Green fluorescent protein rendered susceptible to proteolysis: positions for protease-sensitive insertions.

The green fluorescent protein (GFP) is highly resistant to proteolysis and remains uncleaved after prolonged incubation with trypsin or pronase despite several putative tryptic and chymotryptic sites in exposed loops. We have rendered GFP sensitive to proteolysis by inserting five amino acids, IEGRS, in loops at position 157, 172, or 189. Excitation and emission maxima of the three insertion mutants were similar to those of wild type, but quantum yields of mutants Omega172 and Omega189 were lower, indicating increased freedom of the fluorophore. Trypsin cleaved the native (folded) form of each mutant at a unique site defined by the insert. Pronase also yields similar digestion patterns in these variants, but further proteolysis was also observed, suggesting that the primary cleavage relaxes GFP structure and reveals previously inaccessible sites. Fluorescence of Omega189 changed little upon digestion with trypsin but decreased progressively by as much as 40% upon digestion with increasing amounts of pronase. Fluorescence of other variants was not affected significantly by the proteases, further confirming the remarkable stabilities of GFP variants. These constructs define a new conformation-sensitive site around residue 189 of GFP and show that GFP may be useful for design of protease-susceptible molecules for monitoring of specific proteolytic activities in vivo.

Chronic inhalation exposure of rats to nitromethane.

Male and female Long-Evans rats were housed in inhalation chambers and exposed to vapors of nitromethane (NM) at either 100 or 200 ppm. The animals were exposed 7 hr per day, 5 days per week for 2 years. Control groups of rats were also housed in a similar inhalation chamber, but NM was not introduced into the chamber. The animals were observed daily for signs of pharmacologic or toxicologic effect and body weights were recorded periodically. At the 2-year termination of the exposure period, clinical laboratory examinations (serum chemistry and hematology) were performed on selected animals and all surviving animals were sacrificed. All animals were necropsied and subjected to a thorough histopathologic examination. During the study there were no pharmacologic effects from exposure to NM at either 100 or 200 ppm. There was no effect on mortality on either sex at either exposure level. Body weights of male rats exposed to NM were not significantly different from those of control rats, but the body weights of female rats of both exposure groups were slightly less than their controls. There was no effect of exposure of rats of either sex to either level of NM on hematology. There were no clinically significant effects on serum chemistry. There were no effects of exposure to NM on organ weights. There were no significant differences in the nonneoplastic or neoplastic pathology related to exposure to NM.

Hypouricemic effect of allopurinol and the novel xanthine oxidase inhibitor TEI-6720 in chimpanzees.

The hypouricemic effect of a newly synthesized xanthine oxidase/xanthine dehydrogenase inhibitor, TEI-6720, 2-(3-cyano-4-isobutoxyphenyl)-4-methyl-5-thiazolecarboxylic acid, was investigated and compared with that of allopurinol in male chimpanzees (n = 3). When allopurinol (10 mg/kg) was administered orally once a day for three consecutive days, it cumulatively reduced serum urate levels by 29.7, 50.1 and 60.2%, 24, 48 and 72 h, respectively, after the initial dose. This effect was dose dependent at doses of 3 and 10 mg/kg. At 3 mg/kg, the mean serum urate levels were 3.1, 2.4, 2.5 and 2.3 mg/dl before and 24, 48 and 72 h, respectively, after the initial dose. Animals treated with 10 mg/kg of allopurinol showed serum urate levels of 3.3, 2.3, 1.6 and 1.3 mg/dl, respectively. The urate-lowering effect of TEI-6720 was then compared with that of allopurinol at a daily dose of 5 mg/kg (n = 3). Both compounds caused striking reductions in serum and urinary uric acid levels accompanied by an increase in urinary xanthine levels. These effects of TEI-6720 were more potent than those of allopurinol. TEI-6720 reduced serum urate levels by 55.9, 69.6 and 73.6%, 24, 48 and 72 h, respectively, after the first dose, whereas the corresponding values after allopurinol were 28.1, 41.6 and 45.1%. These results suggest that the hypouricemic effect of TEI-6720 may be more potent than that of allopurinol in the treatment of hyperuricemia and gout, and that TEI-6720 may become an effective alternative drug.

Chronic inhalation exposure of rats to vapors of nitroethane.

Male and female Long-Evans rats were exposed in inhalation chambers to vapors of nitroethane at concentrations of 100 or 200 ppm, 7 hr per day, 5 days per week for 2 years. During the study, general observations were made daily and body weights were obtained weekly for the first 6 months of the study and biweekly thereafter. Any rats that were found dead or sacrificed moribund during the 2-year exposure phase of the study were given a thorough gross examination and tissues were retained for microscopic examination. After 2 years of inhalation of nitroethane, all surviving rats were sacrificed and subjected to the same thorough gross examination. Blood samples were obtained from representative groups of animals for hematology and serum chemistry studies. All rats were examined histopathologically. Exposure of the rats to nitroethane had no pharmacologic effects nor were there any effects on mortality of rats of either sex at either level of exposure. Throughout most of the investigation, body weights of both sexes of both exposed groups were slightly less than those of respective controls, but lack of a well-defined dose-response relationship suggested the involvement of factors other than just exposure to nitroethane. There were no effects of exposure to nitroethane on hematology nor were there any biologically significant effects of exposure to nitroethane on clinical chemistry or on organ weights. No significant nonneoplastic or neoplastic pathology was found as a consequence of exposure of the rats to nitroethane.

Persistence of impaired heat tolerance from artificially induced miliaria rubra.

Ten volunteers were heat acclimatized to 48.9 degrees C (Ta), 20% rh for 7 days to complete a 100-min walk on a level treadmill (1.56 m x s-1). Subjects were then divided into experimental (n = 6) and control (n = 4) groups. Miliaria rubra (heat rash) was then induced on the experimental subjects by wrapping them for 3 days in polyethylene plastic. All six developed marked miliaria with involvement of 40-70% of the total body surface area. All subjects were reexposed to walking in the heat on the 7th day after unwrapping, by which time rash was clinically indetectable, and again 14 days after unwrapping. On the first test (day 7) only one of the rashed group, and on the second test (day 14) only two could complete the 100-min walk; the control group finished without difficulty on both days. Body heat storage for the rash group was 2.5 times that of the control group on day 7 and 1.5 as great on day 14; measurements of mean body temperature (Tb) on the rash group indicated a much greater heat stress when compared to their own prerash-acclimatized values or those of the control group. These data demonstrate the potential of "healed" miliaria in the etiology of clinical heat illness.

Heat intolerance as a function of percent of body surface involved with miliaria rubra.

Twenty-four heat-acclimatized male volunteers were wrapped as previously described (Am. J. Physiol. 239 (Regulatory Integrative Comp. Physiol. 8): R226-R232, 1980) but to produce miliaria rubra (heat rash) in specific regions of the body. Three experimental rash groups were involved: 1) the torso (17% total skin surface rashed, n = 6), 2) torso and arms (38%, n = 8), or 3) legs (41%, n = 6), while four subjects served as controls. All subjects were reexposed to walking in the heat on the 7th day after unwrapping, and again 14, 21, and 28 days after unwrapping. When compared to responses for the last heat acclimatization day, tolerance time and sweat rate were lower and mean body temperature and delta heat storage significantly higher for experimental rash subjects contrasted to the controls for up to 21 days; however, no significant differences between the three rashed groups were found. The critical amount of surface area for heat intolerance from heat rash appears to be related to the specific region of the body and associated sweating responses; smaller rashed areas of the trunk, because they have greater potential for abundant sweating, may produce similar responses to heat stress as larger rashed areas of the limbs. Heat intolerance due to rash was not resolved until after 21 days.

Biologic effects of airborne particulate lead on continuously exposed rats and rhesus monkeys.

The biological effects of airborne particulate lead were studied in rats and rhesus monkeys (Macaca mulatta) exposed nearly continuously (22 hours per day) at a concentration of 21.5 mug Pb/cubic meter of air. The year-long exposure elicited an increase in the concentration of lead in the blood to 28 mug/100 ml in the rats and 17 mug/100 ml in the monkeys. Levels of lead in control animals were about 5 mug/100 and 4 mug/100 ml, respectively, in the rats and monkeys. The elevated blood-lead levels reached a maximum during the first few months of exposure and did not increase significantly after that time. Elevated concentrations of lead were also detected in lung, liver, kidney and bone of both species. While concentrations of lead were nearly always less than 1 mug/g in control animals, they rose to 2-3 mug/g in soft tissues of exposed animals and up to 6 mug/g in bone. Differences between lead levels in animals exposed six months or twelve months were very small. The concentration of lead decreased in the soft tissues of animals removed from the chamber after one year's exposure but remained elevated in bone. The activity of the enzyme delta-amino-levulinic acid dehydrase (ALAD) in circulating erythrocytes was inhibited about 70% in rats exposed to the airborne lead. No reduction of the enzyme activity occurred in brain or liver tissue of either the rats or monkeys. Normal levels of ALAD in erythrocytes of the monkeys were too low to permit meaningful measurements. In spite of the reduced ALAD activity in rat erythrocytes, there was no concomitant alteration in the excretion of heme precursors. In all other respects, there appeared to be no deleterious effects on the animals from exposure to the airborne particulate lead. No changes were detected in serum chemistry or hematology nor were there any gross, microscopic or ultrastructural pathologic changes observed.

Clinical studies on men continuously exposed to airborne particulate lead.

Two experiments were conducted to determine the effects of low-level exposure to airborne lead particulates on humans. Male volunteers were exposed 23 hours per day for about 18 weeks to either 10.9 mug Pb/m3 or 3.2 mug Pb/m3 of air. The particulate matter consisted primarily of sub-micron sized particles of alpha lead dioxide. During exposure to 10.9 mug Pb/m3, the mean blood-lead level of the men increased to 37 mug/100 ml while the level in controls remained at about 15 mug/100 ml. Exposure to 3.2 mug Pb/m3 elicited an increase in blood-lead to about 27 mug/100 ml. In both cases, the blood-lead levels appeared to plateau after about three months of exposure and subsequent to that, no further increases were observed. About two months after the men left the exposure chamber, their blood-leads returned to near normal levels. Although urinary excretion of lead was always within the limits usually considered normal, there was a definite increase in urinary lead in the men exposed to 10.9 mug Pb/m3 and a somewhat smaller increase in the men exposed to 3.2 mug Pb/m3. The activity of delta-aminolevulinic acid dehydrase was reduced by about 50% in the erythrocytes of men exposed to 10.9 mug Pb/m3, but returned to normal after exposure was terminated. Practically no changes in the activity of the enzyme were noted in the men exposed to 3.2 mug Pb/m3. Exposure to either level of particulate lead did not cause measurable changes in the excretion of heme precursors nor were there any alterations of serum chemistry or hematology profiles in any of the men.