An Invertebrate Hyperglycemic Model for the Identification of Anti-Diabetic Drugs

Abstract

The number of individuals diagnosed with type 2 diabetes mellitus, which is caused by insulin resistance and/or abnormal insulin secretion, is increasing worldwide, creating a strong demand for the development of more effective anti-diabetic drugs. However, animal-based screening for anti-diabetic compounds requires sacrifice of a large number of diabetic animals, which presents issues in terms of animal welfare. Here, we established a method for evaluating the anti-diabetic effects of compounds using an invertebrate animal, the silkworm, Bombyx mori. Sugar levels in silkworm hemolymph increased immediately after feeding silkworms a high glucose-containing diet, resulting in impaired growth. Human insulin and 5-aminoimidazole-4-carboxamide-1-β-D-ribofuranoside (AICAR), an AMP-activated protein kinase (AMPK) activator, decreased the hemolymph sugar levels of the hyperglycemic silkworms and restored growth. Treatment of the isolated fat body with human insulin in an in vitro culture system increased total sugar in the fat body and stimulated Akt phosphorylation. These responses were inhibited by wortmannin, an inhibitor of phosphoinositide 3 kinase. Moreover, AICAR stimulated AMPK phosphorylation in the silkworm fat body. Administration of aminoguanidine, a Maillard reaction inhibitor, repressed the accumulation of Maillard reaction products (advanced glycation end-products; AGEs) in the hyperglycemic silkworms and restored growth, suggesting that the growth defect of hyperglycemic silkworms is caused by AGE accumulation in the hemolymph. Furthermore, we identified galactose as a hypoglycemic compound in jiou, an herbal medicine for diabetes, by monitoring its hypoglycemic activity in hyperglycemic silkworms. These results suggest that the hyperglycemic silkworm model is useful for identifying anti-diabetic drugs that show therapeutic effects in mammals.

A hyperglycemic silkworm model for evaluating hypoglycemic activity of Rehmanniae Radix, an herbal medicine

“…We previously reported that feeding of a high glucose diet causes hyperglycemia in silkworms (18). The hyperglycemic silkworm model is useful for evaluating the hypoglycemic effect of human insulin (18).…”

Evaluation of anti-diabetic drugs by using silkworm, <i>Bombyx mori </i>

“…The result demonstrated that the total sugar level in hemolymph of the hyperglycemic silkworms was decreased by injection of human insulin (Figure 2A). We also found that human insulin enhanced the phosphorylation of Akt in cells of fat body of silkworm in an in vitro tissue culture system and stimulated glucose uptake into the fat body ( Figure 2B) (19). These effects of human insulin were suppressed by pre-treatment of wortmannin, which is an inhibitor of the phosphoinositide 3-kinase (PI3K), a key factor of insulin-signaling pathway ( Figure 2B).…”

“…As a result, we found that total sugar level in hemolymph of silkworms quickly increased within 30 min by intake of an artificial diet containing high amount of glucose ( Figure 1B). Moreover, amounts of sugar in fat body, muscle, malpighian tubule, and silk gland in silkworms fed the high glucose diet were much higher than those in silkworm fed a normal diet ( Figure 1C) (19). Furthermore, we examined conditions whose silkworms become hyperglycemic by monitoring the effect of the feeding time and the amount of glucose in the diet ( Figures 1D and 1F).…”

“…Identification by structural determination of the active compounds purified by monitoring the hypoglycemic activities using diabetic silkworms is a conceivable approach. We have reported that polygalactose was identified as an active compound in Rehmannia Radix by monitoring the hypoglycemic activities using the hyperglycemic silkworms (19). If large numbers of chemically synthesized compounds are subjected in the evaluation systems using silkworm, it will be possible to select a most active compound having the hypoglycemic activity.…”

Silkworm fungal infection model for identification of virulence genes in pathogenic fungus and screening of novel antifungal drugs

“…We reported that silkworms ingesting a high glucose diet showed the symptoms corresponding to diabetes in mammals (20,21). We screened C. glabrata mutant strains that have low pathogenicity against the diabetic model of silkworms (11).…”