Dietary fructose induces endotoxemia and hepatic injury in calorically controlled primates

Abstract

Background: Controversy exists regarding the causative role of dietary fructose in obesity and fatty liver diseases. Clinical trials have indicated that negative health consequences may occur only when fructose is consumed within excess calories. Animal studies have suggested that fructose impairs intestinal integrity and leads to hepatic steatosis (HS).

Objectives: We assessed nonhuman primates after chronic ad libitum and short-term calorically controlled consumption of a high-fructose (HFr), low-fat diet (24% of calories). Microbial translocation (MT), microbiome, and metabolic health indexes were evaluated.

Design: Seventeen monkeys fed 0.3–7 y of an HFr ad libitum diet were compared with 10 monkeys fed a low-fructose, low-fat diet (control). Ten middle-aged, weight-stable, fructose-naive monkeys were stratified into HFr and control groups fed for 6 wk at caloric amounts required to maintain weight stability. Metabolic endpoints, feces, liver, small and large intestinal biopsies, and portal blood samples were collected.

Results: Monkeys allowed ad libitum HFr developed HS in contrast to the control diet, and the extent of ectopic fat was related to the duration of feeding. Diabetes incidence also increased. Monkeys that consumed calorically controlled HFr showed significant increases in biomarkers of liver damage, endotoxemia, and MT indexes and a trend for greater hepatitis that was related to MT; however, HS did not develop.

Conclusions: Even in the absence of weight gain, fructose rapidly causes liver damage that we suggest is secondary to endotoxemia and MT. HS relates to the duration of fructose consumption and total calories consumed. These data support fructose inducing both MT and ectopic fat deposition in primates.

FIGURE 1.

A: Least-squares mean (±SEM) hepatic steatosis scores adjusted for diet duration, age, and body weight. Scores were calculated from a histologic section examination by duplicate blind reviewers from monkeys fed an ad libitum CTL (n = 10) or HFr (n = 17). The HFr induced greater liver fat deposition (ANCOVA; *P < 0.001). B: Scatterplot of hepatic steatosis scores and duration of consumption of either the CTL (n = 10; open circles) or HFr (n = 17; closed circles). The partial correlation coefficient reflects adjustment for age and body weight (r = 0.61, P < 0.05). Monkeys that ate the CTL had lifelong exposure but are represented at 0.2 y, which reflects the time that they were housed at the same site as HFr monkeys. The majority of these CTL monkey values are superimposed with a steatosis score of 0, and thus, the 10 animals are not discriminated on the graph. CTL, low-fat, low-fructose diet; HFr, low-fat, high-fructose diet.

FIGURE 2.

A: Mean (±SEM) scores for liver pathology as assessed by histologic grading for inflammation from monkeys fed either a CTL (n = 5) or HFr (n = 5) for 6 wk. An ANCOVA P value is shown. B: Representative histologic section from a monkey fed the HFr (histologic score: 3) showing the periportal inflammatory infiltrate seen in fructose-fed monkeys. C: Representative histologic section from a liver biopsy taken from a CTL monkey (histologic score: 0). CTL, low-fat, low-fructose diet; HFr, low-fat, high-fructose diet.

FIGURE 3.

Representative liver histologic sections stained for lipid with oil red O. Low-fat, high fructose–fed monkeys (A) had similar lipid amounts quantified by histology and direct biochemical analysis as did low-fat, low-fructose–fed monkeys (B) (4.66% compared with 3.48% by area, respectively; ANCOVA P = 0.38).

FIGURE 4.

A: Endotoxin concentrations representing microbial translocation were measured from portal plasma samples taken after 6-wk consumption of controlled intakes of either a CTL (n = 5) or HFr (n = 5). *ANCOVA P = 0.05. B: The ligand for LPS (sCD14) significantly increased in the peripheral circulation after only 6 wk in monkeys fed the HFr. *ANCOVA P = 0.02. C: The binding protein for LPS (LBP-1) significantly increased in the peripheral circulation after only 6 wk in monkeys fed the HFr. *ANCOVA P = 0.04. CTL, low-fat, low-fructose diet; HFr, low-fat, high-fructose diet; LBP-1, LPS binding protein-1; sCD14, soluble CD14.

FIGURE 5.

Cluster diagram on the basis of a PCoA of the fecal microbiome. Animal identification numbers are shown on the graph. A: No differences were observed between monkeys fed the CTL (triangles; n = 5) and those fed the HFr (squares; n = 5) at baseline (P = 0.89 for PCoA 1 and P = 0.91 for PCoA 2). B: No differences were also observed at the study end (P = 0.92 for PCoA 1 and P = 0.48 for PCoA 2). CTL, low-fat, low-fructose diet; HFr, low-fat, high-fructose diet; PCoA, principal coordinate analysis.