Juha M. Peltonen

Molecular mechanisms of ligand–receptor interactions in transmembrane domain V of the α2A-adrenoceptor

The structural determinants of catechol hydroxyl interactions with adrenergic receptors were examined using 12 α2‐adrenergic agonists and a panel of mutated human α2A‐adrenoceptors. The α2ASer201 mutant had a Cys → Ser201 (position 5.43) amino‐acid substitution, and α2ASer201Cys200 and α2ASer201Cys204 had Ser → Cys200 (5.42) and Ser → Cys204 (5.46) substitutions, respectively, in addition to the Cys → Ser201 substitution. Automated docking methods were used to predict the receptor interactions of the ligands. Radioligand‐binding assays and functional [35S]GTPγS‐binding assays were performed using transfected Chinese hamster ovary cells to experimentally corroborate the predicted binding modes. The hydroxyl groups of phenethylamines were found to have different effects on ligand affinity towards the activated and resting forms of the wild‐type α2A‐adrenoceptor. Substitution of Ser200 or Ser204 with cysteine caused a deterioration in the capability of catecholamines to activate the α2A‐adrenoceptor. The findings indicate that (i) Cys201 plays a significant role in the binding of catecholamine ligands and UK14,304 (for the latter, by a hydrophobic interaction), but Cys201 is not essential for receptor activation; (ii) Ser200 interacts with the meta‐hydroxyl group of phenethylamine ligands, affecting both catecholamine binding and receptor activation; while (iii) substituting Ser204 with a cysteine interferes both with the binding of catecholamine ligands and with receptor activation, due to an interaction between Ser204 and the para‐hydroxyl group of the catecholic ring.

Oral soft tissue alterations in patients with neurofibromatosis

Our aim was to characterize the type and frequency of oral soft tissue alterations in neurofibromatosis. A total of 103 patients with neurofibromatosis 1 (NF1) and three patients with neurofibromatosis 2 (NF2) were clinically evaluated for their oral soft tissue alterations. Disturbing growths were removed from nine patients with NF1 and from one patient with NF2. The specimens were analyzed using routine histological methods and with immunohistochemistry using antibodies to S100, type IV collagen, CD34, neurofilament, and neuron-specific tubulin (TUBB3). Alterations including oral tumors, overgrowths of gingival soft tissue, and enlarged papillae of the tongue were discovered in 74% of NF1 patients. The results showed that three tumors clinically classified as plexiform neurofibromas and five out of six discrete mucosal tumors displayed histology and immunohistology consistent with that of neurofibroma. The histology of one palatal lesion resembled that of a scar, and the lesion removed from the patient with NF2 was classified as an amyloid tumor. To conclude, oral soft tissue growths are common findings in NF1, but most lesions do not require treatment and the patients may even not be aware of these alterations. Collagen IV, S100, and CD34 are useful biomarkers in the analysis of NF1-related oral soft tissue tumors. The clinicians should recognize that oral soft tissue alterations are relatively common in NF1. Some of the growths are disturbing, and plexiform neurofibromas may bear a risk of malignant transformation.

Effects of metformin treatment on glucose transporter proteins in subcellular fractions of skeletal muscle in (fa/fa) Zucker rats

1 The present study was designed to clarify the cellular mechanism through which the antihyperglycaemic drug, metformin, exerts its effects. For this purpose the contents of glucose transporter protein isoforms GLUT1 and GLUT4 were measured in plasma membrane and intracellular membrane fractions of skeletal muscle obtained from genetically obese, insulin‐resistant Zucker rats. 2 Hindlimb muscles were dissected from metformin‐treated (300 mg kg−1 day−1, p.o., for 12 days) and control rats in basal treatment state, and after acute stimulation with insuhn (22 u kg−1, i.p.). Since metformin treatment reduces food intake, we also used a pair‐fed control group to investigate the effects of altered insulinaemia per se. Glucose transporter levels were analysed by Western blot and slot blot‐techniques. In addition, 2‐deoxy‐[14C]‐glucose uptake in isolated muscle strips was evaluated. 3 No changes were noted in the contents of GLUT1 proteins in any of the subcellular fractions after metformin treatment. The contents of GLUT4 in subcellular fractions were not altered in the basal treatment state. After acute insulin exposure the content of GLUT4 in the intracellular membrane fraction declined significantly in the metformin‐treated group, while no significant effect was seen in the plasma membrane fraction. In agreement with these results, metformin treatment did not alter 2‐deoxyglucose uptake into isolated muscle strips. 4 In conclusion, the present study does not support the concept that metformin would enhance translocation of glucose transporter proteins from the intracellular compartment to the plasma membrane in skeletal muscle in vivo.

Dental age in patients with neurofibromatosis 1

Neurofibromatosis type 1 (NF1) is a common, hereditary, neurocutaneous skeletal condition with a variety of osseous manifestations. Although NF1 also affects craniofacial structures, the literature has only limited information related to the effect of NF1 on dental development. In this study the dental age of 34 Finnish NF1 patients, 8-17 yr of age, was estimated using the Demirjian & Goldstein method. The dental age of children with NF1 was similar to that of a Finnish control population. The findings suggest that NF1 does not affect the timing of tooth development.