Green tea consumption and glutathione S-transferases genetic polymorphisms on the risk of adult leukemia

Glutathione: Lights and Shadows in Cancer Patients

In cases of cellular injury, there is an observed increase in the production of reactive oxygen species (ROS). When this production becomes excessive, it can result in various conditions, including cancerogenesis. Glutathione (GSH), the most abundant thiol-containing antioxidant, is fundamental to re-establishing redox homeostasis. In order to evaluate the role of GSH and its antioxi-dant effects in patients affected by cancer, we performed a thorough search on Medline and EMBASE databases for relevant clinical and/or preclinical studies, with particular regard to diet, toxicities, and pharmacological processes. The conjugation of GSH with xenobiotics, including anti-cancer drugs, can result in either of two effects: xenobiotics may lose their harmful effects, or GSH conjugation may enhance their toxicity by inducing bioactivation. While being an interesting weapon against chemotherapy-induced toxicities, GSH may also have a potential protective role for cancer cells. New studies are necessary to better explain the relationship between GSH and cancer. Although self-prescribed glutathione (GSH) implementation is prevalent among cancer patients with the intention of reducing the toxic effects of anticancer treatments and potentially preventing damage to normal tissues, this belief lacks substantial scientific evidence for its efficacy in reducing toxicity, except in the case of cisplatin-related neurotoxicity. Therefore, the use of GSH should only be considered under medical supervision, taking into account the appropriate timing and setting.

The Effects of Green Tea Catechins in Hematological Malignancies

Green tea catechins are bioactive polyphenol compounds which have attracted significant attention for their diverse biological activities and potential health benefits. Notably, epigallocatechin-3-gallate (EGCG) has emerged as a potent apoptosis inducer through mechanisms involving caspase activation, modulation of Bcl-2 family proteins, disruption of survival signaling pathways and by regulating the redox balance, inducing oxidative stress. Furthermore, emerging evidence suggests that green tea catechins can modulate epigenetic alterations, including DNA methylation and histone modifications. In addition to their apoptotic actions, ROS signaling effects and reversal of epigenetic alterations, green tea catechins have shown promising results in promoting the differentiation of leukemia cells. This review highlights the comprehensive actions of green tea catechins and provides valuable insights from clinical trials investigating the therapeutic potential of green tea catechins in leukemia treatment. Understanding these multifaceted mechanisms and the outcomes of clinical trials may pave the way for the development of innovative strategies and the integration of green tea catechins into clinical practice for improving leukemia patient outcomes.

Association Between the Individual and Combined Effects of the GSTM1 and GSTT1 Polymorphisms and Risk of Leukemia: A Meta-Analysis

Background: Fourteen meta-analyses reported the individual effects of the GSTM1 and GSTT1 polymorphisms on leukemia risk. However, over 40 studies were not included in previously published meta-analyses. Moreover, one key aspect was that previous meta-analyses did not conduct the false-positive test on the aforementioned issues. Furthermore, previous meta-analyses did not observe the combined effects of GSTM1 present/null and GSTT1 present/null polymorphism with leukemia risk. Therefore, we conducted the current study to further analyze these associations. Objectives: This study aimed to investigate the association between the individual and combined effects of the GSTM1 present/null and GSTT1 present/null polymorphisms and the risk of leukemia. Methods: A meta-analysis was performed applying Meta-analyses of Observational Studies in Epidemiology (MOOSE) guidelines. Moreover, false-positive report probability (FPRP) and Bayesian false discovery probability (BFDP) were applied to investigate the false-positive results. Results: The individual GSTM1 and GSTT1 null genotypes and combined effects of the two genes were associated with a significantly increased leukemia risk in overall and several subgroup analyses, such as Asians, Caucasians, and so on. Then, further analysis was conducted using FPRP and BFDP. Significant associations were considered as "positive" results on the GSTM1 null genotype with leukemia risk in overall populations (FPRP < 0.001 and BFDP = 0.006), Asians (FPRP < 0.001 and BFDP < 0.001), and East Asian population (FPRP < 0.001 and BFDP = 0.002). For the GSTT1 null genotype, significant associations were regarded "positive" results in overall populations, acute myeloid leukemia (AML), Asians, and East Asian population. For the combined effects of the GSTM1 and GSTT1 polymorphisms, significant associations were also considered "positive" results in the overall analysis of Asians, Indians, and East Asian population. Conclusion: This study strongly indicates that the individual GSTM1 and GSTT1 null genotypes and combined effects of the two genes are associated with increased leukemia risk in Asians, especially in the East Asian population; the GSTT1 null genotype is associated with increased AML risk; the combined effects of the two genes are associated with increased leukemia risk in Indians.

Effect of Green Tea Supplementation on Antioxidant Status in Adults: A Systematic Review and Meta-Analysis of Randomized Clinical Trials

It is well-established that green tea supplementation has antioxidant properties. However, whether green tea supplementation leads to oxidative stress reduction remains unclear, as clinical investigations on this subject have yielded inconsistent outcomes. Consequently, we aimed to determine the effects of green tea supplementation on oxidative stress in adults. A systematic search of English language publications up to 21 August 2021 was carried out in PubMed, Scopus, Embase, and ISI Web of Science, utilizing pertinent keywords. These searches included randomized controlled trials (RCTs) evaluating the relationship between green tea supplementation, malondialdehyde (MDA), and total antioxidant capacity (TAC) in adults. A random-effects model was used to estimate the weighted mean difference (WMD) and 95% confidence intervals (95% CI). Meta-regression and non-linear dose-response analyses were performed to investigate the association between the dosage of green tea (mg/day) and the duration of the intervention (weeks) with pooled effect size. Sixteen RCTs with seventeen arms including 760 participants met the inclusion criteria. Our results indicated that green tea supplementation had significant effects on TAC (weighted mean difference [WMD]: 0.20 mmol/L; 95% CI: 0.09, 0.30, p < 0.001) and significant heterogeneity between studies (I² = 98.6%, p < 0.001), which was largely related to gender and body mass index (BMI). Subgroup analysis in TAC identified a significant relationship except with low dose supplementation and obese individuals. No relationship between MDA and green tea supplementation was observed in any subgroups; however, meta-regression analysis revealed a linear inverse association between the dosage and significant change in MDA (r = −2117.18, p = 0.017). Our outcomes suggest that green tea supplementation improves TAC and affects MDA based on the dose of the intervention in adults. Future RCTs with longer durations are needed to expand our findings.

Green tea (Camellia sinensis) for the prevention of cancer

BACKGROUND

This review is an update of a previously published review in the Cochrane Database of Systematic Reviews (2009, Issue 3).Tea is one of the most commonly consumed beverages worldwide. Teas from the plant Camellia sinensis can be grouped into green, black and oolong tea, and drinking habits vary cross-culturally. C sinensis contains polyphenols, one subgroup being catechins. Catechins are powerful antioxidants, and laboratory studies have suggested that these compounds may inhibit cancer cell proliferation. Some experimental and nonexperimental epidemiological studies have suggested that green tea may have cancer-preventative effects.

OBJECTIVES

To assess possible associations between green tea consumption and the risk of cancer incidence and mortality as primary outcomes, and safety data and quality of life as secondary outcomes.

SEARCH METHODS

We searched eligible studies up to January 2019 in CENTRAL, MEDLINE, Embase, ClinicalTrials.gov, and reference lists of previous reviews and included studies.

SELECTION CRITERIA

We included all epidemiological studies, experimental (i.e. randomised controlled trials (RCTs)) and nonexperimental (non-randomised studies, i.e. observational studies with both cohort and case-control design) that investigated the association of green tea consumption with cancer risk or quality of life, or both.

DATA COLLECTION AND ANALYSIS

Two or more review authors independently applied the study criteria, extracted data and assessed methodological quality of studies. We summarised the results according to diagnosis of cancer type.

MAIN RESULTS

In this review update, we included in total 142 completed studies (11 experimental and 131 nonexperimental) and two ongoing studies. This is an additional 10 experimental and 85 nonexperimental studies from those included in the previous version of the review. Eleven experimental studies allocated a total of 1795 participants to either green tea extract or placebo, all demonstrating an overall high methodological quality based on 'Risk of bias' assessment. For incident prostate cancer, the summary risk ratio (RR) in the green tea-supplemented participants was 0.50 (95% confidence interval (CI) 0.18 to 1.36), based on three studies and involving 201 participants (low-certainty evidence). The summary RR for gynaecological cancer was 1.50 (95% CI 0.41 to 5.48; 2 studies, 1157 participants; low-certainty evidence). No evidence of effect of non-melanoma skin cancer emerged (summary RR 1.00, 95% CI 0.06 to 15.92; 1 study, 1075 participants; low-certainty evidence). In addition, adverse effects of green tea extract intake were reported, including gastrointestinal disorders, elevation of liver enzymes, and, more rarely, insomnia, raised blood pressure and skin/subcutaneous reactions. Consumption of green tea extracts induced a slight improvement in quality of life, compared with placebo, based on three experimental studies. In nonexperimental studies, we included over 1,100,000 participants from 46 cohort studies and 85 case-control studies, which were on average of intermediate to high methodological quality based on Newcastle-Ottawa Scale 'Risk of bias' assessment. When comparing the highest intake of green tea with the lowest, we found a lower overall cancer incidence (summary RR 0.83, 95% CI 0.65 to 1.07), based on three studies, involving 52,479 participants (low-certainty evidence). Conversely, we found no association between green tea consumption and cancer-related mortality (summary RR 0.99, 95% CI 0.91 to 1.07), based on eight studies and 504,366 participants (low-certainty evidence). For most of the site-specific cancers we observed a decreased RR in the highest category of green tea consumption compared with the lowest one. After stratifying the analysis according to study design, we found strongly conflicting results for some cancer sites: oesophageal, prostate and urinary tract cancer, and leukaemia showed an increased RR in cohort studies and a decreased RR or no difference in case-control studies.

AUTHORS' CONCLUSIONS

Overall, findings from experimental and nonexperimental epidemiological studies yielded inconsistent results, thus providing limited evidence for the beneficial effect of green tea consumption on the overall risk of cancer or on specific cancer sites. Some evidence of a beneficial effect of green tea at some cancer sites emerged from the RCTs and from case-control studies, but their methodological limitations, such as the low number and size of the studies, and the inconsistencies with the results of cohort studies, limit the interpretability of the RR estimates. The studies also indicated the occurrence of several side effects associated with high intakes of green tea. In addition, the majority of included studies were carried out in Asian populations characterised by a high intake of green tea, thus limiting the generalisability of the findings to other populations. Well conducted and adequately powered RCTs would be needed to draw conclusions on the possible beneficial effects of green tea consumption on cancer risk.

A Review of Dietary (Phyto)Nutrients for Glutathione Support

Glutathione is a tripeptide that plays a pivotal role in critical physiological processes resulting in effects relevant to diverse disease pathophysiology such as maintenance of redox balance, reduction of oxidative stress, enhancement of metabolic detoxification, and regulation of immune system function. The diverse roles of glutathione in physiology are relevant to a considerable body of evidence suggesting that glutathione status may be an important biomarker and treatment target in various chronic, age-related diseases. Yet, proper personalized balance in the individual is key as well as a better understanding of antioxidants and redox balance. Optimizing glutathione levels has been proposed as a strategy for health promotion and disease prevention, although clear, causal relationships between glutathione status and disease risk or treatment remain to be clarified. Nonetheless, human clinical research suggests that nutritional interventions, including amino acids, vitamins, minerals, phytochemicals, and foods can have important effects on circulating glutathione which may translate to clinical benefit. Importantly, genetic variation is a modifier of glutathione status and influences response to nutritional factors that impact glutathione levels. This narrative review explores clinical evidence for nutritional strategies that could be used to improve glutathione status.

Anticancer Effects of Green Tea and the Underlying Molecular Mechanisms in Bladder Cancer

Green tea and green tea polyphenols (GTPs) are reported to inhibit carcinogenesis and malignant behavior in several diseases. Various in vivo and in vitro studies have shown that GTPs suppress the incidence and development of bladder cancer. However, at present, opinions concerning the anticancer effects and preventive role of green tea are conflicting. In addition, the detailed molecular mechanisms underlying the anticancer effects of green tea in bladder cancer remain unclear, as these effects are regulated by several cancer-related factors. A detailed understanding of the pathological roles and regulatory mechanisms at the molecular level is necessary for advancing treatment strategies based on green tea consumption for patients with bladder cancer. In this review, we discuss the anticancer effects of GTPs on the basis of data presented in in vitro studies in bladder cancer cell lines and in vivo studies using animal models, as well as new treatment strategies for patients with bladder cancer, based on green tea consumption. Finally, on the basis of the accumulated data and the main findings, we discuss the potential usefulness of green tea as an antibladder cancer agent and the future direction of green tea-based treatment strategies for these patients.

Coffee and green tea consumption and subsequent risk of acute myeloid leukemia and myelodysplastic syndromes in Japan

Although coffee and green tea are suggested to reduce the risk of some types of cancers, only a few epidemiological studies have investigated their effect on the risk of acute myeloid leukemia (AML) and myelodysplastic syndromes (MDS). Here, we investigated the association of coffee and green tea consumption and the risk of AML and MDS in a large-scale population-based cohort study in Japan. A total of 95,807 Japanese subjects (45,937 men and 49,870 women; age 40-69 years at baseline) were followed to the end of 2012, for an average of 18 years. Hazard ratios (HRs) and 95% confidence intervals (95% CIs) for the association between coffee and green tea consumption at baseline and the risk of AML and MDS were assessed using a Cox proportional hazards model with adjustment for potential confounders. During 1,751.956 person-years, we identified 85 AML cases and 70 MDS cases. Our findings showed no significant association between coffee consumption and the risk of AML, or between green tea consumption and the risk of AML or MDS. In contrast, we observed a decreasing dose-response relationship between coffee consumption and the risk of MDS among men (almost none: reference, 1-4 times/week: HR = 0.83, 95% CI: 0.43-1.62; ≥1cups/day: HR = 0.47, 0.22-0.99, p for trend = 0.049). Stratified analysis by smoking status suggested that the observed relative risk for AML and MDS of coffee drinkers relative to non-coffee drinkers might be due to residual confounding by smoking. These findings deserve further investigation in future studies.