The acute-phase protein response to human immunodeficiency virus infection in human subjects.

Although several studies have shown that asymptomatic human immunodeficiency virus infection elicits an increase in whole body protein turnover, it is not known whether this increased protein turnover includes changes in the kinetics of acute-phase proteins (APPs). To answer this question, we measured 1) the plasma concentrations of four positive (C-reactive protein, alpha1-antitrypsin, haptoglobin, and fibrinogen) and four negative APPs [albumin, high-density lipoprotein (HDL)-apolipoprotein (apo) A1, transthyretin, and retinol-binding protein] and 2) the fractional (FSR) and absolute (ASRs) synthesis rates of three positive and three negative APPs using a constant intravenous infusion of [2H5]phenylalanine in five subjects with symptom-free acquired immunodeficiency syndrome (AIDS) and five noninfected control subjects. Compared with the values of the controls, the plasma concentrations, FSRs, and ASRs of most positive APPs were higher in the AIDS group. The negative APPs had faster FSRs in the AIDS group, there was no difference between the ASRs of the two groups, and only HDL-apoA1 had a lower plasma concentration. These results suggest that symptom-free AIDS elicits an APP response that is different from bacterial infections, as the higher concentrations and faster rates of synthesis of the positive APPs are not accompanied by lower concentrations and slower rates of synthesis of most of the negative APPs.

Erythrocyte glutathione deficiency in symptom-free HIV infection is associated with decreased synthesis rate.

Although several studies have documented intra- and extracellular glutathione (GSH) deficiency in asymptomatic human immunodeficiency virus (HIV) infection, the mechanisms responsible for the altered GSH homeostasis remain unknown. To determine whether decreased synthesis contributes to this alteration of GSH homeostasis, a primed-constant infusion of [2H2]glycine was used to measure the fractional and absolute rates of synthesis of GSH in five healthy and five symptom-free HIV-infected subjects before and after supplementation for 1 wk with N-acetylcysteine. The erythrocyte GSH concentration of the HIV-infected group was lower (P < 0.01) than that of the control group (1.4 +/- 0.16 vs. 2.4 +/- 0.08 mmol/l). The smaller erythrocyte GSH pool of the HIV-infected group was associated with a significantly slower (P < 0.01) absolute synthesis rate of GSH (1.15 +/- 0.14 vs. 1.71 +/- 0.15 mmol. l-1. day-1) compared with controls. Cysteine supplementation elicited significant increases in both the absolute rate of synthesis and the concentration of erythrocyte GSH. These results suggest that the GSH deficiency of HIV infection is due in part to a reduced synthesis rate secondary to a shortage in cysteine availability.

Enteral glutamate is the preferential source for mucosal glutathione synthesis in fed piglets.

To measure the source and rate of mucosal glutathione (GSH) synthesis, fed piglets (28 days old; 7.7 kg) received a 6-h infusion of intragastric [U-13C]glutamate (n = 11) either with (n = 5) or without (n = 6) an intragastric infusion of [1-13C]glycine (0-6 h) and [1,2-13C2(U-13C)]glycine (3-6 h). Eighty-four percent of the labeled mucosal GSH-glutamate and 86% of the luminal GSH-glutamate was 13C5. The tracer-to-tracee ratio of GSH-[U-13C]glutamate was 75% of that of mucosal glutamate. Sixty percent of the labeled mucosal glutamate was 13C1, 13C2, or 13C3, but the tracer-to-tracee ratios of these isotopomers in GSH-glutamate were not significantly different from zero. After 3 h of infusion, the tracer-to-tracee ratio of GSH-[U-13C]glycine was 46%, and after 6 h of infusion GSH-[13C1]glycine was 82% of that of mucosal glycine. This suggested that the half-life of mucosal GSH was 2.7 +/- 0.1 h. We concluded that, in fed piglets, mucosal GSH-glutamate derived largely from the direct metabolism of enteral glutamate rather than from glutamate that was metabolized within the mucosa.

Chronic low protein intake reduces tissue protein synthesis in a pig model of protein malnutrition.

To determine the effect of severe chronic protein deficiency on protein synthesis in different tissues and total protein in plasma, and on plasma biochemical constituents involved in amino acid metabolism, we fed diets containing either 20 or 3% protein to two groups of four age-matched piglets. After consuming the diets for 8 wk, the pigs received a primed-constant infusion of 2 H3-leucine for 8 h to measure the fractional synthesis rates (FSR) of tissue protein and total protein in plasma. Plasma urea and amino acid concentrations, particularly indispensable amino acids, were significantly lower in protein-deficient pigs. Fractional protein synthesis rates were lower in skin by 66% (P < 0.01), in jejunal mucosa by 50% (P < 0.05), in masseter muscle by 40% (P < 0.05), and in liver by 25% (P < 0.02); the fractional synthesis rate of the longissimus muscle was not different than controls. Although plasma protein concentration was significantly (P < 0.01) lower in protein-deficient pigs, the fractional synthesis rate of the total intravascular plasma protein pool was not different. We conclude that adaptation to a low protein diet involves a reduction in the rate of protein synthesis in most body tissues, with the most marked changes occurring in skin and intestine, two tissues which frequently exhibit severe functional impairment in protein malnutrition.

Protein-deficient pigs cannot maintain reduced glutathione homeostasis when subjected to the stress of inflammation.

The mechanisms responsible for depletion of systemic glutathione levels in nutritional deprivation and/or in infective and inflammatory conditions have not been fully established. We quantified the effects of protein undernutrition and experimental inflammation on the concentration and synthesis of reduced glutathione in the erythrocytes, liver and jejunal mucosa of young pigs. Two groups of five piglets consumed diets containing either 23 or 3% protein and, after 4 wk, were infused intravenously with [13C2]glycine before and 48 h after subcutaneous injections of turpentine. Erythrocyte, hepatic and intestinal mucosal reduced glutathione was quantified as the monobromobimane derivative by HPLC. Reduced glutathione synthesis was determined by measurements of the tracer/tracee ratio of reduced glutathione-bound glycine. In well-nourished piglets, turpentine injection had no effect on erythrocyte reduced glutathione concentrations or rate of synthesis. Protein undernutrition was associated with lower erythrocyte reduced glutathione concentrations (1.05 +/- 0.04 vs. 1.32 +/- 0.06 mmol/L, P < 0.01) and synthesis (42 +/- 5 vs. 60 +/- 5%/d), and turpentine inflammation caused a further fall in erythrocyte reduced glutathione concentration to 0.96 +/- 0.05 mmol/L, despite a significant (P < 0.05) increase in reduced glutathione synthesis. The combination of protein undernutrition and inflammation had a marked effect on mucosal reduced glutathione concentration (37 +/- 3% of control) and synthesis (65 +/- 5% of control). Hepatic reduced glutathione concentration and synthesis did not differ in the two groups. We conclude that the biosynthetic supply of reduced glutathione is sufficient to withstand an inflammatory challenge in well-nourished piglets but not in protein-deficient animals.

Direct effects of endotoxin on the microcirculation.

Endotoxin (E Coli, Difco), 0.5 mg in 10 ml saline, or whole blood, was infused over a ten-minute period in the retrograde direction into a branch of a mesenteric artery in anesthetized dogs; control infusions were physiologic saline or whole blood without endotoxin. After infusion, the animal's blood was allowed to circulate through the microcirculatory field. Changes in the microcirculation were recorded by cine and still photography. After infusion of endotoxin there was coincident margination of leukocytes and thickening of endothelial cells, then formation of fibrin thrombi in small veins, followed by lyses of the thrombi and extravasation of erythrocytes. Systemic blood pressure did not fall until after endothelial cell thickening and leukocyte margination (five to 25 minutes after infusion). The mean pressure fell to between 30 and 50 mm Hg, even though the dose of endotoxin was less than 1/100 of that required to cause this blood pressure fall when given IV. It is hypothesized that intracellular hydration of endothelial cells causes increased leakage of fluids and extravasation of erythrocytes following endotoxin. If the internal volumes of hexahedron-shaped cells increase without an increase in their surface areas they must assume a more spherical shape, thereby permitting gaps to develop between adjacent cells.