Potassium bromide and the thyroid gland of the rat: morphology and immunohistochemistry, RIA and INAA analysis

Influence of medications on thyroid function in dogs: An update

Erroneous thyroid function test results can occur because of drugs that alter thyroid hormone physiology in one or more aspects, including synthesis, secretion, distribution, and metabolism. Research since publication of the last review in the Journal of Veterinary Internal Medicine (JVIM) 20 years ago has evaluated the effects of amiodarone, zonisamide, inhalant anesthetics, clomipramine, trilostane, and toceranib on thyroid function tests in the dog. In addition, recent work on the effects of glucocorticoids, sulfonamides, phenobarbital, and nonsteroidal anti-inflammatory drugs will be reviewed. Awareness of these effects is necessary to avoid misdiagnosis of hypothyroidism and unnecessary treatment.

New aspects in deriving health-based guidance values for bromate in swimming pool water

Bromate, classified as a EU CLP 1B carcinogen, is a typical by-product of the disinfection of drinking and swimming pool water. The aim of this study was (a) to provide data on the occurrence of bromate in pool water, (b) to re-evaluate the carcinogenic MOA of bromate in the light of existing data, (c) to assess the possible exposure to bromate via swimming pool water and (d) to inform the derivation of cancer risk-related bromate concentrations in swimming pool water. Measurements from monitoring analysis of 229 samples showed bromate concentrations in seawater pools up to 34 mg/L. A comprehensive non-systematic literature search was done and the quality of the studies on genotoxicity and carcinogenicity was assessed by Klimisch criteria (Klimisch et al., Regul Toxicol Pharmacol 25:1–5, 1997) and SciRAP tool (Beronius et al., J Appl Toxicol, 38:1460–1470, 2018) respectively. Benchmark dose (BMD) modeling was performed using the modeling average mode in BMDS 3.1 and PROAST 66.40, 67 and 69 (human cancer BMDL₁₀; EFSA 2017). For exposure assessment, data from a wide range of sources were evaluated for their reliability. Different target groups (infants/toddlers, children and adults) and exposure scenarios (recreational, sport-active swimmers, top athletes) were considered for oral, inhalation and dermal exposure. Exposure was calculated according to the frequency of swimming events and duration in water. For illustration, cancer risk-related bromate concentrations in pool water were calculated for different target groups, taking into account their exposure using the hBMDL₁₀ and a cancer risk of 1 in 100,000. Convincing evidence was obtained from a multitude of studies that bromate induces oxidative DNA damage and acts as a clastogen in vitro and in vivo. Since statistical modeling of the available genotoxicity data is compatible with both linear as well as non-linear dose–response relationships, bromate should be conservatively considered to be a non-threshold carcinogen. BMD modeling with model averaging for renal cancer studies (Kurokawa et al., J Natl. Cancer Inst, 1983 and 1986a; DeAngelo et al., Toxicol Pathol 26:587–594, 1998) resulted in a median hBMDL₁₀ of 0.65 mg bromate/kg body weight (bw) per day. Evaluation of different age and activity groups revealed that top athletes had the highest exposure, followed by sport-active children, sport-active adults, infants and toddlers, children and adults. The predominant route of exposure was oral (73–98%) by swallowing water, followed by the dermal route (2–27%), while the inhalation route was insignificant (< 0.5%). Accepting the same risk level for all population groups resulted in different guidance values due to the large variation in exposure. For example, for an additional risk of 1 in 100,000, the bromate concentrations would range between 0.011 for top athletes, 0.015 for sport-active children and 2.1 mg/L for adults. In conclusion, the present study shows that health risks due to bromate exposure by swimming pool water cannot be excluded and that large differences in risk exist depending on the individual swimming habits and water concentrations.

Increased Thyroid Cancer Incidence in Volcanic Areas: A Role of Increased Heavy Metals in the Environment?

Thyroid cancer incidence is significantly increased in volcanic areas, where relevant non-anthropogenic pollution with heavy metals is present in the environment. This review will discuss whether chronic lifelong exposure to slightly increased levels of metals can contribute to the increase in thyroid cancer in the residents of a volcanic area. The influence of metals on living cells depends on the physicochemical properties of the metals and their interaction with the target cell metallostasis network, which includes transporters, intracellular binding proteins, and metal-responsive elements. Very little is known about the carcinogenic potential of slightly increased metal levels on the thyroid, which might be more sensitive to mutagenic damage because of its unique biology related to iodine, which is a very reactive and strongly oxidizing agent. Different mechanisms could explain the specific carcinogenic effect of borderline/high environmental levels of metals on the thyroid, including (a) hormesis, the nonlinear response to chemicals causing important biological effects at low concentrations; (b) metal accumulation in the thyroid relative to other tissues; and (c) the specific effects of a mixture of different metals. Recent evidence related to all of these mechanisms is now available, and the data are compatible with a cause–effect relationship between increased metal levels in the environment and an increase in thyroid cancer incidence.

Short-term effects of combined treatment with potassium bromide and methimazole in patients with Graves' disease

BACKGROUND

Potassium bromide is used as a sedative and an anti-epileptic drug for children and adolescents. Rodent animal studies have shown that bromide ions inhibit thyroid hormone synthesis by decreasing the iodine concentration in thyroid tissue.

AIM

To observe the short-term clinical effects of combined treatment with potassium bromide and methimazole in patients with Graves' disease.

MATERIALS AND METHODS

Sixty patients with Graves' diseases were randomized in groups. Thirty patients in the combined treatment group were treated with methimazole (10 mg, tid) and potassium bromide (1 g, tid); 30 patients in the methimazole only group were treated with methimazole (10 mg, tid) and starch placebo (1 g, tid). All the patients were treated with metoprolol tartrate (25 mg, bid) to control the symptoms and signs of hyperthyroidism. Patients were treated for one month. Clinical symptoms and potential side effects were monitored. Serum thyroid hormone levels were measured before and after the treatments.

RESULTS

Clinical hyperthyroidism symptoms were improved in both groups, with or without potassium bromide. Patients in the combined treatment group displayed improved clinical hyperthyroidism symptoms 10 days earlier on average (p<0.05). Furthermore, blood thyroid hormone levels decreased to normal levels in 93% (28/30) of patients in the combined treatment group, compared with only 37% (5/30) of patients in the methimazole only group (p<0.05).

CONCLUSIONS

Treatment of patients with Graves' disease with a novel combination therapy consisting of potassium bromide and methimazole resulted in a rapid improvement in clinical symptoms and decreased blood thyroid hormone levels to homeostatic levels faster than methimazole treatment alone.

A systematic review of the safety of potassium bromide in dogs

OBJECTIVE

To critically evaluate and summarize available information on the safety of potassium bromide in dogs.

DESIGN

Systematic review.

SAMPLE

111 references reporting safety information relevant to potassium bromide published between 1938 and 2011.

PROCEDURES

PubMed searches without date limitations were conducted with the terms "potassium bromide" and "sodium bromide" in December 2009 and October 2011. Additional articles were identified through examination of article reference lists and book chapters on seizures in dogs and pharmacology.

RESULTS

Reversible neurologic signs were the most consistently reported toxicoses and were generally associated with adjunctive potassium bromide treatment or high serum bromide concentrations. Dermatologic and respiratory abnormalities were rare in dogs. Insufficient information was available to assess the effects of potassium bromide on behavior or to determine the incidence of vomiting, weight gain, polyphagia, pancreatitis, polyuria, polydipsia, or reproductive abnormalities associated with potassium bromide administration. Evidence suggested that administration of potassium bromide with food may alleviate gastrointestinal irritation and that monitoring for polyphagia, thyroid hormone abnormalities, and high serum bromide concentrations may be beneficial.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggested that potassium bromide is not an appropriate choice for treatment of every dog with seizures and that practitioners should tailor therapeutic regimens and clinical monitoring to each dog. Abrupt dietary changes or fluid therapy may compromise seizure control or increase the likelihood of adverse events. Availability of an appropriately labeled, approved potassium bromide product could provide better assurance for veterinarians and their clients of the quality, safety, and effectiveness of the product for veterinary use.

Analysis of thyroid gland microvascularization in rats induced by ingestion of potassium bromide: a scanning electron microscopy study

The microvascularization of the thyroid gland in rats was studied in animals following ingestion of potassium bromide in various concentrations in drinking water (15, 50 or 100 mg/l) over a period of either 16 or 66 days. Accordingly, animals were divided into six study groups and one control group. Microvascularization was compared among the groups. The pattern of thyroidal follicle distribution within the blood vessels was evaluated by scanning electron microscopy. Animals that ingested potassium bromide presented an increased density and number of meshes in the capillary network of the follicle. The peripheral vessels showed flattening of the walls and in the central portion of the follicle, the distribution of the capillary network did not undergo any morphologic alteration.

The effect of bromide on the ultrastructure of rat thyrocytes

Electron microscopic examination of thyroid tissue following administration of bromide to rats showed marked hypertrophy and hyperplasia in the thyrocytes, microfollicular rearrangement and lowered volume of colloid. The luminal surface of the thyrocytes showed increased size and number of microvilli, often filling the microlumen. Most of the nuclei were irregular in shape with unusual incisions and a higher density of chromatin. Proliferation of ER was seen with significantly dilated cisterns containing low electron density material. The Golgi complex was well developed and larger in rats receiving 10 mg Br/l drinking water (16 days) and 100 mg Br/l (16 and 66 days) than in control rats. Granules and small spherical structures (50-100 nm) appeared in the subapical part of the cytoplasm and their number increased in animals after administration of 50 mg Br-/l (16 and 66 days), 100 mg Br-/l (16 and 66 days), 200 and 400 mg Br-/l (133 days). In contrast, their number was reduced in thyrocytes of rats treated with 100 mg Br/l (16, 66 and 133 days). Colloid droplets were only rarely found. There was no significant change in the amount of mitochondria, secondary lysosomes including phagolysosomes. Some thyrocytes showed signs of necrosis in animals following administration of 10 mg Br/l (16 days, 100 and 400 mg Br/l, 133 days). Clusters of thyrocytes with spongy cytoplasm and bizarre shaped nuclei were found in groups treated with 100 mg Br/l, and 400 mg Br-/l (133 days). These changes, with previously published light microscopical, radioanalytical and biochemical findings, confirm the goitrogenic effect of bromide.

Influence of drugs on thyroid function in dogs

Several drugs can affect thyroid function test results in humans and eventually lead to an erroneous evaluation of thyroid function. These medications can alter the synthesis, secretion, transport, or metabolism of thyroid hormones. Some drugs also directly inhibit the hypothalamic-pituitary-thyroid axis. The effects of drugs on thyroid function in dogs have long been underestimated and have most likely contributed to the overdiagnosis of hypothyroidism in this species. This manuscript 1st reviews pertinent thyroid physiology followed by an overview of drugs for which the effects on canine thyroid function have been studied. The effects of glucocorticoids, propranolol, sulfonamides, phenobarbital, potassium bromide, and nonsteroidal anti-inflammatory agents (NSAIDs) on canine thyroid function are summarized here. Knowledge of the potential effect of these medications on thyroid function should contribute to a more reliable interpretation of thyroid function test results in dogs.

Effect of anticonvulsant dosages of potassium bromide on thyroid function and morphology in dogs

A placebo-controlled experiment was performed to evaluate the effect of potassium bromide on the canine thyroid gland. Basal total thyroxine, free thyroxine, and basal thyrotropin serum concentrations were evaluated over a 6-month period in potassium bromide-treated and control dogs. A thyrotropin-releasing hormone stimulation test was also performed in all dogs at the beginning and conclusion of the study. Thyroid histopathology was compared between treated and control dogs at the end of the study. No difference was detected in any parameter between the two groups at the end of the study. A decline in thyroid hormone concentrations over the course of the study did occur in both groups of dogs. Potassium bromide does not appear to have a significant effect on canine thyroid function or morphology.

Long-term action of potassium bromide on the rat thyroid gland

Male rats fed by a standard diet with determined of bromine and iodine content were exposed to a 133-day oral administration of KBr (100, 200, 400 mg Br-/l drinking water). Their thyroid glands showed increased growth of the epithelial cells reflected by a microfollicular rearrangement of the parenchyma due to proliferation of very small follicles with a low or zero content of colloid. Morphometric analysis of thyroids of Br(-)-exposed animals revealed a significant decrease in the volume of intrafollicular colloid and marked increase in the number of the smallest follicles (areas up to 100 and 100-300 micron 2). In addition, the nuclei of thyrocytes showed an increased number of mitoses. The vascularization was increased as well. In the blood plasma of the Br(-)-exposed animals the T4 concentration was significantly decreased in dependence on the bromine concentrations. Thyroglobulin immunoreactivity in the colloid of Br(-)-exposed animals decreased after administration of 400 mg Br-/l drinking water. Increasing concentrations of Br- in the drinking water caused an increased bromine concentration in the thyroid, a decreased iodine content and a decreased I/Br molar ratio. The changes in the rat thyroid caused by long-term administration of 100 mg Br-/l were similar to hyperplastic parenchymal goitre and were comparable to those induced in previous experiments by the same bromine concentration administered over a 16- and 66-day period respectively.