) in tissue) were identified. Both CNs cleave histidine-containing (Xaa-His) dipeptides such as carnosine where CN2 was found to accept a broader spectrum of substrates. A loss of CN function, resulting in a high carnosine concentration, reduces risk for diabetes and neurological disorders. Although several studies on CN activities and its Michaelis complex were conducted, all shed the light on CN1 activity where the CN2 data is limited. Also, the molecular details on CN1 and CN2 similarity and dissimilarity in structure and function remain unclear. Thus, in this work, molecular dynamics (MD) simulations were employed to study structure and dynamics of human CN1 and CN2 in comparison. The results show that the different catalytic ability of both CNs is due to their pocket size and environment. CN2 can accept a wider range of substrate due to the wider mouth of a binding pocket. The L1 loop seems to play a role in gating activity. Comparing to CN2, CN1 provides more electronegative entrance, more wettability, and higher stability of catalytic metal ion-pair in the active site which allow more efficient water-mediated catalysis. The microscopic understanding obtained here can serve as a basis for CN inhibition strategies resulting in higher carnosine levels and consequently mitigating complications associated with diseases such as diabetes and neurological disorder.

Anserine and Carnosine Induce HSP70-Dependent H2S Formation in Endothelial Cells and Murine Kidney

Anserine and carnosine have nephroprotective actions; hydrogen sulfide (H₂S) protects from ischemic tissue damage, and the underlying mechanisms are debated. In view of their common interaction with HSP70, we studied possible interactions of both dipeptides with H₂S. H₂S formation was measured in human proximal tubular epithelial cells (HK-2); three endothelial cell lines (HUVEC, HUAEC, MCEC); and in renal murine tissue of wild-type (WT), carnosinase-1 knockout (Cndp1-KO) and Hsp70-KO mice. Diabetes was induced by streptozocin. Incubation with carnosine increased H₂S synthesis capacity in tubular cells, as well as with anserine in all three endothelial cell lines. H₂S dose-dependently reduced anserine/carnosine degradation rate by serum and recombinant carnosinase-1 (CN1). Endothelial Hsp70-KO reduced H₂S formation and abolished the stimulation by anserine and could be restored by Hsp70 transfection. In female Hsp70-KO mice, kidney H₂S formation was halved. In Cndp1-KO mice, kidney anserine concentrations were several-fold and sex-specifically increased. Kidney H₂S formation capacity was increased 2-3-fold in female mice and correlated with anserine and carnosine concentrations. In diabetic Cndp1-KO mice, renal anserine and carnosine concentrations as well as H₂S formation capacity were markedly reduced compared to non-diabetic Cndp1-KO littermates. Anserine and carnosine induce H₂S formation in a cell-type and Hsp70-specific manner within a positive feedback loop with CN1.

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.

Longitudinal proteomics study of serum changes after allogeneic HSCT reveals potential markers of metabolic complications related to aGvHD

Even though hematopoietic stem cell transplantation (HSCT) allows successful treatment for many malignant and non-malignant disorders, its curative potential remains limited by severe side effects, including infections and other transplant-related complications such as graft-versus-host disease (GvHD). This study examined changes in serum proteome via high-performance two-dimensional gel electrophoresis (2-DE) during HSCT to search for diagnostic biomarkers for post-HSCT complications. Longitudinal proteomic analysis revealed proteins related to metabolic complications and hemolytic anemia. Retinol-binding protein 4 (RBP4), a reliable marker of insulin resistance, was identified, and is possibly associated with the onset mechanism of acute graft-versus-host disease (aGvHD) and/or skin GvHD. Although the cause of insulin resistance is not fully understood, it is thought to be associated with adipocytes inflammation induced by RBP4, iron overload and hemolytic anemia after HSCT, as observed in this study. The present study has demonstrated that insulin resistance and metabolic complications could be immediate complications after transplantation and are associated with aGvHD. The biomarkers revealed in this study are promising tools to be used for improving the early diagnosis of HSCT-associated complications, especially aGvHD, possibly even before clinical manifestations.

Natural and Synthetic Agents Targeting Reactive Carbonyl Species against Metabolic Syndrome

Reactive carbonyl species (RCS) may originate from the oxidation of unsaturated fatty acids and sugar in conditions of pathology. They are known to have high reactivity towards DNA as well as nucleophilic sites of proteins, resulting in cellular dysfunction. It has been considered that various pathological conditions are associated with an increased level of RCS and their reaction products. Thus, regulating the levels of RCS may be associated with the mitigation of various metabolic and neurodegenerative disorders. In order to perform a comprehensive review, various literature databases, including MEDLINE, EMBASE, along with Google Scholar, were utilized to obtain relevant articles. The voluminous review concluded that various synthetic and natural agents are available or in pipeline research that hold tremendous potential to be used as a drug of choice in the therapeutic management of metabolic syndrome, including obesity, dyslipidemia, diabetes, and diabetes-associated complications of atherosclerosis, neuropathy, and nephropathy. From the available data, it may be emphasized that various synthetic agents, such as carnosine and simvastatin, and natural agents, such as polyphenols and terpenoids, can become a drug of choice in the therapeutic management for combating metabolic syndromes that involve RCS in their pathophysiology. Since the RCS are known to regulate the biological processes, future research warrants detailed investigations to decipher the precise mechanism.

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.

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.

Dexamethasone-Induced Perturbations in Tissue Metabolomics Revealed by Chemical Isotope Labeling LC-MS analysis

Dexamethasone (Dex) is a synthetic glucocorticoid (GC) drug commonly used clinically for the treatment of several inflammatory and immune-mediated diseases. Despite its broad range of indications, the long-term use of Dex is known to be associated with specific abnormalities in several tissues and organs. In this study, the metabolomic effects on five different organs induced by the chronic administration of Dex in the Sprague–Dawley rat model were investigated using the chemical isotope labeling liquid chromatography-mass spectrometry (CIL LC-MS) platform, which targets the amine/phenol submetabolomes. Compared to controls, a prolonged intake of Dex resulted in significant perturbations in the levels of 492, 442, 300, 186, and 105 metabolites in the brain, skeletal muscle, liver, kidney, and heart tissues, respectively. The positively identified metabolites were mapped to diverse molecular pathways in different organs. In the brain, perturbations in protein biosynthesis, amino acid metabolism, and monoamine neurotransmitter synthesis were identified, while in the heart, pyrimidine metabolism and branched amino acid biosynthesis were the most significantly impaired pathways. In the kidney, several amino acid pathways were dysregulated, which reflected impairments in several biological functions, including gluconeogenesis and ureagenesis. Beta-alanine metabolism and uridine homeostasis were profoundly affected in liver tissues, whereas alterations of glutathione, arginine, glutamine, and nitrogen metabolism pointed to the modulation of muscle metabolism and disturbances in energy production and muscle mass in skeletal muscle. The differential expression of multiple dipeptides was most significant in the liver (down-regulated), brain (up-regulation), and kidney tissues, but not in the heart or skeletal muscle tissues. The identification of clinically relevant pathways provides holistic insights into the tissue molecular responses induced by Dex and understanding of the underlying mechanisms associated with their side effects. Our data suggest a potential role for glutathione supplementation and dipeptide modulators as novel therapeutic interventions to mitigate the side effects induced by Dex therapy.

Focusing on the functional characterization of the anserinase from Oreochromis niloticus

Carnosine, anserine and homocarnosine are the three most representative compounds of the histidine dipeptides family, widely distributed in mammals in different amounts depending on the species and the tissue considered. Histidine dipeptides are mainly degraded by two different carnosinase homologues: a highly specific metal-ion dependent carnosinase (CN1) located in serum and brain and a non-specific cytosolic form (CN2). The hydrolysis of such dipeptides in prokaryotes and eukaryotes is also catalyzed by the anserinase (ANSN). Such naturally occurring dipeptides represent an interesting topic because they seem to have numerous biological roles such as potential neuroprotective and neurotransmitter functions in the brain and therefore ANSN results to be a very interesting target of study. We here report, for the first time, cloning, expression of ANSN from the fish Oreochromis niloticus both in a mammalian and in a prokaryotic system, in order to perform deep functional studies by enzymatic assays in the presence of different metals and substrates. Furthermore, by means of a mass spectrometry-based proteomic approach, we analysed protein sequence and the potential presence of post-translational modifications in the mammalian recombinant protein. Finally, a preliminary structural characterization was carried out on ANSN produced in Escherichia coli.

Therapeutic potential of carbonyl-scavenging carnosine derivative in metabolic disorders

Obesity and overnutrition increase levels of reactive sugar- and lipid-derived aldehydes called reactive carbonyl species (RCS). Increased tissue and circulating RCS levels have been tied to insulin resistance and inflammation, but previous pharmacological approaches to target RCS have had equivocal outcomes. In this issue of the JCI, Anderson et al. present evidence for the development and implementation of carnisonol, a compound that is biologically stable in vivo and shows impressive effects on improving metabolism and inflammation in rodent models of diet-induced obesity and metabolic dysfunction.

Development and validation of a sensitive LC-MS/MS assay for the quantification of anserine in human plasma and urine and its application to pharmacokinetic study

Carnosine (beta-alanyl-L-histidine) and its methylated analogue anserine are present in relevant concentrations in the omnivore human diet. Several studies reported promising therapeutic potential for carnosine in various rodent models of oxidative stress and inflammation-related chronic diseases. Nevertheless, the poor serum stability of carnosine in humans makes the translation of rodent models hard. Even though anserine and carnosine have similar biochemical properties, anserine has better serum stability. Despite this interesting profile, the research on anserine is scarce. The aim of this study was to explore the bioavailability and stability of synthesized anserine by (1) performing in vitro stability experiments in human plasma and molecular modelling studies and by (2) evaluating the plasma and urinary pharmacokinetic profile in healthy volunteers following different doses of anserine (4-10-20 mg/kg body weight). A bio-analytical method for measuring anserine levels was developed and validated using liquid chromatography-electrospray mass spectrometry. Both plasma (C_MAX: 0.54-1.10-3.12 µM) and urinary (C_MAX: 0.09-0.41-0.72 mg/mg creatinine) anserine increased dose-dependently following ingestion of 4-10-20 anserine mg/kg BW, respectively. The inter-individual variation in plasma anserine was mainly explained by the activity (R² = 0.75) and content (R² = 0.77) of the enzyme serum carnosinase-1. Compared to carnosine, a lower interaction energy of anserine with carnosinase-1 was suggested by molecular modelling studies. Conversely, the two dipeptides seems to have similar interaction with the PEPT1 transporter. It can be concluded that nutritionally relevant doses of synthesized anserine are well-absorbed and that its degradation by serum carnosinase-1 is less pronounced compared to carnosine. This makes anserine a good candidate as a more stable carnosine-analogue to attenuate chronic diseases in humans.

Carnosine supplementation reduces plasma soluble transferrin receptor in healthy overweight or obese individuals: a pilot randomised trial

Abnormalities of iron homeostasis have been linked to insulin resistance, type 2 diabetes and cardiovascular disease. Carnosine, an over-the-counter food supplement with chelating properties, has been shown to decrease serum iron and improve glucose metabolism in diabetic rodents. We have previously demonstrated that carnosine supplementation prevented worsening of glucose metabolism in healthy overweight and obese middle-aged adults. Yet, the impact of carnosine on markers of iron metabolism in humans has not been investigated. We aimed to determine whether carnosine supplementation has an effect on iron parameters in overweight and obese, otherwise healthy adults. We included 26 participants, who were randomly allocated to receive 1 g carnosine (n = 14) or identical placebo (n = 12) twice daily for 12 weeks. Iron parameters including iron, ferritin, transferrin, soluble transferrin receptor, total iron binding capacity and iron saturation were measured in serum or plasma by standard commercial assays. Carnosine supplementation decreased plasma soluble transferrin receptor compared to placebo (mean change difference ± standard error: - 0.07 ± 0.03 mg/l, p = 0.04). None of the other iron parameters were different between carnosine and placebo groups. At follow-up, soluble transferrin receptor was associated inversely with urinary carnosine concentrations and positively with serum carnosinase-1 activity (both p < 0.02). Our findings suggest that carnosine may modulate iron metabolism in high-risk groups which could ameliorate insulin resistance and prevent type 2 diabetes. Larger human clinical trials are required to confirm our results.

Carnosinase, diabetes mellitus and the potential relevance of carnosinase deficiency

Carnosinase (CN1) is a dipeptidase, encoded by the CNDP1 gene, that degrades histidine-containing dipeptides, such as carnosine, anserine and homocarnosine. Loss of CN1 function (also called carnosinase deficiency or aminoacyl-histidine dipeptidase deficiency) has been reported in a small number of patients with highly elevated blood carnosine concentrations, denoted carnosinaemia; it is unclear whether the variety of clinical symptoms in these individuals is causally related to carnosinase deficiency. Reduced CN1 function should increase serum carnosine concentrations but the genetic basis of carnosinaemia has not been formally confirmed to be due to CNDP1 mutations. A CNDP1 polymorphism associated with low CN1 activity correlates with significantly reduced risk for diabetic nephropathy, especially in women with type 2 diabetes, and may slow progression of chronic kidney disease in children with glomerulonephritis. Studies in rodents demonstrate antiproteinuric and vasculoprotective effects of carnosine, the precise molecular mechanisms, however, are still incompletely understood. Thus, carnosinemia due to CN1 deficiency may be a non-disease; in contrast, carnosine may potentially protect against long-term sequelae of reactive metabolites accumulating, e.g. in diabetes and chronic renal failure.