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Publications and Student Theses

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Comvita are committed to helping people live healthier, happier and more vibrant lives through natural products which are backed by science.

Comvita, in conjunction with our research collaborators, have published our research in many peer-reviewed journals. Our research supports the efficacy of our natural ingredients, as well as using science to better understand and harness our natural ingredients.

Below is a list of currently available journal articles and student theses titles. Scientific research is an ongoing priority at Comvita and we currently have several research projects underway.

Honey Research

Phenolic compounds and methylglyoxal in some New Zealand Manuka and Kanuka honeysFood Chemistry, Volume 120, Issue 1, pages 78-86, 1 May 2010.

Abstract:

The principal phenolic compounds and methylglyoxal were analysed in New Zealand Leptospermum scoparium (manuka) and Kunzea ericoides (kanuka) honeys. These honeys shared six phenolic acids as primary components and differentiation was possible as relative proportions varied. Manuka honey contained an elevated concentration of a trimethoxybenzoic acid and methylglyoxal; and 2-methoxybenzoic acid and methylglyoxal concentrations were linearly correlated in fresh manuka honey. Kanuka honey contained an elevated concentration of methoxyphenyllactic acid. The concentration of the phenolic components increased with maturation in both honey types; and this profile development, along with a corresponding increase of methylglyoxal concentration, was linear in manuka honey. Nectar analysed from the plant species contained the same phenolic components as the honeys. These results demonstrated the phenolic profile could be used to differentiate the honey types, heat treatment of honey could be identified, and the presence of these components may contribute to the efficacy of these honeys in therapeutic uses.

Isolation and characterisation of arabinogalactan-proteins from New Zealand kanuka honey.Food Chemistry, Volume 128, Issue 4, Pages 949-956, 15 October 2011.

Abstract: Fractionation of manuka, kanuka and clover honeys indicated the >10 kDa fraction contained small amounts of type II arabinogalactans (AGs), which are often present as arabinogalactan proteins (AGPs). AGPs were isolated from the >10 kDa fraction of kanuka honey using β-glucosyl Yariv reagent and their composition and structure analysed. Constituent sugar, glycosyl linkage and NMR spectroscopy analysis of the purified AGP fraction revealed a predominance of neutral sugars, mainly galactose and arabinose, linked in a highly-branched structure typical of type II AGs. The molecular weight of the major component of the purified AGPs was ∼110 kDa, as determined by size-exclusion chromatography-multi-angle laser light scattering (SEC-MALLS). The Yariv supernatant fraction contained less total sugar, especially galactose, and more protein than purified AGPs. Linkage analysis indicated this fraction also contained an AG-type polymer in addition to various other polysaccharides and SEC-MALLS indicated the molecular weight of the major component was ∼32 kDa.

Arabinogalactan proteins contribute to the immunostimulatory properties of New Zealand honeys. Immunopharmacology and Immunotoxicology, 34(4):598-607, August 2012.

Abstract: Context: Factors in honey that improve wound healing are poorly understood, but are thought to include lipopolysaccharide (LPS), apalbumin-1 and -2, and a 5.8 kDa component that stimulate cytokine release from macrophages. Objective: To characterize the ability of New Zealand honeys to elicit the release of tumor necrosis factor-α (TNF-α) from monocytic cell lines as a model for early events within a wound site. Materials and methods: The ability of kanuka (Kunzea ericoides), manuka (Leptospermum scoparium), and clover (Trifolium spp.) honeys to stimulate the release of TNF-α from monocytic cell lines THP-1 and U937 was assayed by ELISA. Results: All three honeys stimulated TNF-α release from THP-1 cells, with kanuka honey being the most active. The activity of kanuka honey was associated with a high molecular weight (>30 kDa) component that was partially heat labile and inhibitable with polymyxin B. LPS concentrations in the honeys were too low to adequately explain the level of immunostimulation. The contribution of type II arabinogalactan proteins (AGPs) we recently identified in kanuka honey was tested, as AGPs are known immunostimulators. AGPs purified from kanuka honey stimulated the release of TNF-α from THP-1 and U937 cells. Discussion: Here we demonstrated that AGPs we recently identified in kanuka honey have immunostimulatory activity. We propose that the immunostimulatory properties of individual honeys relate to their particular content of LPS, apalbumins, the 5.8 kDa component and AGPs. Conclusion: The immunostimulatory activity of kanuka honey may be particularly dependent on AGPs derived from the nectar of kanuka flowers.

The effect of New Zealand kanuka, manuka and clover honeys on bacterial growth dynamics and cellular morphology varies according to the species. PLOS ONE, February 2013.

Abstract: Treatment of chronic wounds is becoming increasingly difficult due to antibiotic resistance. Complex natural products with antimicrobial activity, such as honey, are now under the spotlight as alternative treatments to antibiotics. Several studies have shown honey to have broad-spectrum antibacterial activity at concentrations present in honey dressings, and resistance to honey has not been attainable in the laboratory. However not all honeys are the same and few studies have used honey that is well defined both in geographic and chemical terms. Here we have used a range of concentrations of clover honey and a suite of manuka and kanuka honeys from known geographical locations, and for which the floral source and concentration of methylglyoxal and hydrogen peroxide potential were defined, to determine their effect on growth and cellular morphology of four bacteria: Bacillus subtilis, Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa. While the general trend in effectiveness of growth inhibition was manuka>manuka-kanuka blend>kanuka>clover, the honeys had varying and diverse effects on the growth and cellular morphology of each bacterium, and each organism had a unique response profile to these honeys. P. aeruginosashowed a markedly different pattern of growth inhibition to the other three organisms when treated with sub-inhibitory concentrations of honey, being equally sensitive to all honeys, including clover, and the least sensitive to honey overall. While hydrogen peroxide potential contributed to the antibacterial activity of the manuka and kanuka honeys, it was never essential for complete growth inhibition. Cell morphology analysis also showed a varied and diverse set of responses to the honeys that included cell length changes, cell lysis, and alterations to DNA appearance. These changes are likely to reflect the different regulatory circuits of the organisms that are activated by the stress of honey treatment.

Honeybee apisimin and plant arabinogalactans in honey costimulate monocytes. Food Chemistry, Volume 168, pages 34-40 July 2014

Abstract: Here we determined whether immunostimulatory plant-derived arabinogalactan proteins (AGPs) and the honeybee-derived protein apisimin are present in varieties of New Zealand honey. Apisimin is a protein of unknown function secreted from the glands of honeybees into Royal Jelly, forming a complex with apalbumin1 capable of stimulating lymphocyte proliferation. AGPs were abundant in kanuka honey with lesser amounts in manuka, kowhai and clover honeys, but absent from Royal Jelly. Apisimin was present in all honeys, as well as Royal Jelly. We report that apisimin shares with honey AGPs the ability to stimulate the release of TNF-α from blood monocytes. Further, it synergizes with AGPs to enhance the release of TNF-α, via a mechanism not involving the formation of a complex with AGPs. In summary, this study provides evidence that AGPs and apisimin are commonly present in different floral varieties of honey, and hence contribute to their immunostimulatory properties.

Student Theses

  • Investigation of the immunostimulatory effects of some New Zealand honeys and characterization of an active component (Master of Technology in Food Technology at Massey University), Swapna Gannabathula, June 2010.
  • Antimicrobial effect of Manuka honey and kanuka honey alone and in combination with the bio-actives against the growth of Propionibacterium acnes ATCC 6919 (Master of Technology in Food Technology at Massey University), Qiong Wu, June 2011.
  • Interaction of Manuka honey derived phenolic compounds with natural beeswax (Diploma of Food Processing and Biotechnology at Berlin Institute for Technology and Food Chemistry), Jennifer Kuehne, December 2011.
  • Fluorescence screening of indigenous New Zealand Honeys (Master of Biological Sciences at The University of Auckland), Jessie Bong Nee Jan, July 2012.
  • The inhibitory effects of polyphenolic compounds from a range of natural products against selected enzymes (Master of Science at The University of Auckland), Bin Lin, July 2013.
  • Profiling and quantification of immunostimulatory compounds in different types of honey(Master of Science at The University of Auckland), Alex George Anthony Samy, July 2014
  • Characterisation of the in vitro antioxidant properties of therapeutic honeys of the world(Bachelor of Science, Honours at The University of Auckland), Jeffry Sutanto Tang, November 2013

Olive Leaf Extract Research

Olive (Olea europaea L.) Leaf Polyphenols Improve Insulin Sensitivity in Middle-Aged Overweight Men: A Randomized, Placebo-Controlled, Crossover Trial. PLOS ONE, March 2013.

Abstract: Background: Olive plant leaves (Olea europaea L.) have been used for centuries in folk medicine to treat diabetes, but there are very limited data examining the effects of olive polyphenols on glucose homeostasis in humans. Objective: To assess the effects of supplementation with olive leaf polyphenols (51.1 mg oleuropein, 9.7 mg hydroxytyrosol per day) on insulin action and cardiovascular risk factors in middle-aged overweight men. Design: Randomized, double-blinded, placebo-controlled, crossover trial in New Zealand. 46 participants (aged 46.4±5.5 years and BMI 28.0±2.0 kg/m2) were randomized to receive capsules with olive leaf extract (OLE) or placebo for 12 weeks, crossing over to other treatment after a 6-week washout. Primary outcome was insulin sensitivity (Matsuda method). Secondary outcomes included glucose and insulin profiles, cytokines, lipid profile, body composition, 24-hour ambulatory blood pressure, and carotid intima-media thickness. Results: Treatment evaluations were based on the intention-to-treat principle. All participants took >96% of prescribed capsules. OLE supplementation was associated with a 15% improvement in insulin sensitivity (p = 0.024) compared to placebo. There was also a 28% improvement in pancreatic β-cell responsiveness (p = 0.013). OLE supplementation also led to increased fasting interleukin-6 (p = 0.014), IGFBP-1 (p = 0.024), and IGFBP-2 (p = 0.015) concentrations. There were however, no effects on interleukin-8, TNF-α, ultra-sensitive CRP, lipid profile, ambulatory blood pressure, body composition, carotid intima-media thickness, or liver function. Conclusions: Supplementation with olive leaf polyphenols for 12 weeks significantly improved insulin sensitivity and pancreatic β-cell secretory capacity in overweight middle-aged men at risk of developing the metabolic syndrome. Trial Registration: Australian New Zealand Clinical Trials Registry #336317.

Human absorption and metabolism of oleuropein and hydroxytyrosol ingested as olive (Olea europaea L.) leaf extract. Molecular Nutrition and Food Research, April 2013.

Abstract: Phenolic compounds derived from the olive plant (Olea europaea L.), particularly hydroxytyrosol and oleuropein, have many beneficial effects in vitro. Olive leaves are the richest source of olive phenolic compounds, and olive leaf extract (OLE) is now a popular nutraceutical taken either as liquid or capsules. To quantify the bioavailability and metabolism of oleuropein and hydroxytyrosol when taken as OLE, nine volunteers (five males) aged 42.8 ± 7.4 years were randomized to receive either capsulated or liquid OLE as a single lower (51.1 mg oleuropein, 9.7 mg hydroxytyrosol) or higher (76.6 mg oleuropein, 14.5 mg hydroxytyrosol) dose, and then the opposite strength (but same formulation) a week later. Plasma and urine samples were collected at fixed intervals for 24 h post-ingestion. Phenolic content was analyzed by LC-ESI-MS/MS. Conjugated metabolites of hydroxytyrosol were the primary metabolites recovered in plasma and urine after OLE ingestion. Peak oleuropein concentrations in plasma were greater following ingestion of liquid than capsule preparations (0.47 versus 2.74 ng/mL; p = 0.004), but no such effect was observed for peak concentrations of conjugated (sulfated and glucuronidated) hydroxytyrosol (p = 0.94). However, the latter peak was reached earlier with liquid preparation (93 versus 64 min; p = 0.031). There was a gender effect on the bioavailability of phenolic compounds, with males displaying greater plasma area under the curve for conjugated hydroxytyrosol (11,600 versus 2550 ng/mL; p = 0.048). All conjugated hydroxytyrosol metabolites were recovered in the urine within 8 h. There was wide inter-individual variation. OLE effectively delivers oleuropein and hydroxytrosol metabolites to plasma in humans.

Secoiridoids delivered as olive leaf extract induce acute improvements in human vascular function and reduction of an inflammatory cytokine: a randomised, double-blind, placebo-controlled, cross-over trial. British Journal of Nutrition, June 2015 http://dx.doi.org/10.1017/S0007114515001269

Abstract: The leaves of the olive plant (Olea europaea) are rich in polyphenols, of which oleuropein and hydroxytyrosol (HT) are most characteristic. Such polyphenols have been demonstrated to favourably modify a variety of cardiovascular risk factors. The aim of the present intervention was to investigate the influence of olive leaf extract (OLE) on vascular function and inflammation in a postprandial setting and to link physiological outcomes with absorbed phenolics. A randomised, double-blind, placebo-controlled, cross-over, acute intervention trial was conducted with eighteen healthy volunteers (nine male, nine female), who consumed either OLE (51 mg oleuropein; 10 mg HT), or a matched control (separated by a 4-week wash out) on a single occasion. Vascular function was measured by digital volume pulse (DVP), while blood collected at baseline, 1, 3 and 6 h was cultured for 24 h in the presence of lipopolysaccharide in order to investigate effects on cytokine production. Urine was analysed for phenolic metabolites by HPLC. DVP-stiffness index and ex vivo IL-8 production were significantly reduced (P,0·05) after consumption of OLE compared to the control. These effects were accompanied by the excretion of several phenolic metabolites, namely HT and oleuropein derivatives, which peaked in urine after 8–24 h. The present study provides the first evidence that OLE positively modulates vascular function and IL-8 production in vivo, adding to growing evidence that olive phenolics could be beneficial for health.

Impact of phenolic-rich olive leaf extract on blood pressure, plasma lipids and inflammatory markers: a randomised controlled trial. European Journal of Nutrition, March 2016.

Abstract: PURPOSE: Dietary polyphenols have been demonstrated to favourably modify a number of cardiovascular risk markers such as blood pressure (BP), endothelial function and plasma lipids. We conducted a randomised, double-blind, controlled, crossover trial to investigate the effects of a phenolic-rich olive leaf extract (OLE) on BP and a number of associated vascular and metabolic measures. METHODS: A total of 60 pre-hypertensive [systolic blood pressure (SBP): 121-140 mmHg; diastolic blood pressure (DBP): 81-90 mmHg] males [mean age 45 (±SD 12.7 years, BMI 26.7 (±3.21) kg/m2] consumed either OLE (136 mg oleuropein; 6 mg hydroxytyrosol) or a polyphenol-free control daily for 6 weeks before switching to the alternate arm after a 4-week washout. RESULTS: Daytime [-3.95 (±SD 11.48) mmHg, p = 0.027] and 24-h SBP [-3.33 (±SD 10.81) mmHg, p = 0.045] and daytime and 24-h DBP [-3.00 (±SD 8.54) mmHg, p = 0.025; -2.42 (±SD 7.61) mmHg, p = 0.039] were all significantly lower following OLE intake, relative to the control. Reductions in plasma total cholesterol [-0.32 (±SD 0.70) mmol/L, p = 0.002], LDL cholesterol [-0.19 (±SD 0.56) mmol/L, p = 0.017] and triglycerides [-0.18 (±SD 0.48), p = 0.008] were also induced by OLE compared to control, whilst a reduction in interleukin-8 [-0.63 (±SD 1.13) pg/ml; p = 0.026] was also detected. Other markers of inflammation, vascular function and glucose metabolism were not affected. CONCLUSION: Our data support previous research, suggesting that OLE intake engenders hypotensive and lipid-lowering effects in vivo. Student Theses • Olive leaf phenolics and cardiovascular risk reduction (Doctoral thesis at the University of Reading, UK), Stacey Lockyer, 2014   Other Research Areas

Abstract: Nutritional genomics reflects gene/nutrient interactions, utilising high-throughput genomic tools in nutrition research. The field also considers the contribution of individual genotypes to wellness and the risk of chronic disease (nutrigenetics), and how such genetic predisposition may be modified by appropriate diets. For example, high consumption of brassicaceous vegetables, including broccoli, has regularly associated with low cancer risk. Bioactive chemicals in broccoli include glucosinolates, plant pigments including kaempferol, quercetin, lutein and carotenoids, various vitamins, minerals and amino acids. Cancer prevention is hypothesised to act through various mechanisms including modulation of xenobiotic metabolising enzymes, NF-E2 p45-related factor-2 (Nrf2)-mediated stress-response mechanisms, and protection against genomic instability. Broccoli and broccoli extracts also regulate the progression of cancer through anti-inflammatory effects, effects on signal transduction, epigenetic effects and modulation of the colonic microflora. Human intervention studies with broccoli and related foods, using standard biomarker methodologies, reveal part of a complex picture. Nutrigenomic approaches, especially transcriptomics, enable simultaneous study of various signalling pathways and networks. Phenotypic, genetic and/or metabolic stratification may identify individuals most likely to respond positively to foods or diets. Jointly, these technologies can provide proof of human efficacy, and may be essential to ensure effective market transfer and uptake of broccoli and related foods.

Student Theses

Studentship Programme

Student participation is a key part of Comvita’s research model. Several PhD and Masters students from various universities conduct science projects under the supervision of Comvita’s full-time researchers. For more information on studentship opportunities, visit HERE.

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