Endogenous and Exogenous Thyrotoxicosis and Risk of Incident Cognitive Disorders in Older Adults

Importance

Thyroid hormone is among the most common prescriptions in the US and up to 20% may be overtreated. Endogenous hyperthyroidism may be a risk factor for dementia, but data are limited for iatrogenic thyrotoxicosis.

Objective

To determine whether thyrotoxicosis, both endogenous and exogenous, is associated with increased risk of cognitive disorders.

Design, Setting, and Participants

This cohort study performed a longitudinal time-varying analysis of electronic health records for patients receiving primary care in the Johns Hopkins Community Physicians Network between January 1, 2014, and May 6, 2023. Patients 65 years and older with at least 2 visits 30 days apart to their primary care physicians were eligible. None of the 65 931 included patients had a history of low thyrotropin (TSH) level or cognitive disorder diagnoses within 6 months of their first visit. Data analysis was performed from January 1 through August 5, 2023.

Exposure

The exposure variable was a low TSH level, characterized based on the clinical context as due to endogenous thyrotoxicosis, exogenous thyrotoxicosis, or unknown cause, excluding those attributable to acute illness or other medical factors such as medications.

Main Outcomes and Measures

The outcome measure was cognitive disorders, including mild cognitive impairment and all-cause dementia, to improve sensitivity and account for the underdiagnosis of dementia in primary care.

Results

A total of 65 931 patients were included in the analysis (median [IQR] age at first visit, 68.0 [65.0-74.0] years; 37 208 [56%] were female; 46 106 [69.9%] were White). Patients exposed to thyrotoxicosis had cognitive disorder incidence of 11.0% (95% CI, 8.4%-14.2%) by age 75 years vs 6.4% (95% CI, 6.0%-6.8%) for those not exposed. After adjustment, all-cause thyrotoxicosis was significantly associated with risk of cognitive disorder diagnosis (adjusted hazard ratio, 1.39; 95% CI, 1.18-1.64; P < .001) across age groups. When stratified by cause and severity, exogenous thyrotoxicosis remained a significant risk factor (adjusted hazard ratio, 1.34; 95% CI, 1.10-1.63; P = .003) with point estimates suggestive of a dose response.

Conclusions and Relevance

In this cohort study among patients 65 years and older, a low TSH level from either endogenous or exogenous thyrotoxicosis was associated with higher risk of incident cognitive disorder. Iatrogenic thyrotoxicosis is a common result of thyroid hormone therapy. With thyroid hormone among the most common prescriptions in the US, understanding the negative effects of overtreatment is critical to help guide prescribing practice.

Levothyroxine Dosing in Older Adults: Recommendations Derived From The Baltimore Longitudinal Study of Aging

OBJECTIVE

As thyroid hormone metabolism slows with advancing age, treatment dosing requirements change. Guidelines recommend titration from a low starting dose for older adults with hypothyroidism while providing weight-based estimates for younger populations. However, rapid replacement may be appropriate with acute onset of overt hypothyroidism. Therefore, a weight-based recommendation specific to older adults is needed.

METHODS

We determined mean levothyroxine dose using actual and ideal body weight (IBW) ratios for the outcome of euthyroid on therapy relative to assay-specific and proposed age-specific ranges for independently living participants aged ≥65 years in the Baltimore Longitudinal Study of Aging. We examined risk factors to identify those at highest risk of overtreatment using regression analyses adjusted for potential covariables and clustering to account for multiple visits per individual.

RESULTS

One hundred eighty-five participants aged ≥65 years were on levothyroxine at 645 eligible visits. At euthyroid visits, participants were on an average dose of 1.09 μg/kg (1.35 μg/kg IBW), with 84% of euthyroid individuals on a dose of <1.6 μg/kg. Average euthyroid dose did not differ by sex using either actual body weight (ABW) or IBW. For obese individuals, mean euthyroid dose was lower if calculated using ABW (0.9 μg/kg vs 1.14 μg/kg; P < .01) but similar if calculated using IBW (1.42 vs 1.32 μg/kg IBW; P = .41) compared with those with a body mass index of <30.

CONCLUSION

Thyroid hormone dose per body weight estimates for replacement in older adults (1.09 μg/kg ABW or 1.35 μg/kg IBW) are one-third lower than current weight-based dose recommendations for younger populations.

Endocrine Dysfunction From Immune Checkpoint Inhibitors: Pearls and Pitfalls in Evaluation and Management

Immune checkpoint inhibitors (ICPis) have proven extremely efficacious in cancer therapy but also lead to a plethora of immune-related adverse events (irAEs). The endocrine irAEs are not only quite common but also may pose a challenge to the clinician while managing a patient with cancer treated with ICPis. The clinical features of endocrine dysfunction are usually nonspecific and may overlap with concurrent illnesses, underlying the importance of accurate hormone testing and efforts toward case-finding. The management of endocrine irAEs is unique in the focus being on hormone replacement rather than curtailing the autoimmune process. Although the management of thyroid irAEs appears straightforward, adrenal insufficiency and insulin-dependent diabetes can be life-threatening if not promptly recognized and treated. This clinical review synthesizes the studies to provide pearls and pitfalls in the evaluation and management of endocrine irAEs with specific reference to guidelines from oncologic societies.

Higher thyroid hormone has a negative association with lower limb lean body mass in euthyroid older adults: Analysis from the Baltimore Longitudinal study of aging

Background: Hyperthyroidism is associated with lower lean body mass, as a result of catabolic actions of thyroid hormone. Therefore, higher thyroid hormone levels could be a factor in the development of sarcopenia and age associated functional decline. The relationship between thyroid hormone and muscle mass in ambulatory, euthyroid older adults is not known. Method: We used mixed-effects models to estimate the cross-sectional relationships (accounting for inter-person variability) between thyroid axis hormone measures and lower limb composition or sarcopenia at visits in the Baltimore Longitudinal Study of Aging (BLSA) at which DEXA scans were available and both thyrotropin (TSH) and free thyroxine (FT4) were in the reference range. Analyses were adjusted for levothyroxine use, age, race, sex, BMI, smoking, alcohol intake, cholesterol, and systolic blood pressure. Results: 1442 euthyroid participants (median age 68, 50% female, and 69% white) contributed to 5306 visits from 2003 to 2019. FT4 was negatively associated with lower limb lean mass (beta: 88.49; 95% Confidence Interval (CI): 122.78, -54.20; p < 0.001) and positively associated with sarcopenia (OR: 1.11%, 95% CI: 1.01, 1.22) in the whole cohort. Additionally, higher FT4 was associated with lower leg lean mass (beta: 66.79; 95% CI: 102.24, -31.33; p < 0.001) and sarcopenia (OR:1.09%, 95% CI:1.01, 1.18) in older adults, but not in younger adults alone. Conclusion: In euthyroid older adults, higher FT4 is associated with lower leg lean mass and higher odds of sarcopenia. Understanding the relationship between thyroid hormone and sarcopenia is needed to improve clinical decision-making and avoid functional decline from excess thyroid hormone use in older adults.

Management of Immune-Related Adverse Events in Patients Treated With Immune Checkpoint Inhibitor Therapy: ASCO Guideline Update

PURPOSE

To increase awareness, outline strategies, and offer guidance on the recommended management of immune-related adverse events (irAEs) in patients treated with immune checkpoint inhibitor (ICPi) therapy.

METHODS

A multidisciplinary panel of medical oncology, dermatology, gastroenterology, rheumatology, pulmonology, endocrinology, neurology, hematology, emergency medicine, nursing, trialists, and advocacy experts was convened to update the guideline. Guideline development involved a systematic literature review and an informal consensus process. The systematic review focused on evidence published from 2017 through 2021.

RESULTS

A total of 175 studies met the eligibility criteria of the systematic review and were pertinent to the development of the recommendations. Because of the paucity of high-quality evidence, recommendations are based on expert consensus.

RECOMMENDATIONS

Recommendations for specific organ system-based toxicity diagnosis and management are presented. While management varies according to the organ system affected, in general, ICPi therapy should be continued with close monitoring for grade 1 toxicities, except for some neurologic, hematologic, and cardiac toxicities. ICPi therapy may be suspended for most grade 2 toxicities, with consideration of resuming when symptoms revert ≤ grade 1. Corticosteroids may be administered. Grade 3 toxicities generally warrant suspension of ICPis and the initiation of high-dose corticosteroids. Corticosteroids should be tapered over the course of at least 4-6 weeks. Some refractory cases may require other immunosuppressive therapy. In general, permanent discontinuation of ICPis is recommended with grade 4 toxicities, except for endocrinopathies that have been controlled by hormone replacement. Additional information is available at www.asco.org/supportive-care-guidelines.

Management of Immune-Related Adverse Events in Patients Treated With Chimeric Antigen Receptor T-Cell Therapy: ASCO Guideline

PURPOSE

To increase awareness, outline strategies, and offer guidance on the recommended management of immune-related adverse events (irAEs) in patients treated with chimeric antigen receptor (CAR) T-cell therapy.

METHODS

A multidisciplinary panel of medical oncology, neurology, hematology, emergency medicine, nursing, trialists, and advocacy experts was convened to develop the guideline. Guideline development involved a systematic literature review and an informal consensus process. The systematic review focused on evidence published from 2017 to 2021.

RESULTS

The systematic review identified 35 eligible publications. Because of the paucity of high-quality evidence, recommendations are based on expert consensus.

RECOMMENDATIONS

The multidisciplinary team issued recommendations to aid in the recognition, workup, evaluation, and management of the most common CAR T-cell-related toxicities, including cytokine release syndrome, immune effector cell-associated neurotoxicity syndrome, B-cell aplasia, cytopenias, and infections. Management of short-term toxicities associated with CAR T cells begins with supportive care for most patients, but may require pharmacologic interventions for those without adequate response. Management of patients with prolonged or severe CAR T-cell-associated cytokine release syndrome includes treatment with tocilizumab with or without a corticosteroid. On the basis of the potential for rapid decline, patients with moderate to severe immune effector cell-associated neurotoxicity syndrome should be managed with corticosteroids and supportive care.Additional information is available at www.asco.org/supportive-care-guidelines.

Additional Surgery for Occult Risk Factors After Lobectomy in Solitary Thyroid Nodules is Predicted by Cytopathology Classification and Tumor Size

OBJECTIVE

Clinical practice for differentiated thyroid cancer is moving towards lobectomy rather than total thyroidectomy in patients at low risk of recurrence. However, recurrence risk assessment depends on post-operative findings, while the surgical decision is based on preoperative factors. We determined the preoperative predictors of occult higher-risk pathology and rates of completion thyroidectomy among surgical candidates with nonbenign thyroid nodules 10 to 40 mm and no evidence of extrathyroidal extension or metastasis on preoperative evaluation.

METHODS

Thyroid surgery cases at a single institution from 2005-2015 were reviewed to identify those meeting American Thyroid Association (ATA) criteria for lobectomy. ATA-based risk stratification from postoperative surgical pathology was compared to preoperative cytopathology, ultrasound, and clinical findings.

RESULTS

Of 1,995 thyroid surgeries performed for nonbenign thyroid nodules 10 to 40 mm, 349 met ATA criteria for lobectomy. Occult high-risk features such as tall cell variant, gross extrathyroidal invasion, or vascular invasion were found in 36 cases (10.7%), while intraoperative lymphadenopathy led to surgical upstaging in 13 (3.7%). Intermediate risk features such as moderate lymphadenopathy or minimal extrathyroidal extension were present in an additional 44 cases. Occult risk features were present twice as often in Bethesda class 6 cases (35%) as in lower categories (12 to 17%). In multivariable analysis, Bethesda class and nodule size, but not age, race, sex, or ultrasound features, were significant predictors of occult higher-risk pathology.

CONCLUSION

Most solitary thyroid nodules less than 4 cm and with cytology findings including atypia of undetermined significance through suspicious for papillary thyroid cancer would be sufficiently treated by lobectomy.

ABBREVIATIONS

ATA = American Thyroid Association; CND = central neck dissection; DTC = differentiated thyroid cancer; ETE = extrathyroidal extension; FNA = fine needle aspiration; FTC/HCC = follicular thyroid carcinoma/Hurthle cell carcinoma; NIFTP = noninvasive follicular thyroid neoplasm with papillary-like nuclear features; OR = odds ratio; PTC = papillary thyroid cancer; US = ultrasound.

Interpreting Elevated TSH in Older Adults

Thyroid function is most often monitored clinically through measurement of the regulatory hormone, thyrotropin (TSH). Subclinical hypothyroidism is generally defined as a TSH level above the reference range while thyroid hormone levels remain within the reference range. Elevated TSH is more common among older adults, leading to high rates of treatment, and over-treatment, in this population. However, the use of levothyroxine in older adults with mild TSH elevations has begun to be called into question by observations that demonstrate a lack of harm from not treating and a lack of benefit from treating. Importantly, these findings suggest that the existing diagnostic algorithm for subclinical hypothyroidism, based on isolated TSH elevation, may be inappropriate for older adults. Age-specific reference ranges have been suggested as a way to avoid inappropriate treatment, but that strategy continues to rely on population norms rather than disease definitions to drive clinical decisions. Recent insight into age-related variability in the underlying pathophysiology that impacts on thyroid function tests demonstrates the need for new clinical tools to allow the targeted use of therapy where it will have benefit.

Management of Immune-Related Adverse Events in Patients Treated With Immune Checkpoint Inhibitor Therapy: American Society of Clinical Oncology Clinical Practice Guideline

Purpose To increase awareness, outline strategies, and offer guidance on the recommended management of immune-related adverse events in patients treated with immune checkpoint inhibitor (ICPi) therapy. Methods A multidisciplinary, multi-organizational panel of experts in medical oncology, dermatology, gastroenterology, rheumatology, pulmonology, endocrinology, urology, neurology, hematology, emergency medicine, nursing, trialist, and advocacy was convened to develop the clinical practice guideline. Guideline development involved a systematic review of the literature and an informal consensus process. The systematic review focused on guidelines, systematic reviews and meta-analyses, randomized controlled trials, and case series published from 2000 through 2017. Results The systematic review identified 204 eligible publications. Much of the evidence consisted of systematic reviews of observational data, consensus guidelines, case series, and case reports. Due to the paucity of high-quality evidence on management of immune-related adverse events, recommendations are based on expert consensus. Recommendations Recommendations for specific organ system-based toxicity diagnosis and management are presented. While management varies according to organ system affected, in general, ICPi therapy should be continued with close monitoring for grade 1 toxicities, with the exception of some neurologic, hematologic, and cardiac toxicities. ICPi therapy may be suspended for most grade 2 toxicities, with consideration of resuming when symptoms revert to grade 1 or less. Corticosteroids may be administered. Grade 3 toxicities generally warrant suspension of ICPis and the initiation of high-dose corticosteroids (prednisone 1 to 2 mg/kg/d or methylprednisolone 1 to 2 mg/kg/d). Corticosteroids should be tapered over the course of at least 4 to 6 weeks. Some refractory cases may require infliximab or other immunosuppressive therapy. In general, permanent discontinuation of ICPis is recommended with grade 4 toxicities, with the exception of endocrinopathies that have been controlled by hormone replacement. Additional information is available at www.asco.org/supportive-care-guidelines and www.asco.org/guidelineswiki .

Management of Immune-Related Adverse Events in Patients Treated With Immune Checkpoint Inhibitor Therapy: American Society of Clinical Oncology Clinical Practice Guideline

Purpose To increase awareness, outline strategies, and offer guidance on the recommended management of immune-related adverse events in patients treated with immune checkpoint inhibitor (ICPi) therapy. Methods A multidisciplinary, multi-organizational panel of experts in medical oncology, dermatology, gastroenterology, rheumatology, pulmonology, endocrinology, urology, neurology, hematology, emergency medicine, nursing, trialist, and advocacy was convened to develop the clinical practice guideline. Guideline development involved a systematic review of the literature and an informal consensus process. The systematic review focused on guidelines, systematic reviews and meta-analyses, randomized controlled trials, and case series published from 2000 through 2017. Results The systematic review identified 204 eligible publications. Much of the evidence consisted of systematic reviews of observational data, consensus guidelines, case series, and case reports. Due to the paucity of high-quality evidence on management of immune-related adverse events, recommendations are based on expert consensus. Recommendations Recommendations for specific organ system-based toxicity diagnosis and management are presented. While management varies according to organ system affected, in general, ICPi therapy should be continued with close monitoring for grade 1 toxicities, with the exception of some neurologic, hematologic, and cardiac toxicities. ICPi therapy may be suspended for most grade 2 toxicities, with consideration of resuming when symptoms revert to grade 1 or less. Corticosteroids may be administered. Grade 3 toxicities generally warrant suspension of ICPis and the initiation of high-dose corticosteroids (prednisone 1 to 2 mg/kg/d or methylprednisolone 1 to 2 mg/kg/d). Corticosteroids should be tapered over the course of at least 4 to 6 weeks. Some refractory cases may require infliximab or other immunosuppressive therapy. In general, permanent discontinuation of ICPis is recommended with grade 4 toxicities, with the exception of endocrinopathies that have been controlled by hormone replacement. Additional information is available at www.asco.org/supportive-care-guidelines and www.asco.org/guidelineswiki .

Unstable Thyroid Function in Older Adults Is Caused by Alterations in Both Thyroid and Pituitary Physiology and Is Associated with Increased Mortality

BACKGROUND

Average thyrotropin (TSH) levels are known to be higher in older adults when measured in cross-sectional populations. Possible etiologies include differential survival, neutral aging changes, or increased disease prevalence at older ages. This study aimed to elucidate the mechanisms underlying changing thyroid function during aging, and to determine the association of changes with survival, by analyzing the individual thyroid axis over time.

METHODS

Individual patterns of changing TSH and free thyroxine (fT4) were determined in 640 participants in the Baltimore Longitudinal Study of Aging who had at least three measures of serum TSH and fT4, not on medications, over an average of seven years of follow-up. Participants with changing phenotypes were identified based on quintiles for both slopes. Those with alterations in primary thyroid gland function demonstrated intact negative feedback (rising TSH with declining fT4 or declining TSH with rising fT4). Other participants had a parallel rise or fall of TSH and fT4 levels, consistent with pituitary dysfunction. Predictors of phenotype were analyzed by logistic regression. Differential survival between thyroid aging phenotypes was analyzed using multivariate Cox regression.

RESULTS

While the majority of participants at all ages had stable thyroid function, changes were more common among older adults, with 32.3% of those aged >80 years but only 9.5% of those aged <60 years demonstrating thyroid function changes in the highest and lowest quintiles. Regression to the mean accounts for some of the changes, for example increased baseline TSH was associated with a falling TSH pattern (odds ratio = 1.4 [confidence interval 1.1-1.7] per 1 mIU/L). Importantly, changing thyroid function in either the upper or lower quintiles of slope for TSH and fT4 was associated with increased risk of death compared to stable thyroid status (hazard ratio = 5.4 [confidence interval 3.1-9.5]).

CONCLUSIONS

Changing thyroid hormone function is increasingly common at older ages and is associated with decreased survival. Nonetheless, the tendency for abnormal thyroid function tests to resolve, along with altered pituitary responsiveness underlying some TSH elevations, suggests that an elevated TSH level should be not assumed to represent subclinical hypothyroidism in older adults. Thus, caution is appropriate when determining the need for thyroid hormone supplements in older adults.

Free Thyroxine and Functional Mobility, Fitness, and Fatigue in Euthyroid Older Men and Women in the Baltimore Longitudinal Study of Aging

BACKGROUND

Emerging evidence suggests that mildly down-regulated thyroid function in older persons may protect and/or reflect maintained health.

METHODS

Using observational data collected between January 2006 and March 2014 on a volunteer sample of 602 men and women aged 68-97 years with normal thyroid function participating in the Baltimore Longitudinal Study of Aging, this study examines the concurrent relationship between reported walking ability, usual and rapid gait speed, endurance walk performance, fatigability, and reported energy level with respect to free thyroxine (FT4) within the normal range (0.76-1.50ng/dL) as a continuous variable and categorized as low (lower quartile), medium (interquartile), or high (upper quartile).

RESULTS

Adjusting for sex, age, race, height, weight, exercise and smoking, reported walking ability, usual and rapid gait speed, 400-m time, fatigability, and reported energy level were less favorable with increasing FT4 (p = .013 to <.001). In sex-strata, similar associations were observed except for walking ability in men and energy level in women. Categorical analyses revealed that persons with low FT4 exhibited better functional mobility, fitness, and reported energy than persons with intermediate or high levels (p < .05 for all). Persons with high-normal versus medium FT4 had slower usual and rapid gait speed (p < .05) only.

CONCLUSION

Older adults with low-normal FT4 exhibit better mobility, fitness, and fatigue profiles. Mildly down-regulated thyroid function appears to align with better function in old age and may serve as a biomarker of healthy longevity.

Thyroid Hormone Therapy and Risk of Thyrotoxicosis in Community-Resident Older Adults: Findings from the Baltimore Longitudinal Study of Aging

BACKGROUND

Both endogenous and exogenous thyrotoxicosis has been associated with atrial fibrillation and low bone mineral density. Therefore, this study investigated the risk factors associated with prevalent and incident thyrotoxicosis and the initiation of thyroid hormone therapy in a healthy, aging cohort.

METHODS

A total of 1450 ambulatory community volunteer participants in the Baltimore Longitudinal Study of Aging examined at the NIA Clinical Research Unit in Baltimore, MD, have undergone longitudinal monitoring of serum thyrotropin (TSH) and thyroid hormone (free thyroxine and free triiodothryonine) levels as well as medication use every one to four years, depending on age, between 2003 and 2014.

RESULTS

The prevalence of low TSH was 9.6% for participants on thyroid hormone and 0.8% for nontreated individuals (p < 0.001). New cases occurred at a rate of 17.7/1000 person-years of exposure to thyroid hormone therapy [CI 9-32/1000] and 1.5/1000 person-years in the unexposed population [CI 0.7-2.9/1000]. Women were more likely to be treated and more often overtreated than men were. The adjusted hazard ratio (HR) for thyrotoxicosis between treated and untreated women was 27.5 ([CI 7.2-105.4]; p < 0.001) and 3.8 for men ([CI 1.2-6.3]; p < 0.01). White race/ethnicity and older age were risk factors for thyroid hormone therapy but not overtreatment. Body mass index was not associated with starting therapy (HR = 1.0). Thyroid hormone initiation was highest among women older than 80 years of age (3/100 person-years). For one-third of treated participants with follow-up data, overtreatment persisted at least two years.

CONCLUSIONS

Iatrogenic thyrotoxicosis accounts for approximately half of both prevalent and incident low TSH events in this community-based cohort, with the highest rates among older women, who are vulnerable to atrial fibrillation and osteoporosis. Physicians should be particularly cautious in treating subclinical hypothyroidism in elderly women in light of recent studies demonstrating no increased risk of cardiovascular morbidity or death for individuals with elevated TSH levels <10 mIU/L.

Patterns of interferon-alpha-induced thyroid dysfunction vary with ethnicity, sex, smoking status, and pretreatment thyrotropin in an international cohort of patients treated for hepatitis C

BACKGROUND

Interferon-alpha (IFNα)-induced thyroid dysfunction occurs in up to 20% of patients undergoing therapy for hepatitis C. The diversity of thyroid disease presentations suggests that several different pathological mechanisms are involved, such as autoimmunity and direct toxicity. Elucidating the relationships between risk factors and disease phenotype provides insight into the mechanisms of disease pathophysiology.

METHODS

We studied 869 euthyroid patients from the ACHIEVE 2/3 trial, a randomized international clinical trial comparing pegylated-IFNα2a weekly or albumin-IFNα2b every 2 weeks for up to 24 weeks in patients with hepatitis C, genotype 2 or 3, from 136 centers. The study population was 60% male and 55% white. Serum thyrotropin (TSH) and free thyroxine were measured before therapy, monthly during treatment from week 8, and at 4- and 12-week follow-up visits.

RESULTS

Overall, 181 (20.8%) participants had at least one abnormal TSH during the study. Low TSH occurred in 71 (8.2%), of whom 30 (3.5%) had a suppressed TSH below 0.1 mU/L. Hypothyroidism occurred in 53 patients (6.1%), with peak TSH above 10 mU/L in 12 patients (1.4%). Fifty-seven patients had a biphasic thyroiditis (6.6%), with extreme values for the nadir and/or peak TSH in all but one. Medical therapy was given to one thyrotoxic patient, four hypothyroid patients, and 26 biphasic thyroiditis patients. Multivariate logistic regression analysis demonstrated that biphasic thyroiditis is associated with being female and higher pretreatment serum TSH, whereas being Asian or a current smoker decreased the risk of thyroiditis. Hypo- and hyperthyroidism are most strongly predicted by the pretreatment TSH.

CONCLUSIONS

Biphasic thyroiditis accounted for the majority (58%) of clinically relevant IFNα-induced thyroid dysfunction. We confirmed our recent findings in a related cohort that female sex is a risk factor for thyroiditis but not hypothyroidism. Further, in this large multiethnic study, the risk of thyroiditis is dramatically increased, specifically for white women. Smoking was found to be protective of thyroiditis. These results support closer monitoring of women and those with a serum TSH at the extremes of the normal range during therapy so that prompt intervention can mitigate the consequences of thyroid dysfunction associated with IFNα treatment.

Phenotypes of interferon-α-induced thyroid dysfunction among patients treated for hepatitis C are associated with pretreatment serum TSH and female sex

CONTEXT

Thyroid dysfunction is a common complication of interferon-α (IFNα) therapy, with many phenotypic patterns and the potential for significant morbidity.

OBJECTIVE

Our objective was to gain mechanistic insight and predict clinical presentations by determining the risk factors for distinct subtypes of IFNα-induced thyroid dysfunction.

DESIGN

ACHIEVE-1, a randomized trial conducted from 2005-2009, compared long-acting preparations of IFNα in 1323 patients with hepatitis C, genotype 1.

SETTING

A total of 149 outpatient clinics in North America, Europe, and Australia participated.

PATIENTS

We studied 1233 patients who were euthyroid at baseline. This population is 60% male and 82% Caucasian.

INTERVENTIONS

Patients were treated with pegylated IFNα2a weekly or albumin-IFNα2b every 2 wk for 48 wk. Serum TSH and free T(4) were measured before therapy and 12 or more times over 60 weeks.

MAIN OUTCOME MEASURES

Thyroid dysfunction was defined as a TSH outside the normal range during the course of therapy. Low serum TSH indicated thyrotoxicosis, elevated TSH indicated hypothyroidism, and both abnormalities occurred in biphasic thyroiditis.

RESULTS

Of previously euthyroid patients, 16.7% developed abnormal TSH values during therapy, including 24 with TSH below 0.1 mU/liter, 69 with TSH over 5.5 mU/liter, and 76 with biphasic thyroiditis. Biphasic thyroiditis was over 8-fold more common among women than men using multivariate logistic regression analysis [odds ratio (OR) = 8.4; 95% confidence interval (CI) = 4.5-15.8]. Thyrotoxicosis was most strongly associated with a lower pretreatment TSH (OR = 4.1 per -1 mU/liter decline; 95% CI = 1.9-9), whereas hypothyroidism was strongly associated with higher pretreatment TSH (OR = 3.9 per 1 mU/liter increase; 95% CI = 3-5.2).

CONCLUSIONS

Biphasic thyroiditis is common among women treated for hepatitis C with IFNα. Lower and higher pretreatment serum TSH are associated with greater likelihood of thyrotoxicosis and hypothyroidism, respectively. Antithyroid antibody levels were not available for the cohort, and thus we cannot clarify the role of pretreatment thyroid autoimmunity as a risk factor. Our results do show that readily identifiable patient characteristics are risk factors for specific patterns of IFN-induced thyroid dysfunction. These findings suggest that distinct mechanisms may underlie subtypes of thyroid dysfunction associated with immune-modulatory therapy for hepatitis C.

Coumarins are competitive inhibitors of cytochrome P450 1B1, with equal potency for allelic variants

OBJECTIVES

Coumarins are naturally occurring chemicals with potential as chemopreventive agents, several with known action on the cytochrome P450 1A family. We examined whether cytochrome P450 1B1 (CYP1B1) was inhibited by coumarins, whether such inhibition was competitive, and whether inhibition varied between common polymorphic variants of this enzyme.

METHODS

We tested the inhibition properties of four coumarins, bergamottin, isopimpinellin, isoimperatorin, and imperatorin in an assay for oxidation of (-)benzo[a]pyrene-7R-trans-7,8-dihyrodiol (B[a]P-7,8-diol) by CYP1B1 using yeast-microsome expressed enzymes. These assays were performed with wild-type enzyme and five single-amino acid polymorphic variants.

RESULTS

All four coumarins are competitive inhibitors of CYP1B1, with Ki values equal to 587, 11, 6 and 1 muM respectively. Inhibition parameters were consistent between five haplotypes of CYP1B1, three representing common haplotypes in Asians, African-Americans and European-Americans, and two with baseline kinetic parameters previously shown to be potentially different from wild-type.

CONCLUSIONS

Coumarins are capable of inhibiting carcinogen activation by CYP1B1 with varying potencies, and their efficacy as chemopreventive agents is not likely to be affected by polymorphism in this enzyme.

Single amino acid mutations, but not common polymorphisms, decrease the activity of CYP1B1 against (-)benzo[a]pyrene-7R-trans-7,8-dihydrodiol

Genetic differences that underlie inter-individual variation in the metabolism of common carcinogens are important potential sources of cancer susceptibility. Cytochrome P450 1B1 (CYP1B1), a central enzyme in the activation of the ubiquitous environmental carcinogen benzo[a]pyrene (B[a]P), has several genetic variants. This study investigated six rare mutations and four common polymorphisms for their effects on B[a]P metabolism. Five missense mutations associated with congenital glaucoma (Gly61Glu, Gly365Trp, Asp374Asn, Pro437Leu and Arg469Tryp) dramatically decreased the capacity of CYP1B1 to convert (-)benzo[a]pyrene-7R-trans-7,8-dihyrodiol (B[a]P-7,8-diol) to (+/-)benzo[a]pyrene-r-7,t-8-dihydrodiol-9,10-epoxides. These five mutations resulted in enzymes with 3-12% of normal activity when assayed in vitro using an Saccharomyces cerevisiae microsomal expression system. A 10 bp deletion mutation produced no detectable protein or activity. In contrast, proteins containing all possible combinations of four common single nucleotide polymorphisms (Arg48Gly, Ala199Ser, Val432Leu, Asn453Ser) had modest effects on B[a]P-7,8-diol metabolism. Michaelis-Menten analysis suggested that two alleles, Arg48, Ala119, Val432, Ser453 (RAVS) and Arg48, Ala119, Leu432, Ser453 (RALS), have KM values 2-fold lower than Arg48, Ala119, Val432, Ser453 (RAVN): 1.4+/-0.3 and 1.3+/-0.4 microM, respectively, compared with 2.8+/-0.8 microM (P<0.05). However, these differences could not be confirmed with direct measurements of rate at low substrate concentration. There were no significant differences for either of two other kinetic parameters, kcat or kcat/KM. Allele frequency analysis in three populations reveals the Ser453 variant is rare among those of Asian (<1%) and African ancestry (<4%), and more common in individuals of European ancestry (16%). Haplotypes containing the Ser453 variant were uncommon; only RALS was detectable in our small populations. The RALS allele occurred between 0.5% in Asians and 15% in Europeans. Our study demonstrates that rare, disease-associated mutations in CYP1B1 significantly decrease the enzyme's metabolism of B[a]P-7,8-diol; however, our results do not identify any major differences in this metabolism due to four common single amino acid polymorphisms.