Jan Rounds

Glutamine preserves liver glutathione after lethal hepatic injury.

Glutathione (GSH) is a major antioxidant that protects tissues from free radical injury. Glutamine augments host defenses and may be important in GSH synthesis. Acetaminophen toxicity causes hepatic GSH depletion and hepatic necrosis. The authors hypothesized that glutamine-supplemented nutrition would enhance liver GSH stores and diminish hepatic injury and death after acetaminophen overdose. Wistar rats received either a standard total parenteral nutrition (TPN) solution (STD) or an isocaloric, isonitrogenous glutamine-supplemented solution (GLN). On the 5th day of feeding, animals were given acetaminophen (400 mg/kg intraperitoneally) and then killed at various time points/Standard TPN solution animals had a rapid depletion of hepatic glutathione, whereas GLN animals were resistant to this drop and rapidly repleted hepatic GSH stores. Glutamine-supplemented animals maintained higher plasma glutamine concentrations, had lesser elevations in hepatic enzymes, and sustained significantly fewer complications compared with STD animals. The authors conclude that glutamine-supplemented nutrition preserves hepatic glutathione, protects the liver, and improves survival during acetaminophen toxicity. Glutamine may augment host defenses by enhancing antioxidant protection.

Improving Nutritional Screening of Hospitalized Patients: The Role of Prealbumin

BACKGROUND Limited resources prevent hospitals from having all patients formally evaluated by a nutrition expert. Thus, hospitals rely on nutrition-screening tools to identify malnourished patients. The purpose of this study was to determine the effectiveness of a nutrition-screening protocol, prealbumin (PAB), retinol binding protein (RBP), and albumin (ALB) in identifying malnourished hospitalized patients. METHODS A nutrition screening protocol was prospectively used in medical and surgical patients and consisted of a nurse administering a questionnaire to patients and requesting formal evaluation by a registered dietitian (RD) only if nutritional issues were identified. Patients also had ALB, PAB, and RBP drawn, which were used to both screen and identify the malnourished. PAB, RBP, and ALB were compared as predictors of RD classification of patient nutritional status. RESULTS The nutrition-screening protocol classified 104 of 320 patients (33%) as malnourished. However, 43% of the patients were not deemed at nutritional risk according to this protocol and therefore did not receive RD assessment. PAB was a significant predictor of RD-determined nutritional status (p < .05), whereas RBP and ALB were not. PAB screening/assessment identified 50% (162/320) of the patients as being malnourished. Notably, 50% of the patients (71 of 142) who were not evaluated by an RD were identified as malnourished using PAB criteria. The nutrition-screening protocol took 1.2 days longer to determine malnourishment compared with PAB (p = .0021). CONCLUSIONS Use of screening questionnaires may miss or delay identification of malnourished patients. PAB screening/assessment may improve identification of those patients requiring nutrition intervention and thus enhance the care of hospitalized individuals.

Diurnal rhythmicity in glucose uptake is mediated by temporal periodicity in the expression of the sodium-glucose cotransporter (SGLT1)

BACKGROUND Intestinal transport exhibits distinct diurnal rhythmicity. Understanding the mechanisms behind this may reveal new therapeutic strategies to modulate intestinal function in disease states such as diabetes and obesity, as well as short bowel syndrome. Although diurnal rhythms have been amply documented for several intestinal transporters, the complexity of transepithelial transport has precluded definitive attribution of rhythmicity in glucose uptake to a single transporter. To address this gap, we assessed temporal changes in glucose transport mediated by the Na(+)/glucose cotransporter SGLT1. METHODS SGLT1 expression was assessed at 4 times during the day: ZT3, ZT9, ZT15, and ZT21 (ZT, Zeitgeber time; lights on at ZT0; n = 8/ time). SGLT1 activity, which is defined as glucose uptake sensitive to the specific SGLT1 inhibitor phloridzin, was measured in everted intestinal sleeves. Changes in Sglt1 expression were assessed by real-time polymerase chain reaction (PCR) and immunoblotting. RESULTS Glucose uptake was significantly higher at ZT15 in jejunum (P < 0.05 vs ZT3). Phloridzin significantly reduced glucose uptake and completely abolished its rhythmicity. Sglt1 mRNA levels were significantly greater at ZT9 and ZT15 in jejunum and ileum, respectively (P < 0.05 vs ZT3), whereas SGLT1 protein levels were significantly greater at ZT15 in jejunum (P < 0.05 vs ZT3). CONCLUSIONS Our results definitively link diurnal changes in intestinal glucose uptake capacity to changes in both SGLT1 mRNA and protein. These findings suggest that modulation of transporter expression would enhance intestinal function and provide an impetus to elucidate the mechanisms that underlie diurnal rhythmicity in transcription. Modulation of intestinal function would benefit the management of malnutrition as well as diabetes and obesity.

Metabolic responses to interleukin-1: centrally and peripherally mediated.

OBJECTIVE The purpose of this study was to differentiate between the catabolic effects of interleukin-1 (IL-1) when infused into the central nervous system or into the periphery. SUMMARY BACKGROUND DATA After injury and infection, IL-1 has been found in the central nervous system. Chronic intracerebrovascular infusion of IL-1 produces protein catabolism, anorexia, and fever. However, IL-1 may act directly on liver and bone marrow to elicit metabolic responses. Although IL-1 is thought to be involved in a number of metabolic responses associated with injury-inflammation, the sites of action are unclear. METHODS Rats were implanted with chronic infusion pumps and received diluent or three doses of IL-1 infused subcutaneously for 6 days, and a variety of response variables were measured. In a second study, doses were adjusted so that similar systemic catabolic responses were obtained from peripheral and intracerebroventricular infusion of IL-1. The acute-phase responses then were compared in the two groups of animals receiving IL-1 by different routes. RESULT Subcutaneously infused IL-1 elicited catabolic responses in a dose-response manner. Similar catabolic responses were achieved by infusing one tenth of the dose of IL-1 given subcutaneously into the central nervous system. Although similar systemic responses (protein catabolism, anorexia, fever, and weight loss) were observed with both routes of infusion, the subcutaneous infusion produced a much greater lymphocytosis, elevation in acute-phase reactants, and fall in serum iron and albumin. CONCLUSIONS The IL-1 appears to have different effects depending on the site of production and site of action. Regionalization of signal proteins such as IL-1 should be taken into consideration when devising specific anticytokine treatment strategies.

Glucagon-like peptide 2 is an endogenous mediator of postresection intestinal adaptation.

BACKGROUND After massive small bowel resection, the remnant intestine undergoes compensatory adaptation. We tested the hypothesis that glucagon-like peptide-2 (GLP-2) is an endogenous mediator of postresection intestinal adaptation. METHODS Rats were allocated to 1 of 4 groups: groups 1 and 2 rats underwent mid-small bowel transection and reanastomosis; groups 3 and 4 rats underwent 75% mid-small bowel resection and reanastomosis. Groups 2 and 4 rats were administered 1.8 mg of antirat GLP-2 antibody twice daily beginning immediately after the surgical procedure; groups 1 and 3 rats were administered rabbit serum (control). Ileal specimens were harvested on postoperative day 7. RESULTS Ileal mucosa from group 3 animals displayed morphologic and proliferative indices of adaptation. Each of these indices of adaptation was inhibited by GLP-2 immunoneutralization (group 4). Morphologic and proliferative parameters in the ileum from animals that had undergone transection with reanastomosis were unaffected by GLP-2 immunoneutralization. CONCLUSIONS These results suggest that GLP-2 is an endogenous mediator of postresection intestinal adaptation.

Parenteral Glutathione Monoester Enhances Tissue Antioxidant Stores

Glutathione (GSH) is a potent endogenous antioxidant that protects major organs from oxidant injury. However, present nutrition regimens may inadequately support tissue stores of this tripeptide during critical illness. To determine whether GSH reserves can be enhanced in vivo with intravenous (IV) supplements, rats underwent central venous catheterization, were given chow and water ad libitum during a 2-day recovery period, and were then randomized to receive one of three treatments as an IV bolus: (1) dextrose, (2) glutathione (GSH), or (3) glutathione monoethyl ester. GSH monoethyl ester is transported into cells more easily than is GSH. Tissue and plasma samples were analyzed for GSH at 2 and 4 hours after drug administration. Liver, renal, and ileal mucosal GSH were significantly increased in the GSH-monoethyl ester rats compared with dextrose-treated animals. In addition, plasma GSH was dramatically increased after monoester injection. In contrast, GSH administration depressed liver GSH stores and did not significantly affect GSH concentration in the other organs analyzed. Plasma GSH concentration was elevated 2 hours after GSH administration. We conclude that: (1) the monoethyl ester of glutathione can be used in vivo to enhance tissue and plasma GSH concentration and (2) IV GSH administration does not significantly increase tissue GSH levels and may paradoxically depress hepatic GSH in normal rats. Because the malnourished and critically ill are likely to have depleted GSH stores, nutrition strategies that include the provision of GSH monoester may lend additional support to those organs that are at risk for injury from oxygen free radicals during catabolic states.

Glutamine prevents pancreatic atrophy and fatty liver during elemental feeding.

Rats fed an elemental, enteral diet (STD) developed pancreatic atrophy and hepatic steatosis following 60% jejunoileal intestinal resection. An isonitrogenous, isocaloric 2 g/100 ml glutamine-supplemented diet (GLN) significantly attenuated the development of pancreatic atrophy and hepatic steatosis associated with elemental feeding. Pancreatic weight, DNA, and protein were 27, 22, and 40% increased, respectively, in GLN animals. The pancreata of all animals appeared normal by light and electron microscopic examination. GLN animals had 12% less total liver wet weight, 3% less hepatic water content, and 47% less hepatic fat relative to STD rats. Histologic examination of the liver revealed extensive centrilobular fatty vacuolization in STD animals whereas GLN rats had normal looking hepatic parenchyma. Glutamine should be viewed as an important nutrient in elemental diets with trophic effects on the pancreas and protective effects against the development of hepatic steatosis.

Capsaicin-sensitive vagal afferents modulate posttranscriptional regulation of the rat Na/glucose cotransporter SGLT1

INTRODUCTION the intestinal Na(+)/glucose cotransporter (SGLT1) displays rapid anticipatory diurnal rhythms in mRNA and protein expression. The vagus nerve has been implicated in the entrainment of some transporters. We aimed to clarify the influence of the vagus nerve on the diurnal entrainment pathway for SGLT1 and examine the role of vagal afferent fibers. METHODS male Sprague-Dawley rats were randomized to three groups, total subdiaphragmatic vagotomy, selective deafferentation of the vagus with capsaicin, or sham laparotomy. Postoperatively, animals were maintained in a 12-h light-dark cycle with food access limited to night. On the ninth postoperative day, animals were euthanized to harvest jejunal mucosa at 6-h intervals starting at 10 AM. Whole cell SGLT1 protein was measured by semiquantitative densitometry of immunoblots. Sglt1 and regulatory subunit RS1 mRNA was assessed by quantitative PCR. Fluorogold tracer technique was used to confirm adequacy of the vagotomy. RESULTS the diurnal rhythm in intestinal SGLT1, with a 5.3-fold increase in Sglt1 mRNA at 4 PM, was preserved in both vagotomy and capsaicin groups. However, the rhythmicity in SGLT1 protein expression (2.3-fold peak at 10 PM; P = 0.041) was abolished following either total vagotomy or deafferentation. Lack of change in RS1 mRNA suggests this is independent of the RS1 regulatory pathway. CONCLUSION SGLT1 transcription is independent of the vagus. However, dissociation of the protein rhythm from the underlying mRNA signal by vagotomy suggests the vagus may be involved in posttranscriptional regulation of SGLT1 in an RS1 independent pathway. Disruption following afferent ablation by capsaicin suggests this limb is specifically necessary.

Superiority of blood over saline resuscitation from hemorrhagic shock: a 31P magnetic resonance spectroscopy study.

OBJECTIVE To study the relation between blood and saline administration, postresuscitation hematocrit (Hct) level, and metabolic recovery after hemorrhagic shock. SUMMARY BACKGROUND DATA It is generally believed that crystalloid can be substituted, in whole or in part, for blood during resuscitation of hemorrhagic shock. This is based on the belief that Hct can be safely reduced but should not fall below a critical level. METHODS Male rats weighing 200 g were subjected to an isobaric hemorrhagic shock at a mean arterial pressure of 30 mmHg for 14 minutes, after which they were randomized to one of three resuscitation regimens. Control group (n = 36) were resuscitated by return of all shed blood. Mid-Hct (n = 39) and low-Hct (n = 60) groups were depleted of one third and one half of their circulating blood volumes, respectively, and were resuscitated with three times that volume of normal saline. Skeletal muscle intracellular energetics and pH were measured serially using 31P magnetic resonance spectroscopy at baseline, during shock, and after resuscitation. Arterial blood was sampled at the same time points. The number of surviving animals in each group at 24 hours was recorded. RESULTS After resuscitation, surviving rats in the low-Hct group demonstrated a greater consumption of high-energy phosphocreatine stores than did the other groups (control = 0.479 +/- 0.003, mid-Hct = 0.465 +/- 0.004, low-Hct = 0.457 +/- 0.007, mean +/- standard error of the mean; p < 0.01 low-Hct vs. other groups by analysis of variance). The rats that received saline resuscitation developed a relative intracellular acidosis (control = 7.29 +/- 0.02, mid-Hct = 7.25 +/- 0.02, low-Hct = 7.23 +/- 0.02; p < 0.05 controls vs. other groups by analysis of variance). At 24 hours, the death rates were significantly different among the groups: control = 1 of 36 rats (2.8%), mid-Hct = 6 of 39 (15.4%), and low-Hct = 14 of 60 (23.3%) (p < 0.05 by chi square analysis). CONCLUSION The oxygen-carrying capacity of resuscitation fluid has an important impact on intracellular metabolism and outcome.

Circadian variation in intestinal dihydropyrimidine dehydrogenase (DPD) expression: A potential mechanism for benefits of 5FU chrono-chemotherapy

BACKGROUND 5-fluorouracil (5FU) is associated with significant GI side-effects. Randomized trials have shown a 50% reduction in severe diarrhea with chrono-chemotherapy versus conventional regimens at similar doses. Dihydropyrimidine dehydrogenase (DPD) is the rate-limiting enzyme in 5FU breakdown. We hypothesized that DPD has a circadian expression pattern, accounting for the reduced GI side effects of chrono-modulated 5FU therapy. METHODS Fifty-one rats were killed at 3-hourly intervals over 24 hours. DPD and thymidylate synthase (TS) mRNA in jejunal and colonic mucosa were measured using qRT-PCR. Cosinor analysis was used for statistical comparison. RESULTS There was a significant circadian rhythm in the DPD mRNA expression in jejunum (1.7-fold, P < .001) and colon (1.5 fold, P < .01), with a peak expression in early sleep phase, and a trough at mid-wake cycle. TS also followed a circadian rhythm in jejunal mucosa with a peak at early rest phase. CONCLUSION This rhythm in DPD expression may explain the benefit of chrono-chemotherapy. The peak of DPD expression in sleep phase in rats corresponds to time for lower GI adverse effects in chrono-chemotherapy in human trials. We believe better understanding of this process allows development of novel approaches to optimize the timing of chemotherapy without the administrative challenges of chronotherapy.