Spontaneous onset of nonalcoholic steatohepatitis and hepatocellular carcinoma in a mouse model of metabolic syndrome.

Metabolic syndrome is a worldwide healthcare issue and a dominant risk factor for the development of incurable diseases that affect the entire body. The hepatic manifestations of this syndrome include nonalcoholic fatty liver disease (NAFLD) and its progressive variant nonalcoholic steatohepatitis (NASH). The basic pathogenesis of NAFLD/NASH remains controversial because it is difficult to clarify the disease process of NASH on the basis of metabolic syndrome alone. To determine the pathogenesis and effective treatment, an excellent animal model of NASH is required. Tsumura Suzuki obese diabetes (TSOD) male mice spontaneously develop diabetes mellitus, obesity, glucosuria, hyperglycemia, and hyperinsulinemia without any special treatments such as gene manipulation. In this study, we examined the histopathological characteristics of visceral fat and liver of 56 male TSOD mice aged 4-17 months and 9 male Tsumura Suzuki non-obesity (control) mice aged 6-12 months. In the visceral fat, enlargement of adipocytes and perivascular and pericapsular CD8-positive lymphoid aggregation were observed in 4-month-old mice. Abnormal expression of tumor necrosis factor-α, interleukin-6, and lipid peroxidation endo products was observed in macrophages. In the liver, microvesicular steatosis, hepatocellular ballooning, and Mallory bodies were observed in 4-month-old mice, with severity worsening with increasing time. These pathological findings in the liver mimic those seen in patients with NASH. Interestingly, small liver nodules with high cellularity and absence of portal tracts were frequently observed after 12 months. Most of them showed nuclear and structural atypia, and mimicked human hepatocellular carcinoma. The degree of steatosis in the non-tumor portions of the liver improved when the liver nodules developed. These findings were not observed in control mice. Here, we report that TSOD male mice spontaneously developed NAFLD without any special treatment, and that these mice are a valuable model for assessing NASH and NASH carcinogenesis owing to metabolic syndrome.

Advantages and disadvantages of hyperbaric oxygen treatment in mice with obesity hyperlipidemia and steatohepatitis.

The effect of hyperbaric oxygen treatment (HBOT) was examined using MSG mice, which are an animal model of obesity, hyperlipidemia, diabetes, and nonalcoholic fatty liver disease. Nineteen MSG male mice were divided into HBOT treated and control groups at 12 weeks of ages. The HBOT group was treated with hyperbaric oxygen from 12 to 14 weeks (first phase) and then from 16 to 18 weeks (second phase). Interestingly, the body weight of the HBOT group was significantly lower (P < 0.01) than that of the control group. In contrast, the serum lipid level did not show significant changes between the two groups. As for the effects of increasing oxidative stress, the liver histology of the HBOT group showed severer cellular damage and aberrant TNF-α expression. HBOT has the advantage of improving obesity in patients with metabolic syndrome, but the fault of causing organ damage by increasing oxidative stress.

Insulin resistance and low sympathetic nerve activity in the Tsumura Suzuki obese diabetic mouse: a new model of spontaneous type 2 diabetes mellitus and obesity.

Tsumura Suzuki obese diabetic (TSOD) mouse is a new model of type 2 diabetes mellitus and obesity. The TSOD mice had hypoadiponectinemia. To assess the glucose utilization and insulin sensitivity, we examined the effect of insulin (1U/kg) on peripheral tissue glucose uptake in vivo in the TSOD and Tsumura Suzuki nonobese mouse using 2-deoxy-d-[(3)H]glucose. The rates constant of glucose uptake in basal condition without insulin were similar in the peripheral tissues in both strains. Insulin-stimulated glucose uptake by skeletal muscles and adipose tissues in vivo was diminished in the TSOD mice. In addition, we assessed norepinephrine turnover in brown adipose tissue and adrenal epinephrine (E) content and E turnover because disturbances in the sympathetic activities relate to many features in obese and diabetic syndrome. In these mice, the rate of norepinephrine turnover was decreased, and adrenal E content was at most one half of the Tsumura Suzuki nonobese mice and E turnover had extremely low rates. The TSOD mice showed hypercorticosteronemia. These results suggest that TSOD mice have insulin resistance and both low sympathetic nervous activities and low adrenomedullary activity, and have high adrenocortical activity, which are significant features of the TSOD mouse.

Type 2 diabetes mellitus in obese mouse model induced by monosodium glutamate.

The number of diabetic patients is increasing every year, and new model animals are required to study the diverse aspects of this disease. An experimental obese animal model has reportedly been obtained by injecting monosodium glutamate (MSG) to a mouse. We found that ICR-MSG mice on which the same method was used developed glycosuria. Both female and male mice were observed to be obese but had no polyphagia, and were glycosuric by 29 weeks of age, with males having an especially high rate of incidence (70.0%). Their blood concentrations of glucose, insulin, total cholesterol, and triglycerides were higher than in the control mice at 29 weeks. These high concentrations appeared in younger males more often than in females, and were severe in adult males. Also, the mice at 54 weeks of age showed obvious obesity and increased concentrations of glucose, insulin, and total cholesterol in the blood. The pathological study of ICR-MSG female and male mice at 29 weeks of age showed hypertrophy of the pancreatic islet. This was also observed in most of these mice at 54 weeks. It was recognized as a continuation of the condition of diabetes mellitus. From the above results, these mice are considered to be useful as new experimental model animals developing a high rate of obese type 2 (non-insulin dependent) diabetes mellitus without polyphagia.

Diabetic complications in a new animal model (TSOD mouse) of spontaneous NIDDM with obesity.

The TSOD mouse has been established as an inbred strain with spontaneous development of diabetes mellitus as the first clinical signs of diabetes. Polydipsia and polyuria are observed at about 2 months old only in male mice, after which hyperglycemia and hyperinsulinemia are detected. Following these symptoms obesity gradually develops until about 12 months old. In histopathological examination of the pancreas, severe hypertrophy of pancreatic islets was observed due to proliferation and swelling of B cells. In the kidney, thickening of the basement membrane in glomeruli and an increase of the mesangial area were observed at 18 months old. Motor neuropathy in TSOD mice began to appear at 14 months old and most male mice at 17 months old showed weakness of front and hind paws caused by neuron degeneration in the peripheral nerve. In sensory neuropathy, the threshold in the tail pressure test decreased significantly at 12 months old. Light microscopic and electron microscopic examination of sciatic nerves showed a decrease in the density of nerve fibers by the endoneural fibrosis and loss of these fibers. Degenerative changes of myelinated fibers, separation of myelin sheaths with intralamellar edema and remyelination were frequently observed. In the severely affected nerve fibers, the lamellar structure was completely destroyed and macrophages migrated around the myelin sheath or invaded the intramyelin space. Considering these findings similar to non-insulin dependent diabetes mellitus (NIDDM) in humans, the TSOD mouse should be a useful model for the pathogenic study of diabetic complications, especially of peripheral neuropathy.

Dopamine-receptor stimulation in the prefrontal cortex ameliorates stress-induced rotarod impairment.

Exposure to chronic stress is thought to play an important role in the etiology of depression. In this disorder, dopaminergic dysfunction in the prefrontal cortex (PFC) is thought to be involved. Indeed, chronic stress reduces dopaminergic transmission in the rat PFC or induces a behaviorally depressive state. However, a relationship between the reduced dopaminergic activity and the behavior of the chronically stressed rats has not been proven. Here, we examined the effects of local application of a dopamine Type I (D(1)) receptor-specific agonist, SKF 81297, in the PFC on the chronic-stress-induced depressive state using a rotarod test. The chronic stress produced by water immersion and restraint for 4 weeks followed by recovery for 10 days impaired the rotarod performance without changing the traction performance or locomotor activity. Although intra-PFC infusion of 1 or 10 ng of SKF 81297 did not affect this impairment, 100 ng of SKF 81297 significantly ameliorated it. These results suggest that the chronic-stress-induced depressive state is caused by a D(1) receptor-mediated hypodopaminergic mechanism in the PFC. These findings will further understanding of the mechanisms underlying the pathophysiology of depression.

A dietary restriction influences the progression but not the initiation of MSG-Induced nonalcoholic steatohepatitis.

The metabolic syndrome is a major worldwide health care issue and a dominant risk factor for cardiovascular disease. The liver manifestations of this syndrome include nonalcoholic fatty liver disease (NAFLD) and its progressive variant nonalcoholic steatohepatitis (NASH). Although significant research has been performed, the basic pathogenesis of NAFLD/NASH remains controversial and effective treatments are still unavailable. We have previously reported on a murine model of NASH induced by the neonatal injection of monosodium glutamate (MSG), which includes the clinical manifestations of central obesity, diabetes, hyperlipidemia, and ultimately liver inflammation, fibrosis, and cancer. Although MSG is considered a safe food additive, its administration to pregnant rats increases the voracity and growth hormone levels in the offspring. To further understand the biology of this model, we have investigated the influence of the calorie intake on these clinical manifestations by feeding animals a restrictive diet. MSG-treated animals fed a restrictive diet continue to manifest obesity and early stage NASH but have improvements in serum lipid profiles. At 12 months of age, mice had manifestations of obesity, whether animals were fed a restricted or control diet, but animals fed a restrictive diet had a reduction in the progression of NASH. In conclusion, MSG appears to be a critical factor in the initiation of obesity, whereas calorie intake may modulate the progression of disease.

Dose dependent development of diabetes mellitus and non-alcoholic steatohepatitis in monosodium glutamate-induced obese mice.

AIMS: We have recently reported that monosodium glutamate (MSG) induces severe obesity with diabetes mellitus and/or non-alcoholic fatty liver disease (NAFLD)/non-alcoholic steatohepatitis (NASH) in Crj:CD-1(ICR) neonatal mice. In this study, we investigated the effects of varying the dose of MSG on the resulting obesity and diabetes mellitus. MAIN METHODS: Crj:CD-1(ICR) neonatal mice were administered MSG in one of several courses: once-daily subcutaneous injections of 2mg/g for 5 consecutive days (2 mg/g x 5 group), a single subcutaneous injection of 4 mg/g (4 mg/g x 1 group) and once-daily subcutaneous injections of 4 mg/g for 5 consecutive days (4 mg/g x 5 group). KEY FINDINGS: In all the MSG treatment groups, severe obesity developed by 29 weeks of age. The onset of diabetes mellitus and liver lesions (resembling those of human NAFLD/NASH) were observed before 54 weeks of age. The obesity, diabetes mellitus and liver lesions were most severe in the 4 mg/g x 1 group. In the 4 mg/g x 5 group, increases in body weight and body length were inhibited by MSG's severe toxicity. SIGNIFICANCE: A single 4 mg/g dose of MSG is the most suitable as the obese model and induces not only severe obesity and diabetes mellitus, but also liver changes resembling human NAFLD/NASH. A small amount of MSG in the newborn develops obesity and the other complications without hyperphagia after a long term.

Monosodium glutamate (MSG): a villain and promoter of liver inflammation and dysplasia.

Chronic inflammation is a common theme in a variety of disease pathways, including autoimmune diseases. The pathways of chronic inflammation are well illustrated by nonalcoholic steatohepatitis (NASH), which is of a serious concern due to its increasing prevalence in the westernized world and its direct correlation with lifestyle factors, particularly diet. Importantly, NASH may ultimately lead to the development of hepatocellular carcinoma. We previously reported that injection of monosodium glutamate (MSG) in ICR mice leads to the development of significant inflammation, central obesity, and type 2 diabetes. To directly address the long-term consequences of MSG on inflammation, we have performed serial analysis of MSG-injected mice and focused in particular on liver pathology. By 6 and 12 months of age, all MSG-treated mice developed NAFLD and NASH-like histology, respectively. In particular, the murine steatohepatitis at 12 months was virtually undistinguishable from human NASH. Further, dysplastic nodular lesions were detected in some cases within the fibrotic liver parenchyma. We submit that MSG treatment of mice induces obesity and diabetes with steatosis and steatohepatitis resembling human NAFLD and NASH with pre-neoplastic lesions. These results take on considerable significance in light of the widespread usage of dietary MSG and we suggest that MSG should have its safety profile re-examined and be potentially withdrawn from the food chain.