In vivo measurement of solute transport rates in a bioartificial organ.

A radioactive tracer technique was used to evaluate the in vivo mass transfer properties of a tissue engineered bioartificial organ. To obtain these measurements, bioartificial organs were first implanted in ten rats and allowed to vascularize for 4 weeks. After vascularization, radioactive inulin was placed within the cell chamber of the device. Following the addition of tracer, blood samples were taken over a 4-h time period and inulin levels were determined. The results of these experiments were interpreted using a compartmental model that describes the transport of inulin from the cell chamber, across the immunoisolation membrane, and into the neovascularized region contained within the adjacent scaffold material. Nonlinear regression analysis of the plasma inulin levels using a four-compartment pharmacokinetic model provided estimates of the membrane permeability, the product of the capillary wall surface area and capillary permeability, and the glomerular filtration rate (GFR). The permeability of the membrane was found to be 3.50 x 10(-5) +/- 1.15 x 10(-5) cm/sec (95% confidence interval, n = 10), which compares favorably to previous in vitro permeability data for this membrane. The capillary wall permeability was found to be 0. 0087 6 0.0029 cm(3)/sec/100 g of tissue. This compares well to a reported value for inulin of 0.01 cm(3)/sec/100 g of tissue. The GFR was found to be 0.44 +/- 0.07 ml/h/g BW, which compares well with a reported value of 0.40 ml/hr/g BW. The inulin tracer technique reported here is a useful tool for assessing the in vivo transport characteristics of a bioartificial organ as well as the vascularization within tissue engineered structures.

Invasive disease due to Haemophilus influenzae serotype f: clinical and epidemiologic characteristics in the H. influenzae serotype b vaccine era. The Haemophilus influenzae Study Group.

With the decline in the rate of infections caused by Haemophilus influenzae serotype b, H. influenzae serotype f (Hif) is becoming a relatively important cause of invasive disease due to H. influenzae. We identified 91 cases of invasive Hif infections in a multistate area over a 6-year period. The incidence of invasive Hif disease was 0.5 case per 1,000,000 population in 1989 and 1.9 cases per 1,000,000 population in 1994. The proportion of all invasive H. influenzae disease caused by Hif rose from 1% in 1989 to 17% in 1994. Seventy-two percent of cases occurred in adults, and 26% of cases occurred in children younger than 5 years of age. Respiratory tract infections accounted for 82% of adult cases, and most adults had significant underlying diseases. In children, pneumonia and meningitis each accounted for 40% of cases, respectively. Overall mortality was 30% among adults, and 21% among children. Molecular typing demonstrated limited overall diversity in Hif isolates. Continued surveillance is warranted to evaluate the trend toward the increasing incidence of Hif disease that was noted in this study.

Effects of pH and thiols on the kinetics of yeast glyoxalase I. An evaluation of the random pathway mechanism.

The disproportionation of alpha-ketoaldehydes, catalyzed by yeast glyoxalase I, has been reported to involve a random pathway mechanism where one branch utilizes the hemimercaptal of glutathione and the alpha-ketoaldehyde in a one-substrate pathway, and the other branch utilizes first glutathione and then the alpha-ketoaldehyde in an ordered two-substrate pathway. The relative importance of the two pathways has been evaluated at 5 degrees in the pH range 3-7, using methylglyoxal and phenylglyoxal as representative aliphatic and aromatic alpha-ketoaldehydes, by comparing initial rates of hemimercaptal formation in the absence of enzyme with initial rates of product formation in the presence of high enzyme concentrations. If the enzyme is not added last, the initial rates of product formation are the same as the initial rates of adduct formation even under conditions where it could be shown that dehydration of the hydrated alpha-ketoaldehyde is not entirely rate determining. If the enzyme is added after hemimercaptal formation, there is a "burst" of product formation equivalent to the amount of hemimercaptal, followed by a slower reaction, consistent with the one-substrate pathway. Additional support for this pathway was obtained from a study of the effects of added thiol reagents on the "burst" kinetics. The broad specificity of yeast glyoxalase I for both aliphatic and aromatic alpha-ketoaldehydes, reflected in Vmax values which are insensitive to the nature of the alpha-ketoaldehyde drops abruptly if the side chain of the alpha-ketoaldehyde is sterically crowded. The hemimercaptal of tert-butylglyoxal has a Vmax 300-fold smaller than Vmax for methylglyoxal; 2,4,6-trimethylphenylglyoxal is essentially inactive as a substrate even though the closely related compound 2,4-dimethylphenylglyoxal is a normal substrate. Analysis of the Vmax and Km (or Ki) values of these alpha-ketoaldehydes suggests that sterically crowded side chains affect both enzyme-substrate formation and the catalytic reaction.