Short-Term, Combined Fasting and Exercise Improves Body Composition in Healthy Males

Fasting enhances the beneficial metabolic outcomes of exercise; however, it is unknown whether body composition is favorably modified on the short term. A baseline-follow-up study was carried out to assess the effect of an established protocol involving short-term combined exercise with fasting on body composition. One hundred seven recreationally exercising males underwent a 10-day intervention across 15 fitness centers in the Netherlands involving a 3-day gradual decrease of food intake, a 3-day period with extremely low caloric intake, and a gradual 4-day increase to initial caloric intake, with daily 30-min submaximal cycling. Using dual-energy X-ray absorptiometry analysis, all subjects substantially lost total body mass (-3.9 ± 1.9 kg; p < .001) and fat mass (-3.3 ± 1.3 kg; p < .001). Average lean mass was lost (-0.6 ± 1.5 kg; p < .001), but lean mass as a percentage of total body mass was not reduced. The authors observed a loss of -3.9 ± 1.9% android fat over total fat mass (p < .001), a loss of -2.2 ± 1.9% gynoid over total fat mass (p < .001), and reduced android/gynoid ratios (-0.05 ± 0.1; p < .001). Analyzing 15 preselected single-nucleotide polymorphisms in 13 metabolism-related genes revealed trending associations for thyroid state-related single-nucleotide polymorphisms rs225014 (deiodinase 2) and rs35767 (insulin-like growth factor1), and rs1053049 (PPARD). In conclusion, a short period of combined fasting and exercise leads to a substantial loss of body and fat mass without a loss of lean mass as a percentage of total mass

Expression of Thyroid Hormone Transporters in the Human Hypothalamus

Context: Transport of thyroid hormone across the plasma membrane is required for proper thyroid hormone action and metabolism. Several specific thyroid hormone transporters have been identified capable of facilitating uptake and/or efflux of thyroid hormones. Monocarboxylate transporter (MCT)-8, MCT10, and organic anion transporting polypeptide 1C1 (OATP1C1) are the best-characterized specific thyroid hormone transporters to date. Objective: Our earlier studies in the human hypothalamus have shown that MCT8 is present in neurons of the hypothalamic paraventricular nucleus (PVN) and infundibular nucleus (IFN) and in tanycytes. We hypothesized that also MCT10 and OATP1C1 are present in specific areas of the human hypothalamus. Design: We studied postmortem brain samples of patients with known serum thyroid hormone levels using immunocythochemistry to investigate the distribution of MCT10 and OATP1C1 in the hypothalamus. Results: We found strong neuronal MCT10 immunocytochemical staining in a number of hypothalamic nuclei, including the PVN, IFN, and supraoptic nucleus. Intense staining was also observed in neurons of the lateral hypothalamus including the perifornical area. OATP1C1 immunoreactivity was present in glial cells throughout the hypothalamus. In addition, staining was present in capillary walls and in neurons of the PVN, IFN, and supraoptic nucleus. Conclusion: The strong expression of MCT10 and OATP1C1 in the human hypothalamus indicates a possible role in the regulation of the hypothalamus-pituitary-thyroid axis. (J Clin Endocrinol Metab 96: E967-E971, 2011

Acute intermittent porphyria-related leukoencephalopathy

Objective: To identify the genetic etiology of a distinct leukoencephalopathy with autosomal recessive inheritance in a single family. Methods: We analyzed available MRIs and retrospectively reviewed clinical information and laboratory investigations. We performed whole-exome sequencing to find the causal gene variants. Results: We identified 3 family members with a similar MRI pattern characterized by symmetrical signal abnormalities in the periventricular and deep cerebral white matter, thalami, and central part of the pons. Cerebellar atrophy was noted in advanced disease stages. Clinical features were childhood-onset slowly progressive spastic paraparesis, cerebellar ataxia, peripheral neuropathy, and in 2 patients, optic atrophy as well as vertical gaze and convergence palsies and nystagmus. Whole-exome sequencing revealed compound heterozygous missense variants in the HMBS gene, both associated with the autosomal dominant disorder acute intermittent porphyria. Sanger sequencing of 6 healthy siblings confirmed the bi-allelic location of the variants and segregation with the disease. Patients had a slight and moderate increase in urinary and plasma porphobilinogen and 5′-aminolevulinic acid, respectively, and a 50% to 66% decrease in hydroxymethylbilane synthase enzyme activity compared to normal. Conclusions: Bi-allelic HMBS variants have been reported before as cause of severe encephalopathy with early childhood fatality in acute intermittent porphyria. Our cases demonstrate childhood onset, but milder and slower disease progression in middle-aged patients. With this, a novel phenotype can be added to the disease spectrum associated with bi-allelic HMBS variants: a leukoencephalopathy with early onset, slowly progressive neurologic symptomatology, and long life expectancy

Evidence for a Homodimeric Structure of Human Monocarboxylate Transporter 8

The human monocarboxylate transporter 8 (hMCT8) protein mediates transport of thyroid hormone across the plasma membrane. Association of hMCT8 mutations with severe psychomotor retardation and disturbed thyroid hormone levels has established its physiological relevance, but little is still known about the basic properties of hMCT8. In this study we present evidence that hMCT8 does not form heterodimers with the ancillary proteins basigin, embigin, or neuroplastin, unlike other MCTs. In contrast, it is suggested that MCT8 exists as monomer and homodimer in transiently and stably transfected cells. Apparently hMCT8 forms stable dimers because the complex is resistant to denaturing conditions and dithiothreitol. Cotransfection of wild-type hMCT8 with a mutant lacking amino acids 267–360 resulted in formation of homo-and heterodimers of the variants, indicating that transmembrane domains 4–6 are not involved in the dimerization process. Furthermore, we explored the structural and functional role of the 10 Cys residues in hMCT8. All possible Cys>Ala mutants did not behave differently from wild-type hMCT8 in protein expression, cross-linking experiments with HgCl2 and transport function. Our findings indicate that individual Cys residues are not important for the function of hMCT8 or suggest that hMCT8 has other yet-undiscovered functions in which cysteines play an essential role

In Vitro and Mouse Studies Supporting Therapeutic Utility of Triiodothyroacetic Acid in MCT8 Deficiency

Monocarboxylate transporter 8 (MCT8) transports thyroid hormone (TH) across the plasma membrane. Mutations in MCT8 result in the Allan-Herndon-Dudley syndrome, comprising severe psychomotor retardation and elevated serum T-3 levels. Because the neurological symptoms are most likely caused by a lack of TH transport into the central nervous system, the administration of a TH analog that does not require MCT8 for cellular uptake may represent a therapeutic strategy. Here, we investigated the therapeutic potential of the biologically active T-3 metabolite Triac (TA3) by studying TA3 transport, metabolism, and action both in vitro and in vivo. Incubation of SH-SY5Y neuroblastoma cells and MO3.13 oligodendrocytes with labeled substrates showed a time-dependent uptake of T-3 and TA3. In intact SH-SY5Y cells, both T-3 and TA3 were degraded by endogenous type 3 deiodinase, and they influenced gene expression to a similar extent. Fibroblasts from MCT8 patients showed an impaired T-3 uptake compared with controls, whereas TA3 uptake was similar in patient and control fibroblasts. In transfected cells, TA3 did not show significant transport by MCT8. Most importantly, treatment of athyroid Pax8-knockout mice and Mct8/Oatp1c1-double knockout mice between postnatal days 1 and 12 with TA3 restored T-3-dependent neural differentiation in the cerebral and cerebellar cortex, indicating that TA3 can replace T-3 in promoting brain development. In conclusion, we demonstrated uptake of TA3 in neuronal cells and in fibroblasts of MCT8 patients and similar gene responses to T-3 and TA3. This indicates that TA3 bypasses MCT8 and may be used to improve the neural status of MCT8 patients

Mutations in MCT8 in Patients with Allan-Herndon-Dudley-Syndrome Affecting Its Cellular Distribution

Monocarboxylate transporter 8 (MCT8) is a thyroid hormone (TH)-specific transporter. Mutations in the MCT8 gene are associated with Allan-Herndon-Dudley Syndrome (AHDS), consisting of severe psychomotor retardation and disturbed TH parameters. To study the functional consequences of different MCT8 mutations in detail, we combined functional analysis in different cell types with live-cell imaging of the cellular distribution of seven mutations that we identified in patients with AHDS. We used two cell models to study the mutations in vitro: 1) transiently transfected COS1 and JEG3 cells, and 2) stably transfected Flp-in 293 cells expressing a MCT8-cyan fluorescent protein construct. All seven mutants were expressed at the protein level and showed a defect in T-3 and T-4 transport in uptake and metabolism studies. Three mutants (G282C, P537L, and G558D) had residual uptake activity in Flp-in 293 and COS1 cells, but not in JEG3 cells. Four mutants (G221R, P321L, D453V, P537L) were expressed at the plasma membrane. The mobility in the plasma membrane of P537L was similar to WT, but the mobility of P321L was altered. The other mutants studied (insV236, G282C, G558D) were predominantly localized in the endoplasmic reticulum. In essence, loss of function by MCT8 mutations can be divided in two groups: mutations that result in partial or complete loss of transport activity (G221R, P321L, D453V, P537L) and mutations that mainly disturb protein expression and trafficking (insV236, G282C, G558D). The cell type-dependent results suggest that MCT8 mutations in AHDS patients may have tissue-specific effects on TH transport probably caused by tissue-specific expression of yet unknown MCT8-interacting proteins. (Molecular Endocrinology 27: 801-813, 2013