N-acetyl Histidine Research Articles

Development and Evaluation of Curcumin Encapsulated Self-assembled Nanoparticles as Potential Remedial Treatment for PCOS in a Female Rat Model.

PurposePolycystic ovary syndrome (PCOS) is one of the most common endocrinopathies affecting women of reproductive age and leads to metabolic disorders and infertility. The present study was conducted to investigate the therapeutic effects of curcumin (Cur) encapsulated arginine (Arg) and N-acetyl histidine (NAcHis) modified chitosan (Arg-CS-NAcHis/Cur) nanoparticles (NPs).MethodsIn this study, amphiphilic chitosan (CS) conjugate was developed by modification with hydrophilic arginine (Arg) and hydrophobic N-acetyl histidine (NAcHis) group (Arg-CS-NAcHis). The synthesized conjugate was well characterized by FTIR and NMR studies. Self-assembled nanoparticles based on the synthesized conjugate were developed by simple sonication method and characterized for the physicochemical properties of zeta potential, particle size and drug encapsulation. Next, in vitro drug release, cytotoxicity, and cellular uptake studies of the NPs were evaluated. Finally, the developed nanoparticles were examined for their therapeutic potential against estradiol valerate (EV) induced PCOS rats by evaluating hormone level changes and ovarian morphology.ResultsThe results showed that zeta potential of the nanoparticles was 39.8±2.52 mV and the average size was 200 nm. The in vitro drug release profile showed sustained release pattern. Cytotoxicity and cellular uptake studies also showed preferential effectiveness than free curcumin. Both the biochemical and histopathological studies showed positive effects in reverting the symptoms of PCOS rats to normalcy.ConclusionCurcumin encapsulated arginine and N-acetyl histidine modified chitosan (Arg-CS-NAcHis/Cur) nanoparticles have been successfully developed. The present study suggested that treatment of the nanoparticles might reverse many of the PCOS symptoms. Therefore, these nanoparticles might be used as promising new candidate for delivery of curcumin to treat PCOS.

An epidemiological study of cataracts in wild and farmed lumpfish (Cyclopterus lumpus L.) and the relation to nutrition.

Twelve groups of farmed lumpfish and one of wild lumpfish were screened for cataract and sampled for fish muscle tissue, whole heart and both eye lenses to investigate possible relations between cataract and tissue free amino acid concentrations. Cataract prevalence ranged from 20% to 100%, with the highest average score of 7.3 (max 8) and incidences of severe cataract (>5) in all groups. Cataract could not be explained by suboptimal histidine concentrations in the feed. Neither muscle nor cardiac tissues had concentrations of free histidine compounds. The lumpfish lens contained N-acetylhistidine (NAH), of which low concentrations were strongly related to cataract severity. However, no correlation between lens NAH and cataract severity was found in the present sample set. Wild lumpfish had higher levels compared to farmed lumpfish, suggesting that the farmed lumpfish may have been deficient in histidine or have a higher utilization of NAH due to osmotic problems. Thus, cataract in farmed lumpfish may be related to primary or secondary disturbed nutrient metabolism or malnutrition, shown by the high levels of specific amino acids in different tissues, which may cause osmotic imbalance and cataract development. This nutritional or environmental-related welfare problem deserves further research.

Synthesis and evaluation of pH-sensitive, self-assembled chitosan-based nanoparticles as efficient doxorubicin carriers.

A novel pH-responsive polymer based on amphiphilic N-acetyl histidine and arginine-grafted chitosan was synthesized using N-acetyl histidine as hydrophobic segment and arginine as hydrophilic segment by 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide-mediated coupling reactions as anticancer drug delivery system for doxorubicin. The structure of the synthesized polymer was confirmed by Fourier transform infrared and 1H nuclear magnetic resonance analysis. Due to self-association behavior, N-acetyl histidine and arginine-grafted chitosan structured nanoparticles with in size range of 204 nm. N-acetyl histidine and arginine-grafted chitosan with different substitution degree of N-acetyl histidine were initially prepared and characterized. The critical micelle concentration decreased with increasing substitution degree of N-acetyl histidine. Furthermore, N-acetyl histidine and arginine-grafted chitosan nanoparticles exhibited an acidic pH-triggered aggregation and disassembling nature. The doxorubicin-encapsulated nanoparticles based on synthesized conjugate ( N-acetyl histidine and arginine-grafted chitosan/doxorubicin nanoparticles) showed a sustained drug release pattern, which could be hastened under acidic pH conditions but delayed with increasing substitution degree of N-acetyl histidine. Anticancer effects demonstrated that N-acetyl histidine and arginine-grafted chitosan/doxorubicin nanoparticles could suppress both sensitive and resistant human breast tumor cell line (MCF-7) efficiently in a dose- and time-dependent pattern. Confocal microscopy results evidenced increased cellular uptake and enhanced retention of the synthesized nanoparticles in drug-resistant cells demonstrating better efficacy of nanoparticles over native doxorubicin. These results suggest that N-acetyl histidine and arginine-grafted chitosan/doxorubicin nanoparticles might be promising carriers for delivery of hydrophobic drug doxorubicin against drug-resistant tumors.

Chemically induced dynamic nuclear polarization study of the reduction of histidine radical in the reactions with aromatic amino acids

In order to model the involvement of histidine radicals in the electron transfer reactions in proteins, we investigated the kinetics of the reduction of hisitidine radicals in the reactions with aromatic amino acid residues by means of chemically induced dynamic nuclear polarization with microsecond time resolution. Histidine radicals were generated in photochemical reaction with triplet-excited 3,3’,4,4’-benzophenone tetracarboxylic acid. The intermolecular electron transfer from N-acetyl derivatives of tyrosine and tryptophan to the radical of N-acetyl histidine was studied in neutral and basic aqueous solutions. It was found that the rate constant of reduction of short-lived histidine radical in the reactions with tyrosine anion is k r = (1.9±0.5)•108 L mol–1 s–1, which is more than two orders of magnitude higher than that of reduction of histidine radical with neutral tyrosine (k r = (1.2±0.4)•106 L mol–1 s–1). In the reduction of histidine radical with N-acetyl tryptophan, the protonated states of reagents do not change, when pH of aqueous solution varies from neutral to basic and the reaction rate coefficient remains constant being k r = (1.3±0.4)•106 L mol–1 s–1.

Active Tumor Permeation and Uptake of Surface Charge-Switchable Theranostic Nanoparticles for Imaging-Guided Photothermal/Chemo Combinatorial Therapy.

To significantly promote tumor uptake and penetration of therapeutics, a nanovehicle system comprising poly(lactic-co-glycolic acid) (PLGA) as the hydrophobic cores coated with pH-responsive N-acetyl histidine modified D-α-tocopheryl polyethylene glycol succinate (NAcHis-TPGS) is developed in this work. The nanocarriers with switchable surface charges in response to tumor extracellular acidity (pHe) were capable of selectively co-delivering indocyanine green (ICG), a photothermal agent, and doxorubicin (DOX), a chemotherapy drug, to tumor sites. The in vitro cellular uptake of ICG/DOX-loaded nanoparticles by cancer cells and macrophages was significantly promoted in weak acidic environments due to the increased protonation of the NAcHis moieties. The results of in vivo and ex vivo biodistribution studies demonstrated that upon intravenous injection the theranostic nanoparticles were substantially accumulated in TRAMP-C1 solid tumor of tumor-bearing mice. Immunohistochemical examination of tumor sections confirmed the active permeation of the nanoparticles into deep tumor hypoxia due to their small size, pHe-induced near neutral surface, and the additional hitchhiking transport via tumor-associated macrophages. The prominent imaging-guided photothermal therapy of ICG/DOX-loaded nanoparticles after tumor accumulation induced extensive tumor tissue/vessel ablation, which further promoted their extravasation and DOX tumor permeation, thus effectively suppressing tumor growth.

Importance of polarization transfer in reaction products for interpreting and analyzing CIDNP at low magnetic fields

The magnetic field dependence of Chemically Induced Dynamic Nuclear Polarization (CIDNP) was studied for the amino acids N-acetyl histidine, N-acetyl tryptophan and N-acetyl tyrosine. It is demonstrated that at low field CIDNP is strongly affected by polarization redistribution in the diamagnetic molecules. Such a polarization transfer is of coherent nature and is due to spin coherences formed together with non-equilibrium population of the spin states. These coherences clearly manifest themselves in an oscillatory time dependence of polarization. Polarization transfer effects are most pronounced at nuclear spin Level Anti-Crossings (LACs), which also result in sharp features in the CIDNP field dependence. Thus, polarization transfer is an important factor, which has to be taken into account in order to interpret low-field CIDNP data on both qualitative and quantitative level. Possible applications of polarization transfer phenomena are also discussed in the paper. In particular, the role of LACs in spin order transfer is highlighted: LACs provide a new tool for precise manipulation of spin hyperpolarization and NMR enhancement of selected target spins.

Imidazole catalyzes chlorination by unreactive primary chloramines

Hypochlorous acid and simple chloramines (RNHCl) are stable biologically derived chlorinating agents. In general, the chlorination potential of HOCl is much greater than that of RNHCl, allowing it to oxidize or chlorinate a much wider variety of reaction partners. However, in this study we demonstrate by kinetic analysis that the reactivity of RNHCl can be dramatically promoted by imidazole and histidyl model compounds via intermediary formation of the corresponding imidazole chloramines. Two biologically relevant reactions were investigated—loss of imidazole-catalyzed chlorinating capacity and phenolic ring chlorination using fluorescein and the tyrosine analog, 4-hydroxyphenylacetic acid (HPA). HOCl reacted stoichiometrically with imidazole, N-acetylhistidine (NAH), or imidazoleacetic acid to generate the corresponding imidazole chloramines which subsequently decomposed. Chloramine (NH2Cl) also underwent a markedly accelerated loss in chlorinating capacity when NAH was present, although in this case N-α-acetylhistidine chloramine (NAHCl) did not accumulate, indicating that the catalytic intermediate must be highly reactive. Mixing HOCl with 1-methylimidazole (MeIm) led to very rapid loss in chlorinating capacity via formation of a highly reactive chlorinium ion (MeImCl+) intermediate; this behavior suggests that the reactive forms of the analogous imidazole chloramines are their conjugate acids, e.g., the imidazolechlorinium ion (HImCl+). HOCl-generated imidazole chloramine (ImCl) reacted rapidly with fluorescein in a specific acid-catalyzed second-order reaction to give 3′-monochloro and 3′,5′-dichloro products. Equilibrium constants for the transchlorination reactions HOCl + HIm = H2O + ImCl and NH2Cl + HIm = NH3 + ImCl were estimated from the dependence of the rate constants on [HIm]/[HOCl] and literature data. Acid catalysis again suggests that the actual chlorinating agent is HImCl+; consistent with this interpretation, MeIm markedly catalyzed fluorescein chlorination by HOCl. Time-dependent imidazole-catalyzed HPA chlorination by NH2Cl was also demonstrated by product analyses. Quantitative assessment of the data suggests that physiological levels of histidyl groups will react with primary chloramines to generate a flux of imidazole chloramine sufficient to catalyze biological chlorination via HImCl+, particularly in environments that generate high concentrations of HOCl such as the neutrophil phagosome.

Coherent transfer of nuclear spin polarization in field-cycling NMR experiments

Coherent polarization transfer effects in a coupled spin network have been studied over a wide field range. The transfer mechanism is based on exciting zero-quantum coherences between the nuclear spin states by means of non-adiabatic field jump from high to low magnetic field. Subsequent evolution of these coherences enables conversion of spin order in the system, which is monitored after field jump back to high field. Such processes are most efficient when the spin system passes through an avoided level crossing during the field variation. The polarization transfer effects have been demonstrated for N-acetyl histidine, which has five scalar coupled protons; the initial spin order has been prepared by applying RF-pulses at high magnetic field. The observed oscillatory transfer kinetics is taken as a clear indication of a coherent mechanism; level crossing effects have also been demonstrated. The experimental data are in very good agreement with the theoretical model of coherent polarization transfer. The method suggested is also valid for other types of initial polarization in the spin system, most notably, for spin hyperpolarization.

Creating Long-Lived Spin States at Variable Magnetic Field by Means of Photochemically Induced Dynamic Nuclear Polarization.

We have shown that long-lived spin states (LLS) can be selectively populated by photogenerated chemically induced dynamic nuclear polarization (CIDNP) over a wide range of magnetic fields. Relaxation times of LLS of the β-CH2 protons in N-acetyl histidine and partially deuterated histidine have been measured. Our experiments demonstrate that CIDNP enables creating LLS in the amino acid in a field range of up to a few Tesla and that their lifetimes can be 45 times longer than T1. The advantage of the method is thus two-fold: it allows one to accumulate high levels of spin hyperpolarization and to preserve them for periods of time far exceeding T1. Therefore, photo-CIDNP is a technique suitable for creating long-lived spin order in biologically relevant molecules.

Effects of chronic and periodic exposures to ammonia on the eye health in juvenile Atlantic halibut (Hippoglossus hippoglossus)

The effects of chronic and periodic peaks of un-ionised ammonia (UIA-N) exposure on eye health and cataract formation in juvenile Atlantic halibut, Hippoglossus hippoglossus, were examined. Fish with mean initial weight 51.7 g (SD 13.2) were exposed to five treatments consisting of control group and three groups (ChronicLow, ChronicMedium and ChronicHigh,) chronically exposed with UIA-N of 0.06, 0.12 to 0.17 mg/l, respectively, for 62 days at 11.9°C, pH 8.0 and salinity 34‰. Furthermore, a fifth group (HighPulse) was exposed to the same high levels as ChronicHigh for a short daily period (peak of 15 mg/l 30 min after exposure, 10 mg/l 1 h after exposure and 1.2 mg/l 3 h after exposure). In the subsequent period of the experimental study (from day 63 until day 100), no ammonia was added to the water. Mean weights were significantly lower in groups exposed to chronically high ambient ammonia concentrations compared to corresponding control group throughout the experimental period. The sampled fish exhibited signs of mild cataract formation, although the results showed no clear evidence that the ammonia treatments contributed to differences. Minor differences were found in measured muscle free amino acids, which could be used to explain potential changes in buffering capacity. The eye histidine status differed significantly at day 62, and osmotic differences in the eye lenses (measured as differences in N-acetyl histidine) were found in all group exposed to chronic levels of ammonia.

N-acetylhistidine, a novel osmolyte in the lens of Atlantic salmon (Salmo salar L.)

Volume homeostasis is essential for the preservation of lens transparency and this is of particular significance to anadromous fish species where migration from freshwater to seawater presents severe osmotic challenges. In Atlantic salmon (Salmo salar L.), aqueous humor (AH) osmolality is greater in fish acclimated to seawater compared with young freshwater fish, and levels of lens N-acetylhistidine (NAH) are much higher in seawater fish. Here we investigate NAH as an osmolyte in the lenses of salmon receiving diets either with or without histidine supplementation. In the histidine-supplemented diet (HD) histidine content was 14.2 g/kg, and in the control diet (CD) histidine content was 8.9 g/kg. A transient increase in AH osmolality of 20 mmol/kg was observed in fish transferred from freshwater to seawater. In a lens culture model, temporary decreases in volume and transparency were observed when lenses were exposed to hyperosmotic conditions. A positive linear relationship between extracellular osmolality and lens NAH content was also observed, whereas there was no change in lens histidine content. Hypoosmotic exposure stimulated [(14)C]-histidine efflux by 9.2- and 2.6-fold in CD and HD lenses, respectively. NAH efflux, measured by HPLC, was stimulated by hypoosmotic exposure to a much greater extent in HD lenses. In vivo, lens NAH increased in response to elevated AH osmolality in HD but not CD fish. In conclusion, NAH has an important and novel role as a compatible osmolyte in salmon lens. Furthermore, it is the major osmolyte that balances increases in AH osmolality when fish move from freshwater to seawater. A deficiency in NAH would lead to a dysfunction of the normal osmoregulatory processes in the lens, and we propose that this would contribute to cataract formation in fish deficient in histidine.

Tumor targeting efficiency of bare nanoparticles does not mean the efficacy of loaded anticancer drugs: Importance of radionuclide imaging for optimization of highly selective tumor targeting polymeric nanoparticles with or without drug

The better understanding of polymeric nanoparticles as a drug delivery carrier is a decisive factor to get more efficient therapeutic response in vivo. Here, we report the non-invasive imaging of bare polymeric nanoparticles and drug-loaded polymeric nanoparticles to evaluate biodistribution in tumor bearing mice. To make nano-sized drug delivery carrier, glycol chitosan was modified with different degrees of hydrophobic N-acetyl histidine (NAcHis-GC-1, -2, and -3). The biodistribution of polymeric nanoparticles and drug was confirmed by using gamma camera with 131I-labeled NAcHis-GC and 131I-labeled doxorubicin (DOX) and by using in vivo live animal imaging with near-infrared fluorescence Cy5.5-labeled NAcHis-GC. Among bare nanoparticles, NAcHis-GC3 (7.8% NAcHis content) showed much higher tumor targeting efficiency than NAcHis-GC1 (3.3% NAcHis content) and NAcHis-GC2 (6.8% NAcHis content). In contrast, for drug-loaded nanoparticles, DOX-NAcHis-GC1 displayed two-fold higher tumor targeting property than DOX-NAcHis-GC3. These data imply that the biodistribution and tumor targeting efficiency between bare and drug-loaded nanoparticles may be greatly different. Therapeutic responses for NAcHis-GC nanoparticles after drug loading were also evaluated. In xenograft animal model, we could find out that DOX-NAcHis-GC1 with higher tumor targeting of DOX has more excellent therapeutic effect than DOX-NAcHis-GC3 and free DOX. These results mean that the hydrophobic core stability might be a critical factor for tumor targeting efficiency of nanoparticles. The present study indicates that by using molecular imaging, we can select more appropriate nanoparticles with the highest tumor targeting properties, leading to exerting more excellent therapeutic results in cancer therapy.

Prostate Cancer-Targeted Imaging Using Magnetofluorescent Polymeric Nanoparticles Functionalized with Bombesin

In this work, the aim was to prepare and characterize a magnetofluorescent polymeric nanoparticle for prostate cancer imaging in vivo. Glycol chitosan (GC) was chemically modified with N-acetyl histidine (NAHis) as a hydrophobic moiety, and bombesin (BBN) was conjugated to the hydrophobically modified GC for use in targeting gastric-releasing peptide receptors (GRPR) overexpressed in prostate cancer cells. NAHis-GC conjugates were labeled with the near-infrared (NIR) fluorophore Cy5.5 (C-NAHis-GC conjugate). BBN-conjugated C-NAHis-GC nanoparticles (BC-NAHis-GC nanoparticles) showed significantly higher binding to the PC3 cell surface than nanoparticles without BBN, and the cellular binding was clearly inhibited by BBN. The tumor-to-muscle ratios of C- and BC-NAHis-GC nanoparticles were 2.26 +/- 0.66 and 5.37 +/- 0.43, respectively. The tumor accumulation of BC-NAHis-GC nanoparticles was clearly reduced by co-injection of BBN. Further, iron oxide nanoparticles (IO) were loaded into BC-NAHis-GC nanoparticles to investigate the possibility of use as a probe for MRI. IO-BC-NAHis-GC nanoparticles were well observed in the PC3 cells, and the blocking with BBN significantly reduced the cellular binding of the nanoparticles. These results demonstrate that the BBN conjugation to NAHis-GC nanoparticles improves their tumor accumulation in PC3-bearing mice in comparison to nanoparticles without BBN, suggesting that BC-NAHis-GC nanoparticles may be useful for prostate cancer imaging.

Influence of histidine on the release of all-trans retinoic acid from self-assembled glycol chitosan nanoparticles

Objective: In this study, the influence of N-acetyl histidine (NAHis) on the all-trans retinoic acid (ATRA) release from the NAHis-conjugated self-assembled glycol chitosan (GC) nanoparticles was investigated. Methods: NAHis was conjugated to GC as a hydrophobic moiety to prepare the self-assembled nanoparticles, and ATRA was incorporated into the inner core of the NAHis–GC nanoparticles. The ATRA release from NAHis–GC nanoparticles was performed at 37°C in a phosphate-buffered saline buffer (pH 5.5 or 7.4) for 48 hours. Results: At a pH of 5.5, less than 20% (w/w) of total loading amount of ATRA was released from the nanoparticles after 48 hours. In contrast, two times greater amount of ATRA was released at a pH of 7.4. The ATRA release rate from the NAHis–GC nanoparticles was significantly slower at a pH of 5.5 than at a pH of 7.4. Conclusion: The release profiles of ATRA that was incorporated into the NAHis–GC nanoparticles were controlled by the NAHis content in the GC nanoparticles.

Effect of plant-based feed ingredients on osmoregulation in the Atlantic salmon lens

Lenses of adult Atlantic salmon fed with a plant oil and plant protein-based diet (plant diet) were compared to lenses of fish fed a diet based on traditional marine ingredients (marine diet) with respect to biochemical composition and functionality ex vivo. After 12 months of feeding, plant diet-fed fish had smaller lenses with higher water contents and lower concentrations of histidine (His) and N-acetylhistidine (NAH) than fish fed with the marine diet. Cataract development in both dietary groups was minimal and no differences between the groups were observed. Lens fatty acid and lipid class composition differed minimally, although a significant increase in linoleic acid was observed. The lenses were examined for their ability to withstand osmotic disturbances ex vivo. Culture in hypoosmotic and hyperosmotic media led to increase and decrease of lens volume, respectively. Lenses from plant diet-fed fish were less resistant to swelling and shrinking, released less NAH into the culture medium, and accumulated His and NAH at higher rates than lenses from marine diet-fed fish. Culture in hypoosmotic medium resulted in higher cataract scores than in control and hyperosmotic medium. mRNA expression of selected genes, including glutathione peroxidase 4 and SPARC (secreted protein acidic and rich in cysteine), was affected by diet and osmotic treatment. It can be concluded that lenses of farmed Atlantic salmon are affected by the diet composition, both in biochemical composition and physiological functionality in relation to osmoregulation.

Solution interactions between the uranyl cation [formula omitted] and histidine, N-acetyl-histidine, tyrosine, and N-acetyl-tyrosine

Complexes of the uranyl cation [ UO 2 2 + ] with histidine (His), N-acetyl-histidine (NAH), tyrosine (Tyr), and N-acetyl-tyrosine (NAT) were studied by UV–visible and NMR spectroscopy, and by potentiometric titration. Protonation constants for each ligand are reported, as are cumulative formation constants for uranyl–amino acid complexes. Coupling constant data ( J CH) for uranyl–histidine complexes indicate that inner-sphere solution interactions between histidine and uranyl cation are solely at the carboxylate site. At 25 °C the major uranyl–histidine complex has a cumulative formation constant of log β 110 = 8.53, and a proposed formula of [UO 2HisH 2(OH) 2] +; the stepwise formation constant, log K UL, is estimated to be ⩽5.6 (≈8.53 − (−6.1) − (−6.1) − 15.15). Outer-sphere interactions, H-bonding or electrostatic interactions, are proposed as contributing a significant portion of the stability to the ternary uranyl–hydroxo-amino acid complexes. The temperature dependent protonation constants of histidine and formation constants between uranyl cation and histidine are reported from 10 to 35 °C; at 25 °C, Δ G = −43.3 kJ/mol.

N-acetyl histidine-conjugated glycol chitosan self-assembled nanoparticles for intracytoplasmic delivery of drugs: Endocytosis, exocytosis and drug release

Nano-sized vesicular systems (nanoparticles), ranging from 10 nm to 1000 nm in size, have potential applications as drug delivery systems. Successful clinical applications require the efficient intracellular delivery of drug-loaded nanoparticles. Here we describe N-acetyl histidine-conjugated glycol chitosan (NAcHis-GC) self-assembled nanoparticles as a promising system for intracytoplasmic delivery of drugs. Because N-acetyl histidine (NAcHis) is hydrophobic at neutral pH, the conjugates formed self-assembled nanoparticles with mean diameters of 150−250 nm. In slightly acidic environments, such as those in endosomes, the nanoparticles were disassembled due to breakdown of the hydrophilic/hydrophobic balance by the protonation of the imidazole group of NAcHis. Cellular internalization and drug release of the pH-sensitive self-assembled nanoparticles were investigated by flow cytometry and confocal microscopy. NAcHis-GC nanoparticles internalized by adsorptive endocytosis were exocytosed or localized in endosomes. The amount of exocytosed nanoparticles was dependent on the pre-incubation time prior to removal of free nanoparticles from the culture media. Flow cytometry and confocal microscopy showed that NAcHis-GC nanoparticles released drugs into the cytosol and cell cycle analysis demonstrated that paclitaxel-incorporated NAcHis-GC nanoparticles were effective in inducing arrest of cell growth.

Dietary histidine affects lens protein turnover and synthesis of N-acetylhistidine in Atlantic salmon (Salmo salar L.) undergoing parr-smolt transformation

This study was conducted to investigate protein synthesis rates and metabolism of histidine (His)-derivatives in lenses of Atlantic salmon (Salmo salar L.) of different dietary His background during parr–smolt transformation. Two populations of Atlantic salmon parr of equal origin were established in freshwater (FW), 3 months prior to transfer to seawater (SW). The populations were fed either a control diet (CD) containing 8.9 g kg-1 His or the same diet added crystalline His to a total level of 14.2 g kg-1 (HD). On the basis of these two populations, 14C His force-feeding studies were performed; in FW 3 weeks prior to sea transfer and in SW 6 weeks after transfer. The studies were conducted by force-feeding the respective diets enriched with 14C labelled His, with subsequent measurements of incorporation of 14C His into lens free amino acid pool, as well as into lens proteins and other free His pool fractions. The latter included the major lens imidazole N-acetylhistidine (NAH). Lens concentrations of His and NAH were clearly influenced by dietary His history, both in parr and smolt. The lens His and NAH concentrations in the CD population were considerably lower in SW than in FW, while in the HD group the His level was equal and the NAH level 50% higher in SW than in FW. Fractional synthesis rate for NAH, KS (NAH), in FW was 8.2 and 4.2 µmol g-1 day-1 for fish in the CD and HD populations, respectively. The corresponding KS (NAH) values in SW were 5.1 and 33.0 µmol g-1 day-1. Our data show that free His is rapidly converted to NAH in the lens, and that NAH seems to have a very high turnover, especially in salmon reared in SW. Fractional synthesis rate for lens proteins, KS (PROTEIN), ranged between 1.8 and 17.3% day-1 (182 and 2791 µg g-1 day-1, respectively), and was generally higher in SW than in FW (P < 0.01). In SW, KS (PROTEIN) was highest in fish in the HD population (P < 0.05), whereas lens protein retention in the HD group was significantly lower than the CD group (P = 0.01). In a second model assuming that His from lens NAH is available for protein synthesis, calculated values of KS (PROTEIN) ranged between 0.17% day-1 (17.6 µg g-1 day-1) and 0.48% day-1 (70.2 µg g-1 day-1). Cataract scores recorded in the His populations at a later point (day 204), showed that the CD fish had significantly higher mean cataract scores than individuals in the HD population (P < 0.01), confirming that low levels of lens His and NAH are associated with cataract development.

Histidine nutrition and genotype affect cataract development in Atlantic salmon, Salmo salar L.

The aim of this study was to investigate effects of dietary levels of histidine (His) and iron (Fe) on cataract development in two strains of Atlantic salmon monitored through parr-smolt transformation. Three experimental diets were fed: (i) a control diet (CD) with 110 mg kg(-1) Fe and 11.7 g kg(-1) His; (ii) CD supplemented with crystalline His to a level of 18 g kg(-1) (HD); and (iii) HD with added iron up to 220 mg kg(-1) (HID). A cross-over design, with two feeding periods was used. A 6-week freshwater (FW) period was followed by a 20-week period, of which the first three were in FW and the following 17 weeks in sea water (SW). Fish were sampled for weighing, cataract assessment and tissue analysis at five time points. Cataracts developed in all groups in SW, but scores were lower in those fed high His diets (P < 0.05). This effect was most pronounced when HD or HID was given in SW, but was also observed when these diets were given in FW only. Histidine supplementation had a positive effect on growth performance and feed conversion ratio (P < 0.05), whereas this did not occur when iron was added. Groups fed HD or HID had higher lens levels of His and N-acetyl histidine (NAH), the latter showing a marked increase post-smoltification (P < 0.05). The HD or HID groups also showed higher muscle concentrations of the His dipeptide anserine (P < 0.05). There was a strong genetic influence on cataract development in the CD groups (P < 0.001), not associated with tissue levels of His or NAH. The role of His and His-related compounds in cataractogenesis is discussed in relation to tissue buffering, osmoregulation and antioxidation.

Mechanisms of reactions of flavin mononucleotide triplet with aromatic amino acids

Chemical reactions between the photoexcited triplet state of flavin mononucleotide and the aromatic amino acids, N-acetyl tryptophan (TrpH), N-acetyl tyrosine (TyrOH), and N-acetyl histidine (HisH) in aqueous solution have been studied in the pH range 2–12. Across the whole pH range, the principal mechanism of reaction of both TrpH and TyrOH is shown to be electron transfer. For HisH, the mechanism and rate of the reaction depend on the protonation state of the reactants. In acidic conditions (pH<4), reaction does not occur. At 4<pH<11, the reaction proceeds via hydrogen atom abstraction with a rate constant varying from 3.0×10 6 to 2.5×10 8 M −1 s −1. In extremely basic solution (pH>12) the mechanism switches to electron transfer.