Starvation alters the activity and mRNA level of glutaminase and glutamine synthetase in the rat intestine

Effects of postprandial starvation on mRNA expression of endocrine-, amino acid and peptide transporter-, and metabolic enzyme-related genes in zebrafish (Danio rerio)

The goal of this study was to systematically evaluate the molecular activities of endocrine-, amino acid and peptide transporters-, and metabolic enzyme-related genes in 35-day-old mixed-sex zebrafish (Danio rerio) after feeding . Zebrafish with initial body weights ranging from 9 to 11 mg were fasted for 384 h in a controlled indoor environment. Fish were sampled at 0, 3, 6, 12, 24, 48, 96, 192, and 384 h after fed. Overall, the present study results show that the regulatory mechanism that insulin-like growth factor I negative feedback regulated growth hormone is conserved in zebrafish, as it is in mammals, but that regulation of growth hormone receptors is highly intricate. Leptin and cholecystokinin are time-dependent negative feedback signals, and neuropeptide Y may be an important positive neuropeptide for food intake in zebrafish. The amino acid/carnitine transporters B(0,+) (ATB(0,+)) and broad neutral (0) amino acid transporter 1(B(0)AT1) mRNA levels measured in our study suggest that protein may be utilized during 24-96 h of fasting in zebrafish. Glutamine synthetase mRNA levels were downregulated, and glutamate dehydrogenase, alanine aminotransferase, aspartate transaminase, and trypsin mRNA levels were upregulated after longtime fasting in this study. The mRNA expression levels of fatty acid synthetase decreased significantly (P < 0.05), whereas those of lipoprotein lipase rapidly increased after 96 h of fasting. Fasting activated the expression of glucose synthesis genes when fasting for short periods of time; when fasting is prolonged, the mRNA levels of glucose breakdown enzymes and pentose phosphate shunt genes decreased.

The protective effects of riluzole on manganese-induced disruption of glutamate transporters and glutamine synthetase in the cultured astrocytes

Chronic exposure to excessive manganese (Mn) can lead to manganism, a type of neurotoxicity accomplished with extracellular glutamate (Glu) accumulation. To investigate this accumulation, this study focused on the role of astrocyte glutamate transporters (GluTs) and glutamine synthetase (GS), which have roles in Glu transport and metabolism, respectively. And the possible protective effects of riluzole (a glutamatergic modulator) were studied in relation to Mn exposure. At first, the astrocytes were exposed to 0, 125, 250, and 500 μM MnCl(2) for 24 h, and 100 μM riluzole was pretreated to astrocytes for 6 h before 500 μM MnCl(2) exposure. Then, [(3)H]-glutamate uptake was measured by liquid scintillation counting; Na(+)-K(+) ATPase and GS activities were determined by a colorimetric method; glutamate/aspartate transporter (GLAST), glutamate transporter-1 (GLT-1), and GS mRNA expression were determined by RT-PCR and protein levels were measured by western blotting. The results showed that Mn inhibited Glu uptake, Na(+)-K(+) ATPase and GS activities, GLAST, GLT-1, and GS mRNA, and protein in a concentration-dependent manner. And they were significantly higher for astrocytes pretreated with 100 μM riluzole than the group exposed to 500 μM MnCl(2). The results suggested that Mn disrupted Glu transport and metabolism by inhibiting GluTs and GS. Riluzole activated protective effects on enhancing GluTs and GS to reverse Glu accumulation. In conclusion, Mn exposure results in the disruption of GLAST, GLT-1, and GS expression and function. Furthermore, riluzole attenuates this Mn toxicity.

Berberine attenuates lipopolysaccharide-induced impairments of intestinal glutamine transport and glutaminase activity in rat

Berberine was reported to protect against the intestinal injury and improve the survival rate in sepsis, and glutamine deficiency was considered to be correlated with mortality in sepsis. We found that berberine pretreatment ameliorated lipopolysaccharide-induced direct intestinal injury and mucosal hypoplasia and attenuated impairments of intestinal glutamine transport and glutaminase activity, B(0)AT1 mRNA and protein expressions, and glutaminase protein expression. These findings showed the first time that berberine pretreatment could improve intestinal recovery and attenuate the impairment of glutamine transport and glutaminase activity in rat sepsis. This might be one of the mechanisms for the beneficial effect of berberine on sepsis.

Regulation of muscular glutamate metabolism by high-protein diet in broiler chicks

The major taste active component, glutamate (Glu), improves the taste of meat. In this study, we investigated the effect of a short-term high-protein (HCP) diet on the intramuscular free Glu content to improve the taste of meat. Furthermore, we elucidated how the muscle free Glu content was controlled by the HCP diet. Chicks (14 days old) were fed the control diet or HCP diet for 10 days. Plasma and muscle free amino acid concentrations, and activity and messenger RNA (mRNA) expression of muscle enzymes related to Glu metabolism were determined. Muscle free Glu content was increased (P < 0.01) by 51%. Activity and mRNA expression of glutaminase (GA), which is one of the major Glu-related enzymes, were significantly decreased (P < 0.05) in the HCP group because of feedback inhibition. The mRNA expression of lysine α-ketoglutarate reductase (LKR), which is the enzyme involved in lysine (Lys) degradation and Glu production, was significantly increased (P < 0.001) in the HCP group. These results suggest that short-term dietary HCP feeding is an effective treatment for improving the taste of meat. Furthermore, our results suggest that the free Glu content in muscle is regulated by GA and LKR.

The protective effect of riluzole on manganese caused disruption of glutamate-glutamine cycle in rats

The mechanisms underlying the disruption of glutamate-glutamine cycle (Glu-Gln cycle) in manganism are still unknown. To approach the concrete mechanisms, the rats were i.p. injected with different doses of MnCl(2) (0, 8, 40, and 200 micromol/kg), and the levels of Mn, Glu, and Gln, the morphological and ultrastructural changes, activities of Na(+)-K(+)-ATPase, GS, and PAG, mRNA and protein expression of GS, GLAST, and GLT-1 in the striatum were investigated. In addition, the effect of 21.35 micromol/kg riluzole (Na(+) channel blocker) was studied at 200 micromol/kg MnCl(2). It was observed that (1) Mn and Glu levels and PAG activity increased; (2) many pathological changes occurred; (3) Gln levels, Na(+)-K(+)-ATPase and GS activities, and GS, GLAST, and GLT-1 mRNA and protein expression inhibited, does dependently. Furthermore, the research indicated that pretreatment of riluzole reversed toxic effects of MnCl(2) significantly. These results suggested that Glu-Gln cycle was disrupted by Mn exposure dose dependently; riluzole might antagonize Mn neurotoxicity.

Protective effects of bombesin on endotoxin-induced intestinal injury in rats

AIM: To investigate the protective effects of bombesin on endotoxin-induced intestinal injury in SD rats.

METHODS: A total of 96 SD rats were divided randomly into 3 groups. Group A was served as control group and administrated normal saline (1 mL/kg). Group B was the model group and treated with LPS (intraperitoneally, 5 mg/kg). Rats in Group C were firstly treated with bombesin (subcutaneously, 10 μg/kg, three times a day) for 7 d, and then injected with LPS intraperitoneally. Following LPS administration, intestinal tissues were collected at 2, 6, 24 h separately for Malondialdehyde (MDA) and GSH-PX study, and blood samples were collected for IL-6 and IL-10 study.

RESULTS: According to the macroscopic and microscopic findings, group C showed significantly lower damage and inflammation compared with group B. At 2, 6, 24 h, the intestinal MDA levels were significantly lower in group C than in group B (3.4092 ± 0.7765 vs 8.4359 ± 0.5589; 4.6588 ± 0.3311 vs 10.9375 ± 1.00094; 4.6324 ± 0.2278 vs 10.5074 ± 1.0142, all P < 0.01), but still higher than that in group A. The intestinal GSH-PX levels were significantly higher in group C than in group B (2 h: 1231.83 ± 74.68 vs 766.67±57.94; 6 h: 2113.34 ± 81.42 vs 749.09 ± 56.72; 24 h: 1950.48 ± 72.74 vs 785.62 ± 62.43, all P < 0.01). At 2, 24 h, the IL-6 levels were lower in group C than in group B (2 h: 553.70 ± 23.03 vs 652.81 ± 27.09; 6 h: 494.52 ± 40.68 vs 606.68 ± 43.60; 24 h: 571.56 ± 52.54 vs 602.73 ± 25.19, all P < 0.01), but still higher than in group A. At every time, the IL-10 levels were higher in group C than in group B (2 h: 601.58 ± 30.65, vs 478.76 ± 23.49; 6 h: 653.77 ± 35.75 vs 469.35 ± 11.27; 24 h: 714.04 ± 29.55 vs 635.17 ± 29.15, all P < 0.01).

CONCLUSION: Bombesin has the function of anti-oxidation and anti-inflammation by increasing the levels of GSH-PX and IL-10 and decreasing the levels of MDA and IL-6.

Glutamine gluconeogenesis in the small intestine of 72 h-fasted adult rats is undetectable

Recent reports have indicated that 48-72 h of fasting, Type 1 diabetes and high-protein feeding induce gluconeogenesis in the small intestine of adult rats in vivo. Since this would (i) represent a dramatic revision of the prevailing view that only the liver and the kidneys are gluconeogenic and (ii) have major consequences in the metabolism, nutrition and diabetes fields, we have thoroughly re-examined this question in the situation reported to induce the highest rate of gluconeogenesis. For this, metabolically viable small intestinal segments from 72 h-fasted adult rats were incubated with [3-13C]glutamine as substrate. After incubation, substrate utilization and product accumulation were measured by enzymatic and NMR spectroscopic methods. Although the segments utilized [13C]glutamine at high rates and accumulated 13C-labelled products linearly for 30 min in vitro, no substantial glucose synthesis could be detected. This was not due to the re-utilization of [13C]glucose initially synthesized from [13C]glutamine. Arteriovenous metabolite concentration difference measurements across the portal vein-drained viscera of 72 h-fasted Wistar and Sprague-Dawley rats clearly indicated that glutamine, the main if not the only gluconeogenic precursor taken up, could not give rise to detectable glucose production in vivo. Therefore we challenge the view that the small intestine of the adult rat is a gluconeogenic organ.

Effects of enteral glutamine supplement on endotoxin translocation and mucosal immune barrier in starved rats

AIM: To investigate the changes in intestinal structure and function as well as the effect of enteral glutamine (GLN) supplement on the endotoxin translocation and immunological function in starved rats.

METHODS: Ninety male Sprague Dawley rats were randomly divided into 3 groups: normal control group (n = 10), starved group (group A, n = 40) and GLN group (group B, n = 40). The rats were sacrificed 3, 5, 7 and 9 d after starvation, respectively. Blood samples were collected from portal vein for the detection of plasma endotoxin and tissue samples removed from ileocecum were observed under light microscope for morphological changes. A contrasting study on the expression of secretary immunoglobulin A (sIgA) and the numbers of CD4⁺, CD8⁺ T lymphocytes were also performed between control group and other groups by immunohistochemical staining method.

RESULTS: The atrophy of intestinal mucosa and villa were observed 3 d after starvation in group A, with the degeneration, necrosis, and shedding of partial mucosal epithelial cells. The changes were gradually deteriorated till the 9^th day after starvation. Those pathological changes were lighter in group B than those in group A on the 3^rd day after starvation and restored to normal on the 5^th day. As the starvation time prolonged, the atrophy, degeneration and necrosis of the mucosal epithelial cells appeared again in group B, but were still lighter than those in group A. The levels of endotoxin were significantly higher 3, 5, 7 and 9 d after starvation in both group A and B than those in the controls, and there were also marked differences between group B and A (322.4 ± 65.1, 389.4 ± 32.6, 464.4 ± 76.6, 413.7 ± 67.2 EU/L vs 527.1 ± 74.9, 546.3 ± 65.7, 623.9 ± 85.9, 587.5 ± 140.8 EU/L, all P < 0.01). The expression of sIgA and the numbers CD4⁺ and CD8⁺ T lymphocytes in intestinal mucosa were reduced significantly in group A and B, in compared with those in the controls (P < 0.05 or P < 0.01), and there were higher levels of sIgA and CD4⁺ and CD8⁺ T lymphocytes in group B than those in group A (P < 0.01).

CONCLUSION: The structure of intestinal mucosa is damaged in the earlier stage of starvation in rats, accompanied by endotoxin translocation and dysfunction of intestinal mucosal immune barrier. Early enteral nourishment of glutamine is helpful for inhibiting endotoxin translocation and improve immune function of intestinal mucosa.

Effect of a short-term fast on intestinal disaccharidase activity and villus morphology of piglets suckling insulin-like growth factor-I transgenic sows1

The objectives of this study were to use transgenic sows that overexpress IGF-I in milk to investigate the effect of a short-term fast on piglet intestinal morphology and disaccharidase activity and to determine how milk-borne IGF-I influences the response to fasting. After farrowing, litters were normalized to 10 piglets. On d 6, piglets (n = 30) suckling IGF-I transgenic (TG) sows and piglets (n = 30) suckling nontransgenic sows (control) were assigned randomly to three treatments: fed piglets (0 h), which remained with the sow until euthanized on d 7, or fasted piglets, which were removed from the sow at either 6 or 12 h before euthanasia on d 7. Serum IGF-I and IGFBP, intestinal weight and length, jejunal protein and DNA content, disaccharidase activity, and villus morphology were measured. Fasting for 12 h resulted in a negative weight change between d 6 and 7 (quadratic response to fasting; P < 0.001). Piglets suckling TG sows tended to have greater intestinal length (P = 0.068), but no effect of IGF-I overexpression was noted for intestinal weight. Fasting, however, resulted in linear (P < 0.001) and quadratic (P = 0.002) decreases in intestinal weight. Serum IGF-I did not differ between control and TG sows, but decreased linearly (P = 0.003) with fasting. Serum IGFBP-4 decreased (linear and quadratic; P < or = 0.02) with fasting, whereas IGFBP-1 increased quadratically (P < 0.001) with fasting. Jejunal villus height, width, and crypt depth were all increased with fasting (linear and quadratic; P < 0.04). Disaccharidase activity was not affected by fed state; however, piglets suckling TG sows had greater jejunal lactase-phlorhizin hydrolase (P < 0.01) and sucrase-isomaltase (P = 0.02) activities than control piglets. In summary, intestinal weight, villus morphology, serum IGF-I, serum IGFBP-1 and -4, and piglet BW change were altered (P < or = 0.02) in response to fasting. Thus, the duration of food deprivation before euthanization should be considered when designing experiments to assess intestinal development or the IGF axis, as the magnitude of differences between the fed and fasted state may exceed those expected as a result of experimental treatment.

Exercise Restores Immune Cell Function in Energy-Restricted Rats

OBJECTIVE

To evaluate the effect of chronic moderate-intensity exercise upon the alterations of immune system cell function induced by energy restriction.

METHODS

Forty male Wistar rats were randomly assigned to the following groups: sedentary animals fed ad libitum (SF, N = 10) or submitted to energy restriction (SER, N = 10, receiving 50% of the mean amount of chow consumed by SF); and trained animals fed ad libitum (TF, N = 10) or submitted to energy restriction (TER, N = 10), who exercised on a treadmill (at 60-65%VO(2max) 5 d.wk(-1) for 10 wk(-1), after 30 d under the restriction protocol. The incorporation of [2-(14)C]-thymidine by lymphocytes obtained from the spleen and mesenteric lymph nodes, plasma glucose and glutamine concentration, and cytokine production by cells cultivated in the presence of glutamine were measured in all groups, 24 h after the last exercise session. Two-way ANOVA and Tukey's posttest were employed for the statistical analysis.

RESULTS

Training induced an increase in the proliferative response and in the production of gamma-interferon and interleukin-1 (P < 0.05) in cells from the spleen and lymph nodes of SER, in which these parameters were diminished when compared with SF (P < 0.05). SER spleen and lymph node cells produced more TNF (26 and 42%, respectively) and IL-2 (49 and 42%, respectively) than SF. The Th1-like diversion of the immune response observed in SER persisted after training. Partial recovery of the decreased SER plasma glutamine concentration and muscle glutamine synthase mRNA was observed.

CONCLUSIONS

Training induced the recovery of the proliferative capacity of lymphocytes from SER, probably due to the partial restoration of plasma glutamine levels, but did not interfere with the diversion towards a Th1-type immune response induced by food restriction.

Induction of control genes in intestinal gluconeogenesis is sequential during fasting and maximal in diabetes

We studied in rats the expression of genes involved in gluconeogenesis from glutamine and glycerol in the small intestine (SI) during fasting and diabetes. From Northern blot and enzymatic studies, we report that only phosphoenolpyruvate carboxykinase (PEPCK) activity is induced at 24 h of fasting, whereas glucose-6-phosphatase (G-6-Pase) activity is induced only from 48 h. Both genes then plateau, whereas glutaminase and glycerokinase strikingly rebound between 48 and 72 h. The two latter genes are fully expressed in streptozotocin-diabetic rats. From arteriovenous balance and isotopic techniques, we show that the SI does not release glucose at 24 h of fasting and that SI gluconeogenesis contributes to 35% of total glucose production in 72-h-fasted rats. The new findings are that 1) the SI can quantitatively account for up to one-third of glucose production in prolonged fasting; 2) the induction of PEPCK is not sufficient by itself to trigger SI gluconeogenesis; 3) G-6-Pase likely plays a crucial role in this process; and 4) glutaminase and glycerokinase may play a key potentiating role in the latest times of fasting and in diabetes.

Enteral feeding and gut atrophy

PURPOSE OF REVIEW

Because of the hypothesis that enteral feeding prevents intestinal mucosal atrophy and bacterial translocation, when fasting or malnutrition is present, nutrition support by the enteral route is usually preferred, if it is available. If nutrients are provided only parenterally intestinal mucosal mass falls dramatically in rats, but the relevance of this finding to humans has not been documented. This article reviews findings in the last 2 years relating to this dilemma.

RECENT FINDINGS

Most work continues to be done in rats and pigs, two species that demonstrate mucosal atrophy with fasting. The earlier demonstration of effects of administration of hormones and glutamine have been corroborated, but proper controls for hormones (related peptides) or glutamine (most importantly glutamate) have usually not been included. In humans mucosal atrophy does not occur except modestly (approximately 10% decrease in thickness) in some reports during catabolic conditions, such as in critical-care units. Even so, no evidence for reversal by enteral feeding has as yet been provided. On the other hand, evidence for specific gene adaptation with or without mucosal atrophy has begun to appear in animals and humans.

SUMMARY

The focus on mucosal atrophy has obscured the adaptation that may occur simultaneously to minimize the atrophy. Attention to gene adaptation during fasting and malnutrition may provide evidence, in future, for appropriate therapeutic interventions.