Structurally diverse deformed phenanthrenes from Strophioblachia fimbricalyx with cytotoxic activities by inducing cell apoptosis.

A group of phenanthrene derivatives with different deformed types, including four previously undescribed derivatives (1-4), an undescribed natural product (5) and five known compounds (6-10), were isolated from the leaves and stems of Strophioblachia fimbricalyx by molecular networking based on UPLC-MS/MS method. Their structures were established by 1D/2D NMR spectroscopy, HRESIMS, quantum chemistry calculation, and single crystal X-ray diffraction. In biogenic pathways, series of deformed phenanthrenes were all suspected to be derived from 6/6/6 tricyclic phenanthrenes with a gem-dimethyl unit in one ring as characteristic components of Strophioblachia. Fimbricalyxone (1) and trigoxyphin M (6) with a 6/6/5 tricyclic carbon skeleton were reported for the first time from the genus and fimbricalyxanhydride C (2) is the first example of anhydride type bearing a rare 8,9-oxycycle. All the isolates were evaluated for their cytotoxic activity against three tumor cell lines, and compounds 8 and 10 exhibited significant activity with IC50 values of 4.65-9.02 µM, and the structure-activity relationship of the deformed phenanthrenes was discussed. In addition, the X-ray structure of 8 and 10 and the antineoplastic activity of 10 are reported herein for the first time. Trigohowilol G (10) inhibiting the proliferation of A549 cells might be related to cell cycle distribution and the induction of S phase arrest, and it induced cell apoptosis through Bad/Bax/Cleaved PARP1 pathway.

EET intervention on Wnt1, NOV, and HO-1 signaling prevents obesity-induced cardiomyopathy in obese mice.

We have previously reported that epoxyeicosatrienoic acid (EET) has multiple beneficial effects on vascular function; in addition to its antiapoptotic action, it increases insulin sensitivity and inhibits inflammation. To uncover the signaling mechanisms by which EET reduces cardiomyopathy, we hypothesized that EET infusion might ameliorate obesity-induced cardiomyopathy by improving heme oxygenase (HO)-1, Wnt1, thermogenic gene levels, and mitochondrial integrity in cardiac tissues and improved pericardial fat phenotype. EET reduced levels of fasting blood glucose and proinflammatory adipokines, including nephroblastoma overexpressed (NOV) signaling, while increasing echocardiographic fractional shortening and O2 consumption. Of interest, we also noted a marked improvement in mitochondrial integrity, thermogenic genes, and Wnt 1 and HO-1 signaling mechanisms. Knockout of peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) in EET-treated mice resulted in a reversal of these beneficial effects including a decrease in myocardial Wnt1 and HO-1 expression and an increase in NOV. To further elucidate the effects of EET on pericardial adipose tissues, we observed EET treatment increases in adiponectin, PGC-1α, phospho-AMP-activated protein kinase, insulin receptor phosphorylation, and thermogenic genes, resulting in a "browning" pericardial adipose phenotype under high-fat diets. Collectively, these experiments demonstrate that an EET agonist increased Wnt1 and HO-1 signaling while decreasing NOV pathways and the progression of cardiomyopathy. Furthermore, this report presents a portal into potential therapeutic approaches for the treatment of heart failure and metabolic syndrome.NEW & NOTEWORTHY The mechanism by which EET acts on obesity-induced cardiomyopathy is unknown. Here, we describe a previously unrecognized function of EET infusion that inhibits nephroblastoma overexpressed (NOV) levels and activates Wnt1, hence identifying NOV inhibition and enhanced Wnt1 expression as novel pharmacological targets for the prevention and treatment of cardiomyopathy and heart failure.Listen to this article's corresponding podcast at http://ajpheart.physiology.org/content/early/2017/05/31/ajpheart.00093.2017.

Cyp2c44 gene disruption is associated with increased hematopoietic stem cells: implication in chronic hypoxia-induced pulmonary hypertension.

We have recently demonstrated that disruption of the murine cytochrome P-450 2c44 gene (Cyp2c44) exacerbates chronic hypoxia-induced pulmonary artery remodeling and hypertension in mice. Subsequently, we serendipitously found that Cyp2c44 gene disruption also increases hematopoietic stem cell (HSC) numbers in bone marrow and blood. Therefore, the objective of the present study was to investigate whether CYP2C44-derived eicosanoids regulate HSC proliferation/cell growth and whether increased HSCs contribute to chronic hypoxia-induced remodeling of pulmonary arteries in Cyp2c44 knockout mice. Our findings demonstrated that lack of CYP2C44 epoxygenase, which catalyzed the oxidation of arachidonic acid to epoxyeicosatrienoic (EETs) and hydroxyeicosatetraenoic (HETE) acids, increases the numbers of 1) HSCs (CD34+, CD117+, and CD133+), 2) proangiogenic (CD34+CD133+ and CD34+CD117+CD133+) cells, and 3) immunogenic/inflammatory (CD34+CD11b+, CD133+CD11b+, F4/80+, CD11b+, and F4/80+CD11b+) macrophages in bone marrow and blood compared with wild-type mice. Among the various CYP2C44-derived arachidonic acids, only 15-HETE decreased CD117+ cell numbers when applied to bone marrow cell cultures. Interestingly, CD133+ and von Willebrand factor-positive cells, which are derived from proangiogenic stem cells, are increased in the bone marrow, blood, and lungs of mice exposed to chronic hypoxia and in remodeled and occluded pulmonary arteries of CYP2C44-deficient mice. In conclusion, our results demonstrate that CYP2C44-derived 15-HETE plays a critical role in downregulating HSC proliferation and growth, because disruption of the Cyp2c44 gene increased HSCs that potentially contribute to chronic hypoxia-induced pulmonary arterial remodeling and occlusion.NEW & NOTEWORTHY This study demonstrates that cytochrome P-450 2C44 plays a critical role in controlling the phenotype of hematopoietic stem cells and that when this enzyme is knocked out, stem cells are differentiated. These stem cells give rise to increased circulating monocytes and macrophages and contribute to the pathogenesis of chronic hypoxia-induced pulmonary artery remodeling and hypertension.

Cyp2c44 gene disruption exacerbated pulmonary hypertension and heart failure in female but not male mice.

Epoxyeicosatrienoicacids (EETs), synthesized from arachidonic acid by epoxygenases of the CYP2C and CYP2J gene subfamilies, contribute to hypoxic pulmonary vasoconstriction (HPV) in mice. Despite their roles in HPV, it is controversial whether EETs mediate or ameliorate pulmonary hypertension (PH). A recent study showed that deficiency of Cyp2j did not protect male and female mice from hypoxia-induced PH. Since CYP2C44 is a functionally important epoxygenase, we hypothesized that knockout of the Cyp2c44 gene would protect both sexes of mice from hypoxia-induced PH. We tested this hypothesis in wild-type (WT) and Cyp2c44 knockout (Cyp2c44 (-/-)) mice exposed to normoxia (room air) and hypoxia (10% O2) for 5 weeks. Exposure of WT and Cyp2c44 (-/-) mice to hypoxia resulted in pulmonary vascular remodeling, increased pulmonary artery resistance, and decreased cardiac function in both sexes. However, in female Cyp2c44 (-/-) mice, compared with WT mice, (1) pulmonary artery resistance and right ventricular hypertrophy were greater, (2) cardiac index was lower, (3) left ventricular and arterial stiffness were higher, and (4) plasma aldosterone levels were higher, but (5) there was no difference in levels of EET in lungs and heart. Paradoxically and unexpectedly, we found that Cyp2c44 disruption exacerbated hypoxia-induced PH in female but not male mice. We attribute exacerbated PH in female Cyp2c44 (-/-) mice to elevated aldosterone and as-yet-unknown systemic factors. Therefore, we suggest a role for the human CYP2C genes in protecting women from severe PH and that this could be one of the underlying causes for a better 5-year survival rate in women than in men.

Oxidized HDL is a potent inducer of adipogenesis and causes activation of the Ang-II and 20-HETE systems in human obese females.

BACKGROUND: Oxidized-HDL (OX-HDL) has been reported to increase coronary events in obese patients; however, OX-HDL has not been studied in subjects with the metabolic syndrome. A high body mass index (BMI) correlates positively with higher levels of metabolic syndrome biomarkers including vasoconstrictors and adipokines. We hypothesize that a subject with a high BMI would present with higher levels of OX-HDL, 20-HETE and Angiotensin II (Ang II) with a reciprocal reduction in serum adiponectin. METHODS: Female subjects with a BMI of 17-25 and a BMI of 30-40, without overt cardiovascular disease, were enrolled in the study. All patients had a history and physical exam documenting the absence of signs and symptoms of cardiovascular disease. Appropriate screening was done and documented. Blood pressure was taken at two discrete points. The BP data are presented as the average. Changes in the relationship between BMI, OX-HDL, 20-HETE, Ang II, TNFα, isoprostane and adiponectin were examined. In addition, the effects of OX-HDL, 20-HETE and Ang II on adipogenesis were examined in human MSC derived adipocytes. RESULTS: Subjects with a high BMI>30 displayed an increase in OX-HDL and isoprostane (P<0.05) compared to those with the lower BMI<25 which was associated with an increase in Ang II and 20-HETE (p<0.05). Serum TNFα levels increased in subjects with a high BMI, compared to subjects with the lower BMI (p<0.05). In contrast, adiponectin levels were increased in subjects with a low BMI compared to obese subjects (p<0.05). In MSC derived adipocytes OX-HDL increased adipogenesis 6 fold at a concentration of 50ng compared to untreated adipocytes. Adipocytes treated with Ang II and 20-HETE also displayed increased adipogenesis (p<0.05), which was attenuated by endogenous increases of the anti-oxidant heme oxygenase-1. Our study demonstrates that OX-HDL presents a unique inflammatory biomarker profile in obese females with the metabolic syndrome at risk for developing cardiovascular disease. CONCLUSIONS: Females with increased BMI (30-40) exhibit a marked increase in OX-HDL and isoprostane levels, which was associated with an increase in 20-HETE, TNF α and Ang II and decreased levels of adiponectin when compared to a group with a low BMI. OX-HDL had a more powerful adipogenic effect when compared to 20-HETE and Ang II. Our study demonstrates that OX-HDL presents a unique inflammatory biomarker profile in obese females with the metabolic syndrome at risk for developing cardiovascular disease. This represents a novel mechanism by which females with a high BMI and controlled blood pressure remain "at risk" for the development of the metabolic syndrome as a result of increased adipogenesis by OX-HDL and activation of the 20-HETE and Ang II systems.

Increased epoxyeicosatrienoic acids and reduced soluble epoxide hydrolase expression in the preeclamptic placenta.

BACKGROUND: Epoxyeicosatrienoic acids (EETs) derived from cytochrome P450 (CYP)-dependent metabolism of arachidonic acid are increased in the plasma of women with preeclampsia as compared with normal pregnancy and are significantly higher in fetal than in maternal plasma and erythrocytes. We hypothesized that differences in EET synthesis or metabolism in the feto-placental unit contributed to the observed differences in circulating EETs. METHOD: To evaluate EETs, formation as well as the expression of relevant CYP isoforms and the metabolizing enzyme, soluble epoxide hydrolase (sEH), biopsies of placenta were collected from 19 normal pregnancy and 10 preeclampsia at the time of cesarean section delivery. EETs were extracted from tissue homogenates and analyzed by liquid chromatography coupled with tandem mass spectrometry. RESULTS: Both cis-EETs and trans-EETs were detected in the placenta. Concentration of total EETs was higher in the placenta from preeclampsia compared with normal pregnancy (2.37 ±â€Š1.42 ng/mg vs. 1.20 ±â€Š0.72 ng/mg, mean ±â€ŠSD, P < 0.01), especially the 5,6-, 8,9- and 11,12-EETs, measured in a subgroup of tissue samples (normal pregnancy = 10, preeclampsia = 5). By immunohistochemistry, sEH, CYP2J2, CYP4A11 were present in placental villi with different pattern distribution, whereas CYP2C8 was not detectable. Neither were CYP2J2, CYP4A11, and CYP2C8 detected in the umbilical cord. Western blot analysis of placenta homogenates showed reduced expression of sEH in preeclampsia as compared with normal pregnancy. CONCLUSION: Increased EETs in the placenta and umbilical cord are associated with the presence of CYP2J2, whereas reduced expression of sEH in preeclampsia may be the key factor of increased EETs in the placenta.

20-HETE contributes to ischemia-induced angiogenesis.

Angiogenesis is an important adaptation for recovery from peripheral ischemia. Here, we determined whether 20-hydroxyeicosatetraenoic acid (20-HETE) contributes to ischemia-induced angiogenesis and assessed its underlying molecular and cellular mechanisms using a mouse hindlimb-ischemia angiogenesis model. Hindlimb blood flow was measured by Laser Doppler Perfusion Imaging and microvessel density was determined by CD31 and tomato lectin staining. We found that systemic and local administration of a 20-HETE synthesis inhibitor, DDMS, or a 20-HETE antagonist, 6,15-20-HEDGE significantly reduced blood flow recovery and microvessel formation in response to ischemia. 20-HETE production, measured by LC/MS/MS, was markedly increased in ischemic muscles (91±11 vs. 8±2pg/mg in controls), which was associated with prominent upregulation of the 20-HETE synthase, CYP4A12. Immunofluorescence co-localized increased CYP4A12 expression in response to ischemia to CD31-positive EC in the ischemic hindlimb microvessels. We further showed that ischemia increased HIF-1α, VEGF, and VEGFR2 expression in gracilis muscles and that these increases were negated by DDMS and 6,15-20-HEDGE. Lastly, we showed that ERK1/2 of MAPK is a component of 20-HETE regulated ischemic angiogenesis. Taken together, these data indicate that 20-HETE is a critical contributor of ischemia-induced angiogenesis in vivo.

Involvement of gap junctions between smooth muscle cells in sustained hypoxic pulmonary vasoconstriction development: a potential role for 15-HETE and 20-HETE.

In response to hypoxia, the pulmonary artery normally constricts to maintain optimal ventilation-perfusion matching in the lung, but chronic hypoxia leads to the development of pulmonary hypertension. The mechanisms of sustained hypoxic pulmonary vasoconstriction (HPV) remain unclear. The aim of this study was to determine the role of gap junctions (GJs) between smooth muscle cells (SMCs) in the sustained HPV development and involvement of arachidonic acid (AA) metabolites in GJ-mediated signaling. Vascular tone was measured in bovine intrapulmonary arteries (BIPAs) using isometric force measurement technique. Expression of contractile proteins was determined by Western blot. AA metabolites in the bath fluid were analyzed by mass spectrometry. Prolonged hypoxia elicited endothelium-independent sustained HPV in BIPAs. Inhibition of GJs by 18ß-glycyrrhetinic acid (18ß-GA) and heptanol, nonspecific blockers, and Gap-27, a specific blocker, decreased HPV in deendothelized BIPAs. The sustained HPV was not dependent on Ca(2+) entry but decreased by removal of Ca(2+) and by Rho-kinase inhibition with Y-27632. Furthermore, inhibition of GJs decreased smooth muscle myosin heavy chain (SM-MHC) expression and myosin light chain phosphorylation in BIPAs. Interestingly, inhibition of 15- and 20-hydroxyeicosatetraenoic acid (HETE) synthesis decreased HPV in deendothelized BIPAs. 15-HETE- and 20-HETE-stimulated constriction of BIPAs was inhibited by 18ß-GA and Gap-27. Application of 15-HETE and 20-HETE to BIPAs increased SM-MHC expression, which was also suppressed by 18ß-GA and by inhibitors of lipoxygenase and cytochrome P450 monooxygenases. More interestingly, 15,20-dihydroxyeicosatetraenoic acid and 20-OH-prostaglandin E2, novel derivatives of 20-HETE, were detected in tissue bath fluid and synthesis of these derivatives was almost completely abolished by 18ß-GA. Taken together, our novel findings show that GJs between SMCs are involved in the sustained HPV in BIPAs, and 15-HETE and 20-HETE, through GJs, appear to mediate SM-MHC expression and contribute to the sustained HPV development.

Red blood cells (RBCs), epoxyeicosatrienoic acids (EETs) and adenosine triphosphate (ATP).

In addition to serving as carriers of O(2), red blood cells (RBCs) regulate vascular resistance and the distribution of microvascular perfusion by liberating adenosine triphosphate (ATP) and epoxyeicosatrienoic acids (EETs) upon exposure to a low O(2) environment. Therefore, RBCs act as sensors that respond to low pO(2) by releasing millimolar amounts of ATP, a signaling molecule, and lipid mediators (EETs). The release of EETs occurs by a mechanism that is activated by ATP stimulation of P2X(7) receptors coupled to ATP transporters, which should greatly amplify the circulatory response to ATP. RBCs are reservoirs of EETs and the primary sources of plasma EETs, which are esterified to the phospholipids of lipoproteins. Levels of free EETs in plasma are low, about 3% of circulating EETs. RBC EETs are produced by direct oxidation of arachidonic acid (AA) esterified to glycerophospholipids and the monooxygenase-like activity of hemoglobin. On release, EETs affect vascular tone, produce profibrinolysis and dampen inflammation. A soluble epoxide hydrolase (sEH) regulates the concentrations of RBC and vascular EETs by metabolizing both cis- and trans-EETs to form dihydroxyeicosatrienoic acids (DHETs). The function and pathophysiological roles of trans-EETs and erythro-DHETs has yet to be integrated into a physiological and pathophysiological context.

Roles of CYP2C29 and RXR gamma in vascular EET synthesis of female mice.

We aimed to identify which cytochrome P-450 (CYP) family/subfamily, as well as related transcription factor(s), is responsible for the estrogen-dependent synthesis of epoxyeicosatrienoic acids (EETs) to initiate shear stress-induced vasodilation. Microarray analysis indicated a significant upregulation of CYP2C29 and retinoid X receptor gamma (RXRgamma) in isolated mesenteric arteries/arterioles of female endothelial nitric oxide synthase-knockout mice, a result that was validated by real-time RT-PCR. The cannulated vessels were then perfused with 2 and 10 dyn/cm(2) shear stress, followed by collection of the perfusate to determine EET concentrations and isoforms. Shear stress dose-dependently stimulated the release of EETs into the perfusate, associated with an EET-mediated vasodilation, in which predominantly 14,15-EET and 11,12-EET contributed to the responses ( approximately 87.4% of total EETs). Transfection of vessels with CYP2C29 siRNA eliminated the release of EETs into the perfusate, which was evidenced by an abolished vasodilation, and confirmed by RT-PCR and Western blot analyses. Knockdown of RXRgamma in these vessels significantly inhibited the production of EETs, parallel to a reduced vasodilation. RXRgamma siRNA not only silenced the vascular RXRgamma expression, but synchronously downregulated CYP2C29 expression, leading to a reduced EET synthesis. In conclusion, our data provide the first evidence for a specific signaling cascade, by which estrogen potentially activates the CYP2C29 gene in the absence of nitric oxide, to synthesize EETs in response to shear stress, via an RXRgamma-related regulatory mechanism.

Contribution of epoxyeicosatrienoic acids to flow-induced dilation in arteries of male ERalpha knockout mice: role of aromatase.

We studied the roles of estrogen receptors (ER) and aromatase in the mediation of flow-induced dilation (FID) in isolated arteries of male ERalpha-knockout (ERalpha-KO) and wild-type (WT) mice. FID was comparable between gracilis arteries of WT and ERalpha-KO mice. In WT arteries, inhibition of NO and prostaglandins eliminated FID. In ERalpha-KO arteries, N(omega)-nitro-L-arginine methyl ester (L-NAME) inhibited FID by approximately 26%, whereas indomethacin inhibited dilations by approximately 50%. The remaining portion of the dilation was abolished by additional administration of 6-(2-proparglyoxyphenyl)hexanoic acid (PPOH) or iberiotoxin, inhibitors of epoxyeicosatrienoic acid (EET) synthesis and large-conductance potassium channels, respectively. By using an electrophysiological technique, we found that, in the presence of 10 dyne/cm(2) shear stress, perfusate passing through donor vessels isolated from gracilis muscle of ERalpha-KO mice subjected to L-NAME and indomethacin elicited smooth muscle hyperpolarization and a dilator response of endothelium-denuded detector vessels. These responses were prevented by the presence of iberiotoxin in detector or PPOH in donor vessels. Gas chromatography-mass spectrometry (GC-MS) analysis indicated a significant increase in arterial production of EETs in ERalpha-KO compared with WT mice. Western blot analysis showed a significantly reduced endothelial nitric oxide synthase expression but enhanced expressions of aromatase and ERbeta in ERalpha-KO arteries. Treatment of ERalpha-KO arteries with specific aromatase short-interfering RNA for 72 h, knocked down the aromatase mRNA and protein associated with elimination of EET-mediation of FID. Thus, FID in male ERalpha-KO arteries is maintained via an endothelium-derived hyperpolarizing factor/EET-mediated mechanism compensating for reduced NO mediation due, at least in part, to estrogen aromatized from testosterone.

Erythrocyte-derived epoxyeicosatrienoic acids.

Red blood cells (RBCs) are reservoirs for cis- and trans-epoxyeicosatrienoic acids (EETs) that can be released. The sources of EET release from RBCs include direct synthesis from arachidonic acid, peroxidation of phospholipids and EETs esterified into cellular phospholipids. The release of EETs from RBCs can be through cytosolic phospholipase A2 (PLA2), secretory PLA2 and other responses associated with ATP release from RBCs. The erythrocyte ATP, purinergic receptors, ATP-binding cassette transporters, PLA2 and cytoskeleton rearrangement may all participate in EET release in the microcirculatory deformation of RBCs. EETs are vasodilatory and are candidate endothelium-derived hyperpolarizing factors. Due to the anti-hypertensive, fibrinolytic, and anti-thrombotic properties of EETs, their release from RBCs is replete with implications for the control of circulation and rheological characteristics of the circulating blood.

Estrogen elicits cytochrome P450--mediated flow-induced dilation of arterioles in NO deficiency: role of PI3K-Akt phosphorylation in genomic regulation.

This study investigated the mechanisms responsible for the estrogen-dependent, cytochrome P450 (CYP)-mediated dilator responses to shear stress in arterioles of NO-deficient female rats and mice. Flow-induced dilation (FID) was assessed in isolated arterioles from N(G)-nitro-L-arginine methyl ester (L-NAME)-treated male and ovariectomized female rats before and after overnight incubation with 17beta-estradiol (17beta-E2, 10(-9) mol/L). In control conditions, prostaglandins (PGs) mediated FID, because indomethacin (INDO) abolished the responses. After incubation of the vessels with 17beta-E2, the basal tone of arterioles was significantly reduced and FID was augmented. INDO did not affect the dilation of the vessels incubated with 17beta-E2. Dilations of these vessels, however, were eliminated by PPOH and miconazole, inhibitors of CYP/epoxygenase. Simultaneous incubation of the vessels with 17beta-E2 plus ICI, 182,780, an estrogen receptor antagonist, or wortmannin, an inhibitor of phosphatidylinositol 3-kinase (PI3K) phosphorylation or the transcriptional inhibitor DRB, prevented the reduced arteriolar tone and the enhanced CYP-mediated FID caused by incubation of vessels with 17beta-E2. Western blot analysis indicated a significantly increased phospho-Akt level in arterioles incubated with 17beta-E2 compared with those without 17beta-E2. The enhanced phospho-Akt in response to 17beta-E2 was localized, by immunohistochemistry, to arteriolar endothelial cells. Moreover, GC-MS analysis indicated a significantly increased production of epoxyeicosatrienoic acids, vasodilator metabolites of CYP/epoxygenase, in arterioles incubated with 17beta-E2, a response that was prevented by ICI 182780 and wortmannin, respectively. Thus, estrogen, via a receptor-dependent, PI3K/Akt-mediated pathway, transcriptionally upregulates CYP activity, leading to an enhanced arteriolar response to shear stress.

Functional expression of human heme oxygenase-1 (HO-1) driven by HO-1 promoter in vitro and in vivo.

We developed a retrovirus-mediated human heme oxygenase-1 (HO-1) gene expression system and assessed the impact of heme on the inducibility of the HO-1 gene in rat lung microvessel (RLMV) endothelial cells and in newborn Sprague-Dawley (SD) rats. Overexpression of the HO-1 gene driven by HO-1 promoter (HOP) resulted in an increase in HO-1 protein and HO activity by 4.8- and 1.3-fold, respectively, compared to the viral LTR promoter. The increased HO-1 gene expression was associated with the enhancement of CO production. In cells transduced by HOP-driven HO-1 gene, there was a decrease in basal cyclooxygenase (COX) activity as measured by PGE(2). The degree of HO-1 expression and, consequently, the levels of cellular heme were directly related to COX activity. Supplementation with heme markedly increased PGE(2) and cGMP synthesis. In all (6/6) of newborn SD rats injected with retrovirus LSN-HOP-HO-1, both HO-1 and neo(r) transcripts were expressed in tissues. We hypothesize that degree of HO-1 gene expression resulted in a differential rate of cellular heme-dependent enzyme gene expression, which may play a vital role in maintaining cellular homeostasis.