Taurine inhibits development of atherosclerotic lesions in apolipoprotein E-deficient mice

1. The effects of taurine on the development of atherosclerotic lesions were investigated in apolipoprotein (apo) E-deficient mice, an animal model with severe hypercholesterolaemia and extensive atherosclerosis. These mice were fed a normal laboratory chow containing 2% taurine for 12 weeks. 2. Serum total cholesterol was significantly elevated after 12 weeks treatment with taurine. This elevation was due to increases in very low-density lipoprotein- and low-density lipoprotein-cholesterol. 3. Despite such effects on serum lipoproteins, analysis using en face oil red O staining revealed that taurine reduced the area of arterial lipid accumulation by 28%, as measured quantitatively as an index of atherosclerosis. Histological examination also demonstrated a decrease in the size of aortic lesions in taurine-treated mice. 4. Serum levels of thiobarbituric acid reactive substances (TBARS) in apoE-deficient mice were higher than in normolipidaemic C57BL/6J mice. Serum TBARS levels were significantly decreased by 12 weeks treatment of apoE-deficient mice with taurine. 5. Thus, taurine prevents the formation of atherosclerotic lesions, independently of serum cholesterol levels, and the results suggest that the anti-oxidative effects of taurine are related to its anti-atherosclerotic actions.     

白鲜皮水提物对ApoE-/-小鼠动脉粥样硬化晚期病变形成的影响

目的研究白鲜皮水提物(cortex dictamni aqueous extract,CDAE)对载脂蛋白E基因缺损小鼠主动脉弓粥样硬化晚期病变形成的影响及其机制。方法将40只ApoE-/-小鼠随机分成空白对照组和CDAE高、中、低3剂量组(CDAE3.2、1.6、0.8 g·kg-1),每组10只。从第12周龄开始给药至18周龄。实验结束时测定给药前后总胆固醇、甘油三酯、高密度脂蛋白胆固醇、低密度脂蛋白胆固醇水平。取各组小鼠主动脉弓,OCT包埋,每只小鼠制作80张病理切片(厚6μm),计算各组主动脉弓粥样硬化病变的面积。体外实验测定CDAE给药后平滑肌细胞的增殖和迁移能力。结果CDAE给药后可明显减少动脉粥样硬化斑块面积,CDAE中、高剂量组给药后ApoE-/-小鼠动脉粥样硬化病变面积均小于对照组(P<0.05,P<0.01),各给药组血脂水平均有不同程度的下降。体外实验表明,CDAE可明显抑制大鼠血管平滑肌细胞的增殖和PDGF诱导的平滑肌细胞迁移。结论CDAE对ApoE-/-小鼠动脉粥样硬化晚期病变形成具有明显的抑制作用,其作用机制可能与降低血脂水平,抑制平滑肌细胞的增殖和迁移能力有关。     

Endothelium dysfunction in LDL receptor knockout mice: a role for H2O2

1. In this study, the role of endogenous H(2)O(2) as an endothelium-dependent relaxant factor was characterised in aortas from C57BL/6J and LDL receptor-deficient mice (LDLR(-/-)). 2. Aortic rings from LDLR(-/-) mice showed impaired endothelium-dependent relaxation to acetylcholine (ACh; 0.001-100 micro M) and to the Ca(2+) ionophore A23187 (0.001-3 micro M) compared with aortic rings from control mice. Endothelium-independent relaxation produced by the NO donor, 3-morpholino-sydnonimine (SIN-1) was not different between strains. 3. Pretreatment of vessels with L-NNA (100 micro M) or L-NNA (100 micro M) plus L-NAME (300 micro M) plus haemoglobin (10 micro M) markedly decreased, but did not abolish the relaxation to ACh in control mice. In the aortas from LDLR(-/-) mice treated with L-NNA (100 micro M), ACh induced a contractile effect. Catalase (800 and 2400 U ml(-1)) shifted to the right the endothelium-dependent relaxation to ACh in aortas from control but not from LDLR(-/-) mice. Aminotriazole (50 mM), which inhibits catalase, abolished its effect on control mice. Treatment of vessels with L-NNA and catalase abolished vasorelaxation induced by ACh. Indomethacin (10 micro M) did not modify the concentration-response curve to ACh. Superoxide dismutase (300 U ml(-1)) did not change ACh-induced relaxation in both strains. 4. Exogenous H(2)O(2) produced a concentration-dependent relaxation in endothelium-denuded aortic rings, which was not different between strains. 5. It is concluded that H(2)O(2) greatly contributes to relaxation to ACh in aorta from control mice. Endothelial-dependent relaxation to ACh is impaired in LDLR(-/-) mice. Reduced biosynthesis or increased inactivation of H(2)O(2) is the possible mechanism responsible for endothelial dysfunction in aortas of atherosclerosis-susceptible LDLR(-/-) mice.     

S-nitroso-N-acetylcysteine (SNAC) prevents myocardial alterations in hypercholesterolemic LDL receptor knockout mice by antiinflammatory action

We investigated the ability of S-nitroso-N-acetylcyseine (SNAC) to prevent structural and functional myocardial alterations in hypercholesterolemic mice. C57BL6 wild-type (WT) and LDL-R-/- male mice (S) were fed a standard diet for 15 days. LDL-R-/- mice (S) showed an 11% increase in blood pressure, 62% decrease in left atrial contractility, and lower CD40L and eNOS expression relative to WT. LDL-R-/- mice fed an atherogenic diet for 15 days (Chol) showed significant increased left ventricular mass compared to S, which was characterized by: (1) 1.25-fold increase in the LV weight/body weight ratio and cardiomyocyte diameter; (2) enhanced expression of the NOS isoforms, CD40L, and collagen amount; and (3) no alteration in the atrial contractile performance. Administration of SNAC to Chol mice (Chol + SNAC) (0.51 micromol/kg/day for 15 day, IP) prevented increased left ventricular mass, collagen deposit, NOS isoforms, and CD40L overexpression, but it had no effect on the increased blood pressure or atrial basal hypocontractility. Deletion of the LDL receptor gene in mice resulted in hypertension and a marked left atrial contractile deficit, which may be related to eNOS underexpression. Our data show that SNAC treatment has an antiinflammatory action that might contribute to prevention of structural and functional myocardial alterations in atherosclerotic mice independently of changes in blood pressure.     

Inhalation exposure of gas-metal arc stainless steel welding fume increased atherosclerotic lesions in apolipoprotein E knockout mice

Epidemiological studies suggest that welding, a process which generates an aerosol of inhalable gases and metal rich particulates, increases the risk for cardiovascular disease. In this study we analyzed systemic inflammation and atherosclerotic lesions following gas metal arc-stainless steel (GMA-SS) welding fume exposure. Apolipoprotein E knockout (apoE^−/−) mice, fed a Western diet, were exposed to GMA-SS at 40 mg/m³ for 3 h/day for ten days (∼8.26 μg daily alveolar deposition). Mice were sacrificed two weeks after exposure and serum chemistry, serum protein profiling and aortic lesion area were determined. There were no significant changes in serum total cholesterol, triglycerides or alanine aminotransferase. Serum levels of uric acid, a potent antioxidant, were decreased perhaps suggesting a reduced capacity to combat systemic oxidative stress. Inflammatory serum proteins interleukin 1 beta (IL-1β) and monocyte chemoattractant protein 3 (MCP-3) were increased two weeks after GMA-SS exposure. Analysis of atherosclerotic plaques showed an increase in lesion area as the result of GMA-SS exposure. In conclusion, GMA-SS exposure showed evidence of systemic inflammation and increased plaque progression in apoE^−/− mice. These results complement epidemiological and functional human studies that suggest welding may result in adverse cardiovascular effects.     

Opioid receptor knockout mice]

mu, delta, kappa opioid receptors are target molecules for analgesia, reward and many physiological functions of opiates. Opioid receptor knockout mice generated by gene-targeting technology which can introduce mutation into specified locus provide invaluable animal models to elucidate the in vivo function of opiates and develop new therapeutic drugs. The disruptions of mu receptor expression decreases the nociceptive threshold to thermal stimuli and increases the threshold to visceral chemical stimuli paradoxically. Analgesia, reward, respiratory depression, constipation, immunosuppression and physical dependence induced by morphine are absent in mice lacking the mu receptor. These data show that the mu receptor is a molecular target for most effects of morphine, both therapeutic and side effects. mu Receptor expression is required for most delta receptor-mediated and some kappa receptor analgesic effects. These results support substantial roles for mu receptor in the analgesic properties of delta, kappa receptors. Cocaine and ethanol reward require mu receptor systems' intactness. Mice lacking the mu receptor will be a useful tool to study complex interactions between endogenous opiate and dopamine systems.     

Acetylcholine receptor knockout mice]

To identify the functions of nicotinic or muscarinic acetylcholine receptor (nAChR or mAChR) subtypes, mice lacking beta 2 nAChR, alpha 4 nAChR, alpha 7 nAChR, M1 mAChR, and M2 mAChR have been generated. All these mice grow to normal size, and show no obvious physical or neurological deficit. However, pharmacological, biochemical, electrophysiological, neuroanatomical, and behavioural analyses revealed important functions of these AChR subunits. The beta 2 nAChR is most widely expressed in the central nervous system, and is involved in the functional high-affinity nicotine receptor regulating cognitive performance and the mesolimbic dopamine system. Aged beta 2-/- mutant mice showed neocortical degeneration and impaired spatial learning, and may serve as one possible animal model for dementias. The alpha 4 nAChR is associated mainly with the beta 2 subunit, and may form a component of the nicotinic pain pathways modulating the antinociceptive effect of nicotine. The alpha 7 nAChR mediates fast nicotinic currents in the hippocampus, and is not essential for normal neuronal development nor neurological function. The M1 mAChR mediates M current modulation in sympathetic neurons and the induction of seizure activity in the pilocarpine model of epilepsy. The M2 mAChR functions in the extrapyramidal system, hypothalamus, and spinal and/or spraspinal muscarinic pain pathways, and is possibly involved in locomotor performance, temperature control, and antinociceptive responses, respectively.     

Dopamine receptor knockout mice]

Dopaminergic systems are transmitted by dopamine receptors which couple to GTP binding proteins. Five subtypes of dopamine receptors were so far cloned. To study the functions of each dopamine receptors, mice lacking each of D1R, D2R, D3R and D4R dopamine receptors have been generated. Histological analyses of D1R knockout mice indicated that the expression of dynorphin is reduced in the striatum. In contrast with wild-type mice, D1R knockout mice exhibit a dose dependent decrease in locomotion. D2R knockout mice display a hypoactivity. The expression of enkephalin mRNA in the striatum is increased in the D2R knockout mice. D2R knockout mice showed hyperplastic changes of intermediate lobe of the pituitary and the increased expression of POMC in the pituitary in D2R knockout mice. D3R knockout mice are more active than wild-type mice in a novel environment and they exhibit enhanced behavioral sensitivity to cocaine and amphetamine. D4R knockout mice show a hypoactivity, but they display locomotor supersensitivity to ethanol, cocaine, and methamphetamine. Dopamine synthesis and its conversion to DOPAC are elevated in the dorsal striatum from D4R knockout mice.     

Serotonin receptor knockout mice]

The neurotransmitter serotonin is known to play a key role in determining emotional state in higher animals, especially in humans. Pharmacological studies have highlighted a subset of serotonin receptor subtypes (1A, 2B and 2C) worthy of knockout analysis. Several groups investigated knockout phenotype and determined the physiological function of these receptors, although the phenotype of the mouse seems somewhat paradoxical. However, the results strongly suggest that serotonin receptors are mainly involved in emotion (i.e., anxiety, aggressive behavior, obesity and epilepsy).     

Cognitive performance in neurokinin 3 receptor knockout mice

Rationale The neurokinin 3 (NK₃) receptor is a novel target under investigation for improvement of the symptoms of schizophrenia due to its ability to modulate dopaminergic signaling. However, research on effects of NK₃ antagonism with animal models has been hindered because of species differences in the receptor between humans, rats, and mice. Objectives The aim of the present study is to further knowledge on the role of NK₃ in cognitive functioning by testing the effect of knockout of the NK₃ receptor on tests of working memory, spatial memory, and operant responding. Materials and methods NK₃ knockout mice generated on a C57Bl/6 background were tested in delayed matching to position (DMTP), spontaneous alternation, Morris water maze, and active avoidance tasks. Results NK₃ knockout mice showed better performance in the DMTP task, though not delay dependently, which points to an effect on operant performance but not on working memory. No differences were seen between the groups in spontaneous alternation, another indication that working memory is not affected in NK₃ knockouts. There was no impairment in knockout mice in Morris water maze training, and the mice also showed faster response latency in the active avoidance task during training. Conclusions Collectively, these results support a role for the NK₃ receptor in performance of operant tasks and in spatial learning but not in working memory.     

Anxiolytic activity of progesterone in progesterone receptor knockout mice

Progesterone is an anxiolytic steroid that could play a role in the regulation of anxiety in women. However, the mechanism by which progesterone decreases anxiety is incompletely understood. Progesterone affects the function of the brain by two distinct mechanisms. Progesterone regulates reproductive behavior by activating intracellular progesterone receptors (PRs). In addition, progesterone is believed to influence neuronal activity through its conversion to allopregnanolone, a neurosteroid that acts as a positive allosteric modulator of GABAA receptors. The extent to which the anxiolytic action of progesterone requires PRs is uncertain. In this study, we utilized PR knockout (PRKO) mice bearing a targeted null mutation of the PR gene that abrogates the function of both PR-A and PR-B subtypes to determine the requirement for PRs in the anxiolytic actions of progesterone. The absence of PR receptor protein expression in PRKO brain was confirmed by immunocytochemistry. In PRKO mice and their isogenic wild-type (WT) littermates, progesterone administration was associated with a dose-dependent rise in plasma allopregnanolone concentrations and corresponding anxiolytic effects in the elevated plus maze test. PRKO mice exhibited a greater anxiolytic response than WT animals although the allopregnanolone levels were similar in the two genotypes. Allopregnanolone also exhibited anxiolytic effects, but the magnitude of the response was similar in both genotypes. Pretreatment of PRKO mice with finasteride, a 5alpha-reductase inhibitor that blocks the conversion of progesterone to allopregnanolone, completely prevented the anxiolytic activity of progesterone, but had no effect on the response to allopregnanolone, demonstrating that allopregnanolone (or other 5alpha-reduced metabolites of progesterone) accounts for the response to the parent steroid hormone. These results provide direct evidence that the anxiolytic action of progesterone does not require PRs. However, PR activation by progesterone may influence the anxiolytic response since PRKO mice were more sensitive to progesterone.     

Regulation of muscarinic acetylcholine receptor function in acetylcholinesterase knockout mice

Acetylcholinesterase (AChE) hydrolyzes acetylcholine to terminate cholinergic neurotransmission. Overstimulation of cholinergic receptors by excess acetylcholine is known to be lethal. However, AChE knockout mice live to adulthood, although they have weak muscles, do not eat solid food, and die early from seizures. We wanted to know what compensatory factors allowed these mice to survive. We had previously shown that their butyrylcholinesterase activity was normal and had not increased. In this report, we tested the hypothesis that AChE-/- mice adapted to the absence of AChE by downregulating cholinergic receptors. Receptor downregulation is expected to reduce sensitivity to agonists and to increase sensitivity to antagonists. Physiological response to the muscarinic agonists, oxotremorine (OXO) and pilocarpine, showed that AChE-/- mice were resistant to OXO-induced hypothermia, tremor, salivation, and analgesia, and to pilocarpine-induced seizures. AChE+/- mice had an intermediate response. The muscarinic receptor binding sites measured with [3H]quinuclinyl benzilate, as well as the protein levels of M1, M2, and M4 receptors measured with specific antibodies on Western blots, were reduced to be approximately 50% in AChE-/- brain. However, mRNA levels for muscarinic receptors were unchanged. These results indicate that one adaptation to the absence of AChE is downregulation of muscarinic receptors, thus reducing response to cholinergic stimulation.     

Small heterodimer partner overexpression partially protects against liver tumor development in farnesoid X receptor knockout mice

Farnesoid X receptor (FXR, Nr1h4) and small heterodimer partner (SHP, Nr0b2) are nuclear receptors that are critical to liver homeostasis. Induction of SHP serves as a major mechanism of FXR in suppressing gene expression. Both FXR^−/− and SHP^−/− mice develop spontaneous hepatocellular carcinoma (HCC). SHP is one of the most strongly induced genes by FXR in the liver and is a tumor suppressor, therefore, we hypothesized that deficiency of SHP contributes to HCC development in the livers of FXR^−/− mice and therefore, increased SHP expression in FXR^−/− mice reduces liver tumorigenesis. To test this hypothesis, we generated FXR^−/− mice with overexpression of SHP in hepatocytes (FXR^−/−/SHP^Tg) and determined the contribution of SHP in HCC development in FXR^−/− mice. Hepatocyte-specific SHP overexpression did not affect liver tumor incidence or size in FXR^−/− mice. However, SHP overexpression led to a lower grade of dysplasia, reduced indicator cell proliferation and increased apoptosis. All tumor-bearing mice had increased serum bile acid levels and IL-6 levels, which was associated with activation of hepatic STAT3. In conclusion, SHP partially protects FXR^−/− mice from HCC formation by reducing tumor malignancy. However, disrupted bile acid homeostasis by FXR deficiency leads to inflammation and injury, which ultimately results in uncontrolled cell proliferation and tumorigenesis in the liver.     

Prevention of atherosclerotic lesion development in mice by taurine

The antiatherosclerotic effects of taurine were evaluated in two murine models. In C57BL/6J mice fed a high-fat diet, 6-month treatment with taurine decreased serum atherogenic low-density lipoprotein (LDL) and very low-density lipoprotein (VLDL) cholesterol by 44%. The same treatment increased antiatherogenic high-density lipoprotein (HDL) cholesterol by 25%. Hepatic cholesterol content was also decreased by taurine. Taurine improved the area of oil red O positive arterial lipid accumulation by 20%. Hepatic cholesterol 7 alpha-hydroxylase activity, a rate-limiting enzyme of bile acid synthesis from cholesterol, was doubled in taurine-treated mice, suggesting stimulation of cholesterol catabolism to bile acid as the cholesterol-lowering mechanism seen with taurine. Thus, taurine prevented the progression of atherosclerotic lesions, and concomitantly improved the serum lipoprotein profile. In another murine model, in apolipoprotein-E-deficient mice fed regular chow, a 3-month treatment with taurine prevented accumulation of arterial lipids by 31%, despite a significant increase in serum LDL and VLDL cholesterol levels. Serum thiobarbituric acid reactive substances (TBARS) in apolipoprotein-E-deficient mice were significantly higher than those in wild type mice and treatment with taurine lowered serum TBARS level by 26%. Thus, taurine prevents the development of atherosclerotic lesions and this antioxidative effect may play an important role in the antiatherosclerotic effect that is unrelated to serum cholesterol levels.     

Oral administration of royal jelly inhibits the development of atopic dermatitis-like skin lesions in NC/Nga mice

We have shown previously that in addition to IL-4, IL-5 and IL-10, antigen-specific interferon-gamma (IFN-gamma) production by spleen cells from ovalbumin (OVA)/Alum-immunized mice is inhibited by the administration of royal jelly (RJ). Since it has been shown that both Th1 and Th2 cytokines play pathogenic roles in the generation of atopic dermatitis (AD), we have examined whether RJ suppresses the development of AD-like skin lesions in NC/Nga mice induced by repeated application of picryl chloride (PiCl) under specific pathogen-free (SPF) conditions. Oral administration of RJ to the PiCl-treated NC/Nga mice inhibited the development of AD-like skin lesions in these mice as exemplified by the significant decrease in the total skin severity scores and the decrease in hypertrophy, hyperkeratosis, and infiltration of the epidermis and corium by inflammatory cells. IFN-gamma production by spleen cells from PiCl-treated NC/Nga mice in response to TNP-KLH was partially but significantly inhibited by the oral administration of RJ, while IFN-gamma production by Con A-stimulated spleen cells was not affected. Since inducible nitric oxide (NO) synthase (iNOS)-derived NO has been suggested as an important immunoregulatory mediator in inflammatory autoimmune diseases, we have also examined the expression of iNOS in the dorsal skin lesions of PiCl-treated NC/Nga mice. Interestingly, the expression of iNOS was significantly increased in the skin lesions of RJ-administered mice compared with those of control PBS-administered mice. Thus, our results suggest that RJ suppresses the development of AD-like skin lesions in PiCl-treated NC/Nga mice, possibly by a combination of down-regulating TNP-specific IFN-gamma production and up-regulating iNOS expression.     

Angiotensin type 2 receptor is expressed in human atherosclerotic lesions.

OBJECTIVE: Expression of the angiotensin type 2 receptor (AT2-receptor) occurs in many animal models of atherosclerosis. However, its expression in human plaques and its functional role remains undetermined. This study examined AT2-receptor expression in human atherosclerotic plaque and also explored its potentially important functional role in atherosclerosis. MATERIAL AND METHODS: We analysed carotid atherosclerotic plaques obtained from 14 Caucasian patients who had previously undergone endarterectomy for symptomatic carotid artery stenosis. Half of all subjects received treatment with an angiotensin receptor blocker (ARB) (n=7); the remaining subjects received no intervention in the renin-angiotensin system (n=7). Immunohistochemistry measured tissue expression of smooth muscle cells (a-actin), macrophages (CD68 antibody), collagen (picro-sirius), and AT2-receptor (AT2-receptor antibody). RESULTS: AT2-receptor expression occurred consistently in all specimens. Although cellular localisation varied, AT2-receptor expression levels correlated with macrophage levels (p<0.01). Compared to conventional treatment, ongoing ARB treatment affected neither AT2-receptor levels nor plaque composition. CONCLUSIONS: AT2-receptor is expressed in human atherosclerotic plaque. Furthermore, we detected no functionally important role of AT2-receptor expression and found no evidence that ARB treatment regulates AT2-receptor expression.     

Unresponsiveness of mu-opioid receptor knockout mice to lipopolysaccharide-induced fever

Recently, we demonstrated that lipopolysaccharide (LPS)-induced fever could be suppressed by a selective mu-opioid receptor antagonist, indicating that the mu-opioid system is involved in the LPS fever. In the present study, to confirm the role of the mu-opioid system in the pathogenesis of LPS fever, we used mice lacking the mu-opioid receptor. In the wild type (WT), following intraperitoneal (i.p.) injection of 100 microg kg(-1) of LPS, body temperature (T(b)) increased approximately 1 degrees C and remained elevated during the 360-min recording period. In the mu-opioid receptor knockout (MOR-KO) mice, the administration of 100 microg kg(-1) i.p. of LPS did not induce fever during the recording period. Saline by itself, given i.p., did not alter the T(b), either in WT or MOR-KO. These results confirm that the mu-opioid system is involved in LPS-induced fever.     

Irgm1 knockout indirectly inhibits regeneration after skeletal muscle injury in mice

Immunity-related GTPase family M1 protein (lRGM1) plays an important role in host resistance to infection, immune inflammation, and tumors, and it is expressed in various tissues and cells, including the central nervous system, cardiovascular system, bone marrow-derived cells, glioma, and melanoma. However, the effect of IRGM1 in the muscles has not been reported to date. In this study, Irgm1^−/− mice were used to evaluate the effect of lrgm1 on regeneration after skeletal muscle injury. The tibialis anterior muscle in Irgm1^−/− mice was poorly repaired after BaCl₂-induced injury, whereas lrgm1 knockout itself had no significant effect on the differentiation of myoblasts. However, the microenvironment of Irgm1^−/− mice with a high interferon-gamma level inhibited the differentiation of myoblasts in vivo. These results suggest that lrgm1 knockout indirectly inhibits skeletal muscle regeneration after injury, providing new insights into the biological function of IRGM1.