Biological effects of Spirometra erinacei plerocercoids in several species of rodents

Cloning and characterization of the rat free fatty acid receptor GPR120: in vivo effect of the natural ligand on GLP-1 secretion and proliferation of pancreatic beta cells

We have recently found that GPR120, which is abundantly expressed in intestine, functions as a receptor for unsaturated long-chain free fatty acids (FFAs) and that GPR120 stimulation promotes the secretion of glucagons-like peptide-1 (GLP-1) in the mouse (Hirasawa et al., Nat Med 11:90-94, 2005). In this study, we cloned and characterized rat GPR120 (rGPR120), and then we examined the in vivo effects of acute and long-term administration of the natural ligand alpha-linolenic acid (alpha-LA). The cloned rat GPR120 complimentary DNA had a seven transmembrane structure, and a homology comparison of human, mouse, and rat GPR120 revealed that the rat GPR120 (rGPR120) shares 85 and 98% sequence identity with the human and mouse GPR120 proteins, respectively. The tissue distribution and ligand properties of rGPR120 were similar to those of mouse GPR120. In addition, alpha-LA provoked a transient increase in [Ca2+]i levels in HEK293 cells expressing rGPR120. Furthermore, administration of alpha-LA to the rat increased plasma GLP-1 levels, and long-term administration of alpha-LA led to proliferation of pancreatic beta cells, probably because of the enhanced GLP-1 secretion. These results show that rat GPR120 is a G-protein-coupled receptor whose ligand is a free fatty acid, and it may play an important role in the FFA-associated physiological responses.

Susceptibility of Chinese hamsters (Cricetulus griseus) to the infection of Babesia microti

Chinese hamsters were examined for the susceptibility to the infection with Babesia microti based on the hematological parameters during the course of infection. A marked decrease in the RBC count, Ht value, Hb concentration, and an increase in WBC count due to the development of neutrophils or monocytes were recognized with the progress of parasitemia. Remarkable clinical findings were anemia and persistent infection with a low level of parasite burden in the chronic and convalescent stages. From these findings, it was concluded that Chinese hamsters were susceptible to infection with B. microti and would be useful for infection examination with the parasite.

An unusual host-parasite relationship: the growth hormone-like factor from plerocercoids of spirometrid tapeworms

Accelerated body growth is associated with experimental infections with the plerocercoid stage of the pseudophyllidean tapeworm, Spirometra mansonoides. The growth response is due to a protein that is synthesized and released by plerocercoids in the host. Plerocercoid growth factor (PGF) is transported by the blood, interacts with growth hormone (GH) receptors and mimics many of the biological actions of GH. Purification and characterization of PGF reveals that the GH-like factor is a 27.5 kDa cysteine proteinase. Sequencing of a cDNA for PGF revealed 40-50% homology to mammalian cysteine proteinases, but no homology to any GH. The GH-like factor/proteinase is found in abundance in the tegument of plerocercoids where the proteinase activity would be most effective in aiding tissue invasion, and possibly evasion, of the host's immune response to the parasite. The advantage of the GH-like activity is less clear, but it may affect the species survival by suppressing specific elements of the host's immune system and by improving the probability that the infected host will be eaten by a definitive host by increasing morbidity and/or mortality, conditions which are associated with long-term exposure to elevated levels of GH and PGF.

Hepatotrophic activity in mouse serum infected with plerocercoids of Spirometra erinacei

To investigate the mechanism by which liver weight increases during plerocercoid infections as well as the possible existence of a hepatocyte-growth-factor (HGF)-like substance in the serum of mice infected with Spirometra erinacei plerocercoids, liver DNA synthesis was measured in vivo and in vitro. Infection with S. erinacei plerocercoids significantly stimulated DNA synthesis in mouse parenchymal hepatocytes prior to the increase in liver weight, at least partly by stimulating the induction of the salvage pathways of pyrimidine biosynthesis. Furthermore, infected mouse serum directly stimulated DNA synthesis in cultured mouse parenchymal hepatocytes. These results suggest that an HGF-like substance is present in the serum of mice infected with S. erinacei plerocercoids.

Decrease of liver glycogen content in golden hamsters infected with plerocercoids of Spirometra erinacei

Liver glycogen content decreased in golden hamsters experimentally infected with plerocercoids of Spirometra erinacei. The activity of glycogen synthase a decreased significantly in infected animals, whereas that of glycogen phosphorylase a was not significantly affected. These observations suggest that changes in glycogen content were not attributable to increased glycogenolysis, but rather resulted from suppressed glycogenesis. Plasma immunoreactive insulin (IRI) concentrations in infected animals were slightly lower than those in controls, but the differences were not statistically significant. Plasma glucagon concentrations were significantly higher in infected animals. These results suggest that the suppression of glycogen synthase activity in S. erinacei-infected hamsters was attributable to enhanced levels of glucagon and that enhanced secretion of glucagon was caused by parasite-induced hypoglycemia.

Effect of infection with Spirometra erinacei plerocercoid on thyroid hormone in mice

Young, male ICR mice were given tap water or distilled water containing 200 mg/l propylthiouracil (PTU) and were then infected with 10 plerocercoids of Spirometra erinacei to investigate the effect of plerocercoid infection on thyroid hormone in their hosts. Plerocercoid infection stimulated growth in PTU-induced hypothyroid mice as if they had never received PTU treatment: there were increases in weight in the liver, skeletal muscle, and spleen, as well as enhancement of the head and body length, in spite of a greater decrease in serum T4 levels than was observed in PTU-treated controls. Furthermore, the intact mice infected with plerocercoids showed a decrease in serum T4 levels as well as in the concentration of T4-binding globulin. These observations suggest that the growth stimulation and the decrease in concentrations of serum T4 and T4-binding globulin associated with plerocercoid infection in mice probably resulted from secretion of a growth hormone-like substance produced by plerocercoids of S. erinacei.

Plerocercoid growth factor: a Homologue of human growth hormone

Plerocercoids of the tapeworm, Spirometra mansonoides, produce a factor with characteristics similar to those of mammalian growth hormone (GH). Plerocercoid growth factor (PGF) stimulates growth and mimics other actions of GH but does not possess the anti-insulin/diabetogenic activities intrinsic to mammalian growth hormones. Duplication of activities unique to human GH, chemical and physical similarities, plus crossreactivity with strictly specific anti-hGH monoclonal antibodies, underlie the hypothesis that S. mansonoides has obtained and expresses a human gene for GH. In this article, Kirk Phares discusses the similarities between the two hormones.

Carbohydrate metabolism in intact golden hamsters infected with plerocercoids of Spirometra erinacei (Cestoda: Diphyllobothriidae)

This study was performed to investigate the mechanism involved in a decrease in the serum glucose of golden hamsters infected with plerocercoids of Spirometra erinacei. The concentration of glucagon, the activity of glucose-6-phosphatase in the liver, and the in vivo incorporation of 2-deoxy-D-[1,2-3H]glucose into various organs increased in plerocercoid-infected hamsters compared with controls. Furthermore, the serum from the plerocercoid-infected hamsters enhanced the in vitro incorporation of [U-14C]glucose into adipose tissues, compared with control serum. The serum levels of immunoreactive insulin and somatomedin associated with nonsuppressible insulin-like activity in experimental animals, however, were not significantly different from those in controls. Therefore, we conclude that the decrease in serum glucose associated with plerocercoid infection is not the result of a decrease in gluconeogenesis, but the result of an increased utilization of glucose in the peripheral tissues.

Lipid metabolism in golden hamsters infected with plerocercoids of Spirometra erinacei (Cestoda: Pseudophyllidea)

Golden hamsters infected with Spirometra erinacei plerocercoids develop a hypertriglyceridaemia characterized by an increase in very low-density lipoprotein. Acyl-CoA synthetase activity, the rate of fatty acid synthesis in the liver and triglyceride production studies showed that the activation and synthesis of fatty acid and production of triglyceride in plerocercoid-infected hamsters were not significantly different from the controls. Lipase activity in post-heparin plasma was found to be suppressed in plerocercoid-infected golden hamsters. The presence of plerocercoids also resulted in a significant reduction in serum thyroxine, but the hypertriglyceridaemia associated with plerocercoid infection was not reversed by injecting the infected hamsters with 2 micrograms/day doses of L-thyroxine. The levels of serum immunoreactive insulin in plerocercoid-infected hamsters were not significantly different from the controls. We conclude that the hypertriglyceridaemia, associated with plerocercoid infection in hamsters, results predominantly from a suppression of triglyceride degradation, and that the suppression of lipase activity is probably not the result of hypothyroidism or the lack of insulin, but the result of secretion of growth hormone-like substances.

Evidence of the growth factor in mouse serum infected with Spirometra erinacei plerocercoids

To investigate the action of the growth factor secreted by Spirometra erinacei plerocercoids, various organ weights, body weight and head-body length were measured in Snell normal and dwarf mice after injection with the serum from mice and rats. Serum from mice infected with the plerocercoids caused significant increases in the weights of the liver and spleen, in the same manner as mice infected with the plerocercoids. However, serum from rats infected with plerocercoids did not cause significant changes in these parameters. The growth factor in the serum of mice infected with plerocercoids was stable at -20 degrees C for at least 6 months and easily passed through the peritoneum.