Investigating the Relationship Between Smoking Behavior and Global Brain Volume

Background

Previous studies have shown that brain volume is negatively associated with cigarette smoking, but there is an ongoing debate about whether smoking causes lowered brain volume or a lower brain volume is a risk factor for smoking. We address this debate through multiple methods that evaluate directionality: Bradford Hill's criteria, which are commonly used to understand a causal relationship in epidemiological studies, and mediation analysis.

Methods

In 32,094 participants of European descent from the UK Biobank dataset, we examined the relationship between a history of daily smoking and brain volumes, as well as an association of genetic risk score to ever smoking with brain volume.

Results

A history of daily smoking was strongly associated with decreased brain volume, and a history of heavier smoking was associated with a greater decrease in brain volume. The strongest association was between total gray matter volume and a history of daily smoking (effect size = -2964 mm3, p = 2.04 × 10-16), and there was a dose-response relationship with more pack years smoked associated with a greater decrease in brain volume. A polygenic risk score for smoking initiation was strongly associated with a history of daily smoking (effect size = 0.05, p = 4.20 × 10-84), but only modestly associated with total gray matter volume (effect size = -424 mm3, p = .01). Mediation analysis indicated that a history of daily smoking mediated the relationship between the smoking initiation polygenic risk score and total gray matter volume.

Conclusions

A history of daily smoking is strongly associated with a decreased total brain volume.

Modification of estrogen's association with Alzheimer's disease risk by genetic polymorphisms

Contrasting effects of estrogen treatment on cognitive function and Alzheimer's disease (AD) risk have been reported. It may be that genetic factors modify these relations. In the present study, 696 participants from the Oxford Project to Investigate Memory and Ageing were included (355 AD cases, 341 controls). Those individuals with other types of dementia and those using hormone treatment had been excluded. Analyses controlled for body mass index, age at blood sampling, and education. Analyses of variance revealed main effects, but not an interaction, for apolipoprotein E (APOE) and Catechol-O-methyl transferase (COMT) genotypes on estradiol (E2) levels in men (p=0.003 and p=0.10, respectively), but not in women (p=0.82 and p=0.49, respectively). Men carrying the APOE ε4 allele had lower E2 levels, while those carrying the COMT Val/Val alleles had higher E2 levels compared to Met/Val (p<0.05) allele carriers. Higher estrone (E1) levels and carrying the APOE ε4 allele (but not COMT alone, or in combination with the APOE genotype) were independent risk factors for AD. Similar to earlier studies, the heterozygous COMT genotype (Met/Val) showed a synergistic effect with the APOE ε4 allele being non-significantly associated with lower cognitive function. In conclusion, the present study suggests that elevated E1 levels significantly increase AD risk in both men and women. However, interactions between APOE ε4 and genetic polymorphisms related to sex steroid metabolism and AD risk need to be further investigated.

Who gets the liver transplant? The use of responsibility as the tie breaker

Is it possible to invoke the use of moral responsibility as part of the selection criteria in the allocation of livers for transplant? Criticism has been applied to the difficulties inherent in including such a criterion and also the effect that employing such a judgement might have upon the relationship between the physician and patient. However, these criticisms rely on speculation and conjecture and do not relate to all the arguments put forward in favour of applying moral responsibility. None of the present arguments against using moral responsibility in the allocation of livers for transplant are good enough to warrant its dismissal.

Safety and immunogenicity of New Zealand strain meningococcal serogroup B OMV vaccine in healthy adults: Beginning of epidemic control

As the first step towards control of a strain specific epidemic of meningococcal disease in New Zealand (NZ), this study, an observer-blind, randomised controlled trial in 75 healthy adults, evaluated safety and immunogenicity of two different dosages of a meningococcal group B vaccine administered in a three dose regime. The "tailor-made" outer membrane vesicle (OMV) vaccine (candidate vaccine) developed using a New Zealand meningococcal group B strain (B:4:P1.7b,4) was well tolerated with no vaccine related serious adverse events. Similar local and systemic reactions were observed in those receiving the New Zealand candidate vaccine and the control parent Norwegian vaccine (MenBvac). A four-fold rise in serum bactericidal antibodies (SBAb) against the vaccine strain 4-6 weeks after the third vaccination was achieved in 100% of New Zealand candidate vaccine 2,519 microg participants and in 87% of 50 microg participants. The safety and immunogenicity profile observed in this study of healthy adults enabled studies in children to be initiated using 25 microg dosage.

A putative type III secretion gene cluster is widely distributed in the Burkholderia cepacia complex but absent from genomovar I

Using probes constructed from Ralstonia solanacearum and Burkholderia pseudomallei, putative type III secretion (TTS) genes were identified in Burkholderia cepacia J2315 (genomovar III). A cosmid clone containing DNA with homology to five TTS genes was sub-cloned and regions were sequenced in order to design oligonucleotides for polymerase chain reaction assays. These indicated that two putative TTS genes (bcscQ and bcscV) were present in all members of the B. cepacia complex with the exception of strains from genomovar I. Southern blot assays confirmed this observation, suggesting that the lack of a TTS gene cluster may define a major difference between B. cepacia genomovar I and other members of the B. cepacia complex, including genomovar III. In contrast to TTS gene clusters in other bacteria, a putative gene homologous to the virB1 gene of Brucella suis was located directly downstream of bcscQR.

Effect of Cis-Trans Ratio on the Physical Properties of 1,4 Polybutadienes

The physical properties of vulcanized 1,4 polybutadienes, prepared by heterogeneous catalysis and ranging from 95 per cent cis to nearly 100 per cent trans configuration, were investigated in gum and tread formulations. Comparisons were made at equal effective (physical) degree of crosslinking for both gum- and carbon black-reinforced stocks and for black stocks at equal 300 per cent modulus. In general, as polybutadienes require less sulfur for adequate vulcanization than trans polybutadienes. Vulcanizates of all 1,4 polybutadienes exceeding 15 per cent in cis content are completely rubbery at ordinary temperatures. Polybutadiene of 93 per cent trans content yields tough, leathery, crystalline vulcanizates at 80° F, which become rubbery at moderately elevated temperatures. Without exception the important physical properties change little between 25 and 80 per cent cis content. At both ends of this range the tensile strength of both gum and black stocks rises as a consequence of increasing chain regularity. However, in gum tensile strength not even the highest cis polybutadienes are equivalent to natural or synthetic cis-polyisoprenes. Black stocks of very good tensile strength with elongations ranging from 500 to 700 per cent are obtained with both cis- and trans-polybutadienes. At the crosslinking level for optimum tensile strength, modulus increases with trans content. The cis-polybutadienes have excellent resilience and low hysteresis and maintain their resilience to temperatures as low as −40° F. The latter is true even of the highest as polymers which crystallize at these temperatures. The tendency to crystallize rapidly at low temperatures disappears between 87 and 82 per cent cis content so that polymers of moderately high cis unsaturation have exceptional low-temperature characteristics. These polymers remain completely rubbery down to their brittle point (ca. −85° C). The excellent resilience of cis-polybutadiene is particularly apparent in carbon black-reinforced stocks. Because of the inherently low modulus of these stocks and their low sulfur requirement, these may be vulcanized to rather high degrees of crosslinking. This results in further improvements in resilience and heat build-up with only moderate sacrifices in tensile strength and ultimate elongation. Vulcanizates of 70 to 80 per cent trans-polybutadienes exhibit evidence of crystallinity over a wide range of temperatures and are probably not completely melted at room temperature. Although their resilience is less than that of the high cis-polybutadienes, it is still somewhat better than that of SBR, particularly at low temperatures. The 1,4 polybutadienes are more resistant to oxidative scission than emulsion polybutadiene or SBR and are greatly superior to natural rubber in this respect. The dominant effect in the aging of 1,4 polybutadienes is crosslinking. Because of their low sulfur requirements the cis polybutadienes offer a particular advantage in aging resistance. None of the polybutadienes exhibits ozone resistance comparable to Hevea.