| 31. |
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| 32. |
- Chen, Dong Lei, 1985-, et al.
(author)
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Development of cyclic shedding teeth from semi-shedding teeth : the inner dental arcade of the stem osteichthyan Lophosteus
- 2017
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In: Royal Society Open Science. - : ROYAL SOC. - 2054-5703. ; 4:5
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Journal article (peer-reviewed)abstract
- The numerous cushion-shaped tooth-bearing plates attributed to the stem-group osteichthyan Lophosteus superbus, which are argued here to represent the ancient form of inner dental arcade, display a unique and presumably primitive way of tooth shedding by basal hard tissue resorption. They carry regularly spaced, recumbent, gently recurved teeth arranged in transverse tooth files that diverge towards the lingual margin of the cushion. Three-dimensional (3D) reconstruction from propagation phase contrast synchrotron microtomography (PPC-SRμCT) reveals remnants of the first-generation teeth embedded in the basal plate that have never been discerned in any taxa. These teeth were shed by semi-basal resorption with the periphery of their bases retained as dentine rings. The rings are highly overlapped, which evidences tooth shedding prior to adding the next first-generation tooth. Later teeth at the same sites underwent cyclical replacing and shedding through basal resorption, producing stacks of buried resorption surfaces separated by bone of attachment. The number and spatial arrangement of resorption surfaces elucidates that basal resorption of replacement teeth had taken place at the older tooth sites before the addition of the youngest first-generation teeth at the lingual margin. Thus the replacement tooth buds cannot have been generated by a single permanent dental lamina, but must have arisen either from successional dental laminae associated with the predecessor teeth, or directly from the dental epithelium of these teeth. The virtual histological dissection of these Late Silurian microfossils broadens our understanding of the development of the gnathostome dental systems and the acquisition of the osteichthyan-type of tooth replacement.
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| 33. |
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| 34. |
- Chen, Donglei, 1985-, et al.
(author)
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The developmental relationship between teeth and dermal odontodes in the most primitive bony fish Lophosteus
- 2020
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In: eLIFE. - 2050-084X. ; 9
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Journal article (peer-reviewed)abstract
- The ontogenetic trajectory of a marginal jawbone of Lophosteus superbus (Late Silurian, 422 Million years old), the phylogenetically most basal stem osteichthyan, visualized by synchrotron microtomography, reveals a developmental relationship between teeth and dermal odontodes that is not evident from the adult morphology. The earliest odontodes are two longitudinal founder ridges formed at the ossification center. Subsequent odontodes that are added lingually to the ridges turn into conical teeth and undergo cyclic replacement, while those added labially achieve a stellate appearance. Stellate odontodes deposited directly on the bony plate are aligned with the alternate files of teeth, whereas new tooth positions are inserted into the files of sequential addition when a gap appears. Successive teeth and overgrowing odontodes show hybrid morphologies around the oral-dermal boundary, suggesting signal cross-communication. We propose that teeth and dermal odontodes are modifications of a single system, regulated and differentiated by the oral and dermal epithelia.
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| 35. |
- Chen, Donglei, et al.
(author)
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The stem osteichthyan Andreolepis and the origin of tooth replacement
- 2016
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In: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 539:7628, s. 237-
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Journal article (peer-reviewed)abstract
- The teeth of gnathostomes (jawed vertebrates) show rigidly patterned, unidirectional replacement that may or may not be associated with a shedding mechanism. These mechanisms, which are critical for the maintenance of the dentition, are incongruently distributed among extant gnathostomes. Although a permanent tooth-generating dental lamina is present in all chondrichthyans, many tetrapods and some teleosts, it is absent in the non-teleost actinopterygians. Tooth-shedding by basal hard tissue resorption occurs in most osteichthyans (including tetrapods) but not in chondrichthyans. Here we report a three-dimensional virtual dissection of the dentition of a 424-million-year-old stem osteichthyan, Andreolepis hedei, using propagation phase-contrast synchrotron microtomography, with a reconstruction of its growth history. Andreolepis, close to the common ancestor of all extant osteichthyans, shed its teeth by basal resorption but probably lacked a permanent dental lamina. This is the earliest documented instance of resorptive tooth shedding and may represent the primitive osteichthyan mode of tooth replacement.
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| 36. |
- Chen, Donglei, et al.
(author)
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Three-dimensional histology of tooth cushions of Lophosteus from the Upper Silurian of Estonia
- 2011
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In: Abstracts. ; , s. 5-6
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Conference paper (other academic/artistic)abstract
- Lophosteus superbus from the Late Silurian of Estonia is one of the oldest and most plesiomorphic osteichthyans described to date. Unfortunately at present it is known only from fragmented dermal microremains. The affinities of Lophosteus are therefore controversial with the taxon placed as either basal to both actinopterygians and sarcopterygians, or ambiguously linked to either placoderms or acanthodians. To confound matters further, the character states diagnosing actinopterygians and sarcopterygians have recently been brought into question, and even monophyly of the traditional placoderm and acanthodian clades has been challenged. As a possible stem osteichthyan, Lophosteus could thus be central to our understanding of early gnathostome evolution and the origin of the osteichthyan body plan. Often the best-preserved, although incompletely documented, elements of Lophosteus are tooth cushions. These tooth-bearing arched ossicles could arguably be homologous with the parasymphysial tooth whorls in chondrichthyans, acanthodians, and sarcopterygians, or even the parasymphysial tooth plates in tetrapodomorphs. High-resolution synchrotron scans of 6 isolated tooth cushions from the Upper Silurian of Estonia has permitted a detailed reconstruction of their three-dimensional architecture. The absence of an enamel layer and the presence of large hollows (bigger than normal osteocytes) in the deepest lamellar layer confirmed assignment of the specimens to Lophosteus. The external surface displays irregularly distributed denticles and there are large parallel vessels running horizontally on the basal bone that feed the denticle rows internally. The odontodes have two distinct generations (with successive odontodes accreted between those of the preceding buried generation) and are organised in a similar manner to those found on Lophosteus scales. This new histological data on vascularization provides insight into early gnathostome tooth patterning and could contribute to future phylogenetic assessments.
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| 37. |
- Chen, Junsheng, et al.
(author)
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Enhanced Size Selection in Two-Photon Excitation for CsPbBr3 Perovskite Nanocrystals
- 2017
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In: Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 8:20, s. 5119-5124
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Journal article (peer-reviewed)abstract
- Cesium lead bromide (CsPbBr3) perovskite nanocrystals (NCs), with large two-photon absorption (TPA) cross-section and bright photoluminescence (PL), have been demonstrated as stable two-photon-pumped lasing medium. With two-photon excitation, red-shifted PL spectrum and increased PL lifetime is observed compared with one-photon excitation. We have investigated the origin of such difference using time-resolved laser spectroscopies. We ascribe the difference to the enhanced size selection of NCs by two-photon excitation. Because of inherent nonlinearity, the size dependence of absorption cross-section under TPA is stronger. Consequently, larger size NCs are preferably excited, leading to longer excited-state lifetime and red-shifted PL emission. In a broad view, the enhanced size selection in two-photon excitation of CsPbBr3 NCs is likely a general feature of the perovskite NCs and can be tuned via NC size distribution to influence their performance within NC-based nonlinear optical materials and devices.
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| 38. |
- Chen, Ricky Hao, et al.
(author)
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Is there a need to optimise pyrazinamide doses in patients with tuberculosis? A systematic review
- 2023
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In: International Journal of Antimicrobial Agents. - : ELSEVIER. - 0924-8579 .- 1872-7913. ; 62:3
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Research review (peer-reviewed)abstract
- Pyrazinamide (PZA) is a first-line antituberculosis drug with potent sterilising activity. Variability in drug exposure may translate into suboptimal treatment responses. This systematic review, conducted according to PRISMA guidelines, aimed to evaluate the concentration-effect relationship. In vitro/in vivo studies had to contain information on the infection model, PZA dose and concentration, and microbiological outcome. Human studies had to present information on PZA dose, measures of drug exposure and maximum concentration, and microbiological response parameter or overall treatment outcome. A total of 34 studies were assessed, including in vitro (n = 2), in vivo (n = 3) and clinical studies (n = 29). Intracellular and extracellular models demonstrated a direct correlation between PZA dose of 15-50 mg/kg/day and reduction in bacterial count between 0.50-27.7 log(10) CFU/mL. Consistent with this, higher PZA doses (>150 mg/kg) were associated with a greater reduction in bacterial burden in BALB/c mice models. Human pharmacokinetic studies displayed a linear positive correlation between PZA dose (i.e. 21.4-35.7 mg/kg/day) and drug exposure (AUC range 220.6-514.5 mg center dot h/L). Additionally, human studies confirmed a dose-effect relationship, with an increased 2-month sputum culture conversion rate at AUC/MIC targets of 8.4-11.3 with higher exposure/susceptibility ratios leading to greater efficacy. A 5-fold variability in AUC was observed at PZA dose of 25 mg/kg. A direct concentration-effect relationship and increased treatment efficacy with higher PZA exposure to susceptibility ratios was observed. Taking into account variability in drug exposure and treatment response, further studies on dose optimisation are justified.
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| 39. |
- Chen, Yaohua Sophie, et al.
(author)
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COVID-19-related loneliness and social isolation in caregivers of people with brain health challenges : The CLIC-Caregiver Global Survey
- 2021
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In: Alzheimer's & dementia : the journal of the Alzheimer's Association. - : Wiley. - 1552-5279. ; 17
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Journal article (peer-reviewed)abstract
- BACKGROUND: Prior to COVID-19, >90% of caregivers of people with brain health challenges (dementia, mental ill health, intellectual disability) experienced high levels of distress, burden, loneliness and social isolation. The COVID-19 pandemic has significantly increased these impacts, particularly since these caregivers are often older and physically vulnerable themselves. The aim of this cross-sectional study is to explore coping and caregiver burden, loneliness and social isolation in caregivers of people with brain health challenges during the COVID-19 pandemic. METHOD: CLIC-Caregiver was a cross-sectional, online, and global survey (June 2nd - November 15th , 2020) using self-administered questionnaires directed at informal caregivers of people with long-term brain health challenges. The study was embedded within a larger survey of loneliness and social isolation for general public ('Comparing Loneliness and Isolation in COVID-19' (CLIC)), including validated loneliness and isolation tools. Translated into ten different languages such as Arabic, French, Romanian, etc, the survey was disseminated over 100 countries. Respondents were included in the CLIC-caregiver sub-study if they answered yes to the question 'Do you provide care and support to a family member or friend with a long-term or life-limiting health problem or disability (including mental health)'. The CLIC project received the initial global ethical approval from Ulster University. The data were fully anonymized. RESULT: From the CLIC main study, 5243 (25%) identified themselves as caregivers. This proportion varied in different countries, from 12 % in Romania to 65% in France. 2323 (44%) had care recipients with dementia, 1761 with physical conditions (disability or long-term illness), 832 with enduring mental health problems, and 404 with intellectual disability. Measures of caregiver burden, loneliness and social isolation will be compared across geographic regions, sociodemographic factors, and risk factors for poor outcomes sought. Findings will be distributed to relevant stakeholders in the form of a project report, with region and country-specific outcomes. This will support recommendations and actions supporting caregivers of people with brain health challenges. CONCLUSION: This represents the largest, most widespread survey on the impact of the COVID-19 pandemic on caregivers of people with long-term conditions to date. It will be an important resource for support agencies and to inform policy.
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| 40. |
- Chen, Yaohua Sophie, et al.
(author)
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COVID-19-related loneliness, social isolation and burden in informal caregivers worldwide
- 2022
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In: Alzheimer's and Dementia. - : Wiley. - 1552-5260 .- 1552-5279. ; 18:S8
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Journal article (peer-reviewed)abstract
- Background: Informal caregivers may experience high levels burden. Prior to COVID-19, loneliness and social isolation, and especially the discordance between them, were recognized for rapid aging-related cognitive decline. The COVID-19 has significantly increased social isolation and loneliness in caregivers. Thus, we aimed to explore the variables that were associated with higher care burden among all caregivers and only among caregivers for people living with dementia, and whether the increased burden could be associated with a discrepancy between loneliness and social isolation. Method: ‘Comparing Loneliness and Isolation in COVID-19’ was an online global survey of over 20,000 respondents, including 5243 caregivers across 50 countries with enduring brain or/and physical health conditions. We first used a multilevel modelling to identify risk factors associated with higher burden. Then, we defined profiles of discrepancy between loneliness and social isolation, based on the differences between standardized score on a scale of loneliness and of social connectedness and estimated the association between the discrepancy and higher burden. Result: In our sample, 74% of caregivers were female, 44% were caring for people with dementia, and 22% for people with multiple conditions, including dementia. The most prevalent age group was 60-69 years old. Factors significantly associated with higher care burden were being female, having poorer financial situation, worse mental health during the pandemic, caring for people with dementia or intellectual disabilities, caring in the same home, being diagnosed with COVID, and changes of care abilities. 40% of caregivers consistently reported high level of loneliness and social isolation, 38% reported consistent lower levels of both, and two groups reported discordance (low levels of loneliness and high social isolation in 13%; high levels of loneliness and mild social isolation in 12%). The latter group was at the highest risk of self-reported increased and intense care burden. Conclusion: This represents the largest, most widespread survey on the impact of the COVID-19 pandemic on caregivers of people with long-term conditions to date and reflects the importance of capturing the nuances in the relationship between loneliness and social isolation in caregivers. It will be an important resource for support agencies and to inform policy.
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