Effect of exercising in water on the fibrocartilage of the deep digital flexor tendon in rats with induced diabetes.

Individuals with diabetes mellitus (DM) are affected four times more by tendinopathies than non-diabetics. On the other hand, physical activity helps to DM control. However, the effects of physical exercise in water (PEW) on the fibrocartilages present in the tendons of animals affected by DM are unknown. In this sense, the aim of this study was to analyze the structural organization and chemical composition of fibrocartilage present in the intermediate region of the deep digital flexor tendon (DDFT) of Wistar rats with alloxan-induced DM. Diabetic and non-diabetic animals were randomly separated into four experimental groups (n = 10): Non-Trained Control (NTC), Trained Control (TC), Non-Trained Diabetic (NTD), and Trained Diabetic (TD). TC and TD animals underwent the exercise protocol (total weekly training load - week 1: 14,375; 2: 16,500; 3: 18,375; 4: 20,000) and then were euthanized to collect tendon samples for analysis. The matrix basophilia was more intense in the TC and TD groups. The Decorin immunohistochemical test results showed greater intensity in the NTD and TD groups. The wet weight of the fibrocartilaginous region of the tendon (NTC:19.9 ± 0.06; TC:22.3 ± 0.05; NTD:20.3 ± 0.08; TD:21.8 ± 0.04 mg - p = 0.048), glycosaminoglycan amounts (NTC:3.21 ± 0.18; TC:3.98 ± 0.44; NTD:3.32 ± 0.19; TD:3.79 ± 0.28 µg/mg of fresh tissue - p = 0.046), and intumescence in water (NTC:13.8 ± 3.8; TC:24.3 ± 3.9; NTD:14.9 ± 3.9; TD:28.2 ± 5.3 % w/w - p = 0.042) were higher in the TC and TD groups. The TD group showed the highest levels of type I collagen and matrix metalloproteinase (MMP)-13. The TC group showed the highest and TD the lowest TGF-ß1 levels. In conclusion, the PEW was able to stimulate the deposition of proteoglycans, without inducing chemical changes that would cause histopathological modifications in fibrocartilage in the DDFT of adult rats. Thus, PEW preserves the structural organization of these tissues in tendons of animals affected by DM.

Assessment of serum endocan levels in patients with beta-thalassemia minor

SUMMARY OBJECTIVE: Beta-thalassemia minor is a blood disease caused by a hereditary decrease in beta-globin synthesis, frequently leading to hypochromic microcytic anemia. Formerly called endothelial cell-specific molecule 1, endocan is a proteoglycan released by vascular endothelial cells in many organs. Our aim was to investigate the relationship between the beta-thalassemia minor patients and the healthy control group in terms of serum endocan level. METHODS: The study was performed in a total of 80 subjects. They were divided into two groups, the beta-thalassemia minor group (n=40) and the healthy control group (n=40). Serum endocan levels, age, sex, body mass index value, and tobacco use data of these groups were compared. RESULTS: No statistically significant difference was detected between the two groups in terms of age, sex, and body mass index values (p>0.05). Endocan levels were measured to be 206.85±88.1 pg/mL in the beta-thalassemia minor group and 236.1±162.8 pg/mL in the control group with no significant difference between the groups in terms of serum endocan levels (p>0.05). CONCLUSIONS: In our study, there was no change in endocan level in beta-thalassemia minor. This might be because serum endocan levels are affected by multi-factorial reasons. Serum endocan levels may be altered secondarily to decreased beta-globin chain, increased sympathetic activity due to anemia, or platelet dysfunction induced by oxidative stress in beta-thalassemia minor. Further multicenter studies involving more patients are necessary to demonstrate this.

Proteoglycan-driven Autophagy: A Nutrient-independent Mechanism to Control Intracellular Catabolism.

Proteoglycans are rapidly emerging as versatile regulators of intracellular catabolic pathways. This is predominantly achieved via the non-canonical induction of autophagy, a fundamentally and evolutionarily conserved eukaryotic pathway necessary for maintaining organismal homeostasis. Autophagy facilitated by either decorin, a small leucine-rich proteoglycan, or perlecan, a basement membrane heparan sulfate proteoglycan, proceeds independently of ambient nutrient conditions. We found that soluble decorin evokes endothelial cell autophagy and breast carcinoma cell mitophagy by directly interacting with vascular endothelial growth factor receptor 2 (VEGFR2) or the Met receptor tyrosine kinase, respectively. Endorepellin, a soluble, proteolytic fragment of perlecan, induces autophagy and endoplasmic reticulum stress within the vasculature, downstream of VEGFR2. These potent matrix-derived cues transduce key biological information via receptor binding to converge upon a newly discovered nexus of core autophagic machinery comprised of Peg3 (paternally expressed gene 3) for autophagy or mitostatin for mitophagy. Here, we give a mechanistic overview of the nutrient-independent, proteoglycan-driven programs utilized for autophagic or mitophagic progression. We propose that catabolic control of cell behavior is an underlying basis for proteoglycan versatility and may provide novel therapeutic targets for the treatment of human disease.

The Tumor Microenvironment: Focus on Extracellular Matrix.

The extracellular matrix (ECM) regulates the development and maintains tissue homeostasis. The ECM is composed of a complex network of molecules presenting distinct biochemical properties to regulate cell growth, survival, motility, and differentiation. Among their components, proteoglycans (PGs) are considered one of the main components of ECM. Its composition, biomechanics, and anisotropy are exquisitely tuned to reflect the physiological state of the tissue. The loss of ECM's homeostasis is seen as one of the hallmarks of cancer and, typically, defines transitional events in tumor progression and metastasis. In this chapter, we discuss the types of proteoglycans and their roles in cancer. It has been observed that the amount of some ECM components is increased, while others are decreased, depending on the type of tumor. However, both conditions corroborate with tumor progression and malignancy. Therefore, ECM components have an increasingly important role in carcinogenesis and this leads us to believe that their understanding may be a key in the discovery of new anti-tumor therapies. In this book, the main ECM components will be discussed in more detail in each chapter.

Role of cell surface proteoglycans in cancer immunotherapy.

Over the past few decades, understanding how tumor cells evade the immune system and their communication with their tumor microenvironment, has been the subject of intense investigation, with the aim of developing new cancer immunotherapies. The current therapies against cancer such as monoclonal antibodies against checkpoint inhibitors, adoptive T-cell transfer, cytokines, vaccines, and oncolytic viruses have managed to improve the clinical outcome of the patients. However, in some tumor entities, the response is limited and could benefit from the identification of novel therapeutic targets. It is known that tumor-extracellular matrix interplay and matrix remodeling are necessary for anti-tumor and pro-tumoral immune responses. Proteoglycans are dominant components of the extracellular matrix and are a highly heterogeneous group of proteins characterized by the covalent attachment of a specific linear carbohydrate chain of the glycosaminoglycan type. At cell surfaces, these molecules modulate the expression and activity of cytokines, chemokines, growth factors, adhesion molecules, and function as signaling co-receptors. By these mechanisms, proteoglycans influence the behavior of cancer cells and their microenvironment during the progression of solid tumors and hematopoietic malignancies. In this review, we discuss why cell surface proteoglycans are attractive pharmacological targets in cancer, and we present current and recent developments in cancer immunology and immunotherapy utilizing proteoglycan-targeted strategies.

Proteoglycans and glycosaminoglycans as regulators of cancer stem cell function and therapeutic resistance.

In contrast to the bulk of the tumor, a subset of cancer cells called cancer stem cells (CSC; or tumor-initiating cells) is characterized by self-renewal, unlimited proliferative potential, expression of multidrug resistance proteins, active DNA repair capacity, apoptosis resistance, and a considerable developmental plasticity. Due to these properties, CSCs display increased resistance to chemo- and radiotherapy. Recent findings indicate that aberrant functions of proteoglycans (PGs) and glycosaminoglycans (GAGs) contribute substantially to the CSC phenotype and therapeutic resistance. In this review, we summarize how the diverse functions of the glycoproteins and carbohydrates facilitate acquisition and maintenance of the CSC phenotype, and how this knowledge can be exploited to develop novel anticancer therapies. For example, the large transmembrane chondroitin sulfate PG NG2/CSPG4 marks stem cell (SC) populations in brain tumors. Cell surface heparan sulfate PGs of the syndecan and glypican families modulate the stemness-associated Wnt, hedgehog, and notch signaling pathways, whereas the interplay of hyaluronan in the SC niche with CSC CD44 determines the maintenance of stemness and promotes therapeutic resistance. A better understanding of the molecular mechanisms by which PGs and GAGs regulate CSC function will aid the development of targeted therapeutic approaches which could avoid relapse after an otherwise successful conventional therapy. Chimeric antigen receptor T cells, PG-primed dendritic cells, PG-targeted antibody-drug conjugates, and inhibitory peptides and glycans have already shown highly promising results in preclinical models.

Proteoglycans as potential biomarkers in odontogenic tumors.

Proteoglycans (PGs) are essential for normal cellular development; however, alterations of their concentrations can promote tumor growth. To date, a limited number of studies report the presence of PGs in odontogenic tumors (OTs); therefore, the main purpose of this work is to gather the information published on the study of PGs. The search reported 26 articles referring to the presence of different PGs in distinct OTs from 1999 to May 2017. PGs seem to play an important role during OTs' development as they are involved in several tumor processes; however, the number of reports on the study of these molecules is low. Thus, more studies are necessary in order to gain a better understanding of the underlying pathophysiology of OTs.

Vitamin D Deficiency and Rheumatoid Arthritis.

Vitamin D (VitD) is a hormone primarily synthesized in human skin under the stimulation of ultraviolet radiation. Beyond its endocrine role in bone metabolism, VitD is endowed with remarkable immunomodulatory properties. The effects of VitD on the immune system include the enhancement of microbicidal ability of monocytes/macrophages and the down-modulation of inflammatory cytokines produced by T lymphocytes. VitD deficiency is involved in many health problems, including immune-mediated diseases such as autoimmune disorders. Rheumatoid arthritis (RA) is a chronic inflammatory systemic autoimmune disease that compromises the joints, causing cartilage destruction and bone erosion. RA treatment usually consists of combined therapies that generally suppress the entire immune response leading to increased susceptibility to infections. This review describes the main effects of VitD on innate and adaptive immune system and also VitD status in inflammatory rheumatic diseases such as RA. Despite some controversies, the majority of reports reinforce the idea that lower VitD levels correlate with more severe clinical manifestations in RA and other rheumatic diseases. Therefore, supplementation with VitD to achieve normal serum levels is worthwhile as an aforethought. Original data concerning the potential applicability of 1,25-dihydroxyvitamin D3 (VitD3), the active form of vitamin D, as a tolerogenic adjuvant are also included. In this sense, the effect of VitD3 associated with proteoglycan (PG), which is a specific cartilage antigen, was tested in the course of experimental arthritis. This association significantly lowered clinical scores and local histopathological alterations. Even though local analysis of T cell subsets and cytokine production did not reveal any difference between the experimental groups, VitD3+PG association significantly reduced cytokine production by spleen cells. These results suggest that VitD3 played a role as a tolerogenic adjuvant by down-modulating the course of experimental RA. Considering this tolerogenic effect of VitD3+PG association, further investigations will reveal its plausible use in human RA.

Carbohydrate-Carbohydrate Interactions Mediated by Sulfate Esters and Calcium Provide the Cell Adhesion Required for the Emergence of Early Metazoans.

Early metazoans had to evolve the first cell adhesion mechanism addressed to maintain a distinctive multicellular morphology. As the oldest extant animals, sponges are good candidates for possessing remnants of the molecules responsible for this crucial evolutionary innovation. Cell adhesion in sponges is mediated by the calcium-dependent multivalent self-interactions of sulfated polysaccharides components of extracellular membrane-bound proteoglycans, namely aggregation factors. Here, we used atomic force microscopy to demonstrate that the aggregation factor of the sponge Desmapsamma anchorata has a circular supramolecular structure and that it thus belongs to the spongican family. Its sulfated polysaccharide units, which were characterized via nuclear magnetic resonance analysis, consist preponderantly of a central backbone composed of 3-α-Glc1 units partially sulfated at 2- and 4-positions and branches of Pyr(4,6)α-Gal1→3-α-Fuc2(SO3)1→3-α-Glc4(SO3)1→3-α-Glc→4-linked to the central α-Glc units. Single-molecule force measurements of self-binding forces of this sulfated polysaccharide and their chemically desulfated and carboxyl-reduced derivatives revealed that the sulfate epitopes and extracellular calcium are essential for providing the strength and stability necessary to sustain cell adhesion in sponges. We further discuss these findings within the framework of the role of molecular structures in the early evolution of metazoans.

Endocan-1 concentrations in maternal and fetal plasma and placentae in pre-eclampsia in the third trimester of pregnancy.

INTRODUCTION: Endocan-1 has been proposed as a possible biomarker and predictor of vascular endothelial related pathologies. Thus, we hypothesised that Endocan-1 levels would be up-regulated in maternal plasma and placentae from women with pre-eclampsia. The aim of our study was to compare Endocan-1 concentrations in maternal/fetal plasma and placentae from normotensive and pre-eclamptic pregnancies. METHODS: Observational and case-controlled study, at the São Lucas Hospital, Brazil. Placental biopsies, maternal/umbilical venous (fetal) plasma were taken from 67 normotensive and 50 pre-eclamptic women. Endocan-1 levels were quantified using MagPlex(TH)-C and analysed by Analysis of Covariance and Pearson correlation. The null hypothesis was rejected at p<0.05. RESULTS: Higher levels of Endocan-1 were found in maternal plasma in the pre-eclamptic group (mean ratio=1.49; 95% confidence interval: 1.19-1.85, p=0.001), with a moderate effect size (Cohen's D=0.84). Placental Endocan-1 levels (µg/g) were lower in pre-eclampsia (1.52 [1.10, 2.40] vs. 2.24 [1.32, 3.75], p=0.033) and fetal Endocan-1 concentration (ng/ml) did not show any difference between groups (3.10 [2.60, 4.54] vs. 2.91 [2.20, 3.66] p=0.085). In addition, an up-regulation of maternal plasma Endocan-1 in the pre-eclamptic group was observed when stratified in relation to gestational age, systolic blood pressure and proteinuria (p<0.05, for all). Furthermore, a positive correlation between Endocan-1 concentration in maternal vs. fetal plasma was also found (r=0.258, p=0.015). For the matched samples, a negative correlation between Endocan-1 in maternal/fetal plasma with birthweights, placental weights and gestational age at delivery was observed (p<0.05 for all). DISCUSSION: Endocan-1 is increased in women with pre-eclampsia for all strata, which highlight the importance of this molecule as a possible biomarker. The negative correlations between Endocan-1 and clinical data suggest that this molecule may also be involved with prematurity and low birth weight, which warrants further investigations.

HTLV-1 infects human mesenchymal stromal cell in vitro and modifies their phenotypic characteristics.

The typical characteristics of mesenchymal stem cells (MSCs) can be affected by inflammatory microenvironment; however, the exact contribution of HTLV-1 to MSC dysfunction remains to be elucidated. In this study, we demonstrated that MSC cell surface molecules VCAM-1 and ICAM-1 are upregulated by contact with HTLV-1, and HLA-DR was most highly expressed in MSCs co-cultured with MT2 cells. The expression levels of VCAM-1 and HLA-DR were increased in MSCs cultured in the presence of PBMCs isolated from HTLV-1-infected symptomatic individuals compared with those cultured with cells from asymptomatic infected individuals or healthy subjects. HTLV-1 does not impair the MSC differentiation process into osteocytes and adipocytes. In addition, MSCs were efficiently infected with HTLV-1 in vitro through direct contact with HTLV-1-infected cells; however, cell-free virus particles were not capable of causing infection. In summary, HTLV-1 can alter MSC function, and this mechanism may contribute to the pathogenesis of this viral infection.

The metabolic dynamics of cartilage explants over a long-term culture period

INTRODUCTION: Although previous studies have been performed on cartilage explant cultures, the generalized dynamics of cartilage metabolism after extraction from the host are still poorly understood due to differences in the experimental setups across studies, which in turn prevent building a complete picture. METHODS: In this study, we investigated the response of cartilage to the trauma sustained during extraction and determined the time needed for the cartilage to stabilize. Explants were extracted aseptically from bovine metacarpal-phalangeal joints and cultured for up to 17 days. RESULTS: The cell viability, cell number, proteoglycan content, and collagen content of the harvested explants were analyzed at 0, 2, 10, and 17 days after explantation. A high percentage of the cartilage explants were found to be viable. The cell density initially increased significantly but stabilized after two days. The proteoglycan content decreased gradually over time, but it did not decrease to a significant level due to leakage through the distorted peripheral collagen network and into the bathing medium. The collagen content remained stable for most of the culture period until it dropped abruptly on day 17. CONCLUSION: Overall, the tested cartilage explants were sustainable over long-term culture. They were most stable from day 2 to day 10. The degradation of the collagen on day 17 did not reach diseased levels, but it indicated the potential of the cultures to develop into degenerated cartilage. These findings have implications for the application of cartilage explants in pathophysiological fields.

Heparanase isoform expression and extracellular matrix remodeling in intervertebral disc degenerative disease

OBJECTIVE: To determine the molecules involved in extracellular matrix remodeling and to identify and quantify heparanase isoforms present in herniated and degenerative discs. INTRODUCTION: Heparanase is an endo-beta-glucuronidase that specifically acts upon the heparan sulfate chains of proteoglycans. However, heparanase expression in degenerative intervertebral discs has not yet been evaluated. Notably, previous studies demonstrated a correlation between changes in the heparan sulfate proteoglycan pattern and the degenerative process associated with intervertebral discs. METHODS: Twenty-nine samples of intervertebral degenerative discs, 23 samples of herniated discs and 12 samples of non-degenerative discs were analyzed. The expression of both heparanase isoforms (heparanase-1 and heparanase-2) was evaluated using immunohistochemistry and real-time RT-PCR analysis. RESULTS: Heparanase-1 and heparanase-2 expression levels were significantly higher in the herniated and degenerative discs in comparison to the control tissues, suggesting a possible role of these proteins in the intervertebral degenerative process. CONCLUSION: The overexpression of heparanase isoforms in the degenerative intervertebral discs and the herniated discs suggests a potential role of both proteins in the mediation of inflammatory processes and in extracellular matrix remodeling. The heparanase-2 isoform may be involved in normal metabolic processes, as evidenced by its higher expression in the control intervertebral discs relative to the expression of heparanase-1.

Noncrystalline uric acid inhibits proteoglycan and glycosaminoglycan synthesis in distal tubular epithelial cells (MDCK)

Hyperuricemia is associated with renal stones, not only consisting of uric acid (UrAc) but also of calcium oxalate (CaOx). Glycosaminoglycans (GAGs) are well-known inhibitors of growth and aggregation of CaOx crystals. We analyzed the effect of noncrystalline UrAc on GAG synthesis in tubular distal cells. MDCK (Madin-Darby canine kidney) cells were exposed to noncrystalline UrAc (80 µg/mL) for 24 h. GAGs were labeled metabolically and characterized by agarose gel electrophoresis. The expression of proteoglycans and cyclooxygenase 2 (COX-2) was assessed by real-time PCR. Necrosis, apoptosis and prostaglandin E2 (PGE2) were determined by acridine orange, HOESCHT 33346, and ELISA, respectively. CaOx crystal endocytosis was evaluated by flow cytometry. Noncrystalline UrAc significantly decreased the synthesis and secretion of heparan sulfate into the culture medium (UrAc: 2127 ± 377; control: 4447 ± 730 cpm) and decreased the expression of perlecan core protein (UrAc: 0.61 ± 0.13; control: 1.07 ± 0.16 arbitrary units), but not versican. Noncrystalline UrAc did not induce necrosis or apoptosis, but significantly increased COX-2 and PGE2 production. The effects of noncrystalline UrAc on GAG synthesis could not be attributed to inflammatory actions because lipopolysaccharide, as the positive control, did not have the same effect. CaOx was significantly endocytosed by MDCK cells, but this endocytosis was inhibited by exposure to noncrystalline UrAc (control: 674.6 ± 4.6, CaOx: 724.2 ± 4.2, and UrAc + CaOx: 688.6 ± 5.4 geometric mean), perhaps allowing interaction with CaOx crystals. Our results indicate that UrAc decreases GAG synthesis in MDCK cells and this effect could be related to the formation of UrAc and CaOx stones.

The extracellular matrix of the lung and its role in edema formation

The extracellular matrix is composed of a three-dimensional fiber mesh filled with different macromolecules such as: collagen (mainly type I and III), elastin, glycosaminoglycans, and proteoglycans. In the lung, the extracellular matrix has several functions which provide: 1) mechanical tensile and compressive strength and elasticity, 2) low mechanical tissue compliance contributing to the maintenance of normal interstitial fluid dynamics, 3) low resistive pathway for an effective gas exchange, d) control of cell behavior by the binding of growth factors, chemokines, cytokines and the interaction with cell-surface receptors, and e) tissue repair and remodeling. Fragmentation and disorganization of extracellular matrix components comprises the protective role of the extracellular matrix, leading to interstitial and eventually severe lung edema. Thus, once conditions of increased microvascular filtration are established, matrix remodeling proceeds fairly rapidly due to the activation of proteases. Conversely, a massive matrix deposition of collagen fiber decreases interstitial compliance and therefore makes the tissue safety factor stronger. As a result, changes in lung extracellular matrix significantly affect edema formation and distribution in the lung.

A matriz extracelular é um aglomerado tridimensional demacromoléculas composta por: fibras colágenas (principalmente, tipos I e III), elastina, glicosaminoglicanos e proteoglicanos. No pulmão, a matriz extracelular tem várias funções, tais como: 1) promover estresse tensil e elasticidade tecidual, 2) contribuir para a manutenção da dinâmica de fluidos no interstício, 3) propiciar efetiva troca gasosa, 4) controlar a função celular através de sua ligação com fatores de crescimento, quimiocinas, citocinas e interação com receptores de superfície, e 5) remodelamento e reparo tecidual. A fragmentação e a desorganização da matriz extracelular pode acarretar edema intersticial e, eventualmente, edema alveolar grave. Logo, quando há aumento da filtração microvascular ocorre rápido remodelamento da matriz por ativação de proteases. Destarte, a deposição de fibras colágenas reduz a complacência intersticial limitando o edema. Em conclusão, modificações na matriz extracelular podem afetar a formação e distribuição do edema no pulmão.

Estudo histoquímico das proteoglicanas da fáscia transversal e bainha anterior do músculo reto abdominal em homens adultos, portadores de hérnia inguinal tipo II e IIIA de NYHUS / Proteoglicans hystochemical study of fascia transversalis and anterior sheath of abdominal rectus muscle of adult males with NYHUS types II and IIIA inguinal hernias

OBJETIVO: Avaliar, de maneira quantitativa, as proteoglicanas na fáscia transversal e na bainha anterior do músculo reto abdominal de pacientes homens, adultos, portadores de hérnia inguinal tipo II e IIIA de NYHUS. MÉTODO: Foram constituídos três grupos de estudo: um grupo controle, composto por dez cadáveres com óbito até 24 horas e de dois grupos, cada um com vinte pacientes, portadores de hérnias tipo II e IIIA de NYHUS. Foram retiradas amostras da fáscia transversal e da bainha anterior do músculo reto abdominal que foram coradas com Alcian Blue, pH 2,5. As lâminas foram analisadas no programa IMAGELAB de avaliação histológica informatizada. RESULTADOS: Observou-se menor quantidade de proteoglicanas nos pacientes com hérnia inguinal, em relação ao grupo controle. Essa diferença foi estatisticamente significante. CONCLUSÃO: A concentração de proteoglicanas na matriz extracelular está diminuída na fáscia transversal e na bainha anterior do músculo reto abdominal de pacientes homens adultos, portadores de hérnia inguinal tipo II e IIIA de NYHUS, em relação ao grupo controle, constituído por cadáveres não portadores de hérnia inguinal.

BACKGROUND: To quantify the presence of proteoglycans in fascia transversalis and anterior sheath of the abdominal rectus muscle, from males, adults, with Nyhus type II and IIIA inguinal hernia. METHODS: The samples were divided in three groups: Group I - twenty patients with Nyhus type II inguinal hernia; Group II - twenty patients with Nyhus type IIIa inguinal hernias. Group III - control comprised of ten cadavers with no more than 24 hours death and no hernias; Fascia transversalis and anterior sheath of the abdominal rectus muscle samples were collected and stained with alcian blue pH2,5. Computerized hystological evaluation (IMAGELAB) was used to analyse the samples prepared as described above. RESULTS: A smaller quantity of proteoglycan was found in patients with inguinal hernia as compared to control group and this was stastically significant. CONCLUSION: Patient with Nyhus type II and IIIa inguinal hernias had a smaller amount of proteoglycans in fascia transversalis and anterior sheath of the abdominal rectus muscle. The role of these findings regardind the etiology of inguinal hernias remains to be better evaluated by further research.