Characterization of a selective, iron-chelating antifungal compound that disrupts fungal metabolism and synergizes with fluconazole

Fungal infections are a growing global health concern due to the limited number of available antifungal therapies as well as the emergence of fungi that are resistant to first-line antimicrobials, particularly azoles and echinocandins. Development of novel, selective antifungal therapies is challenging due to similarities between fungal and mammalian cells. An attractive source of potential antifungal treatments is provided by ecological niches co-inhabited by bacteria, fungi, and multicellular organisms, where complex relationships between multiple organisms have resulted in evolution of a wide variety of selective antimicrobials. Here, we characterized several analogs of one such natural compound, collismycin A. We show that NR-6226C has antifungal activity against several pathogenic Candida species, including C. albicans and C. glabrata, whereas it only has little toxicity against mammalian cells. Mechanistically, NR-6226C selectively chelates iron, which is a limiting factor for pathogenic fungi during infection. As a result, NR-6226C treatment causes severe mitochondrial dysfunction, leading to formation of reactive oxygen species, metabolic reprogramming, and a severe reduction in ATP levels. Using an in vivo model for fungal infections, we show that NR-6226C significantly increases survival of Candida-infected Galleria mellonella larvae. Finally, our data indicate that NR-6226C synergizes strongly with fluconazole in inhibition of C. albicans. Taken together, NR-6226C is a promising antifungal compound that acts by chelating iron and disrupting mitochondrial functions.IMPORTANCEDrug-resistant fungal infections are an emerging global threat, and pan-resistance to current antifungal therapies is an increasing problem. Clearly, there is a need for new antifungal drugs. In this study, we characterized a novel antifungal agent, the collismycin analog NR-6226C. NR-6226C has a favorable toxicity profile for human cells, which is essential for further clinical development. We unraveled the mechanism of action of NR-6226C and found that it disrupts iron homeostasis and thereby depletes fungal cells of energy. Importantly, NR-6226C strongly potentiates the antifungal activity of fluconazole, thereby providing inroads for combination therapy that may reduce or prevent azole resistance. Thus, NR-6226C is a promising compound for further development into antifungal treatment.

Effects on specific promoter DNA methylation in zebrafish embryos and larvae following benzo[a]pyrene exposure

Benzo[a]pyrene (BaP) is an established carcinogen and reproductive and developmental toxicant. BaP exposure in humans and animals has been linked to infertility and multigenerational health consequences. DNA methylation is the most studied epigenetic mechanism that regulates gene expression, and mapping of methylation patterns has become an important tool for understanding pathologic gene expression events. The goal of this study was to investigate aberrant changes in promoter DNA methylation in zebrafish embryos and larvae following a parental and continued embryonic waterborne BaP exposure. A total of 21 genes known for their role in human diseases were selected to measure percent methylation by multiplex deep sequencing. At 96hpf (hours post fertilization) compared to 3.3hpf, dazl, nqo1, sox3, cyp1b1, and gstp1 had higher methylation percentages while c-fos and cdkn1a had decreased CG methylation. BaP exposure significantly reduced egg production and offspring survival. Moreover, BaP decreased global methylation and altered CG, CHH, and CHG methylation both at 3.3 and 96hpf. CG methylation changed by 10% or more due to BaP in six genes (c-fos, cdkn1a, dazl, nqo1, nrf2, and sox3) at 3.3hpf and in ten genes (c-fos, cyp1b1, dazl, gstp1, mlh1, nqo1, pten, p53, sox2, and sox3) at 96hpf. BaP also induced gene expression of cyp1b1 and gstp1 at 96hpf which were found to be hypermethylated. Further studies are needed to link aberrant CG, CHH, and CHG methylation to heritable epigenetic consequences associated with disease in later life.

Lateral line depigmentation (LLD) in channel catfish, Ictalurus punctatus (Rafinesque)

Head and lateral line erosion (HLLE) is a chronic dermatopathy affecting a number of fish that presents as depigmented skin along the lateral line system of the trunk and head. We present microbiological, immunological and histopathological features of this lesion in channel catfish, Ictalurus punctatus (Rafinesque), that developed after exposure to a chronic nutritional stress. Depigmention was limited to skin that was adjacent to the lateral line. The epidermis of affected fish was thin and reduced to a one-cell-thick layer over the lateral line. Melanocytes were depleted at the dermo-epidermal junction and formed aggregates in the epidermis. Innate immunity was weaker in affected fish than that previously measured in well-fed channel catfish. Because the pathology and apparent aetiology of HLLE described in various fish species are highly variable, HLLE appears to be a clinical sign, rather than a disease or syndrome. Thus, we propose that this clinical sign be referred to as lateral line depigmentation (LLD), because this description more accurately encompasses all cases of this presentation reported in fish. As nutritional requirements of channel catfish and lateral line neuroanatomy are well-known, the ability to reproducibly induce LLD in this species could provide a useful model for understanding its pathogenesis.

Development of an ELISA for quantification of the antimicrobial peptide piscidin 4 and its application to assess stress in fish

Antimicrobial peptides (AMP) are an integral component of innate immunity. One of the most widespread AMP in fish are the piscidins, which have potent, broad-spectrum activity against viruses, bacteria, fungi, and parasites. The widespread phylogenetic distribution of piscidins suggests that they might play an important host defense role in many fish. Quantifying their expression is important in understanding how and where they function. Using a novel piscidin (piscidin 4) that we recently isolated from commercially cultured hybrid striped bass (white bass, Morone chrysops Rafinesque, female symbolxstriped bass, Morone saxatilis Walbaum male symbol), we optimized the conditions for measuring this piscidin via sandwich ELISA. We used an antibody to the highly conserved amino terminus of all piscidins as the capture antibody and a peroxidase-labeled antibody specific for the carboxy terminus of piscidin 4 as the detecting antibody. Specificity of the detecting antibody was confirmed by lack of cross-reactivity with other piscidins in ELISA, as well as specificity for piscidin 4 in tissue extracts via Western blotting. The accuracy of the test, defined as piscidin 4 recovery, was 96-103%. Precision, measured by the coefficient of variation, was 13-19%, and parallelism, determined by linearity of the response, had an r(2)>0.99. The ELISA paralleled the results obtained via Western blotting. Piscidin 4 levels expressed in gill tissue of healthy hybrid striped bass were well within concentrations that are lethal to important fish pathogens. Mean gill piscidin 4 in healthy hybrid striped bass was significantly greater than in either nutritionally stressed fish or in diseased (ectoparasite-infested) fish, suggesting that piscidin 4 can be significantly downregulated with stress or disease. These data suggest that the piscidin 4 ELISA might be a useful indicator of disease susceptibility, providing a new, sensitive tool for rapid screening of population health.

Targeted deletion of the ATP binding domain of left-right dynein confirms its role in specifying development of left-right asymmetries

Vertebrates develop distinct asymmetries along the left-right axis, which are consistently aligned with the anteroposterior and dorsoventral axes. The mechanisms that direct this handed development of left-right asymmetries have been elusive, but recent studies of mutations that affect left-right development have shed light on the molecules involved. One molecule implicated in left-right specification is left-right dynein (LRD), a microtubule-based motor protein. In the LRD protein of the inversus viscerum (iv) mouse, there is a single amino acid difference at a conserved position, and the lrd gene is one of many genes deleted in the legless (lgl) mutation. Both iv and lgl mice display randomized left-right development. Here we extend the analysis of the lrd gene at the levels of sequence, expression and function. The complete coding sequence of the lrd gene confirms its classification as an axonemal, or ciliary, dynein. Expression of lrd in the node at embryonic day 7.5 is shown to be symmetric. At embryonic day 8.0, however, a striking asymmetric expression pattern is observed in all three germ layers of the developing headfold, suggesting roles in both the establishment and maintenance of left-right asymmetries. At later times, expression of lrd is also observed in the developing floorplate, gut and limbs. These results suggest function for LRD protein in both ciliated and non-ciliated cells, despite its sequence classification as axonemal. In addition, a targeted mutation of lrd was generated that deletes the part of the protein required for ATP binding, and hence motor function. The resulting left-right phenotype, randomization of laterality, is identical to that of iv and lgl mutants. Gross defects in ciliary structure were not observed in lrd/lrd mutants. Strikingly, however, the monocilia on mutant embryonic node cells were immotile. These results prove the identity of the iv and lrd genes. Further, they argue that LRD motor function, and resulting nodal monocilia movement, are required for normal left-right development.

Detection and identification of Mycobacterium directly from BACTEC bottles by using a DNA-rRNA probe

Detection and identification of mycobacterial species using DNA-rRNA probes from colonies has been used for some time. Guidelines for probe use with a specific minimum growth index (GI) cutoff from BACTEC 12B bottles or its use with 7H9 broth has not been defined. This study defined this minimum GI guideline. Clinical specimens received during the study period were decontaminated and directly inoculated into BACTEC 12B bottles and appropriate solid media. An initial probe test was performed at a GI reading of > or = 100. An additional probe test was made at GI of > or = 300. A total of 1377 specimens were processed with 98 specimens containing 99 isolates of Mycobacterium. Of these, 82 were M. avium complex (MAC), six were M. tuberculosis (Mtb), and 11 were other species. At a GI of > or = 100, 82% of MAC were detected; at a GI of > or = 300, 89% were detected. All Mtb were detected at a GI of > or = 100. The probes correctly identified all isolates from backup 7H9 broths. There were no false-positive probe results for any of the isolates from either BACTEC 12B or 7H9 media. Therefore, the DNA-rRNA probe test at a GI of > or = 300 saves considerable time (on average, 21 days saved) for the detection and identification of Mtb and MAC. This time saving compares with waiting for the production of colonies while retaining acceptable sensitivity and excellent specificity.

A cluster of Mycobacterium gordonae isolates from bronchoscopy specimens

During a 2.5-year period, 52 patients at Yale-New Haven Hospital had Mycobacterium gordonae recovered from specimens obtained by suction at bronchoscopy; 2 of them also had smears positive for acid-fast bacilli. Almost all of the isolates came from patients bronchoscoped by the same physician, one of 4 who performed the procedure during that period. Only this physician added one drop of green dye, stored in a 100-ml bottle, to the cocaine used for topical anesthesia during the procedure; cultures of the dye yielded Mycobacterium gordonae. Contamination with this organism, a cause of positive acid-fast smears, may result in an initial inappropriate diagnosis of Mycobacterium tuberculosis.