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The Remarkable Anti-Cancer Benefits of Phenethyl isothiocyanate (PEITC)

Phenethyl isothiocyanate (PEITC) is one of a number of naturally occurring isothiocyanates.  In order to understand PEITC, you first have to start with their precursors, glucosinolates.

Glucosinolates constitute a natural class of organic compounds that contain sulfur and nitrogen and are derived from glucose and an amino acid.  For each glucosinolates there is a central carbon atom which is bound to a different side group.  The different side groups is what distinguishes each glucosinolate. Some of the more important and well researched glucosinolates include:

  • Glucotropaeolin
  • Gluconasturtiin
  • Glucoraphanin
  • Glucobrassicin
  • Glucocapparin
  • Progoitrin
  • Sinigrin
  • Sinalbin

Glucosinolates occur in various plants and vegetables including the families Brassicaceae (cruciferous vegetables).  Among the vegetables that contain glucosinolates are:

  • arugula
  • bok choy (pak choi)
  • broccoli
  • broccoli raab or rabe
  • broccoli sprouts
  • brussels sprouts
  • cabbages (savoy, red)
  • capers
  • cauliflower
  • cauliflower sprouts
  • Chinese cabbage
  • collards
  • daikon radish
  • garden cress
  • horseradish
  • kale
  • kohlrabi
  • maca root
  • mustard greens
  • mustard seeds
  • papaya seeds
  • radishes
  • turnip
  • wasabi japonica
  • watercress

The total number of documented glucosinolates from nature can be estimated to around 132, as of 2011.  1

Table 1. Glucosinolate Content of Selected Cruciferous Vegetables
Food (raw) Serving Total Glucosinolates (mg)
Brussels sprouts ½ cup (44 g)
104
Garden cress ½ cup (25 g)
98
Mustard greens ½ cup, chopped (28 g)
79
Turnip ½ cup, cubes (65 g)
60
Cabbage, savoy ½ cup, chopped (45 g)
35
Kale 1 cup, chopped (67 g)
67
Watercress 1 cup, chopped (34 g)
32
Kohlrabi ½ cup, chopped (67 g)
31
Cabbage, red ½ cup, chopped (45 g)
29
Broccoli ½ cup, chopped (44 g)
27
Horseradish 1 tablespoon (15 g)
24
Cauliflower ½ cup, chopped (50 g)
22
Bok choy (pak choi) ½ cup, chopped (35 g)
19

Source:  Linus Pauling Institute – Isothiocyanates

Isothiocyanates are biologically active hydrolysis (breakdown) products of glucosinolates.  Isothiocyanates are biologically inert and are only synthesized and formed by the conversion of the glucosinolate by the enzyme myrosinase.  Myrosinase coexists with but is physically separated from glucosinolates under normal conditions.

When vegetables that contain glucosinolates are chewed (plant tissue is damaged), myrosinase is released to convert the glucosinolate into a specific isothiocyanate.  In addition to myrosinase activity in the mouth saliva, the the intestinal microflora of both humans and animals also possess myrosinase activity.  2   

The enzyme myrosinase is activated by cutting or chewing the raw vegetables.  Heating of the vegetables (cooking) can destroy myrosinase activity.  3  Eating raw vegetables can releases 100% of the myrosinase enzyme and all of the isothiocyanates available, whereas cooking of the vegetables can reduce isothiocyanate content, depending on the method of cooking.  4 

This is why it is recommended that cruciferous vegetables be streamed or lightly boiled to preserve the glucosinolate content and not destroy all of the myrosinase enzymes.

Table 2. Food Sources of Selected Isothiocyanates and Their Glucosinolate Precursors
Isothiocyanate Glucosinolate (precursor) Food Sources
Allyl Isothiocyanate (AITC) Sinigrin Broccoli, Brussels sprouts, cabbage, horseradish, mustard, radish
Benzyl Isothiocyanate (BITC) Glucotropaeolin Cabbage, garden cress, Indian cress
Phenethyl-Isothiocyanate (PEITC) Gluconasturtiin Watercress
Sulforaphane (SFN) Glucoraphanin Broccoli, Brussels sprouts, cabbage

Source:  Linus Pauling Institute – Isothiocyanates

Each glucosinolate is a precursor to a different isothiocyanate.  There are four (4) different isothiocyanates that have been identified.  Each isothiocyanate has a specific glucosinolate precursor:

  • Sinigrin is the precursor to allyl isothiocyanate
  • Glucotropaeolin is the precursor to benzyl isothiocyanate
  • Gluconasturtiin is the precursor to phenethyl isothiocyanate
  • Glucoraphanin is the precursor to sulforaphane

 

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Figure 1:  Glucosinolates precursors to isothiocyanates  (Source:  Mechanisms of Action of Isothiocyanates in Cancer Chemoprevention: An Update)

Image result for glucosinolates myrosinase pathway

Figure 2:  Glucosinolates Hydrolysis by Myrosinase  (Source:  Linus Pauling Institute – Isothiocyanates)

Examples of vegetables with different glucosinolates are:

  • broccoli is a rich source of the glucosinolate glucoraphanin
  • cabbage is rich in sinigrin
  • watercress is high in gluconasturtiin

 

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Figure 3:  Examples of isothiocyanates in vegetables  (Source:  Mechanisms of Action of Isothiocyanates in Cancer Chemoprevention: An Update)

Isothiocyanates are known to science to have potent anticancer effects.  The research on these anticancer effects come from an analysis of the four isothiocyanates:
  • allyl isothiocyanate (AITC)
  • benzyl isothiocyanate (BITC)
  • phenethyl isothiocyanate (PEITC)
  • sulforaphane

Phenethyl isothiocyanate (PEITC) is one of the best studied members of the isothiocyanate family.  This is due to the fact that PEITC has generated a great deal of research interest due to its cancer chemopreventive activity.  5  6

PEITC is a naturally occurring isothiocyanate that is found in some cruciferous vegetables:

  • broccoli
  • horseradish (Armoracia rusticana)
  • radish
  • turnips
  • watercress

PEITC is present as the precursor gluconasturtiin in cruciferous plants. 

Watercress has the highest content of PEITC, due to the high levels of gluconasturtiin, which is actually named after watercress (Nasturtium officinale).

watercress11

Figure 4:  Watercress

PEITC is known to not only prevent the initiation phase of carcinogenesis process but also to inhibit the progression of tumorigenesis. 7  PEITC targets multiple proteins to suppress various cancer-promoting mechanisms such as cell proliferation, progression and metastasis. PEITC (along with BITC) were the most effective isothiocyanates in inducing apoptosis.  8   PEITC has been shown to induce apoptosis in certain cancer cell lines, and, in some cases, is even able to induce apoptosis in cells that are resistant to some currently used chemotherapeutic drugs.  9

Another important benefit of PEITC is that it protects against DNA damage.  10   

PEITC’s other mechanism of action is proposed to involve inhibition of cytochrome P450 enzymes, which oxidize compounds such as benzo[a]pyrene and other polycyclic aromatic hydrocarbons (PAHs).

PEITC has been widely studied and shows great promise in inhibiting the proliferation of cancer cells and their ability to form tumors.  11

Following is a list of the molecular targets and major mechanism of action of PEITC in various cancer types:  12

Molecular targets and major mechanism of action of PEITC in various cancer types

Cancer typeReference(s)
Breast1
2
3
4
5
Cervical6
Cholangio carcinoma7
Colon8
Gastric9
Glioma10
Leukemia11
12
Liver13
Lung14
15
16
17
18
Melanoma19
Multiple Myeloma (MM)20
Myeloid leukemia21
Myeloma22
Oral23
24
Oral squamous carcinoma25
Ovarian26
27
Pancreatic28
29
Prostate30
31
32
33
34
35
36
Sarcoma37

 


Informational References

Linus Pauling Institute – Isothiocyanates

 


Resources:

Life Extension – Triple Action Cruciferous Vegetable Extract

 

 

Steaming is the Most Health-Promoting Form of Cooking Cruciferous Vegetables

An interesting study was published in August 2009 in the Journal Zhejiang University Science B entitled Effects of different cooking methods on health-promoting compounds of broccoli in which the researchers determined that of the five cooking methods, including:

  • steaming
  • microwaving
  • boiling
  • stir-frying
  • stir-frying followed by boiling (stir-frying/boiling)

steaming retained the highest levels of chlorophyll, vitamin C, soluble proteins and soluble sugars.  1 

In addition, steaming demonstrated less modifications to total aliphatic and indole glucosinolates which led to the lowest loss of total glucosinolates.  Whereas, stir-frying and stir-frying/boiling presented the highest loss of glucosinolates.

The researchers concluded that stir-frying and stir-frying/boiling cause great losses of chlorophyll, soluble protein, soluble sugar, vitamin C, and glucosinolates, but the steaming method appears the best in retention of the nutrients in cooking broccoli.

The researchers determined the main aliphatic glucosinolates in the tested broccoli were:

  • glucoraphanin
  • glucoiberin

The main indole glucosinolates were:

  • glucobrassicin
  • neoglucobrassicin

The chlorophyll content in boiled, stir-fried/boiled, stir-fried, and microwaved broccoli was reduced by 27%, 23%, 18%, and 16%, respectively (P<0.05), while it was almost unchanged in steamed broccoli.  3

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Figure 1:  Each value is mean±SD of three replicate samples. Values not sharing a common letter are significantly different at P<0.05. Cooking methods: 1. Raw; 2. Boiled; 3. Streamed; 4. Microwaved; 5. Stir-fried; 6. Stir-fried/boiled  (Source:  Effects of different cooking methods on health-promoting compounds of broccoli)


 

The highest contents of total soluble proteins and soluble sugars (2.6 m/g FW and 3.5 mg/g FW, respectively) in broccoli were obtained after steaming. The lowest retention of total soluble proteins was observed in broccoli after boiling and stir-frying/boiling, while the lowest retention of total soluble sugars was found in broccoli after stir-frying/boiling and stir-frying.  4

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Figure 2:  Each value is mean±SD of three replicate samples. Values not sharing a common letter are significantly different at P<0.05. Cooking methods: 1. Raw; 2. Boiled; 3. Streamed; 4. Microwaved; 5. Stir-fried; 6. Stir-fried/boiled  (Source:  Effects of different cooking methods on health-promoting compounds of broccoli)


 

The greatest loss of vitamin C was observed in broccoli after stir-frying/boiling and boiling (38% and 33%, respectively) treatments, followed by microwaving and stir-frying (16% and 24%, respectively) treatments. In contrast, steaming did not cause any significant loss of vitamin C, compared with the raw sample.  5

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Figure 3:  Each value is mean±SD of three replicate samples. Values not sharing a common letter are significantly different at P<0.05. Cooking methods: 1. Raw; 2. Boiled; 3. Streamed; 4. Microwaved; 5. Stir-fried; 6. Stir-fried/boiled  (Source:  Effects of different cooking methods on health-promoting compounds of broccoli)


 

The contents of total aliphatic and indole glucosinolates in broccoli after different cooking treatments are presented in Fig.​Fig.4.4. Total aliphatic glucosinolates were significantly decreased by 55%, 54%, 60%, and 41%, respectively in stir-fried, stir-fried/boiled, microwaved, and boiled broccoli (P<0.05). However, the contents of total aliphatic glucosinolates remained almost unchanged in steamed broccoli.  6

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Figure 4:  Each value is mean±SD of three replicate samples. Values not sharing a common letter are significantly different at P<0.05. DW: dry weight. Cooking methods: 1. Raw; 2. Boiled; 3. Streamed; 4. Microwaved; 5. Stir-fried; 6. Stir-fried/boiled  (Source:  Effects of different cooking methods on health-promoting compounds of broccoli)


 

The main glucosinolate found in broccoli is glucoraphanin.  When raw or steamed broccoli is consumed consumed, the enzyme myrosinase transforms glucoraphanin into raphanin and into sulforaphane, which exhibits anti-cancer and antimicrobial properties in experimental models.   2

Other important glucosinolates include:

  • Glucotropaeolin is the precursor to benzyl isothiocyanate
    • Glucotropaeolin is a phytochemical from Tropaeolum majus, which is commonly known as garden nasturtium, Indian cress or monks cress.
  • Gluconasturtiin is the precursor to phenethyl isothiocyanate
    • Gluconasturtiin is named from its occurrence in watercress (Nasturtium officinale) and horseradish (Armoracia rusticana)
  • Sinigrin is the precursor to allyl isothiocyanate
    • Sinigrin is found in some plants of the Brassicaceae family such as Brussels sprouts, broccoli, and the seeds of black mustard (Brassica nigra)

 


Resources:

Sur La Table® Bamboo Steamers

Bella 7-Liter Multi-Tier Food Steamer

 


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