Functions of pregnane X receptor in self-detoxification

Diarrhea induced by insufficient fat absorption in weaned piglets: Causes and nutrition regulation

Fat is one of the three macronutrients and a significant energy source for piglets. It plays a positive role in maintaining intestinal health and improving production performance. During the weaning period, physiological, stress and diet-related factors influence the absorption of fat in piglets, leading to damage to the intestinal barrier, diarrhea and even death. Signaling pathways, such as fatty acid translocase (CD36), pregnane X receptor (PXR), and AMP-dependent protein kinase (AMPK), are responsible for regulating intestinal fat uptake and maintaining intestinal barrier function. Therefore, this review mainly elaborates on the reasons for diarrhea induced by insufficient fat absorption and related signaling pathways in weaned-piglets, with an emphasis on the intestinal fat absorption disorder. Moreover, we focus on introducing nutritional strategies that can promote intestinal fat absorption in piglets with insufficient fat absorption-related diarrhea, such as lipase, amino acids, and probiotics.

Regulation of PXR in drug metabolism: chemical and structural perspectives

INTRODUCTION

Pregnane X receptor (PXR) is a master xenobiotic sensor that transcriptionally controls drug metabolism and disposition pathways. PXR activation by pharmaceutical drugs, natural products, environmental toxins, etc. may decrease drug efficacy and increase drug-drug interactions and drug toxicity, indicating a therapeutic value for PXR antagonists. However, PXR's functions in physiological events, such as intestinal inflammation, indicate that PXR activators may be useful in certain disease contexts.

AREAS COVERED

We review the reported roles of PXR in various physiological and pathological processes including drug metabolism, cancer, inflammation, energy metabolism, and endobiotic homeostasis. We then highlight specific cellular and chemical routes that modulate PXR activity and discuss the functional consequences. Databases searched and inclusive dates: PubMed, 1 January 1980 to 10 January 2024.

EXPERT OPINION

Knowledge of PXR's drug metabolism function has helped drug developers produce small molecules without PXR-mediated metabolic liabilities, and further understanding of PXR's cellular functions may offer drug development opportunities in multiple disease settings.

Recent advances in the pharmacological applications and liver toxicity of triptolide

Triptolide is a predominant active component of Triptergium wilfordii Hook. F, which has been used for the treatment of cancers and autoimmune diseases such as rheumatoid arthritis, systemic lupus erythematosus and diabetic nephropathy. Therefore, triptolide and its derivates are considered to have promising prospects for development into drugs. However, the clinical application of triptolide is limited due to various organ toxicities, especially liver toxicity. The potential mechanism of triptolide-induced hepatotoxicity has attracted increasing attention. Over the past five years, studies have revealed that triptolide-induced liver toxicity is involved in metabolic imbalance, oxidative stress, inflammations, autophagy, apoptosis, and the regulation of cytochrome P450 (CYP450) enzymes, gut microbiota and immune cells. In this review, we summarize the pharmacological applications and hepatotoxicity mechanism of triptolide, which will provide solid theoretical evidence for further research of triptolide.

Effects of Isosakuranetin on Pharmacokinetic Changes of Tofacitinib in Rats with N-Dimethylnitrosamine-Induced Liver Cirrhosis

Tofacitinib, a Janus kinase 1 and 3 inhibitor, is used to treat rheumatoid arthritis. It is mainly metabolized by the cytochromes p450 (CYP) 3A1/2 and CYP2C11 in the liver. Chronic inflammation eventually leads to cirrhosis in patients with rheumatoid arthritis. Isosakuranetin (ISN), a component of Citrus aurantium L., has hepatoprotective effects in rats. This study was performed to determine the effects of ISN on the pharmacokinetics of tofacitinib in rats with N-dimethylnitrosamine-induced liver cirrhosis (LC). After intravenous administration of 10 mg/kg tofacitinib to control (CON), LC, and LC treated with ISN (LC-ISN) rats, the total area under the plasma concentration-time curves (AUC) from time zero to infinity increased by 158% in LC rats compared to those in CON rats; however, the AUC of LC-ISN rats decreased by 35.1% compared to that of LC rat. Similar patterns of AUC changes were observed in the LC and LC-ISN rats after oral administration of 20 mg/kg tofacitinib. These results can be attributed to decreased non-renal clearance (CL_NR) and intestinal intrinsic clearance (CL_int) in the LC rats and increased intestinal and hepatic CL_int in the LC-ISN rats. Our findings imply that ISN treatment in LC rats restored the decrease in either CL_NR or CL_int, or both, through increased hepatic and intestinal expression of CYP3A1/2 and CYP2C11, which is regulated by the induction of pregnane X receptor (PXR) and constitutive androstane receptor (CAR).

Lycopene Preventing DEHP-Induced Renal Cell Damage Is Targeted by Aryl Hydrocarbon Receptor

Di (2-ethylhexyl) phthalate (DEHP) is an environmentally persistent and bioaccumulative plasticizer. Accumulation of DEHP in the body can eventually cause kidney damage. As a type of natural carotenoid, lycopene (LYC) has a potential protective effect on renal cells, but the protective mechanism has not yet been elucidated. The major goal of this study was to see how effective LYC was at treating DEHP-induced nephrotoxicity in mice. ICR mice were treated with DEHP (500 mg/kg BW/day or 1000 mg/kg BW/day) or LYC (5 mg/kg BW/day) for 28 days. Through histopathology and ultrastructure, we found that LYC attenuated DEHP-induced renal tubular cell and glomerular damage. LYC relieved DEHP-induced kidney injury evidenced by lower levels of blood urea nitrogen (Bun), creatinine (Cre), and uric acid (Uric). Meanwhile, the reduced expression of kidney injury molecule-1 (Kim-1) also supported it. Notably, LYC can alleviate the activity or content of cytochrome P450 system (CYP450s) interfered with by DEHP. In addition, LYC treatment reduced nuclear accumulation of DEHP-induced aromatic hydrocarbon receptor (AhR) and AhR nuclear transporter (Arnt), and its downstream target genes such as cytochrome P450-dependent monooxygenase (CYP) 1A1, 1A2, and 1B1 expression significantly decreased to normal in the LYC treatment group. In summary, LYC can mediate the AhR/Arnt signaling system to prevent kidney toxicity in mice caused by DEHP exposure.

Serine Supplementation Alleviates Doxorubicin-Induced Oxidative Damage in Skeletal Muscle of Mice

Muscle weakness affects physical activity and quality of life of patients. Serine, a nutritionally non-essential amino acid has been reported to enhance protein synthesis and implicate in biosynthesis of multiple bioactive molecules. It remains unknown whether it can protect mice against oxidative stress-induced muscles weakness. This study was conducted to test the hypothesis that serine administration alleviates doxorubicin-induced oxidative damage in skeletal muscle of mice. Mice pre-treated with or without serine were intraperitoneally injected with either doxorubicin or equal volume of saline. Reactive oxygen species (ROS) accumulation, activity of antioxidant enzymes, oxidation product of protein, DNA, and lipid, activity of mitochondrial complex, and protein level of nuclear-factor-erythroid-2-related factor 2 (NRF2)/constitutive-androstane-receptor (CAR) signaling in skeletal muscle of mice were determined. Compared with the control, doxorubicin exposure led to oxidative damage as shown by increased ROS accumulation, decreased activity of antioxidant enzymes, and enhanced oxidative product of protein, DNA, and lipid in the skeletal muscle of mice. These effects of doxorubicin were associated with increased activity of complex I and reduced glutathione. Interestingly, doxorubicin-induced oxidative damage was alleviated by serine administration. Further study showed that the beneficial effect of serine was associated with enhanced NRF2/CAR signaling. Our result showed that serine attenuated doxorubicin-induced muscle weakness in mice. Serine supplementation might be a nutritional strategy to improve the function of skeletal muscle in patients exposed to doxorubicin.

Obesity induced by high-fat diet is associated with critical changes in biological and molecular functions of mesenchymal stromal cells present in visceral adipose tissue

The mesenchymal stromal cells (MSCs) residing within the stromal component of visceral adipose tissue appear to be greatly affected by obesity, with impairment of their functions and presence of senescence. To gain further insight into these phenomena, we analyzed the changes in total proteome content and secretome of mouse MSCs after a high-fat diet (HFD) treatment compared to a normal diet (ND). In healthy conditions, MSCs are endowed with functions mainly devoted to vesicle trafficking. These cells have an immunoregulatory role, affecting leukocyte activation and migration, acute inflammation phase response, chemokine signaling, and platelet activities. They also present a robust response to stress. We identified four signaling pathways (TGF-β, VEGFR2, HMGB1, and Leptin) that appear to govern the cells' functions. In the obese mice, MSCs showed a change in their functions. The immunoregulation shifted toward pro-inflammatory tasks with the activation of interleukin-1 pathway and of Granzyme A signaling. Moreover, the methionine degradation pathway and the processing of capped intronless pre-mRNAs may be related to the inflammation process. The signaling pathways we identified in ND MSCs were replaced by MET, WNT, and FGFR2 signal transduction, which may play a role in promoting inflammation, cancer, and aging.

Fumonisins B1 exposure triggers intestinal tract injury via activating nuclear xenobiotic receptors and attracting inflammation response

Fumonisins (FBs) are mycotoxins that are widely distributed in crops and feed, and ingestion of FBs -contaminated crops is harmful to animal health. Furthermore, it is unknown if Fumonisins B1 (FB1) can cause intestinal toxicity. To investigate FB1-induced intestinal toxicity, mice were treated with 0 or 5 mg/kg FB1 by gavage administration for 42 days. Histopathology indicated that FB1 exposure caused proliferation of intestinal epithelial cells, intestinal villi and epithelial layer shedding, intestinal gland atrophy, and necrosis. Notably, FB1 interfered with nuclear xenobiotic receptors (NXR) homeostasis by regulating the level of aryl hydrocarbon receptor (AHR), constitutive androstane receptor (CAR), pregnane X receptor (PXR) and downstream target genes (CYP450s). Moreover, abnormal expression of inflammatory cytokines (IL-1β, IL-2, IL-4, IL-10, and TNF-α) indicated the occurrence of inflammation. The present study provides new insights regarding the mechanism of FB1-induced intestinal toxicity through activating the NXR system and by triggering inflammatory responses in the intestinal tract in mice.

[Pregnane X receptor promotes programmed cell death protein 4 expression in HepG2 cells]

OBJECTIVE

To investigate the role of pregnane X receptor (PXR) in the regulation of programmed cell death proteins (PDCDs) in HepG2 cells and explore the underlying molecular mechanism.

METHODS

HepG2 cells were treated with PXR agonist rifampicin (10 μmol/L) or SR12813 (1 μmol/L) for 24 h, using DMSO as the negative control. HepG2 cells were infected with constitutively activated PXR adenovirus (VP-PXR) for 36 h, with the cells infected with Mock as the negative control. The mRNA levels of PDCD2, PDCD4, PDCD5, and PDCD6 and the expression of miRNA21 were detected using qRT-PCR, and the protein level of PDCD4 was detected with Western blotting. Bioinformatic analysis was performed to predict the potential PXRresponsive elements (PXREs) motifs in the promotor region of human PDCD4.

RESULTS

The expressions of PDCD5 and PDCD6 mRNA did not differ significantly between rifampicin-treated and the control cells, while PDCD4 mRNA expression increased (t=4.209, P=0.008) and PDCD2 mRNA decreased significantly (t=-2.875, P=0.017) in rifampicin-treated cells. The mRNA expressions of PDCD2, PDCD5 and PDCD6 showed no significant difference between SR12813-treated cells and the control cells, while PDCD4 mRNA expression increased obviously in SR12813-treated cells (t=4.574, P=0.006). The PXR target gene MDR1 also increased significantly in the rifampicin- and SR12813-treated cells compared with the control cells (P=0.020 and 0.01, respectively). Infection of the cells with VP-PXR adenovirus resulted in significantly increased expression of PDCD4 and MDR1 mRNA as compared with Mock group (t=3.343, P=0.000; t=3.343, P=0.024, respectively) without causing obvious changes in PDCD2 and PDCD6 mRNA expressions. The protein level of PDCD4 increased significantly in both rifampicin (t= 2.779, P=0.025) group and VP- PXR group (t=3.066, P=0.012). The expression of miRNA21, the negative regulatory factor of PDCD4, did not differ significantly between PXR agonist group and the control group. Informatic analysis revealed the presence of putative PXREs in the 5'-flanking region of PDCD4 gene.

CONCLUSIONS

Our findings demonstrate that PXR agonism in HepG2 cells increases the expression of PDCD4, which is independent of miRNA21 pathway, and PDCD4 may be a target gene of PXR in HepG2 cells.

Nuclear receptor AHR-mediated xenobiotic detoxification pathway involves in atrazine-induced nephrotoxicity in quail (Coturnix C. coturnix)

Atrazine (ATR), one of the most widely used pesticides in agricultural production, are gradually concerned due to potential ecosystem and health risks. Further, the induction of ATR nephrotoxicity and detoxification response is still unknown. To evaluate ATR-induced nephrotoxicity, quails were treated with 0, 50, 250 or 500 mg/kg ATR by gavage administration for 45 days. Histopathology indicated that ATR exposure caused renal tubular epithelial cell swelling and endoplasmic reticulum degeneration, suggesting that ATR exposure causes renal impairment even renal diseases. Notably, ATR interfered cytochrome P450 system (CYP450s) homeostasis by enhancing contents or activities of CYP450s (total CYP450, Cyt b5, AH, APND, NCR and ERND) and the expression of CYP450 isoforms (CYP1A, CYP1B, CYP2C and CYP3A). ATR triggered phase II detoxifying reaction, reflected by the elevated GSH level, GST activity and the up-regulation of GST isoforms (GSTa, GSTa3 and GSTt1) and GSH synthetase (GCLC). Moreover, ABC transporters were activated to expel ATR from the body by increasing expression of MRP1 and P-GP gene. Accompanying these alterations, the nuclear receptors (AHR, CAR and PXR) were activated by ATR in a dose-dependent manner. Analysis results of present study demonstrated that the induction of phase II detoxifying enzyme system and ABC transporters could be modulated by nuclear receptors response and CYP450s disturbance in low-dose ATR-treated quail. In conclusion, all data suggested that nuclear receptors AHR-mediated detoxification pathway was involved in ATR-induced nephrotoxicity. These results provided new evidence about the nephrotoxic effects of ATR on the response of biotransformation and detoxification system.

Intervention with α-Ketoglutarate Ameliorates Colitis-Related Colorectal Carcinoma via Modulation of the Gut Microbiome

The intestinal microbiome plays a crucial role in promoting intestinal health, and perturbations to its constitution may result in chronic intestinal inflammation and lead to colorectal cancer (CRC). α-Ketoglutarate is an important intermediary in the NF-κB-mediated inflammatory pathway that maintains intestinal homeostasis and prevents initiation of intestinal inflammation, a known precursor to carcinoma development. The objective of this study was to assess the potential protective effects of α-ketoglutarate intervention against CRC development, which may arise due to its known anti-inflammatory and antitumour effects. CRC was induced in C57BL/6 mice using azoxymethane (AOM) and dextran sulfate sodium (DSS). Tumour frequency, histological rating, and colonic microbiota were assessed in colonic samples. The findings demonstrated that α-ketoglutarate offered significant protection against CRC development in mice. Furthermore, α-ketoglutarate also exhibited immunomodulatory effects mediated via downregulation of interleukin (IL)-6, IL-22, tumour necrosis factor (TNF)-α, and IL-1β cytokines. Finally, intervention with α-ketoglutarate tended to minimise the frequency of opportunistic pathogens (Escherichia and Enterococcus) while increasing the populations of Akkermansia, Butyricicoccus, Clostridium, and Ruminococcus. Taken together, our findings show that dietary α-ketoglutarate intervention may protect against inflammation-related CRC.

The nuclear receptors PXR and LXR are regulators of the scaffold protein PDZK1

PDZK1 (NHERF3) interacts with membrane proteins whereby modulating their spatial arrangement, membrane stability, and function. One of the membrane proteins shown to be stabilized by interaction with PDZK1 is the HDL-receptor SR-BI (SCARB1). Testing the influence of TO 901317, a known activator of liver X receptor alpha (LXRα, NR1H3) which is a central regulator of the lipid homeostasis, Grefhorst et al. reported in 2012 that administration of TO 901317 did not affect PDZK1 expression and reduced the amount of SR-BI protein in mouse liver. Considering that TO 901317 also activates the xenosensor pregnane X receptor (PXR, NR1I2), it was aim of this study to further investigate the influence of LXRα and PXR activation on transcription of PDZK1. First, we tested the transactivation of PDZK1 by LXRα or PXR in cell-based reporter gene assays comparing the effect of prototypical ligands to that of TO 901317. Ligand mediated activation of LXRα increased, while that of PXR lowered luciferase activity. Further, we located the most likely binding site for LXRα and PXR on the PDZK1 promoter between -85 bp and -54 bp. The transcriptional regulation by LXRα was further supported showing enhanced mRNA expression of PDZK1 in HepG2 cells treated with the selective LXRα-agonist GW3965, while treatment with TO 901317 reduced the protein amount of PDZK1. Taken together, we provide evidence that both LXRα and PXR are transcriptional regulators of PDZK1 supporting the previous notion that the scaffold protein is part of cholesterol homeostasis and drug metabolism.

Prevention of Oxidative Stress by α-Ketoglutarate via Activation of CAR Signaling and Modulation of the Expression of Key Antioxidant-Associated Targets in Vivo and in Vitro

α-Ketoglutarate (AKG) can act as an antioxidant both in vitro and in vivo. However, the mechanisms of the protective effects of AKG are still not well understood. We evaluated the effects of AKG supplementation on the regulation of the constitutive-androstane-receptor (CAR) pathway in porcine intestinal cells and piglets exposed to H₂O₂. Our data showed that AKG treatment significantly increased not only the intra- and extracellular levels of AKG (26.9 ± 1.31 μmol/g protein, 1064.4 ± 39.80 μmol/L medium) but also those of Asp (29.3 ± 0.21 μmol/g, 4.20 ± 0.11 μmol/L), Gln (24.82 ± 1.50 μmol/g, 1087.80 ± 16.10 μmol/L), and Glu (91.90 ± 3.6 μmol/g, 19.76 ± 1.00 μmol/L). There was approximately a 4-fold increase in α-ketoglutarate dehydrogenase mRNA levels in enterocytes and a simultaneous reduction in ROS levels ( P < 0.05). Moreover, AKG treatment increased the activities of the antioxidant enzymes and the efficiency of cellular respiration ( P < 0.05). AKG also regulated the mRNA levels of the target genes involved in antioxidant responses and xenobiotic detoxification in enterocytes. Increases in the protein levels of SOD1, SOD2, CAR, RXRα, and UCP2 and marked reductions in the expression levels of Nrf2 and Keap1 proteins ( P < 0.05) were observed after AKG administration in the H₂O₂-induced piglets. Our results indicated that AKG may protect against oxidative stress by activating CAR signaling and modulating the expression of key antioxidant-related targets, which improves cellular respiration and antioxidant capacity. The in vivo and in vitro effects of AKG suggest that it may prove to be useful in the reduction of oxidative stress in animal and human trials and subsequent prevention of gastrointestinal pathologies.

Poly(ADP-ribosyl)ated PXR is a critical regulator of acetaminophen-induced hepatotoxicity

Acetaminophen (APAP) overdose is the most frequent cause of acute liver failure and remains a critical problem in medicine. PARP1-dependent poly(ADPribosyl)ation is a key mediator of cellular stress responses and functions in multiple physiological and pathological processes. However, whether it is involved in the process of APAP metabolism remains elusive. In this study, we find that PARP1 is activated in mouse livers after APAP overdose. Pharmacological or genetic manipulations of PARP1 are sufficient to suppress the APAP-induced hepatic toxicity and injury, as well as reduced APAP metabolism. Mechanistically, we identify pregnane X receptor (PXR) as a substrate of PARP1-mediated poly(ADP-ribosyl)ation. The poly(ADP-ribosyl)ation of PXR in ligand-binding domain activates PXR competitively and solidly, facilitates its recruitment to target gene CYP3A11 promoter, and promotes CYP3A11 gene transcription, thus resulting in increases of APAP pro-toxic metabolism. Additionally, PXR silence antagonizes the effects of PARP1 on APAP-induced hepatotoxicity. These results identifies poly(ADP-ribosyl)ation of PXR by PARP1 as a key step in APAP-induced liver injury. We propose that inhibition of PARP1-dependent poly(ADP-ribosyl)ation might represent a novel approach for the treatment of drug-induced hepatotoxicity.

Stable cellular models of nuclear receptor PXR for high-throughput evaluation of small molecules

Pregnane & Xenobiotic Receptor (PXR) is one of the 48 members of the ligand-modulated transcription factors belonging to nuclear receptor superfamily. Though PXR is now well-established as a 'xenosensor', regulating the central detoxification and drug metabolizing machinery, it has also emerged as a key player in several metabolic disorders. This makes PXR attractive to both, researchers and pharmaceutical industry since clinical success of small drug molecules can be pre-evaluated on PXR platform. At the early stages of drug discovery, cell-based assays are used for high-throughput screening of small molecules. The future success or failure of a drug can be predicted by this approach saving expensive resources and time. In view of this, we have developed human liver cell line-based, dual-level screening and validation protocol on PXR platform having application to assess small molecules. We have generated two different stably transfected cell lines, (i) a stable promoter-reporter cell line (HepXREM) expressing PXR and a commonly used CYP3A4 promoter-reporter i.e. XREM-luciferase; and (ii) two stable cell lines integrated with proximal PXR-promoter-reporter (Hepx-1096/+43 and Hepx-497/+43). Employing HepXREM, Hepx-1096/+43 and Hepx-497/+43 stable cell lines > 25 anti-cancer herbal drug ingredients were screened for examining their modulatory effects on a) PXR transcriptional activity and, b) PXR-promoter activity. In conclusion, the present report provides a convenient and economical, dual-level screening system to facilitate the identification of superior therapeutic small molecules.

Pregnane X receptor mediates sorafenib resistance in advanced hepatocellular carcinoma

BACKGROUND

Kinase inhibitor sorafenib is the most widely used drug for advanced HCC clinical treatment nowadays. However, sorafenib administration is only effective for a small portion of HCC patients, and the majority develop sorafenib-resistance during treatment. Thus, it is urgent to discover the endogenous mechanism and identify new pharmaceutical targets of sorafenib-resistance.

METHODS

Pregnane X receptor (PXR) was detected by immunohistochemistry and quantitative PCR. GST-pull down and LC-MS/MS was used to detect the interaction of PXR and Sorafenib. To test the properties of HCC tumor growth and metastasis, in vivo tumor explant model, FACS, trans-well assay, cell-survival inhibitory assay and Western blot were performed. In terms of mechanistic study, additional assays such as ChIP and luciferase reporter gene assay were applied.

RESULTS

In the present work, we found high PXR level in clinical specimens is related to the poor prognosis of Sorafenib treated patients. By the mechanistic studies, we show that sorafenib binds to PXR and activates PXR pathway, and by which HCC cells develop sorafenib-resistance via activating. Moreover, PXR overexpression helps HCC cells to persist to sorafenib treatment.

CONCLUSION

This study reports the endogenous sorafenib-resistance mechanism in HCC cells, which offers an opportunity to design new therapeutic approaches for HCC treatment.

GENERAL SIGNIFICANCE

PXR mediates sorafenib-resistance in HCC cells and targeting PXR can be a useful approach to facilitate HCC treatment.

Administration of alpha-ketoglutarate improves epithelial restitution under stress injury in early-weaning piglets

Alpha-ketoglutarate (AKG) is an important cellular metabolite that participates in energy production and amino acid metabolism. However, the protective effects and mechanism of AKG on mucosal lesions have not been well understood. This study was conducted to investigate the effects of dietary AKG supplementation on epithelial restitution in early-weaning piglets under Escherichia coli lipopolysaccharide (LPS) induction. A total of 32 weaned piglets were used in a 2 × 2 factorial design; the major factors were dietary treatment (basal diet or AKG diet) and inflammatory challenge (LPS or saline). The results showed that AKG supplementation improved the growth performance and intestinal morphology in the LPS-induced early-weaning piglets. Compared with the basal diet, the AKG diet remarkably decreased the concentration and mRNA expression of intestinal inflammatory cytokines (IL-1β, IL-6, and IL-12) in the LPS-induced piglets. Moreover, AKG administration upregulated the mRNA expression of nutrient-sensing transporters (GLUT-2, SGLT-1, PEPT-1, I-FABP2) in the small intestine of both saline- and LPS-treated piglets, and improved the distribution and expression of tight-junction genes andproteins (ZO-1, Occludin, Claudins, E-cadherin). Collectively, our findings indicate that AKG has the potential to alleviate intestinal inflammatory response and improve epithelial restitution and nutrient-sensing ability under stress injury in early-weaning piglets, and it also provides an experimental basis for enteral use of AKG in swine production and clinical application to prevent intestinal epithelial damage.