Serum levels and metabolic clearance of the isoflavones genistein and daidzein in hemodialysis patients

Genistein and daidzein are biologically active isoflavones that are especially abundant in soybeans. After intestinal absorption, circulating genistein and daidzein are eliminated primarily by the kidneys. This study was undertaken to assess the metabolism of genistein and daidzein in patients with end-stage renal disease (ESRD) on hemodialysis therapy, and to test whether this treatment modality can replace the lack of kidney function, with respect to the elimination of the isoflavones. Twenty-three hemodialysis patients and 10 healthy subjects were studied. While consuming a self- selected low isoflavone diet, baseline blood levels were undetectable in eight of 10 healthy subjects and in 14 of 23 dialysis patients. The remaining participants had detectable levels, with the nine dialysis patients displaying much higher blood concentrations than the two healthy control subjects. After the evening intake of one dose of an isoflavone-rich soy protein isolate drink, the early morning blood levels of genistein and daidzein were higher in seven dialysis patients than in eight healthy subjects (genistein 1271 ± 321 versus 425 ± 104, P < 0.05; daidzein 1304 ± 352 versus 292 ± 78, P < 0.05). The blood clearance of the isoflavones was studied in two healthy subjects and in three dialysis patients. Genistein and daidzein were eliminated within 2 d in the healthy subjects, but had not returned to baseline in two of three ESRD patients, 7 d after intake. The half-life of both compounds was estimated to be 10-fold longer in the ESRD patients than in the healthy subjects. Finally, genistein and daidzein levels were measured before and after dialysis in five patients, both while on their regular diet and after one dose of a soy protein isolate drink. In both instances, the dialysis treatment did not affect the blood isoflavone levels. In conclusion, approximately one-third of hemodialysis patients eating the standard American renal diet experience high blood levels of the isoflavones genistein and daidzein, while the remaining two-thirds have undetectable levels. After ingestion of isoflavone-rich food such as soy products, all patients have detectable levels that remain very high for several days due to lack of renal excretion.