Personal Care Magazine: Developing Efficient Probiotics in Ageing

Article originally published in Personal Care November 2024 Issue

With ageing a growing concern for many populations around the world, researchers in the personal care industry are constantly trying to understand how to solve age-related skin problems including wrinkles, pigmentation, and dryness. The gut-skin axis has been identified as an important bidirectional relationship between the gut microbiome and skin health, with recent studies suggesting that the gut microbiome can influence skin health. The dysregulation of the microbiome has been seen in numerous inflammatory skin conditions such as atopic dermatitis, rosacea, and psoriasis. Understanding how the gut microbiome is involved in regulating skin health may lead to development of treatments for these skin disorders through microbiome adjustment.

Improving skin health through probiotics is becoming a popular concept and by regulating skin health and gut–skin axis interactions, probiotics have the potential to be used as tools to suppress and improve skin diseases in multiple ways.

Benefits of probiotics

Maintaining general health is a key challenge for an ageing population, therefore, understanding whether probiotics can help as we get older is vital. The International Scientific Association for Probiotics and Prebiotics defines probiotics as “live microorganisms that, when administered in adequate amounts, confer a health benefit on the host”. Probiotics have been shown in clinical trials to have positive effects on various health outputs including digestive health, skin health, weight management and dental health.

Probiotics are measured in colony forming units (CFU) which represents the number of alive and active microorganisms (bacteria, fungi, viruses etc) in one serving of a probiotic dietary supplement. CFU is the mark that many consumers use as a guide to purchase probiotics, with many probiotic supplements containing 1 to 10 billion CFU per dose and some containing up to 50 billion CFU. However, higher CFU counts do not necessarily improve the product’s health effects. Taking more probiotics or products with a higher CFU might mean that there is a larger amount in the gastrointestinal tract but proving that there is a better positive health response with higher CFU is challenging.

While the emphasis on CFU in probiotic products is evident, it also highlights a broader issue: the general lack of consumer awareness regarding the distinctions between different bacterial strains. Despite the varied impacts of these strains, as demonstrated in clinical trials, the understanding of their biology and the mechanisms of interactions with the host is lacking.

Many clinical studies are performed to determine the success of probiotics. While these studies are necessary to show that a strain provides a beneficial effect, they do not develop an understanding of why the bacterial strain works.

Testing probiotic formulas and ethical testing alternatives

Due to an increasing number of skin-related health problems and diseases being linked to ageing, methods to identify probiotics that can help in such cases are urgently required. Manufacturers of probiotics and postbiotics are investing heavily in novel methods that allow for efficient, high-throughput and identification of formulations that can help human and animal health.

Preclinical evaluation of probiotic strains adheres to a stringent three-step process; the first of which involves in-depth characterisation of the bacterial strain. This includes both phenotypic and genotypic methods to ensure accurate classification and distinguish it from potentially harmful bacteria. Then the comprehensive safety assessment takes place which considers the strain’s history of safe use, its antibiotic resistance profile, and potential for causing harm through in vitro and in vivo models. Finally, efficacy testing investigates the strain’s functional characteristics and potential health benefits using in vitro assays and animal models relevant to the proposed health claim.

However, the European Union (EU) implemented a ban on testing cosmetics on animals and on selling cosmetics tested on animals in 2009, this has meant that the personal care industry has had to find alternatives to test that products are safe and effective.

In vitro assays are typically used to screen potential bacterial strains and to establish basic biological mechanism. They are designed with components of cells that have been isolated to monitor biochemical and functional reactions to determine the impact of probiotics. An in vitro model of the human gut helps compensate for the limitations of animal models in studying the human gut–microbiome interaction and are crucial in the clarification of the mechanism of microbial action or in the high-throughput screening and functional evaluation of probiotics. While useful as a precursor to predict the viability of a probiotic, the isolated assay cannot evaluate the safety of the product on other organs, for example skin, over the long term.

Utilising Caenorhabditis elegans (C. elegans), a small nematode worm, which can be cultured in conjunction with specific bacterial strains, offers insights into specific age-related outcomes of exposure to probiotics in the gut-skin axis. The worm can be used to measure how probiotics improve gut health and provides the perfect bridge between animal models and cell models. As an invertebrate, C. elegans offers a sustainable option for testing products, consuming less energy, water, and resources than rodents. In addition, C. elegans is a more ethical model as it encounters no regulatory or ethical restrictions. C. elegans studies can significantly enrich and compliment data from other models and in vitro experiments.

Microscopic nematodes as a model for discovery

C. elegans is a free-living nematode that feeds on bacteria in rotting vegetation. Through the extensive achievements of research groups across the world, C. elegans has become a powerful model system to study diverse aspects of biology such as programmed cell death, gene silencing, and neuronal function among others, while also being the first model organism in which single gene mutations are found that slowed ageing, and thereby has become powerful model for ageing studies. It has emerged to be extremely useful for nutraceutical discoveries.

C. elegans is a great model for whole organism physiology meaning interactions taking place between different organs or the gut-skin axis can be monitored. Researchers can look at movement, gut integrity, and metabolic health, as well as a cuticle formed from an epidermal layer that mirrors several functions of human skin. The integrity of the cuticle can be monitored as the worms age to see if probiotics have the desired beneficial effects.

Due to the worm’s short yet well-defined life cycle of three days and short lifespan of around three weeks, it is very well suited to study the biology of ageing and testing age-related skin problems. C. elegans is inexpensive to maintain, grows rapidly, and is genetically uniform, making it an excellent choice for large-scale experiments. In addition, large test populations can be used, addressing the heterogeneous nature of ageing. Researchers can deliver ageing data within a couple of weeks versus several months. In vivo data with functional endpoints can be provided in just fourteen days to de-risk probiotic compound development and accelerate research. This approach helps the transition from in vitro studies to human studies, by testing probiotics earlier in a whole organism, without regulatory requirements.

Benefits of using C. elegans in probiotic research

The worm’s translatability to humans, with up to 60-80 percent gene homology with cell types and organs found in humans, enables rational predictions of what could happen in humans treated with the same probiotic product. Importantly, C. elegans can be associated with a single strain of bacteria, making it straightforward to assess the effects of a single probiotic strain on development, movement, and ageing.

Furthermore, genetic manipulation in both C. elegans and the bacterial strain can provide valuable insights into the underlying mechanisms. Targeted mutations of genes in either the worm or the bacteria can be used to explore specific pathways potentially modulated by the probiotic. This approach can identify key genes and functions essential for the probiotic’s efficacy.

Once a specific probiotic strain’s efficacy is linked to the genes responsible for a particular function, researchers can leverage this knowledge to efficiently screen and identify other promising strains with similar genetic composition. This targeted screening strategy streamlines the identification of potentially efficacious probiotic candidates and can speed up research. C. elegans can serve as a powerful screening tool for identifying novel probiotic strains with specific functionalities. The rapid life cycle and ease of manipulation in C. elegans enables researchers to efficiently evaluate large bacterial libraries for their potential health benefits. This approach can accelerate the discovery and development of new probiotic products addressing various skin-related health concerns.

C. elegans opens new perspectives in developing assays to investigate the cytotoxicity of new bioactive molecules or microbial pathogenicity and host defence mechanisms and gives new strategies to understand the mode of action (specific chemical, virulence factor). C. elegans allows a microorganism to be assessed in a whole animal with an integrated point of view, considering the gene expression using transcriptomic and proteomic approaches as well as metabolomics and physiology of the entire organism. While the bacterial communities that can colonise the C. elegans digestive tract contain a smaller number relative to humans, this feature enables the comprehensive study of simplified mock communities to understand the foundational mechanisms that govern host–microbe interactions.

C. elegans offers a highly controlled and reproducible experimental system. Its short life cycle, well-defined anatomy, and ease of cultivation allow for consistent results across replicate experiments. This is particularly advantageous in probiotic research, where complex interactions between the host and numerous microbial factors can occur. The standardized nature of the C. elegans model minimizes variables, facilitating robust and reliable data generation.

Using C. elegans in practice

The short life cycle of C. elegans means that research can be done on ageing very quickly and by testing the bioactive ingredients of natural products, researchers can identify the effectiveness and mechanisms of action in products.

The genetics of C. elegans combined with the genetics in the probiotic strain can be used to understand which genes are important for positive effects on health. A study used C. elegans to identify the mechanism of a probiotic strain that suppresses age-dependent neurodegeneration. The data generated suggests that disrupted lipid metabolism contributes to neurodegeneration and that dietary intervention with Lacticaseibacillus rhamnosus HA-114 restores lipid homeostasis and energy balance through mitochondrial β-oxidation.

Another study investigated probiotic interventions affecting stress and longevity involving the potential therapeutic value of Lactococcus lactis and Leuconostoc mesenteroides isolated from organic basil using a C. elegans model. The results emphasised the potential probiotic applicability of these biomarkers for predicting early health responses.

To develop a model to understand skin ageing, a recent study developed two methods to assess C. elegans’ cuticle, which forms the barrier between the animal and its environment, and is formed from a layer of epidermal cells. It found that with age the cuticle stiffens and that collagen mutations alter the integrity of the cuticle by significantly changing its elasticity. Using this approach, probiotics that slow ageing can be assessed for their ability to maintain integrity of the C. elegans equivalent of skin.

Conclusion

As ageing becomes an ever-increasing problem around the world, age-related health issues are on the rise. There is growing evidence that there is an important relationship between the gut microbiome and skin health, with gut microbiome dysregulation a common symptom in many skin-related diseases. This has led to the nutraceutical industry developing treatments for age-related skin problems through the use of probiotics. To test those probiotics, there is a need for a more ethical and sustainable whole-body organism that can speed up time to result and help researchers fully understand the mode of action of bacterial strains.

C. elegans emerges as a powerful tool not only for probiotic development, but also for the creation of ingredients in pharmaceuticals and nutraceuticals. This tiny nematode worm has revolutionised biological understanding and streamlined product development. Its short lifespan, human gene homology, well-defined anatomy, and ease of cultivation makes it a popular assay choice to investigate the toxicity of new bioactive molecules or microbial pathogenicity in a whole organism. By facilitating the rapid elimination of early-stage risks, C. elegans saves companies significant time and resources. This translates to increased confidence moving into clinical trials, as researchers gain a deeper understanding of a probiotic’s mechanisms and expected benefits on the body and other organs including the skin.

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