Recent Progress in Discovering the Role of Carotenoids and Metabolites in Prostatic Physiology and Pathology-A Review-Part II: Carotenoids in the Human Studies

Revisiting carotenoids as dietary antioxidants for human health and disease prevention

Humans are unique indiscriminate carotenoid accumulators, so the human body accumulates a wide range of dietary carotenoids of different types and to varying concentrations. Carotenoids were once recognized as physiological antioxidants because of their ability to quench singlet molecular oxygen (1O2). In the 1990s, large-scale intervention studies failed to demonstrate that supplementary β-carotene intake reduces the incidence of lung cancer, although its antioxidant activity was supposed to contribute to the prevention of oxidative stress-induced carcinogenesis. Nevertheless, the antioxidant activity of carotenoids has attracted renewed attention as the pathophysiological role of 1O2 has emerged, and as the ability of dietary carotenoids to induce antioxidant enzymes has been revealed. This review focuses on six major carotenoids from fruit and vegetables and revisits their physiological functions as biological antioxidants from the standpoint of health promotion and disease prevention. β-Carotene 9',10'-oxygenase-derived oxidative metabolites trigger increases in the activities of antioxidant enzymes. Lutein and zeaxanthin selectively accumulate in human macular cells to protect against light-induced macular impairment by acting as antioxidants. Lycopene accumulates exclusively and to high concentrations in the testis, where its antioxidant activity may help to eliminate oxidative damage. Dietary carotenoids appear to exert their antioxidant activity in photo-irradiated skin after their persistent deposition in the skin. An acceptable level of dietary carotenoids for disease prevention should be established because they can have deleterious effects as prooxidants if they accumulate to excess levels. Finally, it is expected that the reason why humans are indiscriminate carotenoid accumulators will be understood soon.

The role of matrix metalloproteinases in pathogenesis, diagnostics, and treatment of human prostate cancer

The prostate gland is highly susceptible to oncogenic transformation, many times more than other sex tissues, such as seminal vesicles. In fact, prostate cancer (PCa) will be diagnosed in one in seven lifetime patients, making PCa the subject of intense research aimed at clarifying its biology and providing adequate treatment. PCa is the fourth most common cancer in the world in terms of the overall population and the second most common cancer for the male population. It is postulated that the development of PCa may be influenced by dietary factors, physical and sexual activity, androgens, obesity, and inflammation, but their role in the development of prostate cancer still remains unclear. Extracellular matrix metalloproteinases (MMPs) and tissue metalloproteinase inhibitors (TIMPs) play an important role in many physiological and pathological processes, including proliferation, migration, invasion, cell differentiation, participation in inflammatory processes and angiogenesis. Numerous studies point to a direct relationship between MMPs and both local tumor invasion and the formation of distant metastases. High activity of MMPs is observed in solid tumors of various origins, which positively correlates with a poor overall survival rate. Although biochemical diagnostic markers of PCa are currently available, from the point of view of clinical practice, it seems particularly important to develop new and more sensitive markers allowing for early diagnosis and long-term monitoring of patients after PCa treatment, and the assessment of MMP activity in urine and serum of patients are potential factors that could play such a role.

Progress on the detoxification of aflatoxin B1 using natural anti-oxidants

Aflatoxins are toxic secondary metabolites produced by Aspergillus fungi. The most toxic among them is Aflatoxin B1 (AFB1) which is known to have genotoxic, immunotoxic, teratogenic, carcinogenic, and mutagenic toxic effects (amongst others). The mechanisms responsible for its toxicity include the induction of oxidative stress, cytotoxicity, and DNAdamage. Studies have found that natural anti-oxidants can reduce the damage that AFB1 inflicts on the body by alleviating oxidative stress and inhibiting the biotransformation of AFB1. Therefore, this review outlines the latest progress in research on the use of natural anti-oxidants as antidotes to aflatoxin poisoning and their detoxification mechanisms. It also considers the problems that may possibly arise from their use and their application prospects. Our aim is to provide a useful reference for the prevention and treatment of AFB1 poisoning.

Carotenoids: Dietary Sources, Extraction, Encapsulation, Bioavailability, and Health Benefits-A Review of Recent Advancements

Natural carotenoids (CARs), viz. β-carotene, lutein, astaxanthin, bixin, norbixin, capsanthin, lycopene, canthaxanthin, β-Apo-8-carotenal, zeaxanthin, and β-apo-8-carotenal-ester, are being studied as potential candidates in fields such as food, feed, nutraceuticals, and cosmeceuticals. CAR research is advancing in the following three major fields: (1) CAR production from natural sources and optimization of its downstream processing; (2) encapsulation for enhanced physical and chemical properties; and (3) preclinical, clinical, and epidemiological studies of CARs’ health benefits. This review critically discusses the recent developments in studies of the chemistry and antioxidant activity, marketing trends, dietary sources, extraction, bioaccessibility and bioavailability, encapsulation methods, dietary intake, and health benefits of CARs. Preclinical, clinical, and epidemiological studies on cancer, obesity, type 2 diabetes (T2D), cardiovascular diseases (CVD), osteoporosis, neurodegenerative disease, mental health, eye, and skin health are also discussed.

What Is the Current Direction of the Research on Carotenoids and Human Health? An Overview of Registered Clinical Trials

Carotenoids have been the object of numerous observational, pre-clinical and interventional studies focused on elucidating their potential impacts on human health. However, the large heterogeneity among the trials, in terms of study duration and characteristics of participants, makes any conclusion difficult to draw. The present study aimed to explore the current carotenoid research trends by analyzing the characteristics of the registered clinical trials. A total of 193 registered trials on ClinicalTrials.gov and ISRCTN were included in the revision. Eighty-three studies were performed with foods, one-hundred-five with food supplements, and five with both. Among the foods tested, tomatoes and tomato-based foods, and eggs were the most studied. Lutein, lycopene, and astaxanthin were the most carotenoids investigated. Regarding the goals, 52 trials were focused on studying carotenoids’ bioavailability, and 140 studies investigated the effects of carotenoids on human health. The main topics included eye and cardiovascular health. Recently, the research has focused also on two new topics: cognitive function and carotenoid–gut microbiota interactions. However, the current research on carotenoids is still mostly focused on the bioavailability and metabolism of carotenoids from foods and food supplements. Within this context, the impacts/contributions of food technologies and the development of new carotenoid formulations are discussed. In addition, the research is still corroborating the previous findings on vision and cardiovascular health. Much attention has also been devoted to new research areas, such as the carotenoid–microbiota interactions, which could contribute to explaining the metabolism and the health effects of carotenoids; and the relation between carotenoids and cognitive function. However, for these topics the research is still only beginning, and further studies are need.

Redox regulation by carotenoids: Evidence and conflicts for their application in cancer

Carotenoids have been constantly investigated since the early fifty for their chemical, biochemical and biological properties being presence in foods. Among the more than 1100 carotenoids synthesized by plants and microorganisms, approximately 50 are present in the human diet, and about 20 can be detected in human blood and tissues. Review articles that discuss the anticancer and cancer preventing activity of phytochemicals have often in common the difficulty to find a coherency between the results deriving from experimental studies and the controversial or weak clinical indications arising from epidemiological and interventional studies. In this scenario, the class of carotenoids does not represent an exception. In fact, according with World Cancer Research Fund, strong evidence exists that high-dose supplementation of β-carotene increases the risk of lung cancer, while for other types of cancer, the protective or harmful effects of food-containing carotenoids or carotenoid supplements have been considered limited, suggestive or unlikely. The analysis of the mechanistic evidence is complicated by the double nature of carotenoids being molecules acting either as antioxidant or pro-oxidant compounds. The present review analyzes the ambiguity and the unexpected results deriving from the epidemiological and interventional studies and discusses how the effects of carotenoids on cancer risk can be explained by understanding their capacity to modulate the cellular antioxidant response, depending on the concentration applied and the cellular metabolism. In the final part, a new global approach is proposed to study the contribution of carotenoids, but also of other phytochemicals, to disease prevention, including cancer.

Adolescent Plant Product Intake in Relation to Later Prostate Cancer Risk and Mortality in the NIH-AARP Diet and Health Study

BACKGROUND

Although fruit and vegetable intake during adolescence, a potentially sensitive time period for prostate cancer (PCa) development, has been proposed to protect against PCa risk, few studies have investigated the role of adolescent plant product intake in PCa development.

METHODS

Intake of various vegetables, fruit, and grains by males at ages 12-13 y was examined in relation to later PCa risk and mortality in the NIH-AARP Diet and Health Study. Cox proportional hazards regression was used to calculate HRs and 95% CIs of nonadvanced (n = 14,238) and advanced (n = 2,170) PCa incidence and PCa mortality (n = 760) during 1,729,896 person-years of follow-up.

RESULTS

None of the plant products examined were associated consistently with all PCa outcomes. However, greater adolescent intakes of tomatoes (P-trend = 0.004) and nonstarch vegetables (P-trend = 0.025) were associated with reduced risk of nonadvanced PCa, and greater intakes of broccoli (P-trend = 0.050) and fruit juice (P-trend = 0.019-0.025) were associated with reduced risk of advanced PCa and/or PCa mortality. Positive trends were also observed for greater intakes of fruit juice (P-trend = 0.002), total fruit (P-trend = 0.014), and dark bread (P-trend = 0.035) with nonadvanced PCa risk and for greater intakes of legumes (P-trend < 0.001), fiber (P-trend = 0.001), and vegetable protein (P-trend = 0.013-0.040) with advanced PCa risk or PCa mortality.

CONCLUSIONS

Our findings do not provide strong evidence to suggest that adolescent plant product intake is associated with reduced PCa risk.

Synthetic Retinoids as Potential Therapeutics in Prostate Cancer-An Update of the Last Decade of Research: A Review

Prostate cancer (PC) is the second most common tumor in males. The search for appropriate therapeutic options against advanced PC has been in process for several decades. Especially after cessation of the effectiveness of hormonal therapy (i.e., emergence of castration-resistant PC), PC management options have become scarce and the prognosis is poor. To overcome this stage of disease, an array of natural and synthetic substances underwent investigation. An interesting and promising class of compounds constitutes the derivatives of natural retinoids. Synthesized on the basis of the structure of retinoic acid, they present unique and remarkable properties that warrant their investigation as antitumor drugs. However, there is no up-to-date compilation that consecutively summarizes the current state of knowledge about synthetic retinoids with regard to PC. Therefore, in this review, we present the results of the experimental studies on synthetic retinoids conducted within the last decade. Our primary aim is to highlight the molecular targets of these compounds and to identify their potential promise in the treatment of PC.

Therapeutic effect of iodised serum milk protein, lycopene and their combination on benign prostatic hyperplasia induced in rats

Benign prostatic hyperplasia (BPH) is a common chronic disease in ageing men. Synthetic inhibitors of 5α-reductase commonly used in BPH treatment have limited effectiveness and may cause side effects. Evaluation of iodised serum milk protein and lycopene therapeutic effect in rat BPH model was the aim of the present study. BPH was induced in male Wistar rats by surgical castration and subsequent testosterone administrations (25 mg/kg, 7 injections). Rats with induced BPH received lycopene (5 mg/kg), iodised serum milk protein (200 µg/kg) or their combination for 1 month daily. The efficacy of the treatment was evaluated by the prostate weight, prostatic index and ventral lobe epithelium thickness. In lycopene and iodised serum milk protein-treated rats, prostate weight and prostatic index were significantly reduced compared to control group; and lycopene and iodised serum milk protein used in combination yielded an additive effect. Thus, further investigation of combined supplementation with micronutrients and plant-derived substances in BPH models may help to find new opportunities or its safe and effective treatment.

Mechanistic aspects of carotenoid health benefits - where are we now?

Dietary intake and tissue levels of carotenoids have been associated with a reduced risk of several chronic diseases, including cardiovascular diseases, type 2 diabetes, obesity, brain-related diseases and some types of cancer. However, intervention trials with isolated carotenoid supplements have mostly failed to confirm the postulated health benefits. It has thereby been speculated that dosing, matrix and synergistic effects, as well as underlying health and the individual nutritional status plus genetic background do play a role. It appears that our knowledge on carotenoid-mediated health benefits may still be incomplete, as the underlying mechanisms of action are poorly understood in relation to human relevance. Antioxidant mechanisms - direct or via transcription factors such as NRF2 and NF-κB - and activation of nuclear hormone receptor pathways such as of RAR, RXR or also PPARs, via carotenoid metabolites, are the basic principles which we try to connect with carotenoid-transmitted health benefits as exemplified with described common diseases including obesity/diabetes and cancer. Depending on the targeted diseases, single or multiple mechanisms of actions may play a role. In this review and position paper, we try to highlight our present knowledge on carotenoid metabolism and mechanisms translatable into health benefits related to several chronic diseases.

Recent Progress in Discovering the Role of Carotenoids and Their Metabolites in Prostatic Physiology and Pathology with a Focus on Prostate Cancer-A Review-Part I: Molecular Mechanisms of Carotenoid Action

Among the vast variety of plant-derived phytochemicals, the group of carotenoids has continuously been investigated in order to optimize their potential application in the area of dietary intervention and medicine. One organ which has been especially targeted in many of these studies and clinical trials is the human prostate. Without doubt, carotenoids (and their endogenous derivatives—retinoids and other apo-carotenoids) are involved in intra- and intercellular signaling, cell growth and differentiation of prostate tissue. Due to the accumulation of new data on the role of different carotenoids such as lycopene (LC) and β-carotene (BC) in prostatic physiology and pathology, the present review aims to cover the past ten years of research in this area. Data from experimental studies are presented in the first part of the review, while epidemiological studies are disclosed and discussed in the second part. The objective of this compilation is to emphasize the present state of knowledge regarding the most potent molecular targets of carotenoids and their main metabolites, as well as to propose promising carotenoid agents for the prevention and treatment of prostatic diseases.

Recent Progress in Discovering the Role of Carotenoids and Metabolites in Prostatic Physiology and Pathology-A Review-Part II: Carotenoids in the Human Studies

Among the vast variety of plant-derived phytochemicals, the group of carotenoids has continuously been investigated in order to optimize their potential application in the area of dietary intervention related to chronic diseases. One organ that has been especially targeted in many of these studies and clinical trials is the human prostate. Without doubt, carotenoids (and their endogenous derivatives-retinoids and apo-carotenoids) are involved in a plethora of intra- and intercellular signaling, cell growth, and differentiation of prostate tissue. Due to the accumulation of new data on the role of different carotenoids, such as lycopene (LYC) and β-carotene (BC), in prostatic physiology and pathology, the present review aimed to cover the past ten years of research in this regard. Data from experimental studies are presented in the first part of the review, while epidemiological studies are disclosed in this second part. The objective of this compilation was to emphasize the present state of knowledge about the most potent molecular targets of carotenoids, as well as to propose promising carotenoid agents for the prevention and possible treatment of prostatic diseases.