Effect Of High Glucose Conditions Research Articles

The influence of high glucose conditions on macrophages and its effect on the autophagy pathway.

Macrophages are central cells in mediating the inflammatory response. We evaluated the effect of high glucose conditions on the inflammatory profile and the autophagy pathway in Bone-Marrow Derived Macrophages (BMDM) from diabetic (D-BMDM) (alloxan: 60mg/kg, i.v.) and non-diabetic (ND-BMDM) C57BL/6 mice. BMDM were cultured in medium with normal glucose (5.5 mM), or high glucose (25 mM) concentration and were primed with Nigericin (20µM) stimulated with LPS (100 ng/mL) at times of 30 minutes; 2; 4; 6 and 24 hours, with the measurement of IL-6, IL-1β and TNF-α cytokines. We have further identified changes in the secretion of pro-inflammatory cytokines IL-6, IL-1β and TNF-α, where BMDM showed increased secretion of these cytokines after LPS + Nigericin stimulation. In addition, changes were observed in the autophagy pathway, where the increase in the autophagic protein LC3b and Beclin-1 occurred by macrophages of non-diabetic animals in hyperglycemic medium, without LPS stimulation. D-BMDM showed a reduction on the expression of LC3b and Beclin-1, suggesting an impaired autophagic process in these cells. The results suggest that hyperglycemia alters the inflammatory pathways in macrophages stimulated by LPS, playing an important role in the inflammatory response of diabetic individuals.

Diminished schwann cell repair responses play a role in delayed diabetes-associated wound healing.

Diabetes mellitus is the most common metabolic disease associated with impaired wound healing. Recently, Schwann cells (SCs), the glia of the peripheral nervous system, have been suggested to accelerate normal skin wound healing. However, the roles of SCs in diabetic wound healing are not fully understood. In this study, Full-thickness wounds were made in the dorsal skin of C57/B6 mice and db/db (diabetic) mice. Tissue samples were collected at different time points, and immunohistochemical and immunofluorescence analyses were performed to detect markers of de-differentiated SCs, including myelin basic protein, Sox 10, p75, c-Jun, and Ki67. In addition, in vitro experiments were performed using rat SC (RSC96) and murine fibroblast (L929) cell lines to examine the effects of high glucose conditions (50mM) on the de-differentiation of SCs and the paracrine effects of SCs on myofibroblast formation. Here, we found that, compared with that in normal mice, wound healing was delayed and SCs failed to rapidly activate a repair program after skin wound injury in diabetic mice. Furthermore, we found that SCs from diabetic mice displayed functional impairments in cell de-differentiation, cell-cycle re-entry, and cell migration. In vitro, hyperglycemia impaired RSC 96 cell de-differentiation, cell-cycle re-entry, and cell migration, as well as their paracrine effects on myofibroblast formation, including the secretion of TGF-β and Timp1. These results suggest that delayed wound healing in diabetes is due in part to a diminished SC repair response and attenuated paracrine effects on myofibroblast formation.

Monocyte Chemotactic Proteins Mediate the Effects of Hyperglycemia in Chondrocytes: In Vitro Studies.

Chemokines are secreted by a large variety of cells. They are involved in controlling cell trafficking, maturation, and differentiation. However, the specific responses and effects of chemokines on specific skeletal cell types under high glucose conditions have not been investigated. Chondrocytes play an important role in osteoarthritis and fracture healing. Delayed fracture healing is one of the major health complications caused by diabetes, so the goal of this study was to evaluate the response of several chemokines to high glucose conditions in chondrocyte cells and analyze their role in the catabolic effect of hyperglycemia. ATDC5 chondrocytes were cultured in normal and high glucose media, and mRNA expression levels of several chemokines and chondrocyte differentiation markers were quantified. Bindarit, a specific inhibitor of monocyte chemotactic proteins (MCPs), was used to determine the role of MCPs in mediating the effects of high glucose conditions in chondrocyte cells. High glucose treatment upregulated the expression of three Mcps, as well as the expression of matrix metalloproteinase 13 (Mmp13) and Osteocalcin (Oc). Furthermore, bindarit treatment downregulated Mmp13 and Oc but upregulated Collagen 2 (Col2) mRNA levels in chondrocytes treated with high glucose. Moreover, treatment of chondrocytes with ascorbic acid reduced the effect of high glucose conditions on the expression of chemokines and Mmps. These data together suggest that MCPs mediate the catabolic effect of high glucose in chondrocytes.

Upregulation of TGF-β type II receptor in high glucose-induced vascular smooth muscle cells.

Mortality in patients with diabetes mellitus is estimated above 65% due to cardiovascular diseases. Theaim of study was to investigate the effects of high-glucose conditions on TGF-β type II receptor (TGFBR2) expression levels, cell viability, and migration rate in vascular smooth muscle cells (VSMCs). VSMCs were incubated in 30 mM and 50 mM of glucose for 24 h, 48 h, and 72 h periods. The gene and protein expression levels were investigated by Real-time qRT-PCR and western blotting techniques, respectively. The cell viability was evaluated by MTT assay. VSMC migration rate was also studied by wound healing assay. The TGFBR2 gene and protein expression levels were significantly upregulated in all the groups treated with glucose in 24 h, 48 h, and 72 h periods. The cell viability was not significantly affected in values of 30 mM and 50 mM of glucose. The increase of migration rate of VSMCs was not significant. Theresults suggested the increased expression levels of TGFBR2 in the response to high glucose conditions may modulate the cellular events through the signaling pathway network in VSMCs.

High Glucose Affects Proliferation, Reactive Oxygen Species and Mineralization of Human Dental Pulp Cells.

Diabetes is a group of metabolic disorders that can lead to damage and dysfunction of many organs including the dental pulp. Increased inflammatory response, reduction of dentin formation and impaired healing were reported in diabetic dental pulp. Hyperglycemia, which is a main characteristic of diabetes, was suggested to play a role in many diabetic complications. Therefore our aim was to investigate the effects of high glucose levels on proliferation, reactive oxygen species (ROS) production and odontogenic differentiation of human dental pulp cells (HDPCs). HDPCs were cultured under low glucose (5.5mM Glucose), high glucose (25 mM Glucose) and mannitol (iso-osmolar control) conditions. Cell proliferation was analyzed by MTT assay for 11 days. Glutathione and DCFH-DA assay were used to assess ROS and antioxidant levels after 24 h of glucose exposure. Odontogenic differentiation was evaluated and quantified by alizarin red staining on day 21. Expression of mineralization-associated genes, which were alkaline phosphatase, dentin sialophosphoprotein and osteonectin, was determined by RT-qPCR on day 14. The results showed that high glucose concentration decreased proliferation of HDPCs. Odontogenic differentiation, both by gene expression and mineral matrix deposit, was inhibited by high glucose condition. In addition, high DCF levels and low reduced glutathione levels were observed in high glucose condition. However, no differences were observed between mannitol and low glucose conditions. In conclusion, the results clearly showed the negative effect of high glucose condition on HDPCs proliferation and differentiation. Moreover, it also induced ROS production of HDPCs.

Effect of high glucose condition on glucose metabolism in primary astrocytes

In the brain, glucose enters astrocytes through glucose transporter (GLUT1) and either enters glycolysis or the glycogen shunt. Astrocytes meet the energy needs of neurons by building up and breaking down their glycogen supply. High glucose exposure causes astrocyte dysregulation, but its effects on glucose metabolism are relatively unknown. We hypothesized that high glucose conditioning induces a glycogenic state in the astrocyte, resulting in an inefficient mobilization of substrates when challenged with glucose deprivation. Using neonatal rat astrocytes, we used normal glucose (NG, 5.5 mM) vs. high glucose (HG, 25 mM) feeding media and measured cell membrane GLUT1 expression, glucose analog uptake, glycogen content, and cellular bioenergetics. This study demonstrates that HG conditioning causes increased glucose analog uptake (p < 0.05) without affecting GLUT1 membrane expression when compared to NG conditioned astrocytes. Increased glucose uptake in HG astrocytes is associated with higher baseline glycogen content compared to NG exposed astrocytes (p < 0.05). When challenged with glucose deprivation, HG astrocytes break down more than double the amount of glycogen molecules compared to NG astrocytes, although they break down a similar percentage of the starting glycogen stores (NG = 62%, HG = 55%). Additionally, HG conditioning negatively impacts astrocyte maximal respiration and glycolytic reserve capacity assessed by the Seahorse mitochondrial stress test and glycolytic stress test, respectively (p < 0.05). These results suggest that HG conditioning shifts astrocytes towards glycogen storage at baseline. Despite increased glycogen storage, HG astrocytes demonstrate decreased metabolic efficiency and capacity putting them at higher risk during extended periods of glucose deprivation.

Effects of high glucose conditions on the expansion and differentiation capabilities of mesenchymal stromal cells derived from rat endosteal niche

BackgroundMesenchymal stromal cells in the endosteal niche lining compact bone (CB-MSCs) represent a heterogeneous population, all of which contribute to bone repair and remodelling. Hyperglycaemia associated with type 2 diabetes mellitus (T2DM) can delay and impair the bone healing process. Therefore, this study investigated the influences of high (25 mM) glucose conditions on CB-MSC populations isolated from male Wistar rats, versus normal (5.5 mM) glucose conditions; in terms of proliferation (population doublings, PDs), senescence characteristics, stem cell marker expression, colony forming efficiencies (CFEs); and osteogenic/adipogenic differentiation, following extended culture in vitro.ResultsCB-MSCs under both normoglycaemic and hyperglycaemic conditions demonstrated similar morphologies and rapid exponential growth to >300PDs, although high glucose conditions promoted more rapid and persistent proliferation beyond ~50PDs, with few indications of senescence. Limited senescence was confirmed by minimal SA-β-galactosidase staining, low senescence marker (p53, p21waf1, p16INK4a) expression and positive telomere maintenance marker (rTERT, TR) expression. However, telomere lengths varied throughout culture expansion, with hyperglycaemia significantly reducing telomere lengths at PD50 and PD200. Furthermore, CB-MSCs expanded in normal and high glucose conditions remained non-transformed, exhibiting similar MSC (CD73/CD90/CD105), multipotency (CD146) and embryonic (Slug, Snail) markers throughout extended culture, but negligible hematopoietic (CD34/CD45) or pluripotency (Nanog, Oct4) markers. Hyperglycaemia significantly increased CFEs at PD50 and PD100, which decreased at PD200. CB-MSC osteogenic differentiation was also inhibited by hyperglycaemia at PD15, PD100 and PD200, but not at PD50. Hyperglycaemia inhibited CB-MSC adipogenic differentiation to a lesser extent at PD15 and PD50, with reduced adipogenesis overall at PD100 and PD200.ConclusionThis study demonstrates the limited negative impact of hyperglycaemia on the proliferative and stem cell characteristics of heterogeneous CB-MSC populations, although minor sub-population(s) appear more susceptible to these conditions leading to impaired osteogenic/adipogenic differentiation capabilities. Such findings potentially highlight the impact of hyperglycaemia on CB-MSC bone repair capabilities in situ.

Autophagy preserves the osteogenic ability of periodontal ligament stem cells under high glucose conditions in rats

ObjectiveTo investigate how a high glucose environment influences the osteogenic ability of periodontal ligament stem cells (PDLSCs) and the function of autophagy in this process, we explored whether the osteogenic ability of PDLSCs could be protected by autophagy. DesignPDLSC proliferation and osteogenesis were evaluated by CCK-8 and western blotting under gradient glucose conditions. The Autophagy RT2 Profiler PCR Array was used to screen autophagy-related mRNA expression during PDLSC osteoblastic differentiation on 5.5 mM + osteogenic induction (OI) medium or 25 mM + OI medium on day 3. Autophagy was regulated by an inducer (rapamycin) and inhibitor (bafilomycin) to investigate its protective effects on PDLSCs. A periodontal trauma model was established in diabetic rats to verify the effects of enhanced autophagy activity on PDLSCs. ResultsA high glucose concentration (25 mM) impeded PDLSC proliferation on day 1, and compared with the control condition, high glucose also decreased the osteogenic ability of PDLSCs. The Autophagy RT2 Profiler PCR Array showed obvious fluctuations in many autophagy-related genes, such as ULK1 (9.27), MTOR (3.15), MAP1LC3B (4.22), GABARAPL1 (7.09), ATG10 (6.5), AMPK14 (4.47), WIPI1 (3.29), and IGF1 (24.65). Compared with the control condition, an autophagy inducer or inhibitor markedly impaired or enhanced osteogenic differentiation in cells. The diabetic rat periodontal trauma model demonstrated that periodontium tissue partly recovered in the autophagy-enhanced cell injection diabetic rat group. ConclusionsHigh glucose inhibited the activity of PDLSCs, and regulating autophagy protected cell function. Upregulating autophagy partially reversed the adverse effect of high glucose conditions on PDLSCs.

The effects of high glucose condition on rat tenocytes in vitro and rat Achilles tendon in vivo.

ObjectivesThe aim of this study was to investigate the effect of hyperglycaemia on oxidative stress markers and inflammatory and matrix gene expression within tendons of normal and diabetic rats and to give insights into the processes involved in tendinopathy.MethodsUsing tenocytes from normal Sprague-Dawley rats, cultured both in control and high glucose conditions, reactive oxygen species (ROS) production, cell proliferation, messenger RNA (mRNA) expression of NADPH oxidase (NOX) 1 and 4, interleukin-6 (IL-6), matrix metalloproteinase (MMP)-2, tissue inhibitors of matrix metalloproteinase (TIMP)-1 and -2 and type I and III collagens were determined after 48 and 72 hours in vitro. In an in vivo study, using diabetic rats and controls, NOX1 and 4 expressions in Achilles tendon were also determined.ResultsIn tenocyte cultures grown under high glucose conditions, gene expressions of NOX1, MMP-2, TIMP-1 and -2 after 48 and 72 hours, NOX4 after 48 hours and IL-6, type III collagen and TIMP-2 after 72 hours were significantly higher than those in control cultures grown under control glucose conditions. Type I collagen expression was significantly lower after 72 hours. ROS accumulation was significantly higher after 48 hours, and cell proliferation after 48 and 72 hours was significantly lower in high glucose than in control glucose conditions. In the diabetic rat model, NOX1 expression within the Achilles tendon was also significantly increased.ConclusionThis study suggests that high glucose conditions upregulate the expression of mRNA for NOX1 and IL-6 and the production of ROS. Moreover, high glucose conditions induce an abnormal tendon matrix expression pattern of type I collagen and a decrease in the proliferation of rat tenocytes.Cite this article: Y. Ueda, A. Inui, Y. Mifune, R. Sakata, T. Muto, Y. Harada, F. Takase, T. Kataoka, T. Kokubu, R. Kuroda. The effects of high glucose condition on rat tenocytes in vitro and rat Achilles tendon in vivo. Bone Joint Res 2018;7:362–372. DOI: 10.1302/2046-3758.75.BJR-2017-0126.R2

Heat shock protein 70 modulates neural progenitor cells dynamics in human neuroblastoma SH-SY5Y cells exposed to high glucose content.

In the current experiment, detrimental effects of high glucose condition were investigated on human neuroblastoma cells. Human neuroblastoma cell line SH-SY5Y were exposed to 5, 40, and 70 mM glucose over a period of 72 h. Survival rate and the proliferation of cells were analyzed by MTT and BrdU incorporation assays. Apoptosis was studied by the assays of flow cytometry and PCR array. In order to investigate the trans-differentiation capacity of the cell into mature neurons, we used immunofluorescence imaging to follow NeuN protein level. The transcription level of HSP70 was shown by real-time PCR analysis. MMP-2 and -9 activities were shown by gelatin Zymography. According to data from MTT and BrdU incorporation assay, 70 mM glucose reduced cell viability and proliferation rate as compared to control (5 mM glucose) and cells treated with 40 mM glucose (P < 0.05). Cell exposure to 70 mM glucose had potential to induced apoptosis after 72 h (P < 0.05). Our results also demonstrated the sensitivity of SH-SY5Y cells to detrimental effects of high glucose condition during trans-differentiation into mature neuron-like cells. Real-time PCR analysis confirmed the expression of HSP70 in cells under high content glucose levels, demonstrating the possible cell compensatory response to an insulting condition (pcontrol vs 70 mM group <0.05). Both MMP-2 and -9 activities were reduced in cells being exposed to 70 mM glucose. High glucose condition could abrogate the dynamics of neural progenitor cells. The intracellular level of HSP70 was proportional to cell damage in high glucose condition.

High glucose levels affect spermatogenesis: an in vitro approach.

Besides known factors that may cause male infertility, systemic diseases such as diabetes mellitus may further exacerbate a decline in male fertility. This metabolic disease, clinically characterised by a hyperglycaemic phenotype, has devastating consequences in terms of human health, with reproductive dysfunction being one of the associated clinical complications. Nonetheless, the mechanisms responsible for such alterations are still poorly understood due to the multiplicity of factors involved in the induced pathophysiological changes. With this in mind, we focused on the main mediator of diabetes-associated alterations and performed an in vitro approach to address the effects of high glucose conditions on spermatogenesis, avoiding other confounding in vivo factors. Mouse (5 days post partum) testis fragments were cultured on agar gel stands at a gas-liquid interface with either 5, 25 or 50mM D-glucose for 3 weeks. Stereological analysis revealed that high D-glucose levels increased Sertoli cell number (P<0.05) and decreased tubular luminal area (P<0.01), suggesting an impairment of this somatic cell type. Moreover, higher proliferative activity in a TM4 Sertoli cell line exposed to high D-glucose was found (P<0.05) without compromising cell viability (P>0.05), further suggesting altered Sertoli cell maturation. Overall, high D-glucose concentrations may lead to impairment of Sertoli cell function, which, given their significant role in spermatogenic control, may compromise male fertility.

Effect of high-glucose conditions on human periodontal ligament endothelial cells: in vitro analysis

Endothelial cells participate in key aspects of vascular biology, such as maintenance of capillary permeability and regulation of inflammation. According to previous reports, endothelial cells have revealed highly specific characteristics depending on the organs and tissues. In particular, periodontal endothelial cells have a higher permeability than vascular endothelial cells of other types of tissue. Periodontal disease is not only a chronic disease in oral, but also affect the entire body. Diabetes and periodontal disease are closely related, with periodontal disease even been referred to as the sixth complication of disease. However, no reports have investigated the pathophysiology of microvascular in periodontal tissue once diabetes has developed. Therefore, the aim of the present study is to investigate changes in the properties of human periodontal endothelial cells (HPDLECs) that were cultured under high-glucose conditions. We isolated HPDLECs from human periodontal ligament cells. HPDLECs were cultured under high-glucose (5.5, 11.0, 22.0mM) and investigated proliferation, apoptosis, tube formation and the expression of cell adhesion molecules. A 5.5mM (100mg/dl) control was used in this study. HPDLECs stimulated with high glucose concentration exhibited suppression of cell proliferation and an increased percentage of apoptosis-positive cells. This results suggested that apoptosis was caused by TNF-α expression. The expression levels cell adhesion molecules increased. These results suggest that when HPDLECs are stimulated with a high glucose concentrations, PKC in the intracellular cell substrate is activated, increasing the expression of intercellular and vascular adhesion molecules. Thus, the results of this study demonstrate that diabetes exacerbates periodontal disease.

Effect of high glucose condition on rat tenocytes

Effect of high glucose condition on rat tenocytes

High glucose concentrations per se do not adversely affect human sperm function in vitro

Diabetes mellitus (DM) represents one of the greatest concerns to global health and it is associated with diverse clinical complications, including reproductive dysfunction. Given the multifactorial nature of DM, the mechanisms that underlie reproductive dysfunction remain unclear. Considering that hyperglycemia has been described as a major effector of the disease pathophysiology, we used an in vitro approach to address the isolated effect of high glucose conditions on human sperm function, thus avoiding other in vivo confounding players. We performed a complete and integrated analysis by measuring a variety of important indicators of spermatozoa functionality (such as motility, viability, capacitation status, acrosomal integrity, mitochondrial superoxide production and membrane potential) in human sperm samples after incubation with d- and l-glucose (5, 25, or 50 mM) for 24 and 48 h. No direct effects promoted by 25 or 50 mM d-glucose were found for any of the parameters assessed (P>0.05), except for the acrosome reaction, which was potentiated after 48 h of exposure to 50 mM d-glucose (P<0.05). Interestingly, non-metabolizable l-glucose drastically increased superoxide production (P<0.05) and suppressed sperm motility (P<0.05) and capacitation (P<0.05) after 24 h of treatment, whereas mitochondrial membrane potential (P<0.05), acrosomal integrity (P<0.01) and viability (P<0.05) were later decreased. The overall results suggest that high glucose levels per se do not influence human sperm function in vitro, which stresses the importance of other factors involved in DM pathology. Nevertheless, the absence of metabolizable glucose contributes to a severe impairment of sperm function and thus compromises male fertility.

Effects of high glucose on the production of heparan sulfate proteoglycan by mesangial and epithelial cells

Changes in heparan sulfate metabolism may be important in the pathogenesis of diabetic nephropathy. Recent studies performed on renal biopsies from patients with diabetic nephropathy revealed a decrease in heparan sulfate glycosaminoglycan staining in the glomerular basement membrane without changes in staining for heparan sulfate proteoglycan-core protein. To understand this phenomenon at the cellular level, we investigated the effect of high glucose conditions on the synthesis of heparan sulfate proteoglycan by glomerular cells in vitro. Human adult mesangial and glomerular visceral epithelial cells were cultured under normal (5 mM) and high glucose (25 mM) conditions. Immunofluorescence performed on cells cultured in 25 mM glucose confirmed and extended the in vivo histological observations. Using metabolic labeling we observed an altered proteoglycan production under high glucose conditions, with predominantly a decrease in heparan sulfate compared to dermatan sulfate or chondroitin sulfate proteoglycan. N-sulfation analysis of heparan sulfate proteoglycan produced under high glucose conditions revealed less di- and tetrasaccharides compared to larger oligosaccharides, indicating an altered sulfation pattern. Furthermore, with quantification of glomerular basement membrane heparan sulfate by ELISA, a significant decrease was observed when mesangial and visceral epithelial cells were cultured in high glucose conditions. We conclude that high glucose concentration induces a significant alteration of heparan sulfate production by mesangial cells and visceral epithelial cells. Changes in sulfation and changes in absolute quantities are both observed and may explain the earlier in vivo observations. These changes may be of importance for the altered integrity of the glomerular charge-dependent filtration barrier and growth-factor matrix interactions in diabetic nephropathy.

High glucose and hyperosmolality stimulate hepatocyte growth factor secretion from cultured human mesangial cells.

Hepatocyte growth factor is a recently cloned potent mitogen to hepatocytes, but its extrahepatic roles are not completely defined. It causes proliferation of endothelial and epithelial cells implicating potential action in the glomerulus. We aimed to determine whether cultured human mesangial cells secrete hepatocyte growth factor and the effect of high glucose conditions. Mesangial cells were isolated from the normal cortex of a child's kidney. After differential glomerular sieving and trypsin digestion of glomeruli, mesangial cells were cultured in 20% fetal calf serum/RPMI. Glucose concentration in the medium was adjusted to 5 mmol/l, 11 mmol/l, 25 mmol/l or 5 mmol/l/20 mmol/l mannitol to correct for osmolality. After 0, 24, 48, 72 h incubation, hepatocyte growth factor was measured in the supernatant by enzyme immuno assay using recombinant hepatocyte growth factor and monoclonal antibodies to human hepatocyte growth factor. Hepatocyte growth factor was secreted by cultured mesangial cells. High glucose and hyperosmolar conditions caused a 100-200% increase in hepatocyte growth factor secretion at 48-72 h (p = 0.001). Hepatocyte growth factor secretion at 48 h in 5 mmol/l glucose was 16.46 +/- 1.09 ng/ml (mean +/- SEM), 11 mmol/l glucose: 32.98 +/- 4.54, 25 mmol/l glucose: 33.32 +/- 7.89, 5 mmol/l glucose/20 mmol/l mannitol: 34.05 +/- 3.64; at 72 h in 5 mmol/l glucose: 23.92 +/- 2.85 ng/ml, 11 mmol/l glucose: 28.26 +/- 2.03, 25 mmol/l glucose: 62.04 +/- 12.2, 5 mmol/l glucose/20 mmol/l mannitol: 45.76 +/- 6.25. Trypan blue exclusion demonstrated membrane integrity.(ABSTRACT TRUNCATED AT 250 WORDS)

The Effect of High-Glucose Condition on Insulin Binding to IM-9 Lymphocytes

The long-term effect of high-glucose condition on insulin binding to IM-9 cells was studied by incubating the cells in RPMI-1640 medium containing 450 mg/dl of glucose. Insulin binding began to decrease after incubation for 6 days in high-glucose-treated cells, and significantly decreased after 14 days due to the reduction of receptor affinity. The number of binding sites for insulin did not change by the treatment. Thus, high-glucose condition per se does not appear to induce the decrease of the number of insulin receptors on target cells, as observed in diabetic patients.