Plausible authentication of manuka honey and related products by measuring leptosperin with methyl syringate

Manuka honey as a non-antibiotic alternative against Staphylococcus spp. and their small colony variant (SCVs) phenotypes

The antibiotic resistance (ABR) crisis is an urgent global health priority. Staphylococci are among the problematic bacteria contributing to this emergency owing to their recalcitrance to many clinically important antibiotics. Staphylococcal pathogenesis is further complicated by the presence of small colony variants (SCVs), a bacterial subpopulation displaying atypical characteristics including retarded growth, prolific biofilm formation, heightened antibiotic tolerance, and enhanced intracellular persistence. These capabilities severely impede current chemotherapeutics, resulting in chronic infections, poor patient outcomes, and significant economic burden. Tackling ABR requires alternative measures beyond the conventional options that have dominated treatment regimens over the past 8 decades. Non-antibiotic therapies are gaining interest in this arena, including the use of honey, which despite having ancient therapeutic roots has now been reimagined as an alternative treatment beyond just traditional topical use, to include the treatment of an array of difficult-to-treat staphylococcal infections. This literature review focused on Manuka honey (MH) and its efficacy as an anti-staphylococcal treatment. We summarized the studies that have used this product and the technologies employed to study the antibacterial mechanisms that render MH a suitable agent for the management of problematic staphylococcal infections, including those involving staphylococcal SCVs. We also discussed the status of staphylococcal resistance development to MH and other factors that may impact its efficacy as an alternative therapy to help combat ABR.

Anti-bacterial, anti-biofilm and anti-quorum sensing activities of honey: A review

ETHNOPHARMACOLOGICAL RELEVANCE

Man has used honey to treat diseases since ancient times, perhaps even before the history of medicine itself. Several civilizations have utilized natural honey as a functional and therapeutic food to ward off infections. Recently, researchers worldwide have been focusing on the antibacterial effects of natural honey against antibiotic-resistant bacteria.

AIM OF THE STUDY

This review aims to summarize research on the use of honey properties and constituents with their anti-bacterial, anti-biofilm, and anti-quorum sensing mechanisms of action. Further, honey's bacterial products, including probiotic organisms and antibacterial agents which are produced to curb the growth of other competitor microorganisms is addressed.

MATERIALS AND METHODS

In this review, we have provided a comprehensive overview of the antibacterial, anti-biofilm, and anti-quorum sensing activities of honey and their mechanisms of action. Furthermore, the review addressed the effects of antibacterial agents of honey from bacterial origin. Relevant information on the antibacterial activity of honey was obtained from scientific online databases such as Web of Science, Google Scholar, ScienceDirect, and PubMed.

RESULTS

Honey's antibacterial, anti-biofilm, and anti-quorum sensing activities are mostly attributed to four key components: hydrogen peroxide, methylglyoxal, bee defensin-1, and phenolic compounds. The performance of bacteria can be altered by honey components, which impact their cell cycle and cell morphology. To the best of our knowledge, this is the first review that specifically summarizes every phenolic compound identified in honey along with their potential antibacterial mechanisms of action. Furthermore, certain strains of beneficial lactic acid bacteria such as Bifidobacterium, Fructobacillus, and Lactobacillaceae, as well as Bacillus species can survive and even grow in honey, making it a potential delivery system for these agents.

CONCLUSION

Honey could be regarded as one of the best complementary and alternative medicines. The data presented in this review will enhance our knowledge of some of honey's therapeutic properties as well as its antibacterial activities.

Formation of Protein-Bound Maillard Reaction Products during the Storage of Manuka Honey

Honey from the nectar of the Manuka tree (Leptospermum scoparium) grown in New Zealand contains high amounts of antibacterial methylglyoxal (MGO). MGO can react with proteins to form peptide-bound Maillard reaction products (MRPs) such as Nε-carboxyethyllysine (CEL) and "methylglyoxal-derived hydroimidazolone 1" (MG-H1). To study the reactions of MGO with honey proteins during storage, three manuka honeys with varying amounts of MGO and a kanuka honey (Kunzea ericoides) spiked with various MGO concentrations up to 700 mg/kg have been stored at 37 °C for 10 weeks, and the formation of protein-bound MRPs has been analyzed via high-performance liquid chromatography-mass spectrometry (HPLC-MS/MS) following isolation of the protein fraction and enzymatic hydrolysis. During storage, contents of protein-bound CEL and MG-H1 increased continuously, directly depending on the MGO content. For honeys with large amounts of MGO, a slower formation of Nε-fructosyllysine (FL) was observed, indicating competing reactions of glucose and MGO with lysine. Furthermore, the lysine modification increased with storage independently from the MGO concentration. Up to 58-61% of the observed lysine modification was explainable with the formation of CEL and FL, indicating that other reactions, most likely the formation of Heyns products from lysine and fructose, may play an important role. Our results can contribute to the authentication of manuka honey.

Accelerated loss of diastase in mānuka honey: Investigation of mānuka specific compounds

Diastase is used internationally as a quality monitor for excessive heat treatment and prolonged storage of honey; honey must contain an activity of at least 8 diastase numbers (DN) for it to be considered export quality. Freshly harvested mānuka honey can have diastase activity close to the export threshold of 8 DN without excess heating, increasing susceptibility for export failure. This research investigated the effect of compounds unique to or high in concentration in mānuka honey on diastase activity. Investigation of the effect of methylglyoxal, dihydroxyacetone, 2-methoxybenzoic acid, 3-phenyllatic acid, 4-hydroxyphenyllactic acid and 2'-methoxyacetophenone on diastase activity was carried out. Mānuka honey was stored at 20 and 27 °C and clover honey spiked with compounds of interest were stored at 20, 27 and 34 °C and monitored overtime. Methylglyoxal and 3-phenyllactic acid were found to accelerate the loss of diastase above the loss normally observed with time and elevated temperature.

Benefits of Manuka Honey in the Management of Infectious Diseases: Recent Advances and Prospects

The benefits of honey have been recognized since ancient times for treating numerous diseases. However, in today's modern era, the use of traditional remedies has been rapidly diminishing due to the complexities of modern lifestyles. While antibiotics are commonly used and effective in treating pathogenic infections, their inappropriate use can lead to the development of resistance among microorganisms, resulting in their widespread prevalence. Therefore, new approaches are constantly required to combat drug-resistant microorganisms, and one practical and useful approach is the use of drug combination treatments. Manuka honey, derived from the manuka tree (Leptospermum scoparium) found exclusively in New Zealand, has garnered significant attention for its biological potential, particularly due to its antioxidant and antimicrobial properties. Moreover, when combined with antibiotics, it has demonstrated the ability to enhance their effectiveness. In this review, we delve into the chemical markers of manuka honey that are currently known, as well as detail the impact of manuka honey on the management of infectious diseases up to the present.

Thorough Investigation of the Phenolic Profile of Reputable Greek Honey Varieties: Varietal Discrimination and Floral Markers Identification Using Liquid Chromatography–High-Resolution Mass Spectrometry

Honey is a highly consumed commodity due to its potential health benefits upon certain consumption, resulting in a high market price. This fact indicates the need to protect honey from fraudulent acts by delivering comprehensive analytical methodologies. In this study, targeted, suspect and non-targeted metabolomic workflows were applied to identify botanical origin markers of Greek honey. Blossom honey samples (n = 62) and the unifloral fir (n = 10), oak (n = 24), pine (n = 39) and thyme (n = 34) honeys were analyzed using an ultra-high-performance liquid chromatography hybrid quadrupole time-of-flight mass spectrometry (UHPLC-q-TOF-MS) system. Several potential authenticity markers were revealed from the application of different metabolomic workflows. In detail, based on quantitative targeted analysis, three blossom honey markers were found, namely, galangin, pinocembrin and chrysin, while gallic acid concentration was found to be significantly higher in oak honey. Using suspect screening workflow, 12 additional bioactive compounds were identified and semi-quantified, achieving comprehensive metabolomic honey characterization. Lastly, by combining non-targeted screening with advanced chemometrics, it was possible to discriminate thyme from blossom honey and develop binary discriminatory models with high predictive power. In conclusion, a holistic approach to assessing the botanical origin of Greek honey is presented, highlighting the complementarity of the three applied metabolomic approaches.

Feeding Sugars to Stingless Bees: Identifying the Origin of Trehalulose-Rich Honey Composition

The beneficial disaccharide, trehalulose, is a feature of stingless bee honey, while not dominant in any other foods. By experimentally feeding sugar solutions to confined colonies of the Australian stingless bee Tetragonula carbonaria, the origin of trehalulose has now been established. Complete conversion of fed sucrose was observed, by analysis of the honey, forming trehalulose (64-72%) with lesser erlose (18-23%), fructose (9-12%), and minor glucose detected. Remarkably, feeding solutions of glucose/fructose (1:1) mixtures did not result in trehalulose/erlose formation. Hence, stingless bees with natural access to floral nectar high in sucrose will produce honey high in trehalulose, with its associated beneficial properties. Any temptation to artificially increase trehalulose content by feeding sucrose to stingless bees would produce "fake" honey lacking key natural phytochemicals available to the foraging bee. The sucrose-fed fake and natural honey were however readily distinguished via isotope ratio mass spectrometry δ¹³C values, to combat such potential indirect adulteration.

Methylglyoxal binds to amines in honey matrix and 2'-methoxyacetophenone is released in gaseous form into the headspace on the heating of manuka honey

Reports on the thermal stability of manuka honey in terms of food processing have been few. This study investigated changes in nine characteristic chemicals of manuka honey during heating. Among these, methylglyoxal (MGO) and 2'-methoxyacetophenone (MAP) were significantly decreased by heating at 90 °C. To elucidate the mechanism for this decrease, artificial honey was prepared from sugars and water with MAP or MGO and then heated. The decrease of MGO was enhanced with l-proline, lysine, or arginine derivatives, accompanied by formation of 2-acetyl-1-pyrroline, MGO-derived lysine dimer, or argpyrimidine, respectively, suggesting that an amino-carbonyl reaction is one pathway for the loss of MGO. The decrease of MAP in the artificial honey depended on the volume of headspace in a vessel. MAP from heated manuka honey was also detected in the gas phase, indicating that MAP was vaporized. Heating could thus reduce the beneficial and/or signature molecules in honey.

Dynamics of the Cellular Metabolism of Leptosperin Found in Manuka Honey

Leptosperin (methyl syringate β-d-gentiobioside) is abundantly found in manuka honey, which is widely used because of its antibacterial and possible anti-inflammatory activities. The aim of this study was to examine the molecular mechanism underlying the metabolism of leptosperin. Five phytochemicals (leptosperin, methyl syringate (MSYR), glucuronate conjugate of MSYR (MSYR-GA), sulfonate conjugate of MSYR (MSYR-S), and syringic acid (SYR)) were separately incubated with HepG2 and Caco-2 cells. After incubation, we found that the concentration of MSYR decreased, whereas the concentrations of SYR, MSYR-GA, and MSYR-S increased. By profiling with inhibitors and carboxylesterases (CES1, 2), we found that the conversion from MSYR to SYR was mediated by CES1. Lipopolysaccharide-stimulated RAW264.7 cells restored MSYR-GA to MSYR possibly by the secreted β-glucuronidase. All of the mice administered with leptosperin, MSYR, or manuka honey showed higher MSYR (13.84 ± 11.51, 14.29 ± 9.19, or 6.66 ± 2.30 nM) and SYR (1.85 ± 0.66, 6.01 ± 1.20, or 8.16 ± 3.10 nM) levels in the plasma compared with that of the vehicle controls (3.33 ± 1.45 (MSYR) and 1.85 ± 0.66 (SYR) nM). The findings of our study indicate that the unique metabolic pathways of these compounds may account for possible functionalities of manuka honey.

Bioactive Components and Antioxidant and Antibacterial Activities of Different Varieties of Honey: A Screening Prior to Clinical Application

This study assessed 16 different honey samples in order to select the best one for therapeutic purposes. First, a study of honey's main bioactive compounds was carried out. Then phenolic profiles were determined and specific compounds quantified using a HPLC system coupled to a mass spectrometer. Then, antioxidant activity, by three in vitro methods, and antibacterial activity against reference strains and clinical isolates were evaluated. Great variability among samples was observed regarding ascorbic acid (between 0.34 ± 0.00 and 75.8 ± 0.41 mg/100 g honey; p < 0.001), total phenolic compounds (between 23.1 ± 0.83 and 158 ± 5.37 mg/100 g honey; p < 0.001), and total flavonoid contents (between 1.65 ± 0.11 and 5.93 ± 0.21 mg/100 g honey; p < 0.001). Forty-nine different phenolic compounds were detected, but only 46 of them were quantified by HPLC. The concentration of phenolic compounds and the phenolic profiles varied widely among samples (between 1.06 ± 0.04 and 18.6 ± 0.73 mg/100 g honey; p < 0.001). Antioxidant activity also varied significantly among the samples. All honey varieties exhibited antibacterial activity against both reference and clinical strains (effective concentrations ranged between 0.05 and 0.40 g/mL depending on the honey sample and bacteria tested). Overall, samples with better combinations of bioactive properties were avocado and chestnut honeys.

A green triple-locked strategy based on volatile-compound imaging, chemometrics, and markers to discriminate winter honey and sapium honey using headspace gas chromatography-ion mobility spectrometry

A simple and environmentally approach using untargeted imaging of volatile substances combined with chemometrics and markers response was proposed for discriminating different species of honey with headspace gas-chromatography-ion-mobility (HS-GC-IMS). The 3D HS-GC-IMS imaging and their response differences enabled the clear discrimination between winter honey and sapium honey. Principal component analysis (PCA) and partial least-squares discrimination analysis (PLS-DA) were employed to discriminate different honey. Markers of two kinds of honey were identified and confirmed with a user-built imaging database combined with multivariate analysis. Benzaldehyde dimer and phenylacetaldehyde dimer were found to be reliable markers of winter honey, and phenylethyl acetate dimer was of sapium honey. Adulteration identification of the honey samples with different adulteration ratios were subjected to this triple-locked strategy analysis. The results demonstrate that HS-GC-IMS imaging coupled with chemometrics and marker identification is a useful triple-locked strategy to discriminate honey from different floral origins and adulterated honey.

Antibacterial activity of Manuka honey and its components: An overview

The importance of honey for medicinal purposes is well documented in some of the world's oldest literature. Honey is well known and studied for its antimicrobial properties. The medicinal properties in honey originate from the floral source used by bees. Manuka honey is a dark monofloral honey rich in phenolic content, and currently it is gaining much attention for its antimicrobial activity. Researchers have found that honey is effective against a wide range of pathogens. The antibacterial potency of Manuka honey was found to be related to the Unique Manuka Factor (UMF) rating, which is correlated with the methylglyoxal and total phenols content. It is reported that different types of Manuka honey have differing effects and Gram-negative bacteria are more resistant than Gram-positive bacteria. Bacterial resistance to honey as antimicrobial agent has yet to be identified, possibly due to the presence of a complex mixture of methylglyoxal and other components. Honey is also reported to alter a bacterium's shape and size through septal ring alteration, which affects cell morphology and growth. Research has shown that Manuka honey of different UMF values has medicinal properties of interest and it can be beneficial when used as a combination treatment with other antimicrobial agents.

Authentication of Romanian honeys based on physicochemical properties, texture and chemometric

The purpose of this study was to investigate the physico-chemical properties (free acidity, pH, a_w, ash content, moisture content, color (L*, a*, b*, hue-angle, chroma and yellow index), fructose, glucose and sucrose content) and textural parameters (viscosity, hardness, adhesion, springiness, cohesiveness, chewiness and gumminess) of 50 samples of honey of different botanical origin (acacia, polyfloral, honeydew, sunflower and tilia). In order to achieve the authentication of the honey samples analyzed, their data have been subjected to linear discriminant analysis (LDA) and principal component analysis (PCA).The PCA and LDA have proved the possibility of honey authentication using the physico-chemical and textural properties. LDA classified correctly 92.0% of the honeys based on their botanical origin, using the cross validation. In the LDA projection, the textural parameters (chewiness, hardness, cohesiveness, springiness) dominated the two functions.

New approach: Chemical and fluorescence profiling of NZ honeys

New Zealand manuka (Leptospermum scoparium) and kanuka (Kunzea ericoides) honeys contain a unique array of chemical markers useful for chemical fingerprinting. We investigated the presence of 13 potential marker compounds in nectars of the major honey crop species. We confirmed that leptosperin, lepteridine, 2'-methoxyacetophenone, and 2-methoxybenzoic acid are exclusive to manuka nectar whereas lumichrome is unique to kanuka nectar. 3-Phenyllactic acid and 4-hydroxyphenyllactic acid are present in manuka and kanuka nectars. Leptosperin, lepteridine, 3-phenyllactic acid, and 4-hydroxyphenyllactic acid are chemically stable over prolonged storage, but not 2-methoxybenzoic acid and 2'-methoxyacetophenone. Accordingly, leptosperin and lepteridine are definitive chemical markers for authentication of manuka honey. An optimal concentration cut-off was established for the floral source-specific markers: leptosperin (94mg/kg), lepteridine (2.1mg/kg), 2'-methoxyacetophenone (2.0mg/kg) for manuka honey, and lumichrome (4.5mg/kg) for kanuka honey. The use of leptosperin and lepteridine as fluorescence markers for manuka honey authentication is reinforced.

Characterization of a Monoclonal Antibody against Syringate Derivatives: Application of Immunochemical Detection of Methyl Syringate in Honey

Syringic acid is one of the key skeletal structures of plant-derived chemicals. The derivatives of syringic acid have certain biological functions. In this study, a monoclonal antibody to syringic acid-based phytochemicals was prepared and characterized. The obtained antibody reacted with methyl syringate, syringic acid, and leonurine. Methyl syringate is a characteristic compound found in manuka honey, other honey varieties, and plants. Manuka honey was fractionated using HPLC, and the reactivity of the fractions with the antibody was examined. The antibody reacted with the fraction in which methyl syringate was eluted. The amount of methyl syringate in honeys as estimated by ELISA using the antibody had a good linearity compared with that estimated by HPLC. These results suggest that the antibody is applicable for the immunochemical detection of syringic acid derivatives in plants and foods.

Neutrophil myeloperoxidase and its substrates: formation of specific markers and reactive compounds during inflammation

Myeloperoxidase is an inflammatory enzyme that generates reactive hypochlorous acid in the presence of hydrogen peroxide and chloride ion. However, this enzyme also uses bromide ion or thiocyanate as a substrate to form hypobromous or hypothiocyanous acid, respectively. These species play important roles in host defense against the invasion of microorganisms. In contrast, these enzyme products modify biomolecules in hosts during excess inflammation, indicating that the action of myeloperoxidase is both beneficial and harmful. Myeloperoxidase uses other endogenous compounds, such as serotonin, urate, and l-tyrosine, as substrates. This broad-range specificity may have some biological implications. Target molecules of this enzyme and its products vary, including low-molecular weight thiols, proteins, nucleic acids, and lipids. The modified products represent biomarkers of myeloperoxidase action. Moderate inhibition of this enzyme might be critical for the prevention/modulation of excess, uncontrolled inflammatory events. Some phytochemicals inhibit myeloperoxidase, which might explain the reductive effect caused by the intake of vegetables and fruits on cardiovascular diseases.

Fluorescence markers in some New Zealand honeys

The fluorescence characteristics of various New Zealand honeys were investigated to establish if this technique might detect signatures unique to manuka (Leptospermum scoparium) and kanuka (Kunzea ericoides) honeys. We found unique fluorescence profiles for these honeys which distinguished them from other New Zealand honey floral types. Two excitation-emission (ex-em) marker wavelengths each for manuka and kanuka honeys were identified; manuka honey at 270-365 (MM1) and 330-470 (MM2) nm and kanuka honey at 275-305 (KM1) and 445-525 (KM2) nm. Dilution of manuka and kanuka honeys with other honey types that did not possess these fluorescence profiles resulted in a proportional reduction in fluorescence signal of the honeys at the marker wavelengths. By comparison, rewarewa (Knightia excelsa), kamahi (Weinmannia racemosa), and clover (Trifolium spp.) honeys did not exhibit unique fluorescence patterns. These findings suggests that a fluorescence-based screening approach has potential utility for determining the monoflorality status of manuka and kanuka honeys.

Immunochemical authentication of manuka honey using a monoclonal antibody specific to a glycoside of methyl syringate

Leptosperin, a novel glycoside of methyl syringate, is exclusively present in manuka honey derived from the Leptospermum species Leptospermum scoparium. Quantification of leptosperin might thus be applicable for authentication of honey. The concentration of leptosperin has high linearity with antibacterial activity. We established a monoclonal antibody to leptosperin and characterized the antibody in detail by a competitive enzyme-linked immunosorbent assay (ELISA), comparing the results with those of the high-performance liquid chromatography (HPLC) method for validation. The antigen in manuka honey was confirmed as leptosperin by HPLC fractionation with quantitation by an ELISA. Leptosperin contents of 50 honey samples were analyzed by an established ELISA, which can handle 20 samples (duplicate) on one 96-well plate. Significant coincidence with the chemical quantitation was observed. Immunochemical quantitation of leptosperin would be an economical and facile method for the possible authentication of manuka honey, allowing many honey samples to be processed and analyzed by an ELISA simultaneously.