An in vivo invertebrate evaluation system for identifying substances that suppress sucrose-induced postprandial hyperglycemia

TrCla4 promotes actin polymerization at the hyphal tip and mycelial growth in Trichophyton rubrum

IMPORTANCE

Superficial fungal infections, such as athlete's foot, affect more than 10% of the world's population and have a significant impact on quality of life. Despite the fact that treatment-resistant fungi are a concern, there are just a few antifungal drug targets accessible, as opposed to the wide range of therapeutic targets found in bacterial infections. As a result, additional alternatives are sought. In this study, we generated a PAK TrCla4 deletion strain (∆Trcla4) of Trichophyton rubrum. The ∆Trcla4 strain exhibited deficiencies in mycelial growth, hyphal morphology, and polarized actin localization at the hyphal tip. IPA-3 and FRAX486, small chemical inhibitors of mammalian PAK, were discovered to limit fungal mycelial proliferation. According to our findings, fungal PAKs are interesting therapeutic targets for the development of new antifungal medicines.

Products of Sericulture and Their Hypoglycemic Action Evaluated by Using the Silkworm, Bombyx mori (Lepidoptera: Bombycidae), as a Model

Simple Summary

The use of invertebrates as animal models is gaining attention within the scientific community due to numerous advantages during the development of the experiments, low cost of rearing, and fewer ethical problems. The well-documented biology of the silkworm (Bombyx mori) makes this insect an ideal candidate to be used in different fields of research. In this study, we demonstrated the feasibility of using the silkworm to evaluate the hypoglycemic action of various products of sericulture included in the diet after promoting glucose or sucrose-induced hyperglycemia in silkworms. The postprandial antihyperglycemic activity of fibroin, sericin, and powder made from pupae of silkworms is confirmed. These natural products are therefore ideal candidates for the prevention and treatment of diabetes, obesity, and other lifestyle-related diseases.

Abstract

Sericulture generates different natural products with potential medical applications. Silk peptides, worms, or even pupae are commonly employed in traditional Asian medicine with a wide variety of purposes, and some scientific work has been focused on their antidiabetic properties. This work evaluates the postprandial antihyperglycemic activity of fibroin, sericin, and powder made from either larvae or pupae of silkworms, and Bombyx mori L. (Lepidoptera: Bombycidae), employing the silkworm itself as an animal model. The results indicate a reduction in the glucose levels in hemolymph after sucrose or glucose-induced hyperglycemia when these products are included in the diet of the worms.

Facilitating Drug Discovery in Human Disease Models Using Insects

Drugs are developed through basic studies and clinical trials. In basic studies, researchers seek drug candidates using in vitro evaluation systems and subsequently examine their effectiveness in animal experiments as in vivo evaluations. Drug candidates identified in basic studies are tested to determine whether they are effective against human diseases in clinical trials. However, most drug candidates identified in in vitro evaluation systems do not show therapeutic effects in animal experiments due to pharmacokinetics and toxicity problems in the in vivo evaluations. This review outlines drug discovery using insect disease models that allow us to perform in vivo screening. Since insects have various advantages as experimental animals such as low cost for rearing and few ethical concerns, researchers can perform large-scale in vivo screening to find drug candidates. Silkworms are insects frequently used for studies of drug efficacy, pharmacokinetics, and toxicity. Based on silkworm research, I describe the benefits of using insect disease models for drug discovery. The use of insect disease models for in vivo screening is expected to facilitate drug discovery.

Adenosine Receptor Modulates Permissiveness of Baculovirus (Budded Virus) Infection via Regulation of Energy Metabolism in Bombyx mori

Although the modulation of host physiology has been interpreted as an essential process supporting baculovirus propagation, the requirement of energy supply for host antivirus reactions could not be ruled out. Our present study showed that metabolic induction upon AcMNPV (budded virus) infection of Bombyx mori stimulated virus clearance and production of the antivirus protein, gloverin. In addition, we demonstrated that adenosine receptor signaling (AdoR) played an important role in regulating such metabolic reprogramming upon baculovirus infection. By using a second lepidopteran model, Spodoptera frugiperda Sf-21 cells, we demonstrated that the glycolytic induction regulated by adenosine signaling was a conservative mechanism modulating the permissiveness of baculovirus infection. Another interesting finding in our present study is that both BmNPV and AcMNPV infection cause metabolic activation, but it appears that BmNPV infection moderates the level of ATP production, which is in contrast to a dramatic increase upon AcMNPV infection. We identified potential AdoR miRNAs induced by BmNPV infection and concluded that BmNPV may attempt to minimize metabolic activation by suppressing adenosine signaling and further decreasing the host's anti-baculovirus response. Our present study shows that activation of energy synthesis by adenosine signaling upon baculovirus infection is a host physiological response that is essential for supporting the innate immune response against infection.

Polysaccharides of a fermented food, natto, suppress sucrose-induced hyperglycemia in an in vivo evaluation system and inhibit glucose uptake by human intestinal cells

Natto is a well-known traditional Japanese food produced by fermenting soybeans with Bacillus subtilis var natto. Here we found that the water-soluble viscous fraction of natto inhibits sucrose- or glucose-induced hyperglycemia in silkworms. The water-soluble viscous fraction treated with DNase I, RNase A, and proteinase K, followed by phenol extraction also suppressed sucrose-induced hyperglycemia in silkworms. The enzyme-treated polysaccharide fraction of natto inhibits glucose uptake by Caco-2 cells, human intestinal epithelial cells. These findings suggest that the polysaccharide components of natto selected on the basis of their suppressive effects on sucrose-induced hyperglycemia in silkworms inhibit glucose uptake by human intestinal cells.

Evaluation of the silkworm lemon mutant as an invertebrate animal model for human sepiapterin reductase deficiency

Human sepiapterin reductase (SR) deficiency is an inherited disease caused by SPR gene mutations and is a monoamine neurotransmitter disorder. Here, we investigated whether the silkworm lemon mutant could serve as a model of SR deficiency. A point mutation in the BmSPR gene led to a five amino acid deletion at the carboxyl terminus in the lemon mutant. In addition, classical phenotypes seen in SR deficient patients were observed in the lemon mutant, including a normal phenylalanine level, a decreased dopamine and serotonin content, and an increased neopterin level. A recovery test showed that the replenishment of l-dopa significantly increased the dopamine level in the lemon mutant. The silkworm lemon mutant also showed negative behavioural abilities. These results suggest that the silkworm lemon mutant has an appropriate genetic basis and meets the biochemical requirements to be a model of SR deficiency. Thus, the silkworm lemon mutant can serve as a candidate animal model of SR deficiency, which may be helpful in facilitating accurate diagnosis and effective treatment options of SR deficiency.

Suppressive effects of whey protein hydrolysate on sucrose-induced hyperglycemia in silkworms

Silkworms are useful for evaluating substances that suppress postprandial hyperglycemia by oral administration. In this study, orally administered whey protein hydrolysate (WPH), obtained by enzymatic treatment of whey protein, suppressed sucrose-induced hyperglycemia in silkworms in a dose-dependent manner. WPH also inhibited glucose-induced hyperglycemia in silkworms. These findings suggest that WPH contains a bioactive peptide that inhibits glucose uptake from the intestinal tract and thereby suppresses sucrose-induced hyperglycemia.

Additive effects of Kothala himbutu (Salacia reticulata) extract and a lactic acid bacterium (Enterococcus faecalis YM0831) for suppression of sucrose-induced hyperglycemia in an in vivo silkworm evaluation system

Using a silkworm evaluation system, we previously evaluated various substances that suppress postprandial hyperglycemia. Enterococcus faecalis YM0831, a lactic acid bacterium that inhibits glucose uptake by the human intestinal Caco-2 cell line, exhibited hyperglycemia-suppressing effects in the silkworm system. In the present study, we found that Kothala himbutu (Salacia reticulata) extract, a traditional medicine containing α-glucosidase inhibitors, suppressed sucrose-induced hyperglycemia in the silkworm system. Moreover, combined oral administration of lactic acid bacteria YM0831 with Kothala himbutu extract had stronger suppressive effects on sucrose-induced hyperglycemia than single administration of either component. These findings suggest that the silkworm system provides a simple way to evaluate the effects of supplements on the suppression of blood glucose level induced by sucrose ingestion.

Enterococcus faecalis YM0831 suppresses sucrose-induced hyperglycemia in a silkworm model and in humans

Hyperglycemia caused by excessive intake of sucrose leads to lifestyle-related diseases such as diabetes. Administration of a lactic acid bacterial strain to mice suppresses sucrose-induced hyperglycemia, but evidence for a similar effect in humans is lacking. Here we show that Enterococcus faecalis YM0831, identified using an in vivo screening system with silkworms, suppressed sucrose-induced hyperglycemia in humans. E. faecalis YM0831 also suppressed glucose-induced hyperglycemia in silkworms. E. faecalis YM0831 inhibited glucose uptake by the human intestinal epithelial cell line Caco-2. A transposon insertion mutant of E. faecalis YM0831, which showed decreased inhibitory activity against glucose uptake by Caco-2 cells, also exhibited decreased inhibitory activity against both sucrose-induced and glucose-induced hyperglycemia in silkworms. In human clinical trials, oral ingestion of E. faecalis YM0831 suppressed the increase in blood glucose in a sucrose tolerance test. These findings suggest that E. faecalis YM0831 inhibits intestinal glucose transport and suppresses sucrose-induced hyperglycemia in humans.

Establishment of a gnotobiotic silkworm model

Gnotobiotic animals are useful for investigation of the effects of specific lactic acid bacteria on individual animals. Here we report that lactic acid bacteria colonize and proliferate in the intestinal tract of germ-free silkworms. When silkworms hatching from formalin-treated eggs were reared to fifth-instar larvae with an artificial diet containing antibiotics, bacteria and fungi were not observed in their intestines. An antibiotic-free diet supplemented with viable lactic acid bacteria, such as Enterococcus faecalis 0831-07, Lactococcus lactis 11/19-B1, or Leuconostoc carnosum #7-2, was fed to the germ-free silkworms for 1 day. After feeding the larvae on a diet without lactic acid bacteria for 5 days, each type of lactic acid bacterium was found in the intestine. Moreover, an increase in the number of Enterococcus faecalis 0831-07 was observed in the intestine 2-5 days after ingestion. These findings suggest that we successfully established a method to construct a gnotobiotic silkworm model.

Inhibitory effects of alpha-cyclodextrin and its derivative against sucrose-induced hyperglycemia in an in vivo evaluation system

Cyclodextrins (CyDs) are cyclic oligosaccharides consisting of six to eight glucose residues. Administration of α-CyD (six glucose residues) inhibits sucrose-induced hyperglycemia in humans. Here we show that oral administration of α-CyD and dimethyl α-CyD suppresses sucrose-induced hyperglycemia in an in vivo evaluation system using silkworms. On the other hand, β-CyD (seven glucose residues), γ-CyD (eight glucose residues), and their derivatives did not show the suppressive effect. These findings suggest that dimethyl α-CyD is a new inhibitor against sucrose-induced hyperglycemia and the silkworm system is useful for evaluation of suppressive activities of α-CyD derivatives against postprandial hyperglycemia.

Pharmaceutical significance of Leuconostoc mesenteroides KS-TN11 isolated from Nile Tilapia, Oreochromis niloticus

Aquatic animals are known for their myriad of beneficial bacteria with diverse biologically active compounds. The current study was aimed to isolate and characterize potentially beneficial lactic acid bacteria from Nile Tilapia and evaluate their pharmaceutical applications. The fish samples were dissected and stomach, intestine, and gills were collected and serially diluted for the isolation of lactic acid bacteria (LAB) on BCP agar media. Identification of isolate was carried by biochemical and molecular characterization using API kit and 16S rRNA gene sequencing analysis, respectively. Further, KS-TN11 was assessed for α-glucosidase inhibitory potential using the chromogenic method. A lactic acid bacterium KS-TN11 was isolated from the stomach of Nile Tilapia and identified as Leuconostoc mesenteroides. Effect of KS-TN11 on lipid accumulation in adipocytes was done by using Oil Red O staining. The isolate showed strong antibacterial activity against a number of pathogenic bacteria in vitro. In addition, L. mesenteroides KS-TN11 KS-TN11 (50 mg/ml and 100 mg/ml) tends to inhibit adipogenesis in 3T3-L1 adipocytes and thus may have possible anti-obesity effects. Moreover, L. mesenteroides KS-TN11 exhibited substantial α–glucosidase inhibitory activities by 41.33% at 50 mg/ml and 64% at 100 mg/ml, respectively. The bacterium showed potent antibacterial activity against a number of pathogenic bacteria; in addition to alpha-glucosidase activity, and inhibition of lipid accumulation in 3T3-L1 cell line. These results reinforce KS-TN11 as a novel bacterium with an impending pharmaceutical application.

Estimation of lactic acid bacterial cell number by DNA quantification

Lactic acid bacteria are provided by fermented foods, beverages, medicines, and supplements. Because the beneficial effects of medicines and supplements containing functional lactic acid bacteria are related to the bacterial cell number, it is important to establish a simple method for estimating the total number of lactic acid bacterial cells in the products for quality control. Almost all of the lactic acid bacteria in the products are dead, however, making it difficult to estimate the total number of lactic acid bacterial cells in the products using a standard colony-counting method. Here we estimated the total lactic acid bacterial cell number in samples containing dead bacteria by quantifying the DNA. The number of viable Enterococcus faecalis 0831-07 cells decreased to less than 1 × 10^-8 by 15 min of heat treatment at 80°C. The amount of extracted DNA from heat-treated cells was 78% that of non-heated cells. The number of viable Lactobacillus paraplantarum 11-1 cells decreased to 1 × 10^-4 after 4 days culture. The amount of extracted DNA of the long-cultured cells, however, was maintained at 97%. These results suggest that cell number of lactic acid bacteria killed by heat-treatment or long-term culture can be estimated by DNA quantification.