Ageing is a spontaneous and inevitable biological process. One well-studied theories is cellular ageing, which arises from intrinsic factors within the cell. Cellular ageing refers to the gradual decline in cellular function over time and is closely associated with the accumulation of molecular damage. A key contributor to this process is oxidative stress, primarily driven by free radicals [1].

Free radicals are chemical species with an unpaired electron that are generally very reactive [2]. In recent years, scientific research has shown that superoxide anion (O₂⁻) free radicals are among the primary contributors to the ageing process. These highly reactive molecules are natural byproducts of metabolic processes, such as mitochondrial respiration, enzymatic reactions, and immune responses, particularly during mitochondrial electron transport [3]. When excess O₂⁻ is produced or inadequately neutralised by the body's antioxidant defences, O₂⁻ can oxidise and cause significant damage to cellular molecules, including DNA, proteins, and lipids [4]. This oxidative stress causes the gradual decline of cellular function, contributing to tissue ageing and the development of age-related diseases such as cancer, cardiovascular disorders, and neurodegenerative conditions [5].

Superoxide dismutase (SOD) and catalase (CAT) are essential antioxidant enzymes that play a critical role in protecting cells from oxidative damage caused by reactive oxygen species (ROS), such as O₂⁻. SOD catalyses the disproportionation reaction of O₂⁻ into hydrogen peroxide (H₂O₂) and oxygen (O₂). Although H₂O₂ is less reactive than O₂⁻, it can still be harmful at high concentrations by inducing oxidative stress. Catalase then rapidly converts hydrogen peroxide into water and oxygen, thereby preventing the accumulation of hydrogen peroxide and reducing the risk of oxidative damage to cellular components such as DNA, proteins, and lipids [6,7]. Together, SOD and CAT form a defence system against oxidative stress and contribute to maintaining cellular homeostasis.

Fig. 1 The catalytic reactions of SOD and CAT enzymes within the superoxide anion body

The skin, as the largest and most externally exposed organ of the human body, is continuously subjected to a wide range of internal and external environmental stressors. Consequently, skin aging remains one of the most prominent concerns in dermatological and cosmetic research. Among various functional cosmetic ingredients, anti-aging agents are widely recognized as among the most technologically advanced and scientifically complex. For cosmetic enterprises, developing highly effective anti-aging solutions—supported by superior active ingredients and innovative formulation technologies—represents a critical area of investigation. Addressing skin aging through an understanding of its underlying mechanisms and root causes constitutes a fundamental strategy. Among the prevailing theories of aging, the free radical theory stands out as one of the most influential. In 1990, Professor Sohal, a leading authority in aging research in the United States, formally introduced the concept of oxidative stress, proposing that an imbalance between oxidative and antioxidant processes in the body leads to excessive accumulation of reactive oxygen species (ROS), which serves as a primary driver of the aging process. Therefore, reducing excess ROS through multiple intervention strategies has become a widely adopted approach in anti-aging skincare [8].

1. Natural enzyme extraction: Superoxide dismutase (SOD) and catalase (CAT) are isolated and purified from animal and plant sources, such as earthworms and microalgae. However, this method is associated with low yield and poor stability, which limit its scalability and long-term application.

2. Nanozyme technology: Nanomaterials based on metal–organic frameworks (MOFs), such as AuNPs@MOF, have been developed to mimic the dual enzymatic activities of SOD and CAT. While these nanozymes exhibit promising catalytic performance in vitro, their biological safety remains a concern due to potential cytotoxicity, limited biodegradability, and unclear long-term effects in vivo.

3. Traditional fermentation: Recombinant SOD and CAT can be produced using microbial expression systems, such as Escherichia coli. Despite its industrial potential, this approach faces several challenges, including low enzymatic activity, inconsistent expression levels, and high costs associated with downstream purification processes.

Therefore, our research project addresses the prevalent issue of skin aging in contemporary society by developing anti-aging cosmetic formulations based on the SOD-CAT enzymatic cascade system. We systematically investigate the application of composite enzymes in cosmetics through gene sequence optimization, comprehensive antioxidant activity assessments from multiple perspectives, and stability evaluation under relevant conditions. Furthermore, a deeper understanding of the role of superoxide anion radicals in the aging process is expected to make a significant contribution to anti-aging research, particularly in the development of targeted antioxidant therapies and lifestyle interventions designed to minimize oxidative damage.