Polysaccharide-Targeting Lipid Nanoparticles to Kill Gram-Negative Bacteria

The rapid increase and spread of Gram-negative bacteria resistant to many or all existing treatments threaten a return to the preantibiotic era. The presence of bacterial polysaccharides that impede the penetration of many antimicrobials and protect them from the innate immune system contributes to resistance and pathogenicity. No currently approved antibiotics target the polysaccharide regions of microbes. Here, describe monolaurin-based niosomes, the first lipid nanoparticles that can eliminate bacterial polysaccharides from hypervirulent Klebsiella pneumoniae, are described. Their combination with polymyxin B shows no cytotoxicity in vitro and is highly effective in combating K. pneumoniae infection in vivo. Comprehensive mechanistic studies have revealed that antimicrobial activity proceeds via a multimodal mechanism. Initially, lipid nanoparticles disrupt polysaccharides, then outer and inner membranes are destabilized and destroyed by polymyxin B, resulting in synergistic cell lysis. This novel lipidic nanoparticle system shows tremendous promise as a highly effective antimicrobial treatment targeting multidrug-resistant Gram-negative pathogens.

Coassembled Nitric Oxide-Releasing Nanoparticles with Potent Antimicrobial Efficacy against Methicillin-Resistant Staphylococcus aureus (MRSA) Strains

Nitric oxide (NO)-releasing nanoparticles are effective nanomedicines with diverse therapeutic advantages compared with small molecule-based NO donors. Here, we report a new class of furoxan-based NO-releasing nanoparticles using a simple, creative yet facile coassembly approach. This is the first time we demonstrated that the coassembled NO-releasing nanoparticles with poly(ethylene glycol)₁₀₁-block-poly(propylene glycol)₅₆-block-poly(ethylene glycol)₁₀₁ (Pluronic F127) had potent antimicrobial efficacies against methicillin-resistant Staphylococcus aureus (MRSA) strains. Nanoparticles obtained from the coassembly of either 4-(1-(3-methylpentan-5-ol)oxyl)(3-phenylsulfonyl) furoxan (compound 1) or 4-methoxy(3-phenylsulfonyl) furoxan (compound 2) with Pluronic F127 exhibit 4-fold improved antimicrobial activities compared to their self-assembled counterparts without Pluronic F127. 5(6)-Carboxylfluorescein (CF) leakage experiments further reveal that both coassembled NO-releasing nanoparticles show stronger interactions with lipid bilayers than those self-assembled alone. Subsequently, their strong plasma membrane-damaging capabilities are confirmed under both high-resolution optical microscopy and scanning electron microscopy characterizations. This coassembly approach could be readily applied to other small molecule-based antimicrobials, providing new solutions and important insights to further antimicrobial recipe design.

A polytherapy based approach to combat antimicrobial resistance using cubosomes

A depleted antimicrobial drug pipeline combined with an increasing prevalence of Gram-negative ‘superbugs’ has increased interest in nano therapies to treat antibiotic resistance. As cubosomes and polymyxins disrupt the outer membrane of Gram-negative bacteria via different mechanisms, we herein examine the antimicrobial activity of polymyxin-loaded cubosomes and explore an alternative strategy via the polytherapy treatment of pathogens with cubosomes in combination with polymyxin. The polytherapy treatment substantially increases antimicrobial activity compared to polymyxin B-loaded cubosomes or polymyxin and cubosomes alone. Confocal microscopy and neutron reflectometry suggest the superior polytherapy activity is achieved via a two-step process. Firstly, electrostatic interactions between polymyxin and lipid A initially destabilize the outer membrane. Subsequently, an influx of cubosomes results in further membrane disruption via a lipid exchange process. These findings demonstrate that nanoparticle-based polytherapy treatments may potentially serve as improved alternatives to the conventional use of drug-loaded lipid nanoparticles for the treatment of “superbugs”.

An increasing prevalence of Gram-negative bacteria increases the interest in nanotherapies to treat antibiotic resistance. Here, the authors examine the antimicrobial activity of polymyxin-loaded cubosomes and explore a polytherapy treatment of pathogens with cubosomes in combination with polymyxin.

Polymyxin-Induced Lipid A Deacylation in Pseudomonas aeruginosa Perturbs Polymyxin Penetration and Confers High-Level Resistance

Polymyxins are last-line antibiotics against life-threatening multidrug-resistant Gram-negative bacteria. Unfortunately, polymyxin resistance is increasingly reported, leaving a total lack of therapies. Using lipidomics and transcriptomics, we discovered that polymyxin B induced lipid A deacylation via pagL in both polymyxin-resistant and -susceptible Pseudomonas aeruginosa. Our results demonstrated that the deacylation of lipid A is an "innate immunity" response to polymyxins and a key compensatory mechanism to the aminoarabinose modification to confer high-level polymyxin resistance in P. aeruginosa. Furthermore, cutting-edge neutron reflectometry studies revealed that an assembled outer membrane (OM) with the less hydrophobic penta-acylated lipid A decreased polymyxin B penetration, compared to the hexa-acylated form. Polymyxin analogues with enhanced hydrophobicity displayed superior penetration into the tail regions of the penta-acylated lipid A OM. Our findings reveal a previously undiscovered mechanism of polymyxin resistance, wherein polymyxin-induced lipid A remodeling affects the OM packing and hydrophobicity, perturbs polymyxin penetration, and thereby confers high-level resistance.

Annexin V-containing cubosomes for targeted early detection of apoptosis in degenerative retinal tissue

ANX–PS–Phy cubosomes could be applied as a safe and robust drug delivery vehicle for targeting damaged, apoptotic cells in ocular diseases.

Intraocular Pressure Induced Retinal Changes Identified Using Synchrotron Infrared Microscopy

Infrared (IR) spectroscopy has been used to quantify chemical and structural characteristics of a wide range of materials including biological tissues. In this study, we examined spatial changes in the chemical characteristics of rat retina in response to intraocular pressure (IOP) elevation using synchrotron infrared microscopy (SIRM), a non-destructive imaging approach. IOP elevation was induced by placing a suture around the eye of anaesthetised rats. Retinal sections were collected onto transparent CaF₂ slides 10 days following IOP elevation. Using combined SIRM spectra and chemical mapping approaches it was possible to quantify IOP induced changes in protein conformation and chemical distribution in various layers of the rat retina. We showed that 10 days following IOP elevation there was an increase in lipid and protein levels in the inner nuclear layer (INL) and ganglion cell layer (GCL). IOP elevation also resulted in an increase in nucleic acids in the INL. Analysis of SIRM spectra revealed a shift in amide peaks to lower vibrational frequencies with a more prominent second shoulder, which is consistent with the presence of cell death in specific layers of the retina. These changes were more substantial in the INL and GCL layers compared with those occurring in the outer nuclear layer. These outcomes demonstrate the utility of SIRM to quantify the effect of IOP elevation on specific layers of the retina. Thus SIRM may be a useful tool for the study of localised tissue changes in glaucoma and other eye diseases.

Responses of the green-lipped mussel Perna viridis (L.) to suspended solids

Laboratory experiments were conducted to investigate the lethal and sublethal effects of suspended solids on the survival and physiological, behavourial and morphological changes of the green-lipped mussel Perna viridis collected from Tolo Harbour, Hong Kong. Results showed that P. viridis survived in all test conditions of suspended solids from 0 to 1,200 mg/l over a period of 96 h. Physiological responses of the green-lipped mussel under 14-d exposure of suspended solids from 0 to 600 mg/l, followed by 14-d recovery in natural seawater, revealed no significant changes (p > 0.05) in oxygen consumption and dry gonosomatic index for treatments in different concentrations of suspended solids and exposure time. Changes in clearance rate were only found to be significant (p < 0.001) with exposure time. Responses in behavourial and morphological changes of the green-lipped mussel were also studied under similar experimental treatments and exposure time. Byssus production was significantly (p < 0.001) related to exposure time. Gill damage, however, was significantly greater in treatments (p < 0.001). Present findings suggested that P. viridis could tolerate a high level of suspended solids in the laboratory. There were dose-dependent effects of suspended solids on morphology of gill filaments. Implications of survival and responses of the green-lipped mussel to suspended solids in the marine environment are discussed.

The effects of testicular denervation on spermatogenesis in the Sprague-Dawley rat

In the rat, regression of spermatogenesis during the chronic stages of spinal cord injury (SCI) occurs in the presence of normal function of the pituitary-testis hormone axis, thus suggesting that nonendocrine mechanisms might be involved. The current study examined whether disruption of neural input to the testis contributes to the cascade that leads to the regression of spermatogenesis. Four weeks after denervation of the superior spermatic nerve (SSN), testis weight was 25% lower (p < 0.01) than that of the contralateral sham-operated testis. Defects in spermatogenesis including phagocytosis of mature spermatids, vacuolization of spermatid nuclei, delayed spermiation and incomplete cellular associations were observed in >60% of the tubules. In the remaining 30-40% of tubules, the seminiferous epithelium was severely regressed. While cutting the inferior spermatic nerve (ISN) alone did not affect spermatogenesis significantly, it enhanced the effect of SSN denervation on both spermatogenesis and testis weight (p < 0.01). Spermatogenesis was totally regressed in the SSN/ISN-denervated testes. At this time, quantitatively normal spermatogonial proliferation was maintained in SSN- or ISN-denervated testes. Twelve weeks after surgery, regression of the seminiferous epithelium characterized by absence of proliferating spermatogonia, while undifferentiating spermatogonia were present, was observed in all SSN-denervated testes. At this time, regression of the seminiferous epithelia also occurred in >30% of the tubules in ISN-denervated testes. At both times, serum follicle-stimulating hormone, luteinizing hormone and testosterone levels were normal and >60% of normal testicular testosterone concentrations were maintained in the denervated testes. These results indicate that disruption of neural input to the testis is not a cause for the decrease in spermatogonial proliferation during the acute phase of SCI, but may contribute to the chronic effects of SCI on spermatogenesis.

Ureteroneocystostomy: to drain or not to drain

PURPOSE

Indications for the use of external abdominal drains after ureteral reimplantation are not well defined. We determine the nature of the drainage fluid as well as the current use of drains by pediatric urologists.

MATERIALS AND METHODS

We prospectively evaluated 15 consecutive patients 7 months to 19 years old who underwent unilateral or bilateral intravesical ureteroneocystostomy for primary vesicoureteral reflux. All patients were treated with a urethral Foley catheter and closed suction Jackson-Pratt abdominal drain. Fluid from the Jackson-Pratt drain and Foley catheter was analyzed for urea and creatinine on postoperative day 1, and compared to serum values. The Foley catheter was removed after the urine became clear, and the Jackson-Pratt drain was removed after drainage was 5 ml. or less for 12 hours. In addition, a questionnaire was distributed to 268 pediatric urologists to determine current practice regarding the use of routine postoperative drains.

RESULTS

Urea and creatinine from the Jackson-Pratt drains in all 15 patients were consistent with serum values. The Foley catheter and Jackson-Pratt drain were removed an average of 3 and 4 days postoperatively, respectively. There were 186 responses from the 268 questionnaires distributed (69.4%). Of the pediatric urologists surveyed 70.4% performed intravesical ureteral reimplantation exclusively, 5.9% extravesical reimplantation exclusively and 23.7% both techniques. Of the group surveyed 73.1% placed external abdominal Jackson-Pratt or Penrose drains, although 26.5% of those who routinely used external drains believed that they were probably unnecessary. Of the physicians who placed drains 53.7% believed that the drainage fluid had some component of urine.

CONCLUSIONS

In our small prospective study group we demonstrated that external abdominal drainage fluid is consistent with serum despite the popular belief that it may have some component of urine. The gynecological literature has shown repeatedly that there is no increase in morbidity after radical hysterectomy and pelvic lymph node dissection when no external abdominal drains are used. Although to our knowledge there are no previous reports of drain use after ureteral reimplantation, 26.9% of pediatric urologists currently do not place external abdominal drains with no apparent increase in morbidity. Larger prospective cohorts with long-term followup are needed to address adequately the issue of whether drains are needed after uncomplicated ureteral reimplantation.

Partial purification and characterization of neutral proteases in lymph nodes of rats with experimental allergic encephalomyelitis

Two kinds of neutral protease activities in lymph nodes from Lewis rats with acute experimental allergic encephalomyelits (EAE) have been separated and partially purified and characterized. A soluble enzyme preparation enriched by gel filtration and ion-exchange chromatography hydrolyzes myelin basic protein, polylysine, and other basic proteins with an optimum pH at 6.0-6.5. It is inhibited by p-chloromercuribenzoate, and thus appears to be a mixture of thiol proteases. Another fraction containing proteolytic enzyme activity is strongly bound to the insoluble lymph node residue, and it also hydrolyzes myelin basic protein and histone, but not polylysine. It has a pH optimum above 7.5, is inhibited by phenylmethylsulfonyl fluoride, thus resembling elastase, but does not hydrolyze elastin-Congo red. The insoluble enzyme preparation hydrolyzes basic protein to 4-5 peptides in a pattern on polyacrylamide gels resembling that of the hydrolysis of basis protein by whole lymphocytes; the soluble enzyme mixture produces small fragments not retained on gels. Lymphocytes are a major component of the cells infiltrating the nervous system in experimental allergic encephalomyelitis, and neutral proteases contained in these cells may contribute to the degradation of myelin, especially of the basic protein.