Age-related decline in the taurine content of the skin in rodents

Investigation of the anti-skin aging effects of taurine through mendelian randomization analysis of its relationship with immune cells

BACKGROUND

Aging skin, exacerbated by external factors like UV radiation and pollutants, is a major cosmetic concern. Taurine, renowned for its antioxidant and anti-inflammatory properties, may combat skin aging. We performed mendelian randomization (MR) analysis to investigate the causal link between taurine and immune cells linked to skin aging.

OBJECTIVES

To investigate the association between taurine and immune cells using mendelian randomization, to thereby explore the mechanism through which taurine exerts anti-aging effects on the skin via immune modulation.

METHODS

A MR approach was employed using taurine-level data from the Ieu Open GWAS Project and immunocyte traits from a large European cohort. MR-Egger regression, weighted median estimation, and inverse variance weighting all provided statistical insights into causality. Sensitivity analyses assessed the heterogeneity and pleiotropy among the genetic instruments used.

RESULTS

MR analysis identified a causal relationship between taurine levels and 10 immunocyte phenotypes, with taurine found to be negatively and positively associated with three and seven phenotypes, respectively. Sensitivity analysis revealed no significant heterogeneity or pleiotropy, suggesting reliable MR findings.

CONCLUSION

This study provides insights into the immunological pathways by which taurine contributes to skin anti-aging effects, suggesting that increasing taurine levels could offer a novel strategy for anti-aging skincare.

Multifunctional Hydrogel Microneedle Patches Modulating Oxi-inflamm-aging for Diabetic Wound Healing

Oxidative stress, chronic inflammation, and immune senescence are important pathologic factors in diabetic wound nonhealing. This study loads taurine (Tau) into cerium dioxide (CeO2) to develop CeO2@Tau nanoparticles with excellent antioxidant, anti-inflammatory, and anti-aging properties. To enhance the drug penetration efficiency in wounds, CeO2@Tau is encapsulated in gelatin methacryloyl (GelMA) hydrogel to prepare CeO2@Tau@Hydrogel@Microneedle (CTH@MN) patch system. Microneedle technology achieves precise and efficient delivery of CeO2@Tau, ensuring their deep penetration into the wound tissue for optimal efficacy. Rigorous in vitro and in vivo tests have confirmed the satisfactory therapeutic effect of CTH@MN patch on diabetic wound healing. Mechanistically, CTH@MN attenuates oxidative damage and inflammatory responses in macrophages by inhibiting the ROS/NF-κB signaling pathway. Meanwhile, CTH@MN activated autophagy-mediated anti-aging activity, creating a favorable immune microenvironment for tissue repair. Notably, in a diabetic mouse wound model, the multifunctional CTH@MN patch significantly promotes wound healing by systematically regulating the oxidation-inflammation-aging (oxi-inflamm-aging) pathological axis. In conclusion, the in-depth exploration of the CTH@MN system in this study provides new strategies and perspectives for treating diabetic non-healing wounds.

Taurine and Polyphenol Complex Repaired Epidermal Keratinocyte Wounds by Regulating IL8 and TIMP2 Expression

The healing process after acne lesion extraction provides a miniature model to study skin wound repair mechanisms. In this study, we aimed to identify solutions for acne scars that frequently occur on our faces. We performed acne scar cytokine profiling and found that Interleukin 8 (IL8) and Tissue inhibitor of metalloproteinases 2 (TIMP2) were significant factors at the wounded site. The effect of chlorogenic acid and taurine on human epidermal cells and irritated human skin was investigated. Chlorogenic acid and taurine regulated IL8 and TIMP2 expression and accelerated keratinocyte proliferation. Moreover, tight junction protein expression was upregulated by chlorogenic acid and taurine synergistically. Further, these compounds modulated the expression of several inflammatory cytokines (IL1α, IL1β, and IL6) and skin hydration related factor (hyaluronan synthase 3; HAS3). Thus, chlorogenic acid and taurine may exert their effects during the late stages of wound healing rather than the initial phase. In vivo experiments using SLS-induced wounds demonstrated the efficacy of chlorogenic acid and taurine treatment compared to natural healing, reduced erythema, and restored barrier function. Skin ultrasound analysis revealed their potential to promote denser skin recovery. Therefore, the wound-restoring effect of chlorogenic acid and taurine was exerted by suppression of inflammatory cytokines, and induction of cell proliferation, tight junction expression, and remodeling factors.

Subcellular one carbon metabolism in cancer, aging and epigenetics

The crosstalk between metabolism and epigenetics is an emerging field that is gaining importance in different areas such as cancer and aging, where changes in metabolism significantly impacts the cellular epigenome, in turn dictating changes in chromatin as an adaptive mechanism to bring back metabolic homeostasis. A key metabolic pathway influencing an organism's epigenetic state is one-carbon metabolism (OCM), which includes the folate and methionine cycles. Together, these cycles generate S-adenosylmethionine (SAM), the universal methyl donor essential for DNA and histone methylation. SAM serves as the sole methyl group donor for DNA and histone methyltransferases, making it a crucial metabolite for chromatin modifications. In this review, we will discuss how SAM and its byproduct, S-adenosylhomocysteine (SAH), along with the enzymes and cofactors involved in OCM, may function in the different cellular compartments, particularly in the nucleus, to directly regulate the epigenome in aging and cancer.

Taurine deficiency associated with dilated cardiomyopathy and aging

Taurine (2-aminoethanesulfonic acid) is a free amino acid found ubiquitously and abundantly in mammalian tissues. Taurine content in the heart is approximately 20 mM, which is approximately 100 times higher than plasma concentration. The high intracellular concentration of taurine is maintained by the taurine transporter (TauT; Slc6a6). Taurine plays various roles, including the regulation of intracellular ion dynamics, calcium handling, and acting as an antioxidant in the heart. Some species, such as cats and foxes, have low taurine biosynthetic capacity, and dietary taurine deficiency can lead to disorders such as dilated cardiomyopathy and blindness. In humans, the relationship between dietary taurine deficiency and cardiomyopathy is not yet clear, but a genetic mutation related to the taurine transporter has been reported to be associated with dilated cardiomyopathy. On the other hand, many studies have shown an association between dietary taurine intake and age-related diseases. Notably, it has recently been reported that taurine declines with age and is associated with lifespan in worms and mice, as well as healthspan in mice and monkeys. In this review, we summarize the role of dietary and genetic taurine deficiency in the development of cardiomyopathy and aging.

Functions and Metabolism of Amino Acids in the Hair and Skin of Dogs and Cats

The hair and skin of domestic cats or dogs account for 2% and 12-24% of their body weight, respectively, depending on breed and age. These connective tissues contain protein as the major constituent and provide the first line of defense against external pathogens and toxins. Maintenance of the skin and hair in smooth and elastic states requires special nutritional support, particularly an adequate provision of amino acids (AAs). Keratin (rich in cysteine, serine and glycine) is the major protein both in the epidermis of the skin and in the hair. Filaggrin [rich in some AAs (e.g., serine, glutamate, glutamine, glycine, arginine, and histidine)] is another physiologically important protein in the epidermis of the skin. Collagen and elastin (rich in glycine and proline plus 4-hydroxyproline) are the predominant proteins in the dermis and hypodermis of the skin. Taurine and 4-hydroxyproline are abundant free AAs in the skin of dogs and cats, and 4-hydroxyproline is also an abundant free AA in their hair. The epidermis of the skin synthesizes melanin (the pigment in the skin and hair) from tyrosine and produces trans-urocanate from histidine. Qualitative requirements for proteinogenic AAs are similar between cats and dogs but not identical. Both animal species require the same AAs to nourish the hair and skin but the amounts differ. Other factors (e.g., breeds, coat color, and age) may affect the requirements of cats or dogs for nutrients. The development of a healthy coat, especially a black coat, as well as healthy skin critically depends on AAs [particularly arginine, glycine, histidine, proline, 4-hydroxyproline, and serine, sulfur AAs (methionine, cysteine, and taurine), phenylalanine, and tyrosine] and creatine. Although there are a myriad of studies on AA nutrition in cats and dogs, there is still much to learn about how each AA affects the growth, development and maintenance of the hair and skin. Animal-sourced foodstuffs (e.g., feather meal and poultry by-product meal) are excellent sources of the AAs that are crucial to maintain the normal structure and health of the skin and hair in dogs and cats.

Taurine accelerates the synthesis of ceramides and hyaluronic acid in cultured epidermis and dermal fibroblasts

Taurine is a sulfur-containing amino acid derivative that can be found in the majority of mammalian tissues. Taurine is also present in the skin and is involved in maintaining skin homeostasis by exerting osmoregulatory and antioxidant effects. Previous studies have indicated that taurine treatment is effective against age-, ultraviolet- or detergent-induced skin dysfunction. To determine the mechanism responsible for the beneficial actions of taurine in the skin, the present study aimed to evaluate the effects of taurine on epidermal components (ceramides and filaggrin) and on the dermal extracellular matrix, in three-dimensionally (3D) cultured epidermis and dermal fibroblasts, respectively. These cells were cultured in the presence of 3-50 mM taurine, and cells or culture medium were collected for analysis. The effects of taurine on transepidermal water loss (TEWL) in the skin and the expression of inflammatory cytokines, including IL-1α, IL-1β and IL-1 receptor antagonist, were investigated in acetone-treated 3D-cultured epidermis using a Tewameter and reverse transcription-quantitative PCR (RT-qPCR), respectively. The mRNA expression levels of MMP-1 and hyaluronic acid (HA) production were measured in skin dermal fibroblasts using RT-qPCR and ELISA, respectively. Taurine was found to suppress acetone-induced elevation in TEWL in 3D-cultured epidermis. Taurine also stimulated the mRNA expression of ceramide synthase 4 and filaggrin, a major structural protein in the stratum corneum, in 3D-cultured epidermis. In skin dermal fibroblasts, taurine inhibited the IL-1α-stimulated mRNA and protein expression of MMP-1. In addition, taurine treatment increased HA synthase-2 mRNA expression and in turn HA production. Results from the present study suggest that the protective effect of taurine on the skin is associated with the enhancement of epidermal barrier component expression and modulation of dermal extracellular matrix metabolism.

Taurine deficiency as a driver of aging

Aging is associated with changes in circulating levels of various molecules, some of which remain undefined. We find that concentrations of circulating taurine decline with aging in mice, monkeys, and humans. A reversal of this decline through taurine supplementation increased the health span (the period of healthy living) and life span in mice and health span in monkeys. Mechanistically, taurine reduced cellular senescence, protected against telomerase deficiency, suppressed mitochondrial dysfunction, decreased DNA damage, and attenuated inflammaging. In humans, lower taurine concentrations correlated with several age-related diseases and taurine concentrations increased after acute endurance exercise. Thus, taurine deficiency may be a driver of aging because its reversal increases health span in worms, rodents, and primates and life span in worms and rodents. Clinical trials in humans seem warranted to test whether taurine deficiency might drive aging in humans.

Taurine rescues pancreatic β-cell stress by stimulating α-cell transdifferentiation

The semi-essential ubiquitous amino acid taurine has been shown to alleviate obesity and hyperglycemia in humans; however, the pathways underlying the antidiabetic actions have not been characterized. We explored the effect of chronic taurine exposure on cell biology of pancreatic islets, in degenerative type 1-like diabetes. The latter was modeled by small dose of streptozotocin (STZ) injection for 5 days in mice, followed by a 10-day administration of taurine (2% w/v, orally) in the drinking water. Taurine treatment opposed the detrimental changes in islet morphology and β-/α-cell ratio, induced by STZ diabetes, coincidentally with a significant 3.9 ± 0.7-fold enhancement of proliferation and 40 ± 5% reduction of apoptosis in β-cells. In line with these findings, the treatment counteracted an upregulation of antioxidant (Sod1, Sod2, Cat, Gpx1) and downregulation of islet expansion (Ngn3, Itgb1) genes induced by STZ, in a pancreatic β-cell line. At the same time, taurine enhanced the transdifferentiation of α-cells into β-cells by 2.3 ± 0.8-fold, echoed in strong non-metabolic elevation of cytosolic Ca²⁺ levels in pancreatic α-cells. Our data suggest a bimodal effect of dietary taurine on islet β-cell biology, which combines the augmentation of α-/β-cell transdifferentiation with downregulation of apoptosis. The dualism of action, stemming presumably from the intra- and extracellular modality of the signal, is likely to explain the antidiabetic potential of taurine supplementation.

Protective effect of taurine on UVB-induced skin aging in hairless mice

Taurine, a sulfur-containing amino acid derivative, exists at a high concentration in the skin and is considered to play an important role in maintaining moisture homeostasis. This study investigated the effects of oral taurine supplementation on epidermal moisture content and wrinkle formation, as well as skin taurine content, using ultraviolet B (UVB)-irradiated hairless mice. Wrinkles were induced by exposing hairless mice to UVB radiation (70-100 mJ/cm²). Taurine was dissolved in drinking water at a concentration of 0.3 or 3% (w/v) and given to the mice ad libitum for 2-10 weeks. Taurine was then extracted from the dorsal skin, and the skin taurine content was determined using high-performance liquid chromatography (HPLC). The wrinkles were evaluated using a wrinkle score and the quantitative wrinkle area ratio. The exposure of the mice to UVB radiation for 4 weeks resulted in a decreased moisture content and increased transepidermal water loss (TEWL) in the skin, while taurine supplementation suppressed these changes. Oral supplementation with taurine for 8 weeks ameliorated the development of UVB-induced wrinkle formation. Furthermore, oral taurine supplementation for 4 weeks decreased pre-stablished wrinkles in a dose-dependent manner. Although the UVB radiation reduced the epidermal taurine content, oral taurine supplementation partly restored the taurine content in the epidermis. The present study showed that oral taurine supplementation is able to suppress UVB-induced wrinkle formation, which may be associated with the regulation of moisture content in the epidermis. The beneficial effects of taurine on skin aging may be attributed to its osmoregulatory role.