Model discrimination in dynamic molecular systems: application to parotid de-differentiation network.

In modern systems biology the modeling of longitudinal data, such as changes in mRNA concentrations, is often of interest. Fully parametric, ordinary differential equations (ODE)-based models are typically developed for the purpose, but their lack of fit in some examples indicates that more flexible Bayesian models may be beneficial, particularly when there are relatively few data points available. However, under such sparse data scenarios it is often difficult to identify the most suitable model. The process of falsifying inappropriate candidate models is called model discrimination. We propose here a formal method of discrimination between competing Bayesian mixture-type longitudinal models that is both sensitive and sufficiently flexible to account for the complex variability of the longitudinal molecular data. The ideas from the field of Bayesian analysis of computer model validation are applied, along with modern Markov Chain Monte Carlo (MCMC) algorithms, in order to derive an appropriate Bayes discriminant rule. We restrict attention to the two-model comparison problem and present the application of the proposed rule to the mRNA data in the de-differentiation network of three mRNA concentrations in mammalian salivary glands as well as to a large synthetic dataset derived from the model used in the recent DREAM6 competition.

Scintigraphic assessment of salivary function after intensity-modulated radiotherapy for head and neck cancer: correlations with parotid dose and quality of life.

OBJECTIVE: We investigated salivary function using quantitative scintigraphy and sought to identify functional correlations between parotid dose and quality of life (QoL) for head and neck cancer (HNC) patients receiving intensity-modulated radiotherapy (IMRT). MATERIALS AND METHODS: Between August, 2007 and June, 2008, 31 patients treated IMRT for HNC were enrolled in this prospective study. Salivary excretion function (SEF) was previously measured by salivary scintigraphy at annual intervals for 2 years after IMRT. A dose-volume histogram of each parotid gland was calculated, and the normal tissue complication probability (NTCP) was used to determine the tolerance dose. QoL was longitudinally assessed by the EORTC QLQ-C30 and H&N35 questionnaires prior to RT, and at one, three, 12 and 24 months after RT. RESULTS: A significant correlation was found between the reduction of SEF and the mean parotid dose measured at 1 year (correlation coefficient, R(2)=0.651) and 2 years (R(2)=0.310) after IMRT (p<0.001). The TD(50) of the parotid gland at 1 year after IMRT is 43.6 Gy, comparable to results from western countries. We further found that contralateral parotid and submandibular gland function preservation was correlated with reduced sticky saliva and a better QoL compared to the functional preservation of both parotid glands, as determined by the EORTC QLQ-H&N35 questionnaire. CONCLUSION: A significant correlation was found between the reduction of SEF and the mean parotid dose. Preservation of contralateral parotid and submandibular gland function predicts a better QoL compared to preservation of the function of both parotid glands.

FDG-PET assessment of the effect of head and neck radiotherapy on parotid gland glucose metabolism.

PURPOSE: Functional imaging with [F-18]-fluorodeoxyglucose positron emission tomography (FDG-PET) provides the opportunity to define the physiology of the major salivary glands before and after radiation therapy. The goal of this retrospective study was to identify the radiation dose-response relationship of parotid gland glucose metabolism in patients with head and neck squamous cell carcinoma (HNSCC). MATERIALS AND METHODS: Forty-nine adults with HNSCC were identified who had curative intent intensity-modulated radiation therapy (IMRT) and FDG-PET imaging before and after treatment. Using a graphical user interface, contours were delineated for the parotid glands on axial CT slices while all authors were blinded to paired PET slices. Average and maximal standard uptake values (SUV) were measured within these anatomic regions. Changes in SUV and volume after radiation therapy were correlated with parotid gland dose-volume histograms from IMRT plans. RESULTS: The average parotid gland volume was 30.7 mL and contracted 3.9 ± 1.9% with every increase of 10 Gy in mean dose (p = 0.04). However, within the first 3 months after treatment, there was a uniform reduction of 16.5% ± 7.3% regardless of dose. The average SUV(mean) of the glands was 1.63 ± 0.48 pretreatment and declined by 5.2% ± 2.5% for every increase of 10 Gy in mean dose (p = 0.04). The average SUV(max) was 4.07 ± 2.85 pretreatment and decreased in a sigmoid manner with mean dose. A threshold of 32 Gy for mean dose existed, after which SUV(max) declined rapidly. CONCLUSION: Radiation dose responses of the parotid glands can be measured by integrated CT/FDG-PET scans. Retrospective analysis showed sigmoidal declines in the maximum metabolism but linear declines in the average metabolism of the glands with dose. Future studies should correlate this decline in FDG uptake with saliva production to improve treatment planning.

The impact of dose on parotid salivary recovery in head and neck cancer patients treated with radiation therapy.

PURPOSE: A common side effect experienced by head and neck cancer patients after radiation therapy (RT) is impairment of the parotid glands' ability to produce saliva. Our purpose is to investigate the relationship between radiation dose and saliva changes in the 2 years after treatment. METHODS AND MATERIALS: The study population includes 142 patients treated with conformal or intensity-modulated radiotherapy. Saliva flow rates from 266 parotid glands are measured before and 1, 3, 6, 12, 18, and 24 months after treatment. Measurements are collected separately from each gland under both stimulated and unstimulated conditions. Bayesian nonlinear hierarchical models were developed and fit to the data. RESULTS: Parotids receiving higher radiation produce less saliva. The largest reduction is at 1-3 months after RT followed by gradual recovery. When mean doses are lower (e.g., <25 Gy), the model-predicted average stimulated saliva recovers to pretreatment levels at 12 months and exceeds it at 18 and 24 months. For higher doses (e.g., >30 Gy), the stimulated saliva does not return to original levels after 2 years. Without stimulation, at 24 months, the predicted saliva is 86% of pretreatment levels for 25 Gy and <31% for >40 Gy. We do not find evidence to support that the overproduction of stimulated saliva at 18 and 24 months after low dose in 1 parotid gland is the result of low saliva production from the other parotid gland. CONCLUSIONS: Saliva production is affected significantly by radiation, but with doses <25-30 Gy, recovery is substantial and returns to pretreatment levels 2 years after RT.

A Bayesian mixture model relating dose to critical organs and functional complication in 3D conformal radiation therapy.

A goal of cancer radiation therapy is to deliver maximum dose to the target tumor while minimizing complications due to irradiation of critical organs. Technological advances in 3D conformal radiation therapy has allowed great strides in realizing this goal; however, complications may still arise. Critical organs may be adjacent to tumors or in the path of the radiation beam. Several mathematical models have been proposed that describe the relationship between dose and observed functional complication; however, only a few published studies have successfully fit these models to data using modern statistical methods which make efficient use of the data. One complication following radiation therapy of head and neck cancers is the patient's inability to produce saliva. Xerostomia (dry mouth) leads to high susceptibility to oral infection and dental caries and is, in general, unpleasant and an annoyance. We present a dose-damage-injury model that subsumes any of the various mathematical models relating dose to damage. The model is a nonlinear, longitudinal mixed effects model where the outcome (saliva flow rate) is modeled as a mixture of a Dirac measure at zero and a gamma distribution whose mean is a function of time and dose. Bayesian methods are used to estimate the relationship between dose delivered to the parotid glands and the observational outcome-saliva flow rate. A summary measure of the dose-damage relationship is modeled and assessed by a Bayesian chi(2) test for goodness-of-fit.

Immunohistochemical assessment of fractalkine, inflammatory cells, and human herpesvirus 7 in human salivary glands.

Human fractalkine (CX3CL1), a delta-chemokine, is implicated in the mediation of multiple cell functions. In addition to serving as a chemotactic factor for mononuclear cell subtypes, membrane-bound fractalkine may promote viral infection by interacting with virions that encode putative fractalkine-binding proteins. Fractalkine expression in normal epithelial tissues studied to date is either constitutive or is upregulated with inflammation. In salivary glands, the expression of fractalkine is unknown. Moreover, salivary glands are a major site for the persistent and productive infection by human herpesvirus (HHV)-7, which encodes two putative fractalkine-binding gene products, U12 and U51. Surprisingly, the cellular distribution of HHV-7 in major salivary glands has not been explored. We therefore determined by immunohistochemistry the cellular localization of fractalkine in three different salivary glands: parotid, submandibular, and labial glands. Fractalkine expression was highly variable, ranging from high to undetectable levels. We further examined the association of fractalkine with inflammatory cell infiltration or HHV-7 infection of salivary epithelial cells. Inflammatory cells were always adjacent to epithelial cells expressing fractalkine, consistent with a function of fractalkine in inflammatory cell recruitment and/or retention in salivary glands. In contrast, HHV-7-infected epithelial cells did not always express fractalkine, suggesting that fractalkine may not be an absolute requirement for viral entry.

Scintigraphic assessment of early and late parotid gland function after radiotherapy for head-and-neck cancer: a prospective study of dose-volume response relationships.

PURPOSE: To investigate the value of scintigraphy as an indirect measurement of parotid function after radiotherapy (RT). METHODS AND MATERIALS: Ninety-six patients with primary or postoperative RT for various malignancies in the head-and-neck region were prospectively evaluated. Parotid gland scintigraphy was performed before RT and 6 weeks and 1 year after RT. The uptake, excretion fraction of the saliva from the parotid gland to the oral cavity (SEF), and the ratios of uptake and SEF after and before treatment were calculated. CT-based treatment planning was used to derive dose-volume histograms of the parotid glands. To establish the effects of both the radiation dose and the volume of the parotid gland irradiated, the normal tissue complication probability model proposed by Lyman was fit to the data. RESULTS: The mean maximal uptake of 192 parotid glands decreased significantly from 3329 counts (ct)-/s before RT to 3084 ct/s and 3005 ct/s at 6 weeks and 1 year after RT. The SEF before treatment was 44.7%. The SEF decreased to 18.7% at 6 weeks after RT, but recovered to a SEF of 32.4% at 1 year after RT. A significant correlation was found between the uptake 1 year after RT and the mean parotid dose. The reduction in post-RT SEF correlated significantly with the mean parotid gland dose. The normal tissue complication probability model parameter TD50 was found to be 29 and 43 Gy at 6 weeks and 1 year after RT, respectively, when a complication was defined as a posttreatment SEF parotid ratio of <45%. CONCLUSIONS: The effects of radiation on parotid gland function using scintigraphy could be well established. A statistically significant correlation between the SEF ratio and the mean parotid dose was shown, with some recovery of function at 1 year after RT, comparable with the flow results. When direct flow measurements are not feasible, parotid scintigraphy appears to be a good indicator of gland function.

The assessment of proliferating cell nuclear antigen (PCNA) immunostaining in human benign and malignant epithelial lesions of the parotid gland.

Immunoreactivity of proliferating cell nuclear antigen (PCNA) was assessed in formalin-fixed, paraffin-embedded sections from human normal parotid gland (N; n = 12), chronic sialadenitis (CS; n = 8), Warthin's tumour (W; n = 10), benign pleomorphic adenoma (BPA; n = 11), mucoepidermoid carcinoma (MEC; n = 14), carcinoma in pleomorphic adenoma (CPA; n = 10) and adenoid cystic carcinoma (ACC; n = 12) of the parotid gland, using the monoclonal antibody PC 10. The morphometric parameters measured comprised PCNA labelling induces (PI = the numerical percentage of PCNA positive nuclei) and volume densities of PCNA positive nuclei(VV, PEP = the relative volume of positive nuclei per unit volume of reference epithelium). All parameters were expressed in relation to total positive, as well as to strongly- and weakly-positive nuclei. In general, the values of PCNA parameters increased progressively in benign lesions in comparison with the N group, and in malignant neoplasms in comparison with non-neoplastic groups and benign lesions. The strongly-positive parameters showed more statistically significant differences than weakly-positive ones, suggesting that weakly-stained nuclei may include some non-cycling cells and, therefore, that weakly-positive parameters may not be reliable proliferation markers. Values for all parameters in CPA were significantly higher than those in BPA, suggesting that these parameters may be used as diagnostic discriminators. Spearman rank correlation analysis showed a highly positive correlation between the morphometric parameters and the severity of the lesions. Furthermore, the mean values of PISP were significantly higher in patients who died of the malignant tumours than in those patients who survived. Our results indicate that PCNA indices might be useful markers for discriminating between benign (BPA) and malignant tumours of the parotid gland and that the parameter PISP may have prognostic applications.

Anti-HIV antibody in saliva: an assessment of the role of the components of saliva, testing methodologies and collection systems.

The various components of saliva, namely mixed saliva, parotid saliva, submandibular saliva, crevicular fluid and minor (labial) gland secretions, were collected from 63 known HIV antibody seropositive patients. A commercial test system, Wellcozyme HIV 1+2, and an antibody capture ELISA (GACELISA), were compared for sensitivity against all components. Sensitivity of the GACELISA system was 100% in 123 mixed saliva, 121 parotid saliva and 127 labial fluid samples, and 98% in 99 submandibular samples and 127 crevicular fluid samples. Respective figures for Wellcozyme 1+2 were 92%, 55%, 73%, 66% and 63%. Mixed saliva was most easily, conveniently and effectively collected using a plain Salivette. In 241 Salivette samples examined from the 63 patients, GACELISA proved 100% sensitive, and Wellcozyme 95% sensitive. Another form of Salivette impregnated with citric acid was unsuitable for GACELISA and gave a false negative value of 45%. In 197 samples from the gingival margin taken by a dry swab, GACELISA showed a sensitivity of 98% and Wellcozyme 81%. The most sensitive method for demonstrating anti-HIV antibody in saliva is to collect mixed saliva with the plain Salivette system and assay anti-HIV antibody levels by GACELISA.

In vitro methods for the assessment of the inhibitory effects of antidepressants in rat parotid glands.

The present study evaluates suitable in vitro methods for the assessment of the inhibiting properties of four principally different antidepressant drugs. This was done by comparing the acute effects of antidepressants on autonomic receptor binding (homogenates) together with parallel tests evaluating the biological activities of the receptor systems in collagenase-isolated rat parotid acini. The responses were measured as receptor-activated changes in cyclic nucleotide formation and acinar oxygen consumption. Muscarinic acetylcholine receptor binding, carbachol-induced cGMP formation, and oxygen consumption all reflected the various inhibiting effects of the antidepressants tested. Measurements of the carbachol-induced O2 consumption was however, the most sensitive method and may be considered a well-suited and reliable parameter concerning the expected severity of anticholinergic side-effects caused by medication. The disturbing 'dry mouth' symptoms following treatment with amitriptyline or mianserin are however, also attributed to their substantial adrenoceptor-blocking effects, which are best demonstrated by alpha 1-adrenoceptor binding studies in combination with measurements of the adrenaline-induced O2 consumption in the rat parotid gland.

A new assessment in vitro of human salivary lubrication using a compliant substrate.

The lubrication effect of salivary secretions was assessed in terms of separating a rigid object from a compliant substrate. There was little difference among the various secretions of a single donor. The viscosity of salivas increased as a function of time. Neither the friction testing nor viscometry provided an adequate model of the tissue-coating function ascribed to saliva.