Guilherme Suarez-Kurtz

The Genomic Ancestry of Individuals from Different Geographical Regions of Brazil Is More Uniform Than Expected

Based on pre-DNA racial/color methodology, clinical and pharmacological trials have traditionally considered the different geographical regions of Brazil as being very heterogeneous. We wished to ascertain how such diversity of regional color categories correlated with ancestry. Using a panel of 40 validated ancestry-informative insertion-deletion DNA polymorphisms we estimated individually the European, African and Amerindian ancestry components of 934 self-categorized White, Brown or Black Brazilians from the four most populous regions of the Country. We unraveled great ancestral diversity between and within the different regions. Especially, color categories in the northern part of Brazil diverged significantly in their ancestry proportions from their counterparts in the southern part of the Country, indicating that diverse regional semantics were being used in the self-classification as White, Brown or Black. To circumvent these regional subjective differences in color perception, we estimated the general ancestry proportions of each of the four regions in a form independent of color considerations. For that, we multiplied the proportions of a given ancestry in a given color category by the official census information about the proportion of that color category in the specific region, to arrive at a “total ancestry” estimate. Once such a calculation was performed, there emerged a much higher level of uniformity than previously expected. In all regions studied, the European ancestry was predominant, with proportions ranging from 60.6% in the Northeast to 77.7% in the South. We propose that the immigration of six million Europeans to Brazil in the 19th and 20th centuries - a phenomenon described and intended as the “whitening of Brazil” - is in large part responsible for dissipating previous ancestry dissimilarities that reflected region-specific population histories. These findings, of both clinical and sociological importance for Brazil, should also be relevant to other countries with ancestrally admixed populations.

Warfarin pharmacogenetics: a single VKORC1 polymorphism is predictive of dose across 3 racial groups

Warfarin-dosing algorithms incorporating CYP2C9 and VKORC1 -1639G>A improve dose prediction compared with algorithms based solely on clinical and demographic factors. However, these algorithms better capture dose variability among whites than Asians or blacks. Herein, we evaluate whether other VKORC1 polymorphisms and haplotypes explain additional variation in warfarin dose beyond that explained by VKORC1 -1639G>A among Asians (n = 1103), blacks (n = 670), and whites (n = 3113). Participants were recruited from 11 countries as part of the International Warfarin Pharmacogenetics Consortium effort. Evaluation of the effects of individual VKORC1 single nucleotide polymorphisms (SNPs) and haplotypes on warfarin dose used both univariate and multi variable linear regression. VKORC1 -1639G>A and 1173C>T individually explained the greatest variance in dose in all 3 racial groups. Incorporation of additional VKORC1 SNPs or haplotypes did not further improve dose prediction. VKORC1 explained greater variability in dose among whites than blacks and Asians. Differences in the percentage of variance in dose explained by VKORC1 across race were largely accounted for by the frequency of the -1639A (or 1173T) allele. Thus, clinicians should recognize that, although at a population level, the contribution of VKORC1 toward dose requirements is higher in whites than in nonwhites; genotype predicts similar dose requirements across racial groups.

NEUTRALIZATION OF LETHAL AND MYOTOXIC ACTIVITIES OF SOUTH AMERICAN RATTLESNAKE VENOM BY EXTRACTS AND CONSTITUENTS OF THE PLANT ECLIPTA PROSTRATA (ASTERACEAE)

Ethanolic extracts of the aerial parts of Eclipta prostrata L. (Asteraceae) neutralized the lethal activity of the venom of South American rattlesnake (Crotalus durissus terrificus) when mixed in vitro before i.p. injection into adult Swiss mice. Samples of ethanolic extract corresponding to 1.8 mg of dry extract per animal neutralized up to four lethal doses of the venom (LD50 = 0.08 micrograms venom/g animal). Three substances isolated from the plant--wedelolactone (0.54 mg/animal), sitosterol (2.3 mg/animal) and stigmasterol (2.3 mg/animal)--were able to neutralize three lethal doses of the venom. Aqueous extracts of the plant inhibited the release of creatine kinase from isolated rat muscle exposed to the crude venom. The protection conferred against the myotoxic effects of the venom could be demonstrated also in vivo, when the venom was preincubated with the extract prior to injection into mice.

Inhibition of the myotoxic and hemorrhagic activities of crotalid venoms by Eclipta prostrata (Asteraceae) extracts and constituents

The antimyotoxic and antihemorrhagic effects of Eclipta prostrata (EP) and three of its constituents (wedelolactone, WE; stigmaterol, ST; and sitosterol, SI) were investigated. The myotoxicity of crotalid venoms (Bothrops jararaca, Bothrops jararacussu and Lachesis muta), purified myotoxins (bothropstoxin, BthTX; bothropasin; and crotoxin), and polylysine was quantified in vitro by the release rate of creatine kinase (CK) from rat or mouse extensor digitorum muscles, and in vivo by the plasma CK activity in mice. The in vitro myotoxicity of the crotalid venoms and myotoxins was neutralized by simultaneous exposure of the muscles to an aqueous extract of EP or to WE. ST and SI were less effective than WE, but interacted synergistically with it. Both the EP extract and WE failed to neutralize the in vitro myotoxic effects of polylysine. The in vivo myotoxicity of venoms and myotoxins was neutralized by their preincubation with the EP extract or WE. Intravenous administration of the plant extract or WE attenuated the increase in plasma CK activity induced by subsequent intramuscular injections of the crotalid venoms or the myotoxins. EP and WE inhibited the hemorrhagic effect of B. jararaca venom, as well as the phospholipase A2 activity of crotoxin and the proteolytic activity of B. jararaca venom. The data provide direct evidence for antimyotoxic and antihemorrhagic effects of EP and WE against the crotalid venoms responsible for most cases of envenomation by snakebites in Brazil. These effects are interpreted as consequences of antiproteolytic and antiphospholipase A2 activities of EP and its constituents.

Pharmacogenetics of warfarin: development of a dosing algorithm for brazilian patients.

A dosing algorithm including genetic (VKORC1 and CYP2C9 genotypes) and nongenetic factors (age, weight, therapeutic indication, and cotreatment with amiodarone or simvastatin) explained 51% of the variance in stable weekly warfarin doses in 390 patients attending an anticoagulant clinic in a Brazilian public hospital. The VKORC1 3673G>A genotype was the most important predictor of warfarin dose, with a partial R2 value of 23.9%. Replacing the VKORC1 3673G>A genotype with VKORC1 diplotype did not increase the algorithms predictive power. We suggest that three other single‐nucleotide polymorphisms (SNPs) (5808T>G, 6853G>C, and 9041G>A) that are in strong linkage disequilibrium (LD) with 3673G>A would be equally good predictors of the warfarin dose requirement. The algorithms predictive power was similar across the self‐identified “race/color” subsets. “Race/color” was not associated with stable warfarin dose in the multiple regression model, although the required warfarin dose was significantly lower (P = 0.006) in white (29 ± 13 mg/week, n = 196) than in black patients (35 ± 15 mg/week, n = 76).

Ether à go-go potassium channel expression in soft tissue sarcoma patients.

BackgroundThe expression of the human Eag1 potassium channel (Kv10.1) is normally restricted to the adult brain, but it has been detected in both tumour cell lines and primary tumours. Our purpose was to determine the frequency of expression of Eag1 in soft tissue sarcoma and its potential clinical implications.ResultsWe used specific monoclonal antibodies to determine the expression levels of Eag1 in soft tissue sarcomas from 210 patients by immunohistochemistry. Eag1 was expressed in 71% of all tumours, with frequencies ranging from 56% (liposarcoma) to 82% (rhabdomyosarcoma). We detected differences in expression levels depending on the histological type, but no association was seen between expression of this protein and sex, age, grade or tumour size. Four cell lines derived from relevant sarcoma histological types (fibrosarcoma and rhabdomyosarcoma) were tested for Eag1 expression by real-time RT-PCR. We found all four lines to be positive for Eag1. In these cell lines, blockage of Eag1 by RNA interference led to a decrease in proliferation.ConclusionEag1 is aberrantly expressed in over 70% sarcomas. In sarcoma cell lines, inhibition of Eag1 expression and/or function leads to reduced proliferation. The high frequency of expression of Eag1 in primary tumours and the restriction of normal expression of the channel to the brain, suggests the application of this protein for diagnostic or therapeutic purposes.

RELEASE OF SARCOPLASMIC ENZYMES FROM SKELETAL MUSCLE BY BOTHROPS JARARACUSSU VENOM: ANTAGONISM BY HEPARIN AND BY THE SERUM OF SOUTH AMERICAN MARSUPIALS

The venom of B. jararacussu induced a time- and dose-dependent (2-100 micrograms/ml) increase in the rate of release of sarcoplasmic enzymes (CK and LDH) from isolated rat and frog muscles. This effect, which we attribute to sarcolemmal damage by the venom, persisted in a Ca2+-free media, suggesting that phospholipase A activity was not required. The venom-induced enzyme release from the isolated muscles was reversibly inhibited by the sera (1-10 microliters/ml) of the marsupials Didelphis marsupialis aurita and Philander opossum, by an acidic glycoprotein fraction isolated from the opossum serum (50 micrograms/ml), and by heparin (50 micrograms/ml). Incubation of the B. jararacussu venom with opossum sera or heparin prevented the increase in plasma CK level observed in mice in which the snake venom (2.5-5.0 micrograms/g) was injected i.m. It is suggested that formation of acid-base complexes between basic myotoxins of B. jararacussu venom and either acidic components in the marsupial sera or the polyanionic heparin could account for the inhibition of the in vitro and in vivo effects of the venom on the release of sarcoplasmic enzymes from skeletal muscles.

CYP2C9 genotypes and the pharmacokinetics of tenoxicam in Brazilians

Cytochrome P450 (CYP) 2C9, the product of the polymorphic gene CYP2C9, provides the major catabolic pathway for several anti‐inflammatory drugs, including tenoxicam. Our objectives were (1) to determine the frequency of 2 common CYP2C9 variant alleles (*2 and *3) in the Brazilian population and (2) to evaluate the effects of these polymorphisms on the pharmacokinetics of tenoxicam.

Self-reported skin color, genomic ancestry and the distribution of GST polymorphisms

Background and objective Skin color and self-reported ethnicity have systematically been used in the pharmacogenetic/-genomic literature as phenotypic proxies for geographical ancestry. Population admixture, however, challenges the appropriateness of this approach. We compared the effectiveness of color-based and marker-based biogeographical ancestry classifications in typing polymorphisms in GSTM1, GSTM3 and GSTT1 in the heterogeneous Brazilian population. Methods Individual DNA from 335 healthy Brazilians was typed for a set of insertion/deletion polymorphisms, previously validated as ancestry informative markers. GSTM1-null and GSTT1-null polymorphisms were detected by multiplex PCR and the GSTM3*B polymorphism by restriction-fragment length polymorphism. Nonlinear logistic regression modeling was developed to describe the association between the GST polymorphisms and ancestry estimated by the ancestry informative markers. Results Analysis of the ancestry informative markers data with the Structure software revealed the existence of only two significant clusters, one of which was inferred to be an estimate of the African component of ancestry. Nonlinear logistic regression showed that the odds of having the GSTM1-null genotype decreases (P<0.0004, Wald statistics), whereas the odds of having the GSTM3*B allele increases (P<0.0001) with the increase of the African component of ancestry, throughout the range (0.13–0.95) observed in the population sample. The African component of ancestry proportion was not associated with GSTT1-null frequency. Within the self-reported Black and Intermediate groups, there were significant differences in ancestry informative markers between GSTM1-null and non-null individuals, and between carriers and noncarriers of the GSTM3*B allele. Conclusions Interethnic admixture is a source of cryptic population structure that may lead to spurious genotype–phenotype associations in pharmacogenetic/-genomic studies. Logistic regression modeling of GST polymorphisms shows that admixture must be dealt with as a continuous variable, rather than proportioned in arbitrary subcategories for the convenience of data quantification and analysis.

Worldwide allele frequency distribution of four polymorphisms associated with warfarin dose requirements

The aim of the study is to improve our understanding of the worldwide allele frequency distribution of four genetic polymorphisms known to influence warfarin dosing (VKORC1 rs9923231, CYP2C9 rs1799853, CYP2C9 rs1057910 and CYP4F2 rs2108622). These four polymorphisms were genotyped in the Human Genome Diversity Project-Centre Etude Polymorphism Humain (HGDP-CEPH) worldwide sample (N=963), as well as in a sample of individuals of European, East Asian and South Asian ancestry living in Canada (N=316). The VKORC1 rs9923231 single nucleotide polymorphism (SNP) showed an extensive geographic differentiation, with the derived T allele appearing at very high allele frequencies in East Asian populations. Results from several tests of positive selection indicate that this unusual distribution may be the result of positive selection in East Asia. Understanding the worldwide distribution of markers determining warfarin dosing is important for the future application of pharmacogenomic-based algorithms to different population groups.