Putative contributors to the secular increase in obesity: exploring the roads less traveled

OBJECTIVE

To investigate plausible contributors to the obesity epidemic beyond the two most commonly suggested factors, reduced physical activity and food marketing practices.

DESIGN

A narrative review of data and published materials that provide evidence of the role of additional putative factors in contributing to the increasing prevalence of obesity.

DATA

Information was drawn from ecological and epidemiological studies of humans, animal studies and studies addressing physiological mechanisms, when available.

RESULTS

For at least 10 putative additional explanations for the increased prevalence of obesity over the recent decades, we found supportive (although not conclusive) evidence that in many cases is as compelling as the evidence for more commonly discussed putative explanations.

CONCLUSION

Undue attention has been devoted to reduced physical activity and food marketing practices as postulated causes for increases in the prevalence of obesity, leading to neglect of other plausible mechanisms and well-intentioned, but potentially ill-founded proposals for reducing obesity rates.

Measuring the genetic influence in modulating the human life span: gene-environment interaction and the sex-specific genetic effect

New approaches are needed to explore the different ways in which genes affect the human life span. One needs to assess the genetic effects themselves, as well as gene-environment interactions and sex dependency. In this paper, we present a new model that combines both genotypic and demographic information in the estimation of the genetic influence on life spans. Based on Cox's proportional hazard assumption, the model measures the risks for each gene as well as for gene-environment and gene-sex interactions, while controlling for confounding factors. A two-step MLE is introduced to obtain a non-parametric form of the baseline hazard function. The model is applied to genotypic data from Italian centenarian studies to estimate relative risks of candidate genes, risks due to interactions and initial frequencies of different genes in the population. Results from models that either do or do not take into consideration individual heterogeneity are compared. It is shown that ignoring the existence of heterogeneity can lead to a systematic underestimation of genetic effects and effects due to interactions.

Enhancement of bone growth by sustained delivery of recombinant human bone morphogenetic protein-2 in a polymeric matrix

PURPOSE

The purpose of this study was to develop a polymeric sustained delivery system for recombinant human bone morphogenetic protein-2 (BMP-2) and to evaluate local bone growth induced by the sustained release of BMP-2 in an animal model.

METHODS

BMP-2 was incorporated in biodegradable poly(D,L-lactide-co-glycolide) (PLGA) microspheres to obtain different release rates. Two sustained and an immediate release implants were produced by suspending the BMP-2 loaded PLGA microspheres in aqueous sodium carboxymethylcellulose (CMC), lyophilizing, and cutting the dried materials to the size of the animal bone defects. The local in vivo release at the implantation site in rat calvarial defects was determined by gamma scintigraphy using radiolabeled BMP-2. The local bone induction in the critical size of rabbit calvarial defects was evaluated six weeks post implantation.

RESULTS

The immediate release implant showed about 65% initial drug release within 24 h and the remaining BMP-2 quickly exhausted from the implantation site within 7 days. The sustained release implants, showing 45-55% initial release followed by a prolonged release for 21 days, released a greater amount of BMP-2 at the implantation site and maintained higher serum BMP-2 for the longer period of time compared to the immediate release implant. Significant bone growth was observed in all BMP-2 treated defects while the defects without treatment or with BMP-2-free implant showed minimal bone healing. 75-79% of rabbit calvarial defect area was healed with newly induced bone matrix by the sustained release implants in 6 weeks as compared to 45% recovery from the immediate release implant.

CONCLUSION

The sustained delivery of BMP-2 based on the biodegradable PLGA microsphere system resulted in faster and more complete bone healing in the animal model.

Hypertrophic cardiomyopathy. Tools for identifying risk and alleviating symptoms

Hypertrophic cardiomyopathy is characterized by left or right ventricular hypertrophy that is usually asymmetric and involves the interventricular septum. The condition has numerous genetic, anatomic, and clinical variations and continues to stimulate interest and investigation into causes and treatment options. New genetic forms of the disorder are being identified because of the rapid growth of molecular genetics. However, even with technological advances and a large database of information, risk stratification and treatment of hypertrophic cardiomyopathy remain difficult and controversial. Because of the high risk of sudden death, it is imperative that patients be advised against participation in competitive sports.

Genes, demography, and life span: the contribution of demographic data in genetic studies on aging and longevity

In population studies on aging, the data on genetic markers are often collected for individuals from different age groups. The purpose of such studies is to identify, by comparison of the frequencies of selected genotypes, "longevity" or "frailty" genes in the oldest and in younger groups of individuals. To address questions about more-complicated aspects of genetic influence on longevity, additional information must be used. In this article, we show that the use of demographic information, together with data on genetic markers, allows us to calculate hazard rates, relative risks, and survival functions for respective genes or genotypes. New methods of combining genetic and demographic information are discussed. These methods are tested on simulated data and then are applied to the analysis of data on genetic markers for two haplogroups of human mtDNA. The approaches suggested in this article provide a powerful tool for analyzing the influence of candidate genes on longevity and survival. We also show how factors such as changes in the initial frequencies of candidate genes in subsequent cohorts, or secular trends in cohort mortality, may influence the results of an analysis.

Posterior chamber phakic intraocular lens for hyperopia

PURPOSE

A Phase I U.S. FDA clinical study of a plate haptic posterior chamber phakic intraocular lens (STAAR Surgical Implantable Contact Lens) for treatment of hyperopia was conducted at 4 sites in the United States. The purpose of this report is to assess the short-term safety and efficacy.

METHODS

Ten patients with hyperopia between +2.50 and +10.875 D were implanted in one eye each with the posterior chamber plate phakic intraocular lens and were examined at baseline and 1 day, 1 week, 1, 3, and 6 months after surgery. Mean baseline hyperopia was +6.63 D.

RESULTS

At 6 months postoperatively, 7 of 10 eyes (70%) had an uncorrected visual acuity of 20/20 or better and 10 of 10 (100%) had 20/40 or better. Eight of ten eyes (80%) had a spectacle-corrected visual acuity within 1 line of baseline; the other two eyes (20%) had an improvement of 3 lines. Mean 6-month postoperative spherical equivalent refraction was +0.20 +/- 0.61D (range, -0.50 to +1.50 D), a reduction of 6.025 D from baseline. Eight of 10 eyes (80%) were within +/-0.50 D of emmetropia, 9 eyes (90%) were within +/-1.00 D, and all eyes (100%) were within +/-1.50 D. No operative or postoperative complications or adverse reactions were observed.

CONCLUSIONS

Results support the short-term safety, efficacy, and predictability of the STAAR Surgical Implantable Contact Lens (plate haptic posterior chamber phakic intraocular lens) in the treatment of hyperopia.

Contrast limited adaptive histogram equalization image processing to improve the detection of simulated spiculations in dense mammograms

The purpose of this project was to determine whether Contrast Limited Adaptive Histogram Equalization (CLAHE) improves detection of simulated spiculations in dense mammograms. Lines simulating the appearance of spiculations, a common marker of malignancy when visualized with masses, were embedded in dense mammograms digitized at 50 micron pixels, 12 bits deep. Film images with no CLAHE applied were compared to film images with nine different combinations of clip levels and region sizes applied. A simulated spiculation was embedded in a background of dense breast tissue, with the orientation of the spiculation varied. The key variables involved in each trial included the orientation of the spiculation, contrast level of the spiculation and the CLAHE settings applied to the image. Combining the 10 CLAHE conditions, 4 contrast levels and 4 orientations gave 160 combinations. The trials were constructed by pairing 160 combinations of key variables with 40 backgrounds. Twenty student observers were asked to detect the orientation of the spiculation in the image. There was a statistically significant improvement in detection performance for spiculations with CLAHE over unenhanced images when the region size was set at 32 with a clip level of 2, and when the region size was set at 32 with a clip level of 4. The selected CLAHE settings should be tested in the clinic with digital mammograms to determine whether detection of spiculations associated with masses detected at mammography can be improved.

Implantable contact lens for moderate to high myopia: phase 1 FDA clinical study with 6 month follow-up

PURPOSE

To assess the short-term safety and efficacy of the implantable contact lens (ICL) to treat moderate to high myopia.

SETTING

Phase 1 U.S. Food and Drug Administration clinical study of the ICL conducted at four sites in the United States.

METHODS

Ten patients with myopia of 7.00 diopters (D) or greater had implantation of a Staar Surgical ICL and were examined preoperatively (baseline) and 1 day, 1 week, and 1, 3, and 6 months postoperatively. Mean preoperative myopia was 7.75 D (range 7.25 to 9.37 D).

RESULTS

Six months postoperatively, 5 of 10 eyes (50%) had an uncorrected visual acuity (UCVA) of 20/20 or better, and all eyes had a UCVA of 20/30 or better. All eyes had a best spectacle-corrected visual acuity (BSCVA) of 20/20 or better and 6 eyes (60%), of 20/15 or better. Six eyes (60%) had an improvement of one or more lines of BSCVA. Mean postoperative spherical equivalent was -0.025 D +/- 0.47 (SD). Eight eyes (80%) were within +/- 0.250 D of emmetropia, and all were within +/- 1.125 D. No intraoperative or postoperative complications or adverse reactions were observed.

CONCLUSIONS

The results support the short-term safety, efficacy, and predictability of ICL implantation to treat moderate to high myopia.

Does intensity windowing improve the detection of simulated calcifications in dense mammograms?

This study attempts to determine whether intensity windowing (IW) improves detection of simulated calcifications in dense mammograms. Clusters of five simulated calcifications were embedded in dense mammograms digitized at 50-microns pixels, 12 bits deep. Film images with no windowing applied were compared with film images with nine different window widths and levels applied. A simulated cluster was embedded in a realistic background of dense breast tissue, with the position of the cluster varied. The key variables involved in each trial included the position of the cluster, contrast level of the cluster, and the IW settings applied to the image. Combining the ten IW conditions, four contrast levels and four quadrant positions gave 160 combinations. The trials were constructed by pairing 160 combinations of key variables with 160 backgrounds. The entire experiment consisted of 800 trials. Twenty student observers were asked to detect the quadrant of the image in which the mass was located. There was a statistically significant improvement in detection performance for clusters of calcifications when the window width was set at 1024 with a level of 3328, and when the window width was set at 1024 with a level of 3456. The selected IW settings should be tested in the clinic with digital mammograms to determine whether calcification detection performance can be improved.

Ablation zone centration after photorefractive keratectomy and its effect on visual outcome

PURPOSE

To determine the relation between ablation zone decentration, measured by corneal topography, and visual and refractive outcome, contrast sensitivity, glare, and subjective reports of halos after photorefractive keratectomy (PRK).

SETTING

Eye Foundation, University of Missouri-Kansas City School of Medicine.

METHODS

This study comprised 70 eyes of 70 patients enrolled into Phase III of the clinical investigation of the VISX 20/20 excimer laser for the correction by PRK of 1.00 to 6.00 diopters of pre-existing sphere. All patients were treated with 5.0 mm ablation zones. Preoperative and postoperative corneal topography in 67 eyes was done using the EyeSys system. Ablation zone decentration was measured relative to the pupillary center at all postoperative visits as determined from the difference or change map.

RESULTS

Mean distance between the ablation zone center and the pupillary center was 0.62 mm +/- 0.34 (SD) (range 0.07 to 1.67 mm). Twenty seven of 66 patients with corneal topography (40.9%) had decentrations less than 0.5 mm; decentrations in 6 eyes (9.1%) were 1.0 mm or more from the pupillary center. No correlation was observed between the magnitude of decentration and 1 year postoperative best spectacle-corrected acuity (r = -.04, P = .76), uncorrected acuity (r = -.03, P = .84), or spherical equivalent (r = -.07, P = .59); preoperative uncorrected acuity (r = .04, P = .73) or spherical equivalent (r = -.02, P = .90); or reduction in spherical equivalent (r = .02, P = .89). The magnitude of decentration was correlated with preoperative spectacle-corrected acuity (r = -.37, P = .002). There was no difference in contrast sensitivity, glare, or halos between the cases with less than 0.5 mm of decentration and those with 0.5 mm or more of decentration.

CONCLUSIONS

The degree of ablation zone decentration did not affect postoperative Snellen visual acuity or contrast sensitivity.

Evaluation of a medical ethics consultation service: opinions of patients and health care providers

PURPOSE

To study the perceived effectiveness of bioethics consultation as evaluated by both professional staff and patients and their families.

PATIENTS AND METHODS

An evaluation questionnaire was forwarded to physicians, nurses and patients or family members who were associated with 20 sequential cases referred for ethics consultation during a 2-year period. Respondents were asked to rate the consult as very helpful, somewhat helpful, or not helpful concerning a variety of issues related to the care of the patients. Responses were reviewed for agreement or disagreement between the three sample groups.

RESULTS

Ninety-six percent of physicians and 95% of nurses sampled felt that the consult was helpful, compared with only 65% of the patient/family responses. Lack of communication between patients and staff was cited as a problem in all cases in which the consult was deemed unhelpful by patients and family.

CONCLUSIONS

Patients or family members and professional staff have different perceptions regarding the value of bioethics consultation. When asked for comments, patients/family members cite lack of communication with professional staff as their primary reason for responding negatively. Earlier mobilization of consultative staff, rigorous training of consultants in techniques of conflict resolution, and education of primary caregivers regarding recognition of communication problems may serve to narrow this perceptual divergence.

Efficacy and safety of excimer laser photorefractive keratectomy and radial keratotomy for bilateral myopia

PURPOSE

To compare the safety and efficacy of radial keratotomy (RK) and photorefractive keratectomy (PRK) to correct myopia.

METHODS

In this randomized, prospective, parallel-group study, 33 patients with bilateral myopia of 1.00 to 5.00 diopters (D) had PRK in one eye and RK in the other. The order of surgeries and treatment assignments were randomized, and the bilateral surgeries were within 1 week for each patient. Data were collected using standardized procedures. Clinical measurements and satisfaction surveys were taken in masked fashion.

RESULTS

Eyes that had PRK had statistically significantly more residual myopia than RK-treated eyes at 3, 6, and 12 months postoperatively. This result was attributed to the use of an older excimer laser PRK algorithm that was used at the initiation of the study. No eye that had PRK was overcorrected by 0.50 D or more at 1 year postoperatively, while seven eyes that had RK were overcorrected by at least 0.50 D and six were overcorrected by 1.00 D. Eyes that had PRK had a statistically significant mean shift in the myopic direction between 6 and 12 months postoperatively; two RK eyes had hyperopic shifts of 1.00 D. Three RK eyes and two PRK eyes failed to achieve an uncorrected visual acuity of 20/40 or better by 12 months postoperatively. No eye lost any best corrected visual acuity.

CONCLUSION

The two procedures were comparably safe and effective in treating mild to moderate myopia under this protocol. Eyes that had PRK were somewhat more myopic at 1 year after surgery, attributable to the older PRK ablation algorithm. Adoption of newer (current) laser algorithms has improved the predictability of PRK. There was also evidence of reduced variability of outcome in the PRK group. The PRK eyes did not exhibit hyperopic shifts during the 1 year follow-up.

Small incision surgery with the STAAR Elastimide three-piece posterior chamber intraocular lens

One hundred twelve patients scheduled for uncomplicated cataract removal were randomly assigned to receive a STAAR Elastimide three-piece foldable intraocular lens inserted through a 4.0 mm incision or a STAAR poly(methyl methacrylate) (PMMA) lens inserted through a 7.0 mm incision. The same surgeon performed all surgeries using identical techniques, except for incision size and number of sutures. Patients receiving Elastimide lenses had significantly better uncorrected visual acuity postoperatively than patients receiving PMMA lenses and also had significantly less keratometric cylinder, surgically induced cylinder (vector method), and refractive cylinder. The Elastimide foldable lens offers the advantages of small incision surgery for patients who require a three-piece lens.

Long-term (5- to 12-year) follow-up of metal-blade radial keratotomy procedures

OBJECTIVE

To evaluate the long-term stability of the refractive outcome after metal-blade radial keratotomy procedures.

DESIGN

A cohort of 146 patients who underwent 225 consecutive metal-blade radial keratotomy procedures that were performed under a uniform protocol between November 1979 and August 1981 was monitored prospectively, with 64% of the patients followed up for at least 5 years.

MAIN OUTCOME MEASURES

Changes in spherical equivalent and changes in average keratometry were evaluated within the following periods: 3 months to 1 year; 1 to 2 years; 2 to between 3 and 4 years (mean, 3.7 years); between 3 and 4 (mean, 3.7 years) to between 5 and 12 years (mean, 8.5 years); and 1 to between 5 and 12 years (mean, 8.5 years).

RESULTS

Total mean change in refraction between 1 year and the average of 8.5 years of follow-up was 1.01 diopters (D) (SD, 1.13 D). At 1 year, 31% of the cases were at least 1 D hyperopic, whereas at an average of 8.5 years, 48% were at least 1 D hyperopic. Fifty-four percent of the cases had shifted in the hyperopic direction by 1 D or more. Stepwise regression analysis failed to identify significant predictive factors for the hyperopic shifts.

CONCLUSIONS

The trend toward progressive hyperopic shifts within this cohort has continued with time. Other long-term studies have documented similar, although somewhat smaller, hyperopic shifts among both patients treated with metal-blade and patients treated with diamond-blade procedures. Causative factors for the hyperopic shift have not been identified. It remains to be seen if eyes undergoing current, more cautious surgical approaches to radial keratotomy will also experience this phenomenon.

Changing practice patterns in refractive surgery: results of a survey of the American Society of Cataract and Refractive Surgery

A questionnaire on refractive surgical practice was sent to the entire membership of the American Society of Cataract and Refractive Surgery in 1992. One thousand eight hundred and forty-one (1,841) of the 4,950 members returned the survey for a response rate of 37.2%. The questionnaire was designed to be self-administered and elicited information on types of refractive procedures performed in the survey year and the preceding year, as well as the intent to perform refractive procedures in the future. Surgeons who perform radial keratotomy (RK) increased from 22% in 1991 to 30% in 1992; 45% expected to perform RK in 1993-1994. The following categories of information were requested: characteristics of RK patients, techniques used by the surgeon, characteristics of the surgeon's overall practice, type of RK training, surgical outcome, and prevalence of complications. The results of this survey indicate that the use of RK and astigmatic keratotomy (AK), as well as other refractive procedures, is steadily increasing. Radial keratotomy was mainly performed on patients 20 to 49 years of age who had low to moderate myopia. The majority of surgeons used four to eight radials, centrally directed incisions, and single depth settings. Three quarters of the surveyed RK surgeons used the Casebeer nomogram. The survey results indicated that 42% of surgeons performing photorefractive keratectomy (PRK) did not perform RK or other refractive procedures, suggesting that growth in the practice of PRK following FDA approval may come from both current RK surgeons and novice refractive surgeons.

Implantation in children

With the development of posterior chamber lenses and continuous curvilinear capsulorhexis, and with the availability of viscoelastic agents, the use of intraocular lenses (IOLs) in children is becoming more popular. Since 1982, we have implanted posterior chamber IOLs (PC-IOLs) in the capsular bags of 61 cataractous eyes of 46 children and adolescents. The goal was in-the-bag placement facilitated by the use of a small capsulectomy, and, since 1984, by the use of the continuous curvilinear capsulorhexis. Forty-four cataracts were congenital, 13 were traumatic, and 4 were developmental. Cataract extraction with IOL implantation was performed in 16 (26%) preschool cases (ages 2 through 5), in 31 (51%) child cases (ages 6 through 12), and 14 (23%) adolescent cases (ages 13 through 18). Surgical and postoperative complications were minimal. Visual results were good. Fifty-six percent of preschoolers, 87% of children, and 86% of adolescents achieved 20/40 or better best corrected vision, with 79% of the total cohort achieving 20/40 or better. Overall, 35% achieved an uncorrected visual acuity of 20/40 or better. All but two cases had improvement in best corrected vision; if 20/20 was not attained, the cause was mainly due to deprivation amblyopia. Forty-eight percent of patients were within a diopter of emmetropia.

Effect of a superficial and a deep scleral pocket incision on the incidence of hyphema

Deep tunnel scleral pocket incisions were developed to control surgically induced astigmatism following cataract and intraocular lens implantation surgery. A more superficial, shallow scleral pocket incision was developed to reduce the rate of postoperative hyphema. To test its effectiveness, a randomized prospective clinical study was performed. One hundred twenty-nine eyes of 129 patients were randomized: 66 to receive a deep tunnel pocket and 63 to receive the superficial pocket. In both groups the incision was made 3 mm posterior to the limbus. For the deep pocket cases, a blade setting of 0.27 mm was used and the wound was dissected forward toward the entry site, creating a long, deep, narrow tunnel. For the superficial wound cases, a 0.17 mm blade setting was used and the entire wound was dissected to the edge of the anatomic limbus, creating a thin scleral flap. The left side was then fanned out toward the left with the entry site slightly into clear cornea. At one day after surgery, 22 cases (34%) in the deep pocket group and four cases (6%) in the superficial pocket group had hyphemas. The difference in hyphema rates was statistically significant (P less than .001).

Effect of posterior chamber intraocular lens design and surgical placement on postoperative outcome

Intraocular lens (IOL) design, optical configuration, and placement have potential effects on postoperative outcome. Laboratory studies have suggested that one-piece, biconvex designs may reduce or delay posterior capsular opacification and that in-the-bag fixation of the posterior chamber IOL may reduce inflammation. To document the clinical significance of IOL design and placement, we conducted a randomized, prospective, clinical trial. Six hundred uncomplicated capsulorhexis and phacoemulsification patients were randomized in a three-factor design to receive an IOL that was one-piece or three-piece, had a biconvex, plano-convex, or laser ridge optic, and was bag-or sulcus-fixated. Treatment differences were related to lens placement. Patients with bag-fixated IOLs had less posterior capsular opacification, fewer YAG laser capsulotomies, a higher percentage of centered lenses, less inflammation, and fewer late posterior capsular striae than those with sulcus-fixated IOLs. In the latter group, patients with three-piece IOLs had fewer posterior capsular striae at three months postoperatively. All six occurrences of haptic loop distortion were in patients with three-piece IOLs. Patients with the one-piece design had less late inflammation than those with the three-piece design. Fewer YAG capsulotomies were necessary at one year in patients with the biconvex design than in those with the plano-convex or laser ridge configurations. Operative complications, endothelial cell loss, and postoperative complications were not IOL-related.

Multifocal versus monofocal intraocular lenses. Visual and refractive comparisons

In a unilateral prospective clinical trial, 77 cases were randomized to receive a 3M multifocal IOL or a conventional monofocal implant. Multifocal cases had better uncorrected near vision than monofocal cases at the two to four month visit. Thirty percent of the multifocal cases had near acuity J1, while only 4% of the monofocal cases had that acuity. Eighty-seven percent of multifocal cases and 71% of monofocal cases had near acuities of J1 to J3. With distance correction in place, 54% of multifocal cases had near acuities of J1 to J2, while only 28% of monofocal cases had comparable acuities (P = .04). There have been no serious postoperative complications in either group.

Effect of suture material on postoperative astigmatism

Two hundred patients were enrolled in a randomized, prospective clinical trial comparing the use of 10-0 nylon, 10-0 polypropylene (Prolene), 11-0 polyester (Mersilene), and 10-0 polyethylene (Novafil) suture materials on the amount and decay curves of surgically induced astigmatism following intraocular lens (IOL) surgery. Patients with Mersilene and nylon sutures had the highest amounts of induced with-the-rule (WTR) cylinder (significantly more than Prolene) at one day after surgery. However, the WTR cylinder decayed rapidly for nylon during the first three months but more slowly for Mersilene because of its lack of stretchability. The Prolene group had the lowest level of induced WTR cylinder at one day, but against-the-rule (ATR) drift occurred, leaving cases with ATR astigmatism by a year. The nylon group had the second highest amount of induced WTR cylinder at one day, which had decayed to ATR cylinder by five months. Between one and two years postoperatively, the nylon group experienced a significant ATR shift. The amount of early induced WTR cylinder seemed to be related to the knot-tying technique and tissue gripping characteristics, whereas the shape of the decay curve was related to the material characteristics of the suture.

Effect of small incision intraocular lens surgery on postoperative inflammation and astigmatism. A study of the AMO SI-18NB small incision lens

A single center, single surgeon, randomized, prospective clinical trial was performed comparing the effectiveness of small (3.5 mm to 4.0 mm) incision intraocular lens surgery and a larger (6.0 mm) incision in improving uncorrected visual acuity and reducing post-operative inflammation and surgically induced astigmatism. One hundred twelve eligible unilateral cases were randomized to receive a 3.5 mm to 4.0 mm incision with implantation of an Allergan Medical Optics three-piece SI-18NB silicone lens (56 cases) or a 6.0 mm incision with implantation of a three-piece biconvex poly(methyl methacrylate) lens (56 cases). At one day after surgery, significantly (P less than .01) more patients with 3.5 mm incisions had 20/40 or better uncorrected visual acuity than patients with 6.0 mm incisions (45% vs 20%). Forty percent of patients with 6.0 mm incisions vs 14% of patients with 3.5 mm incisions had visual acuities of 20/100 or worse. At one day after surgery, the larger incision group had significantly higher (P less than .01) mean keratometric cylinder (2.28 diopters vs 1.28 diopters in the small incision group). The two groups were comparable by three months. Laser flare/cell meter measurements were taken for each group but showed no significant differences in mean flare or cell measurements between the groups.

Hyperopic thermokeratoplasty: clinical evaluation

A new procedure, hyperopic thermokeratoplasty (HTK), developed in the Soviet Union for the correction of hyperopia, uses controlled thermal burns of the corneal stroma with a retractable probe tip preset to penetrate the cornea at 95% depth. The coagulations are applied in a radial pattern for spherical hyperopia. Only the peripheral cornea is treated and the effect is titrated by varying the optical zone and number of rays. The thermal effect flattens the peripheral cornea and steepens the central cornea. In this report, we prospectively evaluated the refractive results of a group of 61 HTK patients. Mean preoperative spherical equivalent was 3.9 diopters (D). Mean follow-up to date is 5.2 months, with 44% of cases evaluated at six months and 31% at one year. The initial effect of surgery (at one day) was a mean decrease in hyperopia of 6.0 D (standard error of the mean [S.E.] = 0.3 D), resulting in a mean spherical equivalent of -2.1 D (S.E. = 0.2 D). There was a steep regression of effect between one day and two months at which point average refraction was close to emmetropia. After two months, there was a gradual but continuing regression of effect, leveling off after six months. At five to six months, 63% of cases were undercorrected by at least a diopter; at 9 to 12 months, 83% of cases were undercorrected. The overall change in spherical equivalent at each time increased as optical zone size decreased.(ABSTRACT TRUNCATED AT 250 WORDS)

Purification and characterization of an oxygen-insensitive NAD(P)H nitroreductase from Enterobacter cloacae

The reductive products of several nitroaromatic compounds have been found to be toxic, mutagenic, and carcinogenic. The nitroreductases present in intestinal microflora have been implicated in the biotransformation of these compounds to their deleterious metabolites. A "classical" nitroreductase has been purified from Enterobacter cloacae 587-fold using a protocol which yields approximately 1 mg of purified nitroreductase from 10 liters of cell culture. An analysis of the physical properties of the nitroreductase indicates that the enzyme is active as a monomer with a calculated molecular mass of 27 kDa. FMN has been identified as a required flavin cofactor and is present at a stoichiometry of 0.88 mol of FMN bound/mol of active enzyme. The enzyme was found capable of reducing nitrofurazone under aerobic conditions indicating that the mechanism involves an obligatory two-electron transfer. Thus, this enzyme can be classified as an oxygen-insensitive nitroreductase. The purified nitroreductase can utilize either NADH or NADPH as a source of reducing equivalents and can reduce a variety of nitroaromatic compounds including nitrofurans and nitrobenzenes as well as quinones. Studies in which the rates of nitroreduction for a series of para substituted nitrobenzene derivatives were determined suggest that a linear free energy relationship exists between the rate and the redox midpoint potential of the substrate.

Continuous monitoring of adenosine 5'-triphosphate in the microenvironment of immobilized enzymes by firefly luciferase

The study of enzymes sequestered in artificial or biological systems is generally conducted by indirect methodology with macroscopic measurements of reactants in the bulk medium. This paper describes a new approach with firefly luciferase to monitor ATP concentration directly in the microenvironment of enzymes producing or consuming ATP. Upon addition of ATP to immobilized firefly luciferase, the onset of light production is slower than that observed with the soluble enzyme, due to a slower diffusion of ATP to the immobilized enzyme. With immobilized pyruvate kinase, a relative accumulation of ATP inside the beads is demonstrated, as measured with coimmobilized firefly luciferase. The accumulation of product (ATP) is enhanced when the bead suspension is not stirred. This ATP in the beads is relatively inaccessible to soluble hexokinase added to the bulk medium. Similarly, a rapid ATP depletion in the microenvironment of immobilized hexokinase is demonstrated. This microscopic event is kinetically distinguishable from the slower macroscopic depletion of substrate in the bulk medium. The rate of depletion in the microenvironment depends on the local activity of the immobilized enzyme but not on the total amount of enzyme in suspension, as does the macroscopic phenomenon. The theoretical principles for the interaction of diffusion and catalysis in these systems are briefly summarized and discussed. These results are relevant to various molecular mechanisms proposed for membrane-bound enzyme action and regulation, derived from macroscopic kinetic measurements assuming a negligible diffusion control.

Photographic detection of luminescence in Escherichia coli containing the gene for firefly luciferase

The gene for firefly luciferase (luc) can be used as a generalized genetic probe. A method that aids in the analysis of shuttle vectors containing luc by allowing verification in Escherichia coli of a functional coding sequence is presented here. Colonies containing a functional form of luc are detected on film after luciferin is added to initiate the luminescent reaction. Two conditions, lowering the pH of the environment and maintaining aerobic conditions, were found to greatly improve the sensitivity of the assay. This technique may be useful in the development of genetic constructs that alter the natural coding sequence of luc, such as in gene fusions.

Firefly luciferase gene: structure and expression in mammalian cells

The nucleotide sequence of the luciferase gene from the firefly Photinus pyralis was determined from the analysis of cDNA and genomic clones. The gene contains six introns, all less than 60 bases in length. The 5' end of the luciferase mRNA was determined by both S1 nuclease analysis and primer extension. Although the luciferase cDNA clone lacked the six N-terminal codons of the open reading frame, we were able to reconstruct the equivalent of a full-length cDNA using the genomic clone as a source of the missing 5' sequence. The full-length, intronless luciferase gene was inserted into mammalian expression vectors and introduced into monkey (CV-1) cells in which enzymatically active firefly luciferase was transiently expressed. In addition, cell lines stably expressing firefly luciferase were isolated. Deleting a portion of the 5'-untranslated region of the luciferase gene removed an upstream initiation (AUG) codon and resulted in a twofold increase in the level of luciferase expression. The ability of the full-length luciferase gene to activate cryptic or enhancerless promoters was also greatly reduced or eliminated by this 5' deletion. Assaying the expression of luciferase provides a rapid and inexpensive method for monitoring promoter activity. Depending on the instrumentation employed to detect luciferase activity, we estimate this assay to be from 30- to 1,000-fold more sensitive than assaying chloramphenicol acetyltransferase expression.

The sulfhydryls of firefly luciferase are not essential for activity

Firefly luciferase, containing an average of seven free sulfhydryls per two 50 000-dalton polypeptides, was modified by various sulfhydryl reagents. The differential reactivities of the sulfhydryls in luciferase protected by substrates allow one to define three categories of these groups: Class SH-III contains three sulfhydryls that are not involved in enzymatic activity. Class SH-II contains two sulfhydryls whose modification by different reagents causes varying effects on activity ranging from 0 to 60% inactivation. These sulfhydryls are not essential but may be important structurally or sterically. Class SH-I contains two sulfhydryls that are protected by substrates, either dehydroluciferyl adenylate or dehydroluciferin alone, and are located at or near the active site. The SH-I sulfhydryls are vicinal in the enzyme as demonstrated by their ability to form a disulfide bond. They have also been shown to exist on a single polypeptide chain. Modification of the SH-I groups by most reagents results in complete loss of enzymatic activity; reaction with methyl methanethiosulfonate produces an enzyme that emits only red light whereas native luciferase emits yellow-green light. Evidence is presented that the modified enzyme, while catalytically active, has a distorted active site. It is concluded that these two SH-I sulfhydryls are not essential for activity.

Bioluminescent assays using coimmobilized enzymes

In summary the use of immobilized luciferases along with other enzymes offers a method for measuring a wide variety of metabolites or enzymes. The assays are rapid, sensitive, and specific and can be automated. It is anticipated that many more assays for different compounds will be developed in the future.

Cloning of firefly luciferase cDNA and the expression of active luciferase in Escherichia coli

A cDNA library was constructed from firefly (Photinus pyralis) lantern poly(A)+ RNA, using the Escherichia coli expression vector lambda gt11. The library was screened with anti-P. pyralis luciferase (Photinus luciferin:oxygen 4-oxidoreductase, EC 1.13.12.7) antibody, and several cDNA clones expressing luciferase antigens were isolated. One clone, lambda Luc1, contained 1.5 kilobase pairs of cDNA that hybridized to a 1.9- to 2.0-kilobase band on a nitrocellulose blot of electrophoretically fractionated lantern RNA. Hybridization of the cloned cDNA to lantern poly(A)+ RNA selected an RNA that directed the in vitro synthesis of a single polypeptide. This polypeptide comigrated with luciferase on NaDodSO4/PAGE and produced bioluminescence upon the addition of luciferin and ATP. A 1.8-kilobase-pair cDNA was isolated by probing the firefly cDNA library with the cDNA from lambda Luc1. This cDNA contained sufficient coding information to direct the synthesis of active firefly luciferase in E. coli.

Decreased mitochondrial creatine kinase activity in dystrophic chicken breast muscle alters creatine-linked respiratory coupling

Dystrophic chicken breast muscle mitochondria contain significantly less mitochondrial creatine kinase than normal breast muscle mitochondria. Breast muscle mitochondria from normal 16- to 40-day-old chickens contain approximately 80 units of mitochondrial creatine kinase per unit of succinate:INT (p-iodonitrotetrazolium violet) reductase, a mitochondrial marker, while dystrophic chicken breast muscle mitochondria contain 36-44 units. Normal chicken heart muscle mitochondria contain about 10% of the mitochondrial creatine kinase per unit of succinate:INT reductase as normal breast muscle mitochondria. The levels in heart muscle mitochondria from dystrophic chickens are not affected significantly. Evidence is presented which shows that the reduced level of mitochondrial creatine kinase in dystrophic breast muscle mitochondria is responsible for an altered creatine linked respiration. First, both normal and dystrophic breast muscle mitochondria respire with the same state 3 and state 4 respiration. Second, the post-ADP state 4 rate of respiration of normal breast muscle mitochondria in the presence of 20 mM creatine continues at the state 3 rate. However, the state 4 rate of dystrophic breast muscle mitochondria and mitochondria from other muscle types with a low level of mitochondrial creatine kinase, such as heart muscle and 5-day-old chicken breast muscle, is slower than the state 3 rate. Third, dystrophic breast mitochondria synthesize ATP at the same rate as normal breast muscle mitochondria but rates of creatine phosphate synthesis in 20-50 mM Pi are reduced significantly. Finally, increasing concentrations of Pi displace mitochondrial creatine kinase from mitoplasts of normal and dystrophic breast muscle mitochondria with the same apparent KD, indicating that the outer surface of the inner mitochondrial membrane and the mitochondrial creatine kinase from dystrophic muscle are not altered.

Synthesis of active firefly luciferase by in vitro translation of RNA obtained from adult lanterns

Poly (A)+ RNA was isolated from the lanterns of adult fireflies, Photinus pyralis. The Poly (A)+ RNA was translated in a cell-free translation mixture from rabbit reticulocytes and the synthesis of enzymatically active firefly luciferase was demonstrated. The translation products were immunoprecipitated with anti-luciferase and then subjected to SDS gel electrophoresis. It was shown that a newly synthesized polypeptide exhibited an identical electrophoretic mobility as the purified enzyme.

Two kinetically distinguishable ATP sites in firefly luciferase

Results are presented which indicate that firefly luciferase has two catalytically active sites. One site, Km of 1.1 X 10(-4) M ATP, is responsible for the initial flash and is apparently product inhibited for further light production. The second site, Km of 2 X 10(-5) M ATP, catalyzes the continuous low production of light. ATP or AMP is a potent inhibitor of the initial flash when LH2-AMP is used to initiate the light reaction but appears to have no affect on the second site low level light emission. Both sites must be occupied by ATP for the formation of one L-AMP. Thus, ATP appears to function both as a catalytically active substrate and a regulator for light emission.

Bioluminescence assays for bile acids in the detection and follow-up of experimental liver injury

We evaluated the usefulness of recently developed bioluminescence assays for serum bile acids (BA) in the detection and follow-up of experimental liver injury. Liver damage was induced in rats by either D-galactosamine or CCl4, and BA were compared to SGPT and aminopyrine breath test (ABT). In severe liver injury, following D-galactosamine administration, all three methods revealed a significant difference from control values. The degree of abnormality was, however, far greater with SGPT and BA than with ABT. In moderate liver injury, induced by CCl4, the increase in BA was not significant. Values of SGPT and BA showed a very good correlation (3 alpha-OH: r = 0.88; 7 alpha-OH: r = 0.90; 12 alpha-OH: r = 0.83; p less than 0.001 for all correlations). Application of different assays for 3 alpha-OH, 7 alpha-OH and 12 alpha-OH BA allowed us to assess changes in individual BA. A 96-hr follow-up study in D-galactosamine-treated animals showed an increase in BA up to 48 hr and a decrease thereafter. The bioluminescence assays for BA are simple, rapid and require only 10 microliter of serum. Thus, these assays may be the method of choice in detecting and monitoring liver injury in small laboratory animals.

The effect of inorganic phosphate on creatine kinase in respiring rat heart mitochondria

The ability of creatine to stimulate the respiration of rat heart mitochondria in vitro is reversibly affected by the concentration of inorganic phosphate. The rate of oxygen consumption due to post-ADP state-4 respiration in the presence of 20 mM creatine is reduced significantly when the potassium phosphate concentration is raised from 5 to 20 mM. State-3 respiration is reduced only by potassium phosphate concentrations higher than 20 mM. The rate of synthesis of creatine phosphate is also affected by phosphate concentration, and the apparent Km of the coupled reactions for ADP is significantly higher at 25 mM phosphate as compared to that at 5 mM phosphate. These observations are consistent with the hypothesis that inorganic phosphate acts as an effector molecule, regulating creatine phosphate synthesis by favoring the dissociation of mitochondrial creatine kinase from the mitochondrial membrane. Such regulation may be important in the case of cells undergoing partial or severe ischemia, where changes in phosphate concentration within this range have been reported.

A bioluminescence assay for total 3 alpha-hydroxy bile acids in serum using immobilized enzymes

A bioluminescence assay for bile acids was developed using a co-immobilized 3 alpha-hydroxysteroid dehydrogenase, diaphorase, and bacterial luciferase. The assay was specific for bile acids containing a free 3 alpha-hydroxyl group, as well as androsterone. Light output was linear over a bile acid concentration range of 1-20 000 pmol. Intra-assay precision was 6.2-8.2% and the recovery of added standards was 92-110%. Comparison of results using the bioluminescence assay with those using gas liquid chromatography revealed an excellent correlation (r = 0.99, n = 31). Since the bioluminescence assay is rapid, sensitive, specific, and uses inexpensive reagents, it appears to be an ideal method for the measurement of total bile acids in serum.

How to prevent losses of protein by adsorption to glass and plastic

An improved procedure for reducing the loss of protein by adsorption to glass or plastic surfaces is reported. For working with proteins at the microgram level, the solvent is modified by adding glycerol (50% final concentration) or Triton X-100 (0.2 mM final concentration). Coating the plastic or glass surfaces with proteins such as bovine serum albumin or other materials is not as effective; adding proteins such as bovine serum albumin to the solvent is counterproductive.

A bioluminescent assay for 12-alpha-hydroxy bile acids using immobilized enzymes

A bioluminescent assay for 12-alpha-hydroxy bile acids was developed using enzymes coimmobilized onto Sepharose 4B. The immobilized enzymes used were a bacterial 12-alpha-hydroxysteroid dehydrogenase, bacterial luciferase, and NADPH:FMN oxidoreductase or bacterial diaphorase. The assay was specific for 12-alpha-hydroxy bile acids and the lower limit of detection was 4 pmol/0.5 ml assay volume with a linear range of 4 to 2000 pmol. Intraassay precision was from 7.8 to 8.2%. Values obtained with this assay showed good agreement with those obtained by gas-liquid chromatography. The system using diaphorase was not stable at 4 degrees C in the absence of added thiol compounds, but could be stabilized by the addition of glutathione (0.5 mM). The assay is a convenient, a rapid, and an extremely sensitive method for the measurement of 12-alpha-hydroxy bile acid concentrations in the serum of patients or experimental animals.

Bioluminescent immunoassays

The procedures described here have been developed for only a few antigens at present. It seems very likely that they can be extended to any other antigen of choice. For sensitivities in the picomole range, the luciferase-antigen procedure is satisfactory. For increased sensitivity, the glucose-6-phosphate dehydrogenase-antigen is the method of choice. With some minor modifications the sensitivity of this assay can certainly be increased. The lower limits of detection will ultimately be determined by the affinity of the antibody for the antigen, not by the detection system.

Bioluminescence measurement of primary bile acids using immobilized 7 alpha-hydroxysteroid dehydrogenase: application to serum bile acids

A simple, rapid, and sensitive bioluminescence method for measuring primary bile acids has been developed and validated. The method is based on enzymatic dehydrogenation of bile acids using a bacterial 7 alpha-hydroxysteroid dehydrogenase that is co-immobilized on Sepharose 4B beads with NADH:FMN oxidoreductase and a bacterial luciferase. The assay is specific for 7 alpha-hydroxy bile acids and has a detection limit of 0.5 pmol/tube, with a linear range of 0.5-50 pmol/tube. The assay shows good precision (6-8% intra-assay; 8-10% inter-assay). The values obtained with the bioluminescence assay showed good agreement with those obtained by gas-liquid chromatography, radioimmunoassay, or endpoint enzymatic assays. When applied to the measurement of serum bile acids, there was no interference from serum albumin, and the effect of other dehydrogenase activity in serum could be eliminated by heating the sample prior to assay. Since the method is rapid (1 minute), extremely sensitive (requires only 10 microliters of serum), and specific, it appears to be the best method currently available for the measurement of serum primary bile acids.