Ledipasvir-Sofosbuvir for Treating Chronic Hepatitis C: A NICE Single Technology Appraisal-An Evidence Review Group Perspective

The National Institute for Health and Care Excellence (NICE) invited Gilead, the company manufacturing ledipasvir-sofosbuvir (LDV/SOF), to submit evidence for the clinical effectiveness and cost effectiveness of LDV/SOF for treating chronic hepatitis C. The School of Health and Related Research (ScHARR) Technology Assessment Group was commissioned as the Evidence Review Group (ERG). This paper describes the company's submission (CS), the ERG review and the subsequent decision of the NICE Appraisal Committee (AC). The ERG produced a critical review of the clinical effectiveness and cost-effectiveness evidence of LDV/SOF based upon the CS. The clinical effectiveness data for LDV/SOF were taken from ten trials: three phase III trials and seven phase II trials. Trials compared different durations of LDV/SOF, with and without ribavirin (RBV). There were no head-to-head trials comparing LDV/SOF with any comparator listed in the NICE scope. Data from the trials were mostly from populations with genotype 1 (GT1) disease, although some limited data were available for populations with genotypes 3 and 4. For GT1 treatment-naïve patients, sustained viral response for 12 weeks (SVR12) rates for LDV/SOF ranged from 93.1 to 99.4 % for subgroups of patients with non-cirrhotic disease, whilst SVR rates of 94.1 to 100 % were reported for subgroups of patients with compensated cirrhosis. For GT1 treatment-experienced patients, SVR12 rates ranging from 95.4 to 100 % were reported for subgroups of non-cirrhotic patients, and SVR rates ranging from 81.8 to 100 % were reported within subgroups of patients with compensated cirrhosis. Comparator data were not searched systematically as part of the submission, but were based on the company's previous NICE submission of sofosbuvir, with additional targeted searches. The ERG's critical appraisal of the company's economic evaluation highlighted a number of concerns. The ERG's base case analyses suggested that the incremental cost-effectiveness ratios (ICERs) for LDV/SOF (+RBV) are dependent on (a) treatment durations, (b) whether patients have been previously treated and (c) whether patients have liver cirrhosis or not. The AC concluded that it was appropriate to use the approach taken in the ERG's exploratory analyses, in line with the marketing authorisation, which considered people with and without cirrhosis separately, and estimated the cost effectiveness for each recommended treatment duration of LDV/SOF.

Systematic review, network meta-analysis and exploratory cost-effectiveness model of randomized trials of minimally invasive techniques versus surgery for varicose veins

BACKGROUND

A Health Technology Assessment was conducted to evaluate the relative clinical effectiveness and cost-effectiveness of minimally invasive techniques (foam sclerotherapy (FS), endovenous laser ablation (EVLA) and radiofrequency ablation (RFA)) for managing varicose veins, in comparison with traditional surgery.

METHODS

A systematic review of randomized clinical trials (RCTs) was undertaken to assess the effectiveness of minimally invasive techniques compared with other treatments, principally surgical stripping, in terms of recurrence of varicose veins, Venous Clinical Severity Score (VCSS), pain and quality of life. Network meta-analysis and exploratory cost-effectiveness modelling were performed.

RESULTS

The literature search conducted in July 2011 identified 1453 unique citations: 31 RCTs (51 papers) satisfied the criteria for effectiveness review. Differences between treatments were negligible in terms of clinical outcomes, so the treatment with the lowest cost appears to be most cost-effective. Total FS costs were estimated to be lowest, and FS was marginally more effective than surgery. However, relative effectiveness was sensitive to the model time horizon. Threshold analysis indicated that EVLA and RFA might be considered cost-effective if their costs were similar to those for surgery. These findings are subject to various uncertainties, including the risk of bias present in the evidence base and variation in reported costs.

CONCLUSION

This assessment of currently available evidence suggests there is little to choose between surgery and the minimally invasive techniques in terms of efficacy or safety, so the relative cost of the treatments becomes one of the deciding factors. High-quality RCT evidence is needed to verify and further inform these findings.

Clinical effectiveness and cost-effectiveness of minimally invasive techniques to manage varicose veins: a systematic review and economic evaluation

BACKGROUND

Varicose veins are enlarged, visibly lumpy knotted veins, usually in the legs. Uncomplicated varicose veins can cause major discomfort and some complications. They are part of chronic venous disease (CVD), which is reported to have a substantial negative impact on health-related quality of life (HRQoL). Traditional treatments for varicose veins involve surgical stripping and ligation and liquid sclerotherapy (LS), but can be invasive and painful. New minimally invasive treatments offer an alternative. These treatments typically involve use of laser, radiofrequency or foam sclerosant. They are increasingly widely used and offer potential benefits such as reduced complications, faster recovery, fewer physical limitations and improved quality of life.

OBJECTIVE

The aim of this report is to evaluate the clinical effectiveness, safety and cost-effectiveness of the minimally invasive techniques of foam sclerotherapy (FS), endovenous laser ablation (EVLA) and radiofrequency ablation (RFA) in comparison with other techniques, including traditional surgical techniques, LS and conservative management, in the management of varicose veins.

DATA SOURCES

A systematic search was made of 11 bibliographic databases of published and unpublished literature from their inception to July 2011: MEDLINE; EMBASE; Cumulative Index to Nursing and Allied Health Literature; The Cochrane Library; Biological Abstracts; Science Citation Index (SCI); Social Sciences Citation Index; Conference Proceedings Citation Index-Science; UK Clinical Research Network; Current Controlled Trials; and ClinicalTrials.gov.

REVIEW METHODS

A systematic review of randomised controlled trials (RCTs) to assess the clinical effectiveness of minimally invasive techniques compared with other treatments, principally surgical stripping, in terms of recurrence of varicose veins, retreatment and clinical symptoms, as measured by the Venous Clinical Severity Score (VCSS), pain and quality of life. Network meta-analysis and exploratory cost-effectiveness modelling were performed.

RESULTS

The literature search identified 1453 unique citations, of which 34 RCTs (54 papers) satisfied the criteria for the clinical effectiveness review. The minimally invasive techniques reported clinical outcomes similar to surgery. Rates of recurrence were slightly lower for EVLA, RFA and FS, especially for longer follow-up periods; VCSS score was lower for EVLA and FS than for stripping, but slightly higher for RFA; short-term pain was less for FS and RFA but higher for EVLA; higher quality-of-life scores were reported for all evaluated interventions than for stripping. Differences between treatments were therefore negligible in terms of clinical outcomes, so the treatment with the lowest cost appears to be most cost-effective. Our central estimate is that total FS costs were lowest and FS is marginally more effective than stripping. However, this result was sensitive to the model time horizon. Threshold analysis indicated that EVLA and RFA might be considered cost-effective if their costs are equivalent to stripping. These findings are subject to uncertainty on account of the risk of bias present in the evidence base and the variation in costs.

LIMITATIONS

The relative clinical effectiveness and cost-effectiveness of the techniques are principally based on rates of post-operative technical recurrence rather than symptomatic recurrence, as this was the reported outcome in all trials. The true proportion of treated individuals who are likely to present with symptoms of recurrence requiring retreatment is therefore not certain. A figure reflecting the likely proportion of treated individuals who would experience symptomatic recurrence requiring retreatment (with its associated costs), therefore, had to be calculated by the authors based on a small number of studies. The findings of this report also need to be verified by data from future trials with longer follow-up and using more standardised outcome measures.

CONCLUSIONS

This assessment of the currently available evidence suggests there is little to choose between the minimally invasive techniques in terms of efficacy or cost, and each offers a viable, clinically effective alternative to stripping. FS might offer the most cost-effective alternative to stripping, within certain time parameters. High-quality RCT evidence is needed. Future trials should aim to measure and report outcomes in a standardised manner, which would permit more efficient pooling of their results.

STUDY REGISTRATION

PROSPERO number CRD42011001355.

FUNDING

The National Institute for Health Research Health Technology Assessment programme.

Home telemonitoring or structured telephone support programmes after recent discharge in patients with heart failure: systematic review and economic evaluation

BACKGROUND

Remote monitoring (RM) strategies have the potential to deliver specialised care and management to patients with heart failure (HF).

OBJECTIVE

To determine the clinical effectiveness and cost-effectiveness of home telemonitoring (TM) or structured telephone support (STS) strategies compared with usual care for adult patients who have been recently discharged (within 28 days) from acute care after a recent exacerbation of HF.

DATA SOURCES

Fourteen electronic databases (including MEDLINE, EMBASE, PsycINFO and The Cochrane Library) and research registers were searched to January 2012, supplemented by hand-searching relevant articles and contact with experts. The review included randomised controlled trials (RCTs) or observational cohort studies with a contemporaneous control group that included the following RM interventions: (1) TM (including cardiovascular implanted monitoring devices) with medical support provided during office hours or 24/7; (2) STS programmes delivered by human-to-human contact (HH) or human-to-machine interface (HM).

REVIEW METHODS

A systematic review and network meta-analysis (where appropriate) of the clinical evidence was carried out using standard methods. A Markov model was developed to evaluate the cost-effectiveness of different RM packages compared with usual care for recently discharged HF patients. TM 24/7 or using cardiovascular monitoring devices was not considered in the economic model because of the lack of data and/or unsuitability for the UK setting. Given the heterogeneity in the components of usual care and RM interventions, the cost-effectiveness analysis was performed using a set of costing scenarios designed to reflect the different configurations of usual care and RM in the UK.

RESULTS

The literature searches identified 3060 citations. Six RCTs met the inclusion criteria and were added to the 15 trials identified from the previous systematic reviews giving a total of 21 RCTs included in the systematic review. No trials of cardiovascular implanted monitoring devices or observational studies met the inclusion criteria. The methodological quality of the studies varied widely and reporting was generally poor. Compared with usual care, RM was beneficial in reducing all-cause mortality for STS HH [hazard ratio (HR) 0.77, 95% credible interval (CrI) 0.55 to 1.08], TM during office hours (HR 0.76, 95% CrI 0.49 to 1.18) and TM 24/7 (HR 0.49, 95% CrI 0.20 to 1.18); however, these results were statistically inconclusive. The results for TM 24/7 should be treated with caution because of the poor methodological quality of the only included study in this network. No favourable effect on mortality was observed with STS HM. Similar reductions were observed in all-cause hospitalisations for TM interventions, whereas STS interventions had no major effect. A sensitivity analysis, in which a study was excluded because it provided better-than-usual support to the control group, showed larger beneficial effects for most outcomes, particularly for TM during office hours. In the cost-effectiveness analyses, TM during office hours was the most cost-effective strategy with an estimated incremental cost-effectiveness ratio (ICER) of £11,873 per quality-adjusted life-year (QALY) compared with usual care, whereas STS HH had an ICER of £228,035 per QALY compared with TM during office hours. STS HM was dominated by usual care. Similar results were observed in scenario analyses performed using higher costs of usual care, higher costs of STS HH and lower costs of TM during office hours.

LIMITATIONS

The RM interventions included in the review were heterogeneous in terms of monitored parameters and HF selection criteria and lacked detail in the components of the RM care packages and usual care (e.g. communication protocols, routine staff visits and resources used). As a result, the economic model developed scenarios for different RM classifications and their costs were estimated using bottom-up costing methods. Although the users can decide which of these scenarios is most representative of their setting, uncertainties still remain about the assumptions made in the estimation of these costs. In addition, the model assumed that the effectiveness of the interventions was constant over time, irrespective of the duration of deployment, and that the intervention was equally effective in different age/severity groups.

CONCLUSION

Despite wide variation in usual care and RM strategies, cost-effectiveness analyses suggest that TM during office hours was an optimal strategy (in most costing scenarios). However, clarity was lacking among descriptions of the components of RM packages and usual care and there was a lack of robust estimation of costs. Further research is needed in these areas.

STUDY REGISTRATION

PROSPERO registration no. CRD42011001368.

FUNDING

The National Institute for Health Research Health Technology Assessment programme.

Systematic review, meta-analysis and economic modelling of diagnostic strategies for suspected acute coronary syndrome

BACKGROUND

Current practice for suspected acute coronary syndrome (ACS) involves troponin testing 10-12 hours after symptom onset to diagnose myocardial infarction (MI). Patients with a negative troponin can be investigated further with computed tomographic coronary angiography (CTCA) or exercise electrocardiography (ECG).

OBJECTIVES

We aimed to estimate the diagnostic accuracy of early biomarkers for MI, the prognostic accuracy of biomarkers for major adverse cardiac adverse events (MACEs) in troponin-negative patients, the diagnostic accuracy of CTCA and exercise ECG for coronary artery disease (CAD) and the prognostic accuracy of CTCA and exercise ECG for MACEs in patients with suspected ACS. We then aimed to estimate the cost-effectiveness of using alternative biomarker strategies to diagnose MI, and using biomarkers, CTCA and exercise ECG to risk-stratify troponin-negative patients.

DATA SOURCES

We searched MEDLINE, MEDLINE In-Process & Other Non-Indexed Citations; Cumulative Index of Nursing and Allied Health Literature (CINAHL), EMBASE, Web of Science, Cochrane Central Database of Controlled Trials (CENTRAL), Cochrane Database of Systematic Reviews (CDSR), NHS Database of Abstracts of Reviews of Effects (DARE) and the Health Technology Assessment database from 1985 (CTCA review) or 1995 (biomarkers review) to November 2010, reviewed citation lists and contacted experts to identify relevant studies.

REVIEW METHODS

Diagnostic studies were assessed using the Quality Assessment of Diagnostic Accuracy Studies (QUADAS) tool and prognostic studies using a framework adapted for the project. Meta-analysis was conducted using bayesian Markov chain Monte Carlo simulation. We developed a decision-analysis model to evaluate the cost-effectiveness of alternative biomarker strategies to diagnose MI, and the cost-effectiveness of biomarkers, CTCA or exercise ECG to risk-stratify patients with a negative troponin. Strategies were applied to a theoretical cohort of patients with suspected ACS. Cost-effectiveness was estimated as the incremental cost per quality-adjusted life-year (QALY) of each strategy compared with the next most effective, taking a health-service perspective and a lifetime horizon.

RESULTS

Sensitivity and specificity (95% predictive interval) were 77% (29-96%) and 93% (46-100%) for troponin I, 80% (33-97%) and 91% (53-99%) for troponin T (99th percentile threshold), 81% (50-95%) and 80% (26-98%) for quantitative heart-type fatty acid-binding protein (H-FABP), 68% (11-97%) and 92% (20-100%) for qualitative H-FABP, 77% (19-98%) and 39% (2-95%) for ischaemia-modified albumin and 62% (35-83%) and 83% (35-98%) for myoglobin. CTCA had 94% (61-99%) sensitivity and 87% (16-100%) specificity for CAD. Positive CTCA and positive-exercise ECG had relative risks of 5.8 (0.6-24.5) and 8.0 (2.3-22.7) for MACEs. In most scenarios in the economic analysis presentation, high-sensitivity troponin measurement was the most effective strategy with an incremental cost-effectiveness ratio (ICER) of less than the £20,000-30,000/QALY threshold (ICER £7487-17,191/QALY). CTCA appeared to be the most cost-effective strategy for patients with a negative troponin, with an ICER of £11,041/QALY. However, when a lower MACE rate was assumed, CTCA had a high ICER (£262,061/QALY) and the no-testing strategy was optimal.

LIMITATIONS

There was substantial variation between the primary studies and heterogeneity in their results. Findings of the economic model were dependent on assumptions regarding the value of detecting and treating positive cases.

CONCLUSIONS

Although presentation troponin has suboptimal sensitivity, measurement of a 10-hour troponin level is unlikely to be cost-effective in most scenarios compared with a high-sensitivity presentation troponin. CTCA may be a cost-effective strategy for troponin-negative patients, but further research is required to estimate the effect of CTCA on event rates and health-care costs.

FUNDING

The National Institute for Health Research Health Technology Assessment programme.

Systematic review of the efficacy of cilostazol, naftidrofuryl oxalate and pentoxifylline for the treatment of intermittent claudication

BACKGROUND

A systematic review and network meta-analysis was undertaken to consider the evidence for the efficacy and tolerability of placebo, cilostazol, naftidrofuryl oxalate and pentoxifylline in patients with intermittent claudication due to peripheral arterial disease (PAD).

METHODS

MEDLINE, Embase, Cochrane Library, Cumulative Index to Nursing and Allied Health Literature, Web of Science, Conference Proceedings, BIOSIS, National Research Register and MetaRegister databases were searched. Eligible studies were randomized controlled trials (RCTs) and published systematic reviews of patients with intermittent claudication due to PAD and whose symptoms persisted despite a period of conservative management. Study selection was conducted by one reviewer with involvement from a clinician. Data were extracted by one reviewer with no blinding to authors or journal, and checked by a second reviewer. Outcome measures were maximum walking distance (MWD) and pain-free walking distance (PFWD).

RESULTS

The review identified 1876 citations; 26 RCTs met the inclusion criteria for the systematic review. Eleven trials provided data relevant for the meta-analysis. Naftidrofuryl oxalate was ranked first for both MWD and PFWD (probability of 0·947 and 0·987, respectively, of being the best treatment) followed by cilostazol and pentoxifylline. For naftidrofuryl oxalate, cilostazol and pentoxifylline, MWD increased by 60 (95 per cent credible interval 20 to 114) per cent, 25 (11 to 40) per cent and 11 (-1 to 24) per cent respectively relative to placebo, and PFWD increased by 49, 13 and 9 per cent.

CONCLUSION

Naftidrofuryl oxalate and cilostazol are both effective treatments for claudication; naftidrofuryl oxalate is likely to be the most effective, with minimal serious adverse events.

Trabectedin for the treatment of relapsed ovarian cancer

The paper presents a summary of the evidence review group (ERG) report into the clinical effectiveness and cost-effectiveness of trabectedin for the treatment of relapsed platinum-sensitive ovarian cancer, based upon a review of the manufacturer's submission to the National Institute for Health and Clinical Excellence (NICE) as part of the single technology appraisal process. The submission addressed only part of the decision problem and did not provide evidence to compare trabectedin (Yondelis®, PharmaMar) and pegylated liposomal doxorubicin hydrochloride (PLDH) (Caelyx®, Schering-Plough) with key comparators. The submission's direct comparison evidence came from one reasonable-quality randomised controlled trial (RCT) of trabectedin and PLDH versus PLDH alone (ET743-OVA-301). The results of the RCT were subdivided into the entire platinum-sensitive population (> 6-month relapse after initial platinum-based chemotherapy) and partially platinum-sensitive (≥ 6- to 12-month relapse) and fully platinum-sensitive (> 12-month relapse) populations. The outcomes included were overall survival, progression-free survival measured by three types of assessor, response rates, adverse effects of treatment, health-related quality of life and cost per quality-adjusted-life-year (QALY) gained. A mixed treatment comparison (MTC) meta-analysis comparing trabectedin and PLDH with single-agent PLDH within the entire platinum-sensitive population, with paclitaxel or with topotecan also formed part of the submission. The RCT data showed that trabectedin plus PLDH compared with PLDH monotherapy had a significant effect on overall survival only within the partially platinum-sensitive subgroup. PFS results reported by the independent radiologists showed significant effects in favour of the trabectedin and PLDH arm for the entire and partially platinum-sensitive populations only. Rates of grade 3 and 4 adverse events were mostly higher in the trabectedin and PLDH arm than in the PLDH alone arm. There were several issues regarding the undertaking of the MTC, and thus the data were not considered robust. Furthermore, the ERG did not believe the MTC to be necessary to answer the decision problem. The manufacturer submitted a de novo cost-effectiveness model. The main analysis compared trabectedin in combination with PLDH versus paclitaxel, topotecan and PLDH (each as monotherapy) in the entire platinum-sensitive population, using results estimated from the MTC. Additional analyses were presented comparing trabectedin in combination with PLDH versus PLDH monotherapy using direct evidence from the OVA-301 trial for the fully, partially and entire platinum-sensitive populations. The cost per QALY gained for trabectedin in combination with PLDH versus PLDH monotherapy was estimated to be £ 70,076 in the main analysis. In the additional analyses, the cost per QALY gained for trabectedin in combination with PLDH versus PLDH monotherapy was £ 94,832, £ 43,996 and £ 31,092 for the entire, partially and fully platinum-sensitive populations, respectively. Additional work was undertaken by the ERG using patient-level data and amending some assumptions to provide a better statistical fit to the Kaplan-Meier data than the exponential distribution assumed by the manufacturer. The ERG base-case estimate of the cost per QALY of trabectedin in combination with PLDH ranged from £46,503 to £54,607 in the partially platinum-sensitive population. At the time of writing, trabectedin in combination with PLDH for the treatment of women with relapsed platinum-sensitive ovarian cancer is not recommended by NICE in the final appraisal determination.

Trabectedin for the treatment of relapsed ovarian cancer

The paper presents a summary of the evidence review group (ERG) report into the clinical effectiveness and cost-effectiveness of trabectedin for the treatment of relapsed platinum-sensitive ovarian cancer, based upon a review of the manufacturer’s submission to the National Institute for Health and Clinical Excellence (NICE) as part of the single technology appraisal process. The submission addressed only part of the decision problem and did not provide evidence to compare trabectedin (Yondelis®, PharmaMar) and pegylated liposomal doxorubicin hydrochloride (PLDH) (Caelyx®, Schering-Plough) with key comparators. The submission’s direct comparison evidence came from one reasonable-quality randomised controlled trial (RCT) of trabectedin and PLDH versus PLDH alone (ET743-OVA-301). The results of the RCT were subdivided into the entire platinum-sensitive population (> 6-month relapse after initial platinum-based chemotherapy) and partially platinum-sensitive (≥ 6- to 12-month relapse) and fully platinum-sensitive (> 12-month relapse) populations. The outcomes included were overall survival, progression-free survival measured by three types of assessor, response rates, adverse effects of treatment, health-related quality of life and cost per quality-adjusted-life-year (QALY) gained. A mixed treatment comparison (MTC) meta-analysis comparing trabectedin and PLDH with single-agent PLDH within the entire platinum-sensitive population, with paclitaxel or with topotecan also formed part of the submission. The RCT data showed that trabectedin plus PLDH compared with PLDH monotherapy had a significant effect on overall survival only within the partially platinum-sensitive subgroup. PFS results reported by the independent radiologists showed significant effects in favour of the trabectedin and PLDH arm for the entire and partially platinum-sensitive populations only. Rates of grade 3 and 4 adverse events were mostly higher in the trabectedin and PLDH arm than in the PLDH alone arm. There were several issues regarding the undertaking of the MTC, and thus the data were not considered robust. Furthermore, the ERG did not believe the MTC to be necessary to answer the decision problem. The manufacturer submitted a de novo cost-effectiveness model. The main analysis compared trabectedin in combination with PLDH versus paclitaxel, topotecan and PLDH (each as monotherapy) in the entire platinum-sensitive population, using results estimated from the MTC. Additional analyses were presented comparing trabectedin in combination with PLDH versus PLDH monotherapy using direct evidence from the OVA-301 trial for the fully, partially and entire platinum-sensitive populations. The cost per QALY gained for trabectedin in combination with PLDH versus PLDH monotherapy was estimated to be £70,076 in the main analysis. In the additional analyses, the cost per QALY gained for trabectedin in combination with PLDH versus PLDH monotherapy was £94,832, £43,996 and £31,092 for the entire, partially and fully platinum-sensitive populations, respectively. Additional work was undertaken by the ERG using patient-level data and amending some assumptions to provide a better statistical fit to the Kaplan–Meier data than the exponential distribution assumed by the manufacturer. The ERG base-case estimate of the cost per QALY of trabectedin in combination with PLDH ranged from £46,503 to £54,607 in the partially platinum-sensitive population. At the time of writing, trabectedin in combination with PLDH for the treatment of women with relapsed platinum-sensitive ovarian cancer is not recommended by NICE in the final appraisal determination.

A simple numerical procedure for estimating nonlinear uncertainty propagation

Accurately determining the effect of the propagation of uncertainty in nonlinear applications can be awkward and difficult. The Monte Carlo approach requires statistically significant numbers of function evaluations (typically 10(5) or more) and analytical methods are intractable for all but the simplest cases. This paper derives and demonstrates a method to estimate the propagation of uncertainty in nonlinear cases by representing the function in a piecewise fashion with straight line segments. The probability density function of the result can be calculated from the transformation of the line segments. The mean and confidence intervals of the result can then be calculated from the probability density function. For the special case of a normal distribution in the independent variable, calculation of the mean and confidence intervals requires evaluation of only the error function (erf). A simple example is presented to demonstrate the technique. Variations on the basic approach are presented and discussed.

Bayesian methods for design and analysis of cost-effectiveness trials in the evaluation of health care technologies

We review the development of Bayesian statistical methods for the design and analysis of randomized controlled trials in the assessment of the cost-effectiveness of health care technologies. We place particular emphasis on the benefits of the Bayesian approach; the implications of skew cost data; the need to model the data appropriately to generate efficient and robust inferences instead of relying on distribution-free methods; the importance of making full use of quantitative and structural prior information to produce realistic inferences; and issues in the determination of sample size. Several new examples are presented to illustrate the methods. We conclude with a discussion of the key areas for future research.

Dynamic modelling of a challenge-escalation cross-over study of treatment of capsaicin-induced coughing

In a complex seven-period cross-over trial to study the effects of a drug in attenuating capsaicin-induced coughing, counts of numbers of coughs were recorded 32 times in each period. Subjects were subjected to four escalating levels of capsaicin at each of one and five hours after treatment, with counts of coughs being recorded in four one-minute intervals at each level. Such longitudinal count studies often show considerable individual variability about any regression curve that might be fitted. We develop a non-linear autoregressive model for such count data that also allows for overdispersion.

A framework for cost-effectiveness analysis from clinical trial data

We present a general Bayesian framework for cost-effectiveness analysis (CEA) from clinical trial data. This framework allows for very flexible modelling of both cost and efficacy related trial data. A common CEA technique is established for this wide class of models through linking mean efficacy and mean cost to the parameters of any given model. Examples are given in which efficacy may be measured as a continuous, binary, ordinal or time-to-event outcome, and in which costs are modelled as distributed normally, log-normally, as a mixture or non-parametrically. A case study is presented, illustrating the methodology and illuminating the role of prior information.

Bayesian assessment of sample size for clinical trials of cost-effectiveness

The authors present an analysis of the choice of sample sizes for demonstrating cost-effectiveness of a new treatment or procedure, when data on both cost and efficacy will be collected in a clinical trial. The Bayesian approach to statistics is employed, as well as a novel Bayesian criterion that provides insight into the sample size problem and offers a very flexible formulation.

Bayesian cost-effectiveness analysis from clinical trial data

A key tool for assessing the relative cost-effectiveness of two treatments in health economics is the incremental C/E acceptability curve. We present Bayesian computations for this curve in the case where data on both costs and efficacy are available from a clinical trial. Analysis is given under various formulations of prior information. A case study is analysed in which reasonable prior information is shown to strengthen substantially the posterior inference, leading to a more conclusive assessment of cost-effectiveness. Calculations can be performed using readily available Bayesian software.

The social ecology of the co-occurrence of substance use and early coitus among poor, urban black female adolescents

Currently, the profession of social work has proclaimed the need for an empirical research agenda to broaden its knowledge base. The profession's positivists rightly argue that a sound knowledge base is derived from rigorous scientific empirical methods. Unquestionably, the profession's unique contribution to the study of human development has been its emphasis on environmental effects and individual adaptation. Presently, social scientists embrace an ecological perspective when studying how social environmental effects are mediated. As researchers shift to a social ecological perspective, an empirical contextual model will allow the study of racial/ethnic differences in the incidence of adolescent problem behaviors (Stevens, 1998). An examination of the social ecology of poor, urban black female adolescents was undertaken to examine claims of the co-occurrence of early coitus and substance use, behaviors evident in black adolescents. An ecological framework operationalized by the constructs structural strain, kinscriptions, and community bridging is used to explicate how coital behavior among black females may not co-occur with drug use. The article's exegesis is directed by four postulates that help clarify the relationship of social ecology to the linkage of early coital behavior and substance use. The article concludes with adolescent narratives that illumine the cogency of the ecological analysis.

CD44 expression in the developing and growing rat intervertebral disc

CD44 has been identified at the time of extracellular matrix formation and expansion in several sites of the developing embryo (Wheatley et al. [1993] Development 119:295-306). The nucleus pulposus, consisting of a hydrated extracellular matrix tissue at birth, not previously closely analyzed, was examined for expression of CD44 in the developing and aging rat intervertebral disc. CD44 was identified solely on notochordal cells from the first onset of intervertebral disc formation (day 15 embryo) through the loss of notochordal cells from the nucleus pulposus (12-24 months of age). No CD44 expression was found in the notochordal cells prior to disc formation or in any cells other than the notochordal cells in the annulus fibrosus or nucleus pulposus of the intervertebral disc. Using reverse transcriptase-polymerase chain reaction methodology, the single 365 amino acid CD44 standard, CD44s, open reading frame was amplified from notochordal cells isolated from the nucleus pulposus. Western blot analysis of a cultured nucleus pulposus notochordal cells total protein extract identified a single CD44 species devoid of chondroitin sulfate with a mass of approximately 85 kDa, characteristic of CD44s. Cell surface detection for CD44 was co-localized with hyaluronan and proteoglycans at first appearance of disc formation in the nucleus pulposus.

Teenage parents and welfare reform: findings from a survey of teenagers affected by living requirements

An important component of welfare reform aimed at minor teenage parents is a requirement that the teenager live in an appropriate living situation, typically with a parent or guardian. The State of Massachusetts developed Teen Living Programs as an alternate living arrangement for minor teenage parents receiving welfare who are unable to live with family members. This article reports on a survey of 199 teenage parents who lived in the Teen Living Programs. Three research questions were asked: Who are the teenagers served by these programs? What services were provided? To what extent have teenagers attained key outcomes? Outcomes measured included educational attainment, employment, welfare status, homelessness, and subsequent pregnancy. Implications for social policy, further program development, and clinical intervention are discussed.

Inference for the cost-effectiveness acceptability curve and cost-effectiveness ratio

The aim of this article is to consider Bayesian and frequentist inference methods for measures of incremental cost effectiveness in data obtained via a clinical trial. The most useful measure is the cost-effectiveness (C/E) acceptability curve. Recent publications on Bayesian estimation have assumed a normal posterior distribution, which ignores uncertainty in estimated variances, and suggest unnecessarily complicated methods of computation. We present a simple Bayesian computation for the C/E acceptability curve and a simple frequentist analogue. Our approach takes account of errors in estimated variances, resulting in calculations that are based on distributions rather than normal distributions. If inference is required about the C/E ratio, we argue that the standard frequentist procedures give unreliable or misleading inferences, and present instead a Bayesian interval.

A 14-year experience with 6 cm as a criterion for surgical treatment of abdominal aortic aneurysm

BACKGROUND

It remains unclear when to recommend operation for an asymptomatic abdominal aortic aneurysm (AAA). This study examined a prospective series of patients for whom standard criteria were applied.

METHODS

Some 584 consecutive patients with an AAA of diameter 3 cm or greater detected by ultrasonographic screening have been observed for up to 14 years. Repeat ultrasonographic examinations have been performed at intervals. Surgery was not considered unless the aneurysm measured 6 cm in diameter, expanded at a rate equivalent to at least 1 cm per year, caused the patient symptoms, or an iliac aneurysm was present that required treatment.

RESULTS

Operation was performed on 127 patients; the majority (80; 63 per cent) had an aneurysm that reached 6 cm in diameter. Use of the above criteria prevented rupture in all but 24 (4 per cent) of the 584 patients over the 14-year interval. Of these 24 patients, 11 were unfit for planned surgery and eight declined operation or follow-up. Rupture in the five remaining patients (1 per cent) who were available for treatment compared favourably with the reported 30-day mortality rate for elective surgical treatment of 1.4-12 per cent.

CONCLUSION

Repeated observation is preferable to surgical intervention until an aortic aneurysm measures 6 cm in diameter, expands by 1 cm per annum or causes symptoms. Presented as a poster to the 52nd Annual Meeting of the Society for Vascular Surgery, San Diego, California, USA, June 1998

Pseudoachondroplastic dysplasia: an Iowa review from human to mouse

Lamellar inclusions of the rough endoplasmic reticulum in growth plate chondrocytes, first identified (1972) in the Department of Orthopaedic Surgery, University of Iowa, has become the cytochemical hallmark for the pseudoachondroplastic dysplasia (PSACH) phenotype, linking an endoplasmic reticulum storage disorder with the osteochondrodysplasia. Since this original observation, great advances have been made, leading to the molecular understanding of this altered longitudinal bone growth anomaly. A PSACH canine model suggested that abatement of cumulative vertical growth of growth plate chondrocytes seen in PSACH results from (1) altered extracellular matrix constraints for horizontal growth and (2) uncoupling of endochondral and perichondral growth that causes metaphyseal flaring. PSACH, an autosomal dominant disease, is linked to mutation of the cartilage oligomeric matrix protein (COMP) gene. Amino acid substitutions, deletions, or additions is proposed to alter COMP structure that cause its retention in the rough endoplasmic reticulum of growth plate chondrocytes, leading to (1) compositional and structural change of the extracellular matrix, and (2) altered cellular proliferation and volume expansion. Normal growth and development occurs in COMP gene knockout mice that do not synthesis COMP, demonstrating that a mutant COMP, not absence of COMP, is required for the PSACH phenotype. The mechanism by which mutant COMP induces a PSACH phenotype remains to be elucidated. At the University of Iowa a cell culture system has been developed whereby mutant COMP transgenes are introduced into chondrocytes and the expressed product COMP is retained in the endoplasmic reticulum. This readily manipulated system makes it possible to decipher systematically the system's cellular secretory processing pathway, in order to clarify the mechanism(s) by which the mutant COMP is retained within the endoplasmic reticulum. Concurrent with this is the development of transgenic mice expressing the mutant COMP used in the cell culture system. This will make it possible to establish that expression of a human PSACH-linked mutant COMP will produce a PSACH phenotype. A PSACH animal model will provide a means to characterize the mechanism of altered longitudinal bone growth and to test gene therapy approaches for correcting the anomaly.

Spatial and temporal expression of CD44 isoforms in the developing and growing joints of the rat limb

Hyaluronan is an integral component of proteoglycan-rich extracellular matrices such as hyaline cartilage. Hyaluronan is commonly found in embryonic tissue and is important in the formation of hydrated matrices that allow cellular expansion and migration. Cell surface hyaluronan-binding proteins such as CD44 are presumed to be important in the cellular interactions with hyaluronan in both of these processes. The primary aim of this study was to document the spatial and temporal expressions of CD44 isoforms during the development and growth of the diarthrodial joints of rat limbs. With use of in situ hybridization and immunohistochemistry, the CD44s isoform is selectively identified as localized to a single cell layer on opposing sides of the joint at the first appearance of joint cavitation (on the 18th day of gestation). After joint formation in the neonate, the expression of the CD44s isoform in the cells at the joint surface is lost. These findings suggest that the CD44s isoform has a role in the development of the diarthrodial joint, presumably through interaction with hyaluronan.

African American female adolescent identity development: a three-dimensional perspective

African American female adolescents have unique identity issues that structure developmental tasks. Qualitative data from a longitudinal research project are used to explicate a three-dimensional model of the identity developmental process in early-age African American female adolescents. The limitations of a gender analysis model of voice and connection are noted. It is suggested that the African American female adolescent experiences a relational crisis in both racial and gender identity development. Moreover, African American female adolescents develop skillful, unique, expressionistic, and assertive styles of relating to negotiating perceived hostile environments. Practice implications for child welfare are outlined.

Spatial distribution of CD44 and hyaluronan in the proximal tibia of the growing rat

CD44 has been described as a cell surface hyaluronan receptor present on a variety of different cells, and it is generally assumed to be prevalent in most connective tissues that contain hyaluronan. A major aim of this study was to test that presumption by localizing CD44 and hyaluronan within several tissues of the proximal tibia of the growing rat. Comparison of these profiles would reveal whether CD44 and hyaluronan co-localize with high fidelity, as would be expected if CD44 were a major hyaluronan binding protein. Using in situ hybridization and immunohistochemistry, CD44 was identified on osteoclasts, chondroclasts, osteocytes, hematopoietic marrow cells, synovial cells, and connective tissue fibroblasts (ligaments, tendons, and fascia). Although the majority of osteocytes expressed CD44, reduced expression was observed for osteoblasts and ostcoprogenitor cells. Additionally. CD44 was not detected on chondrocytes from epiphyseal and metaphyseal growth cartilages or in meniscal fibrocartilage. Using biotinylated G1 domain from aggrecan and link protein, hyaluronan was observed in the maturational and hypertrophic zones of all growth cartilages, the synovium and other fibroblastic connective tissues, regional areas of the periosteum and endosteum (around osteoblasts, osteoprogenitor cells, and osteoclasts), osteocyte lacunae, and surrounding blood vessels. In regions of co-localization for CD44 and hyaluronan, it seems that CD44 is a likely hyaluronan binding protein in several tissues of the proximal tibia. However, it does not appear to be the predominant hyaluronan binding protein in growing cartilages of the weanling rat.

Expression of CD44 isoforms in human prostate tumor cell lines

We have examined the expression of the transmembrane glycoproteins CD44 in four human prostate tumor cell lines. Expression was examined at the protein level by flow cytometric analysis and Western blot, and at the mRNA level by reverse transcription-polymerase chain reaction (RT-PCR). All four cell lines (DU145, LNCaP, PC3, and ND1) expressed the standard CD44 isoform (CD44s) at the mRNA level and all cell lines except LNCaP expressed CD44s at the protein level. All four cell lines contained one or more isoforms containing the v6 region (exon 10) at the mRNA level, which has been associated with metastatic potential. However, a subpopulation of LNCaP and ND1 cells showed protein expression of v6. In addition, soluble CD44 isoforms were identified in cultured supernatants from all cell lines except LNCaP. These results show that CD44 isoforms are expressed on human prostate tumor cell lines, including the expression of variant isoforms containing the v6 region, and provide a rationale for the further study of this cellular adhesion molecule in prostate cancer. In addition, preliminary results indicate altered expression of CD44 in human prostatic adenocarcinomas examined immunohistochemically.

Cellular deformation reversibly depresses RT-PCR detectable levels of bone-related mRNA

Osteoblastic cells respond to mechanical stimuli with alterations in proliferation and/or phenotypic expression. In some cases, these responses occur within only a few applications of stimuli (i.e. 'cycle-dependent trigger response') rather than in a dose-dependent manner. To explore potential mechanisms of the cycle dependent trigger response, we raised the following questions: (1) Does strain of bone cells alter gene expression; if so, how quickly does it occur and how long does it last? (2) Are alterations in message level strain magnitude dependent? (3) Are alterations in steady-state message levels cycle dependent? Cultures were evaluated for osteocalcin mRNA one week following a daily stretch application at four stretch magnitudes and four cycle numbers and compared to nonstretched controls. Steady state mRNA message was ascertained prior to and at 10, 20, 30, 60, 120, 180, and 240 min following initiation of stretch. Following mRNA isolation, first strand cDNA synthesis was performed and fluorometrically quantitated. A reverse transcriptase based PCR (RT-PCR) approach allowed assessment of osteocalcin mRNA levels from microcultures (50,000 cells per 10 microliters culture or 5000 cells mm2) of rat calvarial osteoblasts. Optimized PCR was performed using primers to the bone specific protein, osteocalcin (OC) and two 'housekeeping' genes, beta-actin and GAP-DH. PCR products were separated on 4% agarose gels and band intensities digitized with relative quantitation based on internal standards in each gel. The lowest magnitude of stretch (- 1 KPa) at 1800 cycles per day reproducibly depressed message for osteocalcin, but not beta-actin when assayed immediately following the cessation of strain application. By three hours following the initiation of stretch, message levels returned to control values. At the time of stretch cessation, the 1800 cycle stretch regimen diminished (p < 0.0001) steady-state osteocalcin message independently of the four stretch magnitudes. Stretch for 300 cycles failed to depress (p = 0.05) osteocalcin message cultures at any time, but 600 cycles depressed message by 30 min. By one and two hours, cultures stretch 600, 900, and 1800 cycles showed similar levels of message depression. Four hours following the initiation of stretch, message levels returning to nonstrained levels in all groups. We conclude that alterations in cell response to strain are in part mediated by gene expression, that alterations last 3-4 h in this system, and that the message mechanism itself exhibits a trigger-response dependency to cycle number.

Recombinant and native zymogen forms of human complement factor D

We have expressed a full-length cDNA clone encoding human factor D by using a baculovirus expression system. The purified recombinant protein reacted with Ab against native factor D, but was hemolytically inactive and slightly larger than factor D. These results suggested that the recombinant protein was the elusive zymogen of factor D. Amino acid sequencing demonstrated that the recombinant factor D consisted of two proenzyme forms with respective activation peptides, AAPPRGR and APPRGR. Catalytic amounts of trypsin converted recombinant profactor D to its enzymatically active form, exhibiting SDS-PAGE mobility and specific hemolytic activity similar to those of native factor D. About 90% of trypsin-activated recombinant profactor D had the same NH2-terminus as factor D. Human thrombin, kallikrein, and plasmin could also activate recombinant profactor D, but relatively high concentrations of these enzymes were required and the specific hemolytic activity of the "activated" profactor D was about one-third that of native factor D. Trypsin-activatable profactor D was also purified from the urine of a patient with Fanconi's syndrome. This native profactor D represented less than 1.0% of the total antigenic factor D in the patient's urine and had a Gly-Arg dipeptide as the activation peptide. Apparently, urine profactor D was produced by cleavage of pre-profactor D at Arg-(-3) by a serine protease with trypsin-like specificity, which probably is different from the putative leader peptidase that produces the recombinant profactor D. Urine profactor D was inhibited by diisopropyl fluorophosphate although the recombinant proenzyme was resistant to this inhibitor.

Recombinant and native zymogen forms of human complement factor D

We have expressed a full-length cDNA clone encoding human factor D by using a baculovirus expression system. The purified recombinant protein reacted with Ab against native factor D, but was hemolytically inactive and slightly larger than factor D. These results suggested that the recombinant protein was the elusive zymogen of factor D. Amino acid sequencing demonstrated that the recombinant factor D consisted of two proenzyme forms with respective activation peptides, AAPPRGR and APPRGR. Catalytic amounts of trypsin converted recombinant profactor D to its enzymatically active form, exhibiting SDS-PAGE mobility and specific hemolytic activity similar to those of native factor D. About 90% of trypsin-activated recombinant profactor D had the same NH2-terminus as factor D. Human thrombin, kallikrein, and plasmin could also activate recombinant profactor D, but relatively high concentrations of these enzymes were required and the specific hemolytic activity of the "activated" profactor D was about one-third that of native factor D. Trypsin-activatable profactor D was also purified from the urine of a patient with Fanconi's syndrome. This native profactor D represented less than 1.0% of the total antigenic factor D in the patient's urine and had a Gly-Arg dipeptide as the activation peptide. Apparently, urine profactor D was produced by cleavage of pre-profactor D at Arg-(-3) by a serine protease with trypsin-like specificity, which probably is different from the putative leader peptidase that produces the recombinant profactor D. Urine profactor D was inhibited by diisopropyl fluorophosphate although the recombinant proenzyme was resistant to this inhibitor.

Isolation and characterization of bovine gingival proteoglycans versican and decorin

1. We have isolated, chemically and immunologically characterized versican and decorin from bovine gingiva. 2. Versican was of large molecular weight and the molecular size of the core protein was estimated to be greater than 200 kDa. 3. The glycosaminoglycan chains were susceptible to chondroitinase ABC and N-linked oligosaccharides were present on the protein core of the molecule. 4. Immunological studies provided evidence that a hyaluronic acid binding region was present in the core protein of versican. 5. The overall structure was similar to that of versican isolated from bovine sclera. 6. Decorin had a molecular weight of 102 kDa and its glycosaminoglycan chain was completely digested by specific glycosidases. 7. The partially deglycosylated core protein had a molecular weight of 55 kDa and N-linked oligosaccharides were present on the molecule.

Molecular cloning of rat and human type IX collagen cDNA and localization of the alpha 1(IX) gene on the human chromosome 6

Type IX collagen is found in hyaline cartilage, where it is associated with type II collagen in quarter-staggered collagen fibrils. Chicken type IX collagen has been extensively characterized and shown to contain molecules with three triple-helical domains, interspersed with non-triple-helical sequences. The molecule contains three, genetically distinct, subunits and one of these subunits carries a covalently bound glycosaminoglycan side chain. In the present report, we describe for the first time the primary structure of mammalian type IX collagen chains, based on cloning and sequencing of cDNA from rat and human cDNA libraries. The results suggest that mammalian alpha 1(IX) chains have the same multi-domain structure as the avian protein. We also demonstrate, by in situ hybridization of chromosome spreads, that the human alpha 1(IX) collagen gene is located on the long arm of chromosome 6. The cloning of human type IX collagen cDNA provides a probe for molecular studies of human chondrodysplasias that may involve abnormalities in this extracellular collagen-proteoglycan.

N-terminal carbamylation of the hyaluronic acid-binding region and the link protein from the chondrosarcoma proteoglycan aggregate

The ternary complex consisting of a 65-kDa peptide originating from the proteoglycan core protein and a 43-kDa link protein bound to hyaluronic acid was purified from a clostripain digest of the rat chondrosarcoma aggregating proteoglycan and 14C-carbamylated with potassium [14C]cyanate. At a pH of 8.0, 14C-carbamylation of the alpha-NH2 groups in the N-terminal amino acids was favored over carbamylation of epsilon-NH2 groups in the lysinyl residues for both the 65- and 43-kDa species. Two-dimensional tryptic peptide maps revealed a single major, distinctly different, fluorographic spot for each. These tryptic peptides had approximate masses of 4.5 kDa (from the 65-kDa species) and 3.0 kDa (from the 43-kDa species) on sodium dodecyl sulfate-polyacrylamide gel electrophoresis gels and each contained greater than 60% of the total radioactivity associated with its original polypeptide. Primary amino acid sequencing of the 65-kDa species gave a defined sequence for the first 4 N-terminal residues, whereas sequencing through the first 4 residues of a fully carbamylated species gave no dabsylated derivative for the first residue but identical residues in position 2-4 as for the noncarbamylated species and loss of radioactive derivative. Digests of 14C-carbamylated ternary complex with alpha-chymotrypsin resulted in a limit 14C-carbamylated 55-kDa species which contained greater than 85% of the radiolabel originally in the 65-kDa peptide. Similarly, trypsin generated two radiolabeled species, 60 and 58 kDa. These limit digest peptides (55, 60, 58 kDa) all contained the 4.5-kDa N-terminal tryptic peptide. Thus peptides removed from the 65-kDa peptide digestion with either alpha-chymotrypsin or trypsin were on the carboxyl end of the molecule.

Characteristics of the core protein of the aggregating proteoglycan from the Swarm rat chondrosarcoma

A ternary complex of hyaluronic acid-binding region and link protein bound to hyaluronic acid was isolated from limit clostripain digests of proteoglycan aggregates isolated from the Swarm rat chondrosarcoma. Under these conditions, the hyaluronic acid-binding region has a molecular weight of approximately equal to 65,000 (HA-BR65). N-terminal amino acids in the complex were selectively 14C-carbamylated. The resulting derivatized HA-BR65 was isolated, and tryptic peptide maps were prepared and developed on two-dimensional TLC sheets. A single, labeled peptide was obtained which gave a Mr by approximately equal to 8,000 by SDS-PAGE. Chymotrypsin digestion of the ternary complex reduced the molecular weight of HA-BR65 to a polypeptide of approximately equal to 55,000 (HA-BR55) which still retains the same N-terminal tryptic peptide. Partial digestion of proteoglycan aggregates with clostripain generated a series of larger intermediates with the hyaluronic acid-binding region. Direct SDS-PAGE analysis revealed one major intermediate with approximately equal to 109,000 (HA-BR109) as well as HA-BR65. After chondroitinase digestion, two additional prominent intermediates were observed on a SDS-PAGE gel at Mr approximately equal to 120,000 (HA-BR120) and approximately equal to 140,000 (HA-BR140). All the intermediates were recognized by a monoclonal antibody specific for the hyaluronic acid-binding region, and all of them contained the same N-terminal tryptic peptide. The results indicate that the N terminus of the core protein is at the hyaluronic acid-binding end of the proteoglycan and that the chondroitin sulfate chains are first present on the core protein in a region between 109,000 and 120,000 molecular weight away from the N terminus.

Proteoglycan structure and metabolism in normal and osteoarthritic cartilage of guinea pigs

Sulfated proteoglycan structure and metabolism in osteoarthritic articular cartilage from the hind-limb joints of guinea pigs in which the disease had been surgically induced were evaluated and compared with those from nonoperated or sham-operated controls. In these studies, conducted on animals receiving high and low dietary levels of ascorbic acid, the effect of vitamin C on these variables was also examined. Sulfated proteoglycan biosynthesis per unit of DNA as reflected by in vivo uptake of 35S-sulfate was stimulated both by arthritic development and high dietary vitamin C. Under these conditions, the specific activities, 35S-cpm/micrograms uronic acid, of the proteoglycans were elevated. Neither arthritic development nor variation in dietary levels of vitamin C altered the structure of the proteoglycans. Two species of proteoglycans that exhibited the same electrophoretic mobilities in agarose/acrylamide gels, the same elution profiles on high performance liquid chromatography,, and the same galactosamine/glucosamine ratios were found in all normal and osteoarthritic cartilage specimens tested. The specific activities of these two specimens tested. The specific activities of these two species were dissimilar. In all samples, the larger of the two species had a higher specific activity.

L-ascorbic acid: effects on aortic glycosaminoglycan 35S incorporation in rabbit-induced atherogenesis

The effects of L-ascorbic acid on 35S-incorporation into thoracic aorta glycosaminoglycans and upon aorta cholesterol levels were determined in hypercholesterolemic rabbits. No significant difference was observed in serum free or esterified cholesterol levels between animals receiving L-ascorbic acid supplementation or saline while maintained on a cholesterol diet (0.5%). A 15-fold higher serum cholesterol was observed in animals on the cholesterol diet to those animals which received a normal rabbit (Purina) diet. L-Ascorbic acid increased sulfated glycosaminoglycans concentrations in hypercholesterolemic rabbits which paralleled lower tissue free and esterified cholesterol levels. The 35S-specific activity of glycosaminoglycans in hypercholesterolemic animals receiving saline was much greater than in those animals receiving L-ascorbic acid. This suggests that L-ascorbic acid plays a role in the maintenance of adequate levels of aortic sulfated glycosaminoglycans. This then is a suggested biochemical mechanism of L-ascorbic acids interaction in the atherogenic process.