A Boron-Dependent Antibiotic Derived from a Calcium-Dependent Antibiotic.

The prevalence of drug-resistant bacterial pathogens foreshadows a healthcare crisis. Calcium-dependent antibiotics (CDAs) are promising candidates to combat infectious diseases as many of them show modes of action (MOA) orthogonal to widespread resistance mechanisms. The calcium dependence is nonetheless one of the hurdles toward realizing their full potential. Using laspartomycin C (LspC) as a model, we explored the possibility of reducing, or even eliminating, its calcium dependence. We report herein a synthetic LspC analogue (B1) whose activity no longer depends on calcium and is instead induced by phenylboronic acid (PBA). In LspC, Asp1 and Asp7 coordinate to calcium to anchor it in the active conformation; these residues are replaced by serine in B1 and condense with PBA to form a boronic ester with the same anchoring effect. Using thin-layer chromatography, MS, NMR, and complementation assays, we demonstrate that B1 inhibits bacterial growth via the same MOA as LspC, i.e., sequestering the cell wall biosynthetic intermediate undecaprenyl phosphate. B1 is as potent and effective as LspC against several Gram-positive bacteria, including methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus. Our success in converting a CDA to a boron-dependent antibiotic opens a new avenue in the design and functional control of drug molecules.

The Effect of Increasing Nickel Content on the Microstructure, Hardness, and Corrosion Resistance of the CuFeTiZrNix High-Entropy Alloys.

In recent years, high-entropy alloys (HEAs) that contain fine grains of intermetallic compounds (IMCs) have gained increasing attention as they have been shown to exhibit both high mechanical strength and strong corrosion resistance. One such class of HEAs is that of CuFeTiZrNi alloys. In this study, we have investigated the effect of increasing Ni content on the microstructure, hardness, and corrosion resistance of the CuFeTiZrNix alloys (where x = 0.1, 0.3, 0.5, 0.8, 1.0 in a molar ratio). The alloys used in this study were prepared in an arc melting furnace and then annealed at 900 °C. First-principles calculations of the bulk modulus were also performed for each alloy. The results revealed that increasing the Ni content had several effects. Firstly, the microstructure of the CuFeTiZrNix alloys changed from B2_BCC and Laves_C14 in the CuFeTiZrNi0.1 and CuFeTiZrNi0.3 alloys to FCC, B2_BCC, and Laves_C14 in the CuFeTiZrNi0.5 alloys; and to FCC, B2_BCC, Cu51Zr14, and Laves_C14 in the CuFeTiZrNi0.8 and CuFeTiZrNi1.0 alloys. Secondly, IMCs arising from a combination of the refractory elements (Ti and Zr) and atomic size differences were found in the interdendritic region. Thirdly, as the Ni content in the CuFeTiZrNix alloys increased, the hardness decreased, but the corrosion resistance increased.

ß-Amyloid Induces Pathology-Related Patterns of Tau Hyperphosphorylation at Synaptic Terminals.

A synergy between ß-amyloid (Aß) and tau appears to occur in Alzheimer disease (AD), but the mechanisms of interaction, and potential locations, are little understood. This study investigates the possibility of such interactions within the cortical synaptic compartments of APP/PS1 mice. We used label-free quantitative mass spectrometry to study the phosphoproteome of synaptosomes, covering 2400 phosphopeptides and providing an unbiased survey of phosphorylation changes associated with amyloid pathology. Hyperphosphorylation was detected on 36 synaptic proteins, many of which are associated with the cytoskeleton. Importantly, tau is one of the most hyperphosphorylated proteins at the synapse, upregulated at both proline-directed kinase (PDK) sites (S199/S202, S396/S404) and nonPDK sites (S400). These PDK sites correspond to well-known pathological tau epitopes in AD patients, recognized by AT8 and PHF-1 antibodies, respectively. Hyperphosphorylation at S199/S202, a rarely examined combination, was further validated in patient-derived human synaptosomes by immunoblotting. Global surveys of upregulated phosphosites revealed 2 potential kinase motifs, which resemble those of cyclin-dependent kinase 5 (CDK5, a PDK) and casein kinase II (CK2, a nonPDK). Our data demonstrate that, within synaptic compartments, amyloid pathology is associated with tau hyperphosphorylation at disease-relevant epitopes. This provides a plausible mechanism by which Aß promotes the spreading of tauopathy.

The effect of indocyanine green pretreatment on the parameters of transscleral diode laser thermotherapy-induced threshold coagulation of the ciliary body.

BACKGROUND AND OBJECTIVE: To study the effect of indocyanine green (ICG) pretreatment on threshold parameters of transscleral diode laser thermotherapy-induced threshold coagulation of the ciliary body. The procedure was termed 'cyclothermotherapy' based on the long duration (15-60 seconds) of diode laser application. STUDY DESIGN/MATERIALS AND METHODS: The right eyes of nine young adult New Zealand white rabbits underwent transscleral cyclothermotherapy (TCT, Group 1), TCT following ICG pretreatment (Group 2), and external manipulation of the ciliary body alone (Group 3). Rabbits were sacrificed after 24 hours; specimens were evaluated with gross examination and light microscopy. RESULTS: Thresholds were 30 J/cm2 (TCT) and 4.5 J/cm2 (TCT with ICG). Widespread structural damage was seen in the ciliary processes and the ciliary body in Groups 1 and 2. In Group 3, external manipulation of the ciliary body caused hemorrhage and structural damage confined to the ciliary processes. CONCLUSION: ICG pretreatment reduced the energy necessary to cause a threshold lesion with TCT in nonpigmented rabbits.

The role of recombinant lysine-plasminogen and recombinant urokinase and sulfur hexafluoride combination in inducing posterior vitreous detachment.

PURPOSE: To determine the optimal method of generating plasmin in vitreous using recombinant lysine-plasminogen and recombinant urokinase and to determine its efficacy in inducing posterior vitreous detachment when combined with sulfur hexafluoride. METHODS: Plasmin concentration of the rabbit vitreous after separate and combined intravitreal administrations of recombinant lysine-plasminogen and recombinant urokinase was tested in 78 rabbits to determine the optimal method of administration. The safety and efficacy of these agents and sulfur hexafluoride in inducing complete posterior vitreous detachment (total separation of the vitreous apart from vitreous base) were also evaluated. RESULTS: The highest plasmin concentration in vitreous was measured 10 minutes after injection. Intravitreal administration of recombinant lysine-plasminogen and recombinant urokinase did not cause any toxicity findings up to concentrations of 100 microg and 200 IU, respectively, on funduscopy, electroretinography, and histopathologic studies. When combined with sulfur hexafluoride injection, separate intravitreal administrations of 75 microg/0.1 mL of recombinant lysine-plasminogen and 15 IU/0.1 mL of recombinant urokinase induced complete posterior vitreous detachment in 75% of the eyes compared with 13% in eyes that received sulfur hexafluoride injection combined with balanced salt solution, recombinant lysine-plasminogen, or recombinant urokinase. CONCLUSIONS: Plasmin was effectively generated in the vitreous after separate intravitreal administrations of recombinant lysine-plasminogen and recombinant urokinase. When combined with intravitreal gas injection, this method of plasmin production induced complete posterior vitreous detachment in 75% of the eyes.

The effect of intraoperative retinal manipulation on the underlying retinal pigment epithelium: an experimental study.

PURPOSE: Retinal pigment epithelial changes described after vitreoretinal surgery may result from localized compression injury caused by intentional or inadvertent contact with vitreoretinal instruments. The authors evaluated these changes resulting from manipulation of the retina without frank retinal injury. METHODS: One eye each of six pigmented rabbits underwent surgery during which the inner retinal surface was touched at several points with a 20-gauge silicone-tipped subretinal fluid cannula without causing a retinal break or subretinal hemorrhage. The rabbits were followed-up with indirect ophthalmoscopy, fundus photography, and fluorescein angiography, and were killed at 1 hour, 1 week, or 2 weeks. Light microscopy was used for histopathologic evaluation. RESULTS: On fluorescein angiography, diffuse leakage noted at the injury sites significantly decreased by the fourth day and almost completely disappeared by the second week. Disruption of photoreceptor outer segments and retinal pigment epithelium in the early specimens, and irregular pigmentation, proliferation, and migration of the retinal pigment epithelium at 1 and 2 weeks were the prominent features on histopathologic examination. CONCLUSIONS: Intraoperative manipulation of the attached retina may cause significant pigment epithelium displacement and proliferation and varying degrees of disorganization of normal retinal architecture in the absence of clinically evident retinal breaks and subretinal hemorrhages.

Transpupillary thermotherapy threshold parameters: funduscopic, angiographic, and histologic findings in pigmented and nonpigmented rabbits.

PURPOSE: To evaluate the effect of pigmentation on threshold fluence levels, needed to produce visible and angiographic lesions, of transpupillary thermotherapy (TTT) in rabbits. METHODS: Six pigmented and nine nonpigmented rabbits underwent TTT with an 810-nm diode laser coupled to a slit-lamp biomicroscope using a spot size of 2 or 3 mm. The power ranged from 80 to 200 mW with 1 to 3 minutes of laser exposure for pigmented rabbits and 750 to 1800 mW with 1 minute of exposure for albino rabbits. These parameters were also evaluated after compression of the globe using the contact lens to induce blanching of the optic nerve head. After the experiment, the eyes were enucleated under deep anesthesia, and the animals were killed immediately. RESULTS: In pigmented rabbits, the threshold fluence with the 2-mm spot size was 229 J/cm2 without compression and 153 J/cm2 with compression. With the 3-mm spot size, the threshold decreased from 200 to 150 mW as the duration of exposure lengthened (2 or 3 minutes), increasing the fluence from 170 to 382 J/cm2. In nonpigmented rabbits, the threshold fluence with the 2-mm spot size was 2,865 J/cm2 without compression and 2,674 J/cm2 with compression. With the 3-mm spot size, the threshold fluence of 1,528 J/cm2 was not affected by compression. Histopathologic studies showed transretinal damage at the lowest levels necessary to achieve angiographic evidence of a treatment lesion or a barely visible funduscopic lesion at the time of treatment. CONCLUSIONS: Nonpigmented rabbits required more than a 12-fold increase in total TTT fluence compared with pigmented rabbits with the 2-mm spot size and a ninefold increase with the 3-mm spot size. Inner and outer retinal damage was seen histopathologically at these levels.

Transpupillary thermotherapy threshold parameters: effect of indocyanine green pretreatment.

PURPOSE: To evaluate the effect of combined treatment with systemic indocyanine green (ICG) on threshold fluence levels of transpupillary thermotherapy (TTT) in rabbits. METHODS: Four pigmented rabbits and 13 nonpigmented rabbits were studied. TTT was performed on normal rabbit choriocapillaris using an 810-nm diode laser via slit-lamp biomicroscope delivery through a Goldmann macular lens. Laser spot size, power, and duration of laser exposure were varied to achieve a range of TTT fluences for threshold testing in both albino and pigmented rabbit fundi. Intravenous ICG pretreatment at doses of 0.41 to 10 mg/kg was initiated at varying times before TTT treatment. After the experiment, the eyes were enucleated under deep anesthesia, the animals were killed, and the eyes were prepared for light microscopy. RESULTS: When intravenous ICG pretreatment was employed, there was a dose-dependent decrease in the TTT fluence threshold as compared with known threshold values. At threshold fluences, histopathologic sections revealed damage to all layers of the retina in addition to choriocapillaris damage. CONCLUSION: Intravenous ICG pretreatment can be used to lower the TTT threshold fluence and irradiance required to create angiographically visible lesions in the normal rabbit choriocapillaris. Damage was seen in all layers of the retina and choriocapillaris at threshold levels when TTT was used alone or in combination with ICG pretreatment.

The role of scleral buckle in experimental posterior penetrating eye injury.

PURPOSE: Although episcleral buckles are frequently placed as an additional procedure to vitreoretinal surgery, little is known about their independent effect after ocular trauma. The authors created a posterior penetrating ocular injury model to evaluate the isolated role of primary episcleral buckle placement. METHODS: Twenty eyes underwent surgery. The penetrating injury consisted of two 5-mm circumferential incisions placed five clock hours apart and 8 mm behind the limbus. A segmental episcleral buckle was placed over a randomly chosen injury site after wound closure. The degrees of fibrous proliferation, traction, and the presence of retinal detachment were evaluated on follow-up examinations. After enucleation and initial fixation, tissue sectioning was performed, and the greatest dimension of the fibrous proliferation at both wound sites was measured with a caliper. RESULTS: Two eyes were excluded from the study. Three eyes developed a retinal detachment; the remaining 15 eyes showed varying degrees of proliferation and traction on the retina. The greatest dimension of the fibrous proliferation at the buckle site (1.22 +/- 1 mm) was significantly different from that at the nonbuckle site (2 +/- 1.45 mm, P = 0.01). CONCLUSIONS: Primary episcleral buckle placement at the time of surgical repair reduces vitreous traction from the buckle site and decreases the degree of fibrovascular proliferation.