White tea WTEA as a promising agent against sufertility/infetility promoted by diabetes mellitus: synesgistic or single component effect

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Effect of white tea on the reproductive function of diabetic or prediabetic individuals

Publication . Dias, Tânia Isabel Rodrigues Amaral; Oliveira, Pedro Fontes; Silva, Branca Maria Cardoso Monteiro da; Casal, Susana

The prevalence of diabetes mellitus (DM) has been increasing in young men worldwide. Patients with DM have a dysfunction on insulin secretion and/or insulin action, resulting in hyperglycemia. Insulin dysregulation affects glucose homeostasis in the body, having a deleterious impact on male fertility. Sertoli cells (SCs) are essential for the maintenance of male reproductive potential as they provide the physical and nutritional support that allows the differentiation of germ cells into fully competent spermatozoa. SCs function highly relies on glucose metabolism, which is their preferred substrate. Many diabetic patients are subfertile or infertile due to altered SCs function, impaired spermatogenesis and poor sperm quality. The primary strategy to counteract DM and its complications includes nutritional changes and physical activity. However, these interventions are usually unsuccessful alone and need to be complemented with medication. Still, the efficacy of conventional drugs is limited, they are expensive and have several secondary effects. In recent years, natural products, including tea and its components, demonstrated promising antioxidant and antidiabetic properties. Besides, the treatment of prediabetes can be an effective approach as it can occur up to 10 years before the progression of the disease to a more severe state. In this research project, we aimed to unravel the effects of white tea (WTEA) on male reproductive function and its protective role against reproductive dysfunctions induced by prediabetes. Further, we aimed to investigate if the effects of WTEA are due to a combined effect of all WTEA components or to a predominant effect of one of its most bioactive components. WTEA is the rarest and less studied type of tea, but it presents a potent antioxidant potential due to its high catechin content. Through proton nuclear magnetic resonance (1H-NMR), we verified that this type of tea is particularly rich in caffeine, epigallocatechin gallate (EGCG) and L-theanine. Using an in vitro model of rat SCs or human SCs (hSCs) we evaluated the effects of WTEA extract (0.5 mg/mL) and its main bioactive compounds (caffeine, EGCG and L-theanine) on cells metabolism, mitochondrial functionality and oxidative profile. WTEA extract modulated rat SCs metabolism and stimulated the production of lactate, which is essential for germ cells survival. Supplementation of hSCs culture media with 50 μM of caffeine, EGCG, or L-theanine for 24 hours induced alterations in hSCs metabolism that are important for the improvement of male reproductive potential. It resulted in an increase or maintenance of lactate production, showing a protective role against oxidative damages. However, at 50 μM, these compounds also induced some alterations in hSCs proliferation and mitochondrial functionality that may compromise hSCs function. The WTEA extract (0.5 mg/mL) showed a better improvement on SCs, highlighting the importance of the combined effect of all the tea components for its beneficial effect. We also conducted ex vivo studies using rat epididymal spermatozoa to evaluate the potential of WTEA extract (0.5 mg/mL or 1 mg/mL) and the three selected components as an additive for a sperm storage medium at room temperature for short periods. In these studies, the concentrations of caffeine (71 μg/mL) EGCG (82 μg/mL) and L-theanine (19 μg/mL), were selected based on their concentration in the WTEA extract. Sperm viability decreases over time in refrigerated samples, thus in certain cases the short-term storage at room temperature can be advantageous, such as for samples transport or assisted reproductive technology. These studies allowed us to conclude that the WTEA extract (especially at 1 mg/mL) was a better additive to the sperm storage medium at room temperature than each of the components alone, as it kept spermatozoa viability for 3 days equivalently to values obtained at the collection time. Although the combination of the three selected components together showed a higher improvement in spermatozoa viability, it also stimulated protein oxidation, supporting the beneficial combined effect of all the components constituting the WTEA extract. This led us to study the in vivo effect of a regular consumption of WTEA on the reproductive function of a rat model of prediabetes. The prediabetic rats showed alterations in the testicular and epididymal metabolism, resulting in poor sperm quality. WTEA ingestion by prediabetic rats for two months prevented many of the metabolic dysfunctions induced by the disease in the testis and epididymis, resulting in the improvement of sperm motility and viability. Our results indicate that WTEA regular consumption can be a cost-effective strategy to improve prediabetes-induced reproductive dysfunctions, paving the way for WTEA to be used for the development of new antioxidant therapies for the improvement of male fertility.

2019-10Doctoral thesis

Open access

8-(3-phenylpropyl)-1,3,7-triethylxanthine is a synthetic caffeine substitute with stronger metabolic modulator activity

Publication . Carrageta, David F; Dias, Tânia R.; Jarak, Ivana; Alves, Marco G; Oliveira, P.F.; Walt, Mietha Van Der; Terre'Blanche, Gisella; Monteiro, Mariana P.; Silva, Branca M.

Caffeine is one of the most worldwide consumed methylxanthines. It is well-known for its thermogenic and cell metabolism modulating effects. Based on methylxanthines' chemical structure, 8-(3-phenylpropyl)-1,3,7-triethylxanthine (PTX) is a novel adenosine antagonist with higher receptor affinity than caffeine. Therefore, we hypothesized that PTX metabolic effects could be stronger than those of caffeine. For that purpose, murine 3T3-L1 cells were cultured in the presence of increasing doses of PTX or caffeine (0.1, 1, 10 and 100 μM) for 24 h. Cytotoxicity was evaluated by reduction of tetrazolium salt (MTT) and lactate dehydrogenase (LDH) release. Cell metabolites released to the culture medium were identified and quantified by proton nuclear magnetic resonance (1H NMR). Cellular oxidative profile was also evaluated. Our results showed that PTX displayed no signs of cytotoxicity at all studied concentrations. When compared with caffeine, PTX increased glucose, pyruvate, and glutamine consumption, as well as lactate, alanine, and acetate production. Additionally, PTX decreased protein oxidation, thus protecting against oxidative stress-induced damage. These results illustrate that PTX is a stronger and less cytotoxic caffeine substitute with potential applications as metabolic modulator and a good candidate for novel drug design.

2018Journal article

Open access

Implications of epigallocatechin-3-gallate in cultured human Sertoli cells glycolytic and oxidative profile

Publication . Dias, Tânia R.; Alves, Marco G; Silva, Joaquina; Barros, Alberto; Sousa, Mário; Casal, Susana; Silva, Branca M.; Oliveira, Pedro F.

Sertoli cells are crucial for the success of spermatogenesis, which is the biological process that ensures male fertility. These cells present high metabolic rates, being often subjected to high oxidative stress levels that, if uncontrolled, may compromise male fertility. Since the most abundant tea catechin, epigallocatechin-3-gallate (EGCG), has demonstrated a potent preventive activity against oxidative stress, we have evaluated its effect at concentrations of 5 and 50μM, on the metabolism, mitochondrial functionality and oxidative profile of human Sertoli cells (hSCs). While, the highest concentration of EGCG (50μM) increased glucose and pyruvate consumption, it decreased the conversion of pyruvate to alanine to sustain a regular lactate production. However, despite maintaining Krebs cycle functionality, EGCG (50μM) decreased mitochondrial membrane potential of hSCs, which could compromise the normal rates of ATP production. Interestingly, oxidative damages to proteins and lipids decreased in this experimental group, which may be valuable for the nutritional support of spermatogenesis.

2017Journal article

Open access