1
|
Creeden JF, Gordon DM, Stec DE, Hinds TD. Bilirubin as a metabolic hormone: the physiological relevance of low levels. Am J Physiol Endocrinol Metab 2021; 320:E191-E207. [PMID: 33284088 PMCID: PMC8260361 DOI: 10.1152/ajpendo.00405.2020] [Citation(s) in RCA: 87] [Impact Index Per Article: 29.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Recent research on bilirubin, a historically well-known waste product of heme catabolism, suggests an entirely new function as a metabolic hormone that drives gene transcription by nuclear receptors. Studies are now revealing that low plasma bilirubin levels, defined as "hypobilirubinemia," are a possible new pathology analogous to the other end of the spectrum of extreme hyperbilirubinemia seen in patients with jaundice and liver dysfunction. Hypobilirubinemia is most commonly seen in patients with metabolic dysfunction, which may lead to cardiovascular complications and possibly stroke. We address the clinical significance of low bilirubin levels. A better understanding of bilirubin's hormonal function may explain why hypobilirubinemia might be deleterious. We present mechanisms by which bilirubin may be protective at mildly elevated levels and research directions that could generate treatment possibilities for patients with hypobilirubinemia, such as targeting of pathways that regulate its production or turnover or the newly designed bilirubin nanoparticles. Our review here calls for a shift in the perspective of an old molecule that could benefit millions of patients with hypobilirubinemia.
Collapse
Affiliation(s)
- Justin F Creeden
- Department of Neurosciences, University of Toledo College of Medicine and Life Sciences, Toledo, Ohio
| | - Darren M Gordon
- Department of Neurosciences, University of Toledo College of Medicine and Life Sciences, Toledo, Ohio
| | - David E Stec
- Department of Physiology & Biophysics, Cardiorenal and Metabolic Diseases Research Center, University of Mississippi Medical Center, Jackson, Mississippi
| | - Terry D Hinds
- Department of Pharmacology and Nutritional Sciences, University of Kentucky College of Medicine, Lexington, Kentucky
| |
Collapse
|
2
|
Hinds TD, Creeden JF, Gordon DM, Spegele AC, Britton SL, Koch LG, Stec DE. Rats Genetically Selected for High Aerobic Exercise Capacity Have Elevated Plasma Bilirubin by Upregulation of Hepatic Biliverdin Reductase-A (BVRA) and Suppression of UGT1A1. Antioxidants (Basel) 2020; 9:antiox9090889. [PMID: 32961782 PMCID: PMC7554716 DOI: 10.3390/antiox9090889] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2020] [Revised: 09/12/2020] [Accepted: 09/16/2020] [Indexed: 12/15/2022] Open
Abstract
Exercise in humans and animals increases plasma bilirubin levels, but the mechanism by which this occurs is unknown. In the present study, we utilized rats genetically selected for high capacity running (HCR) and low capacity running (LCR) to determine pathways in the liver that aerobic exercise modifies to control plasma bilirubin. The HCR rats, compared to the LCR, exhibited significantly higher levels of plasma bilirubin and the hepatic enzyme that produces it, biliverdin reductase-A (BVRA). The HCR also had reduced expression of the glucuronyl hepatic enzyme UGT1A1, which lowers plasma bilirubin. Recently, bilirubin has been shown to activate the peroxisome proliferator-activated receptor-α (PPARα), a ligand-induced transcription factor, and the higher bilirubin HCR rats had significantly increased PPARα-target genes Fgf21, Abcd3, and Gys2. These are known to promote liver function and glycogen storage, which we found by Periodic acid–Schiff (PAS) staining that hepatic glycogen content was higher in the HCR versus the LCR. Our results demonstrate that exercise stimulates pathways that raise plasma bilirubin through alterations in hepatic enzymes involved in bilirubin synthesis and metabolism, improving liver function, and glycogen content. These mechanisms may explain the beneficial effects of exercise on plasma bilirubin levels and health in humans.
Collapse
Affiliation(s)
- Terry D. Hinds
- Department of Pharmacology and Nutritional Sciences, University of Kentucky College of Medicine, Lexington, KY 40508, USA
- Correspondence: (T.D.H.J.); (D.E.S.)
| | - Justin F. Creeden
- Department of Neurosciences, University of Toledo College of Medicine, Toledo, OH 43614, USA; (J.F.C.); (D.M.G.)
| | - Darren M. Gordon
- Department of Neurosciences, University of Toledo College of Medicine, Toledo, OH 43614, USA; (J.F.C.); (D.M.G.)
| | - Adam C. Spegele
- Department of Physiology and Pharmacology, University of Toledo College of Medicine, Toledo, OH 43614, USA; (A.C.S.); (L.G.K.)
| | - Steven L. Britton
- Department of Anesthesiology, Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, MI 48109, USA;
| | - Lauren G. Koch
- Department of Physiology and Pharmacology, University of Toledo College of Medicine, Toledo, OH 43614, USA; (A.C.S.); (L.G.K.)
| | - David E. Stec
- Center for Excellence in Cardiovascular-Renal Research, Department of Physiology & Biophysics, University of Mississippi Medical Center, 2500 North State St, Jackson, MS 392161, USA
- Correspondence: (T.D.H.J.); (D.E.S.)
| |
Collapse
|
3
|
Gordon DM, Blomquist TM, Miruzzi SA, McCullumsmith R, Stec DE, Hinds TD. RNA sequencing in human HepG2 hepatocytes reveals PPAR-α mediates transcriptome responsiveness of bilirubin. Physiol Genomics 2019; 51:234-240. [PMID: 31074682 DOI: 10.1152/physiolgenomics.00028.2019] [Citation(s) in RCA: 49] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Bilirubin is a potent antioxidant that reduces inflammation and the accumulation of fat. There have been reports of gene responses to bilirubin, which was mostly attributed to its antioxidant function. Using RNA sequencing, we found that biliverdin, which is rapidly reduced to bilirubin, induced transcriptome responses in human HepG2 hepatocytes in a peroxisome proliferator-activated receptor (PPAR)-α-dependent fashion (398 genes with >2-fold change; false discovery rate P < 0.05). For comparison, a much narrower set of genes demonstrated differential expression when PPAR-α was suppressed via lentiviral shRNA knockdown (23 genes). Gene set enrichment analysis revealed the bilirubin-PPAR-α transcriptome mediates pathways for oxidation-reduction processes, mitochondrial function, response to nutrients, fatty acid oxidation, and lipid homeostasis. Together, these findings suggest that transcriptome responses from the generation of bilirubin are mostly PPAR-α dependent, and its antioxidant function regulates a smaller set of genes.
Collapse
Affiliation(s)
- Darren M Gordon
- Center for Hypertension and Personalized Medicine, Department of Physiology & Pharmacology, University of Toledo College of Medicine , Toledo, Ohio
| | - Thomas M Blomquist
- Department of Pathology, University of Toledo College of Medicine , Toledo, Ohio
| | - Scott A Miruzzi
- Department of Neuroscience, University of Toledo College of Medicine , Toledo, Ohio
| | - Robert McCullumsmith
- Department of Neuroscience, University of Toledo College of Medicine , Toledo, Ohio
| | - David E Stec
- Department of Physiology & Biophysics, Mississippi Center for Obesity Research, University of Mississippi Medical Center , Jackson, Mississippi
| | - Terry D Hinds
- Center for Hypertension and Personalized Medicine, Department of Physiology & Pharmacology, University of Toledo College of Medicine , Toledo, Ohio
| |
Collapse
|
4
|
Weaver L, Hamoud AR, Stec DE, Hinds TD. Biliverdin reductase and bilirubin in hepatic disease. Am J Physiol Gastrointest Liver Physiol 2018; 314:G668-G676. [PMID: 29494209 PMCID: PMC6032063 DOI: 10.1152/ajpgi.00026.2018] [Citation(s) in RCA: 59] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The buildup of fat in the liver (hepatic steatosis) is the first step in a series of incidents that may drive hepatic disease. Obesity is the leading cause of nonalcoholic fatty liver disease (NAFLD), in which hepatic steatosis progresses to liver disease. Chronic alcohol exposure also induces fat accumulation in the liver and shares numerous similarities to obesity-induced NAFLD. Regardless of whether hepatic steatosis is due to obesity or long-term alcohol use, it still may lead to hepatic fibrosis, cirrhosis, or possibly hepatocellular carcinoma. The antioxidant bilirubin and the enzyme that generates it, biliverdin reductase A (BVRA), are components of the heme catabolic pathway that have been shown to reduce hepatic steatosis. This review discusses the roles for bilirubin and BVRA in the prevention of steatosis, their functions in the later stages of liver disease, and their potential therapeutic application.
Collapse
Affiliation(s)
- Lauren Weaver
- 1Department of Physiology and Pharmacology, Center for Hypertension and Personalized Medicine, University of Toledo College of Medicine, Toledo, Ohio
| | - Abdul-rizaq Hamoud
- 1Department of Physiology and Pharmacology, Center for Hypertension and Personalized Medicine, University of Toledo College of Medicine, Toledo, Ohio
| | - David E. Stec
- 2Department of Physiology and Biophysics, Mississippi Center for Obesity Research, University of Mississippi Medical Center, Jackson, Mississippi
| | - Terry D. Hinds
- 1Department of Physiology and Pharmacology, Center for Hypertension and Personalized Medicine, University of Toledo College of Medicine, Toledo, Ohio
| |
Collapse
|
5
|
Hamoud AR, Weaver L, Stec DE, Hinds TD. Bilirubin in the Liver-Gut Signaling Axis. Trends Endocrinol Metab 2018; 29:140-150. [PMID: 29409713 PMCID: PMC5831340 DOI: 10.1016/j.tem.2018.01.002] [Citation(s) in RCA: 132] [Impact Index Per Article: 22.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/27/2017] [Revised: 01/02/2018] [Accepted: 01/05/2018] [Indexed: 02/08/2023]
Abstract
Bilirubin is a component of the heme catabolic pathway that is essential for liver function and has been shown to reduce hepatic fat accumulation. High plasma bilirubin levels are reflective of liver disease due to an injurious effect on hepatocytes. In healthy liver, bilirubin is conjugated and excreted to the intestine and converted by microbes to urobilinoids, which are reduced to the predominant pigment in feces, stercobilin, or reabsorbed. The function of urobilinoids in the gut or their physiological relevance of reabsorption is not well understood. In this review, we discuss the relationship of hepatic bilirubin signaling to the intestinal microbiota and its regulation of the liver-gut axis, as well as its capacity to mediate these processes.
Collapse
Affiliation(s)
- Abdul-Rizaq Hamoud
- Center for Hypertension and Personalized Medicine, Department of Physiology & Pharmacology, University of Toledo College of Medicine, Toledo, OH 43614, USA
| | - Lauren Weaver
- Center for Hypertension and Personalized Medicine, Department of Physiology & Pharmacology, University of Toledo College of Medicine, Toledo, OH 43614, USA
| | - David E Stec
- Department of Physiology & Biophysics, Mississippi Center for Obesity Research, University of Mississippi Medical Center, Jackson, MS 39216, USA
| | - Terry D Hinds
- Center for Hypertension and Personalized Medicine, Department of Physiology & Pharmacology, University of Toledo College of Medicine, Toledo, OH 43614, USA.
| |
Collapse
|
6
|
Deetman PE, Kwakernaak AJ, Bakker SJL, Dullaart RPF. Low-normal free thyroxine confers decreased serum bilirubin in type 2 diabetes mellitus. Thyroid 2013; 23:1367-73. [PMID: 23638994 PMCID: PMC3822386 DOI: 10.1089/thy.2013.0156] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
BACKGROUND Bilirubin may confer cardiovascular protection because of its strong antioxidative properties. Both thyroid dysfunction and the diabetic state affect bilirubin metabolism. Here we tested whether low-normal thyroid function affects serum bilirubin among euthyroid subjects with and without type 2 diabetes mellitus (T2DM). METHODS Serum total bilirubin, thyrotropin and free thyroxine (free T4), transaminases, insulin sensitivity (homeostasis model assessment), and lipids were measured in 74 T2DM and 82 nondiabetic subjects with thyrotropin and free T4 levels within the euthyroid range. RESULTS Bilirubin was positively related to free T4 in T2DM subjects (r = 0.370, p < 0.001), but not in nondiabetic subjects (r = 0.047, p = 0.68). In age- and sex-adjusted multiple linear regression analysis, free T4 was found to interact positively with the presence of T2DM on serum bilirubin (interaction term: β = 0.251, p = 0.024). This interaction remained present after additional adjustment for alcohol intake, aspartate aminotransferase and insulin sensitivity (interaction term: β = 0.222, p = 0.043), or alternatively for cholesterol and triglycerides (interaction term: β = 0.203, p = 0.057). CONCLUSIONS Lower free T4 levels within the euthyroid range confer decreased bilirubin in T2DM. Low-normal thyroid function could enhance atherosclerosis susceptibility in T2DM by decreasing serum bilirubin.
Collapse
Affiliation(s)
- Petronella E Deetman
- Department of Internal Medicine, University of Groningen and University Medical Center Groningen , Groningen, The Netherlands
| | | | | | | |
Collapse
|
7
|
Van Hoydonck PG, Temme EH, Schouten EG. Serum bilirubin concentration in a Belgian population: the association with smoking status and type of cigarettes. Int J Epidemiol 2001; 30:1465-72. [PMID: 11821365 DOI: 10.1093/ije/30.6.1465] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
BACKGROUND The endogenous antioxidant serum bilirubin may scavenge free radical species from cigarette smoke. Smokers are expected to have lower serum bilirubin levels than never smokers, but this has never been evaluated in a random population sample of women and men. In addition, in vitro studies indicate that filter cigarette smoke might enhance bilirubin oxidation more than non-filter cigarette smoke. METHODS In this paper, data were analysed from the Belgian Interuniversity Research on Nutrition and Health (BIRNH) study. We investigated the association of smoking and type of cigarettes with serum bilirubin concentrations in men and women using multiple regression models taking into account differences in baseline and smoking characteristics. RESULTS In men, current smokers had lower crude and adjusted serum bilirubin concentrations compared with never smokers (P = 0.0001). For women, the association between smoking and serum bilirubin concentrations adjusted for age was in the same direction as for men, but did not reach statistical significance. Male former smokers had serum bilirubin concentrations in between those of current smokers and never smokers, while female former smokers had even higher (+ 0.50 micromol/l) serum bilirubin concentrations than never smokers. Male subjects smoking filter cigarettes showed a higher serum bilirubin concentration than those smoking cigarettes without a filter (adjusted difference: 0.49 micromol/l; P = 0.03). The duration of smoking was inversely and significantly related to serum bilirubin concentrations (P = 0.0003). CONCLUSION Smoking may lower serum bilirubin concentrations in men, especially in those smoking non-filter cigarettes. The duration of smoking is a more important determinant for serum bilirubin concentrations than the number of cigarettes smoked per day, which may indicate the cumulative negative effects of smoking on the endogenous antioxidant system. Results for females pointed in the same direction, but were less clear, possibly due to low numbers of smoking women, who were largely young and smoked mainly filter cigarettes for a shorter period of time.
Collapse
Affiliation(s)
- P G Van Hoydonck
- University of Leuven, Department of Public Health, Division of Nutritional Epidemiology, Kapucijnenvoer 33-35, B3000 Leuven, Belgium.
| | | | | |
Collapse
|