Androgenic steroids in Over-the-Counter dietary Supplements: Analysis for association with adverse health effects.

From 2012 to 2013, approximately 16 New York residents reported vague, nonspecific adverse health effects which included fatigue, loss of scalp hair, and muscle aches. One patient was hospitalized for liver damage. An epidemiological investigation identified a common factor among these patients; the consumption of B-50 vitamin and multimineral supplements from the same supplier. To investigate whether these nutritional supplements might have been responsible for the adverse health effects observed, comprehensive chemical analyses of marketed lots of the supplements were performed. To determine presence of organic components and contaminants, organic extracts of samples were prepared and analyzed using gas chromatography-mass spectrometry (GC-MS), liquid chromatography-tandem mass spectrometry (LC-MS/MS), liquid chromatography high-resolution mass spectrometry (LC-HRMS), and nuclear magnetic resonance (NMR). These analyses revealed the presence of significant levels of methasterone (17ß-hydroxy-2α,17α-dimethyl-5α-androstane-3-one), an androgenic steroid and schedule III-controlled substance; dimethazine, an azine-linked dimer of methasterone; and methylstenbolone (2,17α-dimethyl-17ß-hydroxy-5α-androst-1-en-3-one), a related androgenic steroid. Methasterone and extracts of certain supplement capsules were identified as highly androgenic in luciferase assays by using an androgen receptor promoter construct. This androgenicity persisted for several days after cell exposure to the compounds. The presence of these components in implicated lots were associated with adverse health effects and the hospitalization of one patient and the presentation of symptoms of severe virilization in a child. These findings underscore the need for more rigorous oversight of the nutritional supplement industry.

NMR and X-ray analysis of structural additivity in metal binding site-swapped hybrids of rubredoxin.

BACKGROUND: Chimeric hybrids derived from the rubredoxins of Pyrococcus furiosus (Pf) and Clostridium pasteurianum (Cp) provide a robust system for the characterization of protein conformational stability and dynamics in a differential mode. Interchange of the seven nonconserved residues of the metal binding site between the Pf and Cp rubredoxins yields a complementary pair of hybrids, for which the sum of the thermodynamic stabilities is equal to the sum for the parental proteins. Furthermore, the increase in amide hydrogen exchange rates for the hyperthermophile-derived metal binding site hybrid is faithfully mirrored by a corresponding decrease for the complementary hybrid that is derived from the less thermostable rubredoxin, indicating a degree of additivity in the conformational fluctuations that underlie these exchange reactions. RESULTS: Initial NMR studies indicated that the structures of the two complementary hybrids closely resemble "cut-and-paste" models derived from the parental Pf and Cp rubredoxins. This protein system offers a robust opportunity to characterize differences in solution structure, permitting the quantitative NMR chemical shift and NOE peak intensity data to be analyzed without recourse to the conventional conversion of experimental NOE peak intensities into distance restraints. The intensities for 1573 of the 1652 well-resolved NOE crosspeaks from the hybrid rubredoxins were statistically indistinguishable from the intensities of the corresponding parental crosspeaks, to within the baseplane noise level of these high sensitivity data sets. The differences in intensity for the remaining 79 NOE crosspeaks were directly ascribable to localized dynamical processes. Subsequent X-ray analysis of the metal binding site-swapped hybrids, to resolution limits of 0.79 A and 1.04 A, demonstrated that the backbone and sidechain heavy atoms in the NMR-derived structures lie within the range of structural variability exhibited among the individual molecules in the crystallographic asymmetric unit (approximately 0.3 A), indicating consistency with the "cut-and-paste" structuring of the hybrid rubredoxins in both crystal and solution. CONCLUSION: Each of the significant energetic interactions in the metal binding site-swapped hybrids appears to exhibit a 1-to-1 correspondence with the interactions present in the corresponding parental rubredoxin structure, thus providing a structural basis for the observed additivity in conformational stability and dynamics. The congruence of these X-ray and NMR experimental data offers additional support for the interpretation that the conventional treatment of NOE distance restraints contributes substantially to the systematic differences that are commonly reported between NMR- and X-ray-derived protein structures.

Contribution of the multi-turn segment in the reversible thermal stability of hyperthermophile rubredoxin: NMR thermal chemical exchange analysis of sequence hybrids.

Pyrococcus furiosus (Pf) rubredoxin is the most thermostable protein characterized to date. Reflecting the complications arising from irreversible denaturation of this protein, predictions of which structural regions confer differential thermal stability have utilized kinetic stability measurements, hydrogen exchange protection factors, long range hydrogen bond NMR spin couplings, and molecular dynamics simulations, and have primarily implicated the three-stranded beta-sheet and the adjacent metal binding site. Herein, NMR chemical exchange experiments demonstrate reversible two-state unfolding at the thermal transition temperature (T(m)) for hybrids of Pf and the mesophile Clostridium pasteurianum (Cp) rubredoxins which interchange residues 14-33, the so-called multi-turn segment. This complementary pair of hybrid rubredoxins exhibits largely additive incremental thermal stabilizations vs. the parental proteins. Both stabilization free energy measurements as well as incremental T(m) values indicate that a minimum of 37% of the total differential thermal stability resides in this multi-turn segment. Such a proportionality between DeltaDeltaG and incremental T(m) values is predicted for hybrid pairs exhibiting thermodynamic additivity in which the differential stability is predominantly enthalpic.