Fatty acid induced insulin resistance in rat-1 fibroblasts overexpressing human insulin receptors: impaired insulin-stimulated mitogen-activated protein kinase activity

Summary Saturated fatty acids cause insulin resistance but the underlying molecular mechanism is still unknown. We examined the effect of saturated non-esterified fatty acids on insulin binding and action in transfected Rat-1 fibroblasts, which over-expressed human insulin receptors. Incubation with 1.0 mmol/l palmitate for 1–4 h did not affect insulin binding, insulin receptor autophosphorylation, insulin-stimulated tyrosine kinase activity toward poly(Glu⁴:Tyr¹), pp185 and Shc phosphorylation and PI3-kinase activity in these cells. However, the dose response curve of insulin-stimulated glucose transport was right-shifted. Palmitate inhibited the maximally insulin-stimulated mitogen activated protein (MAP) kinase activity toward synthetic peptide to 7 % that of control. The palmitate treatment influenced neither cytosolic protein kinase A activity nor cAMP levels. These results suggested that 1) palmitate did not inhibit the early steps of insulin action from insulin binding to pp185 or Shc phosphorylation but inhibited insulin-stimulated MAP kinase, and that 2) palmitate decreased insulin sensitivity as manifested by inhibited insulin-stimulated glucose uptake. In conclusion, the mechanism of saturated non-esterified fatty acid induced insulin resistance in glucose uptake may reside at post PI3-kinase or Shc steps, including the level of MAP kinase activation. [Diabetologia (1997) 40: 894–901] Received: 15 January 1997 and in revised form: 9 April 1997     

The radioprotective 105/MD-1 complex contributes to diet-induced obesity and adipose tissue inflammation

Recent accumulating evidence suggests that innate immunity is associated with obesity-induced chronic inflammation and metabolic disorders. Here, we show that a Toll-like receptor (TLR) protein, radioprotective 105 (RP105)/myeloid differentiation protein (MD)-1 complex, contributes to high-fat diet (HFD)-induced obesity, adipose tissue inflammation, and insulin resistance. An HFD dramatically increased RP105 mRNA and protein expression in stromal vascular fraction of epididymal white adipose tissue (eWAT) in wild-type (WT) mice. RP105 mRNA expression also was significantly increased in the visceral adipose tissue of obese human subjects relative to nonobese subjects. The RP105/MD-1 complex was expressed by most adipose tissue macrophages (ATMs). An HFD increased RP105/MD-1 expression on the M1 subset of ATMs that accumulate in eWAT. Macrophages also acquired this characteristic in coculture with 3T3-L1 adipocytes. RP105 knockout (KO) and MD-1 KO mice had less HFD-induced adipose tissue inflammation, hepatic steatosis, and insulin resistance compared with wild-type (WT) and TLR4 KO mice. Finally, the saturated fatty acids, palmitic and stearic acids, are endogenous ligands for TLR4, but they did not activate RP105/MD-1. Thus, the RP105/MD-1 complex is a major mediator of adipose tissue inflammation independent of TLR4 signaling and may represent a novel therapeutic target for obesity-associated metabolic disorders.     

Evaluation of monitoring: respiratory system and oxygenation

The role of various monitors contributing to achieving and standardizing safety has been increasing in the management of general anesthesia. In particular, sufficient oxygenation is one of the most basic requirements to ensure the safety of patients under general anesthesia. In this report, pulse oximetry, mixed venous oxygen saturation, and central venous oxygen saturation are reexamined as monitors, based on evaluation of the respiratory system and tissue oxygenation, in order to evaluate their usefulness in measurements. Regarding pulse oximeters, the models with added functions are introduced, and in this article mixed venous and central venous oxygen saturation, the early goal-directed therapy (EGDT) and the core of the Surviving Sepsis Campaign (SSC) guidelines from 2008, are examined.     

Safety and efficacy of oral rehydration therapy until 2?h before surgery: a multicenter randomized controlled trial

Purpose

In many countries, patients are generally allowed to have clear fluids until 2?C3?h before surgery. In Japan, long preoperative fasting is still common practice. To shorten the preoperative fasting period in Japan, we tested the safety and efficacy of oral rehydration therapy until 2?h before surgery.

Methods

Three hundred low-risk patients scheduled for morning surgery in six university-affiliated hospitals were randomly assigned to an oral rehydration solution (ORS) group or to a fasting group. Patients in the ORS group consumed up to 1,000?ml of ORS containing balanced glucose and electrolytes: 500?ml between 2100 the night before surgery and the time they woke up the next morning and 500?ml during the morning of surgery until 2?h before surgery. Patients in the fasting group started fasting at 2100 the night before surgery. Primary endpoints were gastric fluid volume and pH immediately after anesthesia induction. Several physiological measures of hydration and electrolytes including the fractional excretion of sodium (FENa) and the fractional excretion of urea nitrogen (FEUN) were also evaluated.

Results

Mean (SD) gastric fluid volume immediately after anesthesia induction was 15.1 (14.0) ml in the ORS group and 17.5 (23.2) ml in the fasting group (P?=?0.30). The mean difference between the ORS group and fasting group was ?2.5?ml. The 95% confidence interval ranged from ?7.1 to +2.2?ml and did not include the noninferior limit of +8?ml. Mean (SD) gastric fluid pH was 2.1 (1.9) in the ORS group and 2.2 (2.0) in the fasting group (P?=?0.59). In the ORS group, mean FENa and FEUN immediately after anesthesia induction were both significantly greater than those in the fasting group (P?P?Conclusions Oral rehydration therapy until 2?h before surgery is safe and feasible in the low-risk Japanese surgical population. Physicians are encouraged to use this practice to maintain the amount of water in the body and electrolytes and to improve the patient??s comfort.     

Pathway-specific modulation of nucleus accumbens in reward and aversive behavior via selective transmitter receptors

The basal ganglia–thalamocortical circuitry plays a central role in selecting actions that achieve reward-seeking outcomes and avoid aversive ones. Inputs of the nucleus accumbens (NAc) in this circuitry are transmitted through two parallel pathways: the striatonigral direct pathway and the striatopallidal indirect pathway. In the NAc, dopaminergic (DA) modulation of the direct and the indirect pathways is critical in reward-based and aversive learning and cocaine addiction. To explore how DA modulation regulates the associative learning behavior, we developed an asymmetric reversible neurotransmission-blocking technique in which transmission of each pathway was unilaterally blocked by transmission-blocking tetanus toxin and the transmission on the intact side was pharmacologically manipulated by local infusion of a receptor-specific agonist or antagonist. This approach revealed that the activation of D1 receptors and the inactivation of D2 receptors postsynaptically control reward learning/cocaine addiction and aversive learning in a direct pathway-specific and indirect pathway–specific manner, respectively. Furthermore, this study demonstrated that aversive learning is elicited by elaborate actions of NMDA receptors, adenosine A2a receptors, and endocannabinoid CB1 receptors, which serve as key neurotransmitter receptors in inducing long-term potentiation in the indirect pathway. Thus, reward and aversive learning is regulated by pathway-specific neural plasticity via selective transmitter receptors in the NAc circuit.     

Carboxyl-directed Pegylation of Brain-derived Neurotrophic Factor Markedly Reduces Systemic Clearance with Minimal Loss of Biologic Activity

Purpose. Brain-derived neurotrophic factor (BDNF) was modified by carboxyl-directed protein pegylation in order to both retain biologic activity of the neurotrophin and reduce the rate of systemic clearance of this cationic protein in vivo. Since the modification of surface lysine residues of neurotrophins results in loss of biologic activity, the present studies examine the feasibility of placing polyethyleneglycol (PEG) polymers on carboxyl residues of surface glutamate or aspartate residues of BDNF. Methods. PEG molecules with terminal hydrazide (Hz) moieties of molecular weight 2,000 (PEG²⁰⁰⁰-Hz) or 5,000 (PEG⁵⁰⁰⁰-Hz) Daltons were coupled to BDNF carboxyls using carbodiimide. Results. The systemic clearances of the BDNF-PEG²⁰⁰⁰ and BDNF-PEG⁵⁰⁰⁰ were reduced 67% and 91%, respectively, compared to unconjugated BDNF. The brain volume of distribution (V_D) of BDNF-PEG⁵⁰⁰⁰ was not significantly different from the cerebral plasma volume. Cell survival studies and TrkB auto-phosphorylation assays showed that the biologic activity of BDNF was not changed following pegylation with PEG²⁰⁰⁰, and was minimally impaired following pegylation with PEG⁵⁰⁰⁰. Conclusions. These experiments describe the first carboxyl-directed pegylation of a neuropeptide, and show this formulation substantially reduces the systemic distribution and elimination of the neurotrophic factor. The biologic activity of the neurotrophin is retained with carboxyl-directed pegylation.