Hypothalamic-Pituitary-Thyroid Axis Set Point Alterations Are Associated With Body Composition in Androgen-Deprived Men

Relationship between TSH and free thyroxine in outpatient cancer patient population

BACKGROUND

The inverse log-linear relationship between Thyroid-stimulating hormone (TSH) and free thyroxine (FT4) is well established and reliably used for evaluation of hypothalamus-pituitary-thyroid (HPT) axis function. However, there are limited data regarding oncologic states in the TSH-FT4 relationship. The purpose of this study was to evaluate thyroid pituitary hypothalamic feedback regulation by the inverse log TSH and FT4 relationship in the cancer patient population at the Ohio State University Comprehensive Cancer Center (OSUCCC-James).

METHODS

This retrospective study analyzed the correlation between TSH and FT4 results from 18846 outpatient subjects collected in August 2019-November 2021 at the Department of Family Medicine (OSU Wexner Medical Center), Department of Oncology (OSUCCC-James). Patients with diagnoses related to cancers were included in the oncology group. Patients with diagnoses not related to cancers were included in the non-oncology group. Patients of the Department of Endocrinology, Department of Cardiology, Department of Obstetrics & Gynecology and Department of Hematology were excluded from this study. Time of collection for TSH and FT4 was from 7am to 7 pm. Data were analyzed by morning (7am-12pm) and afternoon (12pm-7pm). Spearman correlation and non-linear fit were used for data analysis. Sex differences were analyzed as well in each group.

RESULTS

Overall, an inverse correlation was observed between TSH and FT4 in both groups (non-oncology and oncology) regardless of sample collection time and sex differences. Further analysis by linear model in log TSH and FT4 showed a significant inverse fit in males compared with females in the group of oncology, both in the afternoon (p < 0.05). Data were further analyzed by ranges of FT4, as lower or higher (pathophysiology) or within (physiology) the reference interval of FT4. There was no statistical significance between the non-oncology and oncology groups, but relatively good correlation in non-oncology group in either physiologic or pathophysiologic FT4 levels and sample collection time. Interestingly, the best correlation between TSH and FT4 was found in the non-oncology group at pathophysiologic FT4 concentrations (abnormally high). In addition, at pathophysiologic FT4 concentrations (abnormally low), the oncology group demonstrated a significant TSH response in the morning than in the afternoon (p < 0.05).

CONCLUSIONS

Though overall the TSH-FT4 curves showed an inverse relationship, there are variations of TSH-FT4 relationship for collection times when considering FT4 in physiologic or pathophysiologic states. The results advance understanding of TSH response, which is beneficial for the interpretation of thyroid disease. We recommend re-evaluation for interpretation of pituitary hypothalamic axis by TSH results when FT4 is abnormally high in oncology patients or low in non-oncology patients, due to poor predictability and the potential for misdiagnosis. A better understanding of the complex nature of the TSH-FT4 relationship may need further study with better defining subclinical states of cancer patients.

Energy balance in cancer survivors at risk of weight gain: a review

PURPOSE

The study of energy balance [i.e., energy intake (EI) and energy expenditure (EE)] is a powerful tool for understanding body weight regulation and may contribute to our understanding of rapid weight gain risk in certain cancer survivors post-diagnosis. The purpose of this review was to summarize studies that assessed longitudinal, prospective changes in components of energy balance from diagnosis/start of treatment to any duration of follow-up in cancer survivors with prior evidence of weight gain (breast, prostate, thyroid, gynecologic, testicular, and acute lymphoblastic leukemia) RESULTS: The available literature suggests that energy balance components may be altered in cancer survivors who have a heightened risk of weight gain post-diagnosis. The evidence for EI was overall inconsistent. Conversely, decreases in resting and physical activity EE during the active phases of treatment (e.g., chemotherapy, hypothyroid state) were commonly noted, which then slowly rebounded towards baseline levels at the end of treatment and during follow-up assessments. Much of this evidence is based on data collected from breast cancer survivors, which highlights a paucity of data currently available on other cancer types.

CONCLUSIONS

While there is growing acknowledgement that weight management interventions in cancer survivors are needed, it is important to recognize that changes in both behavioral (EI, physical activity EE) and passive (resting EE, thermic effect of food) components of energy balance may occur post-diagnosis. This information can help to inform weight management interventions which often entail modifications in diet and/or physical activity.

The Effects of 8 Weeks of Levothyroxine Replacement Treatment on Metabolic and Anthropometric Indices of Insulin Resistance in Hypothyroid Patients

BACKGROUND

Insulin resistance (IR) is an independent cardiovascular risk factor. IR predisposes to metabolic syndrome and diabetes. Meanwhile, little evidence exists about the effect of levothyroxine replacement treatment (LRT) on IR in hypothyroid patients.

OBJECTIVE

To investigate metabolic and anthropometric indices of IR in hypothyroid patients before and after 8 weeks of LRT.

METHODS

This pre-post study evaluated the 8 weeks outcomes of LRT on 66 patients with recently diagnosed hypothyroidism. Outcome measures included body mass index (BMI), waist circumferences (WC), waist to hip ratio (WHR), waist to height ratio (WHtR), body fat percent (BF%), free thyroxin (FT4), triglyceride (TG), low density lipoprotein (LDL), fasting plasma levels of glucose (FPG) and insulin. Sex- specific cut offs of two metabolic indices i.e. the triglyceride-glucose (TyG) and the homeostasis model assessment (HOMA) were used for IR diagnosis. The changes in TyG and HOMA were also compared after LRT.

RESULTS

Participants were overt and subclinical hypothyroidism 71% and 29%, respectively. After LRT the mean values of the following anthropometric indices significantly decreased: weight (79.61 vs. 78.64), BMI (29.53 vs. 29.2), WC (98.25 vs. 97.39) and BF% (35.34 vs. 34.95). After LRT the HOMA and TyG had no significant changes relative to their initial values. Also, IR that was determined on the basis of these metabolic indices more commonly observed in participants.

CONCLUSION

Despite decreasing some anthropometric indices, the diagnosis of IR based on metabolic indices increased following 8 weeks LRT in hypothyroid cases.

Persisting adverse body composition changes 2 years after cessation of androgen deprivation therapy for localised prostate cancer

OBJECTIVE

Hypogonadism from androgen deprivation therapy (ADT) for prostate cancer causes adverse body composition changes associated with insulin resistance and decreased quality of life (QoL). Our objective was to assess whether adverse body composition changes improve after cessation of ADT.

DESIGN

Prospective case-control study in a tertiary referral hospital. Thirty-four men newly commencing ADT (cases, median age: 67.6 years (interquartile range: 64.6-72.0)) and 29 age-matched (70.6 years (65.3-72.9)) prostate cancer controls not on ADT were assessed 2 years after cessation of ADT (median: 4.4 years).

METHODS

Serum testosterone, body composition, handgrip strength, frailty and QoL were measured. Using a mixed model, the mean adjusted differences (MADs (95% CI)) between groups from baseline to study end are reported.

RESULTS

Twenty-seven cases and 19 controls completed the study. Median duration of ADT was 2.3 years (interquartile range: 1.8-3.1). Two years after cessation of ADT, total testosterone remained lower (MAD: -3.4 nmol/L (-6.3 to -0.5), P < 0.022), fat mass (2214 g (490-3933), P = 0.025) and insulin resistance (homeostasis model assessment of insulin resistance: 0.69 (0.31-1.07), P < 0.001) remained higher in cases, whereas lean mass (-1450 g (-2259 to -640), P < 0.001) and physical component of QoL remained lower than controls (-11.9 (-16.4 to -7.4), P < 0.001).

CONCLUSION

Two years after ADT cessation, metabolically adverse changes in body composition, increased insulin resistance and reduced QoL persisted. This may be related to incomplete testosterone recovery. Persisting adverse effects need to be considered in the risk to benefit assessment of ADT and proactive mitigation should continue after cessation of treatment.

Advances in applied homeostatic modelling of the relationship between thyrotropin and free thyroxine

INTRODUCTION

The relationship between pituitary TSH and thyroid hormones is central to our understanding of thyroid physiology and thyroid function testing. Here, we generated distribution patterns by using validated tools of thyroid modelling.

METHODS

We simulated patterns of individual set points under various conditions, based on a homeostatic model of thyroid feedback control. These were compared with observed data points derived from clinical trials.

RESULTS

A random mix of individual set points was reconstructed by simulative modelling with defined structural parameters. The pattern displayed by the cluster of hypothetical points resembled that observed in a natural control group. Moderate variation of the TSH-FT4 gradient over the functional range introduced further flexibility, implementing a scenario of adaptive set points. Such a scenario may be a realistic possibility for instance in treatment where relationships and equilibria between thyroid parameters are altered by various influences such as LT4 dose and conversion efficiency.

CONCLUSIONS

We validated a physiologically based homeostatic model that permits simulative reconstruction of individual set points. This produced a pattern resembling the observed data under various conditions. Applied modelling, although still experimental at this stage, shows a potential to aid our physiological understanding of the interplay between TSH and thyroid hormones. It should eventually benefit personalised clinical decision making.

Thyroid Allostasis-Adaptive Responses of Thyrotropic Feedback Control to Conditions of Strain, Stress, and Developmental Programming

The hypothalamus-pituitary-thyroid feedback control is a dynamic, adaptive system. In situations of illness and deprivation of energy representing type 1 allostasis, the stress response operates to alter both its set point and peripheral transfer parameters. In contrast, type 2 allostatic load, typically effective in psychosocial stress, pregnancy, metabolic syndrome, and adaptation to cold, produces a nearly opposite phenotype of predictive plasticity. The non-thyroidal illness syndrome (NTIS) or thyroid allostasis in critical illness, tumors, uremia, and starvation (TACITUS), commonly observed in hospitalized patients, displays a historically well-studied pattern of allostatic thyroid response. This is characterized by decreased total and free thyroid hormone concentrations and varying levels of thyroid-stimulating hormone (TSH) ranging from decreased (in severe cases) to normal or even elevated (mainly in the recovery phase) TSH concentrations. An acute versus chronic stage (wasting syndrome) of TACITUS can be discerned. The two types differ in molecular mechanisms and prognosis. The acute adaptation of thyroid hormone metabolism to critical illness may prove beneficial to the organism, whereas the far more complex molecular alterations associated with chronic illness frequently lead to allostatic overload. The latter is associated with poor outcome, independently of the underlying disease. Adaptive responses of thyroid homeostasis extend to alterations in thyroid hormone concentrations during fetal life, periods of weight gain or loss, thermoregulation, physical exercise, and psychiatric diseases. The various forms of thyroid allostasis pose serious problems in differential diagnosis of thyroid disease. This review article provides an overview of physiological mechanisms as well as major diagnostic and therapeutic implications of thyroid allostasis under a variety of developmental and straining conditions.

Recent Advances in Thyroid Hormone Regulation: Toward a New Paradigm for Optimal Diagnosis and Treatment

In thyroid health, the pituitary hormone thyroid-stimulating hormone (TSH) raises glandular thyroid hormone production to a physiological level and enhances formation and conversion of T4 to the biologically more active T3. Overstimulation is limited by negative feedback control. In equilibrium defining the euthyroid state, the relationship between TSH and FT4 expresses clusters of genetically determined, interlocked TSH-FT4 pairs, which invalidates their statistical correlation within the euthyroid range. Appropriate reactions to internal or external challenges are defined by unique solutions and homeostatic equilibria. Permissible variations in an individual are much more closely constrained than over a population. Current diagnostic definitions of subclinical thyroid dysfunction are laboratory based, and do not concur with treatment recommendations. An appropriate TSH level is a homeostatic concept that cannot be reduced to a fixed range consideration. The control mode may shift from feedback to tracking where TSH becomes positively, rather than inversely related with FT4. This is obvious in pituitary disease and severe non-thyroid illness, but extends to other prevalent conditions including aging, obesity, and levothyroxine (LT4) treatment. Treatment targets must both be individualized and respect altered equilibria on LT4. To avoid amalgamation bias, clinically meaningful stratification is required in epidemiological studies. In conclusion, pituitary TSH cannot be readily interpreted as a sensitive mirror image of thyroid function because the negative TSH-FT4 correlation is frequently broken, even inverted, by common conditions. The interrelationships between TSH and thyroid hormones and the interlocking elements of the control system are individual, dynamic, and adaptive. This demands a paradigm shift of its diagnostic use.