# The In Vitro Antioxidant and Immunomodulatory Effects of the Irish Monofloral Ivy and Heather Honey Varieties

## TL;DR

This study explores the antioxidant and immune-modulating effects of two types of Irish honey, finding they may help reduce oxidative stress and influence immune responses.

## Contribution

The study is the first to investigate the bioactive properties of Irish ivy and heather honey on immune cells in vitro.

## Key findings

- Heather honey had the highest total phenolic content, while ivy honey activated Nrf2, a key antioxidant regulator.
- Both honey types upregulated antioxidant enzymes and modulated pro- and anti-inflammatory cytokines.
- Manuka honey showed the strongest radical scavenging activity compared to the Irish varieties.

## Abstract

Honey has long been valued for its medicinal properties, yet the therapeutic potential of Irish monofloral honey remains largely unexplored. This study investigates the antioxidant and immunomodulatory effects of Irish ivy (Hedera helix) and heather (Calluna vulgaris) honey samples on PMA-differentiated THP-1 macrophages, a well-characterised immune model. Antioxidant capacity was assessed through free radical scavenging assays, DPPH and ORAC, while qPCR analysis examined the key inflammatory markers. Both the heather and ivy honey varieties demonstrated antioxidant activity, with heather honey exhibiting the highest total phenolic content (TPC), and ivy honey stimulating Nrf2 activation. Manuka honey showed the strongest radical scavenging capacity, as reflected in its higher ORAC and DPPH values. These findings suggest that the different honey varieties may exert antioxidant effects through distinct mechanisms. Exposure to honey reduced oxidative stress and upregulated the expression of a key antioxidant transcription regulator (Nrf2) and an associated downstream antioxidant defence enzyme, superoxide dismutase (SOD). Additionally, both the honey types exhibited immunomodulatory effects, upregulating pro-inflammatory cytokines, such as TNF-α and IL-1β, while increasing the expression of the anti-inflammatory cytokine IL-10. These findings suggest potential bioactive properties that warrant further investigation. Given the growing interest in alternative treatments for inflammation-related conditions, further research is warranted to determine whether the observed in vitro effects translate into clinically relevant outcomes. This study expands the current understanding of Irish monofloral honey, reinforcing its potential as a functional bioactive compound with relevance in antioxidant therapies, immune modulation, and wound healing.