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Background: Esmolol is marketed as a racemate (RS-esmolol) with hypotension being the most frequently reported adverse event. Previously, it has been shown that the S-enantiomer (S-esmolol) possesses all of the heart rate (HR) control. The authors studied whether S-esmolol alone mitigates hypotension at similar degrees of HR control compared with RS-esmolol. Methods: The effects of RS- and S-esmolol on blood pressure (BP) were compared at multiple infusion rates producing similar HR control in dogs (N = 21). Differences in BP were further interrogated by monitoring global cardiovascular function and included the R-enantiomer (R-esmolol) (N = 3). Results: S-esmolol at half the rate (μg kg−1 min−1) of RS-esmolol provided the same degree of HR control over all infusion rates. RS-esmolol lowered BP by 3, 6, 11, 20, and 38 mmHg at 90, 300, 600, 1,000, and 2,000 μg kg−1 min−1, compared with 2, 4, 5, 10, and 16 mmHg at 45, 150, 300, 500, and 1,000 μg kg−1 min−1 for S-esmolol. Decreased BP with RS-esmolol was attributed to decreases in left ventricular developed pressure (LVDP) (−34 mmHg), LVdP/dt+max (−702 mmHg/s), and cardiac output (−1 l/min). R-esmolol also decreased BP (−10 mmHg), LVDP (−10 mmHg), LVdP/dt+max (−241 mmHg/s), and cardiac output (to −0.2 l/min). S-esmolol reversed these trends toward pre-esmolol values by increasing BP (+13 mmHg), LVDP (+12 mmHg), LVdP/dt+max (+76 mmHg/s), and cardiac output (+0.4 l/min). Conclusions: R-enantiomer provided no HR control, but contributed to the hypotension with RS-esmolol, which appears to be due to negative inotropy. Thus, an S-enantiomer formulation of esmolol may provide similar HR control with less hypotension.

The nuclear receptor retinoid X receptor (RXR) is a ligand-activated transcription factor. To create receptors for a new ligand, a structure-based approach was used to generate a library of ≈380,000 mutant RXR genes. To discover functional variants within the library, we used chemical complementation, a method of protein engineering that uses the power of genetic selection. Wild-type RXR has an EC 50 of 500 nM for 9- cis retinoic acid (9cRA) and an EC 50 of >10 μM for the synthetic retinoid-like compound LG335 in yeast. The library produced ligand–receptor pairs with LG335 that have a variety of EC 50 values (40 nM to >2 μM) and activation levels (10–80% of wild-type RXR with 9cRA) in yeast. The variant I268V;A272V;I310L;F313M has an EC 50 for LG335 of 40 nM and an EC 50 for 9cRA of >10 μM in yeast. This variant has essentially the reverse ligand specificity of wild-type RXR and is transcriptionally active at a 10-fold-lower ligand concentration in yeast. This EC 50 is 25-fold lower than the best receptor we have engineered through site-directed mutagenesis, Q275C;I310M;F313I. Furthermore, the variants' EC 50 values and activation levels in yeast and mammalian cells correlate. This protein engineering method should be extendable to produce other functional ligand–receptor pairs, which can be selected and characterized from libraries within weeks. Coupling large library construction with chemical complementation could be used to engineer proteins that bind virtually any small molecule for conditional gene expression, applications in metabolic engineering, and biosensors and to engineer enzymes through genetic selection.

Genetic analyses have identified a wide spectrum of mutations in the CYP4V2 gene from patients suffering from Bietti’s crystalline corneoretinal dystrophy, and mutations in the CYP4F22 gene have been linked to lamellar ichthyosis. These strong gene–disease associations will be better understood if we can elucidate the substrate specificity of the heretofore “orphan” P450s and unravel the biochemical pathways that go awry in disease states. The complex biotransformations that underlie eicosanoid signaling, however, pose great challenges for the enzymologist seeking to assign specific metabolic roles to these members of the CYP4 family. Inductive reasoning and modeling are crucial tools for designing the experiments that will define disease progression in terms of CYP function.

Background Molecular switch systems that activate gene expression by a small molecule are effective technologies that are widely used in applied biological research. Nuclear receptors are valuable candidates for these regulation systems due to their functional role as ligand activated transcription factors. Previously, our group engineered a variant of the retinoid × receptor to be responsive to the synthetic compound, LG335, but not responsive to its natural ligand, 9-cis-retinoic acid. Results This work focuses on characterizing a molecular switch system that quantitatively controls transgene expression. This system is composed of an orthogonal ligand/nuclear receptor pair, LG335 and GRQCIMFI, along with an artificial promoter controlling expression of a target transgene. GRQCIMFI is composed of the fusion of the DNA binding domain of the yeast transcription factor, Gal4, and a retinoid × receptor variant. The variant consists of the following mutations: Q275C, I310M, and F313I in the ligand binding domain. When introduced into mammalian cell culture, the switch shows luciferase activity at concentrations as low as 100 nM of LG335 with a 6.3 ± 1.7-fold induction ratio. The developed one-component system activates transgene expression when introduced transiently or virally. Conclusions We have successfully shown that this system can induce tightly controlled transgene expression and can be used for transient transfections or retroviral transductions in mammalian cell culture. Further characterization is needed for gene therapy applications.