Vidimce Josif, Pillay Johara, Shrestha Nirajan, Dong Lan-Feng, Neuzil Jiri, Wagner Karl-Heinz, Holland Olivia Jane, Bulmer Andrew Cameron
School of Medical Science, Griffith University, Gold Coast, QLD, Australia.
Institute of Biotechnology, Czech Academy of Sciences, Prague, Czechia.
Front Pharmacol. 2021 Mar 8;12:586715. doi: 10.3389/fphar.2021.586715. eCollection 2021.
Circulating bilirubin is associated with reduced adiposity in human and animal studies. A possible explanation is provided by data that demonstrates that bilirubin inhibits mitochondrial function and decreases efficient energy production. However, it remains unclear whether hyperbilirubinemic animals have similar perturbed mitochondrial function and whether this is important for regulation of energy homeostasis. To investigate the impact of unconjugated hyperbilirubinemia on body composition, and mitochondrial function in hepatic tissue and skeletal muscle. 1) Food intake and bodyweight gain of 14-week old hyperbilirubinemic Gunn ( = 19) and normobilirubinemic littermate (control; = 19) rats were measured over a 17-day period. 2) Body composition was determined using dual-energy X-ray absorptiometry and by measuring organ and skeletal muscle masses. 3) Mitochondrial function was assessed using high-resolution respirometry of homogenized liver and intact permeabilized extensor digitorum longus and soleus fibers. 4) Liver tissue was flash frozen for later gene (qPCR), protein (Western Blot and citrate synthase activity) and lipid analysis. Female hyperbilirubinemic rats had significantly reduced fat mass (Gunn: 9.94 ± 5.35 vs. Control: 16.6 ± 6.90 g, < 0.05) and hepatic triglyceride concentration (Gunn: 2.39 ± 0.92 vs. Control: 4.65 ± 1.67 mg g, < 0.01) compared to normobilirubinemic controls. Furthermore, hyperbilirubinemic rats consumed fewer calories daily ( < 0.01) and were less energetically efficient (Gunn: 8.09 ± 5.75 vs. Control: 14.9 ± 5.10 g bodyweight kcal, < 0.05). Hepatic mitochondria of hyperbilirubinemic rats demonstrated increased flux control ratio (FCR) via complex I and II (CI+II) (Gunn: 0.78 ± 0.16 vs. Control: 0.62 ± 0.09, < 0.05). Similarly, exogenous addition of 31.3 or 62.5 μM unconjugated bilirubin to control liver homogenates significantly increased CI+II FCR ( < 0.05). Hepatic gene expression was significantly increased in hyperbilirubinemic females while and was significantly greater in male hyperbilirubinemic rats ( < 0.05). Finally, hepatic mitochondrial complex IV subunit 1 protein expression was significantly increased in female hyperbilirubinemic rats ( < 0.01). This is the first study to comprehensively assess body composition, fat metabolism, and mitochondrial function in hyperbilirubinemic rats. Our findings show that hyperbilirubinemia is associated with reduced fat mass, and increased hepatic mitochondrial biogenesis, specifically in female animals, suggesting a dual role of elevated bilirubin and reduced UGT1A1 function on adiposity and body composition.
在人体和动物研究中，循环胆红素与肥胖程度降低有关。有数据表明胆红素会抑制线粒体功能并减少能量的有效产生，这可能为此提供了一种解释。然而，目前尚不清楚高胆红素血症动物是否具有类似的线粒体功能紊乱，以及这对能量稳态调节是否重要。为了研究未结合型高胆红素血症对身体组成以及肝脏组织和骨骼肌中线粒体功能的影响。1）在17天的时间里测量了14周龄的高胆红素血症Gunn大鼠（n = 19）和正常胆红素血症同窝大鼠（对照；n = 19）的食物摄入量和体重增加情况。2）使用双能X射线吸收法并通过测量器官和骨骼肌质量来确定身体组成。3）使用高分辨率呼吸测定法评估匀浆肝脏以及完整通透的趾长伸肌和比目鱼肌纤维的线粒体功能。4）将肝脏组织速冻以备后续进行基因（qPCR）、蛋白质（蛋白质免疫印迹和柠檬酸合酶活性）和脂质分析。与正常胆红素血症对照组相比，高胆红素血症雌性大鼠的脂肪量显著减少（Gunn组：9.94±5.35克 vs. 对照组：16.6±6.90克，P < 0.05），肝脏甘油三酯浓度也显著降低（Gunn组：2.39±0.92 vs. 对照组：4.65±1.67毫克/克，P < 0.01）。此外，高胆红素血症大鼠每日消耗的卡路里较少（P < 0.01），能量效率也较低（Gunn组：8.09±5.75 vs. 对照组：14.9±5.10克体重/千卡，P < 0.05）。高胆红素血症大鼠的肝脏线粒体通过复合体I和II（CI+II）表现出增加的通量控制率（FCR）（Gunn组：0.78±0.16 vs. 对照组：0.62±0.09，P < 0.05）。同样，向对照肝脏匀浆中额外添加31.3或62.5μM未结合胆红素会显著增加CI+II FCR（P < 0.05）。高胆红素血症雌性大鼠的肝脏基因表达显著增加，而雄性高胆红素血症大鼠的[具体基因名称未给出]和[具体基因名称未给出]显著更高（P < 0.05）。最后，高胆红素血症雌性大鼠的肝脏线粒体复合体IV亚基1蛋白表达显著增加（P < 0.01）。这是第一项全面评估高胆红素血症大鼠身体组成、脂肪代谢和线粒体功能的研究。我们的研究结果表明，高胆红素血症与脂肪量减少以及肝脏线粒体生物合成增加有关，特别是在雌性动物中，这表明胆红素升高和UGT1A1功能降低对肥胖和身体组成具有双重作用。
