Omega-3 fatty acids supplementation on major cardiovascular outcomes: an umbrella review of meta-analyses of observational studies and randomized controlled trials.

OBJECTIVE: Omega-3 fatty acids are commonly used as a lipid-lowering agent or dietary supplement for the purpose of prevention of cardiovascular diseases. However, even large-scale clinical trials have not shown significant results demonstrating clear clinical benefits in cardiovascular diseases. Thus, this umbrella review aims to summarize and evaluate the evidence of clinical effects of omega-3 fatty acids supplementation on cardiovascular outcomes through comprehensive analyses of previous randomized controlled trials (RCTs) or observational cohort studies. MATERIALS AND METHODS: We conducted relevant publication search in PubMed, Embase, and Cochrane Database of Systematic Reviews. We retrieved and analyzed 3,298 articles published until August 28th, 2019. RESULTS: We identified 29 relevant articles and analyzed 83 meta-analyses of RCTs or cohort studies therefrom. As a result, we identified 12 cardiovascular outcomes that are related to omega-3 fatty acids supplementation. Among them, total mortality from major cardiovascular causes (RR 0.92, 95% CI 0.86 to 0.98) had significant inverse associations, and moreover, statistical significances were maintained even in subgroup analysis of large-scale RCTs including more than 1,000 patients (RR 0.94, 95% CI 0.88 to 0.99). CONCLUSIONS: Our umbrella review study shows that omega-3 fatty acids supplementation have a clinical benefit in reducing mortality from cardiovascular causes. However, many studies still have shown conflicting results, and therefore, further studies will be needed to verify the clinical benefit of omega-3 supplementation.

Licorice and its active compound glycyrrhizic acid ameliorates cisplatin-induced nephrotoxicity through inactivation of p53 by scavenging ROS and overexpression of p21 in human renal proximal tubular epithelial cells.

OBJECTIVE: Nephrotoxicity is one of the major side effects that limit the use of cisplatin in cancer therapy. Cisplatin-induced apoptosis in renal cells is associated with reactive oxygen species (ROS)-mediated p53 activation. Licorice (Glycyrrhiza uralensis Fischer) is one of the most widely used medicinal herbs in Korea, China and Japan. The aim of the study was to evaluate the protective effects of licorice extract (LE) and its active compound glycyrrhizic acid (GA) against cisplatin-induced nephrotoxicity in human renal proximal tubular epithelial (HK-2) cells. MATERIALS AND METHODS: HK-2 cells were pretreated with LE or GA for 1 h and then treated with 40 µM of cisplatin for indicated times under the serum-free condition. Cell viability was evaluated by MTT assay. Apoptosis was evaluated by flow cytometric analysis and caspase-3 activity. The intracellular ROS levels were determined by DCFH-DA assay. The expression and phosphorylation levels of protein were evaluated by Western blot and densitometry analysis. RESULTS: When treating HK-2 cells with LE or GA, both of them alleviated cisplatin-induced cytotoxicity and apoptosis. LE and GA inhibited caspase-3 activity and polymerase (PARP) cleavage in cisplatin-treated cells. LE and GA also inhibited p53 expression and its phosphorylation as well as ROS production in cells exposed to cisplatin. Meanwhile, LE and GA enhanced cisplatin-induced p21 expression, which then led to S-phase arrest in cell cycle and limited cell growth. Presumably, increased p21 expression may contribute to cellular prevention from cisplatin-induced apoptosis, because p21 is the key molecule to cytoprotection during cisplatin-induced nephrotoxicity. CONCLUSIONS: These results suggest that LE and GA ameliorate cisplatin-induced apoptosis through reduction of ROS-mediating p53 activation and promotion of p21 expression in HK-2 cells.

Glechoma hederacea Suppresses RANKL-mediated Osteoclastogenesis.

Glechoma hederacea (GH), commonly known as ground-ivy or gill-over-the-ground, has been extensively used in folk remedies for relieving symptoms of inflammatory disorders. However, the molecular mechanisms underlying the therapeutic action of GH are poorly understood. Here, we demonstrate that GH constituents inhibit osteoclastogenesis by abrogating receptor activator of nuclear κ-B ligand (RANKL)-induced free cytosolic Ca(2+) ([Ca(2+)]i) oscillations. To evaluate the effect of GH on osteoclastogenesis, we assessed the formation of multi-nucleated cells (MNCs), enzymatic activity of tartrate-resistant acidic phosphatase (TRAP), expression of nuclear factor of activated T-cells cytoplasmic 1 (NFATc1), and [Ca(2+)]i alterations in response to treatment with GH ethanol extract (GHE) in primarily cultured bone marrow-derived macrophages (BMMs). Treatment of RANKL-stimulated or non-stimulated BMMs with GHE markedly suppressed MNC formation, TRAP activity, and NFATc1 expression in a dose-dependent manner. Additionally, GHE treatment induced a large transient elevation in [Ca(2+)]i while suppressing RANKL-induced [Ca(2+)]i oscillations, which are essential for NFATc1 activation. GHE-evoked increase in [Ca(2+)]i was dependent on extracellular Ca(2+) and was inhibited by 1,4-dihydropyridine (DHP), inhibitor of voltage-gated Ca(2+) channels (VGCCs), but was independent of store-operated Ca(2+) channels. Notably, after transient [Ca(2+)] elevation, treatment with GHE desensitized the VGCCs, resulting in an abrogation of RANKL-induced [Ca(2+)]i oscillations and MNC formation. These findings demonstrate that treatment of BMMs with GHE suppresses RANKL-mediated osteoclastogenesis by activating and then desensitizing DHP-sensitive VGCCs, suggesting potential applications of GH in the treatment of bone disorders, such as periodontitis, osteoporosis, and rheumatoid arthritis.

Needs regarding care and factors associated with unmet needs in disease-free survivors of surgically treated lung cancer.

BACKGROUND: To evaluate the long-term needs of lung cancer survivors and to explore factors associated with unmet need. PATIENTS AND METHODS: We recruited lung patients treated with curative surgery from 2001 through 2006 at two centers in Korea. Needs in the domains of information, supportive care, education and counseling, and socioeconomic support were measured. We selected the four most frequently reported items of unmet need among 19 items in four domains. RESULTS: The most frequently reported unmet needs were Complementary and alternative medicine (CAM) and folk remedies (59.8%) in the Information domain, Counseling and treatment of depression and anxiety (63.5%) in the Supportive care domain, diet, exercise and weight control (55.1%) in the Education and counseling domain and Financial support (90.4%) in the socioeconomic support domain. Unmet needs for psychological treatment was significantly greater in participants who were employed (adjusted odds ratio [aOR], 2.25; 95% confidential interval [CI], 1.12 to 4.53). Unmet needs for diet, exercise and weight control were significantly greater in participants who had not received chemotherapy (aOR, 1.76; 95% CI, 1.09 to 2.85). Unmet need for financial support was greater in participants who were married (aOR, 4.14, 95%CI, 1.12 to 15.22) and those who had not received chemotherapy (aOR, 5.91, 95%CI, 1.91 to 18.31). CONCLUSION: There were substantial unmet needs for information regarding psychological support, education for diet and exercise, and financial support among lung cancer survivors.

Protective effect of the roots extract of Platycodon grandiflorum on bile duct ligation-induced hepatic fibrosis in rats.

The aim of the present study was to evaluate the protective effect of aqueous extract from Platycodon grandiflorum (BC703) on bile duct ligation (BDL)-induced hepatic fibrosis in rats. BDL rats were divided into three groups, which orally received distilled water or BC703 (10 or 50 mg/kg/day) for consecutive 28 days. Antifibrotic effects of BC703 on BDL-induced hepatic fibrosis in rats were estimated by assessing serum levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST), total bilirubin (TBIL), blood urea nitrogen (BUN), transforming growth factor-beta 1 (TGF-ß1) and hepatic levels of malondialdehyde (MDA), glutathione (GSH), total superoxide dismutase (SOD) and nitric oxide (NO). The biochemical observations were supplemented by histopathological examination of liver samples stained with hematoxylin and eosin and Masson's trichrome stain. ALT, AST, TBIL and BUN were elevated in the group treated with BDL alone than in the sham-operated group. These elevations were significantly decreased by BC703 treatment. Hepatic GSH and SOD levels, depressed by BDL, were also increased in the BC703 group. In addition, increases in hepatic MDA and NO levels in the BDL-induced cholestasis were attenuated by BC703 treatment. Furthermore, BC703 treatment significantly reduced the serum level of fibrogenic cytokine, TGF-ß1. Histopathological studies further substantiated the protective effect of BC703 on BDL-induced hepatic fibrosis in rat. BC703 may have beneficial effects not only on hepatic fibrosis by cholestasis but also on hepatic fibrosis development in patients with chronic hepatic disease.

First Report of an Armillaria Root Disease Pathogen, Armillaria gallica, Associated with Several New Hosts in Hawaii.

The loss and decline of native tree species caused by invasive plant pathogens is a major threat to the endangered endemic forests of the Hawaiian Islands (3). Thus, it is critical to characterize existing pathogens to evaluate potential invasiveness. In August 2005, rhizomorphs and mycelial bark fans of genet HI-4 were collected from dead/declining, mature trees of introduced Monterey pine (Pinus radiata) on the southern flank of Mauna Kea, Hawaii (approximately 19°42'55″N, 155°26'48″W, elevation 2,175 m). In March of 2008, three additional genets (HI-11, HI-13, and HI-16) were collected as rhizomorphs at a site named Pu'u La'au (west slope of the Mauna Kea Forest Reserve area, approximately 19°50'00″N, 155°35'35″W, elevation 2,275 to 2,550 m), approximately 20 km west-northwest of the HI-4 collection. These genets were collected from apparently healthy loblolly pine (Pinus taeda) that were introduced, apparently healthy mamane (Sophora chrysophylla; an endemic tree species of Hawaii), dead and dying mamane, and apparently healthy Methley plum (Prunus cerasifera × Prunus salicina) that was planted. All isolates were determined to have identical sequences in the intergenic spacer-1 rDNA region (GenBank Accession No. DQ995357). On the basis of somatic paring tests against North American Armillaria tester strains and 99% nucleotide sequence identities to GenBank Accession Nos. AY190245 and AY190246, these isolates were identified as Armillaria gallica. Past surveys have noted A. mellea sensu lato and A. nabsnona on numerous hosts in Hawaii, including mamane (3,4). However, to our knowledge, this is the first confirmed report of A. gallica in Hawaii, where it was found on mamane, Monterey pine, loblolly pine, and Methley plum. A. gallica has been widely categorized as a beneficial saprophyte, an opportunistic pathogen, or an aggressive pathogen (2). A recent study suggests that A. gallica can be highly pathogenic in some areas of the eastern United States and it is an important component of forest decline (2), especially under increasing stressors such as climate change. The isolation of A. gallica from declining stands on both introduced and endemic hosts under drought conditions suggests this pathogen is a contributing factor to forest decline on the island of Hawaii. Because the mamane tree is an important component of the native forest stands and essential to the endangered palila bird (Loxioides bailleui), which feeds almost exclusively on its green seeds (1), continued monitoring of Armillaria root disease is warranted. References: (1) P. C. Banko et al. J. Chem. Ecol. 28:1393, 2002. (2) N. J. Brazee and R. L. Wick. For. Ecol. Manage. 258:1605, 2009. (3) R. E. Burgan and R. E. Nelson. USDA For. Serv. Tech. Rep. PSW-3, 1972. (4) J. W. Hanna et al. Plant Dis. 91:634, 2007.

Dihydroartemisinin enhances radiosensitivity of human glioma cells in vitro.

PURPOSE: The antimalarial agent, artemisinin, also confers cancer-specific cytotoxic effects by reacting with ferrous iron atoms to form free radicals. Here, we investigated the radiosensitizing effects of dihydroartemisinin on glioma cells and assessed some possible mechanisms for these effects. MATERIALS AND METHODS: U373MG glioma cells treated with various concentrations of dihydroartemisinin plus radiation, and efficiency of radiosensitization was assessed by clonogenic survival assay. Expression and activity of antioxidant enzymes, glutathione-S-transferase (GST) were quantified by western blot and enzymatic activity analyses, respectively. RESULTS: Dihydroartemisinin showed higher cytotoxicity in the glioma cell lines than in the liver, breast or cervical cancer cell lines. In clonogenic survival assays, treatment with dihydroartemisinin alone dose-dependently reduced the number of U373MG colonies, while treatment with dihydroartemisinin plus gamma-irradiation showed far lower clonal survival than cultures treated with radiation or dihydroartemisinin alone. The radiosensitizing effect of dihydroartemisinin was blocked significantly by the free radical scavengers, NAC and TIRON, indicating association with dihydroartemisinin-induced ROS generation. In addition, the radiation-induced expression of endogenous GST was suppressed by treatment with dihydroartemisinin. The radiosensitizing effect of dihydroartemisinin was also markedly enhanced by the addition of holotransferrin CONCLUSION: Taken together, our results strongly suggest that dihydroartemisinin triggers production of ROS and inhibits GST activity, leading to effective and therapeutically relevant radiosensitization of human glioma cells.

Hypothalamic AMP-activated protein kinase mediates counter-regulatory responses to hypoglycaemia in rats.

AIMS/HYPOTHESIS: Appropriate counter-regulatory hormonal responses are essential for recovery from hypoglycaemia. Although the hypothalamus is known to be involved in these responses, the molecular mechanisms have not been fully elucidated. AMP-activated protein kinase (AMPK) functions as a cellular energy sensor, being activated during energy depletion. As AMPK is expressed in the hypothalamus, an important site of neuroendocrine regulation, the present study was undertaken to determine whether hypothalamic AMPK mediates counter-regulatory responses to hypoglycaemia. MATERIALS AND METHODS: Hypoglycaemia was induced by i.p. injection of regular insulin (6 U/kg) in Sprague-Dawley rats. Hypothalamic AMPK phosphorylation and activities were determined 1 h after i.p. insulin injection. To investigate the role of hypothalamic AMPK activation in mediating counter-regulatory responses, an AMPK inhibitor, compound C, was pre-administered intracerebroventricularly (i.c.v.) or dominant-negative (DN)-AMPK was overexpressed in the hypothalamus before induction of hypoglycaemia. RESULTS: Insulin-induced hypoglycaemia increased hypothalamic AMPK phosphorylation and alpha2-AMPK activities in rats. The change was significant in the arcuate nucleus/ventromedial hypothalamus (ARC/VMH) and paraventricular nuclei (PVN). Prior i.c.v. administration of compound C attenuated hypoglycaemia-induced increases in plasma concentrations of corticosterone, glucagon and catecholamines, resulting in severe and prolonged hypoglycaemia. ARC/VMH DN-AMPK overexpression impaired early counter-regulation, as evidenced by reduced glucagon and catecholamine responses. In contrast, PVN DN-AMPK overexpression attenuated late counter-regulation and corticosterone responses. CONCLUSIONS/INTERPRETATION: Systemic hypoglycaemia causes hypothalamic AMPK activation, which is important for counter-regulatory hormonal responses. Our data indicate that hypothalamic AMPK acts as a fuel gauge, sensing the whole-body energy state and regulating not only energy homeostasis but also neuroendocrine functions.

Neuroprotective effect of Ginkgo biloba L. extract in a rat model of Parkinson's disease.

The neuroprotective effects of a standardized extract of Ginkgo biloba L. (EGb 761) were investigated on 6-hydroxydopamine (6-OHDA)-induced neurotoxicity in the nigrostriatal dopaminergic system of the rat brain. Rats were given a week of pretreatment with daily administrations of EGb 761. Unilateral striatal injection of 6-OHDA was followed by treatment with EGb 761 for a week. Serial measurement of contralateral forepaw adjusting steps revealed a progressive deficit in motor activity. At 8 weeks after 6-OHDA lesion the number of contralateral forepaw adjusting steps was significantly higher in rats that were treated with high doses of EGb 761 (100 mg/kg daily) than in those treated with low doses (50 mg/kg) or with the vehicle. Dopamine neuron loss in the substantia nigra and a depletion in striatal dopamine corresponded with behavioural deficit. These data suggest that the neuroprotective effects of EGb 761 reduce the behavioural deficit in 6-OHDA lesions in rat and also indicates a possible role for the extract in the treatment of Parkinson's disease.

Hematopoietic effect of ginsenoside Rg3 in ICR mouse primary cultures and its application to a biological response modifier.

Ginsenoside Rg3, which is obtained as a by-product during the steaming of red ginseng, at 300 microg/ml enhanced the proliferation of the total spleen and bone marrow (BM) cells in both the cyclophosphamide (CYC)-treated and non-CYC-treated groups.

Effects of melanocortin receptor ligands on thyrotropin-releasing hormone release: evidence for the differential roles of melanocortin 3 and 4 receptors.

The hypothalamic melanocortin system is important in the central regulation of food intake and body weight. We have previously demonstrated that intracerebroventricular administration of alpha-melanocyte stimulating hormone (alpha-MSH), a nonselective MC3 and MC4 receptor agonist, stimulated plasma thyroid-stimulating hormone, and agouti-related protein (AgRP), an MC3 and MC4 receptor antagonist, suppressed it. In this study, we investigated the effects of MC3 and MC4 receptor (MC3-R and MC4-R) selective agonists and antagonists on the release of thyrotropin-releasing hormone (TRH) from hypothalamic explants in vitro. alpha-MSH stimulated TRH release from the rat hypothalamic explants (alpha-MSH 100 nm 230 +/- 22.9% basal, P < 0.005). In contrast, gamma 2-MSH, a selective MC3-R agonist, suppressed TRH release (gamma 2-MSH 10 microns 76.2 +/- 7.4% basal, P < 0.05). AgRP (83-132), a nonselective MC3/4-R antagonist, induced no change in TRH release whilst JKC-363 (cyclic [Mpr11, D-Nal14, Cys18, Asp22-NH2]-beta-MSH 11-22), a selective MC4-R antagonist, suppressed it (JKC-363 10 nm 57.2 +/- 11.5% basal, P < 0.05). Both AgRP (83-132) and JKC-363 blocked alpha-MSH stimulated TRH release but only AgRP (83-132) blocked the inhibitory effect of gamma 2-MSH on TRH release. These data suggest differential roles for the MC3 and MC4 receptors in TRH release; MC3-R agonism inhibiting and MC4-R agonism stimulating TRH release.

Calreticulin enriched as an early-stage encapsulation protein in wax moth Galleria mellonella larvae.

To investigate the molecular mechanism of the early-stage encapsulation reaction in insects, we purified a 47kDa protein from injected beads into Galleria mellonella larvae. When a cDNA clone was isolated, the 47kDa protein showed high homology with Drosophila and human calreticulin. Western blotting analysis showed that the 47kDa protein was present in the hemocytes, but not in the plasma. When the early-stage encapsulated beads were coated with 47kDa protein antibody and reinjected into G. mellonella larvae, any further encapsulation reaction was inhibited. These results suggest that calreticulin is involved in non-self recognition in invertebrate cellular defense reactions.

Protective effects of Debo on zinc-induced apoptosis of C6 glial cells via modulation of intracellular antioxidant, reduced glutathione.

In the present study, the mechanical basis of a traditional herbal prescription, Debo. on cytotoxic damage of the brain cells including C6 glial and PC12 cells has been studied. Traditionally, Debo has been employed for the purpose of preventing responses to trauma, ischemia, and other diseases in the nervous system. C6 glial cells were exposed to oxidative stress through the imployment of ZnCl2, and generates H2O2 and hydroxyl radicals by fenton reaction. ZnCl2-induced death of C6 glial cells, which was revealed as apoptosis by chromatin condensation as well as DNA fragmentation. Pretreatment of Debo significantly prevented apoptotic death of C6 glial cells via inhibition of H2O, generation as well as the recovering of an antioxidant, reduced glutathione (GSH). Also, deprivation of serum and glucose, found in ischemia, deceased the viability of PC12 cells up to 60% via generation of H2O2. However, Debo significantly protected cells from ischemic damage through decrease in H2O, generation. Furthermore, Debo markedly inhibited the transcriptional activation of NF-kappaB by ZnCI, in C6 glial cells. These results suggest that Debo may function as an antioxidant system against free radicals and be applicable to protect brain cells against oxidative or ischemic stresses.

The induction of BDNF and c-fos mRNA in the hippocampal formation after febrile seizures.

In this study we investigated the expression of brain-derived neurotrophic factor (BDNF) and c-fos mRNA in the hippocampal formation after febrile seizures (FSs) with in situ hybridization histochemistry using riboprobes. The induction of BDNF mRNA was firstly observed in the dentate gyrus at 30 min after FSs. The expression in the dentate gyrus peaked at 3 h and returned to basal level at 24 h. It was also observed in the CA3 of hippocampus from 2 to 3 h. The induction of c-fos mRNA was observed in the dentate gyrus at 30 min and 1 h. These observations suggest that BDNF and c-fos are the genes whose expression can be altered by FSs and might be related to pathologic alterations after FSs.

Acanthopanax senticosus root inhibits mast cell-dependent anaphylaxis.

BACKGROUND: Mast cells synthesize and secrete chemical mediators which play a central role in anaphylaxis. METHODS: The effect of Acanthopanax senticosus root (ASR) on mast cell-dependent anaphylaxis was investigated. RESULTS: ASR inhibited compound 48/80-induced systemic anaphylactic shock at the dose of 1.0 g/kg by 50%. When ASR was given as pre-treatment at concentrations ranging from 0.01 to 2.0 g/l, the histamine release from rat peritoneal mast cells induced by compound 48/80 was reduced in a dose-dependent manner. ASR (2.0 g/kg) also inhibited passive cutaneous anaphylaxis activated by anti-dinitrophenyl (DNP) IgE to 53.17+/-6.62%. Moreover, ASR inhibited tumor necrosis factor-alpha production in a concentration-dependent manner, and the treatment of 1 g/l blocked the production by 32.5+/-3.50% compared to saline value. CONCLUSIONS: ASR may possess effective anti-anaphylactic activity.

Effects of (-)-epigallocatechin-3-gallate, the main component of green tea, on the cloned rat brain Kv1.5 potassium channels.

The interaction of (-)-epigallocatechin-3-gallate (EGCG), the main component of green tea (Camellia sinensis), with rat brain Kv1.5 channels (rKv1.5) stably expressed in Chinese hamster ovary (CHO) cells was investigated using the whole-cell patch-clamp technique. EGCG inhibited rKv1.5 currents at +50 mV in a concentration-dependent manner, with an IC50 of 101.2+/-6.2 microM. Pretreatment with protein tyrosine kinase (PTK) inhibitors (10 microM genistein, 100 microM AG1296), a tyrosine phosphatase inhibitor (500 microM sodium orthovanadate), or a protein kinase C (PKC) inhibitor (10 microM chelerythrine) did not block the inhibitory effect of EGCG on rKv1.5. The inhibition of rKv1.5 by EGCG displayed voltage-independence over the full activation voltage range positive to +10 mV. EGCG had no effect on the midpoint potential or the slope factor for steady-state activation and inactivation. EGCG did not affect the ion selectivity of rKv1.5. The activation (at +50 mV) kinetics was significantly slowed by EGCG. During repolarization (at -40 mV), EGCG also slowed the deactivation of the tail currents, resulting in a crossover phenomenon. Reversal of inhibition was detected by the application of repetitive depolarizing pulses and of identical double pulses, especially during the early part of the activating pulse, in the presence of EGCG. EGCG-induced inhibition of rKv1.5 showed identical affinity between EGCG and the multiple closed states of rKv1.5. These results suggest that EGCG interacts directly with rKv1.5 channels. Furthermore, by analyzing the kinetics of the interaction between EGCG and rKv1.5, we conclude that the inhibition of rKv1.5 channels by EGCG includes at least two effects: EGCG preferentially binds to the channel in the closed state, and blocks the channel by pore occlusion while depolarization is maintained.

Heterologous expression of cytochrome P450 2D6 mutants, electron transfer, and catalysis of bufuralol hydroxylation: the role of aspartate 301 in structural integrity.

Cytochrome P450 (P450) 2D6 is a polymorphic human enzyme involved in the oxidation of >50 drugs, most of which contain a basic nitrogen. In confirmation of previous work by others, substitutions at Asp301 decreased rates of substrate oxidation by P450 2D6. An anionic residue (Asp, Glu) at this position was found to be important in proper protein folding and heme incorporation, and positively charged residues were particularly disruptive in bacterial and also in baculovirus expression systems. Truncation of 20 N-terminal amino acids had no significant effect on catalytic activity except to attenuate P450 2D6 interaction with membranes and NADPH-P450 reductase. The truncation of the N-terminus increased the level of bacterial expression of wild-type P450 2D6 (Asp301) but markedly reduced expression of all codon 301 mutants, including Glu301. Reduction of ferric P450 2D6 by NADPH-P450 reductase was enhanced in the presence of the prototypic substrate bufuralol. Bacterial flavodoxin, an NADPH-P450 reductase homolog, binds tightly to P450 2D6 but is inefficient in electron transfer to the heme. These results collectively indicate that the acidic residue at position 301 in P450 2D6 has a structural role in addition to any in substrate binding and that the N-terminus of P450 2D6 is relatively unimportant to catalytic activity beyond a role in facilitating binding to NADPH-P450 reductase.