Comparison of the Cytotoxic Mechanisms of Different Garlic (Allium sativum L.) Cultivars with the Crucial Involvement of Peroxisome Proliferator-Activated Receptor Gamma

Garlic (Allium sativum L.) is one of the oldest known useful plants, valued for thousands of years. This plant contains many biologically active compounds, including polyphenols, sterols, cysteine-sulfoxides, carbohydrates, proteins, and amino acids. The aim of our study was to compare the antioxidant potential, cytotoxicity, and apoptosis induction properties of four garlic cultivars—Harnaś, Ornak, Violeta, and Morado—in human squamous carcinoma (SCC-15) cells, colon adenocarcinoma (CACO-2) cells, and normal fibroblasts (BJ). Additionally, we investigated the mRNA and protein expression of peroxisome proliferator-activated receptor gamma (PPARγ), microtubule-associated protein 1 light chain 3 (LC3A), superoxide dismutase 1 (SOD1), and catalase (CAT) after treatment with the studied garlic extracts. Our study demonstrated that high ROS production was correlated with the strong toxicity of the garlic extracts. All studied extracts produced a lesser increase in ROS in normal BJ fibroblasts and were less toxic to these cells. The expression patterns of PPARγ, LC3A, SOD1, and CAT, along with chromatographic analysis, suggest differing mechanisms among the garlic cultivars. The highest levels of catechin, a known PPARγ agonist, were detected in the Harnaś (3.892 µg/mL) and Ornak (3.189 µg/mL) cultivars. A high catechin content was correlated with similar changes in PPARγ and related SOD1 and LC3A. Our findings showed the health-promoting and anticancer properties of garlic. However, we could not definitively identify which polyphenol or how it is involved in PPARγ activation. Further studies are required to elucidate the role of PPARγ in the mechanism of action of garlic extracts.