Inhibition of vitamin B12 metabolism by OH-cobalamin c-lactam in rat oligodendrocytes in culture: a model for studying neuropathy due to vitamin B12 deficiency.

Vitamin B12 is implicated in methylation processes. Myelin basic protein is methylated on one arginine group. A defect in methylation could produce an unstable protein, leading to neurological disorders. In order to study myelin basic protein, we have developed the cultures of newborn rat oligodendrocytes in vitamin B12-depleted medium. As these cells do not grow without serum, vitamin B12 is always present. We overcame this problem by using OH-cobalamin c-lactam, an antagonist of B12. To ensure that the system was vitamin B12 deficient, we measured the concentrations of homocysteine and methylmalonic acid whose accumulations reflect a vitamin B12 deficiency. Methylmalonic acid was measured by mass spectrometry and homocysteine by HPLC. We obtained a powerful model for studying the influence of B12 deficiency on the synthesis of myelin compounds.

Hydrolysis of phospholipids by purified milk lipoprotein lipase. Effect of apoprotein CII, CIII, A and E, and synthetic fragments.

Different pyrene-labeled phospholipid monolayer vesicles were used as substrates for the bovine milk lipoprotein lipase activity. The effects of synthetic fragments of apoprotein C II were measured on the hydrolysis of 1-myristoyl-2[9(1pyrenyl)-nonanoyl] phosphatidylcholine in vesicles: The activating capacity of fragments 30-78 and 43-78, 50-78 and 55-78, compared to entire apo CII, were similar to that obtained with hydrolysable triglycerides. Our study shows that the longer the carboxy terminal fragment is, the higher is the activation. The phospholipid hydrolysis activity represents in the presence of apo C II, 36% of the triglycerides hydrolysis activity. Phospholipid hydrolysis is less dependent on activator than triglycerides hydrolysis (100% and 300% of increase with apo CII for phosphatidyl-choline and triglycerides respectively). The ratio hydrolysis without apo C II/hydrolysis with apo CII was different when other phospholipids than myrystoyl-phospatidylcholine were assayed: phosphatidyl-serine, ethanolamine, -choline, -glycerol, or diglycerides and butanoylglycerols. Fragment CIII(1) (1-40) which did not bind to lipids, had no inhibitory effect. The entire sugar moiety and the first 40 amino acids are not required for the total inhibition of LPL. Inhibition was also obtained with Apo A I, A II,C I and fragments of apo E.

A new fluorometric method for measuring the action of C apolipoproteins on milk lipoprotein lipase.

Monolayer vesicles containing pyrene-labelled nonanoyltriglyceride (1-2 ditetradecyl 3-pyrene nonanoyl glyceride) were used as a substrate to measure bovine milk lipoprotein lipase activity. The activation of lipoprotein lipase by synthetic fragments of apolipoprotein C II and apo C III was measured. Fragments 30-78 and 43-78 had actions similar to that of the entire apo C II. Fragments 50-78 and 55-78 were 50% active, fragment 60-78 was 10% active and fragment 66-78 was inactive. Thus the activating capacity depended on the length of the carboxyterminal fragment. Replacing tyrosine 62 in apo C II by glycine removed all lipoprotein lipase activating capacity, while making Tyr 62 less accessible for binding to lipids and enzyme decreased apo C II activating capacity. Apo C III1 inhibited both basal lipoprotein lipase activity (no apo C II) and lipoprotein lipase activated by apo C II. Apo C III, fragment A (1-40) which did not bind lipids, had no inhibitory effect, while fragment B(41-79) had the same effect as whole apo C III,. Apo AI, AII and C I also inhibited lipoprotein lipase. The fluorometric assay is easy to perform, and suitable for metabolic studies such as fatty-acid exchanges between lipoproteins, as it produces no alteration in the reaction products. It also avoids the use of a radio-labelled substrate.

Effect of the apolipoprotein C-II/C-III1 ratio on the capacity of purified milk lipoprotein lipase to hydrolyse triglycerides in monolayer vesicles.

The effect of the apolipoprotein C-II/C-III1 ratio on the capacity of purified bovine milk lipoprotein lipase to hydrolyse triglycerides was measured in a controlled model of pyrene-labeled nonanoyltriglycerides (1-2 ditetradecyl 3-pyrene nonanoyl glyceride) monolayer vesicles. Monolayer was composed of triglycerides, a non-hydrolysable phospholipid ether and cholesterol, a model system where the quality of the interface can be controlled. LPL released fatty acids from pyrene-triglycerides which were transferred from the lipoprotein structure to albumin. This transfer induces a decrease in the excimer production and in the excimer fluorescence intensity. Apolipoprotein C-II and C-III0 and C-III1 were purified from apolipoprotein VLDL. The 2 fragments, C-III1 A (peptide 1-40) and C-III1 B (peptide 41-79), were obtained after thrombin cleavage. Apolipoproteins C-III0 and C-III1 had a similar inhibitory effect on LPL. Inhibition with apo C-III0 or apo C-III1 was 85% of full LPL activity without inhibitor: Apo C-III1 B inhibited 62% of basal activity. It was 27% less effective than apo C-III1. Fragment C-III1 A did not inhibit LPL. The effect of change in both apo C-II (0-0.6 microM) and apo C-III1 (0-1.0 microM) on triglyceride hydrolysis shows the importance of the apo C-II/C-III1 ratio for the release of free fatty acids from triglycerides by LPL. The activating effect of apo C-II in the absence of the apo C-III inhibitor was maximal at 0.06 microM. No further activation was obtained between 0.06 and 0.30 microM. Higher concentrations decreased LPL activity. Apo C-III1 (0.1 microM) decreased the maximum activation by apo C-II from 0.0196 to 0.063 nmol/min/nmol LPL. Higher concentrations of apo C-III1 (0.1-0.5 microM) required higher apo C-II concentrations (0.30 microM instead of 0.06 microM) for maximal activation than when apo C-III1 was absent. The activity of the enzyme without apo C-II was decreased by 65% by 0.12 microM apo C-III1. Increasing the apo C-II/apo C-III1 ratio from 0.1 to 1, increased the activation of the enzyme by a given apo C-II concentration. Moreover, for a given apo C-II/C-III1 ratio, the LPL activation increased with the apo C-II concentration (between 0 and 0.010 microM), until a plateau was reached. This is important, as the change in the C-II/C-III1 ratio is not the only factor affecting LPL activity, and inhibition by apo C-III1 also depends on the overall quantity of apolipoproteins. Extrapolation of these results suggests that hyperlipoproteinemia seems to be more likely due to overproduction of VLDL, than to a decrease in lipoprotein lipase activity.

Political and economic determinants of insurance regulation in mental health.

This article studies determinants of two important sets of laws regulating insurance coverage for mental health care: mandated inclusion of minimum coverage for psychotherapy, and mandated coverage for psychologist services, the so-called freedom of choice (FOC) laws. Political market models are developed and estimated to examine the passage of mandates and FOC laws among all fifty states from 1968 through 1983. Findings indicate that a number of groups influence whether these laws are passed, including psychologists and the state, which acts both in its own interests as a direct provider of services and to protect the public's interest. A state's political system and socioeconomic environment also influence the likelihood of passage of these regulations. Our findings run counter to the assumption often made by policymakers and researchers that regulations exclusively serve the interests of providers.

Firearm-related assaults on Los Angeles roadways.

During the summer of 1987, we investigated a series of firearm assaults occurring on Los Angeles County (California) roadways. Using law enforcement records, we identified 137 incidents of roadway assaults with firearms. Of these 137 incidents, 39% were brandishings and 61% were shootings. Of the shootings, 20% resulted in injuries; two were fatal. We compared the findings for June through August 1987 with findings for earlier years and found that the incidence rate of freeway firearm assault had increased each year from 1985 through 1987 for both freeway shootings and brandishings. We also found a positive association between freeway congestion and freeway firearm assaults in 1987.

The epidemiology of injuries in Atlanta day-care centers.

From June 1987 through May 1988, we collected reports of injuries among 5300 children who attended 71 day-care centers in Atlanta, Ga. One hundred forty-three injuries severe enough for the child to require medical or dental care were reported, including 63 lacerations (44.1%), 23 fractures (16.1%), 5 crush injuries (3.5%), 4 dislocations (2.8%), 2 human bites (1.4%), and 2 concussions (1.4%). The head was the site of 98 (68.5%) injuries. Peak hours for injuries were 11 AM and 4 PM, the peak day was Monday, and the peak season was summer. After adjustment for hours and dates of attendance, the rate was 1.77 injuries per 100,000 child-hours in day care; among preschool-aged children, infants had the lowest rate (0.77) and 2-year-old children had the highest rate (2.26). Almost 47% of injuries occurred on the playground; falls were involved in 70% of such injuries. Because 33% of all injuries resulted from falls on the playground, impact-absorbing playground surfaces may be a possible intervention to reduce injuries.

Fall injuries among the elderly. Community-based surveillance.

Falls are a leading cause of fatal and nonfatal injuries among the elderly in the United States. Despite the importance of fall injuries, epidemiological studies of falls among the elderly have identified neither their causes nor the methods to prevent them. Therefore, we established a community-based surveillance system in Miami Beach, Florida, as part of a study to assess falls among the elderly. A total of 1,827 fall injury events occurred in this community between July 1985 and June 1986. More than 85% (1,567) of the persons who fell and received care were seen in an emergency room. The remaining cases were identified from one of the three other sources used: fire rescue reports, inpatient medical records, or medical examiner reports. Most falls (97%) were coded as accidental (E880-E888). More than 100 people sought medical assistance for a fall each month. The time of the injury was known for 68% (1,244) of the people who fell. Seventy-four percent of these falls (921) occurred during daylight hours. Fifty-four percent of the falls (986) occurred in and around the home, and 38% of these had a particular area of the home recorded: 42% occurred in the bedroom, 34% in the bathroom, 9% in the kitchen, 5% on the stairs, 4% in the living room, and the remaining 6% in other areas. This surveillance system will help us use the study to clarify the causes of falls in the elderly and identify and evaluate appropriate prevention efforts. It will also help others in designing and implementing other injury surveillance systems.

Analysis of unlinked infant death certificates from the NIMS project.

The National Infant Mortality Surveillance (NIMS) project used linked birth and infant death certificates to calculate birth weight-specific infant mortality risks for the 1980 U.S. birth cohort. Record linkage depends on complete registration of vital events, interstate exchange of vital records, accurate information on certificates, and a comprehensive linkage system. States reported 2,604 unlinked infant death certificates for 1980, ranging from 0 to 397 per State. Age at death for these infants ranged from 1 minute to 11 months. More than 41 percent of the unlinked death certificates were for postneonates, compared with 32.5 percent found in the cohort's total infant death experience. Only 38.2 percent of the unlinked infant death certificates showed strictly intrastate events (birth and death occurrence, and residence at death all in one State), compared with 92.9 percent in the cohort's total infant death experience. Estimates of the percentage successfully linked by State ranged from 86.0 to 100.0. After adjusting for the certainly unlinked infant death certificates, nine States' infant mortality risks increased by more than 0.2 per 1,000 live births. Improvements are needed both within and between States to ensure more complete birth and infant death certificate linkage.