Soluble P-selectin moderates complement-dependent reperfusion injury of ischemic skeletal muscle

Insulin resistance and insulin hypersecretion in the metabolic syndrome and type 2 diabetes: Time for a conceptual framework shift

While few dispute the existence of the metabolic syndrome as a clustering of factors indicative of poor metabolic health, its utility above that of its individual components in the clinical care of individual patients is questioned. This is likely a consequence of the failure of clinicians and scientists to agree on a unifying mechanism to explain the metabolic syndrome. Insulin resistance has most commonly been proposed for this role and is generally considered to be a root causative factor for not only metabolic syndrome but also for its associated conditions of non-alcoholic fatty liver disease (NAFLD), polycystic ovary syndrome (PCOS), obesity-related type 2 diabetes (T2D) and atherosclerotic cardiovascular disease (ASCVD). An alternative view, for which evidence is mounting, is that hyper-responsiveness of islet β-cells to a hostile environment, such as westernised lifestyle, is primary and that the resulting hyperinsulinaemia drives the other components of the metabolic syndrome. Importantly, within this new conceptual framework, insulin resistance, while always a biomarker and state of poor metabolic health, is not considered to be harmful, but a protective adaptive response of critical tissues including the myocardium against insulin-induced metabolic stress. This major shift in how metabolic syndrome can be considered puts insulin hypersecretion into position as the unifying mechanism. If shown to be correct, this new conceptual framework has major implications for the future prevention and management of the metabolic syndrome, including its associated conditions of NAFLD, PCOS, obesity-related T2D and ASCVD.

Pretreatment with Fish Oil-Based Lipid Emulsion Modulates Muscle Leukocyte Chemotaxis in Murine Model of Sublethal Lower Limb Ischemia

This study investigated the effects of a fish oil- (FO-) based lipid emulsion on muscle leukocyte chemotaxis and inflammatory responses in a murine model of limb ischemia-reperfusion (IR) injury. Mice were assigned randomly to 1 sham (sham) group, 2 ischemic groups, and 2 IR groups. The sham group did not undergo the ischemic procedure. The mice assigned to the ischemic or IR groups were pretreated intraperitoneally with either saline or FO-based lipid emulsion for 3 consecutive days. The IR procedure was induced by applying a 4.5 oz orthodontic rubber band to the left thigh above the greater trochanter for 120 min and then cutting the band to allow reperfusion. The ischemic groups were sacrificed immediately while the IR groups were sacrificed 24 h after reperfusion. Blood, IR-injured gastrocnemius, and lung tissues were collected for analysis. The results showed that FO pretreatment suppressed the local and systemic expression of several IR-induced proinflammatory mediators. Also, the FO-pretreated group had lower blood Ly6C^hiCCR2^hi monocyte percentage and muscle M1/M2 ratio than the saline group at 24 h after reperfusion. These findings suggest that FO pretreatment may have a protective role in limb IR injury by modulating the expression of proinflammatory mediators and regulating the polarization of macrophage.

Establishment and Application of in Vitro Membrane Potential Assays in Cell Lines with Endogenous or Recombinant Expression of ATP-Sensitive Potassium Channels (Kir6.2/SUR1) Using a Fluorescent Probe Kit

The flow of current through the adenosine triphosphate (ATP)-sensitive potassium channel (KATP) of the isoform Kir6.2/SUR1 regulates the resting membrane potential in the pancreatic β-cell. In combination with the cellular glucose metabolism, it is an important minute-to-minute regulator of insulin secretion and whole-body glucose homeostasis. The same KATPisoform is further reported to be present in glucagon-secreting α-cells, intestinal L-cells, and glucose-responsive neurons in the hypothalamus. All in all, this makes Kir6.2/SUR1 an interesting drug target. Using a commercially available fluorescent membrane potential probe kit and a conventional 96-well fluorescence plate reader, the authors have developed and established qualitative membrane potential assays used to screen for potassium channel closers (KCCs) and openers (KCOs) in insulin- and glucagon-secreting cell lines as well as in cells with recombinant expression of the human Kir6.2/SUR1 channel complex. Both glucose- and KCC-induced depolarization could be demonstrated. The magnitudes of these responses and KCO-induced repolarization at high glucose displayed some variation between the different cell lines but a similar rank order of test compounds. Some cell types required the presence of a KCC, such as tolbutamide, to display significant effects of KCOs. The authors find that robust and reliable functional in vitro assays compatible with medium-throughput screening and high-throughput screening can be developed as a base for finding new, more potent, and isoform-selective KCCs and KCOs.

Glutamine Administration After Sublethal Lower Limb Ischemia Reduces Inflammatory Reaction and Offers Organ Protection in Ischemia/Reperfusion Injury

BACKGROUND

This study investigated the effects of intravenous glutamine (GLN) administration on the expression of adhesion molecules and inflammatory mediators in a mice model of hind limb ischemia/reperfusion (IR) injury.

METHODS

There were 3 IR groups and 1 normal control (NC) group. The NC group did not undergo the IR procedure. Mice in the IR groups underwent 90 minutes of limb ischemia followed by a variable period of reperfusion. Ischemia was performed by applying a 4.5-oz orthodontic rubber band to the left thigh. Mice in one IR group were sacrificed immediately after reperfusion. The other 2 IR groups were injected once with either 0.75 g GLN/kg body weight (G group) or an equal volume of saline (S group) via tail vein before reperfusion. Mice in the S and G groups were subdivided and sacrificed at 4 or 24 hours after reperfusion.

RESULTS

IR enhanced the inflammatory cytokine gene expressions in muscle. Also, plasma interleukin (IL)-6 levels, blood neutrophil percentage, and the adhesion molecule and chemokine receptors expressed by leukocytes were upregulated after reperfusion. The IR-induced muscle inflammatory mediator gene expressions, blood macrophage percentage, and plasma IL-6 concentration had declined at an early or a late phase of reperfusion when GLN was administered. Histologic findings also found that remote lung injury was attenuated during IR insult.

CONCLUSIONS

A single dose of GLN administration immediately after sublethal lower limb ischemia reduces the inflammatory reaction locally and systemically; this may offer local and distant organ protection in hind limb IR injury.

Identification of extracellular matrix and cell adhesion molecule genes associated with muscle development in pigs

Extracellular matrix (ECM) and cell adhesion molecule (CAM) genes are involved in the regulation of skeletal muscle development; however, their roles in skeletal muscle development in pigs are still poorly understood. 65 days postcopulation (dpc) is a critical time point in pig development. Therefore, we analyzed expression of ECM and CAM genes in the longissimus dorsi muscles at 65 dpc from Landrace (lean-type: L65), Tongcheng (obese-type: T65), and Wuzhishan pigs (miniature-type: W65) using microarray technology. A total of 35 genes were differently expressed between the breeds, and of them, 18, 18, and 20 genes, were observed in the comparisons of L65 versus T65, L65 versus W65, and T65 versus W65 (L65/T65, L65/W65, and T65/W65), respectively. In L65/T65, differently expressed genes were widely distributed, whereas in L65/W65 and T65/W65, they mostly focused on the genes encoding CAMs and ECMs proteins. Moreover, the largest number of up-regulated genes involved in skeletal muscle development was detected in L65, a moderate number in W65, and the smallest number was in T65. Cluster analysis suggested that T65 showed a more similar expression pattern to L65 than W65. In addition, we validated that five genes from microarray data were more highly expressed in the prenatal as compared to postnatal periods in Landrace and Tongcheng pigs and showed a greater range of high-level expression during gestation in Landrace than Tongcheng pigs. Our data indicated that ECM and CAM genes are differently expressed among the three breeds, and more complicated molecular events involving CAMs and ECMs were observed in Wuzhishan pigs. This study advances our knowledge of the molecular basis of phenotypic variation and provides a helpful resource for the identification of candidate genes associated with meat production traits in pigs.

Coagulation and innate immune responses: can we view them separately?

The horseshoe crab is often referred to as a "living fossil," representative of the oldest classes of arthropods, almost identical to species in existence more than 500 million years ago. Comparative analyses of the defense mechanisms used by the horseshoe crab that allowed it to survive mostly unchanged throughout the millennia reveal a common ancestry of the coagulation and innate immune systems that are totally integrated-indeed, almost inseparable. In human biology, we traditionally view the hemostatic pathways and those regulating innate immune responses to infections and tissue damage as entirely separate entities. But are they? The last couple of decades have revealed a remarkable degree of interplay between these systems, and the linking cellular and molecular mechanisms are rapidly being delineated. In this review, we present some of the major points of intersection between coagulation and innate immunity. We attempt to highlight the potential impact of these findings by identifying recently established paradigms that will hopefully result in the emergence of new strategies to treat a range of inflammatory and hemostatic disorders.

Beta cell mass in diabetes: a realistic therapeutic target?

Beta cell deficiency underlies both type 1 and type 2 diabetes, and restoration or replacement of beta cell function is therefore the logical long-term solution to therapy. This review sets out to describe the defects in beta cell mass and function in both forms of diabetes, summarises current understanding of the underlying causes of beta cell death, and the methodological limitations of determining beta cell mass in vivo. Finally, the potential effects of current and future treatment regimens on beta cell mass and turnover are considered.

Too much of a good thing: why it is bad to stimulate the beta cell to secrete insulin

In many countries, first- or second-line pharmacological treatment of patients with type 2 diabetes consists of sulfonylureas (such as glibenclamide [known as glyburide in the USA and Canada]), which stimulate the beta cell to secrete insulin. However, emerging evidence suggests that forcing the beta cell to secrete insulin at a time when it is struggling to cope with the demands of obesity and insulin resistance may accelerate its demise. Studies on families with persistent hyperinsulinaemic hypoglycaemia of infancy (PHHI), the primary defect of which is hypersecretion of insulin, have shown that overt diabetes can develop later in life despite normal insulin sensitivity. In addition, in vitro experiments have suggested that reducing insulin secretion from islets isolated from patients with diabetes can restore insulin pulsatility and improve function. This article will explore the hypothesis that forcing the beta cell to hypersecrete insulin may be counterproductive and lead to dysfunction and death via mechanisms that may involve the endoplasmic reticulum and oxidative stress. We suggest that, in diabetes, therapeutic approaches should be targeted towards relieving the demand on the beta cell to secrete insulin.

Role of myocardial nitric oxide in diabetic ischemia-reperfusion dysfunction: studies in mice with myocyte-specific overexpression of endothelial nitric-oxide synthase

We investigated the role of nitric oxide (NO) in myocardial ischemia-reperfusion injury of diabetic mice with myocyte-specific overexpression of endothelial NO synthase (NOS). Four weeks after diabetes induction with streptozotocin (blood glucose approximately 29 mM), isolated isovolumic heart function and cellular NO metabolites in response to brief normothermic ischemia-reperfusion were determined. Under normoxic conditions transgenic (TG) hearts from nondiabetic and diabetic animals generated less left-ventricular developed pressure compared with wild-type (WT) control hearts, and this abnormality was unaffected by NOS inhibition. During ischemia, the rise in end-diastolic pressure was less in the TG than WT group of nondiabetic hearts, whereas the transgene had no effect in the diabetic group. Similarly, the transgene also improved reperfusion systolic and diastolic function in nondiabetic but not in diabetic hearts. NOS inhibition worsened reperfusion function in diabetic hearts. Postischemic nitrite and cGMP formation were higher in nondiabetic TG than WT hearts, but in diabetic hearts cGMP was no longer elevated. The formation of reactive oxygen species (superoxide and peroxynitrite) during early reperfusion, measured by electron spin resonance spectroscopy, was similar in nondiabetic WT and TG hearts, but it was significantly higher in diabetic TG hearts. Stimulating endogenous NO production with 10 microM bradykinin more strongly reduced myocardial O(2) consumption in diabetic TG than diabetic WT hearts perfused in normoxia, whereas there was no difference after ischemia-reperfusion. Thus, providing additional endogenous NO is sufficient to protect nondiabetic hearts against ischemia-induced injury, but for a similar protection in diabetic hearts, effective scavenging of reactive oxygen species is also important.

A novel model of acute murine hindlimb ischemia

The McGivney hemorrhoidal ligator (MHL), a band designed to cause tissue necrosis, is the preferred experimental tool to create hindlimb ischemia-reperfusion (I/R) injury in rodents. This report defines and compares the ex vivo band tension exerted by MHL and orthodontic rubber bands (ORBs) along with select in vivo characteristics of I/R. As to method, ex vivo band tension was measured over relevant diameters using a tensiometer. In vivo assessment of murine limb perfusion during ischemia with ORB and MHL was compared using laser Doppler imaging and measurement of wet weight-to-dry weight ratio. Neuromuscular scoring and histological extent of muscle fiber injury after I/R with MHL and ORB were also compared. A dose-response curve, between the duration of ORB-induced I/R with both mitochondrial activity (methyl-thiazol-tetrazolium) or tail perfusion [laser Doppler imaging (LDI)], was generated. As a results, ex vivo measurements showed that ORB exerted significantly less force than the MHL. Despite less tension in ORB, in vivo testing of the ORB confirmed complete ischemia by both LDI and wet weight-to-dry weight ratio. After I/R, caused by ORB, there was significantly less neuromuscular dysfunction. Histological assessment confirmed similar degrees of muscle fiber injury after I/R with either the MHL or ORB. Increasing durations of ischemia created by the ORB followed by reperfusion significantly decreased mitochondrial activity and tail perfusion after 24 h of ischemia. In conclusions, ORB produced similar levels of tissue ischemia in murine models of limb I/R with fewer levels of nonspecific injury. ORB may be the preferred model for selected studies of limb I/R.

Time course of COX-1 and COX-2 expression during ischemia-reperfusion in rat skeletal muscle

The aim of this study was to assess cyclooxygenase (COX)-1 and COX-2 expression in skeletal muscle after an ischemia-reperfusion (I/R). Male Sprague-Dawley rats were subjected to unilateral hindlimb ischemia for 2 h and then euthanized after 0, 1, 2, 4, 6, 10, 24, and 72 h of reperfusion. The COX protein and mRNA were assessed in control and injured gastrocnemius muscle. Muscle damage was indirectly determined by plasma creatine kinase activity and edema by weighing wet muscle. Creatine kinase activity in plasma increased as early as 1 h after reperfusion and returned to control levels by 72 h of reperfusion. Edema was observed at 6 and 10 h of reperfusion, but histological investigations showed an absence of tissular inflammatory cell infiltration. COX-1 mRNA was expressed in control muscle and was increased at 72 h of reperfusion, but the levels of associated COX-1 protein detected in control and injured gastrocnemius muscle were similar. COX-2 mRNA was not, or only slightly, detectable in control muscle and after I/R. In contrast, I/R induced major overexpression of COX-2 immunoreactivity at 6 and 10 h of reperfusion with a maximum at 10 h, whereas COX-2 protein was undetectable in control muscle. In conclusion, hindlimb I/R induced a large overexpression of COX-2 but not COX-1 protein between 6 and 10 h after injury. These results suggest a role for COX-2 enzyme in such pathophysiological conditions of the skeletal muscle.

Influence of Temperature on Short-Chain Fatty Acid Production by Pig Cecal Bacteria In Vitro

We studied the effect of incubation temperature on the production of shortchain fatty acids (SCFA) by pig cecal bacteria in vitro in order to assess short-term influences of body temperature on bacterial metabolism in the large intestine. We employed a 200 mL scale continuous culture system using cecal bacteria from commercially slaughtered pigs as innoculum. The culture was maintained at 30, 37, 40 or 42 degrees C and continuously diluted by continuous feeding of bicarbonate buffer (pH 7.4) added with lactose (10 g/L) and by simultaneous continuous efflux both at 4.17 mL/h. We monitored SCFA concentration of the culture for 12 h, which represents their production rate. Concentrations of SCFA increased during the first several hours and plateaued at around 11 h of incubation. Incubation temperature significantly affected mean concentrations from 1 to 12 h of acetic (40 degrees C>42 degrees C= 37 degrees C>30 degrees C), propionic (40 degrees C>42 degrees C=30 degrees C), n-butyric (42 degrees C>37 degrees C>30 degrees C, 40 degrees C>30 degrees C) and n-valeric (42 degrees C=40 degrees C>37 degrees C>30 degrees C) acids, and total SCFA (40 degrees C>42 degrees C= 37 degrees C> 30 degrees C) (p<0.05). These results indicate that both hyperthermia and hypothermia depress the microbial breakdown of carbohydrates.

Platelet activation leads to activation and propagation of the complement system

Inflammation and thrombosis are two responses that are linked through a number of mechanisms, one of them being the complement system. Various proteins of the complement system interact specifically with platelets, which, in turn, activates them and promotes thrombosis. In this paper, we show that the converse is also true: activated platelets can activate the complement system. As assessed by flow cytometry and immunoblotting, C3 deposition increased on the platelet surface upon cell activation with different agonists. Activation of the complement system proceeded to its final stages, which was marked by the increased generation of the anaphylotoxin C3a and the C5b-9 complex. We identified P-selectin as a C3b-binding protein, and confirmed by surface plasmon resonance binding that these two proteins interact specifically with a dissociation constant of 1 μM. Using heterologous cells expressing P-selectin, we found that P-selectin alone is sufficient to activate the complement system, marked by increases in C3b deposition, C3a generation, and C5b-9 formation. In summary, we have found that platelets are capable of activating the complement system, and have identified P-selectin as a receptor for C3b capable of initiating complement activation. These findings point out an additional mechanism by which inflammation may localize to sites of vascular injury and thrombosis.

Two SUR1-specific Histidine Residues Mandatory for Zinc-induced Activation of the Rat KATP Channel

Zinc at micromolar concentrations hyperpolarizes rat pancreatic beta-cells and brain nerve terminals by activating ATP-sensitive potassium channels (KATP). The molecular determinants of this effect were analyzed using insulinoma cell lines and cells transfected with either wild type or mutated KATP subunits. Zinc activated KATP in cells co-expressing rat Kir6.2 and SUR1 subunits, as in insulinoma cell lines. In contrast, zinc exerted an inhibitory action on SUR2A-containing cells. Therefore, SUR1 expression is required for the activating action of zinc, which also depended on extracellular pH and was blocked by diethyl pyrocarbonate, suggesting histidine involvement. The five SUR1-specific extracellular histidine residues were submitted to site-directed mutagenesis. Of them, two histidines (His-326 and His-332) were found to be critical for the activation of KATP by zinc, as confirmed by the double mutation H326A/H332A. In conclusion, zinc activates KATP by binding itself to extracellular His-326 and His-332 of the SUR1 subunit. Thereby zinc could exert a negative control on cell excitability and secretion process of pancreatic beta-and alpha-cells. In fact, we have recently shown that such a mechanism occurs in hippocampal mossy fibers, a brain region characterized, like the pancreas, by an important accumulation of zinc and a high density of SUR1-containing KATP.

Infusion of routinely stored blood may limit reperfusion injury to acutely ischemic myocardial cells

Emergency thrombolysis and restoration of blood supply to acutely ischemic myocardium kills many reversibly injured muscle cells by free radicals generation and calcium influx. Such reversibly injured cells form the major bulk during the initial 10-20 min of ischaemia and in an era where emergency recanalization of arteries is possible, reperfusion injury becomes significant. Therefore, researchers have been trying to find out ways to limit the reperfusion injury by using antioxidants, complement inhibitors or by reperfusion of leucodepleted autologous blood. Red cell concentrates routinely available in blood banks are already depleted of plasma and hence calcium (chelated to the anticoagulant), leukocytes and most viable plasma proteins including complement. They have reduced oxygen content by virtue of storage; hence there might be less free radical generation. So infusion of such a blood through an intracoronary catheter might limit reperfusion injury. Addition of antioxidants or controlling the oxygen content while infusing this blood might give additional benefits. This hypothesis might be tested in animals by inducing controlled ischaemia with reperfusion of homologous cross-matched and group tested blood followed by cardiac radioactive scans. If the experimental results permit, clinical trials might be carried out eventually.

IgM binding to injured tissue precedes complement activation during skeletal muscle ischemia-reperfusion

BACKGROUND

Skeletal muscle reperfusion injury is mediated by IgM natural antibodies and by complement activation, as shown by the attenuation of reperfusion injury seen in mice with no natural IgM [] and in mice deficient in complement C3 and C4 []. We postulate that tissue, when ischemic, expresses neoantigens to which preformed natural IgM antibodies bind, in turn producing harmful complement activation and reperfusion injury.

MATERIALS AND METHODS

C57Bl/6 mice were subjected to 2 h of tourniquet-induced hind limb ischemia followed by variable periods of reperfusion. Two hours of ischemia and 3 h of reperfusion produced severe muscle necrosis and edema. Deposition of IgM and C3 in tissue was assessed using immunohistochemistry on both frozen and Formalin-fixed tissue samples.

RESULTS

IgM binding to the endothelium and muscle bundles of the hind limb began during the ischemic period and continued throughout reperfusion up to 6 h. C3 deposition was not present during ischemia and, in contrast, began to appear at 1 h of reperfusion and increased progressively thereafter.

CONCLUSIONS

These data demonstrate that IgM binding to ischemic tissues precedes the damaging complement activation by a significant period of time. This has important therapeutic implications when considering anti-inflammatory therapy for reperfusion injury.

Gene deletion of P-Selectin and ICAM-1 does not inhibit neutrophil infiltration into peritoneal cavity following cecal ligation-puncture

Background

Neutrophil infiltration is one of the critical cellular components of an inflammatory response during peritonitis. The adhesion molecules, P-selectin and intercellular adhesion molecule (ICAM)-1, mediate neutrophil-endothelial cell interactions and the subsequent neutrophil transendothelial migration during the inflammatory response. Despite very strong preclinical data, recent clinical trials failed to show a protective effect of anti-adhesion therapy, suggesting that the length of injury might be a critical factor in neutrophil infiltration. Therefore, the objective of this study was to determine the role of P-selectin and ICAM-1 in neutrophil infiltration into the peritoneal cavity during early and late phases of peritonitis.

Methods

Peritonitis was induced in both male wild-type and P-selectin/ICAM-1 double deficient (P/I null) mice by cecal ligation-puncture (CLP). Peripheral blood and peritoneal lavage were collected at 6 and 24 hours after CLP. The total leukocyte and neutrophil contents were determined, and neutrophils were identified with the aid of in situ immunohistochemical staining. Comparisons between groups were made by applying ANOVA and student t-test analysis.

Results

CLP induced a severe inflammatory response associated with a significant leukopenia in both wild-type and P/I null mice. Additionally, CLP caused a significant neutrophil infiltration into the peritoneal cavity that was detected in both groups of mice. However, neutrophil infiltration in the P/I null mice at 6 hours of CLP was significantly lower than the corresponding wild-type mice, which reached a similar magnitude at 24 hours of CLP. In contrast, in peritonitis induced by intraperitoneal inoculation of 2% glycogen, no significant difference in neutrophil infiltration was observed between the P/I null and wild-type mice at 6 hours of peritonitis.

Conclusions

The data suggest that alternative adhesion pathway(s) independent of P-selectin and ICAM-1 can participate in neutrophil migration during peritonitis and that the mode of stimuli and duration of the injury modulate the neutrophil infiltration.

A noninvasive murine model of hind limb ischemia-reperfusion injury

BACKGROUND

This study describes a novel murine method of the Controlled Tension Tourniquet (CTT). The CTT applies a measured circumferential tension to hind limbs using a tourniquet attached to digital strain gauges, and is useful for investigating hind limb ischemia reperfusion (IR).

MATERIALS AND METHODS

Mice were subjected to 1, 3, or 6 h of unilateral hind limb ischemia followed by either 4 or 24 h of reperfusion. Blood flow in the ischemic, reperfused, and contralateral limbs was monitored using a Laser Doppler Imager. Edema in the IR limbs was documented by changes in the wet weight to dry weight ratio. Myeloperoxidase and tetrazolium based mitochondrial activity assays indicated neutrophil infiltration and tissue viability, respectively.

RESULTS

During reperfusion following 1, 4, or 6 h, flow stabilized at 100%, 53%, and 23% of baseline levels, respectively. Edema was present all in IR limbs after 4 h of reperfusion, but increased with the duration of ischemia. After 24 h of reperfusion neutrophil infiltration was equivalent in all IR limbs after all intervals of ischemia. After 24 h of reperfusion, tissue viability after 1 h of ischemia was equivalent to sham or contralateral limbs. At 3 or 6 h of ischemia and 24 h reperfusion decreased tissue viability to 40% of sham and contralateral limbs.

CONCLUSIONS

The CTT provides a reproducible, noninvasive model of acute limb ischemia, which reflects the biochemical indices of microvascular injury, inflammation and flow characteristic of reperfusion injury.

Glucose-induced translational control of proinsulin biosynthesis is proportional to preproinsulin mRNA levels in islet beta-cells but not regulated via a positive feedback of secreted insulin

Proinsulin biosynthesis is regulated in response to nutrients, most notably glucose. In the short term (</=2h) this is due to increases in the translation of pre-existing mRNA. However, prolonging glucose stimulation (24 h) also increases preproinsulin mRNA levels. It has been proposed that secreted insulin from the pancreatic beta-cell regulates its own synthesis through a positive autocrine feedback mechanism. Here the comparative contributions of translation and mRNA levels on the levels of proinsulin biosynthesis were examined in isolated pancreatic islets. Also, the autocrine role of insulin upon four beta-cell functions (insulin secretion, proinsulin translation, preproinsulin mRNA levels, and total protein synthesis) was investigated in parallel. The results showed that proinsulin biosynthesis is regulated, in the short term (1 h), solely at the level of translation, through an approximately 6-fold increase in response to glucose (2.8 mm versus 16.7 mm glucose). In the longer term, when preproinsulin mRNA levels have increased approximately 2-fold, a corresponding increase was observed in the fold response of proinsulin translation to a stimulatory glucose concentration (>/=10-fold). Importantly, neither exogenously added nor secreted insulin were found to play any role in regulating insulin secretion, proinsulin translation, preproinsulin mRNA levels, or total protein synthesis. The results presented here indicate that long term nutritional state sets the preproinsulin mRNA level in the beta-cell at which translation control regulates short term changes in rates of proinsulin biosynthesis in response to glucose, but this is not mediated by any autocrine effect of insulin.

The endothelium in sepsis: source of and a target for inflammation

OBJECTIVE

To discuss a possible role of the endothelium in sepsis.

DATA SOURCES

Studies published in biomedical journals and our own experimental results.

STUDY SELECTION

Studies on endothelial mechanisms in the context of sepsis.

DATA EXTRACTION AND SYNTHESIS

Changes in endothelial cells on activation by inflammatory stimuli are reviewed briefly; potential mechanisms that lead to endothelial damage during sepsis are discussed.

CONCLUSIONS

The endothelium is a key organ involved in the pathogenesis of sepsis. Dysfunction of or injury to the endothelium may be involved in the pathogenesis of multiple organ failure and should be discriminated from activation resulting from stimulation with inflammatory stimuli. Identification of the molecular mechanisms that contribute to endothelial dysfunction or damage is likely to provide novel targets for the treatment of sepsis.