Realities in ossiculoplasty

The results of ossiculoplasty are frequently reported in terms of closure of the air-bone gap. This parameter is a reliable indicator of the degree of technical success, and is useful in comparing different materials and types of reconstructions. However, assessment of the operated ear alone does not evaluate the effect of surgery on binaural hearing ability, leading to the situation where sub-optimal advice may be given to patients pre-operatively. This article advocates a more patient orientated method of assessing the results of ossiculoplasty. Previous studies have indicated that the operated ear must reach an air conduction level of 30 dB for the speech frequencies, or be within 15 dB of the other ear, to ensure that the patient will gain significant benefit. A graphical method for the prediction of patient benefit is presented, and compared to the rule of thumb quoted above. The implications for surgeons and patients considering ossiculoplasty are obvious. Many statements routinely made to patients prior to surgery for conductive hearing loss are unduly optimistic and unrelated to the realities of reported results. There is a need to determine what types of such hearing losses can be helped surgically, and more importantly to what extent the patients hearing disability can be relieved.     

Studies on the molecular pharmacology of GR63178A. A novel pentacyclic pyrolloquinone anticancer drug.

GR63178A (NSC D611615) is the second pentacyclic pyrolloquinone to be evaluated clinically as an anticancer drug. Its mechanism of action is unknown but may be related either to its quinone group or planar ring system. In this report we have investigated the ability of GR63178A to bind non-covalently to DNA, inhibit topoisomerase II and undergo reduction to reactive free radical species. Using two DNA duplexes, a 12-mer oligonucleotide which is a preferred sequence for minor groove binders and a hexamer which is a preferred sequence for intercalators, no evidence of significant binding with GR63178A was found. Neither GR63178A nor GR54374X (its 9-hydroxy metabolite) inhibited purified human topoisomerase II in a decatenation assay. Free radical chemistry was studied by both pulse radiolysis and ESR spectroscopy as well as by in vitro drug incubations with NADPH-fortified rat liver microsomes and purified cytochrome P450 reductase. The one-electron reduction potential of GR63178A was -207 mV +/- 10 which is much more positive than other quinone-containing anticancer drugs such as doxorubicin, mitomycin C and mitozantrone. GR63178A underwent enzyme-catalysed quinone reduction more readily than doxorubicin but produced significantly fewer reactive oxygen species. No evidence was detected of drug-induced, radical-mediated DNA damage in vitro using pBR322 plasmid DNA. Disproportionation of the GR63178A semi-quinone free radical proceeded with a rate constant of 1 x 10(9) M-1 sec-1 under anaerobic conditions, one order of magnitude faster than doxorubicin. The preferential disproportionation of the semi-quinone may explain our inability to detect a free radical signal by ESR. The hydroquinone of GR63178A was stable and exhibited strong visible absorption with a bathochromic shift of 120 nm over the parent drug. These unusual properties may be due to the hydroquinone undergoing a form of keto-enol tautomerization. Thus, GR63178A free radical formation does not appear to result in significant drug activation. In conclusion, GR63178A is unlikely to mediate its antitumour activity by DNA binding, topoisomerase II inhibition or free radical formation in direct contrast to similar anthracycline- and anthraquinone-based anticancer drugs.     

Opposite rank order of potency for alpha-2 adrenoceptor agonists on water and solute excretion in the rat: two sites and/or receptors?

Preliminary studies determined that, unlike other purported alpha-2 adrenoceptor agonists, 2,6-dimethyl clonidine (2,6-DMC) increased urine flow rate independent of vasopressin. We therefore compared the dose-response curves of three alpha-2 adrenoceptor agonists, clonidine, UK 14,304 and 2,6-DMC. Unilaterally nephrectomized Sprague-Dawley rats were anesthetized and the left kidney was exposed and the ureter cannulated. A 31-gauge needle was advanced into the renal artery to permit direct intrarenal infusion of the study drugs. All three agonists produced a dose-related increase in urine flow rate and sodium excretion. A clear opposite rank order of potency was observed when the urine flow rate was analyzed as free water and osmolar clearance. For free water clearance, clonidine much greater than UK 14,304 much greater than 2,6-DMC, with 2,6-DMC producing little change. The effect on osmolar clearance was opposite with 2,6-DMC much greater than clonidine = UK 14,304. The V2 antagonist [1-(beta-mercapto-beta,beta-pentamethylene-proprionic acid), 2-d-isoleucine,4-isoleucine]arginine-vasopressin blocked the effects of clonidine but not 2,6-DMC. In a water-loaded rat model, 2,6-DMC but not clonidine increased the delivery of filtrate out of the proximal segments of the nephron. These results are consistent with the postulate that lower doses of 2,6-DMC increase solute excretion independent of vasopressin, possibly in proximal segments of the nephron. Clonidine on the other hand increases free water clearance and this effect is mediated through an interaction with the renal actions of vasopressin. Whether these disparate effects represent two distinct receptors or two sites of alpha-2 adrenoceptors in the kidney is not known.     

Antigen-induced tolerance by intrathymic modulation of self-recognizing inhibitory receptors

CD1d-restricted invariant natural killer T cell (iNKT cells) have a limited T cell receptor (TCR) repertoire and share characteristics common to T cells and natural killer cells. While intrathymic selection facilitates the production of T cells carrying self major histocompatibility complex-restricted TCRs, natural killer cells carry an appropriate repertoire of self major histocompatibility complex-recognizing receptors to avoid self-reactivity. Here we show that chronic exposure to specific glycolipid antigen resulted in iNKT cell disappearance and thymus-dependent repopulation of iNKT cells with increased expression of inhibitory Ly-49 molecules that resulted in impaired responsiveness. Thymic selection of peripheral Ly-49-expressing iNKT cell repertoire inhibited cytokine production and other functions in vivo. These observations emphasize the acquisition of self-recognizing inhibitory receptors on NKT cells as a previously unknown mechanism of thymic tolerance after chronic antigen exposure.     

Inefficient clustering of tyrosine-phosphorylated proteins at the immunological synapse in response to an antagonist peptide

Interactions of T cells with MHC plus peptide in the peripheral lymphoid system are important for their survival. In this study we investigated further the molecular consequences of such interactions using F5 TCR transgenic mice and peptides previously shown to induce either negative or positive selection in the thymus. Following TCR ligation with the negatively selecting agonist peptide, mature CD8(+) cells proliferated and up-regulated the activation marker CD69. Interestingly, ligation of this TCR with MHC molecules loaded with high concentrations of the positively selecting peptide also resulted in the aforementioned changes, but with slower kinetics. Analysis of the biochemical changes that occur following stimulation with these peptides showed that phosphorylation of key signaling molecules, such as ZAP-70, CD3zeta, Vav, SLP-76, LAT, and ERK-1 and 2, could be detected after exposure to agonist but not antagonist peptide. Confocal microscopy, however, revealed infrequent phosphorylation 'patches' at the site of contact between T cells and APC presenting the antagonist peptide. Our data suggest that peptides capable of inducing positive selection in the thymus can be recognized by mature T cells and cause proliferation, up-regulation of CD69 and accumulation of phosphorylated proteins at the immunological synapse with low efficiency; however no phosphorylation of signaling molecules can be detected using conventional biochemical assays.     

Silent adenoma subtype 3 of the pituitary--immunohistochemical and ultrastructural classification: a review of 29 cases

The silent adenoma subtype 3 (SAS-3) of undetermined cellular derivation is a seemingly nonfunctioning aggressive pituitary tumor with a high recurrence rate. At the time of diagnosis SAS-3s are macro- or giant adenomas particularly aggressive in young individuals, especially women. They are usually associated with mild hyperprolactinemia and are unremarkable by histology. Immunohistochemistry, demonstrating scattered immunoreactivity mostly for GH, PRL, TSH, and alpha-subunit, is not diagnostic. Presently, only TEM permits conclusive diagnosis. Ultrastructurally, the large polar adenoma cells contain abundant RER, masses of SER, extensive multipolar Golgi apparatus, and unevenly clustered mitochondria, displaced by RER and SER, which may show close spatial relationship to RER. Cell membranes often form plexiform interdigitations. Nuclear pleomorphism and nuclear inclusions are common. The 100- to 200-nm secretory granules accumulate heavily in cell processes, which is a hallmark of glycoprotein hormone cell differentiation. The endothelial cells may contain tubuloreticular inclusions. Complete surgical removal of the large often invasive tumors is difficult necessitating postoperative treatment. SAS-3 is sensitive to conventional radiation. Some tumors express somatostatin receptors and respond well to somatostatin analogues, offering long-term control in patients with residual tumor. Possible derivation of SAS-3 from rostral thyrotrophs, a cell type presently known in rodents is contemplated.