Protective effects of glycyrrhizin, a natural sweetener, against precocious puberty via gut microbiome

Background: Precocious puberty (PP) can result in various negative consequences. The standard treatment for this condition, involves the use of gonadotropin-releasing hormone agonist (GnRHa). However, this treatment option can be expensive and invasive. On another note, there has been a recent rise in the global use of non-nutritive sweeteners as substitutes for sugar. One such sweetener is glycyrrhizin, which is derived from natural sources and has shown several health benefits. Consequently, our project aims to explore whether oral glycyrrhizin can provide protective effects against PP in both humans and animals.
Methods: In our human study involving the Taiwan Puberty Longitudinal Study (TPLS) cohort, we enlisted 1823 children aged 6-17 from four hospitals in Taiwan. These participants were surveyed regarding their consumption of glycyrrhizin using a validated food frequency questionnaire. Additionally, we gathered baseline characteristics such as age, gender, level of physical activity, sleep quality score, total energy intake, and body mass index. We employed generalized linear models to examine the correlation between glycyrrhizin intake and the likelihood of PP. In the animal part of the study, we deliberately administered glycyrrhizin (in the form of monoammonium glycyrrhizinate – MAG) to rodents. We divided young female Sprague-Dawley rats into various groups: Control, Danazol, MAG, Danazol + Low-MAG (100 ug/kg/day), Danazol + Medium-MAG (200 ug/kg/day), and Danazol + High-MAG (400 ug/kg/day). A PP model was induced by injecting danazol on postnatal day (PND) 5, followed by MAG administration starting from PND 13. We monitored the timing of vaginal opening and collected stool samples for microbiome and short-chain fatty acid (SCFA) analyses. Furthermore, we harvested the hypothalamus to investigate the expression of puberty-related genes. To further explore the causal relationship between glycyrrhizin intake and PP risk, we conducted fecal microbiota transplantation (FMT).
Results: Consuming glycyrrhizin was linked to a reduced risk of PP in children, particularly girls, from the TPLS cohort following a dose-dependent manner. Furthermore, glycyrrhizin intake was associated with changes in the human gut microbiome. In the animal study, the administration of MAG led to a delay in the timing of vaginal opening, accompanied by lower levels of estradiol compared to the Danazol group. The long-term use of MAG was determined to be safe. Rats receiving medium and high doses of MAG exhibited significantly different beta diversity in their gut microbiome compared to the Danazol group. Additionally, MAG consumption, regardless of the amount, reduced the Firmicutes/Bacteroidetes ratio. Analysis using LEfSE identified the top enriched taxa in each group, many of which showed negative correlations with levels of SCFAs in stool samples. Functional analysis (Kyoto Encyclopedia of Genes and Genomes) revealed that several upregulated metabolic pathways observed in the Danazol group were mitigated with low and medium doses of MAG. MAG also reduced the expression of certain genes associated with functionally-controlled pathways of GnRH, including Kiss1, GPR54, and GnRH. Findings from FMT further supported the causal relationship between glycyrrhizin consumption and alleviation of PP, as well as the mediating role of the gut microbiome.
Conclusions: Glycyrrhizin shows potential to shield both humans and animals from PP by influencing the gut microbiome. Given its established long-term safety, glycyrrhizin could serve as an alternative alongside GnRHa for managing PP.