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Insulin upregulates betatrophin expression via PI4K/Akt pathway

Posted by Puhan L, Xi C, Zeqing Z, et al. on 2017-08-14 19:08:03

Abstract

Betatrophin is regarded as a liver-produced hormone induced by insulin resistance (IR). However, it remains largely unknown how IR regulates betatrophin expression. To study whether IR could regulate betatrophin expression and the corresponding molecular mechanisms, betatrophin levels were examined in 6 in vitro IR models which were established using human hepatocytes L02 with different agents, including tumor necrosis factor-α, interleukin-1β, dexamethasone, palmitate, high glucose and insulin and betatrophin levels were elevated only in the insulin group. These results suggest that it is insulin, not IR that promotes betatrophin expression. In the meantime, PI3K/Akt pathway was activated by insulin and suppressed by above agents that caused IR. Insulin-upregulated betatrophin expression was suppressed by PI3K/Akt inhibitors and IR, suggesting that insulin upregulates and IR decreases betatrophin production through PI3K/Akt pathway. Consistently, the treatment of insulin in mice dose-dependently upregulated betatrophin levels, and the administration of metformin in IR mice also stimulated betatrophin production since published study showed metformin improved PI3K/Akt pathway and IR. In humans, compared with those without insulin treatment, serum betatrophin levels were increased in type 2 diabetic patients with insulin treatment. In conclusion, insulin stimulates betatrophin secretion through PI3K/Akt pathway and IR may play an opposite role.

Zinc Supplementation Protects against CadmiumAccumulation and Cytotoxicity in Madin-Darby BovineKidney Cells

Posted by Ding Z, Jingying L, Jianfeng G, et al. on 2017-08-06 19:07:40

Abstract

Cadmium ions (Cd2+) have been reported to accumulate in bovine tissues, although Cd2+ cytotoxicity has not been investigated thoroughly in this species. Zinc ions (Zn2+) have been shown to antagonize the toxic effects of heavy metals such as Cd2+ in some systems. The present study investigated Cd2+ cytotoxicity in Madin-Darby bovine kidney (MDBK) epithelial cells, and explored whether this was modified by Zn2+. Exposure to Cd2+ led to a dose- and time-dependent increase in apoptotic cell death, with increased intracellular levels of reactive oxygen species and mitochondrial damage. Zn2+ supplementation alleviated Cd2+-induced cytotoxicity and this protective effect was more obvious when cells were exposed to a lower concentration of Cd2+ (10 mM), as compared to 50 mM Cd2+. This indicated that high levels of Cd2+ accumulation might induce irreversible damage in bovine kidney cells. Metallothioneins (MTs) are metal-binding proteins that play an essential role in heavy metal ion detoxification. We found that co-exposure to Zn2+ and Cd2+ synergistically enhanced RNA and protein expression of MT-1, MT-2, and the metal-regulatory transcription factor 1 in MDBK cells. Notably, addition of Zn2+ reduced the amounts of cytosolic Cd2+ detected following MDBK exposure to 10 mM Cd2+. These findings revealed a protective role of Zn2+ in counteracting Cd2+ uptake and toxicity in MDBK cells, indicating that this approach may provide a means to protect livestock from excessive Cd2+ accumulation.

Abstract

Current therapeutic approaches of Alzheimer’s disease (AD) are symptomatic and of modest efficacy, and there is no available effective cure or prevention of AD; hence, the need arise to search for neuroprotective agents to combat AD. The current study aimed at investigating the neuroprotective effect of nanodiamond (ND), adamantine-based nanoparticles, in aluminum-induced cognitive impairment in rats, an experimental model of AD. AD was induced by aluminum chloride (17 mg/kg, p.o. for 6 weeks) and confirmed by Morris water maze and Y-maze behavioral tests. Biochemical and histological analyses of the hippocampus were also performed. Aluminum-treated rats showed behavioral, biochemical, and histological changes similar to those associated with AD. ND improved learning and memory and reversed histological alterations. At the molecular levels, ND mitigated the increase of hippocampal beta-amyloid (Aβ42) and beta-site amyloid precursor protein cleaving enzyme-1 (BACE1) together with down-regulation of phosphorylated tau protein. It also modulated the excitatory glutamate neurotransmitter level. Furthermore, ND boosted the brain-derived neurotrophic factor (BDNF) and mitochondrial transcription factor-A (TFAM), suppressed the proinflammatory cytokine tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6), and curbed oxidative stress by hampering of inducible nitric oxide synthase (iNOS). Moreover, ND augmented the hippocampal levels of phosphorylated signal transducer and activator of transcription-3 (p-STAT3) and B cell leukemia/lymphoma-2 (Bcl-2) anti-apoptotic protein while diminished nuclear factor-kappaB (NF-κB) and caspase-3 (casp-3) expression. These findings indicate the protective effect of ND against memory deficits and AD-like pathological aberrations probably via modulating NF-kB and STAT3 signaling, effects mediated likely by modulating N-methyl-D-aspartate (NMDA) receptors.

Tributyltin in male mice disrupts glucose homeostasis as well as recovery after exposure: mechanism analysis

Posted by Bingshui L, Jiaojiao G, Zhihui X, et al. on 2017-07-24 19:17:56

Abstract

Organotin compounds such as tributyltin (TBT) and triphenyltin can induce diabetes and insulin resistance. However, the development of diabetes caused by organotins and its underlying mechanisms remain unclear. In the present study, male KM mice were orally administered with TBT (0.5, 5, and 50 μg/kg) once every 3 days for 45 days. Their body weights increased and reached a significant difference compared to the control, and the fasting blood glucose levels were significantly elevated. The fasting levels of serum insulin and adiponectin increased, while glucagon levels decreased in the animals treated with TBT. The expression of the insulin receptor (IR) signaling cascade, including IR, IR substrate, phosphatidylinositol 3-kinase, Akt, and glucose transporter 4, was inhibited both in the skeletal muscle and the liver, which might be a main reason for the hyperglycemia and hyperinsulinemia. After removing the TBT stress for 60 days, the animals which had received exposure to TBT could recover normoglycemia, accompanied with a recovery of the suppressed IR signal pathway and fasting insulin levels. However, the fasting levels of serum adiponectin and glucagon were lower than that of the control mice, which would remain a potential risk inducing the disruption of glucose homeostasis.

Quercetin and tin protoporphyrin attenuate hepatic ischemia reperfusion injury: role of HO-1

Posted by Yara A, Hassan M. E, Yousra A, et al. on 2017-07-24 01:44:52

Abstract

Ischemia reperfusion (IR) injury occurs in many clinical situations such as organ transplantation and hepatectomies resulting in oxidative stress and immune activation. Heme oxygenase-1(HO-1) is the rate-limiting step in the heme-degradation pathway and has a critical cytoprotective role. Induction of HO-1 improves liver I/R injury. Quercetin, a plant pigment (flavonoid), is an antioxidant and HO-1 inducer. Tin protoporphyrin (SnPP) is a HO-1 inhibitor. This study was designed to investigate the protective effect of quercetin in hepatic I/R injury and the role of HO-1. Wister rats were randomly divided into four groups (sham, I/R, quercetin, and SnPP). Liver ischemia was induced for 45 min then reperfusion was allowed for 1 h. Quercetin and surprisingly SnPP ameliorate the deleterious effect of I/R by reducing the oxidative stress and hepatocyte degeneration. Both agents decreased the elevated inflammatory cytokines and improved the inhibition of the antiapoptotic marker, Bcl2. They induced HO-1 content and expression. Quercetin has better cytoprotective effect than SnPP. These findings suggest that quercetin has a hepatoprotective effect against I/R injury via HO-1 induction and unexpectedly, SnPP showed the similar effect. Quercetin has more prominent protective effect than SnPP because of its superior ability to induce HO-1.

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