Absence of LTBP-3 attenuates the aneurysmal phenotype but not spinal effects on the aorta in Marfan syndrome.

Fibrillin-1 is an elastin-associated glycoprotein that contributes to the long-term fatigue resistance of elastic fibers as well as to the bioavailability of transforming growth factor-beta (TGFß) in arteries. Altered TGFß bioavailability and/or signaling have been implicated in aneurysm development in Marfan syndrome (MFS), a multi-system condition resulting from mutations to the gene that encodes fibrillin-1. We recently showed that the absence of the latent transforming growth factor-beta binding protein-3 (LTBP-3) in fibrillin-1-deficient mice attenuates the fragmentation of elastic fibers and focal dilatations that are characteristic of aortic root aneurysms in MFS mice, at least to 12 weeks of age. Here, we show further that the absence of LTBP-3 in this MFS mouse model improves the circumferential mechanical properties of the thoracic aorta, which appears to be fundamental in preventing or significantly delaying aneurysm development. Yet, a spinal deformity either remains or is exacerbated in the absence of LTBP-3 and seems to adversely affect the axial mechanical properties of the thoracic aorta, thus decreasing overall vascular function despite the absence of aneurysmal dilatation. Importantly, because of the smaller size of mice lacking LTBP-3, allometric scaling facilitates proper interpretation of aortic dimensions and thus the clinical phenotype. While this study demonstrates that LTBP-3/TGFß directly affects the biomechanical function of the thoracic aorta, it highlights that spinal deformities in MFS might indirectly and adversely affect the overall aortic phenotype. There is a need, therefore, to consider together the vascular and skeletal effects in this syndromic disease.

Comparison of 10 murine models reveals a distinct biomechanical phenotype in thoracic aortic aneurysms.

Thoracic aortic aneurysms are life-threatening lesions that afflict young and old individuals alike. They frequently associate with genetic mutations and are characterized by reduced elastic fibre integrity, dysfunctional smooth muscle cells, improperly remodelled collagen and pooled mucoid material. There is a pressing need to understand better the compromised structural integrity of the aorta that results from these genetic mutations and renders the wall vulnerable to dilatation, dissection or rupture. In this paper, we compare the biaxial mechanical properties of the ascending aorta from 10 murine models: wild-type controls, acute elastase-treated, and eight models with genetic mutations affecting extracellular matrix proteins, transmembrane receptors, cytoskeletal proteins, or intracellular signalling molecules. Collectively, our data for these diverse mouse models suggest that reduced mechanical functionality, as indicated by a decreased elastic energy storage capability or reduced distensibility, does not predispose to aneurysms. Rather, despite normal or lower than normal circumferential and axial wall stresses, it appears that intramural cells in the ascending aorta of mice prone to aneurysms are unable to maintain or restore the intrinsic circumferential material stiffness, which may render the wall biomechanically vulnerable to continued dilatation and possible rupture. This finding is consistent with an underlying dysfunctional mechanosensing or mechanoregulation of the extracellular matrix, which normally endows the wall with both appropriate compliance and sufficient strength.

Differential ascending and descending aortic mechanics parallel aneurysmal propensity in a mouse model of Marfan syndrome.

Marfan syndrome (MFS) is a multi-system connective tissue disorder that results from mutations to the gene that codes the elastin-associated glycoprotein fibrillin-1. Although elastic fibers are compromised throughout the arterial tree, the most severe phenotype manifests in the ascending aorta. By comparing biaxial mechanics of the ascending and descending thoracic aorta in a mouse model of MFS, we show that aneurysmal propensity correlates well with both a marked increase in circumferential material stiffness and an increase in intramural shear stress despite a near maintenance of circumferential stress. This finding is corroborated via a comparison of the present results with previously reported findings for both the carotid artery from the same mouse model of MFS and for the thoracic aorta from another model of elastin-associated glycoprotein deficiency that does not predispose to thoracic aortic aneurysms. We submit that the unique biaxial loading of the ascending thoracic aorta conspires with fibrillin-1 deficiency to render this aortic segment vulnerable to aneurysm and rupture.

The associations of adipokines with selected markers of the renin-angiotensinogen-aldosterone system: the multi-ethnic study of atherosclerosis.

Among obese individuals, increased sympathetic nervous system (SNS) activity results in increased renin and aldosterone production, as well as renal tubular sodium reabsorption. This study determined the associations between adipokines and selected measures of the renin-angiotensinogen-aldosterone system (RAAS). The sample consisted of 1970 men and women from the Multi-Ethnic Study of Atherosclerosis who were free of clinical cardiovascular disease at baseline and had blood assayed for adiponectin, leptin, plasma renin activity (PRA) and aldosterone. The mean age was 64.7 years and 50% were female. The mean (s.d.) PRA and aldosterone were 1.45 (0.56) ng ml(-1) and 150.1 (130.5) pg ml(-1), respectively. After multivariable adjustment, a 1-s.d. increment of leptin was associated with a 0.55 ng ml(-1) higher PRA and 8.4 pg ml(-1) higher aldosterone (P<0.01 for both). Although adiponectin was not significantly associated with PRA levels, the same increment in this adipokine was associated with lower aldosterone levels (-5.5 pg ml(-1), P=0.01). Notably, the associations between aldosterone and both leptin and adiponectin were not materially changed with additional adjustment for PRA. Exclusion of those taking antihypertensive medications modestly attenuated the associations. The associations between leptin and both PRA and aldosterone were not different by gender but were significantly stronger among non-Hispanic Whites and Chinese Americans than African and Hispanic Americans (P<0.01). The findings suggest that both adiponectin and leptin may be relevant to blood pressure regulation via the RAAS, in that the associations appear to be robust to antihypertension medication use and that the associations are likely different by ethnicity.

Estimating risks of de novo kidney diseases after living kidney donation.

De novo post donation renal diseases, such as glomerulonephritis or diabetic nephropathy, are infrequent and distinct from the loss of GFR at donation that all living kidney donors experience. Medical findings that increase risks of disease (e.g. microscopic hematuria,borderline hemoglobin A1C) often prompt donor refusal by centers. These risk factors are part of more comprehensive risks of low GFR and end-stage renal disease (ESRD) from kidney diseases in the general population that are equally relevant. Such data profile the ages of onset, rates of progression, prevalence and severity of loss of GFR from generically characterized kidney diseases. Kidney diseases typically begin in middle age and take decades to reach ESRD, at a median age of 64. Diabetes produces about half of yearly ESRD and even more lifetime near-ESRD. Such data predict that (1) 10- to 15-year studies will not capture the lifetime risks of post donation ESRD; (2)normal young donors are at demonstrably higher risk than normal older candidates; (3) low-normal predonation GFRs become risk factors for ESRD when kidney diseases arise and (4) donor nephrectomy always increases individual risk. Such population-based risk data apply to all donor candidates and should be used to make acceptance standards and counseling more uniform and defensible.

Pregnancy-specific glycoprotein 1 (PSG1) activates TGF-ß and prevents dextran sodium sulfate (DSS)-induced colitis in mice.

Transforming growth factor-ßs (TGF-ßs) are secreted from cells as latent complexes and the activity of TGF-ßs is controlled predominantly through activation of these complexes. Tolerance to the fetal allograft is essential for pregnancy success; TGF-ß1 and TGF-ß2 play important roles in regulating these processes. Pregnancy-specific ß-glycoproteins (PSGs) are present in the maternal circulation at a high concentration throughout pregnancy and have been proposed to have anti-inflammatory functions. We found that recombinant and native PSG1 activate TGF-ß1 and TGF-ß2 in vitro. Consistent with these findings, administration of PSG1 protected mice from dextran sodium sulfate (DSS)-induced colitis, reduced the secretion of pro-inflammatory cytokines, and increased the number of T regulatory cells. The PSG1-mediated protection was greatly inhibited by the coadministration of neutralizing anti-TGF-ß antibody. Our results indicate that proteins secreted by the placenta directly contribute to the generation of active TGF-ß and identify PSG1 as one of the few known biological activators of TGF-ß2.

Higher leptin is associated with hypertension: the Multi-Ethnic Study of Atherosclerosis.

Adipokines are secreted from adipose tissue, influence energy homeostasis and may contribute to the association between obesity and hypertension. Among 1897 participants enrolled in the Multi-Ethnic Study of Atherosclerosis, we examined associations between blood pressure and leptin, tumor necrosis factor-α (TNFα), resistin and total adiponectin. The mean age and body mass index (BMI) was 64.7 years and 28.1, respectively, and 50% were female. After adjustment for risk factors, a 1-s.d.-increment higher leptin level was significantly associated with higher systolic (5.0 mm Hg), diastolic (1.9), mean arterial (2.8) and pulse pressures (3.6), as well as a 34% higher odds for being hypertensive (P<0.01 for all). These associations were not materially different when the other adipokines, as well as BMI, waist circumference or waist-to-hip ratio, were additionally added to the model. Notably, the associations between leptin and hypertension were stronger in men, but were not different by race/ethnic group, BMI or smoking status. Adiponectin, resistin and TNFα were not independently associated with blood pressure or hypertension. Higher serum leptin, but not adiponectin, resistin or TNFα, is associated with higher levels of all measures of blood pressure, as well as a higher odds of hypertension, independent of risk factors, anthropometric measures and other selected adipokines.

Albuminuria and the risk of incident stroke and stroke types in older adults.

BACKGROUND: The kidney biomarker that best reflects risk of stroke is unknown. We sought to evaluate the association of stroke with 3 kidney biomarkers: albuminuria, cystatin C, and glomerular filtration rate. METHODS: These 3 biomarkers were determined in 3,287 participants without history of stroke from the Cardiovascular Health Study, a longitudinal cohort study of men and women age 65 years and older from 4 US communities. The biomarkers were albuminuria ascertained using urinary albumin-to-creatinine ratio (UACR) from morning spot urine, creatinine-based estimated glomerular filtration rate (eGFR), and cystatin C. Outcomes were incident stroke (any, ischemic, or hemorrhagic) during follow-up between 1996 and 2006. RESULTS: A total of 390 participants had an incident stroke: 81% ischemic, 12% hemorrhagic, and 7% unclassified. In adjusted Cox regression models, UACR was more strongly related to any stroke, ischemic stroke, and hemorrhagic stroke than eGFR and cystatin C. The hazard ratio (HR) of any stroke comparing the top to bottom quintile of UACR was 2.10 (95% confidence interval [CI] 1.47-3.00), while HR for eGFR was 1.29 (95% CI 0.91-1.84) and for cystatin C was 1.22 (95% CI 0.85-1.74). When considering clinically relevant categories, elevated UACR was associated with increased hazard of any stroke and ischemic stroke regardless of eGFR or cystatin C categories. CONCLUSIONS: UACR was the kidney biomarker most strongly associated with risk of incident stroke. Results in this elderly cohort may not be applicable to younger populations. These findings suggest that measures of glomerular filtration and permeability have differential effects on stroke risk.

Extracellular microfibrils in development and disease.

Fibrillins are the structural components of extracellular microfibrils that impart physical properties to tissues, alone or together with elastin as elastic fibers. Genetic studies in mice have revealed that fibrillin-rich microfibrils are also involved in regulating developmental programs and homeostatic processes through the modulation of TGF-beta/BMP signaling events. A new paradigm has thus emerged whereby the spatiotemporal organization of microfibrils dictates both the cellular activities and physical properties of connective tissues. These observations have paved the way to novel therapeutic approaches aimed at counteracting the life-threatening complications in human conditions caused by dysfunctions of fibrillin-rich microfibrils.

Osteopetrosis-like phenotype in latent TGF-beta binding protein 3 deficient mice.

LTBPs are extracellular matrix proteins resembling fibrillins. LTBP-1, 3, and 4 covalently bind latent TGF-beta and modulate tissue levels of this potent cytokine through regulation of its secretion, localization, and/or activation. To address LTBP function in vivo, we generated Ltbp-3 null mice. Ltbp-3-/- animals developed craniofacial abnormalities due to early ossification of the skull base synchondroses and displayed reduced body size. In addition, histological examination of Ltbp-3-/- skeletons revealed an increase in bone mass. The osteoblast numbers and mineral apposition rates were decreased in Ltbp-3-/- mice, whereas the osteoclast numbers were similar in null and wild type mice. Histological examination revealed persistence of cartilage remnants in Ltbp-3-/- trabecular bone. Taken together, these results indicate that the Ltbp-3-/- high bone mass phenotype was due to a defect in bone resorption. We hypothesize that lack of Ltbp-3 results in decreased levels of TGF-beta in bone and cartilage, which leads to compromised osteoclast function and decreased bone turnover.

Latent TGF-beta binding proteins.

Latent TGF-beta binding proteins are multidomain proteins with a common, highly repetitive structural organization and partially overlapping expression patterns. Latent TGF-beta binding protein-1, -3 and -4 bind latent TGF-beta. TGF-betas are normally secreted as latent complexes, consisting of the mature TGF-beta dimer non-covalently bound to its processed propeptide dimer plus a latent TGF-beta binding protein. The latent TGF-beta binding protein is covalently bound to the propeptide. These binding proteins may perform at least two functions: structural, as components of the matrix, and regulatory, as modulators of TGF-beta availability.

Exercise delays the hypoxic thermal response in rats.

Exercise exacerbates acute mountain sickness. In infants and small mammals, hypoxia elicits a decrease in body temperature (Tb) [hypoxic thermal response (HTR)], which may protect against hypoxic tissue damage. We postulated that exercise would counteract the HTR and promote hypoxic tissue damage. Tb was measured by telemetry in rats (n = 28) exercising or sedentary in either normoxia or hypoxia (10% O2, 24 h) at 25 degrees C ambient temperature (Ta). After 24 h of normoxia, rats walked at 10 m/min on a treadmill (30 min exercise, 30 min rest) for 6 h followed by 18 h of rest in either hypoxia or normoxia. Exercising normoxic rats increased Tb ( degrees C) vs. baseline (39.68 +/- 0.99 vs. 38.90 +/- 0.95, mean +/- SD, P < 0.05) and vs. sedentary normoxic rats (38.0 +/- 0.09, P < 0.05). Sedentary hypoxic rats decreased Tb (36.15 +/- 0.97 vs. 38.0 +/- 0.36, P < 0.05) whereas Tb was maintained in the exercising hypoxic rats during the initial 6 h of exercise (37.61 +/- 0.55 vs. 37.72 +/- 1.25, not significant). After exercise, Tb in hypoxic rats reached a nadir similar to that in sedentary hypoxic rats (35.05 +/- 1.69 vs. 35.03 +/- 1.32, respectively). Tb reached its nadir significantly later in exercising hypoxic vs. sedentary hypoxic rats (10.51 +/- 1.61 vs. 5.36 +/- 1.83 h, respectively; P = 0.002). Significantly greater histopathological damage and water contents were observed in brain and lungs in the exercising hypoxic vs. sedentary hypoxic and normoxic rats. Thus exercise early in hypoxia delays but does not prevent the HTR. Counteracting the HTR early in hypoxia by exercise exacerbates brain and lung damage and edema in the absence of ischemia.

Bone defects in latent TGF-beta binding protein (Ltbp)-3 null mice; a role for Ltbp in TGF-beta presentation.

The latent transforming growth factor (TGF)-beta binding proteins (LTBP)-1, -3 and -4 bind the latent form of the multipotent cytokine TGF-beta. To examine the function of the LTBPs, we made a null mutation of Ltbp-3 by gene targeting. The homozygous mutant animals developed cranio-facial malformations by 12 days. By three months, there was a pronounced rounding of the cranial vault, extension of the mandible beyond the maxilla, and kyphosis. The mutant animals developed osteosclerosis of the long bones and vertebrae as well as osteoarthritis between 6 and 9 months of age. These latter phenotypic changes were similar to those described for mice that have impaired TGF-beta signaling. Thus, we suggest that Ltbp-3 plays an important role in regulating TGF-beta bioavailability as the phenotype of the Ltbp-3 null mouse appears to result from decreased TGF-beta signaling. Histological examination of the skulls from null animals revealed no effects on calvarial suture closure. However, the synchondroses in the skull base were obliterated within 2 weeks of birth. This is in contrast to the wild-type synchondroses, which remain unossified throughout the life of the animal and enable growth of the skull base through endochondral ossification. Histological changes in mutant basooccipital-basosphenoid synchondrosis were observed 1.5 days after birth. Compared with wild-type or heterozygous littermates, the basooccipital-basosphenoid synchondrosis of Ltbp-3 null mice contained increased numbers of hypertrophic chondrocytes. The expression of bone sialoprotein-1 (a marker for osteoblasts) was observed in cells surrounding the synchondrosis at postnatal day 1.5 indicating ectopic ossification. The expression of Indian hedgehog (Ihh) (a marker for chondrocytes committed to hypertrophic differentiation) was found through the basooccipital-basosphenoid synchondrosis, whereas the expression of parathyroid hormone related protein (PTHrP), which inhibits chondrocyte differentiation, appeared to be diminished in Ltbp-3 null mice. This suggests that Ltbp-3 may control chondrocyte differentiation by regulating TGF-beta availability. TGF-beta may regulate PTHrP expression either downstream of Ihh or independently of Ihh signaling.

Physician control of pediatric antimicrobial use in Beijing, China, and its rural environs.

BACKGROUND: Antibiotic resistance is recognized as an increasing problem in China. It is widely believed that because antibiotics are available without a prescription, changing physician prescribing behaviors will not decrease inappropriate usage. This study identified the sources of antibiotics and the important influence that physicians have on antibiotic use by children in one region of China. METHODS: Trained medical professionals surveyed parents of children attending several kindergartens in urban Beijing and rural Gu'An, Hebei County. Parents completed a questionnaire concerning the children's recent illnesses, care-seeking patterns and antibiotic use. The team also observed hospital- and non-hospital-based pharmacy purchases of antibiotics for children, assessed the proportion accompanied by a prescription and then interviewed parents about factors influencing those purchases. RESULTS: Of 241 urban and 143 rural kindergarten parents, 76 to 82% usually obtained children's antibiotics from a hospital pharmacy (with a prescription). For 84% the first source of care was usually a physician (primarily western medicine, sometimes traditional Chinese medicine). Only 5% of antibiotics were obtained from independent vendors without prior physician consultation. Among 229 observed antibiotic purchases 72% occurred at hospital-based facilities, even after longer observation times at nonhospital pharmacies. Prescriptions accompanied all hospital-based antibiotic purchases, contrasting with 18% of nonhospital transactions (P < 0.001). Together 86% of parents self-reported that the observed purchase stemmed from a doctor's recommendation. CONCLUSIONS: Doctors directly and indirectly controlled the majority of antibiotic usage for childhood illnesses in Beijing and Gu'An (Hebei County). Physician education and implementation of treatment guidelines might substantially reduce inappropriate antimicrobial usage and help prevent antimicrobial resistance in this region.

Tamoxifen and estrogen effects on TGF-beta formation: role of thrombospondin-1, alphavbeta3, and integrin-associated protein.

We have found that the enhanced activation of latent TGF-beta by human breast carcinoma cell lines either treated with tamoxifen or deprived of estrogen is dependent upon thrombospondin-1 (TSP-1) since activation was blocked by anti-TSP-1 antibodies or by a TSP antagonist peptide. However, TGF-beta formation upon tamoxifen exposure to estrogen withdrawal is associated with decreased levels of soluble TSP-1. A concomitant increase in the expression of the TSP-1 receptors alphavbeta3 and integrin-associated protein (IAP) occurs under these conditions, and antibodies to TSP-1 or to these receptors inhibit increased TGF-beta formation. Therefore, increased cell surface associated TSP-1 enhances latent TGF-beta activation.

Ambient temperature modulates hypoxic-induced changes in rat body temperature and activity differentially.

When rats, acclimated to an ambient temperature (T(a)) of 29 degrees C, are exposed to 10% O(2) for 63 h, the circadian rhythms of body temperature (T(b)) and level of activity (L(a)) are abolished, T(b) falls to a hypothermic nadir followed by a climb to a hyperthermic peak, L(a) remains depressed (Bishop B, Silva G, Krasney J, Salloum A, Roberts A, Nakano H, Shucard D, Rifkin D, and Farkas G. Am J Physiol Regulatory Integrative Comp Physiol 279: R1378-R1389, 2000), and overt brain pathology is detected (Krasney JA, Farkas G, Shucard DW, Salloum AC, Silva G, Roberts A, Rifkin D, Bishop B, and Rubio A. Soc Neurosci Abstr 25: 581, 1999). To determine the role of T(a) in these hypoxic-induced responses, T(b) and L(a) data were detected by telemetry every 15 min for 48 h on air, followed by 63 h on 10% O(2) from rats acclimated to 25 or 21 degrees C. Magnitudes and rates of decline in T(b) after onset of hypoxia were inversely proportional to T(a), whereas magnitudes and rates of T(b) climb after the hypothermic nadir were directly proportional to T(a). No hyperthermia, so prominent at 29 degrees C, occurred at 25 or 21 degrees C. The hypoxic depression of L(a) was least at 21 degrees C and persisted throughout the hypoxia. In contrast, T(a) was a strong determinant of the magnitudes and time courses of the initial fall and subsequent rise in T(b). We propose that the absence of hyperthermia at 21 and 25 degrees C as well as a persisting hypothermia may protect the brain from overt pathology.

The latent transforming growth factor-beta-binding protein-1 promotes in vitro differentiation of embryonic stem cells into endothelium.

The latent transforming growth factor-beta-binding protein-1 (LTBP-1) belongs to a family of extracellular glycoproteins that includes three additional isoforms (LTBP-2, -3, and -4) and the matrix proteins fibrillin-1 and -2. Originally described as a TGF-beta-masking protein, LTBP-1 is involved both in the sequestration of latent TGF-beta in the extracellular matrix and the regulation of its activation in the extracellular environment. Whereas the expression of LTBP-1 has been analyzed in normal and malignant cells and rodent and human tissues, little is known about LTBP-1 in embryonic development. To address this question, we used murine embryonic stem (ES) cells to analyze the appearance and role of LTBP-1 during ES cell differentiation. In vitro, ES cells aggregate to form embryoid bodies (EBs), which differentiate into multiple cell lineages. We analyzed LTBP-1 gene expression and LTBP-1 fiber appearance with respect to the emergence and distribution of cell types in differentiating EBs. LTBP-1 expression increased during the first 12 d in culture, appeared to remain constant between d 12 and 24, and declined thereafter. By immunostaining, fibrillar LTBP-1 was observed in those regions of the culture containing endothelial, smooth muscle, and epithelial cells. We found that inclusion of a polyclonal antibody to LTBP-1 during EB differentiation suppressed the expression of the endothelial specific genes ICAM-2 and von Willebrand factor and delayed the organization of differentiated endothelial cells into cord-like structures within the growing EBs. The same effect was observed when cultures were treated with either antibodies to TGF-beta or the latency associated peptide, which neutralize TGF-beta. Conversely, the organization of endothelial cells was enhanced by incubation with TGF-beta 1. These results suggest that during differentiation of ES cells LTBP-1 facilitates endothelial cell organization via a TGF-beta-dependent mechanism.

Circadian rhythms of body temperature and activity levels during 63 h of hypoxia in the rat.

The hypothermic response of rats to only brief ( approximately 2 h) hypoxia has been described previously. The present study analyzes the hypothermic response in rats, as well as level of activity (L(a)), to prolonged (63 h) hypoxia at rat thermoneutral temperature (29 degrees C). Mini Mitter transmitters were implanted in the abdomens of 10 adult Sprague-Dawley rats to continuously record body temperature (T(b)) and L(a). After habituation for 7 days to 29 degrees C and 12:12-h dark-light cycles, 48 h of baseline data were acquired from six control and four experimental rats. The mean T(b) for the group oscillated from a nocturnal peak of 38.4 +/- 0.18 degrees C (SD) to a diurnal nadir of 36.7 +/- 0.15 degrees C. Then the experimental group was switched to 10% O(2) in N(2). The immediate T(b) response, phase I, was a disappearance of circadian rhythm and a fall in T(b) to 36.3 +/- 0.52 degrees C. In phase II, T(b) increased to a peak of 38.7 +/- 0.64 degrees C. In phase III, T(b) gradually decreased. At reoxygenation at the end of the hypoxic period, phase IV, T(b) increased 1.1 +/- 0.25 degrees C. Before hypoxia, L(a) decreased 70% from its nocturnal peak to its diurnal nadir and was entrained with T(b). With hypoxia L(a) decreased in phase I to essential quiescence by phase II. L(a) had returned, but only to a low level in phase III, and was devoid of any circadian rhythm. L(a) resumed its circadian rhythm on reoxygenation. We conclude that 63 h of sustained hypoxia 1) completely disrupts the circadian rhythms of both T(b) and L(a) throughout the hypoxic exposure, 2) the hypoxia-induced changes in T(b) and L(a) are independent of each other and of the circadian clock, and 3) the T(b) response to hypoxia at thermoneutrality has several phases and includes both hypothermic and hyperthermic components.