Protective effect of black relative to white race against non-alcoholic fatty liver disease in patients with severe obesity, independent of type 2 diabetes.

Severe obesity (body mass index ⩾35 kg m-2) and type 2 diabetes (T2D) are potent and additive risk factors for non-alcoholic fatty liver disease (NAFLD), including non-alcoholic steatohepatitis (NASH). Scant available evidence indicates that black relative to white patients with severe obesity are less susceptible to NAFLD, but it is unclear if T2D abolishes this apparent racial disparity. Therefore, we compared biopsy-proven NAFLD and its progression between black (n=71) and white (n=155) patients with severe obesity stratified by presence or absence of T2D. Although prevalence of T2D was similar between races (37%, P>0.9), whites were significantly more likely than blacks to have NAFLD, NASH and advanced fibrosis (defined as bridging fibrosis and/or cirrhosis). Importantly, T2D was associated with increased odds of NAFLD, NASH and advanced fibrosis (defined as bridging fibrosis or cirrhosis) in whites only (P<0.05). In turn, a higher proportion of blacks than whites with T2D were free of NAFLD (58 versus 22%, P<0.01). These preliminary findings question translation of the powerful interconnection between T2D and NAFLD in whites with severe obesity to blacks and point to an important role of race in the pathophysiology and treatment of these diseases.

Comparing Normothermic Machine Perfusion Preservation With Different Perfusates on Porcine Livers From Donors After Circulatory Death.

The utilization of normothermic machine perfusion (NMP) may be an effective strategy to resuscitate livers from donation after circulatory death (DCD). There is no consensus regarding the efficacy of different perfusates on graft and bile duct viability. The aim of this study was to compare, in an NMP porcine DCD model, the preservation potential of three different perfusates. Twenty porcine livers with 60 min of warm ischemia were separated into four preservation groups: cold storage (CS), NMP with Steen solution (Steen; XVIVO Perfusion Inc., Denver, CO), Steen plus red blood cells (RBCs), or whole blood (WB). All livers were preserved for 10 h and reperfused to simulate transplantation for 24 h. During preservation, the NMP with Steen group presented the highest hepatocellular injury. At reperfusion, the CS group had the lowest bile production and the worst hepatocellular injury compared with all other groups, followed by NMP with Steen; the Steen plus RBC and WB groups presented the best functional and hepatocellular injury outcomes, with WB livers showing lower aspartate aminotransferase release and a trend toward better results for most parameters. Based on our results, a perfusate that contains an oxygen carrier is most effective in a model of NMP porcine DCD livers compared with Steen solution. Specifically, WB-perfused livers showed a trend toward better outcomes compared with Steen plus RBCs.

Characterization of hypothermic intestinal ischemia-reperfusion injury in dogs. Effects of glycine.

The effects of 48 hr of hypothermic (4 degrees C ischemia) and short-term reperfusion. (I-R) on intestinal function and metabolism were studied in dogs utilizing Collins flush alone or with the putative cytoprotectant amino acid, glycine. Intestinal blood flow after hypothermic ischemia in Collins-flushed segments briefly rose at reperfusion, rapidly declined after 5 min, and plateaued over the 60-minute reperfusion period. Paired intestinal segments flushed with 5 mM glycine demonstrated parallel changes in blood flow over the reperfusion period, but the blood flow values were significantly higher (100-300%), relative to the Collins segments. Intestinal oxygen consumption (VO2) was about 50% of normal nonischemic intestinal segments at all times after reperfusion. The glycine-flushed intestinal segments significantly consumed about 100% more oxygen, relative to the paired control intestines. Intestinal fluid and protein flux into the lumen significantly increased after I-R in both glycine- and Collins-flushed segments. Mucosal tissue myeloperoxidase (MPO) activity, a biochemical marker of neutrophils, significantly increased after 48 hr of cold ischemia with Collins flush and 1 hr of reperfusion, relative to tissue obtained before ischemia. The reperfusion-induced increase in MPO activity was abolished in intestinal segments flushed with glycine. Mucosal synthesis of the chemoattractant leukotriene B4 (LTB4) significantly increased after I-R and glycine flush abolished these increases. Nitric oxide synthesis by mucosal tissue in Collins-flushed segments subjected to 48 hr of hypothermic ischemia and 1 hr of reperfusion was significantly higher, compared with nonischemic tissue or mucosal tissue subjected to cold ischemia without reperfusion. Glycine flush did not alter this pattern of NO synthesis. Light microscopic analysis in both Collins- and glycine-flushed segments revealed that intestinal hypothermic ischemia and reperfusion caused significant morphologic changes characterized by loss of villus epithelium, decreased villus height, and venous congestion. These data indicate that glycine significantly improve oxygenation after hypothermic ischemia and reperfusion and prevented the I-R-induced increase in tissue neutrophil infiltration and leukotriene synthesis.

Eicosanoid synthesis inhibition and renal allograft function during acute rejection.

The effects of the dual cyclooxygenase-lipoxygenase inhibitor 3-amino-1-(m[trifluoromethyl]phenyl)-2-pyrazoline (BW755C) (10 mg/kg, p.o., b.i.d.) on renal blood flow, glomerular filtration rate (GFR), and eicosanoid production were examined in anesthetized dogs that had undergone unilateral renal allotransplantation. Rejecting renal allograft blood flow significantly declined over a 5-day period compared to the nonrejecting native kidney. In animals treated with BW755C, renal allograft blood flow was maintained over the postoperative 5-day period at levels comparable to blood flow to the native kidneys. While GFR and urine flow progressively declined in the rejecting kidney, treatment with BW755C prevented the fall in GFR and even augmented urine flow. Allograft renal cortical production or thromboxane B2 (TXB2) and leukotriene B4 (LTB4) in animals treated with BW755C was not significantly different than production by the native contralateral kidneys. Furthermore, BW755C reduced cellular infiltration and tissue damage in allografts compared to nontreated renal allografts. The selective cyclooxygenase inhibitor, indomethacin (5 mg/kg, p.o., b.i.d.) exerted no effect on renal allograft GFR or urine output but reduced allograft blood flow after 4 days compared to nontreated allografts. In conclusion, inhibition of arachidonate cyclooxygenase and lipoxygenase metabolism improves renal allograft function and reduces tissue damage while selective inhibition of the cyclooxygenase pathway does not improve renal allograft function. These data indicate that products of arachidonate-lipoxygenase metabolism potentiate the loss of renal function and tissue destruction associated with renal allograft rejection.

Arginine-specific suppression of mixed lymphocyte culture reactivity by Kupffer cells--a basis of portal venous tolerance.

Portal venous administration of alloantigen abrogates the DTH response and prolongs heart and kidney allograft survival. Within the hepatic microenvironment, negligible L-arginine levels result from the effects of the highest tissue arginase activity of any organ (25 times greater than kidney). This study evaluated the effects of arginine availability on Kupffer cell immune function in the rat mixed lymphocyte culture. When 5 x 10(5) Wistar-Furth unfractionated lymph node cells (LNC) were cultured with 5 x 10(5) irradiated Lewis LNC in standard RPMI-1640 medium containing 1200 microM L-arginine, the proliferative response was not effected by the addition of 1 x 10(5) WF KC. However, when L-arginine-depleted medium (6 microM) was used, the MLC response was markedly reduced by the addition of KC. This was specific to arginine since media depletion of L-lysine, a similar basic amino acid, did not affect MLC/KC responses. When syngeneic WF KC were added as antigen-presenting cells to fractionated stimulator and responder T lymphocytes, WF/LEW MLC proliferation was restored in standard and L-lysine-depleted media, but did not increase in L-arginine-depleted RPMI 1640 medium. These responses correlated with a fivefold increase in KC prostaglandin-E2 (PGE2) production in the L-arginine-depleted medium. These findings support the hypothesis that diminished immune responsiveness in the low-arginine hepatic environment is effected, at least in part, by locally increased production of the immunosuppressant prostaglandin-E2.

Arachidonate lipoxygenase products and renal allograft rejection in dogs.

The production of 12-hydroxyeicosatetraenoic acid (12-HETE) and leukotriene B4 (LTB4) was studied in renal tissue obtained from renal allografts and normal kidneys of nonimmunosuppressed dogs that had undergone unilateral renal allotransplantation. We have shown that allografted renal cortex undergoing rejection synthesizes significantly greater quantities of 12-HETE than normal or autotransplanted control renal cortex. There was no significant increase in 12-HETE production by allografted medulla undergoing rejection. Production of LTB4 was significantly greater in the rejecting renal cortex compared to control renal cortex but was not different in the rejecting compared to normal renal medulla. Production of 12-HETE and LTB4 was significantly inhibited by the lipoxygenase-cyclooxygenase inhibitor BW755C, suggesting that production of these compounds was enzyme catalyzed. Histologic examination of renal tissue undergoing rejecting revealed varying degrees of tissue destruction and cellular infiltration. These histologic parameters correlated with the magnitude of 12-HETE production in the allografts. Our findings therefore indicate that arachidonate lipoxygenase products are generated in increased amounts by renal cortical tissue undergoing rejection and suggest that these products may be involved in the rejection process.

Lymphocyte suppression by Kupffer cells prevents portal venous tolerance induction: a study of macrophage function after intravenous gadolinium.

Ag administration into the portal vein can induce specific tolerance to that Ag, known as portal venous tolerance. Because intrahepatic mechanisms of tolerance induction are still largely undefined, we studied the in vitro response of OVA-sensitized Lewis rat lymphocytes to OVA presented by normal syngeneic rat Kupffer cells (KC) or KC that had been treated in vivo with gadolinium chloride (GD), a rare earth metal, which prevents the induction of portal venous tolerance. KC (2.5 x 10(4)) were able to present OVA to 5 x 10(5) OVA-sensitized APC-depleted lymphocytes as effectively as could lymph node APC. However, the use of GD-treated KC was associated with a significantly (P < 0.001) impaired response of OVA-sensitized APC-depleted lymphocytes to OVA. Although GD nearly abrogated in vivo phagocytosis of fluorescent latex beads by both KC and adherent splenocytes, expression of the class II MHC molecule (Ia) by KC was only slightly reduced by GD treatment. Unresponsiveness of OVA-sensitized lymphocytes to OVA was not related to enhanced PGE2 release by GD-treated KC, as determined both by PGE2 levels in culture supernatants and by cyclooxygenase inhibition. However, the marked ability of GD-treated KC to inhibit the response to OVA by primed lymph node populations containing lymphocytes and APCs supports an active suppressive mechanism. Prevention of the induction of portal venous tolerance by GD, the lack of in vitro KC Ag presentation by GD-treated KC, and active immunosuppression by GD-treated KC support a model of tolerance induction within the liver wherein Ag presentation and lymphocyte proliferation are necessary for the development of tolerance.

The Kupffer cell in endotoxin tolerance: mechanisms of protection against lethal endotoxemia.

Kupffer cells (KC) of the hepatic sinusoid respond to endotoxemia by producing mediators which promote or inhibit systemic inflammatory responses. Sublethal lipopolysaccharide (LPS) pretreatment confers tolerance to the lethality of a subsequent LPS exposure. However, the precise role of the KC in endotoxin tolerance (ET) remains unclear. This study evaluated the effect of ET induction upon the rat KC production of the mediators tumor necrosis factor-alpha (TNF-alpha), prostaglandin E2 (PGE2), and interleukin-6 (IL-6), and upon the in vivo phagocytic capacity of the KCs. 3 days prior to KC isolation, age-matched rats received either 5 mg/kg LPS (ET) or normal saline (nontolerant, NT), which protected 100% of the ET rats against an LPS dose 3 days later which was lethal in 72% of NT rats. On an in vitro LPS rechallenge, ET KC produced significantly lower amounts of TNF than NT KC (p < .01). In contrast, the ET KC produced significantly more PGE2 (p < .05) and IL-6 (p < .001) than the NT KC. The percentage of KC phagocytosing fluorescent latex spheres in vivo was increased 7-fold in the ET rats. Thus, ET induction, which protects rats against subsequent lethal endotoxemia, selectively alters KC mediator production and phagocytic capacity. These findings strongly implicate the KC in the mediation of early endotoxin tolerance.

A biologic basis for limited Kupffer cell reactivity to portal-derived endotoxin.

Despite continuous exposure to gut-derived endotoxin (lipopolysaccharide) under normal conditions, Kupffer cells (KC) fail to generate detrimental cytokine responses. KC function within a unique microenvironment in which high hepatic arginase activities (25 times greater than those activities in the kidney) result in negligible local L-arginine levels. To evaluate the relevance of this profound arginine deficiency on the physiologic function of KC, the kinetics of tumor necrosis factor (TNF-alpha) production and autoregulatory eicosanoid prostaglandin E2 (PGE2) production were compared in lipopolysaccharide-stimulated KC cultured with (1200 mumol/L) and without (10 mumol/L) L-arginine media. In (+)arginine culture the KC TNF-alpha production peaked early before decreasing as PGE2 production increased. In (-)arginine culture, however, KC TNF-alpha production was significantly (p less than 0.01) reduced, whereas PGE2 production was amplified (p less than 0.01). When cyclooxygenase blockade with indomethacin completely prevented KC production of PGE2 in (-)arginine culture, TNF-alpha production was upregulated (p less than 0.001 vs (-)arginine; p not significant vs (+)arginine). These arginine-specific depression of TNF-alpha responses appeared unique to KC because both TNF-alpha and PGE2 levels increased when peritoneal, pleural, and alveolar macrophages were stimulated by lipopolysaccharide in (-)arginine medium. This PGE2-dependent autoregulation of potentially harmful lipopolysaccharide-induced TNF-alpha responses may reflect an evolutionary adaptation by KC to their local hepatic environment and strategic anatomic position in the portal circuit, which optimally removes endotoxin and naturally protects the host.

Hemodynamic effects of periodic G(z) acceleration in meconium aspiration in pigs.

The hemodynamic effects of periodic acceleration (pG(z)), induced in the spinal axis with noninvasive motion ventilation (NIMV), were studied in a piglet model of pulmonary hypertension associated with meconium aspiration. Animals (n = 12) were anesthetized, paralyzed, intubated, and supported by conventional mechanical ventilation (CMV). Thirty minutes after tracheal instillation of meconium solution (6 ml/kg), either CMV (n = 6) was continued or NIMV (n = 6) was initiated. Changes in systemic and pulmonary hemodynamics and arterial blood gases were tracked for 2 h after aspiration. Thermodilution, cardiac output, and heart rate were not significantly different after meconium aspiration in the pG(z) group relative to the CMV controls. Aortic pressure and systemic vascular resistance were significantly lower (approximately 30%) after meconium aspiration in NIMV animals relative to CMV animals. Pulmonary arterial pressure and pulmonary vascular resistance were also significantly lower, by 100%, after aspiration of meconium in the NIMV animals compared with the CMV controls. Meconium aspiration significantly decreased total respiratory compliance by approximately 50% and increased total respiratory resistance by approximately 100% in both CMV and NIMV animals, but such alterations did not differ between the two groups. Both CMV and NIMV satisfactorily supported ventilation in these paralyzed animals. In conclusion, NIMV through pG(z) in the spinal axis decreased systemic and pulmonary vascular resistance in piglets after meconium aspiration.

Noninvasive motion ventilation (NIMV): a novel approach to ventilatory support.

A motion platform was developed that oscillates an animal in a foot-to-head direction (z-plane). The platform varies the frequency and intensity of acceleration, imparting periodic sinusoidal inertial forces (pG(z)) to the body. The aim of the study was to characterize ventilation produced by the noninvasive motion ventilator (NIMV) in animals with healthy and diseased lungs. Incremental increases in pG(z) (acceleration) with the frequency held constant (f = 4 Hz) produced almost linear increases in minute ventilation (VE). Frequencies of 2-4 Hz produced the greatest VE and tidal volume (VT) for any given acceleration between +/-0.2 and +/-0.8 G. Increasing the force due to acceleration produced proportional increases in both transpulmonary and transdiaphragmatic pressures. Increasing transpulmonary pressure by increasing pG(z) produced linear increases in VT, similar to spontaneous breathing. NIMV reversed deliberately induced hypoventilation and normalized the changes in arterial blood gases induced by meconium aspiration. In conclusion, a novel motion platform is described that imparts periodic sinusoidal acceleration forces at moderate frequencies (4 Hz) to the whole body in the z-plane. These forces, when properly adjusted, are capable of highly effective ventilation of normal and diseased lungs. Such noninvasive ventilation is accomplished at airway pressures equivalent to atmospheric or continuous positive airway pressure, with acceleration forces less than +/-1 G(z).

Organ interactions in sepsis. Host defense and the hepatic-pulmonary macrophage axis.

Endotoxin (lipopolysaccharide [LPS]) and tumor necrosis factor (TNF-alpha) have been implicated in the pathogenesis of sepsis-induced adult respiratory distress syndrome. To evaluate the possible interaction of the hepatic-pulmonary macrophage axis in the adult respiratory distress syndrome, we compared the kinetics of immunosuppressive prostaglandin E2, TNF-alpha, and interleukin 6 production in LPS-stimulated Kupffer cells and alveolar macrophages (AMs). Interleukin 6 production by Kupffer cells was significantly higher than for equal numbers of AMs. Kupffer cell TNF-alpha levels peaked early before decreasing as regulatory prostaglandin E2 levels rose. In contrast, AM TNF-alpha levels rose sharply and remained significantly higher than for Kupffer cells throughout culture coincident with negligible prostaglandin E2 production. Kupffer cell sequestration of LPS may normally invoke a coordinated cytokine response able to locally induce acute-phase hepatocytes. In hepatic failure, however, LPS spillover to the lung may promote adult respiratory distress syndrome by inducing unregulated AM TNF-alpha production within the pulmonary microenvironment.

Prostanoids and hypothermic renal preservation injury.

The effect of 48 hours of hypothermic renal ischemia utilizing Euro-Collins flush and short term reperfusion on renal prostaglandin synthesis was studied in dogs. Hypothermic ischemia followed by 60 minutes of reperfusion in-vivo resulted in significant elevations in renal Thromboxane B2 (TXB2) production in the outer cortex, inner cortex, and medulla, relative to non-ischemic kidneys. Prostaglandin E2 (PGE2) and 6-keto Prostaglandin F1 alpha (6-K PGF1 alpha) production were not significantly affected by ischemia and reperfusion. Enhanced TXB2 production was not seen with ischemia alone (without reperfusion) or with reperfusion with O2 saturated buffer, indicating a blood born source or stimuli. Early postreperfusion renal blood flow after hypothermic ischemia followed a biphasic pattern; blood flow increased for the first 10 minutes of reperfusion to achieve normal values, and then steadily declined over the next 20 minutes. This pattern was not altered by the cyclooxygenase inhibitors Idomethacin (5 mg/kg, P.O.) or Mefenamic acid (10 mg/kg, I.V.). Administration of the TXA2 synthesis inhibitor CGS-12970 (3 mg/kg, I.V.) or the TXA2/endoperoxide receptor antagonist SQ-29548 (80 micrograms/min, I.A.) significantly increased renal blood flow during reperfusion but neither agent altered the basic time dependent pattern observed in the control group. These data indicate that 48 hours of hypothermic renal ischemia results in dramatic changes in intrarenal TXA2 synthesis at the time of reperfusion. Enhanced TXA2 production is not dependent on reoxygenation per se, but rather requires reperfusion with blood suggesting a circulatory source.(ABSTRACT TRUNCATED AT 250 WORDS)

Novel CPR with periodic Gz acceleration.

The effects of periodic Gz acceleration (pGz) on cardiovascular function and hemodynamics were determined in a pig model of acute cardiopulmonary resuscitation (CPR). The application of pGz (horizontal head-to-foot oscillations) at 2 Hz increased cardiac output in fibrillated animals proportional to the amplitude of the applied acceleration force that plateaued at 0.7 G. Cardiac output in fibrillating animals was restored to 20% of the values obtained before fibrillation with pGz-CPR and arterial blood gas values were normal during this period. The central vascular pressure gradient driving blood flow was only about 6 mmHg, suggesting low vascular resistance during pGz-CPR. In another study, capillary blood flow was determined before and after pGz-CPR using colored microspheres. Capillary perfusion was detected in all tissue beds studied during pGz-CPR. Significant capillary blood flow was detected in the endocardium and brain stem during pGz-CPR that represented 39 and 197% of control values before fibrillation, respectively. Thus, the cardiac output during pGz-CPR was preferentially distributed to the myocardial and brain tissues. In a final group, animals were successfully resuscitated with return of spontaneous circulation (ROSC) after pGz-CPR for 15 min following cardiac fibrillation with a 3-min non-intervention period. Following ROSC, blood pressure was maintained at pre-arrest values for 2 h without any pharmacological or mechanical support. Arterial blood gases during the pGz-CPR and the ROSC periods were normal and not different from values obtained before fibrillation. None of the control animals (18 min of fibrillation without pGz-CPR) survived the experimental protocol and only two of these six animals briefly returned to spontaneous circulation (<20 min). In conclusion, experimental pGz-CPR produces cardiac output, capillary blood flow, and ventilation sufficient to maintain fibrillating animals for 18 min with ROSC for 2 h without support.

Arachidonic acid and postprandial intestinal hyperemia.

The effects of prostaglandin synthesis on food-induced increases in intestinal blood flow and O2 uptake were examined in the jejunum of anesthetized dogs. Intravenous (40 micrograms X kg-1 X min-1) or intra-arterial (0.8-1.6 microgram X min-1) infusions and luminal placement (6.5 X 10(-4) M or 200 micrograms/ml) of arachidonic acid (AA) significantly attenuated the food-induced jejunal hyperemia. Furthermore, luminal placement of AA significantly attenuated the food-induced increase in jejunal O2 uptake. Changes in blood flow and O2 uptake were significantly correlated both before and after arachidonic acid administration. Although intravenous infusion of AA decreased blood flow, intra-arterial infusion and luminal placement of AA did not significantly alter resting blood flow under free-flow conditions. In another series of experiments, intravenous infusions of AA under constant-flow conditions produced a biphasic response: vascular resistance rose when local blood AA concentration was raised to the range between 1 and 6 micrograms/ml blood and fell when the concentration was raised between 8 and 12 micrograms/ml blood. This study indicates that prostaglandin synthesis has a marked effect on both resting intestinal blood flow and postprandial intestinal hyperemia. The attenuation of the hyperemia may be due to its attenuation of the food-induced increase in intestinal oxidative metabolism.

Thromboxane synthesis inhibitors and postprandial jejunal capillary exchange capacity.

The effects of thromboxane synthesis inhibitors (imidazole and U 63557A; Upjohn) and the cyclooxygenase inhibitor, mefenamic acid, on jejunal capillary filtration coefficients (Kfc) were determined in dogs before and during the presence of predigested food in the jejunal lumen. The jejunal Kfc increased significantly soon after the placement of a predigested test food containing all major constituents of diet. The Kfc remained elevated as long as the food was present in the lumen (15 min). Mefenamic acid (10 mg/kg iv) did not significantly alter resting jejunal Kfc or alter the food-induced increase in Kfc. Imidazole (5.0 mg/min ia) or U 63557A (5.0 mg/kg iv) per se significantly increased jejunal Kfc. Placement of digested food further increased the Kfc to levels significantly higher than those observed before administration of the two thromboxane synthase inhibitors. Production of thromboxane B2 by jejunal tissue was significantly reduced and 6-ketoprostaglandin F1 alpha (the stable hydrolysis product of prostacyclin) production was significantly increased after administration of U 63557A. Our study indicates that the relative production of endogenous thromboxanes and other prostanoids modulates jejunal capillary exchange capacity in the absence or presence of digested food in the jejunal lumen.

Thromboxane synthesis inhibition and postprandial intestinal hyperemia and oxygenation.

The effects of imidazole and U-63557A (Upjohn), inhibitors of thromboxane synthesis, on food-induced changes in intestinal blood flow and oxygen uptake were determined in the jejunum of anesthetized dogs. Intra-arterial (5.0 mg/min ia) infusions of imidazole had no effect on the postprandial intestinal hyperemia but significantly potentiated food-induced increases in oxygen uptake via enhanced oxygen extraction. Furthermore, imidazole had no effect on intestinal glucose absorption. The selective thromboxane synthesis inhibitor U-63557A (5 mg/kg iv) also enhanced oxygen uptake during nutrient absorption and had no effect on the hyperemia or glucose absorption. Our study indicates that inhibition of thromboxane synthesis has no effect on either resting intestinal blood flow or postprandial intestinal hyperemia but significantly enhances postprandial oxygen extraction and uptake. The potentiation of the food-induced increases in oxygen uptake by imidazole and U-63557A appears not to be related to glucose absorption. Endogenous thromboxane therefore appears to inhibit oxygen uptake more than blood flow, and yet does not affect glucose absorption during nutrient absorption.