A dynamical measure of the black hole mass in a quasar 11 billion years ago

Tight relationships exist in the local Universe between the central stellar properties of galaxies and the mass of their supermassive black hole (SMBH)1-3. These suggest that galaxies and black holes co-evolve, with the main regulation mechanism being energetic feedback from accretion onto the black hole during its quasar phase4-6. A crucial question is how the relationship between black holes and galaxies evolves with time; a key epoch to examine this relationship is at the peaks of star formation and black hole growth 8-12 billion years ago (redshifts 1-3)7. Here we report a dynamical measurement of the mass of the black hole in a luminous quasar at a redshift of 2, with a look back in time of 11 billion years, by spatially resolving the broad-line region (BLR). We detect a 40-μas (0.31-pc) spatial offset between the red and blue photocentres of the Hα line that traces the velocity gradient of a rotating BLR. The flux and differential phase spectra are well reproduced by a thick, moderately inclined disk of gas clouds within the sphere of influence of a central black hole with a mass of 3.2 × 108 solar masses. Molecular gas data reveal a dynamical mass for the host galaxy of 6 × 1011 solar masses, which indicates an undermassive black hole accreting at a super-Eddington rate. This suggests a host galaxy that grew faster than the SMBH, indicating a delay between galaxy and black hole formation for some systems.

Plasmodium falciparum Drug Resistance Genes pfmdr1 and pfcrt In Vivo Co-Expression During Artemether-Lumefantrine Therapy

Background: Artemisinin-based combination therapies (ACTs) are the global mainstay treatment of uncomplicated Plasmodium falciparum infections. PfMDR1 and PfCRT are two transmembrane transporters, associated with sensitivity to several antimalarials, found in the parasite food vacuole. Herein, we explore if their relatedness extends to overlapping patterns of gene transcriptional activity before and during ACT administration.

Methods: In a clinical trial performed in Tanzania, we explored the pfmdr1 and pfcrt transcription levels from 48 patients with uncomplicated P. falciparum malaria infections who underwent treatment with artemether-lumefantrine (AL). Samples analyzed were collected before treatment initiation and during the first 24 h of treatment. The frequency of PfMDR1 N86Y and PfCRT K76T was determined through PCR-RFLP or direct amplicon sequencing. Gene expression was analyzed by real-time quantitative PCR.

Results: A wide range of pre-treatment expression levels was observed for both genes, approximately 10-fold for pfcrt and 50-fold for pfmdr1. In addition, a significant positive correlation demonstrates pfmdr1 and pfcrt co-expression. After AL treatment initiation, pfmdr1 and pfcrt maintained the positive co-expression correlation, with mild downregulation throughout the 24 h post-treatment. Additionally, a trend was observed for PfMDR1 N86 alleles and higher expression before treatment initiation.

Conclusion:pfmdr1 and pfcrt showed significant co-expression patterns in vivo, which were generally maintained during ACT treatment. This observation points to relevant related roles in the normal parasite physiology, which seem essential to be maintained when the parasite is exposed to drug stress. In addition, keeping the simultaneous expression of both transporters might be advantageous for responding to the drug action.

Plasmodium falciparum K13 expression associated with parasite clearance during artemisinin-based combination therapy

BACKGROUND

Delayed parasite clearance and, consequently, reduced efficacy of artemisinin-based combination therapies have been linked with Plasmodium falciparum K13 gene SNPs in Southeast Asia. In Africa, significantly prolonged clearance has not yet been observed and the presently restricted variation in parasite clearance cannot be explained by K13 polymorphisms.

OBJECTIVES

Our aim was to study the in vivo pfK13 transcriptional response in patients treated with artemether-lumefantrine and explore whether the pfk13 transcripts can explain the patients' parasite clearance outcomes.

PATIENTS AND METHODS

A total of 47 Tanzanian children with microscopically confirmed uncomplicated P. falciparum malaria were hospitalized and received artemether-lumefantrine treatment (clinical trial ID: NCT00336375). RNA was extracted from venous blood samples collected before treatment initiation and at five more timepoints after treatment. cDNA was synthesized and pfk13 transcripts measured by real-time PCR.

RESULTS

A wide range of pfk13 transcript variation was observed throughout all timepoints after artemether-lumefantrine treatment. Taking parasite clearance data together with the pfk13 transcripts profile, we observed a negative correlation inferring that pfk13 down-regulation is associated with longer parasite clearance time.

CONCLUSIONS

The findings suggest that a reduced PfK13 transcriptional response may represent a first step towards artemisinin tolerance/resistance.

Differential effects of clinically used derivatives and metabolites of artemisinin in the activation of constitutive androstane receptor isoforms

BACKGROUND AND PURPOSE

Widespread resistance to antimalarial drugs requires combination therapies with increasing risk of pharmacokinetic drug-drug interactions. Here, we explore the capacity of antimalarial drugs to induce drug metabolism via activation of constitutive androstane receptors (CAR) by ligand binding.

EXPERIMENTAL APPROACH

A total of 21 selected antimalarials and 11 major metabolites were screened for binding to CAR isoforms using cellular and in vitro CAR-coactivator interaction assays, combined with in silico molecular docking. Identified ligands were further characterized by cell-based assays and primary human hepatocytes were used to elucidate induction of gene expression.

KEY RESULTS

Only two artemisinin derivatives arteether and artemether, the metabolite deoxyartemisinin and artemisinin itself demonstrated agonist binding to the major isoforms CAR1 and CAR3, while arteether and artemether were also inverse agonists of CAR2. Dihydroartemisinin and artesunate acted as weak inverse agonists of CAR1. While arteether showed the highest activities in vitro, it was less active than artemisinin in inducing hepatic CYP3A4 gene expression in hepatocytes.

CONCLUSIONS AND IMPLICATIONS

Artemisinin derivatives and metabolites differentially affect the activities of CAR isoforms and of the pregnane X receptor (PXR). This negates a common effect of these drugs on CAR/PXR-dependent induction of drug metabolism and further provides an explanation for artemisinin consistently inducing cytochrome P450 genes in vivo, whereas arteether and artemether do not. All these drugs are metabolized very rapidly, but only artemisinin is converted to an enzyme-inducing metabolite. For better understanding of pharmacokinetic drug-drug interaction possibilities, the inducing properties of artemisinin metabolites should be considered.

Cytochrome 1A1 and 1B1 gene diversity in the Zanzibar islands

Amodiaquine (AQ) is a 4-aminoquinoline widely used in the treatment of malaria as part of the artemisinin combination therapy (ACT). AQ is metabolised towards its main metabolite desethylamodiaquine mainly by cytochrome P450 2C8 (CYP2C8). CYP1A1 and CYP1B1 play a minor role in the metabolism but they seem to be significantly involved in the formation of the short-lived quinine-imine. To complete the genetic variation picture of the main genes involved in AQ metabolism in the Zanzibar population, previously characterised for CYP2C8, we analysed in this study CYP1A1 and CYP1B1 main genetic polymorphisms. The results obtained show a low frequency of the CYP1A1*2B/C allele (2.4%) and a high frequency of CYP1B1*6 (approximately 42%) followed by CYP1B1*2 (approximately 27%) in Zanzibar islands. Genotype data for CYP1A1 and CYP1B1 show a low incidence of fast metabolisers, revealing a relatively safe genetic background in Zanzibar's population regarding the appearance of adverse effects.

CYP2C8 and antimalaria drug efficacy

Malaria is a major infectious disease. In the last 10 years it has killed more than 20 million people, mainly small children in Africa. The highly efficacious artemisinine combination therapy is being launched globally, constituting the main hope for fighting the disease. Amodiaquine is a main partner in these combinations. Amodiaquine is almost entirely metabolized by the polymorphic cytochrome P450 (CYP) isoform 2C8 to the pharmacologically active desethylamodiaquine. The question remains whether the efficacy of amodiaquine is affected by the gene polymorphism. Genotype-inferred low metabolizers are found in 1-4% of African populations, which corresponds to millions of expected exposures to the drug. In vivo pharmacokinetic data on amodiaquine is limited. By combining it with published in vitro pharmacodynamic and drug metabolism information, we review and predict the possible relevance, or lack of, of CYP2C8 polymorphisms in the present and future efficacy of amodiaquine. Chloroquine and dapsone, both substrates of CYP2C8, are also discussed in the same context.

Quinoline resistance associated polymorphisms in the pfcrt, pfmdr1 and pfmrp genes of Plasmodium falciparum in Iran

Plasmodium falciparum resistance to chloroquine (CQ) has been documented in Iran since the early 1980s and has since gradually increased. Iran is therefore reviewing its national drug policy for malaria control. We describe the prevalence of single nucleotide polymorphisms (SNP) associated with quinoline drug resistance in south eastern Iran. Pre-treatment blood from patients with uncomplicated but symptomatic P. falciparum infection was analysed. Polymorphisms at codons 76, 152, 163 and 220 of the pfcrt gene (chloroquine resistance transporter) and at codons 86, 184, 1034, 1042 and 1246 of the pfmdr1 gene (multidrug resistance) were determined by PCR-RFLP and sequencing. In addition, SNPs on a recently described multidrug resistance protein (pfmrp) and a microsatellite (MS-4760) in the pfnhe-1 (sodium hydrogen exchanger) gene associated with quinoline and quinine resistance, respectively, were investigated for the first time in field samples not from Thailand. pfcrt 76T was found in 99% and pfmdr1 86Y in 72% of the samples. pfmrp 191H and 437S associated with decreased quinoline response were found to be absolutely linked at a frequency of 13.6%. The pfnhe-1 MS-4760 one repeat allele associated to quinine response in vitro was also detected. Sequencing of the pfcrt 72-76 haplotype revealed that SVMNT was the most common allele as previously observed in India. This suggests that pfcrt found in the Iranian P. falciparum population may have the same origin as in the P. falciparum populations in India but different from that normally found in south east Asia. In conclusion, the frequencies of quinoline resistance associated gene polymorphisms in this region suggest a population that has been significantly selected for by the long use of CQ.

Pharmacodynamic interactions of amodiaquine and its major metabolite desethylamodiaquine with artemisinin, quinine and atovaquone in Plasmodium falciparum in vitro

The antimalarial in vitro activities of amodiaquine and desethylamodiaquine in combination with atovaquone, quinine and artemisinin against Plasmodium falciparum were investigated in strains F-32, FCR-3 and K-1. These parasitic strains have different sensitivity profiles to the standard antimalarial chloroquine, but all can be considered sensitive to the test drugs, representing the recommended situation for introduction of two partner drugs in combination therapy. Amodiaquine showed marked synergism when combined with each of the three partner compounds at concentration ratios between 90 and 9x10(-7), including the therapeutically relevant range. The interaction profiles of desethylamodiaquine with quinine and artemisinin also showed predominantly synergism over a wide range of concentration ratios between 70 and 9x10(-7). The responses to all combinations exhibited signs of strain-specificity, but such phenomena were usually observed outside the therapeutic range of the concentration ratios. Synergism was generally more marked with increasing EC values, i.e. at concentrations expected to be therapeutically effective and thus clinically relevant. Even trace quantities of amodiaquine were able to potentiate the activity of structurally unrelated antimalarial drugs.

CYP2C8 polymorphism frequencies among malaria patients in Zanzibar

OBJECTIVE

The determination of the prevalence of the CYP2C8 main alleles in a typical set of malaria patients in Zanzibar, as these patients represent a typical population exposed to amodiaquine, an antimalarial mainly metabolized by CYP2C8. Also, to determine for the first time the frequencies of CYP2C8 alleles in native African populations.

METHODS

Polymerase chain reaction-restriction fragment polymorphism for the identification of CYP2C8*1, CYP2C8*2, CYP2C8*3 and CYP2C8*4 on a random population of 165 unrelated malaria patients.

RESULTS

The allele frequencies found were: CYP2C8*1 (wild type, 83.4%), CYP2C8*2 (13.9%), CYP2C8*3 (2.1%) and CYP2C8*4 (0.6%). In terms of genotypes, 70.4% of the patients showed the CYP2C8*1/ CYP2C8*1 genotypes, while heterozygous between the wild type and other minor alleles were seen in 26.0%. Finally, 3.6% of the patients were homozygous for slow metabolizer alleles. The frequencies observed are equivalent to those documented for African-Americans.

CONCLUSIONS

CYP2C8 non-wild type alleles have a significant prevalence in the East African population studied. The consequent frequency of 3.6% of patients homozygous for slow metabolizer alleles represent a significant fraction of the population potentially in higher risk of adverse effects due to a less efficient metabolism of amodiaquine. As approximately 10(6) first-line treatments are currently performed in Zanzibar per year, this represents a non-negligible absolute number of amodiaquine exposures. This information constitutes a background for the pharmacovigilance programs presently being employed in Zanzibar.

Synergism between amodiaquine and its major metabolite, desethylamodiaquine, against Plasmodium falciparum in vitro

The in vitro activity of the prodrug amodiaquine and its metabolite monodesethyl-amodiaquine has been studied for three strains of Plasmodium falciparum: LS-2, LS-3, and LS-1. Both compounds showed significant activity against all three strains; the activity of amodiaquine was slightly higher than that of the metabolite. By use of a checkerboard design, interaction studies with both compounds yielded evidence of significant synergism; means of the sums of the fractional inhibitory concentrations were 0.0392 to 0.0746 for strain LS-2, 0.1567 to 0.3102 for strain LS-3, and 0.025 to 0.3369 for strain LS-1. In further investigations, the interaction of amodiaquine with monodesethyl-amodiaquine was tested at clinically relevant concentrations of both compounds. In these studies, involving amodiaquine at picomolar and femtomolar concentrations, the compound was found to exert high potentiating activity on monodesethyl-amodiaquine. This interaction produced mean ratios of observed to expected activity of 0.0505 to 0.0642 for strain LS-2, 0.0882 to 0.3820 for strain LS-3, and 0.0752 to 0.2924 for strain LS-1. The synergistic activity was most marked at monodesethyl-amodiaquine/amodiaquine ratios up to 100,000:1 but was still evident at higher ratios.

Detection of atovaquone and Malarone resistance conferring mutations in Plasmodium falciparum cytochrome b gene (cytb)

Clinical treatment failures of the hydroxynaphthoquinone atovaquone or its combination with proguanil (Malarone) in Plasmodium falciparum malaria has been recently documented. These events have been associated to single nucleotide polymorphisms (SNPs) in the parasite cytochrome b gene (cytb). In this report we describe a set of nest PCR-RFLP methods developed for the fast detection of all known cytb mutations associated to resistance to these drugs. The methods were successfully applied for the analysis of phenol-chloroform extracted DNA samples from patients not cured by Malarone, and from an established parasite clone. Further, the protocol for the detection of the A803C mutation was applied to 164 DNA field samples extracted through crude methanol-based protocols, originated from several malaria settings. The PCR-RFLP methods here presented can be used as a valuable for the clinical detection and study of Malarone and atovaquone P. falciparum resistance.

N-acetyltransferase (NAT2) genotype and susceptibility of sporadic Alzheimer's disease

The importance of environmental aggression and individual susceptibility to develop Alzheimer's Disease (AD) has been suggested by epidemiological studies on both typical familial and sporadic AD cases. In order to elucidate functions that can influence the susceptibility to AD pathogenesis, we genotyped a group of 53 sporadic late-onset AD patients, matched control individuals and a larger randomly selected non-demented population for the N-acetyltransferase (NAT2). We determined the relative frequencies of individual allele combinations that define a broad range of acetylator phenotypes. Inter-individual variability in the cytotoxic and genotoxic responses to a wide diversity of environmental chemicals is known to result from the polymorphism of NAT2 as well as other drug-metabolizing-enzyme genes. The results presented are the first to demonstrate a significant difference in the NAT2 genotype profiles of sporadic AD patients compared with the healthy population. A lower frequency of the recessive alleles NAT2*6 (chi-squared 1 d.f. = 12.56, P < 0.0004) and NAT2*5B (chi-squared 1 d.f. = 6.72, P < 0.01) was found among the AD population compared with control individuals, which was concomitant with a significantly higher number of NAT2*4 fully active allele homozygotes and heterozygotes (chi-squared 1 d.f. = 5.69, P = 0.017). The most notable observation was the absence of NAT2*5B/NAT2*6 heterozygotes among cases while being present in 22.5% of control individuals (chi-squared 1 d.f. = 13.08, P = 0.0003). These observations indicate that NAT2 is a potential low-penetrance gene in AD pathogenesis, determining an individual susceptibility trait predisposing to this degenerative disease.

Increased frequency of wild-type arylamine-N-acetyltransferase allele NAT2*4 homozygotes in Portuguese patients with colorectal cancer

Here we report that colorectal cancer patients show a markedly higher frequency (3-fold) of wild-type NAT2*4 allele homozygotes than the control population. However, a marked difference in NAT2*4/NAT2*4 genotype frequency associated with the patients gender was observed pointing to a male-specific effect of this genotype as a risk factor in colon cancer. The arylamine-N-acetyltransferase (E.C. 2.3.1.5.) NAT2, a phase II detoxification enzyme, has been implicated in procarcinogen activation, namely from food contained arylamines, cigarette smoking, as well as environmental amines of various types. NAT2 is encoded by a polymorphic gene presenting several allelic variants encoding partially inactive enzymes expressed in human liver and colon. Epidemiological studies based on phenotype determination have long indicated the importance of the NAT2 active phenotype as a susceptibility factor in colorectal cancer. In the present study we investigated the NAT2 allelic frequencies and genotype distribution in a group of 114 unrelated colorectal cancer patients, in parallel with 201 healthy Portuguese subjects. We first demonstrate that the frequency of the wild-type NAT2*4 allele in the Portuguese sample population (23.4%) does not significantly differ from the values described for other Europeans. Besides the 3-fold higher frequency of NAT2*4 homozygotes found in colorectal cancer subjects, the NAT2*4/NAT2*5A compound genotype, known to determine a faster acetylator phenotype than other heterozygotic combinations, also increased by the same order of magnitude. These two genotypes represent 32% of the patients population versus 11% of the healthy controls. Taken together, our results strongly indicate that NAT2 genotype, particularly NAT2*4 allele zygosity, constitutes an individual susceptibility trait associated with sporadic colorectal cancer development, probably due to the local dietary habits in Portugal.