Free fatty acid-induced alterations in the steroid-binding properties of rat androgen-binding protein

5 alpha-reductase-catalyzed conversion of testosterone to dihydrotestosterone is increased in prostatic adenocarcinoma cells: suppression by 15-lipoxygenase metabolites of gamma-linolenic and eicosapentaenoic acids

Although the androgens, testosterone (T) and its highly active metabolite dihydrotestosterone (DHT) play a role in the development and progression of prostate cancer, the mechanism(s) are unclear. Furthermore, 5 alpha-reductase which catalyze the conversion of T to DHT, has been a target of manipulation in the treatment of prostatic cancer, hence synthetic 5 alpha-reductase activity inhibitors have shown therapeutic promise. To demonstrate that nutrients derived from dietary sources can exert similar therapeutic promise, this study was designed using benign hyperplastic cells (BHC) and malignant tumorigenic cells (MTC) derived from Lobund-Wistar (L-W) rat model of prostatic adenocarcinoma to test the effects of gamma-linolenic acid (GLA), eicosapentaenoic acid (EPA) and their 15-lipoxygenase metabolites on cellular 5 alpha-reductase activity. Our data revealed: (i) that incubation of MTC with [3H]-T resulted in marked conversion to [3H]-DHT when compared to similar incubation with BHC; (ii) that DHT-enhanced activity of 5 alpha-reductase was inhibited 80% by 15S-hydroxyeicosatrienoic acid, the 15-lipoxygenase metabolite of GLA, when compared to 55% by 15S-hydroxyeicosapentaenoic acid, the 15-lipoxygenase metabolite of EPA; and (iii) that their precursor fatty acids, respectively, exerted moderate inhibition. Taken together, the study underscores the biological importance of 15-lipoxygenase metabolites of polyunsaturated fatty acids (PUFAs) in androgen metabolism.

Postprandial free fatty acids stimulate activity of human corticosteroid binding globulin

The effect of postprandial variation of free fatty acids (FFA) on serum corticosteroid binding globulin (CBG) properties and cortisol (hydrocortisone) concentrations were explored in 11 women (20-30 yr) during 8 h after an oral load of tallow (26% C16:0, 18% C18:0, and 43% C18:1), oleic-sunflower (oleic-SF; 73% C18:1), sunflower (SF; 67% C18:2), and mixed oil (MO; 39% C18:1 and 48% C18:2). Serum FFA increased little after SF and MO but more than doubled in the late postprandial period (6 and 8 h) after oleic-SF (due to monounsaturated FFA) or tallow (due to saturated and monounsaturated FFA). CBG concentrations remained unchanged, but in relation with the postprandial elevation of serum FFA, CBG binding activity was increased after tallow or oleic-SF as a result of a combined two- to threefold increase in affinity constant and a 50% reduction in binding sites. Immunological and in vitro binding studies showed the changes in CBG behavior to be conformational and to be mediated mainly by monounsaturated FFA, especially C18:1. The modifications of CBG properties were associated with sustained high concentrations of cortisol (suppression of midday decrease) 6 and 8 h after tallow or oleic-SF. Thus dietary FFA may have an impact on bioavailability of glucocorticoids.

Interactions between phytoestrogens and human sex steroid binding protein

The interactions of human Sex steroid binding protein (SBP) and the lignans [Nordihydrogaiaretic acid (NDGA) enterolactone (Ent), enterodiol (End)] and isoflavonoid phytoestrogens [Equol (Eq), diazein Dad), genistein (Gen)] were studied. The phytoestrogens had different dose-dependent inhibitory effects on steroid binding by SBP. Their relative efficiencies were: Ent> or = NDGA = Eq > Gen for displacing E2 and Eq > Ent > NDGA > Gen for displacing T. End and Dad were much less active. Scatchard analysis suggested that NDGA had similar non- competitive effects on T and E2 binding by reducing the number of binding sites without changing the association constants. But Eq seemed to inhibit E2 binding non-competitively and T binding competitively. NDGA binding to SBP reduced the immunorecognition of SBP by monospecific anti-SBP antibodies, suggesting that NDGA changed SBP immunoreactivity. Unlike NDGA, Eq binding to SBP caused no immunological changes in SBP, indicating qualitative differences in the effects of the lignan and isoflavonoid. Our results indicate that phytoestrogens may modulate the SBP activity and so influence the role of this protein in the delivery of hormonal information to sex steroid-dependent cells.

Structure, function, and regulation of androgen-binding protein/sex hormone-binding globulin

Despite over 20 years of research, the functions of ABP and SHBG remain elusive. The major reason for this lack of knowledge has been the unavailability of natural mutants with clinical defects for study. There is strong evidence that these binding proteins do act to modulate the gene regulatory actions of nuclear sex steroid receptors by controlling the availability of androgens and estrogens. In plasma, SHBG controls the metabolic clearance rate of sex steroids. In addition there is strong evidence that they have a much broader function. The identification of plasma membrane receptors in target tissues and the finding of homologous domains in several developmental proteins support other functions. Moreover, other experiments suggest the proteins may actually be hormones or growth factors. These findings are not compatible with a model that has the proteins only regulating free steroid hormone levels. Obviously, much more experimentation will be necessary to reveal the functions of ABP and SHBG. The recent discoveries have offered several clues to their functions and open new routes for study. These experiments, coupled with newly developed techniques, such as gene knockout by homologous recombination, make one optimistic that the functions of these unique proteins will be deciphered in the near future.