A bioassay method validation framework for laboratory and semi-field tests used to evaluate vector control tools

Vector control interventions play a fundamental role in the control and elimination of vector-borne diseases. The evaluation of vector control products relies on bioassays, laboratory and semi-field tests using live insects to assess the product's effectiveness. Bioassay method development requires a rigorous validation process to ensure that relevant methods are used to capture appropriate entomological endpoints which accurately and precisely describe likely efficacy against disease vectors as well as product characteristics within the manufacturing tolerance ranges for insecticide content specified by the World Health Organization. Currently, there are no standardized guidelines for bioassay method validation in vector control. This report presents a framework for bioassay validation that draws on accepted validation processes from the chemical and healthcare fields and which can be applied for evaluating bioassays and semi-field tests in vector control. The validation process has been categorized into four stages: preliminary development; feasibility experiments; internal validation, and external validation. A properly validated method combined with an appropriate experimental design and data analyses that account for both the variability of the method and the product is needed to generate reliable estimates of product efficacy to ensure that at-risk communities have timely access to safe and reliable vector control products.

Characterising the intensity of insecticide resistance: A novel framework for analysis of intensity bioassay data

Insecticide resistance is a growing problem that risks harming the progress made by vector control tools in reducing the malaria burden globally. New methods for quantifying the extent of resistance in wild populations are urgently needed to guide deployment of interventions to improve disease control. Intensity bioassays measure mosquito mortality at a range of insecticide doses and characterise phenotypic resistance in regions where resistance is already detected. These data are increasingly being collected but tend to exhibit high measurement error and there is a lack of formal guidelines on how they should be analysed or compared. This paper introduces a novel Bayesian framework for analysing intensity bioassay data, which uses a flexible statistical model able to capture a wide variety of relationships between mortality and insecticide dose. By accounting for background mortality of mosquitoes, our approach minimises the impact of this source of measurement noise resulting in more precise quantification of resistance. It outputs a range of metrics for describing the intensity and variability in resistance within the sample and quantifies the level of measurement error in the assay. The functionality is illustrated with data from laboratory-reared mosquitoes to show how the lethal dose varies within and between different strains. The framework can also be used to formally test hypotheses by explicitly considering the high heterogeneity seen in these types of data in field samples. Here we show that the intensity of resistance (as measured by the median lethal dose (LC50) of insecticide) increases over 7 years in mosquitoes from one village in Burkina Faso but remains constant in another. This work showcases the benefits of statistically rigorous analysis of insecticide bioassay data and highlights the additional information available from this and other dose-response data.

Strain Characterisation for Measuring Bioefficacy of ITNs Treated with Two Active Ingredients (Dual-AI ITNs): Developing a Robust Protocol by Building Consensus

Durability monitoring of insecticide-treated nets (ITNs) containing a pyrethroid in combination with a second active ingredient (AI) must be adapted so that the insecticidal bioefficacy of each AI can be monitored independently. An effective way to do this is to measure rapid knock down of a pyrethroid-susceptible strain of mosquitoes to assess the bioefficacy of the pyrethroid component and to use a pyrethroid-resistant strain to measure the bioefficacy of the second ingredient. To allow robust comparison of results across tests within and between test facilities, and over time, protocols for bioefficacy testing must include either characterisation of the resistant strain, standardisation of the mosquitoes used for bioassays, or a combination of the two. Through a series of virtual meetings, key stakeholders and practitioners explored different approaches to achieving these goals. Via an iterative process we decided on the preferred approach and produced a protocol consisting of characterising mosquitoes used for bioefficacy testing before and after a round of bioassays, for example at each time point in a durability monitoring study. We present the final protocol and justify our approach to establishing a standard methodology for durability monitoring of ITNs containing pyrethroid and a second AI.

Developing Consensus Standard Operating Procedures (SOPs) to Evaluate New Types of Insecticide-Treated Nets

In response to growing concerns over the sustained effectiveness of pyrethroid-only based control tools, new products are being developed and evaluated. Some examples of these are dual-active ingredient (AI) insecticide-treated nets (ITNs) which contain secondary insecticides, or synergist ITNs which contain insecticide synergist, both in combination with a pyrethroid. These net types are often termed 'next-generation' insecticide-treated nets. Several of these new types of ITNs are being evaluated in large-scale randomized control trials (RCTs) and pilot deployment schemes at a country level. However, no methods for measuring the biological durability of the AIs or synergists on these products are currently recommended. In this publication, we describe a pipeline used to collate and interrogate several different methods to produce a singular 'consensus standard operating procedure (SOP)', for monitoring the biological durability of three new types of ITNs: pyrethroid + piperonyl butoxide (PBO), pyrethroid + pyriproxyfen (PPF), and pyrethroid + chlorfenapyr (CFP). This process, convened under the auspices of the Innovation to Impact programme, sought to align methodologies used for conducting durability monitoring activities of next-generation ITNs.

The Automatic Classification of Pyriproxyfen-Affected Mosquito Ovaries

Pyriproxyfen (PPF) may become an alternative insecticide for areas where pyrethroid-resistant vectors are prevalent. The efficacy of PPF can be assessed through the dissection and assessment of vector ovaries. However, this reliance on expertise is subject to limitations. We show here that these limitations can be overcome using a convolutional neural network (CNN) to automate the classification of egg development and thus fertility status. Using TensorFlow, a resnet-50 CNN was pretrained with the ImageNet dataset. This CNN architecture was then retrained using a novel dataset of 524 dissected ovary images from An. gambiae s.l. An. gambiae Akron, and An. funestus s.l., whose fertility status and PPF exposure were known. Data augmentation increased the training set to 6973 images. A test set of 157 images was used to measure accuracy. This CNN model achieved an accuracy score of 94%, and application took a mean time of 38.5 s. Such a CNN can achieve an acceptable level of precision in a quick, robust format and can be distributed in a practical, accessible, and free manner. Furthermore, this approach is useful for measuring the efficacy and durability of PPF treated bednets, and it is applicable to any PPF-treated tool or similarly acting insecticide.

Review and Meta-Analysis of the Evidence for Choosing between Specific Pyrethroids for Programmatic Purposes

Simple Summary

A group of insecticides, called pyrethroids, are the main strategy for controlling the mosquito vectors of malaria. Pyrethroids are used in all insecticide-treated bednets, and many indoor residual spray programmes (in which insecticides are sprayed on the interior walls of houses). There are different types of pyrethroids within the class (e.g., deltamethrin and permethrin). Across the world, mosquitoes are showing signs of resistance to the pyrethroids, such as reduced mortality following contact. However, it is unclear if this resistance is uniform across the pyrethroid class (i.e., if a mosquito is resistant to deltamethrin, whether it is resistant to permethrin at the same level). In addition, it is not known if switching between different pyrethroids can be used to effectively maintain mosquito control when resistance to a single pyrethroid has been detected. This review examined the evidence from molecular studies, resistance testing from laboratory and field data, and mosquito behavioural assays to answer these questions. The evidence suggested that in areas where pyrethroid resistance exists, different mortality seen between the pyrethroids is not necessarily indicative of an operationally relevant difference in control performance, and there is no reason to rotate between common pyrethroids (i.e., deltamethrin, permethrin, and alpha-cypermethrin) as an insecticide resistance management strategy.

Abstract

Pyrethroid resistance is widespread in malaria vectors. However, differential mortality in discriminating dose assays to different pyrethroids is often observed in wild populations. When this occurs, it is unclear if this differential mortality should be interpreted as an indication of differential levels of susceptibility within the pyrethroid class, and if so, if countries should consider selecting one specific pyrethroid for programmatic use over another. A review of evidence from molecular studies, resistance testing with laboratory colonies and wild populations, and mosquito behavioural assays were conducted to answer these questions. Evidence suggested that in areas where pyrethroid resistance exists, different results in insecticide susceptibility assays with specific pyrethroids currently in common use (deltamethrin, permethrin, α-cypermethrin, and λ-cyhalothrin) are not necessarily indicative of an operationally relevant difference in potential performance. Consequently, it is not advisable to use rotation between these pyrethroids as an insecticide-resistance management strategy. Less commonly used pyrethroids (bifenthrin and etofenprox) may have sufficiently different modes of action, though further work is needed to examine how this may apply to insecticide resistance management.

Pyriproxyfen-treated bed nets reduce reproductive fitness and longevity of pyrethroid-resistant Anopheles gambiae under laboratory and field conditions

Background

The efficacy of insecticide-treated nets (ITNs) containing the insect growth regulator pyriproxyfen (PPF) and pyrethroid insecticides (PPF-ITNs) is being assessed in clinical trials to determine whether they provide greater protection from malaria than standard pyrethroid-treated ITNs in areas where mosquitoes are resistant to pyrethroids. Understanding the entomological mode of action of this new ITN class will aide interpretation of the results from these trials.

Methods

Anopheles gambiae sensu lato (s.l.) mosquitoes from a susceptible laboratory strain were exposed to PPF-treated netting 24 h, 6 h, and immediately prior to, or 24 h post blood feeding, and the impact on fecundity, fertility and longevity recorded. Pyrethroid-resistant populations were exposed to nets containing permethrin and PPF (PPF-ITNs) in cone bioassays and daily mortality recorded. Mosquitoes were also collected from inside houses pre- and post-distribution of PPF-ITNs in a clinical trial conduced in Burkina Faso; female An. gambiae s.l. were then assessed for fecundity and fertility.

Results

PPF exposure reduced the median adult lifespan of insecticide-susceptible mosquitoes by 4 to 5 days in all exposure times (p < 0.05) other than 6 h pre-blood meal and resulted in almost complete lifelong sterilization. The longevity of pyrethroid-resistant mosquitoes was also reduced by at least 5 days after exposure to PPF-ITNs compared to untreated nets, but was unaffected by exposure to standard pyrethroid only ITNs. A total of 386 blood-fed or gravid An. gambiae s.l. females were collected from five villages between 1 and 12 months before distribution of PPF-ITNs. Of these mosquitoes, 75% laid eggs and the remaining 25% appeared to have normal ovaries upon dissection. In contrast, only 8.6% of the 631 blood-fed or gravid An. gambiae s.l. collected post PPF-ITN distribution successfully oviposited; 276 (43.7%) did not oviposit but had apparently normal ovaries upon dissection, and 301 (47.7%) did not oviposit and had abnormal eggs upon dissection. Egg numbers were also significantly lower (average of 138/female prior distribution vs 85 post distribution, p < 0.05).

Conclusion

Exposure to a mixture of PPF and pyrethroids on netting shortens the lifespan of mosquitoes and reduces reproductive output. Sterilization of vectors lasted at least one year under operational conditions. These findings suggest a longer effective lifespan of PPF-pyrethroid nets than reported previously.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12936-021-03794-z.

New insecticide screening platforms indicate that Mitochondrial Complex I inhibitors are susceptible to cross-resistance by mosquito P450s that metabolise pyrethroids

Fenazaquin, pyridaben, tolfenpyrad and fenpyroximate are Complex I inhibitors offering a new mode of action for insecticidal malaria vector control. However, extended exposure to pyrethroid based products such as long-lasting insecticidal nets (LLINs) has created mosquito populations that are largely pyrethroid-resistant, often with elevated levels of P450s that can metabolise and neutralise diverse substrates. To assess cross-resistance liabilities of the Complex I inhibitors, we profiled their susceptibility to metabolism by P450s associated with pyrethroid resistance in Anopheles gambiae (CYPs 6M2, 6P3, 6P4, 6P5, 9J5, 9K1, 6Z2) and An. funestus (CYP6P9a). All compounds were highly susceptible. Transgenic An. gambiae overexpressing CYP6M2 or CYP6P3 showed reduced mortality when exposed to fenpyroximate and tolfenpyrad. Mortality from fenpyroximate was also reduced in pyrethroid-resistant strains of An. gambiae (VK7 2014 and Tiassalé 13) and An. funestus (FUMOZ-R). P450 inhibitor piperonyl butoxide (PBO) significantly enhanced the efficacy of fenpyroximate and tolfenpyrad, fully restoring mortality in fenpyroximate-exposed FUMOZ-R. Overall, results suggest that in vivo and in vitro assays are a useful guide in the development of new vector control products, and that the Complex I inhibitors tested are susceptible to metabolic cross-resistance and may lack efficacy in controlling pyrethroid resistant mosquitoes.

Repurposing isoxazoline veterinary drugs for control of vector-borne human diseases

Isoxazolines are oral insecticidal drugs currently licensed for ectoparasite control in companion animals. Here we propose their use in humans for the reduction of vector-borne disease incidence. Fluralaner and afoxolaner rapidly killed Anopheles, Aedes, and Culex mosquitoes and Phlebotomus sand flies after feeding on a drug-supplemented blood meal, with IC50 values ranging from 33 to 575 nM, and were fully active against strains with preexisting resistance to common insecticides. Based on allometric scaling of preclinical pharmacokinetics data, we predict that a single human median dose of 260 mg (IQR, 177-407 mg) for afoxolaner, or 410 mg (IQR, 278-648 mg) for fluralaner, could provide an insecticidal effect lasting 50-90 days against mosquitoes and Phlebotomus sand flies. Computational modeling showed that seasonal mass drug administration of such a single dose to a fraction of a regional population would dramatically reduce clinical cases of Zika and malaria in endemic settings. Isoxazolines therefore represent a promising new component of drug-based vector control.

Does mosquito mass-rearing produce an inferior mosquito?

BACKGROUND

The success of the sterile insect technique depends, among other things, on continuous releases of sexually competitive sterile males within the target area. Several factors (including high rearing density and physical manipulation, such as larvae and pupae separation) can influence the quality of males produced in mass-rearing facilities. The different steps in mass production in the laboratory may modify the behaviour of mosquitoes, directly or through loss of natural characters as a result of adaptation to lab rearing, and lead to the competitiveness of sterile male being reduced. In the present study, the objective was to evaluate the effect of mass-rearing conditions on sterile male sexual competitiveness in semi-field cages compared to routine small scale laboratory rearing methods.

METHODS

Anopheles arabiensis immature stages were reared both on a large scale using a rack and tray system developed by the FAO/IAEA (MRS), and on a small scale using standard laboratory rearing trays (SRS). Mosquito life history traits such as pupation rate, emergence rate, adult size as well as the effect of irradiation on adult longevity were evaluated. Moreover, 5-6 day old mosquitoes were released into field cages and left for two nights to mate and the mating competitiveness between sterile mass-reared males and fertile males reared on a small scale when competing for small scale reared virgin females was investigated. Resulting fertility in a treatment ratio of 1:1:1 (100 irradiated males: 100 non-irradiated males: 100 virgin females) was compared to control cages with 0:100:100 (non-irradiated control) and 100:0:100 (irradiated control).

RESULTS

No significant differences in life history parameters were observed between rearing methods. The competitiveness index of mass reared males (0.58) was similar to males reared on a small scale (0.59). A residual fertility rate of 20% was observed in the irradiated control (100:0:100), measured as the percentage of eggs collected from the cages which developed to adulthood. No significant difference was observed (t = 0.2896, df = 4, P = 0.7865) between the rearing treatments (MRS and SRS) in the fertility rate, a measure of mating competitiveness.

CONCLUSIONS

The results showed that the FAO/IAEA mass-rearing process did not affect mosquito life history parameters or the mating competitiveness of males.

Development of Aedes albopictus (Diptera: Culicidae) Larvae Under Different Laboratory Conditions

Critical to successful application of the sterile insect technique against Aedes albopictus (Skuse) is the development of an efficient and standardized rearing protocol to be employed in the mass production system. In this study, several life history traits of Ae. albopictus were analyzed to identify upper and lower thresholds of larval density and diet concentration. Survival to pupation, time to pupation, and sex ratio were evaluated under a range of larval densities (0.5-5 larvae/ml) and food levels (0.05-1.6 mg/larva/d) using two larval diets (one locally developed; one developed by the FAO/IAEA). The larvae reared at 28 °C, at a density of 2 larvae/ml and receiving a food dose equal to 0.6 mg/larva/d of a diet consisting of 50% tuna meal, 50% bovine liver powder (the FAO/IAEA diet), and, as an additive, 0.2 g of Vitamin Mix per 100 ml of diet solution, developed in 5 d and had 90% survival to the pupal stage. With this rearing regime male pupae production 24 h after the onset of pupation was the highest; these pupae were ∼94% male.

Large-scale Anopheles arabiensis egg quantification methods for mass-rearing operations

Background

The success of the sterile insect technique relies, among other things, on the continuous release of over flooding numbers of sexually competitive sterile males into the target area. To produce sufficiently large quantities of sterile males, rearing protocols need to be optimized including the development and validation of a standardized egg quantification method.

Methods

Batches of 1000 freshly laid eggs collected from standard rearing cages were counted, gently dried under laboratory conditions (27 ± 1 °C, 75 ± 5 % RH) and combined so that 1000–8000 eggs were weighed, to calculate the correlation between weight and number. The actual counted egg number and the egg number estimated by weighing were further compared for samples of 1000, 3000 and 4000 eggs collected from both standard and mass-rearing cages. The effect of drying, brushing and weighing on egg hatch rate was evaluated in three samples each of 1000 fresh and 1000 dried eggs, and in batches of 1000, 3000 and 4000 dried eggs. Pupal production and adult life history traits were assessed for dried eggs hatched and reared in mass-rearing trays. Expected egg numbers and actual observed mean egg numbers were compared after gentle drying, and after applying a rapid drying method exposure to wind speed of 1.8 m/s for 30 min.

Results

A significant positive relationship between the number of dried eggs and egg weight was observed and the equation ‘Weight (mg) = (0.00399 × Number of counted eggs) + 0.536 was derived. The actual counted mean egg number and the egg number estimated by weighing were similar for samples from small rearing cages but significantly lower for samples of 3000 and 4000 egg samples collected from mass-rearing cages. No negative effect of the drying, brushing and weighing process on egg hatch rate was observed. No significant difference was observed in any life history trait between adults reared from dried or from fresh eggs up to twenty-one days post emergence. The mean number of eggs counted from a given replicate’s weight was significantly higher for egg batches fast dried with a suction device compared to those dried with a gentle drying method (fast: 1075 ± 9, gentle: 1024 ± 7).

Conclusion

An equation has been derived to allow accurate quantification of dried Anopheles arabiensis eggs based on weight, enabling more accurate quantification of eggs for consistent larval rearing density to be achieved. Eggs can be dried for weighing in a manner which does not impair the quality of resulting adults.

Stimulating Anopheles gambiae swarms in the laboratory: application for behavioural and fitness studies

Background

Male Anopheles mosquitoes that swarm rely in part on features of the environment including visual stimuli to locate swarms. Swarming is believed to be the primary behaviour during which mating occurs in the field, but is not a common behaviour in the laboratory. Features that stimulate male Anopheles gambiae G3 strain swarming were created in novel large indoor cages.

Methods

The following visual features were tested in all combinations to determine which were important for swarm formation. Large cages and fading ceiling lights at dusk alone did not stimulate swarming while a dark foreground and contrasting illuminated background with a contrasting landmark stimulated and localized swarm formation during artificial twilight. Given the need to test transgenic strains in as natural a setting as possible, in this study it was investigated whether induced swarm behaviour and cage size would affect relative mating performance of wild-type and transgenic β2Ppo1 and β2Ppo2 A. gambiae sexually sterile males.

Results

Even using a mosquito colony that has been in laboratory culture for 39 years, swarming behaviour was induced by this novel arrangement. The presence of swarming stimuli was associated with an increase in insemination frequency from 74.3 to 97.7% in large cages. Transgenic males showed a lower competitiveness in large cages compared to small cages regardless of the presence of swarming stimuli.

Conclusions

The results of the present study are discussed in view of the progressive evaluation of genetically modified A. gambiae strains and the potential applications of reproducing swarms in controlled conditions to dissect the mating behaviour of this species and the mechanisms controlling it.

Participation of irradiated Anopheles arabiensis males in swarms following field release in Sudan

Background

The success of the sterile insect technique (SIT) depends the release of large numbers of sterile males, which are able to compete for mates with the wild male population within the target area. Unfortunately, the processes of colonisation, mass production and irradiation may reduce the competitiveness of sterile males through genetic selection, loss of natural traits and somatic damage. In this context, the capacity of released sterile Anopheles arabiensis males to survive, disperse and participate in swarms at occurring at varying distances from the release site was studied using mark-release-recapture (MRR) techniques.

Methods

In order to assess their participation in swarms, irradiated and marked laboratory-reared male mosquitoes were released 50, 100 or 200 m from the known site of a large swarm on three consecutive nights. Males were collected from this large swarm on subsequent nights. Over the three days a total of 8,100 males were released. Mean distance travelled (MDT), daily probability of survival and estimated population size were calculated from the recapture data. An effect of male age at the time of release on these parameters was observed.

Results

Five per cent of the males released over three days were recaptured. In two-, three- and four-day-old males, MDT was 118, 178 and 170 m, and the daily survival probability 0.95, 0.90 and 0.75, respectively. From the recapture data on the first day following each release, the Lincoln index gives an estimation of 32,546 males in the natural population.

Discussion

Sterile An. arabiensis males released into the field were able to find and participate in existing swarms, and possibly even initiate swarms. The survival probability decreased with the age of male on release but the swarm participation and the distance travelled by older males seemed higher than for younger males. The inclusion of a pre-release period may thus be beneficial to male competitiveness and increase the attractiveness of adult sexing techniques, such as blood spiking.

Occurrence of natural Anopheles arabiensis swarms in an urban area of Bobo-Dioulasso City, Burkina Faso, West Africa

The swarming behaviour of natural populations of Anopheles arabiensis was investigated by conducting transect surveys on 10 consecutive days, around dusk, from March to April and from September to October 2012 in Dioulassoba, a district of Bobo-Dioulasso city in Burkina Faso (West Africa). Swarms were observed outside, around identified larval breeding sites on the banks of the Houet River, as well as in the open-air courtyards found at the centre of many homes in the region. Swarms were found to occur in open sunlit spaces, mostly located above physical or visual cues somehow visually distinct from the surrounding area. Overall 67 and 78 swarms were observed, respectively, during the dry season (March-April) and the rainy season (September-October) of 2012, between 1.5m and 4.5m above the ground at their centre. 964 mosquitoes were collected and analysed from dry season swarms, of which most were male, and all were An. arabiensis, as were the few resting mosquitoes collected indoors. Larvae collected from breeding sites found on the banks of the Houet River mostly consisted of An. arabiensis and only a minority of Anopheles coluzzii (formerly identified as An. gambiae M form). Of 1694 mosquitoes analysed from 78 swarms in the rainy season collections, a few An. gambiae (formerly known as An. gambiae S form) males were identified, and the remainders were An. arabiensis. The majority of larvae collected during the wet season from the same breeding sites were identified as An. arabiensis followed by An. coluzzii and An. gambiae. The same pattern of species composition was observed in resting mosquitoes, though the proportion of An. arabiensis was less overwhelming. These data support the conclusion that An. arabiensis is the most prevalent species in this area, though the difference in species composition when using different population sampling techniques is noteworthy. Further studies are required for more detailed investigations of male dispersal, feeding behaviour and mating patterns in this urban setting.

Current status and future challenges for controlling malaria with the sterile insect technique: technical and social perspectives

The intolerable burden of malaria, when faced with high levels of drug resistance, increasing insecticide resistance and meagre resources at the national level, remains a great public health challenge to governments and the research/control community. Efficient control methods against the vectors of malaria are desperately needed. Control strategies for malaria that integrate the transfer of sterile sperm by released males to wild virgin females with other control tactics are currently being developed, and optimised mass-rearing, irradiation and release techniques are being validated in several field sites. However, the success of this strategy as part of wider pest control or health management programmes strongly depends on gaining public understanding and acceptance. Here we attempt to review what progress has been made and the remaining challenges surrounding the use of the sterile insect technique against malaria from technical and social perspectives.

Efficiency of three diets for larval development in mass rearing Aedes albopictus (Diptera: Culicidae)

A fundamental step in establishing a mass production system is the development of a larval diet that promotes high adult performance at a reasonable cost. To identify a suitable larval diet for Aedes albopictus (Skuse), three diets were compared: a standard laboratory diet used at the Centro Agricoltura Ambiente, Italy (CAA) and two diets developed specifically for mosquito mass rearing at the FAO/IAEA Laboratory, Austria. The two IAEA diets, without affecting survival to the pupal stage, resulted in a shorter time to pupation and to emergence when compared with the CAA diet. At 24 h from pupation onset, 50 and 90% of the male pupae produced on the CAA and IAEA diets, respectively, had formed and could be collected. The diet received during the larval stage affected the longevity of adult males with access to water only, with best results observed when using the CAA larval diet. However, similar longevity among diet treatments was observed when males were supplied with sucrose solution. No differences were observed in the effects of larval diet on adult male size or female fecundity and fertility. Considering these results, along with the relative costs of the three diets, the IAEA 2 diet is found to be the preferred choice for mass rearing of Aedes albopictus, particularly if a sugar meal can be given to adult males before release, to ensure their teneral reserves are sufficient for survival, dispersal, and mating in the field.

Density-dependent effects in experimental larval populations of Anopheles arabiensis (Diptera: Culicidae) can be negative, neutral, or overcompensatory depending on density and diet levels

Anopheles arabiensis Patton (Diptera: Culicidae) larvae were reared from hatching to the adult stage in the laboratory under a range of diet and larval concentrations using a factorial design. The range circumscribed most of the larval densities and diet concentrations that would allow larval growth and survival using the particular diet formulation and water volume we tested. We determined how these variables affected three outcomes, as follows: larval development rate, survival, and wing length. As has been reported previously, negative density dependence of survival as a function of increased larval density was the prevalent effect on all outcomes when diet was limiting. When diet was not limiting, density dependence was not observed, and three cases of overcompensatory survival were seen. We discuss these results in the context of diet and larval densities for mass rearing and the effect of larval competition on control strategies.

Female-specific flightless phenotype for mosquito control

Dengue and dengue hemorrhagic fever are increasing public health problems with an estimated 50-100 million new infections each year. Aedes aegypti is the major vector of dengue viruses in its range and control of this mosquito would reduce significantly human morbidity and mortality. Present mosquito control methods are not sufficiently effective and new approaches are needed urgently. A "sterile-male-release" strategy based on the release of mosquitoes carrying a conditional dominant lethal gene is an attractive new control methodology. Transgenic strains of Aedes aegypti were engineered to have a repressible female-specific flightless phenotype using either two separate transgenes or a single transgene, based on the use of a female-specific indirect flight muscle promoter from the Aedes aegypti Actin-4 gene. These strains eliminate the need for sterilization by irradiation, permit male-only release ("genetic sexing"), and enable the release of eggs instead of adults. Furthermore, these strains are expected to facilitate area-wide control or elimination of dengue if adopted as part of an integrated pest management strategy.

Reversible and irreversible non-internalized LDL and methyl LDL accumulation by human fibroblasts

In previous in vivo animal studies, we showed that low density lipoprotein (LDL) accumulated irreversibly at the edges of healing arterial lesions rather than being internalized and degraded. To see if similar LDL accumulation occurs in vitro, fibroblasts from normal and homozygous familial hypercholesterolemic (FH) subjects were incubated at 37 degrees C with 125I-LDL and 125I-methyl LDL; the latter is not recognized by any known LDL receptor. Normal fibroblast accumulation of LDL and methyl LDL (5 microg/ml) plateaued within 1 h at 200 and 100 ng/mg, respectively. With FH cells, both LDL and methyl LDL accumulation plateaued at 100 ng/mg. Lipoprotein accumulation by both cell types rose steeply at concentrations up to 15-25 microg/ml, and less so at higher concentrations. Except for degradation of LDL by normal cells, degradation was minimal, which indicated that much of the lipoprotein accumulation was unaccompanied by internalization. The accumulation of both lipoproteins by both cell types was greater at 37 degrees C than at 4 degrees C, and was inhibited between 43 and 75% by homologous unlabeled lipoprotein. To see if any accumulation was irreversible, cells were incubated with radiolabeled lipoproteins for 3 h (pulse), then with homologous unlabeled lipoproteins for up to 20 h (chase). About 50% of intact radiolabeled lipoprotein rapidly dissociated from cells into the medium in the first 4 h of the chase period. In contrast, between 4 and 20 h, most of the remaining intact LDL and methyl LDL appeared to be irreversibly bound, because it was released at a rate of only 0-1%/h. Thus, we conclude that, under the conditions studied, both reversible and irreversible non-internalized LDL binding play a major role in LDL accumulation by cultured cells.

The Quinapril Ischemic Event Trial (QUIET): evaluation of chronic ace inhibitor therapy in patients with ischemic heart disease and preserved left ventricular function

Angiotensin-converting enzyme inhibitors improve endothelial function, inhibit experimental atherogenesis, and decrease ischemic events. The Quinapril Ischemic Event Trial was designed to test the hypothesis that quinapril 20 mg/day would reduce ischemic events (the occurrence of cardiac death, resuscitated cardiac arrest, nonfatal myocardial infarction, coronary artery bypass grafting, coronary angioplasty, or hospitalization for angina pectoris) and the angiographic progression of coronary artery disease in patients without systolic left ventricular dysfunction. A total of 1,750 patients were randomized to quinapril 20 mg/day or placebo and followed a mean of 27 +/- 0.3 months. The 38% incidence of ischemic events was similar for both groups (RR 1.04; 95% confidence interval 0.89 to 1.22; p = 0.6). There was also no significant difference in the incidence of patients having angiographic progression of coronary disease (p = 0.71). The rate of development of new coronary lesions was also similar in both groups (p = 0.35). However, there was a difference in the incidence of angioplasty for new (previously unintervened) vessels (p = 0.018). Quinapril was well tolerated in patients after angioplasty with normal left ventricular function. Quinapril 20 mg did not significantly affect the overall frequency of clinical outcomes or the progression of coronary atherosclerosis. However, the absence of the demonstrable effect of quinapril may be due to several limitations in study design.

Low-density lipoprotein apheresis therapy during pregnancy

Pregnancy in patients with severe hypercholesterolemia and coronary artery disease results in multiple problems both for mother and fetus; the most potent agents for low-density lipoprotein (LDL) cholesterol reduction, the HMG-CoA reductase inhibitors (statins) cannot be used during pregnancy. We present a case in which LDL apheresis via heparin-induced extracorporeal LDL precipitation was employed safely and efficaciously during pregnancy in a woman with heterozygous familial hypercholesterolemia and stable coronary artery disease.

A new model-based technique for enhanced small-vessel measurements in X-ray ciné-angiograms

Arterial diameter estimation from X-ray ciné angiograms is important for quantifying coronary artery disease (CAD) and for evaluating therapy. However, diameter measurement in vessel cross sections < or =1.0 mm is associated with large measurement errors. We present a novel diameter estimator which reduces both magnitude and variability of measurement error. We use a parametric nonlinear imaging model for X-ray ciné angiography and estimate unknown model parameters directly from the image data. Our technique allows us to exploit additional diameter information contained within the intensity profile amplitude, a feature which is overlooked by existing methods. This method uses a two-step procedure: the first step estimates the imaging model parameters directly from the angiographic frame and the second step uses these measurements to estimate the diameter of vessels in the same image. In Monte-Carlo simulation over a range of imaging conditions, our approach consistently produced lower estimation error and variability than conventional methods. With actual X-ray images, our estimator is also better than existing methods for the diameters examined (0.4-4.0 mm). These improvements are most significant in the range of narrow vessel widths associated with severe coronary artery disease.

Non-pharmacological lowering of low-density lipoprotein by apheresis and surgical techniques

In the past year, new data have appeared on the long-term benefits of low-density lipoprotein apheresis in severely hypercholesterolemic patients who are refractory to lipid-lowering drug therapy. Such data are critical for clinical decision-making, because they confirm the hypothesis that the dramatic reduction in low-density lipoprotein made possible by this technique produces clear-cut clinical benefits. Because of its efficacy and low incidence of side-effects, apheresis for severe drug-refractory hypercholesterolemia has superseded surgical approaches, such as liver transplantation or ileal bypass.

Angiotensin-converting enzyme inhibition as antiatherosclerotic therapy: no answer yet. QUIET Investigators. QUinapril Ischemic Event Trial

Angiotensin-converting enzyme inhibitors have proven to be of clinical benefit in congestive heart failure. Whether they also provide benefit to patients with coronary artery disease in the absence of congestive heart failure via an antiatherosclerotic mechanism is a question the QUinapril Ischemic Event Trial quantitative coronary angiography (QCA) study attempted to answer: 1,750 patients with normal left ventricular function who were undergoing coronary angiography and angioplasty were randomized to 20 mg/day of quinapril versus placebo and followed for 3 years for cardiac end points. A randomly selected subgroup of the total cohort underwent follow-up angiography. The primary QCA end point was the categorical designation of progression versus nonprogression, defined either by QCA or by a cardiac event in patients selected for the QCA trial who had no usable follow-up x-ray film. Secondary end points in patients with 2 angiograms were: new stenosis development, change in minimum lumen diameter index, and change in percent diameter stenosis index. There were 119 progressors among 243 placebo-treated patients (49%) and 111 progressors among 234 quinapril-treated patients (47%) (p = NS). There were 44 patients with new stenosis development in the placebo group (19%) and 50 (22%) in the quinapril group (p = NS). Change in minimum lumen diameter index was -0.21+/-0.03 mm in the placebo group and -0.18+/-0.03 mm in the quinapril group (p = NS). Finally, change in percent diameter stenosis index was +5.1+/-1.0 in the placebo group and +3.5+/-1.0 in the quinapril group (p = NS). Potential confounders of this trial are presented and discussed.

Measurement of the time course of peripheral vasoactivity: results in cigarette smokers

The brachial artery response to flow was assessed non-invasively by ultrasonic measurement of arterial diameter before and 1 min after 5 min of cuff-induced ischemia. It was hypothesized that continuous measurement of arterial diameter and flow velocity would provide a more complete and accurate evaluation of the response to change in blood flow. Therefore, a system to provide this data was developed and its utility in exploring the acute and chronic effects of smoking on arterial function was demonstrated. Brachial artery diameter and flow velocity were measured before, during and for at least 3 min after 5-min of forearm cuff occlusion. Measurements were acquired from 12 habitual smokers (mean 18.3 pack years), after at least 2 h (mean 6.5 h) without smoking ('pre-cigarette') and immediately after smoking one cigarette ('post-cigarette'), as well as from 12 age- and sex-matched lifelong non-smokers. The slope of brachial artery diameter versus time during the occlusion period and the maximum dilation after cuff release relative to the pre-occlusion diameter were significantly decreased in pre-cigarette smokers compared with non-smokers (P < 0.0001 for both comparisons). Importantly, the absolute arterial dilation during the period of increased flow (i.e. reactive hyperemia) was equal for the pre-cigarette smokers and non-smokers (0.31 +/- 0.03 vs. 0.32 +/- 0.04 mm, respectively). Immediately after smoking, the flow response parameters in chronic smokers changed toward non-smoker values (P < 0.001 for post-cigarette vs. pre-cigarette comparisons of the diameter slope during occlusion and the maximum dilation after cuff release relative to pre-occlusion diameter). Thus, continuous diameter measurements in smokers who refrained from smoking demonstrated abnormal constriction of the brachial artery during the low flow period of cuff occlusion, but normal absolute dilation during the period of increased flow. Immediately after smoking, the artery no longer constricted during occlusion. These findings demonstrate the potential value of continuous monitoring of arterial diameter and flow velocity before, during and after application of a vasoactive stimulus.

Histopathology of human coronary atherosclerosis by quantifying its chemical composition with Raman spectroscopy

BACKGROUND

Lesion composition, rather than size or volume, determines whether an atherosclerotic plaque will progress, regress, or rupture, but current techniques cannot provide precise quantitative information about lesion composition. We have developed a technique to assess the pathological state of human coronary artery samples by quantifying their chemical composition with near-infrared Raman spectroscopy.

METHODS AND RESULTS

Coronary artery samples (n=165) obtained from explanted recipient hearts were illuminated with 830-nm infrared light. Raman spectra were collected from the tissue and processed to quantify the relative weights of cholesterol, cholesterol esters, triglycerides and phospholipids, and calcium salts in the examined artery location. The artery locations were then classified by a pathologist and grouped as either nonatherosclerotic tissue, noncalcified plaque, or calcified plaque. Nonatherosclerotic tissue, which included normal artery and intimal fibroplasia, contained an average of approximately 4+/-3% cholesterol, whereas noncalcified plaques had approximately 26+/-10% and calcified plaques approximately 19+/-10% cholesterol in the noncalcified regions. The average relative weight of calcium salts was 1+/-2% in noncalcified plaques and 41+/-21% in calcified plaques. To make this quantitative chemical information clinically useful, we developed a diagnostic algorithm, based on a first set of 97 samples, that demonstrated a strong correlation of the relative weights of cholesterol and calcium salts with histological diagnoses of the same locations. This algorithm was then prospectively tested on a second set of 68 samples. The algorithm correctly classified 64 of these new samples, thus demonstrating the accuracy and robustness of the method.

CONCLUSIONS

The pathological state of a given human coronary artery may be assessed by quantifying its chemical composition, which can be done rapidly with Raman spectroscopic techniques. When Raman spectra are obtained clinically via optical fibers, Raman spectroscopy may be useful in monitoring the progression and regression of atherosclerosis, predicting plaque rupture, and selecting proper therapeutic intervention.

Determination of human coronary artery composition by Raman spectroscopy

BACKGROUND

We present a method for in situ chemical analysis of human coronary artery using near-infrared Raman spectroscopy. It is rapid and accurate and does not require tissue removal; small volumes, approximately 1 mm3, can be sampled. This methodology is likely to be useful as a tool for intravascular diagnosis of artery disease.

METHODS AND RESULTS

Human coronary artery segments were obtained from nine explanted recipient hearts within 1 hour of heart transplantation. Minces from one or more segments were obtained through grinding in a mortar and pestle containing liquid nitrogen. Artery segments and minces were excited with 830 nm near-infrared light, and Raman spectra were collected with a specially designed spectrometer. A model was developed to analyze the spectra and quantify the amounts of cholesterol, cholesterol esters, triglycerides and phospholipids, and calcium salts present. The model provided excellent fits to spectra from the artery segments, indicating its applicability to intact tissue. In addition, the minces were assayed chemically for lipid and calcium salt content, and the results were compared. The relative weights obtained using the Raman technique agreed with those of the standard assays within a few percentage points.

CONCLUSIONS

The chemical composition of coronary artery can be quantified accurately with Raman spectroscopy. This opens the possibility of using histochemical analysis to predict acute events such as plaque rupture, to follow the progression of disease, and to select appropriate therapeutic interventions.

Peripheral vasoactivity in familial hypercholesterolemic subjects treated with heparin-induced extracorporeal LDL precipitation (HELP)

Hypercholesterolemia is associated with abnormalities in arterial vasoactivity which can be reversed with cholesterol-reducing therapies. Heparin-induced extracorporeal LDL precipitation (HELP), an invasive method for treating refractory hypercholesterolemia, causes regression of both xanthomas and atherosclerosis, but its effect on vasoactivity has not been investigated. We tested the effects of HELP on vasoactivity with an ultrasound system for continuous measurement of arterial flow velocity and end-diastolic diameter. We measured brachial artery vasoactivity before, during, and after a 5 min forearm vascular occlusion. Vasoactivity measurements were acquired from 6 subjects with familial hypercholesterolemia (FH) who had been treated chronically with HELP, immediately before and after each of 4 treatments, and from 12 age- and sex-matched normocholesterolemic subjects (2 matched with each HELP subject). Peak arterial dilation after cuff release, relative to the pre-occlusion diameter, was similar for the pre-treatment, post-treatment, and normocholesterolemic groups (0.29 mm pre-treatment, 0.30 mm post-treatment and 0.33 mm normocholesterolemic, P = NS). The slope of arterial diameter during occlusion was also similar for the three groups (-0.10 microm/s pre-treatment, 0.02 microm/s post-treatment, and 0.06 microm/s normocholesterolemic, P = NS). These two parameters are known to be decreased in hypercholesterolemic subjects to an extent which could be readily detected by the power of this study. Interestingly, one homozygous FH subject consistently demonstrated significant improvement in these two parameters immediately after HELP, suggesting an individual difference in arterial physiology. On average, FH patients treated chronically with HELP have similar vasoactivity to age- and sex-matched subjects with low risk for atherosclerosis. This result, in light of the many studies that have associated hypercholesterolemia with abnormal vasoactivity, suggests that chronic HELP therapy improves vasoactivity in patients with severe hypercholesterolemia.

Comparison of B-mode, M-mode and echo-tracking methods for measurement of the arterial distension waveform

Measurements of arterial diameter throughout the cardiac cycle (i.e., the arterial distension waveform) are conducted increasingly to study mechanical properties of the arterial wall and changes associated with disease. The distension waveform of peripheral arteries can be measured noninvasively via ultrasonic echo tracking. M-mode imaging, and B-mode imaging. Of these, echo tracking is the most popular method because of its single micrometer resolution during continuous measurements under ideal conditions. However, high resolution within continuous measurements does not imply high reproducibility between measurements. Therefore, we compared repeated measurements of the amplitude of common carotid artery distension in 26 subjects, obtained sequentially in random order by: 1. Off-line echo tracking of digitized radiofrequency ultrasound; 2. M-mode imaging with automated edge detection; and 3. 30-Hz B-mode imaging with automated edge detection and model-based diameter estimation. In each case, the transducer was hand-held and was removed from the neck between repeated measurements. The amplitude of arterial distension was estimated from the serial diameter measurements by maximum likelihood (ML) estimation, by least-squares fit of a Fourier series model, and by application of a cubic smoothing spline. Within continuous measurements, the standard deviation of the ML distension amplitude for neighboring cardiac cycles was significantly smaller (p > 0.05) with echo-tracking (0.023 mm) than with the B-mode (0.036 mm) or M-mode (0.074 mm) methods. However, between discontinuous measurements on the same subject, the standard deviation of the ML distension amplitude was similar for the echo-tracking (0.076 mm) and B-mode (0.073 mm) methods. The Fourier series model and the cubic smoothing spline slightly reduced the standard deviation of the B-mode and M-mode distension amplitudes, but also reduced the mean amplitude estimate. On the basis of this relative comparison of methods, we conclude that, although echo tracking offers high resolution for continuous measurements, the reproducibility of discontinuous measurements of carotid artery distension is no better with echo tracking than can be obtained from 30-Hz B-mode images.

Baseline clinical and angiographic data in the Quinapril Ischemic Event (QUIET) Trial

The QUinapril Ischemic Event Trial (QUIET) is the first prospective, double-blind, placebo-controlled trial to investigate the long-term antiatherosclerotic effects of angiotensin-converting enzyme inhibition. Normotensive, nonhyperlipidemic subjects (1,750) with normal left ventricular systolic function were randomly assigned to treatment or placebo at percutaneous transluminal coronary angioplasty (PTCA). The primary end point is time to first cardiac ischemic event. Baseline clinical characteristics are (mean +/- SD): age 58 +/- 9 years; blood pressure 123 +/- 15/74 +/- 10 mm Hg; low density lipoprotein cholesterol 124 +/- 27 mg/dL; high density lipoprotein cholesterol 37 +/- 10 mg/dL; and triglycerides 167 +/- 91 mg/dL. In addition, 81% are men; 22% are current smokers; 49% give a history of myocardial infarction. Baseline angiographic characteristics are (mean +/- SD): left ventricular ejection fraction 59% +/- 11%; per patient diameter stenosis (excluding the PTCA segment) 49% +/- 31%; 8.9 +/- 3.5 analyzable segments per patient (excluding the PTCA segment), 3.8 +/- 2.3 of which have visible stenosis. Including the PTCA segment, 52% have single vessel disease and 48% have multivessel disease. Baseline angiographic data for non-PTCA segments will be correlated with cardiac ischemic events which occur after 6 months. Up to 500 subjects will undergo follow-up angiography with quantitative coronary angiographic analysis (QCA) of baseline and follow-up films. The primary QCA end point will be per-patient categorical designation as progressor or nonprogressor based on the presence or absence of > or = 400 microns narrowing in > or = 1 vessels that did not undergo PTCA.

Biodistribution and autoradiographic localization of I-125--labeled synthetic Peptide in aortic atherosclerosis in cholesterol-fed rabbits

I-125 labeled SP4 is a synthetic oligopeptide derived from apolipoprotein B of low-density lipoprotein that has been shown to localized in atherosclerotic plaques in experimental animals. However, its biodistribution and mechanism of localization need to be further elucidated. Twenty-four cholesterol-fed (CF) and 20 normal (NL) New Zealand White rabbits were injected with I-125-SP4 and killed 15 to 30 min (6 NL; 6 CF) or 2 h (14 NL; 18 CF) later. We obtained aortic autoradiograms and activity concentrations (% injected dose/gm) in aortic segments and other tissues. The uptake of I-125-SP4 was higher in CF than in NL rabbits in all aortic segments (p < 0.05). I-125-SP4 was cleared rapidly in both CF and NL rabbits with 60 to 70% of the injected dose cleared from the blood by 1 h. No statistically significant differences in radiotracer biodistribution were observed between NL and CF rabbits although activity tended to be higher in the liver, gallbladder, and intestine in NL rabbits and in the kidney and spleen in CF rabbits. Silver grains were distributed mainly on foam cells of the fatty streaks in aortic microautoradiograms from two additional rabbits that had been injected with I-125-SP4. There were 23,518 plus minus 15,878 (SD) grains/mm(2) in fatty plaques but only 14,669 plus minus 11,035 grains/mm(2) in media muscle (p < 0.0001 [9 sections, 17 areas evaluated] in an atherosclerotic animal) in injected animals and 13,439 plus minus 5,565 grains/mm(2) in media muscle (two sections, four areas) in the normal control animals (NS versus media of atherosclerotic animal). I-125-SP4 specifically localizes in aortic atherosclerotic plaques in CF rabbits. There is no significant difference in tissue distribution between normal and CF rabbits except in the aorta. Preliminarily, it appears that the site of tracer uptake is on foam cells and this suggests the possibility of relative specificity for fatty plaque.

Treatment of hypercholesterolemia with heparin-induced extracorporeal low-density lipoprotein precipitation (HELP)

Familial hypercholesterolemia (FH) can cause early disability and death from premature atherosclerotic cardiovascular disease. Patients homozygous for the disease have very high plasma cholesterol, extensive xanthomatosis, and die from atherosclerosis in childhood or early adulthood. Past attempts to improve the prognosis included removal of cholesterol from the circulation by ileal bypass or biliary diversion. Neither treatment was successful. Direct removal by plasmapheresis of low-density lipoprotein (LDL), the primary carrier of cholesterol in plasma, was first performed on an FH homozygous patient in 1966. The treatment was well tolerated and led to rapid diminution of xanthomas. Other experimental treatments included selective LDL apheresis with monoclonal or polyclonal antibody affinity columns. A method for selective LDL apheresis was developed in 1983 by Armstrong, Seidel, and colleagues based on heparin precipitation of LDL at low pH. This method, called HELP, removes all apolipoprotein B-containing lipoproteins including LDL and lipoprotein (a), as well as some fibrinogen. LDL apheresis by HELP is well tolerated; the incidence of side effects is low, and the treatment has been associated with regression of cardiovascular disease. LDL apheresis, rather than liver transplantation, is the treatment of choice for patients with severe, life-threatening hypercholesterolemia which does not respond to diet and drug therapy.

The application of echo-tracking methods to endothelium-dependent vasoreactivity and arterial compliance measurements

Measurements of endothelium-dependent vasoreactivity and arterial compliance are important metrics of vascular pathophysiology which may be used for the development and evaluation of therapeutic methods. The technique of ultrasonic echo tracking is applicable to measurements of endothelium-dependent vasoreactivity and arterial compliance. To evaluate the application of echo tracking to these measurements, we constructed a system based upon analog-to-digital conversion and storage of the radio frequency (RF) ultrasound signals. Off-line analysis of the RF data with various echo-tracking algorithms demonstrated two potential sources of error: tracking drift and RF transition regions. The tracking drift resulted from the slow accumulation of tracking error. The RF transition regions were associated with disparate motions of neighboring reflectors or the insonation of a new series of tissue layers. As a result of these sources of error, the application of echo tracking to endothelium-dependent vasoreactivity measurements is unlikely to outperform duplex ultrasound methods. The application of echo tracking to arterial compliance measurements via the arterial pressure/diameter relationship may produce variable results due to RF transition regions. Finally, the application of echo tracking to arterial compliance measurements via the pulse wave velocity is relatively insensitive to these sources of error because the pulse-wave velocity measurement depends upon the timing of the peak arterial distension, not on the absolute value of the distension.

New methods for arterial diameter measurement from B-mode images

Arterial diameter is an important parameter of vascular physiology in vivo. Noninvasive measurements of arterial diameter can be used in the assessment of endothelium-dependent vasoreactivity (EDV) and arterial compliance. Measurements of EDV may serve for assessment of early atherosclerosis. The potential value of EDV measurements with specificity for individual subjects is a strong motivation for improvements in the ultrasonic measurement of arterial diameter. This article presents and evaluates new methods for the measurement and tracking of arterial diameter from B-mode images. B-mode images acquired in planes longitudinal to the vessel and in planes rotated slightly off of the vessel axis ("skew") are considered. The cross-sections of arteries in these planes are modeled as parabola pairs or as ellipses. For the brachial artery, the variance of caliper-based diameter estimates (0.0139 mm2) is twice as large as that of elliptical-model-based diameter estimates (0.0072 mm2) and five times as large as parabolic-model-based diameter estimates (0.0027 mm2). Diameter estimates from the skew and longitudinal planes perform equivalently in limited-motion quantitative comparisons. However, diameter estimates from skew planes are less sensitive to translational motions of the artery. Also, translational motions are unambiguously represented in the skew image, thus facilitating compensatory motions of the transducer. The methods described here are relatively simple to implement and may provide adequate resolution for noninvasive assessment of EDV with individual specificity.

Selective removal of plasma low density lipoprotein with the HELP system: biweekly versus weekly therapy

PURPOSE

Biweekly (once every 2 weeks) heparin-induced extracorporeal low-density lipoprotein (LDL) precipitation (HELP) therapy was evaluated for safety and efficacy in selectively reducing LDL cholesterol levels compared with weekly HELP therapy.

PATIENTS AND METHODS

Biweekly treatments were given to high-risk, diet/drug resistant hypercholesterolemic patients (n = 23) after 6 months of weekly HELP therapy. Lipids, lipoprotein cholesterol, apolipoproteins A-I and B, and fibrinogen were measured on plasma samples before and after treatment.

RESULTS

Mean plasma volume treated was 2.8 l and mean treatment duration 1.7 h. Therapy complications were minimal. In 98% of 268 biweekly HELP treatments, LDL cholesterol levels were reduced by > 30%. For patients completing 6 months of biweekly therapy following 6 months' weekly therapy (n = 23), mean LDL cholesterol levels were reduced 138.5 mg/dl (111.2 mg/dl weekly) with a time-averaged decrease from mean pre-apheresis levels of 33% for biweekly therapy (39% weekly). Mean total cholesterol (161.2 mg/dl biweekly versus 132.9 weekly) and apolipoprotein B (104.6 mg/dl versus 92.6) levels were also reduced with each treatment. Mean HDL cholesterol was reduced only 6.1 mg/dl (6.3 mg/dl weekly).

CONCLUSIONS

Biweekly HELP treatments can safely reduce LDL cholesterol levels as consistently as weekly HELP treatments. However, the higher pre-treatment LDL cholesterol levels with biweekly treatments may produce less therapeutic benefit than with weekly therapy.

Homozygous Tangier disease and cardiovascular disease

Decreased levels of plasma high density lipoprotein (HDL) cholesterol have been associated with premature cardiovascular disease (CVD). Tangier disease is an autosomal co-dominant disorder in which homozygotes have a marked deficiency of HDL cholesterol and apolipoprotein (apo) A-I levels (both < 10 mg/dl), decreased low density lipoprotein (LDL) cholesterol levels (about 40% of normal), and mild hypertriglyceridemia. Homozygotes develop cholesterol ester deposition in tonsils (orange tonsils), liver, spleen, gastrointestinal tract, lymph nodes, bone marrow, and Schwann cells. Our purpose was to assess the prevalence of CVD in Tangier disease. We reviewed published clinical information on 51 cases of homozygous Tangier disease, report 3 new cases and provide autopsy information on 3 cases. Mean (+/- S.D.) lipid values of all cases were as follows: total cholesterol 68 +/- 30 mg/dl (32% of normal), triglycerides 201 +/- 118 mg/dl (162% of normal), HDL cholesterol 3 +/- 3 mg/dl (6% of normal) and LDL cholesterol 50 +/- 38 mg/dl (37% of normal). The most common clinical finding in these subjects (n = 54) was peripheral neuropathy which was observed in 54% of cases versus < 1% of control subjects (n = 3130). CVD was observed in 20% of Tangier patients versus 5% of controls (P < 0.05), and in those that were between 35 and 65 years of age, 44% (11 of 25) had evidence of CVD (either angina, myocardial infarction or stroke) versus 6.5% in 1533 male controls and 3.2% in 1597 female controls in this age group (P < 0.01). In 9 patients who died, 2 died prior to age 20 of probable infectious diseases, 3 of documented coronary heart disease at ages 48, 64, and 72, 2 of stroke at ages 56 and 69, one of valvular heart disease, and 1 of cancer. In three autopsy cases, significant diffuse atherosclerosis was observed in one at age 64, moderate atherosclerosis and cerebral infarction in another at age 56, but no atherosclerosis was noted in the third case who died of lymphoma at age 62. In one patient with established coronary heart disease, none of the lipid lowering agents used (niacin, gemfibrozil, estrogen or lovastatin) raised HDL cholesterol levels above 5 mg/dl. However, these agents did have significant effects on lowering triglyceride and LDL cholesterol levels. Our data indicate that there may be heterogeneity in these patients with regard to CVD risk, that peripheral neuropathy is a major problem in many patients, and that CVD is a significant clinical problem in middle aged and elderly Tangier homozygotes.(ABSTRACT TRUNCATED AT 400 WORDS)

External imaging of atherosclerosis in rabbits using an 123I-labeled synthetic peptide fragment

The oligopeptide fragment of apolipoprotein B, SP-4, has demonstrated pronounced uptake in the healing edges of balloon-injured rabbit aortic endothelium. To assess 123I-labeled SP-4 for identification of atherosclerotic plaques by gamma camera imaging, 14 Watanabe heritable hyperlipidemic (WHHL) and 5 normal rabbits were imaged 5 minutes and 12 and 24 hours after intravenous injection of 123I-SP-4. In addition, two WHHL and two normal rabbits were injected with 125I-SP-4 for autoradiography. Twelve of the 14 WHHL, but none of the normal, rabbits had visually apparent focal radioiodine accumulation in the region of the aorta. Focus-to-lung and focus-to-heart count ratios were 2.4 +/- 1.3 and 1.0 +/- 0.4, respectively. Five of the visually positive WHHL rabbits were reimaged 4 and 8 weeks later with 123I-NaI and 123I-SP-2 (an apo E peptide), respectively, as negative controls. Perceptible, but faint, aortic localization of 123I-NaI and of 123I-SP-2 was seen in only one animal each. The distributions of atherosclerotic lesions on photographs of the opened WHHL aortas and of film blackening on 125I-SP-4 autoradiograms were identical. In contrast, the two normal rabbit aortas did not exhibit plaques on photographs or film blackening on autoradiograms. Thus, in an animal model closely simulating human atherosclerotic disease, SP-4 localizes specifically in aortic atherosclerotic lesions.

Low-density lipoprotein modification and arterial wall accumulation in a rabbit model of atherosclerosis

Chemically or enzymatically modified low-density lipoproteins (LDL), with and without changes in surface charge, were studied in vivo in the healing, balloon catheter-deendothelialized rabbit aorta to determine the effect of LDL modification on its accumulation in arterial lesions. In this model, in which healing (reendothelialization) proceeds radially outward from individual aortic branch arteries, it was previously shown by autoradiography that two kinetically distinct compartments accumulated 125I-labeled LDL. In aortic regions which were still deendothelialized, accumulation was diffuse and labile. In contrast, at the edges of the islands of regenerating endothelium, LDL accumulation was intensely focal, as it is in human atherosclerotic lesions, and persisted for at least 40 h after injection in spite of falling levels of radiolabeled LDL in plasma [Chang, M. Y., et al. (1992) Arterioscler. Thromb. 12, 1088-1098]. In the present study, modified LDLs with gradations in charge change were prepared to clarify the role of changes in surface charge on focal aortic LDL accumulation. Oxidized LDL (weakly anionized), desialated LDL (weakly cationized), and reductively methylated LDL (no change in net charge) all accumulated focally. Focal accumulation of native LDL also occurred in ballooned rabbits fed probucol to inhibit LDL oxidation. Strongly anionized succinylated and diazobenzenearsonylated LDL and strongly cationized dimethylpropanediamine LDL did not accumulate focally. The results support the concept that focal sequestration of LDL in arterial lesions is mediated by specific, oxidation-independent patterns of charge and polarity on LDL which are disrupted by major changes in LDL surface charge.

Surface-induced conformational switching in amphiphilic peptide segments of apolipoproteins B and E and model peptides

The conformational and surface-binding properties of a synthetic peptide corresponding to Tyr-apolipoprotein B-100(1000-1016) amide, SP-4, which was previously shown to mimic the focal accumulation pattern of LDL on the healing de-endothelialized rabbit aorta [Shih et al. (1990) Proc. Natl. Acad. Sci. USA 87, 1436-1440], have been investigated. SP-4 behaves as an amphiphilic alpha-helical peptide at the air-water interface and bound to siliconized quartz slides. However, its N alpha-acetylated analogue formed beta-sheet structures at the air-water interface. Nonhomologous peptide models of SP-4 also exhibited mixed alpha-helical and beta-sheet surface-binding behavior. Peptides corresponding to the cationic apolipoprotein (apo) B/E receptor binding regions of apoE (SP-2) and apoB (SP-11) were also studied. SP-2 behaved as an amphiphilic alpha helix, but, surprisingly, SP-11 formed surface-induced beta-sheets. These results demonstrate that all of the peptides studied have surface-binding properties, and suggest further that either alpha-helical or beta-sheet peptide structures may determine the binding of LDL to the arterial wall or the apoB/E receptor.

Enzymatic modification of plasma low density lipoproteins in rabbits: a potential treatment for hypercholesterolemia

Phospholipase A2 (EC 3.1.1.4) hydrolyzes certain phospholipids of low density lipoprotein (LDL). Plasma clearance of phospholipase A2-modified human LDL is up to 17 times faster than that of native human LDL in hypercholesterolemic rabbits. Modification of blood lipoproteins of hypercholesterolemic rabbits was performed by using an extracorporeal circuit containing immobilized phospholipase A2. After 90-min treatments, nearly 30% decreases in plasma cholesterol concentrations were observed. Erythrocyte, leukocyte, and platelet counts showed no net change after treatment. This technique does not require any fluid replacement or sorbent regeneration and offers a potential approach for lowering serum cholesterol and LDL levels.

The QUinapril Ischemic Event Trial (QUIET) design and methods: evaluation of chronic ACE inhibitor therapy after coronary artery intervention

The rationale, trial design, and statistical aspects of QUIET, the QUinapril Ischemic Event Trial, are described. QUIET is a prospective, double-blind placebo-controlled study that will assess the ability of the angiotensin-converting enzyme (ACE) inhibitor quinapril to reduce the rate of cardiac ischemic events and to slow or prevent the development of coronary artery atherosclerosis as assessed by serial angiography in a normolipidemic population without left ventricular dysfunction. The study began in September 1991 and has completed recruitment with 1740 patients across 38 centers (28 U.S., 4 Canada, 6 Europe) by the end of 1992. Patients are randomized to 20 mg of quinapril or placebo once daily and continue in the study for 3 years. Study completion is projected for 1995.

Time course of 125I-labeled LDL accumulation in the healing, balloon-deendothelialized rabbit aorta

We previously showed by qualitative en face autoradiography that after 24 hours of circulation, 125I-labeled low density lipoprotein (LDL) injected in tracer amounts accumulated focally at the edges of regenerating endothelial islands in the balloon catheter-deendothelialized aorta of the normocholesterolemic rabbit. In the present study with the same animal model, we have used quantitative autoradiography to examine 125I-LDL accumulation in the healing aorta as a function of LDL circulation time from 2.5 to 40 hours. The results demonstrated that 125I-LDL accumulation in the healing aorta occurred in two kinetically and biochemically distinct compartments, one of which was in equilibrium with plasma and one of which sequestered LDL. LDL accumulation in the still-deendothelialized aorta (DEA) was diffuse and only moderately intense on autoradiography. It peaked 4 hours after injection; over the following 36 hours the disappearance of 125I-LDL from DEA paralleled the disappearance of 125I-LDL from plasma. In contrast, accumulation of 125I-LDL at the edges of regenerating endothelial islands was focal and intense. LDL accumulation in this compartment also peaked 4 hours after injection but remained elevated even at 40 hours, despite falling plasma levels of LDL. At 24 hours, edge LDL accumulation per unit area was more than five times greater than DEA accumulation. The data indicate that LDL accumulation in specific compartments of the functionally modified arterial wall occurs independently of either acute or chronic hypercholesterolemia. The contrast between labile LDL accumulation in DEA and persistent accumulation at the edges of healing aortic islands indicates that LDL accumulation in the two areas must involve different processes within the arterial wall itself.

99mTechnetium-labeled low density lipoprotein: receptor recognition and intracellular sequestration of radiolabel

99MTechnetium-labeled low density lipoprotein (99MTc-labeled LDL) was developed to detect atherosclerosis by external imaging with the gamma scintillation camera (Lees, et al. J. Nucl. Med. 1985. 26: 1056-1062; Lees, et al. Arteriosclerosis. 1988. 8: 461-470). The present study examined high affinity LDL receptor recognition and intracellular sequestration of 99MTc-labeled LDL by fibroblasts. There were no significant differences between 99MTc-labeled LDL and 125I-labeled LDL in binding parameters or percent inhibition of accumulation, which indicated that 99MTc labeling did not alter receptor recognition of LDL. At 4 degrees C the Kd (+SE) for 99MTc-labeled LDL and 125I-labeled LDL, respectively, was 1.52 +/- 0.24 and 1.45 +/- 0.14 micrograms/ml; Bmax (+/- SE) was 5.45 +/- 0.48 and 4.89 +/- 0.25 ng/well, respectively. Binding was saturated at about 2 micrograms/ml. The complete linearity of 99MTc-labeled LDL accumulation from 0-6 h and the positive slope from 6-24 h indicated that radiolabel that entered cells as 99MTc-labeled LDL was sequestered; pulse-chase experiments, which measured residual cell-associated radioactivity out to 24 h, also showed that radiolabel was trapped. Because radiolabel sequestration was essentially complete, and because 99MTc-labeled LDL was recognized by the LDL receptor equally as well as 125I-labeled LDL, it should be useful not only for imaging atherosclerosis, but also for quantitatively determining sites of utilization and degradation of LDL.

Focal accumulation of an apolipoprotein B-based synthetic oligopeptide in the healing rabbit arterial wall

The functions of surface-accessible domains of apolipoprotein (apo) B, the protein moiety of low density lipoprotein (LDL), are unknown, aside from the LDL receptor-binding domain, which lies toward the carboxyl-terminal end of apoB. Since LDL accumulation in arterial lesions does not depend on recognition of LDLs by a cell-surface receptor, we synthesized an oligopeptide with the sequence of the trypsin-accessible domain of apoB that lies closest to the amino-terminal end of the protein and compared its biological activity to that of another synthetic oligopeptide with the sequence of the heparin- and apoB/apoE receptor-binding domains of apoE. (Tyrosine was added at the amino-terminal end of each peptide to facilitate radiolabeling.) The 18-amino acid apoB-based peptide included residues 1000-1016 of apoB, for which no function has been previously described. In radioautographs, the 125I-labeled peptide accumulated focally at the healing edges of regenerating endothelial islands in the balloon-catheter deendothelialized rabbit aorta. In contrast, the 21-residue apoE-based peptide, which included residues 129-148 of apoE, accumulated diffusely and uniformly throughout the deendothelialized areas of the aorta. The data show that focal binding of the apoB-based peptide can delineate arterial lesions and suggest that this arterial wall-binding domain of apoB mediates accumulation of LDLs in arterial lesions.