Drinking Non-nutritive Sweetness Solution of Sodium Saccharin or Rebaudioside a for Guinea Pigs: Influence on Histologic Change and Expression of Sweet Taste Receptors in Testis and Epididymis

Potential Exacerbation of Polycystic Ovary Syndrome by Saccharin Sodium Using a Letrozole Rat Model

The most common cause of anovulatory infertility is polycystic ovarian syndrome (PCOS), which is closely associated with obesity metabolic and syndrome. Artificial sweetener, notably saccharin sodium (SS), has been utilized in management of obesity in PCOS. However, accumulating evidence points towards SS deleterious effects on ovarian physiology, potentially through activation of ovarian sweet and bitter taste receptors, culminating in a phenotype reminiscent of PCOS. This research embarked on exploration of SS influence on ovarian functions within a PCOS paradigm. Rats were categorized into six groups: Control, Letrozole-model, two SS groups at 2 dose levels, and two groups receiving 2 doses of SS with letrozole. The study underscored SS capability to potentiate PCOS-related anomalies. Elevated cystic profile with outer thin granulosa cells, were discernible. This owed to increased apoptotic markers cleaved CASP-3, mirrored by high BAX and low BCL-2, with p38-MAPK/ERK1/2 pathway. This manifestation was accompanied by activation of taste receptors and disruption of steroidogenic factors; StAR, CYP11A1, and 17β-HSD. Thus, SS showed an escalation in testosterone, progesterone, estrogen, and LH/FSH ratio, insinuating a perturbation in endocrine regulation. It is found that there is an impact of taste receptor downstream signaling on ovarian steroidogenesis and apoptosis instigating pathophysiological milieu of PCOS.

Sweet Taste Receptor T1R3 Expressed in Leydig Cells Is Closely Related to Homeostasis of the Steroid Hormone Metabolism Profile

Taste receptor type 1 subunit 3 (T1R3) is initially expressed in mammal tongue for recognition and response of sweet/umami tastants and is critical to nutrient absorption, even endocrine. In this study, down-regulation of related steroidogenic enzymes such as StAR, 3β-HSD, CYP17A1, and 17β-HSD with the decrease of T1R3 expression was found in Leydig cells treated by a T1R3 inhibitor (lactisole). The abundances of progesterone, 17a-hydroxyprogesterone, androstenedione, testosterone, and deoxycorticosterone were down-regulated by 2.3, 3.5, 1.4, 1.6, and 2.2 times, respectively, after T1R3 inhibition. In addition, opposite results were found in saccharin sodium treatment. T1R3 activation contributed to intracellular cyclic adenosine monophosphate (cAMP) accumulation (14.41 ± 0.58 vs 20.21 ± 0.65) and increased testosterone (20.31 ± 3.49 vs 50.01 ± 7.44) and steroidogenic metabolite levels. Coadministration of human chorionic gonadotropin and saccharin sodium resulted in elevating the testosterone and cAMP levels and enhancing the expression levels of steroidogenic-related factors. Similarly, intratesticular injection of lactisole and saccharin sodium further confirmed that T1R3 inhibition/activation affected the expression of related steroidogenic enzymes and the testosterone levels in mice. The above findings suggest that T1R3 plays a role in testicular steroidogenesis.

The co-expression of steroidogenic enzymes with T1R3 during testicular development in the Congjiang Xiang pig

Testosterone is a key crucial hormone synthesized by steroidogenic enzymes that initiate and maintain spermatogenesis and secondary sexual characteristics in adult males. The taste receptor family 1 subunit 3 (T1R3) is reported to be associated with male reproduction. T1R3 can regulate the expressions of steroidogenic enzymes and affect testosterone synthesis. In this study, we addressed the question of whether the expression of steroid synthase was associated with T1R3 and its downstream-tasting molecules during testicular development. The results showed an overall upward trend in testosterone and morphological development in testes from Congjiang Xiang pigs from pre-puberty to sexual maturity. Gene expression levels of testicular steroidogenic acute regulatory protein (StAR), 3β-hydroxysteroid dehydrogenase (3β-HSD), cytochrome P450c17 (CYP17A1) and 17β-hydroxysteroid dehydrogenase (17β-HSD) were increased from pre-puberty to sexual maturity. Protein expression changes of CYP17A1 and 3β-HSD were consistent with mRNA. The relative abundance of tasting molecules (TAS1R3, phospholipase Cβ2, PLCβ2) was increased from pre-puberty to puberty (P < 0.05), with no further significant changes in expression from puberty to sexual maturity. Steroidogenic enzymes (3β-HSD and CYP17A1) were strongly detected in Leydig cells from pre-puberty to sexual maturity, while tasting molecules were localized in Leydig cells and spermatogenic cells. Correlation analysis showed that the genes mentioned above (except for PLCβ2) were positively correlated with testosterone levels and morphological characteristics of the testes at different developmental stages of Congjiang Xiang pigs. These results suggest that steroidogenic enzymes regulate testosterone synthesis and testicular development, and that taste receptor T1R3, but not PLCβ2, may associate with this process.

Taste receptors affect male reproduction by influencing steroid synthesis

For the male genetic materials to reach and fertilize the egg, spermatozoa must contend with numerous environmental changes in a complex and highly sophisticated process from generation in the testis, and maturation in the epididymis to capacitation and fertilization. Taste is an ancient chemical sense that has an essential role in the animal's response to carbohydrates in the external environment and is involved in the body's energy perception. In recent years, numerous studies have confirmed that taste signaling factors (taste receptor families 1, 2 and their downstream molecules, Gα and PLCβ2) are distributed in testes and epididymis tissues outside the oral cavity. Their functions are directly linked to spermatogenesis, maturation, and fertilization, which are potential targets for regulating male reproduction. However, the specific signaling mechanisms of the taste receptors during these processes remain unknown. Herein, we review published literature and experimental results from our group to establish the underlying signaling mechanism in which the taste receptor factors influence testosterone synthesis in the male reproduction.

The Impact of Non-caloric Sweeteners on Male Fertility: A Systematic Review and Narrative Synthesis in Rodent Models

Understanding the factors which influence fertility is essential for developing appropriate nutritional recommendations for couples trying to conceive. Non-caloric sweeteners (NCS) are increasing in the food chain and despite being no/low calorie, several adverse metabolic consequences have been attributed to their consumption. Their effects on reproduction have been relatively under-researched, particularly in males. This review aims to systematically review the literature for evidence of the effect of NCS on male fertility in rodents, with sperm parameters (sperm quantity and quality) assessed as primary outcomes. Given the lack of information available in humans this review has been carried out using evidence from rodent models. Risk of bias assessment was carried out using the Syrcle risk of bias tool. Nine studies met the inclusion criteria. Forty-four percent showed a negative effect of NCS on male reproductive parameters compared with controls. The effects of NCS on fertility have been conflicting and selected studies have been heterogeneous in relation to study design. It is unclear if NCS has an impact on male reproductive function. There is a need for randomized controlled trials using a standardized protocol for analysis, to formulate a clear message in terms of male fertility.