Nutritional modulation of immune function

New lipids in enteral feeding

PURPOSE OF REVIEW

Lipid sources for enteral nutrition continue to be an exciting area of investigation. It is timely to review recent developments which have largely contributed to thrust enteral feeding into a new era.

RECENT FINDINGS

Although much more research needs to be done, there is a better understanding of the competitive relationships between n-6/n-3 fatty acids in conditions of metabolic and immune stress as well as in autoimmune and degenerative diseases. Although structured lipids are more completely absorbed and cleared, other more important clinical benefits need to be documented before they can be considered cost-effective. Immune enhancing formulas are the subject of controversy and some have been shown to be more effective than others. Enteral formulations with short-chain fatty acids are promising but more experimental work on the normal, and the sick colon is needed. Finally, there are a few isolated studies suggesting that enteral feeding with liposomes and with lipolytic products may have advantages when the digestive phase needs to be circumvented. The era of nutrigenomics, in which the effect of specific lipids on genes and proteins is being explored, is with us. We can look forward to nutrigenetics when the effect of genetic variation on the interaction between diet and disease will guide our practice.

SUMMARY

Clinicians already have access to lipid sources and formulations which allow them to individualize enteral feeding programs. More clinical and technological research needs to be carried out, however, before products can be tailored to produce optimal effects in specific conditions.

Nutritional support in critical care

Despite the key role of nutrition in health and the almost universal use of supplemental feeding in the ICU, there is a lack of high-quality evidence to guide clinical practice. Enteral nutrition is superior to TPN in almost all circumstances and most patients in the ICU can be fed successfully by this route. There is little evidence to support the use of special feeds and the role of immunonutrients remains unproven. Nutritional support cannot completely prevent the adverse effects of catabolic illness and overfeeding should be avoided.

Genomic interactions with disease and nutrition

The putative influence of genomic factors on the responsiveness to nutrient intake is a newly developed field of research. As well, there is growing interest for determining the interactions between nutrient, inflammation and aging and the possible impact on lifespan and disease development. Inflammation adversely affects health in many diseases with an inflammatory basis, such as atherosclerosis, obesity and type 2 diabetes mellitus. The metabolic effects of inflammation are mediated by pro-inflammatory cytokines. Metabolic effects include insulin insensitivity, hyperlipidemia, muscle protein loss and oxidant stress. Aging is also characterized by an increase in inflammatory stress and contains some of the hallmarks of inflammatory disease. It is also a phase of life when inflammatory diseases rise in incidence. Evidence is accumulating that the individual level of cytokine production is influenced by single nucleotide polymorphisms (SNPs) in cytokine genes. The combination of SNPs might control the relative level of inflammatory stress following inflammatory stimuli and diseases. These genomic characteristics might therefore influence lifespan, morbidity and mortality in diseases with an infectious or inflammatory basis.Recent studies indicate that genotypic factors may influence the effectiveness of such immunonutrients as anti-oxidants and n-3 polyunsaturated fatty acids. A better understanding of this aspect of nutrient gene interactions and of the genomic factors which influence the intensity of inflammation in disease will help in the targeting of nutritional therapy.

A randomized trial of the impact of multiple micronutrient supplementation on mortality among HIV-infected individuals living in Bangkok

OBJECTIVES

To examine the impact of high-dose multiple micronutrient supplementation on survival and disease progression among HIV-infected individuals in Thailand.

DESIGN

Randomized placebo-controlled trial.

METHODS

Four-hundred and eighty-one HIV-infected men and women living in and around Bangkok with CD4 cell counts in the range 50 x 10(6)- 550 x 10(6)/l were randomized to receive micronutrients or placebo for a period of 48 weeks. Trial participants were examined clinically 12-weekly and tested for CD4 cell count 24-weekly. A subset were tested for HIV plasma viral load at 48 weeks.

RESULTS

Seventy-nine (16%) trial participants were lost to follow-up and 23 (5%) died. The death rate was lower in the micronutrients arm with the mortality hazard ratios [95% confidence interval (CI)] of 0.53 (0.22-1.25; P = 0.1) overall and 0.37 (0.13-1.06; P = 0.052) and 0.26 (0.07-0.97; P = 0.03) among those with CD4 cell counts < 200 x 10(6)/l and < 100 x 10(6)/l respectively. There was no impact on CD4 cell count or plasma viral load.

CONCLUSIONS

Multiple micronutrient supplementation may enhance the survival of HIV-infected individuals with CD4 cell counts < 200 x 10(6)/l. This could have important public health implications in the developing world where access to antiretrovirals remains poor. The clinical findings need to be reproduced in other settings and the mechanism, which appears to be independent of change in CD4 cell count, merits further investigation.

Role of specific amino acids in nutritional support

Attempts have been made over the past decade to evaluate the role of specific amino acids in the nutritional support of surgical patients. Particular attention has been paid to the branched-chain amino acids, glutamine, and a collection of compounds that have been referred to as 'immunonutrients'. The present review provides an overview of the rationale behind the use of these nutrients and reviews information about their role in patients undergoing surgery. In general, although the use of immunonutrients enhances the nutritional status of patients, and although a number of clinical trials have claimed clinical advantages, there are still doubts about their clinical utility and concerns about their high cost.

Quantitative determination of free intracellular alpha-keto acids in neutrophils

For the first time, a procedure is described for the quantitative analysis of free alpha-keto acid content in human neutrophils (PMNs) relative to single cell number by reversed-phase fluorescence high-performance liquid chromatography. The procedure is minimally invasive and is unsurpassed in the quality of PMN separation, ease of sample preparation as well as sample stability. This method can satisfy the rigorous demands for an ultra-sensitive, comprehensive and rapid intracellular alpha-keto acid analysis in particularly for the surveillance of severe diseases as well as cellular or organ dysfunction.

Glutamine decreases lipopolysaccharide-induced IL-8 production in Caco-2 cells through a non-NF-kappaB p50 mechanism

Glutamine (Gln) supplementation has been shown to decrease production of pro-inflammatory cytokines by the human intestinal mucosa. The mechanism of this is poorly understood. We hypothesize that Gln down-regulates lipopolysaccharide (LPS)-stimulated pro-inflammatory cytokine production in Caco-2 cells by nuclear factor-kappa B (NF-kappaB). Caco-2 cells were incubated with different concentrations of Gln with or without methionine sulfoximine (MS, an inhibitor of glutamine synthetase) before stimulation with LPS. IL-6, IL-8, IL-10 and TNF-alpha protein and mRNA level were determined. NF-kappaB translocation was determined using an ELISA-based kit. IL-8 was the only detectable cytokine/chemokine. The largest amount of IL-8 was secreted by cells in the presence of MS with no Gln in the medium after exposure to LPS. LPS increased IL-8 production, peaking 10h after LPS administration. The addition of Gln (0.5 or 5.0mM) decreased IL-8 peptide and mRNA expression. LPS increased NF-kappaB nuclear translocation in the presence or absence of MS. Neither Gln nor MS altered NF-kappaB nuclear translocation. These results indicate that the lack of glutamine increases IL-8 production by Caco-2 cells after LPS stimulation. However, the glutamine-mediated decrease in LPS-stimulated IL-8 production is not associated with NF-kappaB p50 nuclear binding.

Immunonutrients and neonates

The gastrointestinal tract is the largest surface area of the body and the primary site for microorganisms, foreign antigens and toxins to gain entry to the host's internal milieu. The use of enteral feedings enriched with immune-enhancing ingredients is attracting considerable interest because there is increasing application of enteral feeding and appreciation of the role of the gut in the development of infection and of multiple organ failure in critically ill patients.

CONCLUSION

in this review, we will discuss nutrients, such as glutamine, arginine, omega 3 fatty acids, nucleotides, probiotics, and lactoferrin, and how they might be used as immunonutrients in neonatal clinics.

Inflammatory response in the elderly

PURPOSE OF REVIEW

During ageing there may be the onset of a chronic inflammatory state. This review examines the underlying causes of this phenomenon and the role that genotype plays in its intensity.

RECENT FINDINGS

There are predisposing factors for the chronic inflammation that occurs during ageing. These include increased oxidative stress, a decrease in ovarian function, a decrease in stress-induced glucocorticoid sensitivity of pro-inflammatory cytokine production in men, and an increased incidence of asymptomatic bacteriuria. Obesity induces chronic inflammation. Inflammation is a key factor in the progressive loss of lean tissue and impaired immune function observed in ageing. Polymorphisms in the promoter regions of pro- and anti-inflammatory cytokine genes influence the level of cytokine production and the ageing process. Thus, a genotype for high pro-inflammatory cytokine production results in high cytokine production and may accelerate the rate of tissue loss. Conversely, polymorphisms in the genes for anti-inflammatory cytokines may result in a slowing of tissue loss. In the healthy aged male population, the former polymorphisms are under-represented and the latter over-represented, indicating a genetically determined survival advantage in maintaining inflammation at a low level. Nutrients with anti-inflammatory properties, such as vitamin E and n-3 polyunsaturated fatty acid, may reduce the level of chronic inflammation and thereby ameliorate tissue and functional loss during ageing. New evidence suggests that, for the latter nutrient, gene-nutrient interactions occur that alter the effectiveness of dietary therapy.

SUMMARY

Ageing is associated with increased levels of chronic inflammation. This plays a major role in the decline in immune function and lean body mass. Anti-inflammatory nutrient therapy may slow the rate of decline. The pro- and anti-inflammatory cytokine genotype is linked negatively and positively, respectively, with life-span, because of its influence on inflammation.

Emerging roles of PPARs in inflammation and immunity

Lipids and lipid metabolism have well-documented regulatory effects on inflammatory processes. Recent work has highlighted the role of the peroxisome proliferator-activated receptors (PPARs)--a subset of the nuclear-hormone-receptor superfamily that are activated by various lipid species--in regulating inflammatory responses. Here, we describe how the PPARs, through their interactions with transcription factors and other cell-signalling systems, have important regulatory roles in innate and adaptive immunity.

Inflammatory status and insulin resistance

PURPOSE OF REVIEW

The inflammatory response is essential in the response to pathogens. TNF-alpha, IL-1 and IL-6 are key mediators of the response. They initiate metabolic changes to provide nutrients for the immune system, from host tissues. These changes include hyperlipidemia and increased gluconeogenesis. Insulin resistance and disordering of lipid metabolism occur in obesity, diabetes mellitus, atherosclerosis. This review examines recent research that links inflammation to insulin insensitivity.

RECENT FINDINGS

Population studies show a strong association between indices of inflammation, and abnormal lipid and carbohydrate metabolism, obesity and atherosclerosis. TNF-alpha is produced, by cells of the immune system and by adipocytes. It may provide the link between inflammation and insulin sensitivity. TNF-alpha results in insulin insensitivity, indirectly by stimulating stress hormone production and directly by sustained induction of SOCS-3 which decreases insulin-induced insulin receptor substrate 1 (IRS1) tyrosine phosphorylation and its association with the p85, regulatory subunit of phosphatidylinositol-3 kinase; and by negative regulation of PPAR gamma. Adipose tissue produces both TNF-alpha and leptin. Production of the latter relates positively to adipose tissue mass and through its actions on immune function exerts a pro-inflammatory influence.

SUMMARY

Recent studies on diseases which involve insulin insensitivity (e.g. obesity, type 2 diabetes and atherosclerosis) also show increased cytokine production and markers of inflammation. Evidence at present favours chronic inflammation as a trigger for chronic insulin insensitivity, rather than the reverse situation.

Chronic inflammation alters protein metabolism in several organs of adult rats

Despite the prevalence of chronic inflammatory diseases in developed countries, few studies have considered the metabolic alterations observed in these disorders. To determine which perturbations in protein metabolism occur during chronic inflammation, and the consequences they have on nutritional requirements, a model of ulcerative colitis was adapted for use in adult rats. Adult Sprague-Dawley male rats (9 mo old) received dextran sulfate sodium (DSS) in their drinking water at 50 g/L for 9 d, then at 20 g/L for 18 d. A group of control rats, matched for age and weight, was pair-fed to the treated rats. DSS induced body weight loss and chronic inflammation characterized by an increase of spleen, liver, ileum and colon weights, of blood leukocytes and acute-phase protein levels. The main inflammatory site was the colon, which presented characteristic histological alterations and increased myeloperoxydase activity. Inflammation was accompanied by oxidative stress, characterized by increased plasma protein carbonyl content and increased liver glutathione concentration, but decreased glutathione concentration in muscle. This DSS-induced colitis led to a stimulation of protein synthesis in spleen (+223%), ileum (+40%) and colon (+63%). By contrast, protein synthesis in muscle slowed down (-23%). In conclusion, like acute inflammation, chronic inflammation induced a stimulation of protein metabolism in several splanchnic organs. In muscle, both protein synthesis and degradation were reduced. Taken together, these data are consistent with inadequate amino acid supply to meet the increased requirement resulting from chronic inflammation.

Immunonutrition

Nutrition and immunology are interrelated. Several nutrients like arginine, glutamine, omega-3-fatty acids and nucleotides enhance cellular immunity, modulate tumor cell metabolism and improve clinical outcome in stress situations. Glutamine supplementation has been shown to decrease incidence of sepsis and to reduce length of hospital stay in bone marrow transplant patients, low birth weight infants, surgical and multiple trauma patients. Studies with arginine have shown a reduction in infectious complications and lower mortality, however a better understanding of the biology of arginine is needed. Omega-3-fatty acid supplimentation as in fish oil stimulates the immune system. The beneficial effects of immunonutrition in surgical patients has been demonstrated in several studies. It significantly reduces infectious complications and length of hospital stay. In critically ill patients immunonutrition may decrease infectious complications but it is not associated with a mortality advantage. Pediatric experience is limited, but the future is promising.