Effect of presence/absence of a nasogastric tube in the same person on incidence of aspiration.

OBJECTIVE: To determine what effect, if any, the presence or absence of a nasogastric (NG) tube in the same person had on the incidence of anterograde aspiration. DESIGN: Case series with planned data collection. SETTING: Large, urban, tertiary care teaching hospital. SUBJECTS AND METHODS: Referred sample of 62 consecutively enrolled adult inpatients for fiber-optic endoscopic evaluation of swallowing (FEES). Group 1 (n = 21) had either small-bore (n = 13) or large-bore (n = 8) NG tubes already in place and had a FEES first with the NG tube in place and a second FEES after NG tube removal. Group 2 (n = 41) did not have an NG tube and had a FEES first without an NG tube and a second FEES after placement of a small-bore NG tube. Time between FEES was approximately 5 minutes. Patients were tested with thin liquid and puree food consistencies. Occurrence of aspiration for each consistency dependent on the presence or absence of an NG tube was recorded. RESULTS: There were no significant differences (P > .05) in aspiration status for both liquid and puree consistencies in the same person dependent on presence or absence of either a small-bore or large-bore NG tube. CONCLUSIONS: Since objective swallowing evaluation (eg, FEES) can be performed with an NG tube in place, it is not necessary to remove an NG tube to evaluate for aspiration. Similarly, there is no contraindication to leaving an NG tube in place to supplement oral alimentation until nutritional requirements are achieved.

Nontraumatic cerebrospinal fluid rhinorrhea as a result of pseudotumor cerebri.

OBJECTIVE: The purpose of this study is to demonstrate that pseudotumor cerebri, also known as benign intracranial hypertension, can be an overlooked cause of spontaneous, nontraumatic cerebrospinal fluid (CSF) rhinorrhea. STUDY DESIGN AND METHODS: This study presents a literature review and 2 case reports. The medical records of 2 patients who had nontraumatic CSF rhinorrhea were reviewed. RESULTS: The patients were diagnosed as having spontaneous, nontraumatic CSF rhinorrhea, believed to have been caused by pseudotumor cerebri, and were surgically treated. The patients are obese, middle-aged women. CONCLUSIONS: Cerebrospinal fluid rhinorrhea is most often the result of trauma, but it may also occur spontaneously because of nontraumatic causes in some patients. Pseudotumor cerebri can be an overlooked cause of spontaneous, nontraumatic CSF rhinorrhea. A patient with signs and symptoms of pseudotumor cerebri should be evaluated and treated, if the condition is present, to prevent complications that include irreversible visual loss and CSF rhinorrhea.

Role of active site tyrosines in dynamic aspects of DNA binding by AP endonuclease.

AP endonuclease (AP endo), a key enzyme in repair of abasic sites in DNA, makes a single nick 5' to the phosphodeoxyribose of an abasic site (AP-site). We recently proposed a novel mechanism, whereby the enzyme uses a key tyrosine (Tyr(171)) to directly attack the scissile phosphate of the AP-site. We showed that loss of the tyrosyl hydroxyl from Tyr(171) resulted in dramatic diminution in enzymatic efficiency. Here we extend the previous work to compare binding/recognition of AP endo to oligomeric DNA with and without an AP-site by wild type enzyme and several tyrosine mutants including Tyr(128), Tyr(171) and Tyr(269). We used single turnover and electrophoretic mobility shift assays. As expected, binding to DNA with an AP-site is more efficient than binding to DNA without one. Unlike catalytic cleavage by AP endo, which requires both hydroxyl and aromatic moieties of Tyr(171), the ability to bind DNA efficiently without an AP-site is independent of an aromatic moiety at position 171. However, the ability to discriminate efficiently between DNA with and without an AP-site requires tyrosine at position 171. Thus, AP endo requires a tyrosine at the active site for the properties that enable it to behave as an efficient, processive endonuclease.

Novel role of tyrosine in catalysis by human AP endonuclease 1.

Apurinic/apyrimidinic endonuclease (AP endo, HAP1) recognizes abasic sites in ds DNA and makes a single nick in the backbone 5' to the abasic site. In this report we examine the roles of three conserved tyrosine residues in close proximity to the active site. We show that Tyr(128) and Tyr(269), which interact upstream and downstream of the abasic site, respectively, are involved in recognition and binding of abasic site-containing double stranded DNA. However, the two residues are not equivalent, as their effects are differentiated by changes in salt concentration. In sharp contrast, Tyr(171) is directly involved in catalysis as well as binding. Y171F, Y171H, and Y171A all show decreased catalytic efficiencies 25,000-50,000-fold from the WT enzyme. Both imidazole and basic pH markedly stimulate the WT enzyme. Imidazole stimulates Tyr(171) mutant enzymes when tyrosine is also present but basic pH eliminates remaining mutant activity. These results underscore the importance of tyrosines in AP endo catalysis. They render the current hypotheses regarding enzyme action unlikely and allow us to consider the possibility that the phenolate of Tyr(171) is the nucleophile that attacks the scissile phosphate.