Horacio A. Priestap

Biochemical, Molecular, and Functional Characterization of PISCF-Allatostatin, a Regulator of Juvenile Hormone Biosynthesis in the Mosquito Aedes aegypti

Aedes aegypti PISCF-allatostatin or allatostatin-C (Ae-AS-C) was isolated using a combination of high performance liquid chromatography and enzyme-linked immunosorbent assay (ELISA). The matrix-assisted laser desorption/ionization time-of-flight (TOF) mass spectrum of positive ELISA fractions revealed a molecular mass of 1919.0 Da, in agreement with the sequence qIRYRQCYFNPISCF, with bridged cysteines. This sequence was confirmed by matrix-assisted laser desorption/ionization tandem TOF/TOF mass spectrometry analysis. The corresponding Ae-AS-C cDNA was amplified by PCR, and the sequence of the peptide was confirmed. An in vitro radiochemical assay was used to study the inhibitory effect of synthetic Ae-AS-C on juvenile hormone biosynthesis by the isolated corpora allata (CA) of adult female A. aegypti. The inhibitory action of synthetic Ae-AS-C was dose-dependent; with a maximum at 10–9 m. Ae-AS-C showed no inhibitory activity in the presence of farnesoic acid, an immediate precursor of juvenile hormone, indicating that the Ae-AS-C target is located before the formation of farnesoic acid in the pathway. The sensitivity of the CA to inhibition by Ae-AS-C in the in vitro assay varied during the adult life; the CA was most sensitive during periods of low synthetic activity. In addition, the levels of Ae-AS-C in the brain were studied using ELISA and reached a maximum at 3 days after eclosion. These studies suggest that Ae-AS-C is an important regulator of CA activity in A. aegypti.

MOLECULAR AND FUNCTIONAL CHARACTERIZATION OF A JUVENILE HORMONE ACID METHYLTRANSFERASE EXPRESSED IN THE CORPORA ALLATA OF MOSQUITOES

A juvenile hormone acid methyltransferase (JHAMT) was isolated as an abundant EST in a library of the corpora allata of the adult female mosquito Aedes aegypti. Its full length cDNA encodes a 278-aa protein that has 43% amino acid identity with BmJHAMT, a juvenile hormone acid methyltransferase previously cloned from Bombyx mori. Heterologous expression produced a recombinant protein that metabolizes farnesoic acid (FA) into methyl farnesoate, as well as juvenile hormone acid into juvenile hormone III (JH III) with exquisite stereo specificity. Real time PCR experiments showed that JHAMT mRNA levels are not an unequivocal indicator of JH III synthesis rates; the A. aegypti JHAMT gene, silent in female pupae, was transcriptionally activated just 4-6h before adult eclosion. Radiochemical methyltransferase assays using active and inactive corpora allata glands (CA) dissected from sugar and blood-fed females respectively, clearly indicated that significant levels of JHAMT enzymatic activity are present when the CA shows very low spontaneous rates of JH III synthesis. Having the last enzymes of the JH synthetic pathway readily available all the time might be critical for the adult female mosquito to sustain rapid dynamic changes in JH III synthesis in response to nutritional changes or peripheral influences, such as mating or feeding. These results suggest that this gene has different roles in the regulation of JH synthesis in pupal and adult female mosquitoes, and support the hypothesis that the rate-limiting steps in JH III synthesis in adult female mosquitoes are located before entrance of FA into the synthetic pathway.

Animal pigment bilirubin discovered in plants

The bile pigment bilirubin-IXalpha is the degradative product of heme, distributed among mammals and some other vertebrates. It can be recognized as the pigment responsible for the yellow color of jaundice and healing bruises. In this paper we present the first example of the isolation of bilirubin in plants. The compound was isolated from the brilliant orange-colored arils of Strelitzia nicolai, the white bird of paradise tree, and characterized by HPLC-ESMS, UV-visible, (1)H NMR, and (13)C NMR spectroscopy, as well as comparison with an authentic standard. This discovery indicates that plant cyclic tetrapyrroles may undergo degradation by a previously unknown pathway. Preliminary analyses of related plants, including S. reginae, the bird of paradise, also revealed bilirubin in the arils and flowers, indicating that the occurrence of bilirubin is not limited to a single species or tissue type.

The sesquiterpene lactone dehydroleucodine triggers senescence and apoptosis in association with accumulation of DNA damage markers.

Sesquiterpene lactones (SLs) are plant-derived compounds that display anti-cancer effects. Some SLs derivatives have a marked killing effect on cancer cells and have therefore reached clinical trials. Little is known regarding the mechanism of action of SLs. We studied the responses of human cancer cells exposed to various concentrations of dehydroleucodine (DhL), a SL of the guaianolide group isolated and purified from Artemisia douglasiana (Besser), a medicinal herb that is commonly used in Argentina. We demonstrate for the first time that treatment of cancer cells with DhL, promotes the accumulation of DNA damage markers such as phosphorylation of ATM and focal organization of γH2AX and 53BP1. This accumulation triggers cell senescence or apoptosis depending on the concentration of the DhL delivered to cells. Transient DhL treatment also induces marked accumulation of senescent cells. Our findings help elucidate the mechanism whereby DhL triggers cell cycle arrest and cell death and provide a basis for further exploration of the effects of DhL in in vivo cancer treatment models.

Aristolochic acid I metabolism in the isolated perfused rat kidney.

Aristolochic acids are natural nitro-compounds found globally in the plant genus Aristolochia that have been implicated in the severe illness in humans termed aristolochic acid nephropathy (AAN). Aristolochic acids undergo nitroreduction, among other metabolic reactions, and active intermediates arise that are carcinogenic. Previous experiments with rats showed that aristolochic acid I (AA-I), after oral administration or injection, is subjected to detoxication reactions to give aristolochic acid Ia, aristolactam Ia, aristolactam I, and their glucuronide and sulfate conjugates that can be found in urine and feces. Results obtained with whole rats do not clearly define the role of liver and kidney in such metabolic transformation. In this study, in order to determine the specific role of the kidney on the renal disposition of AA-I and to study the biotransformations suffered by AA-I in this organ, isolated kidneys of rats were perfused with AA-I. AA-I and metabolite concentrations were determined in perfusates and urine using HPLC procedures. The isolated perfused rat kidney model showed that AA-I distributes rapidly and extensively in kidney tissues by uptake from the peritubular capillaries and the tubules. It was also established that the kidney is able to metabolize AA-I into aristolochic acid Ia, aristolochic acid Ia O-sulfate, aristolactam Ia, aristolactam I, and aristolactam Ia O-glucuronide. Rapid demethylation and sulfation of AA-I in the kidney generate aristolochic acid Ia and its sulfate conjugate that are voided to the urine. Reduction reactions to give the aristolactam metabolites occur to a slower rate. Renal clearances showed that filtered AA-I is reabsorbed at the tubules, whereas the metabolites are secreted. The unconjugated metabolites produced in the renal tissues are transported to both urine and perfusate, whereas the conjugated metabolites are almost exclusively secreted to the urine.

Bilirubin present in diverse angiosperms.

Recently, we discovered bilirubin-IXα, a pigment previously known only in animals as a breakdown product of heme, in Strelitzia nicolai. Here, we show that bilirubin-IXα is present in eight species from three diverse angiosperm orders.

The effect of dehydroleucodine in adipocyte differentiation.

Dehydroleucodine (DhL) is a sesquiterpene lactone of the guaianolide group with gastric cytoprotective activity. Recent studies have also demonstrated that DhL inhibits the proliferation of vascular smooth muscle cells. In this study we examined the effect of DhL in the differentiation of 3T3-L1 preadipocytes. The addition of DhL significantly inhibited the differentiation of 3T3-L1 preadipocytes along with a significant decrease in the accumulation of lipid content by a dramatic downregulation of the expression of adipogenic-specific transcriptional factors PPARγ and C-EBPα. However, phosphorylation of AMPKα, Erk1/2 and Akt1 was not inhibited by DhL treatment. Interestingly, we also found that 11,13-dihydrodehydroleucodine, a derivative of DhL with inactivated α-methylene-γ-lactone function, also inhibited the differentiation of 3T3-L1 preadipocytes. Taken together, these data suggest that DhL has an important inhibitory effect in cellular pathways regulating adipocyte differentiation by modulating the PPARγ expression, which is known to play a pivotal role during adipogenesis.

Characterization of an isopentenyl diphosphate isomerase involved in the juvenile hormone pathway in Aedes aegypti

Isopentenyl diphosphate isomerase (IPPI) is an enzyme involved in the synthesis of juvenile hormone (JH) in the corpora allata (CA) of insects. IPPI catalyzes the conversion of isopentenyl pyrophosphate (IPP) to dimethylallyl pyrophosphate (DMAPP); afterward IPP and DMAPP condense in a head-to-tail manner to produce geranyl diphosphate (GPP), this head-to-tail condensation can be repeated, by the further reaction of GPP with IPP, yielding the JH precursor farnesyl diphosphate. An IPPI expressed sequence tag (EST) was obtained from an Aedes aegypti corpora-allata + corpora cardiaca library. Its full-length cDNA encodes a 244-aa protein that shows a high degree of similarity with type I IPPIs from other organisms, particularly for those residues that have important roles in catalysis, metal coordination and interaction with the diphosphate moiety of the IPP. Heterologous expression produced a recombinant protein that metabolized IPP into DMAPP; treatment of DMAPP with phosphoric acid produced isoprene, a volatile compound that was measured with an assay based on a solid-phase micro extraction protocol and direct analysis by gas chromatography. A. aegypti IPPI (AaIPPI) required Mg(2+) or Mn(2+) but not Zn(2+) for full activity and it was entirely inhibited by iodoacetamide. Real time PCR experiments showed that AaIPPI is highly expressed in the CA. Changes in AaIPPI mRNA levels in the CA in the pupal and adult female mosquito corresponded well with changes in JH synthesis (Li et al., 2003). This is the first molecular and functional characterization of an isopentenyl diphosphate isomerase involved in the production of juvenile hormone in the CA of an insect.

Conversion of aristolochic acid I into aristolic acid by reaction with cysteine and glutathione: biological implications.

Aristolochic acid I (AA-I), naturally occurring in Aristolochia plants, is a potent nephrotoxin and carcinogen. Here we report that AA-I suffers hydrogenolysis with loss of the nitro group by reaction with cysteine or glutathione to give aristolic acid. Since the reaction can proceed in aqueous solutions at pH 7.0 and 37 °C, it is inferred that it may also occur in biological systems and contribute to the nephrotoxic effects induced by AA-I.

Dehydro-leucodin: a guaiane-type sesquiterpene lactone.

Dehydroleucodin [systematic name: (1S,6S,2R)-9,13-dimethyl-5-methylene-3-oxatricyclo[8.3.0.02,6]trideca-9,12-diene-4,11-dione], C15H16O3, is a guanolide isolated from Artemisia douglasiana. The fused-ring system contains a seven-membered ring that adopts a chair conformation, a fused planar cyclopentenone ring and a five-membered lactone ring fused in envelope conformation. The absolute structure determined by X-ray analysis agrees with that previously assigned to this compound by NMR studies [Bohlmann & Zdero (1972 ▶). Tetrahedron Lett. 13, 621–624] and also with that of leucodine, a closely related guaianolide [Martinez et al. (1988 ▶). J. Nat. Prod. 51, 221–228].