Five threads: How U-shaped thinking weaves together dogs, men, selenium, and prostate cancer risk

Selenium in Prostate Cancer: Prevention, Progression, and Treatment

Selenium, a trace mineral with various biological functions, has become a focal point in prostate cancer research. This review aims to present a comprehensive overview of selenium's involvement in prostate cancer, covering its impact on prevention, development, treatment, and underlying mechanisms. Observational studies have revealed a link between selenium levels and selenoproteins with prostate cancer progression. However, randomized controlled studies have shown that selenium supplementation does not prevent prostate cancer (HR: 0.95; 95% CI 0.80-1.13). This discrepancy might be attributed to selenoprotein single nucleotide polymorphisms. In the context of combinatorial therapy, selenium has demonstrated promising synergistic potential in the treatment of prostate cancer. Emerging evidence highlights the significant role of selenium and selenoproteins in prostate cancer, encompassing AR signaling, antioxidative properties, cell death, cell cycle regulation, angiogenesis, epigenetic regulation, immunoregulation, epithelial-mesenchymal transformation, and redox signal. In conclusion, selenium's diverse properties make it a promising trace mineral in prostate cancer prevention, development, and treatment and as a platform for exploring novel agents.

Both selenium deficiency and excess impair male reproductive system via inducing oxidative stress-activated PI3K/AKT-mediated apoptosis and cell proliferation signaling in testis of mice

Selenium (Se) deficiency or excess impairs testicular development and spermatogenesis, while the underlying mechanisms in this regard remain unclear. This study was designed to explore the molecular biology of Se deficiency or excess in spermatogenesis in mice. Three-week-old male mice (n = 10 mice/diet) were fed with Se-deficient diet (SeD, 0.02 mg Se/kg), adequate-Se diet (SeA, 0.2 mg Se/kg), or excess-Se diet (SeE, 2.0 mg Se/kg) for 5 months. Compared with SeA, SeD reduced (P < 0.05) the body weight (10.4%) and sperm density (84.3%) but increased (P < 0.05) sperm deformity (32.8%); SeE decreased (P < 0.05) the sperm density (78.5%) and sperm motility (35.9%) of the mice. Meanwhile, both SeD and SeE increased (P < 0.05) serum FSH concentrations (10.4-25.6%) and induced testicular damage in mice in comparison with the SeA. Compared with SeA, SeD increased (P < 0.05) the 8-OHdG concentration by 25.5%; SeE increased (P < 0.05) both MDA and 8-OHdG concentrations by 118.8-180.3% in testis. Furthermore, transcriptome analysis showed that there 1325 and 858 transcripts were altered (P < 0.05) in the testis by SeD and SeE, respectively, compared with SeA. KEGG pathway analysis revealed that these differentially expressed genes were mainly enriched in the PI3K-AKT signaling pathway, which is regulated by oxidative stress. Moreover, western blotting analysis revealed that SeD and SeE dysregulated PI3K-AKT-mediated apoptosis and cell proliferation signaling, including upregulating (P < 0.05) caspase 3, cleaved-caspase 3, BCL-2 and (or) P53 and downregulating (P < 0.05) PI3K, p-AKT, p-mTOR, 4E-BP1, p-4E-BP1 and (or) p-p70S6K in the testis of mice compared with SeA. Additionally, compared with SeA, both SeD and SeE increased (P < 0.05) GPX3 and SELENOO; SeD decreased (P < 0.05) GPX1, TXRND3 and SELENOW, but SeE increased (P < 0.05) production of three selenoproteins in the testis. Conclusively, both Se deficiency and excess impairs male reproductive system in mice, potentially with the induction of oxidative stress and activation of PI3K/AKT-mediated apoptosis and cell proliferation signaling in the testis.

Whole blood trace element and toxic metal concentration in dogs with idiopathic epilepsy and healthy dogs: A case-control study

Background

Idiopathic epilepsy (IE) is the most common neurological disease in dogs. Multiple genes and environmental factors interact to cause clinical signs, although the pathogenesis remains poorly understood. Extensive evidence from recent decades shows that trace elements play a role in epilepsy in humans, and recently it was shown for the first time that also dogs with IE have altered trace element status. On the other hand, toxic metals may cause seizures but research on their role in canine IE is lacking. Therefore, we aimed to investigate trace element and toxic metal concentrations in whole blood from dogs that had been diagnosed with IE and compare them to those of healthy dogs.

Materials and methods

Whole blood concentrations of trace elements (selenium, zinc, copper, manganese, iron, and chromium) and toxic metals (arsenic, cadmium, mercury, and lead) were analyzed from 19 dogs that had been diagnosed with IE by board-certified neurologists and 19 healthy control dogs using inductively coupled plasma mass spectrometry. The concentrations in study and control group were compared using the Mann-Whitney U test.

Results

Dogs diagnosed with IE had significantly higher blood copper concentration (P = 0.007), higher copper/zinc ratio (P = 0.04), and higher selenium concentration (P < 0.001), as well as lower chromium concentration (P = 0.01) when compared to healthy dogs. Treatment of IE with potassium bromide was associated with a significant elevation in blood arsenic concentration (P = 0.01).

Conclusion

In conclusion, the present results support the role of altered trace element status in dogs diagnosed with IE and suggest that copper, selenium, and chromium may be involved in the pathogenesis of canine epilepsy or seizures. The results also suggest that potassium bromide may alter arsenic metabolism in dogs.

Zinc in Prostate Health and Disease: A Mini Review

Introduction-With the high global prevalence of prostate cancer and associated mortalities, it is important to enhance current clinical practices for better prostate cancer outcomes. The current review is towards understanding the value of Zn towards this mission. Method-General information on Zn in biology and multiple aspects of Zn involvement in prostate health and disease were referred to in PubMed. Results-The most influential feature of Zn towards prostate health is its ability to retain sufficient citrate levels for a healthy prostate. Zn deficiencies were recorded in serum, hair, and prostate tissue of men with prostate cancer compared to non-cancer controls. Zn gut absorption, albumin binding, and storage compete with various factors. There are multiple associations of Zn cellular influx and efflux transporters, Zn finger proteins, matrix metalloproteinases, and Zn signaling with prostate cancer outcomes. Such Zn marker variations associated with prostate cancer recorded from biological matrices may improve algorithms for prostate cancer screening, prognosis, and management when coupled with standard clinical practices. Discussion-The influence of Zn in prostatic health and disease is multidimensional, therefore more personalized Zn requirements may be beneficial. Several opportunities exist to utilize and improve understanding of Zn associations with prostate health and disease.

Effect of Dietary Methylseleninic Acid and Se-Methylselenocysteine on Carcinogen-Induced, Androgen-Promoted Prostate Carcinogenesis in Rats

Selenomethionine (SeMet) did not prevent prostate cancer in the SELECT trial and in two hormone-driven rat models. However, we have shown that daily oral bolus administration of next-generation selenium forms, methylseleninic acid (MSeA) and Se-methylselenocysteine (MSeC) at 3 mg Se/kg body weight, inhibits prostate carcinogenesis in the TRAMP and pten-deficient mouse models and In Vivo growth of human prostate cancer cells. Here, we determined whether these Se forms prevent prostate cancer in a chemically induced-androgen promoted carcinogenesis rat model in which SeMet was not preventive. WU rats were treated with methylnitrosourea, and one week later, slow-release testosterone implants when they were randomized to groups fed AIN-93M diet supplemented with 3 ppm selenium as MSeA or MSeC or control diet. Mean survival, tumor incidence in all accessory sex glands combined (dorsolateral and anterior prostate plus seminal vesicle) and the incidence of tumors confined to dorsolateral and/or anterior prostate were not statistically significantly different among the groups. Thus, MSeA and MSeC feeding was not preventive in this model. The contrast with the inhibitory effects of MSeA and MSeC in mouse models may be due to differences in carcinogenic mechanisms, selenium dosage, delivery mode, and pharmacokinetics or fundamental rat-mouse differences in selenium metabolism.

Threshold effects and interactive effects of total zinc and selenium intake on cognitive function in older adults

BACKGROUND & AIMS

The aim of this study was to assess threshold effects and interactive effects of total zinc and selenium intake on cognitive function in older adults.

METHODS

We used data from the National Health and Nutrition Examination Survey (NHANES) 2011-2014. Zinc and selenium intake were obtained through two 24-h dietary recalls. Cognitive performance was evaluated by the Digit Symbol Substitution Test (DSST). Smooth curve fitting, two-piecewise multivariable linear regression models, binary logistic regression model, multiplicative interactions model, and additive interactions model were used to evaluate the association between zinc, selenium intake and their interactive effect on cognitive function.

RESULTS

A total of 2450 participants aged 60 years or older were included. Zinc and selenium intake was non-linearly associated with cognitive function. The inflection point for zinc intake was 8.94 mg/d in males and 7.58 mg/d in females. When zinc intake was below inflection point, zinc intake was positively associated with the DSST test in males (β = 1.02, 95% CI, 0.44 to 1.60) and females (β = 0.94, 95% CI, 0.26 to 1.62). When zinc intake above inflection point, there is no association between zinc intake and the DSST test in both sexs. The inflection point for selenium intake was 186.33 μg/d in males and 68.40 μg/d in females. Among males, the β (95% CIs) was 0.03 (0.01,0.06) to the left side of the inflection point and -0.06 (-0.10, -0.02) to the right of the inflection point. Among females, the β (95% CIs) was 0.13 (0.04,0.22) to the left side of the inflection point and 0.01 (-0.01,0.04) to the right of the inflection point. Besides, zinc and selenium have significant interaction on DSST test only in females (P = 0.028, RERI = 0.418).

CONCLUSIONS

The present study demonstrated that zinc and selenium intake was non-linearly associated with cognitive function in different sex. There was an interactive effect between zinc and selenium intake on improving cognitive function, especially in females.

Biomarkers of disease in human nails: a comprehensive review

Diagnostic, monitoring, response, predictive, risk, and prognostic biomarkers of disease are all widely studied, for the most part in biological fluids or tissues, but there is steadily growing interest in alternative matrices such as nails. Here we comprehensively review studies dealing with molecular or elemental biomarkers of disease, as opposed to semiological, pharmacological, toxicological, or biomonitoring studies. Nails have a long history of use in medicine as indicators of pathological processes and have also been used extensively as a matrix for monitoring exposure to environmental pollution. Nail clippings are simple to collect noninvasively as well as to transport and store, and the matrix itself is relatively stable. Nails incorporate, and are influenced by, circulating molecules and elements over their several months of growth, and it is widely held that markers of biological processes will remain in the nail, even when their levels in blood have declined. Nails thus offer the possibility to not only look back into a subject's metabolic history but also to study biomarkers of processes that operate over a longer time scale such as the post-translational modification of proteins. Reports on ungual biomarkers of metabolic and endocrine diseases, cancer, and psychological and neurological disorders will be presented, and an overview of the sampling and analytical techniques provided.

Differential protein expression due to Se deficiency and Se toxicity in rat liver

There is a U-shaped dose-response between selenium (Se) status and health outcomes, but underlying metabolic processes are unclear. This study aims to identify candidate proteins in liver regulated by dietary Se, ranging from deficiency to toxic. Male rats (n=4) were fed graded Se concentrations as selenite for 28 days. Bulk Se analysis was performed by ICP-MS on both soluble and insoluble fractions. Soluble fraction samples were chromatographically separated for identification of selenocompounds by SEC-ICP-MS and protein quantification by LC-MS/MS. Bioinformatics analysis compared low-Se (0 and 0.08 µg Se g^-1) and high-Se (0.8, 2 and 5 µg Se g^-1) with adequate-Se (0.24 µg Se g^-1) diets. Major breakpoints for Se were seen at 0.8 and 2 µg Se g^-1 in the insoluble and soluble fractions, respectively. Glutathione peroxidase 1 protein abundance reached a plateau at ≥0.08 µg Se g^-1diet; Se bound to selenium binding protein 2 was observed with 2 and 5 µg Se g^-1 Se. The extreme diets presented the highest number of differentially expressed (P value <0.05, FC ≥1.2) proteins in comparison to the adequate-Se diet (0 µg Se g^-1: 45 proteins; 5 µg Se g^-1: 59 proteins); 13 proteins were commonly affected in 0 and 5 µg Se g^-1 treatments. Network analysis revealed that the metabolism of glutathione, xenobiotics and amino acids were enriched in both 0 and 5 µg Se g^-1 diets, indicating a U-shape effect of Se. This similarity is likely due to down-stream effects of lack of essential selenoproteins in Se deficiency and due to toxic effects of Se that exceeds the capacity to cope with excess Se.

Selenium Status Is Associated With Insulin Resistance Markers in Adults: Findings From the 2013 to 2018 National Health and Nutrition Examination Survey (NHANES)

Although literature has been consistently showing an increased risk of type 2 diabetes (T2DM) in populations with high exposure to selenium, there is a lack of information quantifying the association between diabetes-related markers and the nutritional status of selenium. Therefore, we aimed to investigate the association between blood selenium concentration and glucose markers in a representative sample of the US population, which is known to have moderate to high exposure to selenium. This cross-sectional analysis included 4,339 participants ≥18 years from the 2013 to 2018 National Health and Nutrition Examination Survey (NHANES). All participants were assessed for whole blood selenium concentration, fasting plasma insulin and glucose, HbA1c, and HOMA-IR (Homeostatic Model Assessment for Insulin Resistance). In this cohort, all participants presented with adequate selenium status [196.2 (SD: 0.9) μg/L] and 867 (15%) had diabetes mellitus. Selenium was positively associated with insulin, glucose and HOMA-IR in models adjusted for age and sex. When the models were further adjusted for smoking status, physical activity, metabolic syndrome and BMI, the associations with insulin and HOMA-IR remained but the association with glucose was no longer significant. A 10 μg/L increase in selenium was associated with 1.5% (95% CI: 0.4–2.6%) increase in insulin and 1.7% (95% CI: 0.5–2.9%) increase in HOMA-IR in fully adjusted models. There was no evidence of an association between selenium and diabetes prevalence. Our findings corroborate the notion that selenium supplementation should not be encouraged in populations with high dietary intake of selenium.

Risk of breast cancer in relation to dietary intake of selenium and serum selenium as a marker of dietary intake: a prospective cohort study within The Malmö Diet and Cancer Study

Purpose

Selenium has been suggested to be protective against breast cancer, but the evidence remains inconclusive. Hence, it is important to further examine the potential protective effect. This prospective cohort study investigates pre-diagnostic selenium intake in relation to breast cancer risk. In addition, we analyze serum selenium as a marker of dietary intake.

Methods

This study includes 17,035 women in the Malmö Diet and Cancer cohort. Dietary assessment and serum samples were collected at baseline (1991–1996). During 344,584 person-years of follow-up, 1,427 incident cases were retrieved. Cox regression analysis examined breast cancer risks adjusted for potential confounding factors. In addition, odds ratios (ORs) were estimated for 1186 cases and an equal number of controls in relation to quartiles (Q) of selenium intake and groups consisting of a combination of intake and serum selenium levels.

Results

No overall association between selenium intake, or a combination of intake and serum levels, and breast cancer risk was found. The adjusted relative risk for breast cancer in selenium intake Q4 versus Q1 was 0.96 (0.83–1.12) (P_trend = 0.65). Similarly, adjusted the OR for breast cancer in selenium intake for Q4 versus Q1 was 0.97 (0.76–1.23). The kappa value, 0.096 (p = 0.001), showed poor agreement between serum selenium and selenium intake.

Conclusion

Our findings suggest that there is no overall association between selenium intake, or a combination of intake and serum levels, and breast cancer risk. Finally, our results showed a poor correlation between estimated selenium intake and serum selenium.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10552-021-01433-1.

Selenium and Dogs: A Systematic Review

The intent of this review is to summarize the knowledge about selenium and its function in a dog's body. For this purpose, systematic literature search was conducted. For mammals, including dogs, a balanced diet and sufficient intake of selenium are important for correct function of metabolism. As for selenium poisoning, there are no naturally occurring cases known. Nowadays, we do not encounter clinical signs of its deficiency either, but it can be subclinical. For now, the most reliable method of assessing selenium status of a dog is measuring serum or plasma levels. Levels in full blood can be measured too, but there are no reference values. The use of glutathione peroxidase as an indirect assay is questionable in canines. Commercial dog food manufactures follow recommendations for minimal and maximal selenium levels and so dogs fed commercial diets should have balanced intake of selenium. For dogs fed home-made diets, complex data are missing. However, subclinical deficiency seems to affect, for example, male fertility or recovery from parasitical diseases. Very interesting is the role of selenium in prevention and treatment of cancer.

Sex-dependent association between selenium status and cognitive performance in older adults

PURPOSE

Selenium (Se) is an essential nutrient required for maintaining brain health across lifespan, and adequate nutritional Se status has been positively associated with sustained cognitive performance in older adults. However, critical physiological sex differences in Se metabolism have not been specifically assessed in human studies. Therefore, we aimed to investigate sex differences in the association between Se concentration in whole blood and cognitive performance in US older adults.

METHODS

This cross-sectional study included 2016 participants (984 male and 1032 female) ≥ 60 years from the 2011 to 2014 National Health and Nutrition Survey (NHANES). All participants were assessed for whole blood Se concentration and completed the following battery of cognitive tests: Consortium to Establish a Registry for Alzheimer's Disease (CERAD) Word Learning Test, Animal Fluency test, and Digit Symbol Substitution Test (DSST).

RESULTS

In this cohort, all participants presented with adequate Se status (mean 196.7 μg/L; 95% CI 193.5, 200.0), and cohort-wide scores were equivalent to a cognitively healthy population. A sex effect on CERAD recall (P = 0.005) and animal fluency (P = 0.018) was observed in models adjusted for age, diabetes, history of cardiovascular disease, physical activity and body mass index. Se concentration was positively associated with CERAD recall (β: 0.015, 95% CI 0.007, 0.022) and animal fluency (β: 0.017, 95% CI 0.003, 0.030) performance in males only, while no associations were observed for females.

CONCLUSION

This study provides the first evidence for sex differences in the association between Se status and cognitive performance in older adults.

Devising a new dialogue for nutrition science: how life course perspective, U-shaped thinking, whole organism thinking, and language precision contribute to our understanding of biological heterogeneity and forge a fresh advance toward precision medicine

The process of designing and implementing individualized health-promoting interventions, nutritional or otherwise, is fraught with great difficulty owing to the heterogeneity inherent in factors that influence healthy longevity. This article proposes that careful attention to three principles-life course perspective, U-shaped thinking, and whole organism thinking-creates an attitudinal framework that can be used to reframe biological heterogeneity into the clinically relevant question: Who will benefit? The search for tools to cope with the complexity of this heterogeneity has been dominated by technological advances, including state-of-the-art "-omics" approaches and machine-based handling of "big data." Here, it is proposed that language precision and nuanced category usage could provide critical tools for coping with heterogeneity, thereby enabling interventionalists to design and implement strategies to promote healthy longevity with greater precision. The lack of a clear understanding of "Who will benefit?" stands as a major obstacle to the design and implementation of nutritional strategies to optimize healthy longevity. This article opens a new dialogue situating the principles of life course perspective, U-shaped thinking, and whole organism thinking, along with cultivating an attitude of language precision at the very core of accelerating creative discovery and refining practical advance in the field of nutrition science.

Selenium Status in Elderly People: Longevity and Age-Related Diseases

BACKGROUND

Selenium (Se) is a trace element active in selenoproteins, which can regulate oxidative stress. It is generally perceived as an import factor for maintaining health in the elderly.

METHODS

The goal of this review is to discuss selenium concentration in biological samples, primarily serum or plasma, as a function of age and its relation with longevity. The elemental level in various age-related diseases is reviewed.

CONCLUSION

Highest selenium values were observed in healthy adults, while in an elderly population significantly lower concentrations were reported. Variables responsible for contradictory findings are mentioned. Risk and benefits of Se-supplementation still remain under debate.

Selenium Supplementation and Prostate Health in a New Zealand Cohort

Background: There is variable reporting on the benefits of a 200 μg/d selenium supplementation towards reducing prostate cancer impacts. The current analysis is to understand whether stratified groups receive supplementation benefits on prostate health. Methods: 572 men were supplemented with 200 µg/d selenium as selinized yeast for six months, and 481 completed the protocol. Selenium and prostate-specific antigen (PSA) levels were measured in serum at pre- and post-supplementation. Changes in selenium and PSA levels subsequent to supplementation were assessed with and without demographic, lifestyle, genetic and dietary stratifications. Results: The post-supplementation selenium (p = 0.002) and the gain in selenium (p < 0.0001) by supplementation were significantly dependent on the baseline selenium level. Overall, there was no significant correlation between changes in PSA and changes in selenium levels by supplementation. However, stratified analyses showed a significant inverse correlation between changes in PSA and changes in selenium in men below the median age (p = 0.048), never-smokers (p = 0.031), men carrying the GPX1 rs1050450 T allele (CT, p = 0.022 and TT, p = 0.011), dietary intakes above the recommended daily intake (RDI) for zinc (p < 0.05), and below the RDI for vitamin B12 (p < 0.001). Conclusions: The current analysis shows the influence of life factors on prostate health benefits of supplemental selenium.

Redox regulation of protein kinase C by selenometabolites and selenoprotein thioredoxin reductase limits cancer prevention by selenium

The cancer-preventive mechanism of selenium should address the way low concentrations of selenometabolites react with cellular targets without being diffused from the sites of generation, the way selenium selectively kills tumor cells, and the intriguing U-shaped curve that is seen with dietary supplementation of selenium and cancer prevention. Protein kinase C (PKC), a receptor for tumor promoters, is well suited for this mechanism. Due to the catalytic redox cycle, low concentrations of methylselenol, a postulated active metabolite of selenium, react with the tumor-promoting lipid hydroperoxide bound to PKC to form methylseleninic acid (MSA), which selectively reacts with thiol residues present within the vicinity of the PKC catalytic domain to inactivate it. Given that lipid hydroperoxide levels are high in promoting cells, PKC inactivation selectively leads to death in these cells. A biphasic effect of MSA in inducing cell death was observed in certain prostate cancer cell lines; lower concentrations of MSA induced cell death, while higher concentrations failed to do so. Lower concentrations of selenium inactivate more sensitive antiapoptotic isoenzymes of PKC (ε and α), sparing less sensitive proapoptotic isoenzymes (PKCδ and PKCζ). Higher concentrations of selenium also inactivate proapoptotic isoenzymes and consequently make tumor cells resistant to apoptosis. Due to a high-affinity binding of thioredoxin to the PKC catalytic domain, this thiol oxidation is explicitly reversed by thioredoxin reductase (TXNRD), a selenoprotein. Therefore, overexpression of TXNRD in advanced tumor cells could make them resistant to selenium-induced death. Conceivably, this mechanism, at least in part, explains why selenium prevents cancer only in certain cases.

Selenoproteins in colon cancer

Selenocysteine-containing proteins (selenoproteins) have been implicated in the regulation of various cell signaling pathways, many of which are linked to colorectal malignancies. In this in-depth excurse into the selenoprotein literature, we review possible roles for human selenoproteins in colorectal cancer, focusing on the typical hallmarks of cancer cells and their tumor-enabling characteristics. Human genome studies of single nucleotide polymorphisms in various genes coding for selenoproteins have revealed potential involvement of glutathione peroxidases, thioredoxin reductases, and other proteins. Cell culture studies with targeted down-regulation of selenoproteins and studies utilizing knockout/transgenic animal models have helped elucidate the potential roles of individual selenoproteins in this malignancy. Those selenoproteins, for which strong links to development or progression of colorectal cancer have been described, may be potential future targets for clinical interventions.