Evaluation of a Novel Boron-Containing α-D-Mannopyranoside for BNCT.

Boron neutron capture therapy (BNCT) is a unique anticancer technology that has demonstrated its efficacy in numerous phase I/II clinical trials with boronophenylalanine (BPA) and sodium borocaptate (BSH) used as 10B delivery agents. However, continuous drug administration at high concentrations is needed to maintain sufficient 10B concentration within tumors. To address the issue of 10B accumulation and retention in tumor tissue, we developed MMT1242, a novel boron-containing α-d-mannopyranoside. We evaluated the uptake, intracellular distribution, and retention of MMT1242 in cultured cells and analyzed biodistribution, tumor-to-normal tissue ratio and toxicity in vivo. Fluorescence imaging using nitrobenzoxadiazole (NBD)-labeled MMT1242 and inductively coupled mass spectrometry (ICP-MS) were performed. The effectiveness of BNCT using MMT1242 was assessed in animal irradiation studies at the Kyoto University Research Reactor. MMT1242 showed a high uptake and broad intracellular distribution in vitro, longer tumor retention compared to BSH and BPA, and adequate tumor-to-normal tissue accumulation ratio and low toxicity in vivo. A neutron irradiation study with MMT1242 in a subcutaneous murine tumor model revealed a significant tumor inhibiting effect if injected 24 h before irradiation. We therefore report that 10B-MMT1242 is a candidate for further clinical BNCT studies.

Sugar-powered nanoantimicrobials for combating bacterial biofilms.

Bacterial biofilms cause chronic infections due to their inherent tolerance to antimicrobial therapies. We describe and compare the efficacy of two types of sugar (d-glucose and d-mannose)-modified cyclodextrin nanocarriers (CD-GLU and CD-MAN) loaded with antibacterial agents for preventing and eradicating bacterial biofilm. The antibacterial agents comprise a quorum sensing inhibitor (5,6-dimethyl-2-aminobenzimidazole, DMABI) and two antibiotics (erythromycin and rifampicin), and the cyclodextrin nanocarriers were tested on Pseudomonas aeruginosa (Gram-negative) and Staphylococcus aureus (Gram-positive). DMABI loaded in the CD-GLU carrier was significantly more effective at inhibiting the development of Pseudomonas aeruginosa biofilm when compared to either its free form or when it is loaded in CD without grafted sugar moieties. Antibiotics loaded in CD-GLU and CD-MAN carriers were similarly more effective at dispersing pre-formed Pseudomonas aeruginosa biofilms. These antibacterial compounds loaded in the CD-GLU and CD-MAN carriers were somewhat less effective in eradicating Staphylococcus aureus biofilm as compared to Pseudomonas aeruginosa biofilm. This difference is attributed to the different extent of penetration of the sugar-grafted carriers into the biofilms of these two species of bacterial cells. Although the sugar-grafted carrier-antibacterial agent complexes exhibit potent effects against bacterial biofilms, they are not cytotoxic to mammalian cells.

Toxicity of Urban PM10 and Relation with Tracers of Biomass Burning.

The chemical composition of particles varies with space and time and depends on emission sources, atmospheric chemistry and weather conditions. Evidence suggesting that particles differ in toxicity depending on their chemical composition is growing. This in vitro study investigated the biological effects of PM10 in relation to PM-associated chemicals. PM10 was sampled in ambient air at an urban traffic site (Borgerhout) and a rural background location (Houtem) in Flanders (Belgium). To characterize the toxic potential of PM10, airway epithelial cells (Beas-2B cells) were exposed to particles in vitro. Different endpoints were studied including cell damage and death (cell viability) and the induction of interleukin-8 (IL-8). The mutagenic capacity was assessed using the Ames II Mutagenicity Test. The endotoxin levels in the collected samples were analyzed and the oxidative potential (OP) of PM10 particles was evaluated by electron paramagnetic resonance (EPR) spectroscopy. Chemical characteristics of PM10 included tracers for biomass burning (levoglucosan, mannosan and galactosan), elemental and organic carbon (EC/OC) and polycyclic aromatic hydrocarbons (PAHs). Most samples displayed dose-dependent cytotoxicity and IL-8 induction. Spatial and temporal differences in PM10 toxicity were seen. PM10 collected at the urban site was characterized by increased pro-inflammatory and mutagenic activity as well as higher OP and elevated endotoxin levels compared to the background area. Reduced cell viability (-0.46 < rs < -0.35, p < 0.01) and IL-8 induction (-0.62 < rs < -0.67, p < 0.01) were associated with all markers for biomass burning, levoglucosan, mannosan and galactosan. Furthermore, direct and indirect mutagenicity were associated with tracers for biomass burning, OC, EC and PAHs. Multiple regression analyses showed levoglucosan to explain 16% and 28% of the variance in direct and indirect mutagenicity, respectively. Markers for biomass burning were associated with altered cellular responses and increased mutagenic activity. These findings may indicate a role of biomass burning in the observed adverse health effect of particulate matter.

Mannose-Modificated Polyethylenimine: A Specific and Effective Antibacterial Agent against Escherichia coli.

Polyethylenimine (PEI) has antimicrobial activity against Gram-positive (Staphylococcus aureus, S. aureus) and Gram-negative (Escherichia coli, E. coli), bacteria but is highly cytotoxic, and the selective antimicrobial activity against S. aureus is obviously better than that against E. coli. To reduce the cytotoxicity and improve the antibacterial activity against E. coli, we modified PEI with d-mannose through nucleophilic addition between primary amine and aldehyde groups to get mannose-modified polyethylenimine copolymer particles (Man-PEI CPs). The use of mannose may provide good targeting ability toward E. coli pili. The antibacterial activity of Man-PEI CPs was investigated. Man-PEI CPs shows specific and very strong killing capability against E. coli at a concentration of 10 µg/mL, which is the highest antimicrobial efficiency compared to that of unmodified PEI (220 µg/mL). The antibacterial mechanism demonstrated that the enhancement in antibacterial activity is due to specific recognition of the mannose and destroying the cell wall of the bacteria by PEIs. Importantly, the Man-PEI CPs show less cytotoxicity and excellent biocompatibility. The results indicate that Man-PEI CPs have great potential as novel antimicrobial materials to prevent bacterial infections and provide specific applications for killing E. coli.

APC targeted micelle for enhanced intradermal delivery of hepatitis B DNA vaccine.

Chronic hepatitis B is a serious liver disease and puts people at high risk of death from cirrhosis and liver cancer. Although DNA vaccination has been emerged as a potential immunotherapeutic strategy for the treatment of chronic hepatitis B, the efficiencies were not adequate in clinical trials. Here we describe the design, synthesis, and evaluation of mannosylated phenylalanine grafted chitosan (Man-CS-Phe) as a DNA delivery vector for direct transfection of antigen presenting cells to improve cellular and humoral immunity to plasmid-coded antigen. The cationic Man-CS-Phe micelles condense plasmid DNA into nanoscale polyplexes and provide efficient protection of complexed DNA from nuclease degradation. The mannose receptor-mediated enhanced cell uptake and high in vitro transfection efficiency of the polyplexes were demonstrated in RAW 264.7 and DC 2.4 cells using GFP-expressing plasmid DNA. Furthermore, intradermal immunization of BALB/c mice indicated that hepatitis B DNA vaccine/Man-CS-Phe polyplexes not only induced multi-fold higher serum antibody titer in comparison to all other formulations including FuGENE HD, but also significantly stimulated T-cell proliferation and skewed T helper toward Th1 polarization. These results illustrate that the Man-CS-Phe can serve as a promising DNA delivery vector to harness both cellular and humoral arms of immune system.

Cytotoxic mannopyranosides of indole alkaloids from Zanthoxylum nitidum.

Three new mannopyranosides of indole alkaloids, methyl 7-(ß-D-mannopyranosyloxy)-1H-indole-2-carboxylate (1), methyl 7-[(3-O-acetyl-ß-D-mannopyranosyl)oxy]-1H-indole-2-carboxylate (2), and 2-methyl-1H-indol-7-yl ß-D-mannopyranoside (3), were isolated from an EtOH extract of the roots of Zanthoxylum nitidum. Their structures were identified as new compounds on the basis of the spectroscopic analyses. Bioactivity evaluation revealed that these alkaloids possess significant cytotoxicities against all the tested tumor cell lines with IC50 values of less than 30 µM.

Mannose supplements induce embryonic lethality and blindness in phosphomannose isomerase hypomorphic mice.

Patients with congenital disorder of glycosylation (CDG), type Ib (MPI-CDG or CDG-Ib) have mutations in phosphomannose isomerase (MPI) that impair glycosylation and lead to stunted growth, liver dysfunction, coagulopathy, hypoglycemia, and intestinal abnormalities. Mannose supplements correct hypoglycosylation and most symptoms by providing mannose-6-P (Man-6-P) via hexokinase. We generated viable Mpi hypomorphic mice with residual enzymatic activity comparable to that of patients, but surprisingly, these mice appeared completely normal except for modest (~15%) embryonic lethality. To overcome this lethality, pregnant dams were provided 1-2% mannose in their drinking water. However, mannose further reduced litter size and survival to weaning by 40 and 66%, respectively. Moreover, ~50% of survivors developed eye defects beginning around midgestation. Mannose started at birth also led to eye defects but had no effect when started after eye development was complete. Man-6-P and related metabolites accumulated in the affected adult eye and in developing embryos and placentas. Our results demonstrate that disturbing mannose metabolic flux in mice, especially during embryonic development, induces a highly specific, unanticipated pathological state. It is unknown whether mannose is harmful to human fetuses during gestation; however, mothers who are at risk for having MPI-CDG children and who consume mannose during pregnancy hoping to benefit an affected fetus in utero should be cautious.

Mannosylated polyethyleneimine-hyaluronan nanohybrids for targeted gene delivery to macrophage-like cell lines.

Nonviral gene delivery systems have a number of limitations including low transfection efficiency, specificity, and cytotoxicity, especially when the target cells are macrophages. To address these issues, the hypothesis tested in this study was that mannose functionalized nanohybrids composed of synthetic and natural polymers will improve transfection efficiency, cell viability, and cell specificity in macrophages. Robust nanohybrids were designed from hyaluronic acid (HA) and branched polyethyleneimine (bPEI) using carbodiimide chemistry. The reaction product, i.e., branched polyethyleneimine-hyaluronic acid (bPEI-HA) copolymer was subsequently functionalized with mannose at the terminal end of the copolymer to obtain mannosylated-bPEI-HA (Man-bPEI-HA) copolymer. UV spectroscopy and gel retardation studies confirmed the formation of polyplexes at polymer to DNA weight ratio ≥ 2. Alamar Blue and MTT assay revealed that the cytotoxicity of the developed nanohybrids were significantly (P < 0.05) lower than that of unmodified bPEI. Mannose functionalization of these nanohybrids showed specificity for both murine and human macrophage-like cell lines RAW 264.7 and human acute monocytic leukemia cell line (THP1), respectively, with a significant level (P < 0.05) of expression of gaussia luciferase (GLuc) and green fluorescent reporter plasmids. Internalization studies indicate that a mannose mediated endocytic pathway is responsible for this higher transfection rate. These results suggest that hyaluronan-based mannosylated nanohybrids could be used as efficient carriers for targeted gene delivery to macrophages.

Interaction of gold nanoglycodendrimers with algal cells (Chlamydomonas reinhardtii) and their effect on physiological processes.

With the rise of nanotechnologies, the risk of contamination of aquatic ecosystems with nanoparticles is increasing. Glycodendrimer-coated gold nanoparticles have been developed for biomedical applications; however, their effect on microalgae has never been studied. In this report, their interactions with algae were investigated using two strains of Chlamydomonas reinhardtii, a wild type having cell wall and a cell wall-deficient mutant. Cultures were exposed 48 h to 6 and 12 ng ml⁻¹ of gold nanoparticles coated with mannose generation 0 polyamidoamine dendrimer. Culture aggregation was found only for wild type cells, probably because of interactions between mannose and cell wall glycoproteins. Nanoparticles penetrated cytoplasm in both strains; however, inhibition of algal growth and photosynthetic activity was found only in the wild type. We conclude that nanoparticles' deteriorating effect in algae is caused by interactions with the cell wall, causing an aggregation of cell culture, and not by nanoparticle penetration inside the cytoplasm.

Longevity of multiple species of tephritid (Diptera) fruit fly parasitoids (Hymenoptera: Braconidae: Opiinae) provided exotic and sympatric-fruit based diets.

While adult parasitic Hymenoptera in general feed on floral and extrafloral nectars, hemipteran-honeydews and fluids from punctured hosts, Diachasmimorpha longicaudata (Ashmead), an Old World opiine braconid introduced to tropical/subtropical America for the biological control of Anastrepha spp. (Tephritidae), can survive on fruit juices as they seep from injured fruit. An ability to exploit fruit juice would allow such a parasitoid to efficiently forage for hosts and food sources simultaneously. Two New World opiines, Doryctobracon areolatus (Szepligeti) and Utetes anastrephae (Viereck), are also prominent Anastrepha parasitoids and are roughly sympatric. All three species were provided with: (1) pulp and juice diets derived from a highly domesticated Old World fruit (orange, Citrus sinensis L.) that is only recently sympatric with the Mexican flies and parasitoids and so offered little opportunity for the evolution of feeding-adaptations and (2) a less-domesticated New World fruit (guava, Psidium guajava L.), sympatric over evolutionary time with D. areolatus and U. anastrephae. Both sexes of D. longicaudata died when provided guava pulp or juice at a rate similar to a water-only control. D. areolatus and U. anastrephae, presumably adapted to the nutrient/chemical constituents of guava, also died at a similar rate. Survival of all three species on orange pulp and juice was greater than on water, and often equaled that obtained on a honey and water solution. In confirmatory experiments in Mexico, D. areolatus and U. anastrephae, as well as other tephritid parasitoids Doryctobracon crawfordi (Viereck) and Opius hirtus (Fisher), all died at a significantly higher rates when provided guava in comparison to a honey and water diet. Such a result is likely due to guavas being repellent, innutritious or toxic. D. longicaudata clearly consumed guava juice tagged with a colored dye. Dilutions of orange and guava juice resulted in shorter lifespans than dilutions of orange juice and water demonstrating that there while diluted orange juice provided nutrition the addition of guava created toxicity. Given the differences in fruit-food quality, adult opiine food sources would not be obtainable at all oviposition sites and in the case of guava, more additional sites and foraging for food than previously postulated may be required.

Investigation of carbohydrate binding property of a fungal lectin from Xerocomus chrysenteron and potential use on Myzus persicae aphid.

In recent years encoding insecticidal Lectins have been suggested as one of the promising methods against insect pests and have been engineered successfully into a variety of crops including wheat, rice, tobacco and potatoes. Xerocomus chrysenteron Lectin (XCL) has a high hemagglutinating activity and results obtained from sugar specificity assay showed to have specific affinity to Galactose and N-Acetylgalactosamine (GalNAc). In previous studies, XCL was shown to have negative effects on some insect pests, including aphids. In the present study, the effects of different carbohydrates including D-glucose, D-mannose, D-galactose and GalNAc, associated with 0.1% XCL (w/v) in artificial diet was investigated to assess the evolution of the lectin toxicity toward Myzus persicae aphid during 7 days. M. persicae, a polyphagous aphid, showed no significant differences of mortality when fed with the XCL lectin associated with Glucose and Mannose or fed on XCL diet only. At the opposite, the mortality rates related to artificial diet supplemented with Galactose or GalNAc and XCL were significantly reduced. There was then a significant mortality difference between M. persicae fed on an artificial diet incorporated specific carbohydrate binding Lectin with those fed with lectin only. The potential use of this particular fungal Lectin (XCL) with more specific carbohydrate binding will be discussed in relation to the development of bio-insecticide and integrated pest management.

Ablation of mouse phosphomannose isomerase (Mpi) causes mannose 6-phosphate accumulation, toxicity, and embryonic lethality.

MPI encodes phosphomannose isomerase, which interconverts fructose 6-phosphate and mannose 6-phosphate (Man-6-P), used for glycoconjugate biosynthesis. MPI mutations in humans impair protein glycosylation causing congenital disorder of glycosylation Ib (CDG-Ib), but oral mannose supplements normalize glycosylation. To establish a mannose-responsive mouse model for CDG-Ib, we ablated Mpi and provided dams with mannose to rescue the anticipated defective glycosylation. Surprisingly, although glycosylation was normal, Mpi(-/-) embryos died around E11.5. Mannose supplementation even hastened their death, suggesting that man-nose was toxic. Mpi(-/-) embryos showed growth retardation and placental hyperplasia. More than 90% of Mpi(-/-) embryos failed to form yolk sac vasculature, and 35% failed chorioallantoic fusion. We generated primary embryonic fibroblasts to investigate the mechanisms leading to embryonic lethality and found that mannose caused a concentration- and time-dependent accumulation of Man 6-P in Mpi(-/-) fibroblasts. In parallel, ATP decreased by more than 70% after 24 h compared with Mpi(+/+) controls. In cell lysates, Man-6-P inhibited hexokinase (70%), phosphoglucose isomerase (65%), and glucose-6-phosphate dehydrogenase (85%), but not phosphofructokinase. Incubating intact Mpi(-/-) fibroblasts with 2-[(3)H]deoxyglucose confirmed mannose-dependent hexokinase inhibition. Our results in vitro suggest that mannose toxicity in Mpi(-/-) embryos is caused by Man-6-P accumulation, which inhibits glucose metabolism and depletes intracellular ATP. This was confirmed in E10.5 Mpi(-/-) embryos where Man-6-P increased more than 10 times, and ATP decreased by 50% compared with Mpi(+/+) littermates. Because Mpi ablation is embryonic lethal, a murine CDG-Ib model will require hypomorphic Mpi alleles.

Mannose induces an endonuclease responsible for DNA laddering in plant cells.

The effect of D-mannose (Man) on plant cells was studied in two different systems: Arabidopsis roots and maize (Zea mays) suspension-cultured cells. In both systems, exposure to D-Man was associated with a subset of features characteristic of apoptosis, as assessed by oligonucleosomal fragmentation and microscopy analysis. Furthermore, D-Man induced the release of cytochrome c from mitochondria. The specificity of D-Man was evaluated by comparing the effects of diastereomers such as L-Man, D-glucose, and D-galactose. Of these treatments, only D-Man caused a reduction in final fresh weight with concomitant oligonucleosomal fragmentation. Man-induced DNA laddering coincided with the activation of a DNase in maize cytosolic extracts and with the appearance of single 35-kD band detected using an in-gel DNase assay. The DNase activity was further confirmed by using covalently closed circular plasmid DNA as a substrate. It appears that D-Man, a safe and readily accessible compound, offers remarkable features for the study of apoptosis in plant cells.

Regioselective synthesis and biological profiling of butyric and phenylalkylcarboxylic esters derivated from D-mannose and xylitol: influence of alkyl chain length on acute toxicity.

Regiospecific synthesis of 12 novel n-butyric and phenylalkylcarboxylic monoesters of mannose and xylitol was achieved. The strategy adopted, avoided a tedious intramolecular transesterification step, previously described for the synthesis of analogous compounds and permitted the facile synthesis of a new generation of stable derivatives. The general tolerance of the drugs has been assayed after intravenous administration of a bolus dose into mice. Monobutyric esters showed a low toxicity commensurate with the requirements for future development. A relationship was observed between chain length and toxicity. In contrast, phenylacetic, 3-phenylpropionic and 4-phenylbutyric esters were found to be toxic. Phenylbutyric esters induced marked and specific neuromuscular damage. Preliminary biological investigations of the new series of monobutyric esters showed them to retain the benificial biological properties of butyric acid whilst remaining relatively non toxic. They induced an inhibition of in vitro proliferation of 10 human cases of de novo acute myeloid leukemia (AML) primary cultures and AML established cell lines. AML blasts growth appeared to be blocked and cell differentiation was established. Transcription and expression of maturation markers and finally apoptosis were observed. Moreover, human gamma-chain hemoglobin (HbF) synthesis in erythroleukemia cells was stimulated by monobutyric esters. Mannose and xylitol butyric derivatives would appear to have exciting potential in treatment of beta-Hemoglobinopathies, sickle cell anemia and cancer.

Mannose-induced dysmorphogenesis of metanephric kidney. Role of proteoglycans and adenosine triphosphate.

Because various fetal anomalies are seen in diabetic offspring, we examined the effects of sugars on proteoglycans (PGs): extracellular matrix (ECM) macromolecules modulating morphogenesis. 13-d-old mouse metanephric kidney explants were exposed to mannose for 7 d and labeled with [35S]sulfate, [35S]-methionine, or [3H]thymidine. Mannose exposure caused reduction in kidney size and disorganization of ureteric bud branches with inhibition of glomerulogenesis. Tissue autoradiographic and immunofluorescence studies indicated decreased expression of sulfated PGs in ECMs. Helix pomatia lectin binding to D-GalNAc residues of glomerular epithelial cells was also reduced. Biochemical studies revealed decreased synthesis of sulfated PGs. PGs were of lower molecular weight with reduced charge density and increased chondroitin/heparan sulfate ratio. Immunoprecipitation of [35S]methionine-labeled proteins confirmed the reduction of PG core peptides. Intracellular ATP levels were reduced. The addition of 0.1 mM ATP to culture media restored kidney size, the population of glomeruli, and the synthesis and characteristics of PGs to almost normal, with no detectable effect on the replication of cells as determined by [3H]thymidine incorporation. The effect of ATP could be partially blocked by the P2y-purinoreceptor, i.e., reactive blue-2. Data suggest that mannose causes energy depletion by cellular ATP consumption and thus selectively alters the synthesis of heavily glycosylated proteins with rapid turnover, such as PGs, resulting in renal dysmorphogenesis.

Mannose toxicity in Ehrlich ascites tumor cells.

Mannosephosphate isomerase (MPI) showed a higher activity than hexokinase (HKM) in its ability to phosphorylate mannose in the spleen, thymus, brain, liver, striated muscles, kidneys, and testes from BALB/c mice. This led to a HKM/MPI ratio of less than 1 in all the organs and tissues mentioned. In contrast, Ehrlich ascites tumor cells obtained from the peritoneum of BALB/c mice had low MPI activity (half of the HKM activity and, therefore, a ratio of 2). Mannose, which is nontoxic to nontumor cells at a concentration of 0.1 M, induced marked in vitro mortality of the tumor cells. Incubation of Ehrlich ascites tumor cells with mannose resulted in a high accumulation of mannose-6-phosphate and a marked depletion of ATP which did not appear when the cells were incubated with glucose. These facts may explain the selective mortality caused by mannose in the tumor cells studied.

Fuel-mediated teratogenesis: symmetric growth retardation in the rat fetus at term after a circumscribed exposure to D-mannose during organogenesis.

We previously infused the D-glucose epimer D-mannose into pregnant rats to deliver a brief metabolic insult to the early postimplantation conceptus. This insult caused developmental anomalies and growth retardation that were apparent in the embryos 2 days later. We now report the long-range effects on intrauterine development of such a circumscribed metabolic insult during organogenesis. Ten pregnant animals were infused with D-mannose for 12 hours during early neurulation (day 9.5 to 10 of development). Ten control animals were infused with equimolar D-glucose during this same time interval. Mannose infusions produced maternal plasma mananose concentrations in the embryotoxic range; glucose infusions caused only slight and transient hyperglycemia. Fetuses were removed at term and examined for evidence of developmental anomalies and growth retardation. None of 137 fetuses from the mannose group or 138 fetuses from the glucose group exhibited gross anomalies. However, an excess of resorbed conceptions in the mannose group (21 versus six in the glucose group; p less than 0.01) suggested some lethal toxicity from mannose exposure during embryogenesis. Among viable fetuses, the mean body weight of those from the mannose group was significantly reduced compared with those from the glucose group (5.62 +/- 0.04 versus 5.89 +/- 0.03 gm, respectively; p less than 0.001). Reductions of a similar magnitude were noted in the mean wet weight and protein content of fetal brains, hearts, livers, and kidneys from the mannose group (range, 3.4% to 7.1% below the glucose group), indicating a symmetric pattern of fetal growth retardation. In addition, analysis of fetal ossification sites after Alizarin Red S staining revealed a significant delay of skeletal development in the mannose group. These results indicate that a relatively brief metabolic insult to embryos during early organogenesis may cause lethal developmental anomalies as well as growth retardation and delayed skeletal development that are manifested in the fetus at term.

Mechanism of mannose toxicity.

Mannose toxicity in honeybees is due to a marked shortage of mannosephosphate isomerase that leads to a large accumulation of mannose-6-P and a marked depletion of ATP. Drosophila melanogaster and Ceratitis capitata are insensitive to mannose and have excess of mannosephosphate isomerase over hexokinase. 2-Deoxyglucose is as toxic as mannose for honeybees and is toxic also for the other insects studied, which supports the conclusion that the mechanism of mannose toxicity involves large accumulation of a hexosephosphate.

Fuel-mediated teratogenesis. Use of D-mannose to modify organogenesis in the rat embryo in vivo.

The unique embryotoxic properties of D-mannose have been used as the basis for a new technique to secure precise temporal correlations between metabolic perturbations during organogenesis and subsequent dysmorphogenesis. Conscious, pregnant rats were infused with D-mannose or equimolar amounts of D-glucose by "square wave" delivery during the interval in which the neural plate is established and early fusion of neural folds takes place, that is, days 9.5-10.0 of gestation. Infusions of mannose to maternal plasma levels of 150-200 mg/dl did not elicit any toxicity in the mothers: motor activity, eating behavior, and serum components (electrolytes, osmolality, bilirubin) did not differ in glucose- vis-à-vis mannose-infused dams. Embryos were excised by hysterotomy on day 11.6 for evaluation of development. Examination with a dissecting microscope did not disclose developmental abnormalities in any of the 136 embryos from glucose-infused mothers or in 62 additional embryos from mothers that had not received any infusions. By contrast, dysmorphic changes were seen in 17 of 191 embryos (8.9%) from mannose-infused mothers. 14 of the 17 had abnormal brain or neural tube development with incomplete neural tube closure in 9 instances. Abnormal axial rotation was present in 8 of the 191 embryos (4.2%) and lesions of the heart or optic vesicles were seen in 4 (2.1%) and 3 (1.6%), respectively. Embryos from mannose-infused mothers displayed significant retardations in somite number, crown-rump length, and total protein and DNA content. These stigmata of growth retardation were more marked in the 17 dysmorphic embryos. The experiments indicate that D-mannose may be employed in model systems with rodents for precisely timed interruptions of organogenesis in vivo. Initial applications are consistent with our earlier suggestion that multiple dysmorphic changes may supervene after interference with communally observed metabolic dependencies during organogenesis. The studies do not identify the vulnerable site(s) within the conceptus (e.g., investing membranes, embryos, or both). However, the findings suggest that dysmorphic events are manifest most markedly in a general setting of embryo growth retardation.

The honeybee syndrome - implications of the teratogenicity of mannose in rat-embryo culture.

Lethal effects of D-mannose in the honeybee have been recognized for more than a half a century. We observed another toxic effect of D- mannose during culture of rat embryos from the early head-fold stage to the 26-to-29-somite stage (Days 9-1/2 through 11-1 of gestation). The addition to culture mediums of 1.5 mg of D-mannose per milliliter caused growth retardation and faulty neural-tube closure in approximately two thirds of the embryos. Mannose effects occurred during the first 24 hours of culture and were attended by modes inhibition of the glycolysis that constitutes the principal energy pathway at this stage of development. Adding more glucose to preserve glycolytic flux or increasing atmospheric oxygen to promote oxidative metabolism offset the mannose teratogenesis. Our findings highlight the metabolic vulnerabilities that exist during early organogenesis, before oxidative flexibility is established. They may serve as a model to explain the teratogenicity of many other seemingly unrelated agents that could act by perturbing glycolysis at this vulnerable stage.