Further lowering of muscle lipid oxidative capacity in obese subjects after biliopancreatic diversion

A reduced lipid oxidative capacity is considered a risk factor for the development of obesity, but a further impairment of lipid oxidative capacity is observed after weight loss. We aimed to define the mechanisms underlying this phenomenon in skeletal muscle and in particular to study the mitochondrial and peroxisomal lipid oxidative pathways. Thus we measured intramyocellular triglyceride content (IMTG) and the expression of genes of lipid oxidation [peroxisome proliferator-activated receptor-alpha, carnitine palmitoyltransferase 1B, and acyl-coenzyme A (acyl-CoA) oxidase 1] and synthesis (acetyl-CoA carboxylase B) using RT-PCR analysis in muscle biopsies of morbidly obese patients before and after biliopancreatic diversion. Weight reduction significantly decreased IMTG while increasing insulin sensitivity, measured by euglycemic hyperinsulinemic clamp. Moreover, an increase in glucose and a decline in lipid oxidation, as assessed by respiratory chamber, were observed. Weight loss reduced the expression of peroxisome proliferator-activated receptor-alpha (-46.7%), carnitine palmitoyltransferase 1B (-43.1%), acyl-CoA oxidase 1 (-37.8%), and acetyl-CoA carboxylase B (-48.7%). Our results indicate that a defect of both peroxisomal and mitochondrial oxidative pathways at the muscular level may contribute to the reduced fat oxidation in obese subjects after biliopancreatic diversion. They also suggest that a depression of the de novo lipogenesis may account for IMTG depletion.

Expression, localization, and regulation of NOS in human mast cell lines: effects on leukotriene production

Nitric oxide (NO) is a potent radical produced by nitric oxide synthase (NOS) and has pleiotrophic activities in health and disease. As mast cells (MCs) play a central role in both homeostasis and pathology, we investigated NOS expression and NO production in human MC populations. Endothelial NOS (eNOS) was ubiquitously expressed in both human MC lines and skin-derived MCs, while neuronal NOS (nNOS) was variably expressed in the MC populations studied. The inducible (iNOS) isoform was not detected in human MCs. Both growth factor-independent (HMC-1) and -dependent (LAD 2) MC lines showed predominant nuclear eNOS protein localization, with weaker cytoplasmic expression. nNOS showed exclusive cytoplasmic localization in HMC-1. Activation with Ca(2+) ionophore (A23187) or IgE-anti-IgE induced eNOS phosphorylation and translocation to the nucleus and nuclear and cytoplasmic NO formation. eNOS colocalizes with the leukotriene (LT)-initiating enzyme 5-lipoxygenase (5-LO) in the MC nucleus. The NO donor, S-nitrosoglutathione (SNOG), inhibited, whereas the NOS inhibitor, N(G)-nitro-l-arginine methyl ester (L-NAME), potentiated LT release in a dose-dependent manner. Thus, human MC lines produce NO in both cytoplasmic and nuclear compartments, and endogenously produced NO can regulate LT production by MCs.

Disruption of neural signal transducer and activator of transcription 3 causes obesity, diabetes, infertility, and thermal dysregulation

Signal transducer and activator of transcription (STAT)3 is widely expressed in the CNS during development and adulthood. STAT3 has been implicated in the control of neuron/glial differentiation and leptin-mediated energy homeostasis, but the physiological role and degree of involvement of STAT3 in these processes is not defined and controversial because of the lack of a direct genetic model. To address this, we created mice with a neural-specific disruption of STAT3 (STAT3(N-/-)). Surprisingly, homozygous mutants were born at the expected Mendelian ratio without apparent developmental abnormalities but susceptible to neonatal lethality. Mutants that survived the neonatal period were hyperphagic, obese, diabetic, and infertile. Administering a melanocortin-3/4 receptor agonist abrogated the hyperphagia and hypothalamic immunohistochemistry showed a marked reduction in proopiomelanocortin with an increase in neuropeptide Y and agouti-related protein. Mutants had reduced energy expenditure and became hypothermic after fasting or cold stress. STAT3(N-/-) mice are hyperleptinemic, suggesting a leptin-resistant condition. Concomitant with neuroendocrine defects such as decreased linear growth and infertility with accompanying increased corticosterone levels, this CNS knockout recapitulates the unique phenotype of db/db and ob/ob obese models and distinguishes them from other genetic models of obesity. Thus, STAT3 in the CNS plays essential roles in the regulation of energy homeostasis and reproduction.

Decreased muscle acetyl-coenzyme A carboxylase 2 mRNA and insulin resistance in formerly obese subjects

OBJECTIVE

A relationship between free fatty acids, intramuscular triglycerides (TG(M)s), and insulin resistance is widely accepted. The intracellular level of malonyl-coenzyme A (CoA) was suggested to be the possible link. Acetyl-CoA carboxylase (ACC) is a key enzyme in fatty acid metabolism, catalyzing the synthesis of malonyl-CoA, a fatty acid acyl-chain elongation unit, from acetyl-CoA. We assessed ACC2 mRNA expression variations in skeletal muscle of subjects who have undergone biliopancreatic diversion (BPD) operation. BPD, in fact inducing a massive lipid malabsorption, leads to a reversion of insulin resistance.

RESEARCH METHODS AND PROCEDURES

Twelve obese women (BMI > 40 kg/m(2)) were enrolled in the study. Body composition, euglycemic-hyperinsulinemic clamp, and muscle biopsies for lipid analysis and reverse transcription-competitive polymerase chain reaction were performed before and 3 years after BPD.

RESULTS

The average weight loss was around 37%. A significant inverse linear relation was observed between glucose uptake and TG(M) (y = -5.62x - 142.82, R(2) = 0.50, p = 0.01). The reduced amount of ACC2 mRNA directly correlated with both TG(M) (y = 2.11x +69.85, R(2) = 0.70, p = 0.01) and fasting insulin (y = 1.49x + 57.17, R(2) = 0.69, p < 0.01) concentrations.

DISCUSSION

In conclusion, down-regulation of ACC2 mRNA, induced by the lowering of plasma insulin concentration, is related to improvement of insulin sensitivity. We hypothesize that reduced amount of malonyl-CoA, consequent to reduced ACC2 mRNA, enhancing fatty acid oxidation, causes lowering of the intramyocitic triglyceride depot.

Long-term normalization of insulin sensitivity following biliopancreatic diversion for obesity

OBJECTIVE

Assess insulin sensitivity and metabolic status of obese patients with stable weight loss at long term following biliopancreatic diversion (BPD).

MATERIAL AND METHODS

The study was carried out in 36 nondiabetic severely obese patients undergoing BPD. Serum concentration of glucose, insulin and leptin were determined prior to and at 2 y following the operation. Insulin sensitivity was calculated according to the homeostatic model assessment (HOMA IR).

RESULTS

At 2 y following BPD, weight loss in all subjects corresponded to a marked drop in serum leptin concentration and improvement of insulin sensitivity within physiological range. Following the operation, HOMA IR values were positively correlated with serum leptin concentration independently of body mass index values.

DISCUSSION

The stable weight loss following BPD at long term is accompanied by a complete reversal of the preoperative insulin resistance. Serum leptin concentration and HOMA IR data were positively related only postoperatively, suggesting that the action of factors that could influence the relation between leptin and insulin action in the obese status can be reverted.

Retinoblastoma protein functions as a molecular switch determining white versus brown adipocyte differentiation

Adipocyte precursor cells give raise to two major cell populations with different physiological roles: white and brown adipocytes. Here we demonstrate that the retinoblastoma protein (pRB) regulates white vs. brown adipocyte differentiation. Functional inactivation of pRB in wild-type mouse embryo fibroblasts (MEFs) and white preadipocytes by expression of simian virus 40 large T antigen results in the expression of the brown fat-specific uncoupling protein 1 (UCP-1) in the adipose state. Retinoblastoma gene-deficient (Rb-/-) MEFs and stem cells, but not the corresponding wild-type cells, differentiate into adipocytes with a gene expression pattern and mitochondria content resembling brown adipose tissue. pRB-deficient MEFs exhibit an increased expression of the Forkhead transcription factor Foxc2 and its target gene cAMP-dependent protein kinase regulatory subunit RIalpha, resulting in increased cAMP sensitivity. Suppression of cAMP-dependent protein kinase activity in Rb(-/-)MEFs blocked the brown adipocyte-like gene expression pattern without affecting differentiation per se. Immunohistochemical studies revealed that pRB is present in the nuclei of white but not brown adipocyte precursor cells at a developmental stage where both cell types begin to accumulate lipid and brown adipocytes express UCP-1. Furthermore, pRB rapidly undergoes phosphorylation upon cold-induced neodifferentiation and up-regulation of UCP-1 expression in brown adipose tissue. Finally, down-regulation of pRB expression accompanies transdifferentiation of white into brown adipocytes in response to beta3-adrenergic receptor agonist treatment. We propose that pRB acts as a molecular switch determining white vs. brown adipogenesis, suggesting a previously uncharacterized function of this key cell cycle regulator in adipocyte lineage commitment and differentiation.

Brown adipose tissue: function and physiological significance

The function of brown adipose tissue is to transfer energy from food into heat; physiologically, both the heat produced and the resulting decrease in metabolic efficiency can be of significance. Both the acute activity of the tissue, i.e., the heat production, and the recruitment process in the tissue (that results in a higher thermogenic capacity) are under the control of norepinephrine released from sympathetic nerves. In thermoregulatory thermogenesis, brown adipose tissue is essential for classical nonshivering thermogenesis (this phenomenon does not exist in the absence of functional brown adipose tissue), as well as for the cold acclimation-recruited norepinephrine-induced thermogenesis. Heat production from brown adipose tissue is activated whenever the organism is in need of extra heat, e.g., postnatally, during entry into a febrile state, and during arousal from hibernation, and the rate of thermogenesis is centrally controlled via a pathway initiated in the hypothalamus. Feeding as such also results in activation of brown adipose tissue; a series of diets, apparently all characterized by being low in protein, result in a leptin-dependent recruitment of the tissue; this metaboloregulatory thermogenesis is also under hypothalamic control. When the tissue is active, high amounts of lipids and glucose are combusted in the tissue. The development of brown adipose tissue with its characteristic protein, uncoupling protein-1 (UCP1), was probably determinative for the evolutionary success of mammals, as its thermogenesis enhances neonatal survival and allows for active life even in cold surroundings.

Expression of the thermogenic nuclear hormone receptor coactivator PGC-1alpha is reduced in the adipose tissue of morbidly obese subjects

Peroxisome proliferator-activated receptor gamma coactivator 1alpha (PGC1alpha) is an accessory protein which can potentiate the transcriptional activation function of many nuclear hormone receptors. Its tissue distribution and physiological studies suggest that its principal in vivo roles are to promote cold-induced thermogenesis, mitochondrial biogenesis, hepatic gluconeogenesis, and fatty acid beta-oxidation. It is expressed in the white adipose tissue of both humans and rodents, and in rodents it has been suggested to mediate in part the leptin-induced conversion of white adipocytes from fat storing to fat oxidising cells. In this study, quantitative real-time PCR has been used in human tissue to demonstrate that (1) PGC1alpha mRNA levels in subcutaneous fat are three-fold lower in morbidly obese than in slim subjects; (2) there are no differences in PGC1alpha mRNA between omental and subcutaneous mature adipocytes; (3) there is a robust induction of PGC1alpha expression during subcutaneous human preadipocyte differentiation ex vivo. Whether low PGC1alpha expression is a prelude to the development of obesity, or a consequence of that obesity, attempts to upregulate endogenous white adipose tissue expression may prove a valuable new avenue to explore in obesity therapy.

The many lives of leptin

Leptin is a 16,000-Da protein which is secreted by fat but acts within the brain to regulate adiposity. Our Peptides Classic addressed the mystery of how such a large molecule could negotiate the blood-brain barrier (BBB), a structure which normally excludes proteins from the brain. We found that leptin was transported across the BBB by a saturable transport system. This finding was important to understanding how satiety-related peptides and proteins worked, but it was also important to the concept that the BBB is a regulatory interface important in brain-body communication. Obesity in humans and many animals is associated with a leptin resistant state rather than a leptin deficiency. Subsequent work has shown that a defect in the BBB transport of leptin is key in producing and reinforcing this state of resistance. Leptin is pluripotent and the concept of it being primarily an adipostat is being discarded for more encompassing views. Consideration of the BBB data would favor the view that ancestral levels of leptin were much lower than those currently considered normal and are consistent with leptin acting as a metabolic switch, informing the brain when fat reserves are adequate to direct energy expenditures towards activities other than seeking calories.

Excess body fat in men decreases plasma fatty acid availability and oxidation during endurance exercise

The effect of relative body fat mass on exercise-induced stimulation of lipolysis and fatty acid oxidation was evaluated in 15 untrained men (5 lean, 5 overweight, and 5 obese with body mass indexes of 21 +/- 1, 27 +/- 1, and 34 +/- 1 kg/m2, respectively, and %body fat ranging from 12 to 32%). Palmitate and glycerol kinetics and substrate oxidation were assessed during 90 min of cycling at 50% peak aerobic capacity (VO2 peak) by use of stable isotope-labeled tracer infusion and indirect calorimetry. An inverse relationship was found between %body fat and exercise-induced increase in glycerol appearance rate relative to fat mass (r2 = 0.74; P < 0.01). The increase in total fatty acid uptake during exercise [(micromol/kg fat-free mass) x 90 min] was approximately 50% smaller in obese (181 +/- 70; P < 0.05) and approximately 35% smaller in overweight (230 +/- 71; P < 0.05) than in lean (354 +/- 34) men. The percentage of total fatty acid oxidation derived from systemic plasma fatty acids decreased with increasing body fat, from 49 +/- 3% in lean to 39 +/- 4% in obese men (P < 0.05); conversely, the percentage of nonsystemic fatty acids, presumably derived from intramuscular and possibly plasma triglycerides, increased with increasing body fat (P < 0.05). We conclude that the lipolytic response to exercise decreases with increasing adiposity. The blunted increase in lipolytic rate in overweight and obese men compared with lean men limits the availability of plasma fatty acids as a fuel during exercise. However, the rate of total fat oxidation was similar in all groups because of a compensatory increase in the oxidation of nonsystemic fatty acids.

Haptoglobin release by human adipose tissue in primary culture

Haptoglobin is a putative adiposity marker because its concentration in blood is increased in obese humans. The present studies examined haptoglobin release by explants of adipose tissue in primary culture. Haptoglobin was released by explants of human visceral and subcutaneous adipose tissue at a nearly linear rate over 48 h. Explants of visceral adipose tissue released more haptoglobin than did explants of subcutaneous adipose tissue. The release of haptoglobin was quite variable, but there was a close correlation between haptoglobin release by visceral adipose tissue and that by explants of subcutaneous tissue from the same individual. Dexamethasone and niflumic acid, a cyclooxygenase-2 inhibitor, both inhibited haptoglobin release. There was release of haptoglobin by both isolated adipocytes and the adipose tissue matrix remaining after collagenase digestion of human adipose tissue. However, the amount of haptoglobin released by human adipose tissue explants in primary culture was quite low in relationship to the circulating level of haptoglobin.

Obesity wars: molecular progress confronts an expanding epidemic

The worldwide prevalence of obesity is increasing at an alarming rate, with major adverse consequences for human health. This "obesity epidemic" is paralleled by a rapid and substantive increase in our understanding of molecular pathways and physiologic systems underlying the regulation of energy balance. While efforts to address the environmental factors that are responsible for the recent "epidemic" must continue, new molecular and physiologic insights into this system offer exciting possibilities for future development of successful therapies.

Sensory but not parasympathetic nerves are required for ocular vascular remodeling following chronic sympathectomy in rat

Choroidal vascularity increases following chronic sympathetic denervation in rats. The mechanisms of this remodeling are unclear. Since both nitric oxide and substance P/CGRP have been suggested as angiogenic factors in other targets, we hypothesized that sensory or parasympathetic nerves may also participate in ocular vascular remodeling. To test this hypothesis, sympathetic denervation was accomplished by superior cervical ganglionectomy. Sensory denervation was induced by subcutaneous injections of capsaicin on postnatal days 2 and 9, and ocular parasympathetic innervation was ablated by pterygopalatine ganglion excision on postnatal day 60. Eyes were processed and sectioned for light microscopic histomorphometry. Sympathetic denervation for 6 weeks resulted in increased choroidal thickness, vascular luminal area, numbers of large venules and large arterioles, and capillaries in the outer nuclear layer. Capsaicin pretreatment prevented sympathectomy-induced increases in choroidal thickness, vascular luminal area and large venules and large arterioles, whereas pterygopalatine ganglionectomy was without effect. Both sensory and parasympathetic denervation attenuated increases in outer nuclear layer capillaries. These studies indicate that increased choroidal vascularity noted after chronic sympathectomy requires intact sensory innervation.

Regulation of haptoglobin gene expression in 3T3-L1 adipocytes by cytokines, catecholamines, and PPARgamma

Factors which regulate expression of the haptoglobin (acute phase reactant) gene in adipocytes have been examined using 3T3-L1 cells. Haptoglobin expression was observed by Northern blotting in each of the major white adipose tissue depots of mice (epididymal, subcutaneous, mesenteric, and perirenal) and in interscapular brown fat. Expression occurred in mature adipocytes, but not in the stromal-vascular fraction. In 3T3-L1 cells, haptoglobin mRNA was detected from day 4 after the induction of differentiation into adipocytes. Lipopolysaccharide and the cytokines, TNFalpha and interleukin-6, resulted in substantial increases in haptoglobin mRNA in 3T3-L1 adipocytes; the increase (7-fold) was highest with TNFalpha. Increases in haptoglobin mRNA level were also induced by dexamethasone, noradrenaline, isoprenaline, and a beta3-adrenoceptor agonist. In contrast, haptoglobin mRNA was reduced by nicotinic acid and the PPARgamma agonist, rosiglitazone. RT-PCR showed that the haptoglobin gene was expressed in human adipose tissue (subcutaneous, omental). It is concluded that haptoglobin gene expression in adipocytes is stimulated by inflammatory cytokines, glucocorticoids, and the sympathetic system, while activation of the PPARgamma nuclear receptor is strongly inhibitory.

Fatty liver in familial hypobetalipoproteinemia: roles of the APOB defects, intra-abdominal adipose tissue, and insulin sensitivity

Fatty liver is frequent in the apolipoprotein B (apoB)-defective genetic form of familial hypobetalipoproteinemia (FHBL), but interindividual variability in liver fat is large. To explain this, we assessed the roles of metabolic factors in 32 affected family members with apoB-defective FHBL and 33 related and unrelated normolipidemic controls matched for age, sex, and indices of adiposity. Two hour, 75 g oral glucose tests, with measurements of plasma glucose and insulin levels, body mass index, and waist-hip ratios were obtained. Abdominal subcutaneous, intraperitoneal (IPAT), and retroperitoneal adipose tissue masses were quantified by MR imaging, and hepatic fat was quantified by MR spectroscopy. Mean +/- SD liver fat percentage values of FHBL and controls were 14.8 +/- 12.0 and 5.2 +/- 5.9, respectively (P = 0.001). Means for these measures of obesity and insulin action were similar in the two groups. Important determinants of liver fat percentage were FHBL-affected status, IPAT, and area under the curve (AUC) insulin in both groups, but the strongest predictors were IPAT in FHBL (partial R(2) = 0.55, P < 0.0002) and AUC insulin in controls (partial R(2) = 0.59, P = 0.0001). Regression of liver fat percentage on IPAT fat was significantly greater for FHBL than for controls (P < 0.001). In summary, because apoB-defective FHBL imparts heightened susceptibility to liver triglyceride accumulation, increasing IPAT and insulin resistance exert greater liver fat-increasing effects in FHBL.

Impaired mitochondrial activity in the insulin-resistant offspring of patients with type 2 diabetes

BACKGROUND

Insulin resistance appears to be the best predictor of the development of diabetes in the children of patients with type 2 diabetes, but the mechanism responsible is unknown.

METHODS

We performed hyperinsulinemic-euglycemic clamp studies in combination with infusions of [6,6-(2)H(2)]glucose in healthy, young, lean, insulin-resistant offspring of patients with type 2 diabetes and insulin-sensitive control subjects matched for age, height, weight, and physical activity to assess the sensitivity of liver and muscle to insulin. Proton ((1)H) magnetic resonance spectroscopy studies were performed to measure intramyocellular lipid and intrahepatic triglyceride content. Rates of whole-body and subcutaneous fat lipolysis were assessed by measuring the rates of [(2)H(5)]glycerol turnover in combination with microdialysis measurements of glycerol release from subcutaneous fat. We performed (31)P magnetic resonance spectroscopy studies to assess the rates of mitochondrial oxidative-phosphorylation activity in muscle.

RESULTS

The insulin-stimulated rate of glucose uptake by muscle was approximately 60 percent lower in the insulin-resistant subjects than in the insulin-sensitive control subjects (P<0.001) and was associated with an increase of approximately 80 percent in the intramyocellular lipid content (P=0.005). This increase in intramyocellular lipid content was most likely attributable to mitochondrial dysfunction, as reflected by a reduction of approximately 30 percent in mitochondrial phosphorylation (P=0.01 for the comparison with controls), since there were no significant differences in systemic or localized rates of lipolysis or plasma concentrations of tumor necrosis factor alpha, interleukin-6, resistin, or adiponectin.

CONCLUSIONS

These data support the hypothesis that insulin resistance in the skeletal muscle of insulin-resistant offspring of patients with type 2 diabetes is associated with dysregulation of intramyocellular fatty acid metabolism, possibly because of an inherited defect in mitochondrial oxidative phosphorylation.

β-ADRENERGICRECEPTORS ANDREGULATION OFENERGYEXPENDITURE: A Family Affair

The family of adrenergic receptors (ARs) expressed in adipocytes includes three sibling betaARs and two alphaAR cousins. Together they profoundly influence the mobilization of stored fatty acids, secretion of fat-cell derived hormones, and the specialized process of nonshivering thermogenesis in brown adipose tissue. The two types of fat cells that compose adipose tissue, brown and white, are structurally and functionally distinct. Studies on the mechanisms by which individual betaAR regulates these cell-specific functions have recently uncovered new signal transduction cascades involved in processes traditionally ascribed to adenylyl cyclase/cAMP/protein kinase A system. They illustrate how betaAR signaling can orchestrate a coordinated set of intracellular responses for fine control of metabolic balance.

Functional characterization of human mesenchymal stem cell-derived adipocytes

The function of adipocytes derived from human mesenchymal stem cells (hMSC) was investigated for the first time in hMSC from fetal liver (FL) and adult bone marrow (BM) and compared with preadipocytes from human subcutaneous adipose tissue differentiated according to adipocyte-specific protocols. FL- and BM-derived adipocytes displayed both morphological and functional characteristics of mature adipocytes including specific intracellular signaling pathways for tumor necrosis factor-alpha, catecholamine-regulated lipolysis as well as secretion of adiponectin and leptin. Similar to differentiated preadipocytes, hMSC adipocytes displayed lipolytic effects mediated by beta-adrenoceptors and antilipolytic effects mediated by the alpha 2A-adrenoceptor (alpha 2A-AR) and expressed proteins with a pivotal role in human lipolysis, including beta 2-AR, alpha 2A-AR, and hormone-sensitive lipase. We conclude that hMSC-derived adipocytes are morphologically and functionally similar to preadipocytes and display an intact lipolytic signaling pathway and endocrine function. These systems could be of great value in adipocyte research as a renewable source of adipocytes.

Rapid transformation of white adipocytes into fat-oxidizing machines

Adenovirus-induced hyperleptinemia rapidly depletes body fat in normal rats without increasing free fatty acids and ketogenesis, implying that fat-storing adipocytes are oxidizing the fat. To analyze the ultrastructural changes of adipocytes accompanying this functional transformation, we examined the fat tissue by electron microscopy. After 14 days of hyperleptinemia, adipocytes had become shrunken, fatless, and encased in a thick basement-membrane-like matrix. They were crowded with mitochondria that were much smaller than those of brown adipocytes. Their gene expression profile revealed striking up-regulation of peroxisome proliferator-activated receptor gamma coactivator 1alpha (an up-regulator of mitochondrial biogenesis not normally expressed in white fat), increased uncoupling proteins-1 and -2, and down-regulation of lipogenic enzymes. Phosphorylation of both acetyl CoA carboxylase and AMP-activated protein kinase was increased, thus explaining the increase in fatty acid oxidation. The ability to transform adipocytes into unique fat-burning cells may suggest novel therapeutic strategies for obesity.

The epidemiology of congenital cryptorchidism, testicular ascent and orchiopexy

PURPOSE

The frequency, significance and possible etiology of testicular ascent (acquired cryptorchidism) are characterized in light of the known incidence and natural history of congenital cryptorchidism, and data provided by longitudinal and epidemiological studies of ascended testes and orchiopexy rates.

MATERIALS AND METHODS

We comprehensively reviewed the literature addressing the epidemiology of congenital and acquired cryptorchidism and orchiopexy.

RESULTS

The incidence of congenital cryptorchidism in full-term males at birth (2% to 4%) and at age 1 year (approximately 1%) has not increased in the last few decades. The risk of ascent may be as high as 50% in cases where 1 testis is significantly retractile. Ascended testes are typically unilateral (77%), identified in mid childhood and located distal to the inguinal canal (77%). Ascended and significantly retractile testes may be prone to the same germ cell maldevelopment seen in congenital cryptorchidism. Cumulative orchiopexy rates in defined populations are 2% to 4%, and mean age at orchiopexy remains higher than expected (greater than 4 years), despite a long held standard of care that includes recommendation for surgery by age 2. These data suggest that cryptorchidism may be acquired in a significant subset of cases.

CONCLUSIONS

With close monitoring of young boys spontaneous ascent of testes from a scrotal to a suprascrotal position may be observed with time, due to either true or apparent testicular ascent, with possible adverse effects on germ cell development and fertility potential. Patients with significant testicular retractility appear to be at highest risk for acquired cryptorchidism, and should be followed closely at yearly intervals until puberty.

Evidence of a novel quantitative-trait locus for obesity on chromosome 4p in Mexican Americans

Although several genomewide scans have identified quantitative-trait loci influencing several obesity-related traits in humans, genes influencing normal variation in obesity phenotypes have not yet been identified. We therefore performed a genome scan of body mass index (BMI) on Mexican Americans, a population prone to obesity and diabetes, using a variance-components linkage analysis to identify loci that influence BMI. We used phenotypic data from 430 individuals (26% diabetics, 59% females, mean age +/- SD = 43 +/- 17 years, mean BMI +/- SD = 30.0 +/- 6.7, mean leptin (ng/ml) +/- SD = 22.1 +/- 17.1) distributed across 27 low-income Mexican American pedigrees who participated in the San Antonio Family Diabetes Study (SAFDS) for whom a 10-15-cM map is available. In this genomewide search, after accounting for the covariate effects of age, sex, diabetes, and leptin, we identified a genetic region exhibiting the most highly significant evidence for linkage (LOD 4.5) with BMI on chromosome 4p (4p15.1) at 42 cM, near marker D4S2912. This linkage result has been confirmed in an independent linkage study of severe obesity in Utah pedigrees. Two strong positional candidates, the human peroxisome proliferator-activated receptor gamma coactivator 1 (PPARGC1) and cholecystokinin A receptor (CCKAR) with major roles in the development of obesity, are located in this region. In conclusion, we identified a major genetic locus influencing BMI on chromosome 4p in Mexican Americans.

Chronic sympathetic activation: consequence and cause of age-associated obesity?

Primary aging in adult humans is associated with a progressive, tonic activation of the peripheral sympathetic nervous system (SNS). The purpose of this SNS activation and its physiological impact are, however, unknown. We hypothesize that the chronic stimulation of the SNS with aging is driven in part by a progressive accumulation of body fat. This "error" is sensed by the central nervous system via increases in adiposity-sensitive humoral signals (e.g., leptin, insulin) that cross the blood-brain barrier, activate subcortical areas involved in the regulation of energy balance (e.g., ventromedial hypothalamus), and stimulate SNS outflow to peripheral tissues. The SNS activation is intended to increase beta-adrenergic thermogenesis in order to expend excess energy as heat rather than by storage of fat. Recent evidence, however, indicates that these adjustments are not effective in augmenting energy expenditure with aging. Indeed, older sedentary adults demonstrate reduced, not increased, beta-adrenergic stimulation of metabolic rate because of reduced tissue responsiveness, presumably mediated by SNS-induced impairment of beta-adrenergic signaling. As a result, age-associated SNS activation, initiated as a consequence of accumulating adiposity with the intent of preventing further fat storage, ironically, may in time evolve into a potential mechanism contributing to the development of obesity with aging.

Leptin reduces the development of the initial precancerous lesions induced by azoxymethane in the rat colonic mucosa

BACKGROUND & AIMS

Recent studies suggest that leptin, a hormone involved in food intake regulation, released into the circulation and gastrointestinal juice, may be a growth factor for intestine and may be involved in carcinogenesis; however, data are contradictory. This study investigates in rat colonic mucosa (1) the effects of hyperleptinemia on epithelial cell proliferation and development of aberrant crypts, earliest preneoplastic lesions, and (2) whether luminal leptin affects cell proliferation.

METHODS

Leptin (1 mg/kg/d) or vehicle was administered systemically by miniosmotic pump in Fischer 344 rats either for 7 days (BrdU-labeling indices study) or 23 days (azoxymethane-induced colonic lesions study). The effects of injections or continuous infusion of leptin into the colon were also studied.

RESULTS

In systemic leptin-treated rats, plasma leptin levels were 4- to 5-fold increased (P < 0.008 to P < 0.001); labeling indices were higher in proximal colon than in pair-fed control rats (P = 0.006) but unaffected in distal colon. Unexpectedly, in azoxymethane-treated rats, leptin significantly inhibited aberrant crypt foci formation in the middle and distal colon compared with controls (P = 0.006). Under these conditions, plasma insulin levels were reduced by 41%-58%, but gastrin levels were unchanged. In controls, luminal immunoreactive leptin reached the colon. A 3.6-fold increase in intraluminal leptin had no effect on epithelial cell proliferation.

CONCLUSIONS

This study provides the first evidence that leptin reduces the development of chemically induced precancerous lesions in colon, perhaps through decreased insulinemia, and thus does not support an important role for leptin in carcinogenesis promotion. Moreover, the study indicates that leptin is not a potent growth factor for normal intestine.

Comparative analysis of plasma leptin levels in both genders of patients with essential hypertension and healthy subjects

While pathogenesis of hypertension is not clearly deciphered yet, increase in body weight, most of the time, is associated with hypertension. There are reports indicating that leptin, product of the Ob gene mainly synthesized in adipocytes, may have role(s) in hypertension, but contribution of the gender is rather contradictive. In the present study, plasma leptin levels in patients of both genders with hypertension and normotensive controls were measured and the relationship between plasma leptin levels and BMI were evaluated in both sexes. Total of 62 patients (31 M/31 F) diagnosed with essential hypertension who were not under any antihypertensive medication were admitted into the study. The control group was composed of 56 (25 M/31 F) age-, BMI- and sex-matched healthy normotensive volunteers. Plasma leptin levels were determined by a commercial ELISA kit. Plasma leptin and leptin/BMI levels (Mean +/- SEM) of women (n:62) were significantly higher than men (n:56) (20.10 +/- 1.47 ng/ml versus 4.72 +/- 0.50 ng/ml; p < 0.0001). Plasma leptin and leptin/BMI levels of patients of both genders with hypertension were significantly higher than in normotensive subjects (p < 0.05). Leptin and leptin/BMI levels in obese hypertensives were higher than obese normotensives (p < 0.05). Obese hypertensive women had higher leptin and leptin/BMI levels than obese normotensive women (p < 0.05). In conclusion, these results support the hypothesis that a possible link exists between leptin and hypertension. Further studies are needed to clarify how increased levels of leptin affects the pathophysiology of hypertension.

Genetic factors and insulin secretion: gene variants in the IGF genes

IGFs are important regulators of pancreatic beta-cell development, growth, and maintenance. Mutations in the IGF genes have been found to be associated with type 2 diabetes, myocardial infarction, birth weight, and obesity. These associations could result from changes in insulin secretion. We have analyzed glucose-stimulated insulin secretion using hyperglycemic clamps in carriers of a CA repeat in the IGF-I promoter and an ApaI polymorphism in the IGF-II gene. Normal and impaired glucose-tolerant subjects (n = 237) were independently recruited from three different populations in the Netherlands and Germany to allow independent replication of associations. Both first- and second-phase insulin secretion were not significantly different between the various IGF-I or IGF-II genotypes. Remarkably, noncarriers of the IGF-I CA repeat allele had both a reduced insulin sensitivity index (ISI) and disposition index (DI), suggesting an altered balance between insulin secretion and insulin action. Other diabetes-related parameters were not significantly different for both the IGF-I and IGF-II gene variant. We conclude that gene variants in the IGF-I and IGF-II genes are not associated with detectable variations in glucose-stimulated insulin secretion in these three independent populations. Further studies are needed to examine the exact contributions of the IGF-I CA repeat alleles to variations in ISI and DI.

Cardiovascular risk associated with the metabolic syndrome

The term metabolic syndrome refers to a clustering of cardiovascular risk factors, most of which also share insulin resistance as an additional feature. Scientific effort has concentrated on understanding why these diverse cardiovascular risks co-occur in individuals and in determining the presumed common environmental or genetic factors that might underpin this. Clinically important developments include publication of standard definitions of the metabolic syndrome and recommendations for the use of type 2 diabetes and the presence of the metabolic syndrome as critical "risk stratifiers" in cardiovascular disease prevention. The remarkable recent secular increases in the prevalence of type 2 diabetes and obesity in many populations mean that the importance of the metabolic syndrome as a determinant of cardiovascular disease is likely to increase until these trends can be reversed.

Isomers of conjugated linoleic acid differ in their effects on angiogenesis and survival of mouse mammary adipose vasculature

Dietary conjugated linoleic acid (CLA) is a cancer chemopreventive agent that has been shown to inhibit angiogenesis in vivo and in vitro, and to decrease vascular endothelial growth factor (VEGF) and Flk-1 concentrations in the mouse mammary gland. To determine which isomer mediates the antiangiogenic effects of CLA in vivo, the effects of diets supplemented with 5 or 10 g/kg c9,t11- or t10,c12-CLA isomers were compared in CD2F1Cr mice. Both isomers inhibited functional vascularization of a matrigel pellet in vivo and decreased serum VEGF concentrations; the t10,c12 isomer also decreased the proangiogenic hormone leptin (P < 0.05). Additionally, the t10,c12 isomer, but not c9,t11-CLA, rapidly induced apoptosis of the white and brown adipocytes as well as the preexisting supporting vasculature of the mammary fat pad (P < 0.05). Independent of this isomer-specific adipose apoptotic effect, both isomers induced a rapid and reversible decrease in the diameter of the unilocular adipocytes (P < 0.05). The ability of both CLA isomers to inhibit angiogenesis in vivo may contribute to their ability to inhibit carcinogenesis. Moreover, we propose that each CLA isomer uniquely modifies the mammary stromal "soil" in a manner that is useful for chemoprevention of breast cancer.

Effects of acute bouts of running and swimming exercise on PGC-1alpha protein expression in rat epitrochlearis and soleus muscle

The purpose of this study was to elucidate the mechanisms underlying low-intensity exercise-induced peroxisome proliferator-activated receptor-gamma coactivator-1alpha (PGC-1alpha) protein expression in rat skeletal muscles. Rats (5-6 wk old) swam without a load and ran on the treadmill at a speed of 13 m/min, respectively, in two 3-h sessions separated by 45 min of rest. PGC-1alpha content in epitrochlearis muscle (EPI) was increased by 75 and 95%, immediately and 6 h after swimming, respectively, with no increase in PGC-1alpha content in the soleus (SOL). After running, PGC-1alpha content in EPI was unchanged, whereas a 107% increase in PGC-1alpha content was observed in SOL 6 h after running. Furthermore, in EPI and SOL as well as other muscles (triceps, plantaris, red and white gastrocnemius), PGC-1alpha expression was enhanced concomitant with reduced glycogen postexercise, suggesting that expression of PGC-1alpha occurs in skeletal muscle recruited during exercise. PGC-1alpha content in EPI was increased after 18-h in vitro incubation with 0.5 mM 5-aminoimidazole-4-carboxamide ribonucleoside (AICAR) and 4 mM caffeine. However, AICAR incubation did not affect PGC-1alpha content in the SOL, whereas caffeine incubation increased it. These results suggest that exercise-induced PGC-1alpha expression in skeletal muscle may be mediated by at least two exercise-induced signaling factors: AMPK activation and Ca2+ elevation. The number of factors involved (both AMPK and Ca2+, or Ca2+ only) in exercise-induced PGC-1alpha expression may differ among muscles.

Mitochondrial biogenesis as a cellular signaling framework

The identification, more than 50 years ago, of mitochondria as the site of oxidative energy metabolism has prompted studies that have unraveled the complexity of the numerous biosynthetic and degradative reactions, fundamental to cell function, carried out by these organelles. These activities depend on a distinctive mitochondrial structure, with different enzymes and reactions localized in discrete membranes and aqueous compartments. The characteristic mitochondrial structural organization is the product of both synthesis of macromolecules within the mitochondria and the import of proteins and lipids synthesized outside the organelle. Synthesis and import of mitochondrial components are required for mitochondrial proliferation, but rather than producing new organelles, these processes may facilitate the growth of pre-existing mitochondria. Recent evidence indicates that these events are regulated in a complex way by several agonists and environmental conditions, through activation of specific transcription factors and signaling pathways. Some of these are now being elucidated. Generation of nitric oxide (NO) appears to be a novel player in this scenario, possibly acting as a unifying molecular switch to trigger the whole mitochondriogenic process.

[Weight loss in a patient with morbid obesity under treatment with oleoyl-estrone]

BACKGROUND AND OBJECTIVE

Oleoyl-estrone administration in rats results in loss of body fat and sparing protein via decreasing food intake and maintaining energy expenditure. Oleoyl-estrone also decreases insulin resistance and hyperlipidemia and has no direct estrogenic effects. Our objective was to determine whether oral oleoyl-estrone was effective in the treatment of morbid obesity in a voluntary patient.

PATIENT AND METHOD

Oleoyl-estrone (150-300 mol/d) was given to a morbid obese man (BMI: 51.9) over 10 consecutive 21-day trial periods of oral drug intake followed by at least two months of recovery. This treatment was given without additional dietary restrictions. Plasma metabolites, hormones and enzymes were measured before treatment, during active administration and at recovery periods.

RESULTS

Oleoyl-estrone decreased the body weight (38.5 kg in 27 months, final BMI: 40.5). No rebound trends were observed. No significant changes in blood parameters, plasma metabolites, hormones or enzymes were observed as a consequence of the treatment.

CONCLUSIONS

Oleoyl-estrone decreased body weight in this subject without affecting metabolites or hormones, similarly to its effects in animal models. This means that oleoyl-estrone could have a marked potential as an anti-obesity drug.

Absence of hormone-sensitive lipase inhibits obesity and adipogenesis in Lep ob/ob mice

Hormone-sensitive lipase (HSL) plays a crucial role in the hydrolysis of triacylglycerol and cholesteryl ester in various tissues including adipose tissues. To explore the role of HSL in the metabolism of fat and carbohydrate, we have generated mice lacking both leptin and HSL (Lep(ob/ob)/HSL(-/-)) by cross-breeding HSL(-/-) mice with genetically obese Lep(ob/ob) mice. Unexpectedly, Lep(ob/ob)/HSL(-/-) mice ate less food, gained less weight, and had lower adiposity than Lep(ob/ob)/HSL(+/+) mice. Lep(ob/ob)/HSL(-/-) mice had massive accumulation of preadipocytes in white adipose tissues with increased expression of preadipocyte-specific genes (CAAT/enhancer-binding protein beta and adipose differentiation-related protein) and decreased expression of genes characteristic of mature adipocytes (CCAAT/enhancer-binding protein alpha, peroxisome proliferator activator receptor gamma, and adipocyte determination and differentiation factor 1/sterol regulatory element-binding protein-1). Consistent with the reduced food intake, hypothalamic expression of neuropeptide Y and agouti-related peptide was decreased. Since HSL is expressed in hypothalamus, we speculate that defective generation of free fatty acids in the hypothalamus due to the absence of HSL mediates the altered expression of these orexigenic neuropeptides. Thus, deficiency of both leptin and HSL has unmasked novel roles of HSL in adipogenesis as well as in feeding behavior.

Suppression of mitochondrial respiration through recruitment of p160 myb binding protein to PGC-1alpha: modulation by p38 MAPK

The transcriptional coactivator PPAR gamma coactivator 1 alpha (PGC-1alpha) is a key regulator of metabolic processes such as mitochondrial biogenesis and respiration in muscle and gluconeogenesis in liver. Reduced levels of PGC-1alpha in humans have been associated with type II diabetes. PGC-1alpha contains a negative regulatory domain that attenuates its transcriptional activity. This negative regulation is removed by phosphorylation of PGC-1alpha by p38 MAPK, an important kinase downstream of cytokine signaling in muscle and beta-adrenergic signaling in brown fat. We describe here the identification of p160 myb binding protein (p160MBP) as a repressor of PGC-1alpha. The binding and repression of PGC-1alpha by p160MBP is disrupted by p38 MAPK phosphorylation of PGC-1alpha. Adenoviral expression of p160MBP in myoblasts strongly reduces PGC-1alpha's ability to stimulate mitochondrial respiration and the expression of the genes of the electron transport system. This repression does not require removal of PGC-1alpha from chromatin, suggesting that p160MBP is or recruits a direct transcriptional suppressor. Overall, these data indicate that p160MBP is a powerful negative regulator of PGC-1alpha function and provide a molecular mechanism for the activation of PGC-1alpha by p38 MAPK. The discovery of p160MBP as a PGC-1alpha regulator has important implications for the understanding of energy balance and diabetes.

Regulation of mitochondrial biogenesis in muscle by endurance exercise

Behavioural and hereditary conditions are known to decrease mitochondrial volume and function within skeletal muscle. This reduces endurance performance, and is manifest both at high- and low-intensity levels of exertion. A programme of regular endurance exercise, undertaken over a number of weeks, produces significant adaptations within skeletal muscle such that noticeable improvements in oxidative capacity are evident, and the related decline in endurance performance can be attenuated. Notwithstanding the important implications that this has for the highly trained endurance athlete, an improvement in mitochondrial volume and function through regular physical activity also endows the previously sedentary and/or aging population with an improved quality of life, and a greater functional independence. An understanding of the molecular and cellular mechanisms that govern the increases in mitochondrial volume with repeated bouts of exercise can provide insights into possible therapeutic interventions to care for those with mitochondrially-based diseases, and those unable to withstand regular physical activity. This review focuses on the recent developments in the molecular aspects of mitochondrial biogenesis in chronically exercising muscle. Specifically, we discuss the initial signalling events triggered by muscle contraction, the activation of transcription factors involved in both nuclear and mitochondrial DNA transcription, as well as the post-translational import mechanisms required for mitochondrial biogenesis. We consider the importance and relevance of chronic physical activity in the induction of mitochondrial biogenesis, with particular emphasis on how an endurance training programme could positively affect the age-related decline in mitochondrial content and delay the progression of age- and physical inactivity-related diseases.

Epithelial-mesenchymal transition and its implications for fibrosis

Epithelial to mesenchymal transition (EMT) is a central mechanism for diversifying the cells found in complex tissues. This dynamic process helps organize the formation of the body plan, and while EMT is well studied in the context of embryonic development, it also plays a role in the genesis of fibroblasts during organ fibrosis in adult tissues. Emerging evidence from studies of renal fibrosis suggests that more than a third of all disease-related fibroblasts originate from tubular epithelia at the site of injury. This review highlights recent advances in the process of EMT signaling in health and disease and how it may be attenuated or reversed by selective cytokines and growth factors.

Epithelial-mesenchymal transition and its implications for fibrosis

Epithelial to mesenchymal transition (EMT) is a central mechanism for diversifying the cells found in complex tissues. This dynamic process helps organize the formation of the body plan, and while EMT is well studied in the context of embryonic development, it also plays a role in the genesis of fibroblasts during organ fibrosis in adult tissues. Emerging evidence from studies of renal fibrosis suggests that more than a third of all disease-related fibroblasts originate from tubular epithelia at the site of injury. This review highlights recent advances in the process of EMT signaling in health and disease and how it may be attenuated or reversed by selective cytokines and growth factors.

Differential effects of the C1431T and Pro12Ala PPARgamma gene variants on plasma lipids and diabetes risk in an Asian population

We investigated the association of C1431T and Pro12Ala polymorphisms at the peroxisome proliferator-activated receptor gamma (PPARgamma) locus with plasma lipids and insulin resistance-related variables, according to diabetes status, in a large and representative Asian population from Singapore consisting of 2,730 Chinese, 740 Malays, and 568 Indians. Moreover, we estimated the diabetes risk and examined gene-nutrient interactions between these variants and the ratio of polyunsaturated fatty acid to saturated fat (SFA) in determining body mass index (BMI) and fasting insulin. We found differential effects of these gene variants. The Pro12Ala polymorphism was more associated with plasma lipids and fasting glucose concentrations, whereas the C1431T polymorphism was related to the risk of diabetes. Carriers of the 12Ala allele had higher HDL-cholesterol than did Pro12Pro homozygotes (P < 0.05), and the effect of the 12Ala allele on fasting glucose was modified by diabetes status (P < 0.001). After controlling for confounders, carriers of the T allele had decreased risk of diabetes compared with CC homozygotes [odds ratio (OR) 0.73, 95% confidence interval (CI) 0.58-0.93; P = 0.011]; this effect was stronger in Indians (OR 0.38, 95% CI 0.15-0.92; P = 0.032). For both polymorphisms, normal subjects carrying the less prevalent allele had higher BMI (P < 0.05). The PUFA/SFA did not modify the effect of these polymorphisms on BMI or insulin.

Peroxisome proliferator-activated receptor-gamma coactivator 1alpha (PGC-1alpha) regulates triglyceride metabolism by activation of the nuclear receptor FXR

Peroxisome proliferator-activated receptor-gamma coactivator 1alpha (PGC-1alpha) has been shown to regulate adaptive thermogenesis and glucose metabolism. Here we show that PGC-1alpha regulates triglyceride metabolism through both farnesoid X receptor (FXR)-dependent and -independent pathways. PGC-1alpha increases FXR activity through two pathways: (1) it increases FXR mRNA levels by coactivation of PPARgamma and HNF4alpha to enhance FXR gene transcription; and (2) it interacts with the DNA-binding domain of FXR to enhance the transcription of FXR target genes. Ectopic expression of PGC-1alpha in murine primary hepatocytes reduces triglyceride secretion by a process that is dependent on the presence of FXR. Consistent with these in vitro studies, we demonstrate that fasting induces hepatic expression of PGC-1alpha and FXR and results in decreased plasma triglyceride levels in wild-type but not in FXR-null mice. Our data suggest that PGC-1alpha plays an important physiological role in maintaining energy homeostasis during fasting by decreasing triglyceride production/secretion while it increases fatty acid beta-oxidation to meet energy needs.

Cardiac-specific induction of the transcriptional coactivator peroxisome proliferator-activated receptor gamma coactivator-1alpha promotes mitochondrial biogenesis and reversible cardiomyopathy in a developmental stage-dependent manner

Recent evidence has identified the peroxisome proliferator-activated receptor gamma coactivator-1alpha (PGC-1alpha) as a regulator of cardiac energy metabolism and mitochondrial biogenesis. We describe the development of a transgenic system that permits inducible, cardiac-specific overexpression of PGC-1alpha. Expression of the PGC-1alpha transgene in this system (tet-on PGC-1alpha) is cardiac-specific in the presence of doxycycline (dox) and is not leaky in the absence of dox. Overexpression of PGC-1alpha in tet-on PGC-1alpha mice during the neonatal stages leads to a dramatic increase in cardiac mitochondrial number and size coincident with upregulation of gene markers associated with mitochondrial biogenesis. In contrast, overexpression of PGC-1alpha in the hearts of adult mice leads to a modest increase in mitochondrial number, derangements of mitochondrial ultrastructure, and development of cardiomyopathy. The cardiomyopathy in adult tet-on PGC-1alpha mice is characterized by an increase in ventricular mass and chamber dilatation. Surprisingly, removal of dox and cessation of PGC-1alpha overexpression in adult mice results in complete reversal of cardiac dysfunction within 4 weeks. These results indicate that PGC-1alpha drives mitochondrial biogenesis in a developmental stage-dependent manner permissive during the neonatal period. This unique murine model should prove useful for the study of the molecular regulatory programs governing mitochondrial biogenesis and characterization of the relationship between mitochondrial dysfunction and cardiomyopathy and as a general model of inducible, reversible cardiomyopathy.

Upregulation of insulin receptor substrate-2 in pancreatic beta cells prevents diabetes

The insulin receptor substrate-2 (Irs2) branch of the insulin/IGF signaling system coordinates peripheral insulin action and pancreatic beta cell function, so mice lacking Irs2 display similarities to humans with type 2 diabetes. Here we show that beta cell-specific expression of Irs2 at a low or a high level delivered a graded physiologic response that promoted beta cell growth, survival, and insulin secretion that prevented diabetes in Irs2-/- mice, obese mice, and streptozotocin-treated mice; and that upon transplantation, the transgenic islets cured diabetes more effectively than WT islets. Thus, pharmacological approaches that promote Irs2 expression in beta cells, especially specific cAMP agonists, could be rational treatments for beta cell failure and diabetes.

Can endogenous gaseous messengers control mitochondrial biogenesis in mammalian cells?

Mitochondria have been identified as the site of oxidative energy metabolism and of numerous biosynthetic and degradative reactions, which depend on a distinctive mitochondrial structure, with different enzymes and reactions localised in discrete membranes and aqueous compartments. Synthesis and import of mitochondrial components are required for mitochondrial proliferation, but rather than producing new organelles, these processes may facilitate the growth of preexisting mitochondria. Recent evidence indicates that these events are regulated in a complex way by several agonists and environmental conditions, through activation of specific transcription factors and signaling pathways. Some of these are now being elucidated. Generation of nitric oxide (NO) appears to be a novel player in this scenario, possibly acting as a unifying molecular switch to trigger the whole process of the mitochondrial biogenesis.

PGC-1alpha mRNA expression is influenced by metabolic perturbation in exercising human skeletal muscle

Endurance training leads to many adaptational changes in several tissues. In skeletal muscle, fatty acid usage is enhanced and mitochondrial content is increased. The exact molecular mechanisms regulating these functional and structural changes remain to be elucidated. Contractile activity-induced metabolic perturbation has repeatedly been shown to be important for the induction of mitochondrial biogenesis. Recent reports suggest that the peroxisome proliferator-activated receptor gamma coactivator 1alpha (PGC-1alpha)/mitochondrial transcription factor A (Tfam) pathway is involved in exercise-induced mitochondrial biogenesis. In the present study, nine healthy men performed two 45-min bouts of one-legged knee extension exercise: one bout with restricted blood flow, and the other with nonrestricted blood flow to the working muscle. Muscle biopsies were obtained from the vastus lateralis muscle before exercise and at 0, 30, 120, and 360 min after the exercise bout. Biopsies were analyzed for whole muscle, as well as fiber-type specific mRNA expression of myocyte-enriched calcineurin interacting protein (MCIP)-1, PGC-1alpha, and downstream mitochondrial transcription factors. A novel finding was that, in human skeletal muscle, PGC-1alpha mRNA increased more after exercise with restricted blood flow than in the nonrestricted condition. No changes were observed for the mRNA of NRF-1, Tfam, mitochondrial transcription factor B1, and mitochondrial transcription factor B2. Muscle fiber type I and type II did not differ in the basal PGC-1alpha mRNA levels or in the expression increase after ischemic training. Another novel finding was that there was no difference between the restricted and nonrestricted exercise conditions in the increase of MCIP-1 mRNA, a marker for calcineurin activation. This suggests that calcineurin may be activated by exercise in humans and does not exclude that calcineurin could play a role in PGC-1 transcription activation in human skeletal muscle.

Reduced beta-cell mass and altered glucose sensing impair insulin-secretory function in betaIRKO mice

Pancreatic beta-cell-restricted knockout of the insulin receptor results in hyperglycemia due to impaired insulin secretion, suggesting that this cell is an important target of insulin action. The present studies were undertaken in beta-cell insulin receptor knockout (betaIRKO) mice to define the mechanisms underlying the defect in insulin secretion. On the basis of responses to intraperitoneal glucose, approximately 7-mo-old betaIRKO mice were either diabetic (25%) or normally glucose tolerant (75%). Total insulin content was profoundly reduced in pancreata of mutant mice compared with controls. Both groups also exhibited reduced beta-cell mass and islet number. However, insulin mRNA and protein were similar in islets of diabetic and normoglycemic betaIRKO mice compared with controls. Insulin secretion in response to insulin secretagogues from the isolated perfused pancreas was markedly reduced in the diabetic betaIRKOs and to a lesser degree in the nondiabetic betaIRKO group. Pancreatic islets of nondiabetic betaIRKO animals also exhibited defects in glyceraldehyde- and KCl-stimulated insulin release that were milder than in the diabetic animals. Gene expression analysis of islets revealed a modest reduction of GLUT2 and glucokinase gene expression in both the nondiabetic and diabetic mutants. Taken together, these data indicate that loss of functional receptors for insulin in beta-cells leads primarily to profound defects in postnatal beta-cell growth. In addition, altered glucose sensing may also contribute to defective insulin secretion in mutant animals that develop diabetes.

Tumor-host interactions

A number of malignant tumors interact with the host to cause a syndrome of cachexia, characterized by extensive loss of adipose tissue and skeletal muscle mass, but with preservation of proteins in visceral tissues. Although anorexia is frequently present, the body composition changes in cancer cachexia cannot be explained by nutritional deprivation alone. Loss of skeletal muscle mass is a result of depression in protein synthesis and an increase in protein degradation. The main degradative pathway that has been found to have increased expression and activity in the skeletal muscle of cachectic patients is the ubiquitin-proteasome proteolytic pathway. Cachexia-inducing tumors produce catabolic factors such as proteolysis-inducing factor (PIF), a 24 kDa sulfated glycoprotein, which inhibit protein synthesis and stimulate degradation of intracellular proteins in skeletal muscle by inducing an increased expression of regulatory components of the ubiquitin-proteasome proteolytic pathway. While the oligosaccharide chains in PIF are required to initiate protein degradation the central polypeptide core may act as a growth and survival factor. Only cachexia-inducing tumors are capable of elaborating fully glycosylated PIF, and the selectivity of production possibly rests with the acquisition of the necessary glycosylating enzymes, rather than expressing the gene for the polypeptide core. Loss of adipose tissue is probably the result of an increase in catabolism rather than a defect in anabolism. A lipid mobilizing factor (LMF), identical with the plasma protein Zn-alpha2-glycoprotein (ZAG) is found in the urine of cachectic cancer patients and is produced by tumors causing a decrease in carcass lipid. LMF causes triglyceride hydrolysis in adipose tissue through a cyclic AMP-mediated process by interaction with a beta3-adrenoreceptor. Thus, by producing circulating factors certain malignant tumors are able to interfere with host metabolism even without metastasis to that particular site.

Modulatory effect of leptin on nitric oxide production and lipid metabolism in term placental tissues from control and streptozotocin-induced diabetic rats

Leptin production by placental tissues contributes to its circulating levels and functions. The diabetic pathology induces alterations in leptin levels. In the present study, leptin levels were evaluated in placental tissue from control and neonatal streptozotocin-induced (n-STZ) diabetic rats during late gestation. The effects of leptin levels on the generation of nitric oxide (NO), prostaglandin (PG) E2 production and lipid metabolism were examined. Leptin levels were diminished in placentas from n-STZ diabetic rats compared with controls (P < 0.01). These differences were also evident when leptin was evaluated immunohistochemically. Addition of leptin (1 nm) in vitro enhanced NO production in control (66%) and diabetic placentas (134%) by stimulating NO synthase activity (by 38% and 54%, respectively). The addition of leptin increased PGE2 production in placentas from control (173%) and diabetic rats (83%) and produced a 50% decrease in placental lipid levels (phospholipids, triacylglycerides, cholesterol and cholesteryl ester) without involving a reduction in de novo lipid synthesis. These data indicate that leptin enhances the production of placental NO and PGE2, vasoactive agents that modify placental blood flow, and that leptin stimulates placental lipid metabolism, probably generating more lipids for transfer to the fetus. In the diabetic rat, placental leptin was reduced, probably as a response to the maternal environment to locally regulate the transfer of nutrients to the developing fetus.

Mosaic analysis of insulin receptor function

Insulin promotes both metabolism and growth. However, it is unclear whether insulin-dependent growth is merely a result of its metabolic actions. Targeted ablation of insulin receptor (Insr) has not clarified this issue, because of early postnatal lethality. To examine this question, we generated mice with variable cellular mosaicism for null Insr alleles. Insr ablation in approximately 80% of cells caused extreme growth retardation, lipoatrophy, and hypoglycemia, a clinical constellation that resembles the human syndrome of leprechaunism. Insr ablation in 98% of cells, while resulting in similar growth retardation and lipoatrophy, caused diabetes without beta-cell hyperplasia. The growth retardation was associated with a greater than 60-fold increase in the expression of hepatic insulin-like growth factor binding protein-1. These findings indicate that insulin regulates growth independently of metabolism and that the number of insulin receptors is an important determinant of the specificity of insulin action.

β-Phenylethylamines and the isoquinoline alkaloids

This review covers beta-phenylethylamines and isoquinoline alkaloids derived from them, including further products of oxidation. condensation with formaldehyde and rearrangement, some of which do not contain an isoquinoline system, together with naphthylisoquinoline alkaloids, which have a different biogenetic origin. The occurrence of the alkaloids, with the structures of new bases, together with their reactions, syntheses and biological activities are reported. The literature from July 2002 to June 2003 is reviewed, with 568 references cited.