The isoflavones genistein and daidzein increase hepatic concentration of thyroid hormones and affect cholesterol metabolism in middle-aged male rats.

We examined whether isoflavones interfere with thyroid homeostasis, increase hepatic thyroid hormone concentrations and affect cholesterol metabolism in middle-aged (MA) male rats. Thirteen-month-old Wistar rats were injected subcutaneously with 35 mg/kg b.w./day of genistein, daidzein or vehicle (controls) for four weeks. Hepatic Dio1 gene expression was up-regulated by 70% (p < 0.001 for both) and Dio1 enzyme activity increased by 64% after genistein (p < 0.001) and 73% after daidzein treatment (p < 0.0001). Hepatic T3 was 75% higher (p < 0.05 for both), while T4 increased only after genistein treatment. Serum T4 concentrations were 31% lower in genistein- and 49% lower in dadzein-treated rats (p < 0.001 for both) compared with controls. Hepatic Cyp7a1 gene expression was up-regulated by 40% after genistein and 32% after daidzein treatment (p < 0.05 for both), in agreement with a 7α-hydroxycholesterol increase of 50% (p < 0.01) and 88% (p < 0.001), respectively. Serum 24- and 27-hydroxycholesterol were 30% lower (p < 0.05 for both), while only 24-hydroxycholesterol was decreased in the liver by 45% after genistein (p < 0.05) and 39% (p < 0.01) after dadzein treatment. Serum concentration of the cholesterol precursor desmosterol was 32% (p < 0.05) lower only after dadzein treatment alone, while both isoflavones elevated this parameter in the liver by 45% (p < 0.01). In conclusion, isoflavones increased T3 availability in the liver of MA males, despite decreasing serum T4. Hepatic increase of T3 possibly contributes to activation of the neutral pathway of cholesterol degradation into bile acids in the liver. While isoflavones obviously have the potential to trigger multiple mechanisms involved in cholesterol metabolism and oxysterol production, they failed to induce any hypocholesterolemic effect.

Positive effects of naringenin on near-surface membrane fluidity in human erythrocytes.

PURPOSE: Deformability/rheologic behavior of erythrocytes are related to near-surface membrane fluidity. Specific agents can increase erythrocyte membrane fluidity in order to adjust hemodynamics in cardiovascular diseases. Grapefruit flavanone naringenin has been proposed for potential use in an alternative therapy of cardiovascular conditions. In respect to this, we assessed here effects of two nutritionally relevant concentrations of naringenin (0.1 and 1 µg/ml) on near-surface membrane fluidity in human erythrocytes. METHODS: We used electron paramagnetic resonance spectroscopy and fatty acid spin probes (5-DS and 7-DS), the spectra of which are dependent on membrane fluidity. RESULTS: The results showed a significant (p = 0.029) increase of membrane fluidity near the hydrophilic surface in erythrocytes treated with higher concentration of naringenin. In the deeper layer, just below the erythrocyte membrane phospholipid heads, both lower and higher concentration of naringenin significantly increased membrane fluidity (p = 0.036 and p = 0.028, respectively). CONCLUSIONS: These data document the positive and dose dependent effect of naringenin on near-surface membrane fluidity in human erythrocytes, recommending its use in the cardiovascular conditions characterized by disturbed hemodynamics.

Activity, but not mRNA expression of gelatinases correlates with susceptibility to experimental autoimmune encephalomyelitis.

Experimental autoimmune encephalomyelitis (EAE) is a model of multiple sclerosis (MS), inflammatory, demyelinating and neurodegenerative disease of the central nervous system (CNS). Clinically manifested EAE can be induced in Dark Agouti (DA) rats, but not in Albino Oxford (AO) rats by immunization with spinal cord homogenate (SCH) and complete Freund's adjuvant (CFA). Matrix metalloproteinases (MMP) play important roles in various steps of MS and EAE pathogenesis. Expression of gelatinases MMP2 and MMP9, their activator MMP14 and their inhibitor tissue inhibitor of MMP (TIMP)1 in the CNS of AO and DA rats immunized with SCH+CFA was determined. Expression of mRNA for MMP2, MMP9 and MMP14 was higher and expression of TIMP1 mRNA was lower in AO rats. However, gelatinase activity in spinal cords was higher in samples obtained from DA rats. Further, while there was no strain difference in MMP2 and MMP9 mRNA expression in lymph nodes of the immunized rats, gelatinase activity was higher in DA rats. This activity was reduced by antiinflammatory cytokines interleukin (IL)-10 and IL-4. Interestingly, gelatinase activity was detected in the nuclei of cells within the CNS, but not of those in lymph nodes. Our results imply that posttranscriptional regulation of MMP2 and MMP9 expression and/or function determines low gelatinase activity within the CNS and in immune cells of EAE-resistant AO rats.