Usefulness of Opuntia spp. on the Management of Obesity and Its Metabolic Co-Morbidities

The plants of the Opuntia genus mainly grow in arid and semi-arid climates. Although the highest variety of wild species is found in Mexico, Opuntia spp. is widely distributed throughout the world. Extracts of these cacti have been described as important sources of bioactive substances that can have beneficial properties for the prevention and treatment of certain metabolic disorders. The objective of this review is to summarise the presently available knowledge regarding Opuntia ficus-indica (nopal or prickly pear), and some other species (O. streptacantha and O. robusta) on obesity and several metabolic complications. Current data show that Opuntia ficus-indica products used in preclinical studies have a significant capacity to prevent, at least partially, obesity and certain derived co-morbidities. On this subject, the potential beneficial effects of Opuntia are related to a reduction in oxidative stress and inflammation markers. Nevertheless, clinical studies have evidenced that the effects are highly contingent upon the experimental design. Moreover, the bioactive compound composition of nopal extracts has not been reported. As a result, there is a lack of information to elucidate the mechanisms of action responsible for the observed effects. Accordingly, further studies are needed to demonstrate whether Opuntia products can represent an effective tool to prevent and/or manage body weight and some metabolic disorders.

In Vitro Screening and Lipid-Lowering Effect of Prickly Pear (Opuntia Ficus-Indica L. Mill.) Fruit Extracts in 3T3-L1 Pre-Adipocytes and Mature Adipocytes

Opuntia ficus-indica fruits have been widely used due to their nutritional composition and beneficial effects on health, particularly against chronic diseases such as diabetes, obesity, cardiovascular diseases and cancer, among others. In recent years, prickly pear peel and pulp extracts have been characterised, and a high number of bioactive compounds have been identified. This study aimed to analyse the triglyceride-lowering effect of prickly pear peel and pulp extracts obtained from fruits of three varieties (Pelota, Sanguinos, and Colorada) in 3T3-L1 maturing and mature adipocytes. At a concentration of 50 µg/mL, peel extracts from Colorada reduced triglyceride accumulation in pre-adipocytes and mature adipocytes. Additionally, at 25 µg/mL, Pelota peel extract decreased triglyceride content in mature adipocytes. Moreover, maturing pre-adipocytes treated with 50 and 25 µg/mL of Sanguinos pulp extract showed a reduction of triglyceride accumulation. In addition, the lipid-lowering effect of the main individual betalain and phenolic compounds standards were assayed. Piscidic acid and isorhamnetin glycoside (IG2), found in Colorada peel extract, were identified as the bioactive compounds that could contribute more notably to the triglyceride-lowering effect of the extract. Thus, the betalain and phenolic-rich extracts from Opuntia ficus indica fruits may serve as an effective tool in obesity management.

Changes in brown adipose tissue induced by resveratrol and its analogue pterostilbene in rats fed with a high-fat high-fructose diet

Natural bioactive compounds have attracted a great deal of attention since some of them can act as thermogenesis activators. In recent years, special interest has been placed on resveratrol and its analogue pterostilbene, a dimethylether derivative that shows higher bioavailability. The aim of the present study is to compare the effects of resveratrol and its derivative pterostilbene on the thermogenic capacity of interscapular brown adipose tissue (iBAT) in rats under a high-fat high-fructose diet. Rats were divided into four experimental groups: control, high-fat high-fructose diet (HFHF) and HFHF diet supplemented with 30 mg/kg body weight/day of pterostilbene (PT30) or resveratrol (RSV30), for eight weeks. Weights of adipose tissues, iBAT triglycerides, carnitine palmitoyltransferase 1A (CPT1A) and citrate synthase (CS) activities, protein levels of uncoupling protein 1 (UCP1), sirtuins (SIRT1 and 3), AMP-activated protein kinase (AMPK), glucose transporter (GLUT4), fatty acid synthase (FAS), nuclear respiratory factor (NRF1), hormone-sensitive lipase (HSL), adipose triglyceride lipase (ATGL), CD36 and FATP1 fatty acid transporters, peroxisome proliferator-activated receptor gamma coactivator 1 (PGC1) activation and the batokines EPDR1 and NRG4 were assessed in iBAT. The results show that some key proteins related to thermogenesis were modified by either pterostilbene or resveratrol, although the lack of effects on other crucial proteins of the thermogenic machinery suggest that these compounds were not able to stimulate this process in iBAT. Overall, these data suggest that the effects of stilbenes on brown adipose tissue thermogenic capacity depend on the metabolic status, and more precisely on the presence or absence of obesity, although further studies are needed to confirm this hypothesis.

Beneficial Effects of Opuntia spp. on Liver Health

The genus Opuntia spp. includes plants capable of growing in arid, temperate and tropical climates. The vast majority of wild species grow in Mexico, but O. ficus-indica (prickly pear or nopal) is cultivated around the world and it is one of the most studied. This review shows the currently available knowledge concerning the action of O. ficus-indica and other Opuntia species (Opuntia vulgaris, Opuntia robusta, Opuntia streptacantha, Opuntia microdasys, Opuntia dillenii and Opuntia dejecta) on liver health. The available data demonstrate the positive effects of extracts, vinegar, juices or seed oil of the Opuntia genus on the alterations induced in the liver by inadequate feeding patterns or the administration of chemicals. In this regard, the potential beneficial effects of nopal are related to the attenuation of triglyceride accumulation, oxidative stress and/or inflammation. Nevertheless, there is no information concerning the bioactive compound's characterisation in most of these studies; consequently, it is not possible to link the therapeutic effects of these plants to the presence of specific compounds in the nopal extracts. Therefore, further research is needed to confirm if the positive effects observed in animal models are also found in humans, in order to determine whether Opuntia can represent an effective tool to prevent and/or manage hepatic alterations.

Anti-Steatotic Effects of Chlorella vulgaris, Nannochloropsis gaditana and Gracilaria vermiculophylla Algae Extracts in AML-12 Hepatocytes

Non-alcoholic fatty liver disease (NAFLD) is considered the most common chronic liver alteration whose prevalence is increasing in Western countries. Microalgae and macroalgae have attracted great interest due to the high content in bioactive compounds with beneficial effects on health. The aim of the present study is to assess the potential interest of extracts rich in proteins obtained from the microalgae Chlorella vulgaris and Nannochloropsis gaditana and the macroalga Gracilaria vermiculophylla in the prevention of lipid accumulation in AML-12 hepatocytes. Toxicity was not observed at any of the tested doses. Both microalgae and the macroalga were effective in preventing triglyceride accumulation, with Nannochloropsis gaditana being the most effective one. Although the three algae extracts were able to increase different catabolic pathways involved in triglyceride metabolism, the mechanisms underlying the anti-steatotic effect were different in each algae extract. In conclusion, the present study demonstrates that Chlorella vulgaris, Nannochloropsis gaditana and Gracilaria vermiculophylla extracts are able to partially prevent the accumulation of triglycerides induced by palmitic acid in cultured hepatocytes, a model used to mimic the steatosis induced in liver by dietary patterns rich in saturated fat.

Potential usefulness of Mediterranean diet polyphenols against COVID-19-induced inflammation: a review of the current knowledge

The Mediterranean diet is a dietary pattern typical of the populations living in the Mediterranean basin during the 50s-60s of the last century. This diet has demonstrated beneficial effects in the prevention of several pathologies such as cardiovascular diseases, metabolic syndrome, or several cancer types, at least in part, due to its antioxidant compounds. Since the COVID-19 pandemic started, different authors have been studying the effects of certain dietary habits on the presence of COVID-19 and its severity, and the Mediterranean diet is one of them. This review gathers data from studies supporting the potential usefulness of the main phenolic compounds present in the Mediterranean diet, based on their antioxidant and anti-inflammatory effects, as preventive/therapeutic agents against COVID-19. The current evidence supports the potential benefits that hydroxytyrosol, resveratrol, flavonols such as quercetin, flavanols like catechins, and flavanones on the order of naringenin could have on COVID-19. This is due to the increase in the synthesis and translocations of Nrf-2, which increases the activity of antioxidant enzymes and thus reduces ROS production, the scavenging of free radicals, and the suppression of the activity of MMP-9, which is involved in the cytokine storm, and the inhibition of NF-κB.

Scientific Evidence Supporting the Beneficial Effects of Isoflavones on Human Health

Isoflavones are phenolic compounds with a chemical structure similar to that of estradiol. They are present in several vegetables, mainly in legumes such as soy, white and red clover, alfalfa and beans. The most significant food source of isoflavones in humans is soy-derived products. Isoflavones could be used as an alternative therapy for pathologies dependent on hormonal disorders such as breast and prostate cancer, cardiovascular diseases, as well as to minimize menopausal symptoms. According to the results gathered in the present review, it can be stated that there is scientific evidence showing the beneficial effect of isoflavones on bone health and thus in the prevention and treatment of osteoporosis on postmenopausal women, although the results do not seem entirely conclusive as there are discrepancies among the studies, probably related to their experimental designs. For this reason, the results should be interpreted with caution, and more randomized clinical trials are required. By contrast, it seems that soy isoflavones do not lead to a meaningful protective effect on cardiovascular risk. Regarding cancer, scientific evidence suggests that isoflavones could be useful in reducing the risk of suffering some types of cancer, such as breast and endometrial cancer, but further studies are needed to confirm these results. Finally, isoflavones could be useful in reducing hot flushes associated with menopause. However, a limitation in this field is that there is still a great heterogeneity among studies. Lastly, with regard to isoflavone consumption safety, it seems that they are safe and that the most common adverse effect is mild and occurs at the gastrointestinal level.

Activity of Pterostilbene Metabolites against Liver Steatosis in Cultured Hepatocytes

Pterostilbene is a dimethyl ether derivative of resveratrol, less metabolized than its analogue, due to the substitution of two hydroxyl groups with methoxyl groups. Nevertheless, the amounts of pterostilbene phase II metabolites found in plasma and tissues are higher than those of the parent compound. The first aim of this study was to assess whether pterostilbene-4′-O-glucuronide (PT-G) and pterostilbene-4′-O-sulfate (PT-S) were able to prevent triglyceride accumulation in AML12 (alpha mouse liver 12) hepatocytes. This being the case, we aimed to analyze the mechanisms involved in their effects. For this purpose, an in vitro model mimicking the hepatocyte situation in fatty liver was developed by incubating mouse AML12 hepatocytes with palmitic acid (PA). For cell treatments, hepatocytes were incubated with 1, 10 or 25 µM of pterostilbene, pterostilbene-4′-O-glucuronide or pterostilbene-4′-O-sulfate for 18 h. Triglycerides and cell viability were assessed by a commercial kit and crystal violet assay, respectively. Protein expression of enzymes and transporters involved in triglyceride metabolism was analyzed by immunoblot. The results showed for the first time the anti-steatotic effect of pterostilbene metabolites and thus, that they contribute to the preventive effect induced by pterostilbene on steatosis in in vivo models. This anti-steatotic effect is mainly due to the inhibition of de novo lipogenesis.

Key Aspects in Nutritional Management of COVID-19 Patients

This review deals with the relationship among nutrition, the immune system, and coronavirus disease 2019 (COVID-19). The influence of nutrients and bioactive molecules present in foodstuffs on immune system activity, the influence of COVID-19 on the nutritional status of the patients, and the dietary recommendations for hospitalized patients are addressed. Deficient nutritional status is probably due to anorexia, nausea, vomiting, diarrhea, hypoalbuminemia, hypermetabolism, and excessive nitrogen loss. There is limited knowledge regarding the nutritional support during hospital stay of COVID-19 patients. However, nutritional therapy appears as first-line treatment and should be implemented into standard practice. Optimal intake of all nutrients, mainly those playing crucial roles in immune system, should be assured through a diverse and well-balanced diet. Nevertheless, in order to reduce the risk and consequences of infections, the intakes for some micronutrients may exceed the recommended dietary allowances since infections and other stressors can reduce micronutrient status. In the case of critically ill patients, recently published guidelines are available for their nutritional management. Further, several natural bioactive compounds interact with the angiotensin-converting enzyme 2 (ACE2) receptor, the gateway for severe acute respiratory syndrome (SARS) and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Natural bioactive compounds can also reduce the inflammatory response induced by SARS-CoV-2. These compounds are potential beneficial tools in the nutritional management of COVID-19 patients.

Anti-Obesity Effects of Macroalgae

Macroalgae have attracted great interest for their potential applications in nutraceutical and pharmaceutical industries as source of bioactive medicinal products and food ingredients. This review gathers data from in vitro and in vivo studies addressing the anti-obesity effects of macroalgae. Great consensus exists in all reported in vitro studies concerning the reduction induced by seaweed extracts in the expression of transcriptional factors controlling adipogenesis. In animals, macroalgae reduced body fat accumulation and prevented other obesity features, such as dyslipidemia, insulin resistance and fatty liver. These effects are not due to food intake reduction, since few studies have reported such event. Indeed, the effects on metabolic pathways in target tissues/organs seem to play a more relevant role. Macroalgae can reduce de novo lipogenesis, limiting fatty acid availability for triglyceride synthesis in white adipose tissue. This effect has been observed in both cell cultures and adipose tissue from animals treated with macroalgae extracts. In addition, increased fatty acid oxidation and thermogenic capacity, as well as a shift towards healthier gut microbiota composition may contribute to the body fat-lowering effect of macroalgae. Studies in humans are needed to determine whether macroalgae can represent a feasible tool to prevent and/or manage overweight and obesity.

Involvement of 5'-Activated Protein Kinase (AMPK) in the Effects of Resveratrol on Liver Steatosis

This review focuses on the role of 5′AMP-activated protein kinase (AMPK) in the effects of resveratrol (RSV) and some RSV derivatives on hepatic steatosis. In vitro studies, performed in different hepatic cell models, have demonstrated that RSV is effective in preventing liver TG accumulation by activating AMPK, due to its phosphorylation. These preventive effects have been confirmed in studies conducted in animal models, such as mice and rats, by administering the phenolic compound at the same time as the diet which induces TG accumulation in liver. The literature also includes studies focused on other type of models, such as animals showing alcohol-induced steatosis or even steatosis induced by administering chemical products. In addition to the preventive effects of RSV on hepatic steatosis, other studies have demonstrated that it can alleviate previously developed liver steatosis, thus its role as a therapeutic tool has been proposed. The implication of AMPK in the delipidating effects of RSV in in vivo models has also been demonstrated.

Resveratrol and Pterostilbene, Two Analogue Phenolic Compounds, Affect Aquaglyceroporin Expression in a Different Manner in Adipose Tissue

Aquaglyceroporins (AQPs) are transmembrane channels that mediate glycerol release and glycerol uptake. They are involved in fat metabolism, with implications in obesity. The aim was to determine whether the administration of resveratrol and pterostilbene during the six weeks of the experimental period would modify AQPs expression in white and brown adipose tissues from Wistar rats fed an obesogenic diet, and to establish a potential relationship with the delipidating properties of these compounds. Consequently, thirty-six rats were divided into four groups: (a) group fed a standard diet; and three more groups fed a high-fat high-sucrose diet: (b) high-fat high-sucrose group: (c) pterostilbene-treated group (30 mg/kg/d): (d) resveratrol-treated group (30 mg/kg/d). Epididymal, subcutaneous white adipose tissues and interscapular brown adipose tissue were dissected. AQPs gene expression (RT-PCR) and protein expression (western-blot) were measured. In white adipose tissue, pterostilbene reduced subcutaneous adipose tissue weight and prevented the decrease in AQP9 induced by obesogenic feeding, and thus glycerol uptake for triglyceride accumulation. Resveratrol reduced epididymal adipose tissue weight and avoided the decrease in AQPs related to glycerol release induced by high-fat high-sucrose feeding, suggesting the involvement of lipolysis in its body-fat lowering effect. Regarding brown adipose tissue, AQP7 seemed not to be involved in the previously reported thermogenic activity of both phenolic compounds.

Unraveling the in vitro antitumor activity of Vismia baccifera against HepG2: role of hydrogen peroxide

Currently natural products derived from plants are receiving huge attention because of their antitumor activities. In previous work we reported that an aqueous leaf extract of Vismia baccifera induced toxicity in HepG2. The present study focuses on the mechanisms of the cytotoxic actions induced by the extract. Results showed that V. baccifera was innocuous in non-transformed human HH4 hepatocytes. In HepG2 it caused deregulation of antioxidant status (increasing superoxide dismutase expression and decreasing glutathione levels and glutathione peroxidase activity) and accumulation of reactive oxygen species, particularly hydrogen peroxide. The extract induced a) cell cycle arrest at G₂/M phase, b) phosphorylation of ATM (protein kinase ataxia-telangiectasia mutated) and γH2AX (γ-histone family 2A variant), c) caspase-3 activation, and e) deregulation of the Bax/Bcl family, increasing pro-apoptotic proteins. ATM did not seem to be involved in γH2AX activation. Co-incubation with catalase prevented the alterations elicited by V. baccifera in HepG2. Taking together, these results indicate that hydrogen peroxide mediates the HepG2 cytotoxic response and provide evidence for more in-depth studies of the signaling involved.

Influence of oxygen partial pressure on the characteristics of human hepatocarcinoma cells

Most of the in vitro studies using liver cell lines have been performed under atmospheric oxygen partial pressure (21% O₂). However, the oxygen concentrations in the liver and cancer cells are far from this value. In the present study, we have evaluated the influence of oxygen on 1) the tumor cell lines features (growth, steady-state ROS levels, GSH content, activities of antioxidant enzymes, p66 Shc and SOD expressions, metalloproteinases secretion, migration, invasion, and adhesion) of human hepatocellular carcinoma cell lines, and b) the response of the cells to an oxidant stimulus (aqueous leaf extract of the V. baccifera plant species). For this purpose, three hepatocarcinoma cell lines with different p53 status, HepG2 (wild-type), Huh7 (mutated), and Hep3B (deleted), were cultured (6–30 days) under atmospheric (21%) and more physiological (8%) pO₂. Results showed that after long-term culturing at 8% versus 21% O₂, the cellular proliferation rate and the steady-state levels of mitochondrial O₂^- were unaffected. However, the intracellular basal ROS levels were higher independently of the characteristics of the cell line. Moreover, the lower pO₂ was associated with lower glutathione content, the induction of p66 Shc and Mn-SOD proteins, and increased SOD activity only in HepG2. This cell line also showed a higher migration rate, secretion of active metalloproteinases, and a faster invasion. HepG2 cells were more resistant to the oxidative stress induced by V. baccifera. Results suggest that the long-term culturing of human hepatoma cells at a low, more physiological pO₂ induces antioxidant adaptations that could be mediated by p53, and may alter the cellular response to a subsequent oxidant challenge. Data support the necessity of validating outcomes from studies performed with hepatoma cell cultures under ambient O₂.

•

The influence of pO₂ on human hepatocellular carcinoma cell features is analyzed.

•

Low oxygen tension (8% O₂) induces antioxidant adaptations in HepG2.

•

Low O₂ increases the migration and invasion rates of HepG2.

•

Antioxidant adaptations could be p53-dependent.

•

Validating results from in vitro studies using cells cultured at 21% O₂ are required.

Piper and Vismia species from Colombian Amazonia differentially affect cell proliferation of hepatocarcinoma cells

There is an increasing interest to identify plant-derived natural products with antitumor activities. In this work, we have studied the effects of aqueous leaf extracts from Amazonian Vismia and Piper species on human hepatocarcinoma cell toxicity. Results showed that, depending on the cell type, the plants displayed differential effects; thus, Vismia baccifera induced the selective killing of HepG2, while increasing cell growth of PLC-PRF and SK-HEP-1. In contrast, these two last cell lines were sensitive to the toxicity by Piper krukoffii and Piper putumayoense, while the Piperaceae did not affect HepG2 growth. All the extracts induced cytotoxicity to rat hepatoma McA-RH7777, but were innocuous (V. baccifera at concentrations < 75 µg/mL) or even protected cells from basal death (P. putumayoense) in primary cultures of rat hepatocytes. In every case, cytotoxicity was accompanied by an intracellular accumulation of reactive oxygen species (ROS). These results provide evidence for the anticancer activities of the studied plants on specific cell lines and suggest that cell killing could be mediated by ROS, thus involving mechanisms independent of the plants free radical scavenging activities. Results also support the use of these extracts of the Vismia and Piper genera with opposite effects as a model system to study the mechanisms of the antitumoral activity against different types of hepatocarcinoma.