Pioglitazone prevents mice from multiple low-dose streptozotocin-induced insulitis and diabetes.

Macrophage infiltration into pancreatic islets is thought to be an initial event inducing insulitis in the development of type 1 diabetes. Thiazolidinedione is a direct ligand for peroxisome proliferator-activated receptor-gamma, recently reported to inhibit macrophage activation, including cytokine production and type 2 nitric oxide synthase expression. We investigated the effect of pioglitazone, a thiazolidinedione compound, on the development of multiple low-dose streptozotocin (MLDS)-induced autoimmune diabetes in mice. CD-1 mice intraperitoneally injected with five daily sub-diabetogenic doses (30 or 40 mg/kg body weight) of streptozotocin developed mononuclear cell infiltration in and around islets, followed by hyperglycemia. Oral administration of pioglitazone (0.01% food admixture) from 7 days before the first streptozotocin injection prevented or delayed the development of diabetes induced by MLDS. Histologically, pioglitazone blocked the infiltration of mononuclear cells into islets in MLDS mice. Peritoneal macrophages from MLDS mice at day-7 produced significantly large amount of nitric oxide compared with those from control mice. Such activation of peritoneal macrophages was not observed in pioglitazone-treated MLDS mice. These findings suggest that pioglitazone blocks the autoimmune process in the development of MLDS diabetes, partly by inhibiting the macrophage activation.     

链脲佐菌素诱导C57BL/6小鼠发生糖尿病视网膜病变

目的研究糖尿病视网膜病变小鼠的眼底变化。方法给6周龄的C57BL/6小鼠腹腔注射链脲佐菌素(STZ)建立糖尿病模型。模型建立后5 w和10 w,分别行眼内压测量和视网膜电图(ERG)检测以及免疫荧光血管染色检查。结果与对照组小鼠相比较,糖尿病小鼠的眼压升高(P<0.01),ERG的a、b波振幅下降,免疫荧光染色可见糖尿病小鼠视网膜血管异常。结论糖尿病会导致小鼠眼底发生异常改变。这些病理改变可能是糖尿病视网膜病变的重要组成部分。     

The C57BL/6 genetic background confers cardioprotection in iron-overloaded mice

Background

Chronic transfusion therapy causes a progressive iron overload that damages many organs including the heart. Recent evidence suggests that L-type calcium channels play an important role in iron uptake by cardiomyocytes under conditions of iron overload. Given that beta-adrenergic stimulation significantly enhances L-type calcium current, we hypothesised that beta-adrenergic blocking drugs could reduce the deleterious effects of iron overload on the heart.

Methods

Iron overload was generated by intraperitoneal injections of iron dextran (1g/kg) administered once a week for 8 weeks in male C57bl/6 mice, while propranolol was administered in drinking water at the dose of 40 mg/kg/day. Cardiac function and ventricular remodelling were evaluated by echocardiography and histological methods.

Results

As compared to placebo, iron injection caused cardiac iron deposition. Surprisingly, despite iron overload, myocardial function and ventricular geometry in the iron-treated mice resulted unchanged as compared to those in the placebo-treated mice. Administration of propranolol increased cardiac performance in iron-overloaded mice. Specifically, as compared to the values in the iron-overloaded group, in iron-overloaded animals treated with propranolol left ventricular fractional shortening increased (from 31.6% to 44.2%, P =0.01) whereas left ventricular end-diastolic diameter decreased (from 4.1±0.1 mm to 3.5±0.1 mm, P =0.03). Propranolol did not alter cardiac systolic function or left ventricular sizes in the placebo group.

Conclusions

These results demonstrate that C57bl/6 mice are resistant to iron overload-induced myocardial injury and that treatment with propranolol is able to increase cardiac performance in iron-overloaded mice. However, since C57bl/6 mice were resistant to iron-induced injury, it remains to be evaluated further whether propranolol could prevent iron-overload cardiomyopathy.     

Ishige okamurae ameliorates hyperglycemia and insulin resistance in C57BL/KsJ-db/db mice

We investigated the effect of Ishige okamurae extract on blood glucose level and insulin resistance in C57BL/-KsJ-db/db mice. We administered a standard AIN-93G diet with or without IOE to the animals for 6 weeks. After 6 weeks, blood glucose level was improved and blood glycosylated hemoglobin levels were lowered in sample group mice as compared to those in the diabetic control group mice. Hyperinsulinemia was reduced in the I. okamurae extract group mice with type 2 diabetes. With regard to hepatic glucose metabolic enzyme activities, glucokinase activity was enhanced in the IOE group mice, while glucose-6-phosphatase and phosphoenolpyruvate carboxykinase activities in the IOE group mice were significantly lowered than those in the diabetic control group mice. In addition, the hepatic glycogen content was elevated in the IOE group as compared to that in the diabetic control group. The homeostatic index of insulin resistance was lower in the I. okamurae extract group mice than in the diabetic control group mice. These results suggest that a dietary supplement of I. okamurae extract lowers the blood glucose level by altering the hepatic glucose metabolic enzyme activities and improves insulin resistance.     

Berberine ameliorates hyperglycemia in alloxan-induced diabetic C57BL/6 mice through activation of Akt signaling pathway

Recently, it is implicated that the abnormality of Akt signaling pathway is involved in the diabetic pathology. Previous studies have demonstrated that berberine could decrease blood glucose by elevating liver glycogen synthesis. However, the underlying mechanism is still unclear. In the present study, we investigated the effects of berberine on fasting blood glucose, liver glycogen, Akt, Glycogen synthase kinase-3, glucokinase and insulin receptor substrate (IRS) in alloxan-induced diabetic mice, exploring its possible hypoglycemic mechanism. We found that in alloxan-induced diabetic mice, the high blood glucose was significantly lowered by berberine treatment. Liver glycogen content, the expression and activity of glucokinase and the phosphorylated Akt and IRS were all significantly reduced in diabetic mice whereas berberine blocked these changes. Berberine also depressed the increasing of phosphorylated GSK-3β in diabetic mice. Collectively, Berberine upregulates the activity of Akt possibly via insulin signaling pathway, eventually lowering high blood glucose in alloxan-induced diabetic mice.     

Discriminative stimulus effects of ethanol in C57BL/6J and DBA/2J inbred mice

BACKGROUND: Two of the most widely used mouse strains for studying the behavioral effects of ethanol are C57BL/6J (B6) and DBA/2J (D2) mice. These strains exhibit marked differences in behavioral and physiological responses to ethanol. The subjective discriminative stimulus effects of ethanol may play a role in ethanol abuse, but the discriminative stimulus profile of ethanol has not been compared in B6 and D2 mice. Examination of the discriminative stimulus effects of ethanol in B6 and D2 mouse strains may enhance our understanding of the relationship between the subjective effects of ethanol and other ethanol-induced behavioral effects. METHODS: Twelve adult male C57BL/6J mice and 12 male DBA/2J mice were trained to discriminate 1.5 g/kg ethanol from saline in daily 15 min, milk-reinforced operant sessions. After training, ethanol substitution and response-rate suppression dose response curves were determined for ethanol, midazolam, diazepam, pentobarbital, pregnanolone, 4,5,6,7-Tetrahydroisoxazolo[5,4-c]pyridin-3-ol (THIP), dizocilpine, and morphine. RESULTS: D2 mice learned the ethanol discrimination significantly more quickly than did B6 mice. Ethanol, midazolam, pregnanolone, and dizocilpine fully substituted for ethanol in both strains. Pentobarbital was more potent in producing ethanol-like discriminative stimulus effects in D2 than B6 mice. Midazolam and diazepam were significantly more potent in suppressing response rates in D2 than B6 mice. Morphine failed to substitute for ethanol in either strain, but the ED50 for morphine suppression of responding was significantly lower in B6 than D2 mice. CONCLUSIONS: The initial stimulus effects of 1.5 g/kg ethanol may be more salient in D2 than B6 mice. This does not appear to result from differences in the neurotransmitter systems that mediate ethanol's discriminative stimulus effects. In both strains, gamma-aminobutyric acid-positive modulators and a noncompetitive NMDA antagonist substituted for ethanol. However, strain differences did exist in the potency of gamma-aminobutyric acid-positive modulators and morphine for suppressing operant responding.     

Varying susceptibility to myocardial infarction among C57BL/6 mice of different genetic background

Genetically manipulated mouse lines are invaluable to investigate the effects of a single gene on sensitivity to ischemia. When choosing appropriate controls, we were concerned that intrinsic, strain-independent but colony-dependent differences may influence the susceptibility to ischemia. We, therefore, compared the infarct:risk volume ratio (I:R%) after 30-min global ischemia in Langendorff-perfused hearts from outbred C57BL/6 mice with that in wild-type mice derived from heterozygote x heterozygote crosses of two different in-house C57BL/6 mouse lines with targeted disruption of an MKK3 or MAPKAPK2 allele. Despite similar hemodynamic characteristics, I:R% in outbred C57BL/6 hearts was significantlysmaller (40.8 +/- 2.8%) than in C57BL/6 MAPKAPK2 wild types (65.8 +/- 4.5%, P = 0.0003) and significantly larger than in C57BL/6 MKK3 wild types (23.7 +/- 2.9%, P = 0.002). Therefore, inherent colony substrain-dependent differences appear to influence the susceptibility to infarction in response to global ischemia, underscoring the importance of using colony-matched wild-type controls in murine studies of myocardial ischemia.     

Protection by dimethyl urea against hyperglycaemia,but not insulitis,in low-dose streptozotocin-induced diabetes in the mouse

Summary The protective effect of dimethyl urea, a hydroxyl radical scavenger, against low-dose streptozotocin-induced diabetes has been evaluated. Dimethyl urea was given to C57BL/KsJ mice before five daily injections of streptozotocin. The saline pre-treated control animals became gradually hyperglycaemic, whereas the dimethyl urea treated group remained normoglycaemic during the 11 week follow-up period. Two weeks after the first streptozotocin injection, six out of ten dimethyl urea-treated and 12 out of 15 saline-treated mice had insulitis. Four or 11 weeks after the streptozotocin treatment, insulitis was rare in both groups. Multiple injections of dimethyl urea only did not affect the serum glucose concentrations or the islet morphology. It is suggested that dimethyl urea protected against hyperglycaemia by reducing the -cell cytotoxic effects of the low doses of streptozotocin. An increased number of cells would thus be preserved and the animals less prone to develop diabetes, despite the presence of an inflammatory process in the pancreatic gland.     

Characteristics of cardiac aging in C57BL/6 mice

The specific processes that cause aging of the cardiac tissue remain elusive. C57BL/6 (B6) mice are commonly used for investigating age-related diseases in mammals. We thus sought to evaluate the cardiac aging process in B6 mice. Cardiac tissues from the newborn (B6 NB), 2 month-old (B6 2M) and 21–27 month-old B6 mice (B6 aged) were used for the investigation. Several age-related cellular processes were evaluated, including telomere shortening, changes in p53 and p16 expression, changes in mitochondria DNA expression and DNA deletion, and alteration of mitochondria. We found that the aging of the B6 mice cardiac tissue is associated with the maintenance of telomere length, increased expression of p53 and p16, mild changes in mitochondrial DNA expression but widespread DNA deletion, and significant alterations of the mitochondrial ultrastructure within the cardiac tissue. The results of our studies suggest that mitochondrial DNA deletions, which affect the mitochondrial ultrastructure, cytochrome C oxidase activity, and p53 expression, are significantly associated with cardiac aging and may be a source of age-related heart failure.     

Partial glucocorticoid agonist-like effects of imipramine on hypothalamic-pituitary-adrenocortical activity, thymus weight, and hippocampal glucocorticoid receptors in male C57BL/6 mice

Abnormal hypothalamic-pituitary-adrenocortical (HPA) activity may provide clues to the neurochemistry of depression. Psychotic depression has one of the highest rates of elevated HPA activity and is most often responsive to the tricyclic class of antidepressants. Because successful treatment resolves HPA as well as psychiatric symptoms, we hypothesized, in light of evidence that tricyclic antidepressants can affect glucocorticoid receptor function, that these drugs would mimic glucocorticoid feedback inhibition of HPA activity. To test this hypothesis, we measured circadian nadir (morning) and peak (evening) as well as restraint stress-induced levels of plasma ACTH and corticosterone in adrenalectomized (ADX) and sham-ADX (Sham) male C57BL/6 mice after 8 wk of imipramine (20 mg/kg/d, ip) or saline treatment. Antidepressant efficacy was confirmed by decreased immobility in forced-swim testing. When glucocorticoids were low or absent, imipramine mimicked glucocorticoid action in inhibiting evening ACTH in ADX mice and tending to inhibit morning corticosterone in Shams. However, when glucocorticoid levels were high, imipramine appeared to interfere with feedback inhibition by increasing post-stress ACTH and tending to increase evening corticosterone in Sham mice. Imipramine also decreased thymus weight in ADX and increased thymus weight in Sham mice. Imipramine stimulated morning ACTH in ADX mice, possibly by mimicking facilitative effects of high glucocorticoids. Short-term imipramine treatment was capable of inducing nuclear translocation of hippocampal glucocorticoid receptors in ADX mice. We conclude that imipramine effects on glucocorticoid-sensitive endpoints in vivo resemble those of a glucocorticoid partial agonist.     

Serum protein fractions in C57BL mice during growth and senescence

Serum protein fractions havve been studied uantitatively, using a micromethod for starch gel electrophoresis combined with densitometric scans of the gel strips. Observations were made on C₅₇BL male and female mice during the first 2 weeks of life, as well as on young adult and on senile animals. The main findings include:

• 1.(i) a specific embryonic a₁ globulin, the origin of which is unexplained and which disappears within the first 2 weeks of life;
• 2.(ii) a low βB globulin value in neonatal mice which increases during the first 2 weeks and which may tentatively be ascribed to the influence of maternal oestrogens during intrauterine life (cf. iii);
• 3.(iii) some differences between male and female sera, which occur as the animals attain sexual maturity, were experimentally shown to be caused by sex hormones. Most striking of these sex differences is the decreased βB globulin level caused by oestrogens;
• 4.(iv) in senile mice, few changes in serum protein fractions were found, except a marked elevation in the βB globulin fraction in females. This change perhaps is ascribable to decreased oestrogen production in old female mice. It was found experimentally that high oestrone doses may decrease this fraction to the young adult level.

     

Renal vasopressin receptors in ageing C57BL/Icrfat mice

The mechanism of water conservation is impaired in ageing mammals. An age-related defect in the release of vasopressin has been implicated but, more recently, attention has moved to the renal component of the water conservation mechanism. Previous studies using renal cells prepared from mice of different ages have shown that the threshold dose of vasopressin required to elicit a significant rise in cyclic AMP (cAMP) was greater in older animals. The dose-response curve was moved to the right in 35-month-old mice, i.e. the concentration of vasopressin required to give maximum cAMP output was increased. To investigate this further we examined the binding of vasopressin to renal medullary cells maintained in short-term culture, to determine whether the decreased response of cAMP levels to vasopressin is due to changes in hormone-receptor interaction. In 6-month-old male mice the dissociation constant (Kd) was 2.38 nmol/l and the maximum binding of the hormone (Bmax) was 47.6 fmol/10(6) cells, and at 30 months of age Kd was 2.37 nmol/l and Bmax was 47.0 fmol/10(6) cells. In female mice the changes were more complicated because the data for the 6-month-old mice could be split into two groups. It is concluded that there are no age-related differences in the numbers of receptors or their affinity for vasopressin, and that the decreased cAMP response is probably associated with post-receptor mechanisms in this species.     

Studies of Trypanosoma cruzi clones in inbred mice. II. Course of infection of C57BL/6 mice with single-cell-isolated stocks

A study of the course of parasitemia and mortality of C57BL/6 mice infected with the Trypanosoma cruzi Sylvio-X10 strain and two single-cell-isolate clones of the strain confirms our previous report on the existence of intra-strain subpopulations differing in their pathogenicity for inbred mice. In contrast to the generally accepted pattern of mouse strain susceptibility, C57BL/6 mice are more susceptible than C3H/HeN mice when infected with the Sylvio-X10 isolates. In addition, sex-related differences in susceptibility occurred depending upon the strain of the mouse and parasite isolate used. These data infer an interplay of host and parasite genetic factors influencing the outcome of a mouse infection with T. cruzi.     

链脲菌素剂量对C57BL/6J小鼠糖尿病诱导效应的影响

目的 观察不同剂量链脲菌素(STZ)对C57BL/6J小鼠糖尿病诱导效应的影响,探讨其量效关系及最佳剂量范围.方法 将C57BL/6J小鼠按数字随机法分为9个STZ剂量组(A～I组,STZ分别为30、60、80、100、120、150、180、210、240 ms/kg体重),每组15只,腹腔注射;1个对照组,10只,腹腔注射等体积缓冲液.观察各组血糖、体重、血胰岛素和45 d生存率的变化,分析其与STZ剂量的关系.同时取A、C、G及对照组小鼠胰腺、肾脏组织做病理学检杏,并行免疫组化观察胰腺胰岛素及肾脏CD<,68>的表达.结果 C～G组较对照组血糖增高、体重及血胰岛素含量较对照组下降非常显著(P<0.05),且STZ剂量与血糖呈正相关(r=0.984,P<0.05),与血胰岛素含量呈负相关(r=-0.994,P<0.05).C～G组成模率达86.7%～100%,显著高于A、B组的0和40%(P<0.05);45 d生存率为46.7%～73.3%,显著高于H、I组的13.3%和0(P<0.05).A组胰腺、肾脏组织未见明显破坏;C组及G组出现典型的胰岛萎缩变形,胰岛素分泌颗粒减少,肾小球系膜外基质沉着及球周臣噬细胞浸润.结论 C57BL/6J小鼠腹腔注射STZ以80～180 mg/kg体重的剂量制模率高、生存率高,且靶器官损伤典型;该剂量与血糖呈正相关,与血胰岛素含量呈负相关.     

缺氧对C57BL/6J小鼠瘦素及其受体基因表达的影响

目的　研究缺氧对小鼠瘦素及其受体 (包括转运性受体Ra、Rc和功能性受体Rb)mRNA表达变化的影响,以进一步明确瘦素和呼吸功能的关系。方法　利用医学自动测控缺氧仓(XQ Ⅰ型)复制机体常压缺氧状态,将小鼠分为正常对照组、缺氧 24h组、缺氧 48h组,然后利用逆转录 聚合酶链反应(RT-PCR)分别定量检测瘦素及其受体mRNA表达水平。根据cDNA条带的灰度值计算其相对含量,各种产物与磷酸甘油醛脱氢酶 (GADPH)的比值表示其相对表达水平。结果(1)缺氧 24h组和缺氧 48h组瘦素mRNA表达水平分别为 0.903±0.190、0.856±0.336,显著高于正常对照组(0.508±0.207,P均<0.05); (2)缺氧 24h组和缺氧 48h组RamRNA表达水平分别为0 724、0.700,分别为正常对照组 (0 630)的 115%、111%; (3)缺氧 24h组和缺氧 48h组RbmRNA表达水平分别为 0.381±0.038、0.345±0.042,与正常对照组(0.258±0.049)比较差异均有统计学意义(P均<0.05); (4)缺氧 24h组和缺氧 48h组RcmRNA表达水平分别为 0.299、0.292,分别为正常对照组(0.133)表达水平的 224%、219%。结论　缺氧作为一种独立因素可在一定范围内刺激机体瘦素、瘦素受体Ra、Rb、Rc基因表达增加,从而在正向调节机体呼吸功能中发挥重要作用。     

Genetic control of endogenous C-type virus production in pancreatic acinar cells of C57BL/He and C57BL/6J mice.

Electron microscopy revealed very active production of C-type virus particles in the pancreatic acinar cells of untreated normal adult mice of the C57BL/He strain. In C57BL/6J mice, a similar picture was observed after a single intraperitoneal injection of dexamethasone. No viruses were observed in the pancreas of untreated or dexamethasone-treated BALB/c and C3Hf mice. F1 hybrids of both C57BL strains with C3Hf mice produced viruses in the same manner and quantity as the C57BL parents, whereas hybrids with BALB/c mice were entirely negative. Approximately 50% of mice of the first backcross generation of (BALB/c times C57BL/He)F1 hybrids with C57BL/He mice were active producers of C-type particles, while the other 50% were negative. It is suggested that a regulator gene that controls C-type virus production does not function in the pancreatic cells of either C57BL strain, and that BALB/c mice can provide hybrids with an active regulator.     

Cardiac phenotype of mitochondrial creatine kinase knockout mice is modified on a pure C57BL/6 genetic background

Discrepant results for the phenotype of mitochondrial creatine kinase knockout mice (Mt-CK^−/−) could be due to mixed genetic background and use of non-littermate controls. We therefore backcrossed with C57BL/6J for > 8 generations, followed by extensive in vivo cardiac phenotyping. Echocardiography and in vivo LV haemodynamics were performed in independent cohorts at 20-40 weeks and 1 year. No significant differences were observed for ECG, LV volumes, pressures, and systolic or diastolic function compared to littermate controls. Furthermore, responses to dobutamine were not different, indicating preserved contractile reserve. Contrary to published reports using Mt-CK^−/− on a mixed background, we observed normal LV weights even in year old mice, and gene expression of common hypertrophic markers were not elevated. However, previously undetected adaptations were observed: an increase in activity of the cytosolic MM-CK isoenzyme (+ 20% vs WT, P = 0.0009), and of citrate synthase (+ 18% vs WT, P = 0.0007), a marker for mitochondrial volume. In a 3-week voluntary wheel running protocol, Mt-CK^−/− ran significantly less per day (P = 0.009) and attained lower maximum speed compared to controls (P = 0.0003), suggesting impaired skeletal muscle function. MM-CK isoenzyme activity was significantly elevated in soleus but not gastrocnemius muscle of KO mice, and citrate synthase activities were normal in both, suggesting compensatory mechanisms are incomplete in skeletal muscle. Conclusions: in contrast to previous reports using a mixed genetic background, Mt-CK^−/− on a C57BL/6 background do not develop LV hypertrophy or dysfunction even up to 1 year, and this may be explained by a compensatory increase in MM-CK activity and mitochondrial volume.