Wednesday 16 February 2011

Manuka honey - Wikipedia, the free encyclopedia

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Manuka Honey Bush (Leptospermum scoparium)

Manuka honey is a kind of honey claimed to have anti-bacterial properties. It has been known to benefit humans by healing wounds and injuries but causes no damage to cells. It is made by bees in New Zealand that frequent the manuka bush, Leptospermum scoparium.

Contents

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Origin

Manuka honey is gathered in New Zealand from bees feeding on the manuka bush, Leptospermum scoparium, which grows uncultivated throughout the country and has antibacterial properties. However, its antimicrobial activity varies with origin and processing. A survey of 345 samples of New Zealand honeys from 26 different floral sources found a large number with low activity (36% of the samples had activity near or below the level of detection in an agar diffusion assay), the activity of the rest being distributed over a 30-fold range of activity. An unpublished survey of 340 samples of Australian honeys from 78 different floral sources found 68.5% of the samples had activity below the level of detection in an agar diffusion assay.[1][Full citation needed]

Antibacterial properties of Manuka honey

Honey has been used for treating infected wounds for at least two millennia. In c.50 AD, Dioscorides once described honey as being "good for all rotten and hollow ulcers".[cite this quote] Medical science has established that honey has an inhibitory effect to around 60 species of bacteria including aerobes and anaerobes, gram-positives and gram-negatives.[citation needed] 2009 studies in Scotland show that Manuka may be the next step to fighting MRSA (Methicillin-resistant Staphylococcus aureus).[2]

Manuka honey, like other honeys, has an antibacterial property due to the release of hydrogen peroxide which can kill bacteria. Unique to the Leptospermum species of plants, honeys made from these plants contain other non-peroxide compounds with anti-bacterial properties.[3][dubious – discuss]

Hydrogen peroxide activity

Hydrogen peroxide is a well-known antimicrobial agent, initially hailed for its antibacterial and cleansing properties when it was first introduced into clinical practice. In more recent times, it has lost favour because of inflammation and damage to tissue. However, the hydrogen peroxide concentration produced in honey activated by dilution is typically around 1 mmol/l, about 1000 times less than in the 3% solution commonly used as an antiseptic. The harmful effects of hydrogen peroxide are further reduced because honey contains antioxidants which inactivates the free ion catalyzing the formation of oxygen free radicals produced by hydrogen peroxide. Studies in animal models[citation needed] have demonstrated that honey reduces inflammation (seen histologically), compared with various controls, in deep and superficial burns and in full-thickness wounds.

Formation of Hydrogen Peroxide from oxygen free radicals

Although the level of hydrogen peroxide in honey is very low, it is still effective as an antimicrobial agent. It has been reported that hydrogen peroxide is more effective when supplied by continuous generation with glucose oxidase than when added in isolation. A study with Escherichia coli exposed to a constantly replenished stream of hydrogen peroxide, showed that bacterial growth was inhibited by 0.02-0.05 mmol/l hydrogen peroxide, a concentration that was not damaging to fibroblast cells from human skin.[citation needed]

Methyglyoxal

Methylglyoxal

Methylglyoxal, also called pyruvaldehyde or 2-oxopropanal (CH3-CO-CH=O) is the aldehyde form of pyruvic acid. Methylglyoxal is both an aldehyde and a ketone. Methylglyoxal in manuka honey has been shown to originate from dihydroxyacetone, which is present in the nectar of manuka flowers. Manuka honey, which has just been produced, contains low levels of methylglyoxal and high levels of dihydroxyacetone. Storage of these honeys at 37 °C led to a decrease in the dihydroxyacetone content and a related increase in methylglyoxal.

In some honeys treated with catalase to remove the hydrogen peroxide activity, an additional non-peroxide antibacterial factor has been identified. Manuka (Leptospermum scoparium) honey from New Zealand has been found to have substantial levels of non-peroxide antibacterial activity. It is now known that this non-peroxide activity is due to the action of methylglyoxal (MGO). Although very low levels of MGO are found in most honey, the high level of MGO in manuka honey is unique. High levels of methylglyoxal in manuka honey is directly related to its antibacterial property. The non-peroxide antibacterial activity of manuka honey is stable, thus manuka honey does not lose its antibacterial potency when stored for long periods. The non-peroxide antibacterial activity of manuka honey diffuses deeper into skin tissues than hydrogen peroxide. It is also more effective than honey with hydrogen peroxide against some types of bacteria. For example, it is about twice as effective as other honey against Escherichia coli and Enterococci, common causes of infection in wounds.[citation needed]

Methylglyoxal’s antibacterial properties stem from its electrophilic properties; methylglyoxal is believed to attack the nucleophilic centres of the cell’s DNA molecule, possibly changing or destroying the DNA molecule, rending the cell unable to produce new proteins leading to a breakdown of the cell. Cells are able to deal with small quantities of methylglyoxal by metabolising them; methylglyoxal reacts with glutathione forming a hemithioacetal. This is converted into S-D-lactoyl-glutathione by glyoxalase I and then further metabolised into D-lactate by glyoxalase II.[citation needed]

Anti-bacterial ratings

An agar-well diffusion assay is conducted on the bacteria Staphylococcus aureus to test the methylglyoxal’s anti-bacterial activities. Firstly, two wells are created in an agar plate and Staphylococcus aureus are scraped onto each well using an inoculating needle. After soaking small squares of blotter paper with methylglyoxal and phenol solution separately into the wells, each square is set in different ends of the agar plate using forceps and then left upside down in the refrigerator for a few days. After that, a comparison between the size and shape of the bacterial colonies is made to determine the anti-bacterial activities between the two. Varying concentration of phenol solution is used to find one that coincides with the antibacterial potency of the methylglyoxal. This can allow fair comparison with UMF and MGO ratings and determine its accuracy.[4][Full citation needed]

Unique Manuka Factor (UMF)

The UMF or unique manuka factor is a rating system that measures the non-hydrogen peroxide antibacterial potency of manuka honey. The system has a range from 0 to 30 but typical manuka honey has a rating of 10 or more. The higher the UMF rating is, the higher the anti-bacterial activities are. The UMF rating of manuka honey is determined by measuring the antibacterial activity of a given honey with the antibacterial activity of antiseptic phenol, also known as carbolic acid, at various concentrations. Hydrogen peroxide must first be eliminated using the enzyme catalase so that only the non-peroxide compound is measured. The species of bacteria used is Staphylococcus aureus, also known as Golden Staph or Hospital Superbug, a strain of bacteria that poses a huge threat to people.[5] It has a developed antibiotic resistance to penicillins including methicillin, oxacillin, amoxicillin and other antibiotics, and only manuka honey has been known to naturally destroy these bacteria. Thus, Staphylococcus aureus it is commonly used in testing of manuka honey’s antibacterial activity. The numbers are proportional to the potency of a certain percentage of phenol. For example, a UMF rating of 10 is the same as having an antibacterial potency of 10% of phenol solution.

The UMF Ratings (measure of antibacterial strength):

  • 0-4: Not detectable
  • 5-9: Maintenance levels only (similar to table honey and not recommended for special therapeutic use)
  • 10-15: Useful levels endorsed by the Honey Research Unit at The University of Waikato[citation needed]
  • 16 and over: Superior levels with very high activity.

Methylglyoxal (MGO) rating

According to some manuka honey manufacturers, the UMF system is unreliable. The ratings are made by the Active Manuka Honey Association (AMHA), which compares a batch of honey against the bacteria-killing ability of different concentrations of a standard disinfectant. Another way proposed to measure the effectiveness of manuka honey would be by measuring methylglyoxal (MGO) content. This compound is found in high concentrations in manuka honey – up to 100 times greater than ordinary honey – according to German researchers[who?], and is thought to give it its antiseptic edge. The minimum concentration of MGO in honey necessary to kill major bacteria types is found to be 100 mg/kg, having an equivalent antibacterial rating of 10%. As MGO is the compound directly responsible for the antibacterial activities, MGO rating is said to be a more accurate form of rating for Manuka honey.[by whom?]

Extraction of MGO by HPLC

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High Pressure Liquid Chromatography

The main processes involved in the extraction of methylglyoxal are Reverse Phase High Performance Liquid Chromatography (RP-HPLC), coupled with ultraviolet (UV) detection. RP-HPLC separates molecules based on the differences in their hydrophobicity. In this case, methyglyoxal (MGO) is separated from samples of manuka honey through this process.[6] Manuka honey samples of a certain UMF rating are first dissolved in HPLC grade water with catalase solution. Then, they will be treated with Ortho-Phenylenediamine (OPD) in phosphate buffer, which will react with the 1,2 dicarbonyl compounds to form corresponding quinoxaline derivatives. After which, these constituents of the analyte mixture are passed by a high-pressure pump in an organic solvent called the mobile-phase over stationary-phase particles with pores large enough for them to enter into the HPLC column. Organic solvent like acetonotrile or methanol is used because it decreases the mobile phase polarity and thus reduces the hydrophobic interaction between the solutes and the stationary phase, promoting de-sorption. During this process, the interactions between the solutes and the hydrophobic surface of the stationary phase remove the constituents from the flowing mobile-phase stream which can be recycled for another use again. As the concentration of organic solvent in the eluant increases, it reaches a critical value for each constituent which results in their de-sorptions from the hydrophobic stationary-phase surface, allowing it to elute from the column in the flowing mobile phase. Since this elution depends on the precise distribution of hydrophobic residues in each species, each constituent elutes from the column at a characteristic time, and the resulting peak can be used to confirm its identity and quantify it.[7]

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Structure of Agar Jelly- Agarose Polymer and Agaropectin

After methyglyoxal is extracted, an agar well-diffusion assay will be conducted on the bacteria mentioned earlier, Staphylococcus aureus, to test the methylglyoxal’s anti-bacterial activities. The agar well-diffusion assay aims to detect the growth of bacteria colonies by their appearances and sizes as well as the rate at which certain inhibitors and anti-bacterial properties can slow down their growth. The steps of this experimentation are as follows. Firstly, two wells are created in an agar plate and Staphylococcus aureus are scraped onto each well using an inoculating needle. After soaking small squares of blotter paper with methylglyoxal and phenol solution separately into the wells and labeling them respectively, each square is set in different ends of the agar plate using a forceps and then left upside down in the refrigerator for a few days. After that, a comparison between the size and shape of the bacterial colonies is made to determine the anti-bacterial activities between the two. Varying concentration of phenol solution will be experimented to find one that coincides with the antibacterial potency of the methylglyoxal. This can allow fair comparison with UMF rating and determination of its accuracy. For example, if the UMF rating for the honey samples is 10, and the anti-bacterial activity of the methylglyoxal coincides with either more or less than 10% of antiseptic phenol, then it can be concluded that the UMF rating is not accurate as the anti-bacterial strength of manuka honey varies, but if they are the same, then it means that the rating system is accurate.

Other functions of MGO

Besides being the main constituent for anti-bacterial properties for manuka honey, Methyglyoxal is also found to be involved in the formation of advanced glycation end products (AGE) by reacting with free amino groups of lysine and arginine. If immune cells are unable to detoxify the highly reactive methylglyoxal that is formed during cellular metabolism of sugars, amino acids, and fatty acids, it will result in a reduced Glo1 (Glyoxalase 1) activity which causes the accumulation of AGE. Research has also shown that heat shock protein 27 is actually a specific target of posttranslational modification by methylglyoxal in human metastatic melanoma cells and this process caused an in cell-sensitization to anti-tumor apoptosis.[citation needed]

See also

Notes

  1. ^ Peter Charles Molan (Dec 2001); Honey as a topical antibacterial agent for treatment of infected wounds
  2. ^ Ker Than. How Honey Curbs the MRSA Superbug, National Geographic News, 8 September 2009.
  3. ^ Methylglyoxal in Manuka Honey – Correlation with Antibacterial Properties, http://benefitofmanukahoney.com/2010/07/methylglyoxal-in-manuka-honey-–-correlation-with-antibacterial-properties/
  4. ^ Elvira Mavric, Silvia Wittmann, Gerold Barth, Thomas Henle, (21 Jan 2008), Identification and Quantification of Methylglyoxal as the Dominant Antibacterial Constituent of Manuka Honey
  5. ^ Methicillin Resistant Staph Auereus, ManukaHoneyUSA website: http://www.manukahoneyusa.com/mrsa.htm
  6. ^ Christopher. J. Adams, Cherie H. Boulta, Benjamin J. Deadman, Judie M. Farra, Megan N.C. Grainger, Merilyn Manley-Harris and Melanie J. Snow, Chemistry Department, University of Waikato ; Isolation by HPLC and Characterization of the Bioactive Fraction of Manuka Honey (Leptospermum scoparium) from New Zealand
  7. ^ Andrew Guzzetta. (July 22, 2001). Reverse Phase HPLC Basics for LC/MS. Ionsource Tutorial website: http://www.ionsource.com/tutorial/chromatography/rphplc.htm

External links

  • Christopher J. Adams, Merilyn Manley-Harris, Peter C. Molan, 2009, The origin of methylglyoxal in New Zealand manuka (Leptospermum scoparium) honey
  • Koichi Inoue, Shiho Murayama, Fumie Seshimo, Kazue Takeba, Yoshihiro Yoshimura and Hiroyuki Nakazawa, 2005, Identification of phenolic compound in manuka honey as specific superoxide anion radical scavenger using electron spin resonance (ESR) and liquid chromatography with coulometric array detection

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