Richard N. Garrison

Obesity, inflammation, and the potential application of pharmaconutrition

Obesity is an emerging problem worldwide. Hospitalized obese patients often have a worse outcome than patients of normal weight, particularly in the setting of trauma and critical care. Obesity creates a low-grade systemic inflammatory response syndrome (SIRS) that is similar (but on a much smaller scale) to gram-negative sepsis. This process involves up-regulation of systemic immunity, is characterized clinically by insulin resistance and the metabolic syndrome, and puts the patient at increased risk for organ failure, infectious morbidity, and mortality. Through lipotoxicity and cytokine dysregulation, obesity may act to prime the immune system, predisposing to an exaggerated subsequent immune response when a second clinical insult occurs (such as trauma, burns, or myocardial infarction). Specialized nutrition therapy for such patients currently consists of a hypocaloric, high-protein diet. However, this approach does not address the putative pathophysiologic mechanisms of inflammation and altered metabolism associated with obesity. A number of dietary agents such as arginine, fish oil, and carnitine may correct these problems at the molecular level. Pharmaconutrition formulas may provide exciting innovations for the nutrition therapy of the obese patient.

SELECTIVE MICROVASCULAR ENDOTHELIAL CELL DYSFUNCTION IN THE SMALL INTESTINE FOLLOWING RESUSCITATED HEMORRHAGIC SHOCK

Following resuscitation (RES) from hemorrhagic shock (HEM), intestinal microvessels develop progressive vasoconstriction that impairs mucosal blood flow, despite central hemodynamic RES. These events might have clinical consequences secondary to occult intestinal ischemia. We hypothesized that the microvascular impairments were due to progressive endothelial cell dysfunction and an associated reduction in the dilator, nitric oxide (NO), following HEM/RES. Male Sprague-Dawley rats, were monitored for central hemodynamics and the terminal ileum was studied with in vivo videomicroscopy. HEM was 50% of baseline mean arterial pressure (MAP) for 60 min, and RES was with shed blood + 1 volume of normal saline (NS), Following HEM/RES, acetylcholine (10-7, 10-5 M) was topically applied and ileal inflow (A1) and premucosal arteriolar diameters were measured to assess endothelial-cell function at 60 and 120 min post-RES. Normalization of MAP, cardiac output, and heart rate demonstrated adequate systemic resuscitation. Post-RES vasoconstriction developed in A1 (-25%) and premucosal (-28%) arterioles with an associated reduction in A1 flow (-47%). However, there was a selective impairment of endothelialdependent dilation that was manifested only in the smaller premucosal arterioles and not in the inflow, A1 arterioles. This suggests that multiple mechanisms are involved in the development of the post-RES vasoconstriction. The premucosal response was likely mediated by endothelial cell dysfunction, while the A1 response was probably the result of enhanced vasoconstrictor forces. This early microvascular dysfunction might contribute to the late sequelae of intestinal ischemia and might alter microvascular responses to subsequent systemic insults.

Nitric oxide synthase inhibition aggravates intestinal microvascular vasoconstriction and hypoperfusion of bacteremia.

Nitric oxide (NO) is an important hemodynamic mediator of sepsis; however, its visceral microcirculatory effects are largely unknown. To determine the role of systemic nitric oxide synthase (NO-S) inhibition on the microcirculation of the small intestine (SI), an intact loop of SI was exteriorized from decerebrate rats into a controlled tissue bath. Videomicroscopy was used to measure arteriolar diameters (A1, A3) and optical Doppler velocimetry was used to quantitate flow. In nonbacteremic controls inhibition of NO-S by N omega-nitro-L-arginine methyl ester (L-NAME; 1 mg/kg IV) caused vasoconstriction (A1 = -7%; A3 = -24% baseline values) and reduced A1 flow by 26%. Bacteremic controls received 10(9) Escherichia coli IV, which resulted in arteriolar constriction and hypoperfusion (A1 = -16%; A3 = -21%; A1 flow = -44%), despite increased cardiac output (+33%). Treatment of bacteremic rats with L-NAME corrected the increased cardiac output (-3%), but exacerbated vasoconstriction (A1 = -24%; A3 = -27%) and did not improve A1 flow (-49%). These data indicate that (1) NO mediates basal microvascular tone of the SI; (2) hyperdynamic bacteremia causes arteriolar constriction and hypoperfusion of the SI; and (3) although systemic NO-S inhibition normalizes cardiac output and increases blood pressure, it aggravates vasoconstriction in the SI and does not improve hypoperfusion.

Complement Activation Mediates Intestinal Injury after Resuscitation from Hemorrhagic Shock

BACKGROUND Endothelial cell injury after hemorrhage and resuscitation (HEM/RES) might contribute to intestinal hypoperfusion and mucosal ischemia. Our recent work suggests that the injury might be the result of complement activation. We hypothesized that HEM/RES causes complement-mediated endothelial cell dysfunction in the small intestine. METHODS Male Sprague-Dawley rats (195-230 g) were anesthetized and HEM to 50% of baseline mean arterial pressure for 60 minutes. Just before RES, animals received either soluble complement receptor-1 (sCR1, 15 mg/kg) to inhibit complement activation or saline vehicle. Resuscitation was with shed blood and an equal volume of saline. Two hours after RES, the small bowel was harvested to evaluate intestinal nitric oxide synthase activity (NOS), neutrophil influx, histology, and oxidant injury. RESULTS HEM/RES induced tissue injury, increased neutrophil influx, and reduced NOS activity by 50% (vs. SHAM), all of which were completely prevented by sCR1 administration. There were no observed differences in oxidant injury between the groups. CONCLUSION Histologic tissue injury, increased neutrophil influx, and impaired NOS activity after HEM/RES were all prevented by complement inhibition. Direct oxidant injury did not seem to be a major contributor to these alterations. Complement inhibition after HEM might ameliorate reperfusion injury in the small intestine by protecting the endothelial cell, reducing neutrophil influx and preserving NOS function.

Fluid resuscitation attenuates early cytokine mRNA expression after peritonitis.

OBJECTIVE To study the hypothesis that fluid resuscitation alters cytokine gene expression after experimental murine peritonitis. MATERIALS AND METHODS Mice underwent cecal ligation and puncture (CLP) to induce peritonitis and were randomized to receive variable amounts of normal saline (0, 0.25, 1.0 ml. subcutaneously) and serum (0 or 0.1 mL) after operation. Hepatic and small intestinal (ileal) tissue were harvested at 3 or 6 hours after CLP, and total tissue RNA was extracted. Reverse transcriptase polymerase chain reaction was used to provide relative quantitation of tumor necrosis factor-alpha and interleukin (IL)-1 beta messenger RNA (mRNA) compared with beta-actin. RESULTS CLP without resuscitation resulted in significant increases in hepatic tumor necrosis factor-alpha mRNA (1190% at 6 hours compared with normal animals), and IL-1 beta mRNA (1475%), and intestinal IL-1 beta mRNA (1243%). Volume administration attenuated cytokine expression at both 3 and 6 hours, and saline seemed to have more potent effects than serum. The volume of resuscitation correlated with survival at 18 hours. Survival in the saline (1 mL) + serum group was 90% at 18 hours compared with 20 to 40% in the groups with little or no resuscitation. Overall, there were no survivors at 30 hours. CONCLUSIONS Fluid resuscitation (amount, composition, timing) should be an important consideration in the utilization of experimental infection models. Furthermore, optimization of the patients intravascular volume status during sepsis may have important effects on immune responses, in addition to improving hemodynamic variables.

Utility of inframalleolar arterial bypass grafting

Sixty-five patients received 68 inframalleolar arterial grafts for severe rest pain, foot ulceration, or gangrene. Patients were elderly with an average age of 68 years (median 72); most had several operative risk factors. Reversed saphenous vein grafts were used early, but most conduits were in situ vein grafts. The recipient vessel was the dorsalis pedis artery in 39 patients, the posterior tibial in 27, and tarsal branches in two. Preoperative angiography was routinely performed with biplanar and digital arterial techniques, but in nearly a third a suitable bypass vessel was not identified preoperatively. When vessels were identified there was usually only a single patent artery suitable for bypass grafting below the knee. There were five postoperative deaths (7.6%). Eight grafts (11%) required early revision for thrombosis or retained valve, and six were salvaged and remained patent. Poor vein quality appeared responsible for the two early failures. Six late graft occlusions occurred from 4 to 39 months (mean 14 months). Three of these patients had no recurrence of their ulceration, but two required amputation, and one has continued rest pain. One additional amputation was required in a patient with a patent graft. Eleven late deaths (16%) occurred (nine with patent grafts) primarily of cardiac causes.

Mechanisms of Direct Peritoneal Resuscitation–Mediated Splanchnic Hyperperfusion Following Hemorrhagic Shock

Conventional resuscitation (CR) from hemorrhagic shock causes a persistent and progressive splanchnic vasoconstriction and hypoperfusion despite hemodynamic restoration with intravenous fluid therapy. Adjunctive direct peritoneal resuscitation (DPR) with a clinical peritoneal dialysis solution instilled into the peritoneal cavity has been shown to restore splanchnic tissue perfusion, down-regulate the gut-derived exaggerated systemic inflammatory response, promote early fluid mobilization, and improve overall outcome. This study was conducted to define the molecular mechanisms of DPR-induced gut hyperperfusion after hemorrhagic shock. Male rats were bled to 50% baseline mean arterial pressure and resuscitated with the shed blood plus two volumes of saline (CR). In vivo videomicroscopy and Doppler velocimetry were used to assess terminal ileal microvascular diameters and blood flow. Direct peritoneal resuscitation animals received CR and topical application of a clinical glucose-based peritoneal dialysis solution (Delflex). Inhibitors, glibenclamide (K+ATP channels), N-monomethyl-L-arginine (L-NMMA) (nitric oxide synthase), 8-cyclopentyl-1,3-diprophylxanthine (DPCPX) (A1 adenosine receptor), tetrabutylammonium (K+Ca2+ channels), and mefenamic acid (cyclooxygenase) were topically applied (individually or in combination) with DPR according to protocol; BQ-123 (endothelin A receptor antagonist) and BQ-788 (endothelin B receptor antagonist) were used topically with CR to define the mechanism of post-CR vasoconstriction and hypoperfusion. Conventional resuscitation caused a persistent progressive intestinal vasoconstriction and hypoperfusion that can be abolished with endothelin antagonists. In contrast, adjunctive DPR caused an instantaneous sustained vasodilation and hyperperfusion. Glibenclamide or L-NMMA partially attenuated DPR-induced vasodilation, whereas the addition of DPCPX to the two inhibitors eliminated the dilation. Cyclooxygenase and K+Ca2+channels were not active in DPR-mediated microvascular effects. In conclusion, DPR improves splanchnic tissue perfusion by endothelium-dependent mechanisms mediated by activations of glibenclamide-sensitive K+ channels (KATP), adenosine A1 receptor subtype activation, and nitric oxide release. Direct peritoneal resuscitation preserves endothelial dilatory functions, thereby overriding any endothelium-derived constrictor response triggered by hemorrhagic shock and CR.

Lazaroids prevent acute cyclosporine-induced renal vasoconstriction.

BACKGROUND Cyclosporine (CsA)-induced nephrotoxicity may be due to intrarenal vasoconstriction and glomerular hypoperfusion. Several factors, including endothelin and prostanoids, are suggested mediators of this response. Recent evidence suggests that CsA leads to increased oxygen-derived free radical (ODFR) production and lipid peroxidation in renal tissue. Whether this leads to alterations in renal vessel reactivity is unclear. Lazaroids, such as U74389G, are radical-quenching antioxidants that inhibit ODFR-induced lipid peroxidation and may improve renal function after ischemia and reperfusion. We hypothesized that ODFRs contribute to CsA-induced alterations of the renal microcirculation. METHODS Rat hydronephrotic kidneys were studied by video microscopy. Interlobular arteriolar diameter and flow, afferent and efferent arteriolar diameters, and cardiac output were measured at 15-min intervals for 120 min. U74389G or its vehicle was infused 15 min before topical application of CsA to the kidney. The results were compared with U74389G alone and normal saline. RESULTS CsA administration caused renal microvascular vasoconstriction (10-25% below baseline) and hypoperfusion (35% below baseline). Both vasoconstriction and hypoperfusion were significantly attenuated by U74389G (5-8% and 20% below baseline, respectively). CONCLUSIONS Inhibition of lipid peroxidation by U74389G maintained renal blood flow during acute CsA administration. These data suggest that ODFRs are involved in the renal microvascular response to CsA. Inhibition of ODFR-induced lipid peroxidation may help prevent CsA-induced glomerular hypoperfusion. Lazaroids may prove an effective adjunct in reducing CsA-induced nephrotoxicity.

Role of muscle microvasculature during hyperdynamic and hypodynamic phases of endotoxin shock in decerebrate rats

Microcirculatory derangements in skeletal muscle could act to change cardiac output during endotoxemia. To explore this idea, we measured arteriole and venule responses to low-dose and high-dose endotoxemia in the rat cremaster muscle by direct in vivo videomicroscopy. Our data indicate that cardiac output increased in the low-dose group and decreased in the high-dose group. In both animal groups, a differential arteriolar response occurred to give small arteriole dilation and large arteriole constriction while venous diameters did not change. We conclude that: 1) changes in cardiac output during endotoxemia are not related to microvascular responses in skeletal muscle, and 2) the microvascular responses in skeletal muscle could be responsible for the decreased systemic vascular resistance during high cardiac output endotoxemia, but not for the elevated systemic vascular resistance during low cardiac output endotoxemia.

Nitric oxide mediates redistribution of intrarenal blood flow during bacteremia

The normal or hyperdynamic circulatory response during the early phases of the systemic septic response is associated with renal microvascular constriction and can result in renal dysfunction. Intrarenal redistribution of blood flow from the outer cortex to the medulla appears to account for decreased glomerular filtration in spite of normal or elevated renal blood flow, but the mechanisms of this response are not well described. Nitric oxide is recognized as an important regulator of regional blood flow during both normal and pathologic conditions including sepsis, and we hypothesized that alterations in nitric oxide contribute to redistribution of renal blood flow during sepsis. The current study used laser Doppler fluximetry and clearance of p-aminohippuric acid (effective renal plasma flow, ERPF) to study intrarenal distribution of blood flow during basal conditions and during normodynamic Escherichia coli bacteremia, with and without inhibition of nitric oxide. Inhibition of nitric oxide in normal animals resulted in a decrease in ERPF (-19%) with a decrease in cortical flux (-39%) without alteration of medullary flux. Bacteremia resulted in a decrease in cortical flow (-17%), an increase in medullary flow (36%), and a modest reduction (-9%) in ERPF. Inhibition of nitric oxide synthase during bacteremia worsened cortical flow (-43%), reversed the increase in medullary flux (-42%), and further impaired ERPF (-28%). These data suggest that nitric oxide regulates renovascular tone during normal conditions and bacteremia, and indicate that it is a prime mediator of intrarenal redistribution of blood flow during sepsis.