Publications

BACKGROUND

Assessing adverse effects from environmental chemical exposure is integral to public health policies. Toxicology assays identifying early biological changes from chemical exposure are increasing our ability to evaluate links between early biological disturbances and subsequent overt downstream effects. A workshop was held to consider how the resulting data inform consideration of an "adverse effect" in the context of hazard identification and risk assessment.

OBJECTIVES

Our objective here is to review what is known about the relationships between chemical exposure, early biological effects (upstream events), and later overt effects (downstream events) through three case studies (thyroid hormone disruption, antiandrogen effects, immune system disruption) and to consider how to evaluate hazard and risk when early biological effect data are available.

DISCUSSION

Each case study presents data on the toxicity pathways linking early biological perturbations with downstream overt effects. Case studies also emphasize several factors that can influence risk of overt disease as a result from early biological perturbations, including background chemical exposures, underlying individual biological processes, and disease susceptibility. Certain effects resulting from exposure during periods of sensitivity may be irreversible. A chemical can act through multiple modes of action, resulting in similar or different overt effects.

CONCLUSIONS

For certain classes of early perturbations, sufficient information on the disease process is known, so hazard and quantitative risk assessment can proceed using information on upstream biological perturbations. Upstream data will support improved approaches for considering developmental stage, background exposures, disease status, and other factors important to assessing hazard and risk for the whole population.

BACKGROUND

Percutaneous coronary intervention (PCI) is performed in many patients with stable coronary artery disease, despite evidence of little clinical benefit over optimal medical therapy.

OBJECTIVE

To examine physicians' beliefs, practices, and decision-making regarding elective PCI.

DESIGN

Six focus groups, three with primary care physicians and three with cardiologists. Participants discussed PCI using hypothetical case scenarios. Transcripts were analyzed using grounded theory, and commonly expressed themes regarding the decision-making pathway to PCI were identified.

PARTICIPANTS

Twenty-eight primary care physicians and 20 interventional and non-interventional cardiologists in Butte County, Orange County, and San Francisco Bay Area, California, in 2006.

RESULTS

A number of factors led primary care physicians to evaluate non-symptomatic or minimally symptomatic patients for coronary artery disease and refer them to a cardiologist. The use of screening tests often led to additional testing and referral, as well as fear of missing a coronary stenosis, perceived patient expectations, and medicolegal concerns. The end result was a cascade such that any positive test would generally lead to the catheterization lab, where an "oculostenotic reflex" made PCI a virtual certainty.

CONCLUSIONS

The widespread use of PCI in patients with stable coronary artery disease--despite evidence of little benefit in outcomes over medical therapy--may in part be due to psychological and emotional factors leading to a cascade effect wherein testing leads inevitably to PCI. Determining how to help physicians better incorporate evidence-based medicine into decision-making has important implications for patient outcomes and the optimal use of new technologies.

During acute human immunodeficiency virus type 1 (HIV-1) infection, early host cellular immune responses drive viral evolution. The rates and extent of these mutations, however, remain incompletely characterized. In a cohort of 98 individuals newly infected with HIV-1 subtype B, we longitudinally characterized the rates and extent of HLA-mediated escape and reversion in Gag, Pol, and Nef using a rational definition of HLA-attributable mutation based on the analysis of a large independent subtype B data set. We demonstrate rapid and dramatic HIV evolution in response to immune pressures that in general reflect established cytotoxic T-lymphocyte (CTL) response hierarchies in early infection. On a population level, HLA-driven evolution was observed in approximately 80% of published CTL epitopes. Five of the 10 most rapidly evolving epitopes were restricted by protective HLA alleles (HLA-B*13/B*51/B*57/B*5801; P = 0.01), supporting the importance of a strong early CTL response in HIV control. Consistent with known fitness costs of escape, B*57-associated mutations in Gag were among the most rapidly reverting positions upon transmission to non-B*57-expressing individuals, whereas many other HLA-associated polymorphisms displayed slow or negligible reversion. Overall, an estimated minimum of 30% of observed substitutions in Gag/Pol and 60% in Nef were attributable to HLA-associated escape and reversion events. Results underscore the dominant role of immune pressures in driving early within-host HIV evolution. Dramatic differences in escape and reversion rates across codons, genes, and HLA restrictions are observed, highlighting the complexity of viral adaptation to the host immune response.