Biomedical subjects

J R Perfect

Publications and source records attributed to J R Perfect.

At least 37 records · Page 2Linked to original sources

PubMed2001

Identification and characterization of the Cryptococcus neoformans phosphomannose isomerase-encoding gene, MAN1, and its impact on pathogenicity.

The polysaccharide capsule surrounding Cryptococcus neoformans comprises manose, xylose and glucuronic acid, of which mannose is the major constituent. The GDP-mannose biosynthesis pathway is highly conserved in fungi and consists of three key enzymes: phosphomannose isomerase (PMI), phosphomannomutase (PMM) and GDP-mannose pyrophosphorylase (GMP). The MAN1 gene, encoding for the PMI enzyme, was isolated and sequenced from C. neoformans, and a disruption of the MAN1 gene was generated. One MAN1 disruption mutant, man1, which showed poor capsule formation, reduced polysaccharide secretion and morphological abnormalities, was chosen for virulence studies. In both the rabbit and the mouse models of invasive cryptococcosis, man1 was shown to be severely impaired in its virulence, with complete elimination of the yeast from the host. A reconstituted strain of man1 was constructed using gene replacement at the native locus. The wild-type and reconstituted strains were significantly more virulent than the knock-out mutant in both animal models. Our findings reveal that PMI activity is essential for the survival of C. neoformans in the host. The fact that the man1 mutant was not pathogenic suggests that blocking mannose synthesis could be fungicidal in the mammalian host and thus an excellent target for antifungal drug development.

Amino Acid Sequence↗

PubMed2001

Two cyclophilin A homologs with shared and distinct functions important for growth and virulence of Cryptococcus neoformans.

Cyclophilin A is the target of the immunosuppressant cyclosporin A (CsA) and is encoded by a single unique gene conserved from yeast to humans. In the pathogenic fungus Cryptococcus neoformans, two homologous linked genes, CPA1 and CPA2, were found to encode two conserved cyclophilin A proteins. In contrast to Saccharomyces cerevisiae, in which cyclophilin A mutations confer CsA resistance but few other phenotypes, cyclophilin A mutations conferred dramatic phenotypes in C. neoformans. The Cpa1 and Cpa2 cyclophilin A proteins play a shared role in cell growth, mating, virulence and CsA toxicity. The Cpa1 and Cpa2 proteins also have divergent functions. cpa1 mutants are inviable at 39 degrees C and attenuated for virulence, whereas cpa2 mutants are viable at 39 degrees C and fully virulent. cpa1 cpa2 double mutants exhibited synthetic defects in growth and virulence. Cyclophilin A active site mutants restored growth of cpa1 cpa2 mutants at ambient but not at higher temperatures, suggesting that the prolyl isomerase activity of cyclophilin A has an in vivo function.

Amino Acid Sequence↗

PubMed2001

Rapamycin and less immunosuppressive analogs are toxic to Candida albicans and Cryptococcus neoformans via FKBP12-dependent inhibition of TOR.

Candida albicans and Cryptococcus neoformans cause both superficial and disseminated infections in humans. Current antifungal therapies for deep-seated infections are limited to amphotericin B, flucytosine, and azoles. A limitation is that commonly used azoles are fungistatic in vitro and in vivo. Our studies address the mechanisms of antifungal activity of the immunosuppressive drug rapamycin (sirolimus) and its analogs with decreased immunosuppressive activity. C. albicans rbp1/rbp1 mutant strains lacking a homolog of the FK506-rapamycin target protein FKBP12 were found to be viable and resistant to rapamycin and its analogs. Rapamycin and analogs promoted FKBP12 binding to the wild-type Tor1 kinase but not to a rapamycin-resistant Tor1 mutant kinase (S1972R). FKBP12 and TOR mutations conferred resistance to rapamycin and its analogs in C. albicans, C. neoformans, and Saccharomyces cerevisiae. Our findings demonstrate the antifungal activity of rapamycin and rapamycin analogs is mediated via conserved complexes with FKBP12 and Tor kinase homologs in divergent yeasts. Taken together with our observations that rapamycin and its analogs are fungicidal and that spontaneous drug resistance occurs at a low rate, these mechanistic findings support continued investigation of rapamycin analogs as novel antifungal agents.

Antifungal Agents↗

PubMed2001

Fungal phospholipase activity and susceptibility to lipid preparations of amphotericin B.

It has been postulated that phospholipases of fungal origin can affect in vitro susceptibility testing of amphotericin B lipid complex (ABLC). We used specific phospholipase-deficient mutants of Candida albicans and Cryptococcus neoformans in susceptibility testing and demonstrated that extracellular fungal phospholipase activity does not influence the in vitro susceptibilities of these two fungi to ABLC.

Amphotericin B↗

PubMed2001

Cyclic AMP-dependent protein kinase controls virulence of the fungal pathogen Cryptococcus neoformans.

Cryptococcus neoformans is an opportunistic fungal pathogen that infects the human central nervous system. This pathogen elaborates two specialized virulence factors: the antioxidant melanin and an antiphagocytic immunosuppressive polysaccharide capsule. A signaling cascade controlling mating and virulence was identified. The PKA1 gene encoding the major cyclic AMP (cAMP)-dependent protein kinase catalytic subunit was identified and disrupted. pka1 mutant strains were sterile, failed to produce melanin or capsule, and were avirulent. The PKR1 gene encoding the protein kinase A (PKA) regulatory subunit was also identified and disrupted. pkr1 mutant strains overproduced capsule and were hypervirulent in animal models of cryptococcosis. pkr1 pka1 double mutant strains exhibited phenotypes similar to that of pka1 mutants, providing epistasis evidence that the Pka1 catalytic subunit functions downstream of the Pkr1 regulatory subunit. The PKA pathway was also shown to function downstream of the Galpha protein Gpa1 and to regulate cAMP production by feedback inhibition. These findings define a Galpha protein-cAMP-PKA signaling pathway regulating differentiation and virulence of a human fungal pathogen.

Animals↗

PubMed2000

Identification of the MATa mating-type locus of Cryptococcus neoformans reveals a serotype A MATa strain thought to have been extinct.

Cryptococcus neoformans is an opportunistic fungal pathogen with a defined sexual cycle involving mating between haploid MATa and MATalpha cells. Here we describe the isolation of part of the MATa mating-type locus encoding a Ste20 kinase homolog, Ste20a. We show that the STE20a gene cosegregates with the MATa mating type in genetic crosses, maps within the mating-type locus on a 1.8-Mb chromosome, and is allelic with the MATalpha locus. We identify the first MATa isolate of the most common pathogenic variety of C. neoformans (serotype A, variety grubii) which had been thought to be extinct. This serotype A MATa strain is sterile, fails to produce mating pheromone, and is less virulent than a serotype A MATalpha strain in an animal model. Our studies illustrate an association of mating type with virulence and suggest that, like Candida albicans, pathogenic isolates of C. neoformans may be largely asexual.

Amino Acid Sequence↗

PubMed2000

Identification and characterization of a highly conserved calcineurin binding protein, CBP1/calcipressin, in Cryptococcus neoformans.

Calcineurin is the conserved target of the immunosuppressants cyclosporin A and FK506. Using the yeast two-hybrid system, we identified a novel calcineurin binding protein, CBP1, from the pathogenic fungus Cryptococcus neoformans. We show that CBP1 binds to calcineurin in vitro and in vivo, and FKBP12-FK506 inhibits CBP1 binding to calcineurin. Cryptococcus neoformans cbp1 mutant strains exhibit modest defects in growth under stress conditions and virulence, similar to but less severe than the phenotypes of calcineurin mutants. Saccharomyces cerevisiae mutants lacking the CBP1 homolog RCN1 are, like calcineurin mutants, sensitive to lithium cation stress. CBP1 shares a central peptide sequence motif, SPPxSPP, with related proteins in S.CEREVISIAE:, Schizosaccharomyces pombe, Drosophila melanogaster, Caenorhabditis elegans and humans, and peptides containing this motif altered calcineurin activity in vitro. Interestingly, the human CBP1 homolog DSCR1 is encoded by the Down's syndrome candidate region interval on chromosome 21, is highly expressed in the heart and central nervous system, and may play a role in calcineurin functions in heart development, neurite extension and memory.

Amino Acid Motifs↗

PubMed2000

Practice guidelines for the management of cryptococcal disease. Infectious Diseases Society of America.

An 8-person subcommittee of the National Institute of Allergy and Infectious Diseases (NIAID) Mycoses Study Group evaluated available data on the treatment of cryptococcal disease. Opinion regarding optimal treatment was based on personal experience and information in the literature. The relative strength of each recommendation was graded according to the type and degree of evidence available to support the recommendation, in keeping with previously published guidelines by the Infectious Diseases Society of America (IDSA). The panel conferred in person (on 2 occasions), by conference call, and through written reviews of each draft of the manuscript. The choice of treatment for disease caused by Cryptococcus neoformans depends on both the anatomic sites of involvement and the host's immune status. For immunocompetent hosts with isolated pulmonary disease, careful observation may be warranted; in the case of symptomatic infection, indicated treatment is fluconazole, 200-400 mg/day for 36 months. For those individuals with non-CNS-isolated cryptococcemia, a positive serum cryptococcal antigen titer >1:8, or urinary tract or cutaneous disease, recommended treatment is oral azole therapy (fluconazole) for 36 months. In each case, careful assessment of the CNS is required to rule out occult meningitis. For those individuals who are unable to tolerate fluconazole, itraconazole (200-400 mg/day for 6-12 months) is an acceptable alternative. For patients with more severe disease, treatment with amphotericin B (0.5-1 mg/kg/d) may be necessary for 6-10 weeks. For otherwise healthy hosts with CNS disease, standard therapy consists of amphotericin B, 0.7-1 mg/kg/d, plus flucytosine, 100 mg/kg/d, for 6-10 weeks. An alternative to this regimen is amphotericin B (0.7-1 mg/kg/d) plus 5-flucytosine (100 mg/kg/d) for 2 weeks, followed by fluconazole (400 mg/day) for a minimum of 10 weeks. Fluconazole "consolidation" therapy may be continued for as along as 6-12 months, depending on the clinical status of the patient. HIV-negative, immunocompromised hosts should be treated in the same fashion as those with CNS disease, regardless of the site of involvement. Cryptococcal disease that develops in patients with HIV infection always warrants therapy. For those patients with HIV who present with isolated pulmonary or urinary tract disease, fluconazole at 200-400 mg/d is indicated. Although the ultimate impact from highly active antiretroviral therapy (HAART) is currently unclear, it is recommended that all HIV-infected individuals continue maintenance therapy for life. Among those individuals who are unable to tolerate fluconazole, itraconazole (200-400 mg/d) is an acceptable alternative. For patients with more severe disease, a combination of fluconazole (400 mg/d) plus flucytosine (100-150 mg/d) may be used for 10 weeks, followed by fluconazole maintenance therapy. Among patients with HIV infection and cryptococcal meningitis, induction therapy with amphotericin B (0.7-1 mg/kg/d) plus flucytosine (100 mg/kg/d for 2 weeks) followed by fluconazole (400 mg/d) for a minimum of 10 weeks is the treatment of choice. After 10 weeks of therapy, the fluconazole dosage may be reduced to 200 mg/d, depending on the patient's clinical status. Fluconazole should be continued for life. An alternative regimen for AIDS-associated cryptococcal meningitis is amphotericin B (0.7-1 mg/kg/d) plus 5-flucytosine (100 mg/kg/d) for 6-10 weeks, followed by fluconazole maintenance therapy. Induction therapy beginning with an azole alone is generally discouraged. Lipid formulations of amphotericin B can be substituted for amphotericin B for patients whose renal function is impaired. Fluconazole (400-800 mg/d) plus flucytosine (100-150 mg/kg/d) for 6 weeks is an alternative to the use of amphotericin B, although toxicity with this regimen is high. In all cases of cryptococcal meningitis, careful attention to the management of intracranial pressure is imperative to assure optimal c

AIDS-Related Opportunistic Infections↗

PubMed2000

Agents for treatment of invasive fungal infections.

The incidence of fungal infections continues to rise as the population of immunocompromised individuals increases. Despite the enlarging numbers of infections, there are only a few antifungal agents for treatment of deep-seated, invasive infections. These agents include amphotericin B, flucytosine, terbinafine, and several azoles. Progress has been made in understanding the role of these agents in a variety of infections and this article examines in detail these agents and their prophylactic, empiric, and therapeutic uses in invasive mycoses. This article focuses on general concepts of antifungal therapies and provides a detailed review of each antifungal agent available for treatment of deep-seated mycoses.

Antifungal Agents↗

PubMed2000

RAS1 regulates filamentation, mating and growth at high temperature of Cryptococcus neoformans.

Cryptococcus neoformans is a basidiomycete yeast and opportunistic human pathogen of increasing clinical importance due to the increasing population of immunocompromised patients. To further investigate signal transduction cascades regulating fungal pathogenesis, we have identified the gene encoding a RAS homologue in this organism. The RAS1 gene was disrupted by transformation and homologous recombination. The resulting ras1 mutant strain was viable, but failed to grow at 37 degrees C, and exhibited significant defects in mating and agar adherence. The ras1 mutant strain was also avirulent in an animal model of cryptococcal meningitis. Reintroduction of the wild-type RAS1 gene complemented these ras1 mutant phenotypes and restored virulence in animals. A dominantly active RAS1 mutant allele, RAS1Q67L, induced a differentiation phenotype known as haploid fruiting, which involves filamentation, agar invasion and sporulation in response to nitrogen deprivation. The ras1 mutant mating defect was suppressed by overexpression of MAP kinase signalling elements and partially suppressed by exogenous cAMP. Additionally, cAMP also suppressed the agar adherence defect of the ras1 mutant. However, the ability of the ras1 mutant strain to grow at elevated temperature was not restored by cAMP or MAP kinase overexpression. Our findings support a model in which RAS1 signals in C. neoformans through cAMP-dependent, MAP kinase, and RAS-specific signalling cascades to regulate mating and filamentation, as well as growth at high temperature which is necessary for maintenance of infection.

Animals↗

PubMed2000

Fungal meningitis.

Fungi provide many benefits to humans. However, some of these fungi have the ability to become human pathogens. All the major fungal pathogens can produce meningitis. From the common cryptococcal meningitis to the rare fungal meningitis caused by a dimorphic or filamentous fungus, medical issues are discussed in this review on a fungus-specific basis. Both primary (Cryptococcus, Blastomyces, Histoplasma, Coccidioides, and other dimorphic fungi) and secondary (Aspergillus, Candida, and a series of molds) fungal pathogens can produce life-threatening central nervous system infections. These infections require immediate and precise diagnosis and carefully selected management strategies to optimize outcomes. In this review, we examine the epidemiology, pathogenesis, clinical manifestations, and treatment for fungal meningitis in all the major fungal groups.

Aspergillus fumigatus↗

PubMed2000

Treatment of methicillin-resistant staphylococcus aureus infections with quinupristin-dalfopristin in patients intolerant of or failing prior therapy. For the Synercid Emergency-Use Study Group.

Safety and efficacy of quinupristin-dalfopristin (an injectable streptogramin antibiotic) were evaluated in the treatment of a variety of infections due to methicillin-resistant Staphylococcus aureus (MRSA) in patients either intolerant of or failing prior therapy. The influence of resistance phenotypes on treatment outcome was also assessed. This worldwide, multicentre, open-label, non-comparative, emergency-use clinical study enrolled patients with one or more of nine predefined, culture-confirmed infections with MRSA, who had no clinically appropriate alternative antibiotic therapy. The recommended quinupristin-dalfopristin dose was 7.5 mg/kg administered iv every 8 h for a duration judged appropriate by the investigator. There were no restrictions on prior or concomitant treatment with other antibiotics. Clinical, microbiological and laboratory assessments were performed at baseline, during study drug treatment, within 24 h after the last dose, and 7-21 days post-therapy. Ninety patients [age (mean +/- S.D.) 57.4 +/- 18.5 years] with significant underlying medical illnesses were treated at 63 centres in five countries. The most common indications were bone and joint infection (44.4% of patients) and skin and skin structure infection (16.7%). The mean (+/- S.D.) daily dose and treatment duration was 20.2 +/- 2.9 mg/kg/day for 28.5 +/- 22.3 days, most frequently administered every 8 h. The overall success rate (defined as a clinical outcome of either cure or improvement and a bacteriological outcome of eradication or presumed eradication) was 71.1% in the all-treated population (n = 90) and 66.7% in patients who were both clinically and bacteriologically evaluable (n = 27). Success rates for endocarditis, respiratory tract infection and bacteraemia of unknown source were below the population mean. The macrolide-lincosamide-streptogramin type B resistance phenotype did not appear to alter the response rate. The most common non-venous adverse events related to study medication were arthralgias (10.8%), myalgias (8.6%) and nausea (8.6%). Quinupristin-dalfopristin should be considered as a treatment option for infections caused by MRSA, especially in patients intolerant of or failing alternate therapy.

Adolescent↗

PubMed2000

Immunosuppressive and nonimmunosuppressive cyclosporine analogs are toxic to the opportunistic fungal pathogen Cryptococcus neoformans via cyclophilin-dependent inhibition of calcineurin.

Cyclosporine (CsA) is an immunosuppressive and antimicrobial drug which, in complex with cyclophilin A, inhibits the protein phosphatase calcineurin. We recently found that Cryptococcus neoformans growth is resistant to CsA at 24 degrees C but sensitive at 37 degrees C and that calcineurin is required for growth at 37 degrees C and pathogenicity. Here CsA analogs were screened for toxicity against C. neoformans in vitro. In most cases, antifungal activity was correlated with cyclophilin A binding in vitro and inhibition of the mixed-lymphocyte reaction and interleukin 2 production in cell culture. Two unusual nonimmunosuppressive CsA derivatives, (gamma-OH) MeLeu(4)-Cs (211-810) and D-Sar (alpha-SMe)(3) Val(2)-DH-Cs (209-825), which are also toxic to C. neoformans were identified. These CsA analogs inhibit C. neoformans via fungal cyclophilin A and calcineurin homologs. Our findings identify calcineurin as a novel antifungal drug target and suggest nonimmunosuppressive CsA analogs warrant investigation as antifungal agents.

Animals↗

PubMed2000

Synergistic antifungal activities of bafilomycin A(1), fluconazole, and the pneumocandin MK-0991/caspofungin acetate (L-743,873) with calcineurin inhibitors FK506 and L-685,818 against Cryptococcus neoformans.

Cryptococcus neoformans is an opportunistic fungal pathogen that causes life-threatening infections of the central nervous system. Existing therapies include amphotericin B, fluconazole, and flucytosine, which are limited by toxic side effects and the emergence of drug resistance. We recently demonstrated that the protein phosphatase calcineurin is required for growth at 37 degrees C and virulence of C. neoformans. Because calcineurin is the target of potent inhibitors in widespread clinical use, cyclosporine and FK506 (tacrolimus), it is an attractive drug target for novel antifungal agents. Here we have explored the synergistic potential of combining the calcineurin inhibitor FK506 or its nonimmunosuppressive analog, L-685,818, with other antifungal agents and examined the molecular basis of FK506 action by using genetically engineered fungal strains that lack the FK506 target proteins FKBP12 and calcineurin. We demonstrate that FK506 exhibits marked synergistic activity with the H(+)ATPase inhibitor bafilomycin A(1) via a novel action distinct from calcineurin loss of function. FK506 also exhibits synergistic activity with the pneumocandin MK-0991/caspofungin acetate (formerly L-743,873), which targets the essential beta-1,3 glucan synthase, and in this case, FK506 action is mediated via FKBP12-dependent inhibition of calcineurin. Finally, we demonstrate that FK506 and fluconazole have synergistic activity that is independent of both FKBP12 and calcineurin and may involve the known ability of FK506 to inhibit multidrug resistance pumps, which are known to export azoles from fungal cells. In summary, our studies illustrate the potential for synergistic activity of a variety of different drug combinations and the power of molecular genetics to define the mechanisms of drug action, as well as identify a novel action of FK506 that could have profound implications for therapeutic or toxic effects in other organisms, including humans.

Anti-Bacterial Agents↗

PubMed2000

Urease as a virulence factor in experimental cryptococcosis.

Urease catalyzes the hydrolysis of urea to ammonia and carbamate and has been found to be an important pathogenic factor for certain bacteria. Cryptococcus neoformans is a significant human pathogenic fungus that produces large amounts of urease; thus we wanted to investigate the importance of urease in the pathogenesis of cryptococcosis. We cloned and sequenced the genomic locus containing the single-copy C. neoformans urease gene (URE1) and used this to disrupt the native URE1 in the serotype A strain H99. The ure1 mutant strains were found to have in vitro growth characteristics, phenoloxidase activity, and capsule size similar to those of the wild type. Comparison of a ure1 mutant with H99 after intracisternal inoculation into corticosteroid-treated rabbits revealed no significant differences in colony counts recovered from the cerebrospinal fluid. However, when these two strains were compared in both the murine intravenous and inhalational infection models, there were significant differences in survival. Mice infected with a ure1 strain lived longer than mice infected with H99 in both models. The ure1 strain was restored to urease positivity by complementation with URE1, and two resulting transformants were significantly more pathogenic than the ure1 strain. Our results suggest that urease activity is involved in the pathogenesis of cryptococcosis but that the importance may be species and/or infection site specific.

Animals↗

PubMed2000

The G-protein beta subunit GPB1 is required for mating and haploid fruiting in Cryptococcus neoformans.

Cryptococcus neoformans is an opportunistic fungal pathogen with a defined sexual cycle. The gene encoding a heterotrimeric G-protein beta subunit, GPB1, was cloned and disrupted. gpb1 mutant strains are sterile, indicating a role for this gene in mating. GPB1 plays an active role in mediating responses to pheromones in early mating steps (conjugation tube formation and cell fusion) and signals via a mitogen-activated protein (MAP) kinase cascade in both MATalpha and MATa cells. The functions of GPB1 are distinct from those of the Galpha protein GPA1, which functions in a nutrient-sensing cyclic AMP (cAMP) pathway required for mating, virulence factor induction, and virulence. gpb1 mutant strains are also defective in monokaryotic fruiting in response to nitrogen starvation. We show that MATa cells stimulate monokaryotic fruiting of MATalpha cells, possibly in response to mating pheromone, which may serve to disperse cells and spores to locate mating partners. In summary, the Gbeta subunit GPB1 and the Galpha subunit GPA1 function in distinct signaling pathways: one (GPB1) senses pheromones and regulates mating and haploid fruiting via a MAP kinase cascade, and the other (GPA1) senses nutrients and regulates mating, virulence factors, and pathogenicity via a cAMP cascade.

Amino Acid Sequence↗

PubMed2000

Antifungal pharmacodynamics: review of the literature and clinical applications.

Invasive fungal infections are seen with growing frequency, likely due to increases in numbers of patients at risk of infection. Optimal selection and dosing of antifungal agents are important, as these infections are often refractory to available therapy. In contrast to antibacterials, studies examining the pharmacodynamic properties of antifungals and their application in treating invasive disease often are lacking. Agents administered for invasive infections are amphotericin B, flucytosine, and azole antifungals. Several drugs are under investigation, such as posiconazole, voriconazole, and the echinocandins, and preliminary pharmacodynamic data likely will help shape dosing regimens. Clinical trials that investigated dosage and administration, as well as the potential benefits of combination and sequential therapy, are addressed. In addition, antifungal susceptibility and animal models of infection are discussed.

Animals↗

PubMed2000

Anastomotic infections in lung transplant recipients.

OBJECTIVES: Anastomotic infections are an uncommon but potentially devastating complication after lung transplantation. The incidence, microbiology, predisposing factors, and clinical outcomes of anastomotic infections have not been well described. METHODS: We performed a retrospective chart review of the first 283 lung or heart-lung transplant recipients performed at Duke University Medical Center and identified all cases of anastomotic infection. RESULTS: Fifteen patients (5.3%) developed anastomotic infections. Aspergillus caused infection in six patients, Candida in eight patients and Staphylococcus aureus in one patient. Bilateral or right lung transplantation and the use of induction immunosuppression with monoclonoal or polyclonal antibodies are associated with a higher incidence of anastomotic infections. All patients with fungal anastomotic infections were treated with a combination of systemic and inhaled antifungal agents. All patients had improvement of their anastomotic sites after treatment and no patients developed anastomotic dehiscence. CONCLUSIONS: Anastomotic infection is an infrequent complication after lung transplantation, and is caused predominately by fungal pathogens. In contrast to previous reports, anastomotic dehiscence did not occur in any patient in our series. Treatment with the combination of inhaled and systemic antimicrobial agents may have favorably affected clinical outcomes.

Adult↗