Thiol Reduction of 3′-Azidothymidine to 3′-Aminothymidine: Kinetics and Biomedical Implications

The ability of thiols to reduce 3-azidothymidine (AZT) to 3-aminothymidine has been investigated. Incubation with glutathione, dithiothreitol (DTT), or mercaptoethanol at pH 7.2 and 37°C leads to quantitative reduction of the azido moiety to an amine. The reaction is first order in AZT and first order in reducing agent (mono- or dithiol). The second-order rate constants are 2.77 × 10^–3, 6.55 × 10^–5, and 6.35 × 10^–6 M ^–l sec^–1 for the dithiothreitol, glutathione, and mercaptoethanol reductions, respectively. The thiol reduction of alkyl azide to amine under mild conditions is a synthetic method particularly suitable for water-soluble azido compounds that are sensitive to catalytic hydrogenation. The potential for the mono- or dithiol-mediated reduction of alkyl azides under biological conditions must be considered when conducting studies of azido drugs.     

Suggested approaches for research protocols involving the potential for life-threatening reactions

These guidelines are intended to reduce the potential for serious or life-threatening reactions when clinical research is conducted. The following issues were addressed: identifying the risks involved in the research, providing adequate safeguards in the protocol design and during withholding of medication, anticipating risks, minimizing the chances for human error, providing resuscitative equipment sufficient to deal with the most serious anticipated life-threatening reactions, planning for medical support in case of a life-threatening emergency, and optimizing the use of medical personnel and expertise to handle emergency situations. The guidelines also discuss important general issues about protocol design and implementation and the human subject consent form, which should facilitate the approval of protocols by the governing institutional review board.The guidelines are not meant to be inflexible or applicable to all research situations. However, it is our hope that they will allow for clinical research to be conducted in a manner that affords the research subjects a high degree of protection from unnecessary and possibly fatal injuries.     

Content analysis of helping group interactions: Toward a developmental perspective

Age comparative content anaylses were carried out for eleven support-discussion groups. Comparisons of six groups of elderly persons and five groups of college youth revealed that the older more frequently discuss bodily changes, family relations, significant others and external sources of self respect. The young were more concerned with physical vulnerabilities. The elderly were more likely to discuss matters in terms of the past. The results are considered in the light of a life stage developmental conception of group behavior which could have implications for helping interventions.     

Essential role of a kinesin-like protein in Arabidopsis trichome morphogenesis

Little is known about how cell shape is controlled. We are using the morphogenesis of trichomes (plant hairs) on the plant Arabidopsis thaliana as a model to study how cell shape is controlled. Wild-type Arabidopsis trichomes are large, single epidermal cells with a stalk and three or four branches, whereas in zwichel (zwi) mutants the trichomes have a shortened stalk and only two branches. To further understand the role of the ZWI gene in trichome morphogenesis we have cloned the wild-type ZWICHEL (ZWI) gene by T-DNA tagging, and report here that it encodes a member of the kinesin superfamily of microtubule motor proteins. Kinesin proteins transport diverse cellular materials in a directional manner along microtubules. Kinesin-like proteins are characterized by a highly conserved “head” region that comprises the motor domain, and a nonconserved “tail” region that is thought to participate in recognition and binding of the appropriate cargo.     

Levothyroxine dose requirements for thyrotropin suppression in the treatment of differentiated thyroid cancer.

We have compared the dose of levothyroxine (L-T4) required to suppress serum TSH to given levels in two clinical groups: 1) 44 patients with thyroid cancer whose thyroid glands had been ablated by surgical thyroidectomy and 131I treatment, and 2) 113 patients with thyroidal failure due either to spontaneous primary hypothyroidism (31 patients) or after 131I treatment for Graves' hyperthyroidism (82 patients). The dose of L-T4 needed to attain serum TSH levels in the euthyroid range (0.5-6.2 microU/mL) was significantly greater (P less than 0.01) in patients with thyroid cancer (2.11 micrograms/kg.day) than in the patients with primary hypothyroidism associated with nonmalignant disease (1.63 micrograms/kg.day). Similarly, patients with thyroid cancer required a higher dose of L-T4 to suppress serum TSH to a given subnormal level. These findings suggest that the secretion of hormone from residual thyroid tissue in patients who have not been subjected to near-total thyroid ablation contributes substantially to the circulating levels of serum T4 and T3. We, therefore, infer that residual thyroidal secretion in the patients with hypothyroidism due to benign causes is relatively independent of TSH stimulation. Further subdivision of patients with benign hypothyroidism revealed that patients with Graves' who developed hypothyroidism after 131I treatment showed a lower mean dose requirement than patients with spontaneous hypothyroidism. This raises the possibility that continued secretion of thyroid-stimulating immunoglobulin in such patients might account for the lower dose requirement in the combined group with hypothyroidism. Our studies also have allowed us to make serial observations in 4 patients with thyroid cancer who exhibited elevated levels of serum thyroglobulin. In this limited series, maximal suppression of serum thyroglobulin was produced by doses of L-T4, which reduced circulating TSH to 0.4 mU/L.     

Proportional assist ventilation. Results of an initial clinical trial.

The response to proportional assist ventilation (PAV) was tested in four normal subjects during heavy exercise and in five ventilator-dependent patients recovering from assorted medical disorders. The apparatus consisted of a rolling-seal piston coupled to a motor that generated pressure in proportion to inspired flow and inspired volume, with the gains adjusted such that the proportionality between airway pressure (Paw) and instantaneous patient-generated pressure (Pmus) was approximately 1:1 (i.e., machine-amplified patient effort by a factor of 2). Normal subjects responded to PAV by decreasing their own effort, as judged from esophageal pressure, such that the changes in ventilation and breathing pattern were rather small (VE: 64.8 +/- 3.6 during PAV versus 56.0 +/- 4.3, p less than 0.01; VT: 2.39 +/- 0.24 versus 2.02 +/- 0.17, p less than 0.05; f: 27.5 +/- 1.9 versus 28.0 +/- 2.2, NS). In patients, elastance ranged from 20 to 35 cm H2O cm/L, resistance ranged from 5 to 10 cm H2O/L/s, and maximal inspiratory pressure ranged from -16 to -65 cm H2O. After a period of observation during synchronized intermittent mechanical ventilation (SIMV) the patient was switched to PAV and maintained on it for 1 to 3 h. No patient had to be replaced on SIMV because of discomfort or deterioration in any of the monitored variables. During PAV peak airway pressure was less than half the value observed with the IMV breaths (16.6 +/- 2.4 versus 35.4 +/- 3.4 cm H2O, p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)