Ultrastructural changes in the secretion granules of the hypopharyngeal glands of the honeybee infected by Nosema apis and after treatment with fumagillin

Liposome-based RNAi delivery in honeybee for inhibiting parasite Nosema ceranae

Nosema ceranae, a parasite that parasitizes and reproduces in the gut of honeybees, has become a serious threat to the global apiculture industry. RNA interference (RNAi) technology can be used to inhibit N. ceranae growth by targeting silencing the thioredoxin reductase (TrxR) in N. ceranae. However, suitable carriers are one of the reasons limiting the application of RNAi due to the easy degradation of dsRNA in honeybees. As a vesicle composed of a lipid bilayer, liposomes are a good carrier for nucleic acid delivery, but studies in honeybees are lacking. In this study, liposomes were used for double-stranded RNA (dsRNA) dsTrxR delivery triggering RNAi to inhibit the N. ceranae growth in honeybees. Compared to naked dsTrxR, liposome-dsTrxR reduced N. ceranae numbers in the midgut and partially restored midgut morphology without affecting bee survival and gut microbial composition. The results of this study confirmed that liposomes could effectively protect dsRNA from entering the honeybee gut and provide a reference for using RNAi technology to suppress honeybee pests and diseases.

Potential of Fumagillin and Agaricus blazei Mushroom Extract to Reduce Nosema ceranae in Honey Bees

Depending on the infection level and colony strength, Nosema ceranae, a microsporidian endoparasite of the honey bee may have significant consequences on the health, reproduction and productivity of bee colonies. Despite exerting some side effects, fumagillin is most often used for Nosema control. In this study, in a cage experiment, N. ceranae infected bees were treated with fumagillin or the extract of Agaricus blazei mushroom, a possible alternative for Nosema control. Bee survival, Nosema spore loads, the expression levels of immune-related genes and parameters of oxidative stress were observed. Fumagillin treatment showed a negative effect on monitored parameters when applied preventively to non-infected bees, while a noticeable anti-Nosema effect and protection from Nosema-induced immunosuppression and oxidative stress were proven in Nosema-infected bees. However, a protective effect of the natural A. blazei extract was detected, without any side effects but with immunostimulatory activity in the preventive application. The results of this research suggest the potential of A. blazei extract for Nosema control, which needs to be further investigated.

Novel Insight Into the Development and Function of Hypopharyngeal Glands in Honey Bees

Hypopharyngeal glands (HGs) are the most important organ of hymenopterans which play critical roles for the insect physiology. In honey bees, HGs are paired structures located bilaterally in the head, in front of the brain between compound eyes. Each gland is composed of thousands of secretory units connecting to secretory duct in worker bees. To better understand the recent progress made in understanding the structure and function of these glands, we here review the ontogeny of HGs, and the factors affecting the morphology, physiology, and molecular basis of the functionality of the glands. We also review the morphogenesis of HGs in the pupal and adult stages, and the secretory role of the glands across the ages for the first time. Furthermore, recent transcriptome, proteome, and phosphoproteome analyses have elucidated the potential mechanisms driving the HGs development and functionality. This adds a comprehensive novel knowledge of the development and physiology of HGs in honey bees over time, which may be helpful for future research investigations.

Fumagillin: an overview of recent scientific advances and their significance for apiculture

Fumagillin is a potent fungal metabolite first isolated from Aspergillus fumigatus. It is widely used in apiculture and human medicine against a variety of microsporidian fungal infections. It has been the subject of research in cancer treatments by employing its angiogenesis inhibitory properties. The toxicity of fumagillin has limited its use for human applications and spurred the development of analogues using structure-activity relationships relating to its angiogenesis properties. These discoveries may hold the key to the development of alternative chemical treatments for use in apiculture. The toxicity of fumagillin to humans is important for beekeeping, because any residues remaining in hive products pose a direct risk to the consumer. The analytical methods published to date measure fumagillin and its decomposition products but overlook the dicyclohexylamine counterion of the salt form widely used in apiculture.

Fumagillin-induced chromosome aberrations in mouse bone-marrow cells

The genotoxicity of fumagillin was evaluated assessing the mitotic index and chromosome aberrations in mouse bone-marrow cells. Mice were given fumagillin orally in doses 5, 10 and 20 mg/kg bw. All doses significantly (p<0.001) reduced the mitotic index. The medium and maximum doses led to significant (p<0.01 and p<0.001, respectively) increases in numeric aberrations. The highest dose induced both structural and numeric aberrations (p<0.001), and insertions on the first pair of autosomes that were amplified in the 1C and 1E regions. These results pointed to the genotoxic potential of fumagillin in the range of medium and maximum doses applied. <br><br><font color="red"><b> This article has been retracted. Link to the retraction <u><a href="http://dx.doi.org/10.2298/ABS150320032E">10.2298/ABS150320032E</a><u></b></font>

In vitro evaluation of the clastogenicity of fumagillin

Fumagillin, an antibiotic compound produced by Aspergillus fumigatus, is effective against microsporidia and various Amoeba species, but is also toxic when administered systemically to mammals. Furthermore, a recent in vivo study by Stanimirovic Z et al. 2007: (Mutat Res 628:1-10) indicated genotoxic effects of fumagillin. The aim of the present study was to investigate and explain the clastogenic effects of fumagillin (in the form of fumagillin dicyclohexylamine salt) on human peripheral blood lymphocytes in vitro by sister-chromatid exchanges (SCE), chromosome aberrations (CA), and micronucleus (MN) tests. The mitotic index (MI), proliferation index (PI), and nuclear division index (NDI) were calculated to evaluate the cytotoxic potential of fumagillin. Five concentrations of fumagillin (0.34, 0.68, 1.02, 3.07, and 9.20 microg/ml) were applied to lymphocyte cultures. All the tested concentrations of fumagillin increased the frequency of SCE per cell significantly (P < 0.001 or P < 0.01) compared with the negative control. A significant (P < 0.001) increase in frequency of structural CA was observed at the three highest concentrations in comparison with the negative control. In addition, the three highest test concentrations increased MN formation and decreased MI, PI, and NDI significantly compared with the negative control. The present results indicate that fumagillin is clastogenic and cytotoxic to cultured human lymphocytes.

Evaluation of genotoxic effects of fumagillin by cytogenetic tests in vivo

Fumagillin is a naturally secreted antibiotic of the fungus Aspergillus fumigatus. It is used in veterinary medicine against microsporidiosis of bees and fish. In this study, the genotoxicity of fumagillin (in the form of fumagillin dicyclohexylamine) was evaluated in mouse bone-marrow cells using the mitotic index (MI), the chromosome aberration (CA) assay, and the micronucleus (MN) test. Fumagillin was administered to BALB/c mice by gavage, at doses of 25, 50, 75 mg/kg body weight (bw), repeated for 7 days at 24-h intervals, with water-sugar syrup as a negative control and cyclophosphamide (40 mg/kg bw) as a positive control. All experimental doses of fumagillin induced a significant decrease (p<0.001) in MI (3.47+/-0.04%, 3.17+/-0.01%, and 2.27+/-0.02%, respectively) in comparison with the negative control (6.00+/-0.01%). Fumagillin significantly (p<0.001) increased the frequency of MN (4.98+/-0.35, 8.45+/-0.57, and 12.02+/-0.37, respectively) over negative control (1.04+/-0.28). Significantly increased frequencies (p<0.01 or p<0.001) of numerical chromosomal aberrations (aneuploidies and polyploidies) and structural chromosomal aberrations such as gaps, breaks, and centric rings were observed at the highest experimental dose of fumagillin (75 mg/kg bw) compared with the negative control. However, with respect to the induction of Robertsonian translocations, both the intermediate (50 mg/kg bw) and highest (75 mg/kg bw) experimental dose caused a significant (p<0.001) increase (7.12+/-0.26 and 9.00+/-0.10, respectively) in comparison with the negative control (0.00+/-0.00). Chromosomes 4 and 19 participated in these Robertsonian translocations. Regarding total cytogenetic changes, a significant increase (p<0.001) was observed in both the intermediate dose group (17.36+/-1.83) and the highest dose group (59.49+/-1.92) compared with the negative control (7.00+/-1.35). These results suggest that fumagillin has genotoxic (clastogenic) potential in mammals in vivo.