Publications

Thrombospondin is a high-molecular-weight glycoprotein constituent of extracellular matrices of several cells in culture. Immunoreactive thrombospondin is also present within the normal human renal mesangium. To determine whether this thrombospondin could be a synthetic product of the intrinsic glomerular mesangial cells, we examined cultured human glomerular mesangial cells for the ability to synthesize and secrete thrombospondin. Well-characterized human mesangial cells were found to synthesize and secrete thrombospondin, as determined by specific immunostaining at the light- and electron-microscopic levels. Furthermore, metabolically labeled thrombospondin was immunoprecipitated from the conditioned medium of cultured cells. These studies suggest that the thrombospondin present within the normal mesangium is of intrinsic glomerular cell origin. Mesangial thrombospondin may be an important mediator of cellular function, particularly in disease states characterized by intrinsic glomerular cell proliferation.

Sulfur dioxide (SO2) and sulfites are well-described causes of bronchoconstriction in persons with asthma that are chemically related and, therefore, may share a common mechanism of action. When either sulfur species dissolves in aqueous solutions, a pH-dependent equilibrium is established predominantly among bisulfite ion (HSO3-), sulfite ion (SO3=), and SO2. In addition, hydrogen ions may be released. To assess the relative bronchoconstricting potencies of these chemical forms and the role of acidity caused by the release of hydrogen ions in SO2- and sulfite-induced bronchoconstriction, we administered to 10 asthmatic subjects nebulized sodium sulfite (Na2SO3) solutions at pH 9 containing 95% sulfite, at pH 6.6 containing 80% bisulfite, and at pH 4 containing 99% bisulfite but greater than an order of magnitude more SO2 than the pH 6.6 solutions. Subjects inhaled increasing concentrations of aerosolized Na2SO3 at each pH during 1 min of tidal breathing. Subjects also breathed buffered acetic acid aerosols with the same acidity of the pH 4 Na2SO3 solutions to control for the airway effects of acid aerosols. To assess sensitivity to SO2 gas, subjects inhaled increasing concentrations of SO2 during eucapneic hyperpnea. Bronchoconstrictor response was assessed by measuring specific airway resistance (SRaw) before and after each challenge. Nine of the 10 subjects developed bronchoconstriction after inhaling the Na2SO3 aerosols at all 3 levels of pH and the SO2 gas. The mean concentration of Na2SO3 solution calculated to increase SRaw by 100% above baseline was significantly different (p less than 0.01) at the various levels of pH: pH 4 (0.17 mg/ml) less than pH 6.6 (0.49 mg/ml) less than pH 9 (2.10 mg/ml).(ABSTRACT TRUNCATED AT 250 WORDS)

We studied the relationship between duration and concentration of exposure in SO2-induced bronchoconstriction in 8 asthmatic subjects. On separate days, we administered SO2 in humidified air through a mouthpiece at 2 concentrations (0.5 and 1.0 ppm) for 3 time periods (1, 3, and 5 min) during eucapnic hyperpnea (60 L/min). Humidified air was administered for 5 min as a control. Bronchoconstriction was assessed by measurement of specific airway resistance (SRaw). The magnitude of the bronchoconstrictor response to both concentrations of SO2 increased progressively over the 3 time periods studied. The mean (+/- SE) increase in SRaw (in L x cm H2O/L/s) and percent increase above baseline (in parentheses) after each exposure to SO2 were as follows: 2.5 +/- 0.3 (34%) after 0.5 ppm for 1 min; 7.5 +/- 4.7 (93%) after 1.0 ppm for 1 min; 13 +/- 3.2 (173%) after 0.5 ppm for 3 min; 31.4 +/- 7.4 (395%) after 1.0 ppm for 3 min; 19.6 +/- 4.0 (234%) after 0.5 ppm for 5 min; 44.1 +/- 9.8 (580%) after 1.0 ppm for 5 min; 3.5 +/- 1.5 (46%) after humidified air for 5 min. For the group, the increases in SRaw caused by inhalation of both concentrations of SO2 for 1 min were small. However, 2 of 8 subjects did develop large increases in SRaw and chest tightness after inhalation of 1.0 ppm for 1 min. Seven of 8 subjects developed wheezing, chest tightness, or dyspnea and used an inhaled bronchodilator after inhalation of 0.5 ppm for 3 and 5 min and 1.0 ppm for 3 minutes.(ABSTRACT TRUNCATED AT 250 WORDS)

Administration of 3,5-dicarbethoxy-2,6-dimethyl-4-ethyl-1,4-dihydropyridine (DDEP) (a structural analog of the dihydropyridine Ca2+ antagonists) to untreated, phenobarbital-, or dexamethasone-pretreated rats results in time-dependent losses of hepatic cytochrome P-450 content. Functional markers for various cytochrome P-450 isozymes have permitted the identification of P-450h, P-450 PB-1/k, and P-450p as the isozymes inactivated preferentially by the drug. DDEP-mediated cytochrome P-450 destruction may be reproduced in vitro, is most prominent after pretreatment of rats with dexamethasone, pregnenolone 16 alpha-carbonitrile or phenobarbital, and is blocked by triacetyloleandomycin. These findings together with the observation that DDEP markedly inactivates hepatic 2 beta- and 6 beta-testosterone hydroxylase and erythromycin N-demethylase tend to indict the steroid-inducible P-450p isozyme as a key protagonist in this event. The precise mechanism of such DDEP-mediated P-450p heme destruction is unclear, but involves prosthetic heme alkylation of the apocytochrome at its active site in what appears to be a novel mechanism-based "suicide" inactivation. Such inactivation appears to involve fragmentation of the heme to reactive metabolites that irreversibly bind to the protein, but the chemical structure of the heme-protein adducts is yet to be established. Intriguingly, such DDEP-mediated P-450p destruction in vivo also results in accelerated loss of immunochemically detectable apocytochrome P-450p. It remains to be determined whether or not this loss is due to enhanced proteolysis triggered by the structural modification of the apocytochrome.