**New Insights Regarding the Potential Health Benefits of Isoflavones**

Corina Danciu, Diana Simona Antal, Florina Ardelean, Aimée Rodica Chiş, Codruţa Şoica, Florina Andrica and Cristina Dehelean

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/67896

#### **Abstract**

Isoflavones are a class of plant secondary metabolites, with an estrogen‐like structure presenting a plethora of biological activities. The chapter discusses important facts about this class of phytoestrogens, from biosynthesis to the latest research about their health benefits. The following major points discussed are: biosynthesis, regulation, isolation, metabolism and bioavailability, isoflavones in diet and intake, and new insights regarding the therapeutic effect including cancer chemoprevention. The chapter ends with a mini review of own research of the anti‐inflammatory and chemopreventive activity of iso‐ flavonoid genistein alone and incorporated in modern pharmaceutical formulations. The chapter updates the interested researchers in the field with the latest progress regarding potential health benefits of isoflavones.

**Keywords:** isoflavones, biosynthesis, regulation, isolation, metabolism, bioavailability, therapeutic effect

### **1. Introduction**

Isoflavonoids, a class of secondary metabolites including over 1000 structures [1], are polyphe‐ nolic derivatives of 1,2‐diphenylpropane, as opposed to the larger group of flavonoids having a 1,3‐diphenylpropane skeleton. They encompass several subgroups, the most prominent being the isoflavones, the rotenoids, the pterocarpans and the coumestans (**Figure 1**). The mul‐ tiplicity of isoflavonoid structures is accounted by different oxidation levels of the backbone, the presence of additional heterocyclic rings and the diversity of substituents. These substances occur

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**Figure 1.** Flavonoid and isoflavonoid backbones. 1: Flavones, 2: Isoflavones, 3: Rotenoids, 4: Pterocarpans and 5: Coumestans.

mostly in free forms as aglycones (**Figure 2**); glycosides are formed with glucose, rhamnose or apiose as the sugar moiety and are mainly O‐glycosides.

Isoflavonoids are a major biochemical marker of the Fabaceae, especially of the subfamily Faboideae [2]. As much as 95% of the isoflavonoid aglycones and about 90% of isoflavones were reported in this family [3]. In recent years, the distribution of isoflavonoids has reliably been proven in a variety of nonlegumes, including bryophytes, gymnosperms and angiosperms. In flowering plants, they occur in over 50 families, and their distribution pattern is unrelated with the degree of phylogenetic closeness. Such families include among monocots such as the Iridaceae, Liliaceae, Asphodelaceae, Poaceae, Zingiberaceae and Cyperaceae as well as a large number of dicots such as Asteraceae, Apiaceae, Malvaceae, Rosaceae, Rutaceae or Solanaceae [1, 4]. Among plant organs, isoflavonoids are mainly present in underground parts, wood and bark as compared to flowers and leaves [1]. *In planta*, they act as anti‐microbial compounds synthesized in response to the attack of pathogens, representing the first identified type of phytoalexins. Isoflavonoids may either be preexistent in plant tissues before microbial attacks or be produced only upon exposure to infection or environmental stressors. The prominent distribution of these secondary metabolites

**Figure 2.** Main isoflavone aglycones: 1: Genistein, 2: Daidzein, 3: Glycitein, 4: Biochanin A and 5: Formononetin.

in legumes is related to their physiological role in nodulation. The isoflavonoids present in root exudates are associated with the attraction of symbiotic *Rhizobium* bacteria and promotion of their growth within root nodules [5], leading to an improved nitrogen uptake.

### **2. Biosynthesis and regulation**

mostly in free forms as aglycones (**Figure 2**); glycosides are formed with glucose, rhamnose or

**Figure 1.** Flavonoid and isoflavonoid backbones. 1: Flavones, 2: Isoflavones, 3: Rotenoids, 4: Pterocarpans and 5:

Isoflavonoids are a major biochemical marker of the Fabaceae, especially of the subfamily Faboideae [2]. As much as 95% of the isoflavonoid aglycones and about 90% of isoflavones were reported in this family [3]. In recent years, the distribution of isoflavonoids has reliably been proven in a variety of nonlegumes, including bryophytes, gymnosperms and angiosperms. In flowering plants, they occur in over 50 families, and their distribution pattern is unrelated with the degree of phylogenetic closeness. Such families include among monocots such as the Iridaceae, Liliaceae, Asphodelaceae, Poaceae, Zingiberaceae and Cyperaceae as well as a large number of dicots such as Asteraceae, Apiaceae, Malvaceae, Rosaceae, Rutaceae or Solanaceae [1, 4]. Among plant organs, isoflavonoids are mainly present in underground parts, wood and bark as compared to flowers and leaves [1]. *In planta*, they act as anti‐microbial compounds synthesized in response to the attack of pathogens, representing the first identified type of phytoalexins. Isoflavonoids may either be preexistent in plant tissues before microbial attacks or be produced only upon exposure to infection or environmental stressors. The prominent distribution of these secondary metabolites

**Figure 2.** Main isoflavone aglycones: 1: Genistein, 2: Daidzein, 3: Glycitein, 4: Biochanin A and 5: Formononetin.

apiose as the sugar moiety and are mainly O‐glycosides.

Coumestans.

258 Flavonoids - From Biosynthesis to Human Health

The biosynthesis of isoflavonoids occurs as a branch of the phenylpropanoid pathway, involved in the biologic obtainment of all flavonoids [6]. The departing point is represented by the amino acid phenylalanine, sequentially converted to cinnamate, p‐coumarate and p‐coumaroyl‐CoA by the relevant enzymes of each step (phenylalanine ammonia‐lyase, cinnamic acid‐4‐hydroxylase, and 4‐coumarate‐CoA ligase, respectively). Subsequently, chalcone synthase is involved in the creation of the 15‐carbon flavonoid backbone from p‐coumaroyl‐CoA; several derivatives may be produced via different branch pathways. The crucial enzyme for isoflavone biosynthesis is isoflavone synthase, a cytochrome P450 monooxygenase, which catalyzes the migration of the aryl moiety and transforms flavanones to isoflavones [7]. The reaction involves keto‐enol tautomerism of flavanones and epoxidation, followed by dehydration [8].

Relevant metabolic pathways for the biosynthesis of the major isoflavonoids genistein (pre‐ cursor naringenin) and daidzein (precursor liquiritigenin) have been well‐studied in soybean (*Glycine max* (L.) Merr.). Their understanding opened possibilities of metabolic engineering, leading to the development of soybean lines with an increased content of isoflavones in comparison to wild‐type seeds. On the other hand, the health benefits of isoflavones prompted strategies to induce the synthesis of these compounds by non‐legume plants (broccoli and tomatoes). This approach could be achieved in plants with an active phenylpropanoid path‐ way [9]. In fact, the flavanone naringenin is not only the substrate of isoflavone synthase, but as well that of flavanone‐3‐hydroxylase, involved in the biosynthesis of flavonols, antho‐ cyanins and condensed tannins. The introduction of the isoflavone synthase gene in plants that do not express this enzyme was able to trigger genistein production in corn [7] and the model cruciferous *Arabidopsis thaliana* [10]. The disadvantage was represented by low isofla‐ vone content, related to the competition between the flavonoid and the isoflavone pathways. Blocking the alternative flavonoid/anthocyanin branch of the phenylpropanoid pathway while upregulating the synthesis of isoflavones by introducing foreign transcription factors yielded very favorable results. Yu et al. could increase up to fourfold the level of isoflavones in soy by introducing the transcription factors C1 and R from corn in soybean (involved in the regulation of the phenylpropanoid pathway genes), and by co‐suppressing flavanone‐3‐ hydroxylase, hence diverting the whole substrate to the isoflavonoid pathway [11]. An addi‐ tional regulation of isoflavone biosynthesis involves the enzymes catalyzing the glycosylation of aglycones, as the majority of isoflavonoids accumulate in conjugated form. In soybean, the malonylglycosides are predominant, followed by glucosides. These conjugates are obtained upon catalysis by malonyl transferase and glycosyl transferase, respectively, in specific posi‐ tions. The engineered obtainment of isoflavonoids in nonlegumes is crucially related to the presence of isoflavonoid‐specific malonyl transferases and glycosyl transferases [12]. In soy, the content and composition of isoflavonoids are subjected to polygenic regulation and highly variable in response to drought, temperature, fertilization, carbon dioxide content and genetic factors [13]. The level of isoflavonoids is higher in wild‐growing populations than in cultivated soybean; this situation is thought to be a consequence of domestication [14].
