Inhibition of Morganella morganii Histidine Decarboxylase Activity and Histamine Accumulation in Mackerel Muscle Derived from Filipendula ulumaria Extracts

Elucidating the potential of chlorogenic acid for controlling Morganella psychrotolerans growth and histamine formation

AIM

To investigate the inhibitory impact of chlorogenic acid (CGA) on the growth of Morganella psychrotolerans and its ability to form histamine.

METHODS AND RESULTS

The antimicrobial effect of CGA on M. psychrotolerans was evaluated using the minimum inhibitory concentration (MIC) method, revealing an MIC value of 10 mg ml-1. The alkaline phosphatase (AKP) activity, cell membrane potential, and scanning electron microscopy images revealed that CGA treatment disrupted cell structure and cell membrane. Moreover, CGA treatment led to a dose-dependent decrease in crude histidine decarboxylase (HDC) activity and gene expression of histidine decarboxylase (hdc). Molecular docking analysis demonstrated that CGA interacted with HDC through hydrogen bonds. Furthermore, in situ investigation confirmed the efficacy of CGA in controlling the growth of M. psychrotolerans and significantly reducing histamine formation in raw tuna.

CONCLUSION

CGA had good activity in controlling the growth of M. psychrotolerans and histamine formation.

Rapidly and accurately screening histidine decarboxylase inhibitors from Radix Paeoniae alba using ultrafiltration-high performance liquid chromatography/mass spectrometry combined with enzyme channel blocking and directional enrichment technique

Histidine Decarboxylase (HDC), an unique enzyme responsible for the synthesis of histamine, which is an important mediator in allergy. Inhibition of HDC activity to decrease histamine production is one way to alleviate allergic symptoms. Traditional Chinese medicines (TCMs) with reported anti-allergy effect is one of important source to search for natural HDC inhibitor. Ultrafiltration combined with high-performance liquid chromatography/mass spectrometry (UF-HPLC/MS) is an effective method for screening HDC inhibitor from TCMs. Nevertheless, false-positive and false-negative results caused by the non-specific binding and the neglection of the trace active compounds are major problems in this method. In this study, an integrated strategy that combined UF-HPLC/MS with enzyme channel blocking (ECB) technique and directional enrichment (DE) technique was developed to seek natural HDC inhibitors from Radix Paeoniae alba (RPA), and at the same time, to reduce false-positive and false-negative results. HDC activity was detected to determine the validity of the screened compounds by RP-HPLC-FD in vitro. Molecular docking was applied to assay the binding affinity and binding sites. As a result, three compounds were screened from low content components of RPA after the DE. Among them, two non-specific compounds were eliminated by ECB, and the specific compound was identified as catechin, which has obvious HDC inhibition activity with IC₅₀ 0.52 mM. Furthermore, gallic acid (IC₅₀ 1.8 mM) and paeoniflorin (IC₅₀>2 mM) from high content components of RPA were determined having HDC inhibitory activity. In conclusion, the integrated strategy of UF-HPLC/MS combined with ECB and DE technique is an effective mode for rapid and accurate screening and identification of natural HDC inhibitors from TCMs.

A single amino acid substitution converts a histidine decarboxylase to an imidazole acetaldehyde synthase

Histidine decarboxylase (HDC; EC 4.1.1.22), an enzyme that catalyzes histamine synthesis with high substrate specificity, is a member of the group II pyridoxal 5'-phosphate (PLP) -dependent decarboxylase family. Tyrosine is a conserved residue among group II PLP-dependent decarboxylases. Human HDC has a Y334 located on a catalytically important loop at the active site. In this study, we demonstrated that a HDC Y334F mutant is capable of catalyzing the decarboxylation-dependent oxidative deamination of histidine to yield imidazole acetaldehyde. Replacement of the active-site Tyr with Phe in group II PLP-dependent decarboxylases, including mammalian aromatic amino acid decarboxylase, plant tyrosine/DOPA decarboxylase, and plant tryptophan decarboxylase, is expected to result in the same functional change, given that a Y-to-F substitution at the corresponding residue (number 260) in the HDC of Morganella morganii, another group II PLP-dependent decarboxylase, yielded the same effect. Thus, it was suggested that the loss of the OH moiety from the active-site Tyr residue of decarboxylase uniquely converts the enzyme to an aldehyde synthase.

One injection to profile the chemical composition and dual-antioxidation activities of Rosa chinensis Jacq

An on-line high-performance liquid chromatography-diode-array-detector-electrospray ionization-ion-trap-time-of-flight-mass spectrometry-total antioxidant capacity detection (HPLC-DAD-ESI-IT-TOF-MS-TACD) system was applied for the identification and evaluation of antioxidants in Rosa chinensis Jacq., an edible flower in food industry and a widely used traditional Chinese medicine. With the help of this platform, the HPLC fingerprint, mass fragmentations, and sample activity profiles against 1,1-diphenylpicryl-2-hydrazyl radical (DPPH•) and ferric reducing antioxidant power (FRAP) were recorded after one injection. Using this technique, 80 compounds were separated and identified by their LC/MS behaviors with the assistance of standard compounds. In addition, 11 different Rosa chinensis Jacq. samples were profiled and then quantified for their DPPH• and FRAP activities. Interestingly, a total of 52 compounds showed antioxidative effects against DPPH• and 61 were active against FRAP. The results demonstrated that the on-line system is a powerful technique for antioxidant discovery in Rosa chinensis Jacq. and other food resources.

Bacterial secretion of histamine within the gut influences immune responses within the lung

BACKGROUND

Histamine is an important immunomodulator influencing both the innate and adaptive immune system. Certain host cells express the histidine decarboxylase enzyme (HDC), which is responsible for catalysing the decarboxylation of histidine to histamine. We and others have shown that bacterial strains can also express HDC and secrete histamine; however, the influence of bacterial-derived histamine on the host immune responses distant to the gut is unclear.

METHODS

The Escherichia coli BL21 (E coli BL21) strain was genetically modified to express the Morganella morganii (M morganii)-derived HDC gene (E coli BL21_HTW). E coli BL21 and E coli BL21_HTW were gavaged to ovalbumin (OVA) sensitized and challenged mice to investigate the effect of bacterial-derived histamine on lung inflammatory responses.

RESULTS

Oral administration of E coli BL21_HTW, which is able to secrete histamine, to wild-type mice reduced lung eosinophilia and suppressed ex vivo OVA-stimulated cytokine secretion from lung cells in the OVA respiratory inflammation mouse model. In histamine receptor 2 (H2R)-deficient mice, administration of histamine-secreting bacteria also reduced inflammatory cell numbers in bronchoalveolar lavage (BAL). However, the suppressive effect of bacterial-derived histamine on BAL inflammation was lost in HDC-deficient mice. This loss of activity was associated with increased expression of histamine degrading enzymes and reduced histamine receptor expression.

CONCLUSION

Histamine secretion from bacteria within the gut can have immunological consequences at distant mucosal sites, such as within the lung. These effects are influenced by host histamine receptor expression and the expression of histamine degrading enzymes.

Cysteine 180 Is a Redox Sensor Modulating the Activity of Human Pyridoxal 5'-Phosphate Histidine Decarboxylase

Histidine decarboxylase is a pyridoxal 5'-phosphate enzyme catalyzing the conversion of histidine to histamine, a bioactive molecule exerting its role in many modulatory processes. The human enzyme is involved in many physiological functions, such as neurotransmission, gastrointestinal track function, cell growth, and differentiation. Here, we studied the functional properties of the human enzyme and, in particular, the effects exerted at the protein level by two cysteine residues: Cys-180 and Cys-418. Surprisingly, the enzyme exists in an equilibrium between a reduced and an oxidized form whose extent depends on the redox state of Cys-180. Moreover, we determined that (i) the two enzymatic redox species exhibit modest structural changes in the coenzyme microenvironment and (ii) the oxidized form is slightly more active and stable than the reduced one. These data are consistent with the model proposed by bioinformatics analyses and molecular dynamics simulations in which the Cys-180 redox state could be responsible for a structural transition affecting the C-terminal domain reorientation leading to active site alterations. Furthermore, the biochemical properties of the purified C180S and C418S variants reveal that C180S behaves like the reduced form of the wild-type enzyme, while C418S is sensitive to reductants like the wild-type enzyme, thus allowing the identification of Cys-180 as the redox sensitive switch. On the other hand, Cys-418 appears to be a residue involved in aggregation propensity. A possible role for Cys-180 as a regulatory switch in response to different cellular redox conditions could be suggested.