HDAC6 at the Intersection of Neuroprotection and Neurodegeneration

Histone deacetylase 6 (HDAC6) catalyzes multiple reactions. We summarize the current knowledge on HDAC6, its targets and functions. Among others, HDAC6 recognizes damaged proteins and assures that these proteins are destroyed by autophagy. On the other hand, HDAC6 also modifies the tracks used by the clearance mechanism so that axonal transport becomes less efficient. We hypothesize that a disturbance in the equilibrium between the different functions of HDAC6 could play an important role in neurodegeneration.     

Regioselective oxidation of cholic acid and its 7β epimer by using o-iodoxybenzoic acid

Rational exploration directed by DFT (density functional theory) based atomic Fukui indices, lead to development of regioselective oxidation of cholic acid and its 7β epimer by o-iodoxybenzoic acid. In case of cholic acid only, 7α-hydroxyl underwent oxidation, where as in its 7β epimer the selectivity was towards 12α-hydroxy group. Since these oxidations are the key steps in synthesis of ursodeoxycholic acid starting from cholic acid these findings may be useful in devising a protection free synthetic route.     

Structure of Sir2Tm bound to a propionylated peptide

Lysine propionylation is a recently identified post‐translational modification that has been observed in proteins such as p53 and histones and is thought to play a role similar to acetylation in modulating protein activity. Members of the sirtuin family of deacetylases have been shown to have depropionylation activity, although the way in which the sirtuin catalytic site accommodates the bulkier propionyl group is not clear. We have determined the 1.8 Å structure of a Thermotoga maritima sirtuin, Sir2Tm, bound to a propionylated peptide derived from p53. A comparison with the structure of Sir2Tm bound to an acetylated peptide shows that hydrophobic residues in the active site shift to accommodate the bulkier propionyl group. Isothermal titration calorimetry data show that Sir2Tm binds propionylated substrates more tightly than acetylated substrates, but kinetic assays reveal that the catalytic rate of Sir2Tm deacylation of propionyl‐lysine is slightly reduced to acetyl‐lysine. These results serve to broaden our understanding of the newly identified propionyl‐lysine modification and the ability of sirtuins to depropionylate, as well as deacetylate, substrates.     

Caloric restriction mimetics: natural/physiological pharmacological autophagy inducers

Nutrient depletion, which is one of the physiological triggers of autophagy, results in the depletion of intracellular acetyl coenzyme A (AcCoA) coupled to the deacetylation of cellular proteins. We surmise that there are 3 possibilities to mimic these effects, namely (i) the depletion of cytosolic AcCoA by interfering with its biosynthesis, (ii) the inhibition of acetyltransferases, which are enzymes that transfer acetyl groups from AcCoA to other molecules, mostly leucine residues in cellular proteins, or (iii) the stimulation of deacetylases, which catalyze the removal of acetyl groups from leucine residues. There are several examples of rather nontoxic natural compounds that act as AcCoA depleting agents (e.g., hydroxycitrate), acetyltransferase inhibitors (e.g., anacardic acid, curcumin, epigallocatechin-3-gallate, garcinol, spermidine) or deacetylase activators (e.g., nicotinamide, resveratrol), and that are highly efficient inducers of autophagy in vitro and in vivo, in rodents. Another common characteristic of these agents is their capacity to reduce aging-associated diseases and to confer protective responses against ischemia-induced organ damage. Hence, we classify them as “caloric restriction mimetics” (CRM). Here, we speculate that CRM may mediate their broad health-improving effects by triggering the same molecular pathways that usually are elicited by long-term caloric restriction or short-term starvation and that imply the induction of autophagy as an obligatory event conferring organismal, organ- or cytoprotection.     

Tetracycline nanoparticles loaded calcium sulfate composite beads for periodontal management

Background

The objective of this study was to fabricate, characterize and evaluate in vitro, an injectable calcium sulfate bone cement beads loaded with an antibiotic nanoformulation, capable of delivering antibiotic locally for the treatment of periodontal disease.

Methods

Tetracycline nanoparticles (Tet NPs) were prepared using an ionic gelation method and characterized using DLS, SEM, and FTIR to determine size, morphology, stability and chemical interaction of the drug with the polymer. Further, calcium sulfate (CaSO₄) control and CaSO₄-Tet NP composite beads were prepared and characterized using SEM, FTIR and XRD. The drug release pattern, material properties and antibacterial activity were evaluated. In addition, protein adsorption, cytocompatibility and alkaline phosphatase activity of the CaSO₄-Tet NP composite beads in comparison to the CaSO₄ control were analyzed.

Results

Tet NPs showed a size range of 130 ± 20 nm and the entrapment efficiency calculated was 89%. The composite beads showed sustained drug release pattern. Further the drug release data was fitted into various kinetic models wherein the Higuchi model showed higher correlation value (R² = 0.9279) as compared to other kinetic models. The composite beads showed antibacterial activity against Staphylococcus aureus and Escherichia coli. The presence of Tet NPs in the composite bead didn't alter its cytocompatibility. In addition, the composite beads enhanced the ALP activity of hPDL cells.

Conclusions

The antibacterial and cytocompatible CaSO₄-Tet NP composite beads could be beneficial in periodontal management to reduce the bacterial load at the infection site.

General significance

Tet NPs would deliver antibiotic locally at the infection site and the calcium sulfate cement, would itself facilitate tissue regeneration.     

Synthesis of 4β-acyloxypodophyllotoxin analogs modified in the C and E rings as insecticidal agents against Mythimna separata Walker

To discover the new natural-product-based insecticidal agents, four series of sixty novel 4β-acyloxypodophyllotoxin analogs modified in the C and E rings were prepared, and their insecticidal activity was tested against the pre-third-instar larvae of oriental armyworm, Mythimna separata (Walker) in vivo at the concentration of 1 mg/mL. It demonstrated that the position of the dioxo group on the E-ring of 4′-demethylepipodophyllotoxin was regioselectively controlled by the chlorine atom at its C-2′ position when 2′-chloro-4′-demethylepipodophyllotoxin was oxidized by sodium periodate. Among all the derivatives, IIIi exhibited the best potent insecticidal activity with the final mortality rate of 63.3%. To alkylacyloxy series, the proper length of the side chain at the C-4 position of Ia–g, IIa–g and IIIa–g was important for their insecticidal activity.     

Screening of the regioselectivity of acetyl xylan esterase from Bacillus pumilus as a catalyst for the deacetylation of glycoside acetates

Regioselective deacetylations of nine glycosides catalyzed by acetyl xylan esterase from Bacillus pumilus have been studied. The glycosides were methyl and benzyl glycosides of the tetraacetates of α-D-glucopyranose, α-D-galactopyranose and α-D-mannopyranose, and the methyl glycosides of tetra-O-acetyl-β-D-glucopyranose, tetra-O-acetyl-β-D-galactopyranose and tetra-O-acetyl-α-D-glucopyranose. The kinetics of successive deacetylations was monitored by GLC and 21 sugar acetates have been identified.     

A Novel Culture Method for High Level Production of Heterologous Protein in Saccharomyces cerevisiae

A high level production system for heterologous protein by cold culture of yeast transformants at 15°C was developed. The yeast transformants, carrying a plasmid containing cDNA for Aspergillus oryzae α-amylase (Taka-amylase A) or human lysozyme synthetic DNA, were cultivated in a selective medium for 1 or 2 days until full growth at 30°C. The yeast cells were harvested by centrifugation from the culture fluid and then were transferred to YPD medium. These inoculated broths were incubated for 2 days at 15°C and then for another 2 days at 30°C. By the cold culture method described above, higher amounts of Taka-amylase A (28.6 mg/liter) and human lysozyme (6.1 mg/liter) were produced by the yeast transformants compared to those by conventional methods.

Heterologous protein productions using YEp, YCp, and YIp types of yeast expression vectors with ADH1 or GAPDH promoter by the cold culture method showed effective productivity of about 2-fold compared to those by the conventional method of culture at 30°C. The high level production of heterologous protein by this method was not specific to the S. cerevisiae strains examined.