HO-2 has been found to be closely associated with sGC, ALA synthase, cytochrome P450 reductase and NOS in the brain (Wu and Wang, 2005). levels in tissue, e.g., kernicterus. Care must be used to ensure that when these compounds are used as therapeutic agents their deleterious effects are minimized or avoided. On balance, however, the strategies to target heme oxygenase-1 as described in this review offer promising therapeutic approaches to clinicians for the effective management of hypertension and renal function. The approaches detailed may prove to be seminal in the development of a new therapeutic strategy to treat hypertension. strong class=”kwd-title” Keywords: Heme oxygenase, Hypertension, Carbon monoxide, Bilirubin, Adiponectin 1. Introduction Heme oxygenase (HO), comprising HO-1 and HO-2, functions as Ibuprofen (Advil) the rate-limiting enzyme in the degradation of heme, a process that leads to formation of equimolar amounts of the bile pigment biliverdin, free iron and carbon monoxide (CO). Biliverdin formed in this reaction is rapidly converted to bilirubin. Heme oxygenase has been reported to be present in all tissues and is located in microsomes (Abraham and Kappas, 2008). Recently HO-1 and HO-2 have been shown to be also present in mitochondria (Di Noia et al., 2006; Turkseven et al., 2007). It is now apparent that HO-2 is constitutively expressed, whereas HO-1 is inducible by Ibuprofen (Advil) a large number of structurally unrelated pharmacological and other agents as well as by a variety of circumstances, that include heat shock and both cellular and oxidant stress. The HO system provides both antioxidant and anti-apoptotic properties due to its byproducts, bilirubin/biliverdin and CO, respectively (Abraham and Kappas, 2008) (Fig. 1). HO-1 is induced by oxidant stress and plays a crucial role in protection against oxidative insult in diabetes and cardiovascular diseases (Abraham and Kappas, 2008). Open in a separate window Fig. EPHB4 1 Functional consequences of the three heme degradation products, biliverdin, iron, and carbon monoxide (CO). Biliverdin is converted to bilirubin in a stereospecific manner by the cytosolic enzyme, biliverdin reductase. Both CO and bilirubin are bioactive molecules while the iron generated by heme degradation is immediately sequestered by associated increases in ferritin. Heme oxygenase (HO), the rate-limiting enzyme in heme degradation exists Ibuprofen (Advil) in two isoforms, HO-1 (inducible) and HO-2 (constitutive). A spectrum of drugs have been used to up-regulate HO-1 expression and HO activity. Stannous chloride (SnCl2) has been reported to lower blood pressure in spontaneously hypertensive rats (Sacerdoti et al., 1989). Metalloporphyrins, such as heme, heme arginate, and CoPP, are also commonly used drugs to induce HO-1 expression and HO activity and have been used to normalize blood pressure in animals and humans (Kordac et al., 1989; Levere et al., 1990; Abraham and Kappas, 2008). However, in discovering the ideal pharmacological drug, one must consider the dose and time of HO-1 induction. Therefore, most of the pharmacological inducers of HO-1, such as hemin and heavy metals, used in experimental studies may show cellular and tissue toxicity if used at high concentrations. Thus, the adverse and long-term effects of increased HO-1 expression and its effect Ibuprofen (Advil) on the heme synthesis pathway must be elucidated before clinical application. Ibuprofen (Advil) Aspirin is known to reduce the incidence of thrombotic occlusive events, such as myocardial infarction and stroke. Aspirin increased HO-1 protein levels and HO activity in a dose-dependent manner in cultured endothelial cells derived from human umbilical vein. Pretreatment of cells with aspirin or bilirubin protected endothelial cells from H2O2-mediated toxicity (Abraham and Kappas, 2008). Another type of drug, statins, the widely used lipid-lowering agents, substantially decrease cardiovascular morbidity and mortality in patients with and without coronary disease. Simvastatin and lovastatin increase HO-1 mRNA levels in cultured endothelial cells derived from human umbilical vein (Abraham and Kappas, 2008). Recently, we reported that L-4F and D-4F mimetic peptides increased levels of aortic HO-1 protein, HO activity, and extracellular superoxide dismutase while decreasing superoxide levels (Abraham and Kappas, 2008; Peterson et al., 2007). Probucol, an antioxidant drug, reduces the risk of restenosis. The protective effect of probucol depends not only on its ability to inhibit lipid oxidation but also on its ability to induce HO-1. Treatment with paclitaxel, possessing antiproliferative effects on vascular smooth muscle cells, resulted in a marked time- and dose-dependent induction of HO-1 mRNA, followed by corresponding increases in HO-1 protein and HO activity (Choi et al., 2004). It has been suggested that HO-1, induced by rapamycin in VSMCs, shows an antiproliferative effect, resulting in the reduction of the restenosis rate (Abraham and Kappas, 2008). Resveratrol, an important component in certain varieties of.
Chemokines and adhesion molecules expressed by inflamed LSECs are also potential targets for anti-inflammatory therapy in liver disease. usually refer to them as liver sinusoidal endothelial cells (LSECs), whereas isolated human cells have also been referred to as human hepatic sinusoidal endothelial cells (HSECs). For the purpose of this Review, we use the term LSEC. The exposure of these sinusoidal endothelial cells to blood originating from both the gut and the systemic circulation means they are ideally situated to remove and recycle blood-borne proteins and lipids. In combination with Kupffer cells (KCs; liver-resident macrophages), LSECs constitute the most powerful scavenger system in the body1. This activity is facilitated by the presence of fenestrae in LSECs, their lack of a AMG 837 classical basement membrane and their expression of promiscuous scavenger receptors combined with the most potent endocytic capacity in the body2. Thus, virus particles3, advanced glycation end products4 and modified LDL cholesterol5 can be cleared from the circulation within minutes by this route. Open in a separate window Fig. 1 Microanatomy of the human liver vascular tree.a | Low-power image of human liver tissue (stained with haematoxylin and eosin) illustrating the lobular organization of the liver, with zonal architecture indicated relative to the position of the portal tract. b | Expanded periportal section of the same image to illustrate the different vascular compartments within the parenchyma. c | Immunohistochemical staining of stabilin 1, which highlights liver endothelial cell distribution within hepatic tissue in a normal liver section. d | A comparison of the structure of liver sinusoidal endothelium and glomerular endothelium. Endothelial cells in different vascular beds are generated from common early embryological precursors and have broadly similar histological appearance and functional AMG 837 roles throughout the body. However, extensive variations in phenotype and function arise as a consequence of local microenvironmental signals dependent on anatomical localization6. The vascular architecture in the human liver is acquired by 17C25 weeks of gestation, but different vessels within the liver have distinct embryonic origins. Thus, portal vessels are derived from vitelline veins, whereas sinusoids develop from capillary vessels of the septum transversum and acquire their distinctive fenestrated phenotype by week 20 of gestation7 under the control of transcription factor GATA4 (ref.8). From this point onward, sinusoidal endothelial cells remain functionally and phenotypically distinct from the other vascular endothelial cells in the liver microenvironment and assume a phenotype that has many similarities with lymphatic endothelial cells9. The unique characteristics of LSECs are presented in Box?1. Both lymphatic and sinusoidal endothelial cells have minimal basement membranes and loosely organized cell junctions10 and share a complement of receptors such as lymphatic vessel endothelial hyaluronic acid receptor (LYVE1)11, prospero homeobox protein 1 (PROX1)12, podoplanin13 and liver/lymph node-specific ICAM3-grabbing non-integrin (LSIGN; also known as CLEC4M)14. It has been shown that the phenotype of sinusoidal endothelial cells varies across the liver acinus; a study of human liver tissue published in 2017 demonstrated that zone 1 LSECs are CD36hi and LYVE1low, whereas zone 2 and zone 3 LSECs are CD36low, LYVE1hi and CD32hi (ref.15). The presence of fenestrations or membranous pores organized into sieve plates is a feature that also distinguishes LSECs from the other hepatic endothelial populations2. Fenestrations are not unique to hepatic endothelial cells and are also MYO7A found in endothelium in endocrine glands such as the pancreas16, kidney17, spleen18 and bone marrow19 and are sometimes observed in tumour vasculature20. However, unlike other fenestrated endothelial AMG 837 populations such as those in the kidney, hepatic fenestrations lack a diaphragm or basal lamina and are grouped into organized sieve plates, rendering LSECs highly permeable (Fig.?1d). Many studies have implicated vascular endothelial growth factor (VEGF) as an essential factor for regulation of fenestrations21, but dynamic changes in hepatic fenestration number and size can occur rapidly in response to agents such as alcohol22, dietary constituents23 AMG 837 and fasting24 or calorie restriction25. The fenestrations act.