Enteral refeeding rapidly restores PN-induced reduction of hepatic mononuclear cell number through recovery of small intestine and portal vein blood flows

Metabolic and nutritional triggers associated with increased risk of liver complications in SARS-CoV-2

Obesity, diabetes, cardiovascular and respiratory diseases, cancer and smoking are risk factors for negative outcomes in severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which can quickly induce severe respiratory failure in 5% of cases. Coronavirus disease-associated liver injury may occur during progression of SARS-CoV-2 in patients with or without pre-existing liver disease, and damage to the liver parenchyma can be caused by infection of hepatocytes. Cirrhosis patients may be particularly vulnerable to SARS-CoV-2 if suffering with cirrhosis-associated immune dysfunction. Furthermore, pharmacotherapies including macrolide or quinolone antibiotics and steroids can also induce liver damage. In this review we addressed nutritional status and nutritional interventions in severe SARS-CoV-2 liver patients. As guidelines for SARS-CoV-2 in intensive care (IC) specifically are not yet available, strategies for management of sepsis and SARS are suggested in SARS-CoV-2. Early enteral nutrition (EN) should be started soon after IC admission, preferably employing iso-osmolar polymeric formula with initial protein content at 0.8 g/kg per day progressively increasing up to 1.3 g/kg per day and enriched with fish oil at 0.1 g/kg per day to 0.2 g/kg per day. Monitoring is necessary to identify signs of intolerance, hemodynamic instability and metabolic disorders, and transition to parenteral nutrition should not be delayed when energy and protein targets cannot be met via EN. Nutrients including vitamins A, C, D, E, B6, B12, folic acid, zinc, selenium and ω-3 fatty acids have in isolation or in combination shown beneficial effects upon immune function and inflammation modulation. Cautious and monitored supplementation up to upper limits may be beneficial in management strategies for SARS-CoV-2 liver patients.

Impaired Gut-Systemic Signaling Drives Total Parenteral Nutrition-Associated Injury

BACKGROUND

Total parenteral nutrition (TPN) provides all nutritional needs intravenously. Although lifesaving, enthusiasm is significantly tempered due to side effects of liver and gut injury, as well as lack of mechanistic understanding into drivers of TPN injury. We hypothesized that the state of luminal nutritional deprivation with TPN drives alterations in gut-systemic signaling, contributing to injury, and tested this hypothesis using our ambulatory TPN model.

METHODS

A total of 16 one-week-old piglets were allocated randomly to TPN (n = 8) or enteral nutrition (EN, n = 8) for 3 weeks. Liver, gut, and serum were analyzed. All tests were two-sided, with a significance level of 0.05.

RESULTS

TPN resulted in significant hyperbilirubinemia and cholestatic liver injury, p = 0.034. Hepatic inflammation (cluster of differentiation 3 (CD3) immunohistochemistry) was higher with TPN (p = 0.021). No significant differences in alanine aminotransferase (ALT) or bile ductular proliferation were noted. TPN resulted in reduction of muscularis mucosa thickness and marked gut atrophy. Median and interquartile range for gut mass was 0.46 (0.30-0.58) g/cm in EN, and 0.19 (0.11-0.29) g/cm in TPN (p = 0.024). Key gut-systemic signaling regulators, liver farnesoid X receptor (FXR; p = 0.021), liver constitutive androstane receptor (CAR; p = 0.014), gut FXR (p = 0.028), G-coupled bile acid receptor (TGR5) (p = 0.003), epidermal growth factor (EGF; p = 0.016), organic anion transporter (OAT; p = 0.028), Mitogen-activated protein kinases-1 (MAPK1) (p = 0.037), and sodium uptake transporter sodium glucose-linked transporter (SGLT-1; p = 0.010) were significantly downregulated in TPN animals, whereas liver cholesterol 7 alpha-hydroxylase (CyP7A1) was substantially higher with TPN (p = 0.011).

CONCLUSION

We report significant alterations in key hepatobiliary receptors driving gut-systemic signaling in a TPN piglet model. This presents a major advancement to our understanding of TPN-associated injury and suggests opportunities for strategic targeting of the gut-systemic axis, specifically, FXR, TGR5, and EGF in developing ameliorative strategies.

Role of the Gut⁻Liver Axis in Driving Parenteral Nutrition-Associated Injury

For decades, parenteral nutrition (PN) has been a successful method for intravenous delivery of nutrition and remains an essential therapy for individuals with intolerance of enteral feedings or impaired gut function. Although the benefits of PN are evident, its use does not come without a significant risk of complications. For instance, parenteral nutrition-associated liver disease (PNALD)—a well-described cholestatic liver injury—and atrophic changes in the gut have both been described in patients receiving PN. Although several mechanisms for these changes have been postulated, data have revealed that the introduction of enteral nutrition may mitigate this injury. This observation has led to the hypothesis that gut-derived signals, originating in response to the presence of luminal contents, may contribute to a decrease in damage to the liver and gut. This review seeks to present the current knowledge regarding the modulation of what is known as the “gut–liver axis” and the gut-derived signals which play a role in PN-associated injury.

The influence of dietary restriction on hepatic mononuclear cell numbers and functions in mice

BACKGROUND

Surgical patients with gastrointestinal malignancies are at increased risk for malnutrition. However, the mechanism by which dietary restriction (DR), one form of malnutrition, impairs hepatic immunity remains to be clarified. The present study was designed to examine the influence of DR on hepatic mononuclear cell (MNC) numbers, subpopulations, and cytokine productions (tumor necrosis factor α [TNF-α], interferon gamma [IFN-γ], and interleukin 10 [IL-10]) in response to lipopolysaccharide (LPS) in mice. Immunoglobulin (Ig) A levels in the gallbladder and histopathologic changes in the liver were also assessed.

MATERIAL AND METHODS

Male Institute of Cancer Research mice were randomly assigned to three dietary groups: ad libitum (AD), mild restriction (MR), and severe restriction (SR). The AD, MR, and SR groups received daily mouse chow in amounts of 190, 133, and 76 g/kg, respectively, for 7 d. After the mice had been fed for 7 d, hepatic MNCs were isolated. Total hepatic MNCs were counted and subpopulations were determined by flow cytometry. Cytokine productions (TNF-α, IFN-γ, and IL-10) by hepatic MNCs in response to LPS were measured. Blood samples were analyzed for hepatobiliary biochemical parameters. IgA levels in gallbladder bile were measured with enzyme-linked immunosorbent assay. In addition, liver histologies were examined.

RESULTS

Hepatic MNC numbers were significantly lower in the MR and SR groups than in the AD group, with no significant difference between the MR and SR groups. The percentage of B cells was significantly lower in the SR group than in the MR and AD groups, whereas the T-cell percentage was higher in the SR group than in the MR and AD groups. The percentage of Kupffer cells was significantly lower in the SR group than in the AD group, whereas that in the MR group was midway between those in the SR and AD groups. TNF-α and IL-10 levels in hepatic MNC culture supernatants were increased LPS-dose dependently in the AD group. However, the increase was slight in the MR group and absent in the SR group. The IgA levels in gallbladder bile were significantly lower in the SR and MR groups than in the AD group. On the basis of hematoxylin and eosin staining of hepatic sections, livers from the SR group showed atrophic hepatocytes and sinusoidal dilatation, whereas these changes were absent in the AD group.

CONCLUSIONS

DR decreases hepatic MNC number with subpopulation changes, reduces IgA levels in gallbladder bile, blunts cytokine production by hepatic MNCs, and induces pathologic damage in the liver, which may be an important mechanism underlying the impaired host defense associated with malnutrition.

Nutrition and gut immunity

The human intestine contains huge amounts of nonpathologic bacteria surviving in an environment that is beneficial to both the host and the bacterial populations. When short pauses in oral intake occur with minimal alterations in the mucosa-microbial interface, critical illness, with its attendant acidosis, prolonged gastrointestinal tract starvation, exogenous antibiotics, and breakdown in mucosal defenses, renders the host vulnerable to bacterial challenge and also threatens the survival of the bacteria. This review examines the altered innate and adaptive immunologic host defenses that occur as a result of altered oral or enteral intake and/or injury.