Antioxidant effects of α-lipoic acid against epididymal oxidative damage in adult offspring rats exposed to maternal hypothyroidism stress.

It is well known that the epididymis promotes post-testicular sperm maturation events. However, its malfunction during congenital hypothyroidism is relatively less understood as compared to the testis. The present study evaluated the probable effect of α-lipoic acid on epididymal oxidative stress parameters in rats exposed to antithyroid drug, carbimazole during fetal period. Time-mated pregnant rats in unexposed and carbimazole (1.35 mg/Kg body weight exposed were allowed to deliver pups and weaned. At postnatal day 100, the F1 male pups were assessed for epididymal endpoints. Among the epididymal regions, significant elevation of lipid peroxidation levels, superoxide anion, and hydrogen peroxide contents with a concomitant reduction in the activity levels of superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase and reduced glutathione levels were observed in cauda epididymis of carbimazole exposed rats over controls. Significant elevation in sperm DNA fragmentation (comet assay), accelerated cauda epididymal sperm transit time and reduction in epididymal sialic acid content was observed in carbimazole exposed rats. RT-qPCR studies revealed that embryonic exposure to carbimazole resulted in down regulation of androgen receptor, nuclear factor eryrthoid 2 like 2, 5α-reducatse 1 mRNA levels, while up regulation of caspase 3 mRNA was observed in epididymal regions of rats. In addition, fetal exposure to carbimazole resulted in disorganization of cauda epididymal architecture in rats. Conversely, supplementation of α-lipoic acid (70 mg/Kg bodyweight) during PND 3 to 14 restored epididymal functions in carbimazole exposed rats and the ameliorative effects of lipoic acid could be attributed to its antioxidant and steroidogenic effects.

Transcriptomic profiling identified altered expression of genes associated with testicular functions in adult F1 rats exposed to carbimazole during fetal period.

The central goal of this study was to investigate the alterations in transcriptome of testis in F1 generation adult rats exposed to carbimazole prenatally. At post-natal day 100, the testis of rats delivered to carbimazole exposed (time-mated pregnant rats orally administered with carbimazole from gestation day 9 to 21) and control (untreated pregnant rats) groups were subjected to transcriptomic analysis using NGS platform. A total of 187 differentially expressed (up regulated: 49 genes; down regulated: 138) genes were identified in carbimazole exposed rats over controls and the major processes associated with these altered testicular transcripts were examined. Functional clustering analysis suggest that the involvement of identified DEGs were linked to intrinsic and extrinsic apoptotic pathways, mitochondrial solute carriers slc25a members, nuclear receptors/zinc family members, steroidogenic pathway and cholesterol synthesis, and growth factors and protein kinases and thus represent potential mediators of the developmental toxic effects of carbimazole in F1 generation rats. Based on the findings, it can be concluded that prenatal exposure to carbimazole prominently affects expression of multiple transcripts implicating key regulatory events associated with testicular functions, spermatogenesis and steroidogenesis in rats at their adulthood. These results support our earlier findings and hypothesis. This background information obtained at the testicular transcriptome during gestational hypothyroidism might be helpful for future studies and experiments to gain additional in-depth analysis and to develop strategies to protect F1 generation male reproductive health. SIGNIFICANCE: The rationale for the paper described thyroid gland changes in the off springs. Antithyroid drugs are widely used to control thyroid disorders and used to control thyroid hormone levels during surgeries. Carbimazole is one of the antithyroid drugs and is a parent molecule of methimazole. Both the drugs can able to cross placenta. During fetal period, the development of thyroid gland is not completely formed and hence, the fetus entirely depends on the maternal thyroid hormones. Therefore, it is conceivable that the disturbances at the level of maternal thyroid hormones could interfere with the development of vital organs such as testis and glands including thyroid gland (Kala et al., 2012). To address this notion, the present study was designed and executed.

Metformin alleviates the dysregulated testicular steroidogenesis and spermatogenesis induced by carbimazole in levothyroxine-primed rats.

Most of the published experiments about carbimazole (CMZ)-induced testicular injury are constructed in normal healthy animals, which lakes the translational identification. Despite metformin (MET) having advantageous effects on injured testicles, its impact on thyroid function is arguable. In the current levothyroxine (LT4)/CMZ model, Wistar rats were primed by LT4 for sixty days. CMZ was then given individually or simultaneously with different doses of MET, 100, 200, and 400 mg, daily for thirty days. Serum was assessed for thyroid profile panel, sex hormones, and gonadotropin levels. Testicular tissues were examined for steroidogenesis, spermatogenesis, inflammation, and apoptosis. Histopathology of thyroid and testes were examined, besides thyroidal nuclear factor (NF)-kB expression. MET in a dose-response manner improved the LT4/CMZ-induced testicular toxicity by increasing the steroidogenic acute regulatory protein (StAR), and 17-ß-hydroxysteroid dehydrogenase (17ßHSD) activities, the proliferating cell nuclear antigen (PCNA), sperm count and motility, sex hormones, and gonadotropin levels. MET-400 mg markedly decreased the elevated NF-kB expressions, tumour necrosis factor (TNF)-α, caspase-3, and BAX, and increased BCL-2. LT4/CMZ could be used as translational animal modelling. MET displayed a dose-dependent ameliorative effect on the LT4/CMZ model without significant harmful effects on thyroid functions. MET-testicular protective roles in diabetics with thyroidal diseases should be explored.

Pharmacokinetics of controlled-release carbimazole tablets support once daily dosing in cats.

Carbimazole, a prodrug of methimazole, is used in the treatment of hyperthyroidism in cats. The pharmacokinetics of methimazole was investigated in healthy cats following oral administration of 15 mg of carbimazole as a controlled-release tablet (Vidalta), Intervet). The controlled-release tablet did not produce a pronounced concentration peak and methimazole was present in the circulation for a sustained period, compared with a conventional tablet formulation. The time to reach peak concentrations after carbimazole administration was quite long (t(max) 6 h). The absolute bioavailability of carbimazole was around 88 +/- 11%. Repeated oral administration daily for 13 consecutive days did not lead to accumulation of methimazole in plasma. The extent of absorption of carbimazole was about 40% higher when administered to cats that had been fed compared to fasted cats. The relative oral bioavailability of methimazole following administration of the controlled-release tablets was similar to that of a conventional release formulation (83 +/- 21%). The pharmacokinetics of this controlled-release formulation of carbimazole supports its use as a once daily treatment (both as a starting dose and for maintenance therapy) for cats with hyperthyroidism.

Assessment of povidone-iodine disinfectant compatibility with antimicrobial incise drape and adhesion inhibition on the skin using a gas chromatography/mass spectrometry approach.

According to orthopedists' reports, substitution of the original for a generic povidone-iodine (PVP-I) disinfectant could have led to some adhesion problems of antimicrobial incise drapes on the field of operation with the consequence of increasing the infection risk. Three methods have been used to assess the case: (a) a gas chromatography/mass spectrometry (GC-MS) approach quantifying methimazole formation from carbimazole, (b) in vitro adhesion experiments on a smooth glass plate surface and (c) the analysis of intrasurgical procedures. GC-MS results confirmed the higher potency of the original compared to the generic PVP-I. In vitro comparison of the adhesion on a PVP-I-pretreated glass surface showed no difference between the disinfectants and no significant destruction of the adhesive layer. However, due to different surgery preparation procedures, the remaining free skin surface granting sufficient adhesion differed if the intervening surgeon himself or his assistant prepared the field of operation. As a conclusion, the original PVP-I disinfectant is confirmed as the first-choice disinfectant for the field of operation. Adhesion problems were arising with new surgical staff and thus different preparation procedures. Exchanging PVP-I disinfectants cannot explain the adhesion problems of drapes and antimicrobial incise foils on the skin.

Evaluation of olfactory and auditory system effects of the antihyperthyroid drug carbimazole in the Long-Evans rat.

Carbimazole (2-carbethoxythio-1-methylimidazole) is a thiocarbamide drug used in the treatment of hyperthyroidism in humans. Side effects associated with carbimazole treatment are reported to include impaired taste, impaired olfaction, and hearing loss. The structurally similar antihyperthyroid drug methimazole (1-methyl-2-mercaptoimidazole), also reportedly associated with impaired taste and olfaction in humans, has recently been demonstrated by this laboratory to be an olfactory toxicant by both the oral and intraperitoneal routes of exposure in rodents. A systematic evaluation of sensory system effects of these compounds, either in rodents or humans, is not available in the literature. Male Long-Evans rats were used to evaluate the auditory and olfactory toxicity of carbimazole by two routes of exposure. Histopathological evaluation of nasal cavities from rats administered carbimazole via i.p. and oral routes revealed olfactory mucosal damage and early evidence of repair; a no-observed effect level (NOEL) of 100 mg/kg was observed for orally administered carbimazole. Further, these studies demonstrate evidence for the generation of the olfactory toxic metabolites of carbimazole by the olfactory mucosa itself, as incubation of carbimazole with an olfactory S9 preparation resulted in NADPH-dependent degradation of carbimazole. Evaluation of the auditory startle response in carbimazole-treated rats revealed no deficits, demonstrating that carbimazole does not cause a global loss of hearing in rats.

Clinical significance of esterases in man.

Esterases, hydrolases which split ester bonds, hydrolyse a number of compounds used as drugs in humans. The enzymes involved are classified broadly as cholinesterases (including acetylcholinesterase), carboxylesterases, and arylesterases, but apart from acetylcholinesterase, their biological function is unknown. The acetylcholinesterase present in nerve endings involved in neurotransmission is inhibited by anticholinesterase drugs, e.g. neostigmine, and by organophosphorous compounds (mainly insecticides). Cholinesterases are primarily involved in drug hydrolysis in the plasma, arylesterases in the plasma and red blood cells, and carboxylesterases in the liver, gut and other tissues. The esterases exhibit specificities for certain substrates and inhibitors but a drug is often hydrolysed by more than one esterase at different sites. Aspirin (acetylsalicylic acid), for example, is hydrolysed to salicylate by carboxylesterases in the liver during the first-pass. Only 60% of an oral dose reaches the systemic circulation where it is hydrolysed by plasma cholinesterases and albumin and red blood cell arylesterases. Thus, the concentration of aspirin relative to salicylate in the circulation may be affected by individual variation in esterase levels and the relative roles of the different esterases, and this may influence the overall pharmacological effect. Other drugs have been less extensively investigated than aspirin and these include heroin (diacetylmorphine), suxamethonium (succinylcholine), clofibrate, carbimazole, procaine and other local anaesthetics. Ester prodrugs are widely used to improve absorption of drugs and in depot preparations. The active drug is released by hydrolysis by tissue carboxylesterases. Individual differences in esterase activity may be genetically determined, as is the case with atypical cholinesterases and the polymorphic distribution of serum paraoxonase and red blood cell esterase D. Disease states may also alter esterase activity.

Amiodarone. The dilemma of hyperthyroxinaemia and the treatment of thyrotoxicosis.

The use of amiodarone, a drug which is prescribed increasingly as an anti-anginal and anti-arrhythmic agent, necessitates a high index of suspicion for the development of thyroid disorders, especially thyrotoxicosis. Two cases, which illustrate the diagnostic dilemma of hyperthyroxinaemia and the poor response to antithyroid medication, are described. During amiodarone therapy, the clinical features of thyrotoxicosis may be masked or atypical, and the choice of therapy is complicated by a delayed response to thioamide drugs and possible contraindication for beta-blocking agents which necessitates the use of glucocorticoid drugs in some patients.

Comparative bioavailability of carbimazole and methimazole.

In this study we investigated the oral bioavailability of therapeutic doses of two antithyroid drugs, methimazole and carbimazole, in seven euthyroid subjects. To increase the statistical power deuterium-labeled methimazole was given orally as an internal standard together with the tested drugs. Using a recently described highly sensitive gas chromatographic-mass spectrometric assay for methimazole we found that intake of 15 mg carbimazole resulted in plasma concentrations of methimazole and pharmacokinetic data comparable to intake of an equimolar amount of methimazole, i. e., 9.2 mg. Maximum concentrations of 163 and 149 ng/ml, respectively, were reached in both instances at 0.9 h after intake of 15 mg carbimazole and 10 mg methimazole. The plasma half-life was 5.7 and 5.4 h, respectively. In contrast to previous suggestions the interindividual differences in pharmacokinetics were small. In conclusion, carbimazole was rapidly and totally bioactivated to methimazole, and the drugs should be regarded as equipotent when compared on a molar basis.

Intrathyroidal concentrations of methimazole in patients with Graves' disease.

A sensitive gas chromatographic-mass spectrometric method enabled us to study intrathyroidal concentrations of methimazole in 20 euthyroid patients with Graves' disease on treatment with carbimazole and T4. There was no difference between patients receiving a final dose of carbimazole (10 mg), known to be totally bioactivated to methimazole (6.1 mg), 3-6 h before thyroid excision (518 ng/g thyroid tissue +/- 90 SEM) and patients who received the same dose 17-20 h before excision (727 ng/g thyroid tissue +/- 157 SEM), indicating a slow intrathyroidal turnover of the drug. On the other hand, the serum concentrations were much higher in the first group (102 ng/ml +/- 5 SEM vs. 16 ng/ml +/- 3 SEM), reflecting a short plasma half-life of the drug. The intrathyroidal concentrations of methimazole ranged from 230-1895 ng/g among individual glands but were similar in pieces from different parts of a single gland. These methimazole concentrations are lower than the concentrations reported by others to have an immunosuppressive action on lymphocytes in vitro.

Excretion of methimazole in human milk.

It is universally stated that antithyroid drugs are concentrated in human milk and are thus contraindicated during breast-feeding. We recently showed, however, that propylthiouracil (PTU) was not concentrated in milk and a study has now been made of the excretion of another widely used antithyroid drug carbimazole (CMI) in human milk. Methimazole (MMI) in blood and milk from five lactating women was measured after oral administration of CMI 40 mg, which is rapidly and completely transformed to the active antithyroid compound MMI. One hour after CMI, the mean serum-MMI reached 253 microgram/I and the mean concentration of MMI in milk reached 182 microgram/I. MMI was found to be unionized and not to be protein bound in serum, and it occurred in milk in the same concentration as the serum; the mean milk/serum ratio was 0.98. The mean total amount of MMI excreted in milk over 8 h was 34 microgram (SEM +/- 5, n = 5), i.e. 0.14% of the dose administered.

The pharmacokinetics of methimazole after oral administration of carbimazole and methimazole, in hyperthyroid patients.

1 Methimazole plasma concentrations were measured in two groups of hyperthyroid subjects after the oral administration of either carbimazole or methimazole. 2 With the HPLC method it was also possible to measure the concentration of a methimazole metabolite, 3-methyl-2-thiohydantoin in one patient. 3 Large interindividual differences were observed, especially within the carbimazole group. 4 Incomplete absorption of carbimazole could explain particular high apparent volumes of distribution and apparent clearances.

The pharmacokinetics of methimazole in pregnant patients after oral administration of carbimazole.

1 A high performance liquid chromatographic (HPLC) method was used to study the pharmacokinetics of methimazole after oral administration of carbimazole to women in various stages of pregnancy. 2 In one patient it was possible to conduct the study in the first and third timesters: there was an appreciable increase in the apparent clearance of methimazole. 3 Based on the assumption of complete absorption and hydrolysis of carbimazole to methimazole the mean apparent clearance was found to be significantly higher in pregnant patients receiving 10 mg carbimazole than in non-pregnant patients receiving the same dose.

Bioavailability of two tablet preparations of carbimazole in man.

1. The bioavailability of two 5 mg tablet formulations of carbimazole (Neomercazole [A] and Carbazole [B]) have been compared in six euthyroid subjects. There was considerable inter-patient variation in absolute bioavailability although, for each subject, peak plasma concentrations of methimazole were similar with both formulations. 2. Mean peak plasma concentrations were seen on average 62 min after administration of tablet A as compared to 40 min after tablet B. This is consistent with the finding that the disintegration and dissolution times were shorter for formulation B than for formulation A. The mean area under the plasma concentration curve and the 6 h plasma concentration of methimazole tended to be greater after tablet A. These differences could be of significance in the treatment of thyrotoxicosis.