Instrumental variable method for the causal relationship between soluble receptor for advanced glycation end-products (sRAGE) and risk of pancreatic cancer

This thesis project is motivated by the potential problem of using observational data to draw inferences about a causal relationship in observational epidemiology research when controlled randomization is not applicable. Instrumental variable (IV) method is one of the statistical tools to overcome this problem. Mendelian randomization study uses genetic variants as IVs in genetic association study. In this thesis, the IV method, as well as standard logistic and linear regression models, is used to investigate the causal association between risk of pancreatic cancer and the circulating levels of soluble receptor for advanced glycation end-products (sRAGE). Higher levels of serum sRAGE were found to be associated with a lower risk of pancreatic cancer in a previous observational study (255 cases and 485 controls). However, such a novel association may be biased by unknown confounding factors. In a case-control study, we aimed to use the IV approach to confirm or refute this observation in a subset of study subjects for whom the genotyping data were available (178 cases and 177 controls). Two-stage IV method using generalized method of moments-structural mean models (GMM-SMM) was conducted and the relative risk (RR) was calculated. In the first stage analysis, we found that the single nucleotide polymorphism (SNP) rs2070600 of the receptor for advanced glycation end-products (AGER) gene meets all three general assumptions for a genetic IV in examining the causal association between sRAGE and risk of pancreatic cancer. The variant allele of SNP rs2070600 of the AGER gene was associated with lower levels of sRAGE, and it was neither associated with risk of pancreatic cancer, nor with the confounding factors. It was a potential strong IV (F statistic = 29.2). However, in the second stage analysis, the GMM-SMM model failed to converge due to non- concaveness probably because of the small sample size. Therefore, the IV analysis could not support the causality of the association between serum sRAGE levels and risk of pancreatic cancer. Nevertheless, these analyses suggest that rs2070600 was a potentially good genetic IV for testing the causality between the risk of pancreatic cancer and sRAGE levels. A larger sample size is required to conduct a credible IV analysis.^

Description and analysis of variation in dairy product and concomitant nutrient purchases between Hispanic and non -Hispanic households using a panel of shoppers' purchase records

The purpose of this research was development of a method of estimating nutrient availability in populations as approximated by supermarket purchase records. Demographic information describing 12,516 panel households was obtained from a marketing and advertising program operated by H. E. Butt Grocery Company of San Antonio, Texas. A non-probability sample of 2,161 households meeting expenditure criteria was selected and all purchases of dairy products for this sample of households were organized into a database constructed to facilitate the retrieval, aggregation, and analysis of dairy product purchases and their nutrient contents. Two hypotheses were tested: (1) no difference would be found between Hispanic and non-Hispanic purchases of dairy product categories during the study period and (2) no difference would be found between Hispanic and non-Hispanic purchases of nutrients contained in those dairy products during the thirteen-week study period.^ Food purchase records were used to estimate nutrient exposure on a weekly, per capita basis for Hispanic and non-Hispanic households by linking some 40,000 dairy purchase Universal Product code (UPC) numbers with food composition values contained in USDA Handbook 8-1. Results of this study suggest Hispanic sample households consistently purchased fewer dairy products than did non-Hispanic sample households and consequently had fewer nutrients available from dairy purchases. While weekly expenditures for dairy products among the sample households remained relatively constant during the study period, shifts in the types of dairy products purchased were observed. The effect of ethnicity on dairy product and nutrient purchases was significant over the thirteen-week period. A database consisting of customer, household, and purchase information can be developed to successfully associate food item UPC numbers with a standard reference of food composition to estimate nutrient availability in a population over extended periods of time. ^

Rescue of embryonic lethality in mdmx null mice by loss of p53 suggests a non-overlapping pathway with MDM2 to regulate p53

The tumor suppressor p53 is mutated in over 50% of human sporadic tumors originating from diverse tissues. p53 responds to DNA damage and cell stress by activating the transcription of a variety of target genes, the protein products of which then initiate either growth arrest or apoptosis. ^ A p53 target with a particularly intriguing function is the oncogene MDM2. MDM2 functions, in part, by binding to and inhibiting p53's activity. Overexpression of MDM2, by gene amplification, has been found in 30% of human sarcomas harboring a wild type p53, indicating that an increase in MDM2 levels is sufficient for p53 inactivation. Mice carrying a homozygous null allele for mdm2 exhibit an early embryonic lethality that is completely rescued in a p53-null background. These data indicate that MDM2's only critical function in early mouse embryogenesis is the negative regulation of p53. ^ The mdmx gene is the first additional member of the mdm2 gene family to be isolated. MDMX, like MDM2, contains a RING-finger domain, ATP binding domain and a p53 binding domain, which retains the ability to bind and inhibit p53 transactivation in vitro. However, mdmx does not appear to be transcriptionally regulated by p53. We have cloned and characterized the murine mdmx genomic locus from a mouse 129 genomic library. The mdmx gene contains 11 exons, spans approximately 37 Kb of DNA, and is located on mouse chromosome 1. The genomic organization of the mdmx gene is identical to that of mdm2 except at the 5′ end of the gene near the p53 responsive element. Northern expression analysis of mdmx transcripts during mouse embryogenesis and in adult tissues revealed constitutive and ubiquitous expression throughout adult tissues and embryonic development. To determine the in vivo function of MDMX, mice carrying a null allele of mdmx have been generated. Mdmx homozygous null mice are early embryonic lethal. Mdmx null mice do not develop beyond 9.5 dpc and can be discerned by gross dissection as early as 7.5 dpc. Utilizing TUNEL and BrdU assays on 7.5 dpc histological sections we have determined that the mutant embryos are dying due to increased levels of growth arrest, but not apoptosis. Surprisingly, Mdmx homozygous null mice are viable in a p53 null background, indicating that MDMX is also very important in the negative regulation of p53. ^