Vitamin E Intake and Risk of Renal Cell Carcinoma: A Meta-Analysis of 7 Case-Control Studies

Impact of heavy metals, oxidative stress, expression of VHL, and antioxidant genes in the pathogenesis of renal cell carcinoma

INTRODUCTION

Heavy metals exposure is a known carcinogen in humans. The impact of heavy metals in the pathogenesis of renal cell carcinoma (RCC) is unclear with scant available literature. Though previous studies have evaluated the role of heavy metals in RCC, majority of those studies have evaluated either single or few heavy metals in urine. None of the prior studies have evaluated an extensive panel of heavy metals in blood, urine, and tissue in the same patient along with the serum oxidation status and gene expression to establish a cause-and-effect relationship. This study aims to evaluate the role of extensive panel of heavy metals, oxidative status, and gene expression in RCC.

METHODOLOGY

This observational study recruited RCC patients who visited our tertiary care centre from 2019 to 2023. Age matched healthy volunteers were included as controls. Blood, urine, and tissue samples (tumor and adjacent normal tissue) were collected from RCC patients. Levels of arsenic, copper, manganese, selenium, cadmium, lead, and mercury were measured in each of the samples. Serum oxidative stress markers like glutathione peroxidase (GPX), lipid peroxidase (LPO), and superoxide dismutase (SOD) were measured. Genetic expression of Von Hippel-Lindau (VHL), catalase (CAT), superoxide dismutase (SOD1), and glutathione peroxidase (GPX1) genes were measured in the tumor tissue and adjacent normal parenchyma.

RESULTS

150 cases and 150 age matched controls were enrolled. RCC cases had elevated blood levels of arsenic (P = 0.02), copper (P = 0.01), manganese (P < 0.001), cadmium (P < 0.001), lead (P < 0.001), and mercury (P = 0.02) compared to controls. Urine levels of selenium (P = 0.02), mercury (P = 0.03), and lead (P = 0.04) were higher in cases. Reduced levels of serum GPx (P = 0.02) and higher levels of LPO (P = 0.04) were detected in cases. Elevated levels of copper (P = 0.03), manganese (P = 0.002), selenium (P < 0.001), and cadmium (P < 0.001) were found in the adjacent normal parenchyma compared to the tumor tissue. VHL (P = 0.03) and oxidative stress gene expressions were lower in the tumour tissue compared to the normal parenchyma.

CONCLUSION

Elevated levels of heavy metals in the blood, urine, tissue, and imbalance in the serum oxidative status along with downregulated tumor suppressor VHL and oxidative stress genes in the tumor tissues likely explain the carcinogenic role of heavy metals in RCC. Environmental exposure is the main cause of heavy metal toxicity. Mitigating the environmental exposure of heavy metals and thereby their toxicity might play a role in cancer prevention.

Association between circulating vitamin E and ten common cancers: evidence from large-scale Mendelian randomization analysis and a longitudinal cohort study

BACKGROUND

The association between vitamin E and cancer risk has been widely investigated by observational studies, but the findings remain inconclusive. Here, we aimed to evaluate the causal effect of circulating vitamin E on the risk of ten common cancers, including bladder, breast, colorectal, esophagus, lung, oral and pharynx, ovarian, pancreatic, prostate, and kidney cancer.

METHODS

A Mendelian randomization (MR) analytic framework was applied to data from a cancer-specific genome-wide association study (GWAS) comprising a total of 297,699 cancer cases and 304,736 controls of European ancestry. Three genetic instrumental variables associated with circulating vitamin E were selected. Summary statistic-based methods of inverse variance weighting (IVW) and likelihood-based approach, as well as the individual genotyping-based method of genetic risk score (GRS) were used. Multivariable IVW analysis was further performed to control for potential confounding effects. Furthermore, the UK Biobank cohort was used as external validation, supporting 355,543 European participants (incident cases ranged from 437 for ovarian cancer to 4882 for prostate cancer) for GRS-based estimation of circulating vitamin E, accompanied by a one-sample MR analysis of dietary vitamin E intake underlying the time-to-event analytic framework.

RESULTS

Specific to cancer GWAS, we found that circulating vitamin E was significantly associated with increased bladder cancer risk (odds ratios [OR]_IVW = 6.23, P_IVW = 3.05×10^-3) but decreased breast cancer risk (OR_IVW = 0.68, P_IVW = 8.19×10^-3); however, the significance of breast cancer was dampened (P_{multivariable IVW} > 0.05) in the subsequent multivariable MR analysis. In the validation stage of the UK Biobank cohort, we did not replicate convincing causal effects of genetically predicted circulating vitamin E concentrations and dietary vitamin E intake on the risk of ten cancers.

CONCLUSIONS

This large-scale population study upon data from cancer-specific GWAS and a longitudinal biobank cohort indicates plausible non-causal associations between circulating vitamin E and ten common cancers in the European populations. Further studies regarding ancestral diversity are warranted to validate such causal associations.

The role of diet in renal cell carcinoma incidence: an umbrella review of meta-analyses of observational studies

BACKGROUND

Evidence associating diet with the incidence of renal cell carcinoma (RCC) is inconclusive. We aimed to summarize evidence associating dietary factors with RCC incidence and assess the strength and validity of this evidence.

METHODS

We conducted an umbrella review of systematic reviews or meta-analyses (SRoMAs) that assessed the association between diet and RCC incidence. Through April 2021, PubMed, Web of Science, Embase, The Cochrane Library, Scopus, and WCRF were searched. Two independent reviewers selected studies, extracted data, and appraised the quality of SRoMAs. According to credibility assessment criteria, evidence can be divided into five categories: convincing (class I), highly suggestive (class II), suggestive (class III), weak (class IV), and nonsignificant (class V).

RESULTS

Twenty-nine meta-analyses were obtained after screening. After excluding 7 overlapping meta-analyses, 22 meta-analyses including 502 individual studies and 64 summary hazard ratios for RCC incidence were included: dietary patterns or dietary quality indices (n = 6), foods (n = 13), beverages (n = 4), alcohol (n = 7), macronutrients (n =15), and micronutrients (n =19). No meta-analyses had high methodological quality. Five meta-analyses exhibited small study effects; one meta-analysis showed evidence of excess significance bias. No dietary factors showed convincing or highly suggestive evidence of association with RCC in the overall analysis. Two protective factors had suggestive evidence (vegetables (0.74, 95% confidence interval 0.63 to 0.86) and vitamin C (0.77, 0.66 to 0.90)) in overall analysis. One protective factor had convincing evidence (moderate drinking (0.77, 0.70 to 0.84)) in Europe and North America and one protective factor had highly suggestive evidence (cruciferous vegetables (0.78, 0.70 to 0.86)) in North America.

CONCLUSIONS

Although many meta-analyses have assessed associations between dietary factors and RCC, no high-quality evidence exists (classes I and II) in the overall analysis. Increased intake of vegetables and vitamin C is negatively associated with RCC risk. Moderate drinking might be beneficial for Europeans and North Americans, and cruciferous vegetables might be beneficial to North Americans, but the results should be interpreted with caution. More researches are needed in the future.

TRIAL REGISTRATION

PROSPERO CRD42021246619.

Metabolomics in renal cell carcinoma: From biomarker identification to pathomechanism insights

Renal cell carcinoma (RCC) is a frequently diagnosed cancer with high prevalence, which is inversely associated with survival benefit. Although myriad studies have shed light on disease causality, unfortunately, thus far, RCC diagnosis is faced with numerous obstacles partly due to the insufficient knowledge of effective biomarkers, hinting deeper mechanistic understanding are urgently needed. Metabolites are recognized as final proxies for gene-environment interactions and physiological homeostasis as they reflect dynamic processes that are ongoing or have been taken place, and metabolomics may therefore offer a far more productive and cost-effective route to disease discovery, particularly within the arena for new biomarker identification. In this review, we primarily expatiate recent advances in metabolomics that may be amenable to novel biomarkers or therapeutic targets for RCC, which may expand our armaments to win more bettles against RCC.

Vitamin E and cancer prevention: Studies with different forms of tocopherols and tocotrienols

α-Tocopherol (α-T) is the major form of vitamin E (VE) in animals and has the highest activity in carrying out the essential antioxidant functions of VE. Because of the involvement of oxidative stress in carcinogenesis, the cancer prevention activity of α-T has been studied extensively. Lower VE intake or nutritional status has been shown to be associated with increased cancer risk, and supplementation of α-T to populations with VE insufficiency has shown beneficial effects in lowering the cancer risk in some intervention studies. However, several large intervention studies with α-T conducted in North America have not demonstrated a cancer prevention effect. More recent studies have centered on the γ- and δ-forms of tocopherols and tocotrienols (T3). In comparison with α-T, these forms have much lower systemic bioavailability but have shown stronger cancer-preventive activities in many studies in animal models and cell lines. γ-T3 and δ-T3 generally have even higher activities than γ-T and δ-T. In this article, we review recent results from human and laboratory studies on the cancer-preventive activities of different forms of tocopherols and tocotrienols, at nutritional and pharmacological levels. We aim to elucidate the possible mechanisms of the preventive actions and discuss the possible application of the available information for human cancer prevention by different VE forms.

Micronutrient Intake and Risk of Hematological Malignancies in Adults: A Systematic Review and Meta-analysis of Cohort Studies

There has been accumulating evidence that several micronutrients may play a protective role in the risk of solid cancers. However, their role in hematological malignancies remains to be elucidated; this meta-analysis aims to evaluate the associations between micronutrient intake as well as supplementation and risk of hematological cancer in adults. Eligible cohort studies (examining intake of vitamin A, vitamin C, vitamin D, vitamin E, lycopene, folate, iron, carotenoids, beta-carotene, selenium, pyridoxine) were sought in PubMed up to July 31, 2016. Random-effects models were used for the calculation of pooled relative risks (RR) with their 95% confidence intervals (CI). Twelve cohort studies were deemed eligible. Null associations were noted regarding supplemented vitamin A (pooled relative risk [RR] = 0.92, 95% confidence interval [CI]: 0.80-1.07), supplemented vitamin C (pooled RR = 1.00, 95%CI: 0.90-1.12), total vitamin D (pooled RR = 1.05, 95%CI: 0.91-1.20), supplemented vitamin E (pooled RR = 0.98, 95%CI: 0.88-1.10), and dietary lycopene intake (pooled RR = 1.00, 95%CI: 0.86-1.16) and the risk of non-Hodgkin lymphoma. No summary estimates are provided for other hematological malignancies due to the limited number of studies. Future prospective trials should be conducted for a better understanding of this field; especially regarding Hodgkin lymphoma, leukemia and plasma cell neoplasms, on which data are scarce.

Identification of metabolism-associated genes and pathways involved in different stages of clear cell renal cell carcinoma

The lack of early diagnostic markers and novel therapeutic targets for clear cell renal cell carcinoma (ccRCC) negatively affects patient prognosis. Cancer metabolism is an attractive area for the understanding of the molecular mechanism of carcinogenesis. The present study attempted to identify metabolic changes from the view of the expression of metabolism-associated genes between control samples and those of ccRCC at different disease stages. Data concerning ccRCC gene expression obtained by RNA-sequencing was obtained from The Cancer Genome Atlas and data on metabolism-associated genes were extracted using the Recon2 model. Following analysis of differential gene expression, multiple differentially expressed metabolic genes at each tumor-node-metastasis disease stage were identified, compared with control non-disease samples: Metabolic genes (305) were differentially expressed in stage I disease, 323 in stage II disease, 355 in stage III disease and 363 in stage IV disease. Following enrichment analysis for differential metabolic genes, 22 metabolic pathways were identified to be dysregulated in multiple stages of ccRCC. Abnormalities in hormone, vitamin, glucose and lipid metabolism were present in the early stages of the disease, with dysregulation to reactive oxygen species detoxification and amino acid metabolism pathways occurring with advanced disease stages, particularly to valine, leucine, and isoleucine metabolism, which was substantially dysregulated in stage IV disease. The xenobiotic metabolism pathway, associated with multiple cytochrome P450 family genes, was dysregulated in each stage of the disease. This pathway is worthy of substantial attention since it may aid understanding of drug resistance in ccRCC. The results of the present study offer information to aid further research into early diagnostic biomarkers and therapeutic targets of ccRCC.

Association of Vitamin E Intake with Reduced Risk of Kidney Cancer: A Meta-Analysis of Observational Studies

Background

Several observational studies suggested that vitamin E intake is related to the risk of kidney cancer; however, the results of published studies are inconsistent.

Material/Methods

A meta-analysis was performed to assess the relationship between vitamin E intake and the risk of kidney cancer by searching PubMed and Medline through August 2015. We computed pooled relative risks (RR) and 95%CI of kidney cancer for the highest versus lowest level of vitamin E intake.

Results

A total of 13 observational studies (7 case-control and 6 cohort) were included. The pooled RR (95%CI) of kidney cancer for the highest vs. the lowest level of vitamin E intake was 0.81 (0.69–0.94). In subgroup-analysis, this study found an inverse relationship between vitamin E intake and kidney cancer risk, which was not significantly modified by study design, study population, or sex distribution except in the cohort studies.

Conclusions

Results of the present study suggest an inverse relationship between vitamin E intake and kidney cancer risk. However, additional well designed cohort studies and randomized controlled trials that focus on the relationship between vitamin E intake and kidney cancer risk are needed.