Stereoselective interactions of lactic acid enantiomers with HSA: Spectroscopy and docking application.

Lactic acid enantiomers, normally found in fermented food, are absorbed into the blood and interact with plasma carrier protein human serum albumin (HSA). Unveiling the effect on the function and structure of HSA during chiral interaction can give a better understanding of the different distribution activities of the two enantiomers. Multi-spectroscopic methods and molecular modelling techniques are used to study the interactions between lactic acid enantiomers and HSA. Time-resolved and steady-state fluorescence spectra manifest that the fluorescence quenching mechanism is mainly static in type, due to complex formation. Binding interactions, deduced by thermodynamic calculation, agree with the docking prediction. Docking results and kinetic constants represent chiral-recognizing discriminations consistently. The bindings of lactic acid enantiomers lead to some microenvironmental and slight conformational changes of HSA as shown by circular dichroism (CD), synchronous and three-dimensional fluorescence spectra. This investigation may yield useful information about the possible toxicity risk of lactic acid enantiomers to human health.

Probing the stereoselective interaction of ofloxacin enantiomers with corresponding monoclonal antibodies by multiple spectrometry.

Although stereoselective antibody has immense potential in chiral compounds detection and separation, the interaction traits between stereoselective antibody and the corresponding antigenic enantiomers are not yet fully exploited. In this study, the stereospecific interactions between ofloxacin isomers and corresponding monoclonal antibodies (McAb-WR1 and McAb-MS1) were investigated using time-resolved fluorescence, steady-state fluorescence, and circular dichroism (CD) spectroscopic methods. The chiral recognition discrepancies of antibodies with ofloxacin isomers were reflected through binding constant, number of binding sites, driving forces and conformational changes. The major interacting forces of McAb-WR1 and McAb-MS1 chiral interaction systems were hydrophobic force and van der Waals forces joined up with hydrogen bonds, respectively. Synchronous fluorescence spectra and CD spectra results showed that the disturbing of tyrosine and tryptophan micro-environments were so slightly that no obvious secondary structure changes were found during the chiral hapten binding. Clarification of stereospecific interaction of antibody will facilitate the application of immunoassay to analyze chiral contaminants in food and other areas.

Stereospecific recognition and quantitative structure-activity relationship between antibodies and enantiomers: ofloxacin as a model hapten.

In this study, ofloxacin stereoisomers were chosen as a simple model to investigate the stereospecific recognition of chiral haptens and antibodies. Three polyclonal antibodies were studied and showed a relatively high enantioselectivity and an excellent sensitivity. Comparative molecular field analysis and comparative molecular similarity indices analysis were employed to investigate the chiral recognition between the antibody and the ofloxacin enantiomer, and all the models yielded high correlation and predictive ability. It was found that the chiral discrimination was probably caused by steric hindrance; the antibody stereospecificity could be ascribed to the variation of the R1 and R3 groups of quinolones; the common structure of the quinolones is also essential in the hapten-antibody recognition. The recognition between the chiral haptens and the antibodies was co-affected by multiple interaction forces, and those forces were defined explicitly at the sub-structural level. An illustrative enhanced model with good simplicity and universality was also developed for a better understanding of the stereospecific recognition of ofloxacin enantiomers and antibodies for the first time. This work provides insights into the stereospecific recognition of chiral haptens and antibodies.

Molecular modeling application on hapten epitope prediction: an enantioselective immunoassay for ofloxacin optical isomers.

To deepen our understanding of the physiochemical principles that govern hapten-antibody recognition, ofloxacin enantiomers were chosen as a model for epitope prediction of small molecules. In this study, two monoclonal antibodies (mAbs) mAb-WR1 and mAb-MS1 were raised against R-ofloxacin and S-ofloxacin, respectively. The enantioselective mAbs have a high sensitivity and specificity, and the enantioselectivity is not affected by heterologous coating format reactions. The epitopes of the ofloxacin isomers were predicted using the hologram quantitative structure-activity relationship (HQSAR) and comparative molecular field analysis (CoMFA) approaches. The results consistently show that the epitope of the chiral hapten should be primarily composed of the oxazine ring and the piperazinyl ring and mAbs recognize the hapten from the side of this moiety. The enantioselectivity of mAbs is most likely due to the steric hindrance caused by the stereogenic center of the epitope. Modeling of chiral hapten-protein mimics reveals that ofloxacin isomers remain upright on the surface of the carrier protein. Suggestions to improve the enantioselectivity of antibodies against ofloxacin isomers were also proposed. This study provided a simple, efficient, and general method for predicting the epitopes of small molecules via molecular modeling. The epitope predictions for small molecules may create a theoretical guide for hapten design.

In vitro expansion of DNA triplet repeats with bulge binders and different DNA polymerases.

The expansion of DNA repeat sequences is associated with many genetic diseases in humans. Simple bulge DNA structures have been implicated as intermediates in DNA slippage within the DNA repeat regions. To probe the possible role of bulged structures in DNA slippage, we designed and synthesized a pair of simple chiral spirocyclic compounds [Xi Z, Ouyang D & Mu HT (2006) Bioorg Med Chem Lett 16, 1180-1184], DDI-1A and DDI-1B, which mimic the molecular architecture of the enediyne antitumor antibiotic neocarzinostatin chromophore. Both compounds strongly stimulated slippage in various DNA repeats in vitro. Enhanced slippage synthesis was found to be synchronous for primer and template. CD spectra and UV thermal stability studies supported the idea that DDI-1A and DDI-1B exhibited selective binding to the DNA bulge and induced a significant conformational change in bulge DNA. The proposed mechanism for the observed in vitro expansion of long DNA is discussed.

[Clinical significance of electrophysiological tests of BCR, ICR and PSEP for ED patients].

OBJECTIVE: To assess the clinical significance of electrophysiological tests of bulbocavernosus reflex (BCR), ischiocavernosus reflex (ICR) and pudenda somatosensory evoked potential (PSEP) for patients with erectile dysfunction (ED). METHODS: Electrophysiological tests of BCR, ICR and PSEP were performed for 232 ED patients with IIEF-5 scores of 2-20 (10.39 +/- 5.52), another 21 normal volunteer controls underwent the same tests, and the results were compared. RESULTS: Abnormal results, such as prolonged and advanced latencies, were found in 94 (40.5%) of the patients, which suggested neurotic ED with different degrees of cauda equine nerve injuries. CONCLUSION: Electrophysiological tests of BCR, ICR and PSEP can objectively reveal the functional state of the cauda equine nerve and offer an important support to the diagnosis of nerve-mediated ED.

Interaction of bulged DNA with leucine-containing mimics of NCS-chrom.

Synthesis of chiral spirocyclic helical compounds containing leucine that mimic the molecular architecture of the potent DNA bulge binder obtained from the natural product metabolite NCSi-gb has been accomplished. The interaction between the compounds and DNA was studied by circular dichroism (CD) method. The results suggested that the two synthetic diastereoisomers specifically targeted the bulge site of DNA and induced conformational change of bulged DNA greatly.

Stimulation on DNA triplet repeat strand slippage synthesis by the designed spirocycles.

The designed simpler chiral spirocyclic helical compounds that mimic the molecular architecture of the DNA bulge binder NCSi-gb have been prepared. It has been found that the synthesized spirocyclic compounds have strong stimulation effect on DNA slippage synthesis. Their stimulation activities on DNA strand slippage suggest that they may bind to or induce the formation of a non Watson-Crick structure during in vitro replication of DNA triplet repeats.

[Association between polymorphism of CYP17 gene and serum hormone concentrations in aged men].

OBJECTIVE: To investigate the association between polymorphism of CYP17 gene and serum hormone concentrations in aged men. METHODS: Eighty-three healthy men at the average age of 66.7 were divided into a < 66.7 group (n = 36) and a > 66.7 group (n = 47), and the polymorphism of CYP17 gene in the 5' promoter region was investigated by PCR using DNA from the men's peripheral blood lymphocytes. A new recognition site was created for the restriction enzyme MspA1 I by transition (T --> C) in the risk allele (A2). Three genotypes A1/A1, A1/A2, A2/A2 were established, serum sex-hormone levels measured, and mean hormone concentration evaluated in each genotype and age group. RESULTS: No evidence was found that the testosterone (T) level, estrogen (E2) level and T/E2 ratio were associated with the genotype of CYP17 gene. There was no significant difference in T and E2 levels between the two groups, but there was a significant increase in the T/E2 ratio (P < 0.05). CONCLUSION: A2 allele does not increase sex hormone levels in aged men, but the T/E, ratio was higher in the > 66.7 group than in the < 66.7 group. This may be closely associated with the mechanism of benign prostate hyperplasia and prostate cancer in aged men.