The metabolic syndrome: an emerging risk state for cardiovascular disease

Fat-On-A-Chip Models for Research and Discovery in Obesity and Its Metabolic Comorbidities

The obesity epidemic and its associated comorbidities present a looming challenge to health care delivery throughout the world. Obesity is characterized as a sterile inflammatory process within adipose tissues leading to dysregulated secretion of bioactive adipokines such as adiponectin and leptin, as well as systemic metabolic dysfunction. The majority of current obesity research has focused primarily on preclinical animal models in vivo and two-dimensional cell culture models in vitro. Neither of these generalized approaches is optimal due to interspecies variability, insufficient accuracy with respect to predicting human outcomes, and failure to recapitulate the three-dimensional (3D) microenvironment. Consequently, there is a growing demand and need for more sophisticated microphysiological systems to reproduce more physiologically accurate human white and brown/beige adipose depots. To address this research need, human and murine cell lines and primary cultures are being combined with bioscaffolds to create functional 3D environments that are suitable for metabolically active adipose organoids in both static and perfusion bioreactor cultures. The development of these technologies will have considerable impact on the future pace of discovery for novel small molecules and biologics designed to prevent and treat metabolic syndrome and obesity in humans. Furthermore, when these adipose tissue models are integrated with other organ systems they will have applicability to obesity-related disorders such as diabetes, nonalcoholic fatty liver disease, and osteoarthritis. Impact statement The current review article summarizes the advances made within the organ-onchip field, as it pertains to adipose tissue models of obesity and obesity-related syndromes, such as diabetes, non-alcoholic fatty liver disease, and osteoarthritis. As humanized 3D adipose-derived constructs become more accessible to the research community, it is anticipated that they will accelerate and enhance the drug discovery pipeline for obesity, diabetes, and metabolic diseases by reducing the preclinical evaluation process and improving predictive accuracy. Such developments, applications, and usages of existing technologies can change the paradigm of personalized medicine and create substantial progress in our approach to modern medicine.

Postnatal overnutrition affects metabolic and vascular function reflected by physiological and histological changes in the aorta of adult Wistar rats

Rigorous nutritional care during early life leads to healthy adulthood. Cardiovascular and metabolic disorders, the most prevalent clinical challenges worldwide, are epidemiologically linked to poor nutritional habits throughout life. We aimed to understand whether postnatal overnutrition (PO) initiated during lactation affects metabolic markers and vascular function later in life. To test this hypothetical effect, we studied a PO Wistar rat model based on adjusting litter size at the third day of age to three pups and eight for the control group (C). Systemic parameters such as body weight and food intake were significantly increased in adult rats, measured up to 36 weeks. Moreover, fat mass, triglycerides, insulin and systolic blood pressure were all significantly increased in the PO group. Furthermore, we assessed whether these alterations would affect morphological and functional parameters in isolated vessels. Consistent with systemic alterations of the vasculature, contraction of thoracic aortic rings, determined by dose-response curves to norepinephrine (NE), was significantly reduced in PO rats. Histological stains revealed that the relative area of collagen was higher and the elastic fiber density was lower in the distal rings of PO rats. Altogether, our results highlight the critical importance of having a healthy neonatal nutrition to prevent harmful metabolic and vascular alterations during adulthood.

The prevalence and risk factors of visual impairment among the elderly in Eastern Taiwan

Visual impairment is associated with disability and poor quality of life. This study aimed to investigate the prevalence and associated risk factors of visual impairment among the suburban elderly in Eastern Taiwan. The cross-sectional research was conducted from April 2012 to August 2012. The ocular condition examination took place in suburban areas of Hualien County. Medical records from local infirmaries and questionnaires were utilized to collect demographic data and systemic disease status. Logistic regression models were used for the simultaneous analysis of the association between the prevalence of visual impairment and risk factors. Six hundred and eighty-one residents participated in this project. The mean age of the participants was 71.4±7.3 years. The prevalence of vision impairment (better eye<6/18) was 11.0%. Refractive error and cataract were the main causes of vision impairment. Logistic regression analysis showed that people aged 65-75 years had a 3.8 times higher risk of developing visual impairment (p=0.021), while the odds ratio of people aged > 75 years was 10.0 (p<0.001). In addition, patients with diabetic retinopathy had a 3.7 times higher risk of developing visual impairment (p=0.002), while the odds ratio of refractive error was 0.36 (p<0.001). The prevalence of visual impairment was relatively high compared with previous studies. Diabetic retinopathy was an important risk factor of visual impairment; by contrast, refractive error was beneficial to resist visual impairment. Therefore, regular screening of ocular condition and early intervention might aid in the prevention of avoidable vision loss.

Association of insulin resistance with adipocytokine levels in patients with metabolic syndrome

Metabolic syndrome (MetS) results from the derangement of adipocyte physiology and carbohydrate metabolism. Obesity and insulin resistance (IR) are integral features of MetS. The adipokine alterations in MetS often correlate with IR and body fat content. High adipose tissue content is associated with a decreased production of adiponectin and excessive production of tumour necrosis factor-α (TNF-α) and interleukin-6 (IL-6), all of which induce IR. The present study evaluated the adipokine alterations in MetS and their association with IR. The findings of the current study indicate that MetS is associated with significant decrease in adiponectin and increase in TNF-α and IL-6. The present study also found that the adipocyte derived inflammatory adipokines, TNF-α and IL-6 correlate with IR while the anti-inflammatory adipokines, adiponectin does not correlate with the degree and severity of IR.

Variations over four decades in body mass index trajectories prior to diagnosis of diabetes mellitus: The Manitoba Follow-up Study, 1948-2007

OBJECTIVE

The aim of the study was to explore the variations in body mass index (BMI) trajectories during the 20 years before diagnosis of type 2 diabetes mellitus (T2DM) over four decades between 1968 and 2007.

METHODS

Longitudinal measurements of BMI from 437 men, all with a diagnosis of T2DM, were used in the analysis. A mixed method approach was used to fit individual patterns of BMI measurements during the 20 years before diagnosis of T2DM.

RESULTS

The mean BMI at diagnosis was 26.7 kg/m2 (95% confidence interval, 26.4-27.1). Compared with men whose condition was diagnosed between 1968 and 1977, for men with a diagnosis between 1978 and 2007 the mean BMI about 10 years before diagnosis significantly increased by 0.92 to 1.54 BMI units. Decades also varied in how long there was a persistent increase in BMI during the 20 years before diagnosis. The rate of change in mean BMI among men whose T2DM was diagnosed in the most recent two decades increased by 8.8% to 22.6% during the 10-year interval before diagnosis, but there was no significant difference among men given a diagnosis between 1978 and 1987. The quadratic trend of BMI prior to diagnosis was also significantly affected by age at diagnosis.

CONCLUSION

The BMI trajectories during the 20 years leading up to T2DM varied by decade of diagnosis. The increase in BMI persisted for much longer among relatively younger men with a diagnosis in more recent decades. Strategies to prevent T2DM, informed by the pattern of BMI trajectories, should be customized to consider a potential age-period effect.

Metabolic syndrome: Risk factors among adults in Kingdom of Saudi Arabia

Background:

Metabolic syndrome (MetS) is a cluster of established cardiovascular risk factors that collectively increase predisposition to major chronic diseases, including heart diseases and diabetes mellitus. Citizens of developing countries such as Saudi Arabia are at risk for MetS as a result of industrialization and accessibility to fast foods. In this epidemiologic study, the kingdom-wide prevalence of MetS is determined.

Materials and Methods:

A total of 4578 Saudis aged 15-64 was randomly selected from 20 regions in Saudi Arabia. Anthropometrics were collected, and fasting blood samples collected to ascertain fasting blood glucose and lipid profile. Components of full MetS as defined by the International Diabetes Federation were used for screening.

Results:

The overall prevalence of MetS is 28.3%. Prevalence was significantly higher in males than in females (31.4 vs. 25.2%; P = 0.001). Prevalence of MetS was the highest in the northern and central region, and showed a parallel increase with age, and inversely with educational status. Region was also a significant contributor to MetS. Conclusion: Despite accumulating evidence of an epidemic, MetS remains largely unresolved in the kingdom. Aggressive public campaign should be launched, and policies implemented to control any future damage of MetS in the kingdom.

Renal transplantation: better fat than thin

BACKGROUND

Obesity has been a relative contraindication for renal transplantation. This study evaluates the impact of pretransplant body mass index (BMI) on renal transplant outcomes in a single institution in the era of modern immunosuppression.

MATERIALS AND METHODS

A 10-y retrospective analysis was undertaken of 454 consecutive patients who received a renal transplant at Westmead Hospital from January 1, 2001 to December 31, 2010. The role of pretransplant BMI on patient survival, graft survival, surgical complications, and postoperative complications was studied.

RESULTS

The mean age of transplant of this study population was 45.4 ± 13.0 y. Live donation rate was 53.5%, and 60.6% were male. The median preoperative BMI was 25.6 (range, 14.3-51.4). One-year and 5-y patient survival were 97.4% and 86.6%, respectively, whereas 1-y and 5-y death-censored graft survival were 97.1% and 91.9%, respectively. Patients with BMI >30 did not exhibit any significant difference in survival or graft failure but had higher surgical wound infection rates (hazard ratio 3.95, P < 0.01). Patients with preoperative BMI <18.5 were associated with a six-fold increase in both death and death-censored graft failure (P < 0.01).

CONCLUSIONS

Pretransplant obesity increases wound infection but is not a contraindication to renal transplantation. Future prospective studies are required to further define the impact of low preoperative BMI <18.5.

Description and prediction of the development of metabolic syndrome: a longitudinal analysis using a markov model approach

BACKGROUND

Delineating the natural history of metabolic syndrome (MetS) is prerequisite to prevention. This study aimed to build Markov models to simulate each component's progress and to test the effect of different initial states on the development of MetS.

METHODS

MetS was defined with revised AHA/NHLBI criteria. Each reversible multistate Markov chain consisted of 8 states (no component, five isolated component states, 2-component state, and MetS state). Yearly transition probabilities were calculated from a five-year population-based follow up studywhich enrolled 2,247 individuals with mean aged 32.4 years at study entry.

RESULTS

In men, high BP or a 2-component state was most likely to initiate the progress of MetS. In women, abdominal obesity or low HDL were the most likely initiators. Metabolic components were likely to occur together. The development of MetS was an increasing monotonic function of time. MetS was estimated to develop within 15 years in 12.7% of young men with no component, and 2 components developed in 16.3%. MetS was estimated to develop in 10.6% of women with at the age of 47, and 2 components developed in 14.3%. MetS was estimated to develop in 24.6% of men and 27.6% of women with abdominal obesity, a rate higher than in individuals initiating with no component.

CONCLUSIONS

This modeling study allows estimation of the natural history of MetS. Men tended to develop this syndrome sooner than women did, i.e., before their fifth decade of life. Individuals with 1 or 2 components showed increased development of MetS.

The role of obesity in kidney transplantation outcome

BACKGROUND

The number of obese kidney transplant candidates has been growing. However, there are conflicting results regarding to the effect of obesity on kidney transplantation outcome. The aim of this study was to investigate the association between the body mass index (BMI) and graft survival by using continuous versus categoric BMI values as an independent risk factor in renal transplantation.

METHODS

We retrospectively reviewed 376 kidney transplant recipients to evaluate graft and patient survivals between normal-weight, overweight, and obese patients at the time of transplantation, considering BMI as a categoric variable.

RESULTS

Obese patients were more likely to be male and older than normal-weight recipients (P = .021; P = .002; respectively). Graft loss was significantly higher among obese compared with nonobese recipients. Obese patients displayed significantly lower survival compared with nonobese subjects at 1 year (76.9% vs 35.3%; P = .024) and 3 years (46.2% vs 11.8%; P = .035).

CONCLUSIONS

Obesity may represent an independent risk factor for graft loss and patient death. Careful patient selection with pretransplantation weight reduction is mandatory to reduce the rate of early posttransplantation complications and to improve long-term outcomes.

Serum insulin is significantly related to components of the metabolic syndrome in Japanese working women

BACKGROUND

The aim of this study was to examine the association between serum insulin levels and components of the metabolic syndrome (MetS) in working women.

METHODS

The target subjects were 141 working women. Serum triglyceride, HDL cholesterol, uric acid, plasma insulin and plasma glucose were measured in addition to waist circumference and blood pressure.

RESULTS

MetS was diagnosed based on the modified criteria of the International Diabetes Federation, and was present in 7.1% (10/141) of the study subjects. Stepwise multiple regression analysis showed that some components of MetS were significantly associated with log-transformed values of the serum insulin. The standardized regression coefficient for the waist circumference, high density lipoprotein cholesterol, systolic blood pressure and age were 0.238, -0.333, 0.309 and -0.156, respectively.

CONCLUSIONS

A statistically significant relationship existed between the components of MetS and the serum insulin levels in working women.

Effect of obesity on cardiovascular disease risk factors in African American women

Obesity is a growing health care concern with implications for cardiovascular disease (CVD). Obesity and CVD morbidity and mortality are highly prevalent among African American women. This pilot study examined the association between obesity and the traditional and emerging CVD risk factors in a sample of African American women. Participants comprised 48 women (27 obese, 21 normal weight) aged 18-45. with no known history of CVD. The women completed demographic and 7-day physical activity recall questionnaires. Height and weight were used to determine body mass index (BMI). Hypertension risk was assessed using the average of two resting blood pressure (BP) measurements. Lipid profile, blood glucose, fibrinogen, high-sensitivity C-reactive protein (hs-CRP), plasminogen activator inhibitor-1 (PAI-1), soluble intercellular adhesion molecule-1 (sICAM-1), and E-selectin (eSel) levels were assessed using fasting blood samples. Laboratory findings were interpreted using the American Diabetes Association (ADA) and Adult Treatment Panel (ATP) III reference guidelines as well as manufacturers' reference ranges for the novel CVD risk factors. The most common traditional risk factors were physical inactivity (72.9%), positive family history of CVD (58.3%), and obesity (56.3%). Obese individuals had elevated systolic BP (p = .0002), diastolic BP (p = .0007) and HDL-cholesterol (p = .01), triglyceride (p = .02), hs-CRP (p = .002), and fibrinogen (p = .01), when compared with normal-weight women. The findings suggest an association between obesity and higher prevalence of both traditional and emerging CVD risk factors in young African American women.

Association of plasminogen activator inhibitor-1 and tissue plasminogen activator with type 2 diabetes and metabolic syndrome in Malaysian subjects

Background

Increased plasma plasminogen activator inhibitor-1 (PAI-1) activity and decreased tissue plasminogen activator (tPA) activity could be considered a true component of the metabolic syndrome (MetS) associated with an increased risk of developing cardiovascular diseases (CVD) and fibrinolytic abnormalities. The aim of this study was to investigate the association of tPA and its inhibitor PAI-1 with type 2 diabetes (T2D) and MetS and interrelationship between PAI-1and tPA activities and antigens in Malaysian T2D and normal subjects.

Methods

The plasma activities and antigens of PAI-1 and tPA and the levels of the tPA/PAI-1 complex as well as serum insulin, parameter of the coronary risk panel and plasma glucose at fasting state were studied in 303 T2D subjects (227 with MetS and 76 without MetS), 131 normal non-diabetic non-metabolic subjects and 101 non-diabetic MetS subjects.

Results

The PAI-1 activity was higher in subjects with T2D with MetS (P = 9.8 × 10^-19) and non-diabetic subjects with MetS (P = 3.0 × 10^-15), whereas the tPA activity was lower in T2D with MetS (P = 0.003) as compare to normal subjects. Plasma tPA antigen levels were higher in subjects with T2D with MetS (P = 8.9 × 10^-24), T2D without MetS (P = 1.3 × 10^-13) and non-diabetic MetS subjects (P = 0.002). The activity and antigen of PAI-1 in normal subjects were related to insulin resistance (P = 2.2 × 10^-4; 0.007). Additionally, the PAI-1 activity was associated with an increased waist circumference (P = 2.2 × 10^-4) and decreased HDL-c (P = 0.005), whereas the tPA activity was associated with decreased FBG (P = 0.028). The highest correlation was between PAI-1 activity and its antigen (R² = 0.695, P = 1.1 × 10^-36) in diabetic subjects. The tPA activity negatively correlated with its antigen (R² = -0.444, P = 7.7 × 10^-13) in normal subjects and with the PAI-1 activity and antigen (R² = -0.319, P = 9.9 × 10^-12; R2 = -0.228, P = 3.4 × 10^-6) in diabetic subjects.

Conclusions

PAI-1 and tPA activities and antigens were associated with diabetes and MetS parameters in Malaysian subjects.

Prevalence and interrelationships between cardio-metabolic risk factors in abdominally obese individuals

OBJECTIVE

The aim of this study was to examine the prevalence of metabolic syndrome and identify relationships between clustering and severity of cardio-metabolic risk factors in abdominally obese adults.

METHODS

Cardio-metabolic risk factors were assessed in a sample of 300 abdominally obese volunteers (233 females, 67 males, mean age 43.7 years) who were not being treated for diabetes, hypertension or dyslipidemia. Waist circumference (WC), blood pressure, fasting lipids, and glucose were measured and prevalence of metabolic syndrome was determined according to International Diabetes Federation (IDF) criteria. Correlation analysis and Poisson regression were used to examine associations between the presence of a particular risk factor and the propensity for clustering and derangement of other risk factors, using continuous data for risk factors and categorical data for number of metabolic syndrome components.

RESULTS

In all, 53% had metabolic syndrome and only 16% were free of cardio-metabolic abnormalities. In order of importance, diastolic blood pressure (DBP), high-density lipoprotein cholesterol (HDL), and triglycerides (TGs) were most strongly associated with greater clustering of risk factors, with a one standard deviation difference being associated with a respective difference of 9.65, 1.23, and 0.12 in the number of risk factors present. A greater number of risk factors was associated with an increased derangement for any given risk factor, with this effect being greatest for dyslipidemia, as represented by the TG:HDL ratio.

DISCUSSION

In abdominally obese individuals, DBP was strongly associated with metabolic syndrome component clustering, which may reflect the pathogenic progression of metabolic syndrome, as DBP is likely to be elevated following establishment of other risk factors. Also, dyslipidemia was strongly related to the magnitude of derangement of cardio-metabolic risk factors which may indicate that increases in dyslipidemia may drive the pathogenic progression of metabolic syndrome once acquired.

Serum insulin is significantly related to components of the metabolic syndrome in Japanese working men

The aim of this study was to examine the association between serum insulin levels and components of the metabolic syndrome (MS). The target participants were 3054 working men. MS was diagnosed based on the modified criteria of the International Diabetes Federation and was present in 12.9% of the study patients. Serum lipid profiles, uric acid, insulin, plasma glucose, and hemoglobin A1c were measured. Stepwise multiple regression analysis showed that all the components of MS were significantly associated with log-transformed values of the serum insulin. The standardized regression coefficient for the waist circumference was 5-fold higher than that for fasting plasma glucose, being 0.40 and 0.08, respectively. The standardized regression coefficients for diastolic blood pressure, log-transformed values of serum triglyceride, high-density lipoprotein cholesterol, and age were 0.09, 0.13, -0.16, and -0.11, respectively. A statistically significant relationship existed between the components of MS, especially abdominal obesity, and the serum insulin levels.

Relationship between two indicators of coronary risk estimated by the Framingham Risk Score and the number of metabolic syndrome components in Japanese male manufacturing workers

BACKGROUND

The Framingham Risk Score (FRS) has frequently been used in the United States to predict the 10-year risk of coronary heart disease (CHD). Components of the metabolic syndrome and several lifestyle factors have also been evaluated to estimate the risk of CHD.

METHODS

To determine the relationship between the FRS and components of metabolic syndrome as coronary risk indicators, the authors conducted a cross-sectional study of 2,619 Japanese male workers, ranging in age from 40 to 64 years, at a single workplace. Although the estimation by the FRS and metabolic syndrome involved some different factors, significant association of the risk estimated by the 2 methods was observed.

RESULTS

When logistic regression analysis was conducted with adjustment for several lifestyle factors, the FRS and serum insulin were found to be significantly associated with the risk of likelihood of metabolic syndrome. The odds ratios and 95% confidence intervals of FRS by per standard deviation increment and serum insulin by increasing 1 microIU/mL for the prediction of metabolic syndrome were 2.50 (2.17-2.88) and 1.24 (1.20-1.27), respectively. A preventive effect of abstaining from drinking every day and eating breakfast almost daily against the likelihood of metabolic syndrome was also observed.

CONCLUSIONS

In conclusion, the FRS and insulin were found to be significantly associated with the risk of likelihood of metabolic syndrome, even after controlling for weight change.

Metabolic effects of AEDs: impact on body weight, lipids and glucose metabolism

Epilepsy is a chronic disorder often requiring years of treatment. Accordingly, adverse effects of epilepsy and its treatment can impact general health for many decades. The psychological consequences of epilepsy are well documented, although the metabolic consequences of the treatment of epilepsy have only recently received attention. Antiepileptic drugs (AEDs) are well known to alter weight, causing either weight gain or weight loss. The mechanism by which this occurs remains to be fully understood, although there appears to be an effect on lipid and glucose metabolism. This chapter examines current data available on the adverse effects of individual AEDs on somatic weight, serum lipid profile, and glucose metabolism. These issues are of importance to neurologists caring for patients with epilepsy.

Skin tissue cholesterol is not related to vascular occlusive disease

The objective of the present study was to evaluate the role of skin tissue cholesterol (SkinTc) in predicting the presence of atherosclerosis. SkinTc concentrations were determined in 318 consecutive patients by using the non-invasive PREVU POC Skin Sterol Test. Additionally, a complete lipid status and cardiovascular risk profile according to the PROCAM and Framingham scores as well as an evaluation by carotid duplex sonography and ankle-brachial blood pressure index testing was obtained from all patients. SkinTc concentrations did not differ significantly among patients suffering from cerebrovascular disease (CVD) and peripheral arterial disease (PAD) compared to the corresponding control groups and among patients with a calculated cardiovascular risk > 10% in 10 years compared to patients with a risk < 10% (all p > 0.05). Additionally, SkinTc concentrations were not significantly higher in the 245 patients with at least one documented atherosclerotic disease compared with the remaining 73 patients without evidence of atherosclerosis. In conclusion, SkinTc concentrations determined by the PREVU POC Skin SterolTest are not related to the presence of CVD and PAD or to an elevated cardiovascular risk, indicating that this parameter cannot be used as a reliable indicator of atherosclerosis.

Estrogen and adiposity--utilizing models of aromatase deficiency to explore the relationship

Estrogen has an important role to play in energy homeostasis in both men and mice. Lack of estrogen results in the development of a metabolic syndrome in humans and rodents, including excess adiposity, hepatic steatosis (in male but not female aromatase knockout (ArKO) mice) and insulin resistance. Estrogen replacement results in a prompt reversal of the energy imbalance symptoms associated with estrogen deficiency. A corollary to the perturbed energy balance observed in the ArKO mouse is the death by apoptosis of dopaminergic neurons in the hypothalamic arcuate nucleus of male ArKO mice, an area of the brain pivotal to the regulation of energy uptake, storage, and mobilisation. An extension of our work exploring the relationship between estrogen and adiposity has been to examine the role played by androgens in energy balance. We have demonstrated that an increased androgen to estrogen ratio can promote visceral fat accumulation in the rodent by inhibiting AMPK activation and stimulating lipogenesis. Therefore, understanding the regulation of energy homeostasis is becoming an increasingly fascinating challenge, as the number of contributors, their communications, and the complexity of their interactions, involved in the preservation of this equilibrium continues to increase. Models of aromatase deficiency, both naturally occurring and engineered, will continue to provide valuable insights into energy homeostasis.

Recognizing rare disorders: aromatase deficiency

Aromatase deficiency is rare in humans. Affected individuals cannot synthesize endogenous estrogens. Aromatase is the enzyme that catalyzes conversion of androgens into estrogens, and if aromatase is nonfunctional because of an inactivating mutation, estrogen synthesis cannot occur. If the fetus lacks aromatase activity, dehydroepiandrosterone sulfate produced by the fetal adrenal glands cannot be converted to estrogen by the placenta, so is converted to testosterone peripherally and results in virilization of both fetus and mother. Virilization manifests as pseudohermaphroditism in female infants, with hirsutism and acne in the mother; the maternal indicators resolve following delivery. To date, only seven males and seven females with aromatase deficiency have been reported. Affected females are typically diagnosed at birth because of the pseudohermaphroditism. Cystic ovaries and delayed bone maturation can occur during childhood and adolescence in these girls, who present at puberty with primary amenorrhea, failure of breast development, virilization, and hypergonadotrophic hypogonadism. Affected males, on the other hand, do not present with obvious defects at birth, so are diagnosed much later in life, presenting with clinical symptoms, which include tall stature, delayed skeletal maturation, delayed epiphyseal closure, bone pain, eunuchoid body proportions and excess adiposity. Estrogen replacement therapy reverses the symptoms in male and female patients.

New insights into renal transport of urate

PURPOSE OF REVIEW

This review focuses on recent progress in the understanding of various aspects of renal transport of urate.

RECENT FINDINGS

Since the molecular cloning of the renal apical urate/anion exchanger URAT1 (SLC22A12), several membrane proteins relevant to the transport of urate have been identified. The molecular identification of two sodium-coupled monocarboxylate transporters, SMCT1(SLC5A8) and SMCT2(SLC5A12), and the emerging role of PDZ (PSD-95, DglA, and ZO-1) scaffold for renal apical transporters have led to a new concept of renal urate transport: urate-transporting multimolecular complex, or 'urate transportsome', that may form an ultimate functional unit including the sodium-coupled urate transport system by linking URAT1 and sodium-coupled monocarboxylate transporters or the coordinated apical urate uptake system by balancing reabsorptive (URAT1) and efflux (NPT1/OATv1 and MRP4) transporters. In addition, genetic variations of the URAT1 gene are associated not only with idiopathic renal hypouricemia but also with reduced renal urate excretion.

SUMMARY

Although our knowledge of renal urate handling has been increased by the molecular identification of urate transport proteins and by results of genetic studies on patients with serum urate disorders, current evidence is insufficient to fully understand the precise mechanism governing the bi-directional transport of urate. Further studies are still necessary.

Chronic PYY3-36 treatment promotes fat oxidation and ameliorates insulin resistance in C57BL6 mice

PYY(3-36) is a gut-derived hormone acting on hypothalamic nuclei to inhibit food intake. We recently showed that PYY(3-36) acutely reinforces insulin action on glucose disposal in mice. We aimed to evaluate effects of PYY(3-36) on energy metabolism and the impact of chronic PYY(3-36) treatment on insulin sensitivity. Mice received a single injection of PYY(3-36) or were injected once daily for 7 days, and energy metabolism was subsequently measured in a metabolic cage. Furthermore, the effects of chronic PYY(3-36) administration (continuous and intermittent) on glucose turnover were determined during a hyperinsulinemic-euglycemic clamp. PYY(3-36) inhibited cumulative food intake for 30 min of refeeding after an overnight fast (0.29 +/- 0.04 vs. 0.56 +/- 0.12 g, P = 0.036) in an acute setting, but not after 7 days of daily dosing. Body weight, total energy expenditure, and physical activity were not affected by PYY(3-36). However, it significantly decreased the respiratory quotient. Both continuous and intermittent PYY(3-36) treatment significantly enhanced insulin-mediated whole body glucose disposal compared with vehicle treatment (81.2 +/- 6.2 vs. 77.1 +/- 5.2 vs. 63.4 +/- 5.5 micromol.min(-1).kg(-1), respectively). In particular, PYY(3-36) treatment increased glucose uptake in adipose tissue, whereas its impact on glucose disposal in muscle did not attain statistical significance. PYY(3-36) treatment shifts the balance of fuel use in favor of fatty acids and enhances insulin sensitivity in mice, where it particularly promotes insulin-mediated glucose disposal. Notably, these metabolic effects of PYY(3-36) remain unabated after chronic administration, in contrast to its anorexic effects.

Of mice and men: the evolving phenotype of aromatase deficiency

We are rapidly becoming aware of the importance of estrogen in maintaining virtually all facets of male health. In order for estrogens to be synthesized endogenously, the enzyme responsible for their synthesis from androgens, aromatase, must be functional. The seven known men in whom aromatase is nonfunctional all have a mutation in either exon V or IX of the CYP19 gene, which encodes aromatase. Collectively, these men are reported to have undetectable estrogen; normal to high levels of testosterone and gonadotropins; tall stature with delayed skeletal maturation and epiphyseal closure; osteoporosis; impaired lipid and insulin metabolism; and impaired reproductive function. The aromatase knockout mouse presents with a phenotype that is similar in many aspects and provides a valuable tool with which to examine and manipulate the actions of estrogen. By studying the naturally occurring aromatase-deficient humans, together with studies of the aromatase-knockout mouse, we are expanding our understanding of the essential role of estrogen in male physiology.

Obesity is associated with worsening cardiovascular risk factor profiles and proteinuria progression in renal transplant recipients

Obesity is associated with adverse cardiovascular (CV) parameters and may be involved in the pathogenesis of allograft dysfunction in renal transplant recipients (RTR). We sought the spectrum of body mass index (BMI) and the relationships between BMI, CV parameters and allograft function in prevalent RTR. Data were collected at baseline and 2 years on 90 RTR (mean age 51 years, 53% male, median transplant duration 7 years), categorized by BMI (normal, BMI < or = 24.9 kg/m2; pre-obese, BMI 25-29.9 kg/m2; obese, BMI > or = 30 kg/m2). Proteinuria and glomerular filtration rate (eGFR(MDRD)) were determined. Nine percent RTR were obese pre-transplantation compared to 30% at baseline (p < 0.001) and follow-up (25 +/- 2 months). As BMI increased, prevalence of metabolic syndrome and central obesity increased (12 vs 48 vs 85%, p < 0.001 and 3 vs 42 vs 96%, p < 0.001, respectively). Systolic blood pressure, fasting blood glucose and lipid parameters changed significantly with BMI category and over time. Proteinuria progression occurred in 65% obese RTR (23 (13-59 g/mol creatinine) to 59 (25-120 g/mol creatinine)). BMI was independently associated with proteinuria progression (beta 0.01, p = 0.008) but not with changing eGFR(MDRD.) In conclusion, obesity is common in RTR and is associated with worsening CV parameters and proteinuria progression.

Endothelial Function in the Forearm Circulation of Patients with the Metabolic Syndrome – Effect of Different Lipid-Lowering Regimens

We compared the effect of statin therapy (either alone or combined with ezetimibe) on the inhibition of cholesterol resorption and endothelial function by measuring forearm blood flow in male patients with the metabolic syndrome. Compared to 40 mg atorvastatin alone, combination therapy with 10 mg ezetimibe and 10 mg atorvastatin for 8 weeks resulted in significantly decreased total serum cholesterol and triglycerides levels (n = 14). Endothelium-dependent, acetylcholine-mediated vasodilation was significantly better with combination therapy (p < 0.05). In contrast, endothelium-independent forearm blood flow response to sodium nitroprusside was comparable in both groups. Our data suggest a more effective restoration of endothelial function with the statin/ezetimibe combination compared to statin monotherapy in patients with the metabolic syndrome.

Impact of obesity on renal transplant outcomes

Obesity is a frequent and important consideration to be taken into account when assessing patient suitability for renal transplantation. In addition, posttransplant obesity continues to represent a significant challenge to health care professionals caring for renal transplant recipients. Despite the vast amount of evidence that exists on the effect of pretransplant obesity on renal transplant outcomes, there are still conflicting views regarding whether obese renal transplant recipients have a worse outcome, in terms of short- and long-term graft survival and patient survival, compared with their non-obese counterparts. It is well established that any association of obesity with reduced patient survival in renal transplant recipients is mediated in part by its clustering with traditional cardiovascular risk factors such as hypertension, dyslipidaemia, insulin resistance and posttransplant diabetes mellitus, but what is not understood is what mediates the association of obesity with graft failure. Whether it is the higher incidence of cardiovascular comorbidities jeopardising the graft or factors specific to obesity, such as hyperfiltration and glomerulopathy, that might be implicated, currently remains unknown. It can be concluded, however, that pre- and posttransplant obesity should be targeted as aggressively as the more well-established cardiovascular risk factors in order to optimize long-term renal transplant outcomes.

Renal urate handling: Clinical relevance of recent advances

Urate is the major inert end product of purine degradation in higher primates in contrast to most other mammals because of the genetic silencing of hepatic oxidative enzyme uricase. The kidney plays a dominant role in urate elimination. The kidney excretes 70% of the daily urate production. Therefore, it is important to understand renal urate handling mechanism because the under excretion of urate has been implicated in the development of hyperuricemia that leads to gout. The urate transport systems exist in the proximal tubule but they are complicated because of their bidirectional transport and the species differences. Recently, we have identified the urate-anion exchanger URAT1 (SLC22A12) in the human kidney and found that defects in SLC22A12 lead to idiopathic renal hypouricemia. URAT1 is targeted by uricosuric and antiuricosuric agents that affect urate excretion. Molecular identification of urate transporting proteins will lead to the new drug development for hyperuricemia.