Biliverdin reductase activity in cattle, sheep, rabbits and rats

Cellular Stress Response (Hormesis) in Response to Bioactive Nutraceuticals with Relevance to Alzheimer Disease

Significance: Alzheimer's disease (AD) is the most common form of dementia associated with aging. As the large Baby Boomer population ages, risk of developing AD increases significantly, and this portion of the population will increase significantly over the next several decades. Recent Advances: Research suggests that a delay in the age of onset by 5 years can dramatically decrease both the incidence and cost of AD. In this review, the role of nuclear factor erythroid 2-related factor 2 (Nrf2) in AD is examined in the context of heme oxygenase-1 (HO-1) and biliverdin reductase-A (BVR-A) and the beneficial potential of selected bioactive nutraceuticals. Critical Issues: Nrf2, a transcription factor that binds to enhancer sequences in antioxidant response elements (ARE) of DNA, is significantly decreased in AD brain. Downstream targets of Nrf2 include, among other proteins, HO-1. BVR-A is activated when biliverdin is produced. Both HO-1 and BVR-A also are oxidatively or nitrosatively modified in AD brain and in its earlier stage, amnestic mild cognitive impairment (MCI), contributing to the oxidative stress, altered insulin signaling, and cellular damage observed in the pathogenesis and progression of AD. Bioactive nutraceuticals exhibit anti-inflammatory, antioxidant, and neuroprotective properties and are potential topics of future clinical research. Specifically, ferulic acid ethyl ester, sulforaphane, epigallocatechin-3-gallate, and resveratrol target Nrf2 and have shown potential to delay the progression of AD in animal models and in some studies involving MCI patients. Future Directions: Understanding the regulation of Nrf2 and its downstream targets can potentially elucidate therapeutic options for delaying the progression of AD. Antioxid. Redox Signal. 38, 643-669.

Biliverdin reductase: a target for cancer therapy?

Biliverdin reductase (BVR) is a multifunctional protein that is the primary source of the potent antioxidant, bilirubin. BVR regulates activities/functions in the insulin/IGF-1/IRK/PI3K/MAPK pathways. Activation of certain kinases in these pathways is/are hallmark(s) of cancerous cells. The protein is a scaffold/bridge and intracellular transporter of kinases that regulate growth and proliferation of cells, including PKCs, ERK and Akt, and their targets including NF-κB, Elk1, HO-1, and iNOS. The scaffold and transport functions enable activated BVR to relocate from the cytosol to the nucleus or to the plasma membrane, depending on the activating stimulus. This enables the reductase to function in diverse signaling pathways. And, its expression at the transcript and protein levels are increased in human tumors and the infiltrating T-cells, monocytes and circulating lymphocytes, as well as the circulating and infiltrating macrophages. These functions suggest that the cytoprotective role of BVR may be permissive for cancer/tumor growth. In this review, we summarize the recent developments that define the pro-growth activities of BVR, particularly with respect to its input into the MAPK signaling pathway and present evidence that BVR-based peptides inhibit activation of protein kinases, including MEK, PKCδ, and ERK as well as downstream targets including Elk1 and iNOS, and thus offers a credible novel approach to reduce cancer cell proliferation.

A protective role for heme oxygenase-1 in INS-1 cells and rat islets that are exposed to high glucose conditions

Heme oxygenase-1 (HO-1) has been described as an inducible protein that is capable of cytoprotection via radical scavenging and the prevention of apoptosis. Chronic exposure to hyperglycemia can lead to cellular dysfunction that may become irreversible over time, and this process has been termed glucose toxicity. Yet little is known about the relation between glucose toxicity and HO-1 in the islets. The purposes of the present study were to determine whether prolonged exposure of pancreatic islets to a supraphysiologic glucose concentration disrupts the intracellular balance between reactive oxygen species (ROS) and HO-1, and so this causes defective insulin secretion; we also wanted to evaluate a protective role for HO-1 in pancreatic islets against high glucose levels. The intracellular peroxide levels of the pancreatic islets (INS-1 cell, rat islet) were increased in the high glucose media (30 mM glucose or 50 mM ribose). The HO-1 expression was induced in the INS-1 cells by the high glucose levels. Both the HO-1 expression and glucose stimulated insulin secretion (GSIS) was decreased simultaneously in the islets by treatment of the HO-1 antisense. The HO-1 was upregulated in the INS-1 cells by hemin, an inducer of HO-1. And, HO-1 upregulation induced by hemin reversed the GSIS in the islets at a high glucose condition. These results suggest HO-1 seems to mediate the protective response of pancreatic islets against the oxidative stress that is due to high glucose conditions.

Bile pigments in fishes: a review

Gallbladder (GB) bile of most cyclostomes, elasmobranchs, and teleosts contains appreciable amounts of biliverdin (BV) and bilirubin (BR) conjugates with lesser amounts of unconjugated BR in certain species. Certain elasmobranch and teleost species have been reported to have primarily BV or BR in bile. The appearance of the enzyme BV reductase, which converts BV to BR in mammals, evolved quite early in the evolution of vertebrate species; however, exceptions exist in certain fishes, amphibians, reptiles, and mammals whose bile contains primarily BV. Nearly all analytical studies on bile pigment composition in fishes to date have utilized only GB bile, which may or may not always be representative of the pigments excreted in freshly collected hepatic duct bile. The concentration of BV and BR in GB bile of fishes increases markedly during prolonged fasts. From the limited data currently available, there appears to be no systematic development from primitive to advanced forms in the appearance of certain bile pigments in fishes. While bile of most aquatic species contains appreciable amounts of both BV and BR, it is interesting that the bile of most terrestrial avian and reptilian forms contains primarily BV. The serum of fishes, except for certain bony species such as eels (Anguilleformes) and cottids (Scorpaeniformes), is a light yellow color due to the presence of BR and is similar to that observed in higher vertebrates. Serum from certain eels and cottids is bluish green in color due to the presence of a variety of chromoproteins that contain BV firmly bound as the prosthetic group.

Heme oxygenase-1 inhibits atherogenesis in Watanabe heritable hyperlipidemic rabbits

BACKGROUND

Heme oxygenase-1 (HO-1) is proposed to have a variety of adaptive responses against oxidative stress. To examine the function of HO-1 against atherogenesis in vivo, we observed the effects of HO-1 inhibition on atherosclerotic lesion formation in Watanabe heritable hyperlipidemic rabbits (WHHL). Methods and Results- During 4 weeks of a 1% cholesterol diet, intravenous injections of Sn-protoporphyrin IX to inhibit HO-1 (S group, n=10) and saline as a control (C group, n=10) were given to 3-month-old WHHL rabbits. The percentages of en face atherosclerotic lesion areas in total descending aorta by Sudan IV staining (EFA) and the ratio of intima to media in microscopic atherosclerotic lesions in the ascending aortas (I/M) were calculated. Two different quantitative methods revealed significantly greater atherosclerotic lesions in the S group than the C group (EFA, P<0.001; I/M, P<0.005). HO-1 expression in atherosclerotic lesions was confirmed by Northern blot and immunohistochemical analyses. The dominant cell types expressing HO-1 were macrophages and foam cells, in which oxidized phospholipids were also accumulated. HO inhibition increased plasma and tissue lipid peroxide levels without affecting plasma lipid co osition.

CONCLUSIONS

These results suggest the possibilities that HO-1 has antiatherogenic properties in vivo and that the antiatherogenic properties of HO-1 are conducted through the prevention of lipid peroxidation.

A protective role for heme oxygenase expression in pancreatic islets exposed to interleukin-1beta

Heme oxygenase (HO)-1 expression was investigated in rat isolated pancreatic islets. Freshly isolated islets showed no evidence of HO-1 expression. After a 20-h culture, there was a small increase in HO-1 in control islets, and interleukin-1beta (IL-1beta) induced HO-1 expression above control levels. N(G)-monomethyl-L-arginine inhibited the IL-1beta-induced increase in HO-1. Sodium nitroprusside-generated nitric oxide also increased HO-1 expression. CoCl2 induced a concentration- and time-dependent increase in HO-1, but not heat shock protein 70, expression. Cobalt chloride (CoCl2) protected islets from the inhibitory effects of IL-1beta on glucose-stimulated insulin release and glucose oxidation. Nickel chloride did not mimic the effects of CoCl2. An inhibitor of HO-1 activity, zinc-protoporphyrin IX (ZnPP), prevented the protective effect of CoCl2 on insulin release with IL-1beta but did not affect HO-1 expression or the inhibitory response to IL-1beta alone. ZnPP also inhibited the protective effect of hemin in IL-1beta-treated islets. CoCl2 inhibited the marked increase in islet nitrite production in response to IL-1beta. Cobalt-protoporphyrin IX (CoPP), which increased HO expression and activity, also protected islets from the inhibitory effects of IL-1beta, even though IL-1beta largely blocked the CoPP-induced increase in HO-1 expression. In betaHC9 cells, CoCl2 increased HO-1 expression and HO activity, whereas CoPP directly activated HO. ZnPP inhibited basal and CoCl2-stimulated HO activity. Thus, increased HO-1 expression and/or HO activity in response to CoCl2, CoPP, and hemin, seems to mediate protective responses of pancreatic islets against IL-1beta. HO-1 may be protective of beta-cells because of the scavenging of free heme, the antioxidant effects of the end-product bilirubin, or the generation of carbon monoxide, which might have insulin secretion-promoting effects and inhibitory effects on nitric oxide synthase.

Bile and bilirubin excretion in relation to hepatic energy status during hemorrhagic shock and hypoxemia in rabbits

OBJECTIVE

We investigated the relation between in vivo hepatocyte excretion of bile and bilirubin and hepatic energy status in rabbit models of hemorrhagic shock and hypoxemia.

DESIGN

Randomized animal study.

MATERIALS AND METHODS

After creation of a total biliary fistula, hemorrhagic shock with mean pressure of 50 mm Hg (10 rabbits) or hypoxemia with Pao2 at 35 mm Hg (8 rabbits) was induced for 60 minutes. We determined bile flow, excretion of bilirubin and total bile acids, the plasma level of bilirubin, and arterial ketone body ratio, which reflects hepatic mitochondrial function.

MEASUREMENTS AND MAIN RESULTS

Both the hemorrhagic shock and the hypoxemic models showed decreases in bile flow and excretion of bilirubin and total bile acids as well as increase in the plasma level of bilirubin in association with decreases in the hepatic energy charge and the arterial ketone body ratio.

CONCLUSIONS

Bile flow and the excretion of bilirubin were correlated with the hepatic energy status.

Bile pigments in gallbladder and freshly-secreted hepatic duct bile from fed and fasted rainbow trout, Oncorhynchus mykiss

1. Chromatographic analyses of bile pigments in rainbow trout reveal the presence of primarily unconjugated biliverdin (BV) and bilirubin (BR) glycosyl conjugates. Only trace amounts of unconjugated BR are present in hepatic duct (HD) bile: no beta-glucuronidase activity is detectable. 2. The per cent of BV and BR in HD and gallbladder biles is similar in fasted trout; however, the per cent of BV is significantly increased in HD bile from fed fish. 3. Fasting decreases the rate of choleresis but does not alter the excretory rate of endogenous BV or BR. 4. Erythrocyte life span is estimated to be approximately 500 days.