bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of Chemically Modified Tetracycline, CMT‐8, on Bone Loss and Osteoclast Structure and Function in Osteoporotic States
Authors: SASAKI TAKAHISA , OHYORI NOBUTAKA , DEBARI KAZUHIRO , RAMAMURTHY NUMGAVARAM S. , GOLUB LORNE M.
Published: February 2006

ABSTRACT: We examined the effects of a nonantimicrobial tetracycline analogue, CMT‐8, on bone loss and osteoclasts in ovariectomized (OVX) rats. Three‐month‐old female rats were OVX, and, one week later, distributed into three groups: sham‐operated non‐OVX controls, untreated OVX controls, and CMT‐8‐treated OVX rats. After 145 days of daily drug administration (p.o.), the femurs were dissected and examined histologically. Ovariectomy markedly decreased trabecular and cortical bone volume in the metaphyses compared to sham‐operated controls. Treating the OVX rats with CMT‐8 produced a significant inhibition of trabecular and cortical bone loss and induced new bone formation, in which connectivity of the trabecular struts was increased by bridging the adjacent longitudinal bone trabeculae. Ultrastructurally, CMT‐8 reduced ruffled border formation in osteoclasts, while it caused no structural impairment in osteoblasts. To further evaluate the effects of CMT‐8 on the resorbing activity of osteoclasts, osteoclasts were cultured on dentine slices pretreated with CMT‐8 at concentrations of 2, 10, or 50 μg/ml, and resorption lacuna formation on the dentine surface was found to be reduced, dose‐dependently, by the bound CMT‐8. Our results suggest that CMT‐8 therapy effectively inhibits post‐ovariectomy bone loss not only by inducing new bone formation, but also by inhibiting osteoclastic bone resorption, and that CMT‐8 binding to bone may provide a prolonged release delivery of this anti‐resorptive therapy.
Matrix Metalloproteinase Inhibition: From The Jurassic To The Third Millennium
Authors: WOESSNER J. FREDERICK
Published: February 2006

ABSTRACT: A brief historical introduction to the matrix metalloproteinase (MMP) field, which began in 1962, is followed by an overview of the inhibition of these proteases by natural inhibitors such as α2 macroglobulin and the TIMPs (tissue inhibitors of metalloproteinases) and by synthetic inhibitors, which are largely chelating agents. The latter include thiol, alkylcarbonyl, phosponamidate and hydroxamate compounds, as well as the tetracyclines. A review of the most recent progress concludes with prognostications as to where the field may be going next.
C‐Telopeptide Pyridinoline Cross‐Links: Sensitive Indicators of Periodontal Tissue Destruction
Authors: GIANNOBILE WILLIAM V.
Published: February 2006

ABSTRACT: C‐telopeptides and related pyridinoline cross‐links of bone Type I collagen are sensitive markers of bone resorption in osteolytic diseases such as osteoporosis and osteoarthritis. We have studied the release of C‐telopeptide pyridinoline crosslinks of Type I collagen as measures of bone destruction in periodontal disease. Studies in preclinical animal models and humans have demonstrated the relationship between radiographic bone loss and crevicular fluid C‐telopeptide levels. We have recently found that C‐telopeptide levels correlate strongly with microbial pathogens associated with periodontitis and around endosseous dental implants. Host‐modulation of bone‐related collagen breakdown has been shown by studies in humans demonstrating that MMP inhibition blocks tissue destruction and release of C‐telopeptides in patients with active periodontal disease.
Thirty‐six Years in the Clinic without an MMP Inhibitor: What Hath Collagenase Wrought?
Authors: GREENWALD ROBERT A.
Published: February 2006

ABSTRACT: Vertebrate collagenase was discovered in 1962, and within a few short years, several inhibitors had been identified. At one time or another, virtually every major drug company has had an MMP inhibitor program, but in 1999, there is only one such product on the market. With a potential market for lifelong therapy in rheumatoid arthritis, osteoarthritis, periodontal disease, osteoporosis, and cancer, this is certainly puzzling. The problem is that the chemistry appears to have outstripped the biology. In vitro, there are many inhibitors with nanomolar or picomolar efficacy, but in vivo efficacy in animal models does not always follow. There is also a conceptual problem regarding broad‐spectrum vs. highly specific inhibitors. Designing human trials to demonstrate MMP inhibition and clinical efficacy is a daunting problem, especially if one seeks to distinguish anti‐MMP activity from anti‐inflammatory effect. Adult periodontal disease may be the best available human disease model for development of an MMPI.
Physical and Biological Regulation of Proteoglycan Turnover around Chondrocytes in Cartilage Explants: Implications for Tissue Degradation and Repair
Authors: QUINN THOMAS M. , MAUNG ADRIAN A. , GRODZINSKY ALAN J. , HUNZIKER ERNST B. , SANDY JOHN D.
Published: February 2006

ABSTRACT: The development of clinical strategies for cartilage repair and inhibition of matrix degradation may be facilitated by a better understanding of (1) the chondrocyte phenotype in the context of a damaged extracellular matrix, and (2) the roles of biochemical and biomechanical pathways by which matrix metabolism is mediated. Using methods of quantitative autoradiography, we examined the cell‐length scale patterns of proteoglycan deposition and turnover in the cell‐associated matrices of chondrocytes in adult bovine and calf cartilage explants. Results highlight a rapid turnover in the pericellular matrix, which may indicate spatial organization of PG metabolic pools, and specific biomechanical roles for different matrix regions. Subsequent to injurious compression of calf explants, which resulted in grossly visible tissue cracks and caused a decrease in the number of viable chondrocytes within explants, cell‐mediated matrix catabolic processes appeared to increase, resulting in apparently increased rates of proteoglycan turnover around active cells. Furthermore, the influences of cell‐stimulatory factors such as IL‐1β appeared to be delayed in their effects subsequent to injurious compression, suggesting interactions between biomechanical and biochemical pathways of PG degradation. These results may provide a useful reference point in the development of in vitro models for cartilage injury and disease, and hint at possible new approaches in the development of cartilage repair strategies.
Adamalysins: A Family of Metzincins Including TNF‐α Converting Enzyme (TACE)
Authors: KILLAR LORAN , WHITE JUDITH , BLACK ROY , PESCHON JACQUES
Published: February 2006

ABSTRACT: The adamalysins are a family of proteins in the metzincin super‐family of metalloproteases, which also includes the matrix metalloproteinases. There are two subfamilies of adamalysins: the snake venom metalloproteases (SVMPs) and the ADAMs (proteins containing a disintegrin and metalloprotease domain). At least 23 ADAMs have been identified to date. The ADAMs are expressed by a wide variety of cell types, and are involved in functions as diverse as sperm‐egg binding, myotube formation, neurogenesis, and proteolytic processing of cell surface proteins. An overview of the ADAM family and their functions will be presented. TACE is a unique member of the ADAM family that cleaves membrane‐bound TNF‐α to generate soluble TNF‐α. Mice lacking proteolytically active TACE have been generated and characterized. The TACE knock‐out results in perinatal lethality. Cells from the TACE‐deficient mice release 80‐90% less soluble TNF‐α than do wild‐type cells. Irradiated mice that are reconstituted with TACE knock‐out hematopoeitic stem cells have markedly reduced levels of serum TNF‐α following LPS challenge, compared to irradiated mice reconstituted with wild‐type cells, suggesting that TACE is the major TNF‐α converting enzyme in vivo. TACE‐deficient cells are compromised in the generation of other soluble proteins that are produced as the result of cleavage of a membrane precursor form, suggesting that TACE is involved in multiple shedding events.
MMP Inhibition and Downregulation by Bisphosphonates
Authors: TERONEN OLLI , HEIKKILÄ PIA , KONTTINEN YRJÖ T. , LAITINEN MINNA , SALO TUULA , HANEMAAIJER ROELAND , TERONEN ANNELI , MAISI PÄIVI , SORSA TIMO
Published: February 2006

ABSTRACT: Bisphosphonates are a group of drugs capable of inhibiting bone resorption, and are thus used for the treatment of bone diseases, such as Paget's disease, osteoporosis, and for bone metastases of malignant tumors. Their primary cellular target is considered to be the osteoclast. The molecular mechanisms responsible for the downregulation of bone resorption by bisphosphonates have remain unclear. We have discovered that various matrix metalloproteinases (MMPs) are inhibited in vitro by several bisphosphonates. This novel finding may, in part, explain the efficacy of bisphosphonates in their current indications in humans. In enzyme activity tests using purified and recombinant enzymes, we have observed the inhibition of MMP‐1, ‐2, ‐3, ‐7, ‐8, ‐9, ‐12, ‐13, and ‐14 by clondronate, alendronate, pamidronate, zolendronate, nedrinate, and clodrinate. The IC50s range from 50 to 150 μM. We have also shown that clodronate can downregulate the expression of MT1‐MMP protein and mRNA in several cell lines. Additionally, several bisphosphonates decrease the degree of invasion of malignant melanoma (C8161) and fibrosarcoma (HT1080) cells through artificial basement membrane (Matrigel) in cell cultures at IC50s of 50‐150 μM and below. Having low toxicity and proven to be well tolerated after several years in human use, bisphosphonates have the potential to become one of the main MMP‐inhibitors for MMP‐related human soft and hard tissue‐destructive diseases in the near future.
Retinoid‐Mediated Suppression of Tumor Invasion and Matrix Metalloproteinase Synthesis
Authors: SCHOENERMARK MATTHIAS P. , MITCHELL TERESA I. , RUTTER JONI L. , RECZEK PETER R. , BRINCKERHOFF CONSTANCE E.
Published: February 2006

ABSTRACT: Cancer mortality usually results from the tumor invading the local environment and metastasizing to vital organs, e.g. liver, lung, and brain. Degradation of the extracellular matrix is, therefore, the sine qua non of tumor cell invasion. this degradation is mediated mainly by MMPs, and thus, inhibition of MMP synthesis is a target for anticancer agents. Tumor cells must traverse both the basement membrane (type IV collagen) and the interstitial stroma (type I collagen). Therefore, we used scanning electron microscopy to examine the invasive behavior of several aggressive tumor cell lines, A2058 melanoma cells, and SCC and FaDu squamous cell carcinomas through these matrices; and we monitored the ability of all‐trans retinoic acid and several RAR‐specific ligands to block invasion. We demonstrate that several retinoids, which are specific RAR α, β, or γ agonists/antagonists, selectively inhibited MMP synthesis in the three tumor cell lines. However, there was not a common pattern of MMP inhibition by a particular retinoid. For instance, a RAR α antagonist suppressed MMP‐1 and MMP‐2 synthesis in the melanoma cell line, but not in the FaDu or SCC‐25 cells. On the other hand, synthesis of MMP‐1 and MMP‐9 by the FaDu cells was affected hardly at all, while a RARγ antagonist reduced the levels of MMP‐2. Only all‐trans retinoic acid reduced MMP‐1 synthesis in these cells. We postulate that the differences may be related to a differential pattern of RAR expression in each of these cells, and that the RARs expressed by each cell line may not be targets of these RAR specific compounds. All‐trans retinoic acid is a pan ligand, binding to all three RARs and, therefore, may modulate gene expression more generally. We conclude that the power of these new ligands lies in their specificity, which can be directed towards modulating expression of certain RARs and, thus, of certain MMPs. By blocking MMP synthesis, retinoids may be effective in cancer therapy by decreasing tumor invasiveness.
Insulin Resistance: A Chicken That Has Come to Roost
Authors: REAVEN GERALD M.
Published: February 2006

ABSTRACT: Insulin‐mediated glucose disposal varies approximately 10‐fold in apparently healthy human beings. Insulin (I)‐resistant individuals can remain glucose tolerant if the pancreas compensates for this defect by secreting large amounts of I. Type 2 diabetes develops when I‐resistant persons cannot sustain this state of compensatory hyperinsulinemia (↑ I). However, the ability of ↑ I to prevent decompensation of glucose tolerance is a mixed blessing, and the combination of I resistance and ↑ I predisposes such individuals to develop a series of abnormalities that increase risk of coronary heart disease (CHD). Given the health‐related consequences of I resistance and ↑ I, it has been suggested that a “thrifty” genotype exists that favored evolutionary survival by enhancing I secretion and thereby promoting energy accumulation. An alternative view is that conservation of muscle mass was necessary for survival, and that muscle I resistance was the “thrifty” genotype. This latter hypothesis is more consistent with current data, and there is evidence of a genetic basis for I resistance. In either case, there is little question as to the importance of I resistance and related abnormalities in diseases of Western civilization. However, the strength of the association between I resistance and its consequences varies in magnitude, and it is necessary to emphasize that development of a clinical end‐point will vary as a function of (1) degree of I resistance; (2) “closeness” of I resistance to the end‐point; and (3) the ability to compensate for the effects of I resistance. I resistance is a physiological characteristic, genetically determined, that helped primitive humans to survive. It is greatly aggravated by obesity and physical inactivity, and represents a modern scourge.
Interaction between Aging and Syndrome X: New Insights on the Pathophysiology of Fat Distribution
Authors: BARZILAI NIR , GUPTA GAURAV
Published: February 2006

ABSTRACT: Increased fat mass (FM), and in particular a specific increase in visceral fat (VF), may account for the age‐associated decrease in insulin action and the development of Syndrome X. Utilizing chronic caloric restriction (CR) with aging in a rodent model, we dissociated the effects of VF and FM, and demonstrated that the decrease in VF accumulation was sufficient to prevent the marked decrease in hepatic insulin action. This suggests that the typical increase in VF with aging, rather than aging per se, determines hepatic insulin resistance. To directly assess the role of VF, we studied rats after surgical removal of VF or sham operation. Surgical extraction of VF (which accounts for ∼10% of total fat) improved hepatic insulin action by more than twofold. We studied the role of fat‐derived peptides in the regulation of body composition and insulin action. While VF extraction resulted in decreased gene expression for leptin and TNF‐α in the subcutaneous adipose, administration of leptin selectively decreased visceral fat (∼60%), and enhanced the action of insulin on inhibiting hepatic glucose production (∼80%). Thus, the cause‐effect relationship between the age‐related increase in VF and the decrease in hepatic insulin action may involve the failure of leptin to “cross talk” with other fat depots to regulate fat distribution.
Mechanisms for Hyperglycemia in the Metabolic Syndrome: The Key Role of β‐Cell Dysfunction
Authors: PORTE DANIEL
Published: February 2006

ABSTRACT: Hyperglycemia in Type 2 diabetes represents a steady‐state re‐regulation of plasma glucose to a higher‐than‐normal level after an overnight fast. The underlying pathophysiology represents an interaction between impaired β‐cell function and peripheral and hepatic insulin resistance which leads to abnormal hepatic glucose production. Subjects with the Metabolic Syndrome are at an increased risk for Type 2 diabetes and often have one or both of these disorders present even when glucose tolerance is normal. Thus, sophisticated measures of β‐cell function and insulin sensitivity demonstrate a high frequency in populations characterized as having a high prevalence of atherosclerosis, central obesity, hypertension, and dyslipidemia with or without impaired glucose tolerance. Hyperglycemia compensates for the impairment of β‐cell function and therefore, in our view, the β‐cell is the critical factor in its development. Hyperinsulinemia, a curvilinear compensation for insulin resistance that is closely correlated with central adiposity, is another important predictor of hyperglycemia. In a Japanese‐American population followed for five years, impaired β‐cell function was present at baseline and preceded the accumulation of intraabdominal fat in those who developed Type 2 diabetes five years later. This interaction between these two pathophysiologic abnormalities in this sequence supports the hypothesis that β‐cell dysfunction contributes to the development of central adiposity by reduced CNS insulin signaling.
Cross Talk between Adipocytes and Their Precursors: Relationships with Adipose Tissue Development and Blood Pressure
Authors: AILHAUD GÉRARD
Published: February 2006

ABSTRACT: Adipose tissue is an important source of angiotensinogen (AT). A possible involvement of increased plasma AT has been proposed in hypertension in obese patients, but growing evidence suggests also that the local renin‐angiotensinogen system (RAS), giving rise to angiotensin II (AngII), may act as a distinct system from the plasma RAS. AngII stimulates in vitro the production and release of prostacyclin from adipocytes which in turn promotes the differentiation of precursor cells into new adipocytes (Darimont et al. 1994, Endocrinology 138: 1092‐1096). Cross talk between adipocytes and precursor cells has been validated ex vivo and in vivo as (1) AngII stimulates specifically prostacyclin production, (2) both carbacyclin, a stable analogue of prostacyclin, and AngII promote the formation of new fat cells, and (3) AT (−/−) mice, which have decreased blood pressure (Tanimoto et al. 1994, J. Biol. Chem. 269: 31334‐31336), exhibit both hypertrophy and hypoplasia of adipose tissue compared to wild‐type mice (collaboration with Prof. A. Fukamizu, Tsukuba University, Japan). Altogether the data are consistent with an autocrine/paracrine mechanism implicating AT, AngII, and prostacyclin in adipose tissue development and suggest a new role for local AngII in addition to that of systemic AngII in blood pressure. Hormonal regulation of AT production from adipose tissue is also discussed.
Role of PPARγ in Regulating Adipocyte Differentiation and Insulin‐Responsive Glucose Uptake
Authors: HAMM JONATHAN K. , EL JACK AMR K. , PILCH PAUL F. , FARMER STEPHEN R.
Published: February 2006

ABSTRACT: Adipocyte differentiation is regulated by at least two families of transcription factors, CCAAT/enhancer binding proteins (C/EBPs) and peroxisome proliferator‐activated receptors (PPARs). Induction of PPARγ gene transcription during the differentiation of preadipocytes into adipocytes in vitro occurs following an initial phase of cell proliferation and requires a direct involvement of C/EBPβ, C/EBPδ, and glucocorticoids. Ectopic expression of PPARγ in non‐adipogenic, Swiss 3T3 fibroblasts promotes their conversion into adipocytes as indicated by the accumulation of lipid droplets and the induction of C/EBPα, aP2, insulin‐responsive aminopeptidase (IRAP), and glucose transporter 4 (GLUT4) expression. These PPARγ‐expressing Swiss cells also exhibit a high level of insulin‐responsive glucose uptake that is comparable to that expressed in 3T3‐L1 adipocytes. In contrast, PPARγ‐expressing NIH‐3T3 fibroblasts, despite similar lipid accumulation, adipocyte morphology, and aP2 expression, do not synthesize C/EBPα and fail to acquire insulin sensitivity. In Swiss 3T3 cells ectopically expressing PPARγ, the development of insulin‐responsive glucose uptake correlates with C/EBPα expression. Furthermore, ectopic expression of C/EBPα in NIH‐3T3 cells induces PPARγ expression and adipogenesis, but also restores insulin‐sensitive glucose transport. These results suggest that although PPARγ is sufficient to trigger the adipogenic program, C/EBPα is required for establishment of insulin‐sensitive glucose transport in adipocytes.
Nutrient Modulation of Cellular Insulin Action
Authors: PATTI MARY‐ELIZABETH
Published: February 2006

ABSTRACT: Abundant evidence supports a crucial role for dietary factors in the induction and maintenance of insulin resistance. At the cellular and tissue level, the availability of substrates for cellular energy production may play an important role in metabolic regulation and, in particular, in determining the response to insulin stimulation. The infusion of amino acids or fatty acids decreases insulin‐stimulated glucose disposal in vivo; sustained hyperglycemia also induces insulin resistance. To determine whether nutrients directly affect insulin signaling, we have evaluated the impact of fatty acids, amino acids, and activation of the hexosamine pathway on insulin signaling in both cultured cells and animal models. We demonstrate that fatty acids and amino acids inhibit early post‐receptor steps in insulin action, including tyrosine phosphorylation of insulin receptor substrate (IRS) proteins and activation of phosphatidylinositol 3‐kinase (PI3‐kinase), both in vitro and in several in vivo models. Similarly, activation of the hexosamine pathway by infusion of glucosamine also reduces insulin‐stimulated phosphorylation of IRS proteins, activation of PI3‐kinase, and activation of glycogen synthase. These data suggest that nutrients directly modulate insulin signaling, perhaps via common pathways, and thus contribute to cellular insulin resistance.
Role of PC‐1 in The Etiology of Insulin Resistance
Authors: GOLDFINE IRA D. , MADDUX BETTY A. , YOUNGREN JACK F. , TRISCHITTA VINCENZO , FRITTITTA LUCIA
Published: February 2006

ABSTRACT: Defects in insulin receptor tyrosine kinase activity have been demonstrated in tissues from insulin resistant subjects, but mutations in the insulin receptor gene are rare. Therefore, other molecules that are capable of modulating the insulin receptor most likely play a major role in insulin resistance. In cultured fibroblasts from an insulin resistant patient with Type 2 diabetes, we first identified membrane glycoprotein PC‐1 as an inhibitor of the insulin receptor tyrosine kinase activity. PC‐1 is overexpressed in fibroblasts from other insulin resistant subjects, both with and without Type 2 diabetes. PC‐1 is a large class II exoprotein whose function is unknown. Studies in muscle and fat of insulin resistant subjects, two primary tissues for insulin activation, reveal that elevated levels of PC‐1 are inversely correlated with decreased insulin action both in vivo and in vitro. Transfection and expression of PC‐1 in cultured cells demonstrate that overexpression of PC‐1 produces impairments in insulin receptor tyrosine kinase activity, and the subsequent cellular responses to insulin. These studies indicate, therefore, that PC‐1 is a major factor in the etiology of insulin resistance, and is a potential new therapeutic target for antidiabetic therapy.
Nutritionally Induced Insulin Resistance and Receptor Defect Leading to β‐Cell Failure in Animal Models
Authors: SHAFRIR ELEAZAR , ZIV EHUD , MOSTHAF LUITGARD
Published: February 2006

ABSTRACT: Animals with genetically or nutritionally induced insulin resistance and Type 2 diabetes comprise two groups: those with resilient β‐cells, e.g., ob/ob mice or fa/fa rats, capable of longstanding compensatory insulin hypersecretion and those with labile β‐cells in which the secretion pressure leads to β‐cell degranulation and apoptosis, e.g., db/db mice and Psammomys gerbils (sand rats). Psammomys features low insulin receptor density; on a relatively high energy diet it becomes hyperinsulinemic and hyperglycemic. In hyperinsulinemic clamp the hepatic glucose production is only partially suppressed by insulin, even in the normoglycemic state. The capacity of insulin to activate muscle and liver receptor tyrosine kinase is nearly abolished. GLUT4 content and mRNA are markedly reduced. Hyperinsulinemia was also demonstrated to inhibit insulin signaling and glucose transport in several other species. Among the factors affecting the insulin signaling pathway, phosphorylation of serine/threonine appears to be the prominent cause of receptor malfunction as inferred from the finding of overexpression of PKCɛ isoforms in the muscle and liver of Psammomys. The insulin resistance syndrome progressing in animals with labile β‐cells to overt diabetes and β‐cell failure is a “thrifty gene” characteristic. This is probably also true for human populations emerging from food scarcity into nutritional affluence, inappropriate for their metabolic capacity. Thus, the nutritionally induced hyperinsulinemia, associated with PKCɛ activation may be looked upon from the molecular point of view as “PKCɛ overexpression syndrome.”
Paradoxical Phosphorylation of Skeletal Muscle Glycogen Synthase byin VivoInsulin in Very Lean Young Adult Rhesus Monkeys
Authors: ORTMEYER HEIDI K. , BODKIN NONI L. , HANSEN BARBARA CALEEN
Published: February 2006

ABSTRACT:Calorie restriction (CR) has previously been shown to unexpectedly induce a reversal ofin vivoinsulin action (phosphorylation instead of dephosphorylation) on skeletal muscle glycogen synthase (GS) in four out of six long‐term calorie‐restricted (CR) monkeys. The purpose of the present study was to determine whether this increase in Ka (concentration of glucose 6‐phosphate [G6P] at which GS activity is half‐maximal) during insulin is also present in very lean (VL) young adult monkeys maintained on a controlled feeding regimen. Muscle samples from 10 VL monkeys (10 ± 2% body fat; 7 years old) were obtained before and during a euglycemic hyperinsulinemic clamp and the Ka was determined and compared to the Ka of two other groups of monkeys, one matched in age but fully ad libitum (AL)‐fed (n= 9, 8 ± 1 years old, 20 ± 3% body fat,p= 0.01 vs. VL monkeys), and the other our previously described weight‐clamped long‐term CR monkeys (n= 6, 20 ± 1 years old, 21 ± 2% body fat,p= 0.01 vs. VL monkeys). All of the AL monkeys had the expected decrease in Ka with insulin; however, similar to the 4 out of 6 CR monkeys, 7 out of 10 VL monkeys had an increase in Ka with insulin. The 11 monkeys with an increase in Ka (+Ka) (7 VL + 4 CR) were compared to the 14 monkeys with a decrease in Ka with insulin (−Ka) (3 VL + 2 CR + 9 AL). The +Ka monkeys had lower basal Ka (p= 0.0001), higher basal GS fractional activity (p= 0.0003), lower basal G6P content (p= 0.002), lower glycogen phosphorylase fractional activity (p= 0.01), and lower whole‐body insulin‐mediated glucose disposal rate (p< 0.05) than the −Ka monkeys. We conclude that the condition of steady‐state restrained calorie intake (as in the CR monkeys and in the controlled feeding VL monkeys) produces the paradoxical action ofin vivoinsulin to phosphorylate muscle GS, and raises the possibility that the presence of the unusual response to insulin may serve as a marker in calorie‐restrained individuals for the genotype of obesity, insulin resistance and/or Type 2 diabetes.
Transgenic Mice Lacking White Fat: Models for Understanding Human Lipoatrophic Diabetes
Authors: REITMAN MARC L. , MASON MARK M. , MOITRA JAIDEEP , GAVRILOVA OKSANA , MARCUS‐SAMUELS BERNICE , ECKHAUS MICHAEL , VINSON CHARLES
Published: February 2006

ABSTRACT: The human disease lipoatrophic (or lipodystrophic) diabetes is a rare syndrome in which a deficiency of adipose tissue is associated with Type 2 diabetes. This disease is an interesting contrast to the usual situation in which diabetes is associated with obesity, an excess of fat. Aside from obesity, patients with lipodystrophic diabetes have the other features associated with Metabolic Syndrome X, including hypertension and dyslipidemia. The contrast between diabetes with a lack of fat and diabetes with an excess of fat provides an opportunity to study the mechanisms causing Type 2 diabetes and its complications. Recently, three laboratories have produced transgenic mice that are deficient in white adipose tissue. These mice have insulin resistance and other features of lipoatrophic diabetes, and are a faithful model for the human disease. Here we review the different murine models of fat ablation and compare the murine and human diseases, addressing the questions: Is the lack of fat causative of the diabetes, and if so by what mechanism? How could the other clinical features be explained mechanistically? And finally, what can be gleaned about insight into treatment options?
Glutamate Excitotoxicity and Neuronal Energy Metabolism
Authors: NICHOLLS DAVID G. , BUDD SAMANTHA L. , CASTILHO ROGER F. , WARD MANUS W.
Published: February 2006

ABSTRACT: The bioenergetic properties of the in situ mitochondria play a central role in controlling the susceptibility of neurons to acute or chronic neurodegenerative stress. The mitochondrial membrane potential, ΔΨm, is the parameter that controls three interrelated mitochondrial functions of great relevance to neuronal survival: namely, ATP synthesis, Ca2+ accumulation, and superoxide generation. The in vitro model we study is the rat cerebellar granule cell in primary culture and its susceptibility to NMDA receptor‐mediated necrosis, which is preceded by a delayed failure of cytoplasmic Ca2+ homeostasis (“delayed Ca2+ deregulation,” DCD). DCD is not caused by a failure of mitochondrial ATP synthesis since it also occurs in cells maintained purely by glycolysis. The in situ mitochondria maintain a ΔΨm sufficient for ATP synthesis throughout the exposure of the cells to glutamate until DCD occurs. Even at that stage it appears that mitochondrial depolarization may be an effect of DCD rather than a primary cause. This somewhat unorthodox view resolves a number of apparent paradoxes, such as observations of enhanced superoxide generation by in situ mitochondria during excitotoxic exposure, since isolated mitochondria generate superoxide only under conditions of high ΔΨm. Mitochondrial depolarization by selective inhibitors that do not deplete cellular ATP is acutely neuroprotective.
Fundamental Aspects of Reactive Oxygen Species, or What's the Matter with Oxygen?
Authors: FRIDOVICH IRWIN
Published: February 2006

ABSTRACT: A byproduct of normal aerobic metabolism is the generation of dangerously reactive intermediates of the reduction of O2. These include O2−, H2O2, and HO · and arise because of the predisposition of O2 for univalent reductions. These reactive oxygen species (ROS), and others that they can engender, threaten all cellular macromolecules, and defenses are needed. Among those known to date are: superoxide dismutases to convert O2− into O2+ H2O2; catalases to dismute H2O2 into O2+ H2O; and peroxidases to reduce H2O2 into 2H2O) and to reduce ROOH into ROH and H2O. These defenses are aided by enzymes that repair or recycle oxidatively damaged nucleic acids and proteins. A role for such oxidative damage in aging and neurodegenerative diseases is well supported.
Ca2+‐Mediated Mitochondrial Dysfunction and the Protective Effects of Bcl‐2
Authors: MURPHY ANNE N.
Published: February 2006

ABSTRACT: Mitochondrial Ca2+ sequestration likely contributes to cell death in excitotoxicity and ischemia reperfusion injury, and may also be involved in chronic forms of neurodegeneration in which a compromise in bioenergetic function alters cellular Ca2+ homeostasis. Bcl‐2 overexpression is known to protect against Ca2+‐mediated death; the mechanism of protection remains unresolved. Our data of the ability of Bcl‐2 to potentiate mitochondrial Ca2+ uptake capacity and resistance to Ca2+‐induced damage is discussed in light of current information on apoptotic signaling pathways.
Mitochondrial Membrane Potential and the Permeability Transition in Excitotoxicity
Authors: REYNOLDS IAN J.
Published: February 2006

ABSTRACT: Acute neuronal injury caused by activation of glutamate receptors in neurons, or excitotoxicity, can be triggered by the activation of N‐methyl‐D‐aspartate receptors and the entry of large amounts of Ca2+. Recent studies have suggested that mitochondria have a critical role in the excitotoxicity injury mechanism. Mitochondria accumulate large amounts of Ca2+ following glutamate stimulation, and also generate reactive oxygen species. Moreover, the prevention of mitochondrial Ca2+ accumulation protects neurons from injury. The target for the actions of Ca2+ in the mitochondrial matrix has not yet been established. The permeability transition pore has the characteristics of a mechanism that is well suited to mediate neuronal injury. However, evidence for activation of the permeability transition pore in intact neurons is rather indirect, and these data suffer from some ambiguities that make it difficult to conclude that permeability transition is a critical contributor to mitochondrially mediated neuronal injury.
Oxidative Phosphorylation Disease Diagnosis
Authors: SHOFFNER JOHN M.
Published: February 2006

ABSTRACT: Although the mtDNA encodes only 13 polypeptide subunits of the OXPHOS enzymes, approximately 1,000 proteins are estimated to be necessary for proper OXPHOS function. Over the past 10 years a wide variety of adult and pediatric OXPHOS diseases were found to be caused by or associated with mitochondrial DNA (mtDNA) mutations and nuclear DNA mutations. These advances enhanced the ability to definitively diagnose patients, develop management plans, and provide genetic counseling. Recently described nuclear DNA and mtDNA mutations are enhancing our understanding of this complex group of diseases. The impact of these advances on our understanding of OXPHOS disease pathogenesis will be reviewed.
The α‐Ketoglutarate Dehydrogenase Complex
Authors: REX SHEU KWAN‐FU , BLASS JOHN P.
Published: February 2006

ABSTRACT: The α‐ketoglutarate dehydrogenase complex (KGDHC) is an important mitochondrial constituent, and deficiency of KGDHC is associated with a number of neurological disorders. KGDHC is composed of three proteins, each encoded on a different and well‐characterized gene. The sequences of the human proteins are known. The organization of the proteins into a large, ordered multienzyme complex (a “metabolon”) has been well studied in prokaryotic and eukaryotic species. KGDHC catalyzes a critical step in the Krebs tricarboxylic acid cycle, which is also a step in the metabolism of the potentially excitotoxic neurotransmitter glutamate. A number of metabolites modify the activity of KGDHC, including inactivation by 4‐hydroxynonenal and other reactive oxygen species (ROS). In human brain, the activity of KGDHC is lower than that of any other enzyme of energy metabolism, including phosphofructokinase, aconitase, and the electron transport complexes. Deficiencies of KGDHC are likely to impair brain energy metabolism and therefore brain function, and lead to manifestations of brain disease. In general, the clinical manifestations of KGDHC deficiency relate to the severity of the deficiency. Several such disorders have been recognized: infantile lactic acidosis, psychomotor retardation in childhood, intermittent neuropsychiatric disease with ataxia and other motor manifestations, Friedreich's and other spinocerebellar ataxias, Parkinson's disease, and Alzheimer's disease (AD). A KGDHC gene has been associated with the first two and last two of these disorders. KGDHC is not uniformly distributed in human brain, and the neurons that appear selectively vulnerable in human temporal cortex in AD are enriched in KGDHC. We hypothesize that variations in KGDHC that are not deleterious during reproductive life become deleterious with aging, perhaps by predisposing this mitochondrial metabolon to oxidative damage.
Oxidative Stress and a Key Metabolic Enzyme in Alzheimer Brains, Cultured Cells, and an Animal Model of Chronic Oxidative Deficits
Authors: GIBSON GARY E. , PARK LARRY C. H. , ZHANG HUI , SORBI SANDRO , CALINGASAN NOEL Y.
Published: February 2006

ABSTRACT: Oxidative stress and diminished metabolism occur in several neurodegenerative disorders. Brains from Alzheimer's disease (AD) patients exhibit several indicators of oxidative stress and have reduced activities of the α‐ketoglutarate dehydrogenase complex (KGDHC), a key mitochondrial enzyme. Whether these abnormalities are secondary to neurodegenerative processes or are inherent properties of the cells cannot be determined in autopsy brain. Studies in cultured fibroblasts suggest that AD‐related differences in oxidative stress and KGDHC reflect inherent properties of AD cells. KGDHC is sensitive to oxidative stress whether the enzyme is studied in cells, in purified mitochondria, or as an isolated protein. Reductions of brain KGDHC in living rodents lead to oxidative stress and selective cell death. The results suggest that KGDHC participates in a deleterious cascade of events related to oxidative stress that are critical in selective neuronal loss in neurodegenerative diseases.
The Use of Transgenic and Mutant Mice to Study Oxygen Free Radical Metabolism
Authors: HUANG TING‐TING , CARLSON ELAINE J. , RAINERI INES , GILLESPIE ANNE MARIE , KOZY HEATHER , EPSTEIN CHARLES J.
Published: February 2006

ABSTRACT: To distinguish the role of Mn superoxide dismutase (MnSOD) from that of cytoplasmic CuZn superoxide dismutase (CuZnSOD), the mouse MnSOD gene (Sod2) was inactivated by homologous recombination. Sod2−/− mice on a CD1 (outbred) genetic background die within the first 10 days of life (mean, 5.4 days) with a complex phenotype that includes dilated cardiomyopathy, accumulation of lipid in liver and skeletal muscle, metabolic acidosis and ketosis, and a severe reduction in succinate dehydrogenase (complex II) and aconitase (a TCA cycle enzyme) activities in the heart and, to a lesser extent, in other organs. These findings indicate that MnSOD is required to maintain the integrity of mitochondrial enzymes susceptible to direct inactivation by superoxide. On the other hand, Lebovitz et al. reported an independently derived MnSod null mouse (Sod2tmlLeb) on a mixed C57BL/6 and 129Sv background with a different phenotype. Because a difference in genetic background is the most likely explanation for the phenotypic differences, the two mutant lines were crossed into different genetic backgrounds for further analyses. To study the phenotype of Sod2tmlLeb mice CD1 background, the Sod2tmlLeb mice were crossed to CD1 for two generations before the −/+ mice were intercrossed to generate −/− mice. The life span distribution of CD1〈Sod2−/−〉Leb was shifted to the left, indicating a shortened life span on the CD1 background. Furthermore, the CD1〈Sod2−/−〉Leb mice develop metabolic acidosis at an early stage as was observed with CD1〈Sod2−/−〉Cje. When Sod2tmlCje was placed on C57BL/6J (B6) background, the −/− mice were found to die either during midgestation or within the first 4 days after birth. However, when the B6〈Sod2−/+〉Cje were crossed with DBA/2J (D2) for the generation of B6D2F2〈Sod2−/−〉Cje mice, an entirely different phenotype, similar to that described by Lebovitz et al., was observed. The F2 Sod−/− mice were able to survive up to 18 days, and the animals that lived for more than 15 days displayed neurological abnormalities including ataxia and seizures. Their hearts were not as severely affected as were those of the CD1 mice, and neurological degeneration rather than heart defect appears to be the cause of death.
The Blood‐Brain Barrier and Cerebrovascular Pathology in Alzheimer's Disease
Authors: KALARIA RAJ N.
Published: February 2006

ABSTRACT: The pathology of Alzheimer's disease (AD) is not limited to amyloid plaques and neurofibrillary tangles. Recent evidence suggests that more than 30% of AD cases exhibit cerebrovascular pathology, which involves the cellular elements that represent the blood‐brain barrier. Certain vascular lesions such as microvascular degeneration affecting the cerebral endothelium, cerebral amyloid angiopathy and periventricular white matter lesions are evident in virtually all cases of AD. Furthermore, clinical studies have demonstrated blood‐brain barrier dysfunction in AD patients who exhibit peripheral vascular abnormalities such as hypertension, cardiovascular disease and diabetes. Whether these vascular lesions along with perivascular denervation are coincidental or causal in the pathogenetic processes of AD remains to be defined. In this chapter, I review biochemical and morphological evidence in context with the variable but distinct cerebrovascular pathology described in AD. I also consider genetic influences such as apolipoprotein E in relation to cerebrovascular lesions that may shed light on the pathophysiology of the cerebral vasculature. The compelling vascular pathology associated with AD suggests that transient and focal breach of the blood‐brain barrier occurs in late onset AD and may involve an interaction of several factors, which include perivascular mediators as well as peripheral circulation derived factors that perturb the endothelium. These vascular abnormalities are likely to worsen cognitive disability in AD.
Cellular and Molecular Mechanisms Underlying Perturbed Energy Metabolism and Neuronal Degeneration in Alzheimer's and Parkinson's Diseases
Authors: MATTSON MARK P. , PEDERSEN WARD A. , DUAN WENZHEN , CULMSEE CARSTEN , CAMANDOLA SIMONETTA
Published: February 2006

ABSTRACT: Synaptic degeneration and death of nerve cells are defining features of Alzheimer's disease (AD) and Parkinson's disease (PD), the two most prevalent age‐related neurodegenerative disorders. In AD, neurons in the hippocampus and basal forebrain (brain regions that subserve learning and memory functions) are selectively vulnerable. In PD dopamine‐producing neurons in the substantia nigra‐striatum (brain regions that control body movements) selectively degenerate. Studies of postmortem brain tissue from AD and PD patients have provided evidence for increased levels of oxidative stress, mitochondrial dysfunction and impaired glucose uptake in vulnerable neuronal populations. Studies of animal and cell culture models of AD and PD suggest that increased levels of oxidative stress (membrane lipid peroxidation, in particular) may disrupt neuronal energy metabolism and ion homeostasis, by impairing the function of membrane ion‐motive ATPases and glucose and glutamate transporters. Such oxidative and metabolic compromise may thereby render neurons vulnerable to excitotoxicity and apoptosis. Studies of the pathogenic mechanisms of AD‐linked mutations in amyloid precursor protein (APP) and presenilins strongly support central roles for perturbed cellular calcium homeostasis and aberrant proteolytic processing of APP as pivotal events that lead to metabolic compromise in neurons. Specific molecular “players” in the neurodegenerative processes in AD and PD are being identified and include Par‐4 and caspases (bad guys) and neurotrophic factors and stress proteins (good guys). Interestingly, while studies continue to elucidate cellular and molecular events occurring in the brain in AD and PD, recent data suggest that both AD and PD can manifest systemic alterations in energy metabolism (e.g., increased insulin resistance and dysregulation of glucose metabolism). Emerging evidence that dietary restriction can forestall the development of AD and PD is consistent with a major “metabolic” component to these disorders, and provides optimism that these devastating brain disorders of aging may be largely preventable.
Polyglutamine Domain Proteins with Expanded Repeats Bind Neurofilament, Altering the Neurofilament Network
Authors: NAGAI YOSHITAKA , ONODERA OSAMU , STRITTMATTER WARREN J. , BURKE JAMES R.
Published: February 2006

ABSTRACT: Proteins with expanded polyglutamine (polyQ) repeats cause eight inherited neurodegenerative diseases. Nuclear and cytoplasmic polyQ protein is a common feature of these diseases, but its role in cell death remains debatable. Since the neuronal intermediate filament network is composed of neurofilament (NF) and NF abnormalities occur in neurodegenerative diseases, we examined whether pathologic‐length polyQ domain proteins interact with NF. We expressed polyQ‐green fluorescent fusion proteins (GFP) in a neuroblast cell line, TR1. Pathologic‐length polyQ‐GFP fusion proteins form large cytoplasmic aggregates surrounded by neurofilament. Immunoisolation of pathologic‐length polyQ proteins co‐isolated 68 kD NF protein demonstrating molecular interaction. These observations suggest that polyQ interaction with NF is important in the pathogenesis of the polyglutamine repeat diseases.
Bioenergetics in Huntington's Disease
Authors: GRÜNEWALD THOMAS , BEAL M. FLINT
Published: February 2006

ABSTRACT: Huntington's disease (HD) is an autosomal dominant inherited neurodegenerative disorder with relentless course and prototypical clinical symptoms. In 1993 HD was associated with an expanded CAG triplet repeat stretch on chromosome 4 in the coding region of its target protein, huntingtin. The length of the resulting polyglutamine extensions correlates with lower age of onset and a higher density of ubiquitine‐positive neuronal intranuclear inclusions. Recently it has been proposed that mutant huntingtin induces progressive neuronal cell death by an apoptotic mechanism. There is strong evidence that disturbances in cellular energy homeostasis and oxidative damage contribute to neurodegeneration. This review will summarize and discuss the current concepts that point towards an involvement of free radical‐induced oxidative stress, glutamate excitotoxicity and mitochondrial resporatory chain defects in pathogenesis of HD.
New Vistas for Melanocortins: Finally, an Explanation for Their Pleiotropic Functions
Authors: STRAND FLEUR L.
Published: February 2006

Abstract: This paper presents a historical overview of melanocortin (MC) research from the early investigations of the many noncorticotropic effects of peptide fragments of adrenocorticotropic hormone to the present focus on the discovery and cloning of the MC receptors (MCRs). Final acceptance of the passage of neuropeptides through the blood‐brain barrier provided the scientific basis for the neuropeptide concept, formulated previously by both De Weid and Kastin, that peripherally administered neuropeptides affect neural processes. The discussion includes melanocortin effects on behavior, the cardiovascular system, central and peripheral electrophysiological parameters, food intake, inflammation and analgesia, nerve regeneration and neuroprotection, and development. The localization of specific MCRs in both neural and nonneural tissues is correlated with the pleiotropic effects discussed.
Stress, Corticotropin‐releasing Factor, and Drug Addiction
Authors: KOOB GEORGE F.
Published: February 2006

Abstract: The neuropeptide corticotropin‐releasing factor (CRE) and related neuropeptides not only mediate hormonal responses to stressors but also have a neurotropic role in the central nervous system to mediate behavioral responses to stressors. CRF antagonists effectively block CRF responses and have effects opposite those of CRF in many stress‐related situations. Recent advances suggest that in addition to CRF itself there is another CRF‐related neuropeptide, urocortin, that may be involved in stress‐related responses, particularly those involving appetite. At least two CRF receptors have been discovered to date, CRF‐1 and CRF‐2. CRF may be involved in various aspects of the addiction cycle associated with drugs of abuse. CRF appears to be activated during stress‐induced reinstatement of drug taking as well as acute withdrawal from all major drugs of abuse. CRF is hypothesized to be part of an allostatic change leading to vulnerability to relapse during prolonged abstinence from drugs of abuse.