Isoflavone conjugates are underestimated in tissues using enzymatic hydrolysis

Area of Science:

• Nutritional Biochemistry
• Pharmacokinetics
• Endocrinology

Background:

• Soy isoflavones are linked to numerous health benefits.
• Their absorption results in various forms (free, glucuronide, sulfate conjugates) in bodily fluids.
• Limited data exists on their molecular forms and concentrations within specific organs.

Purpose of the Study:

• To quantify soy isoflavone content in various rat organs.
• To determine the molecular forms (aglycon vs. conjugates) of isoflavones in these tissues.
• To assess the subcellular distribution of isoflavones within the liver.

Main Methods:

• Rats were fed diets containing soy protein isolate.
• Isoflavone content in multiple organs (heart, brain, liver, kidney, etc.) was analyzed using acid and enzymatic hydrolysis.
• Subcellular fractionation was employed to determine isoflavone distribution in liver cells.

Main Results:

• Isoflavones were detected in a wide range of tissues, with the kidney showing the highest concentrations and the heart the lowest.
• Acid hydrolysis released significantly more aglycones than enzymatic digestion, indicating the presence of conjugates.
• In the liver, 28-44% of isoflavones were unconjugated aglycones, primarily located in the cytosol.

Conclusions:

• Soy isoflavones are distributed throughout various rat tissues in both aglycon and conjugated forms.
• The measured concentrations of isoflavone aglycones in tissues are considerably lower than those required for observed in vitro bioactivity.
• This suggests that the biological effects of soy isoflavones in vivo may be limited at the studied concentrations.