Cytotoxic activity of strawberry tree ( Arbutus unedo L.) honey, its extract, and homogentisic acid on CAL 27, HepG2, and Caco-2 cell lines

Arh Hig Rada Toksikol. 2022 Jul 7;73(2):158-168. doi: 10.2478/aiht-2022-73-3653.

Abstract

Strawberry tree (Arbutus unedo L.) honey (STH), also known as "bitter honey", is a traditional medicine widely used in the Mediterranean area. Regardless of geographical origin, it usually has a very high content of phenolic compounds and strong antioxidant capacity. Yet, little is still known about the effects of STH, its phenolic extract (STHE), and its main bioactive compound - homogentisic acid (HGA) - at the cell level. The aim of this study was to estimate total phenolic content, DPPH radical scavenging activity, and ferric reducing antioxidant power of STH made in Croatia and investigate cytotoxic and pro-oxidative effects of STH, STHE and HGA on three human cell lines: tongue squamous cell carcinoma (CAL 27), hepatocellular carcinoma (HepG2), and epithelial colorectal adenocarcinoma cells (Caco-2) cells. These substances were tested at four concentrations (0.5-5× average human daily intake of STH) and over 30 min and 1 and 2 h. Croatian STH had a total phenolic content of 1.67 g gallic acid equivalents (GAE) per kg of honey, DPPH radical scavenging activity of 2.96 mmol Trolox equivalents (TE) per kg of honey, and ferric reducing antioxidant power (FRAP) of 13.5 mmol Fe2+ per kg of honey. Our results show no clear and consistent time- or concentration-dependent cytotoxicity in any of the cell lines. ROS levels in all the three cell types at almost all exposure times were not significantly higher than control. The most important observation is that the tested substances have low cytotoxicity and high biocompatibility, regardless of concentration, which is a good starting point for further research of their biological effects in other models.

Med obične planike (Arbutus unedo L.) (STH), poznat kao “gorki med”, tradicionalno se koristi u narodnoj medicini na sredozemnom području. Bez obzira na zemljopisno podrijetlo, obično ima vrlo visok udio fenolnih spojeva i snažan antioksidacijski kapacitet. Ipak, još uvijek se malo zna o učincima STH-a, njegova ekstrakta (STHE), kao i dominantnoga fenolnog spoja – homogentizinske kiseline (HGA) – na staničnoj razini. Cilj ovoga istraživanja bio je utvrditi ukupni sadržaj fenola, antioksidacijski kapacitet metodom DPPH i FRAP u STH-u, proizvedenome u Hrvatskoj, te ispitati citotoksične i prooksidacijske učinke STH-a, STHE-a i HGA-e na tri ljudske stanične linije: karcinoma pločastih stanica jezika (CAL 27), hepatocelularnoga karcinoma jetre (HepG2) i adenokarcinoma epitela debelog crijeva (Caco-2). STH, STHE i HGA ispitani su u četirima koncentracijama (0,5–5× prosječni dnevni unos STH-a u ljudi) i tijekom 30 minuta te tijekom jednog i dva sata. Hrvatski STH imao je visok ukupan sadržaj fenola (1,67 g ekvivalenata galne kiseline po kg meda i snažan antioksidacijski kapacitet (2,96 mmol Trolox ekvivalenata po kg meda i 13,5 mmol Fe2+ po kg meda). Dobiveni rezultati ne pokazuju jasnu i dosljednu citotoksičnost, ovisno o vremenu ili koncentraciji, ni u jednoj staničnoj liniji. Razine reaktivnih kisikovih vrsta u svim trima tipovima stanica u gotovo svim vremenima izlaganja nisu bile značajno veće od kontrole. Najvažnije je zapažanje da ispitivane tvari imaju nisku citotoksičnost i visoku biokompatibilnost, bez obzira na koncentraciju, što je dobra polazna točka za daljnja istraživanja njihovih bioloških učinaka na drugim modelima.

Keywords: adenokarcinom debelog crijeva; cell viability; colon adenocarcinoma; fenoli; hepatocellular carcinoma; hepatocelularni karcinom jetre; human cell lines; karcinom pločastih stanica jezika; ljudske stanične linije; phenols; preživljenje; reactive oxygen species; reaktivne kisikove vrste; tongue adenosquamous carcinoma.

MeSH terms

  • Antineoplastic Agents* / pharmacology
  • Antioxidants / pharmacology
  • Biphenyl Compounds
  • Caco-2 Cells
  • Carcinoma, Hepatocellular
  • Carcinoma, Squamous Cell
  • Chromans
  • Colorectal Neoplasms
  • Ericaceae* / chemistry
  • Gallic Acid
  • Hep G2 Cells
  • Homogentisic Acid* / pharmacology
  • Honey*
  • Humans
  • Iron / chemistry
  • Liver Neoplasms
  • Phenols / pharmacology
  • Picrates
  • Plant Extracts* / pharmacology
  • Reactive Oxygen Species
  • Tongue Neoplasms
  • Trees / chemistry

Substances

  • Antineoplastic Agents
  • Antioxidants
  • Biphenyl Compounds
  • Chromans
  • Phenols
  • Picrates
  • Plant Extracts
  • Reactive Oxygen Species
  • Gallic Acid
  • 1,1-diphenyl-2-picrylhydrazyl
  • Iron
  • Homogentisic Acid
  • 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid