0711 Select Symptoms From The Epworth Sleepiness Scale Questionnaire And Response To Therapy Of Central Sleep Apnea With Phrenic Nerve Stimulation

Introduction

Some subjects with central sleep apnea (CSA) complain of subjective excessive daytime sleepiness (EDS), as assessed by the Epworth Sleepiness Score (ESS). However, there is considerable variability in the level of chances of dozing for each of the 8 ESS questions, as each reflects a different situation. The aim of this analysis was to examine individual situations of the ESS and determine if transvenous phrenic nerve stimulation (TPNS) resulted in improvements of individual ESS situations which were scored moderate to high (2 and 3) at baseline. Patient Global Assessment (PGA) was also assessed.

Methods

All 151 subjects enrolled in the randomized (Treatment vs Control) remedē System pivotal trial were included in the analysis. All subjects were implanted, but activation in Control arm was delayed 6 months.

Results

Greater than or equal to 50% of patients scored moderate-high on several individual ESS situations: chance of dozing while sitting and reading (57%), watching television (62%), while lying down to rest in the afternoon when circumstances permit (76%). In the active arm, 68%, 44% and 29% of patients with moderate-high at baseline, respectively, for sitting and reading, watching television, and lying down to rest in the afternoon shifted to less than moderate at 6 months. Respective shifts for the control arm were 29%, 23% and 13%. Seventy-two percent of treated subjects with baseline ESS>10 shifted to ≤10 at 6 months compared to 26% of control patients. Additionally, 72% of treated compared to 7% of control subjects with baseline ESS>10 reported markedly or moderately improved QoL.

Conclusion

Results of this randomized controlled trial shows that compared to the control arm, TPNS leads to improvements in various situations of the ESS as well as QoL. The most improved situations were less chance of dozing while reading and watching television.

Support

Respicardia

Days' Supply of Initial Opioid Analgesic Prescriptions and Additional Fills for Acute Pain Conditions Treated in the Primary Care Setting - United States, 2014

During 2017, opioids were associated with 47,600 deaths in the United States, approximately one third of which involved a prescription opioid (1). Amid concerns that overprescribing to patients with acute pain remains an essential factor underlying misuse, abuse, diversion, and unintentional overdose, several states have restricted opioid analgesic prescribing (2,3). To characterize patterns of opioid analgesic use for acute pain in primary care settings before the widespread implementation of limits on opioid prescribing (2,3), patients filling an opioid analgesic prescription for acute pain were identified from a 2014 database of commercial claims. Using a logistic generalized additive model, the probability of obtaining a refill was estimated as a function of the initial number of days supplied. Among 176,607 patients with a primary care visit associated with an acute pain complaint, 7.6% filled an opioid analgesic prescription. Among patients who received an initial 7-day supply, the probability of obtaining an opioid analgesic prescription refill for nine of 10 conditions was <25%. These results suggest that a ≤7-day opioid analgesic prescription might be sufficient for most, but not all, patients seen in primary care settings with acute pain who appear to need opioid analgesics. However, treatment strategies should account for patient and condition characteristics, which might alternatively reduce or extend the anticipated duration of benefit from opioid analgesic therapy.

Patterns of Immediate-Release and Extended-Release Opioid Analgesic Use in the Management of Chronic Pain, 2003-2014

Importance

Many stakeholders are working to improve the safe use of immediate-release (IR) and extended-release/long-acting (ER/LA) opioid analgesics. However, little information exists regarding the relative use of these 2 formulations in chronic pain management.

Objectives

To describe the distribution of IR and ER/LA opioid analgesic therapy duration and examine adding and switching patterns among patients receiving long-term IR opioid analgesic therapy, defined as at least 90 consecutive days of IR formulation use.

Design, Setting, and Participants

A retrospective cohort study of 169 million individuals receiving opioid analgesics from across 90% of outpatient retail pharmacies in the United States from January 1, 2003, to December 31, 2014, using the IQVIA Health Vector One: Data Extract Tool. Analyses were conducted from March 2015 to June 2017.

Exposures

Receipt of dispensed IR or ER/LA opioid analgesic prescription.

Main Outcomes and Measures

Distribution of therapy frequency and duration of IR and ER/LA opioid analgesic use, and annual proportions of patients receiving long-term IR opioid analgesic therapy who added an ER/LA formulation while continuing to use an IR formulation, switched to an ER/LA formulation, or continued receiving IR opioid analgesic therapy only.

Results

Among the 169 280 456 patients included in this analysis, 168 315 458 patients filled IR formulations and 10 216 570 patients filled ER/LA formulations. A similar percentage of women received ER/LA (55%) and IR (56%) formulations, although those receiving ER/LA formulations (72%) were more likely to be aged 45 years or older compared with those receiving IR formulations (46%). The longest opioid analgesic episode duration was 90 days or longer for 11 563 089 patients (7%) filling IR formulations and 3 103 777 patients (30%) filling ER/LA formulations. The median episode duration was 5 days (interquartile range, 3-10 days) for patients using IR formulations and 30 days (interquartile range, 21-74 days) for patients using ER/LA formulations. From January 1, 2003, to December 31, 2014, a small and decreasing proportion of patients with long-term IR opioid analgesic therapy added (3.8% in 2003 to 1.8% in 2014) or switched to (1.0% in 2003 to 0.5% in 2014) an ER/LA formulation.

Conclusions and Relevance

Most patients receiving opioid analgesics, whether for short or extended periods, use IR formulations. Once receiving long-term IR opioid analgesic therapy, patients are unlikely to add or switch to an ER/LA formulation.

Successful Comparison of US Food and Drug Administration Sentinel Analysis Tools to Traditional Approaches in Quantifying a Known Drug-Adverse Event Association

The US Food and Drug Administration's Sentinel system has developed the capability to conduct active safety surveillance of marketed medical products in a large network of electronic healthcare databases. We assessed the extent to which the newly developed, semiautomated Sentinel Propensity Score Matching (PSM) tool could produce the same results as a customized protocol-driven assessment, which found an adjusted hazard ratio (HR) of 3.04 (95% confidence interval [CI], 2.81-3.27) comparing angioedema in patients initiating angiotensin-converting enzyme (ACE) inhibitors vs. beta-blockers. Using data from 13 Data Partners between 1 January 2008, and 30 September 2013, the PSM tool identified 2,211,215 eligible ACE inhibitor and 1,673,682 eligible beta-blocker initiators. The tool produced an HR of 3.14 (95% CI, 2.86-3.44). This comparison provides initial evidence that Sentinel analytic tools can produce findings similar to those produced by a highly customized protocol-driven assessment.

Non-steroidal anti-inflammatory drugs use is associated with reduced risk of inflammation-associated cancers: NIH-AARP study

Background

Chronic inflammation has been linked to cancers, and use of non-steroidal anti-inflammatory drugs (NSAIDs) has been associated with reduced risk of several cancers. To further refine the magnitude of NSAID-related associations, in particular for cancers related to inflammation, such as alcohol-, infection-, obesity-, and smoking-related cancers, as well as for less common cancers, we evaluated the use of NSAIDs and cancer risk in a very large cohort. We used propensity scores to account for potential selection bias and hypothesized that NSAID use is associated with decreased cancer incidence.

Methods

We conducted a prospective study among 314,522 participants in the NIH-AARP Diet and Health Study. Individuals who completed the lifestyle questionnaire, which included NSAID use, in 1996–1997 were followed through 2006. Information on cancer incidence was ascertained by linking to cancer registries and vital status databases.

Findings

During 2,715,994 person-years of follow-up (median 10.1 person-years), there were 51,894 incident cancers. Compared with non-users of NSAIDs, individuals who reported use in the 12 months prior to interview had a significantly lower risk of all inflammation-related cancer, alcohol-related, infection-related, obesity-related, and smoking-related cancers [hazard ratio (HR) (95% CI)) 0.90 (0.87–0.93), 0.80 (0.74–0.85), 0.82 (0.78–0.87), 0.88 (0.84–0.92), and 0.88 (0.85–0.92) respectively)].

Conclusions

After accounting for potential selection bias, our data showed an inverse association between NSAID use and alcohol-related, infection-related, obesity-related, and smoking-related cancers and support the hypothesis that inflammation is related to an increased risk of certain cancers.

Abstract A53: Estrogen metabolism in relation to the risk of aggressive prostate cancer

Introduction and Objective: Existing epidemiologic data do not support an association between circulating levels of sex steroid hormones and risk of prostate cancer. Although it has been suggested that the combined action of androgens and estrogens'specifically their balance'may play a key role in prostate carcinogenesis, epidemiologic studies to evaluate this hypothesis are sparse, have assessed a limited number of sex steroid hormones, and have provided inconsistent results. We investigated associations between serum sex hormones'with a particular focus on estrogen metabolites'and risk of aggressive prostate cancer.

Study Population, Design and Methods: In a case-control study nested within the Prostate, Lung, Colorectal and Ovarian (PLCO) Cancer Screening Trial, we measured 15 parent serum estrogens (estrone and estradiol) and estrogen metabolites, including those in the C-2, -4, or 16 hydroxylation pathways, using a liquid chromatography-tandem mass spectrometry (LC/MS/MS) assay. Cases (n=195) were defined as non-Hispanic white men diagnosed with aggressive prostate cancer (stage III or IV and/or Gleason ≥7) between and 1994 and 2009 who were 55–70 years at diagnosis. Controls (n=195) were non-Hispanic white men who were free from prostate cancer for the duration of follow-up and frequency-matched to cases by age at study entry (5-yr intervals), time since baseline screen (1-yr time windows) and year of blood draw. Only cases and controls included in a previous study that measured serum androgens and sex-hormone binding globulin (SHBG) were eligible. Logistic regression models were used to estimate odds ratios (OR) and 95% confidence intervals (95%CI).

Results: Individual parent estrogens and individual estrogen metabolites were unrelated to risk of aggressive prostate cancer; with the exception of a non-linear inverse relationship between cancer and levels of methylated catechols, namely 2- and 4-methoxyestrone. However, there was an increased risk of aggressive prostate cancer associated with an increasing ratio of 2:16 hydroxyestrone (fourth vs. first quartile: OR 2.44, 95% CI 1.34–4.45, p trend=0.001) and a strong trend of decreasing prostate cancer risk with an increasing ratio of estradiol to testosterone (fourth vs. first quartile: OR 0.27, 95% CI 0.12–0.59, p trend=0.003).

Conclusion: We observed a strong protective effect of higher serum estradiol to testosterone levels in relation to risk of aggressive prostate cancer. Men with higher concentrations of methylated catechols in the 2- and 4-hydroxylation pathway may have a reduced risk of aggressive prostate cancer, while those with higher ratios of 2:16 hydroxyestrone may be at increased risk. These findings suggest a role for sex steroid hormone metabolism in prostate carcinogenesis.

Citation Format: Amanda Black, Paul F. Pinsky, Robert L. Grubb, III, Roni T. Falk, Ann W. Hsing, Lisa W. Chu, Tamra E. Meyer, Tim Veenstra, Xia Xu, Kai Yu, Louise A. Brinton, Robert N. Hoover, Michael B. Cook. Estrogen metabolism in relation to the risk of aggressive prostate cancer. [abstract]. In: Proceedings of the Twelfth Annual AACR International Conference on Frontiers in Cancer Prevention Research; 2013 Oct 27-30; National Harbor, MD. Philadelphia (PA): AACR; Can Prev Res 2013;6(11 Suppl): Abstract nr A53.

Prospective evaluation of serum sarcosine and risk of prostate cancer in the Prostate, Lung, Colorectal and Ovarian Cancer Screening Trial

Metabolomic profiling has identified, sarcosine, a derivative of the amino acid glycine, as an important metabolite involved in the etiology or natural history of prostate cancer. We examined the association between serum sarcosine levels and risk of prostate cancer in 1122 cases (813 non-aggressive and 309 aggressive) and 1112 controls in the Prostate, Lung, Colorectal and Ovarian Cancer Screening Trial. Sarcosine was quantified using high-throughput liquid chromatography-mass spectrometry. A significantly increased risk of prostate cancer was observed with increasing levels of sarcosine (odds ratio [OR] for the highest quartile of exposure [Q4] versus the lowest quartile [Q1] = 1.30, 95% confidence interval [CI]: 1.02, 1.65; P-trend 0.03). When stratified by disease aggressiveness, we observed a stronger association for non-aggressive cases (OR for Q4 versus Q1 = 1.44, 95% CI: 1.11, 1.88; P-trend 0.006) but no association for aggressive prostate cancer (OR for Q4 versus Q1 = 1.03, 95% CI: 0.73, 1.47; P-trend 0.89). Although not statistically significant, temporal analyses showed a stronger association between sarcosine and prostate cancer for serum collected closer to diagnosis, suggesting that sarcosine may be an early biomarker of disease. Interestingly, the association between sarcosine and prostate cancer risk was stronger among men with diabetes (OR = 2.66, 95% CI: 1.04, 6.84) compared with those without reported diabetes (OR = 1.23, 95% CI: 0.95-1.59, P-interaction = 0.01). This study found that elevated levels of serum sarcosine are associated with an increased prostate cancer risk and evidence to suggest that sarcosine may be an early biomarker for this disease.

Neuropsychiatric events in varenicline and nicotine replacement patch users in the Military Health System

AIM

To determine the rate ratio of neuropsychiatric hospitalizations in new users of varenicline compared to new users of nicotine replacement therapy (NRT) patch in the Military Health System (MHS).

DESIGN, SETTING AND PARTICIPANTS

Varenicline (n = 19,933) and NRT patch (n = 15,867) users who initiated therapy from 1 August 2006 to 31 August 2007 within the MHS were included in this retrospective cohort study. After matching according to propensity scores, 10,814 users remained in each cohort. The study population included those with and without a history of neuropsychiatric disease.

MEASUREMENTS

Patients were followed for neuropsychiatric hospitalizations defined by primary neuropsychiatric discharge diagnosis using ICD-9 codes from in-patient administrative claims. Hazard ratios (HR) and 95% confidence intervals (CI) were estimated after propensity score matching on exposure for socio-demographic factors, health-care utilization, comorbidities, medication history and neuropsychiatric history.

FINDINGS

There was no increase in the rate of neuropsychiatric hospitalizations in patients treated with varenicline compared to NRT patch when followed for 30 days (propensity-score matched HR = 1.14, 95% CI: 0.56-2.34). Results were similar after 60 days of follow-up.

CONCLUSIONS

There does not appear to be an increase in neuropsychiatric hospitalizations with varenicline compared with nicotine replacement therapy patch over 30 or 60 days after drug initiation.

The association between inflammation-related genes and serum androgen levels in men: the prostate, lung, colorectal, and ovarian study

BACKGROUND

Androgens and inflammation have been implicated in the etiology of several cancers, including prostate cancer. Serum androgens have been shown to correlate with markers of inflammation and expression of inflammation-related genes.

METHODS

In this report, we evaluated associations between 9,932 single nucleotide polymorphisms (SNPs) marking common genetic variants in 774 inflammation-related genes and four serum androgen levels (total testosterone [T], bioavailable T [BioT]; 5α-androstane-3α, 17β-diol glucuronide [3αdiol G], and 4-androstene-3,17-dione [androstenedione]), in 560 healthy men (median age 64 years) drawn from the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial. Baseline serum androgens were measured by radioimmunoassay. Genotypes were determined as part of the Cancer Genetic Markers of Susceptibility Study genome-wide scan. SNP-hormone associations were evaluated using linear regression of hormones adjusted for age. Gene-based P values were generated using an adaptive rank truncated product (ARTP) method.

RESULTS

Suggestive associations were observed for two inflammation-related genes and circulating androgen levels (false discovery rate [FDR] q-value <0.1) in both SNP and gene-based tests. Specifically, T was associated with common variants in MMP2 and CD14, with the most significant SNPs being rs893226G > T in MMP2 and rs3822356T > C in CD14 (FDR q-value = 0.09 for both SNPs). Other genes implicated in either SNP or gene-based tests were IK with T and BioT, PRG2 with T, and TNFSF9 with androstenedione.

CONCLUSION

These results suggest possible cross-talk between androgen levels and inflammation pathways, but larger studies are needed to confirm these findings and to further clarify the interrelationship between inflammation and androgens and their effects on cancer risk.

A reproducible and high-throughput HPLC/MS method to separate sarcosine from α- and β-alanine and to quantify sarcosine in human serum and urine

While sarcosine was recently identified as a potential urine biomarker for prostate cancer, further studies have cast doubt on its utility to diagnose this condition. The inconsistent results may be due to the fact that alanine and sarcosine coelute on an HPLC reversed-phase column and the mass spectrometer cannot differentiate between the two isomers, since the same parent/product ions are generally used to measure them. In this study, we developed a high-throughput liquid chromatography-mass spectrometry (LC-MS) method that resolves sarcosine from alanine isomers, allowing its accurate quantification in human serum and urine. Assay reproducibility was determined using the coefficient of variation (CV) and intraclass correlation coefficient (ICC) in serum aliquots from 10 subjects and urine aliquots from 20 subjects across multiple analytic runs. Paired serum/urine samples from 42 subjects were used to evaluate sarcosine serum/urine correlation. Both urine and serum assays gave high sensitivity (limit of quantitation of 5 ng/mL) and reproducibility (serum assay, intra- and interassay CVs < 3% and ICCs > 99%; urine assay, intra-assay CV = 7.7% and ICC = 98.2% and interassay CV = 12.3% and ICC = 94.2%). In conclusion, this high-throughput LC-MS method is able to resolve sarcosine from α- and β-alanine and is useful for quantifying sarcosine in serum and urine samples.

Dietary carbohydrate, glycemic index, glycemic load, and risk of prostate cancer in the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial (PLCO) cohort

OBJECTIVE

To evaluate the associations between dietary carbohydrate, glycemic index (GI), glycemic load (GL), and incident prostate cancer in the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial (PLCO) cohort.

METHODS

Between September 1993 and September 2000, 38,343 men were randomized to the screening arm of the trial at one of 10 PLCO centers. A food frequency questionnaire administered at baseline assessed usual dietary intake over the preceding 12 months. Prostate cancer was ascertained by medical follow-up of suspicious screening results and annual mailed questionnaires and confirmed with medical records. Cox proportional hazards regression was used to model the associations of carbohydrate, GI, and GL with prostate cancer risk.

RESULTS

During follow-up (median = 9.2 years), 2,436 incident prostate cancers were identified among 30,482 eligible participants. Overall, there were no associations of baseline carbohydrate, GI, or GL with incident prostate cancer in minimally or fully adjusted models. There were no associations when the 228 advanced and 2,208 non-advanced cancers were analyzed separately.

CONCLUSIONS

Dietary carbohydrate, GI, and GL were not associated with incident prostate cancer in PLCO. The narrow range of GI in this cohort may have limited our ability to detect associations, an issue that future studies should address.

Genome-wide association studies of serum magnesium, potassium, and sodium concentrations identify six Loci influencing serum magnesium levels

Magnesium, potassium, and sodium, cations commonly measured in serum, are involved in many physiological processes including energy metabolism, nerve and muscle function, signal transduction, and fluid and blood pressure regulation. To evaluate the contribution of common genetic variation to normal physiologic variation in serum concentrations of these cations, we conducted genome-wide association studies of serum magnesium, potassium, and sodium concentrations using ∼2.5 million genotyped and imputed common single nucleotide polymorphisms (SNPs) in 15,366 participants of European descent from the international CHARGE Consortium. Study-specific results were combined using fixed-effects inverse-variance weighted meta-analysis. SNPs demonstrating genome-wide significant (p<5×10⁻⁸) or suggestive associations (p<4×10⁻⁷) were evaluated for replication in an additional 8,463 subjects of European descent. The association of common variants at six genomic regions (in or near MUC1, ATP2B1, DCDC5, TRPM6, SHROOM3, and MDS1) with serum magnesium levels was genome-wide significant when meta-analyzed with the replication dataset. All initially significant SNPs from the CHARGE Consortium showed nominal association with clinically defined hypomagnesemia, two showed association with kidney function, two with bone mineral density, and one of these also associated with fasting glucose levels. Common variants in CNNM2, a magnesium transporter studied only in model systems to date, as well as in CNNM3 and CNNM4, were also associated with magnesium concentrations in this study. We observed no associations with serum sodium or potassium levels exceeding p<4×10⁻⁷. Follow-up studies of newly implicated genomic loci may provide additional insights into the regulation and homeostasis of human serum magnesium levels.

Magnesium, potassium, and sodium are involved in important physiological processes. To better understand how common genetic variation may contribute to inter-individual differences in serum concentrations of these electrolytes, we evaluated single nucleotide polymorphisms (SNPs) across the genome in association with serum magnesium, potassium, and sodium levels in 15,366 participants of European descent from the CHARGE Consortium. We then verified the associations in an additional 8,463 study participants. Six different genomic regions contain variants that are reproducibly associated with serum magnesium levels, and only one of the regions had been previously known to influence serum magnesium concentrations in humans. The identified SNPs also show association with clinically defined hypomagnesemia, and some of them with traits that have been linked to serum magnesium levels, including kidney function, fasting glucose, and bone mineral density. We further provide evidence for a physiological role of magnesium transporters in humans which have previously only been studied in model systems. None of the SNPs evaluated in our study are significantly associated with serum levels of sodium or potassium. Additional studies are needed to investigate the underlying molecular mechanisms in order to help us understand the contribution of these newly identified regions to magnesium homeostasis.

Association between genetic variants in the 8q24 cancer risk regions and circulating levels of androgens and sex hormone-binding globulin

BACKGROUND

Genome-wide association studies have identified multiple independent regions on chromosome 8q24 that are associated with cancers of the prostate, breast, colon, and bladder.

METHODS

To investigate their biological basis, we examined the possible association between 164 single nucleotide polymorphisms (SNPs) in the 8q24 risk regions spanning 128,101,433-128,828,043 bp, and serum androgen (testosterone, androstenedione, 3alphadiol G, and bioavailable testosterone), and sex hormone-binding globulin levels in 563 healthy, non-Hispanic, Caucasian men (55-74 years old) from a prospective cohort study (the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial). Age-adjusted linear regression models were used to determine the association between the SNPs in an additive genetic model and log-transformed biomarker levels.

RESULTS

Three adjacent SNPs centromeric to prostate cancer risk-region 2 (rs12334903, rs1456310, and rs980171) were associated with testosterone (P < 1.1 x 10(-3)) and bioavailable testosterone (P < 6.3 x 10(-4)). Suggestive associations were seen for a cluster of nine SNPs in prostate cancer risk region 1 and androstenedione (P < 0.05).

CONCLUSIONS

These preliminary findings require confirmation in larger studies but raise the intriguing hypothesis that genetic variations in the 8q24 cancer risk regions might correlate with androgen levels.

IMPACT

These results might provide some clues for the strong link between 8q24 and prostate cancer risk.

Diabetes genes and prostate cancer in the Atherosclerosis Risk in Communities study

There is a known inverse association between type 2 diabetes (T2D) and prostate cancer (PrCa) that is poorly understood. Genetic studies of the T2D-PrCa association may provide insight into the underlying mechanisms of this association. We evaluated associations in the Atherosclerosis Risk in Communities study between PrCa and nine T2D single nucleotide polymorphisms from genome-wide association studies of T2D (in CDKAL1, CDKN2A/B, FTO, HHEX, IGF2BP2, KCNJ11, PPARG, SLC30A8, and TCF7L2) and four T2D single nucleotide polymorphisms from pre-genome-wide association studies (in ADRB2, CAPN10, SLC2A2, and UCP2). From 1987 to 2000, there were 397 incident PrCa cases among 6,642 men ages 45 to 64 years at baseline. We used race-adjusted Cox proportional hazards models to estimate associations between PrCa and increasing number of T2D risk-raising alleles. PrCa was positively associated with the CAPN10 rs3792267 G allele [hazard ratio (HR) 1.20; 95% confidence interval (CI), 1.00-1.44] and inversely associated with the SLC2A2 rs5400 Thr110 allele (HR, 0.85; 95% CI, 0.72, 1.00), the UCP2 rs660339 Val55 allele (HR, 0.84; 95% CI, 0.73, 0.97) and the IGF2BP2 rs4402960 T allele (HR, 0.79; 95% CI, 0.61-1.02; blacks only). The TCF7L2 rs7903146 T allele was inversely associated with PrCa using a dominant genetic model (HR, 0.79; 95% CI, 0.65-0.97). Further knowledge of T2D gene-PrCa mechanisms may improve understanding of PrCa etiology.

Abstract 4732: Association between genetic variants in the 8q24 cancer risk regions and circulating levels of androgens and sex-hormone binding globulin

Multiple genome-wide association studies have identified several independent non-coding regions in chromosome 8q24 associated with risk for cancers of the prostate, breast, colon, and bladder. To explore their biological basis, we investigated the possible association between 164 single nucleotide polymorphism (SNPs) in the 8q24 risk regions, spanning 128,101,433-128,828,043 bp, and serum androgen (testosterone, androstenedione, and 3αdiol G) and sex hormone-binding globulin levels in 563 healthy, non-Hispanic, Caucasian men (55-74 years old) from a prospective cohort study, the Prostate, Lung, Colorectal, and Ovarian (PLCO) Cancer Screening Trial. Age-adjusted linear regression using SNPs in an additive genetic model showed that three adjacent SNPs centromeric to prostate cancer risk region 2 (rs12334903, rs1456310, and rs980171) were associated with measured total testosterone (P&lt;1.1×10−3) and calculated bioavailable testosterone (P&lt;6.3×10−4). Suggestive associations were seen for a cluster of 9 SNPs in prostate cancer risk region 1 and androstenedione (P&lt;0.05). These preliminary findings, although in need of confirmation in larger studies, suggest that genetic variations in the 8q24 cancer risk regions may correlate with androgen levels, which in turn may provide some clues for the strong link between 8q24 and prostate cancer risk.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4732.

Abstract 924: Possible joint effects between single nucleotide polymorphisms in inflammation genes and serum androgen levels on risk of prostate cancer

Both inflammation and androgens are likely to be involved in the etiology of prostate cancer. There is evidence for cross-talk between androgen and inflammation pathways, yet little is known about the joint contribution of inflammation and androgens to prostate cancer risk. Thus, we evaluated the joint effects of 9,932 tag single nucleotide polymorphisms (SNPs) in 774 inflammation-related genes and four serum androgen measures (total testosterone [T], bioavailable T, 3α-androstanediol glucuronide [3α diol G], and androstenedione) on risk of prostate cancer in 516 incident cancer cases and 560 controls from the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial. SNPs included in this study were genotyped as part of the National Cancer Institute Cancer Genetic Markers of Susceptibility genome-wide association study. Likelihood ratio tests (LRT) were used to compare logistic models of prostate cancer regressed on age, center, the androgen (in quartiles), the SNP (additive genetic coding) and the SNP x hormone interaction term to logistic models of prostate cancer regressed on age, center, and the androgen. False discovery rate (FDR) control was used to adjust for multiple testing. Statistically significant LRT P-values were noted for T and three intronic SNPs in linkage disequilibrium (r2&gt;0.7) within the HIPK2 gene on 7q34 (rs10256326, rs7788362, and rs12539357; FDR-adjusted P=0.04 for all SNPs). For each SNP, the minor allele was associated with a reduced prostate cancer risk in men with serum T levels in the lower three quartiles, but was associated with an increased risk among men in the highest quartile of serum T. LRT P-values of borderline statistical significance were also seen for joint effects of these three SNPs and bioavailable T on risk of prostate cancer (FDR-adjusted P=0.07 for all SNPs). There were no significant joint effects for any of the SNPs with 3αdiol G or androstenedione after adjustment for multiple tests. Our preliminary results suggest that T levels could interact with HIPK2 gene variants to influence prostate cancer risk. HIPK2 is an attractive candidate gene for further evaluation because it codes for a serine/threonine kinase involved in transcriptional regulation, particularly involved in p53-dependent and independent regulation of cell cycle control and apoptosis. Future studies are needed to confirm our preliminary findings and to further understand the possible interaction between T and genetic variants in HIPK2, which could contribute to prostate cancer risk.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 924.

Measuring serum melatonin in epidemiologic studies

BACKGROUND

Epidemiologic data on serum melatonin, a marker of circadian rhythms, and cancer are sparse due largely to the lack of reliable assays with high sensitivity to detect relatively low melatonin levels in serum collected during daylight, as commonly available in most epidemiologic studies.

METHODS

To help expand epidemiologic research on melatonin, we assessed the reproducibility and refined a currently available melatonin RIA, and evaluated its application to epidemiologic investigations by characterizing melatonin levels in serum, urine, and/or plasma in 135 men from several ethnic groups.

RESULTS

Reproducibility was high for the standard 1.0-mL serum [mean coefficient of variation (CV), 6.9%; intraclass correlation coefficient (ICC), 97.4%; n = 2 serum pools in triplicate] and urine-based (mean CV, 3.5%; ICC, 99.9%) assays. Reproducibility for the 0.5-mL refined-serum assay was equally good (mean CV, 6.6%; ICC, 99.0%). There was a positive correlation between morning serum melatonin and 6-sulfatoxymelatonin in 24-hour urine (r = 0.46; P = 0.008; n = 49 subjects). Melatonin levels in serum-plasma pairs had a high correlation (r = 0.97; P < 1x10(-4); n = 20 pairs). Morning serum melatonin levels were five times higher than those from the afternoon (before 9 a.m. mean, 11.0 pg/mL, versus after 11 a.m. mean, 2.0 pg/mL). Chinese men had lower melatonin levels (mean, 3.4 pg/mL), whereas Caucasian, African-American, and Ghanaian men had similar levels (mean, 6.7-8.6 pg/mL).

CONCLUSIONS

These results suggest that melatonin can be detected reliably in serum samples collected in epidemiologic studies in various racial groups.

IMPACT

With improved assays, it may be possible to investigate the role of melatonin and the emerging circadian rhythm hypothesis in cancer etiology in epidemiologic studies.

Androgen receptor CAG repeat length and risk of biliary tract cancer and stones

Biliary tract cancers, encompassing cancers of the gallbladder, extrahepatic bile ducts, and ampulla of Vater, are rare but highly fatal. Gallstones represent the major risk factor for biliary tract cancer, and share with gallbladder cancer a female predominance and an association with reproductive factors and obesity. Although estrogens have been implicated in earlier studies of gallbladder cancer, there are no data on the role of androgens. Because intracellular androgen activity is mediated through the androgen receptor (AR), we examined associations between AR CAG repeat length [(CAG)(n)] and the risk of biliary tract cancers and stones in a population-based study of 331 incident cancer cases, 837 gallstone cases, and 750 controls from Shanghai, China, where the incidence rates for biliary tract cancer are rising sharply. Men with (CAG)(n) >24 had a significant 2-fold risk of gallbladder cancer [odds ratio (OR), 2.00; 95% confidence interval (CI), 1.07-3.73], relative to those with (CAG)(n) < or = 22. In contrast, women with (CAG)(n) >24 had reduced gallbladder cancer risk (OR, 0.69; 95% CI, 0.43-1.09) relative to those with (CAG)(n) < or = 22; P interaction sex = 0.01, which was most pronounced for women ages 68 to 74 (OR, 0.48; 95% CI, 0.25-0.93; P interaction age = 0.02). No associations were found for bile duct cancer or gallstones. Reasons for the heterogeneity of genetic effects by gender and age are unclear but may reflect an interplay between AR and the levels of androgen as well as estrogen in men and older women. Further studies are needed to confirm these findings and clarify the mechanisms involved.

GOSR2 Lys67Arg is associated with hypertension in whites

BACKGROUND

Hypertension is a risk factor for coronary heart disease (CHD), but the causes of hypertension remain largely unknown. Genetic variation is thought to contribute to the etiology of hypertension. We tested a single-nucleotide polymorphism (SNP) (Lys67Arg, rs197922) in the Golgi SNAP Receptor Complex Member 2 (GOSR2) gene for association with hypertension and blood pressure (BP). We chose this SNP because it was nominally associated with CHD in earlier studies. Further, GOSR2 is located in a linkage region for hypertension and BP in human and animal studies.

METHODS

We used logistic and linear regression to test associations of the GOSR2 SNP with hypertension and BP among 3,528 blacks and 9,861 whites from the Atherosclerosis Risk in Communities (ARIC) study. Race-specific regression models of hypertension were adjusted for age and gender. Regression models of BP were further adjusted for antihypertensive medication use.

RESULTS

The GOSR2 Lys67 allele was associated with hypertension in whites (odds ratio (OR) = 1.09, P = 0.01) but not blacks (OR = 0.96, P = 0.47). The Lys67 allele was associated with increased systolic BP (SBP) in both races (0.87 mm Hg, P < 0.001 among whites and 1.05 mm Hg, P = 0.05 among blacks). A similar association in whites was observed for the GOSR2 SNP and SBP in the Women's Genome Health Study (WGHS) (OR = 1.03, P = 0.04). The OR remained unchanged after adjustment for antihypertensive medication use (OR = 1.03, P = 0.11), though it was no longer statistically significant.

CONCLUSIONS

We found evidence that a SNP in GOSR2 is modestly associated with hypertension in whites from the ARIC study and the WGHS.

West Nile virus infection among the homeless, Houston, Texas

Among 397 homeless participants studied, the overall West Nile virus (WNV) seroprevalence was 6.8%. Risk factors for WNV infection included being homeless >1 year, spending >6 hours outside daily, regularly taking mosquito precautions, and current marijuana use. Public health interventions need to be directed toward this high-risk population.

Serological evidence of typhus group rickettsia in a homeless population in Houston, Texas

We tested sera from 176 homeless people in Houston for antibodies against typhus group rickettsiae (TGR). Sera from 19 homeless people were reactive to TGR antigens by ELISA and IFA. Two people had antibodies against Rickettsia prowazekii (epidemic typhus) and the remaining 17 had antibodies against Rickettsia typhi (murine typhus).

Adherence to recommendations for follow-up to abnormal Pap tests

OBJECTIVE

To evaluate whether timely adherence rates differ by race among women with abnormal Pap tests participating in a cost-free or reduced-cost program.

METHODS

Eligible subjects included women aged 47-64 years who received a referral for follow-up care after an abnormal Pap test from 1999 to 2002 in South Carolina (n=330). Adherence was measured as days to receipt of follow-up care after an abnormal Pap test. Cox proportional hazards modeling was used to estimate risk factors associated with time to adherence within 60 and 365 days by race.

RESULTS

African-American and non-Hispanic white women had similar adherence to follow-up. Among white women, those with high-grade lesions were less likely to adhere in a timely manner relative to those with low-grade lesions (hazard ratio 0.6, 95% confidence interval [CI] 0.4-1.0). For African-American women, rural residence (hazard ratio: 0.5, 95% CI 0.2-0.9) and history of abnormal Pap tests (hazard ratio 0.6, 95% CI 0.3-1.0) were associated with decreased adherence, whereas less education (hazard ratio 2.3, 95% CI 1.3-3.9) was associated with increased adherence.

CONCLUSION

Adherence rates do not differ by race. However, risk factors for adherence within race are variable. Interventions tailored to the differential needs of racial and ethnic groups may prove effective toward increasing timely adherence rates.

LEVEL OF EVIDENCE

II.

Meta-analysis of racial disparities in survival in association with socioeconomic status among men and women with colon cancer

BACKGROUND

Few studies have addressed racial disparities in survival for colon cancer by adequately incorporating both treatment and socioeconomic factors, and the findings from those studies have been inconsistent. The objectives of the current study were to systematically review the existing literature and provide a more stable estimate of the measures of association between socioeconomic status and racial disparities in survival for colon cancer by undertaking a meta-analysis.

METHODS

For this meta-analysis, the authors searched the MEDLINE database to identify articles published in English from 1966 to August 2006 that met the following inclusion criteria: original research articles that addressed the association between race/ethnicity and survival in patients with colon or colorectal cancer after adjusting for socioeconomic status. In total, 66 full articles were reviewed, and 56 of those articles were excluded, which left 10 studies for the final analysis.

RESULTS

The pooled hazard ratio (HR) for African Americans compared with Caucasians was 1.14 (95% confidence interval [95% CI], 1.00-1.29) for all-cause mortality and 1.13 (95% CI, 1.01-1.28) for colon cancer-specific mortality. The test for homogeneity of the HR was statistically significant across the studies for all-cause mortality (Q=31.69; P<.001) but was not significant across the studies for colon cancer-specific mortality (Q=7.45; P=.114).

CONCLUSIONS

Racial disparities in survival for colon cancer between African Americans and Caucasians were only marginally significant after adjusting for socioeconomic factors and treatment. Attempts to modify treatment and socioeconomic factors with the objective of reducing racial disparities in health outcomes may have important clinical and public health implications.

Plasmon waveguide resonance spectroscopic evidence for differential binding of oxidized and reduced Rhodobacter capsulatus cytochrome c2 to the cytochrome bc1 complex mediated by the conformation of the Rieske iron-sulfur protein

The dissociation constants for the binding of Rhodobacter capsulatus cytochrome c2 and its K93P mutant to the cytochrome bc1 complex embedded in a phospholipid bilayer were measured by plasmon waveguide resonance spectroscopy in the presence and absence of the inhibitor stigmatellin. The reduced form of cytochrome c2 strongly binds to reduced cytochrome bc1 (Kd = 0.02 microM) but binds much more weakly to the oxidized form (Kd = 3.1 microM). In contrast, oxidized cytochrome c2 binds to oxidized cytochrome bc1 in a biphasic fashion with Kd values of 0.11 and 0.58 microM. Such a biphasic interaction is consistent with binding to two separate sites or conformations of oxidized cytochrome c2 and/or cytochrome bc1. However, in the presence of stigmatellin, we find that oxidized cytochrome c2 binds to oxidized cytochrome bc1 in a monophasic fashion with high affinity (Kd = 0.06 microM) and reduced cytochrome c2 binds less strongly (Kd = 0.11 microM) but approximately 30-fold more tightly than in the absence of stigmatellin. Structural studies with cytochrome bc1, with and without the inhibitor stigmatellin, have led to the proposal that the Rieske protein is mobile, moving between the cytochrome b and cytochrome c1 components during turnover. In one conformation, the Rieske protein binds near the heme of cytochrome c1, while the cytochrome c2 binding site is also near the cytochrome c1 heme but on the opposite side from the Rieske site, where cytochrome c2 cannot directly interact with Rieske. However, the inhibitor, stigmatellin, freezes the Rieske protein iron-sulfur cluster in a conformation proximal to cytochrome b and distal to cytochrome c1. We conclude from this that the dual conformation of the Rieske protein is primarily responsible for biphasic binding of oxidized cytochrome c2 to cytochrome c1. This optimizes turnover by maximizing binding of the substrate, oxidized cytochrome c2, when the iron-sulfur cluster is proximal to cytochrome b and minimizing binding of the product, reduced cytochrome c2, when it is proximal to cytochrome c1.

What predicts adherence to follow-up recommendations for abnormal Pap tests among older women?

OBJECTIVE

To address socio-demographic factors associated with adherence to follow-up recommendations in a high-risk population of women referred for follow-up care after an abnormal Pap test.

METHODS

486 women aged 46-64 served by BCCEDP in two southeastern states between 1999-2002 and referred for follow-up care after an abnormal Pap test were the sampling frame for this cross-sectional study; 204 women completed a phone-based interview in 2004. Cox proportional hazards modeling was used to determine the association of various risk factors with time to adherence.

RESULTS

Among those completing the phone interview (interview rate=61.4%) the mean age was 53.3 years, 64.7% were African-American women, 81.9% had low-grade cervical lesions, and all were either uninsured or under insured. Over 95% received follow-up care for an abnormal Pap test within 365 days of referral. When the BCCEDP criteria of follow-up within 60 days were applied, 52.9% were adherent. Rates of self-reported and program documented adherence differed significantly by state. After adjusting for state of residence, women who reported having symptoms of a chronic disease were more likely to be adherent within 365 days (aHR=1.42; 95% CI=1.00, 2.04). Neither age, race, lesion severity, education, number of dependent adults or children, self-perceived physical health, nor smoking status was associated with time to adherence.

CONCLUSIONS

Findings suggest that institutional factors may be more important than individual factors in predicting time to adherence for an abnormal Pap test.

A case-control study of farming and prostate cancer in African-American and Caucasian men

OBJECTIVE

To determine the risk of prostate cancer associated with farming by duration, recency and specific activities among African-Americans and Caucasians.

METHODS

This population-based case-control study had information on farming-related activities for 405 incident prostate cancer cases and 392 controls matched for age, race and region in South Carolina, USA, from 1999 to 2001. Cases with histologically confirmed, primary invasive prostate cancer who were aged between 65 and 79 years were ascertained through the South Carolina Central Cancer Registry. Appropriately matched controls were identified from the Health Care Financing Administration Medicare Beneficiary File. Data were collected using computer-assisted telephone interviewing, and adjusted odds ratios (aOR) were estimated using unconditional logistic regression.

RESULTS

Farming was associated with increased risk of prostate cancer in Caucasians (aOR 1.8; 95% confidence interval (CI) 1.3 to 2.7) but not in African-Americans (aOR 1.0; 95% CI 0.6 to 1.6). Regarding specific farming activities, farmers who mixed or applied pesticides had a higher risk of prostate cancer (aOR 1.6; 95% CI 1.2 to 2.2). Increased risk of prostate cancer was observed only for those farming <5 years.

CONCLUSIONS

Increased risk of prostate cancer for farmers in this study may be attributable to pesticide exposure. Racial differences in the association between farming and prostate cancer may be explained by different farming activities or different gene-environment interactions by race.

Stabilization against Hyperthermal Denaturation through Increased CG Content Can Explain the Discrepancy between Whole Genome and 16S rRNA Analyses

Based largely upon analysis of ribosomal RNA, a third domain of life, called archaea, had been proposed in addition to bacteria and eukaryotes. However, quantitative analysis of 73 whole genomes shows only a two-domain division of life: into eukaryotes and prokaryotes. Thousands of orthologous genes in archaea and bacteria show an essentially unimodal distribution of sequence identities. Thus, whole genome analyses indicate that archaea are a phylum of bacteria rather than a separate domain of life. In contrast, archaeal rRNA and that of hyperthermophilic bacteria differ from the rRNA of mesophilic bacteria. Thus, there is a bimodal distribution of rRNA sequence identities which differ by 12%. This discrepancy in rRNA and gene content based analyses of whole genomes is likely due to a 15% elevated C:G content of the rRNA of archaea and hyperthermophilic bacteria. The elevated C:G content is consistent with stabilization against thermal denaturation caused by additional hydrogen bonding (3 bonds) in C:G pairs compared to A:U pairs (2 bonds). Based upon this premise, there is no reliable way to correct rRNA for such differences in base composition and it is not possible to quantitatively compare hyperthermophiles with mesophiles by the rRNA method. Furthermore, quantitative study of whole genomes shows that the extent of change in both bacterial and archaeal genes, including rRNA, has reached a limit. Thus, direct sequence comparisons work with closely related genomes, but it is not possible to differentiate the most divergent prokaryotic species, which are currently designated as separate phyla. We believe that the differences in characteristics of archaeal species is based primarily upon selection of genes and pathways compatible with the extreme environmental lifestyle, i.e., hyperthermophily.

Binding of Oxidized and Reduced Cytochrome c2 to Photosynthetic Reaction Centers: Plasmon-Waveguide Resonance Spectroscopy

The dissociation constants for the binding of oxidized and reduced wild-type cytochrome c(2) from Rhodobacter capsulatus and the lysine 93 to proline mutant of cytochrome c(2) to photosynthetic reaction centers (Rhodobacter sphaeroides) has been measured to high precision using plasmon-waveguide resonance spectroscopy. For the studies reported, detergent-solubilized photosynthetic reaction center was exchanged into a phosphatidylcholine lipid bilayer to approximate the physiological environment. At physiologically relevant ionic strengths ( approximately 100 mM), we found two binding sites for the reduced wild-type cytochrome (K(D) = 10 and 150 nM), with affinities that decrease with decreasing ionic strength (2-5-fold). These results implicate nonpolar interactions as an important factor in determining the dissociation constants. Taking advantage of the ability of plasmon-waveguide resonance spectroscopy to reslove the contribution of changes in mass and of structural anisotropy to cytochrome binding, we can demonstrate very different properties for the two binding sites. In contrast, the oxidized wild-type cytochrome only binds to a single site with a K(D) of 10 nM at high ionic strength, and this site has properties similar to the low-affinity site for binding the reduced cytochrome. The binding of oxidized cytochrome c(2) has a strong ionic strength response, with the affinity decreasing approximately 30-fold in going from high to low ionic strength. The K93P mutant binds to a single site in both redox states, which is similar, in terms of mass and structural anisotropy, to the oxidized wild-type site, with the affinity of the mutant oxidized state being approximately 30-fold weaker than that of the oxidized wild-type cytochrome at high ionic strength. Thus, reduced wild-type cytochrome can bind to both the high- and low-affinity sites, while the oxidized wild-type cytochrome and both redox states of the mutant cytochrome can only bind to the low-affinity site, possibly the consequence of the more stable structure of reduced wild-type cytochrome. In aggregate, the results are consistent with a model in which a transient conformational change in the region 88-102 in the cytochrome three-dimensional structure, the so-called hinge region, drives the dissociation of the oxidized cytochrome from the reaction center-cytochrome complex, facilitating turnover.

Protein Dynamics in the Region of the Sixth Ligand Methionine Revealed by Studies of Imidazole Binding To Rhodobacter capsulatus Cytochrome c2 Hinge Mutants,

All class I c-type cytochromes studied to date undergo a dynamic process in the oxidized state, which results in the transient breaking of the iron-methionine-sulfur bond and sufficient movement to allow the binding of exogenous ligands (imidazole in this work). In the case of Rhodobacter capsulatus cytochrome c(2), the sixth heme ligand Met96 and up to 14 flanking residues (positions 88-100, termed the hinge region), located between two relatively rigid helical regions, may be involved in structural changes leading to a transient high-spin species able to bind ligands. We have examined 14 mutations at 9 positions in the hinge region of Rhodobacter capsulatus cytochrome c(2) and have determined the structure of the G95E mutant. Mutations near the N- and C-terminus of the hinge region do not affect the kinetics of movement but allow us to further define that portion of the hinge that moves away from the heme to the 93-100 region in the amino acid sequence. Mutations at positions 93 and 95 can alter the rate constant for hinge movement (up to 20-fold), presumably as a result of altering the structure of the native cytochrome to favor a more open conformation. The structure of one of these mutants, G95E, suggests that interactions within the hinge region are stabilized while interaction between the hinge and the heme are destabilized. In contrast, mutations at positions 98 and 99 alter imidazole binding kinetics but not the hinge movement. Thus, it appears that these mutations affect the structure of the cytochrome after the hinge region has moved away from the heme, resulting in increased solvent access to the bound imidazole or alter interactions between the protein and the bound imidazole.

Rhodobacter capsulatus Photoactive Yellow Protein: Genetic Context, Spectral and Kinetics Characterization, and Mutagenesis

A gene for photoactive yellow protein (PYP) was previously cloned from Rhodobacter capsulatus (Rc), and we have now found it to be associated with genes for gas vesicle formation in the recently completed genome sequence. However, the PYP had not been characterized as a protein. We have now produced the recombinant RcPYP in Escherichia coli as a glutathione-S-transferase (GST) fusion protein, along with the biosynthetic enzymes, resulting in the formation of holo-RcPYP following cleavage of the GST tag. The absorption spectrum (with characteristic peaks at 435 and 375 nm) and the photocycle kinetics, initiated by a laser flash at 445 nm, are generally similar to those of Rhodobacter sphaeroides (RsPYP) but are significantly different from those of the prototypic PYP from Halorhodospira halophila (HhPYP), which has a single peak at 446 nm and has slower recovery. RcPYP also is photoactive when excited with near-ultraviolet laser light, but the end point is then above the preflash baseline. This suggests that some of the PYP chromophore is present in the cis-protonated conformation in the resting state. The excess 435 nm form in RcPYP, built up from repetitive 365 nm laser flashes, returns to the preflash baseline with an estimated half-life of 2 h, which is markedly slower than that for the same reaction in RsPYP. Met100 has been reported to facilitate cis-trans isomerization in HhPYP, yet both Rc and RsPYPs have Lys and Gly substitutions at positions 99 and 100 (using HhPYP numbering throughout) and have 100-fold faster recovery kinetics than does HhPYP. However, the G100M and K99Q mutations of RcPYP have virtually no effect on kinetics. Apparently, the RcPYP M100 is in a different conformation, as was recently found for the PYP domain of Rhodocista centenaria Ppr. The cumulative results show that the two Rhodobacter PYPs are clearly distinct from the other species of PYP that have been characterized. These properties also suggest a different functional role, that we postulate to be in regulation of gas vesicle genes, which are known to be light-regulated in other species.

Amino Acid Sequences and Distribution of High-Potential Iron–Sulfur Proteins That Donate Electrons to the Photosynthetic Reaction Center in Phototropic Proteobacteria

High-potential iron-sulfur protein (HiPIP) has recently been shown to function as a soluble mediator in photosynthetic electron transfer between the cytochrome bc1 complex and the reaction-center bacteriochlorophyll in some species of phototrophic proteobacteria, a role traditionally assigned to cytochrome c2. For those species that produce more than one high-potential electron carrier, it is unclear which protein functions in cyclic electron transfer and what characteristics determine reactivity. To establish how widespread the phenomenon of multiple electron donors might be, we have studied the electron transfer protein composition of a number of phototrophic proteobacterial species. Based upon the distribution of electron transfer proteins alone, we found that HiPIP is likely to be the electron carrier of choice in the purple sulfur bacteria in the families Chromatiaceae and Ectothiorhodospiraceae, but the majority of purple nonsulfur bacteria are likely to utilize cytochrome c2. We have identified several new species of phototrophic proteobacteria that may use HiPIP as electron donor and a few that may use cytochromes c other than c2. We have determined the amino acid sequences of 14 new HiPIPs and have compared their structures. There is a minimum of three sequence categories of HiPIP based upon major insertions and deletions which approximate the three families of phototrophic proteobacteria and each of them can be further subdivided prior to construction of a phylogenetic tree. The comparison of relationships based upon HiPIP and RNA revealed several discrepancies.

Site-specific mutations provide new insights into the origin of pH effects and alternative spectral forms in the photoactive yellow protein from Halorhodospira halophila

Acid/base titrations of wild-type PYP and mutants, either in buffer or in the presence of chaotropes such as thiocyanate, establish the presence of four spectral forms including the following: a neutral form (446-476 nm), an acidic form (350-355 nm), an alkaline form (430-440 nm), and an intermediate wavelength form (355-400 nm). The acidic species is formed by protonation of the oxyanion of the para-hydroxy-cinnamyl cysteine chromophore as a secondary result of acid denaturation (with pK(a) values of 2.8-5.4) and often results in precipitation of the protein, and in the case of wild-type PYP, eventual hydrolysis of the chromophore thioester bond at pH values below 2. Thus, the large and complex structural changes associated with the acidic species make it a poor model for the long-lived photocycle intermediate, I(2), which undergoes more moderate structural changes. Mutations at E46, which is hydrogen-bonded to the chromophore, have only two spectral forms accessible to them, the neutral and the acidic forms. Thus, an intact E46 carboxyl group is essential for observation of either intermediate or alkaline wavelength forms. The alkaline form is likely to be due to ionization of E46 in the folded protein. We postulate that the intermediate wavelength form is due to a conformational change that allows solvent access to E46 and formation of a hydrogen-bond from a water molecule to the carboxylic acid group, thus weakening its interaction with the chromophore. Increasing solvent access to the intermediate spectral form with denaturant concentration results in a continuously blue-shifted wavelength maximum.

Identification of a thiosulfate utilization gene cluster from the green phototrophic bacterium Chlorobium limicola

Chlorobium is an autotrophic, green phototrophic bacterium which uses reduced sulfur compounds to fix carbon dioxide in the light. The pathways for the oxidation of sulfide, sulfur, and thiosulfate have not been characterized with certainty for any species of bacteria. However, soluble cytochrome c-551 and flavocytochrome c (FCSD) have previously been implicated in the oxidation of thiosulfate and sulfide on the basis of enzyme assays in Chlorobium. We have now made a number of observations relating to the oxidation of reduced sulfur compounds. (1) Western analysis shows that soluble cytochrome c-551 in Chlorobium limicola is regulated by thiosulfate, consistent with a role in the utilization of thiosulfate. (2) A membrane-bound flavocytochrome c-sulfide dehydrogenase (which is normally a soluble protein in other species) is constitutive and not regulated by sulfide as expected for an obligately autotrophic species dependent upon sulfide. (3) We have cloned the cytochrome c-551 gene from C. limicola and have found seven other genes, which are also presumably involved in sulfur metabolism and located near that for cytochrome c-551 (SoxA). These include genes for a flavocytochrome c flavoprotein homologue (SoxF2), a nucleotidase homologue (SoxB), four small proteins (including SoxX, SoxY, and SoxZ), and a thiol-disulfide interchange protein homologue (SoxW). (4) We have established that the constitutively expressed FCSD genes (soxEF1) are located elsewhere in the genome. (5) Through a database search, we have found that the eight thiosulfate utilization genes are clustered in the same order in the Chlorobium tepidum genome (www.tigr.org). Similar thiosulfate utilization gene clusters occur in at least six other bacterial species but may additionally include genes for rhodanese and sulfite dehydrogenase.

Characterization of a bacterial tyrosine ammonia lyase, a biosynthetic enzyme for the photoactive yellow protein

During genome sequence analysis of Rhodobacter capsulatus, nearby open reading frames were found that encode a photoactive yellow protein (PYP) and a hypothetical biosynthetic enzyme for its chromophore, a tyrosine ammonia lyase (TAL). We isolated the TAL gene, overproduced the recombinant protein in Escherichia coli, and after purification analyzed the enzyme for its activity. The catalytic efficiency for tyrosine was shown to be approximately 150 times larger than for phenylalanine, suggesting that the enzyme could in fact be involved in biosynthesis of the PYP chromophore. To our knowledge it is the first time this type of enzyme has been found in bacteria.

Radiation-associated valvular heart disease in Hodgkin's disease is associated with characteristic thickening and fibrosis of the aortic-mitral curtain

Radiation-associated valvular dysfunction is characterized by variable aortic and mitral valve thickening. A review of three patients assessed echocardiographically revealed that radiation-associated valvular dysfunction after radiation treatment for Hodgkin's disease may be characterized by a unique and consistent pattern of thickening of the aortic and mitral valves involving the aortic-mitral curtain.

Identification of a small tetraheme cytochrome c and a flavocytochrome c as two of the principal soluble cytochromes c in Shewanella oneidensis strain MR1

Two abundant, low-redox-potential cytochromes c were purified from the facultative anaerobe Shewanella oneidensis strain MR1 grown anaerobically with fumarate. The small cytochrome was completely sequenced, and the genes coding for both proteins were cloned and sequenced. The small cytochrome c contains 91 residues and four heme binding sites. It is most similar to the cytochromes c from Shewanella frigidimarina (formerly Shewanella putrefaciens) NCIMB400 and the unclassified bacterial strain H1R (64 and 55% identity, respectively). The amount of the small tetraheme cytochrome is regulated by anaerobiosis, but not by fumarate. The larger of the two low-potential cytochromes contains tetraheme and flavin domains and is regulated by anaerobiosis and by fumarate and thus most nearly corresponds to the flavocytochrome c-fumarate reductase previously characterized from S. frigidimarina to which it is 59% identical. However, the genetic context of the cytochrome genes is not the same for the two Shewanella species, and they are not located in multicistronic operons. The small cytochrome c and the cytochrome domain of the flavocytochrome c are also homologous, showing 34% identity. Structural comparison shows that the Shewanella tetraheme cytochromes are not related to the Desulfovibrio cytochromes c(3) but define a new folding motif for small multiheme cytochromes c.

Characterization of glutathione amide reductase from Chromatium gracile. Identification of a novel thiol peroxidase (Prx/Grx) fueled by glutathione amide redox cycling

Among the Chromatiaceae, the glutathione derivative gamma-l-glutamyl-l-cysteinylglycine amide, or glutathione amide, was reported to be present in facultative aerobic as well as in strictly anaerobic species. The gene (garB) encoding the central enzyme in glutathione amide cycling, glutathione amide reductase (GAR), has been isolated from Chromatium gracile, and its genomic organization has been examined. The garB gene is immediately preceded by an open reading frame encoding a novel 27.5-kDa chimeric enzyme composed of one N-terminal peroxiredoxin-like domain followed by a glutaredoxin-like C terminus. The 27.5-kDa enzyme was established in vitro to be a glutathione amide-dependent peroxidase, being the first example of a prokaryotic low molecular mass thiol-dependent peroxidase. Amino acid sequence alignment of GAR with the functionally homologous glutathione and trypanothione reductases emphasizes the conservation of the catalytically important redox-active disulfide and of regions involved in binding the FAD prosthetic group and the substrates glutathione amide disulfide and NADH. By establishing Michaelis constants of 97 and 13.2 microm for glutathione amide disulfide and NADH, respectively (in contrast to K(m) values of 6.9 mm for glutathione disulfide and 1.98 mm for NADPH), the exclusive substrate specificities of GAR have been documented. Specificity for the amidated disulfide cofactor partly can be explained by the substitution of Arg-37, shown by x-ray crystallographic data of the human glutathione reductase to hydrogen-bond one of the glutathione glycyl carboxylates, by the negatively charged Glu-21. On the other hand, the preference for the unusual electron donor, to some extent, has to rely on the substitution of the basic residues Arg-218, His-219, and Arg-224, which have been shown to interact in the human enzyme with the NADPH 2'-phosphate group, by Leu-197, Glu-198, and Phe-203. We suggest GAR to be the newest member of the class I flavoprotein disulfide reductase family of oxidoreductases.

An Alternative to the Accepted Phylogeny of Purple Bacteria Based on 16S rRNA: Analyses of the Amino Acid Sequences of Cytochromes C2 and C556 from Rhodobacter (Rhodovulum) sulfidophilus

It is becoming increasingly apparent from complete genome sequences that 16S rRNA data, as currently interpreted, does not provide an unambiguous picture of bacterial phylogeny. In contrast, we have found that analysis of insertions and deletions in the amino acid sequences of cytochrome c2 has some advantages in establishing relationships and that this approach may have broad utility in acquiring a better understanding of bacterial relationships. The amino acid sequences of cytochromes c2 and c556 have been determined in whole or in part from four strains of Rhodobacter sulfidophilus. The cytochrome c2 contains three- and eight-residue insertions as well as a single-residue deletion in common with the large cytochromes c2 but in contrast to the small cytochromes c2 and mitochondrial cytochromes. In addition, the Rb. sulfidophilus protein shares a rare six- to seven-residue insertion with other Rhodobacter cytochromes c2. The cytochrome c556 is a low-spin class II cytochrome c homologous to the greater family of cytochromes c', which are usually high-spin. The similarity of cytochrome c556 to other species of class II cytochromes is consistent with the relationships deduced from comparisons of cytochromes c2. Thus, our results do not support placement of Rb. sulfidophilus in a separate genus, Rhodovulum, which was proposed primarily on the basis of 16S rRNA sequences. Instead, the Rhodobacter cytochromes c2 are distinct from those of other genera and species of purple bacteria and show a different pattern of relationships among species than reported for 16S rRNA.

Antiadrenergic effects of adenosine in pressure overload hypertrophy

In the present study, we sought to evaluate whether the antiadrenergic action of adenosine in the heart is altered in pressure overload hypertrophy produced in rats by suprarenal aortic banding. Epicardial and coronary effluent adenosine and inosine concentrations and release were significantly elevated in compensated pressure overload hypertrophy but not in hearts with left ventricular failure. In pressure overload hearts, the contractile response to beta-adrenergic stimulation was less inhibited by incremental concentrations of either adenosine or the selective A(1) receptor agonist chloro-N:(6)-cyclopentyl adenosine than in controls. Furthermore, the extent of desensitization to the antiadrenergic actions of adenosine in pressure overload hypertrophy appeared to be proportional to the extent of chamber dilation and dysfunction. A 60-minute infusion of adenosine produced a sustained antiadrenergic effect that lasted up to 45 minutes after the infusion was terminated in both controls and hearts with compensated hypertrophy. This effect was not observed in the decompensated left ventricular failure group. Subsequent infusion with adenosine of the A(2A) receptor antagonist 8-(3-chlorostyryl)-caffeine to counteract the proadrenergic effect of A(2A) receptor stimulation did not alter the decreased sensitivity to the antiadrenergic actions of adenosine in hypertrophied hearts. Finally, isolated myocytes from hypertrophied hearts demonstrated a decreased ability to suppress isoproterenol-elicited increases in [Ca(2+)](i) transients in the presence of adenosine and the A(2A) receptor antagonist compared with myocytes from control hearts. Myocardial adenosine concentrations increase during the compensated phase of pressure overload hypertrophy but then decrease when there is evidence of decompensation. The antiadrenergic actions of adenosine transduced via the myocardial A(1) receptor are diminished in pressure overload hypertrophied hearts. These factors may render these hearts more vulnerable to the detrimental effects of chronically increased sympathetic activity.

Reduction in myocardial collagen cross-linking parallels left ventricular dilatation in rat models of systolic chamber dysfunction

BACKGROUND

The transition from compensated left ventricular hypertrophy (LVH) to heart failure is associated with alterations in the myocardial interstitium. We hypothesized that LV dilatation is associated with modifications in collagen cross-linking.

METHODS AND RESULTS

We studied 2 rat models of LV dilatation: (1) pressure-overload hypertrophy with heart failure (POH-F) induced by suprarenal abdominal aortic banding and (2) LVH induced by 7 months of isoproterenol (ISO, 0.04 mg x kg(-1) x d(-1)) administration. In POH-F rats and in rats receiving ISO, LV dilatation and a reduced systolic chamber performance were noted. Myocardial hydroxyproline concentrations ([HPRO]) were increased in the POH-F rats, whereas in rats receiving ISO, [HPRO] was decreased. In POH-F rats, the ratio of myocardial collagen type I to type III was increased, but in rats receiving ISO, myocardial collagen I/III was unchanged. In contrast to the diverse changes in myocardial collagen concentrations and phenotypes observed in the 2 models of LV dilatation, the ratio of myocardial insoluble to soluble (relationship between cross-linked and non-cross-linked) collagen was decreased in both the POH-F and ISO groups. Moreover, administration of captopril (0.22 mmol x kg(-1) x d(-1)), which inhibited the ISO-induced reduction in myocardial insoluble/soluble collagen but not the reduction in [HPRO], prevented the ISO-induced alterations in LV dimensions and performance.

CONCLUSIONS

Because decreases in the ratio of myocardial insoluble to soluble collagen parallel LV dilatation in rats, reductions in myocardial collagen cross-linking may be an important mechanism contributing to LV dilatation in heart disease.

Coupling of hydrogen bonding to chromophore conformation and function in photoactive yellow protein

To understand in atomic detail how a chromophore and a protein interact to sense light and send a biological signal, we are characterizing photoactive yellow protein (PYP), a water-soluble, 14 kDa blue-light receptor which undergoes a photocycle upon illumination. The active site residues glutamic acid 46, arginine 52, tyrosine 42, and threonine 50 form a hydrogen bond network with the anionic p-hydroxycinnamoyl cysteine 69 chromophore in the PYP ground state, suggesting an essential role for these residues for the maintenance of the chromophore's negative charge, the photocycle kinetics, the signaling mechanism, and the protein stability. Here, we describe the role of T50 and Y42 by use of site-specific mutants. T50 and Y42 are involved in fine-tuning the chromophore's absorption maximum. The high-resolution X-ray structures show that the hydrogen-bonding interactions between the protein and the chromophore are weakened in the mutants, leading to increased electron density on the chromophore's aromatic ring and consequently to a red shift of its absorption maximum from 446 nm to 457 and 458 nm in the mutants T50V and Y42F, respectively. Both mutants have slightly perturbed photocycle kinetics and, similar to the R52A mutant, are bleached more rapidly and recover more slowly than the wild type. The effect of pH on the kinetics is similar to wild-type PYP, suggesting that T50 and Y42 are not directly involved in any protonation or deprotonation events that control the speed of the light cycle. The unfolding energies, 26.8 and 25.1 kJ/mol for T50V and Y42F, respectively, are decreased when compared to that of the wild type (29.7 kJ/mol). In the mutant Y42F, the reduced protein stability gives rise to a second PYP population with an altered chromophore conformation as shown by UV/visible and FT Raman spectroscopy. The second chromophore conformation gives rise to a shoulder at 391 nm in the UV/visible absorption spectrum and indicates that the hydrogen bond between Y42 and the chromophore is crucial for the stabilization of the native chromophore and protein conformation. The two conformations in the Y42F mutant can be interconverted by chaotropic and kosmotropic agents, respectively, according to the Hofmeister series. The FT Raman spectra and the acid titration curves suggest that the 391 nm form of the chromophore is not fully protonated. The fluorescence quantum yield of the mutant Y42F is 1.8% and is increased by an order of magnitude when compared to the wild type.

Norepinephrine concentrations in the epicardial transudate reflect early changes in adrenergic activity in the isolated perfused heart

The aim of this study was to establish whether epicardial transudates could be used to uncover small, but physiologically important changes in interstitial NE concentrations under normal and pathological conditions. Norepinephrine (NE) concentrations measured in epicardial transudate fluid were compared to NE levels in the coronary effluent in normal and pressure overload hypertrophied (POH) rat hearts. Hearts were isolated together with the stellate ganglion and perfused in the inverted position. Epicardial surface transudates, representative fluid of the interstitial myocardial compartment, and coronary effluents were collected for determination of NE levels in the presence and absence of stellate ganglion stimulation. The same protocol was repeated in the presence and absence of nisoxetine, a NE uptake blocker. NE concentrations in epicardial transudates were 16- and 19-fold higher than in the coronary effluent in both sham and POH groups, respectively. NE concentrations in the transudates but not in the coronary effluents were significantly higher (1.6-fold) in hearts with POH when compared to normal hearts. Likewise, nisoxetine (10(-5)m) increased (1.3-fold) NE concentrations in the transudates but not in the effluents of sham animals. As expected, stellate ganglion stimulation increased NE concentrations in both transudates and effluents in sham and POH hearts. In conclusion, determination of NE concentrations in epicardial transudates represents a simple, rapid and sensitive method to detect increases in adrenergic activity in normal and abnormal hearts.

Primary structure characterization of a Rhodocyclus tenuis diheme cytochrome c reveals the existence of two different classes of low-potential diheme cytochromes c in purple phototropic bacteria

The complete amino acid sequence of a 26-kDa low redox potential cytochrome c-551 from Rhodocyclus tenuis was determined by a combination of Edman degradation and mass spectrometry. There are 240 residues including two heme binding sites at positions 41, 44, 128, and 132. There is no evidence for gene doubling. The only known homolog of Rc. tenuis cytochrome c-551 is the diheme cytochrome c-552 from Pseudomonas stutzeri which contains 268 residues and heme binding sites at nearly identical positions. There is 44% overall identity between the Rc. tenuis and Ps. stutzeri cytochromes with 10 internal insertions and deletions. The Ps. stutzeri cytochrome is part of a denitrification gene cluster, whereas Rc. tenuis is incapable of denitrification, suggesting different functional roles for the cytochromes. Histidines at positions 45 and 133 are the fifth heme ligands and conserved histidines at positions 29, 209, and 218 and conserved methionines at positions 114 and 139 are potential sixth heme ligands. There is no obvious homology to the low-potential diheme cytochromes characterized from other purple bacterial species such as Rhodobacter sphaeroides. There are therefore at least two classes of low-potential diheme cytochromes c found in phototrophic bacteria. There is no more than 11% helical secondary structure in Rc. tenuis cytochrome c-551 suggesting that there is no relationship to class I or class II c-type cytochromes.

Aging reduces the cardioprotective effect of ischemic preconditioning in the rat heart

Multiple brief periods of ischemia in the mammalian heart elicits protection against morphologic and functional damage caused by longer-duration ischemia. Preconditioning-induced protection against post-ischemic contractile dysfunction has been reported to be depressed with aging of the adult heart. This study was undertaken to determine whether aging of the adult myocardium reduces the preconditioning-induced attenuation of necrosis observed with ischemia. Isolated, perfused hearts obtained from Fischer 344 rats of either 3 (young) or 22 (aged) months of age were paced and instrumented for determination of developed left ventricular pressure. Necrosis was determined with triphenyltetrazolium. In the absence of preconditioning, young and aged adult hearts made globally ischemic for 45 min developed necrosis involving 53+/-6% and 49+/-6% of the myocardium, respectively. Contractile function (+dP/dt(max)) at 90 min of reperfusion was depressed by 80% in young and 52% in aged hearts, compared to values obtained prior to preconditioning. Preconditioning with two 5 min ischemia/5 min reperfusion cycles significantly reduced necrosis development and enhanced reperfusion contractile function in young hearts. However, in aged adult hearts, the preconditioning did not significantly reduce the development of necrosis or enhance reperfusion contractile function. These data suggest that aging reduces the effectiveness of preconditioning in providing cardioprotection against ischemic-induced myocardial necrosis.

A membrane-bound flavocytochrome c-sulfide dehydrogenase from the purple phototrophic sulfur bacterium Ectothiorhodospira vacuolata

The amino acid sequence of Ectothiorhodospira vacuolata cytochrome c-552, isolated from membranes with n-butanol, shows that it is a protein of 77 amino acid residues with a molecular mass of 9,041 Da. It is closely related to the cytochrome subunit of Chlorobium limicola f. sp. thiosulfatophilum flavocytochrome c-sulfide dehydrogenase (FCSD), having 49% identity. These data allowed isolation of a 5.5-kb subgenomic clone which contains the cytochrome gene and an adjacent flavoprotein gene as in other species which have an FCSD. The cytochrome subunit has a signal peptide with a normal cleavage site, but the flavoprotein subunit has a signal sequence which suggests that the mature protein has an N-terminal cysteine, characteristic of a diacyl glycerol-modified lipoprotein. The membrane localization of FCSD was confirmed by Western blotting with antibodies raised against Chromatium vinosum FCSD. When aligned according to the three-dimensional structure of Chromatium FCSD, all but one of the side chains near the flavin are conserved. These include the Cys 42 flavin adenine dinucleotide binding site; the Cys 161-Cys 337 disulfide; Glu 167, which modulates the reactivity with sulfite; and aromatic residues which may function as charge transfer acceptors from the flavin-sulfite adduct (C. vinosum numbering). The genetic context of FCSD is different from that in other species in that flanking genes are not conserved. The transcript is only large enough to encode the two FCSD subunits. Furthermore, Northern hybridization showed that the production of E. vacuolata FCSD mRNA is regulated by sulfide. All cultures that contained sulfide in the medium had elevated levels of FCSD RNA compared with cells grown on organics (acetate, malate, or succinate) or thiosulfate alone, consistent with the role of FCSD in sulfide oxidation.

Crystal structures of an oxygen-binding cytochrome c from Rhodobacter sphaeroides

The photosynthetic bacterium Rhodobacter sphaeroides produces a heme protein (SHP), which is an unusual c-type cytochrome capable of transiently binding oxygen during autooxidation. Similar proteins have not only been observed in other photosynthetic bacteria but also in the obligate methylotroph Methylophilus methylotrophus and the metal reducing bacterium Shewanella putrefaciens. A three-dimensional structure of SHP was derived using the multiple isomorphous replacement phasing method. Besides a model for the oxidized state (to 1.82 A resolution), models for the reduced state (2.1 A resolution), the oxidized molecule liganded with cyanide (1. 90 A resolution), and the reduced molecule liganded with nitric oxide (2.20 A resolution) could be derived. The SHP structure represents a new variation of the class I cytochrome c fold. The oxidized state reveals a novel sixth heme ligand, Asn(88), which moves away from the iron upon reduction or when small molecules bind. The distal side of the heme has a striking resemblance to other heme proteins that bind gaseous compounds. In SHP the liberated amide group of Asn(88) stabilizes solvent-shielded ligands through a hydrogen bond.

Structure and stability effects of the mutation of glycine 34 to serine in Rhodobacter capsulatus cytochrome c(2)

Gly 34 and the adjacent Pro 35 of Rhodobacter capsulatus cytochrome c(2) (or Gly 29 and Pro 30 in vertebrate cytochrome c) are highly conserved side chains among the class I c-type cytochromes. The mutation of Gly 34 to Ser in Rb. capsulatus cytochrome c(2) has been characterized in terms of physicochemical properties and NMR in both redox states. A comparison of the wild-type cytochrome c(2), the G34S mutation, and the P35A mutation is presented in the context of differences in chemical shifts, the differences in NOE patterns, and structural changes resulting from oxidation of the reduced cytochrome. G34S is substantially destabilized relative to wild-type (2.2 kcal/mol in the oxidized state) but similarly destabilized relative to P35A. Nevertheless, differences in terms of the impact of the mutations on specific structural regions are found when comparing G34S and P35A. Although available data indicates that the overall secondary structure of G34S and wild-type cytochrome c(2) are similar, a number of both perturbations of hydrogen bond networks and interactions with internal waters are found. Thus, the impact of the mutation at position 35 is propagated throughout the cytochrome but with alterations at defined sites within the molecule. Interestingly, we find that the substitution of serine at position 34 results in a perturbation of the heme beta meso and the methyl-5 protons. This suggests that the hydroxyl and beta carbon are positioned away from the solvent and toward the heme. This has the consequence of preferentially stabilizing the oxidized state in G34S, thus, altering hydrogen bond networks which involve the heme propionate, internal waters, and key amino acid side chains. The results presented provide important new insights into the stability and solution structure of the cytochrome c(2).