Medicinal honey for cholesterol homeostasis and the structure of delivery hydrogels

Huong, N 2019, Medicinal honey for cholesterol homeostasis and the structure of delivery hydrogels, Doctor of Philosophy (PhD), Science, RMIT University.

Document type: Thesis
Collection: Theses

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Title Medicinal honey for cholesterol homeostasis and the structure of delivery hydrogels
Author(s) Huong, N
Year 2019
Abstract Honey is a sweet reward of nature. Its composition is dominated by monosaccharides (70-80%), water (<20%), disaccharides and higher sugars (5-10%), and minor quantities of phenolic compounds, minerals, vitamins, enzymes and organic acids. Sugars govern its physicochemical properties and technological functions, while non-sugar components, mainly phenolic acids and flavonoids, impart health benefits and make it unique from other sweeteners. Interestingly, honey bees promote the transfer of phytochemicals from floral nectars into honey and make them concentrated in honey, thus, honey is not only an abundant source of antioxidants, but also a carrier of medicinal phytochemicals. Oxidative stress and hypercholesterolemia are detrimental factors in the pathogenesis of atherosclerosis, the leading cause of mortality worldwide. Although different strategies have been developed to combat them, finding an effective natural remedy targeting both is challenging. Accumulated evidence emphasizes the advantages of honey in attenuating such detrimental factors, however, little is known about its mode of action on oxidative damage and lipid metabolism at a molecular level.

Recently, the use of honey as a healthy food or a complementary medicine has attracted great attention. Considerable efforts have been made to incorporate honey into delivery systems including cryogels and hydrogels to enhance its nutraceutical values and overcome its physical limitations. To date, most investigations on the physicochemical properties of honey address its quality standards, whereas understanding structural characteristics and molecular interactions within a honey matrix or a honey-incorporated network is limited.

Therefore, this PhD research was conducted with primary aims to (i) validate the physicochemical quality of four newly developed medicinal honeys and elucidate their effect on some key biomarkers of oxidative stress and lipid metabolism, (ii) establish a concrete basis of structural characteristics of honey for technological applications in food biomedical industries, and (iii) develop a honey-gelatin template as a delivery system for honey's bio-functionality.

In the first experimental chapter, commercial manuka-1 honey with 400 mg/kg methylglyoxal (MGO 400+) and four medicinal honeys (arjuna, guggul, jiaogulan and olive) newly developed in The Pangenomics Laboratory were characterized for their physicochemical and biochemical characteristics. Data indicated that all medicinal honeys tested comply with international regulations for blossom honeys, except for olive honey having substandard content of monosaccharides (49.2%). Arjuna, guggul and olive honeys demonstrated outstanding values of phenolics, flavonoids, radical scavenging activity and antioxidant content. The results encouraged the subsequent examination of their effect on oxidative stress and cholesterol homeostasis in the fatty acid-induced HepG2 cell line. Although the stimulation of Nrf2 gene expression could not be captured for arjuna, guggul and olive honeys, all medicinal honeys up-regulated the expression of NQO1 gene that is associated with cellular defense pathways in a concentration dependent manner, of which higher transcriptional levels were recorded at 2.0%. Manuka-1, guggul honeys (both, 1.0 and 2.0%) and arjuna honey (2.0%) significantly reduced total cellular cholesterol (TC) in the cells. In contrast, jiaogulan and olive honeys did not decrease TC. The transcriptional levels of the tested genes associated with lipid metabolism (AMPKα, SREBP-2, HMGCR, LDLR, LXRα, PPARα) varied according to honey-type and concentration. Manuka and arjuna honeys showed a good agreement between the transcriptional levels of the tested genes and the reduction of TC. Guggul honey modulated genes and decreased TC but further research at various time points is required to elucidate the mechanism. Jiaogulan and olive honeys regulated the genes in a pattern that should lead to reduced TC, but this expectation did not occur, suggesting their ability to esterify free cholesterol into storage form. Although the medicinal honeys (2.0%) activated PPARα, cellular triglyceride content was not reduced upon combined treatment of fatty acids and honey to HepG2 cells.

In the second experimental chapter, a detailed profile of physicochemical and rheological properties of four blossom honeys (tulsi, alfalfa, manuka-1 and -2) were established. The honeys meet international quality regulations and contain high content of phenolics and flavonoids. Manuka-1 and tulsi honeys produce amorphous diffractograms, supported by flat micro DSC thermograms. In contrast, alfalfa and manuka-2 honeys exhibit multiple WAXD peaks that agree to endothermic transition recorded calorimetrically. Calorimetric and mechanical glass transition temperature (Tg) coincide for honey, indicating the dominant role of sugars in the metastable state of honey matrix. Finally, a good fit of modified Arrhenius and WLF equation allows the determination of free volume characteristics within glass transition state and values of activation energy required for molecular motions in the glassy state of the honeys tested.

In the last experimental chapter, molecular interactions and vitrification characteristics of a gelatin hydrogel in the present of manuka-1 honey (10-75%, w/w) were presented. Thermomechanical analyses exhibit a dramatic glass transition region when cooling samples to subzero temperatures. The implementation of synthetic polymer characterization approach pinpoints predicted mechanical Tg for high-solid hydrogels in comparison to calorimetric Tg. Partial replacement of water molecules within the hydrogels leads to stronger interactions of gelatin and honey moieties and creates amorphous systems which are significant for the development of functional foods and biomedical products. The study provides concrete background for further investigations on topical and oral delivery of bioactive compounds from honey-gelatin gels at controlled rates.

To summarize, physicochemical and biochemical characteristics of manuka-1, arjuna, guggul and olive honeys are presented here for the first time and support the development of medicinal honeys that combat oxidative stress and hypocholesterolemia. However, their chemical profiles and their effect on pathways associated with the risk factors need to be further studied to provide solid evidence for using the medicinal honeys in the management of such risks. Comprehensive profiles of viscoelastic and structural characteristics of the blossom honeys and honey-containing hydrogels were established as a concrete foundation to maintain optimal quality of medicinal honeys and develop delivery hydrogels of honey's bio-functionality. To make honey hydrogels closer to clinical availability, swelling and release study should be conducted for the kinetic control and targeted delivery of honey and/or its bioactive compounds.
Degree Doctor of Philosophy (PhD)
Institution RMIT University
School, Department or Centre Science
Subjects Food Chemistry and Molecular Gastronomy (excl. Wine)
Complementary and Alternative Medicine not elsewhere classified
Keyword(s) Honey
Structural properties
Gelatin hydrogels
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Created: Wed, 08 Apr 2020, 09:19:15 EST by Adam Rivett
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