Heat Stress Mitigation by Haematococcus lacustris Extract: Evidence from HaCaT Keratinocytes and Caenorhabditis elegans

Rising temperatures and the occurrence of heat waves due to climate change can increase the risk of various skin disorders. Moreover, elevated temperatures worsen oxidative damage and inflammation caused by other climate change stressors, such as UV exposure. Consequently, there is growing interest in innovative solutions to protect skin health from the effects of pollution and climate change stressors. Among natural cosmeceuticals, carotenoids are recognized for their antioxidant and anti-inflammatory properties. This study evaluated the thermoprotective effects of Hematococcus lacustris (the microalga formerly called Hematococcus pluvialis) extract (HLE), which is considered the richest natural source of carotenoid astaxanthin, against acute hyperthermia, which mimics the conditions of heat waves. In addition, we separately assessed the effects of HLE against UVA and hydrogen peroxide stress, complementing the antioxidant profile of the extract under study. The evaluation was conducted using in vitro tests on human HaCaT keratinocytes and the nematode Caenorhabditis elegans, which is a model organism sensitive to environmental stressors. The treatment of HaCaT keratinocytes with HLE counteracted the intracellular formation of reactive oxygen species and cytotoxicity induced by hyperthermia, UVA, and hydrogen peroxide exposure. Under the same experimental conditions, HLE also restored the impaired expression of stress-sensitive genes, such as matrix metalloproteinase-1, in HaCaT keratinocytes and promoted wound closure mimicking the process of re-epithelization. Lastly, experiments in C. elegans confirm that HLE reduces heat stress-induced oxidative damage and preserves motility, supporting a systemic protective effect consistent with dietary uptake of the extract. These findings suggest that HLE, rich in carotenoid astaxanthin, can protect keratinocytes against oxidative damage and cytotoxicity induced by thermal stress, indicating its potential role in mitigating thermal aging.