Generic enteral formulas: a new idea for the 1990s

Generic equivalent enteral formulas are now commercially available. The purpose of this article is threefold: (1) to define generic equivalents and compare both their nutritional and monetary differences with brand name products, (2) to provide the clinician with factors to consider when evaluating generic formulas--the source and distribution of macronutrients and micronutrients, and patient tolerance, nutritional status and outcome--and (3) to provide information on how to incorporate generic enteral formulas onto an institution's enteral formulary. In today's environment of diminishing health care budgets, generic enteral formulas can play a role in cost containment without sacrificing quality nutritional care.

Determination of combined benzidine in FD&C Yellow No. 6 (Sunset Yellow FCF)

Samples from 67 manufactured lots of FD&C Yellow No. 6 (Sunset Yellow FCF; Colour Index No. 15985) were analysed for combined benzidine. These samples were selected from those submitted to the US Food and Drug Administration for certification between October 1991 and December 1992 by 13 dye distributors. Dithionite was used to reduce any combined benzidine present in the form of azo or disazo dyes to free benzidine. This reduction was followed by extraction, diazotization and coupling with 2-naphthol-3,6-disulfonic acid disodium salt (R salt). The total benzidine was quantified as benzidine-R salt disazo dye by HPLC with detection at 540 nm and a quantification limit of 10 ng benzidine/g FD&C Yellow No. 6. Of the 67 samples analysed, 34 were found to contain more than 10 ng combined benzidine/g. Of these, 30 samples were from one manufacturing company, including three of its subsidaries. The level of combined benzidine found ranged from 11 to 104 ng/g, except for one sample containing 941 ng/g.

Staphylococcal enterotoxin B modulates V beta 8+ TcR-associated T-cell memory against conventional antigen

Primary in vivo challenge with the superantigen staphylococcal enterotoxin B (SEB) induces polyclonal proliferation of an unusually large proportion of circulating T-cells that bear the V beta 8-T-cell receptor (TcR) domain. Early and vigorous proliferation of V beta 8+ T-cells precedes their selective deletion, leaving the host unresponsive upon rechallenge with the native immunogen SEB. Nonetheless, this induction of anergy is incompletely understood. Recently we demonstrated that more cells than just V beta 8+ T-cells undergo clonal proliferation after challenge with SEB (Cell. Immunol. 154, 440, 1994). These findings suggested that non-V beta 8+ T-cells may have a role in the induction of superantigen-induced anergy. To further investigate this, we enumerated CD4+ and CD8+ T-cells in lymph nodes and spleens from Balb/c mice at various times after primary and secondary challenge with either a high or a low dose of SEB. Using these kinetic data we investigated whether challenge with SEB would modulate antigen-specific V beta 8-associated T-memory responses. To this end, the V beta 8+ T-cell-associated responses induced by SEB were compared with the V beta 8+ TcR-associated memory responses induced by the nominal antigen sperm whale myoglobin (SWM). Results indicated that challenge of SWM-primed mice with SEB abrogated the V beta 8-associated SWM-specific T-cell memory for an extended but transient period of time. Moreover, prechallenge with SEB blocked the establishment of de novo V beta + T-cell-mediated immunity. These findings suggest that administration of low and controlled doses of microbial superantigen could provide long-term suppression of antigen-specific cell-mediated immunity.

Experience with enteral nutrition in a hospital population of acutely ill patients

Enteral feeding has unique metabolic and immune advantages. This article describes the successful use of enteral nutrition, alone or in combination with parenteral feeding, in a tertiary-care hospital. Study participants were 89 patients who received enteral feeding during a 6-month period. These critically ill patients (ranging in age from 55 to 71 years) had severity of illness levels of 7 to 25 according to the Acute Physiologic and Chronic Health Evaluation (APACHE II) system and lengths of hospital stay from 27 to 73 days. Mortality was as high as 50% in patients with liver disease (nonmalignant), 35% in patients with cardiothoracic and vascular diseases, and 17% in patients with cancer and other diseases. Despite the severity of illness, patients met their energy and protein intake goals through enteral or combined feeding with total parenteral nutrition. Serial weights (ie, obtained weekly) and serum albumin concentrations did not improve during hospitalization. Complications related to enteral feeding were minimal (< 17% incidence). Differences were noted between survivors and nonsurvivors: nonsurvivors had lower serum albumin concentrations at the time of admission, had longer hospitalizations, and required total parenteral nutrition for more days than the survivors. Nonetheless, even with extremely sick patients, provision of enteral nutrition can be successful using the administration techniques we describe. Enteral nutrition could best be provided by beginning at a slow rate (10 c3/hour), inserting the feeding tube past the pylorus, and feeding according to sensible energy goals (25 kcal/kg of body weight), and using elemental then polymeric formulas.

Early activation and cell trafficking induced by staphylococcal enterotoxin B: effects of high- versus low-dose challenge on induction of anergy

The in vivo challenge with exogenous superantigen, staphylococcal enterotoxin B (SEB), selectively induces vigorous polyclonal proliferation of T cells bearing the V beta 8+ TcR domain, whereafter the responsive cells become anergic. We used kinetic analyses to compare the effects of primary (1 degree) and secondary (2 degrees) challenge with a high and a low dose of SEB and the conventional antigen, sperm whale myoglobin, to determine the differential effects of in vivo challenge with a superantigen compared with a conventional antigen. We demonstrate that SEB induces very early activation-associated intralymphatic proliferation and trafficking of more T cells than can be accounted for by V beta 8+ T cells alone. Overall, this study indicates that challenge with SEB causes an apparent loss of CD4+ T-helper cell function and provides an essential foundation for the understanding of the mechanisms of peripheral tolerance induction and T cell "memory."

Determination of combined benzidine in FD & C yellow no. 5 (tartrazine), using a highly sensitive analytical method

53 samples of FD & C Yellow No. 5 (tartrazine; Colour Index No. 19140) were examined for combined benzidine. These samples, which represent separate lots from 12 dye distributors, were submitted to the US FDA for certification between 28 February 1990 and 27 June 1991. A method was developed to reduce the dye matrix with dithionite so that combined benzidine present in the form of azo or disazo dyes would be converted to free benzidine. Reduction was followed by extraction, diazotization and coupling with pyrazolone T, and the total benzidine present was quantitated as benzidine-pyrazolone T disazo dye (BZPT) by HPLC with detection at 500 nm. The limit of quantitation for benzidine in FD & C Yellow No. 5 by this method is 5 ng/g. 25 samples of FD & C Yellow No. 5 were found to contain 7-83 ng/g of combined benzidine that was released by dithionite reduction. 23 of these samples were from the same manufacturer. The identify of the BZPT from two FD & C Yellow No. 5 samples was confirmed by spectral analysis using HPLC with a photodiode array detector.

Augmentation of HIV-specific lymphoproliferation in HIV-infected individuals by TraT: a novel T-cell immunopotentiating agent

OBJECTIVE

To evaluate the potential of TraT to restore HIV-specific cell-mediated immunity.

DESIGN

CD4+ T cell-associated antiviral and recall antigen-specific lymphoproliferative responses are generally impaired or absent in HIV-infected individuals.

METHODS

Using peripheral blood mononuclear cells (PBMC) from a group of asymptomatic and symptomatic HIV-infected individuals, we compared the immunomodulatory effects of exogenous interleukin-2 (IL-2) with the effects elicited by the bacterial integral membrane protein, TraT.

RESULTS

Exogenous IL-2 enhanced lymphoproliferation induced by an immunodominant synthetic HIV gp41 analogue, gp41[8] (amino acids 593-604), in four out of 10 asymptomatics and six out of 19 symptomatics. In contrast, TraT acted synergistically with gp41[8] to augment HIV-specific proliferation with higher frequency and greater magnitude than exogenous IL-2. Moreover, this TraT-mediated enhancement of HIV-specific lymphoproliferation occurred in the majority of HIV-infected individuals, irrespective of CD4+ T-cell count in peripheral blood or disease status, and thus appears not to be major histocompatibility complex-restricted. TraT also augmented lymphoproliferation induced by well-known recall antigens and other less immunodominant HIV analogues.

CONCLUSIONS

These findings suggest that TraT, in combination with HIV-derived peptides, could be used to maintain or restore cell-mediated immune functions of HIV-infected individuals, as well as cellular immune functions in individuals suffering from other immunodeficiency disorders.

Fish-oil-containing diet and platelet aggregation

Current research suggests that a diet high in fish oil may be useful for immunomodulation in hospitalized patients. However, one of the side effects of fish oil is a prolongation of the bleeding time, specifically by reducing platelet aggregability. Although this effect might be beneficial for patients with cardiovascular disease, it would be a potential concern in certain critically ill patients. To address this concern, we conducted a prospective study of platelet aggregation in 16 surgical patients who were randomly assigned to receive either a diet containing 16.5 g of fish oil in 1500 ml (Impact) or usual care (standard enteral formulas devoid of fish oil). Feeding was successfully accomplished in the patient group receiving a diet that provided approximately 14.2 g of fish oil/day for 1 wk without significantly affecting platelet aggregability. Thus, it appears that, over the short term, this dose of fish oil does not alter platelet function in hospitalized surgical patients.

Nutrition support and the human immunodeficiency virus (HIV)

Nutritional support of patients with HIV or acquired immune deficiency syndrome (AIDS) has many similarities to other disease states in that the same nutritional products and techniques are used. Some patients with HIV, and many with AIDS without secondary infection, experience a metabolic milieu similar to patients with cancer cachexia. In providing dietary counselling to the HIV patient, we encounter many of the obstacles that must be overcome to improve nutrition in cancer: anorexia, gastrointestinal discomfort, lethargy, and poor nutrient utilization, which limit the ability for nutritional repletion. When a secondary infection is superimposed on HIV, patients resemble more highly catabolic trauma patients or patients in the intensive care unit (ICU), where, despite aggressive efforts to feed, there is usually a net nitrogen wasting leading to the more rapid development of cachexia. However, even in this setting, feeding will limit substantially net catabolism when compared to total starvation. Because the nutritional needs of HIV patients vary greatly, individual strategies have to be designed as the patient moves through the stages of disease. Patients are generally able to consume adequate nutrition either as regular food or dietary supplements during the latency period of viral replication. Once secondary infections become prevalent, artificial diets administered by tube or by vein may be required during the period of active secondary infections, with dietary supplements often helpful during more quiescent periods. Patients with HIV are among the most challenging for clinicians providing nutritional support. Knowledge from treatment of patients with other diseases may be useful, but more data must be gathered on the unique aspects of aetiology and treatment of the anorexia, malabsorption, and ultimate wasting associated with AIDS.

Heterogeneous effects of exogenous IL-2 on HIV-specific cell-mediated immunity (CMI)

A characteristic feature associated with HIV-1 infection of the human host is a chronic decline in circulating CD4+ T helper/inducer cell numbers. Impaired cell-mediated immune functions usually occur in parallel with the decline in CD4+ T cells. Activated CD4+ T helper cells are a major source of endogenous IL-2 which is required for the immunoregulation of both antigen-specific B cells and CD8+ T cells. HIV-specific T cell proliferative responses are said to be weak and inconsistent, even during the asymptomatic phase of disease. We thus wished to determine how exogenous IL-2 affected HIV-specific T cell proliferation at different stages of the disease. Our cohort of 81 included both asymptomatic and symptomatic HIV-infected patients as well as uninfected normal donors. Proliferative responses of peripheral blood mononuclear cells (PBMC) that were elicited during culture with an immunodominant gp41-derived synthetic peptide, gp41[8], and which were known to be CD8+ cell-associated in asymptomatics only, were used to analyse the effects of exogenous IL-2. IL-2 had three main effects on HIV-specific proliferation, namely (i) an additive effect, (ii) a synergistic effect, and (iii) an induced effect. More specifically, low dose exogenous IL-2 frequently augmented lymphoproliferation in both asymptomatic and symptomatic gp41[8] responders. In most symptomatics, however, who were predominantly gp41[8] non-responders, exogenous IL-2 induced lymphoproliferation. Flow cytometric analyses using dual immunofluorescence were used to analyse the T cell subset distribution of proliferating PBMC cultures. During culture with gp41[8], both CD4+ and CD8+ T cell numbers increased. However, after the addition of exogenous IL-2 to gp41[8]-containing cultures, CD8+ cell-associated lymphoproliferative responses were preferentially augmented. These results suggest that in symptomatics there is an inadequate supply of endogenous IL-2 to help maintain the strong and effective CD8+ cell-associated anti-viral immunity, and an exogenous supply of IL-2 may be required.

CD8+ T-cells from HIV-infected patients can either augment or abrogate HIV-specific lymphoproliferation

Despite the presence of activated CD8+ T-cells that have been identified in infected individuals, these cells do not overcome natural HIV infection. To understand this better, we analyzed the CD8+ cell-dependent HIV-specific lymphoproliferation that occurs after HIV infection. Our study group of 36 individuals included 11 asymptomatic and 16 symptomatic patients (12 ARC and 4 AIDS), as well as HIV-seronegative controls. After CD8+ cell depletion of PBMC cultures, the remaining cells were tested for proliferation during culture with a well-defined and immunodominant gp41-derived HIV analog, gp41(8). After CD8+ cell depletion, three functional outcomes, which differed in accordance with the disease status of the individual, were consistently recorded, namely (i) an "abrogation effect," (ii) an "augmentation effect," or (iii) "no effect." First, removal of CD8+ cells from PBMC cultures abrogated gp41(8)-specific lymphoproliferation in gp41(8)-specific responders. Paradoxically, in other patients, including 5 symptomatics, the same inhibition of CD8+ cell function caused significant augmentation of gp41(8)-specific lymphoproliferation. These results suggest that the subpopulations of CD8+ T-cells that predominate at different stages of HIV-induced disease have different functional properties, including the ability to modulate HIV-specific cell-mediated immunity.

Glutamine content of whole proteins: implications for enteral formulas

In two recent clinical trials in surgical patients, supplementation of total parenteral nutrition with daily doses of 12 or 20 g of glutamine resulted in a diminished loss of free glutamine in skeletal muscle tissue. Studies in animals exploring the use of both enteral and parenteral glutamine supplementation suggest that glutamine may be an essential nutrient in the maintenance of gut structure and function during critical illness. These findings have led to heightened interest in the glutamine content of enteral formulas. This article describes a method for estimating the glutamine content of whole-protein enteral formulas. The average amount of glutamine in selected, whole-protein formulas ranges from a minimum of 3.55 g/4200 kJ to a maximum of 5.15 g/4200 kJ. Although it is still too early to define the safest and most effective dose of glutamine, there are two points regarding glutamine supplementation that clearly merit further investigation: no clinical trials have been conducted to assess the potential benefits of glutamine supplementation of an enteral diet or to assess the effects of using diets containing protein-bound glutamine rather than free glutamine.

Tolerance to enteral tube feeding diets in hypoalbuminemic critically ill, geriatric patients

Tolerance of elemental (for example, Peptamen [PEP]) or free amino acid (for example, Vivonex TEN [VIV]) tube feeding diets is controversial, especially in the critically ill patient who is hypoalbuminemic. A prospective, randomized trial was conducted to compare differences between feeding PEP (n = 8) or VIV (n = 8) in critically ill, elderly (average age of 66 years) patients. Diets were administered through nasogastric or postpyloric feeding tubes. Eleven patients had diseases of the gastrointestinal tract; all underwent surgical treatment. Patients were fed each diet at full strength, beginning with 20 to 30 milliliters per hour and advancing by 10 to 20 milliliters every day until goal rate was reached, usually on day 4. Assessment was made for ability to comply with rate of tube feeding ordered, compliance with caloric goal and tolerance (as evidenced by abdominal discomfort and diarrhea). Diarrhea was qualitatively defined as more than three stools per day and then quantitatively as the mean number of stools daily. There were no significant differences between the two groups in terms of compliance with prescribed tube feeding order or caloric goal or the presence of diarrhea and abdominal discomfort. There was a significant difference between the two groups in terms of the actual number of stools per day (PEP equals 1.38 versus VIV equals 2.25, p less than 0.02). Serum albumin concentrations upon initiation of the diets were 2.3 grams per deciliter in both groups. We conclude that tolerance to the two diets were similar because it was possible to feed enterally either PEP or VIV in critically ill, hypoalbuminemic patients (serum albumin concentrations of less than 2.5 grams per deciliter) successfully, irrespective of diet. Although there were more stools in the VIV group, this did not reduce compliance with the goals.

Definition of an immunodominant T cell epitope contained in the envelope gp41 sequence of HIV-1

The majority of the immunodominant amino acid sequences of HIV-1 that have been characterized to date are coded for by hypervariable gene sequences. These variable sequences are however interspersed with sequences that are highly conserved between HIV strains. Immunogenic viral products with amino acid sequences that vary minimally between strains, and that consistently elicit both humoral and cellular immune responses, may be ideal for inclusion in a subunit vaccine. We studied HIV-seronegative and HIV-infected persons, classified as asymptomatic (AS), ARC or AIDS. Initially, we assessed the cellular immune status of each subject from results of T cell phenotype analyses, assays for serum levels of surrogate markers of disease progression, and responses to mitogens and recall antigen. In addition, we tested whether three short synthetic peptides derived from the conserved sequences of the envelope gp120 (aa 262-284) and gp41 (aa 579-601), and core p17 (aa 106-125) regions of the HTLV-IIIB isolate, could elicit B cell as well as T cell responses in HIV-infected subjects. Only the gp41-derived sequence was immunogenic at both B and T cell levels. To further characterize the gp41 epitope, we used a series of overlapping synthetic peptides derived from a conserved region of the envelope gp41 (aa 572-613). We thus identified an immunodominant 12-mer peptide sequence, gp41(8)(aa 593-604), which consistently elicited both T cell blastogenic and B cell (antibody) responses in AS HIV-seropositive individuals but not in ARC and AIDS patients. Linear regression analysis showed that in AS persons there was a strong positive correlation (P less than 0.0005) between the absolute CD8+ T cell numbers and the magnitude of blastogenic responses to the gp41(8)(aa 593-604). Furthermore, those AS subjects with T cells that proliferated in response to this gp41 analogue also had significantly greater serum levels of antibody to the same short peptide sequence than symptomatic ARC and AIDS patients. These results suggest that cellular responses to the immunodominant and highly conserved envelope sequences of HIV-1, associated with increased CD8+ T cells, may be important in the pathogenesis of HIV disease.

Potential of parenteral and enteral nutrition in inflammation and immune dysfunction: a new challenge for dietitians

Advances in the understanding of the interrelationship between immunology and nutrition indicate that immune dysfunction in critically ill patients is linked with nutrient deficiency and abnormal acute-phase response to illness. Immune dysfunction requires special nutrition therapy and metabolic support; immunoregulation by nutrition manipulation may lead to specific immunotherapies for defined groups of patients. The success of dietary strategies must be measured not only by metabolic indexes but also by effects on immune function. The health profession must combat immune dysfunction and inflammation for the sick and frail patients under its care.