The antineoplastic effect of carnosine is accompanied by induction of PDK4 and can be mimicked by L-histidine

Integrated Multilayer Omics Reveals the Genomic, Proteomic, and Metabolic Influences of Histidyl Dipeptides on the Heart

Background

Histidyl dipeptides such as carnosine are present in a micromolar to millimolar range in mammalian hearts. These dipeptides facilitate glycolysis by proton buffering. They form conjugates with reactive aldehydes, such as acrolein, and attenuate myocardial ischemia–reperfusion injury. Although these dipeptides exhibit multifunctional properties, a composite understanding of their role in the myocardium is lacking.

Methods and Results

To identify histidyl dipeptide–mediated responses in the heart, we used an integrated triomics approach, which involved genome‐wide RNA sequencing, global proteomics, and unbiased metabolomics to identify the effects of cardiospecific transgenic overexpression of the carnosine synthesizing enzyme, carnosine synthase (Carns), in mice. Our result showed that higher myocardial levels of histidyl dipeptides were associated with extensive changes in the levels of several microRNAs, which target the expression of contractile proteins, β‐fatty acid oxidation, and citric acid cycle (TCA) enzymes. Global proteomic analysis showed enrichment in the expression of contractile proteins, enzymes of β‐fatty acid oxidation, and the TCA in the Carns transgenic heart. Under aerobic conditions, the Carns transgenic hearts had lower levels of short‐ and long‐chain fatty acids as well as the TCA intermediate—succinic acid; whereas, under ischemic conditions, the accumulation of fatty acids and TCA intermediates was significantly attenuated. Integration of multiple data sets suggested that β‐fatty acid oxidation and TCA pathways exhibit correlative changes in the Carns transgenic hearts at all 3 levels.

Conclusions

Taken together, these findings reveal a central role of histidyl dipeptides in coordinated regulation of myocardial structure, function, and energetics.

Viability of Glioblastoma Cells and Fibroblasts in the Presence of Imidazole-Containing Compounds

The naturally occurring dipeptide carnosine (β-alanyl-L-histidine) specifically attenuates tumor growth. Here, we ask whether other small imidazole-containing compounds also affect the viability of tumor cells without affecting non-malignant cells and whether the formation of histamine is involved. Patient-derived fibroblasts and glioblastoma cells were treated with carnosine, L-alanyl-L-histidine (LA-LH), β-alanyl-L-alanine, L-histidine, histamine, imidazole, β-alanine, and L-alanine. Cell viability was assessed by cell-based assays and microscopy. The intracellular release of L-histidine and formation of histamine was investigated by high-performance liquid chromatography coupled to mass spectrometry. Carnosine and LA-LH inhibited tumor cell growth with minor effects on fibroblasts, and L-histidine, histamine, and imidazole affected viability in both cell types. Compounds without the imidazole moiety did not diminish viability. In the presence of LA-LH but not in the presence of carnosine, a significant rise in intracellular amounts of histidine was detected in all cells. The formation of histamine was not detectable in the presence of carnosine, LA-LH, or histidine. In conclusion, the imidazole moiety of carnosine contributes to its anti-neoplastic effect, which is also seen in the presence of histidine and LA-LH. Despite the fact that histamine has a strong effect on cell viability, the formation of histamine is not responsible for the effects on the cell viability of carnosine, LA-LH, and histidine.

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 synthase deficiency is compatible with normal skeletal muscle and olfactory function but causes reduced olfactory sensitivity in aging mice

Carnosine (β-alanyl-l-histidine) and anserine (β-alanyl-3-methyl-l-histidine) are abundant peptides in the nervous system and skeletal muscle of many vertebrates. Many in vitro and in vivo studies demonstrated that exogenously added carnosine can improve muscle contraction, has antioxidant activity, and can quench various reactive aldehydes. Some of these functions likely contribute to the proposed anti-aging activity of carnosine. However, the physiological role of carnosine and related histidine-containing dipeptides (HCDs) is not clear. In this study, we generated a mouse line deficient in carnosine synthase (Carns1). HCDs were undetectable in the primary olfactory system and skeletal muscle of Carns1-deficient mice. Skeletal muscle contraction in these mice, however, was unaltered, and there was no evidence for reduced pH-buffering capacity in the skeletal muscle. Olfactory tests did not reveal any deterioration in 8-month-old mice lacking carnosine. In contrast, aging (18-24-month-old) Carns1-deficient mice exhibited olfactory sensitivity impairments that correlated with an age-dependent reduction in the number of olfactory receptor neurons. Whereas we found no evidence for elevated levels of lipoxidation and glycation end products in the primary olfactory system, protein carbonylation was increased in the olfactory bulb of aged Carns1-deficient mice. Taken together, these results suggest that carnosine in the olfactory system is not essential for information processing in the olfactory signaling pathway but does have a role in the long-term protection of olfactory receptor neurons, possibly through its antioxidant activity.

Profiling and targeting of cellular mitochondrial bioenergetics: inhibition of human gastric cancer cell growth by carnosine

L-Carnosine (β-alanyl-L-histidine) is a naturally occurring dipeptide distributed in various organs of mammalians. We previously showed that carnosine inhibited proliferation of human gastric cancer cells through targeting both mitochondrial bioenergetics and glycolysis pathway. But the mechanism underlying carnosine action on mitochondrial bioenergetics of tumor cells remains unclear. In the current study we investigated the effect of carnosine on the growth of human gastric cancer SGC-7901 cells in vitro and in vivo. We firstly showed that hydrolysis of carnosine was not a prerequisite for its anti-gastric cancer effect. Treatment of SGC-7901 cells with carnosine (20 mmol/L) significantly decreased the activities of mitochondrial respiratory chain complexes I-IV and mitochondrial ATP production, and downregulated 13 proteins involved in mitochondrial bioenergetics. Furthermore, carnosine treatment significantly suppressed the phosphorylation of Akt, while inhibition of Akt activation with GSK690693 significantly reduced the localization of prohibitin-1 (PHB-1) in the mitochondria of SGC-7901 and BGC-823 cells. In addition, we showed that silencing of PHB-1 gene with shRNA markedly reduced the mitochondrial PHB-1 in SGC-7901 cells, and significantly decreased the colony formation capacity and growth rate of the cells. In SGC-7901 cell xenograft nude mice, administration of carnosine (250 mg kg/d, ip, for 3 weeks) significantly inhibited the tumor growth and decreased the expression of mitochondrial PHB-1 in tumor tissue. Taken together, these results suggest that carnosine may act on multiple mitochondrial proteins to down-regulate mitochondrial bioenergetics and then to inhibit the growth and proliferation of SGC-7901 and BGC-823 cells.

Carnosine inhibits glioblastoma growth independent from PI3K/Akt/mTOR signaling

Glioblastoma is a high-grade glioma with poor prognosis even after surgery and standard therapy. Here, we asked whether carnosine (β-alanyl-L-histidine), a naturally occurring dipeptide, exert its anti-neoplastic effect on glioblastoma cells via PI3K/Akt/mTOR signaling. Therefore, glioblastoma cells from the lines U87 and T98G were exposed to carnosine, to the mTOR inhibitor rapamycin and to the PI3K inhibitor Ly-294,002. Pyruvate dehydrogenase kinase (PDK4) expression, known to be a target of PI3K/Akt/mTOR, and which is also affected by carnosine, was analyzed by RT-qPCR, and reporter gene assays with the human PDK4 promoter were performed. Cell viability was assessed by cell-based assays and mTOR and Akt phosphorylation by Western blotting. Rapamycin and Ly-294,002 increased PDK4 mRNA expression in both cell lines but significance was only reached in U87. Carnosine significantly increased expression in both lines. A significant combinatorial effect of carnosine was only detected in U87 when the dipeptide was combined with Ly-294,002. Reporter gene assays revealed no specific effect of carnosine on the human PDK4 promoter, whereas both inhibitors increased reporter gene expression. Rapamycin reduced phosphorylation of mTOR, and Ly-294,002 that of Akt. A significant reduction of Akt phosphorylation was observed in the presence of carnosine in U87 but not in T98G, and carnosine had no effect on mTOR phosphorylation. Cell viability as determined by ATP in cell lysates was reduced only in the presence of carnosine. We conclude that carnosine’s anti-neoplastic effect is independent from PI3K/Akt/mTOR signaling. As the dipeptide reduced viability in tumor cells that do not respond to PI3K or mTOR inhibitors, it appears to be worth to further investigate the mechanisms by which carnosine exerts its anti-tumor effect and to consider it for therapy, especially as it is a naturally occurring compound that has already been used for the treatment of other diseases without indication of side-effects.

The proton-coupled oligopeptide transporters PEPT2, PHT1 and PHT2 mediate the uptake of carnosine in glioblastoma cells

The previous studies demonstrated that carnosine (β-alanyl-L-histidine) inhibits the growth of tumor cells in vitro and in vivo. Considering carnosine for the treatment of glioblastoma, we investigated which proton-coupled oligopeptide transporters (POTs) are present in glioblastoma cells and how they contribute to the uptake of carnosine. Therefore, mRNA expression of the four known POTs (PEPT1, PEPT2, PHT1, and PHT2) was examined in three glioblastoma cell lines, ten primary tumor cell cultures, in freshly isolated tumor tissue and in healthy brain. Using high-performance liquid chromatography coupled to mass spectrometry, the uptake of carnosine was investigated in the presence of competitive inhibitors and after siRNA-mediated knockdown of POTs. Whereas PEPT1 mRNA was not detected in any sample, expression of the three other transporters was significantly increased in tumor tissue compared to healthy brain. In cell culture, PHT1 expression was comparable to expression in tumor tissue, PHT2 exhibited a slightly reduced expression, and PEPT2 expression was reduced to normal brain tissue levels. In the cell line LN405, the competitive inhibitors β-alanyl-L-alanine (inhibits all transporters) and L-histidine (inhibitor of PHT1/2) both inhibited the uptake of carnosine. SiRNA-mediated knockdown of PHT1 and PHT2 revealed a significantly reduced uptake of carnosine. Interestingly, despite its low expression at the level of mRNA, knockdown of PEPT2 also resulted in decreased uptake. In conclusion, our results demonstrate that the transporters PEPT2, PHT1, and PHT2 are responsible for the uptake of carnosine into glioblastoma cells and full function of all three transporters is required for maximum uptake.

Pyruvate attenuates the anti-neoplastic effect of carnosine independently from oxidative phosphorylation

Here we analyzed whether the anti-neoplastic effect of carnosine, which inhibits glycolytic ATP production, can be antagonized by ATP production via oxidative phosphorylation fueled by pyruvate. Therefore, glioblastoma cells were cultivated in medium supplemented with glucose, galactose or pyruvate and in the presence or absence of carnosine. CPI-613 was employed to inhibit the entry of pyruvate into the tricarboxylic acid cycle and 2,4-dinitrophenol to inhibit oxidative phosphorylation. Energy metabolism and viability were assessed by cell based assays and histochemistry.ATP in cell lysates and dehydrogenase activity in living cells revealed a strong reduction of viability under the influence of carnosine when cells received glucose or galactose but not in the presence of pyruvate. CPI-613 and 2,4-dinitrophenol reduced viability of cells cultivated in pyruvate, but no effect was seen in the presence of glucose. No effect of carnosine on viability was observed in the presence of glucose and pyruvate even in the presence of 2,4-dinitrophenol or CPI-613.In conclusion, glioblastoma cells produce ATP from pyruvate via the tricarboxylic acid cycle and oxidative phosphorylation in the absence of a glycolytic substrate. In addition, pyruvate attenuates the anti-neoplastic effect of carnosine, even when ATP production via tricarboxylic acid cycle and oxidative phosphorylation is blocked. We also observed an inhibitory effect of carnosine on the tricarboxylic acid cycle and a stimulating effect of 2,4-dinitrophenol on glycolytic ATP production.

Serum and urine metabolomics study reveals a distinct diagnostic model for cancer cachexia

BACKGROUND

Cachexia is a multifactorial metabolic syndrome with high morbidity and mortality in patients with advanced cancer. The diagnosis of cancer cachexia depends on objective measures of clinical symptoms and a history of weight loss, which lag behind disease progression and have limited utility for the early diagnosis of cancer cachexia. In this study, we performed a nuclear magnetic resonance-based metabolomics analysis to reveal the metabolic profile of cancer cachexia and establish a diagnostic model.

METHODS

Eighty-four cancer cachexia patients, 33 pre-cachectic patients, 105 weight-stable cancer patients, and 74 healthy controls were included in the training and validation sets. Comparative analysis was used to elucidate the distinct metabolites of cancer cachexia, while metabolic pathway analysis was employed to elucidate reprogramming pathways. Random forest, logistic regression, and receiver operating characteristic analyses were used to select and validate the biomarker metabolites and establish a diagnostic model.

RESULTS

Forty-six cancer cachexia patients, 22 pre-cachectic patients, 68 weight-stable cancer patients, and 48 healthy controls were included in the training set, and 38 cancer cachexia patients, 11 pre-cachectic patients, 37 weight-stable cancer patients, and 26 healthy controls were included in the validation set. All four groups were age-matched and sex-matched in the training set. Metabolomics analysis showed a clear separation of the four groups. Overall, 45 metabolites and 18 metabolic pathways were associated with cancer cachexia. Using random forest analysis, 15 of these metabolites were identified as highly discriminating between disease states. Logistic regression and receiver operating characteristic analyses were used to create a distinct diagnostic model with an area under the curve of 0.991 based on three metabolites. The diagnostic equation was Logit(P) = -400.53 - 481.88 × log(Carnosine) -239.02 × log(Leucine) + 383.92 × log(Phenyl acetate), and the result showed 94.64% accuracy in the validation set.

CONCLUSIONS

This metabolomics study revealed a distinct metabolic profile of cancer cachexia and established and validated a diagnostic model. This research provided a feasible diagnostic tool for identifying at-risk populations through the detection of serum metabolites.

Carnosine Inhibits the Proliferation of Human Cervical Gland Carcinoma Cells Through Inhibiting Both Mitochondrial Bioenergetics and Glycolysis Pathways and Retarding Cell Cycle Progression

Carnosine has been demonstrated to play an antitumorigenic role in certain types of cancer. However, its underlying mechanism is unclear. In this study, the roles of carnosine in cell proliferation and its underlying mechanism were investigated in the cultured human cervical gland carcinoma cells HeLa and cervical squamous carcinoma cells SiHa. The results showed that carnosine exerted a significant inhibitory effect on the proliferation of HeLa cells, whereas its inhibitory action on the proliferation of SiHa cells was much weaker. Carnosine decreased the ATP content through inhibiting both mitochondrial respiration and glycolysis pathways in cultured HeLa cells but not SiHa cells. Carnosine reduced the activities of isocitrate dehydrogenase and malate dehydrogenase in TCA (tricarboxylic acid) cycle and the activities of mitochondrial electron transport chain complex I, II, III, and IV in HeLa cells but not SiHa cells. Carnosine also decreased the mRNA and protein expression levels of ClpP, which plays a key role in maintaining the mitochondrial function in HeLa cells. In addition, carnosine induced G1 arrest by inhibiting the G1-S phase transition in both HeLa and SiHa cells. Taken together, these findings suggest that carnosine has a strong inhibitory action on the proliferation of human cervical gland carcinoma cells rather than cervical squamous carcinoma cells. Mitochondrial bioenergetics and glycolysis pathways and cell cycle may be involved in the carnosine action on the cell proliferation in cultured human cervical gland carcinoma cells HeLa.

Specific inhibition by synthetic analogs of pyruvate reveals that the pyruvate dehydrogenase reaction is essential for metabolism and viability of glioblastoma cells

The pyruvate dehydrogenase complex (PDHC) and its phosphorylation are considered essential for oncotransformation, but it is unclear whether cancer cells require PDHC to be functional or silenced. We used specific inhibition of PDHC by synthetic structural analogs of pyruvate to resolve this question. With isolated and intramitochondrial PDHC, acetyl phosphinate (AcPH, K_i^AcPH = 0.1 μM) was a much more potent competitive inhibitor than the methyl ester of acetyl phosphonate (AcPMe, K_i^AcPMe = 40 μM). When preincubated with the complex, AcPH also irreversibly inactivated PDHC. Pyruvate prevented, but did not reverse the inactivation. The pyruvate analogs did not significantly inhibit other 2-oxo acid dehydrogenases. Different cell lines were exposed to the inhibitors and a membrane-permeable precursor of AcPMe, dimethyl acetyl phosphonate, which did not inhibit isolated PDHC. Using an ATP-based assay, dependence of cellular viability on the concentration of the pyruvate analogs was followed. The highest toxicity of the membrane-permeable precursor suggested that the cellular action of charged AcPH and AcPMe requires monocarboxylate transporters. The relevant cell-specific transcripts extracted from Gene Expression Omnibus database indicated that cell lines with higher expression of monocarboxylate transporters and PDHC components were more sensitive to the PDHC inhibitors. Prior to a detectable antiproliferative action, AcPH significantly changed metabolic profiles of the investigated glioblastoma cell lines. We conclude that catalytic transformation of pyruvate by pyruvate dehydrogenase is essential for the metabolism and viability of glioblastoma cell lines, although metabolic heterogeneity causes different cellular sensitivities and/or abilities to cope with PDHC inhibition.

Flor Yeast: New Perspectives Beyond Wine Aging

The most important dogma in white-wine production is the preservation of the wine aroma and the limitation of the oxidative action of oxygen. In contrast, the aging of Sherry and Sherry-like wines is an aerobic process that depends on the oxidative activity of flor strains of Saccharomyces cerevisiae. Under depletion of nitrogen and fermentable carbon sources, these yeast produce aggregates of floating cells and form an air–liquid biofilm on the wine surface, which is also known as velum or flor. This behavior is due to genetic and metabolic peculiarities that differentiate flor yeast from other wine yeast. This review will focus first on the most updated data obtained through the analysis of flor yeast with -omic tools. Comparative genomics, proteomics, and metabolomics of flor and wine yeast strains are shedding new light on several features of these special yeast, and in particular, they have revealed the extent of proteome remodeling imposed by the biofilm life-style. Finally, new insights in terms of promotion and inhibition of biofilm formation through small molecules, amino acids, and di/tri-peptides, and novel possibilities for the exploitation of biofilm immobilization within a fungal hyphae framework, will be discussed.

Cancer stem cell molecular reprogramming of the Warburg effect in glioblastomas: a new target gleaned from an old concept

Prior targeted treatment for glioblastoma multiforme (GBM) with anti-angiogenic agents, such as bevacizumab, has been met with limited success potentially owing to GBM tumor's ability to develop a hypoxia-induced escape mechanism--a glycolytic switch from oxidative phosphorylation to glycolysis, an old concept known as the Warburg effect. New studies points to a subpopulation of cells as a source for treatment-resistance, cancer stem cells (CSCs). Taken together, the induction of the Warburg effect leads to the promotion of CSC self-renewal and undifferentiation. In response to hypoxia, hypoxia-inducible transcription factor is upregulated and is the central driver in setting off the cascade of events in CSC metabolic reprogramming. Hypoxia-inducible transcription factor upregulates GLUT1 to increase glucose uptake into the cell, upregulates HK2 and PK during glycolysis, upregulates LDHA in the termination of glycolysis, and downregulates PDH to redirect energy production toward glycolysis. This review aims to unite these old and new concepts simultaneously and examine potential enzyme targets driven by hypoxia in the glycolytic phenotype of CSCs to reverse the metabolic shift induced by the Warburg effect.

CK2 inhibition induced PDK4-AMPK axis regulates metabolic adaptation and survival responses in glioma

Understanding mechanisms that link aberrant metabolic adaptation and pro-survival responses in glioma cells is crucial towards the development of new anti-glioma therapies. As we have previously reported that CK2 is associated with glioma cell survival, we evaluated its involvement in the regulation of glucose metabolism. Inhibition of CK2 increased the expression of metabolic regulators, PDK4 and AMPK along with the key cellular energy sensor CREB. This increase was concomitant with altered metabolic profile as characterized by decreased glucose uptake in a PDK4 and AMPK dependent manner. Increased PDK4 expression was CREB dependent, as exogenous inhibition of CREB functions abrogated CK2 inhibitor mediated increase in PDK4 expression. Interestingly, PDK4 regulated AMPK phosphorylation which in turn affected cell viability in CK2 inhibitor treated glioma cells. CK2 inhibitor 4,5,6,7-Tetrabromobenzotriazole (TBB) significantly retarded the growth of glioma xenografts in athymic nude mouse model. Coherent with the in vitro findings, elevated senescence, pAMPK and PDK4 levels were also observed in TBB-treated xenograft tissue. Taken together, CK2 inhibition in glioma cells drives the PDK4-AMPK axis to affect metabolic profile that has a strong bearing on their survival.

Graphene Oxides Decorated with Carnosine as an Adjuvant To Modulate Innate Immune and Improve Adaptive Immunity in Vivo

Current studies have revealed the immune effects of graphene oxide (GO) and have utilized them as vaccine carriers and adjuvants. However, GO easily induces strong oxidative stress and inflammatory reaction at the site of injection. It is very necessary to develop an alternative adjuvant based on graphene oxide derivatives for improving immune responses and decreasing side effects. Carnosine (Car) is an outstanding and safe antioxidant. Herein, the feasibility and efficiency of ultrasmall graphene oxide decorated with carnosine as an alternative immune adjuvant were explored. OVA@GO-Car was prepared by simply mixing ovalbumin (OVA, a model antigen) with ultrasmall GO covalently modified with carnosine (GO-Car). We investigated the immunological properties of the GO-Car adjuvant in model mice. Results show that OVA@GO-Car can promote robust and durable OVA-specific antibody response, increase lymphocyte proliferation efficiency, and enhance CD4(+) T and CD8(+) T cell activation. The presence of Car in GO also probably contributes to enhancing the antigen-specific adaptive immune response through modulating the expression of some cytokines, including IL-6, CXCL1, CCL2, and CSF3. In addition, the safety of GO-Car as an adjuvant was evaluated comprehensively. No symptoms such as allergic response, inflammatory redness swelling, raised surface temperatures, physiological anomalies of blood, and remarkable weight changes were observed. Besides, after modification with carnosine, histological damages caused by GO-Car in lung, muscle, kidney, and spleen became weaken significantly. This study sufficiently suggest that GO-Car as a safe adjuvant can effectively enhance humoral and innate immune responses against antigens in vivo.

Carnosine metabolism in diabetes is altered by reactive metabolites

Carnosinase 1 (CN1) contributes to diabetic nephropathy by cleaving histidine-dipeptides which scavenge reactive oxygen and carbonyl species and increase nitric oxide (NO) production. In diabetic mice renal CN1 activity is increased, the regulatory mechanisms are unknown. We therefore analysed the in vitro and in vivo regulation of CN1 activity using recombinant and human CN1, and the db/db mouse model of diabetes. Glucose, leptin and insulin did not modify recombinant and human CN1 activity in vitro, glucose did not alter renal CN1 activity of WT or db/db mice ex vivo. Reactive metabolite methylglyoxal and Fenton reagent carbonylated recombinant CN1 and doubled CN1 efficiency. NO S-nitrosylated CN1 and decreased CN1 efficiency for carnosine by 70 % (p < 0.01), but not for anserine. Both CN1 cysteine residues were nitrosylated, the cysteine at position 102 but not at position 229 regulated CN1 activities. In db/db mice, renal CN1 mRNA and protein levels were similar as in non-diabetic controls, CN1 efficiency 1.9 and 1.6 fold higher for carnosine and anserine. Renal carbonyl stress was strongly increased and NO production halved, CN1 highly carbonylated and less S-nitrosylated compared to WT mice. GSH and NO2/3 concentrations were reduced and inversely related with carnosine degradation rate (r = -0.82/-0.85). Thus, reactive metabolites of diabetes upregulate CN1 activity by post-translational modifications, and thus decrease the availability of reactive metabolite-scavenging histidine dipeptides in the kidney in a positive feedback loop. Interference with this vicious circle may represent a new therapeutic target for mitigation of DN.

L-histidine inhibits biofilm formation and FLO11-associated phenotypes in Saccharomyces cerevisiae flor yeasts

Flor yeasts of Saccharomyces cerevisiae have an innate diversity of Flo11p which codes for a highly hydrophobic and anionic cell-wall glycoprotein with a fundamental role in biofilm formation. In this study, 380 nitrogen compounds were administered to three S. cerevisiae flor strains handling Flo11p alleles with different expression levels. S. cerevisiae strain S288c was used as the reference strain as it cannot produce Flo11p. The flor strains generally metabolized amino acids and dipeptides as the sole nitrogen source, although with some exceptions regarding L-histidine and histidine containing dipeptides. L-histidine completely inhibited growth and its effect on viability was inversely related to Flo11p expression. Accordingly, L-histidine did not affect the viability of the Δflo11 and S288c strains. Also, L-histidine dramatically decreased air-liquid biofilm formation and adhesion to polystyrene of the flor yeasts with no effect on the transcription level of the Flo11p gene. Moreover, L-histidine modified the chitin and glycans content on the cell-wall of flor yeasts. These findings reveal a novel biological activity of L-histidine in controlling the multicellular behavior of yeasts [corrected].

Dual effects of carnosine on energy metabolism of cultured cortical astrocytes under normal and ischemic conditions

OBJECTIVE

The aim of this study was to investigate the effects of carnosine on the bioenergetic profile of cultured cortical astrocytes under normal and ischemic conditions.

METHODS

The Seahorse Bioscience XF96 Extracellular Flux Analyzer was used to measure the oxygen consumption rates (OCRs) and extracellular acidification rates (ECARs) of cultured cortical astrocytes treated with and without carnosine under normal and ischemic conditions.

RESULTS

Under the normal growth condition, the basal OCRs and ECARs of astrocytes were 21.72±1.59 pmol/min/μg protein and 3.95±0.28 mpH/min/μg protein respectively. Mitochondrial respiration accounted for ~80% of the total cellular respiration and 85% of this coupled to ATP synthesis. Carnosine significantly reduced basal OCRs and ECARs and ATP-linked respiration, but it strikingly increased the spare respiratory capacity of astrocytes. The cellular ATP level in carnosine-treated astrocytes was reduced to ~42% of the control. However, under the ischemic condition, carnosine upregulated the mitochondrial respiratory and cellular ATP content of astrocytes exposed to 8h of oxygen-glucose deprivation (OGD) followed by 24 h of recovery under the normal growth condition.

CONCLUSIONS

Carnosine may be an endogenous regulator of astrocyte energy metabolism and a clinically safe therapeutic agent for promoting brain energy metabolism recovery after ischemia/reperfusion injury.