Effects of a diabetes-specific enteral nutrition on nutritional and immune status of diabetic, obese, and endotoxemic rats: interest of a graded arginine supply

Chronic intermittent hypoxia due to obstructive sleep apnea slightly alters nutritional status: a pre-clinical study

Obstructive sleep apnea syndrome (OSAS) is associated with chronic intermittent hypoxia (cIH) that causes disturbances in glucose and lipid metabolism. Animals exposed to cIH show lower body weight and food intake, but the protein-energy metabolism has never been investigated. Here, to address the gap, we studied the impact of cIH on nutritional status in rats. A total of 24 male Wistar rats were randomized into 3 groups (n = 8): a control group (Ctrl), a cIH group (cIH) exposed to cIH (30 s 21-30 s 5% fraction of inspired oxygen, 8 h per day, for 14 days), and a pair-fed group (PF) exposed to normoxia with food intake adjusted to the intake of the cIH group rats with anorexia. Body weight and food intake were measured throughout the study. After 14 days, the rats were euthanized, the organs were collected, weighed, and the liver, intestine mucosa, and muscles were snap-frozen to measure total protein content. Food intake was decreased in the cIH group. Body weight was significantly lower in the cIH group only (-11%, p < 0.05). Thymus and liver weight as well as EDL protein content tended to be lower in the cIH group than in the Ctrl and PF groups. Jejunum and ileum mucosa protein contents were lower in the cIH group compared to the PF group. cIH causes a slight impairment of nutritional status and immunity. This pre-clinical work argues for greater consideration of malnutrition in care for OSAS patients. Further studies are warranted to devise an adequate nutritional strategy.

L-Arginine supplementation inhibits the growth of breast cancer by enhancing innate and adaptive immune responses mediated by suppression of MDSCs in vivo

Background

L-Arg is involved in many biological activities, including the activation of T cells. In breast cancer patients, L-Arg is depleted by nitric oxide synthase 2 (NOS2) and arginase 1 (ARG-1) produced by myeloid-derived suppressor cells (MDSCs). Our aim was to test whether L-Arg supplementation could enhance antitumor immune response and improve survivorship in a rodent model of mammary tumor.

Methods

Tumor volumes in control and L-Arg treated 4 T1 tumor bearing (TB) BALB/c mice were measured and survival rates were recorded. The percentages of MDSCs, dendritic cells (DCs), regulatory T cells (Tregs), macrophages, CD4⁺ T cells, and CD8⁺ T cells were examined by flow cytometry. Additionally, levels of IL-10, TNF-α, and IFN-γ were measured by enzyme-linked immunosorbent assay (ELISA) and nitric oxide (NO) levels were measured by the Griess reaction. IFN-γ, T-bet, Granzyme B, ARG-1 and iNOS mRNA levels were examined by real-time RT-PCR.

Results

L-Arg treatment inhibited tumor growth and prolonged the survival time of 4 T1 TB mice. The frequency of MDSCs was significantly suppressed in L-Arg treated TB mice. In contrast, the numbers and function of macrophages, CD4⁺ T cells, and CD8⁺ T cells were significantly enhanced. The IFN-γ, TNF-α, NO levels in splenocytes supernatant, as well as iNOS, IFN-γ, Granzyme B mRNA levels in splenocytes and tumor blocks were significantly increased. The ARG-1 mRNA level in tumor blocks, the frequency of Tregs, and IL-10 level were not affected.

Conclusion

L-Arg supplementation significantly inhibited tumor growth and prolonged the survival time of 4 T1 TB mice, which was associated with the reduction of MDSCs, and enhanced innate and adaptive immune responses.

In vitro anti-inflammatory effects of citrulline on peritoneal macrophages in Zucker diabetic fatty rats

In type 2 diabetes (T2D) macrophage dysfunction increases susceptibility to infection and mortality. This may result from the associated decreased plasma concentration of arginine, an amino acid that plays an important role in immunity. In vitro, increasing arginine availability leads to an improvement in macrophage function; however, arginine supplementation in diabetic obese patients may be detrimental. The aim of the present study was to assess in vitro whether citrulline, an arginine precursor, could replace arginine in the regulation of macrophage function under a condition of diabetes and obesity. Peritoneal macrophages from diabetic obese or lean rats were incubated for 6 h in an arginine-free medium, in the presence of increasing citrulline concentrations (0·1, 0·5, 1 or 2 mmol/l). Cytokine and NO production was determined. Peritoneal macrophages from either lean or diabetic obese rats produced NO, and at higher levels in the cells from lean rats. In diabetic obese rats, TNF-α production decreased with increasing citrulline concentrations, but was higher than that in the cells from lean rats. In contrast, IL-6 production increased with increasing citrulline concentrations. The present experiment shows that citrulline is effectively used for NO production and regulates cytokine production in macrophages from diabetic obese rats. This effect warrants in vivo evaluation in T2D-related inflammation.