Is laser photocoagulation still effective in diabetic macular edema? Assessment with optical coherence tomography in Nepal

AIM: To find out the outcome of laser photocoagulation in clinically significant macular edema (CSME) by optical coherence tomography (OCT) METHODS: It was a prospective, non-controlled, case series study enrolling 81 eyes of 64 patients with CSME between August 2008 and January 2010. All patients received modified grid photocoagulation with frequency doubled Nd: YAG laser. Each patient was evaluated in terms of best-corrected visual acuity (BCVA) and regression or progression of maculopathy after laser therapy at 1, 3 and 6 months. Spearman’s correlation test was used to show the correlation between BCVA and total macular volume (TMV). Analysis of variance (ANOVA) was used to compare among groups and independent t-test was used to compare in each group. RESULTS: There is high correlation between BCVA and TMV (P≤0.001). BCVA improved in 50.6 %, remained static in 39.5% and deteriorated in 9.9% patients after 6 month of treatment. The Baseline TMV (mean and SD) were 9.26±1.83, 10.4±2.38), 11.5±3.05), 8.89±0.75 and 9.47±1.98mm3 for different OCT patterns, ST (sponge like thickening), CMO (cystoid macular edema), SFD (subfoveal detachment), VMIA (Vitreo macular interface abnormality) and average TMV respectively (P=0.04). After 6 months of laser treatment, the mean TMV decreased from 9.47±1.98mm³ to 8.77±1.31mm³ (P=0.01). In ST there was significant decrease in TMV, P=0.01, Further within these groups at 6 months, they were significantly different, P=0.01. CONCLUSION: OCT showed the different morphological variant of CSME while the response of treatment is different. TMV decreased the most and hence showed the improvement in vision after 6 months of laser treatment. In the era of Anti vascular endothelial growth factors (VEGFs), efficacy of laser seems to be in shadow but it is still first line of treatment in developing nation like Nepal where antiVEGFs may not be easily available and affordable.     

A Novel Polymyxin Derivative That Lacks the Fatty Acid Tail and Carries Only Three Positive Charges Has Strong Synergism with Agents Excluded by the Intact Outer Membrane

Polymyxins are cationic lipopeptides (five cationic charges) and the last resort for the treatment of serious Gram-negative infections caused by multiresistant strains. NAB741 has a cyclic peptide portion identical to that of polymyxin B but carries in the linear peptide portion a threonyl-d-serinyl residue (no cationic charges) instead of the diaminobutyryl-threonyl-diaminobutyryl residue (two cationic charges). At the N terminus of the peptide, NAB741 carries an acetyl group instead of a mixture of methyl octanoyl and methyl heptanoyl residues. NAB741 sensitized Escherichia coli, Klebsiella pneumoniae, Enterobacter cloacae, and Acinetobacter baumannii to antibiotics against which the intact outer membrane is an effective permeability barrier. When tested by using Etest strips on plates containing increasing concentrations of NAB741, the fractional inhibition concentration index (FICI) of the combination of NAB741 with rifampin ranged from ≤0.111 to 0.158 and that with clarithromycin from ≤0.094 to 0.292. When tested by the checkerboard method, the corresponding FICI values against E. coli ATCC 25922 were ≤0.141 to ≤0.155 with rifampin and 0.094 with clarithromycin. In addition, at 4 μg/ml, NAB741 decreased the MICs of azithromycin, mupirocin, fusidic acid, and vancomycin for E. coli strains and E. cloacae by factors ranging from 8 to 200. A sister peptide, NAB752, carrying a threonyl-aminobutyryl residue as the linear peptide portion, was inactive. Furthermore, NAB741 sensitized E. coli to the bactericidal activity of fresh guinea pig serum. The renal clearance of NAB741 was approximately 400-fold, 16-fold, and 8-fold higher than those measured for colistin, NAB7061, and NAB739, respectively.The emergence of progressively more and more multiresistant strains of Gram-negative bacteria is a major public health concern (2, 3, 4, 10, 14, 18). To date, major therapeutic challenges have been caused by such strains of Pseudomonas aeruginosa, Acinetobacter baumannii, and Klebsiella pneumoniae, but an even worse threat is the current development and spread of the carbapenemase-producing multiresistant strains of Escherichia coli, an opportunist capable of causing common infections in otherwise healthy patients outside hospitals. Emerging novel plasmid-encoded resistance determinants, originally found in other Gram-negative species, have already been found in strains of E. coli worldwide (2, 3, 4, 10, 14, 18). Besides KPC and several other carbapenemases (16), they include the qnr-mediated fluoroquinolone resistance determinant (11, 17), as well as the 16S rRNA methylases that confer panresistance to aminoglycosides (8, 9).The options to treat infections caused by multiresistant Gram-negative bacteria are becoming very scarce. Tigecycline is active against most strains of Enterobacteriaceae, but the low blood levels and other pharmacokinetic properties might limit its use in bacteremic pyelonephritis (2, 4, 7). There are no novel classes of agents in clinical development for the treatment of infections by Gram-negative bacteria, and the pipeline will remain dry in the next 10 years (2, 3, 14, 18).Still another approach is to develop agents that permeabilize the outer membrane (OM) of Gram-negative bacteria to other antibacterial agents (23). Polymyxins (polymyxin B and colistin) are cyclic lipodecapeptides, each carrying five free amino groups and a net charge of +5 under physiological conditions. They are bactericidal antibiotics that permeabilize the OM. Very importantly, and in contrast to most of the other cationic peptides, their action is restricted to Gram-negative bacteria (23). Gram-positive bacteria, eukaryotic microbes, and mammalian cells are typically resistant to polymyxins. Furthermore, the OM-permeabilizing action of polymyxins is stereospecific (20). Today, polymyxins are increasingly the last resort for the treatment of serious infections by Gram-negative bacteria caused by the very resistant strains. In spite of their notable specificity, the use of polymyxins is shadowed by their occasional toxicity, especially nephrotoxicity (2, 3).We have previously described novel polymyxin derivatives that carry only three positive charges (24, 25). NAB739 has a cyclic peptide portion identical to that of polymyxin B, but in the linear portion of the peptide, it carries a threonyl-d-serinyl residue (no cationic charge) instead of a diaminobutyryl-threonyl-diaminobutyryl residue (two cationic charges). The MIC₉₀ of NAB739 for E. coli is identical to that of polymyxin B (1 μg/ml) (25). NAB7061 (linear portion of the peptide, threonyl-aminobutyryl [Abu]) lacks direct antibacterial activity but sensitizes the target bacteria to hydrophobic antibiotics (25, 26).In this study, we describe further modifications, including NAB741. It has cyclic and linear peptide portions identical to those of NAB739 but differs from NAB739, NAB7061, and polymyxin B by carrying only an acetyl residue in the N terminus of the peptide instead of a significantly longer hydrophobic residue, i.e., octanoyl in NAB739 and NAB7061 and 6-methyloctanoyl or 6-methylheptanoyl in polymyxin B. We show that NAB741 has preserved the OM-permeabilizing activity of polymyxins. However, as also shown here, differences in the N-terminal moiety and the linear peptide portion affect the renal clearance of the compounds.     

Polymyxin B Induces Apoptosis in Kidney Proximal Tubular Cells

The nephrotoxicity of polymyxins is a major dose-limiting factor for treatment of infections caused by multidrug-resistant Gram-negative pathogens. The mechanism(s) of polymyxin-induced nephrotoxicity is not clear. This study aimed to investigate polymyxin B-induced apoptosis in kidney proximal tubular cells. Polymyxin B-induced apoptosis in NRK-52E cells was examined by caspase activation, DNA breakage, and translocation of membrane phosphatidylserine using Red-VAD-FMK [Val-Ala-Asp(O-Me) fluoromethyl ketone] staining, a terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end labeling (TUNEL) assay, and double staining with annexin V-propidium iodide (PI). The concentration dependence (50% effective concentration [EC₅₀]) and time course for polymyxin B-induced apoptosis were measured in NRK-52E and HK-2 cells by fluorescence-activated cell sorting (FACS) with annexin V and PI. Polymyxin B-induced apoptosis in NRK-52E cells was confirmed by positive labeling from Red-VAD-FMK staining, TUNEL assay, and annexin V-PI double staining. The EC₅₀ (95% confidence interval [CI]) of polymyxin B for the NRK-52E cells was 1.05 (0.91 to 1.22) mM and was 0.35 (0.29 to 0.42) mM for HK-2 cells. At lower concentrations of polymyxin B, minimal apoptosis was observed, followed by a sharp rise in the apoptotic index at higher concentrations in both cell lines. After treatment of NRK-52E cells with 2.0 mM polymyxin B, the percentage of apoptotic cells (mean ± standard deviation [SD]) was 10.9% ± 4.69% at 6 h and reached plateau (>80%) at 24 h, whereas treatment with 0.5 mM polymyxin B for 24 h led to 93.6% ± 5.57% of HK-2 cells in apoptosis. Understanding the mechanism of polymyxin B-induced apoptosis will provide important information for discovering less nephrotoxic polymyxin-like lipopeptides.     

Keratosis obturans: A rare cause of facial nerve palsy

Keratosis obturans, caused by the deposition of desquamated keratin plug in the external auditory canal can present with facial palsy. Young patients presenting with facial palsy, earache, and gradual hearing loss should be suspected for Keratosis obturans.