Author: Alessio Gastino & Giovanni Dal Vecchio

Introduction

Kale (Brassica oleracea var. acephala) is a leafy green vegetable belonging to the Brassicaceae family, including approximately 350 genera, 13 tribes and 3200 species.
The plant is robust and tolerates a broad range of agricultural and climatic conditions. It has a lively pungent flavor with bitter peppery qualities. However, a light frost will produce sweeter and more flavorful kale leaves.

Among the Brassica vegetables, kale has been reported to exhibit the highest concentrations of vitamins, minerals, dietary fiber, carotenoids, glucosinolates,and phenolic compounds, with potential positive health effects in human.

Glucosinolates. are modified aminoacids, carrying an S-glucose functional group and variety of different side chains. Hydrolysis of GLs by myrosinase, an enzyme found both in the same plants and in human bowel microflora, leads to the production of several biologically active compounds such as isothiocyanates, thiocyanates and nitriles, depending on the hydrolysis conditions.
The main phenolic compounds found in Brassica vegetables Flavonoids and phenolic acids, both of which predominantly exist as molecules in conjugated forms. The most ubiquitous subclass of the flavonoids is the flavonols, with the most abundant aglycons quercetin and kaempferol. Another flavonoid subclass found in Brassica is the anthocyanins, responsible for the purple red color. In plant tissue, flavonols and anthocyanins are present as sugar conjugates and are often acylated with hydroxycinnamic acids.

Brassica vegetables can be subjected to various forms of processing to make them more suitable for human consumption. Common processing steps include blanching, freezing, cooking, and, occasionally, warm-holding. Culinary processing affects the plant tissue and the phytochemicals present and may lead to alteration in health-related qualities. Processing may influence phytochemicals positively by releasing compounds and increasing their bioavailability or negatively by physical loss and chemical degradation of the phytochemicals.
Glucosinolates biochemistry, genetics and biological activity.

Kale and its antioxidant effects

Several epidemiological studies have indicated that a high intake of kale products is associated with a reduced risk of a number of chronic diseases, such as atherosclerosis and cancer. These beneficial effects have been partly attributed to the compounds which possess antioxidant activity. The major antioxidants of these vegetables are vitamins C and E, carotenoids, and phenolic compounds, especially flavonoids. These antioxidants scavenge radicals and inhibit the chain initiation or break the chain propagation (the second defense line). Vitamin E and carotenoids also contribute to the first defense line against oxidative stress, because they quench singlet oxygen. Flavonoids as well as vitamin C showed a protective activity to a- tocopherol in human LDL, and they can also regenerate vitamin E, from the achromanoxy radical.
Nutrient antioxidants may act together to reduce reactive oxygen spieces level more effectively than single dietary antioxidants, because they can function as synergists. In addition, a mixture containing both water-soluble and lipid-soluble antioxidants is capable of quenching free radicals in both aqueous and lipid phases For example, with the liposome oxidation method, the activity of combination of quercetin or catechins plus a-tocopherol was significantly higher than the sum of the individual activities. Combinations of a-tocopherol or vitamin C plus phenolic compounds also provided synergistic effects in human erythrocyte membrane ghosts and phosphatidylcholine liposome systems.

Water-soluble antioxidants

Vitamin C

Vitamin C, which includes ascorbic acid and its oxidation product has many biological activities in human body. Biological function of L- ascorbic acid can be defined as an enzyme cofactor, a radical scavenger, and as a donor/acceptor in electron transport at the plasma membrane. Ascorbic acid is able to scavenge the superoxide and hydroxyl radicals, as well as regenerate a-tocopherol.
Dehydroascorbic acid (DHA) (oxidation product of ascorbic acid) is unstable at physiological pH and it is spontaneously and enzymatically converted to 2,3-diketo- gulonic acid. It is the dominant form of vitamin C in kale, with 4-fold higher level than ascorbic acid.

In addition to ascorbic and dehydroascorbic acid, Brassica vegetables include ascorbigens, which are formed as the result of the reaction between ascorbic acid and degradation products of indol-3-ylmethylglucosinolates produced in the myrosinase-catalysed degradation

Phenolic compounds

Phenolic compounds, especially flavonoids, possess different biological functions but the most important is the antioxidant activity. They are able to scavenge reactive oxygen spieces due to their electron donating properties. Their antioxidant effectiveness depends on the stability in different systems, as well as number and location of hydroxyl groups. In many in vitro studies, phenolic compounds demonstrated higher antioxidant activity than antioxidant vitamins and carotenoids.

Lipid-soluble antioxidants

Carotenoids

Carotenoids (carotens and xanthophylls) are yellow, orange, and red pigments present in many fruits and vegetables. Several of them are precursors of vitamin A (i.e. b-carotene, g-carotene, and b-cryptoxanthin), and due to conjugated double bonds they are both radical scavengers and quenchers of singlet oxygen. Lutein and b-carotene are the dominant carotenoids in cruciferous vegetables.

Vitamin E

In addition to carotenoids, vitamin E also belongs to a group of lipid-soluble antioxidants. The biological activity of vitamin E exhibit tocopherols and tocotrienols, especially a-tocopherol. The predominant reaction responsible for tocopherol antioxidant activity is hydrogen atom donation, where a tocopheroxyl radical is formed. Vitamin E shows protective effects against the coronary heart disease due to inhibition of LDL oxidation

Future research should be focused on relationship between the total antioxidant capacity and the content, as well as composition of antioxidants in Brassica vegetables since: (i) the content and composition of antioxidants vary significantly between and within their subspecies, (ii) antioxidant activity and stability of individual phytochemicals differ significantly, (iii) the vegetable processing (blanching, canning), as well as domestic cooking influence antioxidants content and activity.

Natural antioxidants and antioxidant capacity of Brassicavegetables.

Protection against cerebral ischemia/reperfusion

Ischemic stroke is the result of a transient or permanent reduction in cerebral blood flow caused by the occlusion of a cerebral artery via an embolus or local thrombosis. Cerebral ischemia initiates a significant inflammatory cascade, which involves the activation of brain microglia, upregulation of proinflammatory cytokines, such as tumor necrosis factor-alpha (TNF-α), interleukin (IL)-1β and others, infiltration of various types of inflammatory cells (including neutrophils, different subtypes of T cells, monocyte/macrophages and other cells) into the ischemic brain tissue.

Restoration of blood supply to ischemic tissues can cause additional damage that can be more dangerous than the initial ischemia. It has been amply demonstrated that there are a series of reactions following brain reperfusion, such as inflammation and a rapid increase of reactive oxygen species (ROS) and reactive nitrogen species (RNS), which can produce significant quantities of tissue damage, thereby contributing to neuronal cell death.
Therefore, antiinflammatory or antioxidant approach may be a potential therapeutic strategy of preserving against ischemia/reperfusion (I/R) cerebral injury .
Despite advances in the understanding of the cerebral ischemia pathophysiology, therapeutic options remain limited. Numerous clinical trials failed in the past decades because either these agents showed no protective effects in patients or their toxicity/side effects cannot be tolerated by patients.
In many epidemiological studies, consumption of Brassica vegetables seems to have beneficial effects attributed to the huge presence of glucosinolates (GLs) in this family of vegetables. Among them, one of the most studied is RS-glucoraphanin [RS-GRA; 4(RS)-methylsulfinylbutyl glucosinolate] a compound found in Brassicaceae, notably in Tuscan black kale.

By recent achieved data, it is clear that bioactive RS-GRA is active on central and peripheral nervous system, through the mechanisms involved namely the modulation of the inflammatory pathways and the reduction in the activation of cell death by apoptosis. In specific, it was demonstrated that bioactive RS-GRA is able to significantly decrease nuclear factor (NF)-kB translocation and pro-inflammatory cytokines production (IL-1β and TNF-α), as well as the triggering of oxidative species generation (i-NOS, nitrotyrosine, PARP, Nrf2 and GFAP) and neuronal apoptotic death pathway (Caspase 3 and Bax/Bcl-2 unbalance). These effects have been correlated with the release of neurotrophic factors, such as GAP-43, NGF and BDNF, that play a supporting role in the neuroprotective action of bioactive RS-GRA.
Starting from these data, the purpose of new studies is to propose this RS-GRA as a useful drug for the treatment of cerebral ischemia, at least in association with current conventional therapy.

-glucoraphanin purified from Tuscan black kale and bioactivated with myrosinase enzyme protects against cerebral ischemia/reperfusion injury.

The antiproliferative capacities of kale

Studies have shown a relation between consumption of Brassica vegetables and cancer, particularly in the gastrointestinal system.
Human colon cancer development is often characterized in an early stage by hyperproliferation of the epithelium leading to the formation of adenomas. This is mainly a consequence of dysregulated cell cycle control and suppressed apoptosis. Protective effects against colon cancer development should consequently be associated with inhibition of cell proliferation and/or induction of the apoptotic pathway to delete cells carrying mutations and to maintain a normal cell population.
The anticancer effects have usually been dedicated to the glucosinolates and their degradation products, often without a thorough investigation of other potential bioactive compounds found in Brassica vegetables. Thus, it is not well understood which constituents are responsible for these anticancer effects or whether these effects are a consequence of synergistic action of several constituents.
Also flavonoids are shown to possess a remarkable spectrum of biological and pharmacological activities at nontoxic concentrations, suggesting that the significantly affect basic cell functions, such as growth, differentiation, and/or programmed cell death (apoptosis). Some epidemiological studies have provided evidence that a high dietary intake of flavonoids could be associated with low cancer prevalence in humans.

Other studies on human breast cancer cell lines and both estrogen receptor (ER)-positive (ER+; MCF-7 and BT474) and ER-negative (ER−; MDA-MB-231 and BT20) shows mechanisms of action and antiproliferative properties of Brassica oleracea juice.

The effect of juice on cell proliferation was evaluated on DNA synthesis and on cell cycle–related proteins. Juice markedly reduced DNA synthesis in a dose-dependent manner. Cell growth inhibition was accompanied by significant cell death at the higher juice concentrations, although no evidence of apoptosis was found. Interestingly, the juice displayed a preferential activity against breast cancer cells compared with other mammalian cell lines investigated (ECV304, VERO, Hep2, 3T3, and MCF-10A).

At the molecular level, the inhibition of proliferation was associated with significantly reduced CDK6 expression and an increased level of p27 in ER+ cells but not in ER− cells, whereas a common feature in all cell lines was significantly decreased retinoblastoma protein phosphorylation.

To conclude, the edible part of Brassica oleracea contains substances that can markedly inhibit the growth of both ER+ and ER− human breast cancer cells, although through different mechanisms.

Antiproliferative Effects of Fresh and Thermal Processed Green and Red Cultivars of Curly Kale.

Mechanisms of Action and Antiproliferative Properties of Brassica oleracea Juice in Human Breast Cancer Cell Lines.

Kale juice in gastric ulcer

Gastric ulcer is a chronic disease affecting millions of people worldwide. The pathology is the result of an imbalance between the protective agents (such as the mucosal barrier, mucus secretion and cell regeneration) and aggressors of the gastric mucosa (such as acid–pepsin secretion) linked to the process of digestion and other factors, such as excess alcohol consumption, chronic treatment of non-steroidal anti-inflammatories, stress, and infection caused by Helicobacter pylori.
Currently, the treatment is performed mainly with antacids and histamine receptor antagonists-2 (H2-Ras) and proton pump inhibitors can cause serious side effects such as hypersensitivity, arrhythmia, impotence, gynecomastia and hematopoietic disorderes. Therefore, there is a need to search for new, more effective and safer treatments, with less side effects. In this context, plant extracts are among the most promising substances in the search for new therapies for the treatment of gastric- ulcer.

Brassica oleracea, popularly known as “couve”, is the plant that is most commonly used by the Brazilian population for the treatment of gastritis and gastric ulcers.
There are several Brazilian reports indicating that the juice prepared from the leaves of Brassica oleracea, ingested during fasting, leads to relief of symptoms of this disease and also some others such as diabetes mellitus, cirrhosis and rheumatism.
To evaluate the gastroprotective effect.
of the extract of Brassica oleracea, the model of acute ulcer induced by ethanol/HCl was first performed.

The effects of ethanol on the gastric mucosa may be associated with the formation of reactive oxygen species resulting in severe damage to the vascular plexus.
The HCl present in this model accelerates the process of gastric ulcerogenesis and intensifies the lesions, impairing the mucosal protection against chemical agents.
It was demonstrated that the extract presents cytoprotective activity, since it significantly reduced the ethanol/HCl-induced ulcer.

Another protocol experimental used in this study was NSAID- induced ulcer. These drugs act by inhibiting prostaglandin synthesis through cyclooxygenase-1 block. Endogenous prostaglandins are responsible for regulating the secretion of mucus and bicarbonate, blood flow and proliferation of epithelial cells. Therefore, inhibition of prostaglandin synthesis weakens the gastric mucosal defenses, leading to the formation of lesions in the gastric epithelium.
It was suggested the possible involvement of prostaglandin production or mucus in the antiulcer effect presented by the extract.

Through phytochemical analysis of the Brassica oleracea extract, the presence of flavonoids, terpenes and sterols was demonstrated. These secondary metabolite classes are related to the gastroprotector activity. Glucosinolates are associated with antiulcer activity through in vitro inhibition of (H+–K+)-ATPase, reducing the production of HCl.
In conclusion preparations obtained from Brassica oleracea could be also used for the development of a new phytopharmaceutical for the treatment of gastric ulcer.

Gastroprotective activity of hydroalcoholic extract obtained from the leaves of Brassica oleracea var. acephala DC in different animal models.