Chlortetracycline and demeclocycline inhibit calpains and protect mouse neurons against glutamate toxicity and cerebral ischemia

Minocycline is a potent neuroprotective tetracycline in animal models of cerebral ischemia. We examined the protective properties of chlortetracycline (CTC) and demeclocycline (DMC) and showed that these two tetracyclines were also potent neuroprotective against glutamate-induced neuronal death in vitro and cerebral ischemia in vivo. However, CTC and DMC appeared to confer neuroprotection through a unique mechanism compared with minocycline. Rather than inhibiting microglial activation and caspase, CTC and DMC suppressed calpain activities. In addition, CTC and DMC only weakly antagonized N-methyl-D-aspartate (NMDA) receptor activities causing 16 and 14%, respectively, inhibition of NMDA-induced whole cell currents and partially blocked NMDA-induced Ca2+ influx, commonly regarded as the major trigger of neuronal death. In vitro and in vivo experiments demonstrated that the two compounds selectively inhibited the activities of calpain I and II activated following glutamate treatment and cerebral ischemia. In contrast, minocycline did not significantly inhibit calpain activity. Taken together, these results suggested that CTC and DMC provide neuroprotection through suppression of a rise in intracellular Ca2+ and inhibition of calpains.     

1,12-substituted tetracyclines as antioxidant agents

Novel hydroxypyrazoline derivatives of tetracycline and minocycline have been synthesized through the reaction of these tetracyclines with hydrazine. The formation of a new chiral center at C12 is stereospecific to give 12S-12-hydroxy-1,12-pyrazolinotetracycline. A reaction mechanism for the formation of these novel tetracycline derivatives has been proposed. Hydroxypyrazolinotetracyclines exhibit no binding to Mg2+ and Zn2+, features that are required for antibiotic activity and matrix metalloproteinase (MMP) inhibitions, respectively. The modification toward their hydroxypyrazolino derivatives significantly improved the antioxidant activities of tetracycline and minocycline, as shown by three commonly used assays (DPPH, ABTS+, and superoxide scavenging). 12S-Hydroxy-1,12-pyrazolinominocycline is a promising tetracycline-based antioxidant devoid of antibiotic properties and MMP inhibitory activity, which could be beneficial in the treatment of complications related to oxidative stress.     

Pseudomonad cyclopentadecanone monooxygenase displaying an uncommon spectrum of Baeyer-Villiger oxidations of cyclic ketones

Baeyer-Villiger monooxygenases (BVMOs) are biocatalysts that offer the prospect of high chemo-, regio-, and enantioselectivity in the organic synthesis of lactones or esters from a variety of ketones. In this study, we have cloned, sequenced, and overexpressed in Escherichia coli a new BVMO, cyclopentadecanone monooxygenase (CpdB or CPDMO), originally derived from Pseudomonas sp. strain HI-70. The 601-residue primary structure of CpdB revealed only 29% to 50% sequence identity to those of known BVMOs. A new sequence motif, characterized by a cluster of charged residues, was identified in a subset of BVMO sequences that contain an N-terminal extension of approximately 60 to 147 amino acids. The 64-kDa CPDMO enzyme was purified to apparent homogeneity, providing a specific activity of 3.94 micromol/min/mg protein and a 20% yield. CPDMO is monomeric and NADPH dependent and contains approximately 1 mol flavin adenine dinucleotide per mole of protein. A deletion mutant suggested the importance of the N-terminal 54 amino acids to CPDMO activity. In addition, a Ser261Ala substitution in a Rossmann fold motif resulted in an improved stability and increased affinity of the enzyme towards NADPH compared to the wild-type enzyme (K(m) = 8 microM versus K(m) = 24 microM). Substrate profiling indicated that CPDMO is unusual among known BVMOs in being able to accommodate and oxidize both large and small ring substrates that include C(11) to C(15) ketones, methyl-substituted C(5) and C(6) ketones, and bicyclic ketones, such as decalone and beta-tetralone. CPDMO has the highest affinity (K(m) = 5.8 microM) and the highest catalytic efficiency (k(cat)/K(m) ratio of 7.2 x 10(5) M(-1) s(-1)) toward cyclopentadecanone, hence the Cpd designation. A number of whole-cell biotransformations were carried out, and as a result, CPDMO was found to have an excellent enantioselectivity (E > 200) as well as 99% S-selectivity toward 2-methylcyclohexanone for the production of 7-methyl-2-oxepanone, a potentially valuable chiral building block. Although showing a modest selectivity (E = 5.8), macrolactone formation of 15-hexadecanolide from the kinetic resolution of 2-methylcyclopentadecanone using CPDMO was also demonstrated.     

Pseudomonad Cyclopentadecanone Monooxygenase Displaying an Uncommon Spectrum of Baeyer-Villiger Oxidations of Cyclic Ketones

Baeyer-Villiger monooxygenases (BVMOs) are biocatalysts that offer the prospect of high chemo-, regio-, and enantioselectivity in the organic synthesis of lactones or esters from a variety of ketones. In this study, we have cloned, sequenced, and overexpressed in Escherichia coli a new BVMO, cyclopentadecanone monooxygenase (CpdB or CPDMO), originally derived from Pseudomonas sp. strain HI-70. The 601-residue primary structure of CpdB revealed only 29% to 50% sequence identity to those of known BVMOs. A new sequence motif, characterized by a cluster of charged residues, was identified in a subset of BVMO sequences that contain an N-terminal extension of ~60 to 147 amino acids. The 64-kDa CPDMO enzyme was purified to apparent homogeneity, providing a specific activity of 3.94 μmol/min/mg protein and a 20% yield. CPDMO is monomeric and NADPH dependent and contains ~1 mol flavin adenine dinucleotide per mole of protein. A deletion mutant suggested the importance of the N-terminal 54 amino acids to CPDMO activity. In addition, a Ser261Ala substitution in a Rossmann fold motif resulted in an improved stability and increased affinity of the enzyme towards NADPH compared to the wild-type enzyme (K_m = 8 μM versus K_m = 24 μM). Substrate profiling indicated that CPDMO is unusual among known BVMOs in being able to accommodate and oxidize both large and small ring substrates that include C₁₁ to C₁₅ ketones, methyl-substituted C₅ and C₆ ketones, and bicyclic ketones, such as decalone and β-tetralone. CPDMO has the highest affinity (K_m = 5.8 μM) and the highest catalytic efficiency (k_cat/K_m ratio of 7.2 × 10⁵ M⁻¹ s⁻¹) toward cyclopentadecanone, hence the Cpd designation. A number of whole-cell biotransformations were carried out, and as a result, CPDMO was found to have an excellent enantioselectivity (E > 200) as well as 99% S-selectivity toward 2-methylcyclohexanone for the production of 7-methyl-2-oxepanone, a potentially valuable chiral building block. Although showing a modest selectivity (E = 5.8), macrolactone formation of 15-hexadecanolide from the kinetic resolution of 2-methylcyclopentadecanone using CPDMO was also demonstrated.