Association of antiplatelet therapy with clinical outcomes in patients with peripheral artery disease.

BACKGROUND: The beneficial role of dual anti-platelet therapy (DAPT) in coronary artery disease is well established. However, there is limited data describing the effects of DAPT in patients with atherosclerotic peripheral artery disease (PAD). The aim of this meta-analysis is to compare clinical outcomes associated with DAPT versus single anti-platelet therapy (SAPT) in patients with symptomatic PAD. METHODS: We performed a literature search for studies assessing the risk of adverse cardiovascular and limb events in cohorts receiving either DAPT or SAPT. The primary endpoint was all cause mortality. The secondary endpoints included graft failure, amputation, total bleeding, severe bleeding and fatal bleeding. The search included the following databases: Ovid MEDLINE, EMBASE, Web of Science, and Google Scholar. The search was not restricted to time or publication status. RESULTS: A total of 11 studies with 54,331 participants (24,449 on SAPT and 29,882 on DAPT) were included. Patients with PAD treated with SAPT had higher all-cause mortality compared to patients treated with DAPT (OR 1.37, 95 % CI 1.09-1.74; p < 0.01). There was no difference in risk of graft failure or amputation between patients treated with SAPT or DAPT (OR 0.9, 95 % CI 0.77-1.06; p = 0.19; OR 1.11, 95 % CI 0.88-1.41; p = 0.37). Patients treated with SAPT had lower total bleeds compared to patients treated with DAPT (OR 0.53, 95 % CI 0.36-0.77; p < 0.01). However, For SAPT plus AC vs SAPT, a total of 8 studies with 17,100 participants (3447 with SAPT plus AC and 8619 with only SAPT) were included. Patients on SAPT plus AC did not have a statistically significant difference in risk for all-cause mortality, (OR 0.91, 95 % CI 0.67-1.24; p = 0.56). SAPT plus AC had significantly lower risk of MI (OR 0.82, 95 % CI 0.69-0.97; p = 0.02), amputation (OR 0.72, 95 % CI 0.53-0.97; p = 0.03), and graft failure (OR 0.66, 95 % CI 0.48-0.93; p = 0.02). There was no significant different in risk of fatal bleeding be-tween the two groups (OR 1.60, 95 % CI 0.76-3.35; p = 0.22). CONCLUSIONS: In patients with symptomatic PAD, a strategy of DAPT may confer a mortality benefit when compared to SAPT without significantly increasing the risk of serious bleeding events.

Biomarkers and Strain Echocardiography for the Detection of Subclinical Cardiotoxicity in Breast Cancer Patients Receiving Anthracyclines.

The optimal surveillance and management strategies for breast cancer patients receiving anthracycline therapy are limited by our incomplete understanding of the role of biomarkers heralding the onset of cardiotoxicity. The purpose of this study was to determine whether there is a temporal correlation between cardiac biomarkers and subclinical left ventricular dysfunction in breast cancer patients receiving anthracycline chemotherapy. Thirty-one females between 46 and 55 years old with breast cancer treated with anthracycline chemotherapy were prospectively enrolled. Cardiac biomarkers were correlated with echocardiography with speckle tracking at baseline, post-anthracycline therapy, and 6 months post-anthracycline chemotherapy. Subclinical cardiotoxicity was defined as ≥ 10% reduction in global longitudinal strain (GLS). There was a relative reduction in left ventricular ejection fraction (LVEF) ≥ 10% in 5/30 (17%) and 7/27 (26%) patients post-anthracycline therapy and 6 months post-anthracycline therapy, respectively. Subclinical cardiotoxicity was noted in 8/30 (27%) and 10/26 (38%) patients post-anthracycline and 6 months post-anthracycline therapy, respectively. Baseline N-terminal pro B-type natriuretic peptide (NT-proBNP) was the strongest predictor of LVEF (ρ = -0.45; p = 0.019), with post-therapy NT-proBNP values illustrating similar predictive value (ρ = -0.40; p = 0.038). Interim changes in suppression of tumorigenicity 2 (ST2) and galectin-3 correlated with a 6-month change in LVEF (ρ = -0.48; p = 0.012 and ρ = -0.45; p = 0.018, for ST2 and galectin-3, respectively). Changes in galectin-3 from baseline to mid-therapy paralleled changes in GLS. NT-proBNP, ST2, and galectin-3 correlate with reduced LVEF among breast cancer patients receiving anthracycline therapy. Additional trials focusing on a cardiac biomarker approach may provide guidance in the early diagnosis and management of anthracycline-induced cardiotoxicity.

Outcomes of Functional Testing Versus Invasive Cardiac Catheterization for the Evaluation of Intermediate Severity Coronary Stenosis Detected on Cardiac Computed Tomography Angiography.

INTRODUCTION: The aim of this study was to evaluate the effectiveness of functional testing in comparison to invasive coronary angiography (ICA) among acute chest pain patients whose first diagnostic modality was a coronary computed tomography angiogram (CCTA) and were found to have intermediate coronary stenosis, defined as 50%-70% luminal stenosis. METHODS: We conducted a retrospective review of 4763 acute chest pain patients ≥18 years old who received a CCTA as the initial diagnostic modality. Of these, 118 patients met enrollment criteria and proceeded to either stress test (80/118) or directly to ICA (38/118). The primary outcome was 30-day major adverse cardiac event, consisting of acute myocardial infarction, urgent revascularization, or death. RESULTS: There was no difference in 30-day major adverse cardiac event among patients who underwent initial stress testing versus directly referred to ICA (0% vs. 2.6%, P = 0.322) following CCTA. The rate of revascularization without acute myocardial infarction was significantly higher among those who underwent ICA versus stress test [36.8% vs. 3.8%, P < 0.0001; adjusted odds ratio: 9.6, 95% confidence interval, 1.8-49.6]. Patients who underwent ICA had a higher rate of catheterization without revascularization within 30 days of the index admission in comparison to those who underwent initial stress testing (55.3% vs. 12.5%, P < 0.0001; adjusted odds ratio: 26.7, 95% confidence interval, 6.6-109.5). CONCLUSION: Among patients with intermediate coronary stenosis on CCTA, a functional stress test compared with ICA may prevent unnecessary revascularization and improve cardiac catheterization yield without negatively affecting the 30-day patient safety profile.

Diagnostic and Prognostic Role of the Modified Diamond-Forrester Model in Combination With Coronary Calcium Score in Acute Chest Pain Patients.

BACKGROUND: The aim of this study was to evaluate whether pretest probability (PTP) assessment using the Diamond-Forrester Model (DFM) combined with coronary calcium scoring (CCS) can safely rule out obstructive coronary artery disease (CAD) and 30-day major adverse cardiovascular events (MACE) in acute chest pain patients. METHODS: We retrospectively evaluated consecutive patients, age ≥18 years, with no known CAD, negative initial electrocardiogram, and troponin level. All patients had coronary computed tomographic angiography (CCTA) with CCS, and our final cohort consisted of 1988 patients. Obstructive CAD was defined as luminal narrowing of ≥50% in 1 or more vessels by CCTA. Patients were classified according to PTP as low (<10%), intermediate (10%-90%), or high (>90%). RESULTS: The DFM classified 293 (14.7%), 1445 (72.7%), and 250 (12.6%) of patients as low, intermediate, and high risk, respectively, with corresponding 30-day MACE rates of 0.0%, 2.35%, and 14.8%. For patients with intermediate PTP and CCS ≤10, the negative predictive value was 99.2% (95% confidence interval: 98.7-99.8) for 30-day MACE while it was 92.62% (95% confidence interval: 87.9-97.3) for patients with high PTP. Among patients with a high PTP and CCS of zero, the prevalence of 30-day MACE and obstructive CAD remained high (7.07% and 10.1%, respectively). CONCLUSIONS: In acute chest pain patients without evidence of ischemia on initial electrocardiogram and cardiac troponin, low PTP by DFM or the combination of intermediate PTP and CCS ≤10 had excellent negative predictive values to rule out 30-day MACE. CCS is not sufficient to exclude obstructive CAD and 30-day MACE in patients with high PTP.

A Day Seven Reflection Circle to Enhance Resilience in Residents after a Difficult Patient Loss.

This article was migrated. The article was marked as recommended. Caring for the dying patient can have significant impact on physicians in training, and if unaddressed, can lead to burnout and potentially compromised patient care. The literature suggests didactics and real time supportive interventions such as "post code debriefs" may be most effective in addressing the impact of death on physicians. In this paper, we highlight and discuss a reflection that is conducted several days after the event, when resident physicians are more self-aware of their mental hygiene and the residual impact of challenging event on their personal and professional well-being.

Initiation, Continuation, Switching, and Withdrawal of Heart Failure Medical Therapies During Hospitalization.

Patients with worsening heart failure with reduced ejection fraction (HFrEF) spend a large proportion of time in the hospital and other health care facilities. The benefits of guideline-directed medical therapy (GDMT) in the outpatient setting have been shown in large randomized controlled trials. However, the decision to initiate, continue, switch, or withdraw HFrEF medications in the inpatient setting is often based on multiple factors and subject to significant variability across providers. Based on available data, in well-selected, treatment-naïve patients who are hemodynamically stable and clinically euvolemic after stabilization during hospitalization for HF, elements of GDMT can be safely initiated. Inpatient continuation of GDMT for HFrEF appears safe and well-tolerated in most hemodynamically stable patients. Hospitalization is also a potential time for switching from an angiotensin-converting enzyme inhibitor/angiotensin II receptor blocker to sacubitril/valsartan therapy in eligible patients, and is the subject of ongoing study. Therapy withdrawal or need for dose reduction is rarely required, but if needed identifies a particularly at-risk group of patients with progressive HF. If recurrent intolerance to neurohormonal blockers is observed, these patients should be evaluated for advanced HF therapies. There is an enduring need for using the teachable moment of HFrEF hospitalization for optimal initiation, continuation, and switching of GDMT to improve post-discharge patient outcomes and the quality of chronic HFrEF care.

Role of Hyperkalemia in Heart Failure and the Therapeutic Use of Potassium Binders.

Hyperkalemia can be a life-threatening disorder, especially for at-risk patients with heart failure, chronic kidney disease, with diabetes, and patients on certain drugs like renin-angiotensin-aldosterone system antagonists and mineralocorticoid receptor antagonists. There are limited therapeutic options available for hyperkalemia, and they have narrow effectiveness because of their unfavorable side effects profile in long-term and high cost utilization requiring inpatient care. Patiromersorbitex calcium and sodium zirconium cyclosilicate are novel potassium-lowering compounds for the treatment and prevention of hyperkalemia in at-risk population. These therapeutic agents have shown encouraging results in early phase II and phase III clinical trials. However, there is need to further study their efficacy and safety in heart failure population in order to establish their clinical use. The focus of this chapter will be to promote better understanding of potassium homeostasis in heart failure patients and the mechanistic overview of novel drugs, with emphasis on heart failure population.

A Rare Case of Plantar Epithelioma Cuniculatum Arising from a Wart.

A 68-year-old man, a known case of hypertension, coronary artery disease and old cardiovascular accident with right-sided hemiplegia, came with the chief complaints of a large cauliflower like growth with pus discharge on the left heel since 15 years. The patient had sustained a penetrating injury by a thorn on the left heel region few days before the lesion appeared. Dermatological examination revealed a single verrucous lesion measuring 7 × 7 cm on the left heel region associated with discharge of foul smelling cheesy material. There was also a enlarged right inguinal lymph node which was non-tender, firm, measuring 2 cm in diameter with normal overlying skin. X-ray left ankle was done which showed some soft tissue swelling. A skin biopsy showed hyperkeratosis, acanthosis and parakeratosis. Elongated rete ridges with keratinocyte hyperplasia, forming a large mass pressing on the underlying dermis were seen. There was formation of multiple large keratin filled invaginations and crypts. No atypical cells were seen. Based on history, clinical examination and investigations, a diagnosis of epithelium cuniculatum type of verrucous squamous cell carcinoma was made. A wide excision with a flap cover was performed in consultation with the oncosurgeon and the excision sample was sent for histopathological re-examination, which confirmed the diagnosis of epithelioma cuniculatum.

Hematuria following stereotactic body radiation therapy (SBRT) for clinically localized prostate cancer.

BACKGROUND: Hematuria following prostate radiotherapy is a known toxicity that may adversely affect a patient's quality of life. Given the higher dose of radiation per fraction using stereotactic body radiation therapy (SBRT) there is concern that post-SBRT hematuria would be more common than with alternative radiation therapy approaches. Herein, we describe the incidence and severity of hematuria following stereotactic body radiation therapy (SBRT) for prostate cancer at our institution. METHODS: Two hundred and eight consecutive patients with prostate cancer treated with SBRT monotherapy with at least three years of follow-up were included in this retrospective analysis. Treatment was delivered using the CyberKnife® (Accuray) to doses of 35-36.25 Gy in 5 fractions. Toxicities were scored using the CTCAE v.4. Hematuria was counted at the highest grade it occurred in the acute and late setting for each patient. Cystoscopy findings were retrospectively reviewed. Univariate and multivariate analyses were performed. Hematuria-associated bother was assessed via the Expanded Prostate Index Composite (EPIC)-26. RESULTS: The median age was 69 years with a median prostate volume of 39 cc. With a median follow-up of 48 months, 38 patients (18.3%) experienced at least one episode of hematuria. Median time to hematuria was 13.5 months. In the late period, there were three grade 3 events and five grade 2 events. There were no grade 4 or 5 events. The 3-year actuarial incidence of late hematuria ≥ grade 2 was 2.4%. On univariate analysis, prostate volume (p = 0.022) and history of prior procedure(s) for benign prostatic hypertrophy (BPH) (p = 0.002) were significantly associated with hematuria. On multivariate analysis, history of prior procedure(s) for BPH (p < 0.0001) and α1A antagonist use (p = 0.008) were significantly associated with the development of hematuria. CONCLUSIONS: SBRT for prostate cancer was well tolerated with hematuria rates comparable to other radiation modalities. Patients factors associated with BPH, such as larger prostate volume, alpha antagonist usage, and prior history of procedures for BPH are at increased risk for the development of hematuria.

Proctitis following stereotactic body radiation therapy for prostate cancer.

BACKGROUND: Proctitis after radiation therapy for prostate cancer remains an ongoing clinical challenge and critical quality of life issue. SBRT could minimize rectal toxicity by reducing the volume of rectum receiving high radiation doses and offers the potential radiobiologic benefits of hypofractionation. This study sought to evaluate the incidence and severity of proctitis following SBRT for prostate cancer. METHODS: Between February 2008 and July 2011, 269 men with clinically localized prostate cancer were treated definitively with SBRT monotherapy at Georgetown University Hospital. All patients were treated to 35-36.25Gy in 5 fractions delivered with the CyberKnife Radiosurgical System (Accuray). Rectal bleeding was recorded and scored using the CTCAE v.4. Telangiectasias were graded using the Vienna Rectoscopy Score (VRS). Proctitis was assessed via the Bowel domain of the Expanded Prostate Index Composite (EPIC)-26 at baseline and at 1, 3, 6, 9, 12, 18 and 24 months post-SBRT. RESULTS: The median age was 69 years with a median prostate volume of 39 cc. The median follow-up was 3.9 years with a minimum follow-up of two years. The 2-year actuarial incidence of late rectal bleeding ≥ grade 2 was 1.5%. Endoscopy revealed VRS Grade 2 rectal telangiectasias in 11% of patients. All proctitis symptoms increased at one month post-SBRT but returned to near-baseline with longer follow-up. The most bothersome symptoms were bowel urgency and frequency. At one month post-SBRT, 11.2% and 8.5% of patients reported a moderate to big problem with bowel urgency and frequency, respectively. The EPIC bowel summary scores declined transiently at 1 month and experienced a second, more protracted decline between 6 months and 18 months before returning to near-baseline at two years post-SBRT. Prior to treatment, 4.1% of men felt their bowel function was a moderate to big problem which increased to 11.5% one month post-SBRT but returned to near-baseline at two years post-SBRT. CONCLUSIONS: In this single institution cohort, the rate and severity of proctitis observed following SBRT is low. QOL decreased on follow-up; however, our results compare favorably to those reported for patients treated with alternative radiation modalities. Future prospective randomized studies are needed to confirm these observations.

Obstructive voiding symptoms following stereotactic body radiation therapy for prostate cancer.

BACKGROUND: Obstructive voiding symptoms (OVS) are common following prostate cancer treatment with radiation therapy. The risk of urinary retention (UR) following hypofractionated radiotherapy has yet to be fully elucidated. This study sought to evaluate OVS and UR requiring catheterization following SBRT for prostate cancer. METHODS: Patients treated with SBRT for localized prostate cancer from February 2008 to July 2011 at Georgetown University were included in this study. Treatment was delivered using the CyberKnife® with doses of 35 Gy-36.25 Gy in 5 fractions. UR was prospectively scored using the CTCAE v.3. Patient-reported OVS were assessed using the IPSS-obstructive subdomain at baseline and at 1, 3, 6, 9, 12, 18 and 24 months. Associated bother was evaluated via the EPIC-26. RESULTS: 269 patients at a median age of 69 years received SBRT with a median follow-up of 3 years. The mean prostate volume was 39 cc. Prior to treatment, 50.6% of patients reported moderate to severe lower urinary track symptoms per the IPSS and 6.7% felt that weak urine stream and/or incomplete emptying were a moderate to big problem. The 2-year actuarial incidence rates of acute and late UR ≥ grade 2 were 39.5% and 41.4%. Alpha-antagonist utilization rose at one month (58%) and 18 months (48%) post-treatment. However, Grade 3 UR was low with only 4 men (1.5%) requiring catheterization and/or TURP. A mean baseline IPSS-obstructive score of 3.6 significantly increased to 5.0 at 1 month (p < 0.0001); however, it returned to baseline in 92.6% within a median time of 3 months. Late increases in OVS were common, but transient. Only 7.1% of patients felt that weak urine stream and/or incomplete emptying was a moderate to big problem at two years post-SBRT (p = 0.6854). CONCLUSIONS: SBRT treatment caused an acute increase in OVS which peaked within the first month post-treatment, though acute UR requiring catheterization was rare. OVS returned to baseline in > 90% of patients within a median time of three months. Transient Late increases in OVS were common. However, less than 10% of patients felt that OVS were a moderate to big problem at two years post-SBRT.

Clinical characteristics and management of late urinary symptom flare following stereotactic body radiation therapy for prostate cancer.

PURPOSE: Stereotactic body radiation therapy (SBRT) is increasingly utilized as primary treatment for clinically localized prostate cancer. While acute post-SBRT urinary symptoms are well recognized, the late genitourinary toxicity of SBRT has not been fully described. Here, we characterize the clinical features of late urinary symptom flare and recommend conservative symptom management approaches that may alleviate the associated bother. METHODS: Between February 2008 and August 2011, 216 men with clinically localized prostate cancer were treated definitively with SBRT at Georgetown University Hospital. Treatment was delivered using the CyberKnife with doses of 35-36.25 Gy in five fractions. The prevalence of each of five Common Terminology Criteria for Adverse Events (CTCAE) graded urinary toxicities was assessed at each follow-up visit. Medication usage was documented at each visit. Patient-reported urinary symptoms were assessed using the American Urological Association (AUA) symptom score and the Expanded Prostate Cancer Index Composite (EPIC)-26 at 1, 3, 6, 9, 12, 18, and 24 months. Late urinary symptom flare was defined as an increase in the AUA symptom score of ≥5 points above baseline with a degree of severity in the moderate to severe range (AUA symptom score ≥15). The relationship between the occurrence of flare and pre-treatment characteristics were examined. RESULTS: For all patients, the AUA symptom score spiked transiently at 1 month post-SBRT. Of the 216 patients, 29 (13.4%) experienced a second transient increase in the AUA symptom score that met the criteria for late urinary symptom flare. Among flare patients, the median age was 66 years compared to 70 for those without flare (p = 0.007). In patients who experienced flare, CTCAE urinary toxicities including dysuria, frequency/urgency, and retention peaked at 9-18 months, and alpha-antagonist utilization increased at 1 month post-treatment, rose sharply at 12 months post-treatment, and peaked at 18 months (85%) before decreasing at 24 months. The EPIC urinary summary score of flare patients declined transiently at 1 month and experienced a second, more protracted decline between 6 and 18 months before returning to near baseline at 2-year post-SBRT. Statistically and clinically significant increases in patient-reported frequency, weak stream, and dysuria were seen at 12 months post-SBRT. Among flare patients, 42.9% felt that urination was a moderate to big problem at 12 months following SBRT. CONCLUSION: In this study, we characterize late urinary symptom flare following SBRT. Late urinary symptom flare is a constellation of symptoms including urinary frequency/urgency, weak stream, and dysuria that transiently occurs 6-18 months post-SBRT. Provision of appropriate anticipatory counseling and the maintenance of prophylactic alpha-antagonists may limit the bother associated with this syndrome.

Patient-reported urinary incontinence following stereotactic body radiation therapy (SBRT) for clinically localized prostate cancer.

PURPOSE: Urinary incontinence (UI) following prostate radiotherapy is a rare toxicity that adversely affects a patient's quality of life. This study sought to evaluate the incidence of UI following stereotactic body radiation therapy (SBRT) for prostate cancer. METHODS: Between February, 2008 and October, 2010, 204 men with clinically localized prostate cancer were treated definitively with SBRT at Georgetown University Hospital. Patients were treated to 35-36.25 Gray (Gy) in 5 fractions delivered with the CyberKnife (Accuray). UI was assessed via the Expanded Prostate Index Composite (EPIC)-26. RESULTS: Baseline UI was common with 4.4%, 1.0% and 3.4% of patients reporting leaking > 1 time per day, frequent dribbling and pad usage, respectively. Three year post treatment, 5.7%, 6.4% and 10.8% of patients reported UI based on leaking > 1 time per day, frequent dribbling and pad usage, respectively. Average EPIC UI summary scores showed an acute transient decline at one month post-SBRT then a second a gradual decline over the next three years. The proportion of men feeling that their UI was a moderate to big problem increased from 1% at baseline to 6.4% at three years post-SBRT. CONCLUSIONS: Prostate SBRT was well tolerated with UI rates comparable to conventionally fractionated radiotherapy and brachytherapy. More than 90% of men who were pad-free prior to treatment remained pad-free three years following treatment. Less than 10% of men felt post-treatment UI was a moderate to big problem at any time point following treatment. Longer term follow-up is needed to confirm late effects.

Potency preservation following stereotactic body radiation therapy for prostate cancer.

BACKGROUND: Erectile dysfunction after prostate radiation therapy remains an ongoing challenge and critical quality of life issue. Given the higher dose of radiation per fraction using stereotactic body radiation therapy (SBRT) there is concern that post-SBRT impotency would be higher than conventional radiation therapy approaches. This study sought to evaluate potency preservation and sexual function following SBRT for prostate cancer. METHODS: Between February 2008 and March 2011, 216 men with clinically localized prostate cancer were treated definitively with SBRT monotherapy at Georgetown University Hospital. Potency was defined as the ability to have an erection firm enough for intercourse with or without sexual aids while sexual activity was defined as the ability to have an erection firm enough for masturbation and foreplay. Patients who received androgen deprivation therapy (ADT) were excluded from this study. Ninety-seven hormone-naïve men were identified as being potent at the initiation of therapy and were included in this review. All patients were treated to 35-36.25 Gy in 5 fractions delivered with the CyberKnife Radiosurgical System (Accuray). Prostate specific antigen (PSA) and total testosterone levels were obtained pre-treatment, every 3 months for the first year and every 6 months for the subsequent year. Sexual function was assessed with the Sexual Health Inventory for Men (SHIM), the Expanded Prostate Index Composite (EPIC)-26 and Utilization of Sexual Medication/Device questionnaires at baseline and all follow-up visits. RESULTS: Ninety-seven men (43 low-, 50 intermediate- and 4 high-risk) at a median age of 68 years (range, 48-82 years) received SBRT. The median pre-treatment PSA was 5.9 ng/ml and the minimum follow-up was 24 months. The median pre-treatment total serum testosterone level was 11.4 nmol/L (range, 4.4-27.9 nmol/L). The median baseline SHIM was 22 and 36% of patients utilized sexual aids prior to treatment. Although potency rates declined following treatment: 100% (baseline); 68% (6 months); 62% (12 months); 57% (18 months) and 54.4% (24 months), 78% of previously potent patients had erections sufficient for sexual activity at 24 months post-treatment. Overall sexual aid utilization increased from 36% at baseline to 49% at 24 months. Average EPIC sexual scores showed a slow decline over the first two years following treatment: 77.6 (baseline); 68.7 (6 months); 63.2 (12 months); 61.9 (18 months); 59.3 (24 months). All sexual functions including orgasm declined with time. Prior to treatment, 13.4% of men felt their sexual function was a moderate to big problem which increased to 26.7% two years post treatment. Post-treatment testosterone levels gradually decreased with a median value at two year follow-up of 10.7 nmol/L. However, the average EPIC hormonal scores did not illustrate a statistically significant difference two years post-treatment. Review of the radiation doses to the penile bulb in this study, a potential marker of post-treatment sexual function, revealed that the dose was relatively low and at these low doses the percentage of the penile bulb receiving 29.5 Gy did not correlate with the development of ED. CONCLUSIONS: Men undergoing SBRT monotherapy for prostate cancer report sexual outcomes comparable to those reported for conventional radiation modalities within the first 24 months after treatment. Longer follow-up is required to confirm the durability of these findings.

Thermal properties of rhodopsin: insight into the molecular mechanism of dim-light vision.

Rhodopsin has developed mechanisms to optimize its sensitivity to light by suppressing dark noise and enhancing quantum yield. We propose that an intramolecular hydrogen-bonding network formed by ∼20 water molecules, the hydrophilic residues, and peptide backbones in the transmembrane region is essential to restrain thermal isomerization, the source of dark noise. We studied the thermal stability of rhodopsin at 55 °C with single point mutations (E181Q and S186A) that perturb the hydrogen-bonding network at the active site. We found that the rate of thermal isomerization increased by 1-2 orders of magnitude in the mutants. Our results illustrate the importance of the intact hydrogen-bonding network for dim-light detection, revealing the functional roles of water molecules in rhodopsin. We also show that thermal isomerization of 11-cis-retinal in solution can be catalyzed by wild-type opsin and that this catalytic property is not affected by the mutations. We characterize the catalytic effect and propose that it is due to steric interactions in the retinal-binding site and increases quantum yield by predetermining the trajectory of photoisomerization. Thus, our studies reveal a balancing act between dark noise and quantum yield, which have opposite effects on the thermal isomerization rate. The acquisition of the hydrogen-bonding network and the tuning of the steric interactions at the retinal-binding site are two important factors in the development of dim-light vision.

Thermal decay of rhodopsin: role of hydrogen bonds in thermal isomerization of 11-cis retinal in the binding site and hydrolysis of protonated Schiff base.

Although thermal stability of the G protein-coupled receptor rhodopsin is directly related to its extremely low dark noise level and has recently generated considerable interest, the chemistry behind the thermal decay process of rhodopsin has remained unclear. Using UV-vis spectroscopy and HPLC analysis, we have demonstrated that the thermal decay of rhodopsin involves both hydrolysis of the protonated Schiff base and thermal isomerization of 11-cis to all-trans retinal. Examining the unfolding of rhodopsin by circular dichroism spectroscopy and measuring the rate of thermal isomerization of 11-cis retinal in solution, we conclude that the observed thermal isomerization of 11-cis to all-trans retinal happens when 11-cis retinal is in the binding pocket of rhodopsin. Furthermore, we demonstrate that solvent deuterium isotope effects are involved in the thermal decay process by decreasing the rates of thermal isomerization and hydrolysis, suggesting that the rate-determining step of these processes involves breaking hydrogen bonds. These results provide insight into understanding the critical role of an extensive hydrogen-bonding network on stabilizing the inactive state of rhodopsin and contribute to our current understanding of the low dark noise level of rhodopsin, which enables this specialized protein to function as an extremely sensitive biological light detector. Because similar hydrogen-bonding networks have also been suggested by structural analysis of two other GPCRs, beta1 and beta2 adrenergic receptors, our results could reveal a general role of hydrogen bonds in facilitating GPCR function.

Site-specific incorporation of keto amino acids into functional G protein-coupled receptors using unnatural amino acid mutagenesis.

G protein-coupled receptors (GPCRs) are ubiquitous heptahelical transmembrane proteins involved in a wide variety of signaling pathways. The work described here on application of unnatural amino acid mutagenesis to two GPCRs, the chemokine receptor CCR5 (a major co-receptor for the human immunodeficiency virus) and rhodopsin (the visual photoreceptor), adds a new dimension to studies of GPCRs. We incorporated the unnatural amino acids p-acetyl-L-phenylalanine (Acp) and p-benzoyl-L-phenylalanine (Bzp) into CCR5 at high efficiency in mammalian cells to produce functional receptors harboring reactive keto groups at three specific positions. We obtained functional mutant CCR5, at levels up to approximately 50% of wild type as judged by immunoblotting, cell surface expression, and ligand-dependent calcium flux. Rhodopsin containing Acp at three different sites was also purified in high yield (0.5-2 microg/10(7) cells) and reacted with fluorescein hydrazide in vitro to produce fluorescently labeled rhodopsin. The incorporation of reactive keto groups such as Acp or Bzp into GPCRs allows their reaction with different reagents to introduce a variety of spectroscopic and other probes. Bzp also provides the possibility of photo-cross-linking to identify precise sites of protein-protein interactions, including GPCR binding to G proteins and arrestins, and for understanding the molecular basis of ligand recognition by chemokine receptors.