Mechanisms of cell damage and enzyme release

Release of intracellular enzymes to the extracellular space is a marker of cell damage in various diseases, e.g. liver, heart and muscle diseases. In the normal state the plasma membrane is impermeable to enzymes, and enzyme release, therefore, indicates a severe change of the membrane integrity. This review deals with the present knowledge about cellular changes leading to enzyme release, which may be caused either by energy depletion, e.g. in ischemia or shock, or by a direct membrane damage as caused by various toxins and inflammatory products. Inhibition of the energy metabolism results in ATP depletion leading to fluxes of Na+, K+ and Cl- down their gradients across the membrane and swelling of the cell. Subsequently Ca2+ leak into the cell activating phospholipases and the formation of eicosanoids, affecting the cytoskeleton and, perhaps, activating the formation of oxidants. The exact "point of no return" is not known but an uncontrolled Ca2+ activity in the cell probably has an important role in initiating the irreversible changes. The result of these reactions and probably other unknown reactions as well is damage to the membrane. This is evident morphologically at first by the formation of blebs that appears in the reversible phase, and later on by rupturing of the membrane, a sign of irreversible damage. A very small part of the enzyme release may occur in the reversible phase when blebs detach with resealing of the membrane, but the substantial part of enzyme release occurs as a result of irreversible cell damage when ATP has decreased to a low level and a serious disruption of the membrane integrity has taken place. All the secondary affections of the membrane during energy depletion may also occur as a primary direct membrane damage that more or less may affect the energy metabolism secondarily. The cell damage and enzyme release after some types of direct membrane damage is almost independent of the cellular energy metabolism whereas other types of direct membrane damage are counteracted by the cell by energy consuming reactions and, therefore, the final cell damage is a concerted action of the direct membrane damage and the energy depletion. This also means that a direct membrane damage may be more severe for the cell in energy depleted states than in the normal state. As in energy dependent cell damage the substantial part of enzyme release after a direct membrane damage is due to irreversible cellular changes. It appears that although the knowledge of the molecular basis of cell damage and enzyme release has grown there are still many questions to be answered about these complex processes.     

Cytomechanics of axonal development

Mechanical tension is a robust regulator of axonal development of cultured neurons. We review work from our laboratory, using calibrated glass needles to measure or apply tension to chick sensory neurons, chick forebrain neurons, and rat PC12 cells. We survey direct evidence for two different regimes of tension effects on neurons, a fluid-like growth regime, and a nongrowth, elastic regime. Above a minimum tension threshold, we observe growth effects of tension regulating four phases of axonal development: 1. Initiation of process outgrowth from the cell body; 2. Growth cone-mediated elongation of the axon; 3. Elongation of the axon after synaptogenesis, which normally accommodates the skeletal growth of vertebrates; and 4. Axonal elimination by retraction. Significantly, the quantitative relationship between the force and the growth response is surprisingly similar to the simple relationship characteristic of Newtonian fluid mechanical elements: elongation rate is directly proportional to tension (above the threshold), and this robust linear relationship extends from physiological growth rates to far-above-physiological rates. Thus, tension apparently integrates the complex biochemistry of axonal elongation, including cytoskeletal and membrane dynamics, to produce a simple "force input/growth output" relationship. In addition to this fluid-like growth response, peripheral neurons show elastic behaviors at low tensions (below the threshold tension for growth), as do most cell types. Thus, neurites could exert small static forces without diminution for long periods. In addition, axons of peripheral neurons can actively generate modest tensions, presumably similar to muscle contraction, at tensions near zero. The elastic and force-generating capability of neural axons has recently been proposed to play a major role in the morphogenesis of the brain.     

Log-linear allometry of fetal craniofacial growth in Down's syndrome

Trisomy 21 develops as a result of nondisjunction of two homologous chromosomes during either the first or second meiotic division. One of the more important consequences of these genetic alterations is the predictable, although variable disturbance in the architecture of the craniofacial region [1]. Postnatal craniofacial morphology has been extensively studied in Down's syndrome (DS). However, little information is available on human prenatal development of the head and face in such patients. The time at which changes in craniofacial phenotype first emerge in Down's syndrome fetuses and at which physical growth begins to diverge from normal is unknown. To explore these questions, we compared prenatal craniofacial growth in 50 Down's syndrome fetuses with that of 555 fetuses judged to be "typical for body weight and age" using the method of log-linear allometry [2].     

Lobectomy combined with volume reduction for patients with lung cancer and advanced emphysema

Methanol-induced conformational transitions of hen egg white lysozyme were investigated with a combined use of far- and near-UV CD and NMR spectroscopies, ANS binding and small-angle X-ray scattering. Addition of methanol induced no global change in the native conformation itself, but induced a transition from the native state to the denatured state which was highly cooperative, as shown by the coincidence of transition curves monitored by the far- and near-UV CD spectroscopy, by isodichroic points in the far- and near-UV CD spectra and by the concomitant disappearance of individual 1H NMR signals of the native state. The ANS binding experiments could detect no intermediate conformer similar to the molten globule state in the process of the methanol denaturation. However, at high concentration of methanol, e.g., 60% (v/v) methanol/water, a highly helical state (H) was realized. The H state had a helical content much higher than the native state, monitored by far-UV CD spectroscopy, and had no specific tertiary structure, monitored both by near-UV CD and NMR spectroscopy. The radius of gyration in the H state, 24.9 angstroms, was significantly larger than that in the native state (15.7 angstroms). The Kratky plot for the H state did not show a clear peak and was quite similar to that for the urea-denatured state, indicating a complete lack of globularity. Thus we conclude that the H state has a considerably expanded, flexible broken rod-like conformation which is clearly distinguishable from the "molten globule" state. The stability of both N and H states depends on pH and methanol concentration. Thus a phase diagram involving N and H was constructed.     

Refining the level for anticipated hepatotoxicity in acetaminophen poisoning

Treatment of an acetaminophen overdose with N-acetyl cysteine usually is based on the position of the 4-h acetaminophen (APAP) level on the Rumack-Matthew nomogram; however, there is disagreement on the level at which clinically relevant hepatotoxicity occurs. A retrospective review of all acute adult formulation APAP exposures reported to our poison center between 1986 and 1993 was performed and cases corresponding to the "possible risk or toxicity" range on the nomogram were identified. Our current poison center protocol for APAP poisoning does not recommend treatment with N-acetylcysteine (NAC) in low-risk patients if the 4-h serum APAP level or the extrapolated equivalent falls within the possible toxicity range on the nomogram. Seventeen cases met the inclusion criteria for the study and received no NAC; six additional patients met inclusion criteria but received one or two doses of NAC before therapy was discontinued. No patients in either group demonstrated clinical evidence of hepatotoxicity. This pilot study suggests that patients with no risk factors and APAP levels in the "possible risk" range may not require NAC therapy.     

HLA-DRB1 genes and disease severity in rheumatoid arthritis. The MIRA Trial Group. Minocycline in Rheumatoid Arthritis

OBJECTIVE: To examine the effect of alleles encoding the "shared"/"rheumatoid" epitope on rheumatoid arthritis (RA) disease severity in patients who participated in the minocycline in RA (MIRA) trial. METHODS: Of 205 patients with a week-48 visit, blood was available for typing of HLA-DRB1 and HLA-DQB1 in 174 (85%) and successfully completed in 169 (82%). Baseline erosions were used to assess disease severity and new erosions at the last visit served as a proxy for progression. RESULTS: At baseline, there was no association between the presence of erosive disease or rheumatoid factor status and the dose of rheumatoid epitope (homozygous, heterozygous, none) or the specific alleles identified. At the final visit, a gradient was observed for the 3 allelic subgroups (and their gene doses) in the occurrence of new erosions among the Caucasian placebo-treated, but not the minocycline-treated, patients. A treatment group/HLA-DR4 epitope interaction was demonstrated in multivariate analyses. Approximately two-thirds of African-American patients did not have the rheumatoid epitope. CONCLUSION: HLA-DRB1 oligotyping may be useful in predicting the progression of disease in some Caucasian patients. Our study corroborates the infrequency of the epitope among African-American patients with RA.     

Perinuclear antineutrophil cytoplasmic antibodies in patients with Crohn's disease define a clinical subgroup

BACKGROUND & AIMS: Antineutrophil cytoplasmic antibodies (ANCA) have been consistently detected in a subgroup of patients with Crohn's disease (CD). This study was designed to determine whether serum ANCA expression in patients with CD characterizes an identifiable clinical subgroup. METHODS: The study population consisted of 69 consecutive patients with an established diagnosis of CD as determined by a combination of characteristic clinical, radiographic, endoscopic, and histopathologic criteria. Sera from the patients were analyzed for the presence of ANCAs using the fixed neutrophil enzyme-linked immunosorbent assay (ELISA) assay. Perinuclear ANCA (pANCA)-positive and cytoplasmic ANCA (cANCA)-positive results by ELISA were confirmed by indirect immunofluorescence staining. Clinical profiles of the ANCA-positive patients with CD were compared with those of patients with CD not expressing ANCA (ANCA-negative). RESULTS: pANCA-positive patients with CD have endoscopically and/or histopathologically documented left-sided colitis and symptoms of left-sided colonic inflammation, clinically reflected by rectal bleeding and mucus discharge, urgency, and treatment with topical agents. One hundred percent of patients with CD expressing pANCA had "UC-like" features. CONCLUSIONS: In patients with CD, serum pANCA expression characterizes a UC-like clinical phenotype. Stratification of CD by serum pANCA provides evidence of heterogeneity within CD and suggests a common intestinal mucosal inflammatory process among a definable subgroup of patients with CD and UC expressing this marker.     

Laparoscopic vs. open wedge biopsy of the liver

The number of people smoking free-base cocaine, or "crack," has increased dramatically in recent years. Concomitantly, the literature describing complications of such use has grown as well. Adverse pulmonary effects are being increasingly noted, such as respiratory symptoms, pulmonary hemorrhage, pulmonary edema, asthma, and pulmonary barotrauma. These and other pulmonary effects are reviewed.     

After-hours telephone coverage: the application of an area-wide telephone triage and advice system for pediatric practices

BACKGROUND: After-hours telephone calls are a stressful and frustrating aspect of pediatric practice. At the request of private practice pediatricians in Denver, a metropolitan area-wide system was created to manage after-hours pediatric telephone calls and after-hours patient care. This system, the After-Hours Program (AHP), uses specially trained pediatric nurses with standardized protocols to provide after-hours telephone triage and advice for the patients of 92 Denver pediatricians, representing 56 practices. OBJECTIVES: This report describes the AHP, presents data from 4 years' experience with the program, and describes results of our evaluation of the following aspects of the program: subscribing physician satisfaction, parent satisfaction, the accuracy and appropriateness of telephone triage, and program costs. METHODS: After-Hours Program records (including quality assurance data) for all 4 years of operation were retrospectively reviewed, tabulated, and analyzed. The results of two subscribing physician surveys and one parent caller satisfaction survey are presented. A retrospective review of after-hours patient care encounter forms assessed the necessity for after-hours visits triaged by the AHP. An analysis of the total cost of this program to 10 randomly selected subscribing physicians was conducted using current AHP data and a survey of the 10 physicians. RESULTS: In 4 years, 107,938 calls have been successfully managed without an adverse clinical outcome. Minor errors in using protocols occurred in one call out of 1450 after-hours calls. After-hours phoen calls necessitated an after-hours patient visit 20% of the time and generated one after-hours hospital admission out of every 88 calls. Just over half of the patients were managed with home care advice only, and 28% were given home care advice after-hours and seen the next day in the primary physician's office. Of all patients directed by the telephone triage nurses to be seen after hours, 78% were determined to have a condition necessitating after-hours care. Data are presented regarding call volumes by time of day, day of week, patient age, and patient's initial complaint. The 6 most common complaints accounted for more than one half of the calls, and 38 complaints accounted for more than 95% of all after-hours calls. Utilization by subscribing physicians is described. Satisfaction among subscribing pediatricians was 100%, and among parents was 96% to 99% on a variety of issues. The total cost to participating Denver pediatricians (which includes revenues "given up" as a result of not seeing patients after hours) ranged from 1% to 12% of their annual net income, depending on a variety of factors. CONCLUSIONS: Large-scale after-hours telephone coverage systems can be effective and well-received by patients, parents, and primary physicians. Data presented in this report can assist in planning the training of personnel who provide after-hours telephone advice and triage. Controversies associated with this type of program are discussed. Suggestions are made regarding the direction of future programs and research.     

Choroidal neovascular membrane in Best's vitelliform macular dystrophy

The right eye of a 9-year-old white boy with Best's vitelliform macular dystrophy had an intact egg-yolk lesion and a retinal pigment epithelial defect superiorly, suggesting an early pseudohypopyon stage. The disruptive phase of the left eye showed subretinal hemorrhages, a "signet ring," and a subretinal neovascular membrane.