TISSUE MAST CELLS AND ACUTE INFLAMMATION IN EXPERIMENTAL CUTANEOUS MUCORMYCOSIS OF NORMAL, 48/80-TREATED, AND DIABETIC RATS

Development of a Combat-Relevant Murine Model of Wound Mucormycosis: A Platform for the Pre-Clinical Investigation of Novel Therapeutics for Wound-Invasive Fungal Diseases

Wound-invasive fungal diseases (WIFDs), especially mucormycosis, have emerged as life-threatening infections during recent military combat operations. Many combat-relevant fungal pathogens are refractory to current antifungal therapy. Therefore, animal models of WIFDs are urgently needed to investigate new therapeutic solutions. Our study establishes combat-relevant murine models of wound mucormycosis using Rhizopus arrhizus and Lichtheimia corymbifera, two Mucorales species that cause wound mucormycosis worldwide. These models recapitulate the characteristics of combat-related wounds from explosions, including blast overpressure exposure, full-thickness skin injury, fascial damage, and muscle crush. The independent inoculation of both pathogens caused sustained infections and enlarged wounds. Histopathological analysis confirmed the presence of necrosis and fungal hyphae in the wound bed and adjacent muscle tissue. Semi-quantification of fungal burden by colony-forming units corroborated the infection. Treatment with liposomal amphotericin B, 30 mg/kg, effectively controlled R. arrhizus growth and significantly reduced residual fungal burden in infected wounds (p < 0.001). This study establishes the first combat-relevant murine model of wound mucormycosis, paving the way for developing and evaluating novel antifungal therapies against combat-associated WIFDs.

Molecular mechanisms that govern infection and antifungal resistance in Mucorales

SUMMARYThe World Health Organization has established a fungal priority pathogens list that includes species critical or highly important to human health. Among them is the order Mucorales, a fungal group comprising at least 39 species responsible for the life-threatening infection known as mucormycosis. Despite the continuous rise in cases and the poor prognosis due to innate resistance to most antifungal drugs used in the clinic, Mucorales has received limited attention, partly because of the difficulties in performing genetic manipulations. The COVID-19 pandemic has further escalated cases, with some patients experiencing the COVID-19-associated mucormycosis, highlighting the urgent need to increase knowledge about these fungi. This review addresses significant challenges in treating the disease, including delayed and poor diagnosis, the lack of accurate global incidence estimation, and the limited treatment options. Furthermore, it focuses on the most recent discoveries regarding the mechanisms and genes involved in the development of the disease, antifungal resistance, and the host defense response. Substantial advancements have been made in identifying key fungal genes responsible for invasion and tissue damage, host receptors exploited by the fungus to invade tissues, and mechanisms of antifungal resistance. This knowledge is expected to pave the way for the development of new antifungals to combat mucormycosis. In addition, we anticipate significant progress in characterizing Mucorales biology, particularly the mechanisms involved in pathogenesis and antifungal resistance, with the possibilities offered by CRISPR-Cas9 technology for genetic manipulation of the previously intractable Mucorales species.

Hyphae of Rhizopus arrhizus and Lichtheimia corymbifera Are More Virulent and Resistant to Antifungal Agents Than Sporangiospores In Vitro and in Galleria mellonella

Mucorales species cause debilitating, life-threatening sinopulmonary diseases in immunocompromised patients and penetrating wounds in trauma victims. Common antifungal agents against mucormycosis have significant toxicity and are often ineffective. To evaluate treatments against mucormycosis, sporangiospores are typically used for in vitro assays and in pre-clinical animal models of pulmonary infections. However, in clinical cases of wound mucormycosis caused by traumatic inoculation, hyphal elements found in soil are likely the form of the inoculated organism. In this study, Galleria mellonella larvae were infected with either sporangiospores or hyphae of Rhizopus arrhizus and Lichtheimia corymbifera. Hyphal infections resulted in greater and more rapid larval lethality than sporangiospores, with an approximate 10-16-fold decrease in LD50 of hyphae for R. arrhizus (p = 0.03) and L. corymbifera (p = 0.001). Liposomal amphotericin B, 10 mg/kg, was ineffective against hyphal infection, while the same dosage was effective against infections produced by sporangiospores. Furthermore, in vitro, antifungal susceptibility studies show that minimum inhibitory concentrations of several antifungal agents against hyphae were higher when compared to those of sporangiospores. These findings support using hyphal elements of Mucorales species for virulence testing and antifungal drug screening in vitro and in G. mellonella for studies of wound mucormycosis.

Animal Models to Study Mucormycosis

Mucormycosis is a rare but often fatal or debilitating infection caused by a diverse group of fungi. Animal models have been crucial in advancing our knowledge of mechanisms influencing the pathogenesis of mucormycoses, and to evaluate therapeutic strategies. This review describes the animal models established for mucormycosis, summarizes how they have been applied to study mucormycoses, and discusses the advantages and limitations of the different model systems.

Topical cis-urocanic acid prevents ocular surface irritation in both IgE -independent and -mediated rat model

PURPOSE

Our purpose was to investigate the effect of locally administered cis-urocanic (cis-UCA) in two experimental models of allergic conjunctivitis.

METHODS

The compound 48/80 (C48/80)-induced ocular irritation model (IgE-independent) and the ovalbumin (OA)-induced ocular allergy model (IgE-mediated) were used to test and compare the effect of cis-UCA on dexamethasone, ketotifen and olopatadine. In the C48/80 model, clinical severity scoring from photographs, immunohistochemical analysis of nuclear Ki-67 antigen to quantify actively proliferating epithelial cells and of caspase-3 enzyme to identify apoptotic activity in the conjunctival tissue were used. In the OA model, an Evans Blue stain concentration of conjunctival tissue was used to evaluate vascular leakage due to allergic reaction.

RESULTS

The cis-UCA was well tolerated and effective in both the IgE-independent and -mediated rat models. Treatment with C48/80 caused conjunctival hyperaemia, which was significantly inhibited by ketotifen at the 6 h time point (p = 0.014) and by dexamethasone and cis-UCA 0.5% at 12 (p = 0.004) and 24 (p = 0.004) hour time points. In a comparison between the active drug treatments, only ketotifen showed a significant difference (p = 0.023) to cis-UCA treatment at the 1 h time point, otherwise there were no statistically significant differences between the active drugs. Ketotifen, dexamethasone and cis-UCA 0.5% significantly inhibited the C48/80-induced nuclear accumulation of Ki-67, without differences between the active treatment groups. In the OA model, cis-UCA 0.5% did not inhibit the vascular leakage of conjunctiva, whereas cis-UCA 2.5% of was at least equally effective compared to olopatadine, abolishing the allergic vascular leakage response almost completely.

CONCLUSIONS

The present findings in the two AC models suggest that cis-UCA might have anti-allergic potency both in immediate and delayed-type allergic reactions in the eye.

Polymeric "smart" coatings to prevent foreign body response to implantable biosensors

Application of implantable glucose biosensors for "real-time" monitoring is reliant on controlling the negative tissue reaction at the sensor tissue interphase. A novel polymer coating consisting of poly(lactic-co-glycolic) acid (PLGA) microsphere dispersed in poly(vinyl alcohol) (PVA) hydrogels was evaluated in combination with dummy sensors as a "smart" drug eluting biocompatible coating for implantable biosensors to prevent the foreign body response, and thus enhance sensor performance in vivo. The polymeric microspheres slowly release tissue-modifying drugs at the implantation sites to control the inflammation and fibrous encapsulation, while the hydrogel allows rapid analyte diffusion to the sensing elements. Dummy sensors with identical dimensions to that of the functional glucose sensors (0.5×0.5×5mm) were coated with the PLGA/PVA composites using a mold fabrication process. Both normal and diabetic rats were used in the current study to investigate the effect of the diabetic state on tissue sensor interactions. It was evident that the PLGA/PVA hydrogel composite was able to form a uniform coating around the dummy sensor and stayed intact throughout the course of the study (one month). Tissue samples containing dummy sensors that were coated with dexamethasone free composites exhibited acute and chronic inflammation as well as fibrous encapsulation in both normal and diabetic rats. However, the diabetic rats exhibited decreased intensity and delayed onset of the foreign body response following implantation of drug free dummy sensors in comparison to those of normal rats. On the other hand, tissues containing dummy sensors that were coated with dexamethasone containing composites remained normal (i.e. similar to untreated tissues), with no inflammatory reaction or fibrous encapsulation occurring over the one-month period in both the normal and diabetic rats. The feasibility of utilizing PLGA microsphere/PVA hydrogel composites as coatings for implantable biosensors was demonstrated. This polymeric composite is an innovative approach to control the foreign body reaction at the tissue-device interface to prolong biosensor lifetime.

Synovial mast cells: role in acute and chronic arthritis

Mast cells reside in the normal synovium and increase strikingly in number in rheumatoid arthritis and other joint diseases. Given the broad spectrum of activity of this lineage, it has for decades been considered probable that mast cells are involved in the pathophysiology of synovitis. Recent work in murine arthritis has substantiated this suspicion, showing that mast cells can contribute importantly to the initiation of inflammatory arthritis. However, the role of the greatly expanded population of synovial mast cells in established arthritis remains unknown. Here we review the current understanding of mast cell function in acute arthritis and consider the potentially important influence of this cell on key processes within the chronically inflamed synovium, including leukocyte recruitment and activation, fibroblast proliferation, angiogenesis, matrix remodeling, and injury to collagen and bone. We also consider recent evidence supporting an immunomodulatory or anti-inflammatory role for mast cells as well as pharmacologic approaches to the mast cell as a therapeutic target in inflammatory arthritis.

Histamine acting on a histamine type 1 (H1) receptor increases beta-glucuronidase release from human lung macrophages

The effects of histamine on lung macrophages have been studied by both biologic and radioligand experiments. After overnight adherence, lung macrophages spontaneously released beta-glucuronidase (beta-G) at a rate of approximately 7 nmol of hydrolyzed substrate/h/million cells. Histamine at low concentrations (10(-9) to 10(-8) M) resulted in a consistent potentiation of this release. The concentration-effect curve of histamine was bell-shaped, reaching an optimum at 10(-9) M, with concentrations greater than 10(-8) M having no significant effect. At a maximally effective concentration (10(-9) M), histamine evoked a 135 +/- 9.6% (mean +/- SE; n = 8, P less than 0.001) potentiation in the total amount of beta-G released during the first 60 min of incubation. This increase in beta-G release represented both a slight increase in beta-G synthesis as well as an increase in the percentage of beta-G released. When the secreted beta-G is expressed as a percentage of total content, histamine (10(-9) M) evoked a 125 +/- 3.2% (mean +/- SE; n = 27, P less than 0.0005) enhancement. The potentiation of beta-G release by histamine was evident after 45 min of incubation and persisted for up to 6 h. The potentiation of beta-G by histamine was sensitive to inhibition by pyrilamine (10(-7) M).(ABSTRACT TRUNCATED AT 250 WORDS)

Resistance to peritonitis following disruption of peritoneal mast cells

A single ip injection of distilled water osmotically disrupts almost the entire population of peritoneal mast cells in rats. The metachromatic granules released from disrupted mast cells are phagocytosed by peritoneal macrophages increasing their chemotactic and spreading activities. On this basis a study was carried out to determine whether an ip injection of distilled water, by releasing an abundance of these granules for peritoneal macrophage stimulation, protects rats subsequently exposed to peritonitis. We found that a single ip injection of distilled water lowers the mortality in rats exposed to bacterial peritonitis 2-3 weeks later from 80 to 33%.

Host-parasite relationship in opportunistic mycoses

Aspergillosis and mucormycosis are opportunistic fungal infections that share several unique features. The etiologic agents of aspergillosis and mucormycosis are ubiquitous in the environment, but are opportunistic organisms and usually infect only patients predisposed by some underlying disease or treatment. These infections are typically characterized by hyphal tissue invasion and a predilection of the organism for blood vessel invasion with hemorrhage, necrosis, and infarction. Also, these organisms are not dimorphic, like the true pathogenic dimorphic fungi, as they grow both in the environment and within the host in hyphal forms. However, the host must contend with several forms to successfully eliminate them. Each form displays different antigenic and surface features and elicits different host responses. Finally, if germination and hyphal growth occur, the host must compete with a rapidly growing organism that is too large to be ingested by a single cell and so must be handled by extracellular defense mechanisms.

Passive immunization in murine mucormycosis

Antibody raised in mice against mycelial homogenates of Rhizomucor pusillus was effective in passive immunization against pulmonary and disseminated mucormycosis (phycomycosis) in immunocompromised mice. Mice intranasally inoculated and infected with Rh. pusillus and treated with antisera had a statistically significant increased resistance to infection and a diminished secondary dissemination of viable fungal fragments. Histological examination of infected lung tissues showed that antibody treated animals were apparently able to degrade hyphal fragments.

Susceptibility of Zygomycetes to human serum

Seven members of the class Zygomycetes were tested for serum susceptibility. Five of the isolates were inhibited to different degrees by pooled fresh human serum. Heating the serum at 56 degrees C for 30 min to inactivate complement did not abolish the inhibitory activity in the serum. Members of the genera Cunninghamella and Absidia appeared most susceptable to the inhibitory effects of serum while members of the genus Rhizopus were most resistant. One isolate of R. arrhizus appeared to have enhanced growth in the presence of human serum. Our findings suggest certain species of the class Zygomycetes are strongly inhibited by serum, and this may account for the rarity of human infections by these species.

Fungal endocarditis: patients at risk and their treatment

Fungal endocarditis is not rare. It usually develops in patients with abnormal or surgically traumatized hearts, to whose blood fungi have gained access, perhaps during temporary (often iatrogenic) impairment of host defences. Although the blood is cleared rapidly, the fungus can establish itself in the endocardium, where it grows slowly. Thus, clinical and laboratory procedures (including blood and urine cultures) that have permitted early diagnosis and treatment of bacterial endocarditis, are not reliable in early fungal endocarditis. Greater reliance must be placed on serological monitoring of patients who have had transient fungaemia and are at risk of endocarditis. The clinician must consider factors that enhance fungal proliferation and invasion and be cognizant of its dangers - even in the absence of clear signs of infection. Prophylactic measures should be employed to protect the patient at risk, including topical, oral and systemic use of appropriate antifungal agents. Early therapy, the extent and duration of which can be determined by (1) obtaining the MIC of transitory blood or urine isolates - which should not be ignored - and (2) monitoring serology, might eliminate early invaders of the endocardium. Sixty-four reported cures of fungal endocarditis caused by Candida, the most common fungal pathogen, are tabulated, 29 were of classic fungal endocarditis requiring surgery, 3 of whom were seen later by others as fatal recurrences. Those treated early (shortly after candidaemia was diagnosed - mostly in patients on treatment for bacterial endocarditis or after cardiac surgery) survived without need for surgical removal of vegetations or valve replacement. Despite strong suggestive evidence that the first 35 patients tabulated had fungal endocarditis, histological proof exists for only a few who had surgery.

Cures of endocarditis caused by other fungi are noted. Improved surgical and medical therapy has improved the prognosis even of patients with the far-advanced disease. However, development of classic fungal endocarditis has been reported one or more years after cardiac surgery and late recurrences after intensive therapy of fungal endocarditis, that had led to clinical recovery of 2 years or more, have been reported. Serological monitoring of vulnerable patients might alert the physician to recurrence early enough for efficacy of drug therapy, averting fatal outcome or the need for further surgery.

Ocular and orbital phycomycosis

Cerebro-rhino-orbital phycomycosis (CROP) occurs predominantly in individuals with diabetes mellitus in a state of metabolic acidosis. Other forms of metabolic acidosis, especially in infants, may predispose to phycomycotic infections. CROP has also been reported in patients with leukemia or lymphoma. CROP usually begins in the palate or paranasal sinuses and rapidly spreads to the orbital contents. Proptosis, loss of vision, and ophthalmoplegia occur and death from cerebral involvement commonly ensues. The fungus tends to invade arteries and cause thrombosis and tissue infarction. Rhizopus is the most commonly isolated genus in CROP, accounting for almost all cases. The diagnosis can be strongly suspected by the characteristic clinical manifestations. Therapy includes treatment of the underlying disease, surgical excision of the necrotic tissue containing fungal elements and the systemic administration of amphotericin-B. The effect of treatment has improved since the disease was first described, but the condition still has a high mortality, especially if it is not diagnosed early.

A comparison of the content of iron in normal and rheumatoid striated muscle

An investigation has been carried out on the presence of iron in striated muscle from normal individuals and from patients with rheumatoid disease. The methods used for the estimation of iron required a neutron activation analysis of total iron and extraction of hemoglobin in cyanide buffer. The results disclosed that there was a higher deposition of iron in rheumatoid muscle as compared with normals. Iron has a destructive effect on lysosomes and mast cells, the effect of which is an inflammatory reaction which may in part cause "metabolic myopathy" in rheumatoid disease. It is tentatively suggested that this "metabolic myopathy" may cause muscular pain and weakness in rheumatoid disease.

The mast cells of the newborn rat diaphragm and their response to histamine liberators

The mast cell population of rat diaphragm was estimated between birth and adulthood and found to rise with an increase in the age of rat studied. Degranulation of these cells was observed in rats from all age groups, following treatment with compound 48/80 and dextran. The association of mast cells with the blood vessel wall in adult rat diaphragm was not observed in the comparable tissues of newborn rats. These findings are discussed in relationship to the poor vascular permeability reactions exhibited by newborn and young rats.

The mast cell in early rat adjuvant arthritis

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Diabetes and host resistance. I. Effect of alloxan diabetes upon the phagocytic and bactericidal efficiency of rat leukocytes for Pneumococcus

Briscoe, H. Frances (University Medical Center, Jackson, Miss.), and Fred Allison, Jr. Diabetes and host resistance. I. Effect of alloxan diabetes upon the phagocytic and bactericidal efficiency of rat leukocytes for pneumococcus. J. Bacteriol. 90:1537-1541. 1965.-Chronic diabetes mellitus was induced in rats with alloxan monohydrate. Glycosuria persisted for the 6 weeks of study, but ketonuria was never encountered. The cellular composition of peritoneal exudate recovered from diabetic rats after starch aleuronat administration was the same as that obtained from normal rats. The quantity of exudate recovered from the diabetic rats was thought to be less than that obtained from normal rats subjected to the same irritant. Phagocytosis was found to be essentially the same for both diabetic and normal cells when suspended in normal saline. The killing efficiency of harvested peritoneal phagocytes suspended in saline from both diabetic and normal rats for type 1 pneumococcus was compared and no difference between the groups was found.

ACUTE INFLAMMATION AND TISSUE MAST CELLS IN ADRENALECTOMIZED RATS WITH CUTANEOUS MUCORMYCOSIS

The effects of the absence of adrenal tissues on the inflammatory reaction and on the relationship of the tissue mast cells to the inflammatory process have been studied histologically in rats with cutaneous Rhizopus oryzae infection. Degranulation and regranulation of the tissue mast cells at the site of injury have been found to correlate respectively with the onset and subsidence of the exudative cellular phase of inflammation. In the adrenalectomized animals regranulation of these cells and correspondingly termination of the exudative phase are delayed. In the lesions of these rats the numbers of eosinophiles are increased. The proliferative cellular processes of inflammation, although delayed in onset, progress in essentially normal manner but result in some increased collagen deposition. The lack of adrenal secretions does not enhance fungus proliferation and is not associated with spread of the infection. In the present experiments the effectiveness of inflammation does not differ in normal and adrenalectomized rats.

A Function for Tissue Mast Cells

Experimental elimination of mast cells from the peritoneal tissues of the rat by distilled water treatment inhibited the increase of vascular permeability which normally follows a passively induced antigen-antibody reaction in peritoneal tissue. Thus mast cells may contribute to the initiation of inflammation which follows antigen-antibody reactions.