Ketamine-induced hepatoprotection: the role of heme oxygenase-1.

Lipopolysaccharide (LPS) causes hepatic injury that is mediated, in part, by upregulation of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2). Ketamine has been shown to prevent these effects. Because upregulation of heme oxygenase-1 (HO-1) has hepatoprotective effects, as does carbon monoxide (CO), an end product of the HO-1 catalytic reaction, we examined the effects of HO-1 inhibition on ketamine-induced hepatoprotection and assessed whether CO could attenuate LPS-induced hepatic injury. One group of rats received ketamine (70 mg/kg ip) or saline concurrently with either the HO-1 inhibitor tin protoporphyrin IX (50 micromol/kg ip) or saline. Another group of rats received inhalational CO (250 ppm over 1 h) or room air. All rats were given LPS (20 mg/kg ip) or saline 1 h later and euthanized 5 h after LPS or saline. Liver was collected for iNOS, COX-2, and HO-1 (Western blot), NF-kappaB and PPAR-gamma analysis (EMSA), and iNOS and COX-2 mRNA analysis (RT-PCR). Serum was collected to measure alanine aminotransferase as an index of hepatocellular injury. HO-1 inhibition attenuated ketamine-induced hepatoprotection and downregulation of iNOS and COX-2 protein. CO prevented LPS-induced hepatic injury and upregulation of iNOS and COX-2 proteins. Although CO abolished the ability of LPS to diminish PPAR-gamma activity, it enhanced NF-kappaB activity. These data suggest that the hepatoprotective effects of ketamine are mediated primarily by HO-1 and its end product CO.

Structural studies of cytochrome P4501A1: Identification of substrate and cumene hydroperoxide binding regions in the active site of P4501A1 and characterization of the P4501A1 interaction with cytochrome P450 reductase

Cytochromes P450 are a superfamily of heme-thiolate proteins that function in a concert with another protein, cytochrome P450 reductase, as terminal oxidases of an enzymatic system catalyzing the metabolism of a variety of foreign compounds and endogenous substrates. In order to better understand P450s catalytic mechanism and substrate specificity, information about the structure of the active site is necessary. Given the lack of a crystal structure of mammalian P450, other methods have been used to elucidate the substrate recognition and binding site structure in the active center. In this project I utilized the photoaffinity labeling technique and site-directed mutagenesis approach to gain further structural insight into the active site of mammalian cytochrome P4501AI and examine the role of surface residues in the interaction of P4501A1 with the reductase. ^ Four crosslinked peptides were identified by photoaffinity labeling using diazido benzphetamine as a substrate analog. Alignment of the primary structure of cytochrome P4501A1 with that of bacterial cytochrome P450102 (the crystal structure of which is known) revealed that two of the isolated crosslinked peptides can be placed in the vicinity of heme (in the L helix region and β10-β11 sheet region of cytochrome P450102) and could be involved in substrate binding. The other two peptides were located on the surface of the protein with the label bound specifically to Lys residues that were proposed to be involved in reductase-P450 interaction. ^ Alternatively, it has been shown that some of the organic hydroperoxides can support P450 catalyzed reactions in the absence of NADPH, O2 and reductase. By means of photoaffinity labeling the cumene hydroperoxide binding region was identified. Using azidocumene as the photoaffinity label, the tripeptide T501-L502-K503 was shown to be the site where azidocumene covalently binds to P4501A1. The sequence alignment of cytochrome P4501A1 with cytochrome P450102 predicts that this region might correspond to β-sheet structure localized on the distal side of the heme ring near the I helix and the oxygen binding pocket. The role of Thr501 in the cumene hydroperoxide binding was confirmed by mutations of this residue and kinetic analysis of the effects of the mutations. ^ In addition, the role of two lysine residues, Lys271 and Lys279, in the interaction with reductase was examined by means of site-directed mutagenesis. The lysine residues were substituted with isoleucine and enzymatic activity of the wild type and the mutants were compared in reductase- and cumene hydroperoxide-supported systems. The lysine 279 residue has been shown to play a critical role in the P4501A1-reductase interaction. ^

STABILITY AND FOLDING OF MUTANT FORMS OF ISO-1 CYTOCHROME-C FROM SACCHAROMYCES CEREVISIAE

Partially functional forms of iso-1-cytochrome c from Saccharomyces cerevisiae were obtained by replacements of the evolutionarily conserved proline 71 with valine, isoleucine and threonine (Ernst et.al.,1985). Pro-71 lies at the juncture of two short helical regions and is believed to be important for proper local polypeptide chain folding within the iso-1-cytochrome c structure.^ To study folding in the absence of intermolecular disulfide dimer formation the free sulfhydryl group of Cys-102 was modified in both wild type and mutant proteins with an alkylating reagent, methyl methanethiosulfonate. Spectral analysis of the wild type and mutant proteins shows that the native-like functional (or partially functional) folded structure of cytochrome c is retained in the chemically modified derivatives. The replacement of Pro-71 with valine, isoleucine or threonine reduces the intensity of the 696 nm absorbance band which is an indicator of the Met-80 ligation to the heme. Thermal stability and guanidine hydrochloride unfolding studies of the mutant proteins shows a destabilization of the protein as a result of mutation. The degree of destabilization depends on the chemical nature of the substituent amino acid in the mutant protiens.^ Kinetics of folding/unfolding reactions of the proteins were monitored by fluorescence changes using stopped flow mixing to obtain guanidine hydrochloride concentration jumps ending below, within, and above the transition zone. The replacement of Pro-71 alters the rate on one of the fastest phases, $\tau\sb3$, while the two other phases, $\tau\sb1$ & $\tau\sb2$, remain the same.^ Slow refolding kinetic studies indicate that replacement of Pro-71 does not completely eliminate the absorbance or fluorescence detected slow phases leading to the conclusion that Pro-71 is not involved in the generation of the slow phases in the folding kinetics of iso-1-cytochrome c.^ The alkaline conformational change involving the disappearance of the 696 nm absorbance band occurs with increasing pH in the alkaline pH region (Davis et al., 1974). The apparent pK of this conformational change in mutant proteins is shifted as much as two pH units compared to wild type. The equilibrium and kinetic data of alkaline transition for the wild type follows a simple mechanism proposed by Davis et al., (1974) for horse heart cytochrome c. A more complex mechanism is proposed for the behavior of the mutant proteins. ^

CCTeta: A novel soluble guanylyl cyclase-interacting protein

Nitric oxide (NO) transduces most of its biological effects through activation of the heterodimeric enzyme, soluble guanylyl cyclase (sGC). Activation of sGC results in the production of 3′,5 ′-cyclic guanosine monophosphate (cGMP) from 5′ -guanosine triphosphate (GTP). In this thesis, we demonstrate a novel protein interaction between CCT (chaperonin containing t-complex polypeptide) subunit η and the α1β1 isoform of sGC. Using the yeast-two-hybrid system, CCTη was found to interact with the N-terminal portion of β1 subunit of sGC. This interaction was then confirmed in vitro with a co-immunoprecipitation from mouse brain. The interaction between these two proteins was further supported by a co-localization of the proteins within rat brain. Using the yeast-two-hybrid system, CCTη was found to bind to the N-terminal portion of sGC. In vitro assays with purified CCTη and Sf9 lysate expressing sGC resulted in a 33% inhibition of sodium nitroprusside (SNP)-stimulated sGC activity. The same assays were then performed using BAY41-2272, an NO-independent allosteric sGC activator, and CCTη had no effect on this activity. Furthermore, CCTη had no effect on the activity of αβCys105 sGC a constitutively active mutant that lacks a heme group. Of note is the fact that the full-length CCTη-expressing bacterial lysate inhibited the activity of sGC-expressing Sf9 lysate by 48% compared with GST alone. This indicates that the amino terminal 94 amino acids of CCTη are important to the inhibition of sGC activity. Lastly, a 45% inhibition of sGC activity by CCTη was seen in vivo in BE2 cells stably transfected with CCTη and treated with SNP. The fact that the inhibition of sGC was more pronounced with bacterial lysate expressing CCTη versus the purified CCTη implies that some factor in the bacterial lysate enhances the inhibitory effect of CCTη. Because the level of inhibition seen in bacterial lysate and in vivo experiments is similar, might imply that the factor that aids in CCTη effect on sGC is conserved. Together, these data suggest that CCTη is a novel type of sGC inhibitor that inhibits sGC by modifying the binding of NO to the heme group or the subsequent conformational changes induced by NO binding. ^

The role of nitric oxide in small intestinal motility in a model of acute inflammation

Motility responses of the small intestine of iNOS deficient mice (iNOS −/−) and their wildtype littermates (iNOS+/+) to the inflammatory challenge of lipopolysaccharide (LPS) were investigated. LPS administration failed to attenuate intestinal transit in iNOS−/− mice but depressed transit in their iNOS+/+ littermates. Supporting an inhibitory role for sustained nitric oxide (NO) synthesis in the regulation of intestinal motility during inflammation, iNOS immunoreactivity was upregulated in all regions of the small intestine of iNOS+/+ mice. In contrast, neuronal NOS was barely affected. Cyclooxygenase activation was determined by prostaglandin E2 (PGE2) concentration. Following LPS challenge, PGE2 levels were elevated in all intestinal segments in both animal groups. Moreover, COX-1 and COX-2 protein levels were elevated in iNOS+/+ mice in response to LPS, while COX-2 levels were similarly increased in iNOS −/− intestine. However, no apparent relationship was observed between increased prostaglandin concentrations and attenuated intestinal transit. The presence of heme oxygenase 1 (HO-1) in the murine small intestine was also investigated. In both animal groups HO-1 immunoreactivity in the proximal intestine increased in response to treatment, while the constitutive protein levels detected in the middle and distal intestine were unresponsive to LPS administration. No apparent correlation of HO-1 to the suppression of small intestinal motility induced by LPS administration was detected. The presence of S-nitrosylated contractile proteins in the small intestine was determined. γ-smooth muscle actin was basally nitrosylated as well as in response to LPS, but myosin light chain kinase and myosin regulatory chain (MLC20) were not. In conclusion, in a model of acute intestinal inflammation, iNOS-produced NO plays a significant role in suppressing small intestinal motility while nNOS, COX-1, COX-2 and HO-1 do not participate in this event. S-nitrosylation of γ-smooth muscle actin is associated with elevated levels of nitric oxide in the smooth muscle of murine small intestine. ^

New cytochromes P450: Tale of two variants

Cytochrome P450s, a superfamily of heme enzymes found in most living organisms. They are responsible for metabolism of many therapeutic drugs, industrial pollutants, carcinogens, and additives to foodstuffs, as well as some endogenous compounds including fatty acids and steroids. First pass drug metabolism studies represent mainly liver and small intestine elimination, and are viewed as the standard to predict therapeutic outcome. However, drug plasma levels determined after administration do not always correlate with therapeutic efficacy of the drug. Therefore, a possible explanation may come by understanding drug metabolism in extrahepatic tissues and/or at the site of drug action. Identification and characterization of novel tissue specific isoforms of P450 generated by alternative splicing of known P450 genes or as yet unidentified genes is essential to predict pharmacological outcome of drugs or the fate of a carcinogen that act at sites remote from liver. ^ Using RT-PCR, brain-specific cytochrome P450s were detected in samples of human autopsy brain. So far, we have identified two human brain variants including P450 2D7 and P450 1A1. We have shown the presence of the P450 1A1 brain specific splice variant in African Americans, Caucasians and Indians albeit different patterns of liver to brain variant ratio were seen distributed throughout each population. Interestingly, the splice variant was detected only in the brain but not in any other tissues from the same individual. Homology modeling was used to compare the variant 3D structure to the liver form structure and differences in the substrate access channels and substrate binding sites were noticed. Automated computational docking was used to predict the metabolic fate of the potent carcinogenic substrate, benzo[a]pyrene. P450 1A1 brain variant showed no binding orientations that could produce the active metabolite, whereas P450 1A1 liver form did reveal orientations capable of generating active carcinogenic product. In vitro P32 labeling studies verified the docking predictions. Therefore, the data support the hypothesis that P450 brain splice variants mediate the metabolism of xenobiotics by mechanisms distinct from the well-studied liver counterparts. ^

An integrated molecular biology and computational approach to CYP1A1 expression in human brain

The cytochromes P450 comprise a superfamily of heme-containing mono-oxygenases. These enzymes metabolize numerous xenobiotics, but also play a role in metabolism of endogenous compounds. The P450 1A1 enzyme generally metabolizes polycyclic aromatic hydrocarbons, and its expression can be induced by aryl hydrocarbon receptor (AhR) activation. CYP1A1 is an exception to the generality that the majority of CYPs demonstrate highest expression in liver; CYP1Al is present in numerous extrahepatic tissues, including brain. This P450 has been observed in two forms, wildtype (WT) and brain variant (BV), arising from alternatively spliced mRNA transcripts. The CYP1A1 BV mRNA presented an exon deletion and was detected in human brain but not liver tissue of the same individuals. ^ Quantitative PCR analyses were performed to determine CYP1A1 WT and BV transcript expression levels in normal, bipolar disorder or schizophrenic groups. In our samples, we show that CYP1A1 BV mRNA, when present, is found alongside the full-length form. Furthermore, we demonstrate a significant decrease in expression of CYP1A1 in patients with bipolar disorder or schizophrenia. The expression level was not influenced by post-mortem interval, tissue pH, age, tobacco use, or lifetime antipsychotic medication load. ^ There is no indication of increased brain CYP1A1 expression in normal smokers versus non-smokers in these samples. We observed slightly increased CYP1A1 expression only in bipolar and schizophrenic smokers versus non-smokers. This may be indicative of complex interactions between neuronal chemical environments and AhR-mediated CYP1A1 induction in brain. ^ Structural homology modeling demonstrated that P450 1A1 BV has several alterations to positions/orientations of substrate recognition site residues compared to the WT isoform. Automated substrate docking was employed to investigate the potential binding of neurological signaling molecules and neurotropic drugs, as well as to differentiate specificities of the two P450 1A1 isoforms. We consistently observed that the BV isoform produced energetically favorable substrate dockings in orientations not observed for the same substrate in the WT isoform. These results demonstrated that structural differences, namely an expanded substrate access channel and active site, confer greater capacity for unique compound docking positions suggesting a metabolic profile distinct from the wildtype form for these test compounds. ^

Micronutrient intakes and their associations with markers of inflammation, subclinical atherosclerosis, cardiovascular disease, type II diabetes and metabolic syndrome

We investigated cross-sectional associations between intakes of zinc, magnesium, heme- and non heme iron, beta-carotene, vitamin C and vitamin E and inflammation and subclinical atherosclerosis in the Multi-Ethnic Study of Atherosclerosis (MESA). We also investigated prospective associations between those micronutrients and incident MetS, T2D and CVD. Participants between 45-84 years of age at baseline were followed between 2000 and 2007. Dietary intake was assessed at baseline using a 120-item food frequency questionnaire. Multivariable linear regression and Cox proportional hazard regression models were used to evaluate associations of interest. Dietary intakes of non-heme iron and Mg were inversely associated with tHcy concentrations (geometric means across quintiles: 9.11, 8.86, 8.74, 8.71, and 8.50 µmol/L for non-heme iron, and 9.20, 9.00, 8.65, 8.76, and 8.33 µmol/L for Mg; ptrends <0.001). Mg intake was inversely associated with high CC-IMT; odds ratio (95% CI) for extreme quintiles 0.76 (0.58, 1.01), ptrend: 0.002. Dietary Zn and heme-iron were positively associated with CRP (geometric means: 1.73, 1.75, 1.78, 1.88, and 1.96 mg/L for Zn and 1.72, 1.76, 1.83, 1.86, and 1.94 mg/L for heme-iron). In the prospective analysis, dietary vitamin E intake was inversely associated with incident MetS and with incident CVD (HR [CI] for extreme quintiles - MetS: 0.78 [0.62-0.97] ptrend=0.01; CVD: 0.69 [0.46-1.03]; ptrend =0.04). Intake of heme-iron from red meat and Zn from red meat, but not from other sources, were each positively associated with risk of CVD (HR [CI] - heme-iron from red meat: 1.65 [1.10-2.47] ptrend = 0.01; Zn from red meat: 1.51 [1.02 - 2.24] ptrend =0.01) and MetS (HR [CI] - heme-iron from red meat: 1.25 [0.99-1.56] ptrend =0.03; Zn from red meat: 1.29 [1.03-1.61]; ptrend = 0.04). All associations evaluated were similar across different strata of gender, race-ethnicity and alcohol intake. Most of the micronutrients investigated were not associated with the outcomes of interest in this multi-ethnic cohort. These observations do not provide consistent support for the hypothesized association of individual nutrients with inflammatory markers, MetS, T2D, or CVD. However, nutrients consumed in red meat, or consumption of red meat as a whole, may increase risk of MetS and CVD.^

Differential stress response and susceptibility to oxidative injury in alveolar macrophages from C57BL/6J and C3H/HeJ mice following oxidant exposure

Studies have demonstrated a variable response to ozone among individuals and animal species and strains. For instance, C57BL/6J mice have a greater inflammatory response to ozone exposure than C3H/HeJ mice. In these studies, I utilized these strain differences in an effort to derive a mechanistic explanation to the variable strain sensitivity to ozone exposure. Therefore, alveolar macrophages (AM) from C57BL/6J and C3H/HeJ mice were exposed in vitro to hydrogen peroxide ($\rm H\sb2O\sb2$), heat and acetyl ceramide or in vivo to ozone. Necrosis and DNA fragmentation in macrophages from the two murine strains were determined to assess cytotoxicity following these treatments. In addition, synthesis and expression of the stress proteins, stress protein 72 (SP72) and heme oxygenase (HO-1), were examined following treatments. The in vitro experiments were conducted to eliminate the possibility of in vivo confounders (i.e., differences in breathing rates in the two strains) and thus directly implicate some inherent difference between cells from the two murine strains. $\rm H\sb2O\sb2$ and heat caused greater cytotoxicity in AM from C57BL/6J than C3H/HeJ mice and DNA fragmentation was a particularly sensitive indicator of cell injury. Similarly, AM from C57BL/6J mice were more sensitive to ozone exposure than cells from C3H/HeJ mice. Exposure to either 1 or 0.4 ppm ozone caused greater cytotoxicity in macrophages from C57BL/6J mice compared to macrophages from C3H/HeJ mice. The increased sensitivity of AM to injury was associated with decreased synthesis and expression of stress proteins. AM from C57BL/6J mice synthesized and expressed significantly less stress proteins in response to heat and ozone than AM from C3H/HeJ mice. Heat treatment resulted in greater synthesis and expression of SP72. In addition, macrophages from C57BL/6J mice expressed lower amounts of HO-1 than macrophages from C3H/HeJ mice following 0.4 ppm ozone exposure. Therefore, AM from C57BL/6J mice are more susceptible to oxidative injury than AM from C3H/HeJ mice which might be due to differential expression of stress proteins in these cells. ^